Publications

Motivated by the need for climate-change resilience, this article summarizes the results of an international hackathonstyle competition aimed at improving local weather forecasts using machine-learning postprocessing of multiple forecast sources and historical data. The approaches and results of the top teams are presented and compared, including support vector regression, gradient boosting, k-nearest neighbors, long short-term memory networks, and transformer-based architectures. Each approach tailors model architectures, preprocessing, feature selection, and hyperparameter tuning to the characteristics of the target meteorological variables across three case studies in Africa, theMiddle East, and Europe (IEEE Region 8). Six variables are evaluated against ground-truth measurements collected over the seven days following each submission. The results show that careful architectural and feature-engineering choices, informed by domain knowledge, can substantially reduce error relative to the operational European Centre for Medium-Range Weather Forecasts Integrated Forecasting System benchmark. Across the five variables with nontrivial benchmark values, the best per-variable RMSSE reductions reach 59.26%, with an average reduction of 30.46% using postprocessing of historical numerical weather prediction forecasts and local observations, highlighting the significant potential of this technology.

Drilling on the volcanic rifted margin of southern Angola has encountered high volumes of CO2 and evidence for hydrothermal fluid flow, but the sources of CO2, the timing of fluid flow and its impact on basin thermal structure, reservoir evolution and resource distribution have so far remained unresolved. This study integrates in-situ U-Pb geochronology, noble gas and clumped isotope geochemistry, and petrography to reconstruct the burial history and fluid-rock interaction in a CO2-rich Aptian carbonate reservoir. The carbonates have not preserved depositional ages, but they were recrystallized at 111.2 ± 3.4 Ma and 87.7 ± 5.5 Ma, coincident with thermal pulses at temperatures of 114-138°C and 145-149°C (1SE), respectively. Evolved basinal fluids that had interacted with siliciclastics, volcanic and/or basement rocks, but also contained a significant mantle volatile component, were responsible for recrystallization. Decompaction analysis suggests that at least the older event can be considered hydrothermal. The occurrence of such a thermal and fluid pulse within c. 6-16 Ma of deposition will have significantly altered the thermal structure of the basin. The Albian age of fluid flow and calcite recrystallization complements age data from the conjugate Brazilian margin and suggests that this widespread but spatially variable event was genetically linked to the early stages of oceanic spreading. The second fluid pulse coincides with the age of the Peri-Atlantic Alkaline igneous Province (PAAP). This study highlights the importance of early diagenetic fluid flow involving mantle-derived volatiles for basins on the South Atlantic conjugate margins.

Clinoform identification plays a major role in sequence stratigraphy and applied geosciences, offering key insights into sediment fluxes, basin evolution, and natural resource exploration. However, manual interpretation of clinoform geometries in seismic data is time- consuming and labour- intensive. This study proposes a deep learning framework to automate clinoform detection and segmentation. One of the greatest challenges of seismic interpretation with deep learning is the scarcity of labelled training data. To address this, we generated 20,000 synthetic seismic images using process- based forward stratigraphic modelling followed by ray- based seismic modelling, ensuring both geological realism and variability of data. The generated synthetic seismic images were split into training (70%), validation (15%), and testing (15%) sets. The clinoform binary masks were labelled using the top and base layers from the forward stratigraphic models. Then, a YOLOv8m model was trained on this dataset, achieving 86% precision, 82% recall, and 83% Dice coefficient on segmenting clinoforms in the synthetic testing dataset. Qualitative validation on real seismic images confirmed accurate bounding box detection and segmentation of clinoform bodies. These results highlight the potential of deep learning to accelerate seismic interpretation, particularly during early scanning phases, where rapid clinoform analysis supports stratigraphic assessment and reservoir characterisation. The proposed workflow bridges the synthetic- to- real domain gap in seismic data, offering a scalable approach to train algorithms for advancing subsurface analysis.

Geological core images provide subsurface lithological and textural information critical to industry and academia, yet their availability is often limited by high acquisition costs and incomplete core recovery. Formation MicroScanner (FMS) image logs can overcome this limitation by providing continuous, high-resolution measurements of borehole wall resistivity. Recent generative learning approaches have demonstrated the feasibility of translating FMS signals into synthetic core images, thus improving the ability of geologists to interpret this modality. However, existing methods typically rely solely on FMS and overlook the complementary geological context provided by conventional well-log measurements. In this study, we reformulate geological core image generation as a multimodal conditional synthesis problem, jointly conditioned on FMS and depthaligned well-log data. We propose a Log-Gated Dual-Path Conditioning Framework, in which FMS and well-log measurements are encoded through separate modality-specific pathways and integrated through a log-guided gating mechanism to progressively condition the generation process. This design enables structured fusion of heterogeneous geological signals while preserving modality-specific characteristics. Experiments on real-world geological datasets demonstrate that the proposed framework generates highresolution core images that better capture realistic textural structures and lithological patterns compared with singlemodality baselines. These results highlight the importance of structured multimodal conditioning and provide a practical pathway to bridge complex subsurface measurements with interpretable geological representations.

Closed-loop bioelectronic devices offer a promising platform for responsive treatment to heterogeneous disease states. Glioblastoma, an aggressive form of brain cancer, has recently emerged as a focus of bioelectronic medicine through delivery of electrotherapies. This perspective article posits that true progress in the management of this extremely heterogeneous disease requires the integration of continuous monitoring from the tumor microenvironment as well as on-device analytics to enact closed-loop control. Four promising candidate biological changes present in the glioblastoma microenvironment are highlighted (local field potentials, bioimpedance, local pH, biomarkers) alongside the bioelectronic sensors that can enable the development of multifunctional bioelectronic devices to monitor the changes. Finally, three key principles (patient involvement, data analytics, and device fabrication) governing the successful implementation of closed-loop sensors are proposed to create a roadmap for academics and industry partners to successfully develop multimodal devices for the treatment of glioblastoma.

Orbital remote sensing observations are a lynchpin of planetary science research. Hyperspectralinfrared spectroscopy in particular is key for planetary mineralogical exploration, for example, CRISM forMars, as this underpins our understanding of the distribution of specific lithologies and the geological processleading to their formation. Yet routine analysis workflows involving summary parameters have significantlimitations and are highly time‐consuming. This work presents a novel methodology and framework for theanalysis and classification of CRISM SWIR reflectance spectroscopy, leveraging Machine Learning (ML). Wetrain a model to classify 37 minerals previously manually identified on the planet. We show this model is highlyperformant, with test data across Mars and a case study within Jezero crater, where ML results match previousmanual analyses and rover observations. We also adapt Expected Cost (EC) to remote sensing data for use ingeological context for the first time. We demonstrate that EC can be used to dynamically weightmisclassification penalties based on geological context, as a rigorous measure of automated classificationmethods. We envision this model to make analysis of CRISM data more accessible to the planetary sciencecommunity, allowing rapid searches for a vast range of minerals across a global/regional scale. As a result, areasof interest for further satellite or rover exploration can be quickly identified, leading to greater understanding ofgeological processes on Mars

This study presents an innovative approach to automated coral reef monitoring using satellite imagery, addressing challenges in image quality assessment and correction. The method employs Principal Component Analysis (PCA) coupled with clustering for efficient image selection and quality evaluation, followed by a machine learning-based cloud removal technique using an XGBoost model trained to detect land and cloudy pixels over water. The workflow incorporates depth correction using Lyzenga’s algorithm and superpixel analysis, culminating in an unsupervised classification of reef areas using KMeans. Results demonstrate the effectiveness of this approach in producing consistent, interpretable classifications of reef ecosystems across different imaging conditions. This study highlights the potential for scalable, autonomous monitoring of coral reefs, offering valuable insights for conservation efforts and climate change impact assessment in shallow marine environments.

Seismic stratigraphy entails a regional scanning (reconnaissance) of seismic data to identify and annotate seismic reflection terminations. To identify these terminations in modern 3D seismic datasets, interpreters have to examine thousands of inlines and crosslines, which is a time-consuming process. Furthermore, accurate identification of these features relies heavily on human visual observation along with individual expertise. A growing number of studies have shown promising results applying machine learning techniques to identify geological features from seismic data such as salt bodies and faults. However, the identification of seismic reflection terminations has not received the same level of interest and remains a manual process. One of the barriers to utilizing machine learning techniques in seismic interpretation is the lack of “labelled” data. In this study, we evaluate the ability of deep learning Convolutional Neural Networks (CNN) trained on synthetic seismic images to identify seismic reflection terminations. A dataset comprising 160 000 synthetic seismic images that represent conformable and four types of seismic reflection terminations (truncation, toplap, onlap, and downlap) were created using geometric geological modelling and 1D convolution seismic modelling. The dataset was then split into two classes (“Contains Termination” and “No Termination”). A new CNN model architecture named “Seismic Reflection Terminations Attribute (SRT-Ai)” was trained on 80 % of the synthetic seismic dataset. SRT-Ai predicted the test set (remaining 20 %) with an accuracy and precision of 99.9 %. To test its generalization, SRT-Ai was also evaluated on real seismic images, achieving 91 % accuracy and 96 % precision against published interpretations used as reference labels. Qualitative analysis of predictions along seismic sections shows a strong correspondence between the model predictions and manual regional interpretations. SRT-Ai is proposed as a screening tool that will assist seismic interpreters with the identification of major seismic terminations, minimise seismic interpretation uncertainties, reduce the time taken for seismic reconnaissance, and limit the reliance on human visual observation at the early stage of seismic interpretation process.

The use of hyperspectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has uncovered a wide range of previously undetected minerals on the surface of the red planet and has been instrumental in the selection of multiple rover mission landing sites. Yet, due to the aging of the sensor and an increase in noise, a significant portion of CRISM data is deemed too degraded and remains unanalyzed. We present a new data-driven model architecture, Noise2Noise for Mars (N2N4M), designed specifically to denoise hyperspectral data. Our model does not require zero-noise target data, making it well-suited for use in planetary science applications where such data does not exist. We demonstrate its strong performance over benchmark methods, outperforming them on most metrics. We suggest that the reliance on spatial correlations in noise profiles for the deep learning (DL) benchmark methods may be part of the cause of their poor performance when applied to CRISM data. We apply our methodology to two case study sites, each previously studied for hydrated mineralogy, and demonstrate that our model can increase the visual clarity of summary parameters used to highlight areas of interest. This has potential impacts for the characterization of landing sites for upcoming missions such as the ESA’s ExoMars rover mission.

Deep Neural Networks (DNNs) have significantly advanced the field of computer vision. To improve DNN training process, knowledge distillation methods demonstrate their effectiveness in accelerating network training by introducing a fixed learning direction from the teacher network to student networks. In this context, several distillationbased optimization strategies are proposed, e.g., deep mutual learning and self-distillation, as an attempt to achieve generic training performance enhancement through the cooperative training of multiple networks. However, such strategies achieve limited improvements due to the poor understanding of the impact of learning directions among networks across different iterations. In this paper, we propose a novel competitive distillation strategy that allows each network in a group to potentially act as a teacher based on its performance, enhancing the overall learning performance. Competitive distillation organizes a group of networks to perform a shared task and engage in competition, where competitive optimization is proposed to improve the parameter updating process. We further introduce stochastic perturbation in competitive distillation, aiming to motivate networks to induce mutations to achieve better visual representations and global optimum. The experimental results show that competitive distillation achieves promising performance in diverse tasks and datasets.

Core images provide a high-resolution data set of the textures and fabrics of sedimentary rocks, but their availability is often limited by cost and/or poor core recovery. An alternative solution is to utilize advanced high-resolution micro-resistivity images acquired through wireline logging, such as the Formation MicroScanner (FMS). But interpreting FMS image logs requires specialized knowledge that not all geologists possess. In this study, we explore the potential of Generative Adversarial Networks (GANs) in generating realistic core images from FMS logs using supervised image-to-image translation models. We trained a total of 10 models, testing various combinations of FMS data input formats, image processing methods, GAN architecture, and training hyperparameters. The supervised pix2pixHD model trained using concatenated FMS pad images with a batch size of 4 produces the most realistic core images: these have low Root Mean Square Error, high Peak Signal to Noise Ratio and high Structural Similarity Index Method values when compared to the ground truth core images. Our results also stress the importance of a diversified data set to reduce bias and enhance the applicability of the trained models to other wells and fields. Blind testing with geologists shows that classification accuracy for Dunham textures increases from 14% on FMS image logs to 73% on synthetic core images. The approach proposed here has thus the potential to transform the field of subsurface characterization by bridging the gap between the limited availability of core samples and the need for comprehensive geological facies classification.

This study presents an innovative approach to automated coral reef monitoring using satellite imagery, addressing challenges in image quality assessment and correction. The method employs Principal Component Analysis (PCA) coupled with clustering for efficient image selection and quality evaluation, followed by a machine learning-based cloud removal technique using an XGBoost model trained to detect land and cloudy pixels over water. The workflow incorporates depth correction using Lyzenga’s algorithm and superpixel analysis, culminating in an unsupervised classification of reef areas using KMeans. Results demonstrate the effectiveness of this approach in producing consistent, interpretable classifications of reef ecosystems across different imaging conditions. This study highlights the potential for scalable, autonomous monitoring of coral reefs, offering valuable insights for conservation efforts and climate change impact assessment in shallow marine environments.

Giant earthquakes (Mw ≥8.5) along subduction margins pose great hazards to coastal societies. While it is generally accepted that geological margin properties play a role, controls on giant earthquake occurrence remain undetermined. The long intermittence times of giant earthquakes and the comparatively short earthquake record obscure any correlations between margin properties and seismicity. This work presents a new approach to relating margin properties to seismicity. We apply principal component analysis (PCA) to four margin properties to “fingerprint” margins by assigning them a PCA profile, which we compare to giant earthquake occurrence. This approach reduces bias from the short earthquake record because seismicity is not used as a PCA input feature. Using kernel PCA, a nonlinear PCA variant, we find nonlinear patterns in margin properties and suggest that links between properties and seismicity are nonlinear, which helps explain why they have been hard to establish. PCA clusters identify “active and moderate” and “quiet and extreme” margins. We argue that margin segments with “quiet and extreme” PCA profiles but no giant earthquakes since 1900 are as hazardous as those that have ruptured in giant earthquakes recently.

Labelled datasets within geoscience can often be small, with data acquisition both costly and challenging, and their interpretation and downstream use in machine learning difficult due to data scarcity. Deep learning algorithms require large datasets to learn a robust relationship between the data and its label and avoid overfitting. To overcome the paucity of data, transfer learning has been employed in classification tasks. But an alternative exists: there often is a large corpus of unlabeled data which may enhance the learning process. To evaluate this potential for subsurface data, we compare a high-performance semi-supervised learning (SSL) algorithm (SimCLRv2) with supervised transfer learning on a Convolutional Neural Network (CNN) in geological image classification. We tested the two approaches on a classification task of sediment disturbance from cores of International Ocean Drilling Program (IODP) Expeditions 383 and 385. Our results show that semi-supervised transfer learning can be an effective strategy to adopt, with SimCLRv2 capable of producing representations comparable to those of supervised transfer learning. However attempts to enhance the performance of semi-supervised transfer learning with task-specific unlabeled images during self-supervision degraded representations. Significantly, we demonstrate that SimCLRv2 trained on a dataset of core disturbance images can out-perform supervised transfer learning of a CNN once a critical number of task-specific unlabeled images are available for self-supervision. The gain in performance compared to supervised transfer learning is 1% and 3% for binary and multi-class classification, respectively. Supervised transfer learning can be deployed with comparative ease, whereas the current SSL algorithms such as SimCLRv2 require more effort. We recommend that SSL be explored in cases when large amounts of unlabeled task-specific images exist and improvement of a few percent in metrics matter. When examining small, highly specialized datasets, without large amounts of unlabeled images, supervised transfer learning might be the best strategy to adopt. Overall, SSL is a promising approach and future work should explore this approach utilizing different dataset types, quantity, and quality.

Understanding and preserving the deep sea ecosystems is paramount for marine conservation efforts. Automated object (deep-sea biota) classification can enable the creation of detailed habitat maps that not only aid in biodiversity assessments but also provide essential data to evaluate ecosystem health and resilience. Having a significant source of labelled data helps prevent overfitting and enables training deep learning models with numerous parameters. In this paper, we contribute to the establishment of a significant deep-sea remotely operated vehicle (ROV) image classification dataset with 3994 images featuring deep-sea biota belonging to 33 classes. We manually label the images through rigorous quality control with human-in-the-loop image labelling. Leveraging data from ROV equipped with advanced imaging systems, our study provides results using novel deep-learning models for image classification. We use deep learning models including ResNet, DenseNet, Inception, and Inception-ResNet to benchmark the dataset that features class imbalance with many classes. Our results show that the Inception-ResNet model provides a mean classification accuracy of 65%, with AUC scores exceeding 0.8 for each class

Identification of constituent grains in carbonate rocks requires specialist experience. A carbonate sedimentologist must be able to distinguish between skeletal grains that change through geological ages, preserved in differing alteration stages, and cut in random orientations across core sections. Recent studies have demonstrated the effectiveness of machine learning in classifying lithofacies from thin section, core, and seismic images, with faster analysis times and reduction of natural biases. In this study, we explore the application and limitations of convolutional neural network (CNN) based object detection frameworks to identify and quantify multiple types of carbonate grains within close-up core images of carbonate lithologies. We compiled nearly 400 images of high-resolution core images from three ODP and IODP expeditions. Over 9000 individual carbonate components of 11 different classes were manually labelled from this dataset. Using pre-trained weights, a transfer learning approach was applied to evaluate one-stage (YOLO v5) and two-stage (Faster R–CNN) detectors under different feature extractors (CSP-Darknet53 and ResNet50-FPN, respectively). Despite the current popularity of one-stage detectors, our results show Faster R–CNN with ResNet50-FPN backbone provides the most robust performance, achieving 0.73 mean average precision (mAP). Furthermore, we extend the approach by deploying the trained model to two ODP sites from Leg 194 that were not part of the training set (ODP Sites 1196 and 1199), providing a performance comparison with benchmark human interpretation.

The middle part of the Miocene Monterey Formation at Naples Beach, west of Santa Barbara, California, is predominantly composed of organic-rich mudstone interstratified with phosphatic laminae. Minor lithologies include volcanic ash, dolomite, porcelanite and chert, and condensed phosphatic beds. Sediments dated as 14.3–13.5 Ma have average total organic carbon (TOC) values around 8.5 wt%, and organic carbon (OC) accumulation rates are around 565 mg/cm2/k.y. Sediments dated as 13.5–13 Ma are characterized by average TOC values of 12.6 wt% and OC accumulation rates of around 1130 mg/cm2/ k.y. The interval between 13 and 10.6 Ma is marked by condensation; average TOC values are around 8.6 wt%, and OC accumulation rates diminished to around 55 mg/cm2/k.y. The last interval studied is dated as 10.6–9.4 Ma, and average TOC values are around 6 wt%, whereas OC accumulation …

Calcite veins are a common product of hydrothermal fluid circulation. Clumped-isotope palaeothermometry is a promising technique for fingerprinting the temperature of hydrothermal fluids, but clumped-isotope systematics can be reset at temperatures of > ca. 100 °C. To model whether the reconstructed temperatures represent calcite precipitation or closed-system resetting, the precipitation age must be known. LA-ICP-MS U–Pb dating of calcite is a recently developed approach to direct dating of calcite and can provide precipitation ages for modelling clumped-isotope systematics in calcite veins. In this study, clumped-isotope and LA-ICP-MS U–Pb calcite analyses were combined in basalt-hosted calcite veins from three settings in Scotland. Samples from all three localities yielded precipitation temperatures of ca. 75–115 °C from clumped-isotope analysis, but veins from only two of the sites were …

Dolomite is common in carbonate successions. There is an ongoing debate about the origin of ancient massive dolostones. Recent studies suggest widespread syndepositional and early-burial dolomitisation by normal and near-normal seawater, in the rock record, than previously recognised. Seawater dolomitisation is ubiquitous in Cenozoic islands but Cretaceous counterparts are rare, except for Resolution and Allison guyots, Mid-Pacific Mountains. We explored their dolomitisation conditions and the implications on our understanding of Cretaceous normal seawater syndepositional and near-surface dolomitisation. Integrating geochemical and borehole data reveals temporal overlap between 87Sr/86Sr ages of dolomites, and K/Ar and 40Ar/39Ar ages of the basement. Dolomites near basaltic basement exhibit 42-times Fe-enrichment compared to normal seawater dolomites. Host-rock thermal modelling suggested that δ18Odol temperatures are ∼18–29 °C higher than concurrent temperatures. Seismic interpretation and seismic facies forward modelling demonstrate a spatial overlap between dolomites and magmatic sills in both guyots. Accordingly, magmatically driven hydrothermal dolomitisation is proposed, which promoted dolomitisation by providing high heat flow, increasing seawater circulation, and overcoming limited dolomitisation potential of Cretaceous seawater. The H2O–CO2–SO2–HCl-rich magmatic-hydrothermal acidic fluids would mix with seawater causing slight modification by leaching Mg and Fe from basaltic basement. Consequently, magmatically active Cretaceous islands had greater potential for seawater dolomitisation than counterparts with ceased magmatism, due to increased heat flux and slight increase in Mg:Ca of dolomitising fluids. Our findings imply that deep-seated island dolostones don't only form by deep cold seawater below calcite saturation depth. Instead, magmatism appears crucial in this study and potentially other locations (e.g. Xisha Islands). The absence of dolostones in other Cretaceous islands supports previous models of reduced effectiveness of massive dolomitisation by Cretaceous normal seawater, questioning interpretations of syndepositional and near-surface dolomitisation. Thus, caution is advised when interpreting these dolomites by considering additional factors (dolomite geometry, geological settings, and dolomitisation age), as they may share characteristics with syndepositional and near-surface normal seawater dolomites.

Hyperspectral data acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) have allowed for unparalleled mapping of the surface mineralogy of Mars. Due to sensor degradation over time, a significant portion of the recently acquired data is considered unusable. Here a new data-driven model architecture, Noise2Noise4Mars (N2N4M), is introduced to remove noise from CRISM images. Our model is self-supervised and does not require zero-noise target data, making it well suited for use in Planetary Science applications where high quality labelled data is scarce. We demonstrate its strong performance on synthetic-noise data and CRISM images, and its impact on downstream classification performance, outperforming benchmark methods on most metrics. This allows for detailed analysis for critical sites of interest on the Martian surface, including proposed lander sites.

Most of the geologic CO2 entering Earth’s atmosphere and oceans is emitted along plate margins. While C-cycling at mid-ocean ridges and subduction zones has been studied for decades, little attention has been paid to degassing of magmatic CO2 and mineral carbonation of mantle rocks in oceanic transform faults. We studied the formation of soapstone (magnesite–talc rock) and other magnesite-bearing assemblages during mineral carbonation of mantle peridotite in the St. Paul’s transform fault, equatorial Atlantic. Clumped carbonate thermometry of soapstone yields a formation (or equilibration) temperature of 147 ± 13 °C which, based on thermodynamic constraints, suggests that CO2(aq) concentrations of the hydrothermal fluid were at least an order of magnitude higher than in seawater. The association of magnesite with apatite in veins, magnesite with a δ13C of −3.40 ± 0.04‰, and the enrichment of CO2 in hydrothermal fluids point to magmatic degassing and melt-impregnation as the main source of CO2. Melt-rock interaction related to gas-rich alkali olivine basalt volcanism near the St. Paul’s Rocks archipelago is manifested in systematic changes in peridotite compositions, notably a strong enrichment in incompatible elements with decreasing MgO/ SiO2. These findings reveal a previously undocumented aspect of the geologic carbon cycle in one of the largest oceanic transform faults: Fueled by magmatism in or below the root zone of the transform fault and subsequent degassing, the fault constitutes a conduit for CO2-rich hydrothermal fluids, while carbonation of peridotite represents a vast sink for the emitted CO2.

In-situ CO2 mineralisation has been demonstrated as a rapid and secure mechanism of geological CO2 storage through a series of field demonstrations in Icelandic basalts by Carbfix. A key indicator of success in the first of these tests was the discovery of newly precipitated calcite on the monitoring well downhole pump that contained the 14C tracer added to the injected CO2. In this study we use clumped, carbon and oxygen isotope measurements to determine the temperature of CO2 mineralisation and source of parental fluids and CO2 for the calcite found on the pump. Clumped isotope values (Δ47) range from 0.526‰ to 0.540‰, which correspond to mineralisation temperatures of 45–51 ◦C. These are 10–16 ◦C warmer than pre-injection temperatures measured at the pump depth. We attribute the warmer temperatures to continuous water pumping from the monitoring well, drawing up waters from deeper in the storage reservoir to the pump depth. Calculated parent fluid oxygen isotope values (δ18O) match well and local meteoric water records. Calcite carbon isotope values (δ13C) conform to a CarbFix injection source, but are higher than expected given previously established mineralisation yields for CarbFix. This is likely a consequence of the crystal homogenisation process required for analysis, resulting in an averaging of calcite δ13C values. The results of this study validate previous CarbFix findings that subsurface fluid migration and CO2 mineralisation occurred within porous media of the storage reservoir. This is as an example of how isotopic analysis of carbonates and CO2 can contribute to the verification of geological CO2 storage.

The clumped isotope paleo-thermometer has become a valuable proxy for the burial history reconstruction of carbonate formations. To maximise the accuracy of these reconstructions, post-depositional alterations, such as recrystallisation and Δ47 isotope exchange reactions, must be understood. In this study, we examine the isotopic behaviour of calcites and early dolomite samples from the same stratigraphic intervals, and thus with similar burial history. This approach provides additional constraints on the kinetics of Δ47 reordering in dolomite during exhumation. Clumped isotope measurements were performed on 19 calcites and 15 early dolomites from the Permian, Jurassic, and Cretaceous periods from four locations in Oman spanning different burial regimes. The calcite and dolomite samples were collected from the rock matrix, based on the assumption that fine material was more susceptible to recrystallisation. Our results show that calcites and dolomites record different Δ47 values despite being subjected to the same thermal history. The maximum Δ47 temperature recorded in dolomites (181 ± 13 °C) corresponds to the oldest and most deeply buried Permian rock. This value is approximately 35 °C higher than those measured in the co-located and coeval calcite matrix (145 ± 14 °C). This discrepancy suggests that calcite and dolomite have different kinetic parameters. Our data confirm (1) that dolomite Δ47 values are more resistant to alteration during burial and exhumation than Δ47 calcite values, and (2) that dolomite has a higher Δ47 closing temperature than calcite during cooling. The presence of two mineral phases with distinct kinetic parameters in the same stratigraphic unit provides additional constraints on models of burial and uplift. In addition, mineralogical data coupled with Δ47 and burial depths suggest that the progressive development of dolomite cation ordering is driven by temperature elevation, as previously suggested.

The Central Luconia Miocene carbonate platform represents one of the largest regions of Liquified Natural Gas (LNG) production in the world. Although several studies have been conducted, the reservoir diagenesis of this gas-producing region remains poorly understood. To address this issue, a comprehensive and systematic diagenetic study has now been undertaken. Methodologies used included petrography, X-ray diffractometry (XRD), scanning electron microscopy (SEM), backscattered electron microscopy (BSEM), and cathodoluminescent microscopy (CL). Other technologies included elemental analysis using electron probe microanalyzer (EPMA), fluid inclusion microthermometry (FIM), and stable C, O, S, and Sr isotope analyses. The resulting datasets have been integrated so that the paleodiagenetic fluid flow, cementation history, and potential late-stage hightemperature hydrothermal corrosive fluids can be assessed with respect to the effect on reservoir potential.

This study applied clumped isotope analyses to investigate how different limestone components (larger skeletal grains and enclosing matrix) and cements may have varying degrees of susceptibility to recrystallization during progressive burial. The results also provide new constraints on the temperatures of recrystallization and cementation, the nature of the waters involved, the timing of the diagenetic events, and the effect of oil emplacement on inhibiting diagenetic processes. We used clumped isotope measurements from core samples in two giant oilfields, together with petrography and well-constrained thermal histories, to study the reactivity of different limestone fabrics and whether the displacement of pore water by oil affected the recrystallization processes. We recognize seafloor micritization, cementation, and recrystallization as distinct diagenetic processes. The results indicate that skeletal grains record …

A better understanding of constraining paleo fluid circulation along fractures in tectonically complex regions is essential from the scientific perspective and in exploiting sustainable geo-energies such as geothermal resources, but it remains a challenge. Jebel Madar in Oman as a salt dome is an ideal case study because of the complexity of its tectonic evolution and diagenetic process history. Here, we investigated the Cretaceous carbonate-encasing rock of salt domes and calcite-infilling fractures, making them an ideal case study for paleo fluid flow. The objectives were to test two different hypotheses: (1) to verify the previous study based on seismic data that the Hawasina Nappe had been priorly emplaced at the study location and was subsequently completely eroded, and (2) that the complex history of paleo-fluid flow existed in the fractures of the salt dome, and that this system was not yet fully constrained by previous studies, and also including accounting for the presence of any kinetic fractionation. To achieve our objectives, we applied carbonate clumped isotopes on different generations of veins as well as on the carbonate cement of the host rock itself to reconstruct paleo temperatures and the isotopic composition of the paleo-fluids. The carbonate clumped isotope temperatures indicate that calcite vein precipitation occurred between 48 and 171 °C. Assuming that our carbonate clumped isotopes data faithfully capture the recrystallization temperature of the limestone, the geothermal gradient during the Campanian can be estimated at 33.5 °C km−1, implying that the Hawasina Nappe must indeed have been present at the location. We also argue that the evolution of fluid flow in the study area comprises two distinct episodes of fluid circulation. The first episode led to the precipitation of high-temperature calcites followed by closed-system recrystallization during the local emplacement of the Hawasina Nappe. The second episode of fluid circulation occurred at lower temperatures with calcite members representing meteoric diagenetic fluids with evidence of the kinetic fractionation of the clumped isotopes signature in our samples. Our result demonstrates that the new paleotemperature data present new constraints of paleo fluid circulation along the fractures in a salt-domed setting and, importantly, confirms for the first time that the Hawasina Nappe was present at the site of Jebel Madar in the Late Cretaceous.

Previous studies have shown that microorganisms thrive in oligotrophic fracture systems, and metabolisms include consumption and production of methane. In the Laxemar, Götemar, and Forsmark areas of Sweden, ancient microbial activity has previously been demonstrated by large δ13CVPDB variability of carbonate vein infillings within granitic host rocks. Here, we apply carbonate clumped isotope thermometry to reconstruct the temperature of precipitation of the carbonate within these veins. The carbonate clumped isotope temperatures indicate that mineralization took place between 46°C and 108°C, in line with previously published fluid inclusion data (<50°C to 113°C). The new carbonate clumped isotope data more accurately narrows temperatures at the lower end of this range as fluid inclusions are not easily applicable below 80°C, a temperature regime of high importance for paleobiological reconstructions. Our results demonstrate that large volumes of biogenic carbonate cement were formed from low-temperature microbial processes in low-salinity water, succeeding calcite of deep brine origin. The known burial and thermal history of the region combined with our carbonate clumped isotope data place the microbial activity at the end of the Variscan orogeny and later events (e.g., Jurassic). Thus, carbonate clumped isotope thermometry reduces uncertainties in deep biosphere studies by providing more accurate temperature constraints in the low-temperature regime, the biogenic processes, and the origin of the diagenetic fluids.

Modern geological practices, in both industry and academia, rely largely on a legacy of observational data at a range of scales. However, widespread ambiguities in the petrographic description of rock facies reduce the reliability of descriptive data. Previous studies have demonstrated a great potential for the use of convolutional neural networks (CNNs) in the classification of facies from digital images; however, it remains to be determined which of the available CNN architectures performs best for a geological classification task. We evaluate the ability of top-performing CNNs to classify carbonate core images using transfer learning, systematically developing a performance comparison between these architectures on a complex geological dataset. Three datasets with orders of magnitude difference in data quantity (7000–104,000 samples) were created that contain images across seven classes from the modified …

The texture and morphology of igneous zircon indicates magmatic conditions during zircon crystallization and can be used to constrain provenance. Zircons from porphyry copper deposits are typically prismatic, euhedral, and strongly oscillatory zoned which may differentiate them from zircons associated with unmineralized igneous systems. Here, cathodoluminescence images of zircons from the Quellaveco porphyry copper district, Southern Peru, were collected to compare zircon textures between the premineralization Yarabamba Batholith and the Quellaveco porphyry copper deposit. Quellaveco porphyry zircons are prismatic, euhedral, and strongly oscillatory zoned, whereas the batholith zircons are subhedral-anhedral with weaker zoning. We adopt a deep convolutional neural network (CNN) approach to demonstrate that a CNN can classify Quellaveco porphyry zircons with high success. We trial several CNN architectures to classify zircon images: LeNet-5, AlexNet and VGG, including a transfer learning approach where we used the weights of a VGG model pretrained on the ImageNet data set. The VGG model with transfer learning is the most effective approach, with accuracy and receiver operating characteristic-area under curve (ROC-AUC) scores of 0.86 and 0.93, indicating that a Quellaveco porphyry zircon CL image can be ranked higher than a batholith zircon with 93% probability. Visualizing model layer outputs demonstrates that the CNN models can recognize crystal edges, zoning, and mineral inclusions. We trial implementing trained CNN models as unsupervised feature extractors, which can empirically quantify crystal textures and morphology. Therefore, deep learning provides a tool for the extraction of information from large, imaged-based petrographic data sets which can facilitate petrologic and provenance studies.

Clumped isotope values (Δ47) of carbonates forming in high pH conditions do not correspond to mineral precipitation temperatures due to certain effects including kinetic isotope fractionation and dissolved inorganic carbon (DIC) endmember mixing. Field-based archives of these carbonate environments are needed to evaluate and quantify these effects accurately. In this study, we measure the clumped isotope values of anthropogenic carbonates for the first time. Tufa layers were analyzed from samples precipitating in a high pH (>10) stream that drains a major slag heap in north east England. Δ47 values are 0.044‰–0.183‰ higher than expected equilibrium values. Non-linear distribution of clumped isotope data is diagnostic of DIC endmember mixing, rather than partial equilibration of DIC. Episodic dilution of hydroxide-rich stream waters by equilibrated rainfall surface runoff provides the mechanism by which mixing occurs. Δ47 values are ~0.010‰–0.145‰ higher than linear clumped isotope mixing profiles, suggesting that the majority of Δ47 increase results from a combination of endmember non-linear mixing effects and an atmosphere-hydroxide sourcing of DIC. The diagnostic trends and variation in clumped isotope values present in these results demonstrates the potential of anthropogenic carbonate systems as a useful archive for studying and quantifying kinetic effects in clumped isotopes.

Predicting the distribution and heterogeneity of marine Mesozoic organic-rich rocks is a challenging task that requires multi-disciplinary data integration supported by innovative numerical modelling. This study aims at investigating the factors controlling marine organic matter production, accumulation, and preservation along the eastern Arabian intrashelf basins. Such types of basins exhibit an enhanced lateral and vertical facies variability caused by the interplay between shallow and deeper water sedimentation. The work focuses on characterizing the Mid-Upper Jurassic Najmah Formation that presents source rock, reservoir, as well as seal characteristics along Kuwait. It comprises high maturity levels (>0.6% Ro) and TOC values ranging between 2 and 30%. Forward stratigraphic modelling that includes organic matter production, transport, and preservation (i.e., degradation and dilution) was utilized. Models …

Abundant fossil specimens of Scaphechinus mirabilis, now occurring mostly in temperate waters, have been found in the Toukoshan Formation (Pleistocene) in Miaoli County, Taiwan. Environmental changes leading to its extirpation (local extinction) have thus far been elusive. Here, we reconstruct past environmental and oceanic conditions off northwest Taiwan by analyzing clumped isotopes, as well as stable oxygen isotopes, of well-preserved fossil echinoid tests collected from the Toukoshan Formation. Radiocarbon dates suggest that these samples are from Marine Isotope Stage 3 (MIS 3). Paleotemperature estimates based on clumped isotopes indicate that fossil echinoids were living in oceanic conditions that range from 9 to 14 °C on average, comparable with the estimate derived for a modern sample from Mutsu Bay, Japan. Notably, this temperature range is ~ 10 °C colder than today’s conditions off …

The macroscopic movement of subsurface fluids involved in CO2 storage, groundwater, and petroleum engineering applications is controlled by interfacial forces in the pores of rocks. Recent advances in modelling these systems has arisen from approaches simulating flow through a digital representation of the complex pore structure. However, further progress is limited by difficulties in characterising the spatial distribution of the wetting state within the pore structure. In this work, we show how observations of the fluid coverage of mineral surfaces within the pores of rocks can be used as the basis for a quantitative 3D characterisation of heterogeneous wetting states throughout rock pore structures.

Atolls are faithful recorders helping us understand eustatic variations, the evolution of carbonate production through time, and changes in magmatic hotspots activity. Several early Cretaceous Mid-Pacific atolls were previously investigated through ocean drilling, but due to the low quality of vintage seismic data available, few spatial constraints exist on their stratigraphic evolution and large-scale diagenesis. Here, we present results from an integrated core-log-seismic study at Resolution Guyot and comparison with modern and ancient analogues. We identify six seismic-stratigraphic units: (1) platform initiation with aggradation and backstepping through the Hauterivian which ended by platform emersion; (2) reflooding of the platform with progradation and aggradation through the Barremian till the early-Aptian when ocean anoxic event 1a resulted in incipient drowning; (3) platform backstepping till the mid-Aptian when the platform shifted to progradation and aggradation till the mid-Albian; (4) platform emersion; (5) reflooding with backstepping ending at the latest-Albian by platform emersion; and (6) final drowning. The stratigraphic surfaces bounding these units are coeval with some of the Cretaceous eustatic events, which suggest an eustatic control on the evolution of this atoll and confirm that several previously reported sea-level variations in the early Cretaceous are driven by eustasy. Changes in subsidence and carbonate production rates and suspected later magmatism have also impacted the stratigraphic evolution. The suspected later magmatism could lead to environmental perturbations and potentially platform demise. Contrary to previous studies, we identify two emersion events during the mid- and late-Albian which resulted in intensive meteoric dissolution and karstification. The platform margin syndepositional fractures interacted with the subaerial exposure events by focusing the dissolution which formed vertically stacked flank-margin fracture-cave system. The study gives a unique insight into the interplay between eustasy, subsidence, and volcanic activity(ies) on long-term evolution of early Cretaceous shallow-marine carbonates. It also documents the impact and distribution of hypogenic and epigenic fluid-flow in atolls serving as an analogue for isolated carbonate platforms.

As one of the predominant diagenetic products in clastic rocks, calcite cements are typical fingerprints of cement-forming fluids and are key controls on reservoir quality. The Puig-reig anticline, in the south-eastern Pyrenees (Spain), exposes excellent outcrops of conglomerates, sandstones and claystones, which were deposited from a proximal to medial fluvial system and underwent folding, fracturing and cementation. This anticline constitutes an appropriate case study to investigate the origin and distribution of calcite cements during folding evolution and how they affect reservoir quality. Based on structural, petrographic and geochemical analyses (carbon, oxygen, strontium and clumped isotopes and elemental composition), five generations of calcite cements (‘Cc0’to ‘Cc4’) have been identified, filling intergranular porosity of host rocks, faults and four fracture sets (F1 to F4). Calcite cement Cc0 precipitated in intergranular porosity from meteoric fluids in the phreatic zone during the early diagenetic stage. During the most intense phase of thrusting and folding, Cc1 precipitated in intergranular porosity, faults and F1 to F4 fracture sets from hydrothermal fluids that migrated from deeper areas of the Pyrenean chain. During the late stage of fold growth, Cc2 precipitated in faults and their associated fractures in the anticline crest from hydrothermal fluids but at shallower burial depths than that of Cc1. Calcite cement Cc3 mainly precipitated in fractures with the same strike as F1 and F4 fracture sets in the north-western part of the anticline, from formation fluids that probably migrated through the frontal thrust of the south-eastern Pyrenees. During the …

We present a novel multiproxy data set (bulk and clumped isotopes on gastropod shells and variations in ostracod assemblages) of the Hampshire Basin (Southern-England) that sheds light on the connection between the North Sea and the Atlantic Ocean through the English Channel during the deposition of the Barton clay formation (latest Lutetian—Bartonian, middle Eocene; ∼41–40 Ma). During this time period, the English Channel operated as a gateway between the warmer Atlantic Ocean and the colder North Sea waters. High-latitude water mixing combined with the regional hydrological cycle and sea-level variations, may have contributed to mitigate the water temperatures in the Hampshire Basin, with an average recorded of ca. 25°C. In the uppermost part of the section the connection between the two water masses was limited or absent as evidenced by warmer (up to ca. 35°C) Atlantic Ocean temperatures in the Hampshire Basin.

Unconventional shale reservoirs have revolutionized the energy industry. However, the prediction of production based on reservoir geology characterization has largely focused on sweet spot definition rather than on over-arching production trends across multiple plays. This study uses machine learning (ML) techniques to analyze the relationships between well log data and production success within seven North American shale plays. Three ML algorithms were evaluated: stochastic gradient descent kernel trained support-vector machine (SGD-SVM), decision tree (DT), and random forest (RF) classifier. Accuracy of predictions using the SGD-SVM and DT classifiers did not exceed 55%. A fine-tuned RF classifier is the most successful method at predicting well success based on normalized initial production, with an accuracy of 97%. To achieve this result, the RF is trained on the following input features: average play thickness, pore pressure, TVD, and resource concentration. The main factors impacting performance of our algorithm when trying to predict success in unconventional plays are previous understanding of heterogeneities in individual formations, and consistency of data availability across multiple wells. Despite challenges, ML and the RF method in particular show promising applications in the unconventional petroleum industry as a means to streamline production and data collection.

The Cenozoic unconformity above the Late Cretaceous carbonates within the Maverick Basin is a unique feature of Texas (USA). Hypotheses accounting for the unconformity include (1) Cenozoic sediment bypass, and (2) ~6400 m of erosion during the Laramide orogeny. Both hypotheses have different implications for the burial history of the Eagle Ford Group (EFG) and for our understanding of the Laramide orogeny. We generated clumped isotope data and organic maturation proxies from the same location. Carbonate clumped isotope temperatures obtained (113 ± 9 °C) represent recrystallization during burial and a minimum estimate of the maximum burial temperature. This constraint is significantly warmer than apparent organic temperatures derived using an Arrhenius equation (40–55 °C). Organic matter transformation and carbonate recrystallization respond to temperature over different time scales and …

The field of clumped isotope paleothermometry is over a decade old, but the influence of precipitation rate on the fractionation of clumped isotopes between natural carbonates and their environmental solutions remains unclear. Here we apply two different proxies, carbonate clumped isotope paleothermometry and trace element analysis, to investigate whether or not precipitation rates play a major control on the fractionation of clumped isotopes. Twenty-one transect points from three calcite samples coming from veins along fractures (Jebel Madar, Oman) were investigated. The samples selected based on two different types of calcite cements were recognized: (i) Lower temperature macro-columnar calcite, and (ii) Higher temperature calcites within thin vein (“thin-vein calcites”). The Δ47 values vary between 0.513 ± 0.00‰ and 0.667 ± 0.01‰ corresponding to calculated clumped isotope temperatures of 29–59 …

The stable oxygen isotope composition (δ18O) of ammonites and belemnites is a common proxy for Jurassic and Cretaceous sea temperatures. The challenges and uncertainties associated with cephalopod δ18O and other proxy based paleotemperature reconstructions make cephalopods such as ammonites and belemnites a favourable target for carbonate clumped isotope paleothermometry. Our measurements of the clumped isotopic composition of modern cephalopods (Nautilus pompilius, Nautilus macromphalus, Nautilus belauensis and Sepia officianalis), however, confirm significant “vital effects” in clumped isotopic of cephalopod aragonite.

Strongly 13C-depleted authigenic carbonates (e.g., δ13CVPDB <−30‰; VPDB—Vienna Peedee belemnite) in nature are generally believed to form by sulfate-dependent anaerobic oxidation of methane (AOM). However, we demonstrate using geochemical data and thermodynamic calculation that such calcites are most likely derived from biogenic oxidation of methane in sulfate-poor, nonmarine environments during early diagenesis, as observed in the Triassic sandy conglomerates from the Junggar Basin, northwestern China. This process operated through preferential oxidation of 13C-depleted methane by Mn oxides in closed conditions, producing calcites with higher Mn contents and δ13C values in association with more 13C-enriched residual methane as a result of kinetic isotope fractionation. Thus, the Mn-rich and 13C-depleted carbonates are proposed as tracers of Mn-dependent AOM, which should …

Increased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth‐system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ47) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ47 and Δ47 values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference …

The potential for carbonate clumped isotope thermometry to independently constrain both the formation temperature of carbonate minerals and fluid oxygen isotope composition allows insight into long‐standing questions in the Earth sciences, but remaining discrepancies between calibration schemes hamper interpretation of temperature measurements. To address discrepancies between calibrations, we designed and analyzed a sample suite (41 total samples) with broad applicability across the geosciences, with an exceptionally wide range of formation temperatures, precipitation methods, and mineralogies. We see no statistically significant offset between sample types, although the comparison of calcite and dolomite remains inconclusive. When data are reduced identically, the regression defined by this study is nearly identical to that defined by four previous calibration studies that used carbonate‐based …

Predicting reservoir quality and pressure barriers is a challenging task in carbonate systems. In this paper, we present new model results from the Lower Carboniferous Serpukhovian carbonates in the Karachaganak Field (Northern Kazakhstan), which is characterized by complex facies architectures and reservoir compartmentalization. The Serpukhovian sequence at Karachaganak is poorly imaged by seismic due to the presence of thick Permian salt canopies. The carbonate sequence comprises two carbonate build-ups: a larger Main build-up (MBU) in the eastern portion of the field, and a smaller isolated Western build-up (WBU). We used diffusion-based DionisosFlow forward stratigraphic modeling (FSM) coupled with a CougarFlow sensitivity analysis workflow to (1) review sub-salt seismic horizon picks based on process-modeling constraints, (2) understand the regional controls on the stratigraphic stacking …

The field of clumped isotope paleothermometry is over a decade old, but the influence of precipitation rate on the fractionation of clumped isotopes between natural carbonates and their environmental solutions remains unclear. Here we apply two different proxies, carbonate clumped isotope paleothermometry and trace element analysis, to investigate whether or not precipitation rates play a major control on the fractionation of clumped isotopes. Twenty-one transect points from three calcite samples coming from veins along fractures (Jebel Madar, Oman) were investigated. The samples selected based on two different types of calcite cements were recognized: (i) Lower temperature macro-columnar calcite, and (ii) Higher temperature calcites within thin vein (“thin-vein calcites”). The Δ47 values vary between 0.513 ± 0.00‰ and 0.667 ± 0.01‰ corresponding to calculated clumped isotope temperatures of 29–59 …

Calcite veins precipitated in the Estamariu thrust during two tectonic events are studied in order to (i) decipher the temporal and spatial relationships between deformation and fluid migration in a long-lived thrust and (ii) determine the influence of basement rocks on the fluid chemistry during deformation. Structural and petrological observations constrain the relative timing of fluid migration and vein formation, whilst geochemical analyses (δ13C, δ18O, 87Sr∕86Sr, clumped isotope thermometry, and elemental composition) applied to the related calcite cements and host rocks indicate the fluid origin, pathways, and extent of fluid–rock interaction. The first tectonic event, recorded by calcite cements Cc1a and Cc2, is attributed to the Alpine reactivation of the Estamariu thrust. Analytical data indicate that these cements precipitated from heated meteoric fluids (temperatures in the range of 50 to 100 ∘C) that had interacted with basement rocks (87Sr∕86Sr > 0.71) before upflowing through the thrust zone. The second tectonic event, attributed to the Neogene extension, is characterized by the reactivation of the Estamariu thrust and the formation of normal faults and shear fractures sealed by calcite cements Cc3, Cc4, and Cc5. Analytical data indicate that cements Cc3 and Cc4 precipitated from hydrothermal fluids (temperatures between 130 and 210 ∘C and between 100 and 170 ∘C, respectively) that had interacted with basement rocks (87Sr∕86Sr > 0.71) and been expelled through fault zones during deformation. In contrast, cement Cc5 probably precipitated from meteoric waters that likely percolated from the surface through small shear …

We present a multidisciplinary study to decipher the controls of deformation on fluid flow regime in fold and thrust belts using the Lower Pedraforca thrust sheet in the SE Pyrenees as an example. We integrate field-based and petrographic observations and geochemical and geochronological data to differentiate seven types of fractures, eight types of calcite cement (Cc1 to Cc8) and two sets of stylolites during the deformation stretching the studied thrust sheet. During syn-sedimentary hydroplastic normal faulting affecting poorly consolidated Upper Cretaceous and Eocene syn-orogenic sediments, calcite cement did not precipitate. During burial, bed-parallel stylolites formed and Cc1 and Cc2 precipitated from formation waters in a closed palaeohydrological system. During the layer-parallel shortening, Cc3 precipitated from formation waters (~+5.4‰ VSMOW) with 87Sr/86Sr ratios of 0.707922 and at ~70 °C. Cc4 …

Petrographic and geochemical analyses (_18O, _13C, 87Sr/86Sr, clumped isotopes, and elemental composition) coupled with field structural data of synkinematic calcite veins, fault rocks, and host rocks are used to reconstruct the episodic evolution of an outstanding exposed thrust zone in the Southern Pyrenees and to evaluate the fault behavior as a conduit or barrier to fluid migration. The selected thrust displaces the steeply dipping southern limb of the Sant Corneli-Bóixols anticline, juxtaposing a Cenomanian-Turonian carbonate unit against a Coniacian carbonate sequence. Successive deformation events are recorded by distinct fracture systems and related calcite veins, highlighting (i) an episodic evolution of the thrust zone, resulting from an upward migration of the fault tip (process zone development) before growth of the fault (thrust slip plane propagation), and (ii) compartmentalization of the thrust fault zone, leading to different structural and fluid flow histories in the footwall and hanging wall. Fractures within the footwall comprise three systematically oriented fracture sets (F1, F2, and F3), each sealed by a separate generation calcite cement, and a randomly oriented fracture system (mosaic to chaotic breccia), cemented by the same cements as fracture sets F1 and F2. The formation of fractures F1 and F2 and the mosaic to chaotic breccia is consistent with dilatant fracturing within the process zone (around the fault tip) during initial fault growth, whereas the formation of the latest fracture system points to hybrid shear-dilational failure during propagation of the fault. The continuous formation of different fracture systems and related calcite cementation phases evidences that the structural permeability in the footwall was transient and that the fluid pathways and regime evolved due to successive events of fracture opening and calcite cementation. Clumped isotopes evidence a progressive increase in precipitation temperatures from around 50°C to 117°C approximately, interpreted as burial increase linked to thrust sheet emplacement. During this period, the source of fluid changed from meteoric fluids to evolved meteoric fluids due to the water-rock interaction at increasing depths and temperatures. Contrary to the footwall, within the hanging wall, only randomly oriented fractures are recognized and the resulting crackle proto-breccia is sealed by a later and different calcite cement, which is also observed in the main fault plane and in the fault core. This cement precipitated from formation fluids, at around 95°C, that circulated along the fault core and in the hanging wall block, again supporting the interpretation of compartmentalization of the thrust structure. The integration of these data reveals that the studied thrust fault acted as a transverse barrier, dividing the thrust zone into two separate fluid compartments, and a longitudinal drain for migration of fluids. This study also highlights the similarity in deformation processes and mechanisms linked to the evolution of fault zones in compressional and extensional regimes involving carbonate rocks.

We report the results of a multiproxy study that combines structural analysis of a fracture–stylolite network and isotopic characterization of calcite vein cements and/or fault coating. Together with new paleopiezometric and radiometric constraints on burial evolution and deformation timing, these results provide a first-order picture of the regional fluid systems and pathways that were present during the main stages of contraction in the Tuscan Nappe and Umbria–Marche Apennine Ridge (northern Apennines). We reconstruct four steps of deformation at the scale of the belt: burial-related stylolitization, Apenninic-related layer-parallel shortening with a contraction trending NE–SW, local extension related to folding, and late-stage fold tightening under a contraction still striking NE–SW. We combine the paleopiezometric inversion of the roughness of sedimentary stylolites – that constrains the range of burial depth of strata prior to layer-parallel shortening – with burial models and U–Pb absolute dating of fault coatings in order to determine the timing of development of mesostructures. In the western part of the ridge, layer-parallel shortening started in Langhian time (∼15 Ma), and then folding started at Tortonian time (∼8 Ma); late-stage fold tightening started by the early Pliocene (∼5 Ma) and likely lasted until recent/modern extension occurred (∼3 Ma onward). The textural and geochemical (δ18O, δ13C, Δ47CO2 and 87Sr∕86Sr) study of calcite vein cements and fault coatings reveals that most of the fluids involved in the belt during deformation either are local or flowed laterally from the same reservoir. However, the western edge of the ridge …

Fracture-filling rose-like clusters of bladed calcite crystals are found in the northern sector of the Cadí thrust sheet (SE Pyrenees). This unusual calcite crystal morphology has been characterized by using optical and electron microscope, X-ray diffraction, Raman spectroscopy, δ18O, δ13C, 87Sr/86Sr, clumped isotopes, and major and rare earth elements + yttrium (REEs + Y) analysis. Petrographic observations and powder X-ray diffraction measurements indicate that these bladed crystals are mainly made of massive rhombic crystals with the conventional (104) faces, as well as of possibly younger, less abundant, and smaller laminar crystals displaying (108) and/or (1¯08) rhombic faces. Raman analysis of liquid fluid inclusions indicates the presence of aromatic hydrocarbons and occasionally alkanes. Clumped isotopes thermometry reflects that bladed calcite precipitated from meteoric fluids at ~60–65 °C. The 87Sr/86Sr ratios and major elements and REEs content of calcite indicate that these fluids interacted with Eocene marine carbonates. The presence of younger ‘nailhead’ calcite indicates later migration of shallow fresh groundwater. The results reveal that rose-like calcite clusters precipitated, at least in the studied area, due to a CO2 release by boiling of meteoric waters that mixed with benzene and aromatic hydrocarbons. This mixing decreased the boiling temperature at ~60–65 °C. The results also suggest that the high Sr content in calcite, and probably the presence of proteins within hydrocarbons trapped in fluid inclusions, controlled the precipitation of bladed crystals with (104) rhombohedral faces.

The wetting state is an important control on flow in subsurface multi‐fluid phase systems, for example, carbon storage and oil production. Advances in X‐ray imaging allow us to characterize the wetting state using imagery of fluid arrangement within the pores of rocks. We derived a model from equilibrium thermodynamics relating fluid coverage of rock surfaces to wettability and fluid saturation. The model reproduces the behavior measured in a water‐wet, nearly all‐quartz, Bentheimer sandstone imaged during steady‐state imbibition. A shift in fluid surface coverage is observed when the rock is altered to a new wetting state with crude oil. In two multimineralogical (Berea) samples, one water‐wet and the other altered with crude oil, the analysis of fluid surface coverage after imbibition revealed mineral specific wetting preferences only in the altered system. Clays and calcite preferentially alter to an oil‐wet state …

For clumped isotope analysis (Δ47), hydrocarbon and organic molecules present an important contaminant that cannot always be removed by CO2 purification through a Porapak‐Q trap. Low‐temperature oxygen plasma ashing (OPA) is a quick and easy approach for treatment; however, the impact of this treatment on the original carbonate clumped isotope values has never been fully studied.

Peritidal carbonates of the Csukma Formation (Csukma Dolomite Member) in the Villány Hills, SW Hungary, were investigated to determine the nature of the dolomitization and recrystallization processes that affected these rocks during their complex tectonic evolution, and to evaluate if clumped isotope data preserved signals from the original dolomitization event or are indicative of the later recrystallization processes. Sedimentary and petrographic features, as well as geochemical characteristics integrated with the tectonic evolution of the area indicate that dolomitization likely occurred penecontemporaneously via geothermal convection of normal-to-slightly modified seawater in a near-surface to shallow burial setting. This was followed by partial recrystallization of the dolomites in an intermediate burial setting with low water-to-rock ratios. Results of this study suggest that the clumped isotope temperatures of …

A Pluri-Gaussian method is developed for facies variables in three dimensions to model vertical cyclicity related to facies ordering and rhythmicity. Cyclicity is generally characterised by shallowing-upward or deepening-upward sequences and rhythmicity by the repetition of facies at constant intervals along sequences. Both of these aspects are commonly observed in shallow-marine carbonate successions, especially in the vertical direction. A grid-free spectral simulation approach is developed, with a separable covariance allowing a dampened hole-effect to capture rhythmicity in the vertical direction and a different covariance in the lateral plane along strata, as in space-time models. In addition, facies ordering is created by using a spatial shift between two latent Gaussian functions in the Pluri-Gaussian approach. Rapid conditioning to data is performed via Gibbs sampling and kriging using the screening …

Chalk is usually thought to be a homogeneous sediment with a relatively simple early diagenetic history. Here, clumped isotope analyses of samples from a core of Campanian Maastrichtian chalk are presented, indicating that material smaller than 5 µm has a different origin than the coccolith‐dominated coarser fraction. The smallest size fraction (1 to 5 µm) of chalk is dominated by calcite particles without a distinct morphology (micarbs). Clumped isotope data of the micarbs reveals formation temperatures of 14 to 18°C which is 8 to 10°C colder than those derived from coeval coccoliths. The micarbs are interpreted as the product of calcite neoformation, precipitated in the uppermost part of the sediment column (100 metres below sea floor) and linked to early dissolution of aragonitic fossils. These findings prove that early cements can be an abundant component in chalk, and thus challenge the common notion that …

X-ray microcomputed tomography (X-ray μ-CT) is a rapidly advancing technology that has been successfully employed to study flow phenomena in porous media. It offers an alternative approach to core scale experiments for the estimation of traditional petrophysical properties such as porosity and single-phase flow permeability. It can also be used to investigate properties that control multiphase flow such as rock wettability or mineral topology. In most applications, analyses are performed on segmented images obtained employing a specific processing pipeline on the greyscale images. The workflow leading to a segmented image is not straightforward or unique and, for most of the properties of interest, a ground truth is not available. For this reason, it is crucial to understand how image processing choices control properties estimation. In this work, we assess the sensitivity of porosity, permeability, specific surface …

U-Pb dating using laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), δ13C, δ18O, clumped isotopes and 87Sr/86Sr analysis, and electron microprobe have been applied to fracture-filling calcites and host carbonates from the Lower Pedraforca thrust sheet, in the SE Pyrenees. These data are used to determine the type and origin of migrating fluids, the evolution of the palaeohydrological system and timing of fracturing during the emplacement of this thrust sheet, as described in the article “From hydroplastic to brittle deformation: controls on fluid flow in fold and thrust belts. Insights from the Lower Pedraforca thrust sheet (SE Pyrenees)” – Marine and Petroleum Geology (2020). The integration of these data is also used to compare the fluid flow evolution of the Southern Pyrenees with that of other orogens worldwide and to generate a fluid flow model in fold and thrust belts. At a more local …

The Cretaceous Earth, with its greenhouse climate and absence of major ice caps in the polar regions, represents an extreme scenario for modeling future warming. Despite considerable efforts, we are just at the verge of fully understanding the conditions of a warm Earth, and better, more extensive proxy evidence is needed to solve existing discrepancies between the applied temperature proxies. In particular, the Maastrichtian temperature trends are controversial, since data indicate cooling in the South Atlantic and contemporary warming of the North Atlantic. The “heat piracy” hypothesis involves northward heat transport to midlatitudes via oceanic currents and is used to explain the contrasting polar cooling/warming patterns. Here, we present Δ47 and δ18O data from nine coccolith-enriched samples from a shallow core taken from the Danish Basin (Chalk Sea), representing a key location at the northern …

The clumped isotopic composition of carbonate‐derived CO2 (denoted Δ47) is a function of carbonate formation temperature and in natural samples can act as a recorder of paleoclimate, burial, or diagenetic conditions. The absolute abundance of heavy isotopes in the universal standards VPDB and VSMOW (defined by four parameters: R13VPDB, R17VSMOW, R18VSMOW, and λ) impact calculated Δ47 values. Here, we investigate whether use of updated and more accurate values for these parameters can remove observed interlaboratory differences in the measured T‐Δ47 relationship. Using the updated parameters, we reprocess 14 published calibration data sets measured in 11 different laboratories, representing many mineralogies, bulk compositions, sample types, reaction temperatures, and sample preparation and analysis methods. Exploiting this large composite data set (n = 1,253 sample replicates …

The faunal expression of the Paleocene-Eocene Thermal Maximum (PETM) is well documented in deep-sea sediments. However, few studies have examined continental margin sections, especially active margins. The Moreno and Lodo formations, Central California, were deposited along the eastern margin of a north-south trending forearc basin on the convergent margin of California during the Cretaceous through Late Cenozoic. The Tumey Gulch section which includes the Moreno and Lodo formations, is 80 m thick, contains the Paleocene-Eocene boundary and Carbon Isotope Excursion (CIE), and was deposited at abyssal to lower bathyal depths along an active continental margin. Benthic foraminiferal assemblages from this section record faunal changes related to the PETM and a younger hyperthermal, ETM3 which include a disruption of the gradual shallowing of water depths and fluctuation of the CCD …

Much debate exists on the extent to which early dolomites recrystallize and preserve the signature of their primary diagenetic setting. Here, we combine clumped isotopes thermometry with X-ray diffraction and thin section petrography to study dolomite recrystallization under shallow burial (<1 km) conditions. We analysed 26 dolomite samples from two Miocene carbonate platforms on the Marion Plateau, NE Australia. Marion Plateau dolomites provide an ideal case study to examine the effects of recrystallization because of the relative simplicity of the geological setting, with simple subsidence, and several episodes of early dolomitization by normal sea water. Results show that Marion Plateau dolomites are very rich in calcium and their formation temperature inferred from clumped isotopes T(Δ47dol) ranges between 12 and 35 °C. The apparent fluid composition (δ18Ow(app)) falls in the range of sea water …

Shallow marine to peritidal carbonates of the Triassic Csukma Formation in the Mecsek Mts. of SW Hungary are made up of dolomites, limestones and dolomitic limestones that show evidence of a complex diagenetic history. Integration of petrographic, conventional stable oxygen and carbon isotope, clumped isotope, and strontium isotope data with the paleogeography, paleoclimate, and burial history of the region revealed four major diagenetic stages. Stage 1: The peritidal carbonates were dolomitized penecontemporaneously during the Middle Triassic by refluxing evaporatively concentrated brines. Stage 2: Increasing burial during the Late Triassic–Jurassic resulted in recrystallization of the Kán Dolomite Member in an intermediate burial setting. Stage 3: During the Early Cretaceous seawater was drawn down and circulated through rift-related faults, causing renewed recrystallization of the Kán Dolomite …

Structural, petrological and geochemical (δ13C, δ18O, clumped isotopes, 87Sr/86Sr and ICP-MS) analyses of fracture-related calcite cements and host rocks are used to establish a fluid-flow evolution model for the frontal part of the Bóixols thrust sheet (Southern Pyrenees). Five fracture events associated with the growth of the thrust-related Bóixols anticline and Coll de Nargó syncline during the Alpine orogeny are distinguished. These fractures were cemented with four generations of calcite cements, revealing that such structures allowed the migration of different marine and meteoric fluids through time. During the early contraction stage, Lower Cretaceous seawater circulated and precipitated calcite cement Cc1, whereas during the main folding stage, the system opened to meteoric waters, which mixed with the connate seawater and precipitated calcite cement Cc2. Afterwards, during the post-folding stages, connate evaporated marine fluids circulated through newly formed NW-SE and NE-SW conjugate fractures and later through strike-slip faults and precipitated calcite cements Cc3 and Cc4. The overall paragenetic sequence reveals the progressive dewatering of Cretaceous marine host sediments during progressive burial, deformation and fold tightening and the input of meteoric waters only during the main folding stage. This study illustrates the changes of fracture systems and the associated fluid-flow regimes during the evolution of fault-associated folds during orogenic growth.

Carbonate clumped isotope thermometry is based on the thermodynamically dependent relative abundance of 13Csingle bond18O bonds (quantified as Δ47) within the carbonate crystal lattice. The clumping of 13Csingle bond18O in carbonates is based on a self-reaction of isotope exchange that occurs rapidly at near neutral pH. Similar Δ47-temperature relationships between biogenic and inorganically precipitated carbonate in initial studies led to the promise of a proxy free of biologically driven disequilibrium effects, commonly referred to as “vital effects”. This has been largely the case for most organisms investigated. Biologically mediated disequilibrium precipitation has however been reported in corals and cephalopods and brachiopod molluscs. Echinoderms, despite their complex inter-cellular bio-mineralization strategy, large inter-skeletal fractionation of δ18O, δ13C and rapid calcite precipitation have …

The complex geometry of carbonate systems is influenced by a multitude of physical as well as biological processes. The Lower Cretaceous carbonates of Northern Oman are characterised by a variability of regional-scale geometries with expected vertical and lateral facies variations. The main environmental and tectonic controls acting on the depositional processes of the Lower Cretaceous ramps and platforms through space and geological time (in 4 dimensions) are only partially understood. In this study, we use a 4D DionisosFlow Forward Stratigraphic Modelling (FSM) approach to explore the role of: (i) eustasy; (ii) subsidence; (iii) initial paleobathymetry, and (iv) wave energy, to generate carbonate stacking patterns and heterogeneities. Carbonate production was maintained constant through deposition. Multi-disciplinary and multi-scale datasets were used (i.e. seismic, well and field data) to constrain the FSM …

The eastern sector of the south Pyrenean fold and thrust belt developed during the Alpine compression and affected Upper Cretaceous to lower Oligocene foreland basin deposits. In this study, we determine the changes in fluid regime and fluid composition during the growth of this fold and thrust belt, integrating petrographic and geochemical data obtained from fracture-filling cements.

Dolomitization is commonly associated with crustal‐scale faults, but tectonic rejuvenation, diagenetic overprinting and a fluid and Mg mass‐imbalance often makes it difficult to determine the dolomitization mechanism. This study considers differential dolomitization of the Eocene Thebes Formation on the Hammam Faraun Fault block, Gulf of Suez, which has undergone a simple history of burial and exhumation as a result of rifting. Stratabound dolostone bodies occur selectively within remobilized sediments (debrites and turbidites) in the lower Thebes Formation and extend into the footwall of, and for up to 2 km away from, the Hammam Faraun Fault. They are offset by the north–south trending Gebel fault, which was active during the earliest phases of rifting, suggesting that dolomitization occurred between rift initiation (26 Ma) and rift climax (15 Ma). Geochemical data suggest that dolomitization occurred from …

Field work is an important and valued part of geoscience research, but can also serve as a source of stress. Careful planning can help support the mental health and wellness of participants at all career stages.

The Chingshui geothermal field once hosted the first geothermal power plant in Taiwan from 1981 to 1993. After a long period of inactivity, this field is attracting renewed interest to meet the need for clean energy. A 213-m length of cores (IC-21) with continuous recovery, the longest in the Chingshui geothermal field, was recovered from 600 m to 813 m below the surface in 2010. Three types of calcite crystal morphologies have been identified in the veins of the cores of well IC-21: bladed, rhombic and massive crystals. Bladed calcites are generated via degassing under boiling conditions with a precipitation temperature of ∼165 °C and calculated δ18O value of −6.8‰ to −10.2‰ VSMOW for the thermal water. Rhombic calcites grow in low concentration Ca2+ and CO32− meteoric fluids and precipitate at approximately ∼180 °C. Finally, massive calcites are characterized by co-precipitation with quartz in the …

The clumped isotope composition of CaCO3 (Δ47) is a geochemical proxy that can provide mineral formation temperatures and, together with measured carbonate δ18O, inferred fluid δ18O values. Under natural conditions, carbonates form within a relatively wide pH range and varying growth rates which are typically not reflected in laboratory‐based calibrations (mostly ∼pH 8, moderate growth rates). A pH and growth‐rate dependence is known for oxygen isotopes and was also postulated for clumped isotopes. Theoretical predictions suggest that Δ47 values could lie between the carbonate equilibrium value and the value inherited from the dissolved inorganic carbon (predicted offset: +0.04‰ pH &lt; 4 and −0.025‰ at high pH &gt; 12). Here we test whether pH (in addition to temperature) is recorded in the carbonate clumped isotope composition using modern calcites from natural travertine‐forming streams and …

A Pluri-Gaussian method is developed for facies variables in three dimensions to model vertical cyclicity related to facies ordering and rhythmicity. Cyclicity is generally characterised by shallowing-upward or deepening-upward sequences and rhythmicity by the repetition of facies at constant intervals along sequences. Both of these aspects are commonly observed in shallow-marine carbonate successions, especially in the vertical direction. A grid-free spectral simulation approach is developed, with a separable covariance allowing a dampened hole-effect to capture rhythmicity in the vertical direction and a different covariance in the lateral plane along strata, as in space-time models. In addition, facies ordering is created by using a spatial shift between two latent Gaussian functions in the Pluri-Gaussian approach. Rapid conditioning to data is performed via Gibbs sampling and kriging using the screening properties of separable covariances. The resulting facies transiograms can show complex patterns of cyclicity and rhythmicity. Finally, a three dimensional case study of shallow-marine carbonate deposits at outcrop shows the applicability of the modelling method.

Recent research has shown hyperspectral imaging to be a powerful tool to distinguish carbonate phases with slight compositional differences on quarry cliff faces. The traditional remote sensing set-up uses an optimal short distance between the hyperspectral camera mounted on a tripod and a quarry wall characterized by a planar, mostly unweathered surface. Here we present results of a modified workflow geared to the application of ground-based hyperspectral imaging of rough and weathered cliff faces in order to map large scale dolomite bodies from a distance of up to several kilometres. The goal of the study was to determine unique spectral properties of fracture-controlled dolomite bodies in order to be able to distinguish them from a dolomitic host rock. In addition, the impact of weathering on carbonate phases and thus, the modification of the spectral signature between altered and unaltered carbonates is …

The late Miocene‐early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here we present the first continuous late Miocene‐early Pliocene (8.0–4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0–3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest that mean sea surface temperatures (SSTs) are ~27.8 ± 1.1°C (1σ) between 6.4 and 5.5 Ma. The planktic foraminiferal δ18O record implies a 2°C cooling between 7.2 and 6.1 Ma and an up to 3°C warming between 6.1 and 4.4 Ma, consistent with observed tropical alkenone paleo …

This study presents a new approach to geobarometry by combining fluid inclusion and clumped isotope (Δ47) thermometry on carbonate minerals. The offset between homogenisation temperatures of primary fluid inclusions with known composition and Δ47 temperatures of the host mineral allows a direct estimation of the fluid pressure at the time of carbonate crystallisation. This new approach is illustrated via hydrothermal dolomite samples from the Variscan foreland fold‐and‐thrust belt in northern Spain. Clumped isotope analyses yield crystallisation temperatures (107–168°C) which are higher than homogenisation temperatures in corresponding samples (95–145°C). The calculated pressure values suggest that dolomitizing fluids were overpressured during formation of zebra dolomite textures, whereas lower pressures are obtained for dolomite cement from breccia textures. This new approach to …

Constraining basin thermal history is a key part of reservoir characterization in carbonate rocks. Conventional palaeothermometric approaches cannot always be used: fluid inclusions may be reset or not present, while δ18O palaeothermometry requires an assumption on the parent fluid composition. The clumped isotope palaeothermometer, however, is a promising technique for constraining the thermal history of basins. In this study, we test if clumped isotopes record temperatures of recrystallization in deeply-buried dolomitic reservoirs, through comparison with fluid-inclusion data. The studied reservoir is the Cretaceous Pinda Formation, offshore Angola, a deeply-buried dolomitized sedimentary carbonate hydrocarbon reservoir. It provides an ideal test case as samples from industry wells are available over a relatively wide burial depth range of c. 2000–4000 m below seafloor (mbsf) and the constituent …

The Chingshui geothermal field, a moderate-temperature and water-dominated hydrothermal system, was the site of the first geothermal power plant in Taiwan. Many geological, geophysical and geochemical studies using more than 21 drilled wells have been performed since the 1960s. However, there are still controversies regarding the heat and fluid sources due to the tectonically complicated geological setting. To clarify the heat and fluid sources, we analyzed clumped isotopes with carbon and oxygen isotopic compositions of calcite scaling in geothermal wells and veins on outcrops and calculated the δ18O values of the source fluids. Two populations of δ18O values were calculated: −5.8 ± 0.8‰ VSMOW from scaling in the well and −1.0 ± 1.6‰ to 10.0 ± 1.3‰ VSMOW from outcropping calcite veins, indicative of meteoric and magmatic fluid sources, respectively. Meanwhile, two hydrothermal reservoirs at …

Accurate age control of the late Tortonian to early Messinian (8.3–6.0 Ma) is essential to ascertain the origin of benthic foraminiferal O trends and the late Miocene carbon isotope shift (LMCIS), and to examine temporal relationships between the deep-sea, terrasphere and cryosphere. The current Tortonian–Messinian Geological Time Scale (GTS2012) is based on astronomically calibrated Mediterranean sections; however, no comparable non-Mediterranean stratigraphies exist for 8–6 Ma suitable for testing the GTS2012. Here, we present the first high-resolution, astronomically tuned benthic stable isotope stratigraphy (1.5 kyr resolution) and magnetostratigraphy from a single deep-sea location (IODP Site U1337, equatorial Pacific Ocean), which provides unprecedented insight into climate evolution from 8.3–6.0 Ma. The astronomically calibrated magnetostratigraphy provides robust ages, which differ by 2–50 kyr relative to the GTS2012 for polarity Chrons C3An.1n to C4r.1r, and eliminates the exceptionally high South Atlantic spreading rates based on the GTS2012 during Chron C3Bn. We show that the LMCIS was globally synchronous within 2 kyr, and provide astronomically calibrated ages anchored to the GPTS for its onset (7.537 Ma; 50% from base Chron C4n.1n) and termination (6.727 Ma; 11% from base Chron C3An.2n), confirming that the terrestrial C3:C4 shift could not have driven the LMCIS. The benthic records show that the transition into the 41-kyr world, when obliquity strongly influenced climate variability, already occurred at 7.7 Ma and further strengthened at 6.4 Ma. Previously unseen, distinctive, asymmetric saw-tooth patterns in benthic O imply that high-latitude forcing played an important role in late Miocene climate dynamics from 7.7–6.9 Ma. This new integrated deep-sea stratigraphy from Site U1337 can act as a new stable isotope and magnetic polarity reference section for the 8.3–6.0 Ma interval.

Outcrop analogues of the Late Jurassic lower Arab‐D reservoir zone in Saudi Arabia expose a succession of fining‐upward cycles deposited on a distal middle‐ramp to outer‐ramp setting. These cycles are interrupted by erosional scours that incise up to 1·8 m into underlying deposits and are infilled with intraclasts up to boulder size (1 m diameter). Scours of similar size and infill are not commonly observed on low‐angle carbonate ramps. Outcrops have been used to characterize and quantify facies‐body geometries and spatial relationships. The coarse grain size of scour‐fills indicates scouring and boulder transport by debris or hyperconcentrated density flows strengthened by offshore‐directed currents. Longitudinal and lateral flow transformation is invoked to produce the ‘pit and wing’ geometry of the scours. Scour pits and wings erode up to 1·8 m and 0·7 m deep, respectively, and are on average 50 m wide …

Carbonate clumped isotope thermometry examines the thermodynamic preference of 13C–18O bonds to form within the carbonate crystal lattice. The 13C18O16O isotopologue in analyte CO2 has a natural abundance of 44.4 ppm necessitating stringent purification procedures to remove contaminant molecules that may produce significant isobaric effects within range of the mass 47 isotopologue. Strict purifications of analyte CO2 are thus required as well as reliable contamination indicators.

The Triassic-Jurassic boundary is marked by one of the ‘big five’ mass extinctions of the Phanerozoic. This boundary event was accompanied by several carbon cycle perturbations, potentially induced by the opening of the Central Atlantic and associated volcanism, and accompanied by an ocean acidification event. Continuous carbonate successions covering this interval of environmental change are however rare. Here data from a shallow-marine equatorial mixed carbonate-siliciclastic succession is presented, that was studied on a regional scale. Four sections that are 48 km apart were examined on the Musandam Peninsula (United Arab Emirates and Sultanate of Oman). The system was analysed for its sedimentology, vertical and lateral facies changes, and stable carbon and oxygen isotopes. Strontium isotope analysis was used to determine the position of the Triassic-Jurassic boundary horizon. The studied …

An approach to model spatial asymmetrical relations between indicators is presented in a pluri-Gaussian framework. The underlying gaussian random functions are modelled using the linear model of co-regionalization, and a spatial shift is applied to them. Analytical relationships between the two underlying gaussian variograms and the indicator covariances are developed for a truncation rule with three facies and cut-off at 0. The application of this truncation rule demonstrates that the spatial shift on the underlying gaussian functions produces asymmetries in the modelled 1D facies sequences. For a general truncation rule, the indicator covariances can be computed numerically, and a sensitivity study shows that the spatial shift and the correlation coefficient between the gaussian functions provide flexibility to model the asymmetry between facies. Finally, a case study is presented of a Triassic vertical …

ATR-FTIR (attenuated total reflectance Fourier transform infrared) spectroscopy can be used as a rapid and economical tool for qualitative identification of carbonates, calcium sulphates, oxides and silicates, as well as quantitatively estimating the concentration of minerals. Over 200 powdered samples with known concentrations of two, three, four and five phase mixtures were made, then a suite of calibration curves were derived that can be used to quantify the minerals. The calibration curves in this study have an R2 that range from 0.93–0.99, a RMSE (root mean square error) of 1-5 wt.% and a maximum error of 3–10 wt.%. The calibration curves were used on 35 geological samples that have previously been studied using XRD (X-ray diffraction). The identification of the minerals using ATR-FTIR is comparable with XRD and the quantitative results have a RMSD (root mean square deviation) of 14% and 12% for …

Magnesium carbonate minerals produced by reaction of H2O–CO2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes, including (1) deposition of ore-grade, massive-vein cryptocrystalline magnesite; (2) formation of hydrous magnesium carbonates in weathering environments; and (3) metamorphic carbonate alteration of ultramafic rocks. However, the application of traditional geochemical and isotopic methods to infer temperatures of mineralization, the nature of mineralizing fluids, and the mechanisms controlling the transformation of dissolved CO2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved. Clumped-isotope compositions of magnesium carbonates provide a means to determine primary mineralization or (re)equilibration temperature, which permits the …

The Puig-reig anticline, located in the South Pyrenean fold and thrust belt, developed during the Alpine compression, which affected the upper Eocene-lower Oligocene sediments of the Solsona and Berga Formations. In this study, we highlight the controls on formation of joints and reverse, strike-slip and normal faults developed in the crest domain of the Puig-reig anticline as well as the relationships between fluids and these fractures. We integrated structural, petrographic and geochemical studies, using for the first time in the SE Pyrenees the clumped isotopes thermometry to obtain reliable temperatures of calcite precipitation.

Understanding past changes in sea surface temperatures (SSTs) is crucial; however, existing proxies for reconstructing past SSTs are hindered by unknown ancient seawater composition (foraminiferal Mg/Ca and δ18O) or reflect subsurface temperatures (TEX86) or have a limited applicable temperature range ( ). We examine clumped isotope (Δ47) thermometry to fossil coccolith‐rich material as an SST proxy, as clumped isotopes are independent of original seawater composition and applicable to a wide temperature range and coccolithophores are widespread and dissolution resistant. The Δ47‐derived temperatures from &lt;63, &lt;20, &lt;10, and 2–5 μm size fractions of two equatorial Pacific late Miocene‐early Pliocene sediment samples (c1; c2) range between ∼18 and 29°C, with c1 temperatures consistently above c2. Removing the &gt;63 μm fraction removes most nonmixed layer components; however, the Δ47 …

The measurement of complex isotope systems, notably the multiply substituted isotopologues of CO2 derived from carbonates, is challenging from a mass spectrometric point of view, but it is also time consuming and difficult from a data reduction and normalization perspective. Dedicated software often lags behind and currently limits fast, reliable and reproducible data analysis and inter‐laboratory reproducibility.

Large breccia fabrics associated with karst constitute an important structure in massive limestone successions. The dimensions and shapes of breccia structures are controlled by the initial fracture pattern of the limestone and preferential pathways of the karstifying fluids, but subsequently breccia fabrics can also govern the migration of later fluids. Therefore, breccias are highly relevant features to capture for reservoir characterisation. Outcrop analogues for Lower Khuff units in the Middle East present in the Central Oman Mountains reveal brecciated fabrics up to 10s of metres in diameter. These brecciated units are closely associated with dolomite bodies of late diagenetic origin.

The stable isotope compositions of veins provide information on the conditions of fluid–rock interaction and on the origin of fluids and temperatures. In New Caledonia, magnesite and silica veins occur throughout the Peridotite Nappe. In this work, we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore-forming laterization focusing on the Koniambo Massif. For magnesite veins occurring at the base of the nappe, the high δ18O values between 27.8‰ and 29.5‰ attest to a low temperature formation. Clumped isotope analyses on magnesite give temperatures between 26 °C and 42 °C that are consistent with amorphous silica–magnesite oxygen isotope equilibrium. The meteoric origin of the fluid is indicated by calculated δ18Owater values between −3.4‰ to +1.5‰. Amorphous silica associated with …

Quantifying the geometries of evaporite deposits at a <1 km scale is critical in our understanding of similar ancient depositional systems, but is challenging given evaporite mineral dissolution at surface conditions. A high-resolution stratigraphic study of the basal Purbeck Beds in Brightling Mine, UK, provides insight into the three-dimensional architecture, lateral continuity and vertical heterogeneity within an evaporite seal. We conducted a field mapping study, combined with X-ray diffraction, petrographic microscopy, and δ13C and δ18O isotope analysis. The stratigraphic interval contains five facies. In stratigraphic order, these include supratidal porphyritic nodular evaporite, shallow subtidal peloidal packstone with evaporite and two overlying rhythmic sequences of intertidal microbial laminite, subtidal shale, and subtidal laminar marl, capped by nodular anhydrite. The interpreted environment of deposition is a …

Orbital‐scale climate variability during the latest Miocene‐early Pliocene is poorly understood due to a lack of high‐resolution records spanning 8.0–3.5 Ma, which resolve all orbital cycles. Assessing this variability improves understanding of how Earth's system sensitivity to insolation evolves and provides insight into the factors driving the Messinian Salinity Crisis (MSC) and the Late Miocene Carbon Isotope Shift (LMCIS). New high‐resolution benthic foraminiferal Cibicidoides mundulus δ18O and δ13C records from equatorial Pacific International Ocean Drilling Program Site U1338 are correlated to North Atlantic Ocean Drilling Program Site 982 to obtain a global perspective. Four long‐term benthic δ18O variations are identified: the Tortonian‐Messinian, Miocene‐Pliocene, and Early‐Pliocene Oxygen Isotope Lows (8–7, 5.9–4.9, and 4.8–3.5 Ma) and the Messinian Oxygen Isotope High (MOH; 7–5.9 Ma …

The Lower Permian carbonate rock succession of the Oman Mountains represents a stratigraphical surface analogue for Middle Eastern Lower Khuff hydrocarbon reservoirs. The characteristics of the carbonate rocks are highly variable both laterally and vertically due to the superposition of several episodes of dolomitization. A stratabound early dolomitization event affected the well-bedded limestones during Triassic times. Subsequently, a later burial dolomitization led to the emplacement of several hundreds of meter wide and tens of meter thick dolomite bodies. The goal of our study is to understand the distribution and genetic controls on the formation of late diagenetic dolomite bodies.

Carbonate rocks are major hydrocarbon reservoirs in the Middle East and across the world. Capturing the spatial distribution and dimensions of carbonate sedimentary facies is thus of interest for reservoir modelling and for the understanding of process sedimentology. Here we present data from a Middle Jurassic carbonate ramp outcropping on the Musandam Peninsula (Wadi Naqab, Northern United Arab Emirate of Ras-Al-Khaima), which serves as an analogue for the hydrocarbon bearing units in the subsurface of the Middle East with respect to stratigraphic age, lithofacies types, vertical stacking patterns and palaeogeographical setting. Seven closely spaced sections were logged across a 1900 × 1200 × 120 m fault-bounded outcrop offering a pseudo-3D view of the stratigraphy. Sections were correlated bed-by-bed by walking key surfaces and/or by using photopanels, to produce a detailed lithofacies map …

Accurate determination of the thermal history of sedimentary basins is critical to constrain the timing of diagenetic processes. Here, clumped isotope palaeothermometry is used to estimate minimum burial depth of the Lower Cretaceous Qishn Formation in east central Oman. Fossil oysters were collected in a soft argillaceous unit, thin-sectioned, and studied under petrographical and cathodoluminescence microscopy, revealing a variable state of shell preservations with early silica replacement of carbonate and late-stage calcite cementation. Clumped isotopes values varied from 0.602 to 0.666‰, with the best-preserved oyster shell yielding a temperature of 37 ± 4°C and a calculated oxygen isotope ratio in seawater (δ18Oseawater) compatible with Cretaceous seawater having experienced moderate evaporation (1.0–1.5‰ VSMOW). The new minimum estimates for the burial depth of the Qishn Formation is 1.0–1 …

Conventional carbonate–water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials. In spite of a large number of studies, however, there are still large uncertainties in both δ18O- and Δ47-based temperature calibrations. For this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates. In this study we analyzed oxygen, carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines, tufa and cave deposits from natural springs and wells. Together these samples cover a temperature range from 6 to 95 °C. Travertine samples were collected close to the vents of the springs and from pools, and tufa samples were collected from karstic creeks and a cave. The majority of our vent and pool …

Understanding the authigenesis of carbonate fluorapatite through isotopic geochemistry can yield important information on fundamental geologic processes occurring on continental margins around the world. This is particularly true for phosphatic hardgrounds, which are often found in regions of upwelling, but of which questions remain about the initial formation and subsequent diagenesis. Here, we apply standard isotopes (δ13C, δ18O) alongside the novel clumped isotope (Δ47) used in this study for the first time to reconstruct the temperature of formation of carbonate ions within the lattice of sedimentary carbonate fluorapatite. We investigated phosphatic hardgrounds of Miocene age (12.7–10.8 Ma) sampled at El Capitan State Beach in the Monterey Formation. The range of isotopic signatures observed is between +1.5‰ and +8.0‰ for δ13C relative to the Vienna Peedee belemnite (VPDB) standard and …

Carbonate clumped isotopes are applied to an increasing number of geological archives to address a wide range of Earth science questions. However, the effect of changes in salinity on the carbonate clumped isotope technique has not been investigated experimentally yet. In particular, evaporated sea water and diagenetic fluids differ substantially from solutions used to calibrate the clumped isotope thermometer as they exhibit high ionic concentrations of e.g., Na+, Ca2+, Mg2+, and Cl−. High ionic concentrations are known to have an impact on δ18O values, and could potentially impact the successful application of clumped isotopes to the reconstruction of diagenetic processes, including precipitation temperatures and the origin of the diagenetic fluid.

Ancient marine radiaxial calcite cements are commonly exploited as archives of marine porewater properties based on the argument that they lack metabolic effects often assigned to biogenic carbonates. Here we critically test the significance of conventional versus (with respect to these fabrics) less-conventional proxy data from Pennsylvanian, Triassic, and Cretaceous case examples. Conventional proxies include: cathodoluminescence, carbon and oxygen isotope ratios, main and trace elemental concentrations. Less conventionally applied proxies are: clumped isotope “Δ47”, redox-sensitive, and rare earth elements sampled across a succession of Triassic radiaxial fibrous calcites. Radiaxial calcites are subdivided in three groups based on their luminescence characteristics: non-luminescent, patchy luminescent, and bright luminescent. Luminescence patterns are in fair agreement with isotope ratios, in …

Many fields of Earth sciences benefit from the knowledge of mineral formation temperatures. For example, carbonates are extensively used for reconstruction of the Earth’s past climatic variations by determining ocean, lake, and soil paleotemperatures. Furthermore, diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications, for instance, for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs. Carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution. It is based on the temperature-dependent abundance of the rare 13C–18O bonds in carbonate minerals, specified as a _47 value. The clumped isotope thermometer has been calibrated experimentally from 1 °C to 70 °C. However, higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory. In order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high-temperature geological processes we precipitated CaCO3 (mainly calcite) in the laboratory between 23 and 250 °C. We used two different precipitation techniques: first, minerals were precipitated from a CaCO3 supersaturated solution at atmospheric pressure (23–91 °C), and, second, from a solution resulting from the mixing of CaCl2 and NaHCO3 in a pressurized reaction vessel at a pressure of up to 80 bar (25–250 °C). The calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and with other calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70 °C. Our study suggests a universal _47-T calibration (T in K, _47 in ‰): This new _47-T calibration (given in the absolute reference frame), that extends the experimentally calibrated temperature range for clumped isotopes to 250 °C, can be applied to carbonates that grew at intermediate temperatures (20–250 °C).

Calcium carbonate (CaCO3) plays an important role in the natural environment as a major constituent of the skeleton and supporting structure of marine life and has high economic importance as an additive in food, chemicals and medical products. Anhydrous CaCO3 occurs in the three different polymorphs calcite, aragonite and vaterite, whereof calcite is the most abundant and best characterized mineral. In contrast, little is known about the rare polymorph vaterite, in particular with regard to the oxygen isotope fractionation between H2O and the mineral. Synthetic precipitation of vaterite in the laboratory typically involves rapid processes and isotopic non-equilibrium, which excludes isotope studies focused on the characterization of vaterite under equilibrium conditions. Here, we used a new experimental approach that enables vaterite mineral formation from an isotopically equilibrated solution. The solution consists of a ∼0.007molL−1 CaCO3 solution that is saturated with NaCl at room temperature (up to 6.4molL−1). Vaterite precipitated as single phase or major phase (≥94%) in experiments performed between 23 and 91◦C. Only at 80◦Cwasvaterite a minor phase with a relative abundance of 27%.Thehigh mineral yield per experiment of up to 235mg relative to the initially dissolved CaCO3 amount of on average 360mg enables an investigation of the oxygen isotope fractionation between the mineral and water, and the determination of clumped isotope values in vaterite.

Diagenetic heterogeneities are difficult to predict in the subsurface. Nevertheless, such heterogeneities can be crucial in hydrocarbon exploration. Diagenetic processes can significantly alter petrophysical properties of reservoir rocks, especially in carbonate rocks because of the reactive nature of the carbonate minerals. Dolomitization [ie, the transformation of calcite (limestone: Lmst) into dolomite] is a common diagenetic process in carbonate rocks. Resulting dolomite bodies have a different pore network than the original Lmst and respond also differently to tectonic stress causing different fracture networks than in the original Lmst. The paper presents an overview of the learning outcomes gained by studying fracture-related dolomite in outcrops of Oman and subsequent laboratory analysis conducted over the last 4 years. A combined structural, petrographic, and geochemical approach was taken to study three …

Dolomite precipitation models and kinetics are debated and complicated due to the complex and temporally fluctuating fluid chemistry and different diagenetic environments. Using well-established isotope systems (δ18O, δ13C, 87Sr/86Sr), fluid inclusions and elemental data, as well as a detailed sedimentological and petrographic data set, we established the precipitation environment and subsequent diagenetic pathways of a series of Proterozoic to Pleistocene syn-depositional marine evaporative (sabkha) dolomites, syn-depositional non-marine evaporative (lacustrine and palustrine) dolomites, altered marine (“mixing zone”) dolomites and late diagenetic hydrothermal dolomites. These data form the prerequisite for a systematic investigation of dolomite magnesium isotope ratios (δ26Mgdol). Dolomite δ26Mg ratios documented here range, from −2.49‰ to −0.45‰ (δ26Mgmean = −1.75 ± 1.08‰, n = 42). The …

The late Miocene to early Pliocene carbonate-rich sediments recovered at Integrated Ocean Drilling Program (IODP) Site U1338 during the Expedition 320/321 Pacific Equatorial Age Transect (PEAT) program contain abundant calcareous nanno- and microfossils. Geochemical proxies from benthic and planktonic foraminiferal and coccolithophore calcite could be very useful at this location; however, good preservation of the calcite is crucial for the proxies to be robust. Here, we evaluate the preservation of specific benthic and planktonic foraminifer species and coccolithophores in fine fraction sediment at Site U1338 using backscattered electron (topography mode) scanning electron microscopy (BSE-TOPO SEM). Both investigated foraminiferal species, Cibicidoides mundulus and Globigerinoides sacculifer, have undergone some alteration. The C. mundulus show minor evidence for dissolution, and only some specimens show evidence of overgrowth. The Gs. sacculifer show definite signs of alteration and exhibit variable preservation, ranging from fair to poor; some specimens show minor overgrowth and internal recrystallization but retain original features such as pores, spine pits, and internal test-wall growth structure, whereas in other specimens the recrystallization and overgrowth disguise many of the original features. Secondary electron and BSE-TOPO SEM images show that coccolith calcite preservation is moderate or moderate to poor. Slight to moderate etching has removed central heterococcolith features, and a small amount of secondary overgrowth is also visible. Energy dispersive spectroscopy analyses indicate that the main sedimentary components of the fine fraction sediment are biogenic CaCO3 and SiO2, with some marine barite. Based on the investigations in this data report, geochemical analyses on benthic foraminifers are unlikely to be affected by preservation, although geochemical analyses on the planktonic foraminifers should be treated cautiously because of the fair to poor and highly variable preservation.

Predicting spatial distribution, dimension, and geometry of diagenetic geobodies, as well as heterogeneities within these bodies, is challenging in subsurface applications, and can impact the results of reservoir modeling. In this outcrop–based study, we generated a data set of the dimensions of fracture–related dolomite geobodies hosted in Ediacaran (Khufai Formation) limestones of the Oman Mountains that are up to several hundreds of meters long and a few tens of meters wide. The dolomite formed under burial conditions by fluids that interacted with siliciclastic layers, as demonstrated by the enriched Fe (up to 4.4%) and Mn (up to 0.8%) contents and Sr 87/Sr 86 (⁠∼ 0.710⁠) signatures. Dolomitization probably occurred during the Hercynian Orogeny (or pre-Permian) because dolomitization predates some folding and pre-Permian rocks have seen intense deformation related to the Carboniferous Hercynian …

This study investigates one of the few examples of dolomitization of Lower Cretaceous shallow-water limestones from the southern Tethys carbonate platform from outcrops on the Haushi-Huqf High in central-east Oman. Mud-dominated peritidal carbonates rich in microbial mats are replaced by fine crystalline dolomite along at least 60 km in the lower 10 m of the Jurf Formation. Two, meter-thick beds in the overlying Qishn Formation are also dolomitized over lateral distances of one to two kilometers. The stratabound geometry and petrographic relations of the dolomite with all other diagenetic phases indicate that the dolomite precipitated early. The presence of only rare anhydrite relicts suggests that seawater was below gypsum saturation during most of the dolomitization, supporting the hypothesis that Cretaceous slightly evaporated water (δ18Ofluid values range from 2.8‰ to 3.5‰ SMOW) can affect pervasive dolomitization. Despite being composed of peritidal facies with features suggesting high salinity, most of the carbonate succession was not dolomitized, suggesting that the presence of microbial mats exerted a major control on the distribution of dolomite, and that salinity is only a minor control on dolomitization. Clumped-isotope results indicate that the early formed dolomite re-equilibrated with fluids at 44 ± 3°C in a shallow-burial setting. The elevated iron content (on average 6011 ppm) and 87Sr/86Sr (on average 0.70782) with respect to Cretaceous seawater suggests that the burial fluids interacted with Permian clay and feldspars of the Gharif Formation that underlies the Cretaceous carbonates. The vertical gradients of radiogenic Sr and the occurrence of small volumes of coarse crystalline dolomite in stylolites and fractures suggests that burial fluids were driven vertically and laterally by differential compaction, probably during maximum burial in the Late Cretaceous.

For clumped isotope analysis (Δ47), hydrocarbon and organic molecules present an important contaminant that cannot always be removed by CO2 purification through a Porapak‐Q trap. Low‐temperature oxygen plasma ashing (OPA) is a quick and easy approach for treatment; however, the impact of this treatment on the original carbonate clumped isotope values has never been fully studied.

Septarian carbonate concretions contain carbonate precipitated during progressive growth of the concretion and subsequent fracture-filling. As such, they have been used to track variations in _13C and _18O of pore waters during diagenesis and to define diagenetic zones in clastic rocks. However, the _18O value of the carbonate is dependent on precipitation temperature and the _18O value of the pore fluid from which it precipitated. Interpretations must assume one of these parameters, both of which are highly variable through time in diagenetic settings. Carbonate clumped isotopes of the cement can provide independent estimates of temperature of precipitation, allowing the pore-water _18O to be back-calculated. Here, we use this technique on carbonate concretions and fracture fills of the Upper Cretaceous Prairie Canyon Member, Mancos Shale, Colorado. We sampled concretions from two permeable horizons separated by a 5 m shale layer, with one permeable horizon containing concretions with septarian fractures. We show cores precipitated at cooler temperatures (31_°C, _660 m burial depth) than the rims (68_°C (_1980 m burial depth) and relate that to the _13Ccarbonate values to suggest the concretion core precipitated in the methanogenic zone, with increasing input from thermogenically produced CO2. The two concretion-bearing horizons have different back-calculated _18Oporewater values (mean ‰ and 1.13‰ VSMOW) for cements formed at the same temperature and similar _13C values, suggesting the shale layer present between the two horizons acted as a barrier to fluid mixing. Additionally, the _18Ocarbonate of the septarian fractures (‰ VPBD) are due to precipitation at high temperatures (102 to 115_°C) from a fluid with a mean _18Oporewater of 0.32‰ (VSMOW). Therefore, we can tie in the cementation history of the formation to temporal and spatial variations in _18Oporewater.

This study, based in the Haushi‐Huqf area of central east Oman, aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of Lower Cretaceous tidal flat facies within the Tethyan epeiric platform. Field, petrographic and geochemical data were acquired from the Barremian–Aptian Jurf and Qishn formations that crop out in a 500 × 1000 m2 butte, thus allowing for pseudo three‐dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies. The interpretation presented here suggests that the main processes impacting sedimentation in the Lower Cretaceous peritidal environment of the Haushi-Huqf were transport and erosion processes related to storm waves and currents. The vertical evolution of the carbonate system is organized into six types of metre-scale depositional sequences, from …

Understanding the distribution and geometry of reservoir geobodies is crucial for net-to-gross estimates and to model subsurface flow. This article focuses on the process of dolomitization and resulting geometry of diagenetic geobodies in an outcrop of Jurassic host rocks from northern Oman. Field and petrographic data show that a first phase of stratabound dolomite is crosscut by a second phase of fault-related dolomite. The stratabound dolomite geobodies are laterally continuous for at least several hundreds of meters (∼ 1000 ft) and probably regionally and are one-half meter (1.6 ft) thick. Based on petrography and geochemistry, a process of seepage reflux of mesosaline or hypersaline fluids during the early stages of burial diagenesis is proposed for the formation of the stratabound dolomite. In contrast, the fault-related dolomite geobodies are trending along a fault that can be followed for at least 100 m (328 ft …

Diagenesis and fracturing can significantly alter petrophysical properties of subsurface carbonate reservoirs, but the impacts of these processes at the inter-well scale are hard to predict. However, the initial distribution of sedimentary facies is easier to predict, and could template future diagenetic transformation and potentially influence fracturing as well. This paper provides a case study investigating the mutual influence of depositional facies on diagenesis and interpreted early fractures in the Berriasian–Valanginian Habshan Formation in Jebel Madar (Oman). The Habshan Formation mostly comprises ooidal limestones but dolomitized beds a few metres in thickness and laterally correlatable over at least 5 km are present. Discordant (vertical) dolomite streaks are present in the limestone but are rare. The various sedimentary and diagenetic processes were investigated using fieldwork, XRD analysis, petrography …

Stylolites are irregular discontinuity surfaces that are thought to result from localized stress-induced dissolution during burial or tectonic compression. The genesis of stylolites and the controls on stylolitization are still debated, and the interplay between stylolitization, generation of carbonate-rich fluids, diagenetic fluid flow within fractures and matrix, cementation, and porosity modifications is complex. All of these processes have important diagenetic effects potentially altering the intrinsic properties of the host rock, with implications for hydrocarbon exploration and water resources in aquifers. We investigate the process of stylolitization by a macroscopic, petrographic, and geochemical study of pressure-solution features in Eocene to early Oligocene limestones in cores from the Integrated Ocean Drilling Program (IODP) Hole 317-U1352C (Canterbury Basin). The results indicate correlations among stylolite amplitude …

Integrated Ocean Drilling Program Expedition 308 quantified the coupling between sedimentation, consolidation, overpressure, fluid flow, and slope instability in continental margin settings. We summarize and synthesize peer-reviewed hydrogeologic studies published since the end of Expedition 308 that focus on Expedition 308 sites drilled in Ursa Basin: Sites U1322, U1323, and U1324. There is a rich stratigraphic complexity in the Ursa Basin, deepwater Gulf of Mexico. The sandstone-prone Blue Unit is a permeable aquifer overlain by mudstone-prone leveed-channel deposition. Multiple mass transport deposits, each densified relative to surrounding material, are present. Eight coeval surfaces mapped across the drilling transect span ~70 ka to present. Sedimentation rates were >10 mm/y at Site U1324. In situ penetrometer measurements document severe overpressures that begin at or near the seafloor and extend to the base of the drilled holes. Uniaxial consolidation experiments quantified the compression behavior of the sediments and provided an approach to predict pressure from porosity. Laboratory analysis of permeability and compressibility document that the coefficient of consolidation (hydraulic diffusivity) of Ursa Basin mudstones is 10–8 m2/s over the effective stresses encountered during drilling at Ursa Basin (0.1 to 5 MPa). This low and constant value for the coefficient of consolidation is responsible for the presence of high overpressure very near the seafloor. Although permeability is very high, the sediments are also highly compressible. Forward modeling of Ursa Basin sediments shows that overpressure near the seafloor is reasonable given the rock properties and sedimentation rates that are observed. Modeling also illustrates that flow is driven laterally along an underlying aquifer, the Blue Unit. Soon after Blue Unit deposition, lateral flow induced submarine landslides. Later in the evolution of this system, overpressure may have preconditioned the slope to failure by earthquakes of magnitude 5.0.

Dedolomitization is an important diagenetic process that can yield information on the history of paleo-fluids in a given aquifer or outcrop, and by extension it offers a window into past hydrologic conditions. Dedolomitization is also relevant economically as it can alter the porosity and permeability of carbonates, thus affecting reservoir quality. Despite considerable research, the process of dedolomitization is still not entirely understood. Here, new findings from the central Oman Mountains highlight the importance of dolomite chemistry and fluctuating climate on dedolomitization. Petrographic, mineralogical, and geochemical data from both altered and pristine dolomite hosted in Jurassic carbonate rocks from the Sahtan Group and outcropping at Wadi Mistal in the Jebel Akhdar tectonic window reveal two dolomite bodies with different characteristics, stratabound and fault-related dolostone. The (ferroan) dolomite crystals are larger in the fault-related dolostone, whereas the (non-ferroan) dolomite crystals are smaller in the stratabound dolostone. Petrography reveals a complex suite of alteration textures, including pristine dolomite, recrystallized dolomite, and calcitized dolomite (dedolomite). Iron oxides are present pervasively in the altered rocks, and different alteration textures co-occur in the same sample. Relative to unaltered dolomite in this outcrop, the recrystallized dolomite is characterized by similar positive carbon isotope values but less negative oxygen isotope values, and the calcitized dolomite is characterized by even less negative oxygen isotope values and more negative carbon isotope values. Based on field data and petrography, two phases of alteration are evident, an earlier dedolomitization event affecting the stratabound dolomite only, and a more pervasive Pleistocene–Holocene alteration phase associated with surface weathering that affected both the fault-related dolomite and to a lesser extent the stratabound dolomite. Stable isotope results further suggest that the more recent subaerial weathering phase happened under two alternating climate regimes: dedolomitization was triggered by meteoric fluids that interacted with soil-related carbon during humid climatic period(s), whereas recrystallization of ferroan fault-related dolomite happened during more arid climatic period(s) with less developed soils and lower fluid–rock interaction. These results suggest that weathering of ferroan fault-related dolomite can lead to formation of goethite and recrystallized, non-stoichiometric dolomite (with a reset stable oxygen isotope signature), and sometimes to dedolomitization.

The Paleocene-Eocene thermal maximum, a transient global warming event, is characterized by extensive evidence of a more active hydrological cycle. This includes a widespread pulse of kaolinite accumulation on continental margins, viewed as the by-product of either enhanced chemical weathering consistent with much more humid conditions and/or increased erosion of previously deposited laterites. The former would be more consistent with year-round humid conditions, whereas the latter might be indicative of extreme seasonal precipitation patterns. To assess these hypotheses, we present a new high-resolution clay mineral assemblage and oxygen isotope record from Bass River, a site on the New Jersey margin (east coast of North America), which shows a sharp rise in the abundance of kaolinite beginning a few thousand years before the onset of the carbon isotope excursion (CIE). The δ 18 O of the< 2 …

Eustasy is a key parameter to understand sedimentary sequences on continental margins and to reconstruct continental ice volume in the Cenozoic, but timing and magnitude of global sea level changes remain controversial, especially for the Miocene Epoch. We analyzed sediment cores recovered from the Marion Plateau, offshore northeastern Australia, during Ocean Drilling Program (ODP) Leg 194 to define the mechanisms and timing of sequence formation on mixed carbonate-siliciclastic margins, and to estimate the amplitude of Miocene eustatic adjustments. We identified sequence boundaries on seismic reflection lines, significantly revised the existing biostratigraphic age models, and investigated the sedimentary response to sea-level changes across the Marion Plateau. We subdivided the Miocene sediments into three sequence sets comprising a set of prograding clinoforms, a muddy prograding …

We present the results of 276 X-ray diffraction analyses of bulk sediment from Brazos-Trinity IV (Integrated Ocean Drilling Program [IODP] Hole U1320A) and Ursa (IODP Hole U1324B) Basins. The mineralogy at both locations is qualitatively very similar, with quartz and phyllosilicates dominating the assemblages and calcite, dolomite, K-feldspars, plagioclases, and halite present in varying amounts. Ankerite (iron-rich dolomite) was observed in only one sample. Although the composition of the sediment is relatively monotonous, trends in the percent occurrence of each fraction are observed and can be linked to changes in the lithostratigraphic units and core descriptions from Expedition 308. The data presented here will help establish a link between geomechanical behaviors of the sediments and matrix effects driven by mineral composition.

We reconstruct eustatic variations during the latest Paleocene and earliest Eocene (∼58–52 Ma). Dinoflagellate cysts, grain size fractions, and organic biomarkers in marine sections at four sites from three continents indicate an increased distance to the coast during the Paleocene‐Eocene thermal maximum (PETM). The same trend is recognized in published records from other sites around the world. Together, the data indicate a eustatic rise during the PETM, beginning 20 to 200 ka before the globally recorded negative carbon isotope excursion (CIE) at ∼55.5 Ma. Although correlations are tentative, we recognize other global transgressions during Chrons C25n and C24n. The latter may be associated with Eocene Thermal Maximum 2 (∼53.5 Ma) or the “X”‐event (∼52 Ma). These results suggest a link between global sea level and “hyperthermal” intervals, potentially because of the melting of small alpine ice …

The impacts of the Paleocene‐Eocene thermal maximum (PETM) (∼55 Ma), one of the most rapid and extreme warming events in Earth history, are well characterized in open marine and terrestrial environments but are less so on continental margins, a major carbon sink. Here, we present stable isotope, carbonate content, organic matter content, and C:N ratio records through the PETM from new outcrop sections in California and from cores previously drilled on the New Jersey margin. Foraminifer δ18O data suggest that midlatitude shelves warmed by a similar magnitude as the open ocean (5°C–8°C), while the carbon isotope excursion (CIE), recorded both in carbonate and organic matter δ13C records, is slightly larger (3.3–4.5‰) than documented in open ocean records. Sediment accumulation rates increase dramatically during the CIE in marked contrast to the open ocean sites. In parallel, mass accumulation …

Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (1= ffiffi t p) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta. © 2007 Elsevier B.V. All rights reserved.

The Palaeocene/Eocene thermal maximum — a period of intense global warming about 55 million years ago — was associated with a massive release of isotopically distinctive greenhouse gases into the ocean-atmosphere system. It remains unclear, however, whether this input caused or resulted from the global warming and environmental change that characterize the event. Sluijs et al. use high-resolution records of environmental change across the Palaeocene/Eocene boundary from two sediment sections in New Jersey to shed light on this question. They find that the onset of environmental change and surface-ocean warming preceded the input of greenhouse gases by several thousand years at this location. This sequence of events is consistent with the proposal that deep-ocean warming caused the dissociation of submarine gas hydrates, releasing massive amounts of the greenhouse gas methane. But the cause of the early warming remains uncertain.

The Palaeocene–Eocene thermal maximum (PETM) is characterized by a global negative carbon isotope excursion (CIE) and widespread dissolution of seafloor carbonate sediments. The latter feature supports the hypothesis that the PETM and CIE were caused by the rapid release of a large mass (greater than 2000 Gt C) of 12C-enriched carbon. The source of this carbon, however, remains a mystery. Possible sources include volcanically driven thermal combustion of organic-rich sediment, dissociation of seafloor methane hydrates and desiccation and oxidation of soil/sediment organics. A key constraint on the source(s) is the rate at which the carbon was released. Fast rates would be consistent with a catastrophic event, e.g. massive methane hydrate dissociation, whereas slower rates might implicate other processes. The PETM carbon flux is currently constrained by high-resolution marine and terrestrial …

Expedition 308 of the Integrated Ocean Drilling Program (IODP) was the first phase of a two-component project dedicated to studying overpressure and fluid flow on the continental slope of the Gulf of Mexico. We examined how sedimentation, overpressure, fluid flow, and deformation are coupled in a passive margin setting and investigated how extremely rapid deposition of fine-grained mud might lead to a rapid build-up of pore pressure in excess of hydrostatic (overpressure), underconsolidation, and sedimentary mass wasting. Our tests within the Ursa region, where sediment accumulated rapidly in the late Pleistocene, included the first-ever in situ measurements of how physical properties, pressure, temperature, and pore fluid compositions vary within low-permeability mudstones that overlie a permeable, overpressured aquifer, and we documented severe overpressure in the mudstones overlying the aquifer. We also drilled and logged three references sites in the Brazos-Trinity Basin IV and documented hydrostatic pressure conditions and normal consolidation. Post-expedition studies will address how the generation and timing of overpressure control slope stability, seafloor seeps, and large-scale crustal fluid flow. The operations of Expedition 308 provide a foundation for future long-term in situ monitoring experiments in the aquifer and bounding mudstones.

Integrated Ocean Drilling Program (IODP) Expedition 308 is the first stage of a two-component program dedicated to the study of overpressure and fluid flow on the Gulf of Mexico continental slope. Drilling at six sites revealed an active hydrodynamic environment and provided insight into geological processes near the seafloor. We tested a multidimensional flow model by examining how physical properties, pressure, temperature, and pore fluid composition vary within low-permeability mudstones that overlie a permeable and overpressured aquifer. We drilled, logged, and made in situ pressure and temperature measurements in Brazos-Trinity Basin IV off the Texas Gulf Coast where low sedimentation rates and normal pressures were predicted. We contrasted these observations with experiments in the Ursa region off the Mississippi Delta where rapid Pleistocene sedimentation occurred. At Ursa, multiple pore pressure penetrometer measurements recorded values that lie halfway between the hydrostatic pressure and the lithostatic pressure. Porosity-depth profiles suggest that these overpressures are maintained by compaction disequilibrium. Log, core, and seismic data illustrate that this overpressured region was subject to multiple events of slope instability, which generated mass transport deposits. A surprising result is that mudstones beneath Brazos-Trinity Basin IV are undercompacted, and most likely overpressured, relative to mudstones at the basin margin. Interbedded sands and mudstones within Brazos-Trinity Basin IV record a fascinating stratigraphic history that relates turbidite formation to eustatic sea level change. Postcruise science on both areas investigated will combine theoretical modeling and laboratory analysis to further illuminate coupled processes of flow, sedimentation, and deformation on passive continental margins.

Three ODP sites located on the Marion Plateau, Northeast Australian margin, were investigated for clay mineral and bulk mineralogy changes through the early to middle Miocene. Kaolinite to smectite (K/S) ratios, as well as mass accumulation rates of clays, point to a marked decrease in accumulation of smectite associated with an increase in accumulation of kaolinite starting at ∼ 15.6 Ma, followed by a second increase in accumulation of kaolinite at ∼ 13.2 Ma. Both of these increases are correlative to an increase in the calcite to detritus ratio. Comparison of our record with published precipitation proxies from continental Queensland indicates that increases in kaolinite did not correspond to more intense tropical-humid conditions, but instead to periods of greater aridity. Three mechanisms are explored to explain the temporal trends in clay on the Marion Plateau: sea-level changes, changes in oceanic currents …

The temporal variability of geochemical proxies can be used in time intervals characterized by global changes in marine chemistry to achieve improved stratigraphic correlation. The application of this approach in rocks lithified by cementation requires particular attention, as the original isotopic signature may have been modified by diagenetic processes and, when bulk samples are used, could reflect facies-specific compositional changes as opposed to primary changes in the water column. This paper examines sedimentological and chemostratigraphic records from outcrops in the central Mediterranean and cores drilled on the Marion Plateau by the Ocean Drilling Program (ODP) Leg 194, where heterozoan carbonates accumulated during the Miocene. Specifically, the paper addresses how facies and preservation of original marine signatures differentially affect the quality of the dataset. The analysis indicates …

In this paper we explore the relative control of paleoceanography, eustasy, and water temperature over the evolution of a carbonate slope system deposited on the Marion Plateau (Northeastern Australia). Growth of several carbonate platforms started in the early Miocene on this plateau, and although they occurred in low-latitude subtropical waters they are composed mainly of heterozoan organisms. We investigated an upper to distal slope transect drilled during ODP Leg 194 and located close to the Northern Marion Platform. We reconstructed mass accumulation rates of carbonate as well as the evolution in the ratios of carbon and oxygen stable isotopes. Power spectrum analysis of the carbon isotope record revealed the existence of cycles with main frequencies centered around 409 Kyr and 1800 Kyr. We interpret the 409 Kyr cycle as being paced by changes in the eccentricity of the Earth orbit, and we …

δ 18 O benthic values from Leg 194 Ocean Drilling Program Sites 1192 and 1195 (drilled on the Marion Plateau) were combined with deep-sea values to reconstruct the magnitude range of the late middle Miocene sea-level fall (13.6–11.4 Ma). In parallel, an estimate for the late middle Miocene sea-level fall was calculated from the stratigraphic relationship identified during Leg 194 and the structural relief of carbonate platforms that form the Marion Plateau. Corrections for thermal subsidence induced by Late Cretaceous rifting, flexural sediment loading, and sediment compaction were taken into account. The response of the lithosphere to sediment loading was considered for a range of effective elastic thicknesses (10< T e< 40 km). By overlapping the sea-level range of both the deep-sea isotopes and the results from the backstripping analysis, we demonstrate that the amplitude of the late middle Miocene sea …

Ternary plots are used in many fields of science to characterize a system based on three components. Triangular plotting is thus useful to a broad audience in the Earth sciences and beyond. Unfortunately it is typically the most expensive commercial software packages that offer the option to plot data in ternary diagrams. However, they lack features that are paramount to the geosciences, such as the ability to plot data directly into a standardized diagram and the possibility to analyze temporal and stratigraphic trends within this diagram.

We investigated rock outcrops spanning the middle Miocene, global climate-cooling step on the Maltese Islands in order to reconstruct continental weathering rates and terrigenous fluxes, as well as to explore the coupling between these later, regional climate and carbonate accumulations. Sedimentation at this location was dominated during the Oligocene and early Miocene by a transitional platform to slope carbonates but progressively switched to a clay-rich carbonate slope system in the middle Miocene. Around 13 Ma, an abrupt change toward clay-dominated marls occurred, and marl deposition persisted until the Tortonian (ca. 12 Ma), when a shallow-water carbonate ramp was reestablished. Clay mineralogy and bulk-rock oxygen isotope analyses suggest that the deposition of the Blue Clay formation was mainly caused by global climate change and related change in the rate of continental weathering …

The organic- and phosphate-rich interval of the Monterey Formation at El Capitan State Beach (west of Santa Barbara, California, U.S.A.; late early to early late Miocene in age) is composed of a carbonaceous marl (TOC contents between 1.2 and 23.2 wt %) with intercalated phosphate-rich laminae, lenses, and layers. Subordinate lithologies include ash layers, dolomitized horizons, and siliceous beds. We distinguished five lithological units: (1) a gray marl unit lacking major phosphate accumulations (> 16.3 Ma; average TOC content 2% by weight; average sedimentation rate 75 m/My; average TOC accumulation rate 0.19 mg/cm2/yr); (2) a black marl unit including light-colored phosphatic laminae, lenses, and discrete particles (16.3-14.5 Ma; average TOC content 7.5% by weight; average sedimentation rate 20 m/My; average TOC accumulation rate 0.19 mg/cm2/yr); (3) a red marl unit including light-colored …

Estimating the amplitude and timing of past eustatic sea level changes is essential both for the establishment of an accurate Phanerozoic sea level curve and for the interpretation of sediment sequences on continental margins. The magnitude and timing of sea level changes can be estimated in tectonically stable environments by correlating seismic data with lithologic facies, biofacies (for paleowater depths), and chronostratigraphy. During Leg 194, a series of eight sites was drilled through Oligocene-Holocene mixed carbonate and siliciclastic sediments that record the depositional history and past sea level variations on the Marion Plateau, northeast Australia. Seismic sequence stratigraphy provided the geometric framework to locate the drill sites on two carbonate platforms, their slopes, and the plateau for optimal sampling of highstand and lowstand sequences with geometries that enable quantification of Miocene relative sea level variations. At each site, ~500-700 m of sediment was drilled, and five sites penetrated into acoustic basement. During this leg, ~2 km of sediment was recovered from a total cored interval of 5 km. Water depths of the drill sites ranged from 304 to 419 m. In addition to determining sea level magnitudes, Leg 194 drilling also addressed the following scientific themes: The development of carbonate platforms in a current-dominated environment, The development of subtropical carbonate platforms, Facies changes and the development of sequence stratigraphic units controlled by sea level changes in a mixed carbonate and siliciclastic sediment system, The record of Oligocene-Pliocene third-order sea level fluctuations, The mechanisms and causes of fluid flow within pure carbonate and mixed siliciclastic/carbonate depositional environments, and The role of climatic and paleoceanographic change in the subtropical South Pacific and its influence on carbonate platform development. The original hypothesis for Leg 194 drilling postulated that the&nbsp;magnitude of the late middle Miocene (calcareous nannofossil Zones N12-N14; 12.5-11.4 Ma) sea level fall could be estimated from seismic sequences and facies relationships between the top of the Northern Marion Platform (NMP), which was deposited during the sea level highstand, and the base of the Southern Marion Platform (SMP) initiated during the lowstand. Drilling results showed, however, that the southern platform is not solely composed of late Miocene age sediments as previously thought. Instead, ~120-160 m of upper Miocene carbonates overlie a thick middle to lower Miocene platform similar in age to portions of the northern platform. The magnitude of the middle Miocene sea level fall, therefore, was estimated by reconstructing the paleobathymetry of the northern platform top with respect to an upper middle Miocene lowstand ramp immediately adjacent to the platform margin. Physical properties information was used to remove the compaction effects imparted by the overlying sediments at both sites. The base of the lowstand unit after decompaction lies 96 m below the top of the NMP. Paleowater depths estimates are 10-50 m for the platform surface at Site 1193 and 30-50 m for the lowstand unit at Site 1194. Combining the decompaction with the paleowater depth estimates, a late middle Miocene sea level drop between 56 and 116 m is required to produce today's sediment geometries at Sites 1193 and 1194. These values assume infinite crustal strength between the sites. If zero flexural strength is assumed for the crust, the local isostatic compensation would reduce the required magnitude of the sea level drop to 12-53 m. The undisturbed and consistently dipping sediments, as well as the horizontal basement geometry between the two sites, however, show no signs of differential subsidence, and favor the infinite flexural strength model over local isostacy. Lithologic and biostratigraphic data obtained from the Neogene carbonate platforms of the Marion Plateau during Leg 194 reveal that platform architecture was controlled by a series of complexly related factors including sea level change, bottom-current action, and the nature of biological assemblages. Two platform to slope transects were drilled across the Miocene carbonate platforms of the Marion Plateau. An important finding is that the oldest platform phase of the southern carbonate platform developed in a topographic depression as opposed to the more common condition of nucleation on a topographic high. Furthermore, the steep-sided geometry of both Marion Plateau carbonate platforms is typical of tropical to subtropical carbonate platforms. Despite this, cores retrieved during Leg 194 document a cool subtropical faunal assemblage consisting primarily of red algae, bryozoans, and larger foraminifers. These calcite-dominated biogenic sediments have a lower diagenetic potential than their aragonite-dominated counterparts in the tropical realm. Therefore, they can be reworked more easily as they undergo less cementation. In addition, the fragmentation of these sediments leads to the formation of silt- to fine sand-sized particles rather than carbonate mud. Another important finding of Leg 194 is that unlike other carbonate systems, the morphologies of which are predominantly controlled by wind direction, the carbonate platform architecture observed on the Marion Plateau was strongly influenced by high-energy currents near the seafloor, similar to those that exist on the modern Marion Plateau. These currents inhibit sedimentation in the upcurrent position and form wide low-angle clinoforms in the downcurrent position, resulting in an asymmetric platform shape. Pore waters from Leg 194 sediments provide clear evidence that seawater is circulating through the sediments proximal to the carbonate platforms on the Marion Plateau. The dolomitization found in both platforms is itself indirect evidence for past fluid circulation, as dolomite formation on a large scale requires fluid exchange to deliver magnesium to the precursor calcium carbonate sediments. Although sampling of pore waters from within the SMP was not possible because of low recovery, samples taken from the adjacent periplatform sites are characterized by seawater values for most elements. These samples provide evidence that seawater is circulating through these sediments even though they are overlain by ~200 m of hemipelagic deposits. Evidence also indicates that seawater is circulating through the NMP. Acoustic basement was penetrated at five sites during Leg 194, and the basement rocks that were collected differ greatly from those drilled on the Queensland Plateau. Rather than metasedimentary rocks, highly altered volcanic flows and volcaniclastics were recovered. The lack of deformation in hand samples and thin sections suggests that these volcanics may have formed during the Late Cretaceous-Paleocene rifting along northeastern Australia from the Papuan Plateau in the north and the Lord Howe Rise in the south. High-quality paleomagnetic data collected from these basement volcanics, when compared with the Australian apparent polar wander path, may provide age estimates for both the emplacement of the basalts and the timing of their low-temperature alteration.