Diagenesis of phosphatic hardgrounds in the Monterey Formation: A perspective from bulk and clumped isotope geochemistry

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 …

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