The response of heterozoan carbonate systems to Paleoceanographic, climatic and eustatic changes: a perspective from slope sediments of the Marion Plateau (ODP Leg 194)

In this paper we explore the relative control of paleocean-ography, eustasy, and water temperature over the evolution of a car-bonate 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 suggest that the 1800 Kyr cycle could be linked to long-term eustatic changes. Finally, on the basis of the timing of changes in mass accumulation rates of carbonate we infer that the strength and direction of oceanic currents affected sedimen-tation on the Marion Plateau by shifting depocenters of slope sedi-mentation, a process probably further modulated by sea-level changes. We argue that the evolution and demise of the heterozoan carbonate systems present on the Marion Plateau were controlled mainly by the evolution of strong benthic currents, and that eustasy and water temperature alone did not account for the drowning of the platforms in the mid Miocene.

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