Paleoenvironmental Reconstruction of the Late Barremian - Early Aptian Urgonian Platform, Southeast France




Bourdon, Matthew

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The Urgonian platform in Southeast France records cycles of high and low carbonate production rates during the late Barremian - early Aptian, a time period characterized by a global paleoenvironmental and paleoceanographic crisis, the Oceanic Anoxic Event (OAE) 1a. Since other platforms located at other paleolatitudes were not affected by the OAE1a but were eventually replaced by more adapted carbonate-producing ecosystems, it is important to first analyze the latitudes in which the platforms could be found and their corresponding environments. Carbonate systems throughout this time period thus provide an opportunity to understand paleoenvironmental parameters that caused the Urgonian platform to drown in the early Aptian as a potential consequence of the OAE 1a and associate climate change. The OAE1a is the first anoxic event to affect the world during the Cretaceous and is associated with enhanced greenhouse conditions due to increased submarine volcanism. This research hypothesizes that the Urgonian platform was drowned due to an increase in continental weathering and sediment supply at higher latitudes accompanied by cooler seawater temperatures compared to lower latitude where carbonate platforms continued to live and produce carbonate sediment. To complement ongoing research that defines the stratigraphy and ecology of the Urgonian platform using carbon isotope chemostratigraphy and facies analysis, this research uses whole-rock elemental geochemistry (x-ray fluorescence spectrometry) and clumped isotope analysis of rudist shells to infer the quality (e.g., nutrient and detrital input) and temperature of seawater, respectively, at time of deposition, while the location of the OAE 1a will be determined by the evolution of carbon isotope stable isotope composition (δ13C) of carbonate rocks derived from the literature. The data collected from the study will provide a better understanding of the environment where the Urgonian platform thrived and could help predict what will happen to modern-day carbonate-producing reef systems in the context of modern climate change.



carbonate platform, climate proxy, geochemistry, paleoclimate