--> Sedimentologic and Paleoceanographic Controls of Anoxia in the Holocene Cariaco Basin (Venezuela): Implications for Control of Deposition of Cretaceous (Eagle Ford) and Jurassic (Haynesville) Source Rocks in Texas

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Sedimentologic and Paleoceanographic Controls of Anoxia in the Holocene Cariaco Basin (Venezuela): Implications for Control of Deposition of Cretaceous (Eagle Ford) and Jurassic (Haynesville) Source Rocks in Texas

Abstract

The recent worldwide unconventional shale oil and gas boom raises questions about controls on the deposition of organic-rich, fine-grained rocks. Environmental and depositional factors such as upwelling, nutrient supply, preservation, and paleo-oxygenation ultimately contribute to the organic richness and hydrocarbon potential of the source rock. In fine-grained rocks such as mudstones, geochemical investigations have proved useful in identifying productive source intervals for unconventional plays. Most studies on Paleozoic and Mesozoic producing source rocks compare redox-sensitive metals and major elements, TOC, isotopes, and mineralogy to identify sweet spots and probable producing zones. Geochemical and sedimentological studies of modern anoxic basins offer analogues for ancient basins and have the potential to elucidate answers to long-standing questions. However, a direct comparison of a Quaternary anoxic basin (e.g., the Cariaco Basin, offshore Venezuela) to Mesozoic source rocks, such as the Upper Jurassic Haynesville and Upper Cretaceous Eagle Ford Formations of Texas, has not been conducted to date. For this study, we selected three complete slabbed cores from the ODP Site 1002 - Cariaco Basin - and described them for sedimentological structures, facies types, pore types, permeability, grain size, fauna, mineralogy, and ichnofacies. Geochemical analyses in addition to present analyses include major and minor elements indicative for anoxic and euxinic conditions, TOC, and isotopes. The Cariaco Basin and the Eagle Ford and Haynesville cores exhibit similar features, such as alternating layers of organic-rich, laminated marls and planktonic-foram-rich limestones. These alternating deposits exhibit distinct geochemical and sedimentologic signatures probably related to sea-level fluctuations, upwelling, and detrital sediment supply. Characterizing recent mudrocks with detailed controls of water and sediment geochemistry, oceanographic changes, age, and nutrient and sediment flux provide in-depth information for controls on Mesozoic source rocks.