Stratigraphic Control On Source-Rock Distribution: First and Second Order Scale
Published:January 01, 2005
A.Y. Huc, F.S.P. Van Buchem, B. Colletta, 2005. "Stratigraphic Control On Source-Rock Distribution: First and Second Order Scale", The Deposition of Organic-Carbon-Rich Sediments: Models, Mechanisms, and Consequences, Nicholas B. Harris
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We develop and compare a semiquantitative plot showing the distribution the Phanerozoic record of kerogen accumulation in organic-rich black shales (TOC > 3%), to variation in atmospheric CO2, volcanism, sea-level change, and tectonic degassing. Our results suggest that at the first and second stratigraphic order scale, kerogen accumulation is related to periodic tectonically driven increases in atmospheric CO2, enhanced land productivity (CO2 fertilization), aggressive chemical weathering through accelerated soil formation, and flux of nutrients to aquatic bodies, promoting increased marine productivity at the global scale. Moreover, periods of high CO2 are coeval with sea-level rises, forming large anoxia-prone epicontinental seas, which provided conditions favorable for the preservation of organic matter. In this respect, the deposition of major source rocks at this time scale can be speculated as being a result of periodic global “CO2-induced eutrophication”.
At the first-order scale, a time shift is observed between the period of maximum accumulation of prolific source rocks and maximum accumulation of coals. This offset is interpreted by assuming that the depositional settings most favorable for coals were due to global tectonic relaxation at the ends of the two megacycles.
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The Deposition of Organic-Carbon-Rich Sediments: Models, Mechanisms, and Consequences
Depositional models for organic-carbon-rich sediments have been the subjects of both great interest and great controversy for many years. These sediments serve as the ultimate source of virtually all oil and gas. They also represent the interface between biological and geological processes and provide critical evidence for the state of the atmosphere and oceans. Yet despite their importance and decades of research, the origin of these sediments remains the source of vigorous disagreement. The twelve papers in this volume represent the cutting edge of research in this topic. They explore the origin of organic-carbon-rich sediments through a variety of techniques, including sedimentology, geochemistry, paleontology and computer modeling. All papers take multidisciplinary approaches to the topic, and together, they demonstrate the complex interconnected processes that trigger the deposition of organic carbon. This book will appeal to geoscientists in many disciplines, including explorers for petroleum who need models for source rock deposition, organic and inorganic geochemists who study processes in water and sediment, sedimentologists who interpret ancient deposition environments, and climatologists and oceanographers who reconstruct the behavior of the ancient atmosphere and oceans.