Lower Toarcian (Upper Liassic) Black Shales of the Central European Epicontinental Basin: A Sequence Stratigraphic Case Study from the Sw German Posidonia Shale
Published:January 01, 2005
H.-J. Röhl, A. Schmid-Röhl, 2005. "Lower Toarcian (Upper Liassic) Black Shales of the Central European Epicontinental Basin: A Sequence Stratigraphic Case Study from the Sw German Posidonia Shale", The Deposition of Organic-Carbon-Rich Sediments: Models, Mechanisms, and Consequences, Nicholas B. Harris
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During the early Toarcian, black-shale deposition was widespread, and several different models have been proposed to explain environmental conditions and controlling factors. Multidisciplinary investigations combining microfacies analysis, geochemical parameters, and paleoecological data reveal that sea-level variation was the main forcing factor for facies distribution within the Central European Basin. This interpretation is supported by the comparison of several Lower Toarcian sections from Europe.
The results show that a Pliensbachian to early Toarcian regression caused the enclosure of the SW German basin, inducing stagnant conditions. Deposition of organic-matter-rich sediments started in the central part of the basin while contemporaneous sediments in basin-margin areas were affected by reworking. The subsequent slow transgression was of minor extent and led to long-term stagnation, which led to anoxic conditions in the benthic environment. Maximum oxygen depletion existed during the exaratum Subzone times and is indicated by largest fecal pellet sizes, a distinct type of lamination, highest content of organic carbon and sulfur, and a lack of paleocurrents and benthic macrofauna. Enhanced water circulation and improved living conditions in the benthic environment could not have been established until a further sea-level rise. Consequently, the bituminous mudstones of the European Epicontinental Sea were not deposited during a Liassic sea-level maximum.
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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.