Paleopedology and Stable-Isotope Geochemistry of Late Triassic (Carnian-Norian) Paleosols, Durham Sub-Basin, North Carolina, U.S.A.: Implications for Paleoclimate and Paleoatmospheric PCO2
Steven G. Driese, Claudia I. Mora, 2002. "Paleopedology and Stable-Isotope Geochemistry of Late Triassic (Carnian-Norian) Paleosols, Durham Sub-Basin, North Carolina, U.S.A.: Implications for Paleoclimate and Paleoatmospheric PCO2", Sedimentation in Continental Rifts, Robin W. Renaut, Gail M. Ashley
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Paleosols in rift-related Upper Triassic (Camian-Norian) terrestrial deposits of the Durham sub-basin of North Carolina record evidence of a shift from wetter to drier conditions, and slightly elevated atmospheric levels of carbon dioxide. Paleosols in siltstone interbeds of Lithofacies Association IIa (upper Carnian to lower Norian) are characterized by abundant micrite-cemented crayfish burrows, Scoyenia trace fossils, and numerous reduction spots and haloes indicating wet, but not hydric, soil conditions. Paleosols in fluvial-lacustrine sandstone-shale fades of Lithofacies Association IIb (lower Norian) record deposition in semiarid to subhumid climate characterized by seasonal soil-moisture deficits and high evapotranspiration. Pedogenic carbonate in both paleosols includes micritic rhizolith, nodule and burrow-fill morphologies. The carbon-isotope compositions of pedogenic carbonate differ significantly between paleosols within the two lithofacies, indicating different controls imposed by the pedogenic environments. The δ13C values of pedogenic, micritic rhizoliths in the paleosols suggest somewhat elevated pCO2 during the late Carnian-early Norian, two to three times modern levels, and support general estimates of pCO2 based on similar carbonates in time-equivalent paleosols.
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Sedimentation in Continental Rifts
Continental rift basins have long been of interest to sedimentologists. Of all the terrestrial settings, rift basins typically provide the greatest accommodation space, and consequently have some of the longest records of continental sedimentation. These records are a product of a complex interplay between several factors that include geological structure and tectonic activity, volcanism, climate and its temporal variability, hydrology, biology and time. Sedimentation in Continental Rifts is a timely update on this exciting interdisciplinary field and presents new approaches and insights into tectonic and structural controls of sedimentation. Other topics included are lacustrine and fluviatile depositional environments and some lesser-known settings, such as springs, wetlands, and paleosols. Several papers consider the behavior of silica in rift lakes, particularly the roles of microorganisms in silica precipitation, whereas others examine the paleoenvironmental importance of freshwater carbonates. The contents of the volume show that sedimentological research in rift basins has progressed beyond basic facies description and general models, and is now focused on understanding the integrative effects of physical, chemical and biological processes in rifts.