A variety of stable isotope measurements have been found useful in studying processes of environmental change. Measurements of δ13C, δ18O, δ34S and 87Sr/86Sr all can provide information about the conditions of the water column in which sediment deposition occurred, but the most widely applied of these is δ13C. The carbon isotope record for the Triassic System is a complex one; a pronounced negative excursion begins below the base of the Triassic System and continues into the basal Triassic. The succeeding 4 to 6 Ma Lower Triassic interval is marked by isotopic instability, with positive and negative excursions, continuing through the basal Middle Triassic. In contrast to the Lower Triassic, most of the Middle and Upper Triassic display relative isotopic stability, with rising values of δ13C likely reflecting environmental recovery and increasing storage of organic carbon in terrestrial environments. The uppermost Triassic is marked by a pronounced negative excursion near the system boundary that has been linked to significant biotic turnover. The causes of the various excursions remain under investigation, particularly those at the system boundaries, with outgassing during volcanic activity, changes in productivity, ocean anoxia, and seafloor methane releases all suggested as mechanisms both for perturbing the global carbon cycle and for forcing biotic extinction.
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The Triassic Timescale
The Mesozoic Era begins with the approximately 50-million-year-long Triassic Period, a major juncture in Earth history when the vast Pangaean supercontinent completed its assembly and began its fragmentation, and the global biota diversified and modernized after the end-Permian mass extinction, the most extensive biotic decimation of the Phanerozoic. The temporal ordering of geological and biotic events during Triassic time thus is critical to the interpretation of some unique and pivotal events in Earth history. This temporal ordering is mostly based on the Triassic timescale, which has been developed and refined for nearly two centuries. This book reviews the state of the art of the Triassic timescale and includes comprehensive analyses of Triassic radio-isotopic ages, magnetostratigraphy, isotope-based and cyclostratigraphic correlations and timescale -relevant marine and non-marine biostratigraphy.