delta C-13 and delta O-18 values of Triassic brachiopods and carbonate rocks as proxies for coeval seawater and palaeotemperature

摘要

A dataset of 160 isotope delta(13)C and delta(18)O values from Anisian, Ladinian, Carman and Rhaetian articulate brachiopod shells, complemented by 158 carbon and oxygen isotope values from whole rock carbonates, define the first continuous stable isotope baseline trends for the Triassic seawater. The carbon isotope data suggest the existence of several short-term high amplitude excursions in the Early Triassic, followed by a predominance of values around 0.5 +/- 1 parts per thousand during the Middle Triassic, a rise to similar to 3.5 parts per thousand during the Carman, plateau at this level during the Late Carman to Early Norian, and a 1.5 parts per thousand decline in the Middle Norian to values around 2 parts per thousand during the Late Norian-Rhaetian interval. The causation scenarios for these rapid oscillations are at present equivocal, but may in part reflect a biological instability of the carbon cycle following the recovery from the end-Permian extinction event and/or an input of "mantle'-derived CO2 from enhanced volcanic activity.The delta(18)O values from well-preserved brachiopods from the Tethyan realm range front -3.9 to -0.6 parts per thousand V-PDB. These values require open marine Triassic seawater delta(18)O values close to 0 parts per thousand V-SMOW for the calculat