INTERPRETING EARLY TRIASSIC (SMITHIAN) CLIMATE USING OXYGEN ISOTOPES OF CONODONT APATITE

The Early Triassic (~251-245 Ma) is conventionally interpreted to have a warm and ice-free climate. Samples were collected for oxygen isotopic analyses of conodont apatite from six globally distributed locations of Smithian age (northern & western Utah, southern Idaho, northern India, eastern British Columbia, and the Canadian Arctic) ranging from paleotropical to mid-paleolatitudes to better understand the Early Triassic climate. Conodont Alteration Index (CAI), a measure of post-burial thermal alteration based on color, was estimated for each of the locations listed above, and range from 1.5 to 5. In addition, SEM images were taken to identify potential physical alteration of the conodonts.

The Smithian δ¹⁸O values range from ~14.4 to 17.6 ‰. In general, samples with low CAI values and smooth, non-pitted surfaces record higher isotopic values, while those with higher CAI values, pitted and/or secondary surface precipitates have lower isotopic values. Assuming conodonts with CAI values of ≤ 3 record primary/near primary seawater values and ice-free conditions, sea-surface temperatures from ~35 to 38 °C for the paleo-tropical and ~32 to 34 °C for the paleo-subtropical regions (Kolodny et al., 1983). These values indicate that the Smithian ocean was significantly warmer than the present oceans and were likely similar to the extreme greenhouse sea-surface temperatures calculated for mid- to late Cretaceous times.