SHRIMP-RG MEASUREMENTS OF U, Y AND REE PROFILES ON EARLY TRIASSIC CONODONT ELEMENTS FROM NAMMAL, PAKISTAN, AND THEIR IMPLICATIONS FOR BIOTIC RECOVERY AFTER THE END-PERMIAN MASS EXTINCTION

Because the phosphatic feeding elements of conodonts are less prone to diagenetic alteration than carbonate fossils and bulk carbonate rock, they are increasingly used in geochemical studies to assess past ocean conditions (e.g., seawater temperature, redox chemistry).

In particular, conodonts have been used to assess the presence and extent of anoxic waters during and after the end Permian mass extinction and thereby constrain their role in controlling recovery dynamics. Using Laser Ablation-ICPMS measurements of Cerium anomalies and Thorium/Uranium ratios on conodonts from South China, Song et al. (2012) suggested the occurrence of three episodes of anoxia in the Early Triassic. Yet, as discussed in other studies, conodonts tend to be enriched in specific elements (e.g. trace elements) during diagenesis and the full spectrum of Rare Earth Elements plus Yttrium (Y-REE) is needed in order to assess a primary seawater signature.

Using the SHRIMP-RG, we measured the in-situ concentrations of Uranium and of the full Y-REE spectrum in an Early Triassic sequence of exceptionally preserved conodont elements (CAI = 1) from the Nammal section, Salt Range, Pakistan. These same samples were used in a previous study of oxygen isotopes to reconstruct variation in Early Triassic seawater temperatures (Romano et al. 2013). Our new results add to existing evidence that the oxygen isotope values reflect seawater temperatures rather than diagenetic alteration. They also help to further constrain the timing of both global and local (Pakistan, Southern Tethys) anoxic events within the recovery of the end-Permian mass extinction.