THE ROLE OF THE SIBERIAN TRAPS IN THE PERMIAN-TRIASSIC MASS EXTINCTION: ANALYSIS THROUGH CHEMICAL FINGERPRINTING OF MARINE SEDIMENTS USING RARE EARTH ELEMENTS (REES)

The Permian-Triassic boundary (PTB) mass extinction at ~252 Ma was the largest biotic catastrophe in Earth history, resulting in the disappearance of ~90% of marine invertebrate species. Recent work has shown that the most likely trigger for this event was eruption of the Siberian Traps, the largest subaerial flood basalt province of the last 500 million years. However, direct evidence linking the Siberian Traps to the marine mass extinction has been lacking. Volcanic units are commonly characterized by unique rare earth element (REE) signatures, commonly expressed as ratios of light, middle, and heavy REEs (LREE, MREE, and HREE, respectively) and Ce and Eu anomalies. Published studies have shown that the Siberian Traps have an unusual and distinctive REE chemistry (Lightfoot et al., 1990, 1993; Arndt et al., 1993, 1995, 1998; Federenko et al., 1997, 2000). In this study, we analyzed REEs in >400 marine sediment samples from 8 different PTB sections. These data suggest that high-frequency variation in REE sources commenced at the end-Permian extinction horizon and continued into the Early Triassic. The REE signatures of most study samples are consistent with derivation from continental crustal rocks, although selected stratigraphic intervals of the deep-sea Ubara and isolated carbonate-platform Zal sections exhibit patterns of relative HREE enrichment and Eu/Eu* anomalies that are potentially indicative of mantle-derived material. We hypothesize that the REE inventory of these samples was derived primarily from windblown ash emanating from the Siberian Traps. If confirmed, this finding has important implications for the intensity of the end-Permian flood basalt eruptions and their effects on the contemporaneous biosphere.