Paleoenvironment and Paleoclimate Reconstruction through a Life Crisis: the Sedimentology & Geochemistry across the Permo-Triassic Boundary in NW China

Stephanie G. Thomas

Southern Methodist University Department of Geological Sciences

Dallas, TX

sgthomas@smu.edu

The Permian-Triassic extinction is labeled as the most severe extinction event in geologic history, yet the mechanism(s) by which it occurred remain largely elusive. Marine and terrestrial organisms were equally devastated, indicating that the mechanism(s) responsible extended to both marine and terrestrial realms. The terrestrial Permian-Triassic boundary (PTB) is known primarily from the high latitudes of Gondwana. This project will evaluate exposed terrestrial section spanning the PTB from the Junggar Basin, NW China, a northeastern Tethyan locality, with specific focus on paleoenvironmental reconstruction and assessment of pCO₂ through soil-formed proxy minerals across the PTB.

Field efforts will focus on identifying and describing paleosols, placing them accurately within a stratigraphic framework, and collecting samples for XRD, petrography, and elemental and stable isotope analysis of paleopedogenic minerals. Results of fieldwork indicate the presence of paleosol morphologies consistent with perennially wet soil moisture regimes in the Late Permian, whereas paleosols containing soil-formed carbonate and pseudomorphs after gypsum suggest a drier environment characterized by net soil moisture deficiency during the Early Triassic. Chemical analyses may provide quantitative information such as paleotemperature, paleoprecipitation, and atmospheric pCO₂ across the PTB. Preliminary data suggest that the rocks appear to have undergone little diagenetic alteration. Accordingly, the Junggar Basin provides an opportunity to examine pCO₂ variability and environmental change across the PTB through multiple proxy records. Morphological variations will be examined in concert with geochemical data from organic matter and pedogenic minerals to provide the most robust paleoenvironment record possible and greater environmental context for the mass extinction.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid