Date of Award

6-1-2014

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences/Environmental, Earth & Ocean Sciences

First Advisor

Robyn Hannigan

Second Advisor

Rob Etter

Third Advisor

Allen Gontz

Abstract

The Permian-Triassic (PT) extinction is regarded as the largest extinction in Earth's history. While a number of hypotheses have been proposed to explain the cause, tempo, and severity of the mass extinction they are often contradictory. Conceptually, this research focused on integrating the Neo-Tethyan Spiti Valley (Himachal Pradesh, India) sections into the global PT stratigraphy and from this, more clearly understand the local and global geological records preserved in these sections. The purpose of this research was to determine if the geochemical signature of the PT sections in Spiti Valley were altered by post-depositional process, reconstruct the paleo-environment of the Neo-Tethys using geochemistry to identify local/regional and global signatures, interpret global event signatures in relation to the record of marine sections from the Paleo-Tethys, Boreal, and Panthalassa oceans. This research specifically used stable isotopes (C, N, and S), major, and trace element geochemistry of the Upper Permian Gungri Formation (shale) exposed in Spiti Valley to more precisely reconstruct the paleo-environment of the Neo-Tethys. The primary conclusions of this research are that the geochemistry of Spiti Valley sections are not significantly altered by post-depositional and so can be used to reconstruct paleo-environmental conditions. Evaluation of the chemostratigraphy of the sections revealed "event" horizons associated with changes in sedimentation rate and oxygenation prior to the late Permian Regression and the PT boundary. Geochemical evidence suggests that the ferruginous layer, considered by many to be the PT boundary, represents a global sedimentary hiatus. The layer itself formed at a time when the basin was stratified creating a distinct oxic-anoxic boundary where Fe and Mn oxyhydroxide and Fe-Mn oxides were formed at the sediment water interface. The Neo-Tethys was a shallow ocean with poor circulation and limited connectivity to the Paleo-Tethys throughout much of the late Permian and so behaved like a "bath-tub". The ferruginous layer, I conclude, was deposited coincident with the late Permian Regression which is recorded in most marine PT sections. The regression was caused by the closure of the Paleo-Tethys due to the formation of the Cathayasian Bridge. With a precipitous drop in sea level and a well-stratified shallow ocean the ferruginous layer is much like a bath-tub ring. In addition to this major event, the Neo-Tethys PT sections also record other events associated with changes in sedimentation rate with these events time-correlative in most cases. There is no direct evidence of volcanism in the uppermost Permian. There is, however, sufficient evidence of a catastrophic event in the uppermost Permian of the Neo-Tethys that can be associated with a possible bolide impact.

Comments

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