Introduction

The transition from Permian to Triassic (P-T) periods about 252 million years before present was marked by the largest mass extinction event in geological history, that extinguished 90% of terrestrial and 95% of marine species from the face of the Earth.

Contrary to the CretaceousTertiary extinction event, the cause of this biological catastrophe is not well understood and is the subject of current scientific debate. Several hypotheses attribute lowering sea levels, flood volcanism in Siberia, large scale oceanic anoxia, meteorite impact, and submarine methane clathrates to a violently changing paleoenvironment of the Earth during this transition. This transition is well preserved as stratigraphic rock sections across the globe and reflect diverse paleoenvironments ranging from terrestrial to transitional to deeper marine settings.

The Spiti Valley in the Upper Himalayas of India hosts such P-T boundary sections that reflect a portion of the Tethyan ocean. The Spiti sections comprise of Triassic limestones (characterized by the occurrence of marine fossils), overlying the Permian gray shales and the two sharply separated by a thin red oxidized iron rich layer (ferruginous layer). The variable composition, texture and fossil assemblage across this section reflects a period of rapid paleoenvironmental change that demands further investigation.

Fig.1: Permian-Triassic boundary in Spiti, India. Left: Litho-bio Stratigraphy (Shukla et al., 2002); Right: Photograph of the PT section in Atargu, Spiti

Objective

The objective of this project was to microscopically examine the P-T boundary secton from the Spiti Valley of Himachal Pradesh in the Indian Upper Himalayas to characterize the paleoenvironmental conditions in this portion of the Paleotethys. In this Project, a range of microscopic and microprobe techniques were used to search, detect and image evidences and remnants of the prevailing environmental conditions during the Permo Trissic transition.

Rock samples used for this project were collected from the Atargu, Guling and Mud section in the summer of 2009. Imaging was done on polished thin sections of rocks and a few fossils fragments.

Methods

The following methods were used for this project work. All procedures, instrumentation and methods were carried out at the Institute of Optics and the Geology department of University of Rochester, following standard protocols.

1. Light Microscopy: Polarized light and Differential Interference Contrast (DIC) Reflected light

2. Sputter Coating: Polished thin sections of rocks and fossil samples were sputter coated with Gold particles to develop a conductive coating of 100 for imaging under the SEM.

3.Scanning Electron Microscopy (SEM) - Backscattered (BSD) and Secondary Electron (SE2) detectors.

4.Electron flight simulator

5. Energy Dispersive X-ray Spectroscopy (EDS)

6. Atomic Force Microscopy (AFM)

7.Colorization