MINERALOGICAL-GEOCHEMICAL EVIDENCE OF SILICA AND CARBON FLUX IN THE PERMIAN - TRIASSIC PALEO-TETHYS OCEAN

Recently, we reported (Nestell et al., 2015) the taxonomy of foraminifers from the Permian - Triassic Lung Cam section in northern Vietnam, recognizing the foraminiferal species, Hyperammina deformis and Ammodiscus kalhori and microconchids that extended to the Graphic correlation boundary and above. We established the presence of carbon and silica on the surface by laser Raman spectroscopy. Here, we provide detailed analysis of these free specimens in Raman spectroscopy and X-ray diffraction (XRD) studies. We also examined the mineralogy of the fine grained host sediments by XRD. In these detailed examinations of the free specimens of Globivalvulina, microconchids and ostracods, we find their tests are primarily composed of silica and carbon is ubiquitous. We discovered in the bulk sediments hosting the microfossils, Tridymite and Opal A along with ankerite, dolomite, quartz and rare calcite. The discovery of the above mineral assemblage in the Permian – Triassic Paleotethys sediments reflects unique paleoenvironment at the time of extinction. This condition indicates a shift in ocean chemistry involving iron and silica that prevented the precipitation of calcium carbonate in the shells and skeletons of many species.

The changing condition of the ocean brought in silica, iron and carbon in the microfossils and their host sediments. The microorganisms that could adapt to this environment by taking silica to build the shells survived. These include the Hyperammina deformis, Ammodiscus kalhori, ostracods and microconchids. Based on our observation of carbon coatings and silica in the tests of all the specimens, we conclude that seawater was contaminated with excess carbon and silica. We also observed framboidal and discrete pyrite crystals attached to the test walls. Pb isotope ratios of the pyrite cluster reveal that the lead was derived from carbon contaminated seawater. We conclude that the Permian – Triassic transition experienced a severe change in environmental conditions, characterized by high influx of silica and carbon into the Paleo-Tethys Ocean that resulted in the carbonate shelled species to perish. We propose that this carbon and silica in the ocean were sourced from impact-triggered Siberian volcanism similar to the recent proposal to link the end-Cretaceous impact to Deccan volcanism.