Trace Metals, Rare Earths, Carbon and Pb Isotopes as Proxies of Environmental Catastrophe at the Permian – Triassic Boundary in Spiti Himalayas, India

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Nilotpal Ghosh1, Asish R Basu1, Carmala N Garzione2, Arundhuti Ghatak3, Om N Bhargava4, U K Shukla5 and Arun D Ahluwalia6, (1)University of Texas at Arlington, Earth & Environmental Sciences, Arlington, TX, United States, (2)University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY, United States, (3)Indian Institute of Science Education & Research, Earth & Environmental Sciences, Bhopal, India, (4)Indian National Science Academy, Panchkula, India, (5)Banaras Hindu University, Department of Geology, Varanasi, India, (6)Panjab University, Department of Geology, Chandigarh, India
Himalayan sediments from Spiti Valley, India preserve geochemical signatures of the Permian – Triassic (P-Tr) mass extinction in the Neo-Tethys Ocean. We integrate new sedimentological and fossil record with high-resolution geochemical-isotopic data from Spiti that reveals an ecological catastrophe of global proportions. Trace elements of U, Th, Nb, Ta, Zr, Hf, the rare earths (REE) and carbon, oxygen and lead isotopes measured across the P-Tr boundary in Spiti are used as proxies for evaluating abrupt changes in this continental shelf environment.

δ13Corg excursions of 2.4‰ and 3.1‰ in Atargu and Guling P-Tr sections in Spiti Valley are associated with an abrupt fall of biological productivity while δ13Ccarb and δ18Ocarb record of these sediments shows effects of diagenesis. Here, the P-Tr boundary is compositionally distinct from the underlying Late Permian gray shales, as a partly gypsiferous ferruginous layer that allows additional geochemical-isotopic investigation of sedimentary sources. Conspicuous Ce – Eu anomalies in the light REE-enriched Late Permian shales reflect the source composition of the adjacent Panjal Trap basalts of Kashmir. An abrupt change of this source to continental crust is revealed by Nb - Ta and Zr - Hf anomalies at the P-Tr ferruginous layer and continuing through the overlying Early Triassic carbonate rocks. Pb concentration and isotope ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb identify changes in the sedimentary element flux, distinguishing the Late Permian shales from the distinct siliciclastic continental crustal signature in the Early Triassic carbonates. These geochemical-isotopic constraints on the sedimentary geochemistry of one of the most critical transitions in geological record establish the utility of multi-proxy datasets for paleoenvironmental reconstructions.