Geochemistry of Himalayan Black Shales From Krol-Tal Formation: Implications To Past Oceanic Redox State Around The Pc-C Boundary
This project work aims at constraining the oceanic redox state during this period using the chemistry of organic-rich shales from the Lesser Himalaya. Based on chemical, biostratigraphic and chronological investigation, the Krol-Tal Formation boundary of the Lesser Himalaya have been identified as the Pc-C boundary. Fresh and unmetamorphosed black shales with disseminated pyrites were collected from the Maldeota mines. These rocks overly immediate to the Krol-Tal boundary and belong to the Lower Tal Formation. Like any marine sediment, chemical composition of black shales is also regulated by its detrital, authigenic/biogenic components. Abundance of chemical constituents in their authigenic fraction can serve as a proxy for past oceanic condition. For this, we adopted a partial-leaching technique to extract mainly the authigenic part of the shales. Twenty four black shale samples were treated with inverse aqua regia (3:1 volume mixture of HNO3 and HCl) and this oxidizing solution dissolves the authigenic minerals present in the shales. These solutions were analyzed for their trace elements concentrations using a Quadrupole inductively coupled plasma mass spectrometry (Q ICP-MS). The total carbon of the shale samples were measured using a CHNS analyzer, whereas inorganic carbon content was analyzed using a CO2-coulometer. The difference of total and inorganic carbon concentrations yielded the organic carbon concentration for the samples. I have now been involved in interpreting the shale chemistry dataset to reconstruct the seawater chemistry at about 541 Ma.
Keywords: Krol-Tal Formation boundary, Lesser Himalaya, black shale, shale chemistry