Executive Summary : | The transgressive shallow marine deposits of Kutch, Cambay, Jaisalmer, and Barmer basins host glauconitic shale closely associated with hyperthermal events viz. Paleocene Eocene Thermal Maximum (PETM), Eocene Thermal Maximum 2 and 3 (ETM2 and ETM3), Early Eocene Climatic Optimum (EECO), Middle Eocene Climatic Optimum (MECO), and Late Oligocene Warming Event (LOWE). These studies place glauconite as an important proxy to assess the paleogeographic conditions and seawater chemistry during the warm climatic intervals. Glauconite authigenesis requires the transformation of a K-poor, Fe-rich glauconitic-smectite to a K- and Fe-rich glauconite at the sediment-water interface for few Kyr to 1 Myr in areas of low sedimentation rate (Baldermann et al., 2017). Authigenic glauconite formation takes place mostly in the form of very fine silt-sized to fine sand-sized pellets and within the chambers of bioclasts, although pseudomorphic replacement of feldspar, mica and even quartz are not rare. The glauconite pellets show variable K₂O content, ranging from 4 to 8 wt% with moderately high TFe₂O₃ (greater than 20 wt%). Glauconites from the Paleocene-Eocene transitional sediments are distinctively enriched in Al₂O₃ content (greater than 10 wt%.), while those within the middle Eocene and Late Oligocene show considerably lower Al₂O₃ content (less than 8 wt%). The warm climatic condition enhanced the precipitation and runoff, which supplied enhanced nutrients including K, Fe, Al, Si, and Mg into the shallow marine environment, facilitating prolific organic growth and enriching the seawater with cations. Factors such as rapid transgression, reduced sedimentation rate, warm seawater condition, enhanced continental weathering, and enhanced supply of nutrients and decomposition of organic matter favoring dysoxic shallow shelves resulted in abundant glauconite formation during hyperthermal events. Detailed geochemical information regarding the Paleogene glauconites are still lacking, especially the concentration of Rare Earth Elements (REE) and Trace Elements. The enrichment of REE and trace elements have been widely used as a proxy for the depositional conditions as they readily get remobilized and incorporated/adsorbed into sediments (Tribovillard et al., 2006). Authigenic glauconite, can be a potential sink of redox-sensitive REEs and trace metals as it tends to form in an oxygen-depleted, (mildly) reducing environment. Apart from the redox conditions, REE accumulation in glauconite are also useful as a proxy to the paleoceanographic parameters such as sources of the sediment as well as paleo-productivity (Tribovillard et al., 2021, Giresse et al., 2021). Glauconite authigenesis has significant impact on benthic Fe-fluxes, and serves as a major iron sequestrating mineral in sub-oxic depositional environments. This study on the Paleogene glauconites will open a new paradigm into the application of glauconite in a sedimentological as well as paleoclimatic context. |