Authigenic Fe Mineralization in Shallow to Marginal Marine Environments: A Case Study from the Late Paleocene—Early Eocene Cambay Shale Formation

The late Paleocene–early Eocene warm greenhouse conditions, characterized by elevated pCO2 levels in the atmosphere and a dramatic increase sea surface temperature, prompted abundant authigenic glauconite formation within shallow marine sediments worldwide lowering net sedimentation rate, increasing organic productivity expanding oxygen minimum zones to oceans. early marginal Cambay Shale Formation experienced episodes of inundation represented limestone–green shale alternations. shales host light-green, dark-green, brown pellets. A detailed characterization pellets Valia Vastan lignite mines, integrating sedimentological, petrographical, mineralogical, mineral geochemical data, suggests two distinct varieties Fe–silicate formation, viz. chamosite. While glauconitic green are ubiquitous chamosite confined basal part facies alternating with fossiliferous limestone mine. glauconites mine manifest ‘nascent’ ‘slightly evolved’ maturation stage glauconitization, whereas represent ‘evolved’ type. alternation is overlain ~4 m-thick spherulitic mudstone comprising monomineralic sideritic spherulites, reflecting pure FeCO3 composition. transformed from kaolinite-rich clay under dys-oxic depositional conditions. anoxicity microenvironment, possibly amplified rapid oxidation continent-derived matter, facilitated instead glauconite. increased freshwater influx into environment resulted immature, K-poor siderite spherulites overlying relates beginning regressive phase sedimentation.