267 / 2019-07-01 18:44:33

High alumina glauconite formation in the background of Paleocene-Eocene warming events

Glauconite,, Jaisalmer,, PETM,, Transgression,, Eocene

In this study, we report the origin of high alumina glauconite within the shallow marine-originated Khuiala Formation in Jaisalmer Basin, India. Detailed biostratigraphic investigation constrains the age of the Khuiala Formation to Late Paleocene to Early Eocene and the overlying Bandah Formation to Middle Eocene. The basal 40 cm of the Te-Takkar Member is a glauconitic shale/siltstone containing abundant (roughly 50%) glauconite pellets. Glauconitic shale/siltstone grades into a grey shale unit which hosts the Paleocene-Eocene boundary and is rich in planktic foraminifera indicating inner neritic depositional environment. Petrographic investigation reveals that glauconite may form as fecal pellets and very rarely as bioclasts infillings. Major oxide analysis on 119 glauconite grains reveals a high alumina (>10%) nature of the glauconite. Total iron content is moderate (20-25%) of which the majority is Fe3+ (Fe2+/Fe3+ ratio increase upward between 0.02 to 0.04 within the same lithology). Trace element and REE data indicate dys-oxic condition for glauconite formation. Kaolinite is reported as the dominant clay deposited during the Paleocene-Eocene Thermal Maximum. Increased chemical weathering and high run-off is responsible for a high amount kaolinite deposition into the shallow marine environment. The Te-Takkar Member also shows kaolinite as the dominant clay mineral indicating a high run-off/continental input into the depositional environment. Glauconites of similar age are reported from Valia Mines, Gujrat. These glauconites formed at relatively shallow depth compared to modern glauconite formation. We here propose a model for glauconitization in the background of Paleogene warming events in which sub-oxic/dysoxic environment prevailed in the shallow marine environment resulting in widespread glauconite formation. The high alumina content can be attributed to the presence of kaolinite or could be because of the substrate, which is progressively altered to form glauconite.