Unravelling paleoenvironmental dynamics across the cretaceous-paleogene (K-Pg) boundary in the offshore Mannar Basin of the Northern Indian Ocean

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Reconstructing the sedimentary environment and comprehension of the process of mineral enrichment rely significantly on lithofacies, which can be considered a proxy for the paleoenvironment. This study investigates the lithostratigraphic characteristics of the Late Cretaceous to Early Paleocene period, spanning the pivotal Cretaceous-Paleogene (K-Pg) boundary, in the Mannar Basin. Utilizing 25 drill cutting samples from the Dorado exploration well at intervals of 10 meters, ranging from 2800 meters to 3040 meters in depth, various lithofacies were identified using Scanning Electron Microscope (SEM), polarizing microscope, and X-ray diffraction (XRD) analysis. Petrographic examinations revealed a diverse mineral arrangement, ranging from very fine to coarse-grained textures. Dominant minerals identified through XRD analysis include Quartz, Feldspar, Carbonate, and various clay minerals, facilitating shale classification. Five distinct lithofacies were delineated, encompassing calcareous, clayey, calcareous siliceous mixed, calcareous clayey mixed shales, and siliceous rocks. Noteworthy mineralogical compositions include abundant kaolinite, chlorite, and hematite minerals in the Maastrichtian succession, transitioning to montmorillonite, illite, and pyrite dominance in the Early Maastrichtian succession. Through clay mineralogy, this study discerns significant shifts in paleoenvironmental conditions, ranging from anoxic, arid to semi-arid climates during the Campanian to warm/wet, oxidizing environments during Maastrichtian, and finally to arid/semi-arid conditions during the early Paleocene. Additionally, evidence of early burial diagenesis and Late Maastrichtian sea-level regression is identified, contributing to a comprehensive understanding of environmental dynamics during this critical geological period in the Mannar Basin in the Equatorial Margin of the Northern Indian Ocean.