Petrography and geochemistry of the Upper Cretaceous Gryphaea Limestones, Kallankurichi Formation, Ariyalur Group, Trichinopoly, Southern India: Implication for palaeoenvironment

Abstract

Sub-surface Kallankurichi gryphaea limestone formation is observed between Archaean and Quaternary outcrops.  Petrographic observation reveals that mega fossils are absent and it contains abundant skeletal fragments of pelecypods, gastropods, foraminifera, bryozoa, and symbiotic algae. X-ray diffraction (XRD) analyses reveal the mineralogical components of both carbonate and clay minerals. Carbonate minerals include calcite, siderite, witherite, malachite, smithsonite, and rhodochrosite. Clay minerals detected are kaolin, montmorillonite, and palygorskite. Major element composition represents predominance of CaO, SiO₂, Al₂O₃, and Fe₂O₃ oxides, while MgO, MnO, Na₂O, K₂O, TiO₂, and P₂O₅ oxides are depleted. Statistical analyses of correlation coefficient, principal component analysis, and cluster analysis represent the geochemical affinities and aerial distribution similarities among major elements. Palaeoclimate inferred through biotic proxies, major element geochemistry, and clay minerals represents arid and semi-arid climate.