Gypsum–anhydrites in 1.9 Ga Vempalle Formation, Cuddapah basin, India: A note on the Palaeoproterozoic environment and diagenetic condition

Abstract

The Cuddapah basin consists of generally well-preserved Palaeoproterozoic-Neoproterozoic sedimentary and associated volcanic rocks. The detailed lithological studies of sedimentary rocks of Vempalle Formation from the narrow linear belt of 15 km, in the southern margin, show the occurrence of layered gypsum in the cherty dolostone-shale intercalated facies, red shale and phosphatic dolostone facies of the Vempalle Formation. The petromineralogical studies reveal that gypsum is in close association with anhydrites. Microscopically, three different types of gypsum and anhydrite are identified, viz., lath-shaped, equant-shaped and anhedral-shaped grains. The equant variety corresponds to a granular gypsum, whereas the anhedral grains of gypsum exist as the granular and fibrous variety as seen in the hand specimen. The presence of gypsum/anhydrite has been confirmed by the petromineralogical, X-ray diffraction and chemical analytical data. The phosphatic dolostone is the host rock for stratabound type of uranium deposit at Tummalapalle, Cuddapah district, Andhra Pradesh, which is one of the most unique types of uranium mineralisation in the world. Abundant pseudomorphs of gypsum and anhydrite relicts and discontinuous gypsum layers within these dolostones, nodules of chert and gypsum indicate the interrelationship between the diagenesis and genesis of uranium mineralisation which indicates the carbonate precipitation in the sulphate-rich hypersaline environments.

Cuddapah Basin, India: A Collage of Proterozoic Subbasins and Terranes

“…Studies indicated that the 1.9 Ga ultramafic sill (Anand et al, 2001) in the lower part of the Tadpari Formation mineralogically varies from olivine gabbro norite to plagioclase bearing ultramafic rocks (Sesha Sai et al, 2017). Goswami et al (2018) have recorded the presence of bimodal volcanics and tuffs within the Tadpatri Formation.…”

Genesis of Pyrite Concretions: Constraints from Mineral and Geochemical Features of Longtan Formation in Anhui Province, Eastern China

“…The presence of gypsum in the bivalve fossils indicates that the nucleus has likely come from an arid and oxidizing environment [30][31][32]. The main composition of the concretions around the nucleus is diatomite (SiO 2 ·2H 2 O) with no detrital particles and carbonate rocks.…”