Evolving marine sedimentation, redox stratification, and biogeochemical cycling in mid- to low-latitudinal non-frozen waters during late Neoproterozoic global-scale climatic transitions

Abstract

Indian Neoproterozoic successions offer unique insights into global paleoclimatic and biogeochemical transitions. This study presents a detailed sedimentological and geochemical analysis of marine siliciclastic sedimentary rocks from the Cave-Temple Arenite Member of the Kerur Formation, the lowermost formation of the Badami Basin within the Dharwar Craton of the South Indian Shield. Geochronological constraints on overlying carbonate rocks from the Konkankoppa Limestone Member of the uppermost Katageri Formation provide a post-Cryogenian to mid-Ediacaran age of 604 ± 25 (1σ) Ma for the upper limit of marine sedimentation. Sedimentological and geochemical proxies, accompanied with previous geochronological and provenance studies, indicate a rift-related intracratonic basin influenced by tectonic processes associated with the Rodinia supercontinent breakup. Provenance studies reveal sediment contributions predominantly from the Archaean to Mesoproterozoic quartzofeldspathic sources. Marine intervals exhibit distinct stratification, with oxic, brackish to mildly saline shallow waters transitioning to anoxic-euxinic, more saline deeper waters. These conditions emerged above a fluvio-alluvial cycle formed during cold, arid climatic conditions. However, CIA (Chemical Index of Alteration) values suggest subsequent warmer, humid climates during the transgression and evolution of the marine interval. This scenario of climate change and marine transgression likely reflects a global climatic shift during one of the two potential hothouse phases, depending on the estimated minimum and maximum depositional ages spanning approximately from 629 to 579 Ma. These ages correspond either to the post-Marinoan or the post-Gaskiers glaciations, both characterized by intense chemical weathering, high nutrient influx, and enhanced productivity along deeper marine shelves. The studied succession, marked by the absence of glacial deposits and a stratified non-frozen marine setting supposedly situated at mid- to low latitudes, offers evidence for a unique paleoenvironment that harboured active biogeochemical cycles amidst evolving climatic conditions.