Lithostratigraphy, depositional history and sea level changes of the Cauvery Basin, southern India

The sedimentary sequence exposed in the erstwhile Tiruchirapalli district hosts a more or less complete geological record of the Upper Cretaceous-Tertiary period. Systematic field mapping, collation of data on the micro-meso scale lithology, sedimentary structures, petrography, faunal assemblage and facies relationships of these rocks, in the light of modern stratigraphic concepts, helped to enumerate the lithostratigraphic setup and depositional history of the basin. Spatial and temporal variations of the lithologies and revised stratigraphic units are presented in this paper. Many high frequency sea level cycles (presumably fourth or higher order) which stack up to form third order sea level cycles (six in number), which in turn form part of second order cycles (two in number), including seven eustatic sea level peaks, have been recorded in this basin. Trend analysis of sea level curves indicates a gradual increase of the sea level from Barremian to Coniacian and a gradual decrease from Coniacian to Danian. Such lasting sea level trends had their influence on the sedimentation pattern and facies association. It is inferred that depositional bathymetry was maintained at a shallow-moderate level, primarily influenced by a lack of major subsidence during the depositional history of this basin. The study also revealed a prevalent simple basin filling process and dominant control by sea level changes, rather than tectonic movements over the depositional regime

CenomanianTuronian transition in a shallow water sequence of the Sinai, Egypt

Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, δ13C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanianearly Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, low-oxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak δ13C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the δ13C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the δ13C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first δ13C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous δ13C shift, but delayed effects of OAE2 dependent on water depth

Geochemistry and Genesis of Submarine Manganese Crusts

The present manuscript seeks to review the nature, occurrence, origin, genesis and palaeoceanographic accumulation record of marine Mn crusts which are widespread on the sea floor of the World Ocean. Interest in Mn crusts is based on two main topics: scientifically the composition of Mn crusts acts as record for palaeochemistry and palaeoceanography of the environment, and economicially the potential of Co and Pt in the crusts has been considered to be very high