Late Quaternary sediments on the carbonate platform off western India: Analogues of ancient platform carbonates

Abstract

The Late Quaternary carbonate sediments and sedimentary rocks from the platform off western India were reviewed for their genesis and relationship with their ancient counter parts. Submarine cemented and vadose diagenetic limestones were recovered at different locations on the platform and, neomorphic limestones and caliche pisolites were recovered on the continental shelf south of the platform. Dolomites on the platform were primary and formed by microbial processes under hypersaline, sulphate-reducing conditions during the lowered sea levels. Aragonite ooids were formed from the mineralization of microbial filaments that enveloped their cortex portions. Phosphorites were found in organic-rich, aragonite muds on the continental slope adjacent to the platform and formed from the microbial mineralization of organic matter and replacement of carbonate by apatite during early diagenesis. Microbial processes thus played an important role in the formation of dolomites, ooids and phosphorites reported here and those in ancient deposits. Halimeda bioherms on the platform were grown luxuriantly from the nutrients brought by upwelling currents during the Late Pleistocene-Early Holocene sea level transgression and are similar to the Holocene-Recent deposits in the Indo-Pacific region. Lime muds were bio-detrital and formed primarily from the disintegration of Halimeda bioherms and carbonate skeletal on the platform and then exported to the slope. They resemble fine-grained limestones abundantly reported in ancient platforms. Thus, the different carbonate components on the platform are genetically related to their ancient ones and serve as Late Quaternary analogues for the ancient platform carbonates.

The Steptoean Positive Carbon Isotope Excursion (SPICE), inorganic aragonite precipitation and sea water chemistry: Insights from the Middle–Late Cambrian Port au Port Group, Newfoundland

“…Relict oomouldic porosity is also often associated with microbial buildups in the PAP (Figures 3 and 4). Rao and Gopinathan (2019) suggest that aragonite ooids can be the result of calcification of microbial filaments. Microbialites are commonly found in the aftermath of mass extinctions and the abundance is related to atmospheric composition and sea water chemistry (Riding, 2011).…”