PROTEROZOIC GLAUCONITIC PELOIDS FROM SOUTH-INDIA - THEIR ORIGIN AND SIGNIFICANCE

Glauconitic minerals, as peloids, are widespread in the arkosic and su barkosic sandstones of the three Proterozoic units of the Pranhita-God avari Valley, South India. These minerals grew at the expense of detri tal feldspars on a scale so far unknown, and the process offers a viab le alternative model for origin of the glauconitic peloids, particular ly in the Proterozoic and some unfossiliferous Phanerozoic rocks as we ll. Conversion in situ is testified inter alia by the presence of feld spar relies within the peloids. Replacement of the peloids by all othe r authigenic phases and evidence of their compaction and high precemen t porosity of the host sandstones point to preburial authigenesis of t hese minerals near the depositional surface. Glauconitization was enti rely inorganic, and the morphology of the peloids is dictated by that of the precursor grains. Occurrence in rapidly deposited sediments und er semiarid to arid conditions with extensive development of current a nd wave features suggests formation under conditions of warm, open cir culation with high sediment influx and therefore modifies existing ide as about the physical constraints on glauconitization.