Proterozoic glauconitic peloids from South India; their origin and significance

Abstract

Glauconitic minerals, as peloids, are widespread in the arkosic and subarkosic sandstones of the three Proterozoic units of the Pranhita-Godavari Valley, South India. These minerals grew at the expense of detrital feldspars on a scale so far unknown, and the process offers a viable alternative model for origin of the glauconitic peloids, particularly in the Proterozoic and some unfossiliferous Phanerozoic rocks as well. Conversion in situ is testified inter alia by the presence of feldspar relics within the peloids. Replacement of the peloids by all other authigenic phases and evidence of their compaction and high precement porosity of the host sandstones point to preburial authigenesis of these minerals near the depositional surface. Glauconitization was entirely inorganic, and the morphology of the peloids is dictated by that of the precursor grains. Occurrence in rapidly deposited sediments under semiarid to arid conditions with extensive development of current and wave features suggests formation under conditions of warm, open circulation with high sediment influx and therefore modifies existing ideas about the physical constraints on glauconitization.