Microtextures on quartz grains of Campanian-Maastrichtian sediments of Ariyalur Group of Tiruchirapalli Cretaceous, Tamil Nadu - Implication on depositional environments

Studies on the quartz grains of the Campanian-Maastrichtian sediments of th e Ariyalur Group of Tiruchirapalli Cretaceous, Tamil Nadu, using Scanning E lectron Microscope (SEM) have brought out nineteen distinct microtextures. They have been grouped into features based on their mode of origin. Of thes e, thirteen are of mechanical and five mechanical and/or chemical origin wh ile one distinctly chemical. The quartz grains of the Ariyalur Group sedime nts show a wide range of conchoidal fractures, straight steps acid arcuate steps formed during the liberation from the metamorphic and igneous source rocks. The microtextures v's, pits, straight and curved scratches are chara cteristic of the marine environment. The frequency of these features is hig her in the grains from the Sillakkudi, Kallankurichchi and Ottakkovil Forma tions. Rarity of these features on quartz grains from the Kallamedu Formati on is suggestive of variation in transport and depositional conditions. It has been inferred from the microtextures that the source for the quartz gra ins in the Ariyalur Group sediments has been the nearby Precambrian crystal line basement.