Textural and petrographic studies of multistoried sand bodies as observed in quarry sections in West Godavari district, Andhra Pradesh, India

The unfossiliferous Rajahmundry Sandstone beds of Mio-Pliocene age from the Minanagaram and Gangolu quarry sections have been studied for their textural characteristics and petrographic variations. The lithological successions in these sections are dominantly made up of sandstones, and the associated argillaceous and conglomerate facies are secondary. Cyclic sandstone beds with erosional base and upward fining are characteristics of these sand bodies in the quarry faces. Grain size analysis of the Minanagaram quarry samples reveals that they are poorly to moderately sorted and very fine skewed, while the Gangolu samples are more fine-grained, poorly sorted and near symmetrically skewed. Petrographically, ferruginous argillaceous litharenite and ferruginous litharenite are identified in the Minanagaram quarry section and ferruginous argillaceous litharenite alone in the Gangolu quarry. The former quarry section reveals predominance of planar and trough cross-bedded sandstones interspersed with thin polymict type of conglomerate units. The petrofacies in Q-F-L ternary diagrams mainly suggest a continental and recycled orogen source of cratonic interior tectonic setting, in an intense chemical weathering which resulted in quartz-rich sediments formed in a humid climate. Qun-Qnun-Qp ternary plots of detrital quartz suggest plutonic to medium and high rank metamorphic source rocks. Gangolu sequences are fineto medium-grained sandstones inter-bedded with thin conglomerate beds. The lithoclasts are fragments of schists, shales and rare sandstone and are deeply squashed. There is a total absence of polycrystalline quartz grains in these samples. Sedimentary structures such as trough and plane cross beds are common in Minanagaram quarry, where as plane beds dominate Gangolu quarry section indicating a moderate to high flow regime in the later. Diagenetic alteration of such unstable minerals as feldspars and ferromagnesian minerals resulted in the production of hematite and argillaceous cement. As sediments are coarse and partially cemented without showing any pressure solution effects, it is inferred that they have been subjected to shallow burial diagenetic environment. An attempt has been made to draw information on depositional, source area, weathering, transportational, and paleoclimate histories. © 2013 CAFET-INNOVA TECHNICAL SOCIETY.