Petro–chemistry and diagenesis of sandstones of Patherwa Formation, Son Valley, India

Abstract

The sandstone of Patherwa Formation, (Semri Group) is constituted by quartz, feldspar, micas, rock fragments and heavy minerals. Abrupt changes in the grain size are recorded and sandstone is grouped as fine–grained (FGS), medium–grained (MGS), coarse–grained (CGS) and very coarse–grained (VCGS). The field and petrographic divisions are equally reflected in their chemistry. CGS shows highest SiO2 content (mean 86.59 wt%) followed by MGS (mean 80.78 wt%), VCGS (mean 76.51 wt%) and FGS (mean 75.21 wt%). SREE content is highest in FGS (180.51 ppm) and lowest in CGS (129.64 ppm). VCGS possesses anomalously high SREE values (2070.62 ppm). Range of weathering indices including CIA, CIW, PIA and ICV indicates moderate to strong chemical weathering in the provenance. Large range of variation in weathering indices suggests that physical weathering facilitated chemical weathering, under subtropical humid climate. Mechanical compaction led the rearrangement of grains forming point and long contacts while diagenesis dissolved mobile grains which made sandstone highly quartzose. The progressive compaction getting initiated at the sediment–water interface continued till deep burial in a rapidly subsiding basin. Geochemical provenance modelling suggests production of detritus from a predominately granite–gneissic terrain bearing some mafic rocks. Palaeocurrent data indicates sediment supply from two source terrains, i.e. BGC and Bijawar. Synthesis of petrochemical attributes and diagenesis history, assigns a tectonically active setting where generation of positive relief and its desecration was taking place in quick tandem. The most likely such setting is tectonic uplift due to continental collision.