Depositional environment and Provenance of Pilikarar Formation, Central Narmada basin, Hoshangabad District, Madhya Pradesh, India.

Abstract

The Pilikarar Formation comprised of coarser clastics, occur as isolated as well as coalescent cones and exhibit development of bouldery conglomerate lithofacies, with both clast supported and matrix supported varieties; representing debris flow and mud flow deposits of alluvial fan respectively. Caliche nodules and rhizoliths in the middle part of Pilikarar Formation indicate semiarid climatic conditions and related subaerial exposure. Immediacy of this alluvial fan to Son-Narmada-North fault indicates that this fault provided the basin depression, geomorphic contrast together with climate favoured the debris flow process to build alluvial fan.

Granulometric studies of these sediments reveal presence of wide range of size classes, polymodal nature, moderate to very poor sorting, positive skewness and leptokurtic to platykurtic distribution; supplementing fluvial environment of deposition. Thin section studies revealed quartzose arenitic nature, indicating mineralogical maturity of these sediments. The presence of ferruginous cement is suggestive of acidic and oxidising diagenetic conditions. This mineralogical maturity is further supported by high ZTR index together with transparent heavy mineral assemblage of augite, epidote, staurolite, garnet, sillimanite, kyanite, sphene, hornblende, zoisite, monazite, anataze and low values of provenance sensitive indices; related to derivation of these sediments dominantly from Vindhyan Supergroup, with subordinate contribution from Deccan Trap Basalts and Mahakoshal Group. Presence of illite, kaolinite and montmorillonite in these sediments, further supports derivation from soils developed on these rocks. Geochemical composition of these sediments supports mixed provenance and mineralogical maturity of these sediments. Paleotemperature derived from δ¹⁸O content (-1.60 ‰) of calcrete indicate moderate temperature of 21.44°C for Pilikarar Formation, thereby indicating C3-C4 mixed vegetation with dominance of C3 vegetation. The obtained low pCO₂ value of 154.6 ppmV derived from δ¹³C content (-9.25 ‰) and the δ¹⁸O content (-1.60 ‰) suggests evaporation and evapotranspiration as the main process in calcite precipitation, indicating meteoric diagenesis related with semi-arid climatic conditions undergone by Pilikarar sediments.