Provenance of the Gondwana sediments, Palar Basin, Southern India

Abstract

Palar Basin is considered as one of the pericratonic rift basins of East Coast of India. An integrated petrography, clay mineralogy, and heavy mineral studies of sandstone and shale from the Palar Basin South India, Tamil Nadu, have been carried out to decipher their provenance, palaeoclimate, and tectonic setting. The mineralogical make-up of the clastic rocks is largely composed of quartz followed by feldspar, rock fragments with minor amounts of chlorite, glauconite, zircon, garnet, and opaque. Palar sandstones are coarse to medium-grained and mineralogically immature (poorly sorted and few are moderately sorted). The detrital quartz grains consist of well rounded and rounded quartz, monocrystalline quartz with uniform or straight extinction, and polycrystalline grains with five crystals of straight to slightly curved intercrystalline boundaries. Few of the monocrystalline quartz contain inclusions of sillimanite, rutile, and zircon needles and low content of plagioclase and k-feldspar. These petrographic analyses of the sandstone suggest derivation from metamorphic, igneous, and reworked sediments of different grades which infer that the recycling and the clasts were subjected to both long and short transport distances. The recycled orogen provenance suggests that the sandstone has been derived predominantly from low-lying granite and gneissic sources. The framework petrography exhibits (a) higher percentage of quartz, (b) predominance of monocrystalline grains, (c) feldspar affinity, and (d) paucity of rock fragments, and low F/R ratio suggests that the sediments deposited were in a passive continental margin tectonic setting. The presence of euhedral, angular, and subrounded grains of zircon, rutile with reddish and dark boundaries, the high and moderate ZTR Index (zircon-tourmaline-rutile) and the ratio of RuZi (rutile/zircon) and GZi (garnet/zircon) low values reveal that the Palar Basin sediments were sourced from the combination of metamorphic and igneous (granite and gneisses) rock types. The presence of high amount of rock derived clay (illite, chlorite) is predominant than soil derived (kaolinite, smectite) clay minerals. The high content of illite indicates the source of the clay minerals from pre-existing rocks of granite and gneisses, subjected to physical weathering over chemical weathering in a temperate climate (hot/humid) with moderate hydrolysis.