Geochemical and petrographic study helps to understand the source of Upper Cretaceous Fatehgarh Formation, Barmer Basin, Rajasthan, India

Abstract

Quartzose sandstone dominates the Upper Cretaceous sedimentary succession of the Barmer Basin, but its source of sediments is mostly hypothetical. This study elaborates the modal analysis of sandstone, EPMA mineral chemistry of detrital tourmaline and rutile and U-Th-total Pb monazite geochronology within the Fatehgarh Formation to track the possible source rocks. The poorly studied, fluvial- to marine-originated, Upper Cretaceous, roughly 125 m thick, locally cross-stratified formation crops out nearby the Barmer town, Rajasthan. The formation contains mainly sandstone, shale, claystone, conglomerate and evaporite beds forming nonconformity with Lathi Formation/Precambrian Malani Igneous Suites. The Fatehgarh Formation is medium- to coarse-grained, subangular to rounded grains, and moderately to well sorted. The sandstones are cemented by the silica, calcite and iron oxide cement. The QFR modal analysis classified quartzose sandstone and implies craton interior and recycled orogeny provenance for the sandstone. The presence of derital quartz overgrowth and rounded zircon, rutile and tourmaline suggest sediment recycling in the formation. The heavy mineral assemblage of the formation includes primarily tourmaline, zircon, and rutile with leucoxene, Fe-Ti minerals, staurolite, monazite, andalusite and opaque mineral. The EPMA analysis of the tourmaline reveals schorl and dravite varieties of tourmaline. The tourmaline composition Ca-Fe-Mg plot within the fields of ‘Li-poor granites and Ca-poor metapelites and metapsammites’. The tourmaline suggests their derivation from the Paleoproterozoic Pb-Zn deposits of Rajpura-Dariba, Zawarmala, Rampura-Agucha and Mangalwar Complex in the Aravalli-Delhi Fold Belt, and leucogranites of Sewariya-Govindgarh and Balda-Motiya of Delhi Supergroup. The rutile mineral chemistry shows ‘metapelitic origin’ of the majority of rutile grains for the basin. The presence of staurolite and andalusite mineral supports metamorphic source contribution for the sediments. The U-Th-total Pb dating of monazite grains shows major peaks at 950 Ma and 500 Ma. The monazite geochronology corroborates Pan-African and Delhi orogeny- related sediments for the Barmer Basin. The formation shows SW paleocurrent direction. The petrography, mineral chemistry and geochronology indicates the possible source of the sediments from the Marwar Supergroup, Malani Igneous Suites, and Aravalli-Delhi Fold Belts.