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The Delhi rocks are deposited in two sub-basins separated by a median inlier of Pre·Delhi rocks. The Barotiya and Sendra Fonnations occupying the western sub-basin contain significant basic flows and tuffs with associated felsic volcanics. The eastern sub-basin recording a diachronous evolutionary history is the repository of the Rajgarh and Bhim sediments.
Striking similarities are noted in respect of lithology, structure and metamorphism amongst the gneisses and schists of the Pre-Delhi rocks flanking the Delhi Supergroup and also of the median inlier. Structural imprints and contact relationship indicate that these gneisses and schists fonn the basement for the Delhi sediments. Migmatization related to orogeny suggests reactivation of a sialic basement, which along with the tectonic emplacement of basement slices in the Delhi stratigraphy argue in favour of an intra-cratonic development of the Delhi basin.
The western sub-basin shows bimodal volcanism and the various geochemical discriminants suggest an IATor MORB setting, but fail to make a choice between the two. Bimodal volcanism in association with shallow clastic sediments signify ensialic origin in a rifted mobile belt. Structural studies indicate large-scale dextral vergence with steep 'S' surfaces which are characteristic of oblique shear transpressive mobile belt.
