The Paleogene Subathu Formation of India (correlative to the Bhainskati Formation of Nepal, and the Kohat Formation of Pakistan) represents the oldest known foreland basin deposits, and unconformably overlies older strata. The Subathu Formation and equivalents are relatively thin intervals (<150 m) predominantly composed of fossiliferous, organic-rich black shale. These units are interpreted as shallow marine deposits. Marine to shallow marine facies in the form of shales and minor amounts of sand also consists of predominantly green mudstone with minor red facies and were dated back to the upper paleocene to lower mid eocene period based on the existence of Nummulites gathered from biostratigraphical data. petrographic interpretation of the green Subathu Formation were shown to be predominantly sedimentary with minor traces of serpentine schist input. Although the red facies shows a more felsitic and of volcanic origins, it entails that it originates from continental flood basalts of the Indian craton. The Subathu Formation was interpreted to be a preservation of the intense collision between the two plates in the western part of the foreland basin that leads to thrusting. An evidence of a silicified chert breccia strata existing just on top of the rigid precambrian basement was interpreted as a growth fault that developed as a result of compressional tectonics. The thrust slices in the sub-himalayan ranges now preserves some of the Subathu Formation. Although a debate has arise, it is inferred that some locations where the Subathu Formation is exposed are now considered to be the forebulge of the foreland basin as it is overlain by a much younger formation where a time hiatus or an unconformity has occurred. A time hiatus of an approximately 10 MA are inferred based on thermochronology and magnetostratigraphy between the Subathu and the overlying formation, but it is highly controversial.
