Himalayan foreland basin
During the Late Cretaceous and early Cenozoic, the Indian Plate drifted northward a vast distance resulting in the closure of the Neo-Tethys Ocean.
This results in the Eurasian Plate being thrusted up leading to the rise of the Tibetan Plateau, bounded to the south by the collisional Himalayan mountain range.
The foreland basin, much like the Himalayan mountain range, spans approximately 2,000 kilometres (1,200 mi) west to east across Pakistan, India, Nepal, Bhutan and Bangladesh.
The actively subsiding foreland basin lies beneath the Punjab region of Pakistan and the Gangetic plain of India and southernmost Nepal.
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.
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.
[14] 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.
The Dagshai Formation has been dated back to the Oligocene-Miocene Epoch where it consists of primarily fine grained material of alluvial origins.
The Siwalik Group is a coarsening upward siliciclastic succession that makes up the thickest accumulation of detritus derived from the Himalaya in the foreland basin.
[24] The unique part of this multistorey sand complex is the fact that it is underlain by a major erosional surface which extends laterally for hundreds of meters.
The basal part of the Upper Siwalik shows predominantly of crudely stratified conglomerate, sandstone and massive mudstone which suggests a deposition of high energy conditions; this facies assemblage and characteristics are commonly found in gravel transport fans and suggests a deposition by gravelly braided rivers in medial to distal alluvial fan settings.
The chert breccia strata was interpreted as a growth fault in the fold thrust belt as a result of compressional tectonics.
With the collision being an active ongoing process, it progressively generates weight which resulted a downward flexing of the subducting Indian Plate and created an accommodation space to be filled with sediments.
Carbon Isotope data and Pollen analysis indicates of a climatic change around SE Asia which significantly increases humidity of the region.
This erosion then caused a reduction in mass of the Himalaya which made the foreland basin partly invert, rebound, and essentially uplift.
This is supported by the discovery of the older marine deposition of the Subathu formation in parts of the thrust slices in sub-Himalayas, at a high elevation than it would normally be found.
[30] Despite the high TOC levels, the coals exhibit low hydrogen index which indicates the potential to only form gaseous hydrocarbons.
Himalayan deformation was previously thought to stop at the foot of the Himalaya, or the northern boundary of the foreland basin (the Main Frontal Thrust).
