Textural behaviour, facies, and depositional environments of the Middle Siwalik Subgroup of the Jammu area, Jammu Kashmir State, NW Himalaya

摘要

The Middle Siwalik Subgroup is dominantly comprised of multistoried sandstones. However, mudstones also occur at some intervals in the Jammu area, NW Himalaya. These sandstones and mudstones are evaluated for textural and facies analyses for interpreting depositional environments. The sandstones are characterized as very silty sandstone facies and the mudstones are characterized as very silty sandy mudstone facies and very silty slightly sandy mudstone facies. The sandstones are further classified as planar-bedded, trough cross-bedded, and tabular cross-bedded sandstone facies, and the mudstones are classified as laminated mudstone and mottled mudstone facies. Scour-fill facies occurring here is formed due to erosion of mud and filling of sand in the scours. The mottled mudstone facies contains carbonate nodules that formed during pedogenesis. Cumulative frequency curves of both the sandstones and mudstones suggest that the saltation and suspension load dominated during transportation. Mean size versus sorting bivariate plots suggest that both sandstones and mudstones were deposited in a river or a system of the river, and the bulk of the sedimentation occurred on floodplains. Rapid sedimentation and dumping controlled the planar-bedded sandstones that acquired massive thickness. The sheetlike geometries of the sand bodies with large lateral extent suggest that floodplains were of large dimensions during the Middle Siwalik sedimentation. Also, the flow pattern suggests that southerly flowing rivers (Transverse Rivers) deposited the sediments during Middle Siwalik in the Jammu area, northwest Himalaya.