A genetic model of thrust-bounded intermontane basin using scaled sandbox analogue models: an example from the Karewa Basin, Kashmir Himalayas, India

The Himalayan mountain system has many depressions of regional dimensions, which are found oriented mostly E–W to NE–SW, mainly to the north of the main boundary fault (MBF). The Karewa Basin in the Kashmir Himalaya has sediments belonging to late Neogene to Quaternary formations, which represent an almost 1,300-m-thick succession of sand, mud and gravels exposed in the river valleys and the plateau margins of the entire Kashmir Valley. Sandbox analogue experiments show a great variety of wedge shapes showing significant changes in the taper angles due to the change in basal friction. Between two pop-ups or depressions (pop-down) of significant dimensions develop along the strike of the growing wedge. In order to maintain the critical angle, these depressions initially receive material from the hinterland, and later on, from the foreland end of the wedge. The depressions have developed due to the change in the surface slope of the wedge, and receive the eroded material only from the adjacent upheaved portions of the wedge. On continuation of the experiments (in cases where the wedge is highly unstable), these depressions are coupled with the wedge along with their sand-fills. The depositional history of the Karewa sediments indicates a sequential evolutionary pattern of the basin and thus represents a natural analogue of the sandbox experiments.