Original paper

Geomorphology of the Little Rann of Kachchh, W. India: Implication for basin architecture and Holocene palaeo-oceanographic conditions

Maurya, D.M.; Thakkar, M.G.; Khonde, N.; Chamyal, L.S.

Abstract

The present study attempts to describe the geomorphic peculiarities of the Little Rann sedimentary basin. The Little Rann is a unique terrain located in the southeastern part of the seismically active Kachchh palaeorift graben and represents the uplifted floor of a former gulf that existed upto ∼2 ka B.P. In general, the surface of the Little Rann is a flat, almost gradientless expanse that is dotted by several islands. Two linear E-W trending belts of islands, with faults at their southern margin and exposing rocks of late Cretaceous age, are the most significant features of the Little Rann. Based on this, the Little Rann basin is divided into three tectonogeomorphic zones. One is the Outer subbasin that opens to the Gulf of Kachchh in the SW while the Central subbasin and the Inner subbasin are located successively to the north. The outer line of bets particularly the Keshmari bet and the Bhangarwa bet are characterized by well developed wave cut cliffs at their southern margins. The formation of the wave cut cliffs on the southern margins of the islands of the outer belt is conformity with the present day Gulf of Kachchh to the SW of the Little Rann basin. It is envisaged that the Outer subbasin was occupied by a shallow sea that had considerable erosive energy. However, the erosive energy of the waves did not extend further north as the outer belt of islands provided an effective barrier to the waves coming from the open sea towards the SW. We also believe that the Outer subbasin was possibly the deepest part of the basin and therefore may have preserved the maximum thickness of Holocene shallow marine sediments. The Central subbasin may have been shallower while the Inner subbasin formed the shallowest part of the basin as evidenced by the presence of large number of randomly arranged islands. Geomorphic evidence from the Little Rann, including the islands, point to strong control of subsurface structural elements, which influenced the Holocene palaeooceanographic conditions and the marine sedimentation as well. The strong control of structural set up of the South Wagad Fault System (SWFS) on the tectonogeomorphic setting of the Little Rann reveals its potential for neotectonic and seismotectonic studies for unraveling the seismic history of the Kachchh palaeorift.