The miliolite rocks of Kutch and Kathiawar (Western India)

Abstract

The miliolite rocks occurring along the coasts of Kathiawar and as isolated, patchy outcrops in the central plateau of Kathiawar and on the hills of Kutch, are described in this paper. The miliolite rocks from Kutch are described for the first time. The distribution, mode of occurrence, primary structures and the petrography of the rock samples collected from different localities, have been studied. Based on these studies the origin and environment of deposition of these rocks are discussed. The coastal rocks of Kathiawar are arenaceous limestones. The inland rocks and the rocks of Kutch are calcareous sandstones containing pellets which are mainly the rolled tests of Foraminifera. These rocks show uniform lithology in remote unconnected outcrops and are characterized by high degree of sorting, roundness and uniform grain size. Dune-type current-bedding (Fig.1) and alternating coarse- and fine-grained laminations are common. They occur in various levels, at the foot of the hills and high up in their glens. Most favourable occurrences are the hill slopes and valley depressions which are natural barriers and traps for the wind-borne sediments. These characteristics indicate an aeolian origin of these rocks. In this the author differs from the earlier view that the miliolite rocks are of marine origin and that the sea transgressed over Kathiawar and Kutch during their deposition. The author does not believe in the post-Pleistocene uplift of the Kutch-Kathiawar region. It has been shown that the presence of marine fauna alone cannot prove the marine origin of these sediments. From the stratigraphic relationship, palaeontological studies and geomorphological data, a Late Pleistocene to Early Holocene age for the miliolite rocks, has been concluded. It is believed, however, that the coastal rocks of Kathiawar might have been formed earlier than the rocks in the interior of Kathiawar and Kutch and the sediments for the latter were derived from the disintegration of the coastal limestones. It is believed from the distribution of the rocks that the calcareous sands of the Kathiawar coast, rich in marine organisms, were blown towards the northern region by a persistent wind current blowing towards the northwest. This did not permit the sand transportation towards the Indian mainland and the western coast of India where no occurrence of the miliolite rock has been reported.