Jodhpur Sandstone: A Gift of Ancient Beaches to Western Rajasthan

The middle horizon of the latest Proterozoic Jodhpur sandstone is extensively quarried, yielding best quality of building stone as well as much needed valuable geological information. This sandstone shows prolific development of wave ripples and other related structures. It has been observed that the sandstone sequences show ripples developed in a hierarchical order. There are straight crest ripples at the base, followed upward by undulatory ripples, sinuous ripples, interference ripples and adhesion ripples/adhesion warts at the top. Formation of ripples in general and ripple hierarchy in particular is discussed, in the light of wave-generated structures in modern environment. It is deduced that the straight crest ripples have formed under relatively deep-water conditions; whereas undulatory ripples, sinuous ripples and interference ripples developed under gradually shallowing water conditions. The adhesion ripples/adhesion warts indicate subaerial condition of sedimentation. It is envisaged that the hierarchically ripple bedded Jodhpur sandstone sequences represent shallowing upward cycles developed under nearshore-beach environment. These cyclic sequences are critically analyzed. It is suggested that they must have evolved within the confines of shoreface-backshore settings of beach environment. The overail evolution of these ancientbeach sandstone sequences in terms of periodic transgression and sediment aggradation is stressed. Concurrently, the Jodhpur sandstone, as building stone, is considered as a gift of ancient beaches.