Sources and depositional pathways of mid-Holocene sediments in the Great Rann of Kachchh, India: Implications for fluvial scenario during the Harappan Culture

The decline of the Harappan Culture (5300-3300 yrs BP), one of the earliest urban settlements, has often been linked to the demise of a perennial river (vedic Saraswati?) that originated in the Himalayan Mountain Belt and flowed through the Thar Desert into the Arabian Sea. To test this hypothesis we have studied the mid-Holocene (5.5-1.0 ka) sedimentation history of the Great Rann of Kachchh, an uplifted former gulf of the Arabian Sea, which is believed to have housed the delta of the river. Using trace element geochemistry and Sr-Nd isotopic ratios of sediments as tracers we have determined their provenances. Results of our study suggest that the basin received significant sediment contributions (20-30%) from a distinct sub-Himalayan source, apart from the other proximal sources such as the river Indus, Thar Desert and the ephemeral river Luni. It, however, did not receive any sediment from an independent glacier-fed river. Based on geological and geochemical arguments we infer that these sub-Himalayan sediments could have only been transported through a continuous Ghaggar-Hakra-Nara river channel, possibly seasonal, that flowed through the Harappan heartland. The fact that there was no major change in fluvial sedimentation in the Great Rann of Kachchh and it persisted at least until ∼1.0 ka, suggests that drying up of this river system may not have been the primary cause for the decline of the civilization.