The post-glacial (Bølling-Allerød) sedimentary archive preserved in the Eastern Great Rann of Kachchh (EGRK) is used to reconstruct the pattern of Indian Summer Monsoon (ISM) variability, landform evolution, and the impact on the Indus Valley Civilization (IVC). Employing the sedimentology, geochemistry, and chronology supported by statistical analysis, four major phases of strengthened and weakened monsoon conditions are inferred. The pattern of geochemical variability during Phase-I (13.6 ka and 12.7 ka) indicates a relatively wetter condition (improved ISM); following this, during phase-II (11.9 ka and 11.1 ka), the ISM strength weakened. However, the ISM began to restrengthen during the phase-III (11 ka and >5 ka), with fluctuations. The phase-IV (<5 ka) is represented by a gradual decline in the ISM strength. The sediment isotopic analysis (Sr and Nd) reveals that the Indus River was the major contributor (~48%), followed by the contribution from local reworking of Mesozoic lithology from Khadir Island (~35%). The northern Thar Dune field contribution by ephemeral streams was around 14%, whereas the influence of Luni River at Trangadi Bet was insignificant (~3%). The study observed that around 7 ka, hydrological conditions dwindled, which persisted during the IVC, dated to 5.5 ka–3.8 ka in the region. However, despite dwindling freshwater from the branch off northwest-southeast trending paleochannel (via Indus), it has been hypothesized that the IVC in the EGRK (at Dholavira on Khadir Island) was sustained by the ephemeral monsoon-fed channels.
Bhatnagar et al. (Tue,) studied this question.