Optically stimulated luminescence dating of Late Quaternary sediments in NW India: Insights into the Meghalayan drought and decline of Indus valley civilization

The Holocene Epoch has been marked by significant climatic changes on a global scale which has also impacted on the rise and fall of ancient civilizations. Understanding these past climatic changes is crucial for predicting and adapting to future climate variability and its potential impacts on human societies. Geoarchaeological evidence indicates that the main cause of “metamorphosis” or “de-urbanization” of Indus Valley Civilization-one of the world’s early and most advanced civilizations were rapid climate change and declining of Indian Summer Monsoon. The Indus population relied heavily on the agricultural system and monsoonal flooding was its lifeline that was ruined due to the climatic ravaging. This research offers a comprehensive study into the relationship between climate change and the decline of the Indus Valley Civilization during the Holocene Epoch. Records reveal aridification at approx. ~16.3 ka, with a period of enhanced accumulation of dune sand, at around ~12.0 and ~10.2, ~7.5 and ~3.8 ka followed by intervening affluent monsoonal activity at ~15.4, ~13.2, ~6.4, ~4.6 and ~1.5 ka. This climatic fluctuation was also supported by stable oxygen isotope data from bone samples (δ 18 O) w which is enriched by (+3.26‰) in Rakhigarhi cultural mound-4 aged ~7.5 ± 0.4 ka (Late Hakra period) indicating weakening of monsoon. Lowest (δ 18 O) w value of −0.41‰ was found in Rakhigarhi cultural mound-6 yielding ~6.4 ± 0.4 ka (Early Harappan time), suggesting very intense monsoon activity with active fluvial regime which supports the onset of flourishing of Harappan civilization. The (δ 18 O) w enrichment (+2.72‰) in the Kalibangan bone sample (~3.8 ± 0.2 ka, Mature Harappan) indicates a weakened monsoon aligning with the 4.1 ka global event. Combined results reveal climatic shifts linked to major droughts (~8.2 and ~4.2 ka BP), validating the Meghalayan Stage onset (~4.2 ka). This severe arid phase likely transformed the fluvial landscapes of Rakhigarhi and Kalibangan, contributing to the Harappan civilization’s final collapse.