Today the desert margins of northwest India are dry and unable to support large populations, but were densely occupied by the populations of the Indus Civilization during the middle to late Holocene. The hydroclimatic conditions under which Indus urbanization took place, which was marked by a period of expanded settlement into the Thar Desert margins, remains poorly understood. We measured the isotopic values (δ18O and δD) of gypsum hydration water in paleolake Karsandi sediments in northern Rajasthan to infer past changes in lake hydrology, which is sensitive to changing amounts of precipitation and evaporation. Our record reveals that relatively wet conditions prevailed at the northern edge of Rajasthan from ~5.1 ± 0.2 ka BP, during the beginning of the agricultural-based Early Harappan phase of the Indus Civilization. Monsoon rainfall intensified further between 5.0 and 4.4 ka BP, during the period when Indus urban centres developed in the western Thar Desert margin and on the plains of Haryana to its north. Drier conditions set in sometime after 4.4 ka BP, and by ~3.9 ka BP an eastward shift of populations had occurred. Our findings provide evidence that climate change was associated with both the expansion and contraction of Indus urbanism along the desert margin in northwest India.

No abstract

In glacier-fed Baspa River valley, Late Quaternary climatic changes are archived in the terraces, fan and landslide deposits. An initial optically stimulated luminescence (OSL) based stratigraphy of these deposits is developed to deduce geomorphic evolution and palaeoclimatic changes. The data show large alluvial fan progradation around Sangla till c. 45 ka (middle of marine isotope stage 3 or MIS-3) due to glacial retreat and readjustment of glacigenic sediment under warm and humid conditions followed by incision. During the end phase of MIS-3 (>23 ka), intensified precipitation blocked the river course near Sangla and Kharogla by rock avalanches and imposed lacustrine conditions which recorded sedimentation until the beginning of Holocene (c. 11.4 ka). Reduced sedimentation in these lakes during the last glacial maximum (LGM) c. 23–18 ka suggests a cold and arid climate, whereas increased sedimentation during c. 18–11.5 ka indicates a warm and humid climate post-LGM. A palaeolake breach occurred during early Holocene and incision continued throughout the Holocene, with a pulse of fluvial aggradation during c. 9.1–6.5 ka over lacustrine remnant. In the upper reach of the valley (Chitkul area), coeval aggradation continued from >28 ka until c. 19 ka (MIS-3 to LGM) under cold and relatively arid conditions. This study emphasizes that Late Quaternary geomorphic evolution of Baspa valley is well synchronous with glacial fluctuations and the rapid response of the glacifluvial system to Indian summer monsoon (ISM) dynamics.

Geomorphology and sedimentary composition of an archeologically important palaeochannel segment of the Vedic Saraswati River in northwestern Haryana have been evaluated and its temporal relation with the surrounding upland examined with the help of OSL dating. Sediment composition and OSL ages suggest that the channel received enough water supply between 5.9 and 4.3 ka ago, and even before. Several lakes and ponds had developed during this period in the surrounding areas. It was a wet phase in this area as well as in Rajastahn. After ~4.3 ka, the river got starved of regular water supply, became sluggish and finally dried up. Reduced water supply, indicative of decreased rainfall, occurred between 4.3 and 3.4 ka ago. The environmental history of the channel might have influenced the Harrapan archeology of the area.

No abstract