Palaeoenvironmental history of Bap-Malar and Kanod playas of western Rajasthan, Thar desert

Abstract

Two playas in the arid core of the western margin of the Thar desert viz., Bap-Malar and Kanod, have been investigated using palynology, geomorphology, archaeology, AMS-radiocarbon dating, stable isotopes, evaporite mineralogy and geoarchaeology. The principal objective was to obtain a reliable lithostratigraphy of the playa sediments. These are about 7 m thick in the Bap-Malar and > 2.5 to 3 m thick in the Kanod. AMS 14 C dates of > 15 ka BP on pollen from sediment layers indicates that the Bap-Malar playa possibly existed even during the LGM. These playas were full of water during the early Holocene (8 ka BP-5.5 ka BP) and were ephemeral during the Pleistocene-Holocene transition and early to mid to late Holocene. The playas dried almost 1000 years earlier than those occurring on the eastern margin. Pollen of graminaceae, chenopodiaceae/amaranthaceae, cyperaceae etc. and evaporite minerals like gypsum, halite in the profiles indicate that the playas were surrounded by vegetation dominated by grass and that, they remained brackish to saline even during the mid Holocene, lake full stage. Stable dune surfaces, pediments with regoliths, and gravelly channels of ephemeral streams provided a favorable geomorphic niche for nomadic human activity since ∼ 7 ka BP. Though local ecological factors have played an important role in the evolution of the playas, the winter rains, connected with northwesterly depressions, most likely played a vital role in maintaining these playas.

Climate-induced variability in the Late Pleistocene–Holocene fluvial and fluvio-deltaic successions in the Ganga plains, India: A synthesis

“…Although the LGM aridity is recorded at Sambhar, a shallow lake was maintained during this period. AMS 14 C dates of N15 ka BP on pollen from the Bap-Malar playa also reveal that it possibly existed during the LGM and millennial scale differences are recognized in spatially separated playas in the Thar (Deotare et al, 2004). In a recent compilation of Holocene climatic records of India, Prasad and Enzel (2006) showed that a marked positive shift in the hydrological balance in NW India occurred at~6 ka followed by an arid phase and intense dune formation at~5.2 ka.…”

Geochemical signatures of Late Holocene paleo-hydrological changes from Phulera and Pokharan saline playas near the eastern and western margins of the Thar Desert, India

“…Occurrence of palygorskite, albeit in trace amounts, suggests that the Pokharan playa waters turned alkaline for certain periods. This zone at Pokharan is correlated to the ephemeral conditions at Lunkaransar, Didwana, Kanod and Bap-Malar playas (Wasson et al, 1984;Enzel et al, 1999;Deotare et al, 2004). We characterize this phase as one of increasing seasonal rainfall with relatively stable hydrological conditions.…”

“…Earlier paleo-hydrological reconstructions by Wasson et al (1984), Singh et al (1990), Enzel et al (1999), Deotare et al (2004), Sinha and Raymahashay (2004), Roy et al (2006), Sinha et al (2006) suggest that most of the playas were hyper saline during the last glacial maximum (LGM) and until 13-15 ka cal BP and fluctuated between hypersaline and fresh water conditions during 13-7 ka cal BP. Some of the western playas dried around 5-6 ka cal BP, but the eastern playas remained fresh and perennial between 7 and 5 ka cal BP and re-establishment of ephemeral saline conditions occurred after ca.…”

“…Several playas exist in the region and receive inflow only for a few days during the summer monsoon, associated with southwesterly winds, and winter precipitation associated with northeasterly winds and western disturbances (Singhvi and Kar, 1992;Deotare et al, 2004;Prasad and Enzel, 2006). It has been suggested that the processes that lead to the evolution of these playas are: (i) tectonic, via development of basins by the reactivation of lineaments (Sinha-Roy, 1986;Roy, 1999) and (ii) geomorphic, through occlusion of paleo-drainage systems by aeolian sands (Kar, 1990;Singhvi and Kar, 1992 and the references there in).…”

Arid geomorphology

“…Cores from the lake bed indicate that the geochemical evolution of the lake has been ongoing for over 30 ka (Sinha and Raymahashay, 2004). The palaeoenvironmental history of two smaller, more recently formed playas in the western Thar Desert was investigated by Deotare et al (2004). These playas contained perennial lakes during the early Holocene (8-5.5 ka BP) and ephemeral lakes in the mid-to late Holocene before drying out.…”