Holocene history of vegetation and climate of fresh-water Punlota (Degana) Lake in Eastern Rajasthan, India

Abstract

Pollen analysis of 2 m deep sedimentary profile from fresh-water Punlota Lake situated at the outskirt of Degana township in district Nagaur (Eastern Rajasthan), has revealed that around 9,000 years BP, the region had predominantly non-arboreal vegetation, depicting arid climatic conditions. Around 4,200 years BP, savannah type-vegetation covered the region demonstrating increase in the frequency of fern as well as fungal spores- indicating warm and moist conditions. Around 3,000 years BP, savannah vegetation witnessed reduction in tree taxa, ferns and grasses with simultaneous increase in Cyperaceae, Chenopodiaceae, etc., depicting decrease in the warm and moist conditions. Uppermost part of the investigated profile has revealed more or less similar conditions as witnessed in the preceding phase, except for the increase in Poaceae and Caryophyllaceae, reflecting comparatively drier climate.

Simultaneous elemental analysis of the profile reveal that all major (Al, Fe, Ca and Mg) and trace (Mn, Ba, Sr, Pb, Cu, Ni and Zn) elements change in their concentration at the middle of the profile or about 1 m depth from the surface i.e., around 4,200 years BP. Most of these elements abruptly increase by a factor of two or three at this section and maintain relatively higher values up to the surface. Higher elemental abundance above 1 m boundary in the sediment could arise due to accelerated weathering as well as in consequence to the enhancement in the rainfall.

Coupling radiometric data with major change in elemental abundance indicate maximum precipitation around 4,200 years BP, in the region which very well corroborate with the present palynological studies- the first radiocarbon dated Holocene profile from the fresh-water lake in Rajasthan.