Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Chhaya Sharma ¹, M. S. Chauhan ², R. Sinha ³

Affiliations
1 Department of Geology, University of Lucknow, Birbal Sahni Institute of Palaeobotany, Lucknow - 226 007, IN
2 Birbal Sahni Institute of Palaeobotany, Lucknow - 226 007, IN
3 Indian Institute of Technology, Kanpur - 208 016, IN

Abstract

Pollen analysis of a sediment core from Priyadarshini Lake (Core S3), East Antarctica, has revealed the climatic oscillations in the region since Holocene. Three pollen zones have been identified on the basis of recovered pollen taxa and varying frequencies. Between 10,000 and 9,000 yr BP, cold and dry climate prevailed in the region as reflected by the dominance of grasses, Acritarch and very low frequencies of Cosmarium - a fresh water alga. The lake was probably shallow and smaller in dimension during this period. Between 9,000 to 2,400 yr BP, relative increase in grasses is witnessed though in fluctuating frequencies. Cosmarium also exhibits a distinct increasing trend, whereas Acritarch declines considerably. This overall change in the assemblage reflects the onset of warm and moist climate and the lake had a wider expansion during this phase on account of amelioration in climate than witnessed before. Between 2,400 and 1,000 yr BP, relatively reduced frequencies of grasses, coupled with total disappearance of Cosmarium, demonstrate that the climate changed once again to cold and dry. However, 1,000 yr BP onwards, marked increase in grasses coupled with exceedingly high values of Cosmarium implies that the climate ultimately turned warm and moist.

Keywords

Palynology, Holocene, Climate Changes, Priyadarshini Lake, Antarctica.

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D. N. Yadav ¹, M. S. Chauhan ², M. M. Sarin ³

Affiliations
1 Bhabha Atomic Research Centre, Trombay, Mumbai - 400 085, IN
2 Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow - 226 007, IN
3 Earth Science Division, Physical Research Laboratory, Ahemdabad - 380 009, IN

Abstract

A 15 m deep sedimentary core from Jagmotha swamp in northeastern Madhya Pradesh has been analyzed for reconstruction of Late-Quaternary vegetation and climate change based on distribution of major/Trace elements, organic carbon, nitrogen and pollen grains contained in the sediments. The combined geochemical and palynological results indicate a cool and dry climate between 6000 to 5000 yrs BP representing a tree savannah type vegetation followed by warm and moist climate between 5000 to 3000 yrs BP. Such a drastic change in climate promoted tropical mixed deciduous forests in the region. Subsequently, between 3000 to 1200 yrs BP, the climatic condition got further improved with enhanced precipitation in the region marked by the advent of sal tree in the forest floristics. Since then, the climate has been inferred conducive for development of modern sal forests in the region.

Keywords

Palaeoclimate, Palaeovegetation, Late-Quaternary Period, Major/Trace Element Geochemistry, Organic Carbon and Nitrogen, C/N Ratio, Pollen Frequency.

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Anjali Trivedi ¹, M. S. Chauhan ²

Affiliations
1 Department of Geology, Lucknow University, Lucknow - 226 007, IN
2 Birbal Sahni Institute of Palaeobotany, Lucknow - 226 007, IN

Abstract

Pollen analysis of a 33.21 m deep sediment core from Surinsar lake in Jammu region has revealed that between 9,500 and 7,700 yr BP (Pollen zone SL-I), the mixed oak-broad-leaved/chirpine forest occurred in the region under a warm and humid climate. The record of aquatic plants viz. Potamogeton, Typha and freshwater alga Botryococcus in appreciable numbers denotes the existence of the lake since the Early Holocene. Subsequently, mixed chirpine/oakbroad- leaved forests appeared in the area around 7,700 to 6,125 yr BP (Pollen zone SL-II) with the dominance of chirpine (Pinus cf. roxburghii) by the onset of cool and dry climate, attributed to decrease in monsoon rainfall. The expansion of oak and its broad-leaved associates between 6,125 and 4,330 yr BP (Pollen zone SL-III) suggests that the climate turned moderately humid and warm, presumably due to enhanced monsoonal effect. The region has witnessed a brief spell of pluvial environment between 4,330 and 4,000 yr BP (Pollen zone SL-IV) as evidenced by the presence of sandy layer at 15.4-14 m depths. The period of 4,000 to 2,100 yr BP (Pollen zone SL-V) is marked by the prevalence of cool and dry climate as depicted by a sharp decline in oak (Quercus cf. incana) and other broad-leaved taxa and a concurrent increase in chirpine. From 2,100 to 800 yr BP (Pollen zone SL-VI) no palaeofloristic inferences could be drawn due to paucity of pollen, however, the presence of sandy deposit at the corresponding level in lithocolumn implies a pluvial episode by this time. Since 800 yr BP to Present (Pollen zone SL-VII) the slight advance in the oak reflects the ameliorating trend of climate, despite the existing cool and dry climate.

Keywords

Pollen Analysis, Palaeovegetation, Palaeoclimate, Holocene, Surinsar Lake, Jammu.

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M. S. Chauhan ¹, M. F. Quamar ¹

Affiliations
1 Birbal Sahni Institute of Palaeobotany, Lucknow – 226 007, IN

Abstract

Pollen analysis of 2 m deep sediment core from Kiktiha swamp, Shahdol district has revealed that between 1600 and 700 yr BP, tropical deciduous Sal forests comprising Shorea robusta (Sal), Madhuca indica, Terminalia, Lagerstroemia, Aegle marmelos flourished in the region under a warm and moist climate. Between 700 and 300 yr BP the deciduous Sal forests were succeeded by mixed deciduous forests, which turned sparse and less diversified, reflecting a relatively less moist climate attributed to the weak SW monsoon. The unfavourable climate also adversely affected the agricultural practice as evidenced from the diminution of Cerealia and other culture taxa. Since 300 yr BP onwards the modern deciduous Sal forests were re-established with the timely arrival of active SW monsoon. The increase in Cerealia and culture taxa indicates agricultural prosperity.

Keywords

Pollen Analysis, Late Holocene, Vegetation, Climate, Southeastern Madhya Pradesh.

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