Paleoenvironment shifts during MIS 3: Loess and loess paleosols of Kashmir Valley, India
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Ó Indian Academy of Sciences (0123456789().,-volV)(0123456789( ).,-volV)
Paleoenvironment shifts during MIS 3: Loess and loess paleosols of Kashmir Valley, India ASIF ALI1 and HEMA ACHYUTHAN2,* 1
Department of Geology, Anna University, Chennai 600 025, India. Institute for Ocean Management, Anna University, Chennai 600 025, India. *Corresponding author. e-mail: [email protected] 2
MS received 6 November 2019; revised 15 April 2020; accepted 14 May 2020
Kashmir valley receives the rainfall owing to the dominant westerly winds and experiences less impact of the southwest monsoonal rains (SWM). In this valley, loess and loess paleosols occur as a thin veneer covering the landscape. The loess paleosols form an important proxy for paleoclimate reconstruction and understanding the late Quaternary paleoenvironmental shifts. For this purpose, the loess, paleosols within the loess lithosections were lithologged and the sediment samples were subjected to various grainsize textural and geochemical analysis. The U-ratio of the sediments supported by parameters such as TOC, CaCO3 content, ratios of Zr/Rb, Rb/Sr, Ba/Sr, K/Ba, K/Rb, chemical index of alteration (CIA) and clay mineralogy indicate that the loess paleosols have undergone weak to moderate degree of pedogenesis. The U-ratio and Zr/Sr ratio also reCect variations in the wind velocity ranging from weak to moderate conditions for the loess deposition. The Ba/Sr and Rb/Sr ratios signify varied precipitation conditions, particularly with higher precipitation during the paleosol formation. The A–CN–K plot exhibits weaker to intermediate type of weathering of the loess horizons. TiO2% vs. Al2O3% binary plot illustarates mostly basaltic to rhyolite/granite type of rock source and the Panjal Traps is one of the major sources of the loess deposition. The lower end of the exposed Choori and Burzahama lithosections were dated by OSL method to 54 ± 2 ka at 9.5 m depth and 52 ± 2 ka at 8 m of depth, respectively. Geochemical analysis and OSL dating of the Choori and Burzahama lithosections reveal that climate during the marine isotope stage 3 (MIS 3) was dominantly warm and dry (stadial conditions) in Kashmir valley when the loess layers covered the valley and since then the loess horizons have undergone weak to intermediate, moderate type of weathering in cool and dry conditions. Keywords. Loess and loess paleosols; pedogenesis; paleoclimate; weak to moderate weathering; MIS 3.
1. Introduction Marine isotope stage 3 (MIS 3) represents a period between 57 and 29 ka and is often considered to be relatively warmer period during the last glacial cycle. During this period, several abrupt climate warm phases known as the Dansgaard-Oeschger (D-O) events occurred. The warm phases have been followed by cold stages, so-called the Heinrich
events. The D-O and the Heinrich events aAected both Coral as well as faunal life and these have been registered in the Greenland ice core oxygen isotope record that reveal transitions from cold, stadial climate conditions to mild, interstadial c
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