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Paleoenvironment shifts during MIS 3: Loess and loess paleosols of Kashmir Valley, India
Journal of Earth System Science ( IF 1.3 ) Pub Date : 2020-08-28 , DOI: 10.1007/s12040-020-01440-x
Asif Ali , Hema Achyuthan

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 grain-size 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 reflect 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.

中文翻译:

MIS 3期间的古环境变化:印度克什米尔山谷的黄土和黄土古土壤

克什米尔河谷因西风主导而降雨,西南季风雨(SWM)的影响较小。在这个山谷中,黄土和黄土古土壤以覆盖整个景观的薄薄板出现。黄土古土壤是古气候重建和了解第四纪晚期古环境变化的重要代表。为此,对黄土岩石段内的黄土,古土壤进行了岩石成岩作用,并对沉积物样品进行了各种粒度的质地和地球化学分析。TOC,CaCO 3等参数支持的沉积物的U比含量,Zr / Rb,Rb / Sr,Ba / Sr,K / Ba,K / Rb的比值,化学变化指数(CIA)和粘土矿物学表明黄土古土壤经历了弱至中度的成岩作用。U比和Zr / Sr比还反映了风速的变化,其范围从黄土沉积的弱到中等。Ba / Sr和Rb / Sr之比表示不同的降水条件,特别是在古土壤形成过程中,降水量较高。A–CN–K图显示了黄土层风化的弱到中等类型。TiO 2Al 2 O 3%二元积斑说明了玄武岩为流纹岩/花岗岩类型的岩源,而Panjal圈闭是黄土沉积的主要来源之一。裸露的Choori和Burzahama岩石断面的下端通过OSL方法测得分别为9.5 m深度为54±2 ka和8 m深度为52±2 ka。Choori和Burzahama岩石剖面的地球化学分析和OSL测年表明,当黄土层覆盖山谷时,克什米尔山谷的海洋同位素阶段3(MIS 3)的气候主要是温暖干燥的(静止状态)。在凉爽和干燥的条件下经历了弱到中等,中等程度的风化。
更新日期:2020-08-28
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