Palaeoenvironmental and Palaeoclimatic Conditions in the Bhimtal Valley, Kumaun Lesser Himalaya, Between 40 and 24 ka Using Granulometric Analysis

Abstract

In this research, we conducted a detailed granulometric analysis of 9.5 m thick palaeolake succession, exposed at Bilaspur (Bhimtal) in the Kumaun Lesser Himalaya to reconstruct the palaeoenvironmental and palaeoclimatic conditions. We carried out statistical parameters of grain-size data (i.e., standard deviation, kurtosis, and skewness, bivariate plots), and end member modelling analysis (EMMA) and our study reveal sediment’s unimodal and bimodal nature, deposited via fluvial action under low to high energy environmental conditions since the origin of the lake. Some parts of the deposit show poorly sorted and mixed character (leptokurtic to platykurtic) of sediments, indicating that the sediments were primarily transported from the proximal area of the lake basin under low-energy environmental conditions. The finely skewed and poorly sorted sediments show different modes of grain size distribution, which are attributed to fluctuations in the hydrodynamic conditions of the lake. The arid climatic conditions prevailed in the valley from ca. 42 to 40 ka BP, followed by warm and moist conditions from ca. 40 to 39 ka BP. The arid conditions under the low rainfall regime were experienced by the valley from ca. 39 to 30 ka BP, while it exercised another episode of moist and warmer conditions from ca. 30 to 24 ka BP. Further, the end-Member Modelling Analysis (EMMA) shows four end members (EM1-EM4) with different climatic conditions during the deposition, e.g., clay to fine silt-size particles reflecting higher lake levels under warm-wet climatic conditions, coarse silt fraction representing moderate energy conditions, and fine to coarse sand fractions indicating shallow lake-level conditions in the arid climatic conditions as well higher energy flow. The interpretation of energy conditions in the lake and catchment area by using various methods reveals different palaeoenvironmental conditions during the sediment deposition.