Granulometric Composition of the Bottom Sediments in the Torosjarvi Lake (the White Sea Basin)

Abstract

Purpose: The bottom sediments in the small relict the Torosjarvi Lake were studied to track the evolution and more accurately outline the boundaries of the Onego periglacial Lake during the Late Glacial and Holocene times. Methods. The granulometric composition of the bottom sediments was determined using the multifunctional laser diffraction particle size analyser LS 13 320 (by Beckman Coulter, USA) at KarRC RAS Core Facility, and the output was then statistically treated. Results: Two sediment cores were exposed, and their lithostratigraphic descriptions were produced in the field. The granulometric composition of sediments in the 4,40-5,40 m interval (core 2,5) was analyzed in the laboratory. The fractions sizes in this interval were found to range from fine sand to silty clay. The prevalent fraction was coarse silt. Based on granulometric analysis, the palaeo-hydrodynamic sedimentation environments are represented by turbidite deposits in three intervals (4,68-4,69; 5,04-5,05, and 5,14-5,15 m), while the other intervals (4,71-4,81 m and 5,24-5,35 m) fall in the zone deposited by low-velocity streams (homogenous suspension sediments). Conclusions. The granulometric composition of bottom sediment cores from the Lake Torosjarvi revealed a prevalence of the coarse silt fraction (0,01-0,05 mm), which contributed 49,04 % to 62,96 %. The sand fraction accounted for 21,36-38,62 % and was mainly represented by fine sand. The clay fraction accounted for 0,44-1,61 %. A first analysis of changes in sedimentation in the Lake Torosjarvi based on the sediment core in the interval 4,4-5,4 m suggests there occurred five shifts in the dynamic water regimes in the course of the lake formation. The results of this study will be needed in further geoecological and palaeogeographical research.