Grain-surface microtextures in deposits affected by periglacial conditions (Abalakh High-Accumulation Plain, Central Yakutia, Russia)

Abstract

Our paper describes and interprets grain microtexture and microstructure collected from periglacial sediments on the Abalakh High-Accumulation Plain (AHAP) in Central Yakutia. This territory occupies the Lena–Amga Rivers interfluve. In borehole 18/1, five sediment Complexes (I–V) of successive environments were recognized: 1) alluvial in the base of the borehole—Complex I; 2) alluvial-lake—Complex II; 3) lake-complex—Complex III; 4) ice-complex (yedoma)—Complex IV; and finally 5) a Holocene cover—Complex V. Quartz sand-grain and silt-grain microtextural analysis was undertaken in a scanning electron microscope (SEM) and supplemented by mineralogical analyses to reconstruct the sedimentary-accumulation environment, discern the influence of periglacial conditions on the grains, and identify the sediment source(s) for each complex. Based on the results, a conclusion can be reached that the accumulation of Complex I took place as a result of multiple repetitive transportation events recycling the same material and introducing a limited supply of new material into the fluvial environment. Upward in the succession, fluvial-process activities decreased in favour of lake-deposit accumulation. Frozen syngenetic ice-rich silty deposits—yedoma or ice complex—of Complex IV are composed of grains with a precipitated surface, but differ from the underlying deposits in the degree of crusting and mineralogy. Most probably aeolian processes are responsible for their transport. They include a variety of sediments, including older-sourced sediments such as retransported loess and the detritus from mechanical weathering coeval with sediment accumulation. Traces of frost and chemical weathering have been identified on the grain surfaces, the former visible in the form of breakage blocks and conchoidal fracture microtextures and the latter – as surface crusting. However, the frequencies of these microtextures are low, which suggests a relatively high rate of sediment accumulation.