An inlier of Jurassic rocks at the bottom of the Lena River valley

Abstract

An inlier of Jurassic rocks is identified for the first time at the surface of the first terrace above a floodplain composed of Holocene sediments on the left side of the Lena River. It represents a block of Jurassic rocks similar compositionally to rocks in outcrops on the left slope of the river valley. It is shown that the block was displaced along faults in the Holocene. The rocks of the inlier are deformed, and the Paleogene–Neogene sequence covering the plateau (altitude approximately 200 m) is displaced in the stepwise mode to the level corresponding to the bottom of the Lena River valley (altitude approximately 100 m). The Holocene alluvium enveloping the inlier belongs to the constratal type being up to 40 m thick. Steep faceted morphostructures on the left slope of the Lena River valley coincide with the faults. The left slope of the valley is crossed exclusively by young incisions. It is assumed that Holocene movements may be reactivated in the future.