The relief, structure and age of Quaternary deposits of the valley of the Lena River in the Yakutian bend

Abstract

For understanding of the Lena River valley evolution geomorphological and geological structure of the valley in the area from the mouth of the Buotama river to the mouth of the Aldan river (Yakutian bend) studied. Transverse geomorphological profiles through the valley, a map of ruggedness relief density, a geomorphological scheme of the investigated area were constructed. The structure of the terraces was studied, and the sediments were dated by the method of optically stimulated luminescence (OSL) and radiocarbon method. Spore-pollen spectra of terraces and the content of diatom algae in sediments were studied. In the valley we fixed a low and high floodplain up to a height of 10–12 m, two terraces, the height of which varies along the river (5–20 and 30–70 m), and Abalakh plain at an altitude of 100–140 m above the river. Near Yakutsk, the first terrace is called the Sergelyakh and the second terrace is called the Bestyakh. The low floodplain has an age of the first hundred years; the first terrace is dated by 10,000 radiocarbon years, datings of the bestyakh terrace belong to the end of Karginsky time and Sartan time of the Late Pleistocene. The most ancient OSL-datings were obtained from the deposits of the erosion scarp of the Abalakh plain (234–182 thousand years ago). The surface of the bestyakh terrace is decreasing downstream from 60 m at the mouth of the Buotama River to 40 m downstream from the confluence with Aldan River. The deposits of the terrace downstream from the mouth of Aldan River consists of silt mainly by contrast with sand compositions of Lena deposits upstream from the confluence of two rivers. The height of terraces and floodplains varies on the investigated segment of the valley in such a way that the same surface can be worked out in sediments of different ages, or the same age can be distinctive to geological bodies, in which terraces with different altitudes have been developed.