Late Pleistocene-Holocene tectonic asymmetry of the Lena Delta

The Lena Delta is the largest arctic delta in the world (about 29000 km²). Unlike other deltas, its formation was the result of both erosion and accumulation during Late Pleistocene and Holocene. It was caused by combination of continuous sea-level fluctuations and neotectonic movements. The last ones have different speed and direction. From previous studies it is known that western part of delta has uprising tectonic movements while the eastern one is sinking. This asymmetry develops along the fracture extended submeridially across the delta. The aim of this research is to measure the amplitude and speed of these movements by using geomorphologic methods. For that purpose results of German-Russian expedition “Lena” were used. In 2013, 2014, 2015 surface morphology of the biggest delta’s islands Sobo-Sise, Kurungnakh, Jangylakh-Sis and Khardang-Sise located in both eastern and western parts was investigated with high-quality sattelite instruments. These islands consist of the Late Pleistocene Ice Complex (IC) remnants with altitude 20-66 m above sea-level (a.s.l.), eroded by river and sea, and the first accumulative terrace of the delta with 2-15 m a.s.l. IC remnants accumulated in the Late Pleistocene 50-17 ka cal BP. The first terrace was forming in Holocene from 8 ka cal BP to 2 ka cal BP. So, there were made a number of geomorphologic profiles with use of high-quality satellite instruments across river terrace and IC remnants during the expeditions. In this study, we equated them to one level and compared. With use of radiocarbon age and digital elevation models (DEM) data we compared heights and age of islands in eastern and western parts and estimated neotectonic movements’ speed difference. Since 2000 years BP tectonic asymmetry represented in terrace surfaces has been increasing with rate about 2 mm per year. Before 2000 cal BP speed difference approximately values 1 mm per year. Our data correlates with water-flow measurements in the delta, modern water-level observations in Laptev Sea and geophysical investigations.