DETERMINING TIMING AND RATE OF UPLIFT AND EROSION OF NORTHERN SAKHALIN, RUSSIA

Sakhalin, in the Russian Far East, represents a unique study area for developing models of landscape development over geological timescales. Sakhalin lies on a major dextral strike-slip boundary along which Pliocene-Recent transpressional movement has caused significant uplift of poorly lithified Neogene deltaic sediments deposited by the palaeo-Amur River. Much of the uplift has been focused along the fault zones themselves, resulting in the formation of a series of low anticlinal hills which are now being eroded and recycled into the offshore environment. The aim of this study is to quantify the timing, rates and distribution of uplift and erosion and to use this simple model in Sakhalin to test models of tectonic landscape evolution. Several techniques are being used in order to achieve this aim, including: directly estimating volumes of eroded material using DEM data and 3D onshore models; heavy mineral analysis of sediments onshore and offshore to track the timing of denudation of the hills, and of mineralogically diagnostic features such as the ultramafic Schmidt peninsula in northernmost Sakhalin; cosmogenic radionuclide analysis to obtain erosion rates from different catchment areas; and interpretation of seismic data to determine timing of inversion and to obtain offshore sediment volumes.

Indications from conglomerate assemblages and heavy mineral data suggests that parts of northern Sakhalin were being uplifted by the Mid-Pliocene at the latest with evidence of recycling of previously deposited deltaic material being present at this stratigraphic level. Seismic data suggest that the main phase of uplift and deformation occurred after deposition of the main reservoir interval, during the Upper Pliocene. Geomorphological evidence suggests that uplift is still occurring in the present day.