Abstract

This study focuses on the fluvial and tectonic landscape of the North Sakhalin Basin (Russia), where 5 km of Neogene deltaic sediments were deposited across the Okhotsk-Amur plate boundary. The homogeneous, poorly lithified sedimentary sequence created a flat landscape without structural inheritance. These sediments are now being actively deformed by oblique compression. This allows us to investigate the early stages of orogenesis in a strike-slip plate boundary and the response of drainage networks in such a setting, and to construct a model for the topographic evolution along 220 km of the plate boundary. We use fluvial geomorphological indicators (planform morphology, concavity, steepness indices, and knickpoint distribution) as evidence for active landscape deformation. Tectonics and topography are strongly coupled, and neotectonic activity can be observed directly from the landscape. Knickpoints are mostly located on fault planes, suggesting geologically recent activity, or in areas of drainage capture, where they are associated with low concavity indices. Geomorphic indications from longitudinal river profiles and planform morphology suggest that creation of anticlines and disruption of drainage patterns appears to be diachronous in the North Sakhalin Basin, with deformation propagating north and east through time. Minimum uplift and strike-slip displacement rates in the northeast of Sakhalin are 0.63 mm a−1 and 1.95 mm a–1, based on exhumed stratigraphy and offset drainage networks, respectively.

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