DISTINGUISHING SEDIMENT SOURCES AT STRIKE-SLIP PLATE BOUNDARIES: CASE STUDIES FROM SAKHALIN AND CALIFORNIA

Sakhalin has many geological, geomorphological and tectonic parallels with California (e.g. Rozhdestvenskiy, 1973), including the deformation of extensive Neogene deltaic sediments by active dextral strike-slip faulting. Locally derived sediments can be distinguished from deltaic deposits of a continental-scale river in both areas. This study aims to characterize the petrographic and mineralogical differences between the two sediment types in both localities, with a particular focus on the heavy mineral assemblages present in each, and on the role that tectonic setting has on sediment distribution in each basin.

In California, the earliest deltaic sediments of the Colorado River are beautifully exposed in the area west of the Salton Sea. The deltaic deposits become rapidly established as the dominant sediment type in the area, with periodic pulses of locally derived sediments only being found in any significant quantity within a few hundred metres of the basin margin. Locally derived sediments become volumetrically important again in the delta-plain/fluvial part of the sequence where there was much less sediment mixing in the system.

Locally derived sediments in Sakhalin have previously been observed underlying the main deltaic units, although the contact between locally-derived and deltaic sediments is not exposed. After a thick sequence of purely deltaic sediments, an increasing contribution of locally-derived sediments can be observed in the upper part of the deltaic sequence on the island margins and offshore, recording a transition in the tectonic regime from transtension to transpression with a resultant period of uplift on the island.