Late Pleistocene shelf‐edge delta clinoforms along the rift margin of the northern Okinawa Trough

Abstract

Sedimentological study into the architecture of continental margins reveals its importance in predicting the partition of sediment budget between the shelf and the deep‐water settings. The sediment delivery towards the deep‐water basin during sea‐level lowstands can be hindered along rift margins. Here we use a 2D seismic survey from the northern Okinawa Trough to identify a set of clinoform seismic units elongating along the western slope, where the rifting activity occurred later than the late Pleistocene. The clinoform units are interpreted as a shelf‐margin delta complex based on the following observations: (a) the sediments clearly prograde across the eroded paleo‐shelf on the dip‐oriented sections; (b) there is some negative relief along two extensively traceable reflections, indicating the probable existence of paleo‐channels working as the potential pathways of sediment delivery for the shelf‐margin deposits; and (c) an eroded surface is easily recognized in the seismic data, possibly marking the sea‐level lowstand during which the shelf‐margin delta formed. The oxygen isotopes of the core QZ01 are taken as a proxy for the variation of the relative sea level and indicate its fast fluctuation in the past 180 kyr. We interpret how the shelf‐margin delta evolved during the late Pleistocene and propose that the subsidence and the rift faulting lead to the starvation of sediments near the shelf edge. As a result, there could be more sediments depositing along the active rift margin, while few of them would be transported to the deep‐water basin and re‐deposit as turbidites.