Flecker, R.¹, D. I. M. Macdonald²
(1) Bristol University, Bristol, United Kingdom
(2) Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom

ABSTRACT: Topographic Control on Distal Deltaic Sedimentation in a Structurally Active Setting: the Mio-Pliocene Delta of the Palaeo-Amur, Sakhalin, Russian Far East

Distinctive sands deposited in the Mio-Pliocene palaeo-Amur delta crop out continuously across much of northern Sakhalin. Tens of kilometres to the south, several small fault-bound basins on the pre-existing Mesozoic accretionary complex also contain palaeo-Amur deposits. Palinspastic restoration of the strike-slip faults shows that these basins once occupied a frontal position relative to the delta. The fill of these basins comprises biosiliceous and clastic sediments, punctuated by subaerial unconformities. Facies and petrographic analysis suggests that the siliceous sediments are marine in origin, but clastic derivation changed from coarse, local fluvial clastics to a Miocene influx of fine-medium sand from the Amur. These data indicate that the palaeo-high was affected by at least three major subsidence events from late Paleocene to end-Miocene time.
Biosiliceous accumulation is normally interpreted as the result of high ocean productivity in upwelling areas typically at a significant distance from a source of clastic sediment. Here, however, the alternation of subaerial unconformities, fluvial sediments and marine siliceous units suggests that the biosiliceous facies does not represent remote marine deposition, but accumulation on near-shore palaeohighs. Interaction between deltaic sedimentation and siliceous accumulation on these highs results in an unusual mixed facies that appears to indicate distal deltaic deposition in moderate water depths. The sedimentation on the distal, eastern fringe of the Mio-Pliocene palaeo-Amur delta on Sakhalin seems therefore to have been controlled by syn-depositional deformation on active dextral strike-slip faults. These conclusions are supported by analogy with deposits of the same age in the San Joaqin Basin (California).

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.