Geomorphology, Architecture and Genesis of Miocene Isolated Shelf Sand Bodies in the Pearl River Mouth Basin, Northern South China Sea

Abstract

Utilizing a high-quality 3D seismic data set, accompanying well logs and a small amount of drilling cores, the morphology, architecture and genesis of isolated shelf sand bodies have been systematically investigated in this study. In general, the shelf sand bodies in this area can be divided into two phases: phase 1 was only present within the upper part of the Upper Miocene successions while phase 2 sand bodies were well-developed across the late period of Middle Miocene to Late Miocene. On seismic profiles, isolated shelf sand bodies are generally mound-shaped and display high seismic amplitudes. In plan view, most of the isolated shelf sand bodies are band-shaped, orienting NE-SW, and generally one side wider than the other side. The thickness of one single sand body typically ranges from a few meters to more the ten meters, reaching tens of meters at a maximum. On well logs, the shelf sand bodies are both represented by an overall coarsening-upward pattern. Although having similarities mentioned above, the depositional settings, geomorphology and scales of the two phases isolated sand bodies are significant different. Phase 1 shelf sand bodies formed along with a high-amplitude marine transgression period after the Pearl River Mouth Basin just came into the post-rifting stage. They mainly developed in the restricted bay environments caused by the topographic low between the paleo-Pearl River Delta and the carbonate platform in Dongsha Uplift. The significant enhanced tidal flow is thought to primarily contribute to the formation of these isolated shelf sand bodies. In contrast, the phase 2 sand bodies mainly developed on an open-shelf environments when most of the shelf topographic lows were filled up. Also, the formative current might be a composite one, which was speculated to consist of winter oceanic current, SCSBK (South China Sea Branch of Kuroshio) intrusion onto the shelf and internal waves propagating from the Luzon Strait. The development of isolated shelf sand bodies was terminated and replaced by rapid deltaic progradation at 5.5 Ma.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015