Role of Relative Sea Level Change on Geometric Characteristics of Submarine Fans (Onlapping versus Non-Onlapping)

Abstract

Deepwater sediments hold a significant amount of hydrocarbon reserves and have always been the most challenging reservoirs to explore and produce. Conventional sequence stratigraphic model for deepwater clastic system consider that deposition and growth of submarine-fan mostly occurs during relative sea-level fall or lowstand. However, recent studies by various workers have shown that sediments can be supplied to deep water even during rising sea level if the sediment supply is high enough to prograde the entire shelf-edge. In order to apply the concepts of sequence stratigraphy for deep water clastic systems, it is important to understand the various factors other than relative sea-level change, which controls the deep water clastic sedimentation. Various outcrop, subsurface and modern examples have been reviewed to show how factors like rate of sediment supply, shelf-edge width, and gradient along the relative sea level change are significant for developing the sequence stratigraphic model of a deep-water system. Deepwater sediments can either onlap to underlying unconformable surfaces or form a linked shelf-slope-basin system. Brushy Canyon Formation in the Permian Basin is a classic example, which has deposition of carbonates during highstand and deposition of deepwater clastic submarine fans and slope channels onlapping against the underlying sequence boundary during lowstand. A linked lowstand shelf-slope-basin system is found in the Kuitei Basin (East Kalimantan) during Pleistocene. This study also concludes that deepwater submarine fans are not uniquely related to relative sea-level fall/lowstand. Examples were found in Lewis Shale Formation in the Washakie Basin, Oceanside and Carlsbad canyon-channel system in the California Boarderland Basin, and Upper Sobrarbe Formation in the Ainsa Basin (Nothern Spain). Results show that submarine fans and channel-levee systems can develop at any relative sea level, lowstand, highstand or standstill. Shelf-edge delta acts as the sediment source and progradation of these deltas are able to transport coarse sediments to deep water during highstand. The development of highstand submarine fans requires a strong fluvial drive on the deltas. Lowstand submarine fans tend to be bigger thicker and laterally extensive while the highstand submarine fans tend to be smaller and less laterally extensive. Therefore, lowstand deepwater fans are expected to hold more hydrocarbon reserves than highstand fans.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015