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The Influence of Local Gradients on Accommodation Space and Linked Depositional Elements Across a Stepped Slope Profile, Offshore Brunei

By
T. A. (Mac) McGilvery
T. A. (Mac) McGilvery
ConocoPhillips 700 G Street Anchorage, Alaska 99501
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Daniel L. Cook
Daniel L. Cook
Samson Resources Two West Second Street Tulsa, Oklahoma 74103
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Published:
December 01, 2013

Abstract

The modern continental slope offshore Brunei is an outstanding example of the relationship between syndepositional structure, slope accommodation space, and sediment dispersal systems. The bathymetric profile is a “stepped slope” characterized by elongate, structurally controlled mini-basins, in contrast to the elliptical salt withdrawal “intraslope” basins of the Gulf of Mexico. Progressive basinward thrusting, caused by updip sediment loading of the Baram delta and regional tectonics, divides the area into alternating thrust-cored structures and elongate, shelf-margin parallel mini-basins 2-10 km in width and 20-60 km in length. The dominant types of accommodation space are healing and bypass phase slope accommodation space associated with a subordinate amount of ponded accommodation space. The primary control on net deposition versus bypass is local sea floor gradients along sediment dispersal pathways that are structurally controlled. Gradients along primary flow paths range from 0.38O to 1.93O. Local gradients along the basinward margins of thrust structures and along submarine canyon walls are substantially higher (>15.0O). Sediment dispersal pathways can extend for >60km and are quite tortuous across the irregular bathymetry. Four bathymetric features and depositional elements have been defined along these pathways. These include: (1) local cohesive slump complexes up to regional mass transport complexes; cohesive slumps reflect short distance transport by down slope creep, whereas mass transport complexes reflect longer distance debris flows. (2) Submarine canyons have developed by gravity mass wasting along the forelimbs of thrust-cored features. Resultant bathymetric depressions locally act as sediment conduits which link mini-basins across intervening thrust cored structures. (3) Sediment dispersal fairways range from 2-5 km in width and contain multiple straight/erosional or sinuous/leveed channels. (4) Distributary channel/lobe complexes consist of sheet deposits are punctuated by low relief channel features.

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GCSSEPM

Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential

Harry H. Roberts
Harry H. Roberts
Houston, Texas
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Norman C. Rosen
Norman C. Rosen
Houston, Texas
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Richard H. Fillon
Richard H. Fillon
Houston, Texas
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John B. Anderson
John B. Anderson
Houston, Texas
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SEPM Society for Sedimentary Geology
Volume
23
ISBN electronic:
978-0-9836096-7-4
Publication date:
December 01, 2013

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