Mass-Transport Deposits, the dominant sediment in the near-surface interval on the Upper Slope of Sabah, Deepwater Northwest Borneo

Lu, Hongbo¹, Craig Shipp², Chris Hadley¹ (1) Shell International Exploration and Production Inc, Houston, TX (2) Shell Internation Exploration and Production, Houston, TX

The study area is located on the northwest Borneo continental slope with a water depth of 2800-4000 ft (850-1220 m), adjacent to the Brunei border in the Malaysian state of Sabah. The most distinctive feature in this area is a dip-oriented (southeast to northwest) seafloor structure (bulge) with 400-500 ft (120-150 m) of positive relief that dominates the mid to upper slope. A second distinctive feature is complex of mass-transport deposits (MTDs) that occur in the near-surface interval northeast of the bulge with a thickness up to several hundred feet. The MTD complex displays a fan-like shape in map view and is exposed on the seafloor at distal end, while the proximal end near the shelf edge is overlain by 50-100 ft (15-30 m) of hemipelagic drape. Steep slopes on the northeast flank of the bulge seem related to erosion caused by mass failure associated with the MTD complex.

A primary objective of this study was to generate a suite seafloor and near-surface maps to guide the design of subsea infrastructure. The geohazards assessment focused on characterizing seafloor and near-surface geological features, especially the geometry, process, and evolution of the MTD complex. A variety of techniques were used to differentiate seafloor textures and near-surface features on both conventional (3D) and high-resolution (2D and 3D) seismic data sets. Additionally, offset well logs were used to evaluate the internal character of the MTDs.