Deep Water Depositional Systems - Ultra-Deep Makassar Strait, Indonesia

Posamentier, H.W., Veritas Exploration Services, Meizarwin, ARCO Indonesia, and P.S. Wisman, Schlumberger - GeoQuest

Abstract

The ultra deep environment in the Makassar Strait, offshore eastern Kalimantan, Indonesia, is characterized by abundant turbidite, debrite, and sediment wave deposits. Key depositional elements imaged by 3-D seismic data include leveed channels, distributary channels/frontal splays, overbank wedges (levees), overbank splays/sediment waves, bottom-current sediment waves, debris flow sheets, and debris flow lobes. These deposits are systematically deposited within the context of a deep water depositional sequence: (1) debris flow sheets/lobes are observed at the base, overlain by (2) distributary channels or frontal splays that are, in turn overlain by (3) single, prominent leveed channels. This mass flow sequence is then commonly capped by (4) less widespread debris flow sheets or lobes.

Leveed channels of inferred Miocene to Pleistocene age are common in the stratigraphic record of the ultra-deep (i.e., greater than 2000 m water depth) Makassar Strait. These channels are characterized by moderate to high sinuosity and range in width from less than 250 m up to one km, and are associated with overbank wedges approximately one order of magnitude wider. Overbank wedges are characterized by abundant sediment waves. These sediment waves commonly are best developed on outer bends of channel meanders. Sea-floor irregularities have a marked impact on channel pattern as well as stratigraphic architecture. One prominent channel is characterized by a dramatic increase in sinuosity and decrease in channel width just down-system from a toe-thrust ridge, across which it flows.

Leveed channels commonly feed as well as overlie distributary channel complexes or frontal splays. These features can attain widths of greater than 10 km and thicknesses exceeding 80 m. Frontal splays appear to be channelized nearly to their distal extremities.

Debris flow deposits in the form of sheets, lobes, and channel fill are common in the study area. Massive amalgamated debris flow sheets reach thicknesses up to 150 m and widths greater than 20 km. The base of debris flow sheets are characterized by scour and exhibit deep (up to 30 m) and long (greater than 20 km) parallel grooves that diverge basinward.