Contrasting Deepwater Sediment Feeder Systems, Sulawesi, Indonesia

Peter Baillie¹, Philip A. Teas², John Decker², Dan Orange², and Widjanarko^3
1TGS-NOPEC Geophysical Company, Perth Australia
²Black Gold Energy, Jakarta, Indonesia
³MIGAS, Jakarta, Indonesia

Introduction

Sulawesi is located within the Indonesian archipelago near the Equator east of Borneo and north of Java. Formerly know as “Celebes”, it is a K-shaped mountainous island consisting of four narrow peninsulas (“arms”) separated by deep gulfs (“bays”). Geologically it is comprised of a complex series of disparate oceanic and continental tectonic elements which have been brought into (temporary) juxtaposition by a series of predominantly left-lateral Neogene wrench faults.

The climate of Sulawesi is tropical with two seasons, dry from March to September and rainy from October to February. Temperatures range from 21° to 31° along the coast and from 20° to 25° in the highlands. Annual rainfall averages around 1,000–1,500 mm.

Makassar (119°24’17.38” east longitude and 5°8’6.19” south latitude), the main population center for Sulawesi, has average humidity of 67–86%, annual average rainfall of 337mm with January maximum (average 660mm) and August minimum (average 14.4mm), with an average 147 days of rain per year.

Neogene orogenesis in western Sulawesi has resulted in the formation of mountains which currently exceed 3,000 m in height and also the West Sulawesi Fold Belt (Fraser et al., 2003). The age of folding is well-constrained in the Lariang-Karama region where continental alluvial plain and marine deposits of the Plio-Pleistocene Pasangkayu Formation (“Celebes Molasse” of previous workers) formed in response to uplift of the hinterland. Continuing deformation is recorded on offshore seismic sections and syn-depositional folding of younger parts of the Pasangkayu Formation (Calvert and Hall, 2003; Fraser et al., 2003).

Our presentation will report on two spectacularly-imaged deepwater depositional channel systems which drain western Sulawesi; a high-sinuosity system draining northwestwards into the Makassar Strait from Palu Bay (Palu System), the other a low-sinuosity system draining southwards into Bone Bay and the East Java Sea (Bone System).

Database

Ongoing marine hydrographic and coring studies in Indonesia have provided remarkable new data on sediment transport and deposition from the shelf edge to deep marine basins.

TGS, in cooperation with the Indonesian Directorate General of Oil & Gas (Migas), is currently acquiring the Non-Exclusive Indonesia Frontier Basins Project. The project will acquire a variety of data to conduct a comprehensive prospectivity analysis over an area of around one million square kilometers. The studies, involving some 30 sedimentary basins, will have available 35,000 km new 2D seismic data and 400,000 square kilometers of SeaSeepTM – multibeam bathymetry and backscatter, gravity and magnetic data, 1,200 navigated piston cores with geochemical analyses and 120 heat flow probes.

Relevant data from that project, together with earlier vintage non-exclusive seismic data from the Makassar Strait has kindly been made available by TGS and Migas for this presentation.

Palu System

There is no continental shelf offshore of western Sulawesi with the mountains rising steeply east from the Makassar Straits and the continental slope descending rapidly to the flat floor some 2.2 km deep. The Palu River and its extension into Palu Bay are the strong surface expression of the active Palu-Koro wrench fault system.

The Palu System is a deeply-incised, high sinuosity fossil feeder system located northwest of Palu Bay – the feeder system was active until very recent lateral fault movements cut off the sediment supply.

The system has developed on the Pliocene and younger West Sulawesi Foldbelt.

Bone System

Bone Bay is a narrow, deep gulf situated between the South Arm and Southeast Arm of Sulawesi. The gulf is about 400 km long and varies in width from 50 to 180 kilometers., The Bone System is a deep, wide, low-sinuousity channel system which drains towards the East Java Sea.

Seismic data suggests the channel system is Pliocene and younger in age.

Discussion

In our presentation we will present details of the geometry of the depositional systems, information from cores about channel sediments and discuss the origin of the contrasting channel systems.

References

Calvert, S. J. and Hall, R. 2003. The Cenozoic geology of the Lariang and Karama regions, western Sulawesi: new insight into the evolution of the Makassar Strait region. Proceedings Indonesian Petroleum Association 29th Annual Convention, Jakarta, October 14-16, 2003, p. 501–518.

Fraser, T.H., Jackson, B.A., Barber, P.M., Baillie, P. and Myers, K. 2003. The West Sulawesi Fold Belt and other new plays within the North Makassar Straits – a prospectivity review. Proceedings Indonesian Petroleum Association 29th Annual Convention, Jakarta, October 14-16, 2003, p. 431–450.

Figure 1. Multibeam bathymetry image of Palu depositional system, Sulawesi

Figure 2. Multibeam bathymetry in age of Bone depositional system, Sulawesi

AAPG Search and Discovery Article #90079©2008 AAPG Hedberg Conference, Ushuaia-Patagonia, Argentina