Implications of gravity data from East Kalimantan and the Makassar Straits: a solution to the origin of the Makassar Straits?

• Published in: Journal of Asian earth sciences 1999-02, Vol.17 (1), p.61-78
• Main Authors: Cloke, I.R, Milsom, J, Blundell, D.J.B
• Format: Article
• Language: English
• Subjects: Gravity; Kutai; Makassar; Oceanic crust; SE Asia
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/S0743-9547(98)00056-7

Recent free-air gravity data covering the Makassar Straits is integrated with Bouguer gravity data from onshore East Kalimantan to provide new insights into the basement structure of the region. Onshore Kalimantan, gravity highs on the northern margin of the Kutai Basin trend NNE–SSW and N–S and correspond with the axes of inverted Eocene half-grabens. NW–SE trending lows correspond to deep seated basement weaknesses reactivated as normal faults during the Tertiary. An intra-basin gravity high trending NNE–SSW, the Kutai Lakes Gravity High, is modelled as folded high density Paleogene sediments flanked by syn-inversion synclines infilled with low density sediments. Offshore Kalimantan, the Makassar Straits include two basins offset by an en-echelon fault zone, suggestive of an extensional origin. The regional signature of the free-air anomaly data mirrors the bathymetry, but this effect can be reduced by the use of filters in order to examine the basin architecture. The free-air gravity minimum in the Makassar Strait is only −20 mGal, much smaller than that appropriate for a foreland basin, and more indicative of an extensional basin. The steepness of the gradients on the flanks of the basins indicates fault control of their margins. A regional 2D profile across the North Makassar Basin suggests the presence of attenuated crust (