Tectonic reversal in East Barito Basin, south Kalimantan: Consideration of the types of inversion structures and petroleum system significance
Awang Harun Satyana*, Parada D. Silitonga**
** Total Indonesie
Proceedings Indonesian Petroleum Association, Twenty Third Annual Convention, October 1994
The Barito Basin, South Kalimantan, is located between Sundaland to the west and the Meratus Range to the east. Tectonic reversal characterizes Tertiary structural history of the eastern part of the basin. In Paleogene time, extensional deformation prevailed through a period of rifting and subsidence giving rise to a series of NW to SE trending horsts and grabens. In the Neogene, compressional deformation aligned broadly WNW to ESE has reactivated and inverted Paleogene structures producing wrench faults, folds, and reverse faults within the basin. The East Barito inversion structures are examined in detail to define the types of the structures based on Mitra’s (1993) classification of inversion structures. The study concluded that the East Barito inversion structures fall under the type formed by simple fault propagation folding along a planar fault. The structures originated through a number of mechanisms: (1) compressional movement along the restraining bends of wrench faults, (2) en echelon structures adjacent to wrench faults, and (3) direct inversion of NE-SW aligned Paleogene normal faults. The structural-stratigraphic evolution of East Barito inversion structures has provided ideal conditions for the accumulation of hydrocarbons. Growth sedimentation into an extensional basin resulted in early to middle Eocene synrift Lower Tanjung source rocks and reservoir sandstones. Postrift shales of late Eocene to early Oligocene Upper Tanjung provide an effective seal. Structural inversion which commenced in mid-early Miocene and greatly affected the basin from late Miocene to Pliocene has subsided Lower Tanjung source rocks to the depth wherein hydrocarbons could be generated and expelled. Migrated hydrocarbons were entrapped in anticlinal traps formed during the inversion. Plio-Pleistocene inversion might either create new structuraI traps or destroy previous hydrocarbon accumulations. In the latter case, hydrocarbons would remigrate and be trapped in the newly-formed inversion structures. Tanjung Raya fields represent such ideal hydrocarbontrapping conditions. Remaining hydrocarbon potential should be considered before and after the advent of basin inversion.
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