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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association

Abstract


18th Annual Convention Proceedings (Volume 1), 1989
Pages 217-245

Development of the Bengkalis Depression, Central Sumatra and Its Subsequent Deformation – A Model for Other Sumatran Grabens?

P. J. Moulds

Abstract

The Bengkalis Depression is a north-south aligned Paleogene graben 265 kms. in length which traverses Central Sumatra.

The graben appears complex, almost as a chain of interconnected lozenge-shaped depressions whilst several side grabens extend particularly from its western margin. In this model the depression was formed by east-west Palaeogene tension and the observed complexities have been related to basement inhomogeneities.

Subsequent Neogene to Recent compression of the Barisan Tectonic Event has commenced deformation, uplift, erosion and destruction of the graben and its filling sediments progressively from the south. Features resulting from these compressional tectonics are controlled by the same basement inhomogeneities. The distinction of these two tectonic events allows a relatively simple model of graben formation and history to be erected.

The author believes that this model is applicable to other contemporaneous grabens in Sumatra and has traced the major basement structures and their role in controlling graben form. The compression and tectonic overprinting of this earlier extension has produced major basement block uplift, normal fault rejuvenation and strike-slip faulting. The interplay of lines of basement weakness with structural grain and the compression have produced a variety of features such an en echelon folds, (sometimes bisected), chains of anticlines (not en echelon) and Sunda Folds. As the nature of the basement and its structural grain change, so do the effects of the compression. Several examples are discussed.


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