Abstract top ↑
A geological map 1:100,000 of West Central Sumatra was drafted during the "Joint Indonesian-German Uranium Exploration Project" in 1976-1978. A slightly generalized version of this map is here presented on the scale 1:250,000.
A detailed stratigraphy comprises the following types of rock: sedimentary rocks, volcanic rocks, intrusive rocks.
The Structure System of West Central Sumatra:
Four prominent zones of SE trending faults form the main components of the Sumatran Fault Systme in West Central Sumatra. With its associated volcanic activity the Central Barisan Fault Zone constitutes the most significant and striking structural feature in the region.
Dextral displacement of considerable magnitude was evidenced along the Central Barisan Fault Zone by geological mapping.
The structural history of West Central Sumatra and its intimately associated volcanism is governed by processes occurring during the interaction of the Indian Ocean Plate with the Asian Plate and the corresponding subduction zones. Volcanp-plutonic arcs and arc- related lithologies give evidence that Sumatra has formed a part of a convergent margin since the Permian. Major tectonic events occurred during the Middle Cretaceous, the Middle Miocene and the Plio- Pleistocene.
Although evidence for Cenozoic activity is much better substantiated, a pre-Tertiary (Cretaceous) origin and repeated reactivation is postulated for the Sumatran Fault System. Vertical and strike-slip movements resulted from the diagonal subduction of the Indian Plate under the Asian Plate and subsequent thermal doming of the Barisan block.
The Tertiary Deposits of West Central Sumatra:
The Tertiary of West Central Sumatra consists of sediments of the "Breccia and Marl Formation" (Oligocene), the "Quartz-sandstone Formation" (Oligocene-Miocene) and the "Thelisa and Palembang Formations" (Miocene-Pliocene).
The bituminous marl, shale and conglomerate of the "Breccia and Marl Formation", containing an abundant fresh-water fish fauna were deposited in intramontane basins of the Barisan Geanticline. Coal seams have been mined locally.
The "Quartz-sandstone Formation", subdivided into a lower and upper sequence, is composed of conglomerate, sandstone and shale. Coal seams in the lower part are mined at Sawahlunto. Locally, the detritus of the formation was derived from the Pasaman and the Rokan highs, which are parts of the Barisan Geanticline.
The marine deposits (marl, shale, tuff, coral reef limestone) of the "Telisa and Palembang Formations" contain foraminifers of Early Miocene to Middle Miocene age. Presumably, the uppermost part of the series is to be attributed to the "Middle Palembang Beds" (uppermost Miocene to Lower Pliocene).