Sumatra, Sunda Shelf, Natuna - Bibliography of Indonesia Geology

A widespread Plio-Pleistocene compressional event inverted many of the Paleogene rift normal
faults, creating most of today's surface anticlines. The oblique subduction of the Indian Ocean plate
under Sumatra gave rise to the major Sumatra Fault Zone, a NW-SE trending right-lateral strike slip
fault zone across the Barisan Mountains volcanic arc. A similar, parallel fault zone, the Mentawai FZ
is present in the offshore and roughly parallels the front of the accretionary prism.
Sumatra has long been an important hydrocarbon province, with all oil and gas production from the
North, Central and South Sumatra 'back-arc' basins. Initial exploration in the late 1800's- early
1900's focused on drilling surface anticlines, many of them with surface seeps, targeting the
relatively shallow M-L Miocene sandstone reservoirs.
A deeper play, and volumetrically the most important, is in Late Oligocene- basal Miocene fluvialdeltaic
sandstones in anticlinal structures. It was discovered accidentally by drilling 'too deep' into
the thick Early Miocene marine shale section over Christmas in 1922 at Talang Akar-Pendopo in S
Sumatra (Talang Akar field in the Talang Akar Fm). The first discovery in the C Sumatra basin was
in 1939 in the Lirik field and is also in this play. The largest fields oil fields in Sumatra are the giant 3-
5 billion barrels Duri and Minas fields in C Sumatra, discovered in 1941 and 1944.
A third play, which could not be explored in the old days of surface anticline mapping, is in E-M
Miocene reefal carbonate buildups, and was a main focus of 1970's- 1980's exploration. The Arun
field in N Sumatra, discovered in this play in 1971, is one of Indonesia's largest gas fields.
A fourth play, in fractured and weathered Pre-Tertiary basement, has generated interest since the
mid-1980's, but volumes have been relatively minor.
Suggested reading
A recent major review of Sumatra geology is Barber, Crow & Milsom (2005)
II.2. Sunda Shelf (incl. 'Tin Islands', Karimata)
Some 150 papers are in the bibliography primarily on the Sunda Shelf, a broad shallow sea, that
was exposed land during the Pleistocene glacial lowstands. A pattern of Pleistocene relict river
channels draining from Sumatra and Borneo into the South China Sea was mapped by Molengraaff
(1919), Hanebuth et al. (2000), etc.
The Sunda Shelf forms the relatively stable core of 'Sundaland', an area of relatively old continental
terranes (Indochina- E Malaya- SW Borneo?), that amalgamated with Asia before the Permian. Pre-
Tertiary rocks outcrop extensively, or are covered by only a thin veneer of fluvial and shelfal relict
sediments.
The main economic interest of the region is in the 'tin islands' Lingga, Singkep, Bangka and Belitung,
off the NE coast of Sumatra, probably extending to the Karimata islands off SW Kalimantan. They
are the S part of the SE Asian tin belt, which extends from N Burma, Thailand and W Malaysia.
Mining has taken place since the early 1800's and Indonesia has produced ~15% of all tin mined in
the world, mainly from alluvial cassiterite placer deposits eroded from Late Triassic granite
intrusives. Today, reserves are largely depleted.
Bibliography of Indonesia Geology v. 4.1 2 www.vangorselslist.com July 2012