SOUTH SUMATRA BASIN
The
geology of the South Sumatra Basin is a result of tectonic activities that are
closely related to the subduction of the Indi-Australian Plate, which moves
north to northeast to the relatively silent Eurasian Plate. The subduction zone
of the plate covers the area west of Sumatra and south of Java. Some small
plates (micro-plates) that are between the interaction zones also move and
produce convergence zones in various shapes and directions. The subduction of
the Indi-Australian plate can affect rock conditions, morphology, tectonics and
structures in South Sumatra. The tectonic collisions of plates on Sumatra
Island produce a front arc, magmatic, and rear arc.
The
South Sumatra Basin is formed from depression which is surrounded by Pratersier
rock heights. The removal of the Barisan Mountains takes place at the end of
the Limestone accompanied by block faulting. Besides the mountains
The
ranks as block mountains are some of the old rock heights that are still
exposed on the surface are in the Thirteen Mountains, Twelve Mountains, Lingga
Island and Bangka Island which are remnants of the "Sunda Landmass"
high, which is now a Sunda Shelf. The South Sumatra Basin has undergone three
orogenesis processes, the first being in the Middle Mesozoic, the second in the
Late Cretaceous to the Early Tertiary and the third in the Plio-Plistocene.
Plio-Plistocene Orogenesis produces geological structural conditions as seen at
this time. Tectonics and geological structures of the South Sumatra Basin can
be divided into three groups, namely, the Semangko Fault Zone, the folding zone
trending northwest-southeast and the fault zones that are closely related to
Pratersier folds and faults undergoing rejuvenation.
Physiographically,
the South Sumatra Basin is a Tertiary basin with a northwest-southeast
direction, which is bounded by the Semangko Fault and Bukit Barisan in the
southwest, the Sunda Shelf to the northeast, Tinggian Lampung in the southeast
which separates the basin from the Sunda Basin, and the Twelve Mountains. and
the Thirty Mountains in the northwest that separates the South Sumatra Basin
from the Central Sumatra Basin. The position of the South Sumatra Basin as a
back arc basin (Blake, 1989)
Regional Tectonics
Blake
(1989) states that the South Sumatra Basin area is a Tertiary-aged back arc
formed as a result of interactions between Sunda Shelf (as part of the Asian
continental plate) and the Indian Ocean plate. This basin area covers an area
of 330 x 510 km2, of which the southwest is bordered by the Pre-Tertiary
outcrops of Bukit Barisan, to the east by the Sunda Shelf (Sunda Shield), to
the west bordered by the Thirteen Mountains and to the southeast by Tinggian
Lampung.
According
to Salim et al. (1995), the South Sumatra Basin was formed during the Tertiary
(Eocene-Oligocene) Early when the graben series developed as a reaction to the
angular subduction system between the Indian Ocean plate beneath the Asian
Continent plate. According to De Coster, 1974 (in Salim, 1995), it is estimated
that there have been 3 episodes of orogenesis that form the structural
framework of the South Sumatra Basin namely orogenesa Middle Mesozoic, Late
Cretaceous tectonics - Early Tertiary and Plio-Plistocene Orogenesa.
Interaction
between Sunda Exposure (as part of the Asian continental plate) and the Indian
Ocean plate
Sumatra
Tectonic Map
The
first episode, Paleozoic and Mesozoic deposits are metamorphosed, folded and
broken into chunks of structure and intruded by granite batolites and have
formed archetypal basins. According to Pulunggono, 1992 (in Wisnu and Nazirman,
1997), this phase forms a fault trending northwest - southeast in the form of
shear faults.
The
second episode of the Late Cretaceous in the form of an extension phase
produces tensional motion which forms graben and horst in the north-south
general direction. Combined with the results of the Mesozoic orogenesa and the
results of weathering of rocks - Pre-Tertiary rocks, these tensional motion
forms an old structure that controls the formation of the Pre-Talang Akar
Formation.
The
third episode was in the form of a compression phase in Plio - Plistocene which
caused the precipitation pattern to turn into a regression and play a role in
the formation of folding and fault structures so as to form the present
geological configuration. In this tectonic period there was also the removal of
the Bukit Barisan Mountains which produced a Semangko horizontal fault that
developed along the Bukit Barisan Mountains. Horizontal movements that occur
from Early Plistocene to the present affect the conditions of the South and
Central Sumatra Basin so that newly formed faults in this area have almost
parallel developments with the Semangko fault. As a result of this horizontal
movement, the orogenesa that occurs in Plio - Plistocene produces folds that
traverse northwest - southeast but the faults formed are directed northeast -
southwest and northwest - southeast. The type of cesarean contained in this
basin is a rise in fault, horizontal fault and normal fault.
The
appearance of the dominant structure is the structure trending
northwest-southeast as a result of the Plio-Plistocene orogenesis. Thus the
structure pattern that occurs can be distinguished by the old pattern trending
north - south and northwest - southeast as well as a young pattern that
traverses northwest - southeast which is parallel to Sumatra Island.
Regional Stratigraphy
South Sumatra Basin
The
stratigraphy of the South Sumatra Basin area has been widely discussed by
previous geologists, especially those working in the petroleum environment.
Initially the discussion focused on Tertiary sediments, generally never
published and only applied in their own environment.
South
Sumatra Stratigraphy
Previous
researchers have compiled the general stratigraphic sequences of the South
Sumatra Basin, including: Van Bemmelen (1932), Musper (1937), Marks (1956),
Spruyt (1956), Pulunggono (1969), De Coster 2 (1974), Pertamina (1981). Based
on previous researchers, the South Sumatra Basin Stratigraphy is divided into
three groups: Pre-Tertiary rock groups, Tertiary rock groups and Quaternary
rock groups.
1.
Pre-Tertiary Rocks
Pre-Tertiary
Rocks The South Sumatra Basin is the basis of the Tertiary sedimentary basin.
This rock is found as igneous, metamorphic and sedimentary rock (De Coster,
1974) Westerveld (1941), dividing Paleozoic (Permocarbon) rocks in the form of
slate and Mesozoic (Yurakapur) in the form of volcanic facies series and deep
sea facies series. These Pre-Tertiary rocks are thought to have undergone
intensive folds and faults in the Middle Cretaceous to the Late Cretaceous
times and were intruded by igneous rocks since the orogenesis of Middle
Mesozoic (De Coster, 1974).
2.
Tertiary rocks
Based
on previous studies the Tertiary sedimentation sequence in the South Sumatra
Basin is divided into two stages of deposition, namely the stage of oceanic and
sea shrinkage stages. The sediments formed at the stage of the oceanic rock are
called the Telisa Group (De Coster, 1974, Spruyt, 1956), from the age of the
Early Eocene to the Middle Miocene consisting of the Lahat Formation (LAF),
Talang Akar Formation (TAF), Baturaja Formation (BRF) , and Gumai Formation
(GUF). Whereas those formed in the marine shrinkage stage called the Palembang
Group (Spruyt, 1956) from the Middle Miocene - Pliocene age consist of the Air
Benakat Formation (ABF), Muara Enim Formation (MEF), and Kasai Formation (KAF).
a.
Lahat Formation (LAF)
According
to Spruyt (1956), this Formation is located inconsistently above the bedrock,
which consists of thin layers of andesitic tuffs which gradually turn upwards
into tuffaceous clay stones. In addition, andesite breccia intersects with
andesite lava, which is located at the bottom. Tufan claystone, fresh green and
weathered purple to purplish red. According to De Coster (1973) this formation
consisted of tuffs, agglomerates, claystones, tufan sandstones, conglomerates
and breccia that were from the Late Eocene to the Early Oligocene. This
formation is deposited in freshwater. Thickness and lithology varied greatly
from one place to another because of irregular basin forms, then at the Eocene
to Early Miocene age, volcanic activity produced andesite (Westerveld, 1941
vide of side katilli 1941), this activity peaked at the age of Late Oligocene
while the rocks are referred to as "old Andesite Lava" rocks which
also intrusion rocks deposited in the Early Tertiary Period.
b.
Talang Akar Formation (TAF)
The
name Talang Akar originating from Talang Akar Stage (Martin, 1952) other names
that have been used are Houthorizont (Musper, 1937) and Lower Telisa Member
(Marks, 1956). Talang root formations in several places in direct contact are
not in harmony with Pre-Tertiary rocks. This formation in several places is in
harmony with the Lahat Formation (De Coster, 1974), the relationship is called
stratigraphic overlap, it also interprets the stratigraphic relationship
between the two formations, especially in the middle, obtained from the Limau
well drilling data located in the Southwest of Prabumulih City ( Pertamina,
1981), the Talang Akar Formation is divided into two, namely: Members of the
"Gritsand" consist of sandstones, which contain quartz and the grain
size at the bottom is rough and the top is finer. At the top of the sandstone
it turns into a conglomerate sandstone or breccia. Sandstones are white to
grayish brown and contain mica, sometimes there are alternating brown claystone
with coal, in this member there are remnants of plants and coal, the thickness
is between 40 - 830 meters. These sediments are fluviatile to delta deposits
(Spruyt, 1956), also according to Spruyt (1956) the transitional members at the
bottom consist of alternating fine to medium sized quartz sandstones and
claystone and coal seams. Sandstones at the top intersect with thin limestones
and side sandstones, marl, claystone and shale. This member contains fossils of
Molluscs, Crustaceans, remaining large foram fish and small forams, deposited
in the paralis, litoral, delta environment, until the edge of the sea is
shallow and gradually toward the open sea towards the basin. This formation is
from the Late Oligocene to the Early Miocene. The thickness of this formation
in the southern part of the basin reaches 460 - 610 meters, while in the
northern part of the basin has a thickness of approximately 300 meters (De
Coster, 1974).
c.
Baturaja Formation (BRF)
According
to Spruyt (1956), this formation was deposited in harmony above the Talang Akar
Formation. Consisting of reef limestone and sandstone sandstone. Gumai
mountains are exposed from the bottom up in succession of tufan marbles, layers
of coral limestone, white gray sandstone, these limestones contain large
forams, including Spiroclypes spp, Eulipidina Formosa Schl, Molusca and so on.
Thickness between 19 - 150 meters and Early Miocene age. Environment
Precipitation is shallow sea. The naming of the Baturaja Formation was first
put forward by Van Bemmelen (1932) as "Baturaja Stage", Baturaja Kalk
Steen (Musper, 1973) "Crbituiden Kalk" (vd Schilden, 1949; Martin,
1952), "Midle Telisa Members" (Marks, 1956 ), Baturaja Kalk Sten
Formatie (Spruyt, 1956) and Telisa Limestone (De Coster, 1974). The location of
the Baturaja Formation type is in the Baturaja cement plant (Van Bemelen,
1932).
d.
Gumai Formation (GUF)
This
formation is deposited after the Baturaja Formation and is the result of
sediment deposition that occurs when the sea trough reaches its peak. The
relationship with the Baturaja Formation at the edge of the basin or the area
in the shallow basin is harmonious, but in some places in the basin centers or
in deep part of the basin sometimes run with the Baturaja Formation
(Pulonggono, 1986). According to Spruyt (1956) This formation consists of
tufaan napal with bright gray to dark gray. Sometimes there are hard, tuff,
glauconite sandstone layers, tuff breccias, shale clay and a thin layer of
limestone. Sediment deposits in this formation contain a lot of Globigerina
spp, and marl is hardened. Westerfeld (1941) states that the Telisa layers are
a monotonous series of shales and marl containing Globigerina sp with tufa
interlude as well as glauconite sand layers. The age of this formation is Early
Middle Miocene (Tf2) (Van Bemmelen, 1949) whereas according to Pulonggono
(1986) the Early Miocene to Middle Miocene (N9 - N12) age.
e.
Air Benakat Formation (ABF)
According
to Spruyt (1956), this formation is the initial stage of the deposition cycle
of the Palembang Group, namely at the beginning of the deposition of marine
shrinkage. This formation is from the Late Miocene to the Pliocene. The
lithology consists of tuffaceous sandstones, a little or a lot of tuffaceous
clays that intersect with the limestone limestone or the sandstones are getting
more and more the glauconite content decreases. In this formation Globigerina
spp is found, but many contain Rotalia spp. At the top there are many molluscs
and plant remains. In Limau, in the investigation of Spruyt (1956) found clay
flakes which were blue to gray brown, flakes of sandy clay and tuffaceous
sandstones. In the Jambi area found in the form of bluish clay, marl, sand
flakes and sandstones containing Molluscs, glauconite is sometimes coarse.
Deposited in the lower neritic depositional environment and gradually shallow
upper sea level (De Coster, 1974). The thickness of this formation ranges from
250-1550 meters. The location of this type of formation, according to Musper
(1937), is located between Air Benakat and Air Benakat Kecil (approximately 40
km north-northwest of Muara Enim (Lembar Lahat). The other name is "Onder
Palembang Lagen" (Musper, 1937), " Lower Palembang Member
"(Marks, 1956)," Air Benakat and en Klai Formatie "(Spruyt,
1956).
f.
Muara Enim Formation (MEF)
According
to Spruyt (1956) this formation is in fact aligned above the Air Benakat
Formation. This formation can be divided into two members "a" and
members "b". Members of "a" are also called Brown Members
consisting of brown claystone and sandstone to gray brown, fine to medium sized
sandstones. In Palembang there are also coal seams. Members "b" are
also called Blue Green Members consisting of sandstone clay and tufaan
claystone which are green in blue, some layers of coal are dark red, fine
coarse sandstones are white to light gray. In members "a" sometimes
found the content of Foraminifera and Mollusca in addition to coal and plant
residues, while in members "b" other than coal and plant residues are
not found fossils except brackish water foram Haplophragmoides spp (Spruyt,
1956). The thickness of this formation is around 450-750 meters. The member
"a" is deposited in the litoral environment which gradually changes
the environment of brackish and land water (Spruyt, 1956). The location of the
type is located in Muara Enim, Kampong Minyak, Lembar Lahat (Tobler, 1906)
g.
Kasai Formation (KAF)
This
formation ends the ocean shrinkage cycle (De Coster and Adiwijaya, 1973). At
the bottom consists of tufan sandstones with several intervals of tuffaceous
claystone, then there is a conglomerate alternating layers of loose tufan
claystone and sandstone, at the top there is a pumice tuff layer containing
residual plants and cracked wood with a sedimentary cross structure, lignite as
lenses in tufan sandstone and claystone (Spruyt, 1956). Tobler (1906)
discovered Viviparus spp and Union spp freshwater mollusks, whose age was
thought to be Plio-Plistocene. Deposition environment for brackish water to
land. This unit is thrown wide in the eastern part of the sheet and reaches a
thickness of 35 meters.
3.
Alluvial Deposition Unit
The
distribution of this unit includes the river area and the banks of large rivers
in the form of meanders in the middle and on the banks of the river. The
thickness of the alluvial deposits varies, and this unit consists of the
results of frozen rags, sedimentary rocks, loose metamorphic rocks measuring
fine sand to the crust.
Reference:
- Barber, A.J., Crow, M.J., Milsom, J. S., 2005, “Geology, Resources and Tectonic Evolution”, Geological Society London, Geological Society Memoirs No.31.
- Bishop, M.G., 2001, “South Sumatra Basin Province, Indonesia: The Lahat, Talang Akar-Cenozoic Total Petroleum System”. USGS Field Report 99-50-S.
- Eubank, R.T., Makki, A.C., 1981, “Structural Geology of The Central Sumatra Back Arc Basin”. Proceedings Indonesia Petroleum Association, Tenth Annual Convention.
- http://muhammadafit.blogspot.com/2013/11/geologi-indonesia-cekungan-sumatra.html
- http://pswtkertas.tumblr.com/post/32869528255/geologi-regional-cekungan-sumatera-selatan.
Informasi yang sangat bagus :)
BalasHapusijin share 14 tools ini:
http://titihmarket.blogspot.com/2019/03/14-tools-untuk-bisnis-online-2019.html
Salam,
TM