Geologi Regional Cekungan Sumatera Selatan

7/23/2019 Geologi Regional Cekungan Sumatera Selatan

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Geologi Regional Cekungan Sumatera SelatanFebruari 12, 2008 inIndonesia Basin| Tags:Indonesia Basin

Secara fisiografis Cekungan Sumatra Selatan meruakan cekungan Tersier berara! barat laut "

tenggara, #ang dibatasi Sesar Semangko dan Bukit Barisan di sebela! barat da#a, $aaran Sunda di

sebela! timur laut, Tinggian %amung di sebela! tenggara #ang memisa!kan cekungan tersebut

dengan Cekungan Sunda, serta $egunungan &ua Belas dan $egunungan Tiga $ulu! di sebela! barat

laut #ang memisa!kan Cekungan Sumatra Selatan dengan Cekungan Sumatera Tenga!'

Posisi Cekungan Sumatera Selatan sebagai cekungan busur belakang (Blake, 1989)

Tektonik Regional

Blake (1)8)* men#ebutkan ba!+a daera! Cekungan Sumatera Selatan meruakan cekungan busur

belakang berumur Tersier #ang terbentuk sebagai akibat adan#a interaksi antara $aaran Sunda(sebagai bagian dari lemeng kontinen sia* dan lemeng Samudera India' &aera! cekungan ini

meliuti daera! seluas --0 . /10 km2, dimana sebela! barat da#a dibatasi ole! singkaan $raTersier

Bukit Barisan, di sebela! timur ole! $aaran Sunda (Sunda Shield*, sebela! barat dibatasi ole!

$egunungan Tigaulu! dan ke ara! tenggara dibatasi ole! Tinggian %amung'

Menurut Salim et al. (1995), Cekungan Sumatera Selatan terbentuk selama !al "ersier

(#osen $ %ligosen) ketika rangkaian (seri) graben berkembang sebagai reaksi sistem &enun'aman

menuut antara lem&eng Samura *nia i ba!a+ lem&eng Benua sia.

Menurut e Coster, 19- (alam Salim, 1995), i&erkirakan tela+ ter'ai / e&isoe

orogenesa ang membentuk kerangka struktur aera+ Cekungan Sumatera Selatan aitu

orogenesa Meso0oik "enga+, tektonik a&ur k+ir $ "ersier !al an %rogenesa Plio $

Plistosen.
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#&isoe &ertama, ena&an $ ena&an Paleo0oik an Meso0oik termetamor2osa, terli&at

an ter&ata+kan men'ai bongka+ struktur an iintrusi ole+ batolit granit serta tela+ membentuk

&ola asar struktur cekungan. Menurut Pulunggono, 1993 (alam 4isnu an a0irman ,199-),

2ase ini membentuk sesar berara+ barat laut $ tenggara ang beru&a sesar $ sesar geser.

#&isoe keua &aa a&ur k+ir beru&a 2ase ekstensi meng+asilkan gerak $ gerak

tensional ang membentukgrabenan horstengan ara+ umum utara $ selatan. ikombinasikan

engan +asil orogenesa Meso0oik an +asil &ela&ukan batuan $ batuan Pra $ "ersier, gerak gerak

tensional ini membentuk struktur tua ang mengontrol &embentukan 6ormasi Pra $ "alang kar.

#&isoe ketiga beru&a 2ase kom&resi &aa Plio $ Plistosen ang menebabkan &ola

&engena&an beruba+ men'ai regresi an ber&eran alam &embentukan struktur &erli&atan an

sesar se+ingga membentuk kon2igurasi geologi sekarang. Paa &erioe tektonik ini 'uga ter'ai

&engangkatan Pegunungan Bukit Barisan ang meng+asilkan sesar menatar Semangko ang

berkembang se&an'ang Pegunungan Bukit Barisan. Pergerakan +orisontal ang ter'ai mulai

Plistosen !al sam&ai sekarang mem&engaru+i konisi Cekungan Sumatera Selatan an "enga+

se+ingga sesar $ sesar ang baru terbentuk i aera+ ini mem&unai &erkembangan +am&ir

se'a'ar engan sesar Semangko. kibat &ergerakan +orisontal ini, orogenesa ang ter'ai &aa

Plio $ Plistosen meng+asilkan li&atan ang berara+ barat laut $ tenggara teta&i sesar ang

terbentuk berara+ timur laut $ barat aa an barat laut $ tenggara. 7enis sesar ang tera&at&aa cekungan ini aala+ sesar naik, sesar menatar an sesar normal.

enam&akan struktur ang ominan aala+ struktur ang berara+ barat laut $ tenggara

sebagai +asil orogenesa Plio $ Plistosen. engan emikian &ola struktur ang ter'ai a&at

ibeakan atas &ola tua ang berara+ utara $ selatan an barat laut $ tenggara serta &ola mua

ang berara+ barat laut $ tenggara ang se'a'ar engan Pulau Sumatera .


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KERANGKA TEKTONIK DAN PERKEMBANGAN STRUKTUR CEKUNGAN

SUMATRA SELATAN

Kerangka Tektonik Sumatra

Pulau Sumatra terletak i barataa ari ontinen Sundaland an meru&akan 'alur konergensiantara em&eng :inia;ustralia ang menusu& i sebela+ barat em&eng #urasia


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on2igurasi cekungan &aa aera+ Sumatra ber+ubungan langsung engan ke+airan ari

subuksi ang menebabkan non-volcanic fore-arc an volcano-plutonik back-arc. Sumatra

a&at ibagi men'ai 5 bagian (arman an Sii, 3===)

1. Sunda outer-arc ridge, beraa se&an'ang batas cekunganfore-arc Suna an ang

memisa+kan ari lereng trench.3. CekunganFore-arcSuna, terbentang antara akresi non;ulkanik &unggungan outer-arc

engan bagian i ba!a+ &ermukaan an olkanik back-arc Sumatra.

/. CekunganBack-arc Sumatra, meli&uti Cekungan Sumatra >tara, "enga+, an Selatan.

Sistem ini berkembang se'alan engan e&resi ang berbea &aa bagian ba!a+ BukitBarisan.

. Bukit Barisan, ter'ai &aa bagian aial ari &ulauna an terbentuk terutama &aa Perm;arbon +ingga batuan Meso0oik.

5. Intra-arcSumatra, i&isa+kan ole+ upliftberikutna an erosi ari aera+ &engena&an

tera+ulu se+ingga memiliki litologi ang miri& &aafore-arc an back-arc basin.

Struktur Utama Cekungan Sumatra Selatan

Menurut Salim kk (1995) Cekungan Sumatra Selatan meru&akan cekungan belakang busur

karena beraa i belakang Pegunungan Barisan sebagai volcanic-arc-na. Cekungan ini berumur

"ersier ang terbentuk sebagai akibat aana interaksi antara Pa&aran Suna sebagai bagian ariem&eng ontinen sia an em&eng Samuera *nia. aera+ cekungan ini meli&uti aera+

seluas //= 51= km3, bagian barat aa ibatasi ole+ singka&an Pra;"ersier Bukit Barisan, i

sebela+ timur ole+ Pa&aran Suna (Sundaland), sebela+ barat ibatasi ole+ Pegunungan"iga&ulu+ an ke ara+ tenggara ibatasi ole+ "inggian am&ung.

Menurut Suta an Diaoguang (3==5? alam Sata, 3=1=) &erkembangan struktur mau&un eolusi

cekungan se'ak "ersier meru&akan +asil interaksi ari ketiga ara+ struktur utama aitu, berara+

timurlaut;barataa atau isebut Pola 7ambi, berara+ baratlaut;tenggara atau isebut PolaSumatra, an berara+ utara;selatan atau isebut Pola Suna. :al inila+ ang membuat struktur

geologi i aera+ Cekungan Sumatra Selatan lebi+ kom&leks ibaningkan cekungan lainna i

Pulau Sumatra. Struktur geologi berara+ timurlaut;barataa atau Pola 7ambi sangat 'elasteramati i Sub;Cekungan 7ambi. "erbentukna struktur berara+ timurlaut;barataa i aera+

ini berasosiasi engan terbentukna sistem graben i Cekungan Sumatra Selatan. Struktur li&atan

ang berkembang &aa Pola 7ambi iakibatkan ole+ &engakti2an kembali sesar;sesar normal

tersebut &aa &erioe kom&resi2 Plio;Plistosen ang berasosiasi engan sesar menatar (wrench

fault). amun, intensitas &erli&atan &aa ara+ ini tiak begitu kuat.

Pola Sumatra sangat menominasi i aera+ Sub;Cekungan Palembang (Pulunggono an

Cameron, 198). Mani2estasi struktur Pola ematang saat ini beru&a &erli&atan ang berasosiasiengan sesar naik ang terbentuk akibat gaa kom&resi Plio;Pleistosen. Struktur geologi berara+

utara;selatan atau Pola Suna 'uga terli+at i Cekungan Sumatra Selatan. Pola Suna ang &aa

a!alna imani2estasikan engan sesar normal, &aa &erioe tektonik Plio;Pleistosen terakti2kan

kembali sebagai sesar menatar ang sering kali mem&erli+atkan &ola &erli&atan i &ermukaan.


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Gambar 3. #lemen Struktur >tama &aa Cekungan Sumatra Selatan. %rientasi "imurlaut;

barataa atau >tara;Selatan Menun'ukkan >mur #o;%ligosen an Struktur *nersi

Menun'ukkan >mur Plio;Pleistosen (Ginger an 6ieling, 3==5).

Perkembangan Tektonik

Peristi!a "ektonik ang ber&eran alam &erkembangan Pulau Sumatra an Cekungan Sumatra

Selatan menurut Pulonggono kk (1993) aala+
http://ptbudie.files.wordpress.com/2011/10/2.jpg


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6ase kom&resi ang berlangsung ari 7urasik a!al sam&ai a&ur. "ektonik ini

meng+asilkan sesar geser ekstral 44 $ #S# se&erti Sesar ematang, e&aang,

Saka, Pantai Selatan am&ung, MusiLineamentanN S trend. "er'ai wrenchmovement an intrusi granit berumur 7urasik $ a&ur.

Gambar /. 6ase om&resi 7urasik !al Sam&ai a&ur an #li&soi Moel (Pulonggono kk,1993).

6ase tensional &aa a&ur k+ir sam&ai "ersier !al ang meng+asilkan sesar normal

an sesar tumbu+ berara+ $ S an 44 $ #S#. Seimentasi mengisi cekungan atau

terban i atas batuan asar bersamaan engan kegiatan gunung a&i. "er'ai &engisiana!al ari cekungan aitu 6ormasi a+at.

Gambar . 6ase "ensional a&ur k+ir Sam&ai "ersier !al an #li&soi Moel (Pulonggonokk, 1993).
http://ptbudie.files.wordpress.com/2011/10/4.jpghttp://ptbudie.files.wordpress.com/2011/10/3.jpg


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6ase ketiga aitu aana aktiitas tektonik Miosen atau *ntra Miosen menebabkan

&engangkatan te&i;te&i cekungan an iikuti &engena&an ba+an;ba+an klastika. Eaitu

terena&kanna 6ormasi "alang kar, 6ormasi Batura'a, 6ormasi Gumai, 6ormasi irBenakat, an 6ormasi Muara #nim.

6ase keem&at beru&a gerak kom&resional &aa Plio;Plistosen menebabkan sebagian

6ormasi ir Benakat an 6ormasi Muara #nim tela+ men'ai tinggian tererosi, seangkan&aa aera+ ang relati2 turun iena&kan 6ormasi asai. Selan'utna, ter'ai&engangkatan an &erli&atan berara+ barat laut i seluru+ aera+ cekungan ang

mengak+iri &engena&an "ersier i Cekungan Sumatra Selatan. Selain itu ter'ai aktiitas

olkanisme &aa cekungan belakang busur.

Gambar 5. 6ase om&resi Miosen "enga+ Sam&ai Sekarang an #li&soi Moel (Pulonggono

kk, 1993).
http://ptbudie.files.wordpress.com/2011/10/5.jpg


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APLIKASI SEKUEN STRATIGRAI UNTUK DATA !ELLLOG

Sebelum masuk ke tema ini +enakna i&a+ami mengenai sekuen stratigra2i a+ulu. Sebagai

re2erensi bisa ili+at i +alaman +tt&


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og ang biasana igunakan alam analisis stratigra2i ini aala+ log gamma ra (GR) an og

S&ontaneous Potentian (SP) ang meru&akan log ang menceriminkan ukuran butir ari

seimen. alam &enga&alikasian sekuen stratigra2i &erlu iketa+ui marker;marker alam sekuenstratigra2i aitu se&erti

1. Batas sekuen atau sequence boundary(SB); SB-1 dan SB-22. Transgressive Surface

3. Maximum Flooding Surface

Setela+ iketa+ui marker;marker tersebut kemuian a&at ilakukan kronokorelasi untuk setia&

sstem tract-na. &rinsi& kronokorelasi aala+ mengkorelasikan ke'aian;ke'aian geologi angterekam &aa batuan. e'aian geologi bisa ter'ai secara lokal, regional, an global, alam

'angka !aktu menit +ingga ratusan 'uta ta+un, se+ingga rekaman ke'aian ini igolongkan alam

bebera&a ore. Pembagian ore;ore tersebut a&at ibaca i +alaman sekuen stratigra2i sesuailink i atas. Setela+ kerangka kronologi geologi iketa+ui kemuian ilakukan korelasi ang

lebi+ etil biasana aala+ mengunakan &rinsi& litokorelasi se&erti sand to sand correlationan

kemuian a&at ibuat &eta iso&ac+ an &aleogeogra2ina.

Berikut aala+ a&likasi sekuen stratigra2i alam ata log

:*G:S" SES"#MS "RC" (#DD%)
http://ptbudie.files.wordpress.com/2011/04/hst1.jpg


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"RSGR#SS*F# SES"#MS "RC" (#DD%)
http://ptbudie.files.wordpress.com/2011/04/tst.jpg


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S";PR%GR*G 4#G# (#DD%)
http://ptbudie.files.wordpress.com/2011/04/lst-pw.jpg


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S";S%P# 6 C%MP#D (#DD%)
http://ptbudie.files.wordpress.com/2011/04/lst-sfc.jpg


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S";BS* 6%%R 6 (#DD%)
http://ptbudie.files.wordpress.com/2011/04/lst-bff.jpg


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GEOLOGI REGIONAL CEKUNGAN SUMATERA SELATAN

Stratigrafi Regional

Sub Cekungan ambi meruakan bagian Cekungan Sumatra Selatan #ang meruakan

cekungan belakang busur (back arc basin* berumur Tersier #ang terbentuk sebagai akibat

tumbukan antara Sundaland dan %emeng india' Secara 3eografis Sub Cekungan ambi

dibatasi ole! $egunungan Tigaulu! di sebela! utara, Tinggian %amung di bagian selatan,

$aaran Sunda di sebela! timur, dan Bukit Barisan di sebela! barat'

Tatanan stratigrafi Sub Cekungan ambi ada dasarn#a terdiri dari satu siklus besar

sedimentasi dimulai dari fase transgresi ada a+al siklus dan fase regresi ada ak!ir

silkusn#a' Secara detail siklus ini dimulai ole! siklus non marin #aitu dengan diendakann#a

Formasi %a!at ada 4ligosen +al dan kemudian diikuti ole! Formasi Talang kar #ang

diendakan secara tidak selaras di atasn#a' 5enurut di+id6a6a dan &e Coster (1)7-*,

Formasi Talang kar meruakan suatu endaan kias alluial dan endaan sungai teran#am

(braided stream deposit* #ang mengisi suatu cekungan' Fase transgresi terus berlangsung

!ingga 5iosen +al dimana ada kala ini berkembang Batuan karbonat #ang diendakan

ada lingkungan back reef, fore reef, dan intertidal (Formasi Batu Raja*ada bagian atas

Formasi Talang kar' Fase Transgresi maksimum ditun6ukkan dengan diendakann#a

Formasi 3umai bagian ba+a! secara selaras di atas Formasi Batura6a #ang terdiri dari Batu

seri! laut dalam'

Fase regresi dimulai dengan diendakann#a Formasi 3umai bagian atas dan diikuti ole!

engendakan Formasi ir Benakat #ang didominasi ole! litologi Batu asir ada lingkungan

antai dan delta' Formasi ir Benakat diendakan secara selaras di atas Formasi 3umai'

$ada $liosen +al, laut men6adi semakin dangkal dimana lingkungan engendaan beruba!

men6adi laut dangkal, aludal, dataran delta dan non marin #ang dicirikan ole! erselingan


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antara batuasir dan batulemung dengan sisian berua batubara (Formasi 5uara 9nim*'

Tie engendaan ini berlangsung !ingga $liosen k!ir dimana diendakann#a laisan

batuasir tufaan,pumicedan konglemerat'

Batuan Dasar

Batuan $raTersier atau basement terdiri dari komleks batuan $aleooikum dan batuan

5esooikum, batuan metamorf, batuan beku dan batuan karbonat' Batuan $aleooikum

ak!ir dan batuan 5esooikum tersingka dengan baik di Bukit Barisan, $egunungan

Tigaulu! dan $egunungan &uabelas berua batuan karbonat berumur ermian, 3ranit dan

Filit' Batuan dasar #ang tersingka di $egunungan Tigaulu! terdiri dari filit #ang terliat

kuat ber+arna kecoklatan berumur $ermian (Siman6untak, dkk', 1))1*' %ebi! ke ara! ;tara

tersingka 3ranit #ang tela! mengalami elaukan kuat'


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nggota Tuf =ikim tas, diendakan secara selaras dan bergradual di atas nggota

Batuasir =uarsa' Terdiri dari tuf dan batulemung tufan berselingan dengan endaan miri

la!ar'

Formasi %a!at berumur $aleosen !ingga 4ligosen +al'

Formasi Talang Akar

Formasi Talang kar ada Sub Cekungan ambi terdiri dari batulanau, batuasir dan sisian

batubara #ang diendakan ada lingkungan laut dangkal !ingga transisi' 5enurut

$ulunggono, 1)7>, Formasi Talang kar berumur 4ligosen k!ir !ingga 5iosen +al dan

diendakan secara selaras di atas Formasi %a!at' Bagian ba+a! formasi ini terdiri dari

batuasir kasar, seri! dan sisian batubara' Sedangkan di bagian atasn#a berua

erselingan antara batuasir dan seri!'

=etebalan Formasi Talang kar berkisar antara ?00 m " 8/0 m'

Formasi Baturaja

Formasi ini diendakan secara selaras di atas Fm' Talang kar dengan ketebalan antara 200

samai 2/0 m' %itologi terdiri dari batugaming, batugaming terumbu, batugaming

asiran, batugaming seri!an, seri! gamingan dan naal ka#a foraminifera, moluska

dan koral' Formasi ini diendakan ada lingkungan litoralneritik dan berumur 5iosen +al'

Formasi Gumai

Formasi 3umai diendakan secara selaras di atas Formasi Batura6a dimana formasi ini

menandai ter6adin#a transgresi maksimum di Cekungan Sumatera Selatan' Bagian ba+a!

formasi ini terdiri dari seri! gamingan dengan sisian batugaming, naal dan batulanau'

Sedangkan di bagian atasn#a berua erselingan antara batuasir dan seri!'


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=etebalan formasi ini secara umum berariasi antara 1/0 m 2200 m dan diendakan ada

lingkungan laut dalam'

Formasi 3umai berumur 5iosen +al5iosen Tenga!'

Formasi Air Benakat

Formasi ir Benakat diendakan secara selaras di atas Formasi 3umai dan meruakan a+al

ter6adin#a fase regresi' Formasi ini terdiri dari batulemung uti! kelabu dengan sisian

batuasir !alus, batuasir abuabu !itam kebiruan, glaukonitan setemat mengan dung

lignit dan di bagian atas mengandung tufaan sedangkan bagian tenga! ka#a akan fosil

foraminifera' =etebalan Formasi ir Benakat berariasi antara 1001-00 m dan berumur

5iosen Tenga!5iosen k!ir' Formasi ini diendakan ada lingkungan laut dangkal'

Formasi Muara Enim

Formasi 5uara 9nim me+akili ta!a ak!ir dari fase regresi tersier' Formasi ini diendakan

secara selaras di atas Formasi ir Benakat ada lingkungan laut dangkal, aludal, dataran

delta dan non marin' =etebalan formasi ini /00 " 1000m, terdiri dari batuasir,

batulemung , batulanau dan batubara' Batuasir ada formasi ini daat mengandung

glaukonit dan debris olkanik' $ada formasi ini terdaat oksida besi berua konkresi

konkresi dan silisified wood.Sedangkan batubara #ang terdaat ada formasi ini umumn#a

berua lignit'

Formasi 5uara 9nim berumur 5iaosen k!ir " $liosen +al'

Formasi Kasai

Formasi =asai diendakan secara selaras di atas Formasi 5uara 9nim dengan ketebalan 8/0

" 1200 m' Formasi ini terdiri dari batuasir tufan dan tefra riolitik di bagian ba+a!' Bagian

atas terdiri dari tufpumiceka#a kuarsa, batuasir, konglomerat, tuf asiran dengan lensa

rudit mengandung pumice dan tuf ber+arna abuabu kekuningan, ban#ak di6umai sisa

tumbu!an dan laisan tiis lignit serta ka#u #ang terkersikkan'


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Fasies engendaann#a adala! fluvialdan alluvial fan'

Formasi =asai berumur $liosen k!ir$listosen +al'

Sedimen Kuarter

Satuan ini meruakan %itologi termuda #ang tidak terengaru! ole! orogenesa $lio

$listosen' 3olongan ini diendakan secara tidak selaras di atas formasi #ang lebi! tua #ang

teridi dari batuasir, fragmenfragmen konglemerat berukuran kerikil !ingga bongka!, !adir

batuan olkanik andesitikbasaltik ber+arna gela'

Satuan ini berumur resen

Blognya Ahl !eolog "ndonesa
http://geologi.iagi.or.id/http://geologi.iagi.or.id/


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Tulisan geologi popular dari IAGI Ho#e A$out ths %-&ne

"A!"

Cekungan Bengkulu2'' Ma*h 22

tags+ ,ekungan Bengkulu

$y ad#n

Cekungan Bengkulu aala+ sala+ satu cekunganforearci *nonesia. Cekunganforearcartina

cekungan ang ber&osisi i e&an 'alur olkanik (fore - arc? arcH 'alur olkanik). "eta&i, kita

menebutna emikian berasarkan &osisi geologina saat ini. &aka+ &osisi tersebut sua+ ariulu begituI Belum tentu, an inila+ ang +arus kita seliiki. Publikasi;&ublikasi ari :o!les

(198A), Mul+aiono an sikin (1989), :all et al. (199/) an Euli+anto et al. (1995)Jsemuana

iproceedings*P baik untuk i&ela'ari soal Bengkulu Basin.

Berasarkan berbagai ka'ian geologi, ise&akati ba+!a Pegunungan Barisan (alam +al iniaala+ volcanic arc;na) mulai naik i sebela+ barat Sumatra &aa Miosen "enga+. Pengaru+na

ke&aa Cekungan Bengkulu aala+ ba+!a sebelum Misoen "enga+ berarti tiak aaforearc

basinBengkulu sebab &aa saat itu arc;na seniri tiak aa.

Begitula+ ang selama ini iakini, aitu ba+!a &aa sebelum Miosen "enga+, atau Paleogen,

Cekungan Bengkulu masi+ meru&akan bagian &aling barat Cekungan Sumatera Selatan. alu&aa &erioe setela+ Miosen "enga+ atau eogen, setela+ Pegunungan Barisan naik, Cekungan

Bengkulu i&isa+kan ari Cekungan Sumatera Selatan. Mulai saat itula+, Cekungan Bengkulumen'ai cekunganforearcan Cekungan Sumatera Selatan men'ai cekungan backarc(belakang

busur).
http://geologi.iagi.or.id/http://geologi.iagi.or.id/about-2/http://geologi.iagi.or.id/about/http://geologi.iagi.or.id/tag/cekungan-bengkulu/http://geologi.iagi.or.id/http://geologi.iagi.or.id/about-2/http://geologi.iagi.or.id/about/http://geologi.iagi.or.id/tag/cekungan-bengkulu/


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Setting tektonik regional Sumatra (sumber +tt&

i&ela'ari ari stratigra2i Paleogen an eogen keua cekungan itu. a&at iamati ba+!a &aaPaleogen, stratigra2i keua cekungan +am&ir sama. euana mengembangkan sistem graben i

bebera&a tem&at. i Cekungan Bengkulu aa Graben Pagar'ati, Graben eurang;Manna,

Graben *&u+ (&aa saat ang sama i Cekungan Sumatera Selatan saat itu aa graben;graben7ambi, Palembang, ematang, an e&a+iang). "eta&i setela+ eogen, Cekungan Bengkulu

masuk ke&aa cekungan ang lebi+ alam ari&aa Cekungan Sumatera Selatan, ibuktikan ole+

berkembangna terumbu;terumbu karbonat ang masi2 &aa Miosen tas ang +am&ir ekialen

secara umur engan karbonat Parigi i 7a!a Barat (&ara o&erator ang &erna+ beker'a iBengkulu menebutna sebagai karbonat Parigi 'uga). Paa saat ang sama, i Cekungan

Sumatera Selatan lebi+ banak iena&kan seimen;seimen regresi2 (6ormasi ir

Benakat


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seang terangkat. arena &aa eogen, Cekungan Bengkulu men'ai ia&it ole+ ua sistem

sesar besar ang meman'ang i sebela+ barat Sumatera, aitu Sesar Sumatera (Semangko) i

aratan an Sesar Menta!ai i !ilaa+ o22s+ore, seikit i sebela+ timur &ulau;&ulau busur luarSumatera (Simeulue;#nggano). eua sesar ini bersi2at etral. Si2at &ergeseran (slip) ang

sama ari ua sesar menatar ang ber&asangan (couple strike-slipatau duple!) akan bersi2at

trans-tensionatau membuka !ilaa+ ang ia&itna. engan cara itula+ semua cekunganforearci sebela+ barat Sumatera ang ia&it ua sesar besar ini men'ai terbuka ole+ sesar

menatar (trans-tension pull-apart opening) ang mengakibatkan cekungan;cekungan ini

tenggelam se+ingga &una ruang untuk mengembangkan terumbu karbonat eogen ang masi2asalkan tiak terlalu alam.

i cekungan;cekunganforearcutara Bengkulu (Menta!ai, Sibolga, Meulabo+) &un berkembang

terumbu;terumbu eogen ang masi2 akibat &embukaan an &enenggelaman cekungan;

cekungan ini. an, alam unia &erminakan terumbu;terumbu inila+ ang se'ak ak+ir 19A=;antela+ men'ai target;target &emboran eks&lorasi. Saangna, sam&ai saat ini belum ber+asil

itemukan caangan ang komersial, +ana itemukan gas biogenik an oil show(obson et al.,

1998 an Euli+anto, 3===Jproceedings*P untuk keterangan Menta!ai an Sibolga Basins).

Cekungan Bengkulu meru&akan sala+ satu ari ua cekunganforearci *nonesia ang &alingbanak iker'akan o&erator &erminakan (satuna lagi Cekungan Sibolga;Meulabo+). Meski&un

belum ber+asil menemukan minak atau gas komersial, tiak berarti cekungan;cekungan ini

tiak menganung migas komersial. Sebab, target;target &emboran i !ilaa+ ini (total sekitar/= sumur) tak aa satu &un ang menembus target Paleogen engan sistem graben;na ag tela+

terbukti &roukti2 i Cekungan;Cekungan Sumatera "enga+ an Sumatera Selatan.

Cekungan Bengkulu akan meru&akan +ara&an &ertama untuk &enemuan minak i sistem

Paleogenna. Sumur teralam i cekungan ini ang ibor ole+ o&erator 6ina &aa ta+un 1993

(r!ana;1) menemukan oil showsan menembus seimen %ligo;Miosen ang berkualitas baiksebagai batuan inuk minak. emuian, berasarkan ata sumur ini &ula, iketa+ui ba+!a

termal cekungan ini &anas (,5;5 6


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Sekuensn-riftanpost-rifti cekungan ini belum tertembus, i situla+ +ara&an akumulasi

migas beraa. i&erlukan ata seismik ang lebi+ baik untuk target alam an i&erlukan sumur;

sumur alam untuk menembus target;target Paleogen.

Selain ata seismik, rembesan minak i&ermukaan 'uga men'ai ata ang sangat ber+arga

a&abila bisa i&lot i &eta geologi &ermukaan ang cuku& etail, lalu ili+at &enam&anggeologina. anti akan iketa+ui ari batuan mana rembesan itu berasal. Eang tak kala+ &enting

aala+ melakukan serangkaian analisis geokimia ke&aa rembesan minak itu, +al ini akanmemberi ta+u kita si2at batuan inuk ang tela+ menggenerasikan minak tersebut.

Se"ara# tuli$an ini%

"ulisan tentang Cekungan Bengkulu ini ia!ali ari kiriman Pak !ang :S &aa meio Maret3==9 i iagi;net ang beru&a 'a!abanna ter+aa& &ertanaan seorang ma+asis!a tentang cara

terbentukna Cekungan Bengkulu. iriman ini itangga&i ole+ bebera&a orang anggota milis.

engan emikian, &ara anggota milis iagi;net ang berkontribusiJbaik bertana mau&un

men'a!abJalam iskusi mengenai Cekungan Bengkulu ini aala+ !ang :S, 7unrial :airul

:u0aen, Bau ugro+o an Sigit Prabo!o. "erima kasi+ 'uga untuk Eorris 4ibriana atasin2ormasina tentang gambar setting tektonik regional Sumatra.


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Geology f South Sumatra Basin

Filed under: 3eolog# of Indonesia@ !aris A 7:20 am

The South Sumatra basin is located to the east of the Barisan Mountains and extends into theoffshore areas to the northeast and is regarded as a foreland (back-arc) basin bounded by theBarisan Mountains to the southwest, and the Pre-Tertiary of the Sunda Shelf to the northeast(de oster, !"#$)% TheSouth Sumatra basin was formed during east-west extension at the end of the Pre-Tertiary tothe beginning of Tertiary times (&aly et al%, !"'#)%

TT*+ STT+*

The structural features resent in the basin are the result of the three main tectonic e.ents%They are Middle-Meso/oic orogeny, 0ate retaceous-ocene tectonism and the Plio-Pleistocene orogeny% The first two e.ents ro.ided the basement configuration including theformation of half grabens, horsts, and fault block% The last e.ent, the Plio-Pleistoceneorogeny, resulted in formation of the resent northwest-southeast structural features and thederession to the northeast (de oster, !"#$)% Structurally the 1! block is located in thePalembang 2igh% This high is located at the southern edge of a ositi.e feature in the easternmargin of

Sout!

Sumatra

Basin'

STRATIGRAPHY

The sediments of the

Sout!Sumatra

Basin comrise an economic basement of $reTertiar# rocks t!at is oerlain unconformabl# b# a

t!ick Tertiar# seuence' T!e first Tertiar# sedimentation occurred during 9arl# 4ligocene and

gae rise to t!e %a!at Formation consisting of mainl# olcanic rocks, cla#stone and s!ale t!at

+as deosited locall# in t!e graben areas' T!e Talang kar Formation (%ate 4ligocene* oerlies

t!e basement +!ere t!e %a!at Formation is missing' It is a transgresie seuence resulting from

%ate 4ligocene to 5iddle 5iocene subsidence' T!e later sedimentation during mid5iocene to

recent roduced a regressie seuence (de Coster, 1)7?*'

+n most arts of the Palembang 2igh, sediment deosition started in arly Miocene, excet in local low areaswhere terrestrial to nearshore sediments of Talang 3kar 4ormation (ligocene) and terrestrial sediments of0ahat and 0emat 4ormation (o-ligocene) had been deosited% +n many laces, the Talang 3kar, the 0ahatand the 0emat 4ormations cannot be distinguished from each other and hence are called Pre-Batura5aclastics% &uring arly Miocene, carbonate sediments of the Batura5a 4ormation were de.eloed eitherdirectly abo.e the Pre-Tertiary basement or abo.e a thin Talang 3kar 4ormation% ff the Palembang 2igh,hundreds of feet thick of the Talang 3kar 4ormation are resent (4erianto et al%, 1667)%

3roximately !#%7 M8BP the sea le.el droed, and the Batura5a carbonates were exosedand sub5ect to diagenetic rocesses that led to de.eloment of good secondary orosity%3fterward, the sea le.el rose again and the Telisa marine shales (arly-Mid% Miocene) were
http://h4ris.wordpress.com/category/geology-of-indonesia/http://h4ris.wordpress.com/category/geology-of-indonesia/


24/37

deosited% +n around !7%7 M8BP the sea le.el gradually droed again and nearshore toterrestrial sediments of Palembang 4ormation (9er Miocene-Pliocene) were deosited(4erianto et al%, 1667)%

Plio-Pleistocene orogeny (in 1%' M8BP) created the current structures in the region% 3 *:-Sstriking monocline diing to S: is the redominant feature there% The detail Stratigrahy of

South Sumatra Basin is described in other literature, such as &e oster (!"#$) (4erianto et al%,1667)%

;egional sediment sources were generally from the Sunda Plate to the north andPalembang or 0amung 2igh to the east (Sitomul et al%, !""1)% Maximum transgression in themiddle Miocene deosited the marine umai Shale 4ormation seal across the region beforeulift and comression resulted in deosition of shallow marine and continental sandstonesand shales% &e.eloment of the

Barisan5ountains, and ossible olcanic islands to t!e sout! and sout!east, furt!er decreased and t!en

cut off and oer+!elmed marine influences and added ne+ clastic and olcaniclastic sources from

t!ose directions' 9rosion of nort!+est trending anticlines t!at +ere formed during comressionresulted in local $lio$leistocene continental deosits +it!in t!e interening s#nclines' Continued

olcanic actiit# !as coered muc! of t!e surface of t!e

Sout!Sumatra

Basin (Bis!o, 2000*'

PT;09M S8STM

SOURCE ROCK 2ydrocarbons in

Sout!Sumatra

$roince are deried from bot! lacustrine source rocks of t!e %a!at Formation and terrestrial coal

and coal# s!ale source rocks of t!e Talang kar Formation' T!e lacustrine source rocks +ere

deosited in a comle. of !alfgrabens +!ereas t!e subseuent coal and coal# s!ales +ere

deosited in and e.tended be#ond t!e limits of t!e !alfgrabens' T!e Batu a6a %imestone and

t!e 3umai Formation s!ales ma# also be mature and !ae generated !#drocarbons in local areas

(Sar6ono and Sard6ito, 1)8), Bis!o, 2000*'

The middle to late ocene through early ligocene 0ahat or 0emat 4ormation includes theBenakat Shale with oil rone Tye + and ++ kerogen and gas rone Tye +++ kerogen% rganicmaterial in the late ocene through middle Miocene Talang 3kar 4ormation contains oil- and

gas-rone Tye +, ++ and +++ kerogen% The general temerature gradient inSouth Sumatra is $"okm-!(2utchinson, !""< in Bisho, 1666)%

T;3P T8PS

*orthwest to southeast trending anticlines were the first tras exlored and remain the mostimortant tras in the


25/37

South Sumatra basin% &rae, facies-change, and stratigrahic tras are also imortant andmay be attracti.e future targets (Bisho, 1666)%

RESERVOIR ROCK There are se.eral formations in the

Sout!

SumatraBasin +!ic! la# as reseroir rocks, eent basement rocks' T!e# are basement rocks, %a!at

Formation, Talang kar Formation, Batu a6a Formation, 3umai Formation, ir Benakat

Formation, and 5uara 9nim Formation (Bis!o, 2000*'

9lifted areas and aleohighs of Meso/oic and ocene fractured and weathered basementgranite and =uart/ite are effecti.e reser.oirs, in ten fields inSouth Sumatra (Sard5ito et al%, !""!> Bisho, 1666)%

The ocene to ligocene 0ahat 4ormation is comosed of synrift deosits that are as much as!,6#6 m thick% 3lthough locally absent, this formation, is in most locations, more than #


26/37

contact with the o.erlying Muara nim 4ormation% The a.erage orosity of the sandstone is17A (Bisho, 1666)%

The 0ate Miocene to Pliocene Muara nim 4ormation, also known as the Middle Palembang4ormation, was deosited as shallow marine to continental sands, muds, and coals% Theformation thins to the north from a maximum of #76 m in the south% 9lift of the

Barisan

5ountains roided source terrains for clastics from t!e sout! and sout!+est during deosition

of t!e 5uara 9nim Formation (Bis!o, 2000*'

S30 ;

The umai 4ormation reresents the maximum highstand transgression following de.elomentof Batu ;a5a carbonates% Shales of this regional formation seal carbonate reser.oirs andlocally seal a series of stacked sandstone reser.oirs of the Talang 3kar 4ormation (2artanto etal%, !""!)% 2ydrocarbons that are found abo.e the regional seal either ha.e migrated there

due to faults that broke the seal during the comression hase or were generated by theumai 4ormation shales in local areas where this formation might be mature%+ntraformational seals within the Talang 3kar consist of shallow marine and o.erbank shalesthat are imortant seals that comartmentali/e the sandstones (Bisho, 1666)%

References:

3rgakoesoemah ;%M%+%, ;ahar5a M%, :inardhi S%, Tarigan ;%, Maksum T%4%, 3imar 3%, 1667,Telisa Shallow Marine Sandstone As An Emerging Exploration Target In Palembang High, SouthSumatra Basin, +n roceedings +ndonesian Petroleum 3ssociation, Thirtieth 3nnual on.ention,Cakarta

Bisho M% %, 1666, South Sumatra Basin Province, Indonesia The !ahat"Talang A#ar$%eno&oic Total Petroleum S'stem, 9%S% &eartment of The +nterior 9%S% eological Sur.ey,httDEEgeology%cr%usgs%go.EenergyE:orldnergyE4""-76SEro.ince%html

&e oster % 0%, !"#$, The (eolog' o) the %entral and

South

Sumatra

Basins' In roceedings Indonesian $etroleum ssociation, T!ird nnual Conention,

akarta, ' 77 " 110'

&ally M% %, 2ooer B% % &%, and Smith &% %, !"'#, Tertiar' Plate Tectonics and BasinEvolution inIndonesia% +n roceedings +ndonesian Petroleum 3ssociation, Sixteenth 3nnual on.ention,Cakarta, % @""-$1'%

4eriyanto, amil 4%, usnandar 8%, and 8anto 8, 1667, Success)ul Identi)ication o) Thin%arbonate *n Paleo$Basement High Special %ase In Palembang High, South Sumatra Basin, +nroceedings +ndonesian Petroleum 3ssociation, Thirtieth 3nnual on.ention, Cakarta%
http://geology.cr.usgs.gov/energy/WorldEnergy/OF99-50S/province.htmlhttp://geology.cr.usgs.gov/energy/WorldEnergy/OF99-50S/province.html


27/37

2artanto, arsan, :idianto, ko, and Safri/al, !""!, H'drocarbon prospect related to thelocal uncon)ormities o) the +uang area,

South

Sumatra

Basin:$roceedings Indonesian $etroleum ssociation T+entiet! nnual Conention, 4ctober,

1))1, ' 17->'

amal 3%, !""", 2'drocarbon Potential in the Pasemah Bloc#, A rontier Area in SouthSumatra, +n roceedings +ndonesian Petroleum 3ssociation, Twenty Se.enth 3nnualon.ention, Cakarta, % $"-


28/37

U. S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURE!

SOUT& SUMATRA BASIN PRO'INCE( INDONESIA% T&E LA&AT)TALANGAKAR*CENO+OIC TOTAL PETROLEUM S,STEM

b Mic+ele G. Bis+o&1

O-en*ile Re-ort ..*/0S

3===

PROINCE GEOLOG!The on*e *oes an aea o/ ao0#ately 11''' k#2 #aly onshoe Su#ata

"ndonesa (Fg. 1). %0loaton eots hae $een *on*entated onshoe th only a /e dy

holes dlled n oshoe aeas (5eto*onsultants 16). The 5ale#$ang o La#ung Hgh o
http://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/province.html#1Consultanthttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig1.html#TOPhttp://energy.cr.usgs.gov/http://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/province.html#1Consultanthttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig1.html#TOP


29/37

a*h seaates the South Su#ata $asn /o# the Sunda Basn o/ the 7othest 8aa

5on*e 3924 (Fg. 2). Ths hgh seed $oth as a $ae to sed#ent dsesal and as a

sed#ent sou*e tean /o# Meso:o* though #ost o/ the Tetay (de ,oste 14). The

South and ,ental Su#ata Basn 5on*es (3929 39'9) ae dded at the Tgauluh

Mountans (Fg. 2). The esten #agn s the 5lo-5lesto*ene Basan Mountans (Fg. 2).

South Su#ata s dded nto su$-$asns+ 8a#$ 7oth 5ale#$ang ,ental 5ale#$ang

South 5ale#$ang and Banda 8aya Basn (Fg. 2) (lla#s and othes 1


30/37

sans, conglomerates, breccias an clas !ere e&osite in 2aulte an to&ogra&+ic lo!s b alluial, 2luial, an

lacustrine &rocesses (6ig. ). Marine transgression occurre in some areas &ossibl as earl as t+e late #ocene

(Courtene an ot+ers, 199=). 4ies&rea marine transgression 2rom t+e sout+ an sout+!est in t+e late %ligocene

to Miocene resulte in onla& o2 clastic e&osits onto basement rocks, eelo&ment o2 &lat2orm carbonates, ancarbonate buil;u&s on 2ault;block +ig+s. Carbonate an sans !ere also e&osite aroun emergent islans (Cole

an Crittenen, 199-? Courtene an ot+ers, 199=? Sitom&ul an ot+ers, 1993? :artanto an ot+ers, 1991? :uta&ea,

1981? "amtomo an ot+ers, 199-? :amilton, 19-9). "+e oerall transgression !as &unctuate b lo!stans. "+is

resulte in eelo&ment o2 seconar &orosit in some o2 t+e carbonates. o!stans also resulte in submarine 2ans!it+in t+e marine s+ale strata (Cole an Crittenen, 199-? Courtene an ot+ers, 199=? Sitom&ul an ot+ers, 1993?

:artanto an ot+ers, 1991? :uta&ea, 1981? "amtomo an ot+ers, 199-? :amilton, 19-9). Regional seiment sources

!ere generall 2rom t+e Suna Plate to t+e nort+ an Palembang or am&ung :ig+ to t+e east (Sitom&ul an ot+ers,

1993). Maimum transgression in t+e mile Miocene e&osite t+e marine Gumai S+ale 6ormation seal across t+eregion be2ore u&li2t an com&ression resulte in e&osition o2 s+allo! marine an continental sanstones an s+ales

(6ig. ) (Courtene an ot+ers, 199=? Cole an Crittenen, 199-? e Coster, 19-). eelo&ment o2 t+e Barisan

Mountains, an &ossible olcanic islans to t+e sout+ an sout+east, 2urt+er ecrease an t+en cut o22 an

oer!+elme marine in2luences an ae ne! clastic an olcaniclastic sources 2rom t+ose irections (e Coster,19-? Cole an Crittenen, 199-? :amilton, 19-9). #rosion o2 nort+!est trening anticlines t+at !ere 2orme uring

com&ression resulte in local Plio;Pleistocene continental e&osits !it+in t+e interening snclines (e Coster,

19-). Continue olcanic actiit +as coere muc+ o2 t+e sur2ace o2 t+e Sout+ Sumatra Basin (an Bemmelen,

199).

His"or# o$ E%plora"ion%aly e0loaton as guded $y su/a*e sees that ee asso*ated th ant*lnes and led

to the ds*oey o/ =a#ung Mnyak Feld n South Su#ata n 1996 (Fg. 2) (Ma*gego

1eld eotedly *ontaned esees o/ 31.3 MMB?% n the delta* 5lo*ene Muaa

%n# Fo#aton (Fg. 4) (&el and othes 19


31/37

thoughout Su#ata (Ma*gego 1


32/37

(Suseno an ot+ers, 1993). :rocarbon ine (:*) alues are 1/=J39= mg +rocarbon (:C);1 2iel +as been attribute to mature Gumai S+ale

source rocks in t+e a'acent lo! (6ig. 3) (Sar'ono an Sar'ito, 1989).

*n t+e Banar 7aa Basin area (6ig. 3) seeral grabens contain ric+ a+at source rocks (4illiams an ot+ers, 1995).

"+e lacustrine source rocks are oil &rone "&e * an ** kerogen an t+e coal lake margin an eltaic source rockscontain "&e *** kerogen (4illiams an ot+ers, 1995). Seeral !ells +ae teste reseroirs an source rocks in some

o2 t+ese +al2;grabens, encountering gas an oil s+o!s but !it+out commercial success (Petroconsultants, 199A).

nalses o2 t+ese source rocks inicate t+at t+e are 'ust entering t+e oil !ino! (4illiams an ot+ers, 1995).

OER&URDEN ROC'Mane Ioodng /o# the south esulted n deoston o/ the !u#a Fo#aton n the $asns

hle Batu Caa L#estone as deosted on lat/o#s and hghs th #a0#u#

tansgesson ea*hed dung the ealy #ddle Mo*ene (Saono and Sadto 19). ,last*

deoston n*eased dung the late #ddle Mo*ene egesson /o#ng *laystone

sandstone and sltstone n a shallo #ane enon#ent (Saono and Saddto 19).

Shallo #ane and teestal deostonal settngs *ontnued. Beteen 1'''J3''' # o/

oe$uden as deosted untl a desead late 5lo*ene though 5lesto*ene oogeny

*aused /oldng and /aultng (Saono and Sadto 19).

TRAP T,PESort+!est to sout+east trening anticlines !ere t+e 2irst tra&s e&lore an remain t+e most im&ortant tra&s in t+e

Sout+ Sumatra basin (an Bemmelen, 199). %il an gas reseres 2oun in anticlines total /.1 BB%# ultimate

recoerable reseres (Petroconsultants, 199A). "+ese 2iels +ae &rimaril sanstone reseroirs !it+ somelimestones an calcareous sanstones an inclue eer &roucing 2ormation in t+e basin (Petroconsultants, 199A).

"+e anticlines 2orme as a result o2 com&ression t+at began as earl as t+e Miocene but !as most &ronounce

bet!een 3J/ Ma (6ig. A) (Courtene an ot+ers, 199=). Stratigra&+ic &inc+;outs an carbonate builu&s locall

combine !it+ 2ols an anticlines to en+ance t+e e22ectieness o2 t+e &rimar tra& t&e. Recoerable reseres o2 1-8MMB%# are 2oun in bio+erms an carbonate builu& t&e tra&s an A88 MMB%# in 2ault tra&s (Petroconsultants,

199A). ra&e, 2acies;c+ange, an stratigra&+ic tra&s are also im&ortant an ma be attractie 2uture targets.

RESER'OIR ROCKBa$ement Ro1k$
http://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig2.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig2.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig6.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig2.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig2.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig6.html#TOP


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>&li2te areas an &aleo+ig+s o2 Meso0oic an #ocene 2racture an !eat+ere basement granite an uart0ite are

e22ectie reseroirs, !it+ u& to -N &orosit, in ten 2iels in Sout+ Sumatra !it+ gas reseres totaling 1=A MMB%#

ultimate recoerable reseres (Sar'ito an ot+ers, 1991? Petroconsultants, 199A).

La#at 2Lemat( Ol3 Lemat( ,oung Lemat4 ormation"+e #ocene to %ligocene a+at 6ormation (6ig. ) is com&ose o2 snri2t e&osits t+at are as muc+ as 1,=-= m

t+ick. lt+oug+ locall absent, t+is 2ormation, is in most locations, more t+an -A= m t+ick (:utc+inson, 199A). "+e2ormation !as e&osite in continental, lacustrine, an brackis+ lacustrine e&ositional settings (:utc+inson, 199A).

"+is reseroir accounts 2or nearl 88 MMB%# o2 ultimate recoerable reseres (Petroconsultants, 199A).

"+e ikim "u22s, also kno!n as %l emat, are tu22aceous sanstones, conglomerates, breccias, an clas, o2 locallerie &roenance, e&osite in 2aulte an to&ogra&+ic lo!s (:utc+inson, 199A). "+e ikim is inter&rete to b

ate Cretaceous to Paleocene in age an occurs in outcro& an at e&t+ in t+e sout+ern region (:utc+inson, 199A).

"+e olest 2acies o2 t+e Eoung emat is granite !as+ oerlain b coarse clastic e&osits t+at consist o2 sanstones

an breccias !it+ abunant rock 2ragments, clastones, coals, an tu22s (:utc+inson, 199A).

"+e Benakat Member is a gre to bro!n s+ale !it+ tu22aceous s+ale, siltstone, sanstone, coal, carbonate stringers

an glauconitic sanstones t+at occurs in t+e ee& &ortion o2 t+e +al2;graben basins (:utc+inson, 199A). "+is

member !as e&osite in 2res+ to brackis+ !ater lakes an con2ormabl oerlies t+e coarse clastics o2 t+e lo!eremat 6ormation (:utc+inson, 199A).

Talang Akar ormation"+e late %ligocene lo!er "alang kar 6ormation is also re2erre to as t+e Gritsan Member an t+e %ligocene toearl Miocene u&&er "alang kar 6ormation as t+e "ransition Member (Sitom&ul an ot+ers, 1993? "amtomo an

ot+ers, 199-). "+e "alang kar 6ormation is as muc+ as A1= m t+ick (:utc+inson, 199A). *t is a late snri2t to &ost;

ri2t 2ormation t+at is t+ick !+ere t+e unerling a+at 6ormation is t+ickest (6ig. /). "+e "alang kar 6ormation

uncon2ormabl oerlies t+e a+at 6ormation. *t onla&s t+e a+at an t+e basement, etening 2art+er outsie o2 t+ee&ositional basins t+an t+e e&ositional limits o2 t+e a+at 6ormation (:utc+inson, 199A). "+is reseroir consists

o2 uart0ose sanstones, siltstones, an s+ales e&osite in a elta &lain setting t+at c+ange basin!ar, generall to

t+e sout+ an !est, into marginal marine sanstones an s+ales (i!i'a'a an e Coster, 19-/? :utc+inson, 199A?

#ko 4iianto an anang Muksin, 1989). S&eci2ic e&ositional enironments t+at +ae been ienti2ie inclue

o&en marine, nears+ore, elta &lain, elta, istributar c+annel, 2luial, an beac+ (:uta&ea, 1981). "alang kar6ormation sanstones, !+ic+ !ere e&osite uring marine transgressions an regressions, 2orm im&ortant

stratigra&+ic tra&s ("amtomo an ot+ers, 199-). "+ese s+oreline sans are generall aligne east to !est, are

su&&lie !it+ seiment 2rom t+e Suna S+el2 to t+e nort+ an t+e Palembang :ig+ (am&ung :ig+) to t+e east, canbe laterall restricte, an t+icken an t+in in res&onse to to&ogra&+ at t+e time o2 e&osition (i!i'a'a an e

Coster, 19-/? :amilton, 19-9? :uta&ea, 1981? Sitom&ul an ot+ers, 1993). %t+er s+oreline sanstones t+at surroun

basement +ig+s are &rouctie reseroirs 2or seeral 2iels ("amtomo an ot+ers, 199-). :ere t+e ualit o2 t+e

reseroir e&ens on t+e t&e o2 basement rock eroe to &roie t+e clastics.

"+e "alang kar 6ormation reseroir accounts 2or more t+an -5N o2 t+e cumulatie oil &rouction in Sout+ Sumatra("amtomo an ot+ers, 199-). &&roimatel 3 BB%# ultimate recoerable reseres +ae been 2oun in "alang kar

reseroirs (Petroconsultants, 199A). Porosit o2 t+is reseroir rock ranges 2rom 15J/= N an &ermeabilit is as

muc+ as 5 arcies ("amtomo an ot+ers, 199-? Petroconsultants, 199A). Porosit o2 t+e Gritsan Member is

&rimaril seconar an aerages 35N (Sitom&ul an ot+ers, 1993). Porosit o2 t+e "ransitional Member is also&rimaril seconar an cause b t+e issolution o2 grains an etrital clas. "+is cleaner an more mature

sanstone +as 35N aerage &orosit (Sitom&ul an ot+ers, 1993). Clas in bot+ members inclue smectite, illite, an

abunant kaolinite (Sitom&ul an ot+ers, 1993).

Batu Ra"a Lime$tone"+e earl Miocene Batu Ra'a imestone is also kno!n as t+e Basal "elisa imestone (:utc+inson, 199A). "+e

2ormation consists o2 !ies&rea &lat2orm carbonates, 3=J-5 m t+ick, !it+ aitional carbonate builu&s an ree2s,

2rom A=J13= m t+ick (:utc+inson, 199A? :artanto an ot+ers, 1991). "+e Basal "elisa is s+ale an calcareous s+ale
http://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig4.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig3.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig3.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig4.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig3.html#TOP


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e&osite in ee&er !ater as t+e carbonates !ere being eelo&e on t+e &lat2orms an +ig+s (Courtene an ot+ers

199=). t outcro& t+e Batu Ra'a is 53= m t+ick in t+e Garba Mountains area o2 t+e Barisan Mountains (6ig. 3)

(:utc+inson, 199A).

iscoeries in Batu Ra'a limestone an san limestone total oer 1 BB%# ultimate recoerable reseres, !it+ gas

com&rising 'ust oer +al2 o2 t+at amount (Petroconsultants, 199A). %il grait ranges 2rom 3AJA1P*

(Petroconsultants, 199A). Reseroir &orosit ranges 2rom 18J/8N an reseroir &ermeabilit is as muc+ as 1 arc(Petroconsultants, 199A). Porosit +as been en+ance in t+e u&&er &arts o2 t+e 2ormation ue to subaerial e&osure

late in t+e earl Miocene, at a&&roimatel 1-.5 Ma, an also because o2 onl &artiall cemente 2ractures(Courtene an ot+ers, 199=? :artanto an ot+ers, 1991? Sitom&ul an ot+ers, 1993).

Gumai ormation"+e %ligocene to mile Miocene Gumai 6ormation, also kno!n as t+e "elisa 6ormation, is com&ose o2

2ossili2erous marine s+ales !it+ t+in, glauconitic limestones t+at re&resent a ra&i, !ies&rea maimum

transgression (6ig. ) (:artanto an ot+ers, 1991? :utc+inson, 199A). "+e transgression !as to!ar t+e nort+east,an !ater e&t+s !ere s+allo! in t+e nort+east an bat+al in t+e sout+!est (:amilton, 19-9). 6ine;graine

sanstones an siltstones occur on t+e basin margins (:utc+inson, 199A). "+e t+ickness o2 t+e Gumai 6ormation

aries an is as muc+ as 3,-== m t+ick in basins. "+e 2ormation t+ins at basin margins an across +ig+s (:artantoan ot+ers, 1991? :utc+inson, 199A).

"+e Gumai 6ormation is t+e regional seal 2or t+e Batu Ra'a imestone in Sout+ Sumatra but also contains some

reseroir interals. "+ese carbonates contain 1/= MMB%# ultimate recoerable reseres (Petroconsultants, 199A).

"+ese reseres aerage //J53P* grait an are 2oun &rimaril in s+oreline an s+allo! marine sanstones

!it+ 3=N &orosit, +o!eer, :artanto an ot+ers (1991) +ae use !ell logs to ienti2 turbiites an suggest t+att+ese sans coul be e&loration targets in t+e basins. "+ee turbiites suggest t+at a ra&i ro& in sea leel occurre

at t+e en o2 Gumai e&osition in mile Miocene time (:artanto an ot+ers, 1991).

Air Benakat ormation"+e mile Miocene ir Benakat 6ormation, also kno!n as t+e o!er Palembang 6ormation, !as e&osite uring

t+e regression t+at ene e&osition o2 t+e Gumai S+ale. "+e ir Benakat 6ormation c+anges u&!ar 2rom ee&marine to s+allo! marine conitions. Marine glauconitic clas ecrease in 2reuenc an marine sans increase

(:artanto an ot+ers, 1991). "+e 2ormation ranges 2rom 1,===J1,5== m t+ick (:utc+inson, 199A). Coal bes mark

t+e u&&er contact !it+ t+e oerling Muara #nim 6ormation (:utc+inson, 199A). >ltimate recoerable reseresiscoere in s+allo! marine an eltaic sanstone reseroirs !it+in t+e ir Benakat 6ormation total A- MMB%#

(Petroconsultants, 199A). "+e aerage &orosit o2 t+e sanstone is 35N. "+e reseroirs contain oil !it+ aerage -

P* grait an some gas (Petroconsultants, 199A).

Muara Enim ormation"+e late Miocene to Pliocene Muara #nim 6ormation, also kno!n as t+e Mile Palembang 6ormation, !ase&osite as s+allo! marine to continental sans, mus, an coals. "+e 2ormation t+ins to t+e nort+ 2rom a

maimum o2 -5= m in t+e sout+ (6ig. ) (:utc+inson, 199A). %il reseres o2 1-9 MMB%# ultimate recoerable are

locate in Muara #nim sanstone reseroirs !it+ /=N aerage &orosit (Petroconsultants, 199A). >&li2t o2 t+e

Barisan Mountains &roie source terrains 2or clastics 2rom t+e sout+ an sout+!est uring e&osition o2 t+eMuara #nim 6ormation (:amilton, 19-9).

Ka$i Tu55Continental tu22aceous sans, clas, graels, an t+in coal bes o2 t+e asi "u22, also kno!n as t+e >&&er

Palembang 6ormation, are 2oun in alles an snclines 2orme uring e2ormation o2 t+e Barisan Mountains."+ese seiments are erie &rimaril 2rom t+ese mountains (Courtene an ot+ers, 199=? :utc+inson, 199A).

SEAL ROCK"+e Gumai 6ormation re&resents t+e maimum +ig+stan transgression 2ollo!ing eelo&ment o2 Batu Ra'a

carbonates (6ig. / an ) (:artanto an ot+ers, 1991). S+ales o2 t+is regional 2ormation seal carbonate reseroirs an

locall seal a series o2 stacke sanstone reseroirs o2 t+e "alang kar 6ormation (Martainata an 4rig+t, 198?
http://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig2.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig4.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig4.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig4.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig2.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig4.html#TOPhttp://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50S/fig4.html#TOP


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:artanto an ot+ers, 1991). :rocarbons t+at are 2oun aboe t+e regional seal eit+er +ae migrate t+ere ue to

2aults t+at broke t+e seal uring t+e com&ression &+ase or !ere generate b t+e Gumai 6ormation s+ales in local

areas !+ere t+is 2ormation mig+t be mature. *ntra2ormational seals !it+in t+e "alang kar consist o2 s+allo! marine

an oerbank s+ales t+at are im&ortant seals t+at com&artmentali0e t+e sanstones (Courtene an ot+ers, 199=).

UNDISCO'ERED PETROLEUM B, ASSESSMENT UNIT

%ne assessment unit, t+e Sout+ Sumatra assessment unit (/838=1=1), is recogni0e in t+e a+at.S. Geological Sure %&en;6ile Re&ort 9-;A/, one C;R%M.

lett, ".R., Sc+moker, 7.4., an +lbrant, ". S., 3===, ssessment +ierarc+ an initial &roince ranking in>.S.

Geological Sure 4orl #nerg ssessment "eam, >.S. Geological Sure 4orl Petroleum ssessment


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3===Jescri&tion an Results, >.S. Geological Sure igital ata Series S A=, C;R%Ms.

ongle, *. M., 199-, "+e tectonostratigra&+ic eolution o2 S# sia, in6raser, . 7., Matt+e!s, S. 7., an Mur&+, R.

4., es., Petroleum Geolog o2 Sout+east sia Geological Societ S&ecial Publication o. 13A, &. /11;

//9.Macgregor, . S., 1995, "+e e&loration signi2icance o2 sur2ace oil see&age an *nonesian &ers&ectie Proceeings

*nonesian Petroleum ssociation "!ent2ourt+ nnual Conention, %ctober, 1995, &. 9-;1=9.

Martainata, . :., an 4rig+t, 7. :., 198, eelo&ment o2 *bul stratigra&+ic &la, Sout+ Sumatra Basin, b

integration o2 geologic an seismic ata Proceeings *nonesian Petroleum ssociation "+irteent+ nnualConention, Ma, 198, &. 51;A1.

Mouls, P. 7., 1989, eelo&ment o2 t+e Bengkalis e&ression, Central Sumatra an its subseuent e2ormation $ a

moel 2or ot+er Sumatran grabensI Proceeings *nonesian Petroleum ssociation #ig+teent+ nnual

Conention, %ctober, 1989, &. 31-;3A.Petroconsultants, 199A, Petroleum #&loration an Prouction atabase Petroconsultants, *nc., P.%. Bo -=A19,

AA== Sans Point rie, :ouston "D --3-;=A19, >S or Petroconsultants, *nc., P.%. Bo 153, 3

C+emin e la Mairie, 1358 Perl, Genea, S!it0erlan.

Ponto, C. F., 4u, C. :., Pranoto, ., an Stinson, 4. :., 1988, *m&roe inter&retation o2 t+e "alang kare&ositional enironment as an ai to +rocarbon e&loration in t+e R** %22s+ore ort+!est 7aa

contract area Proceeings o2 t+e Seenteent+ nnual Conention *nonesian Petroleum ssociation, . 1,

&. /9-;33.

Pulunggono, .,1985, "+e c+anging &attern o2 ieas on Sunalan !it+in t+e last +unre ears, its im&lications to

oil e&loration Proceeings *nonesian Petroleum ssociation 6ourteent+ nnual Conention, %ctober,1985, &. /-;/-8.

Pulunggono, ., :aro, S. gus, an osuma, C. G., 1993, Pre;"ertiar an "ertiar 2ault sstems as a 2rame!ork

o2 t+e Sout+ Sumatra Basin? a stu o2 sar;ma&s Proceeings *nonesian Petroleum ssociation "!ent6irst nnual Conention, %ctober, 1993, &. //9;/A=.

Sar'ito, 6aianto, #, 'umlati, an :ansen, S., 1991, :rocarbon &ros&ect o2 t+e &re;"ertiar basement in

uang area, Sout+ Sumatra Proceeings *nonesian Petroleum ssociation "!entiet+ nnual Conention,

%ctober, 1991, &. 355;3-8.Sar'ono, S., an Sar'ito, 1989, :rocarbon source rock ienti2ication in t+e Sout+ Palembang sub;basin

Proceeings *nonesian Petroleum ssociation #ig+teent+ nnual Conention, %ctober, 1989, &. 3-;A-.

Sc+ie2elbein, C., an Cameron, ., 199-, Sumatra


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oble, R. ., es., Proceeings o2 t+e Petroleum Sstems o2 Se sia an ustralasia *nonesian Petroleum

ssociation Con2erence, Ma 199-, &. A99;-=8.

ten :aen, :. ., an Sc+ie2elbein, C., 1995, "+e &etroleum sstems o2 *nonesia Proceeings *nonesian

Petroleum ssociation "!ent2ourt+ nnual Conention, %ctober, 1995, &. /;59."o, S. P., unn, M. #., an Bar!ise, . 7. G., 199-, C+aracteri0ing &etroleum c+arge sstems in t+e tertiar o2 S#

sia, in6raser, . 7., Matt+e!s, S. 7., an Mur&+, R. 4., es., Petroleum Geolog o2 Sout+east sia

Geological Societ S&ecial Publication o. 13A, &. 35;-.

>. S. Geological Sure 4orl #nerg ssessment "eam, 3===, >. S. Geological Sure 4orl #nerg Petroleumssessment 3===;escri&tion an Results >SGS igital ata Series S;A=, 2our C;R%Ms.

an Bemmelen, R. 4., 199, "+e Geolog o2 *nonesia, Folume ** #conomic Geolog "+e :ague, 3A5 &&.

4icaksono, P., rmon, 7. 4., an :arono, S., 1993, "+e im&lications o2 basin moelling 2or e&loration $ Suna

Basin case stu, o22s+ore sout+east Sumatra Proceeings o2 t+e "!ent 6irst nnual Conention*nonesian Petroleum ssociation, .1, &. /-9;15.

4illiams, :. :., 6o!ler, M., an #ubank, R. "., 1995, C+aracteristics o2 selecte Palaeogene an Cretaceous

lacustrine source basins o2 Sout+east sia, inambiase, 7. 7., e., :rocarbon :abitat in Ri2t Basins

Geological Societ S&ecial Publication o. 8=, &. 31;383.Euli+anto, B., Situmorang, B., ur'a'ai, ., an Sain, B., 1995, Structural analsis o2 t+e ons+ore Bengklu

6orearc Basin an its im&lication 2or 2uture +rocarbon e&loration actiit Proceeings *nonesian

Petroleum ssociation "!ent2ourt+ nnual Conention, %ctober, 1995, &. 85;9A.

eli22, C. 4., "rollo&e, S. 4., an Maulana, #., 1985, #&loration ccles in t+e corrior block, Sout+ Sumatra

Proceeings, *nonesian Petroleum ssociation 6ourteent+ nnual Conention, %ctober, 1985, &. 3-9;==.

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Geologi Regional Cekungan Sumatera Selatan