editorial board - iagi · kelurahan manggar, balikpapan 76117, kalimantan timur, indonesia, e-mail...

of 31 /31

Upload: others

Post on 28-May-2020

2 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,
Page 2: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 2 Volume 20— February 2011

Herman Darman

Chief Editor

Shell International Exploration and Production B.V. P.O. Box 162, 2501 AN, The Hague – The Netherlands Fax: +31-70 377 4978 E-mail: [email protected]

Minarwan

Deputy Chief Editor

Repsol Exploración SA Paseo de la Castellana, 278-280, Madrid 28046 Spain E-mail: [email protected]

Fuad Ahmadin Nasution

PT. Energi Mega Persada Tbk/EMP Tonga Bakrie 24th Floor, Rasuna Epicentrum, Jl. H.R Rasuna Said Jakarta 12960-Indonesia E-mail: [email protected]

Fatrial Bahesti

NAD-North Sumatra Assets Standard Chartered Building 23rd Floor, Jl Prof Dr Satrio No 164 Jakarta 12950 - Indonesia E-mail: [email protected]

Wayan Ismara Heru Young

University Link coordinator

Legian Kaja, Kuta, Bali 80361, Indonesia E-mail: [email protected]

Julianta Panjaitan

Membership coordinator

PT. Schlumberger Geophysics Nusantara, Data & Consulting Services, Jl. Mulawarman Km. 20, P.O.Box 117, Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail: [email protected]

Editorial Board

• Published 3 times a year in February, June and October.by the Indonesian Sedimentologists Forum (Forum

Sedimentologiwan Indonesia—FOSI), a commission of the Indonesian Association of Geologists (Ikatan

Ahli Geologi Indonesia—IAGI).

• Cover topics related to sedimentary geology, includes their depositional processes, deformation, minerals,

basin fill, etc.

Advisory Board

Prof. Yahdi Zaim—Quarternary Geology—Institute of Technology, Bandung Prof. R. P. Koesoemadinata—Emeritus Professor—Institute of Technology, Bandung

Berita Sedimentologi

Page 3: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Last year, 2010, the Indonesian

Association of Geologist (IAGI)

celebrate the 50th anniversary of

the organization. This event give

a new momentum to the Indone-

sian Sedimentologists Forum

(FOSI) to reactivate the bulletin.

The last ‘Berita Sedimentologi‘

journal was published in 2000 in

paper format. Thereafter many

key people in the editorial board

left Indonesia and we admitted

that the hand-over was not suc-

cessful.

A new editorial board was set

with many new members. We

hope that the coming publication

of Berita Sedimentologi will

achieved the following goal:

• Publish technical journal

regularly

• Facilitate discussions related

to sedimentary geology in

Indonesia and Southeast

Asias region

• Provide opportunities for

knowledge transfers through

generations

The coming Berita Sedimen-

tologi will be published electroni-

cally in PDF format to reduce

cost and give higher flexibility in

journal editing. Electronic journal

also give more freedom to pub-

lish color figures with different

level of resolution. On top of

that, the electronic journal will

also reach larger number of read-

ers as it will be easier to access.

We hope the 3000+ members of

the Indonesian Geologists Asso-

ciation (IAGI) who live in differ-

ent part of the world can get the

benefit of this journal as well.

The editorial board will pick a

theme for each journal and it will

be geographical. For this edition,

for example, we will focus on

SUMATRA.

As a ‘new’ publication we would

like to hear comments from our

readers, especially FOSI and

IAGI members. If you like to

participate in the editorial team.

Please let us know.

Herman Darman

Editor in Chief

From the editors

Bird Foot Print 5

Talang Akar Formation 7

Ombilin Basin 12

Andaman-Sumatra Forearc

18

Langkat structures 22

University news 285

2

Inside this issue:

Number 20 / February 2011

Sedimentological journal of the Indonesian Sedimentologists Forum (FOSI), a commission of the Indonesian Association of Geologist (IAGI)

Berita Sedimentologi

Page 3 Volume 20— February 2011

Page 4: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

T he forum was founded in 1995 as the Indonesian Sedimentolo-gists Forum (FOSI). This or-ganization is a communication

and discussion forum for geologists, es-pecially for those deal with sedimentol-ogy and sedimentary geology in Indone-

sia. The forum was accepted as the sedi-mentological commission of the Indone-sian Association of Geologists (IAGI) in 1996. About 300 members were regis-tered in 1999, including industrial and

academic fellows, as well as students.

FOSI has close international relations with the Society of Sedimentary Geology (SEPM) and the International Associa-

tion of Sedimentologists (IAS).

Fellowship is open to those holding a

recognized degree in geology or a cog-

nate subject and non-graduates who have

at least two years relevant experience.

FOSI has organized 2 international con-

ferences in 1999 and 2001, attended by

more than 150 international participants.

Most of FOSI administrative work will

be handled by the editorial team. IAGI

office in Jakarta will help if necessary.

The official website of FOSI is: http://

www.iagi.or.id/fosi/

About FOSI

the ideal solution, and we may look for

other alternative in the near future. Hav-

ing said that, for the current situation,

Linked is fit for purpose.

International members and students are

welcome to join the organization.

A ny person who has a back-

ground in geoscience and/or

is engaged in the practising

or teaching of geoscience or

its related business may apply for general

membership. As the organization has just

been restarted, we use Linked-in

(www.linkedin.com) as the main data-

base platform. We realize that it is not

FOSI Membership

Page 4 Volume 20— February 2011

Total registered members:

119 February 2011

Page 5: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

T he islands of oceanic southern Asia

(Indonesia, Malaysia, and New

Guinea) have played an influential

role in the development of evolu-

tionary thought, initially because of the his-

toric studies by Alfred Russel Wallace and

later by the discovery of Pleistocene human

remains on Java by Eugene Dubois. Unlike

the majority of Sunda Islands, much of the

central core of Sumatra was emergent from

the early Eocene through the early Miocene.

Freshwater lacustrine sediments of the early

Eocene Sangkarewang Formation have

yielded an abundant diversity of fishes and a

single bird skeleton but no other evidence of

terrestrial vertebrates is known until the Pleis-

tocene. In the summer of 2007 a reconnais-

sance survey of Cenozoic sediments were

initiated in the Ombilin Basin located in the

Barisan Mountains of central Sumatra (Figure

1).The outcrop are well exposed in Sa-

wahlunto and Ombilin Coal Mining areas

consists of alternating conglomerates, quartz

sandstones and shale. In addition to exploring

the Sangkarewang Formation we examined

sediments of the Sawahlunto and overlying

Sawahtambang formations which span the

early part of the Miocene. In the Sawahlunto

Formation we discovered two series of avian

tracks representing two different shorebirds

(Figure 2). These tracks were found at the

base of a thinly laminated, coarsening upward

sandstone overlain by a relatively thin layer

(0.5 meter) of coaly shale, followed by a

quartz-sand conglomerate at the top of the

local section (12 meters total thickness). The

sandstone contains carbonaceous debris and

small to medium, parallel ripples are formed

(Figures 3). One set of tracks has an angle of

90 degrees between digits one and three and

is of relatively small size and probably repre-

sents a gruiform (rail). The second set of

tracks has a 120 degree angle between digits

one and three and was likely made by a cha-

radriid (plover) or scolopacid (sandpiper)

shorebird (Figures 4 and 5). In addition to the

bird tracks, small, circular traces (Skolithos

ichnofacies) are present probably representing

First Evidence of Miocene Avian Tracks from Sumatra Short Announcement

Yahdi Zaim*), Rizal Yan*), Gregg F. Gunnell+), Thomas A. Stidham+), Russell L. Ciochon**) and

Aswan*)

* Department of Geology, Institut Teknologi Bandung – Indonesia

+ Laboratory Paleontology, University of Michigan – USA

** Department of Anthropology, University of Iowa – USA

Page 5 Volume 20— February 2011

Figure 1: Ombilin Basin located in the Barisan Mountains of central Sumatra. On the left is Sing-

karak Lake (Picture from Google Earth,2009)

Figure 2: General Stratigraphy of

the bird foot print location

Page 6: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

tubes of suspension feeding invertebrates such as clams or worms (Figure 6). The presence of these traces suggests that the bird trcks were formed

on an intertidal beach and the birds may well have been feeding on these invertebrates. The presence of these track ways suggest that further explo-

ration of Tertiary sediments in Sumatra is warranted. The avian tracks from the Sawahlunto Formation are as the first discovery of the Bird Foot-

print Fossils in Indonesia.

Page 6 Volume 20— February 2011

Figure 3: Outcrop shows the sandstone contains carbonaceous debris

and small to medium, parallel ripples. The avian tracks are found at the

base of this outcrop.

Figure 4: First discovery of avian tracks, the Bird Footprint Fossils

in Indonesia from Sawahlunto Formation of Early to Middle Mio-

cene in age.

Figure 5: One set of tracks has an angle of 90 degrees between digits

one and three,probably represents a gruiform (rail), and the second set

of tracks has a 120 degree angle between digits.

Figure 6: Small, circular traces (Skolithos ichnofacies) are proba-

bly representing tubes of suspension feeding invertebrates.

Page 7: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Outcrops Conservation of Tanjung Baru or Lower Talang Akar Formation, Baturaja City of Palembang Area - South Sumatra Basin: How important? Premonowati*),

* Department of Geology, Faculty of Mineral Technology, UPN “Veteran” Yogyakarta

Page 7 Volume 20— February 2011

ABSTRACT

Tanjung Baru Formation only outcropped in

one location so called Tanjung Baru,

Palembang, South Sumatra. In total this

formation is expossed in an area of about one

acre. The outcrop is a quartz sandstone

quarry, which has become smaller in size

rapidly because of intensive mining activities

by the local community. The formation is also

called Gritsand Member (GRM) of the Lower

Talang Akar Formation/Lemat Formation/

Lahat Formation. A different name from

Talang Akar Formation was given to this

formation because it has an important role in

the tectonostratigraphy context. Tanjung Baru

Formations has different genetic, location and

section type from that of Talang Akar

Formation. The formation consists of

conglomeratic sandstone of channel deposit.

The sections indicate five times of channeling

with each channel has a geometry of 20 m

long and 9 m thick. This lag sedimentary

deposit consists of fine- to very coarse-

grained sandstones. The erosional base

contact has polymictic conglomeratic

sandstone outcrop with gradded bedding and

planar crossbedding that indicate high energy

deposition like channelized environment in

shallow marine. The fining upward

succession was a result of lateral accretion of

channel shifting or a fluvial channel system

depositional environment. The very fine sand

of channel plug was deposited in a very low

energy environment before the channel was

abandoned. Some parts have shaly and coal

streaks with mafic and feldspatic minerals.

This formation has an indication to be an

excellent reservoir.

The geology of Tanjung Baru Formation is an

important object to study because it is the one

and only outcrop that needs to be conserved.

The objective is to save this outcrop from

extinction. A socialization to the Governor of

South Sumatra Province and Head of

Palembang Regent needs to be done. The

government has to create a regulation to stop

the mining activities, build a boundary for the

outcrops with plantation and put an

information board to explain that it’s a

conservation area. Let all geology students

and also people of all generations to have a

possibility to learn Tanjung Baru Formation

from this outcrop as a geopark.

Introduction

Hydrocarbon production in the South Sumatra

Basin is ranked at the 2nd place after Kutei

Basin in term of total productions. The

primary reservoirs are within the Talang

Akar, Baturaja and Gumai Formations and a

smaller amount in the fractured basement.

The uplifted areas and paleohighs, including

the Mesozoic and Eocene fractured and

weathered basement granite and quartzite, are

effective reservoirs in ten fields in South

Sumatra with gas reserves totaling 106

MMBOE ultimate recoverable reserves

(Sardjito, et al, 1991; Petroconsultants, 1996).

This fact is very important and it is therefore

absolutely urgent for the goverment of

Baturaja District, South Sumatra Province to

conserve and to protect the outcrops of the

Lower TAF. The outcrops have very

important value to Earth Sciences and

exploration in geology, mining and petroleum

engineering. The aim of the conservation is to

avoid outcrop mining for other purposes.

An integrated study (fieldtrip and core

analysis) was held by P.T. Medco E&P

Indonesia (PT. MEPI) for the Graduate

Geoscientists Training 2-2008 at sections

Baturaja-Muara Dua-Palembang and

Palembang Core Storage. The methodology

of outcrop description has been conducted for

the basement rocks to the top formation in

South Sumatra Basin.

The Lemat (Old and Young) Formation has

outcropped in the sandstone quarry at

Tanjung Baru (proposed as locality type and

strato type) and Napalan river in Baturaja

City, Palembang, South Sumatra Province.

The outcrop of Lemat Formation is found in

Tanjung Baru Sandstone Quarry (TAF

equivalent the Gritsand Member). The

Figure 1. Left: South Sumatra Basin configurations. Right: Quarry location of Tanjung Baru sandstone outcrops (See arrow)

Page 8: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 8 Volume 20— February 2011

siliciclastic sediments outcropped in this area

should be named Tanjung Baru sections or

stratotype and it is also the type locality of

Tanjung Baru Formation. The location where

the best siliciclastic sediment outcrop exists is

almost 1 km south of the Baturaja town

(Figure 1).

The promotion of GRM into Tanjung Baru

Formation is necessary due to its

tectonostratigraphy importance. Hutchinson

(1996) concluded that the Eocene to

Oligocene Lahat Formation is composed of

synrift deposits that are as much as 700 -

1,070 m thick. The formation was deposited

in continental, lacustrine, and brackish

lacustrine depositional settings. This reservoir

accounts for nearly 88 MMBOE of ultimate

recoverable reserves (Petroconsultants, 1996).

The oldest facies of the Young Lemat is

granite wash overlain by coarse clastic

deposits consisting of sandstones and breccias

with abundant rock fragments, claystones,

coals, and tuffs (Hutchinson, 1996).

Firstly, the proposed name of Tanjung Baru

Formation is an increase from a member

status of the conglomeratic quartz sandstone

of Lower Talang Akar Formation (Ryacudu,

2005) or the Gritsand Member (GRM).

However, the upper member of the Talang

Akar Formation called the Transition Member

(TRM) is included the Talang Akar

Formation. Lithostratigraphically, in

accordance with SSI (1996), the complete

outcrop of Tanjung Baru Sandstone should be

determined as Tanjung Baru Formation

because of the lithology, mappable,

stratigraphic contact and either lateral or

vertical distribution.

Every year, the outcrops have less volume

due to mining by thelocal community. These

highly valuable outcrops of the Tanjung Baru

Formation have given stratigraphy and

sedimentation models the Oligo-Miocene age

has had outcropped. The outcrops have just

one complete section as type locality and

strato type. They have excellent porosity and

permeability and are analogues to the

reservoir rocks in the South Sumatra Basin.

The comparison with tonase economic value

for mining, the quartz sandstone remains

about 1000 m3. The outcrops should be very

rare therefore it is crucial to be conserved and

protected.

Geology of Baturaja

The South Sumatera Basin is one of a series

of Tertiary back arc basin located in Sumatera

and Java. The basins occupy a geologic

position between the stable micro-continental

block, known as the Sunda Platform, and the

active subduction zone caused by the

northward moving Indian Ocean Plate. The

basin was formed during the Eocene-

Oligocene when a series of northerly trending

grabens developed in response to east-west

interplate extensional movements. These

grabens were filled with locally sourced

volcanoclastics sandstones and shales of the

Lemat Formation in deposi tional

environments ranging from alluvial fan, to

fluvial and lacustrine.

The geology of the studied area, particularly

the Musi Platform, is a structural high area

formed during the Eocene-Oligocene graben-

forming period. It appears to behave as a rigid

structural block through most of the Tertiary.

There is direct evidence to which the area has

been subjected to widespread deformation. To

the west, the platform gradually shallows due

to uplift associated with rising volcanic arc.

Baturaja Limestone is exposed at the foothills

of the Gumai Mountains. The northwestern

and southwestern margins of Musi Platform

are controlled by major faults which bound

Figure 2. Regional Stratigraphy of South Sumatra Basin (Argakoesoemah and Kamal, 2005). Stratigraphic position of Lemat Formation or Tan-

jung Baru outcrops

Tanjung Baru Fm.

Page 9: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 9 Volume 20— February 2011

the Eocene-Oligocene grabens. The

northeastern edge of the block is in the

present day Lematang Trough, a syncline

between the Musi Platform and the Plio-

Pleistocene Lematang fault which has

thousands of feet of overthrusting from the

north. Seismic interpretation of the Lematang

Trough that forms the northeastern margin of

Musi Platform is limited by its proximity to

the overthrust fault.

Stratigraphy

The Tertiary succession overlying the

Mesozoic metamorphic basement consists of

Lemat Formation filling the early half

grabens, unconformably overlain in turn, by

Talang Akar Formation, Baturaja Limestone,

Telisa Formation and Palembang Formation

(Figure 2).

Lemat Formation

Within the Musi Platform, the Lemat

Formation consists of volcanoclastic

sandstones and shales, typical of the unit. The

formation is also known from the graben

areas around the platform and has been

intersected in wells in the Pigi Trough, to the

north, and in the Saungnaga Area, to the

southwest.

Talang Akar Formation

As the subsidence associated with graben

formation waned during the Middle to Late

Oligocene, the interbedded sandstones, shales

and coals of Talang Akar Formation were

deposited across the South Sumatra Basin.

This unit was derived from the northeast

based on the compositional imprint of its

granitic source areas on Sunda Platform. A

general depositional environment sequence

from fluvial in the northeast, to deltaic and

later basinal facies in the southwest can be

reconstructed from sedimentological and

paleontologic evidences. There are evidences

of cyclic deposition within Talang Akar

Formation providing excellent hydrocarbon

reservoirs. The organic rich shales and coals

of the Talang Akar Formation are considered

to be the major oil source for reservoirs in this

unit and the overlying Baturaja Limestone.

The thicker areas of deposition continued to

be controlled by more rapid subsidence over

the Oligocene grabens, and as with Lemat

Formation, deposition was either thin or non-

existent on the structurally higher platform

and horst areas.

Generally over the Musi Platform, the Talang

Akar Formation or Baturaja Limestone lies

unconformably on pre-Tertiary basement.

Talang Akar Formation is interpreted to be a

lacustrine unit deposited on the eroded

basement surface. It is separated from the

more typically sand-prone Talang Akar

Formation deposited on the eastern side of the

basin, by the deep water, shaly sediments

which fill Benakat Gulley. Because of its

isolation from the coarse clastic sediment

source to the northeast, the Talang Akar on

the Musi Platform represents an environment

which is typical for the deposition during this

period. Pre-Telisa clastics in the Pigi Trough

are often tuffaceous and usually lack of good

reservoir quality. As the basin continued to

subside during the lower Miocene, deposition

of the predominantly non-marine Talang Akar

Formation was replaced by widespread

marine deposition of the Telisa Formation.

Tanjung Baru Formation Outcrops

1. Lithology and Stratigraphic Positions

The outcrop of Tanjung Baru Formation

consists of fine- to very coarse-grained

sedimentary rock. It has almost 100 m wide

and 20 – 25 meters thick (Figure 3) and

Figure 3 (Upper) Outcrops of Tanjung Baru quartz sandstone quarry of Lower Talang Akar (TAF)-Baturaja City of Palembang. (Lower) Left:

The outcrops has been dug and remains mining’s tools track. Right: Planar cross bedding of quartz polimictic conglomeratic sandstone.

Page 10: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 10 Volume 20— February 2011

consists of clean quartz conglomerate

sandstone, quartz sandstone, siltstone and

intervals of coals without fossils. Their

stratigraphic position is determined at the

lower part of Talang Akar Formation by fault

and erosional or unconformity contact to the

Upper Oligocene Lahat Group. The presence

of paleosoils and basal conglomerates

indicates an unconformity contact. So, the

Tanjung Baru Formation or Lemat Formation

is approximately Lower Miocene in age.

Quartz conglomerate sandstone; grayish white

color, medium sand to granule grain size,

moderate to poor sorted, subangular -

subrounded, matrix supported, polymictic

conglomerate with quartz dominant as the

fragments, non calcareous, rare basalt and

andesites, feldspar, carbon and mafic

minerals; matrix: quartz, opaque minerals;

silicates cements, 4 – 6 meter thickness.

Observed sedimentary structure includes

graded bedding and in the base there is an

erosional base contact. This outcrop has

initial dip oriented to northwest (N230 o

E/30o). Sediment succession of the upper part

of the Lag Deposit Sandstone (Figure 3) has

planar cross bedding structure, channel plug

(very fine grain size) and some fractures

(uncemented, loose) and shows a fining

upward sequence (Figure 4).

Quartz sandstone; white, fine – medium sand,

grain-supported, moderate to poorly sorted,

and subangular to subrounded, quartz

(abundant), some parts are siltstone of a few

centimeter thick. The light grey siltstone with

silicate cement and without fossils is

distributed in the upper part of the fining

upward sequence. Coals have been found

occasionally and they are a few centimeter

thick.

2. Depositional Environment

Non calcareous sandstone with planar cross

bedding structure, and fining upward

sequences that shows decreasing energy

towards the top can be interpreted as a fluvial

channel system depositional environment. It

shows at least four depositional sequences

which conglomerate as a lag deposit and very

fine sand as channel plug which was

deposited in a very low energy deposition

before channel was abandoned.

Based on the planar cross bedding

sedimentary structure, the sandstone was

deposited by traction current mechanism and

was influenced by highly turbulent current

(Allen, 1988). In the bottom conglomerate,

there was an erosional base-contact which

indicates that this sandstone was deposited in

highly erosional processes environment such

as in channelized environment (Selley, 1970).

The conglomerate at the bottom of this

sequence is predicted as lag deposit which is

channel floor deposit, while fining upward

succession is the result of lateral accretion of

channel shifting (Selley, 1970). Based on all

of interpretations, it is concluded that the

sandstone was deposited in braided channel

which have five, observed channel shifting.

This sandstone has an excellent reservoir

quality.

Genetically, the development of Tanjung

Baru Formation (Gritsand Member) mostly

differed to the TRM Member: the channel

sediments that filled in rift basin after syn-rift

phase. Tectonostratigraphically, the

terminology called: immediate post-rift

(Prosser, 1993) or passive rift fill; however

Talang Akar Formation (TRM) as a

transitional deposits to shallow marine. It

characterized an early regional transgressive

phase in the South Sumatra Basin. This

formation's development is restricted in the

deep zone, but the Talang Akar Formation is

in the platform or basin margin.

Figure 4. (Upper) Left: Tanjung Baru Formation is found at least four (fining upward) sequence of sandstone. Right: Conglomeratic sandstone of

channel deposit in Tanjung Baru sandstone quarry. (Lower) Left: Siltstone of channel deposits, about 10 cm thick in between the massive quartz

sandstone. Right: Lag deposits of channel, with thin orientation of quartz pebble in between the massive quartz sandstone.

Page 11: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 11 Volume 20— February 2011

3. Outcrop Conservations

The outcrop of Tanjung Baru Formation

(Early Miocene) has been characterized as

lithology of excellent reservoir. It is very

ideal and urgent to be conserved. The aims of

the conservation are as follow: a). a very rare

of ideal reservoir characterization for HC

production in the basin; b. Tanjung Baru

Formation has ideal channel system

sedimentation; c). as a learning object for old

reservoirs in the South Sumatra Basin. In

contrast, the sandstone mining will extinguish

the formation records.

Particularly for learning object, the local

government is as follow: Governor, Head of

Baturaja Region (Bupati) have to stop the

sandstone quarry. It is very urgent to protect

and create regulations to stop the mining. The

outcrop should be proposed as a Geopark.

Actually, it is necessary to have plantation

surrounding the outcrops.

Acknowledgment

My thanks to the Management of (PT.

MEPI), Mr. Edi Bambang Setyobudi, Mr.

Asril Kamal, Mr. Dindot Subandrio and

Graduates Geoscientist Training (GGT 2008)

for their valuable suggestions, supports and

discussions.

References

Argakoesoemah, R. M. I. and Kamal, A.,

2005, Ancient Talang Akar deepwater

sediments in South Sumatra Basin: A new

exploration play. Proceedings of the 31st

Indonesian Petroleum Association Annual

Convention,

Hutchison, C. S., 1996, South-East Asian Oil,

Gas, Coal and Mineral Deposits: Clarendon

Press Oxford.

Petroconsultants, 1996, Petroleum

Exploration and Production Database:

Petroconsultants, Inc., P.O. Box 740619,

6600 Sands Point Drive, Houston TX 77274-

0619, USA or Petroconsultants, Inc., P.O.

Box 152, 24 Chemin de la Mairie, 1258 Perly,

Geneva, Switzerland.

Prosser, S., 1993, Rift-related linked

depositional systems and their seismic

expression. Geological Society of London,

Special Publications, 71, 35-66

Komisi Sandi Stratigrafi Indonesia (SSI),

1996, Sandi Stratigrafi Indonesia. Ikatan Ahli

Geologi Indonesia (IAGI), 96 p.

Sardjito, Fadianto, Eddy, Djumlati, and

Hansen, S., 1991, Hydrocarbon prospect of

the pre-Tertiary basement in Kuang area,

South Sumatra: Proceedings Indonesian

Petroleum Association Twentieth Annual

Convention, October, 1991, p. 255-278.

Selley, R.C., 1970, Ancient Sedimentary

Environments and their sub-surface diagnosis.

Chapman and Hall, London, 287p

Page 12: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Half-day visit to Solok-Sawahlunto area, Ombilin Basin: A short observation on non-marine depositional sequences RM Iman Argakoesoemah and Didit Ariady Firmansyah

Page 12 Volume 20— February 2011

Introduction

This is a brief note of our visit to Solok, Sa-

wahlunto area, Ombilin Basin on November

8, 2008 for the purpose of our efforts to

broaden our knowledge on non-marine depo-

sitional sequence and its relationship to the

development of hydrocarbon petroleum sys-

tem in the region. Exposure of the outcrops is

excellent in the form of accessibility and ver-

tical extent of the stack of the sequences.

Unfortunately, as the time was limited, there

was no opportunity to conduct sufficient de-

tailed description of the outcrops. However,

several notes of the broad observation of the

whole large view of the outcrops were made.

Part of them is discussed in this paper.

A total of eight (8) locations (=STA) were

visited during this half-day reconnaissance

trip. The traverse began from Solok using a

car towards northeast to the locations 1 to 8

following the existing main road to Sa-

wahlunto, Figure 1. The outcrops are easily

accessed and visible from the main road.

Some of the outcrops are located immediately

on the edge of the road.

General Overview

The Ombilin Basin has been interpreted as a

small intermontane basin began to occur in

the Late Eocene by north-south tensional

displacements followed by dextral strike-slip

faulting of the Sumatra Fault System in the

Oligocene resulted in a pull-apart develop-

ment of the horst and graben structures in

northwest-southeast trending (Situmorang et

al, 1991; Howells, 1997). The basin uplift in

the Mid-Miocene or later reduced its extent to

the present size where the intermontane basin

is outlined. To the west the basin is presently

bounded by a series of Quaternary to Holo-

cene volcanoes while to the east by the pre-

Tertiary non-volcanic sediments.

The basin began with deposition of the sand-

rich, conglomeratic sequence of alluvial fans

of the basin margins of the Brani Formation

followed by the Sangkarewang, Sawahlunto,

Sawahtambang, and Ombilin Formations

(Koesoemadinata and Matasak, 1981;

Koning, 1985; and Noeradi et al, 2005), Fig-

ure 2. Fresh water lacustrine setting could be

present in the depocentre of the basin. This

transgression stage is stratigraphically repre-

sented by a mega-sequence ranging from non-

marine coarse clastic rift deposits to shales of

deep open marine with the maximum flooding

occurred in the Mid-Miocene.

The Sawahlunto Formation consists of non-

marine argillaceous deposits with numerous

coals and some quartz sandstones. The Ombi-

lin Underground Coalmines situated in Sa-

wahlunto city has produced coals since 1891

from this formation. The estimated reserves

are of about 200 million metric tons. There

are three main coal seams with the most po-

tential up to 18 m thick and average 9.3 m

thick of black and lustrous bituminous coal

rank (Silkina and Toquero, 2008). It should

be noted that large extent of the coals could

also have potential for coalbed methane

(CBM) deposits.

The formation is probably conformable over-

lain by the Sawahtambang Formation. The

age-diagnostic fossils are not present, but

erosion surface could mark the boundary

between both formations as shown by a shift

of Ro value plot in Sinamar-1 well (Koning,

1985). The Sawahtambang has been described

as thick coarse quartz-rich sandstones with

some overbank coaly claystone suggesting

that the formation was deposited in the flu-

vial, braided river setting.

The geothermal gradient in Sinamar-1 (1984)

is only 1.62 degF/100’ (29.6 degC/km) which

is cooler than the average gradient of 3.3

degF/100’ (60.3 degC/km) in the Central

Sumatra Basin. Several oil shows were re-

ported in the sandstones of the Sawahtambang

Formation. One open-hole DST recorded

minor

flow of oil (36 deg API gravity) in the upper

formation and a gas flow exceeding 13

MMCFD (60 deg API gravity) in the middle

part of the formation (Koning, 1985). The

Figure 1. Index map of station (STA) of the observations during visit to Solok-Sawahlunto area.

Page 13: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 13 Volume 20— February 2011

source rocks might be the mature shales

(Ro=0.6%) of the Sangkarewang Formation

(Avg TOC= 2.6%) while the Sawahlunto

coals are still immature with Ro=0.53%

(Fletcher and Yarmanto, 1993). The hydro-

carbon accumulation is considered non-

commercial (Koning and Karsani, 2000). The

later well, South Sinamar-1 (1994) drilling

results is dry.

Brief Outcrop Overview

Several large outcrop exposures are present

along the coalmines in the Sawahlunto area.

Description for a broad mega-sequence over-

view can be conducted from a distance as the

outcrops extend several hundreds of meters

laterally. Some of them could have few hun-

dreds of meters of repeated vertical se-

quences. A closer look will give much better

impression on sedimentary sequences and

lithological description and composition.

Below are a brief description and preliminary

interpretation of the outcrops based on quick

observation and reading materials.

Coaly claystone and coal of the floodplain

deposits have vertically separated each sand-

rich sequence as the river channels move

laterally and vertically with time. These rela-

tively thin floodplain deposits may help corre-

late the sand-rich sequence locally. Some of

them could have been significantly extended

laterally and can be used for local correlation

marker. Thickness of the individual sand-rich

sequence could be tens of meters. Individual

coal layer may not be useful for regional cor-

relation as the main

swampy, floodplain area may not be very

extensive in the Sawahlunto Formation at this

location STA 7, Allied Indo Coal.

Based on the rift basin model, Noeradi et al

(2005) interpreted that the Brani coarse clas-

tics of fanglomerate and other related sedi-

ments representing rift basin margin facies

was deposited during the early syn-rift phase

while the Sawahlunto Formation was depos-

ited during deposition of the late syn-rift. The

Sawahtambang and Ombilin Formations are

considered to be the post-rift phase based on

seismically continuous, widespread reflector

package over the whole basin.

Further geophysical interpretation should be

taken to ensure that the lithological contrast

between the thick sandstone package of the

Sawahtambang Formation and the thick,

open-marine shale package of the Ombilin

Formation shall not lead to the improper in-

terpretation. The impedance or velocity con-

trast between both formations shall be con-

tinuous laterally along the presence of both

formations in the basin unless the lithological

contrast diminishes near the basin margin.

Conclusion and Recomendation

Below are some brief conclusions and recom-

mendations:

(1) Quality of the outcrops is extremely excel-

lent. They are continuous and some of them

are extent to be several hundreds of meters

both in vertical and lateral views. Any de-

tailed geological observations could be made

continuously.

(2) Any outcrops in the Solok-Sawahlunto

region specifically in the area where coal-

mines are present and active should have to

be properly documented. Regular field visit

and detailed geological study should be per-

formed to ensure that the geological informa-

tion is continuously recorded otherwise the

outcrops will disappear shortly due to coal-

mine activity.

(3) Sufficient safety preparation should be

conducted if continuous measured section is

planned since the field condition in some

outcrops need special attention for the pur-

pose of safety precaution.

(4) The outcrops are useful for the study of

non-marine Tertiary sequence stratigraphy

though the deposition and tectonic in the re-

gion are active. Non-marine biostratigraphy

should be conducted to establish the vertical

stratigraphic relationship and lateral regional

correlation across the basin.

(5) In addition to the coalmine purposes fur-

ther exploration for hydrocarbon occurrence

in the basin should remain to be interesting

not only for conventional hydrocarbon but

also for unconventional exploration specifi-

cally coalbed methane.

Note: Any content and interpretation appear

in this paper is solely responsible of the Au-

thors.

References

Fletcher, G. and Yarmanto, 1993, Ombilin

basin field guide book. Indonesian Petroleum

Association, Post Convention Field Trip, 59

pp.

Howells, C., 1997, Tertiary response to

oblique subduction and indentation in Suma-

Figure 2. General lithostratigraphic column of Ombilin Basin (Noeradi et al, 2005)

Page 14: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 14 Volume 20— February 2011

tra, Indonesia: new ideas for hydrocarbon

exploration. Geological Society of London,

Special Publications, v.126, p. 365-374.

Koesoemadinata, R.P. and Th. Matasak,

1981, Stratigraphy and sedimentation – Om-

bilin basin, Central Sumatra (West Sumatra

Province). Indonesian Petroleum Association,

Proceedings of the 10th Annual Convention,

p. 217-249.

Koning, T., 1985, Petroleum geology of the

Ombilin intermontane basin, West Sumatra.

Indonesian Petroleum Association, Proceed-

Figure 3. Repeated stacked sand-rich se-

quences with several lenses of large fluvial

channels. Thickness and width of some chan-

nels should be measurable. The thick, coarser

grain of sediments (dirty white) encased by

light grey argillaceous flood-plain deposits

could be interpreted as part of the main chan-

nel fill, but the thin and discontinuous one of

much smaller channel fills could be inter-

preted as the crevasse splays. However, de-

tailed observation should be made, as the

alluvial fan sequence is present and could be

inter-fingering laterally with the fluvial de-

posits, see Figure 2. The information is im-

portant for interpretation of the variation of

fluvial system (and alluvial fan) depositional

outline and development including non-

marine sequence stratigraphy interpretation

of the region

Figures 4a (above) and 4b (below). This

picture shows several erosion surfaces indi-

cated by irregular sharp-based contact be-

tween fluvial channel (dirty white) and flood

plain (light grey) deposits of the Sawahlunto

Formation at STA 2 location, Korean coal-

mine. The width of some channels is possible

to be measured in the outcrops. It should be

noted that the channels at this location may

not be the main river channels as their sizes

are relatively smaller than those observed in

the basin. The thin, discontinuous, silty sand-

sheets within the swamp are possible deposit

of the crevasse splays. Note: This outcrop

extends laterally several hundred meters.

Page 15: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 15 Volume 20— February 2011

Figure 5. Detailed view of erosion surface

shown by irregular sharp-based contact be-

tween fluvial channel and the underlying

flood plain sediments. The outcrop is very

fresh showing excellent view of micro-

sedimentary structure. Ripple lamination and

others in carbonaceous siltstones with finer

grain of sandstones are present, see the in-

serted photograph. Note: It is Sawahlunto

Formation at STA 3 location, Korean coal-

mine.

Figure 6. Detailed view of erosion surface of

thick sand-rich channels eroded fine-grained

sandstones of the underlying earlier channel.

These thick, stacked sandstone deposits are

interpreted to have been deposited as multi-

story river system channel of the Sawahlunto

Formation at STA 4 location as opposed to

the interpretation of possible proximal allu-

vial fan sediments. Detailed sedimentary

structure of the sandstones and biostratigra-

phy analysis of the intercalated shale be-

tween the channels are crucial just to confirm

the possibility of fresh water lake deposits

present in the depocentre of the basin at this

location. That possibility could enrich alter-

native interpretation of other non-marine

depositions present in the basin. The basin

geometry should be properly mapped, if pos-

sible.

Figures 7a (above) and 7b (below). Possible

inter-fingering contact between the overlying

alluvial fan deposits and underlying mean-

dering swampy sediments of the Sawahlunto

Formation. It should be noted here that the

possibility to have freshwater lacustrine delta

during Sawahlunto deposition should not be

ignored. Therefore, further detailed strati-

graphical and sedimentological observations

are obviously required for this outcrop at this

location and others in the surrounding areas.

Note: The outcrop is located at STA 5.

Page 16: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 16 Volume 20— February 2011

ings of the 14th Annual Convention, p. 117-

137.

Koning, T. and Aulia Karsani, 2000, Abstract:

Exploration in the Ombilin intermontane

basin, West Sumatra. AAPG International

Conference and Exhibition, Bali, Indonesia.

AAPG Search and Discovery Article #90913.

Noeradi, D., Djuhaeni, and Batara Simanjun-

tak, 2005, Rift play in Ombilin basin outcrop,

Figure 8. Close-up of the sedimentary struc-

tures of stacked channels developed in the

Sawahlunto Formation located at STA 5.

Parallel lamination and others with top and

bottom sets of cross-bedding structures can be

recognized along the outcrop. Paleo-current

could be measured accordingly. Any possible

broad direction of the major fluvial shift is

interesting to be exercised.

Figure 9. Large scale of outcrop showing the

presence of thick and large channel sand-

stones that seems to be encased by thick

floodplain deposits (light grey) of the Sa-

wahlunto Formation at STA 6, Allied Indo

Coal mining. Since the lateral extent of the

channel sandstone package is significantly

thick, wide and gentle it could be interpreted

that the equilibrium profile (=base level) of

the fluvial system at the time in this location

rose above the alluvial profile resulted in the

river aggraded the floodplain. This is an

indication of positive fluvial accommodation

took place during deposition of the Sa-

wahlunto.

Figure 10. Development of thin, scattered

crevasse splays within the large and thick

overbank swampy deposits (light grey) of the

Sawahlunto Formation at location STA 7,

Allied Indo Coal mining. The tectonic contri-

bution to the fluvial accommodation in the

basin centre at the time seems to be signifi-

cant resulted in thick fluvial system accumu-

lation as indicated by anomalously thick

floodplain deposits. This is a typical of the

presence of local tectonic sag where the ac-

celerated subsidence took place in the pull-

apart tectonic setting, ie. the Sawahlunto

deposition.

Page 17: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 17 Volume 20— February 2011

West Sumatra. Indonesian Petroleum Asso-

ciation, Proceedings of the 30th Annual Con-

vention, p. 39-51.

Silkina, I. and Napoleon Toquero, 2008, It’s

About Time. Time Technology Pty Ltd, Sci-

entific and Technical Division, PTBA Ombi-

lin Coal Project, 14 pp.

Situmorang, B., Barlian Yulihanto, Agus

Guntur, Romina Himawan, and T. Gamal

Jacob, 2005, Structural development of the

Ombilin basin, West Sumatra. Indonesian

Petroleum Association, Proceedings of the

20th Annual Convention, p. 1-15.

Figure 11. Outcrop of the Sawahtambang

Formation in location STA 8 (Sawahtambang

gorge) showing multi-story, stacked thick

sandstones of the braided river deposits

where some appear to have been amalga-

mated. The formation is well-cropped out in

the basin margin. Towards the basin depocen-

tre, part of the formation has been eroded

following the Mid-Miocene to Pliocene basin

uplift.

Figure 12. Part of the close-up of the outcrop

in Figure 11 above showing detailed sedi-

mentary structures. Cross-bedded sandstones

with composition of mostly quartz are com-

mon in the Sawahlunto Formation.

Figure 13. Outcrop of the Sawahtambang

Formation at the same location (STA 8) as

shown in Figures 11 and 12 above, but it is

located across the main road. Good layered,

multi-story quartz-rich sandstones with ir-

regular shape of the base of the channels can

be observed from a distance.

Page 18: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Seismic Expression of Some Geological Features of Andaman-Offshore West Sumatra Subduction zone Herman Darman—Shell International E&P

Page 18 Volume 20— February 2011

A subduction zone developed in

the south of Myanmar, continue

to the Andaman Sea (India), west

of Sumatra and south of Java

(Indonesia). Two major fault system devel-

oped parallel to the subduction zone, so called

the Mentawai Fault System and Sumatra Fault

system. To the north, where the subduction

zone changes its orientation from NNW-SSE

to NS, a spreading zone developed towards

the east of Andaman Sea (Figure 1). This

zone is a complex and active geological sys-

tem. The 2004 Aceh Tsunami was a major

disaster which was triggered in this subduc-

tion zone.

The Andaman - Offshore West Sumatra sub-

duction system is where part of the Indo-

Australian oceanic plate moving northwards

and going beneath the southern tip of Eura-

sian continental plate. Sumatra Island, which

is part of Indonesian volcanic island arc, oc-

curs parallel to and inland from the boundary

between these two plates. An accretionary

prism or wedge has formed from sediments

that accreted onto the non-subducting plate.

Most of the material in this wedge consists of

marine sediments scraped off from the down-

going slab of Indian oceanic plate with some

erosional products of Sumatra volcanics.

Fore-arc ridge in this system is a chain of

islands (e.g. Andaman, Simeulue, Nias,

Mentawai, and Enggano), formed by the ac-

cretionary wedge. A series of fore-arc basins

developed between the accretionary ridge and

the volcanic arc (Figure 2).

This region is also an active petroleum explo-

ration area. Recently, there are a number of

companies (e.g. Spectrum, TGS and Geco)

provide new and reprocessed seismic lines to

the market. These seismic lines show the

geological features in this subduction system.

1. Andaman Section

2010 articles in Geo-ExPro and AAPG Ex-

plorer displayed seismic sections of Andaman

Sea. These sections were recently reprocessed

by Spectrum in 2010 to support exploration

licenses by the Indian authority. The regional

seismic section shows a submarine volcanic

arc, which separates the back-arc basin from Figure 1: Regional tectonic setting of Andaman—Offshore West Sumatra subduction zone. Sec-

tion 1: Andaman section; Section 2: West Aceh section; Section 3: Simeuleu Section

Page 19: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 19 Volume 20— February 2011

the fore-arc basin. East Andaman fault system

developed bathymetric high called ‘invisible

bank’ in the middle of the fore arc basin. Part

of the fore-arc is shown on the west of the

section. Further west of this section the fore

arc ridge appear to the sea surface as Anda-

man Island (Figure 3).

The interpretation suggest Pliocene-Recent

stratigraphic interval at the shallowest section.

This unit thins in parts due to volcanic activ-

ity and fault movement. Neogene units are

thicker in the back arc basin compare to the

fore-arc basin. The majority of the back-arc

basin is deeper than 3000 MSec. TWT.

A seismic section published in AAPG Ex-

plorer show a Miocene Limestone unit which

this towards the deeper water. The interpreta-

tion also indicates a shelf deposit, shelf edge

and an isolated shoal (Figure 4). The shelf

unit is about 3-4 Msec. TWT deep.

The Neogene unit is underlain by Pre-

Neogene sediments which is thins towards the

volcanic arc. In parts the pre-Neogene se-

quence has been completely eroded away.

This unit seems thicken to the west of the

section in the fore-arc ridge zone. It is be-

lieved that the deeper stratigraphic unit has

limited data control.

2. West Aceh Section (Profile Sumenta 32)

A seismic section published by Malod et al is

a result of Baruna Jaya shallow seismic sur-

vey in 1991. The survey is part of collabora-

tion between Indonesian and France govern-

ment.

This short section shows a reverse fault which

bound the west part of the fore-arc basin

(Figure 5). The fault goes all the way to the

sea floor at about 3.5 sec. TWT, separating

the accretionary prism from the fore-arc ba-

sin. The accretionary prism in the SW of this

section is clearly shown as a bathymetric high

and the fore-arc basin appear as a flat sea

base.

The fore-arc basin was filled with Late Mio-

cene and younger deposits. Flat reflectors

shows that there were very little tectonic im-

pact on this area despite the major earth

quakes and tsunami developed in this region.

Figure 2. Schematic regional cross section of a subduction zone

Figure 3. West to east geoseismic cross section through the northern part of the Andaman fore-arc basin area (after Scaife & Billings, 2010)

Page 20: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 20 Volume 20— February 2011

Unfortunately the seismic section is too short

and too shallow to show the regional picture.

The complex geology in the accretionary

complex result in unclear seismic expression

in this area.

3. Simeuleu Section

In July 2006, Geco acquired 3 deep seismic

sections in offshore west Aceh. (Bunting et al,

2007) to image active faults along the subduc-

tion zone, quantify the volume of water that

penetrated along these faults and provide

information to optimize the location of future

borehole location for the Integrated Ocean

Drilling Program (IODP).

The seismic section is more than 16 sec. TWT

deep and show the oceanic Moho on the SW

of the section. An indication of continental

Moho appears in the NE of the section. The

section also shows the trench and the accre-

tionary wedge of the West Sumatra subduc-

tion zone (Figure 6).

Slightly to the south of this line, TGS shot

some seismic which was focused on the fore-

arc basin. The seismic section clearly shows

the fore-arc ridge and major regional NW

trending fault zone in the SW of the section

(Figure 7). In the NE, present day shelf de-

posit is well imaged. Meulaboh fore-arc basin

has thick post late Miocene deposit adjacent

to the NW trending fault zone as this fault

generate an accommodation space fore about

2 sec. TWT deep.

Conclusion

Recent seismic sections published by Spec-

trum, Geco and TGS, shows different element

of the Andaman-Offshore West Sumatra.

Indonesian BPPT Baruna Jaya shallow seis-

mic, acquired in 1991, shows sea bottom

profiles which are controlled by tectonic fea-

tures. These seismic lines clearly show the

subsea volcanic arc, accretionary wedge, fore-

arc basin, the trench, and boundaries of each

element.

Both carbonate and clastic deposits are shown

on the seismic sections with indication of

potential hydrocarbon.

References

Bunting, T, Chapman, C; Christie, P., Singh,

S., Sledzik, J., 2007, The Science of Tsuna-

mis, Oil Field Review, Autumn 2007

Caife, S., Billings, A., 2010, Offshore Explo-

ration of the Andaman Sea, GEO ExPro, vol

7, no. 5.

Durham, L. S., 2010, India Seismic Gets New

View, AAPG Explorer, October.

Malod, J. A., Kemal, M., Beslier, M. O., De-

plus, C., Diament, M., Karta, K., Mauffret,

A., Patirat, Pl., Pubellier, M., Rgnauld, H.,

Aritonang, P., Zen, M. T., 1993, Deformation

fo the Fore-arc Basin, NW of Sumatra, re-

sponse to oblique subduction, Sumenta Crui-

ese – Baruna Jaya III – 1991.

Figure 4. An example of limestone build-up—the basins’s cap rock. The section length is 28 km.

Data courtesy of Spectum ASA, published in AAPG Explorer—October 2010

Figure 5. Profile SUMENTA 32, west Aceh section showing reverse fault bounding the Aceh

Basin to the west and interpreted as possible strike-slip fault zone. Location of the profile is in

Figure 1..

Page 21: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 21 Volume 20— February 2011

Figure 6. Simeulue Section. A) Preliminary results from the Geco WG1 seismic line with interpretation revewals faulting and deep boundaries. The

main thrust fault can be seen on this image, as well as other reflectors. The Moho, short for the Mohorovicic discontinuity, is the boundary between

the Earth’s crust and the mantle, and can be identified here. B) A seismic section acquired by TGS showing the northwest-southeast trending fault

system as the primary tectonic feature in the west of Meulaboh—Sibolga Basin

Page 22: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Palinspatic 2D Seismic Restoration: Simple Method for Reconstructing Inverted Structure and Basin History, A Case Study in Langkat Area, North Sumatra Basin Fatrial Bahesti—PT Pertamina EP ([email protected])

Page 22 Volume 20— February 2011

Abstract

Numerous published studies have shown that cross-section balancing and valida-tion techniques are a powerful method of structural analysis. The construction of seismic cross-section is of the greatest importance to generate regional study of basin history. For this reason, palinspatic restoration in time domain of seismic data have evoked considerable interest, in particular in areas of extensional and compressional tectonics regime. The basic approaches to restore preserve seis-mic section assume plane strain, or con-servation of cross sectional area. Calcula-tion of equal areas for a section deformed above a decollement or detachment sur-face can be applied by depositional time. It calculates depth to detachment in Langkat area, around 5000 ms in time domain to detachment by restoration techniques. In addition to the analysis of structural traps, cross-section validation can be used in Bampo and Baong Forma-tion as major source rock, especially in the relative timing of hydrocarbon migra-tion. The extension and compression factor results 0.20 and 0.63 for Langkat area without assuming wrench fault zone gives additional strain in calculation. The result, when compared with several ma-jor oil and gas field in Sumatra, gives high compression inverted structure clas-sification that increase confidence for finding any giant field. This technique, when used with other methodologies, such as sequence stratigraphy and basin modelling, allows the interpreter to use all the available data sets to constrain geological models on hydrocarbon prospectivity. It is therefore a valuable methodology in both 3D basin analysis and prospect risking/ranking.

1. Introduction

Whether paleostructure model are resolv-able on seismic reflection surveys, they can significantly affect hydrocarbon mi-gration and trap location, as well as flow

of hydrocarbons. Therefore, understand-ing the evolution of basin structure and physical properties through time should improve geological models and, in turn, significantly reduce exploration risk. Furthermore, whereas these geophysical techniques adequately image the major geological structures, this only provides the present-day structural geometry of the subsurface, which commonly has resulted from multiple tectonic events, thereby increasing the complexity of the analysis. To more realistically model the spatial and temporal development of structural heterogeneities and to address these economical issues, a variety of nu-merical techniques have been developed. They fall into three main categories: (1) the geometric and kinematic approaches; (2) the stochastic approaches; and (3) the physical and geomechanical approaches. The first category includes most of the restoration techniques used by structural geologists to check the consistency of the subsurface structural interpretations. Measures of gaps and overlaps between the restored parts of a model give qualita-tive values to check the strength of the geological interpretation. The geometri-cal methods proposed to restore geologi-cal structures are based on a variety of algorithms, which aim at reproducing natural deformation. For instance, the methods include balancing cross sections by flexural slip (Dahlstrom, 1969; Hos-sack, 1979; Davison, 1986) to model deformation accommodated by slip along an infinite number of bedding interfaces. More simply, mapview restoration has been done using rigid translation and rotation of fault blocks (Dokka and Travis, 1990; Rouby et al., 1993) to model larger scale deformation. These methods are based on geometrical as-sumptions (Rouby et al., 2000), such as preservation of area, minimization of

deformation, minimization of changes in segment length, or minimization of shearing, constant fault slip, fixed faults in space, or discontinuous rigid blocks. Furthermore, these techniques are not based on the fundamental principles of the conservation of mass and momentum, which govern rock deformation. In addi-tion, only strain, which is strongly de-pendent on the geometric restoration algorithm used, is calculated (Erickson et al., 2000; Hennings et al., 2000; Rouby et al., 2000; Sanders et al., 2004). There-fore, physical laws and linear elastic the-ory replace kinematic and geometric constraints used by the existing methods for the restoration of geological struc-tures. Strain heterogeneity may be esti-mated and it is possible effects on bal-ance calculations deduced. The availabil-ity of closely spaced seismic lines, cou-pled with well control, however, can give three-dimensional and stratigraphic con-trol in areas of orogenic contraction.

2. Data and Methods

The geomechanically based restorations described in this study were performed manually using constrain length and ar-eas with CorelDraw, a 2-D seismic has been interpreted to model complex geo-logical structures with a variety of boundary conditions or constraints. In this study, we only consider the 2-D for-mulation to restore geological cross sec-tions. Detachment fault models of extensional basin development have two end-member geometries (Fig. 1A). The first involves listric normal faults that gradually sole into sub-horizontal de-tachments (Wernicke & Burchfiel 1982; Gibbs 1983). In the second case the fault system has a kinked geometry con-sisting of two planar fault segments (Jackson 1987; Groshong 1989). Under both end-member conditions, transla-tion on the sub-horizontal detachment

Page 23: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 23 Volume 20— February 2011

results in potential voids between the hanging wall and footwall blocks, and collapse of the hangingwall results in the formation of a half-graben. The foot-wall block is assumed to remain pas-sive during extension (Gibbs 1983; Groshong 1989). The geometry of the half-graben is governed by (1) the rules of equal-area balancing (Gibbs 1983), (2) the geometry of the fault system, and (3) the nature of the deformation in the hanging wall, i.e., collapse along zones of vertical shear, collapse along antithetic faults of variable dip angles, and the relative amounts of bedding-plane shear within the hanging wall block (Gibbs 1983, 1984; White et al. 1986; Williams & Vann 1987). In gen-eral, half-graben become wider and less deep as the dip angle of the antithetic faults along which the hanging wall col-lapses decreases (Crews & McGrew 1990). The dip angle of the border fault and the depth to detachment also strongly influence the geometry of the basin: for the same amount of net dis-placement on the horizontal detachment, basins become narrower and deeper as the dip of the basin-bounding fault and depth to detachment increase (Morley 1989). In the case of listric faults, a roll-over geometry results in the hanging wall because of the increasing size of the potential void between the hanging wall and footwall blocks toward the listric fault. For the ramp-flat geome-try, a flat-bottomed half-graben results because the width of the potential void between the hanging wall and footwall blocks is constant over considerable por-tion of its length. The basic approaches to section balance assume plane strain, or conservation of cross-sectional area. Calculation of equal areas for a section deformed above a de-collement or detachment surface can be applied to extension as well as contrac-tion. Given the equal-area balancing assumption, the cross-sectional area of the hanging wall basin is given by:

A = hd (1) where h is the net displacement on the hori-zontal detachment and d is the depth of the detachment. The rate of increase in the cross-sectional area of the basin is constant (dA/dh = d), and the change in the rate of area in-crease (d2A/dh2) is zero. This is a feature unique to the detachment fault models. Fig-

ure 1 show the basic approach to section bal-ance for plane strain, or conservational of cross-sectional area. The equation expresses the relationship be-tween the undeformed length, the deformed length of section and the depth to the decolle-ment surface (d). This can be expressed in term of average stratigraphic thickness upon time-depth conversion. It is seen to be identi-cal to those for orogenic contraction with the exception of the change in sign convention for elongation and is likewise independent of the style of deformation. Linear elasticity is used as a tool for restora-tion because its fundamental properties are well suited for such modeling. Therefore, model results can easily be comprehended. Linear elasticity honors the full complement of physical laws that govern geological defor-mation, including conservation of momentum, mass, and energy. As a result, physical laws replace kinematic or geometric assumptions commonly used for restoring geological struc-tures, such as preservation of segment length, surface area, or volume. This is a feature unique to the detachment fault models. The volume of the basin also changes similarly since uniform plane strain conditions prevail (Gibbs 1983). The uni-form plane-strain condition is most likely to be satisfied when the basin is bounded laterally by vertical transfer faults (terminology of Gibbs 1984). (Fig 2).

Sedimentation rates progressively decrease toward the hinge of the basin and precisely mimic the subsidence rates. Since the second increment of displacement is equal to the first, area balance dictates that the newly created volume of the half-graben be equal to that of the first increment. Since the volumetric sedi-mentation rate is constant, the basin again completely fills with fluvial sediments. Notice that the younger wedge of sediments pinches out against the older wedge. This is because the footwall, the basin-bounding fault, and the depocenter of the basin remain fixed during extension, but the hinge of the basin migrates away from the basin-bounding fault. This pattern of fluvial sedimentation and pinchout of younger strata against older strata would continue as long as the displacement rate was uniform. However, a doubling of the amount of displacement also doubles the incremental volume of the basin, which now exceeds the volume of sediments available. Lacustrine deposition occurs. Note that (1) the lacustrine wedge of sediment pinches against older fluvial strata, (2) the maximum sedimentation rate in the lacustrine wedge is higher than the maxima of the two older fluvial wedges, and (3) the depositional surface area of the lacustrine wedge is less than for the fluvial wedges, requiring a higher transverse gradient in sedimentation rates. Given initial fluvial sedimentation, lacustrine sedimentation can only occur if there is an increase in the extension rate and/or if the volumetric sedimentation rate decreases. The chosen volumetric sedimentation rate results in fluvial sedimentation following the first two increments of displacement. After the third increment, the basin is of such a size that lacustrine sedimentation occurs. In general, under conditions of accelerated extension, younger units consistently pinch out against older units, the maximum sedimentation rate in younger units is higher than in older units, and a transition from fluvial to lacustrine is predicted if extension continues long enough and if the effects of accelerated displacement overcome the effects of any increase in the volumetric sedimentation rate. Studies of small normal faults in British coal fields and larger normal faults in the North Sea imaged on a closely-spaced grid of seis-mic lines have shown that the displacement on these faults is generally greatest at or near the center of the fault and decreases to zero at its ends (Barnett et al. 1987; Walsh & Watter-son 1987, 1988, 1989; Gibson et al. 1989). Gibson et al. (1989) used relationships of fault growth model I to generate model half-graben. Specifically, the along-strike dimen-sion of the basin is given by the fault length L:

Fig. 1. Area Balance for Extension. Above: lo

is original length of section which compared

with length in deformed state and area. Below

: the regional projected horizontal, to calcu-

late depth to detachment.

Area A= Area B

l1

lo

( 1- 0)d=A=Bl l

d

Al

l

l

l1

d

( 1- 0)d=A

d=A/

l l

( 1- 0)l l

Page 24: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 24 Volume 20— February 2011

where G is the shear modulus, ∆σ is the stress drop after each seismic event, S is the incre-ment by which slip increases after each slip event (necessary for the fault to grow and for the growth sequence to match the observa-tional data), and D is the maximum displace-ment.

The preceding equations assumed that the normal faults were blind and consequently the displacement of horizons was distributed equally in the footwall and hanging wall blocks. For non-vertical synsedimentary faults (where the fault intersects the free sur-face of the earth), there is an asymmetry be-tween hanging wall and footwall displace-

Fig. 2. Three models of extensional basin development. (A) Linked fault system model involves two end members: (1) listric fault-subhorizontal

detachment and (2) planar kink fault geometry. In both instances horizontal displacement (h) on the detachment fault creates a potential void be-

tween the hanging wall and footwall, which is erased by the collapse of the hanging wall along vertical faults in (1) and antithetic faults dipping at

45° in (2). The deformation is area balanced. Adapted from Gibbs (1983) and Groshong (1989). (B) Domino fault block model in which both the

faults and the intervening fault blocks rotate during extension. i is the initial dip angle of the faults; is the dip after extension; is the dip of a horizon

that was horizontal before extension; F' is the initial fault spacing; F is the fault spacing after extension. Adapted from Wernicke & Burchfiel

(1982). (C) Essential elements of the fault growth model (modified from Gibson et al. 1989). The ruled "ellipse" is the map view of a normal fault in

which displacement is greatest at the fault center and decreases to zero at the ends. Contours represent the elevation change (positive for dotted

contours, negative for solid contours) of the originally horizontal free surface. Note that the footwall uplift is smaller than the hanging wall subsi-

dence. L is the length of the fault, R is the radius of the fault (L/2), T is fault motion toward the reader, A is away. (D) Graph of cumulative basin

volume vs. horizontal component of fault displacement for the models presented in this paper. The change in the rate of increase in basin volume is

zero for the detachment fault model, negative for the domino model, and positive for the two fault growth models.

Page 25: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 25 Volume 20— February 2011

ment of horizons, with the asymmetry in-creasing as the fault dip decreases.

3. Result and Discussion

The picture of the completed seismic line restored onto solid rock deformation using a texture drawing tool. This allows one to fol-low the deformation of the formation layers at each stage of the restoration. The results of the restoration are shown in Figure 2. The changes in fault crosscutting relationships through time. When analyzing the evolution of the sand layers, one observes that they roll back along the fault to their original horizontal position, whereas the free right border of the model translates without any rotation. Dip changes seen across faults on geoseismic lines demon-strate that most faults are listric faults. In the final restored state (stage 6 of Figure 6), the pre-rift beds are tilting as Malacca Platform. In the extensional regimes, it is important to calculate depth to detachment for the base-ment faulting. The brittle-ductile transition occurs at depth of 10-15 km. The depth of detachment estimates with simple equation (Fig.2) and given in time domain around 5000 ms. It gives geometric information, in particu-lar of deep target formation may be in seismic data acquisition in order to optimizing the structural model. Where subsidence and extensional values are required, regionally balance section is critical in providing a structural check on extension and compression factor. Total extension strain gives 0.2 from pre-rift to Mid-Miocene while in plio-pleistocene tectonic gives up to 0.6 compressed. These in turn may be important for hydrocarbon maturation and regional sub-sidence history studies. In the two fluvial wedges, the sedimentation rates (thickness/time) are everywhere equal to the incremental subsidence rates. Sedimenta-tion rates decrease toward the lateral edges and toward the hanging wall hinge of the basin. The maximum sedimentation rate in each fluvial wedge increases in progressively younger strata. In progressively younger syn-rift lacustrine strata, the maximum sedimenta-tion rate is constant or decreases slightly at the center of the basin and increases slightly in those cross sections located closer to the lateral edge of the basin. Within a given lacustrine wedge, sedimentation rates gener-ally increase toward the fault a t the center of the fault trace. The post-rift lacustrine units deposited after fault displacement ceased record a decrease in maximum sedimentation rate because their depositional surface areas increase through time, and thus the thickness of sediment deposited per unit time decreases.

These post-rift strata may be recognized by the large map region over which the sedimen-tation rate is constant within a stratal wedge. This is because these units were deposited over much of their extent on a flat-surface (the undeformed upper surface of the last synrift unit). Several giant oil and gas field have been cal-culated their extensional and compressional factor. Langkat area plotted as challenging area for future exploration based on field classification. However, compressional and extensional factor reveals that inverted tec-tonic occur intensively during basin filling history as following table and graphic :

Future basin filling models should seek to remedy the deficiencies and should be tested against a growing body of fine-scale strati-graphic data for extensional rift-basins (e.g., Olsen & Kent 1990). Nonetheless, the simpli-fying assumptions used in the models pre-sented here should not detract from the main thrust of this paper—that there are inherent tectonic differences among the three end-member models, which yield different stratal geometries and successions in modeling Langkat sub-basin.

4. Conclusions

Improving structural interpretation gains benefit by use of palinspatic restoration with area balancing. In particular, well-understand of the structural pattern and tectonic evolution of such areas can result if such techniques are integrated into seismic interpretation. While seismic section data rarely permit a unique interpretation of structure, balance geoseismic

restoration should be constructed iteratively in order to derive chronologic model. Finally, care should be taken in interpreting very spe-cific results of the basin filling models pre-sented here because: (1) the effects of com-paction and erosion of previously deposited sediments were not considered, (2) fluvial deposits were not allowed to aggrade above the outlet level of the basin, (3) the displace-ment and filling increments in all models were unrealistically large, and (4) the isostatic consequences of sediment loading were not considered. The advance analysis using sophicticated restoration software than manu-ally can reduces interpretational error inherent in seismic data.

Acknowledgements

This paper is an outgrowth of a chapter of the regional study of North Sumatra Basin. I thank to Dirjen Migas and Pertamina EP that has gave authority for publishing this paper as a poster at The HAGI 34th Annual Meeting 2009 in Yogyakarta.

References

Dahlstrom, C. D. A., 1969, Balanced cross section: Canadian Journal of Earth Sciences, v. 6, p. 743– 757. Davison, I., 1986, Listric normal fault pro-files: Calculation using bed-length balance and fault displacement: Journal of Structural Geology, v. 8, p. 209– 210. Dokka, R. K., and C. J. Travis, 1990, Late Cenozoic strike-slip faulting in the Mojave Desert, California: Tectonics, v. 9, p. 311– 340. Erickson, S. G., S. Hardy, and J. Suppe, 2000, Sequential restoration and unstraining of structural cross sections: Application to ex-tensional terranes: AAPG Bulletin, v. 84, p. 234– 249. Gibbs, A. D., 1983, Balanced cross-section construction from seismic sections in areas of extensional tectonics: Journal of Structural Geology, v. 5, p. 153–160. Hennings, P. H., J. E. Olson, and L. B. Thompson, 2000, Combining outcrop data and three-dimensional structural models to characterize fractured reservoirs: An example from Wyoming: AAPG Bulletin, v. 84, p. 830–849. Hossack, J. R., 1979, The use of balanced cross section in the calculation of orogenic contraction: A review: Journal of the Geologi-cal Society (London), v. 136, p. 705– 711. Laurent, M., Frantz, M., 2006, Chronologic modeling of faulted and fractured reservoirs using geomechanically based restoration: Technique and industry applications: AAPG Bulletin, v. 90, p. 1201–1226. Rouby, D., P. R. Cobbold, P. Szatmari, S. Demerican, D. Coelho, and J. A. Rici, 1993, Least-squares palinspastic restoration of re-gion of normal faulting— Application to the

OIL/GAS FIELD Extensional Compressional

RANTAU 0.35 0.43

KUALA SIMPANG BARAT 0.28 0.69

LIRIK 0.25 0.7

BAJUBANG 0.36 0.62

TEMPINO 0.28 0.72

KENALI ASAM 0.57 0.63

SUBAN 0.22 0.36

MUSI 0.15 0.26

PENDOPO 0.5 0.4

TANJUNG MIRING 0.27 0.43

SUNGAI HITAM 0.3 0.8

LANGKAT AREA 0.2 0.63

Page 26: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Page 26 Volume 20— February 2011

Campos Basin (Brasil): Tectonophysics, v. 221, p. 439–452. Rouby, D., H. Xiao, and J. Suppe, 2000, 3-D restoration of complexly folded and faulted surfaces using multiple unfolding mecha-nisms: AAPG Bulletin, v. 84, p. 805– 829. Sanders, C., M. Bonora, D. Richards, E. Kozlowski, C. Sylwan, and M. Cohen, 2004, Kinematic structural restorations and discrete fracture modeling of a thrust trap: A case study from the Tarija Basin, Argentina: Ma-rine and Petroleum Geology, v. 21, p. 845– 855.

Depth to detachment calculating :

A1=A2

22 KM* 3600 ms = 36 KM*DD = 2200 ms

Depth to Detachment due to isostacy

= 3600 + (3600-2200) = 5000 ms

CompressionalStrain = 0.6

Total Extensional Strain = 0.2

D

36 KM

22 KM

3600 ms

Preserved Amplitude Seismic Section

Horizon Interpretation

PalinspaticRestoration (Area Balancing)

Structural Model (Extension/Compressing and

Depth to Detachment Calculating)

33.5 KM

32 KM

30 KM

POST RIFTING PHASE

EARLY MIOCENE: Cont. sea level rise, Belumaiand Peutu Fm deposition as carbonate and clastic carbonate lithology.

RIFTING PHASE

EARLY –LATE OLIGOCENE BAWAH :

Horst-graben filled by Bampo Shale with lacustrine envirinment.

LATE OLIGOCENE : Sea level rise, Bampo shale.

FASA

PRE RIFTING

MID-EOCENE : NSB setting in edge of Sundaland

LATE-EOCENE – EARLY OLIGOCENE : Sea level fall, alluvial fan, conglomeratic sandstone of Parapat&Tampur Formation.

COMPRESSION PHASE

PLIO- PLEISTOSEN : Barisan Orogenic

Fault reactivation, right lateral faulting

Swampy depositional system.

QUIESENCE

TECTONIC PHASE

MID-MIOCENE: Basin stability(subsidence slowly; small uplift) followed by global rising sea level, Lower Baong Fm.

LATE MID-MIOCENE: Diendapakanbatupasirturbitid Duyung, Gebang dengan sumber dariutara. Dan Sembilan sand dari barat(Pegunungan Bukit Barisan sebagai sumbersedimen dari barat)

EARLY MIOCENE : Upper Baong shale, filling accomodation space. Progradational of Keutapang Fm, continued with Seurula&JuluRayeu Fm.

Fig.3. Result of Palinspatic Restoration from

Pre-rift to Compression Stage of a regional

seismic line in Langkat-Medan Area.

Page 27: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

BOOK REVIEW

Sumatra. Geology, Resources and Tectonic Evolution

Fatrial Bahesti (Pertamina)

Page 27 Volume 20— February 2011

B ARBER, A. J., CROW, M. J. &

MILSOM, J. S. 2005. Sumatra.

Geology, Resources and Tectonic

Evolution. Geological Society

Memoir no. 31. ix + 290 pp. London, Bath:

Geological Society of London. ISBN 1

8 6 2 3 9 1 8 0 7 . d o i : 1 0 . 1 0 1 7 /

S0016756806212974.

This book provides collaborative approach of

geology of Sumatra since previous publica-

tion of van Bemmelen, the Dutch geologist

who published a ‘comprehensive and mas-

terly summary’ of the Geology of Indonesia,

initially in 1949. Much of the geological re-

search conducted in Sumatra in the latter part

of the twentieth century has been carried out

by the British Geological Survey and the

University of London SE Asia Research

Group. The whole island has been mapped

geologically at the reconnaissance level and

completed in the mid-1990s, together with

supplementary data obtained by academic

institution and petroleum and mineral explo-

ration companies, has resulted in a vast in-

crease in geological information, which is

summarized in this volume. The editors and

most of the contributors are associated with

these organizations and are thus able to draw

on considerable personal experience. In addi-

tion they have incorporated references to

pretty much every single paper or book to

have dealt with the geology of the island. It

thus follows in the tradition of Van Bem-

melen.

The opening part of this book presents a con-

cise introduction to the topic of Seismology

and Neotectonics that contains some late ad-

ditions which provide a comprehensive sum-

mary of the information that became available

immediately after the 2004 Sumatra’s earth-

quake and tsunami and has a note added in

proof to include data from other after-

shocks up to the end of April 2005. It might

therefore seem prescient to have planned the

publication of a memoir describing the geol-

ogy of Sumatra for 2005. In comparison to

other publications that have followed the

earthquake, this volume can fairly claim to

provide a comprehensive context in which to

place these momentous geological events.

There is much more to the geology of Suma-

tra than its present-day position above an

active subduction zone. It also contains one of

the world’s most prominent strike-slip faults

(the Sumatra Fault), an active volcanic arc, a

partially emergent forearc, and an extensive

back-arc region. It contains a globally signifi-

cant petroleum province, some coal reserves

and more limited mineral resources. The

geological evolution of the island can be

traced back to the Carboniferous or older.

A review of Granites and Pre-Tertiary vol-

canic rocks of Sumatra gives a valuable

history of the exploration and development

of recently oil and gas discovery in fracture

basement system in Sumatra, which played an

important role in establishing the concept, and

provides a general introduction to the geology

of the Northern and Southern Provinces.

There are a few papers in Indonesia con-

cerned with Pre-Tertiary fracture basement

play and magmatism Paleozoic island arc

development on the active margin of Sumatra.

Palaeozoic orogeny in the Sumatra consider

the subduction history of the Sundaland mar-

gin and its implication to describe

pre-tertiary basin present in Suma-

tra.

More specifically, a gap in the cur-

rent treatment is the limited cover-

age of the basins containing hydro-

carbon reserves. Oil company data

is always subject to the constraint

and confidentially, particularly in

Indonesia given the involvement of

Directorate of Oil&Gas in all li-

cences, but it would have been

interesting to see some of the com-

prehensive datasets that must exist

in these areas and would help to

address the thorny question of the

extent to which strike-slip deforma-

tion is associated with the formation

and subsequent inversion of the

Sumatra basins. In addition, the

BGS and University of London

projects were models of construc-

tive collaboration with Indonesian

organizations and it is perhaps a

pity that none of their Indonesian

counterparts are represented

amongst the authors. There is no

doubt that this volume will replace Van

Bemmelen as the standard reference for any-

one working in Sumatra and will no doubt be

the focus of much more work in the years to

come. Additionally, it guides the reader

through further information sources such as

other geological, geophysical, geochemical,

and mineral maps covering the area. It also

points the reader towards the nationally im-

portant archive of resources.

Overall, this is an excellent book and cer-

tainly represents compulsory reading for

undergraduate and postgraduate students

who wish to carry out research and revisiting

of Sumatra’s resources exploration. The

booklet is well referenced. With over 200

pages, and packed with illustrations and

photographs (all black-and-white), it repre-

sents excellent value for money. It also

serves its intended purpose as an excellent

reference guide for more experienced re-

searchers who may need reminding of the

exploration opportunity.

Page 28: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

As Berita Sedimentologi journal aimed to

bridge communications, the editor has pre-

pared a special column for the academia, both

lecturer and students.

University

Page 28 Volume 20— February 2011

Page 29: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Special Publication #95

Cenozoic Carbonate Sys-

tems of Australasia

Edited by: William A. Morgan,

Annette D. George, Paul M.

(Mitch) Harris, Julie A. Kupecz,

and J.F. (Rick) Sarg

The Cenozoic carbonate systems

of Australasia are the product of

a diverse assortment of deposi-

tional and postdepositional proc-

esses, reflecting the interplay of

eustasy, tectonics (both plate and

local scale), climate, and

evolutionary trends that influ-

enced their initiation and development. These

systems, which comprise both landattached

and isolated platforms, were initiated in a

wide variety of tectonic settings (including

rift, passive margin,

and arc-related) and under warm and cool-

water conditions where, locally, siliciclastic

input affected their

development. The lithofacies, biofacies,

growth morphology, diagenesis, and hydro-

carbon reservoir potential of these

systems are products of

these varying influences.

The studies reported in

this volume range from

syntheses of tectonic and

depositional factors influ-

encing carbonate

deposition and controls

on reservoir formation

and petroleum system

development, to local

studies from the South

China Sea, Indonesia,

Kalimantan, Malaysia,

the Marion Plateau, the

Philippines, Western Australia, and New

Caledonia that incorporate outcrop and sub-

surface data, including 3-D seismic imaging

of carbonate platforms and

facies, to understand the interplay of factors

affecting the development of these systems

under widely differing

circumstances.

This volume will be of importance to geo-

scientists interested in the variability of Ceno-

zoic carbonate systems and

the factors that

controlled their

formation, and to

those wanting to

understand the

range of potential

hydrocarbon

reservoirs discovered in these carbonates and

the events that led to favorable reservoir and

trap development.

SEPM Membership for potential members

in Indonesia

Interested on sedimentological international

publications? You can now join SEPM for

US$20/year. For easy access registration

form, go to the following link:

https://www.sepm.org/Forms.aspx?

pageID=224

SEPM NEWS

origin of ooids;

coastal sedi-

ments; forma-

tion of stromato-

lites; impact of

storms on sedi-

ments; and the

formation of

dolomite. The remainder of the papers apply

the study of modern environments and sedi-

mentary processes to ancient sediments.

Other details about IAS is available in:

http://www.sedimentologists.org/

capability of the researcher, and reasonable-

ness of the budget.

SP41 - Perspectives in Carbonate Geology

Swart, P., Eberli, G., McKenzie, J. (Wiley-

Blackwell, 2009 - ISBN 978-1-4051-9380-1)

This special publication Perspectives in Car-

bonate Geology is a collection of papers most

of which were presented at a symposium to

honor the 80th birthday of Bob Ginsburg at

the meeting of Geological Society of America

in Salt Lake City in 2005. The majority of the

papers in this publication are connected with

the study of modern carbonate sediments.

Bob Ginsburg pioneered the concept of com-

parative sedimentology - that is using the

modern to compare to and relate to and under-

stand the ancient. These studies are concerned

with Bob's areas of passion: coral reefs and

sea-level; submarine cementation and forma-

tion of beach rock; surface sediments on

Great Bahama Bank and other platforms;

Up to 10 grants of about 1000€ twice a year

The IAS has established a grant scheme de-

signed to help PhD students with their studies

by offering to support postgraduates in their

fieldwork, data acquisition and analysis, visits

to other institutes to use specialised facilities,

or participation in field excursions directly

related to the PhD research subject. Up

to 10 grants, each of about1000€ are awarded

twice a year. These grants are available for

IAS members only, and only for PhD stu-

dents. Students enrolled in MSc programs are

NOT eligible for grants. Research grants are

NOT given for travel to attend a scientific

conference, NOR for acquisition of equip-

ment. Student travel grants for conferences

can be usually obtained directly from organiz-

ers of the meeting.

The Postgraduate Grant Scheme Guide-

lines provide a summary of required informa-

tion needed for a successful Grant Applica-

tion. Applications are evaluated on the basis

of the scientific merits of the problems, the

IAS NEWS

Page 29 Volume 20— February 2011

Page 30: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Call For Paper

In repeating the previous similar successful

events, joint convention between HAGI and

IAGI: Joint Convention Jakarta in 2003, Joint

Convention Surabaya in 2005, and Joint Con-

vention Bali in 2007, this Joint Convention

Makassar is delivering a theme of Exploring

Eastern Indonesia to represent the spirit of

current exploration and research of geology

and geophysics in Indonesia. Its challenge,

opportunities, process, concept, technology,

remarkable research, and experiences, in ex-

ploring energy (petroleum, mineral, coal,

nuclear, etc.) and understanding the earth

should be discovered on Joint Convention

Makassar 2011.

36th HAGI and 40th IAGI Joint Convention

Makassar 2011

Date

26 – 29 September 2011, Clarion Hotel

Makassar, South Sulawesi

Theme

“Exploring Eastern Indonesia”

Topics

Natural Resources of Indonesia

Mineral and Energy Resources Management

Environmental Issues

Hazard Mitigation

Geodynamics, Seismol-

ogy, Volcanology

Atmospheric Science,

Oceanography, Marine

Geology

Sedimentology and Strati-

graphy

G&G Methods, Technol-

ogy and Application

Engineering Geology

Unconventional Geology

& Geophysics

Mix Energy Sce-

nario and Policy

Abstracts

Authors are invited

to submit the abstracts related to the topics.

Acceptance of paper would be selected on

condition of maximum 300 words, covering

objectives, methods, results, and conclusions,

preferably written in English. Abstract should

not contain figures. Author should indicate

his/her preference in presenting the paper as

oral or poster presentations.

Submit abstract to: [email protected]

Submission deadline: 11 February 2011

Announcement: 15 March 2011

Extended Abstract deadline: 30 April 2011

JCM 2011 Secretariat

Patra Office Tower 20th Floor. Suite 2045

Jl. Gatot Subroto Kav. 32-34

South Jakarta 12950

Tel / Fax:. +62-21-5250040

IAGI NEWS

GTW –

October 2010

The Asia Pa-cific Region saw a success-ful conclusion to its inaugural Geosciences Technology Workshop (GTW) which took place on the 28-29 October 2010 in Singapore. The GTW theme of “Pore Pres-sure and Related Issues – Special Focus: Asia Pacific” was particularly pertinent as the Asia-Pacific region contains numerous rap-idly formed and highly overpressured basins and is an area in which pore pressure predic-tion is particularly challenging. The GTW was attended by 88 delegates and contained 23 presentations from industry experts, among whom were Keynote Presenters Rich-ard Swarbrick of GeoPressure Technology UK and Nader Dutta of Schlumberger USA. Running alongside the GTW were two short courses on Pore Pressure and Petroleum Ge-omechanics, taught by Richard Swarbrick and Mark Tingay (University of Adelaide) respec-

tively.

•University of Pembangunan Nasional

“Veteran” Yogyakarta (Indonesia)

•University of Indonesia (Indonesia)

In this global competition, university teams analyze a dataset (geology, geophysics, land, economics, production infrastructure, and other relevant materials) in the eight (8) weeks prior to their local competition. Each team delivers their results in a 25 minute pres-entation to a panel of industry experts. Stu-dents have the chance to use real technology on a real dataset, receive the feedback from an industry panel, have the opportunity to impress potential employers in the audience, and the chance to win cash awards for their schools. The industry panel of judges will select the winning team on the basis of the technical quality, clarity and originality of its presentation. The judging will take place over 1-3 March 2011. We wish the Teams all the

best!

More information can be obtained

from www.aapg.org/iba

10 Teams to participate in the Asia Pacific

IBA competition

In order to represent the Asia Pacific at the AAPG 2011 Imperial Barrel Award competi-tion at the AAPG ACE2011 in April, 10

teams are vying for this honour :

•Indian Institute of tech-

nology, Bombay (India)

•Indian Institute of Technology Kharagpur

(India)

•Indian Institute of

Technology Roorkee

(India)

•Pandit Deendayal Petroleum University

(India)

•Khon Kaen University (Thailand)

•Chulalongkorn University (Thailand)

•China University of Petroleum (China)

•Institute of Technology Bandung (Indonesia)

AAPG NEWS

Page 30 Volume 20— February 2011

Page 31: Editorial Board - IAGI · Kelurahan Manggar, Balikpapan 76117, Kalimantan Timur, Indonesia, E-mail : julianta_panjaitan@yahoo.com Editorial Board • Published 3 times a year in February,

Size of Advertisement

A5

Width 210 mm

Height 148 mm

US$ 100

Landscape setting

A4

Width 210 mm

Height 297 mm

US$ 150

Portrait setting

This price is for one-off adverts.

For annual contributions and advertisement ,

please contact one of the editors.

For payment method, please contact Herman

Darman ([email protected]).

Sponsorship for FOSI

Guidance for contributors

of 200 DPI resolution, submitted in JPG or

TIFF format.

The whole article, text and figures, should not

exceed 5 pages of A4.

For the setting of the article, contributors can

follow one of the existing article from this or

previous bulletin.

The editorial board welcome articles related

sedimentary rocks in Indonesia, Southeast

Asia and vicinity. The topic and deadline of

the coming Berita Sedimentologi bulletin are

stated below.

Contributors are expected to submit their

article in Microsoft Word, ASCII / Text or

PDF format.

Pictures need to be annotated with minimum

Berita Sedimentologi is

voluntarily prepared by

And for the benefit of

FOSI MEMBERS

Page 31 Volume 20— February 2011

The editorial board will prepare 2011-2012

publications with the following schedule and

topics

2011

February 2011 (this edition): Sumatra

June 2011: Borneo / Kalimantan

• Title deadline: 10 April 2011

• Article deadline: 10 May 2011

October 2011: Java

• Title deadline: 10 August 2011

• Article deadline: 10 September 2011

2012

February 2012: Papua

• Title deadline: 10 December 2011

• Article deadline: 10 January 2012

June 2012: Timor

• Title deadline: 10 April 2011

• Article deadline: 10 May 2011

October 2012: Halmahera

• Title deadline: 10 August 2012

• Article deadline: 10 Septeber 2012

Future Berita Sedimentologi

Note: Depends on the number of articles, editors may change the topic