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IJOG

21IJOG/JGI (Jurnal Geologi Indonesia) - Acredited by LIPI No. 547/AU2/P2MI-LIPI/06/2013, valid 21 June 2013 - 21 June 2016

Indonesian Journal on Geoscience Vol. 1 No. 1 April 2014: 21-34

INDONESIAN JOURNAL ON GEOSCIENCEGeological Agency

Ministry of Energy and Mineral Resources

Journal homepage: h�p://ijog.bgl.esdm.go.idISSN 2355-9314 (Print), e-ISSN 2355-9306 (Online)

Limestone Microfacies of Baturaja Formation along Air Rambangnia Traverse, South OKU, South Sumatra

Sigit Maryanto

Centre for Geological Survey, Geological Agency Jln. Diponegoro No. 57 Bandung - 40122

Manuscript received: February 14, 2012, revised: March 18, 2013, approved: April 1, 2014Corresponding Author: [email protected]

Abstract - Limestones of the Baturaja Formation occur at Air Rambangnia traverse, South Ogan Komering Ulu, South Sumatra, and they are used as objects for microfacies studies. The microfacies studies are based on a detailed petro-graphic analysis of thirty four limestone samples, taken from the traverse. Four types of the limestones are identified such as wackestone, packstone, grainstone, and floatstone. At least five microfacies form the limestone succesion of the Baturaja Formation. They are interpreted as sedimentary facies of very restricted bay and pond, back reef local slope, slope and shelf edge, winnowed platform edge sand, and reef flank facies.

Keywords: Baturaja, limestone, petrography, microfacies, sedimentary facies

Introduction

The term microfacies was first put forward by Brown (1943; in Flugel, 1982). It is defined as extensively discrete paleontology and sedimen-tology aspects, that can be grouped based on the type and number of components in petrographic thin section and polished sample examination. Thereby, microfacies identifies environment of deposition based on petrography data (Maryanto, 2005 and 2008). Based on the type and number of components, Flugel (1982) divides microfacies of limestone into twenty-four types according to the former division of facies zone by Wilson (1975).

Wilson and Rosen (1998) stated that carbonate platform in the western part of Indonesia has ap-peared since the Late Oligocene. Bishop (2000a) concluded that the Early Miocene of Baturaja Formation consists of carbonate platform sedi-ments having totally thickness of 60 - 120 m. Bishop (2000b) divided Baturaja Formation into two lithostratigraphic units based on deposition, i.e. clastic sedimentary facies and limestone or carbonate rock facies.

The researched location was along Air Ram-bangnia River, in between Baturaja and Muaradua towns, administratively belonging to the area of South Ogan Komering Ulu (OKU) Regency, South Sumatra Province (Figure 1). The carbon-ate rocks from Baturaja Formation are well found along the Air Rambangnia traverse. This article was written with the aim to study the environment and deposition mechanism of those limestones based on petrography data in relation to the divi-sion of limestone microfacies.

Methodology

In order to achieve the study purpose, the research method includes field data collection and laboratory analysis. Field data collection is a systematical rock sampling, which is based on the results obtained by making detailed strati-graphic column along Air Rambangnia traverse. Laboratory work was done by quantitatively petrographic analysis with point-counter for as many as 300 counts (Maryanto, 2007a). Important

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Indonesian Journal on Geoscience, Vol. 1 No. 1 April 2014: 21-34

22

aspects of petrography to be identified include: 1. the proportion of major components, such as

carbonate grains, terrigenous grains, matrix, neomorphism materials, cement, and rock porosities

2. identification of the characters of each com-ponents,

3. texture of rocks that include fabric, sorting, grain size, and shapes. The classification is determined according to Dunham (1962) de-veloped by Embry and Klovan (1971). Microfacies interpretation of the limestones

from the Baturaja Formation along Air Rambang-nia traverse is divided according to the standard classification of microfacies from Flugel (1982) and facies zone from Wilson (1975). As a compari-son, there are also references from many authors that discuss microfacies and limestone depositional environment, such as Andreeva (2008), Jones and Desrochers (1992), Kindler and Hearty (1996), Read (1985), and Tucker and Wright (1990).

Geological Review

Regional geology in-between Baturaja and Muaradua area is preceded by Pre-Tertiary rocks

consisting of granite, andesite-basalt, metasedi-ment, mélange, and metamorphic rocks. Uncon-formable overlying the basement rocks there are several Tertiary Formations of Kikim, Talangakar, Baturaja, Gumai, Airbenakat, Muaraenim, Ranau, Kasai, and Alluvium (Gafoer et al., 1986, 1993; Figure 2). Limestone of the Baturaja Formation in general was deposited in the back-reef environ-ment behind the edge of the basin during the Early Miocene (Maryanto, 2007b). Layered limestone can be observed directly along the Air Rambangnia traverse. The rocks are generally sloping ramps to the east (Figure 3), with the total thickness of about 220 m, measurable reach including carbonate rocks from the Baturaja Formation of 196 m thick.

Volcanic rocks of the Kikim Formation are presented as a basement. It consists of volcanic breccias, volcanic sandstone, mudstone, and conglomeratic sandstone, with andesite lava inser-tions. The Baturaja Formation limestone uncon-formably overlies the Kikim Formation (Figure 4).

The lower part of Baturaja Formation was initiated by the presence of grainstone containing some pore-dissolving porosities. Furthermore, the rocks become developed onto layered wackestone-packstone that partially argillaceous with oriented fossils of mollusks (Figure 5) and algae. Several

Figure 1. Location map of South Sumatra Province and the investigated traverse at Air Rambangnia River.

102 E 103 104 105 106 Eo o o o o

oo

oo

oo

o o oo

0303

04 S04 S

02 S02 S

102 E 103

PALEMBANG

Menggala

Kotabumi

Muaradua

Martapura

Baturaja

Lahat

Muaraenim

Prabumulih

Sekayu

Sarolangun

Bangko

Muarabulan

Sungailiat

Pangkalpinang

Kayuagung

Investigated Traverse

105 E104

Manna

Pagaralam

Bengkulu

Curup

ArgamakmurLubuklinggau

JAMBI

BENGKULU

LAMPUNG

BANGKA BELITUNGSOUTH SUMATRAPROVINCE

0 100 Km

N

HINDIA OCEAN

bangka Strait

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Limestone Microfacies of Baturaja Formation along Air Rambangnia Traverse, South OKU, South Sumatra (S. Maryanto)

23

Figure 2. Geological map of Muaradua area, South Sumatra (Gafoer et al., 1993) and locations of Air Rambangnia traverse (Maryanto, 2007a and 2008).

Tomt

Tmg

Tma

Tmpm

Qa

Qtk

Qhv

Qhv

TpokTmg

Tma

Qtk

Tmb

Tmb

Tpok

Tmg

TmaQtk

Qtk

Tmpm

Tma

Tmb

Tmpm

TmaTmg

Tmb

Tpok

Qtk

.

Kjgv

KjgvTpok

Pct

Kgr

Tpokc

Tpokc

Tmg

Qv

Qv

Qtr

QtrQtr

QtrQtr

QtrTma

Tma

Qa

Tmb

Tmpm

Tmg

Tmb

Tmpm

TmgTmpm

Qa

Qa

Qa

Kgr

Pct

Kgr

Kgr

PCt

Tmb

Qa

Kjgv

Kjgv

Km

KJg

Kjg

Qtr

Qtr

Qtk

Qtk

Tmb

KJgs

Pct

Kjgs

Tpok

Qa

Tmb

Tomt

Tpokc

Tomt

Qa

Kgr

Tmpm

Tmb

Tomt

Tma

Pct

Tomt

Air Kiti

Air Kura-kura

Air

Bu

luh

Air T

eban

gka

Air L

ahat

Air Saman

Air Lengkajap

Air Tamba

Air Suban Besar

Air

Laja

Air Kem

u

Air G

ilas

Air Saka

Air Batu-batu

Air

Nap

alan

Air Rambangnia

Air Malau

Air Saka

Air Selabung

Air Komerin

g

Tpok

10

15

15

10

25

17

19

12

15

15

15

15

13

17

2410

15

15

BATURAJA

Batuiputih

Negerisindang

Kungkilan

Penyandingan

Sundan

Sukoraja

Sagarakembang

Negeriratu

Sabahlioh

Tanjungkurung Simpang

Karangagung

Baturaja

Tanjungbringin

Negeriagung

Kotakarang

Sukaraja

Kotamarga

Gedong

MUARADUA

Umbulantelok

Umbulanmeliku

Airbungin

MehangginSaungnaga

Qhv

004

06’

S0

04 3

5’S

004

35’S

004

06’

S0103 54’ E

0103 54’E 0104 15’E

0104 15’ E

INDEX MAP

EXPLANATION:

Alluvium

Tuff Volcanic Unit

Volcanic Unit

Kasai Formation

Ranau Formation

Muaraenim Formation

Airbenakat Formation

Gumai Formation

Baturaja Formation

Talangakar Formation

Kikim Formation

Cawang Mem. Kikim Fm.

Melange Complex

Garba Formation

Insu Mem. Garba Fm.

Situlanglang Mem. Garba Fm.

Garba Granite

Tarap Formation

Air Rambangnia Traverse

Tmb

Tmg

Tma

Tmpm

QTk

QTr

Qhv

Qv

Qa

Tomt

Tpok

Tpokc

Kgr

KJgs

KJgv

Kjg

Km

Pct

0 10 Km

NP

RE

-TE

RT

IAR

YPA

LE

OG

EN

EM

IOC

EN

EQ

UA

RT

ER

NA

RY

SUMATERA

floatstone intercalations are found containing some coral skeletons. Stylobed is interlayering between wackestone-packstone with marl ended the deposi-tion of the lower part of Baturaja Formation.

The middle part of Baturaja Formation is composed of floatstone (Figure 6), of which later evolved into argillaceous wackestone. Interlayers between floatstone with wackestone-packstone

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dominated the sequence, which are later fining upward onto sometimes argillaceous wacke-stone-mudstone. The next lithology is found as floatstone.

The upper part of Baturaja Formation begins with the presence of wackestone-mudstone lay-ers. Stylobedded and or siliceous concretional bedding reaches 80 cm in size are often found in these layers (Figure 7). The concretional bedding sometimes has a parallel direction to the bedding (forming lens) and it shrinks to the upper part. The above concretional beddings are overlain by gradational and planar cross-bedding grain-stones (Figure 8). Carbonate rock sequences in this traverse is ended by wackestone-packstone sometimes with dissolving porosities.

The carbonate rocks of Baturaja Formation partially do not crop out along Air Rambang-nia traverse, especially between sites 306-213. Among that locations, the clastic sedimentary rocks from Muaraenim Formation are exposed in the form of claystone containing limestone boul-ders. The sedimentary rocks are preserved due to a tectonic strike-slip fault in N33oE direction.

Petrography

Based on a detailed petrography analysis, the limestone types recognized are wackestone, packstone, sandy packstone, grainstone, and float-stone. Each of these rocks, including the number and type of the rock components would later be used as the basis for microfacies determination (Table 1).

Wackestone Wackestone group also includes sandy

mudstone-wackestone, which is present as an intercalation. The rocks are generally massive with fine-grained fragmental bioclastic texture. Bioclast always occur and comprises diverse type, size, and amount of fossil. Nevertheless, fossil types composing the rock can be identified, such as red algae, mollusks, and foraminifera. Rarely intraclast or extraclast are preserved in the rocks, the same as the presence of pellets. Terrigenous materials are still observed in some rock samples with limited amounts, scatteredly, and uneven. They are composed of quartz, feldspar, volcanic

Figure 3. Detailed stratigraphic measured map along Air Rambangnia traverse (Maryanto, 2007a and 2008) and sample locations.

Figure 3. Detailed stratigraphy measure map along Air Rambangnia traverse (Maryanto, 2007a & 2008) and sample locations.

0 400 m

N

305

05SM305

EXPLANATION:

Outcrop location

Strike and dip

Fault (predicted)

Number of site

Sample location

River flow direction

10

301

302

303304

305 306

307308

309

310

311

312

313314 315

316

317318

319

320321

322

323324

325 326

327

24

108 7

15

128

10

8

10 1210

SM301ASM302ASM302B

SM303ASM303BSM304ASM304BSM304CSM304D

SM305ASM305BSM305C

SM309

SM310

SM314ASM314BSM315ASM315B

SM316ASM316BSM317ASM317BSM318ASM318B

SM320ASM320BSM321ASM321BSM323A

SM323B

SM323CSM323DSM323E

SM324A

SM324BSM324CSM325ASM325B

Volcanic breccia andsandstone withmudstone andlava intercalations

Conglomeratic sandstone overlainby packstone

Argillaceous wackestone with floatstone intercalations

Bedded wackestone sometimes argillaceous

Clayey sandstone

Argillaceous wackestone

Carbonaceousmudstone and sandstone

Floatstone

Floatstone and wackestonesometimes argillaceous

Bedded floatstone withargillaceous packstone-wackestone

Bedded floatstone with argillaceous packstone-wackestone

Argillaceous wackestone-mudstoneThick bedded floatstone

Argillaceous wackestone-mudstoneArgillaceous wackestone-mudstone

Argillaceous wackestone-mudstonewith lot of concretions

Argillaceous wackestone-mudstonewith concretion bedding

Argillaceous wackestone-mudstoneoverlied by grainstone

Grainstone, wackestone and packstone

Bedded wackestone-packstone

A B

Section A - B

AlluviumKikim Formation Baturaja Formation

B

ATo Muaradua

To Baturaja0S 04 25’ 11,3”0E 104 08’ 40,0”

0S 04 25’ 08,5”0E 104 09’ 30,5”

0 0S 04 25’ 10,0”, E 104 09’ 02,6”

SM326

196 m

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Figure 4. Detailed lithostratigraphy column along Air Rambangnia traverse, OKU Selatan, South Sumatra (Maryanto, 2007a & 2008, with modifications).

A G

E

U N

I T

S

LITH

OLO

GY

SY

MBO

L

LITHOLOGY DESCRIPTION

THIC

KN

ESS

(met

er) A

ND

SAM

PLE

CO

DE

GR

AIN

SIZ

EA

ND

SE

DIM

EN

TAR

YST

RU

CT

UR

E

MIC

RO

FA

CIE

S

CL ST

FSMS

CSGR

PBCO

BO

CL ST MS GR

PBCO

BOFS CS0

55

110

165

220

B A

T U

R A

J A

Volcanic breccia and sandstone cruedly bedded with intercalations of mudstone, conglomeratic sandstone, and andesite lava

SM301A

KIK

IM

EO

CE

NE

-OL

IGO

CE

NE

SM302A

SM302B

SM303ASM303B

SM304A

SM304BSM304C

SM305BSM305ASM304D

SM305C

SM314ASM314BSM315A

SM315B

SM316ASM316BSM317ASM317B

SM318ASM318B

SM320A

SM320B

SM321ASM321B

SM323A

SM323CSM323DSM323ESM323B

SM324A

SM324BSM324C

SM325ASM325B

SM326

Stylobedded grainstone with several dissolution pores

Wackestone-packstone generally argillaceous with fossilsdominated by molluscs and algae

Low

er P

art

Mid

dle

Par

tU

pper

par

t

Wackestone bedded, sometimes argillaceous with floatstonerudstone intercalations

Floatstone coral and lithoclast with molluscs-rich matrix

Wackestone generally argillaceous with molluscs orientation

Floatstone thick bedded and poorly sorted

Floatstone interlayering with packstone-wackestone

Wackestone-mudstone partially argillaceous

Thick bedded floatstone partially develop to rudstonewith wackestone intercalations

Wackestone-mudstone partially with quartzitic concretion

Stylobedded wackestone-mudstone

Wackestone-mudstone partially chalky and recrystallized with lot of concretion fining upward

Grainstone sometimes with cross-bedded structure

Bedded packstone-wackestone with various fossils

E A

R L

Y

M

I O

C E

N E

Fau

lt Z

one

SMF11-FZ6

SMF12-FZ6

SMF10-FZ7

SMF19-FZ8

SMF5-FZ4

SMF10-FZ7

SMF5-FZ4

SMF5-FZ4

SMF10-FZ7

SMF10-FZ7

SMF5-FZ4

SMF5-FZ4

SMF5-FZ4

SMF10-FZ7

SMF19-FZ8

SMF19-FZ8

SMF3-FZ3

SMF10-FZ7

SMF10-FZ7

SMF19-FZ8SMF12-FZ6

SMF12-FZ6SMF12-FZ6

SMF12-FZ6

SMF10-FZ7SMF10-FZ7

SMF10-FZ7

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and sedimentary rock fragments, unidentified rock fragments, phosphate, and glauconite. Car-bonate mud matrix often have changed into mi-crosparite, some even have recrystallized to form pseudosparite together with carbonate grains.

Clay mineral matrix in general is inseparable with carbonate mud matrix. The cement material is always present with very limited quantities, par-ticularly as orthosparite, iron oxides, authigenic clay minerals, and silica.

Packstone Packstone is generally massive with fine- to

medium - grained fragmental bioclastic texture. Bioclast is composed of diverse type, size, and amount of fossil, however, it is predominated by red algae, mollusks, and foraminifera. Intra-clast or exstraclast is present on the coarser size of limestone fragments, spread unevenly, and consists of coralline, bioclastic, and argillaceous limestones. Less amount of very fine pellet some-times changes into microsparite. Sparsely, terrrig-enous materials are still present sporadically dis-tributed, or sometimes excessively influence the rock name to become sandy. The rock matrix is mainly preserved as carbonate mud, which often changes onto microsparite and/or is recrystallized to form pseudosparite together with carbonate grains. Cement materials are always present in the rocks as various amount of orthosparite calcite, and rarely of iron oxides.

Grainstone Grainstone is generally massive with medium-

to coarse - grained fragmental bioclastic texture. Bioclast is quite dominant consisting of various kind, size, and amount of fossil. Intraclast or extraclast is observed unevenly in some coarse-

Figure 5. Massive marl contains a lot of mollusk mouldics, this point is as the lower part of the Baturaja Formation. Photographed in the 303 site of the Air Rambangnia traverse.

Figure 6. Very poorly sorted floatstone composing of the middle part of Baturaja Formation. Photographed in the 314 site of the Air Rambangnia traverse.

Figure 7. Outcrop of wackestone-mudstone containing siliceous concretions, is a constituent of the upper part of Baturaja Formation. Photographed in the 322 site of Air Rambangnia traverse.

Figure 8. Grainstone overlying mudstone-wackestone, pres-ents as a constituent of the upper part of Baturaja Formation. Photographed in the 324 site of Air Rambangnia traverse.

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Table 1. Petrography Analysis Summary of the Limestones from Baturaja Formation along Air Rambangnia Traverse, South Sumatra (Maryanto, 2007a)

SAMPLE CODEDESCRIPTION

SM302B

SM303A

SM303B

SM304A

SM304C

SM304D

SM305A

SM305B

SM305C

SM314A

SM314B

SM315A

SM315B

Structure m m o m m m m m f m o f m m m m o mTexture bf bf bf bf bfc bfc bf bf bf bf bf bf bfSorting m p p p p p p p p vp p vp vpFabric c c c o o o o o o o o o o

Av. grain size (mm) 1.80 0.70 1.40 0.30 0.20 0.20 0.20 0.80 0.20 0.80 0.80 1.20 1.80Grain shape sr sr sr sr sr sr sr sr sr sr sr sr sa

Grain contacts p l c p l c p l c f f f f p f f f p f f p f p lPercentages

Carbonate GrainsGreen algaeRed algaeBryozoansEchinodermsCoralBenthic foraminiferaPlanktonic foraminiferaBrachiopodsMoluscsOstracodsSponge-spiculesBioturbationUnidentified fossilsIntraclasts / extraclastsPellet / peloidsOolite / oncolite

-1.674.332.674.676.001.332.00

15.00---

8.335.33

--

10.671.33

-4.00

-3.00

-1.33

16.33---

6.33---

-1.330.67

--

4.00--

7.33---

24.672.670.67

-

-0.33

-1.33

-8.00

--

5.33---

2.00---

--

0.33--

0.67--

4.00---

9.67---

-0.33

---

0.67--

1.67---

9.67---

-0.670.674.67

-5.671.001.004.332.67

--

5.001.33

--

--

1.001.330.677.33

-0.675.670.67

--

3.671.67

--

-1.67

-0.67

-1.67

-0.675.000.33

--

3.33---

-0.670.671.00

-1.67

-1.336.00

---

5.00---

-1.672.331.331.330.67

-1.3313.001.670.67

-5.335.67

--

-0.671.331.333.336.330.671.334.001.670.67

-6.003.331.33

-

-2.331.671.338.335.000.672.004.672.33

-1.003.004.331.00

-Terrigenous Grains

QuartzFeldsparRock fragmentsGlauconitePhosphateOpaque mineralsCarbon

1.33-

1.33--

0.67-

4.670.336.33

--

0.67-

3.331.33

10.33--

1.33-

2.670.672.00

----

1.00-

1.33----

-------

0.67-

3.00--

0.67-

1.000.671.67

-0.670.67

-

0.670.331.33

----

3.672.332.00

-1.000.670.67

1.000.331.33

----

1.670.33

---

1.33-

0.33-----

0.67Matrix

Carbonate mudClay minerals

--

3.3332.33

-4.67

22.00-

--

--

50.333.00

10.33-

15.00-

6.00-

26.67-

34.006.00

39.33-

Cementing MaterialsOrthospariteIron oxidesAuthigenic claysSilica

9.672.67

--

-3.00

--

-1.672.00

-

0.670.67

-1.33

-1.00

--

2.000.672.332.67

1.673.33

-0.33

4.002.330.67

-

3.001.67

--

4.001.331.672.67

3.333.67

--

8.001.67

--

6.331.67

-1.00

NeomorphismsMicrosparitePseudospariteDolomiteMicritized mudPyrite

16.336.337.001.330.67

-----

-26.006.001.00

-

52.33----

-21.6759.33

--

-24.0051.67

--

5.672.00

-0.67

-

20.335.0028.00

--

9.001.0051.330.67

-

17.008.33

28.332.33

-

7.333.33

16.001.00

-

8.003.00

-0.672.67

5.674.00

-1.330.67

PorositiesIntraparticleMouldicVuggyIntercrystalShelter dan fenestraeFracture

--

1.33---

-1.001.67

-2.331.33

--

1.00---

--

0.67---

---

1.00--

--

4.33---

--

1.00--

0.67

-0.671.67

--

0.67

--

2.00-

1.67-

--

1.67---

--

1.00---

--

0.67---

--

1.33---

Rock Name G SP SP W W W W W W W W W W/F

SMF / FZ 11/6 12/6 12/6 10/7 19/8 19/8 10/7 10/7 19/8 10/7 10/7 10/7 5/4

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Table 1. .............continued (Maryanto, 2007a)


SM316A

SM316B

SM317A

SM317B

SM318A

SM318B

SM320A

SM320B

SM321A

SM321B

SM323A

SM323B

SM323C

Structure m m o m m m m m f m m f m o m o m p mTexture bf bf bf bf bf bf bf bf bf bf bf bf bfSorting vp p p p p p p p p p p p pFabric c c c o c o c c o o o c o

Av. grain size (mm) 1.40 1.45 1.40 0.70 1.60 0.70 1.40 0.40 0.20 0.15 0.15 0.35 0.15Grain shape sr sr sr sr sr r sr sr r sr r r r

Grain contacts p l c p l c p l c f p l c f p l c p l c f f f p l p l c f p lPercentages


-2.331.671.334.67

16.330.330.675.670.67

-1.334.679.330.67

-

-2.331.331.332.67

17.002.331.3313.671.67

--

2.001.330.67

-

4.004.332.331.335.337.000.671.0021.670.33

-1.005.004.001.33

-

-1.33

-1.004.003.330.67

-4.67

---

3.00---

2.673.671.331.004.009.670.672.33

19.33--

0.673.003.002.67

-

-1.001.001.332.671.67

-0.677.670.33

--

6.00-

1.33-

0.675.335.331.332.677.670.671.0012.33

-0.331.336.337.330.67

-

-1.674.331.671.674.332.672.339.671.00

-0.675.004.001.67

-

-1.671.001.33

-4.671.001.678.00

---

6.00---

-1.67

-1.33

-4.002.67

-2.33

---

6.33-

5.00-

-0.67

-5.33

-1.33

16.33-

7.33---

6.00---

-0.670.672.330.671.33

19.674.00

10.333.00

--

6.002.67

--

-0.67

-4.67

-2.338.331.677.332.33

--

6.00---

Terrigenous GrainsQuartzFeldsparRock fragmentsGlauconitePhosphateOpaque mineralsCarbon

1.330.672.33

-0.670.67

-

1.670.671.33

--

0.670.67

1.000.671.670.33

-0.67

-

0.67-

0.67----

2.000.671.33

--

0.67-

0.33------

0.67------

1.670.674.67

-3.000.67

-

--

1.33----

0.33------

1.000.67

--

1.00--

1.33----

0.67-

0.670.67

-0.67

---

MatrixCarbonate mudClay minerals

23.33-

13.67-

10.67-

10.00-

9.33-

10.00-

13.336.00

9.336.00

9.334.00

10.677.00

5.008.00

22.33-

28.338.00


8.001.670.67

-

4.672.67

--

5.671.67

--

1.670.67

--

11.001.67

-0.67

3.001.330.670.67

4.331.331.000.67

5.673.331.33

-

4.001.67

--

0.671.33

--

5.331.33

--

4.333.00

--

3.001.00

--


7.336.004.00

-0.67

17.004.67

-1.33

-

7.003.004.002.67

-

60.336.67

-0.67

-

8.004.00

-1.00

-

56.33--

1.00-

10.673.00

-0.67

-

7.005.006.001.67

-

20.6720.6710.67

-0.67

30.673.0021.670.67

-

27.675.005.00

--

5.672.00

---

11.332.009.67

-0.67


-0.671.33

---

0.67-

2.67---

--

1.67---

--

0.67---

-1.333.67

-0.67

-

-0.672.33

---

-1.334.33

---

--

3.33---

--

1.000.67

--

--

0.67---

0.670.671.67

---

0.67-

8.67---

--

0.67---

Rock Name P/F P P W P W P P W W W P WSMF / FZ 5/4 10/7 5/4 10/7 5/4 10/7 5/4 10/7 10/7 19/8 3/3 10/7 10/7

IJOG


29

Table 1.............continued (Maryanto, 2007a)


SM323D

SM323E

SM324A

SM324B

SM324C

SM325A

SM325B

SM326 EXPLANATION

Structure m m o m p m m m m p m

Structure: m = massive o = with grain orientation p = with several pores f = with joints and fractures

Texture: bf = bioclastic fragmenter cf = clastic fragmenter nc = non-clactic c = crystalline

Sorting: vw = very well sorted w = well sorted m = moderately sorted p = poorly sorted vp = very poorly sorted

Fabric: c = closed o = opened

Grain shape: va = very angular a = angular sa = sub-angular sr = sub-rounded r = rounded wr = well rounded

Grain contact: f = floating p = point l = long c = concave-convex s = sutured

Rock name: BW = Wackestone BW/F = Wackestone/floatstone BP = Packstone BP/F = Packstone/floatstone BG = Grainstone SBP = Sandy packstone

Microfacies: SMF = Standard microfacies (Flugel, 1982) FZ = Facies zone

(Wilson,1975)

Texture bf bf bf bf bf bf bf bfSorting p p m m p p p pFabric c o c c c c c c

Av. grain size (mm) 0.30 0.15 1.20 1.60 1.10 0.80 0.30 0.35Grain shape sr sr sr sr sr sr sr sr

Grain contacts p l f p p l c p l c p l c p l c p l c p l cPercentages


-5.670.674.67

-2.677.672.679.332.67

--

6.334.003.33

-

-4.67

-5.00

-0.674.002.676.332.67

--

4.67-

6.00-

-5.333.3310.332.6722.000.672.0017.00

----

3.670.67

-

-3.332.339.331.3319.671.331.6730.33

----

6.000.67

-

-4.671.676.673.3314.004.674.00

23.000.67

--

4.335.330.67

-

-4.672.003.334.0011.332.672.6714.001.33

--

4.002.330.67

-

-4.331.672.003.0010.335.672.676.331.330.67

-6.00

---

-2.673.334.673.3329.000.672.0011.330.67

--

2.673.331.00

-Terrigenous Grains

QuartzFeldsparRock fragmentsGlauconitePhosphateOpaque mineralsCarbon

---

0.670.67

--

1.00---

0.33--

0.67------

0.67-

0.671.000.33

--

1.00-

1.330.67

---

1.33--

0.67-

0.671.00

1.000.33

-----

0.67---

0.671.33

-Matrix

Carbonate mudClay minerals

9.335.00

17.334.00

--

--

--

6.00-

12.335.00

12.675.67


2.671.33

-13.00

1.001.67

-6.67

14.001.671.33

-

7.671.331.00

-

9.001.330.67

-

4.331.331.000.67

4.676.00

--

3.332.67

--


6.003.007.33

--

5.673.3314.00

--

-6.00

-3.00

-

-6.67

-1.00

-

-3.006.002.00

-

15.004.008.000.67

-

5.33-

7.672.67

-

6.333.004.002.670.67


--

1.33---

0.671.673.33

-2.67

-

--

5.67---

0.670.672.33

---

0.33-

1.67---

--

2.33---

0.67-

10.33---

0.67-

1.00---

Rock Name P W G G G P P PSMF / FZ 10/7 19/8 12/6 12/6 12/6 10/7 10/7 10/7

IJOG


30

sized rocks, and consists of coralline, bioclas-tic, and argillaceous limestones. Pellet is very rarely preserved. A less amount of terrigenous materials are present evenly at the upper part of stratigraphic sequences. They are composed of quartz, feldspar, volcanic and argillaceous, metamorphic, and unidentified rock fragments, very rarely glauconite, phosphate, mica, and opaque minerals. Cement materials are always present in the rocks with a diverse number as orthosparite, iron oxides, authigenic clays, and silica. Most orthosparite is present from phreatic meteoric environment, followed by marine and burial environments. Small amount of iron oxides fills cavities and fractures in the rock. Authigenic clay minerals are preserved as pore-cavity filler. Silica in the form of quartz, feldspar, and zeolite are preserved from the phreatic meteoric environ-ment after cementation by the orthosparite calcite.

Floatstone Floatstone is generally massive with coarse-

grained fragmental bioclastic texture, both with closed fabric or opened fabric. Bioclast is made up of diverse type, size, and amount of fossil. In-traclast or extraclast is sporadically distributed in a few samples, and is composed of coralline, bio-clastic, and argillaceous limestones. Terrigenous materials are preserved in a limited number and spread out unevenly. Carbonate mud matrix often has changed into microsparite. Cement materials are present limitedly within inter and intra particle pores.

Microfacies Interpretation

Wackestone generally has an inversion tex-ture, i.e. coarse grains stuck in carbonate mud matrix, well washed grains, and has various fos-sils. Such limestone was generally deposited in back reef down-slope (SMF10-FZ7). Limestone facies type resides in this deposition environment including argillaceous-rich limestone to some packstone.

In addition to being in the back reef down-slope, wackestone may also be formed in very restricted bays and ponds (SMF19-FZ8). Special characteristic of the limestone deposited in this

depositional environment is the presence of fe-nestrae porosity type, as a result of a tidal activity (Tucker and Wright, 1990).

Coarse-grained packstone can be deposited in another deposition environment. In some cases, packstone can develop into grainstone with the bioclast composed as well of coated and worn red algae. This rock was usually deposited in slopes and shelf edges (SMF12-FZ6). Abrading and leaching of carbonate grains mark the grainstone was deposited in winnowed platform edge sands (SMF11-FZ6).

Packstone can be interpreted as reef-flank fa-cies (SMF5-FZ4), characterized by the presence of bioclasts mostly derived from the reef dwell-ers and reef builders, such as coral and bryozoa reefs (Read, 1985). Packstone and sometimes floatstone with large amount of carbonate mud matrix is interpreted as reef-flank deposits.

This microfacies interpretation can be done to each limestone sample petrography tested. The interpretation microfacies result can be used to trace back the development of facies deposition of a limestone formation, in this case is the Baturaja Formation along the Air Rambangnia traverse.

Discussion

Based on petrographic data (Table 1), the character of each sample can be known and traced to order their stratigraphy. The volcanic rocks of Kikim Formation are deposited unconformably on the limestone of Baturaja Formation, while clastic sedimentary rock of Talangakar Formation is not exposed in this traverse (Sukandi et al., 2006). The lowest part of the Baturaja Formation preceded by grainstone was deposited in the win-nowed platform carbonates, which is above the wave base (SMF11-FZ6). This area is very close to the beach characterized by the presence of ar-gillaceous material from the transgression phase (Andreeva, 2008), making it into the bay or pond (SMF19-FZ8). The depositional environment of the limestones repeated from very restricted pond and bay (SMF19-FZ8; Figure 9) to back-reef local slope (SMF10-FZ7; Figure 10) is due to regres-sive and transgressive phases. These depositional environments are characterized by the presence

IJOG


31

Figure 10. Photomicrograph of wackestone (sample code SM314A) with bioclasts of mollusks (mol) and large foraminifera (for) distributed in carbonate mud matrix (lpr) characterizing the SMF10-FZ7 on back-reef down-slope.

SM314A|----------| 0,5 mm

mol

for

lprpor

Figure 11. Photomicrograph of packstone/floatstone (sample code SM316A) with various bioclasts of red algae (gang) and large foraminifera (for) distributed in carbonate mud matrix (lpr), typifies the SMF5-FZ4 reef-flank area.

SM316A|----------| 0,5 mm

sem

for

lpr

for

gang

of wackestone-packstone interlayers some parts of argillaceous and with floatstone intercalation.

Regression process affects sedimentation in the middle part of Baturaja Formation, initiated by floatstone from reef-flank facies (SMF5-FZ4; Figure 11 and 12). The middle part of the Baturaja Formation is dominated by limestones from that depositional environment. The depositional envi-ronment repeated alternation with back-reef local slope facies (SMF10-FZ7; Wilson, 1975) and their lithology composed of wackestone-packstone.

The lithology from the back-reef local slope (SMF10-FZ7) continued until the upper part of the formation, and it was preceded by the presence of wackestone-mudstone. Regressive phase led the depositional environment to evolve into the very restricted bay or pond (SMF19-FZ8; Flugel,

Figure 9. Photomicrograph of wackestone (sample code SM305C) with very fine - grained size, characterizing the SMF19-FZ8 on very restricted bay or pond.

SM305C|----------| 0,5 mm

Figure 12. Photomicrograph of packstone (sample code SM318A) with various bioclasts of mollusks (mol) and large foraminifera (for) distributed in carbonate mud matrix (lpr), characterizing the SMF5-FZ4 on reef-flank area.

SM318A|----------| 0,5 mm

mol

for

lpr

for

mol

lpr

1982). Furthermore, transgressive phase led to be-come the depositional environment of slopes and shelf edges (SMF12-FZ6; Andreeva, 2008; Fig-ure 13) composed of grainstone with graded and planar cross-bedded structures (Bathurst, 1975; Kendall, 2005). Finally, the lithology sequence ended by the presence of wackestone-packstone deposited at back-reef local slope (SMF10-FZ7; Jones and Desrochers, 1992; Figure 14).

Paleogeographically, the reef complex is located in the east of the researched area, thus the highland is being in the west part (Maryanto, 2005). The Baturaja limestones were deposited, with the influence of a regional transgression, on the Late Oligocene age. The development of depositional environment between time forming

IJOG


32

Figure 14. Photomicrograph of packstone (sample code SM325B) with abraded bioclasts of mollusks (mol), large foraminifera (for), and echinoderms (ech) distributed in carbonate mud matrix, characterizing the SMF10-FZ7 on the back-reef down-slope.

BASEMENT ROCKS

N

N

2

3

4UPPER PART

Fore-reefBack-reefCore-reef Reef-flank

Bay

Tidal Flat

Basin

Local Basin

Local Basin

Local Basin

Lagoon

Tidal Channel

River

Regression

Transgression

INVESTIGATED AREA

1

Open Marine

CalcareousSiliciclastics

Slope

BASEMENT ROCKS

MIDDLE PART


Bay

Tidal Flat

Basin

Lagoon

Tidal Channel

River

INVESTIGATED AREA

Slope

BASEMENT ROCKS

N

LOWER PART


Bay

Tidal Flat

Basin

Lagoon

Tidal Channel

River

Regression

INVESTIGATED AREA

Slope

BASEMENT ROCKS

N

BASEMENT ROCKS


Basin

Lagoon

River

Stable landfollowed by erosion

INVESTIGATED AREA

Slope

Figure 13. Photomicrograph of grainstone (sample code SM324B) with various bioclasts of mollusks (mol), large foraminifera (for), and bryozoans (bry) in carbonate ce-ment, characterizing the SMF12-FZ6 on slope or shelf edge.

Figure 15. Depositional environment development of the Baturaja limestones along Air Rambangnia traverse, OKU Selatan, South Sumatra.

SM324B|----------| 0,5 mm

mol

bry

formol

SM325B|----------| 0,5 mm

lpr

ech

lprfor

mol

IJOG


33

Baturaja Formation is shown in the Figure 15. Depositional environment of the Baturaja Forma-tion varies from very restricted bay or pond area (SMF19-FZ8), back-reef local slope (SMF10-FZ7), slope and shelf edge (SMF12-FZ6), win-nowed platform edge sands (SMF11-FZ6), and reef-flank facies (SMF5-FZ4). In general, the depositional environment is conditioned exis-tence of transgression, characterized by changes in the position of microfacies that increasingly moved away from bay or pond and going onto the reef-flank facies. Depositional phase was still ongoing until the Early Miocene (Maryanto 2007a), which would later be crushed by the Gumai Formation.

Depositional environment forming the Batura-ja Formation along Air Rambangnia traverse has never been the deep sea or the fore-reef area. The position of the fore-reef area is predicted to be far away to east-southeast from the researched area. The research area is located at the volcanic back arc basin, at the basin edge bordering the land area, which at that time was occupied by the Pre-Tertiary rocks, now known as Garba Mountains.

Conclusion

Petrographic analysis was carried out upon thirty four limestone samples taken from Air Rambangnia traverse, OKU Selatan, South Sumatera. It shows out that limestones consist of wackestone, packstone, grainstone, and float-stone.

Stratigraphically, each of the rocks studied repeatedly occurs, but generally they developed in a transgressive depositional environment. The depositional environment is diverse ranging from restricted bay or pond, back-reef local slope, slope or shelf edge, winnowed platform edge sand, and reef-flank facies.

Acknowledgements

The author thanks and appreciates Mr. Herwin Syah for drawing digital pictures, and Mr. Heri-yanto for photographing thin sections.

References

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Kendall C.G.St.C., 2005. Carbonate Petrol-ogy. In: Kendall C.G.St.C. and Alnaji, N.S. (developers). USC Sequence Stratigra-phy.http://strata.geol.sc.edu/ seqstrat.html [27/02/2006].

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