182257582 coal stratigraphy of separi

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Kalimantan Coal and Mineral Resources2010 Proceeding,MGEI IAGI

29 30March2010, Balikpapan, Kalimantan, Indonesia13

Coal Stratigraphyof Separi, East Kalimantan,Indonesia

FajarAlam, YohanesSebayang,WidyoDjunarjanto,Purwadi EkaPrijantoPT Straits ConsultancyServices

Abstract

Separi is an area of 40kmnorth east Samarinda, known as one of the most extensive location for coal mining, as the

area covers the coal bearing formation of Balikpapan Formation. Balikpapan Formation in Separi might separated into

Upper Balikpapan and Lower Balikpapan Formation,asthesandstone become coarser in grains on Upper Balikpapan and

limestone occurrence on Lower Balikpapan. As part of Samarinda Anticlinorium, Separi has a trend of north northeast

south southwest orientation with plungingsouth syncline axis.

A series of extensive exploration program have beendone to Separi Syncline, asoutcrop studyand drilling controlled

with geophysical logginganalysis. Coal stratigraphyof thisarea shows various layer, asthey might pinched out, washed

out or continues, depend on thedepositional systemenvironment.

Sevenzones of depositional coal bearingand typical multi coal seams layer have beenidentified fromold to youngas

follows: Zone 1, mudstone domination with some thin coal seamlayerson upper strata and limestoneon lower strata;

Zone 2, mudstone domination with sandstone intercalation and thin coal seams; Zone 3, sandstone with mudstone

intercalation and Seam H asmajor coal seams; Zone4, mudstone dominated withsandstone beddingand SeamF and G

asmajor coalseam; Zone 5, sandstonedominatedwithSeamDand Easmajor coalseams; Zone6, mudstonedominated

with Seam C as major coal seam; and Zone7, sandstone interbedded with mudstone and Seam A and B asmajor coal

seams. Separiarearefer to fluvialto delta plain depositional environment.

Keyword:Separi Syncline, multi coalseam, fluvial to delta plain

INTRODUCTION

Separi is an area of 40 km north east

Samarinda, known as one of the mostextensive location for coal mining, as the area

covers the coal bearing formation of

Balikpapan Formation (Fig. 1). Practically,economic coal seam distributed along the

wide syncline of Separi as part of the

SamarindaAnticlinorium. The studied area is located approximately

150 kilometers northwest of Balikpapan andapproximately 70 kilometers from the sea.

From Balikpapan, the location could be

reached by planeof approximately 20minutesflight to Samarinda or 2 hours car driving of

approximately 113 km to Samarinda,continued with 1 hour car driving of 40 km.

Geographically, the area cover the

Mulawarman and Bhuana Jaya village in TenggarongSeberang, Kutai Kartanegara.

REGIONALGEOLOGY

Morphology

The Separi area basically consists of mediumundulated to hilly topography as controlled by

tectonic settlement and be part of Samarinda

Anticlinorium; medium undulated spread over

the lowland area as connected to synclinegeometry while hilly area are connected to

anticline geometry as typically with steep dipclose to theaxis.

TectonicSettlementKalimantan is tectonically stable as part of

Sundaland micro plate that characteristically

and structurally quite different to otherislands in Indonesia. Sundaland micro plate is

part of Eurasian Plate that shifted northeastby collision with Asia continental crust.

Basically tectonic pattern in Sundaland micro

plate is developed as friction from stress in itsplate, beside counter rotation movement

fromSundaland micro plate. Other factor thatalso contributed on pattern development of

tectonic in Kalimantan Island is interaction

between Sundaland Plate with Pacific Plateson eastern part, India Australian Plate in

southernpart and SouthChinaSeaPlate. The Kutai Basin is an inverted extensionalbasin located onshore Borneo, to the west of

the Makassar Straits. Basin initiation had

occurred by the middle Eocene and wascontemporaneous with oblique oceanic

spreadingin theMakassar Straits.


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14 Kalimantan Coal and Mineral Resources 2010 Proceeding, MGEI IAGI29 30March2010, Balikpapan, Kalimantan, Indonesia

Seismic profiles across both the northern

and southern marginsof theKutai Basin show

inverted middle Eocene half graben. Thesewere infilled by syn rift successions that

demonstrate considerable lateral and vertical

facies variations. Provenance studies of synrift sediments suggest differing source areas

for individual half graben. Offsets of middleEocene carbonate horizons and thickening of

syn tectonic units seen on seismic sections,indicate late Oligocene extension on NWSE

trending en echelon extensional faults.

Middle Miocene inversion was concentratedon east facing half graben and asymmetric

inversion anticlines are found on both the

northern and southern margins of the KutaiBasin.

A reorientation of the stress direction duringthe late Oligocene was inferred from

extension on en echelon NWSE trending

faults. A rotation of the extensiondirection bybetween 45 and 60° counter clockwise is

suggested by fault and vein

orientations. Neogene micro continentalcollisions with the margins of northern and

eastern Sundaland strongly influenced the

inversion of the basin. Inversion was focusedin the weak attenuated crust underlying the

Kutai Basin and adjacent basins, whereas the

stronger oceanic crust underlying thenorthern Makassar Straits acted as a passive

conduit for compressional stresses (Cloke etal, 1997).

Stratigraphy

Kutai Basin is surrounded by Kuching High in

the west, Mangkalihat High in the north,Barito Basin in the south and Makassar Strait

to the east side. Sedimentation within this

basin always continues from Tertiary torecent. Regression process tends to east side

and happened along the transgressionprocess.

As the area of Samarinda Tenggarong

during early 1980s early 1990s are part of Kaltim Prima Coals concession area before

relinquished, geological research had been

conducted within the area. The area iscovering southern to northern part of

Mahakam River, known as Samarinda Block.

Generally, Lower Kutai Basin consists of fine

clastic Tertiary sediment as sandstone,

mudstone, siltstone and coal from Oligoceneto Holocene formation age (Pamaluan

Formation, Bebuluh Formation, Pulaubalang

Formation, Balikpapan Formation,Kampungbaru Formation and quaternary

alluvium sediment; Fig. 2). According to Landand Jones (1987), coals found in Samarinda

and surroundings area have low ash, highmoisture and generally low sulphur.

Pulaubalang Formation consists of

alternating greywacke and quartz sandstoneintercalations with limestone, claystone, coal

and dacitic tuff. Greywacke; greenish grey,

compact. Quartz sandstone; reddish grey,locally tuffaceous and calcareous. Limestone;

yellowish to light brown, contains largeforaminifera, either as intercalations or as

lenses in quartz sandstone. Age of formation is

Middle Miocene with depositionalenvironment of terrestrial to shallow marine.

Balikpapan Formationconsistsof alternation of

sandstone and clay intercalations with silt,shale, limestone and coal. Quartz sandstone;

white to yellowish, bedding thickness is about

1 3 m, containsof coal fragment layer (5 10cm). Coal; black, thickness 0.30 more than 5

m. Calcareous sandstone, brown, shows

graded bedding and cross bedding. Clay; greyto blackish, locally containsplant remains, iron

oxide. Age of formation is lower Late Mioceneto upper Middle Miocene with depositional

environ ment in regression stage of a deltafront to delta plain. Thickness varies between

1000to 1500m.

Kampungbaru Formation consists of quartzsandstone intercalation with clay, silt and

lignite, commonly soft and easily broken.

Quartz sandstone; white, locally reddish oryellowish, unbedded, easily broken, locally

contains thin layers of iron oxide orconcretionary; tuffaceous or silty, and

intercalation of conglomeratic sandstone. Age

of formation is Late Miocene Plio Pleistocenewith depositional environment of deltaic

shallow marine. Estimated thickness is more

than 500 m. Alluvium consists of gravel, sandand mud, deposited in a fluvial, deltaic and

coastal environment.


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Kalimantan Coal and Mineral Resources 2010 Proceeding,MGEI IAGI


Figure1. ResearchAreain Separi, East Kalimantan

Figure2. Regional Stratigraphyof Samarinda Separi Area (modification fromCloke et al, 1997)


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Figure3. Geological Map of Separi Prangat


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Kalimantan Coal and Mineral Resources 2010 Proceeding,MGEI IAGI


Figure4.Stratigraphiccolumn of Separi


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Figure5.Isopach map of SeamB, EandH

Figure 6. S S Section withCoal Correlation


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RegionalStructuralGeology

Geology of the area consists of complex of folds, known as Samarinda Anticlinorium and

fault structures. Fold structures commonly

oriented northeast southwest with steeper

dip (40

75

o

) on southeast flank rather thanonnorthwest flank. Fault structure developedas thrust fault, normal fault and strike slip

fault. Thrust fault might happen during Last

Miocene and faulted by strike slip fault onlater stage. Otherwise, normal fault happen

onyounger stage of Pliocene.

GEOLOGYOFSEPARI

GeologyandStratigraphyof Separi

Geology of the area structurally is dominated

by fold structure as part of SamarindaAnticlinorium on a trend of north northeast

south southwest (Fig. 3) with stratigraphicformation in the concession area from lower

to thetop are PulaubalangFormation, (Lower

and Upper) Balikpapan Formation andAlluviumsediment (Fig. 4).

Pulaubalang Formation appears on the

eastern part of Separi as the appearance of formation typical lithology: occasional

massive limestone, greywacke, reddish grey

sandstone with no coal beddings due todrilling data of 200 m average depth. Steep

dip of interbedded mudstone (>70o) with veryfine sandstone found as contact indication to

lower part of Balikpapan Formation on part of

the steep anticline, apart between SepariSyncline on the west side to Prangat Syncline

ontheeast side.Balikpapan Formation is differentiated into

Lower Balikpapan Formation and Upper

Balikpapan Formation. Lower BalikpapanFormation consists of mudstone, siltstone,

sandstone, coal and limestone. Upper

Balikpapan Formation consists of quartzsandstone, mudstone, siltstone, coal and

conglomerate. The existence of coal beddingsare common in this formation, as it might act

as thin layer on mudstone, fragmented layer

on sandstone or being a bedding body, inrange of thickness less than 0.30 m to more

than 5 m.

Alluviumsediment in sand and mud content

developed on lowland plane, mostly used as

rice field by local citizens or as swamp areaswith less than 3 m to around 31 m various

depth.

CoalGeologyofSepariCoal occurrences spread over the Upper andLower Balikpapan Formation. Coals dippingare

relatively flat to the axis of syncline and

steeper to the flank ona range of 300.Upper Balikpapan Formation consists of very

fine to coarse grain quartz sandstone,conglomerate, mudstone, interbedded with

siltstone and coal. Lower Balikpapan

Formation consists of fine to very coarse grainquartz sandstone, mudstone, interbeddedwith

siltstone and coal. Close to eastern part of

Separi Syncline, the coals drop in occurrence,as the formation changed to Pulaubalang

Formation.WithinSepari Syncline, coal seams spreading

tend to be thickened along syncline axis and

thinning in syncline flanks on relativedirectionsof north north east and south south

west. As the Separi Syncline is plungingsouth,

coal thickness is also tend to be thickened onsouth direction, asshown in Figure5.

The barren coal area mostly consists of

medium very coarse sandstone withintercalation of mudstone and siltstone;

greywacke, reddish grey sandstone andlimestone occurrence in this area also lead to

formation development as Pulaubalang

Formation. Around the contact betweenbarren coal area of PulaubalangFormationand

multiple coal seams of Lower BalikpapanFormation, steep dip around70 80o ismet as

typical geometry of Samarinda Anticlinorium;

broad syncline with steep dip and narrowanticline. The coal in this block varied in

thickness from less than 0.3 m to around 3 m.

The coals show bright to vitreous luster, hard,conchoidal fracture, but with occasional

spread of pyrite and rarely with white ash lookonitsfracture or cleat.

Coal seam layers in Separi area might be

differentiated into eight seam layers, withvarious interburden(Fig. 6)asfollows:

1. Seam A, depth varied from less than 1 m to

more than 40 meter depth, concentrated in


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20 Kalimantan Coal and Mineral Resources2010 Proceeding, MGEI IAGI29 30March2010, Balikpapan, Kalimantan, Indonesia

the middle part of the Separi Syncline,

thickening southwest along the syncline

axisin variation of 2.5 5 m2. Seam B, depth varied from 9 m to more

than 80 meter depth, concentrated in the

middle part of the Separi Syncline,thickening southwest along the syncline

axis in variationof 0.30 9.5m3. Seam C, depth varied from 6.4 m to more

than 244 meter depth, spread along theSepari Syncline, thickening west

southwest in variationof 0.30 7.5m

4. Seam D, depth varied from 14 m to morethan 370 m, spread along the Separi

Syncline, thickening to west southwest

flank of the syncline in variation of 0.30 3 m

5. Seam E, depth varied from 2.5 m to morethan 410 m, spread along the Separi

Syncline, thickening southwest along the

synclineaxis in variationof 0.30 6m.6. Seam F, depth varied from 6.5 to more

than 600 m, spread along the Separi

Syncline, locally thickening northeast of east flank of the syncline and commonly

thickening southwest of the western flank

of the synclinein variation of 0.30 7.5m7. Seam G, depth varied from 50 m to more

than 710 m, spread along the Separi

Syncline, thickening northeast part of theeast flank of the syncline in variation of

0.30 2.3m8. Seam H, depth varied from 70 910 m,

spread along the Separi Syncline,thickening southwest along the syncline

axis in variationof 0.30 3.4m.

Coal Stratigraphyof Separi

In Separi, most of the area covered in

Balikpapan Formation, as coal bearingformation in Kutai Basin. In this study, coal

depositioneventis limitedonSepari .

Exploration drilling (as covered with

geophysical logging) and short field trip havebeen done to get the data. Six boreholes are

used as a model to get appropriate

subsurface condition of theSepari Syncline asthey might represent lower, middleand upper

part of the syncline. Base on study from drill

hole core for determine the sequence

stratigraphy and be combined with wire linelog signature, Separi Syncline area might be

classified into seven zones of coal deposition,

fromolder to younger, asfollows(Fig. 7):

Zone 1 This zone is dominated by mudstonewith sandstone on upper strata. Mudstone,

whitish grey grey, interlaminated withsiltstone and very fine sandstone with

occasional carbonaceous lamination.

Sandstone on lower part of this zone tends tobe greenish grey, compact, fine grain. On

upper part of this zone, occasionally burned

whitish grey reddish grey fine grainsandstones are interbedded with mudstones.

Some coal seamlayers occurred, ranging 0.20 0.60 m thickness, commonly covered with

carbonaceousclayor shaly coal as their roof or

floor rock.Lower part of thiszone ismarked bygreyish white limestone occurrence within

mudstone. Thicknessesof thiszoneareatleast

120m.

Zone 2 This zone is dominated by mudstone

with sandstone intercalation. Mudstone, grey,interbedded with siltstone (0.20 3 m

thickness) occurred with ironstone nodule.

Sandstone, grey, quartz dominated, bedranging 0.20 m 17 m thick, blocky, fine

medium grain, sometimes interbedded withsiltstone or contain ironstone fragment. Thick

sandstone onupper part of thiszone scoursoncoal. Some coal string and carbonaceous

mudstone occurred, varied from 5 cm to 15

cm. Coal in this zone is associated withcarbonaceous material (carbonaceous

mudstone or shaly coal), ranging 0.30 1 m

thickness, bright dull luster, subconchoidalfracture, deposited on lower delta plain. The

carbonaceous materials tend to be banded incoal seamor in single bed as coal seamroof or

seam floor. Average thickness of this zone is

around250m.

Zone 3 This zone is dominated by sandstone

with mudstone interbedding. Sandstone,whitish grey grey, quartz dominated, very


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Figure7. Depositional Coal Zone of Separi


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Figure8. Outcrop of upper part of Lower Zone Separi Syncline, a) mudstonedominant with intercalationof

sandstone and coal seamlayer, b)finesandstonewith interlaminatedmudstone (ILMS), separating cross

beddingstructureonupper strataand parallel lamination structureonlower strata, c)coal seamlayerswith

15 cmshaly coal asroof rock

Figure9.Outcropof Middle ZoneSepari Syncline, a) thick finegreysandstonewithinterbeddedbrown

sandstone,b) cross beddedsandstonewiththin lamination of coal fragment


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grain and tend to fining upward, varied

thickness 0.30 15 m. Sandstonesin thiszone

tend to beloose with cross beddingsedimentstructure as shown in Pit 4 M outcrop (Fig. 9).

Coal, black, bright dull luster, subconchoidal

brittle fracture. Lower coal ply tend to beinterlaminated with shaly coal, presenting

dirty coal up to 30 cm thickness. Coalthickness ranging in 0.5 2 m, with dominant

coal seams occurrences of Seam C, depositedon lower to upper delta plain. Average

thickness of thiszone is110m.

Zone7

This zone is sandstone interbedded with

mudstoneand coal. Sandstone, whitish grey grey, quartz dominated, very fine coarse

grain in fining upward, thickness varied 0.30m 30 m, coal fragments layer 5 cm 20 cm

thickness, interbedded with brownsandstone.

Brown sandstone, hard, fine grain with ironoxide content (Fig. 10). Coal, black, occasional

parting of shaly coal or carbonaceous

mudstone up to 10cm, occasional occurrenceof resin, bright dull luster, subconchoidal

conchoidal fracture. Dominant coal seams

occurrences in this zone are Seam A and B,deposited on upper delta plain. Average

thickness of thiszone is190 m.

Structural Geologyof Separi

Generally, the concession area is depositedalong the Separi Syncline and on eastern part

turned to west flank of Prangat Syncline. Thesyncline axis is plunging south on strike/dip

direction of N 280o E/4o.

On the eastern part of the Separi Syncline,steep deep contact on the west side is found

to beapproximately 80o but tendto be gentle

to the east, as the dip become only around 4o

and dipping east before meet the axis of

Prangat Syncline. This situation lead bycontact of Pulaubalang Formation and Lower

Balikpapan Formation on steep dip area and

gently dipping to the east as the LowerBalikpapan Formation meet the broad area of

Prangat Syncline.

CONCLUSION

Separi Syncline area might be classified intosevenzone of coal depositionwitheach zone is

characterized by a typical lithological

sequence. It might help to increase theunderstanding of coal stratigraphy of Separi

Syncline area in particular and the Kutai Basinin general.

Zoning of coal deposition within SepariSyncline might be applied for coal exploration

and geological modeling as coal association

with proportion of surrounding lithology mighthelp to develop good model. Thecoal tendsto

get good continuity in lateral spreading on

relative high proportion of mudstoneassociation rather than sandstone association

due to erosionalfactor fromsandstone. This zoning division is expected to be

applied in the planning design, especially for

pit mine design. By looking on lithologysequences in each zone, preliminary

determination might be developed for the

areas needed for geotechnical study of slopestability purposes.

The observations and interpretations

described in thispaper are preliminary, furtherstudies are recommended for better

understanding about coal stratigraphy of

Separi Syncline.

AcknowledgementsWewouldliketo thankthemanagement of PT.

Straits Consultancy Services for permission topublish this paper. The paper based on

exploration work that involved contributions

from numerous geologists and support team.All these people are gratefully acknowledged.

Thank also for Firmansyah S. ,Andrianus D. P.

and Wawan K. for their contributions on dataand picturepreparations.


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Figure10. Outcropof Upper ZoneSepari Syncline, a)thick greysandstonewithcoalfragment atbottom

scouredon mudstone, b) pebble cobble sediment on fine sandstone, c)medium coarsesandstonewith

coal fragment

(a)

(b)

Figure11. Sandstonethickness of SS2 layer and SS3 layer, showinga)relative equal thicknesson both flanks

of theSepari Syncline, b)relativethinningspreadingon southernpart of theSepari Syncline


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182257582 coal stratigraphy of separi

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