Coal Stratigraphy of Separi

�Kalimantan Coal and Mineral Resources 2010� Proceeding, MGEI IAGI29 � 30 March 2010, Balikpapan, Kalimantan, Indonesia

13

Coal Stratigraphy of Separi, East Kalimantan, Indonesia

Fajar Alam, Yohanes Sebayang, Widyo Djunarjanto, Purwadi Eka PrijantoPT Straits Consultancy Services

Abstract

Separi is an area of 40 km north east Samarinda, known as one of the most extensive location for coal mining, as thearea covers the coal bearing formation of Balikpapan Formation. Balikpapan Formation in Separi might separated intoUpper Balikpapan and Lower Balikpapan Formation, as the sandstone become coarser in grains on Upper Balikpapan andlimestone occurrence on Lower Balikpapan. As part of Samarinda Anticlinorium, Separi has a trend of north northeast �south southwest orientation with plunging south syncline axis.

A series of extensive exploration program have been done to Separi Syncline, as outcrop study and drilling controlledwith geophysical logging analysis. Coal stratigraphy of this area shows various layer, as they might pinched out, washedout or continues, depend on the depositional system environment.

Seven zones of depositional coal bearing and typical multi coal seams layer have been identified from old to young asfollows: Zone 1, mudstone domination with some thin coal seam layers on upper strata and limestone on lower strata;Zone 2, mudstone domination with sandstone intercalation and thin coal seams; Zone 3, sandstone with mudstoneintercalation and Seam H as major coal seams; Zone 4, mudstone dominated with sandstone bedding and Seam F and Gas major coal seam; Zone 5, sandstone dominated with Seam D and E as major coal seams; Zone 6, mudstone dominatedwith Seam C as major coal seam; and Zone 7, sandstone interbedded with mudstone and Seam A and B as major coalseams. Separi area refer to fluvial to delta plain depositional environment.

Keyword: Separi Syncline, multi coal seam, fluvial to delta plain

INTRODUCTION

Separi is an area of 40 km north eastSamarinda, known as one of the mostextensive location for coal mining, as the areacovers the coal bearing formation ofBalikpapan Formation (Fig. 1). Practically,economic coal seam distributed along thewide syncline of Separi as part of theSamarinda Anticlinorium.The studied area is located approximately

150 kilometers northwest of Balikpapan andapproximately 70 kilometers from the sea.From Balikpapan, the location could bereached by plane of approximately 20 minutesflight to Samarinda or 2 hours car driving ofapproximately 113 km to Samarinda,continued with 1 hour car driving of 40 km.Geographically, the area cover theMulawarman and Bhuana Jaya village inTenggarong Seberang, Kutai Kartanegara.

REGIONAL GEOLOGY

MorphologyThe Separi area basically consists of mediumundulated to hilly topography as controlled bytectonic settlement and be part of Samarinda

Anticlinorium; medium undulated spread overthe lowland area as connected to synclinegeometry while hilly area are connected toanticline geometry as typically with steep dipclose to the axis.

Tectonic SettlementKalimantan is tectonically stable as part ofSundaland micro plate that characteristicallyand structurally quite different to otherislands in Indonesia. Sundaland micro plate ispart of Eurasian Plate that shifted northeastby collision with Asia continental crust.Basically tectonic pattern in Sundaland microplate is developed as friction from stress in itsplate, beside counter rotation movementfrom Sundaland micro plate. Other factor thatalso contributed on pattern development oftectonic in Kalimantan Island is interactionbetween Sundaland Plate with Pacific Plateson eastern part, India Australian Plate insouthern part and South China Sea Plate.The Kutai Basin is an inverted extensionalbasin located onshore Borneo, to the west ofthe Makassar Straits. Basin initiation hadoccurred by the middle Eocene and wascontemporaneous with oblique oceanicspreading in the Makassar Straits.

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

Seismic profiles across both the northernand southern margins of the Kutai Basin showinverted middle Eocene half graben. Thesewere infilled by syn rift successions thatdemonstrate considerable lateral and verticalfacies variations. Provenance studies of synrift sediments suggest differing source areasfor individual half graben. Offsets of middleEocene carbonate horizons and thickening ofsyn tectonic units seen on seismic sections,indicate late Oligocene extension on NW�SEtrending en echelon extensional faults.Middle Miocene inversion was concentratedon east facing half graben and asymmetricinversion anticlines are found on both thenorthern and southern margins of the KutaiBasin.A reorientation of the stress direction duringthe late Oligocene was inferred fromextension on en echelon NW�SE trendingfaults. A rotation of the extension direction bybetween 45 and 60° counter clockwise issuggested by fault and veinorientations. Neogene micro continentalcollisions with the margins of northern andeastern Sundaland strongly influenced theinversion of the basin. Inversion was focusedin the weak attenuated crust underlying theKutai Basin and adjacent basins, whereas thestronger oceanic crust underlying thenorthern Makassar Straits acted as a passiveconduit for compressional stresses (Cloke etal, 1997).

StratigraphyKutai Basin is surrounded by Kuching High inthe west, Mangkalihat High in the north,Barito Basin in the south and Makassar Straitto the east side. Sedimentation within thisbasin always continues from Tertiary torecent. Regression process tends to east sideand happened along the transgressionprocess.As the area of Samarinda � Tenggarong

during early 1980�s � early 1990�s are part ofKaltim Prima Coal�s concession area beforerelinquished, geological research had beenconducted within the area. The area iscovering southern to northern part ofMahakam River, known as Samarinda Block.

Generally, Lower Kutai Basin consists of fineclastic Tertiary sediment as sandstone,mudstone, siltstone and coal from Oligoceneto Holocene formation age (PamaluanFormation, Bebuluh Formation, PulaubalangFormation, Balikpapan Formation,Kampungbaru Formation and quaternaryalluvium sediment; Fig. 2). According to Landand Jones (1987), coals found in Samarindaand surroundings area have low ash, highmoisture and generally low sulphur.Pulaubalang Formation consists of

alternating greywacke and quartz sandstoneintercalations with limestone, claystone, coaland 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 aslenses in quartz sandstone. Age of formation isMiddle Miocene with depositionalenvironment of terrestrial to shallow marine.Balikpapan Formation consists of alternation ofsandstone and clay intercalations with silt,shale, limestone and coal. Quartz sandstone;white to yellowish, bedding thickness is about1 � 3 m, contains of coal fragment layer (5 � 10cm). Coal; black, thickness 0.30 � more than 5m. Calcareous sandstone, brown, showsgraded bedding and cross bedding. Clay; greyto blackish, locally contains plant remains, ironoxide. Age of formation is lower Late Mioceneto upper Middle Miocene with depositionalenviron ment in regression stage of a deltafront to delta plain. Thickness varies between1000 to 1500 m.

Kampungbaru Formation consists of quartzsandstone intercalation with clay, silt andlignite, commonly soft and easily broken.Quartz sandstone; white, locally reddish oryellowish, unbedded, easily broken, locallycontains thin layers of iron oxide orconcretionary; tuffaceous or silty, andintercalation of conglomeratic sandstone. Ageof formation is Late Miocene � Plio Pleistocenewith depositional environment of deltaic �shallow marine. Estimated thickness is morethan 500 m. Alluvium consists of gravel, sandand mud, deposited in a fluvial, deltaic andcoastal environment.


15

Figure 1. Research Area in Separi, East Kalimantan

Figure 2. Regional Stratigraphy of Samarinda � Separi Area (modification from Cloke et al, 1997)


Figure 3. Geological Map of Separi Prangat


17

Figure 4. Stratigraphic column of Separi


Figure 5. Isopach map of Seam B, E and H

Figure 6. S � S� Section with Coal Correlation


19

Regional Structural GeologyGeology of the area consists of complex offolds, known as Samarinda Anticlinorium andfault structures. Fold structures commonlyoriented northeast � southwest with steeperdip (40 � 75o) on southeast flank rather thanon northwest flank. Fault structure developedas thrust fault, normal fault and strike slipfault. Thrust fault might happen during LastMiocene and faulted by strike slip fault onlater stage. Otherwise, normal fault happenon younger stage of Pliocene.

GEOLOGY OF SEPARI

Geology and Stratigraphy of SepariGeology of the area structurally is dominatedby fold structure as part of SamarindaAnticlinorium on a trend of north northeast �south southwest (Fig. 3) with stratigraphicformation in the concession area from lowerto the top are Pulaubalang Formation, (Lowerand Upper) Balikpapan Formation andAlluvium sediment (Fig. 4).Pulaubalang Formation appears on the

eastern part of Separi as the appearance offormation typical lithology: occasionalmassive limestone, greywacke, reddish greysandstone with no coal beddings due todrilling data of 200 m average depth. Steepdip of interbedded mudstone (>70o) with veryfine sandstone found as contact indication tolower part of Balikpapan Formation on part ofthe steep anticline, apart between SepariSyncline on the west side to Prangat Synclineon the east side.Balikpapan Formation is differentiated into

Lower Balikpapan Formation and UpperBalikpapan Formation. Lower BalikpapanFormation consists of mudstone, siltstone,sandstone, coal and limestone. UpperBalikpapan Formation consists of quartzsandstone, mudstone, siltstone, coal andconglomerate. The existence of coal beddingsare common in this formation, as it might actas thin layer on mudstone, fragmented layeron sandstone or being a bedding body, inrange of thickness less than 0.30 m to morethan 5 m.Alluvium sediment in sand and mud content

developed on lowland plane, mostly used asrice field by local citizens or as swamp areaswith less than 3 m to around 31 m variousdepth.

Coal Geology of SepariCoal occurrences spread over the Upper andLower Balikpapan Formation. Coals dipping arerelatively flat to the axis of syncline andsteeper to the flank on a range of < 20 to > 300.Upper Balikpapan Formation consists of veryfine to coarse grain quartz sandstone,conglomerate, mudstone, interbedded withsiltstone and coal. Lower BalikpapanFormation consists of fine to very coarse grainquartz sandstone, mudstone, interbedded withsiltstone and coal. Close to eastern part ofSepari Syncline, the coals drop in occurrence,as the formation changed to PulaubalangFormation.Within Separi Syncline, coal seams spreading

tend to be thickened along syncline axis andthinning in syncline flanks on relativedirections of north north east and south southwest. As the Separi Syncline is plunging south,coal thickness is also tend to be thickened onsouth direction, as shown in Figure 5.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 toformation development as PulaubalangFormation. Around the contact betweenbarren coal area of Pulaubalang Formation andmultiple coal seams of Lower BalikpapanFormation, steep dip around 70 � 80o is met astypical geometry of Samarinda Anticlinorium;broad syncline with steep dip and narrowanticline. The coal in this block varied inthickness from less than 0.3 m to around 3 m.The coals show bright to vitreous luster, hard,conchoidal fracture, but with occasionalspread of pyrite and rarely with white ash lookon its fracture or cleat.Coal seam layers in Separi area might be

differentiated into eight seam layers, withvarious interburden (Fig. 6) as follows:1. Seam A, depth varied from less than 1 m to

more than 40 meter depth, concentrated in


the middle part of the Separi Syncline,thickening southwest along the synclineaxis in variation of 2.5 5 m

2. Seam B, depth varied from 9 m to morethan 80 meter depth, concentrated in themiddle part of the Separi Syncline,thickening southwest along the synclineaxis in variation of 0.30 � 9.5 m

3. Seam C, depth varied from 6.4 m to morethan 244 meter depth, spread along theSepari Syncline, thickening westsouthwest in variation of 0.30 � 7.5 m

4. Seam D, depth varied from 14 m to morethan 370 m, spread along the SepariSyncline, thickening to west southwestflank 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 SepariSyncline, thickening southwest along thesyncline axis in variation of 0.30 � 6 m.

6. Seam F, depth varied from 6.5 to morethan 600 m, spread along the SepariSyncline, locally thickening northeast ofeast flank of the syncline and commonlythickening southwest of the western flankof the syncline in variation of 0.30 � 7.5 m

7. Seam G, depth varied from 50 m to morethan 710 m, spread along the SepariSyncline, thickening northeast part of theeast flank of the syncline in variation of0.30 � 2.3 m

8. Seam H, depth varied from 70 � 910 m,spread along the Separi Syncline,thickening southwest along the synclineaxis in variation of 0.30 � 3.4 m.

Coal Stratigraphy of SepariIn Separi, most of the area covered inBalikpapan Formation, as coal bearingformation in Kutai Basin. In this study, coaldeposition event is limited on Separi .

Exploration dri ll ing (as covered withgeophysical logging) and short field trip havebeen done to get the data. Six boreholes areused as a model to get appropriatesubsurface condition of the Separi Syncline asthey might represent lower, middle and upper

part of the syncline. Base on study from drillhole core for determine the sequencestratigraphy and be combined with wire linelog signature, Separi Syncline area might beclassified into seven zones of coal deposition,from older to younger, as follows (Fig. 7):

Zone 1 This zone is dominated by mudstonewith sandstone on upper strata. Mudstone,whitish grey � grey, interlaminated withsiltstone and very fine sandstone withoccasional carbonaceous lamination.Sandstone on lower part of this zone tends tobe greenish grey, compact, fine grain. Onupper part of this zone, occasionally burnedwhitish grey � reddish grey fine grainsandstones are interbedded with mudstones.Some coal seam layers occurred, ranging 0.20� 0.60 m thickness, commonly covered withcarbonaceous clay or shaly coal as their roof orfloor rock. Lower part of this zone is marked bygreyish white limestone occurrence withinmudstone. Thicknesses of this zone are at least120 m.

Zone 2 This zone is dominated by mudstonewith sandstone intercalation. Mudstone, grey,interbedded with siltstone (0.20 � 3 mthickness) 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. Thicksandstone on upper part of this zone scours oncoal. Some coal string and carbonaceousmudstone occurred, varied from 5 cm to 15cm. Coal in this zone is associated withcarbonaceous material (carbonaceousmudstone or shaly coal), ranging 0.30 � 1 mthickness, bright � dull luster, subconchoidalfracture, deposited on lower delta plain. Thecarbonaceous materials tend to be banded incoal seam or in single bed as coal seam roof orseam floor. Average thickness of this zone isaround 250 m.

Zone 3 This zone is dominated by sandstonewith mudstone interbedding. Sandstone,whitish grey � grey, quartz dominated, very


21

Figure 7. Depositional Coal Zone of Separi


Figure 8. Outcrop of upper part of Lower Zone Separi Syncline, a) mudstone dominant with intercalation ofsandstone and coal seam layer, b) fine sandstone with interlaminated mudstone (IL MS), separating crossbedding structure on upper strata and parallel lamination structure on lower strata, c) coal seam layers with

15 cm shaly coal as roof rock

Figure 9. Outcrop of Middle Zone Separi Syncline, a) thick fine grey sandstone with interbedded brownsandstone, b) cross bedded sandstone with thin lamination of coal fragment


23

fine � coarse grain, fining upward or blocky, 1� 23 m thickness. Fragments in sandstoneusually consist of coal (<0.5 cm � 6.0 cm) andironstone nodule (<0.5 cm � 4.0 cm).Sometimes, coal fragments occurred as thinlamination in sandstone. Mudstone, grey �dark grey, occasional appearance of ironstonenodule and occasional interlamination withfine sandstone, 1 � 32 m thicknesses. Coal inthis zone relatively occurred as clean coal.Occasional parting in coal seam usuallydeveloped in lower ply, as appearance ofshaly coal, dull � bright luster, subconchoidal� conchoidal fracture. Sometimes shaly coallayer occurred as roof rock or floor rock, up to15 cm thickness. Coal thickness ranging in 0.3m � 2.45 m. Dominant coal seams is Seam H,deposited on upper delta plain. Averagethickness of this zone is around 310 m.

Zone 4 This zone is dominated by mudstonewith sandstone interbedding (Fig. 8a).Mudstone, grey � dark grey, occasionalappearance of ironstone nodule andoccasional interlamination with finesandstone, 1 � 70 m thicknesses. Sandstone,whitish grey � grey, quartz dominated, veryfine � coarse grain, fining upward or blocky,0.4 � 20 m thickness. Fragments in sandstoneusually consist of coal (<0.5 cm � 6.0 cm) andironstone nodule (<0.5 cm � 4.0 cm).Sometimes, coal fragments occurred as thinlamination in sandstone. Sandstone in thiszone sometimes presents direct contact tocoal seam as this condition may lead tothinning of coal seam thickness bysandstone�s scouring on top coal and sandinfilling within coal crack or cleat duringerosion. Occasionally, sandstone mightinterlaminate with mudstone, presentinginterlaminated sandstone with averagethickness 0.15 m (Fig. 8b).Two thick sandstones bedding might

identified in this zone, generally finingupward, as sandstone below Seam F onaverage thickness of 20 m, and sandstone inthe middle between Seam F and E (in zone 5,named as SS3 sandstone) on averageth i c knes s o f 4 0 m w i th mud stoneinterbedding (1 � 3 m). Sandstone in SS3 has a

trend of thinning on southern part of SepariSyncline and relative equal thickness alongboth flanks (Fig. 11). Coal in this zone relativelyoccurred as clean coal. Occasional parting incoal seam usually developed in lower ply, asappearance of shaly coal, dull � bright luster,subconchoidal � conchoidal fracture.Sometimes shaly coal layer occurred as roofrock or floor rock, up to 15 cm thickness (Fig.8c). Coal thickness ranging in 0.3 m � 2.45 m.Dominant coal seams occurrences are Seam Fand G, deposited on upper delta plain. Averagethickness of this zone is around 350 m.

Zone 5 This zone is dominated by sandstonewith siltstone intercalation. Sandstone, grey,quartz dominated, very fine grain on upperstrata, fine � coarse grain in middle and lowerstrata, fining upward, commonly cross beddingwith occasional parallel lamination of siltstone,rare carbonaceous lamination with coalfragments, with thickness varied 0.5 m � >15m. Sandstone between two coal seams (knownas Seam D and E) in this zone might named asSS2 sandstone, as SS3 sandstone have a trendof thinning on southern part of Separi Synclineand relative equal thickness along both flanks(Fig. 11). Siltstone, grey � dark grey, mudstoneinterbedded with occasional carbonaceouslamination and ironstone nodule, 0.2 m � 5 mthickness. Coal, black, occasional occurrenceof shaly coal as parting (commonly less than 5cm), with coal thickness ranging in 0.5 m � 1.5m. Dominant coal seams occurrences of SeamD and E, deposited on fluviatil upper deltaplain. Average thickness of this zone is 60 80m.

Zone 6 This zone is dominated by mudstoneinterbedded with siltstone, sandstone and coalseams. Mudstone, grey � dark grey, showedinterbedding with very fine sandstone ands i l t s tone , ra re in te r l am ina t ion wi thcarbonaceous material with thickness varied0.30 m � 5 m. siltstone, grey, interbedded withmudstone, thickness varied 0.30 m � 4 m.Sandstone, whitish grey � grey, quartzdominated with occasional oxidized mineralinfill as oxidized sandstone or ironstone andcoal fragments, varied from very fine � coarse


grain and tend to fining upward, variedthickness 0.30 � 15 m. Sandstones in this zonetend to be loose with cross bedding sedimentstructure 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, presentingdirty coal up to 30 cm thickness. Coalthickness ranging in 0.5 � 2 m, with dominantcoal seams occurrences of Seam C, depositedon lower to upper delta plain. Averagethickness of this zone is 110 m.

Zone 7This zone is sandstone interbedded withmudstone and coal. Sandstone, whitish grey �grey, quartz dominated, very fine � coarsegrain in fining upward, thickness varied 0.30m � 30 m, coal fragments layer 5 cm � 20 cmthickness, interbedded with brown sandstone.Brown sandstone, hard, fine grain with ironoxide content (Fig. 10). Coal, black, occasionalparting of shaly coal or carbonaceousmudstone up to 10 cm, occasional occurrenceof resin, bright � dull luster, subconchoidal �conchoidal fracture. Dominant coal seamsoccurrences in this zone are Seam A and B,deposited on upper delta plain. Averagethickness of this zone is 190 m.

Structural Geology of SepariGenerally, the concession area is depositedalong the Separi Syncline and on eastern partturned to west flank of Prangat Syncline. Thesyncline axis is plunging south on strike/dipdirection of N 280o E/4o.On the eastern part of the Separi Syncline,

steep deep contact on the west side is foundto be approximately 80o but tend to be gentleto the east, as the dip become only around 4o

and dipping east before meet the axis ofPrangat Syncline. This situation lead bycontact of Pulaubalang Formation and LowerBalikpapan Formation on steep dip area andgently dipping to the east as the LowerBalikpapan Formation meet the broad area ofPrangat Syncline.

CONCLUSION

Separi Syncline area might be classified intoseven zone of coal deposition with each zone ischaracterized by a typical lithologicalsequence. It might help to increase theunderstanding of coal stratigraphy of SepariSyncline area in particular and the Kutai Basinin general.

Zoning of coal deposition within SepariSyncline might be applied for coal explorationand geological modeling as coal associationwith proportion of surrounding lithology mighthelp to develop good model. The coal tends toget good continuity in lateral spreading onrelative high proportion of mudstoneassociation rather than sandstone associationdue to erosional factor from sandstone.

This zoning division is expected to beapplied in the planning design, especially forpit mine design. By looking on lithologysequences in each zone, preliminarydetermination might be developed for theareas needed for geotechnical study of slopestability purposes.

The observations and interpretationsdescribed in this paper are preliminary, furtherstudies are recommended for betterunderstanding about coal stratigraphy ofSepari Syncline.

AcknowledgementsWe would like to thank the management of PT.Straits Consultancy Services for permission topublish this paper. The paper based onexploration work that involved contributionsfrom 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 picture preparations.


25

Figure 10. Outcrop of Upper Zone Separi Syncline, a) thick grey sandstone with coal fragment at bottomscoured on mudstone, b) pebble � cobble sediment on fine sandstone, c) medium � coarse sandstone with

coal fragment

(a)

(b)Figure 11. Sandstone thickness of SS2 layer and SS3 layer, showing a) relative equal thickness on both flanks

of the Separi Syncline, b) relative thinning spreading on southern part of the Separi Syncline


REFERENCES

Alam, F., 2009, Geology of Separi � PrangatSyncline PT Jembayan Muarabara, EastKalimantan, Indonesia (unpublishedreport), Exploration Department PT StraitsConsultancy Services

Cloke, I.R., Moss, S.J. and Craig, J., 1997,Structural Controls on the Evolution of theKutai Basin, East Kalimantan onwww.gl.rhbnc.ac.uk/seasia

Djunarjanto, W., Baroto, T.I., Prijanto, P.E.,Alam, F., 2009, Geologi PT JembayanMuarabara Separi, Kalimantan Timur,Indonesia (Internal Report A 002), PT StraitsConsultancy Services

Land, D.H. and Jones, C.M., 1987, CoalGeology and Exploration of Part of the KuteiBasin in East Kalimantan, Indonesia. In :Coal and Coal bearing Strata: RecentAdvances (Editor A.C. Scott), Spec. Publ.Geol. Soc., London, No. 32, p. 235 � 255.

Putra, S., 1988, Geological Map SamarindaBlock Scale 1:250.000, Kaltim Prima Coal

Documents

Coal Stratigraphy of Separi