182257582 coal stratigraphy of separi
TRANSCRIPT
-
8/16/2019 182257582 Coal Stratigraphy of Separi
1/14
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.
-
8/16/2019 182257582 Coal Stratigraphy of Separi
2/14
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.
-
8/16/2019 182257582 Coal Stratigraphy of Separi
3/14
Kalimantan Coal and Mineral Resources 2010 Proceeding,MGEI IAGI
29 30March2010, Balikpapan, Kalimantan, Indonesia15
Figure1. ResearchAreain Separi, East Kalimantan
Figure2. Regional Stratigraphyof Samarinda Separi Area (modification fromCloke et al, 1997)
-
8/16/2019 182257582 Coal Stratigraphy of Separi
4/14
16 Kalimantan Coal and Mineral Resources 2010 Proceeding, MGEI IAGI29 30March2010, Balikpapan, Kalimantan, Indonesia
Figure3. Geological Map of Separi Prangat
-
8/16/2019 182257582 Coal Stratigraphy of Separi
5/14
Kalimantan Coal and Mineral Resources 2010 Proceeding,MGEI IAGI
29 30March2010, Balikpapan, Kalimantan, Indonesia17
Figure4.Stratigraphiccolumn of Separi
-
8/16/2019 182257582 Coal Stratigraphy of Separi
6/14
18 Kalimantan Coal and Mineral Resources 2010 Proceeding, MGEI IAGI29 30March2010, Balikpapan, Kalimantan, Indonesia
Figure5.Isopach map of SeamB, EandH
Figure 6. S S Section withCoal Correlation
-
8/16/2019 182257582 Coal Stratigraphy of Separi
7/14
Kalimantan Coal and Mineral Resources2010 Proceeding,MGEI IAGI
29 30March2010, Balikpapan, Kalimantan, Indonesia19
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
-
8/16/2019 182257582 Coal Stratigraphy of Separi
8/14
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
-
8/16/2019 182257582 Coal Stratigraphy of Separi
9/14
Kalimantan Coal and Mineral Resources2010 Proceeding,MGEI IAGI
29 30March2010, Balikpapan, Kalimantan, Indonesia21
Figure7. Depositional Coal Zone of Separi
-
8/16/2019 182257582 Coal Stratigraphy of Separi
10/14
22 Kalimantan Coal and Mineral Resources2010 Proceeding, MGEI IAGI29 30March2010, Balikpapan, Kalimantan, Indonesia
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
-
8/16/2019 182257582 Coal Stratigraphy of Separi
11/14
-
8/16/2019 182257582 Coal Stratigraphy of Separi
12/14
24 Kalimantan Coal and Mineral Resources2010 Proceeding, MGEI IAGI29 30March2010, Balikpapan, Kalimantan, Indonesia
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.
-
8/16/2019 182257582 Coal Stratigraphy of Separi
13/14
Kalimantan Coal and Mineral Resources2010 Proceeding,MGEI IAGI
29 30March2010, Balikpapan, Kalimantan, Indonesia25
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
-
8/16/2019 182257582 Coal Stratigraphy of Separi
14/14