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PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION
Thirty-Fifth Annual Convention & Exhibition, May 2011
STRATIGRAPHY AND SEDIMENT PROVENANCE, BARITO BASIN,
SOUTHEAST KALIMANTAN
Duncan Witts*
Robert Hall*
Robert J. Morley**
Marcelle K. BouDagher-Fadel***
ABSTRACT
INTRODUCTION
The Barito Basin is located in southeast Kalimantan.
It contains a thick Cenozoic sedimentary succession
that overlies basement rocks of Paleocene and older
age. This paper presents a revised stratigraphy and
depositional model for the basin and identifies
sediment
source
areas,
based
on
new
lithostratigraphic, biostratigraphic, petrographic and
paleocurrent data collected as part of a field-based
study.
The Barito Basin is located in southeast Kalimantan,
Borneo. The basin contains a thick succession of
sedimentary rocks that are well exposed along the
eastern margin of the basin (Fig. 1). The basin is
bound to the west by the Schwaner Complex,
comprising poorly dated regionally and contact
metamorphosed rocks and Cretaceous granitic
plutons and volcanic rocks. The northern margin is
defined by the ‘Cross Barito High’ (Moss et al.,
1997), an onshore continuation of the NW-SEtrending Adang fault zone. This separates the Barito
Basin from the Kutai Basin to the north. Bounding
the Barito Basin to the east is the Meratus Complex.
This forms a NE-SW-trending belt of uplifted
ophiolitic, subduction-related metamorphic and arctype rocks ranging in age from Jurassic to
Cretaceous (Wakita et al., 1998). The Meratus
Complex is interpreted to record a phase of collision
and accretion along the southern margin of
Sundaland during the mid Cretaceous, and now
separates the Barito Basin from the smaller AsemAsem Basin and the Paternoster Platform to the east.
The stratigraphic similarity between these areas
suggests they were once connected, forming a single
depocentre throughout much of the Paleogene and
Early Neogene, prior to the uplift of the Meratus
Complex.
The oldest sedimentary rocks of the Barito Basin
succession are assigned to the Tanjung Formation.
They include conglomerates, sandstones, siltstones,
mudstones, limestones and coal, deposited in a
fluvio-tidal coastal plain to marginal marine setting.
Palynomorph assemblages indicate deposition began
in the late Middle Eocene and foraminifera show
that it continued until latest Early Oligocene. During
this time, sediment was being sourced from the west
and southwest. The Tanjung Formation is overlain
by the Montalat Formation in the north and the
Berai Formation in the south. These are laterally
equivalent in age and were deposited in marginal
fluvio-deltaic
to
fully
marine
conditions
respectively. Foraminiferal assemblages indicate
this phase of deposition continued until the Early
Miocene. The Warukin Formation overlies these
formations, and includes limestones, mudstones,
siltstones, sandstones and lignites deposited in a
marginal
marine
to
fluviodeltaic
setting.
Palynomorph assemblages date the top of the
formation as Late Miocene. Palaeocurrent data
indicate sediment was being transported from the
west for the oldest part of the formation, and partly
from the east for the younger coal-bearing
sequences. It is suggested that this reversal in
palaeoflow records uplift of the Meratus Mountains.
*
Royal Holloway University of London
** Palynova Limited
*** University College London
A number of models have been proposed to explain
the evolution of the Barito Basin, largely developed
from hydrocarbon exploration. However, due to the
limited number of biostratigraphic analyses and
scarcity of age-diagnostic fossils, the sedimentary
succession has, until this study been poorly dated.
Also, there are no published studies investigating the
provenance of the sandstones. Consequently, the
sediment source areas have never been identified
although the Schwaner Complex is often suggested
as the sediment source during the Paleogene (e.g.
Rose & Hartono, 1978; Hamilton, 1979; Siregar &
Sunaryo, 1980; Courteney et al.1991; van de Weerd
& Armin, 1992; Satyana et al., 1999). This paper
presents results from an extensive field-based study
conducted in the Barito Basin. A revised
stratigraphy is presented, built on existing
nomenclature, and better dated using palynology
and
foraminiferal
assemblages.
Sandstone
petrography, U-Pb dating of zircons and
palaeocurrent data suggest new interpretations of
sandstone provenance. These new data have
significance for hydrocarbon exploration in the
basin and provide important information on the
geological evolution of the surrounding region.
grains older than 1000 Ma. Data were processed
using Isoplot™. A total of 1539 concordant U-Pb
ages
were
obtained.
766
palaeocurrent
measurements were collected from dune cross-beds
within channel sand bars and small-scale ripples. All
measurements were corrected for structural dip. The
Rayleigh’s Test for a Preferred Trend was applied to
all datasets. Critical values are given by Mardia
(1972). Stratigraphic logs, lithofacies analyses, trace
fossils, palynomorphs and foraminifera have been
used to determine depositional environments of the
sedimentary succession.
EOCENE PALYNOLOGICAL ZONATION
METHODS
Palynomorphs and foraminifera have been used to
date the sedimentary succession. Palynological
analysis was conducted by Lemigas in Jakarta. No
palynological zonation for the Eocene of the Sunda
region has been published, and so this study has
provided the basis for such a zonation, described in
summary form below. For the Miocene, reference is
made to the zonation of Morley (1978, 1991).
Foraminifera were analysed at University College
London by Dr. Marcelle BouDagher-Fadel and
sediments have been dated using larger foraminifera
by reference to the Letter Stage scheme of van der
Vlerk & Umbgrove (1927) as modified by Adams
(1970), BouDagher-Fadel & Banner (1999) and
BouDagher-Fadel
(2008)
and
planktonic
foraminifera by reference to Tourmarkine &
Luterbacher (1985) for the Eocene, and Bolli &
Saunders (1985) for the post Eocene. Letter Stages
and planktonic foraminiferal zones are correlated in
BouDagher-Fadel (2008). Sandstone provenance
was determined from detrital modes and U-Pb
dating of detrital zircons. Detrital modes were
determined from 80 sandstones. Zircons from 17
sandstone samples for which the stratigraphic age
was known were dated at University College
London, using LA-ICPMS. The New Wave 213
aperture-imaged,
frequency-quintupled
laser
ablation system (213 nm) was used, coupled to an
Agilent 750 quadrupole-based ICP-MS. Real time
data were processed using GLITTER™. Repeated
measurements of external zircon standard Plesovic
(reference age determined by thermal ionization
mass spectrometry (TIMS) of 337.13±0.37 Ma
(Sláma et al., 2008)) and NIST 612 silicate glass
(Pearce et al., 1997) were used to correct for
instrumental mass bias and depth-dependent interelement fractionation of Pb, Th and U. Data were
filtered using standard discordance tests with a 10%
cut-off. The 206Pb/238U ratio was used to determine
ages less than 1000 Ma and the 207Pb/206Pb ratio for
Since no published palynological zonation is
available to characterise the Middle-Late Eocene
boundary, a reference section was compiled on
which a zonation could be based. Due to limited
exposures, several profiles from the same area were
joined to form a single reference section containing
41 samples. The palynological zones are defined as
follows:
Zone E6 - Middle Eocene
Characterised by the presence of the Middle Eocene
markers
Beaupreadites
matsuokae
and
Polygalacidites clarus in an assemblage dominated
by ‘Indian’ taxa such as Palmaepollenites spp,
Lanagiopollis spp, Lakiapollis ovatus and
Retistephanocolpites williamsi. All are common to
abundant in the Middle Eocene Nanggulan
Formation (Lelono, 2000).
Zone E7 - Late Eocene
Characterised by the first consistent occurrence of
Cicatricosisporites dorogensis, and by the absence
of Meyeripollis nayarkotensis, which ranges from
the base of the overlying zone.
Zone E8 - Late Eocene
Based on the regular presence of Meyeripollis
nayarkotensis and the absence of Magnastriatites
howardi, which ranges from the base of the
overlying zone.
Zone E9 - Late Eocene
Characterised by the overlap of Magnastriatites
howardi and the Eocene marker Proxapertites
operculatus, which has its top at topmost Eocene in
Southeast Asia, India and Africa (Morley, 2000).
STRATIGRAPHY
The sedimentary succession of the Barito Basin
unconformably overlies basement rocks of
Paleocene and older age (Sikumbang, 1986). The
succession comprises five formations that record a
full transgressive to regressive cycle (Fig. 2). The
oldest sedimentary rocks are assigned to the
Tanjung Formation and were deposited in a fluviotidal coastal plain to marginal marine environment.
The formation becomes increasingly marineinfluenced up section. Palynomorph assemblages
date the base of the formation as late Middle Eocene
by reference to palynological zone E6 (see Fig. 2).
The assemblages contain common elements which
relate to the Middle Eocene dispersal of plant taxa
from India (Morley, 1998; Lelono, 2000). The major
part of the Tanjung Formation is Late Eocene and
Early Oligocene. The Late Eocene interval is dated
palynologically by reference to the evolutionary
appearances of Cicatricosisporites dorogensis,
Meyeripollis nayarkotensis and Magnastriatites
howardi. The latter taxon is often thought to have
first appeared in the basal Oligocene (Germeraad et
al. 1968), but is recorded commonly in the Tanjung
Formation stratigraphically below well dated Late
Eocene marine sediments with common planktonics,
which
include
Turborotalia
pomeroli,
Globigerinatheka spp and Hantkenina alabamensis,
indicating the Late Eocene planktonic zone P15P16. The age of the top of the formation is referred
to Letter Stage Td (late Early Oligocene) by
reference to the overlap of the larger foraminifera
Nummulites fichteli and Eulepidina spp.
The Tanjung Formation is overlain by the Berai
Formation in the south and the Montalat Formation
in the far north of the basin. They are laterally
equivalent in age but are lithologically dissimilar.
The Berai Formation records fully marine
conditions, and is characterised by shallow water
platform carbonate rocks. The Montalat Formation
records marginal marine to braid delta deposition
and extends across the Barito/Kutai divide. The base
of the Berai Formation has been referred to Te1 to
lower Te5 Letter Stages (planktonic zone P21-N4)
based on the presence of Heterostegina borneensis
and
association
with
overlying
samples
(BouDagher-Fadel, 2008).
The Warukin Formation overlies the Berai and
Montalat Formations. It records a return to shallow
marine and then terrestrial, fluvio-deltaic conditions.
The base of the formation shows distinct marine
influence and can be referred to upper Te5 to middle
Tf1 Letter Stages (planktonic zone N6-N8) based on
the presence of Miogypsinodella sp., Miogypsina
spp., and L. (N) brouweri and association with
underlying samples (BouDagher-Fadel, 2008). The
top of the formation is older than 7.4 Ma based on
reference to the
palynological zone.
Florschuetzia
meridionalis
The Dahor Formation was not investigated during
this study. It is reported to overly the Warukin
Formation and comprises a succession of polymict
fluviatile and shallow marine sedimentary rocks
(Satyana & Silitonga, 1994; Seeley & Senden, 1994;
Satyana, 1995; Gander et al., 2008) derived from the
Meratus Complex during the Plio-Pleistocene.
SANDSTONE COMPOSITION
Tanjung Formation
Sandstones of the Tanjung Formation are quartz
arenites and sub-litharenites (Folk, 1968) and plot
within the ‘craton interior’ and ‘quartzose recycled’
fields of Dickinson & Suczek (1979), see Fig. 3.
They contain mainly angular monocrystalline and
rounded polycrystalline quartz grains with minor
anhedral feldspars, sub-angular radiolaria-bearing
chert, and lithic fragments. Monocrystalline quartz
has either simple or slightly undulose extinction
pattern and typically contains strings or bands of
fluid inclusions, indicating a plutonic origin.
Polycrystalline quartz has high angles of undulose
extinction, more than three crystals per grain (often
showing alignment), bimodal crystal size within a
single grain, and strings of fluid inclusions. These
features indicate a metamorphic parentage (Smyth et
al., 2008a). Feldspars comprise <1% of the total
composition, and are mainly strained plagioclase
(undulose extinction) suggesting a metamorphic
origin or a post-depositional deformation (Passchier
& Trouw, 2005). Most of the lithic fragments are
schistose.
Montalat Formation
Sandstones from the Montalat Formation are quartz
arenites, sub-arkoses and minor sub-litharenites
(Folk, 1968). The Dickinson & Suczek (1979)
ternary plots suggest a ‘craton interior’ provenance
(Fig. 3). The sandstones are composed of angular
monocrystalline and rounded polycrystalline quartz
grains with minor anhedral feldspars and lithic
fragments. Monocrystalline quartz grains have
simple or slightly undulose extinction pattern and
contain characteristics of a plutonic origin, or are
inclusion-free, exceptionally bright in thin section
and have sharp extinction, suggesting a volcanic
parentage (Smyth et al., 2008a). Polycrystalline
quartz has features indicative of a metamorphic
origin. Feldspars comprise 2.4% of the total
composition. These are mainly strained and
unstrained plagioclase with minor K-feldspar
indicating a predominately metamorphic parentage
with minor input from an acid plutonic source.
Lithic grains include schist and igneous rock
fragments.
Warukin Formation
Sandstones of the Warukin Formation are quartz
arenites, and rare sub-arkoses (Folk, 1968) and plot
mainly within the ‘quartzose recycled’ field of
Dickinson & Suczek (1979), see Fig. 3. They
contain a mixture of angular and rounded
monocrystalline quartz and rounded polycrystalline
quartz grains with minor amounts of anhedral and
rounded feldspar, rounded clasts of radiolariabearing chert and lithic fragments. Monocrystalline
quartz grains contain features suggestive of plutonic
and volcanic origin. A number of rounded grains
with diagenetic quartz overgrowths were identified,
implying multiple recycling. Most of the
polycrystalline quartz grains are of probable
metamorphic origin. Feldspars comprise 1% of the
total composition and are mainly strained
plagioclase and K-feldspar, suggesting metamorphic
and plutonic provenance. Lithic fragments are
mainly composed of schistose material.
All the sandstones of the three formations are
compositionally mature, yet texturally immature
which is relatively unusual. Tropical alteration can
significantly alter the composition of sandstone by
the systematic destruction of unstable lithic
fragments and feldspars during transport, deposition
and storage. Borneo has been situated within
tropical latitudes and climate since the Mesozoic
and we believe the apparent discordance between
compositional and textural maturity has been
produced by intense tropical processes. The standard
plots of detrital modes may therefore mislead in
identifying provenance because they were
developed in mainly non-tropical settings.
PALAEOCURRENT ANALYSIS
Palaeocurrent data for the Tanjung, Montalat and
Warukin Formations are shown in Figs 4 to 6. The
data indicate that during the deposition of the
Tambak Member of the Tanjung Formation (which
accounts for approximately 80% of the formation),
sediment was transported by rivers towards the
north. Orientations of small-scale ripples within the
tidal facies indicate a SW-directed tidal flood. This
implies the coastline was located towards the
northeast. Palaeocurrent measurements from the
Kiwa Member of the Montalat Formation indicate
sediment was being transported towards the
northwest. Palaeocurrent data from the Barabai
Member of the Warukin Formation indicate
sediment was transported towards the east-southeast.
This continued into the lower part of the Tapin
Member. A change is recorded from the top of the
Tapin Member where palaeocurrent data indicate
sediment was being transported towards the west.
GEOCHRONOLOGY
ZIRCONS
OF
DETRITAL
Tanjung Formation
Detrital zircons were analysed from seven samples
collected from the Mangkook and Tambak Members
of the formation. A total of 656 concordant U-Pb
ages were obtained. Ages range from Neoarchean to
Cretaceous (Fig. 7). The most prominent
populations are Cretaceous, of which 32% are Early
Cretaceous (140±5.7 Ma to 99.8±6.1 Ma) and 62%
Late Cretaceous (99.3±4.8 Ma to 70.7±5 Ma), and
Devonian- Carboniferous (415.8±12.6 Ma to
300.5±5.1 Ma) with smaller Permo-Triassic
(295.2±10.5 Ma to 205.7±7.6 Ma), Ordovician Silurian (484.1±15.7 Ma to 417.6±13.2 Ma) and
Proterozoic (2496.7±22 Ma to 544.8±16 Ma)
populations. Jurassic and Archean grains are rare.
Montalat Formation
Detrital zircons were analysed from two samples,
one from each member of the formation. A total of
177 concordant U-Pb ages were obtained. Ages
from the Bentot Member are bimodally distributed,
comprising Cretaceous (122.9±9.3 Ma to 66.9±19.9
Ma) and Proterozoic (2426.2±26.6 Ma to 906.4±44
Ma) populations. The Cretaceous population is
dominated by Early Cretaceous zircons (122.9±9.3
Ma to 99.7±21.7 Ma), and the Proterozoic
population is dominated by Paleoproterozoic grains
(2426.2±26.6 Ma to 1600.8±26.3 Ma). Ages
obtained from the Kiwa Member range from
Cretaceous to Proterozoic. The most prominent
population is Cretaceous (122.6±21.8 Ma to
76.6±19.5 Ma). 79% of which are Late Cretaceous.
There is a small Devonian- Carboniferous
population (398.6±30.5 Ma to 313.2±26.7 Ma), but
zircons of other ages are rare.
Warukin Formation
Detrital zircons from seven samples collected
the Warukin Formation were analysed.
members were represented. A total of
concordant U-Pb ages were obtained, ranging
from
Both
492
from
Mesoarchean to Paleogene. The largest populations
are Cretaceous (143.9±9.3 Ma to 68.6±5.1 Ma),
Permo-Triassic (295.7±18.5 Ma to 204.1±14.5 Ma)
and Proterozoic (2493.0±45.1 Ma to 546.8±20.4
Ma). Jurassic ages form a small population
(190.9±18.1 Ma to 145.8±25.6 Ma). Grains of other
ages are rare.
ZIRCON MORPHOLOGY
Zircon morphology (expressed in terms of width-tolength ratio and prismatic character) is considered to
reflect the physical and chemical conditions present
during crystal growth (Schafer & Dorr, 1997). For
example, elongate or needle-like crystals are
commonly associated with rapidly ascending
magmas, high-level granites and volcanic eruptive
deposits (Corfu et al., 2003), whilst crystals with a
low width-to-length ratio are produced during slowcooling of plutonic intrusions. Representative
images showing zircon morphology are presented in
Fig. 8. Zircon types and their associated ages are
described below.
The Tanjung Formation contains euhedral,
elongate grains (Cretaceous age); euhedral, nonelongate grains (Cretaceous and Jurassic ages);
euhedral, stubby grains (Cretaceous and PermoTriassic ages) and well-rounded and angular grain
fragments (all ages from Neoarchean to Cretaceous).
Zircons from the Montalat Formation include
euhedral, elongate grains (Cretaceous and
Proterozoic ages); euhedral, stubby grains
(Cretaceous age); non-elongate, mostly rounded
grains (Cretaceous and Triassic-Devonian ages);
angular grain fragments (Cretaceous and Proterozoic
ages) and rounded grain fragments (all ages from
Cretaceous to Proterozoic). Zircons from the
Warukin Formation include elongate grains
(Cretaceous, Permo-Triassic and Archean ages);
euhedral, non-elongate grains (Paleogene); euhedral,
stubby grains (Cretaceous, Permian and Proterozoic
ages); rounded, non-elongate grains and rounded
and angular fragments (all ages from Cretaceous to
Mesoarchean). Many of the older, rounded zircons
from each formation have etched and pitted
surfaces, interpreted as features of multiple
recycling.
POSSIBLE SOURCE AREAS
It is commonly believed that the Schwaner Complex
was providing sediment to the Barito Basin area
during much of the Cenozoic, and the Meratus
Complex provided additional sediment into the
basin during the Neogene. Therefore, radiometric
ages from these areas have been compiled. The
Lower Cretaceous Schwaner granites range in age
from 130 Ma to 100 Ma (Williams et al., 1988) and
form the main pluton in the Schwaner Complex,
based on K-Ar analysis of hornblende and biotite.
Zircons from a smaller Upper Cretaceous pluton
yield ages of 87 Ma and 80 Ma (van Hattum et al.,
2006). The Pinoh Metamorphic rocks form an E-Wtrending belt in the north of the Schwaner Complex.
Their exact age is unknown. All that is known for
certain is they are older than the Cretaceous granites
that intrude them. In the Meratus Complex a Lower
Cretaceous granite has a K-Ar age of 115 Ma
(Heryanto et al., 1994) and most metamorphic rocks
have Cretaceous K-Ar ages that range from 140 to
105 Ma (Parkinson et al., 1998). Wakita et al.
(1998) reported 2 Jurassic K-Ar ages of 165 and 180
Ma from metamorphic rocks.
Palaeocurrent data suggest a southern source for the
Tanjung Formation. The Karimunjawa Arch located
to the SW of the Barito Basin (Fig. 1, inset) is
reported to have been elevated throughout the Late
Eocene to Late Miocene (Bishop, 1980; Smyth et
al., 2008b) and supplying sediment into the East and
West Java Basins (Smyth et al., 2008b). It contains
abundant exposures of quartz-rich sandstones,
metasedimentary rocks, and quartz- and mica-rich
phyllites and schists (Smyth, 2008). Zircons were
analysed from Karimunjawa Island situated in the
centre of the arch. A total of 186 concordant U-Pb
ages were obtained (Fig. 9, top). These range from
Proterozoic to Triassic. The dominant populations
are Permo-Triassic (294.9±10.6 Ma to 218.5±5.4
Ma), Carboniferous-Devonian (401.8±9.3 Ma to
317.3±10.2 Ma) and Proterozoic (2439.7±14.8 Ma
to 852.1±24.3 Ma). There is also a small population
of Silurian and rare Ordovician ages.
DISCUSSION
The Barito Basin overlies basement rocks of
distinctly different character. To the west is the
Schwaner Complex, comprising plutonic, volcanic
and metamorphic rocks that represent part of the
pre-Cretaceous continental basement of Sundaland.
To the east is the Meratus Complex. It records
suturing along the Sundaland margin in the mid
Cretaceous, but its subsequent history is poorly
known due to limited exposures, most of which are
located within the Meratus Mountains. The complex
comprises Jurassic and Cretaceous metamorphic
rocks, Cretaceous granitic, ophiolitic and arc rocks
(Sikumbang, 1986; Wakita et al., 1998). Upper
Cretaceous and Paleocene volcanic rocks and
coarse-grained clastic sedimentary rocks of the
Manunggul Formation (Sikumbang, 1986) are also
considered here as part of the basement.
The Tanjung Formation overlies these basement
rocks unconformably. The oldest rocks above the
unconformity are conglomerates and sandstones
with palynomorph-bearing mudstone interbeds of
the Mangkook Member. The mudstones are late
Middle Eocene age. The member records the erosion
and infilling of irregular basement topography and
was deposited by debris flows and braided rivers.
These are overlain by sandstones, siltstones,
mudstones and coals (Tambak Member) deposited
across a wide intertidal floodplain constructed by
rivers flowing towards the north along the present
western flank of the Meratus Complex. The
floodplain extended from the Schwaner Complex in
the west, to the Paternoster Platform in the east, and
from the area now submerged under the Java Sea to
the northern margin of the present Barito Basin.
Overlying the Tambak Member are fine grained
sedimentary rocks of the Pagat Member, deposited
in a marginal to shallow marine setting until the late
Early Oligocene. Subsurface data and surface
mapping show the Tanjung Formation thins to the
west, east and south, with the greatest thicknesses
north of Tanjung (Siregar & Sunaryo, 1980). These
observations suggest a N-S orientation for the axis
of a wide Eocene depocentre, with the thickest part
of the sequence approximately in the position of the
present-day Meratus Mountains. This configuration
suggests that sediment could have been derived
from the east, west or south.
An eastern source (SW Sulawesi) would have
provided texturally immature sediment, rich in
volcanic material. This is not supported by our data.
In addition, there was mid-Eocene extension
between the Paternoster Platform and SW Sulawesi,
and by the Early Oligocene, much of the area to the
east of the basin was below sea level and the site of
carbonate deposition. A western source (Schwaner
Complex) as previously suggested (e.g. Hamilton,
1979) would have supplied texturally immature,
quartz-rich sediment with a significant plutonic
component, and zircons of dominantly Cretaceous
age. These characteristics are observed in all
sandstones of the Tanjung Formation. However, a
Schwaner source does not explain the zircons older
than Cretaceous. Older zircons may have been
derived from the Pinoh Metamorphic Group (in the
Schwaner Complex). However, this seems unlikely
as the rocks are typically zircon-poor, and their
position is inconsistent with palaeocurrent data.
Extensive outcrops of Permo-Triassic granites are
present in the Thai-Malay Peninsula, but transport
from these distant areas would require a complicated
and long drainage pattern in conflict with previous
provenance studies (e.g. Clements, 2008). A
plausible southern source area is the Karimunjawa
Arch and basement areas beneath the East Java Sea.
Hall et al. (2009) and Granath et al. (2011) suggest
this region is underlain by Australian basement,
overlain by a thick Permo-Triassic sequence. This
could have produced the quartz and metamorphic
debris observed in the sandstones, and would also
account for the zircons of Permo-Triassic and older
age. Furthermore, only a simple and relatively short
(<300 km) drainage pattern would be needed to
transport sediment northeast from the Karimunjawa
Arch into the Barito Basin area where flow was then
directed towards the north (Fig. 10). We suggest
both the Schwaner Complex and the Karimunjawa
Arch were supplying sediment to the Barito area
from the late Middle Eocene to late Early
Oligocene.
During Late Oligocene to Early Miocene, extensive
shallow water platform carbonates were deposited
across much of the Barito Basin area, and deep
water sediments were being deposited to the north,
in the southern part of the Kutai Basin (Moss &
Chambers, 1999). Across the northern margin of the
Barito area, a large braid delta formed (Kiwa
Member, Montalat Formation) in which deposition
continued into the Early Miocene. Based on this
palaeogeography, the sandstones of the Kiwa
Member were likely sourced from the Schwaner
Complex and/or uplifted sedimentary successions of
northwest Borneo (e.g. Rajang-Crocker Group).
These would have produced a mixture of texturally
immature and mature fragments, quartz and lithicrich, including radiolaria-bearing chert and plutonic
and
metamorphic
debris.
The
sandstone
compositions and textural features suggest the
Schwaner Complex was the dominant source, which
would also account for the large number of
Cretaceous zircons. It is unlikely that significant
numbers of zircons of older age were derived from
the Pinoh Metamorphic Group as these rocks
typically lack zircons. Alternatively, the small
number of older grains reflects a less important
source
to
the
northwest.
Palaeocurrent
measurements conflict with this interpretation, but
were collected from a relatively small area (<6 km2)
and may record local flow.
By the Early Miocene, deposition of the Warukin
Formation had begun, signifying the onset of a
regression, probably driven by regional tectonic
changes (e.g. Hutchison et al., 2000; Hall, 2002).
Carbonate deposition was replaced by fluvio-deltaic
sedimentation. The Schwaner Complex and
Karimunjawa Arch were emergent to the west and
south respectively, and marine conditions existed to
the east. This palaeogeography suggests sediment
could have been transported from the northwest,
west or south. A northwestern source would be
expected to supply texturally mature quartz- and
lithic-rich material and radiolaria-bearing chert
fragments. Material of this character is present
within the Warukin sandstones, and the age spectra
of zircons are very similar to those of north Borneo
(Fig. 9, bottom). The abundance of first cycle
plutonic and volcanic quartz and a prominent
Cretaceous zircon population strongly suggests
Schwaner derivation, and is supported by
palaeocurrent data. Sediment derived from the
Karimunjawa Arch may be represented by schistose
lithic fragments and polycrystalline quartz, but this
could also have a Pinoh Metamorphic origin. There
is no evidence that the Meratus Complex was
emergent at this time.
By the Late Miocene, the upper part of the Tapin
Member was being deposited in a brackish,
fluviatile environment. Emergent areas included the
Rajang-Crocker Group, Schwaner Complex, and
possibly the Meratus Complex and Karimunjawa
Arch. The sandstones of the Tapin Member contain
many features suggesting a Schwaner Complex and
Rajang-Crocker Group provenance. These include
their compositions, mixed textural maturities and
zircon ages. If uplift of the Meratus Complex had
begun, debris of Meratus basement rocks and
Tanjung Formation would be expected in the
sandstones. However, material of Meratus character
is absent, and despite the abundance of recycled
material, differentiating between recycled RajangCrocker Group and recycled Tanjung Formation
material is difficult. Uplift of the Meratus Complex
could explain the change to west-directed
palaeocurrents at the top of the Tapin Member, and
the absence of Meratus debris may be due to fact
that the Meratus basement rocks were not yet
exposed. We suggest that the sandstones of the
Warukin Formation were mainly derived from the
Schwaner Complex and to a lesser extent the
Rajang-Crocker Group. Towards the top of the
formation, it is probable that material was also
sourced from the Tanjung Formation as a result of
Meratus uplift. Palaeocurrent data suggest uplift
may have begun in the Late Miocene.
CONCLUSIONS
From this study, the following conclusions have
been made:
•
•
•
•
•
•
The oldest sedimentary rocks of the Barito
Basin are late Middle Eocene. This is
considerably younger than some previous
estimates (e.g. Campbell & Ardhana, 1988;
Kusuma & Darin, 1989; Bon et al., 1996).
The sandstones of the Tanjung Formation were
probably derived mainly from the Schwaner
Complex in the eas, and the Karimunjawa Arch
in the southwest.
During the Late Oligocene, an extensive braid
delta formed across the northern margin of the
Barito Basin area, probably fed by material shed
from the Schwaner Complex in the west and the
Rajang-Crocker Group in the northwest.
By the Early Miocene carbonate deposition was
replaced by marginal marine to fluvio-deltaic
deposition, represented by the Warukin
Formation. The top of the formation is assigned
to Late Miocene.
The sandstones of the Warukin Formation were
mainly derived from the Schwaner Complex and
to a lesser extent the Rajang-Crocker Group.
Towards the top of the formation, it is probable
that material was also sourced from the Tanjung
Formation as a result of Meratus uplift.
Palaeocurrent data suggest uplift of the Meratus
Complex may have begun in the Late Miocene.
ACKNOWLEDGEMENTS
We thank the following people for their assistance
and contribution to this study: B. Sapiie from the
Institut Teknologi Banding for his support and help
in organising fieldwork; A. Rudyawan and Y.
Sindhu for their valued assistance in the field; for
discussions concerning the geology and evolution of
Borneo and the Barito Basin we are grateful to J.
Howes, D. Le Heron, G. Nichols, M. Cottam, I.
Watkinson, J.T. Van Gorsel, I. Sevastjanova, B.
Clements, Y. Kusnandar, S. Pollis and E. Deman .
This research was funded by the SEARG .
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Figure 1 – Cenozoic geology of the Barito and Asem-Asem Basins (after Supriatna et al. (1994)).
Figure 2 – Generalised stratigraphy of the Barito Basin. Age diagnostic fauna and flora from this study are
shown. East Indian (EI) Letter Stages correlated with planktonic zones by BouDagher-Fadel
(2008). Numerical ages from GTS2004 (Gradstein et al., 2004).
Figure 3 – Ternary diagrams showing detrital modes of sandstones from the Tanjung, Montalat and
Warukin Formations. (Left) sandstone classification according to Folk (1968). (Right) tectonic
setting according to QmFLt ternary plot of Dickinson & Suczek (1979). Q: quartz, Qm:
monocrystalline quartz, F: feldspar, L: lithics, Lt: total lithics (including polycrystalline quartz).
Figure 4 – Palaeocurrent data for the Tambak Member of the Tanjung Formation. Individual locations with
fluvial data are shown on map. Total fluvial data are shown at top left. In addition, palaeocurrent
data collected from small-scale ripples within tidal facies are shown in blue, centre left. Bin size
is 10° on all plots.
Figure 5 – Palaeocurrent data for the Kiwa Member of the Montalat Formation. Total fluvial data is shown
top left. Bin size is 10° on all plots.
Figure 6 – Palaeocurrent data for Warukin Formation. Total fluvial data for the Barabai Member are shown
bottom left. Total fluvial data for the lower part of the Tapin Member are shown centre left.
Total fluvial data for the top of the Tapin Member are shown top left. Bin size is 10° on all
plots.
Figure 7 – U-Pb ages of zircons analysed from sandstones of the Tanjung, Montalat and Warukin
Formations.
Figure 8 – Examples of zircon morphologies present in the samples analysed. (A) euhedral, elongate, (B,
C) euhedral, non-elongate, (D) rounded, non-elongate. Scale bar is 100µ in all images.
Figure 9 – (Top) U-Pb ages of zircons from Karimunjawa Arch samples. (Bottom) U-Pb ages of zircons
from sandstones of the Rajang-Crocker Groups, northern Borneo (after van Hattum, 2005).
Figure 10 – Map showing suggested flow into the Barito Basin area during the Late Eocene based on data
of this study. Flow into west Java from the Schwaner Complex, reported by Clements (2008)
is also shown.