the lowest part of the OPS. It is considered to represent fragmented upper sections of accreted seamounts.
3.3. Chert Ribbon chert and associated siliceous shale are mostly
reddish brown in color, but some of them are gray and green. The chert is made up mostly of radiolarian skeletons
and and their fragments, and thickness of beds ranges from 1 to 20 cm. The lower part of the chert sequence is sometimes
interbedded with light gray limestone. The chert and lime- stone is underlain by pillow basalt. Chert grades into silic-
eous shale toward the stratigraphic top in some localities. The ages of the chert components are well defined by radi-
olarian biostratigraphy Okamoto et al., 1994; Wakita et al., 1991, 1994a,b, 1997, 1998; Munasri, 1995; Wakita, 1997.
The chert of the Meratus Complex ranges in age from early Middle Jurassic to late Early Cretaceous, while the
chert of the Luk Ulo Complex ranges from Early Cretac- eous to latest Late Cretaceous Fig. 3. The radiolarian
chert of the Luk Ulo and Meratus Complexes was originally pelagic sediment deposited as radiolarian ooze on the ocean
floor.
3.4. Melange The melange of the Luk Ulo Complex in the Karangsam-
bung area, central Java includes clasts of sandstone, shale, siliceous shale, chert, limestone, basalt, rhyolite and schist
within a shale matrix, which is locally sheared. The clasts range in size from 1 mm to several meters, and sometimes
include larger tectonic blocks. The dominant clast type is sandstone, which contains angular to subrounded fragments
of quartz, feldspar and mica, as well as fragments of felsic to basic volcanic rocks. Although the complex itself is inferred
to be a melange, the complex is just an assemblage of various kinds of tectonic blocks. Melanges containing clasts
of various rock types, with highly sheared matrix are loca- lized in some places. They are highly tectonized pebbly
mudstone which stratigraphically grades into a turbidite formation. The shale matrices of the melange were sheared
but not pervasively sheared, and slaty cleavages are devel- oped within the matrix only locally.
Polymict melange in the Bantimala Complex generally occurs in narrow zones between the tectonic slices, and
includes clasts and blocks of chert, sandstone, and siliceous shale with subordinate basalt, limestone and schist
embedded within a variably sheared shale matrix. Frag- ments of metamorphic rocks are very rare. The clasts are
subrounded to subangular, and rhomboidal, spherical, blocky or irregular in shape. Long axes of clasts range
from several millimeters to several hundred meters.
Melange of the Meratus Complex crops out on Pulau Laut. The melange includes clasts and blocks of Jurassic
to Cretaceous chert, siliceous shale, basalt, limestone, marl and manganese carbonate nodules embedded within
a sheared shale matrix. Sandstone or other coarse-grained terrigenous sediments are lacking in the melange. Chert and
limestone are thinly bedded. Basalt is mainly lava, and pillow structures are sometimes preserved. Limestone clasts
are locally dominant in the melange. Fragments of manga- nese carbonate nodules are rare. The clasts are subrounded
to subangular, lenticular to blocky in shape. Clast size ranges from several millimeters to several hundred meters
long. Chert sometimes includes well-preserved radiolarians, ranging in age from Middle Jurassic to Early Cretaceous
late Albian to early Cenomanian age. Siliceous shale clasts include radiolarians of Early Cretaceous age. The
age of melange formation is estimated as slightly younger than the youngest age of the components of the melanges
Fig. 3.
4. Collisional units
The Bantimala Complex is composed mainly of sand- stone, conglomerate, shale, siliceous shale, chert, basalt,
ultramafic rocks, schist, schist breccia and felsic intrusive rocks. Most of the components are similar to those of the
Luk Ulo and Meratus complexes. The Jurassic Paremba sandstone and schist breccia is unique to the Bantimala
Complex. An “unusual unconformity”, with chert atop a schistose basement Haile et al., 1979, the Jurassic
Paremba Sandstone Sukamto and Westermann, 1992, and ultra-high pressure rocks Parkinson et al., 1996,
1998 are the keys to understanding the tectonics of the Bantimala Complex.
The chert of the Bantimala Complex was deposited in a forearc setting, near the provenance of schist breccia and
coarse-grained sandstone, in a relatively short period from the late Albian to early Cenomanian, and is contempora-
neous with the coarse-grained flysch sequence of the Balangbaru Formation. These features suggest that the
chert of the Bantimala Complex was formed in a back-arc or fore-arc setting.
4.1. Allochthon The oldest lithotectonic unit of the Bantimala Complex is
a Jurassic shallow marine formation, the Paremba Sand- stone Fig. 3. The lower part of the Paremba Sandstone is
composed of thinly bedded sandstone and shale, intercalated with thin limestone layers. Some shallow marine sedimen-
tary structures such as ripple and convolute laminations are recognized. The upper part of the Paremba Sandstone
includes substantial conglomerate layers containing pebbles of basalt and schist. Ammonites Middle Liassic Fucini-
ceras, gastropods and brachiopods of Early and Middle Jurassic occur in the Paremba Sandstone Sukamto and
Westermann, 1992.
The Paremba Sandstone and other Jurassic continental clastics in central and East Sulawesi were deposited as sedi-
mentary formations on an allochthonous continental frag- ment detached from Gondwanaland. As the Paremba
K. Wakita Journal of Asian Earth Sciences 18 2000 739–749 743
Sandstone is older than the high PT metamorphic rocks, the formation is older than the accretion and collision stage. The
sandstone is incorporated within the tectonic assemblage in the Bantimala Complex as tectonic slices detached from a
colliding microcontinent in late Cretaceous time.
4.2. High and very high PT metamorphic rocks Metamorphic rocks in the Cretaceous suture zone are
phyllite, quartz-mica schist, greenschist, glaucophane schist, and eclogite. They are mostly of high PT type,
shown by high PT mineral assemblages Miyazaki et al., 1998; Parkinson et al., 1998.
The major types of metamorphic rock in the Luk Ulo, Bantimala,
Meratus and
Pompangeo complexes
are described as follows:
Lok Ulo: Amphibolite-grade schist predominantly garnet-mica-
quartz schist is tectonically intercalated within larger tectonic slices and blocks of sedimentary rocks. Small
amounts of glaucophane rock, garnet amphibolite, lawso- nite eclogite and jadeite-quartz-glaucophane rock occur
as small tectonic blocks in sheared serpentinite along fault zones Miyazaki et al., 1998. The latter two types
were recrystallized at pressures
.18 kbar. Bantimala:
Low grade greenschists and glaucophane-bearing schists occur as imbricate slices in the Bantimala Complex. Peak
P–T conditions have been estimated at around 350– 450
8C and 5–8 kbar Miyazaki et al., 1996; Parkinson et al., 1998, and K–Ar ages are generally in the range
111–114 Ma Hamilton, 1979; Hasan, 1990; Wakita et al., 1996; Parkinson et al., 1998. Very high pressure
metamorphic rocks also occur, but are much less abun- dant. They occur as small tectonic blocks and slabs asso-
ciated with serpentinite and comprise eclogite and garnet- glaucophane rock P 18–24 kbar, T 580–6208C,
coesite-bearing
jadeite quarzites
P . 27
kbar, T 720–7608C and garnet amphibolite Miyazaki et
al., 1996; Parkinson et al., 1998. K–Ar ages of phengite for the VHP rocks are generally older than for the low-
grade schist country rocks: 132 7 Ma, 113 6 Ma and 124 6 Ma garnet-glaucophane rock; Wakita et al.,
1996 and 137 3 Ma eclogite; Parkinson et al., 1998.
Meratus: The complex is a tectonic assemblage of slabs and blocks
consisting of high-pressure metamorphic rocks Hauran Schist and Pelaihari Phyllite distributed in the SW part of
the Meratus Mountains. They occur as wedge-shaped tectonic blocks in fault contact with ultramafic rocks
and Cretaceous formations. The metamorphic rocks are divided into two types, low grade “Pelaihari Phyllite”,
and relatively higher grade “Hauran Schist”. The Hauran Schist includes glaucophane schist, chloritoid-quartz
schist, kyanite-quartz-phengite-chloritoid schist, garnet mica schist, quartz-mica schist, piemontite schist and
amphibolite. The protoliths of the Hauran Schist were predominantly pelitic and basic rocks, although the chlor-
itoid and kyanite-bearing schists are probably derived from bauxites and evaporites. K–Ar ages of micas
range from 110 to 180 Ma Wakita et al., 1998. Some of the metamorphic rocks from the Meratus
Complex of SE Kalimantan are clearly of continental origin. Kyanite-quartz and chloritoid-quartz schists of
the complex are probably derived from continental sedi- mentary cover rocks such as laterite. The same parentage
was proposed for similar metamorphic rocks of the Pompangeo Complex in Central Sulawesi Parkinson,
1991, 1996, 1998a,b.
4.3. Breccia-sandstone-chert sequence Metamorphic rocks in the Bantimala area are unconform-
ably overlain by schist breccia, which grades into radiolar- ian chert through sandstone interbedded with chert Fig. 3;
Haile et al., 1979; Wakita et al., 1994b. The schist breccia is mostly of sedimentary origin and contains angular frag-
ments of schists within a sandstone matrix. The size of fragments ranges from several centimeters to several tens
of centimeters. The metamorphic grade of the schist frag- ments is the same as that of the regional schists in the
Bantimala Complex. The overlying sandstone is rich in mica and quartz fragments, and sometimes contains radi-
olarian remains.
Thin beds of radiolarian chert are intercalated within coarse-gained sandstone. The number of chert beds increase
towards the top of the stratigraphic column. The chert layers range from 1 to 20 cm thick and are interbedded with thinner
shale layers less than 1 cm thick. The chert is rather muddy compared with cherts in other orogenic belts, and is
composed mainly of skeletons and fragments of radiolarians with a small amount of shale. The chert sometimes includes
well-preserved radiolarians of middle Cretaceous late Albian to early Cenomanian age, including Holocryptoca-
nium barbui, Thanarla conica, Archeodictypomitra vulgaris and Phopalosyringium majuroensis.
4.4. Forearc basin unit The Cretaceous forearc basin unit is developed over a wide
area, including South and West Kalimantan and South and West Sulawesi Figs. 2 and 3. The Balangbaru Formation of
South Sulawesi and the Pitap Formation of South Kalimantan have been well investigated Hasan, 1990, 1991; Sikumbang,
1986; Sikumbang and Heryanto, 1994.
Cretaceous flysch sequences of the Balangbaru Forma- tion are widely distributed to the N, NE and SE of the
Bantimala area Hasan, 1990, 1991. The formation is composed of interbedded sandstone and shale, conglomer-
ate, and pebbly shale. The radiolarian assemblage, which includes Rhopalosyringium majuroensis, Thanarla brouweri,
and Pseudodictyomitra sp., indicates that the Balangbaru
K. Wakita Journal of Asian Earth Sciences 18 2000 739–749 744
Formation is contemporaneous with the aforementioned radiolarian chert in the Bantimala Complex Wakita et al.,
1996, although Hasan 1990 reported Late Cretaceous foraminifers from the formation. The equivalent of the
Balangbaru Formation is located in the Barru and Latimo- jong areas of South Sulawesi.
The sandstone of the Balangbaru Formation is composed of quartz, micas, plagioclase and rock fragments of meta-
morphic, shale, and chert. The main provenance for the sandstones of the Balangbaru Formation was the meta-
morphic component of the Bantimala Complex.
The Pitap Formation consists mainly of flysch-type sedi- mentary rocks such as sandstone, siltstone, conglomerate
and shale with subsidiary limestone layers and blocks which contains the foraminifera Orbitolina cf. oculata of
Aptian–Albian age Sikumbang and Heryanto, 1994.
The Pitap Formation of the Meratus Complex and the Barangbaru Formation of the Bantimala Complex were
deposited in a forearc basin. The Selangkai Group of West Kalimantan is equivalent to the Pitap and Barangbaru
Formation. The forearc sedimentary units in West and South Kalimantan and South Sulawesi were accumulated
contemporaneously as terrestrial deposits in the wide region of the forearc basin Fig. 3.
5. Volcanic arc unit
