al., 1994; Wakita et al., 1998. The ages of components of the complex range from Jurassic to early Late Cretaceous
Fig. 3. These rocks are unconformably overlain by Late Cretaceous volcanic rocks and turbidite, such as the Pitap
Alino and Haruyan Pudak Formations. All these Meso- zoic rocks are unconformably covered by Eocene and
younger formations.
Similar complexes crop out in the Latimojong, Barru and Pompangeo areas, Sulawesi, and the Ciletuh and Jiwo Hills
areas in Java. In the Sintang area of West Kalimantan, the Late Cretaceous Selangkai Group includes Cretaceous
radiolarian chert, schist and limestone as olistoliths within turbidite-olistostrome sequences. These olistoliths are
remnants of a former accretionary wedge similar to that which generated the Luk Ulo and Meratus Complexes.
The components of these complexes can be subdivided into accretionary units, collisional units, volcanic arc units,
ophiolitic units, forearc basin units, intrusive and effusive units and cover formations, which reflect differing origins
and tectonic histories.
3. Accretionary units
Accretionary complexes
are characterized
by the
presence of melange, stacked tectonic slices, radiolarian chert underlain by pillow basalt, ophiolite, and recon-
structed “oceanic plate stratigraphy”. Among them, the oceanic plate stratigraphy OPS is the most important
feature
for the
recognition of
ancient accretionary
complexes. 3.1. Oceanic plate stratigraphy
The Luk Ulo Complex, Central Java and Meratus Complex, South Kalimantan include pillow basalt, lime-
stone, chert, siliceous shale, sandstone and shale as tectonic fragments. A succession, consisting in ascending order of
pillow basalt, interbedded limestone and chert, chert, silic- eous shale and turbidite, is preserved in part of the
complexes. Similar successions have also been reconstructed
K. Wakita Journal of Asian Earth Sciences 18 2000 739–749 741
Fig. 2. Major components of Cretaceous accretionary–collision complexes. Cretaceous accretionary–collision complexes are distributed between a continent Sundaland and microcontinents Paternoster, Buton etc.. Late Cretaceous accretionary–complexes are distributed in the following areas, i.e.1. Ciletuh, 2.
Karangsambung, 3. Jiwo Hills, 4. Bantimala, 5. Barru, 6. Latimojong, 7. Pompangeo, 8. Meratus, 9. Pulau Laut. Abbreviation of ages are as follows. JK: Jurassic to Cretaceous, K: Cretaceous, lK: Early Cretaceous, mK: middle Cretaceous, uK: Late Cretaceous, Tp: Paleogene, KT: Cretaceous to Tertiary.
using radiolarian biostratigraphy Wakita et al., 1994a, 1998.
This type of succession is called ‘Oceanic Plate Strati- graphy’ OPS Isozaki et al., 1990; Matsuda and Isozaki,
1991; Wakita, 1997. It is compiled by the following sequence of processes: generation of oceanic plate at the
oceanic ridge; formation of volcanic islands near the ridge, covered by calcareous reefs; sedimentation of calci-
lutite and radiolarian chert on the flank of the volcanic island; deposition of radiolarian skeletons on the oceanic
plate in a pelagic setting; sedimentary mixing of radiolarian remains and terrestrial grains to form siliceous shale in a
hemipelagic setting, and the sedimentation of coarse- grained sandstone and shale at or near the trench of the
convergent margin.
Reconstructed OPS provides us with information on the age range of oceanic subduction, and the age and width of the
subducted oceanic plate. The ‘Luk Ulo oceanic plate’ was generated before the earliest Cretaceous, and seamounts
covered by reef limestone appeared in the Early Cretaceous. Radiolarian biostratigraphy of chert indicates that stable pela-
gic conditions continued from the Hauterivian to Campanian. The overlying siliceous shale and shale indicate the duration of
subduction and sediment accretion at the trench.
3.2. Pillow basalt Pillow basalt is recognized in tectonic blocks in the Luk
Ulo Complex, and as clasts within melanges in the Meratus Complex. The pillow basalt is dark greenish gray in color
and aphyric; it includes small phenocrysts of augite and sometimes pseudomorphs after olivine. It is conformably
overlain by early Cretaceous chert, interbedded with lime- stone in the Luk Ulo Complex. The pillow basalt occupied
K. Wakita Journal of Asian Earth Sciences 18 2000 739–749 742
Fig. 3. Stratigraphic column of major accretionary–complexes in central Indonesia. Ages of major components of the Luk Ulo, Meratus, and Bantimala Complexes are shown in the column. Oceanic plate stratigraphy consists of pillow lava, limestone and chert, chert, siliceous shale and turbidite in ascending
order. The ages of sandstone andor melange indicate the time of accretion wedge formation.
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
