CHARACTERISTICS OF PRE-TERTIARY MELANGE AS DECISIVE FACTOR FOR GEOLOGY NATURE CONSERVANCY OF GUNUNG BADAK,
SUKABUMI-WEST JAVA*)
Rosana, M. F., Syafri, I.,Mardiana, U., Sulaksana, N. Department of Geology, Padjadjaran University
Jl. Raya Bandung Sumedang Km 21, Jatinangor, Sumedang 45363 rosanamf@yahoo.com; rosanamf@melsa.net.id
Abstract
The complex of Gunung Badak is located in the Ciletuh Bay, Sukabumi, West Java.
INTRODUCTION
The mélange complex of Gunung Badak is located in the Ciletuh Bay,
southwest of Sukabumi in southwest Java. The Pelabuhanratu is located about 25 km
northeast of the Gunung Badak, and represent the administrative centre of the area. This
area is the only mélange complex of pre-Tertiary age exposed in West Java. Other areas
in Java where the pre-Tertiary rocks crop out are in Lok Ulo and Jiwo Hill in Central
Java. This study is aimed to identify the characteristics and distribution of lithology of
the mélange complex within the Gunung Badak area. Later on this data is used to
delineate the boundary of the mélange complex in Gunung Badak and proposed those
area as “Cagar Alam Geology” ( Geology Nature Preserve”). At present theGunung
Badak complex is known as “Suaka Alam Cibanteng” or “Cibanteng wildlife reserve”.
The area is part of the Ciletuh complex which is located on the south of present
day active volcanic arc. Offshore lies the java trench, a forearc basin and accretionary
prism associated with the northerly subduction of the India Oceanic Plate (Schiller et at,
1991).
METHODS
This study is intended to identify the characteristics and its distributions of the
mélange complex of the Gunung Badak and surrounded area. Detail geological mapping
and sampling of each lithology where done during the fieldwork. The selected samples
were analyses for petrography, chemical compositions and age dating. Some
information’s also are obtained from previous results of other publications. The data
are then used to determine the boundary of proposed conservation area of the “Geology
Nature Preserve” of the Gunung Badak, Ciletuh, West Java.
RESULTS
The Melange of Gunung Badak complex consists of several small islands
included Manuk, Mandra, Kunti and Karang Haji islands, Ciletuh Bay and Gunung
Badak, and Aseupan Hills. The Gunung Badak complex composed of oldest rocks crop
out, Pre-Tertiary age, in West Java. The lithology consists of ophiolite complex of
peridotite, gabro and basaltic pillow lava; metamorphic rocks consist of serpentinite and
phylitic; and sedimentary rocks of greywacke, nummullites limestone, chert, scally
limestone and polymic breccias. The area also contains one of the most extensive and
best preserved Early Tertiary sequences of Ciletuh Formation of quartz sandstone.
Peridotite of gray to greenish color is best exposed in the northern part of
Gunung Badak. It composed of plagioclase, olivine, augite and enstatite, small amount
This rock is already altered to serpentinite with networks texture due to
tectonometamorphosis.
Gabro mostly exist as small dike like or volcanic neck like within the
peridotite-serpetinite Bukit Aseupan is one of the gabro dike exposed. This rock of dark
gray color, phaneritic texture and composed mainly of basic plagioclase which partly
altered to sericite and clay minerals, pyroxene that mostly altered to chlorite.
Basaltic pillow lava is well exposed in the northern part of Gunung badak foot,
near to Kunti Island. A pillowed structure is very clear with its dark color, and consists
of networking vesicular. Petrography analysis indicated that rock is porphyritic in
texture, mostly felsic plagioclase, pyroxene and chlorite.
Polymict breccia well exposed in Kunti Island, varied in composition,
included phyllite nummulite limestone, schist, quartzite, aphibolite, gness, in a sheared
shale matrix. The Manuk island also composed mainly of polymict breccia, but has
different composition with the Kunti island, it consist of andesite, basalt and chert as a
major clast within the coarse tufaceous sandstone matrix.
Graywacke sandstone is well exposed in Mandra Island, it mainly composed of
fine to coarse greywacke sandstone, silt, locally lenses of breccia and volcanic clast,
carbon and quartz sandstone. This rock is fractured and mostly filled by carbonate and
rarely of quartz.
The southern Gunung Badak and Karang Haji, are well exposed for quartz
sandstone to conglomeratic sandstone of Ciletuh Formation, in these area the thick band
of quartz sandtone and uncompleted turbidite sequence are very clearly seen. The
average sandstone is fine to coarse grained, moderate to well sorted, subangular to
subrounded. The conglomeratic sandstone, most of the larger clasts as pebbles and
cobbles are rounded to wellrounded and composed of quartzite, peridotite, chert, schist,
gabbro, serpetinite, andsite and basalt in fine to coarse sandstone matrix.
The age dating done by Schiller et al, 1991 obtain various ages ranging from
134 Ma from graninitc pebble in conglomerate sandstone; 89.6 Ma from basalt pebble
in polymic breccias; and 22.4 Ma from andesite of breccia fragment from the Kunti
island.
DISSCUSSIONS
The lithology of the Gunung badak complex are mixed of ophiolite rocks with
metamorphic and sedimentary rocks of different environment this suggest that the area
is a mélange complex. The rock units or block are bounded by fault contacts. The
Pre-Tertiary ophiolite and metamorphic rocks are act as the basement of the basin, and
covers is Jampang Formation. The oldest rocks in the Gunung Badak, is exposed due to
the “mega slump” occur and make the Jampang Formation emplaced to the offshore and
these caused the basement rocks are exposed. This phenomenon is clearly seen from the
landsat image which shows the amphitheater like structure within the Ciletuh bay and
Jampang high. Previous research by other geologist suggest that the exposed of the
ophiolite and metamorphic complex within the Gunung Badak area as a product of the
Creatceous subduction of Indo-Australian plate with the Eurasian plate.
The boundary of the conservation area is delineated based on the distribution of
the pre-Tertary of Melange complex within the Gunung Badak and its surrounding area
in the Ciletuh Bay of West Java. This boundary is divided into two zone that category as
the “Main Zone or Kawasan Zona Inti” and “Supporting Zone or Kawasan Zona
Penunjang”. The main zone boundary is placed about 500 m distance from the
pre-Tertary mélange cropped out or interesting geology object within the area, where as
the supporting zone is placed about 1000 ~ 2000 m distance from the cropped out
pre-Tertary mélange cropped out or interesting geology object within the area.
CONCLUSIONS
The lithology of Gunung Badak area is very complex. Field data suggest that
the complex is a mélange. This complex is exposed due to the “mega slump” of the
Jampang Formation. Based on the field and laboratory identification, the boundary of
Geology nature preserve is determined based on it’s the occurrences pre-Tertiary
mélange cropped out and other interesting geology object within the area. The boundary
is divided to category that is main zone and supporting zone boundary.
This boundary later can be used as a based to develop of the area as the “geoturism”
object that can promote the area of Ciletuh bay, West Java as one of the one of the
interesting place to visit especially for people who interesting in geology or earth
sciences. This area also can be promote as the “field laboratory” which can be used for
student who wish to study more detail in geology, especially the mélange of West Java.
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