in Jurassic and Cretaceous Stratigraphy

Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321
Sedimentology and Sr Isotopic Ages of the Bau Limestone Formation
in Northwestern Borneo, Malaysia
32
Y. Kakizaki 1* ,T. Ishikawa 2 ,J. Matsuoka 3 ,T. Hasegawa 1 , A. Kano 4
1. School of Natural System, Kanazawa University, Kanazawa 920-1192, Japan (E-mail: kackey@staff.kanazawa-u.ac.jp)
2. Kochi Core Research, Japan Agency for Marine Science and Technology, Nankoku city, Kochi 783-8502, Japan
3. Kochi Marine research Support Section, Marine Works Japan, Nankoku city, Kochi 783-8502, Japan
4. Division of Evolution of Earth Environments, Kyushu University, Nishi-ward, Fukuoka 819-0395, Japan
The Mid-Mesozoic era (from the Late Jurassic to
the Early Cretaceous) was one of the periods in terms
of the largest deposition of marine carbonate. In the
eutrophied ocean, reef-builders were flourished under
the circumstance of a relatively high CO2 con-
centration and the warm ocean environment. Sedi-
mentology and stratigraphy of the Mid-Mesozoic
carbonate were well studied in Europe, the former
territory of the Tethys Ocean. On the other hand,
information on the Mid-Mesozoic carbonate of Asia
and Pacific realm was limit. Hence, more information
and more studies on them have been expected. Here,
we present the sedimentology and Sr isotopic age of
the Bau Limestone Formation (the Upper Jurassic to
the Lower Cretaceous) in north-western Borneo of
Malaysia, for the first time.
We surveyed at two quarries (Marup and SSF) of
the Gunung Panga Area, located at 30km southwest of
Kuching City (Fig. 1). The lithofacies are mainly
massive limestone yielding mega fossils. The lithology
of the Marup Quarry is subdivided into Bioclastic
wacke-packstone including many cidaris spines and
Bafflestone containing corals. The lithology of the
SSF Quarry is subdivided to 5 facies: Oncoidal Pack-
stone, Peloidal Packstone, Bioclastic Packstone,
Bindstone, and Frame-Bafflestone. At Gunung Panga
Area, mega fossils (especially Rudists and nerineoids)
are yielded at all facies, and sparitic cements occupy
the intergranular spaces.
We surveyed at Bunkit Akut Quarry near
Kuching-Serian Road, which is located at 40km south-
southeast of Kuching City (Fig.1). The limestone is
clearly stratified and slumping fold is developed at the
upper horizon of the surveyed section. Lithofacies are
fine-grained limestone and subdivided into 3 facies:
Calcarenite, Lime mudstone, and bioclastic wacke-
stone. Additionally, mud beddings are intercalated
with limestone at the middle to upper horizon of sur-
veyed section.
Fig.1 Geological map of the Bau Limestone Formation, modified after Wilford (1955)
Because of sparitic cements and hermatypic biota,
the depositional environments of Gunung Panga are
considered to be photic zone influenced by wave. On
the other hand, because of absence of hermatypic biota
and developing of slumping fold, the depositional
environment of Bunkit Akut section is considered to
be deeper than storm wave base, and environment
where siliciclasts were intermittently supplied. Based
on our description, it is concluded that the depositional
environment of the Bau Limestone Formation is