Biostratigraphy and Paleoecology of the Subis Limestone, (Early Miocene) Sarawak, East Malaysia and Correlation with the Neogenes of the Indus Basin, Pakistan.

Abstract

  Detailed micropalaeontological studies of the foraminiferal assemblages were carried out to resolve the biostratigraphy and depositional environment of the Miocene Subis Limestone in northern central Sarawak, East Malaysia. Studies were conducted on the limestone outcrops of three quarries. The Sekaloh and the Garagok Quarries are situated on the southeastern flank of the Subis Hill while the 922 Quarry is situated on the western part of the hill.
Larger benthic foraminifera, indicative of early Miocene (Te5 stage of the East Indian Letter classification), were identified. Six important foraminiferal taxa i.e. Miogypsina, Miogypsinoides, Nephrolepidina, Cyc/oclypeus, Amphistegina and Austrotrillina were examined in detail and their distribution (with the exception of Austrotrillina) were documented. The foraminifera observed in the study area are free living taxa which are indicative of high energy environment. Miogypsina sp., Nephro/epidina sp. and Amphistegina sp. are mostly confined to shallow warm waters of normal oceanic salinities. Amphistegina, in particular are more abundant in shallow, warm, clear waters of high carbonate contents. Thus, the foraminiferal assemblages found in the study area indicate that the Subis Limestone was deposited in a shallow-water turbulent environment.
The Subis Limestone fauna has close similarity with the Gaj Formation of the Indus Basin, Pakistan.