GEOLOGICAL IMPLICATIONS OF NEW BIOSTRATIGRAPHIC DATA FROM EAST AND WEST KALIMANTAN, INDONESIA

This paper presents palaeontological ages based on new nannofossil and foraminiferal studies from a range of sedimentary rocks from the prov inces of West and East Kalimantan, Indonesia. The age of sedimentary r ocks in Kalimantan, away from the main hydrocarbon exploration areas o f the coastal regions, represents a major gap in our basic knowledge o f the island of Borneo. The implications of these new results and exis ting and new correlations are reviewed and suggested. In particular, t he base of the Tertiary section in the Kutai Basin is shown to be uppe r Middle Eocene in age, rather than Late Eocene as originally thought. The limestones of the Batu Belah member of the Ujoh Bilang Formation are dated as NP24-25, Late Oligocene, rather than Early Oligocene as e arlier work had suggested. In the western part of the Mangkalihat Peni nsula area the base of the Tertiary section is determined to be Late O ligocene. Various basement units from both East and West Kalimantan co ntained Late Jurassic to Late Cretaceous microfossils. (C) 1998 Elsevi er Science Ltd. All rights reserved.