Abstract

Exploratory drilling in the offshore portion of the Kutei Basin of East Kalimantan since 1969 has revealed a stratigraphic section consisting of more than 10,000 feet of late Miocene to Recent sediments which exhibit highly variable paleontological and lithological facies. Much of the offshore area of exploratory interest consists of shallow marine facies devoid of planktonic foraminifera. Smaller benthonic foraminifera provide a means of stratigraphic correlation in the shallow marine facies, and five biostratigraphic zones can be recognized: Calcarina Zone, Pleistocene; Ammonia ikebei Zone, Plio-Pleistocene; Asanoina Zone, Pliocene; Pseudorotalia catilliformis Zone, late Miocene and Ammonia yabei Zone, also late Miocene.

A correlation scheme using several zonations based on benthonic foraminifera, planktonic foraminifera and calcareous nannoplankton is required to correlate the various facies in the offshore area. Present studies indicate that much of the offshore late Tertiary section is absent onshore. The Indonesian letter stages are of minimal value as most of the offshore late Tertiary section can only be assigned a generalized Tgh age. Larger foraminifera indicative of Upper Tf have been found associated with late Miocene planktonic foraminifera and calcareous nannoplankton. No biostratigraphic zonation based on smaller benthonic foraminifera has been developed for sediments underlying the A. yabei Zone. In part of the offshore area these sediments contain age significant planktonic microfossils, particularly calcareous nannoplankton, but the problem of correlation is complicated in many localities because of poorly fossiliferous sediments.