ABSTRACT: Miocene deltaic deposition patterns of the Mahakam area

Cibaj, Irfan¹, Agung Wiweko², and Stefano Mora²
(1) Consultant for TotalFina, St. Remy les Chevreuse, France
(2) Total Indonesie, Balikpapan, Indonesia

The Lower to Middle Miocene deltaic deposits of the Kutei basin crop out in the vicinity of the modern Mahakam delta within the Samarinda anticlinorium. The excellent quality of these outcrops is partly related to the narrow anticline structures prevailing in this area.

The series are composed of different elements of deltaic deposits. Distributary channels are filled with conglomerates and coarse-grained sandstones, frequently they are vertically amalgamated. Lateral accretion and abandonment clay plugs are also associated with them.

Mouth bars are dominated by flood deposits (parallel lamination, current ripples, HCS) which are composed of medium-grained sandstones with a coarsening-upwards trend. The bioturbation is highly developed in their lower and distal sections. Delta front "turbidites" are also part of the sedimentation in this setting.

Thick crevasse splay deposits show typically characteristic features. Fine-grained sandstones in thin bed sets exhibiting tangential cross beddings with a finning upwards trend. Coal beds are also very well exposed.

All these elements are well organised in prograding deltaic cycles, which constitute the building blocks of the series. Stacked deltaic cycles show different stratigraphic patterns. The reservoir distribution in the series is related to these stratigraphic stacking patterns. The subsidence and the tectonic activity are the major controlling factors.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia