Abstract

The Kutai Basin, a large sedimentary basin in eastern Kalimantan, hosts significant oil and gas resources within Miocene deltaic systems. We have integrated disparate geological and geophysical surface and subsurface data-sets to re-interpret Tertiary facies distributions in the basin and present models to explain the progressive tectonic evolution of the basin, the resulting depositional environments and their arrangements within the basin in relationship to major basin tectonostratigraphic phases.

The basin was initiated in the Middle Eocene in conjunction with rifting and incipient sea-floor spreading in the North Makassar Straits. The resulting series of N-S/NE-SW trending, discrete, faultbounded depocentres preceeded a sag phase in response to thermal relaxation. Sedimentary fill of the discrete, Eocene depocentres varies depending upon position with respect to sediment source, palaeo-water depths and geometry of the half-grabens. This strongly contrasts with the regionally uniform sedimentary styles that followed in the latter part of the Eocene and the Oligocene. Tectonic uplift, documented along basin margins and related subsidence of the Lower Kutai Sub-basin, occurred during the Late Oligocene. This subsidence is associated with significant volumes of high-level andesitic-dacitic intrusives and associated volcanic rocks. Volcanism, together with uplift of the basin margins, resulted in the erosion and supply of considerable volumes of material eastwards, along with material derived from inverted Paleogene depocentres. During the Miocene, basin-fill continued with an overall regressive style of sedimentation, interrupted by periods of tectonic inversion throughout the Miocene to Pliocene. This new understanding of basin development is important for the appreciation of resource distribution in this basin and similar rift basins of Borneo and SE Asia.