Sedimentological analysis of a Miocene deltaic systems: Air Benakat and Muara Enim Formations, Central Merangin Block, South Sumatra

Abstract

Abstract Outcrop study of Miocene sediments forming the overall regressive Air Benakat-Muara Enim Formation transition in the central Merangin Block (South Sumatra Basin) has allowed identification of a suite of lithofacies which are interpreted as representing deposition in a humid tropical deltaic system. Integration of sedimentological observations and palaeontological information has led to the recognition of a number of sub-environments within the delta system. Delta plain deposition is represented by distributary channel sandstones, which show evidence of tidal influence in their lower reaches, and a variety of interdistributary sediments. The delta front is envisaged to have been an overall mud-dominated environment traversed by sand-bearing sub-sea channels (commonly meandering), with some development of marine bars. A transgressed abandoned delta lobe has also been identified. The main potential reservoir facies are distributary and delta front channel sandstones. A depositional model of a fluvially dominated (with wave and tidal influence) deltaic system, with density current outflow during major river flood discharges, is proposed. This outcrops-based study has obvious application to subsurface analysis of the Miocene section in the Merangin Block, and may be pertinent to other deltaic complexes developed in similar settings.