Sedimentology and stratigraphic architecture of a Miocene retrogradational, tide-dominated delta system: Balingian Province, offshore Sarawak, Malaysia

Abstract

The Balingian Province of NW Borneo is a major hydrocarbon-bearing region with production dominantly from Early Miocene (cycle II) coastal to lower coastal plain deposits. A regional sedimentological synthesis is outlined from the main productive interval of three offshore oilfields, which are representative of the depositional environments and stratigraphic architecture in cycle II. Four types of vertical facies successions are recognized: (1) fluvio-tidal channel; (2) tide-dominated delta front; (3) wave-dominated shoreface; and (4) barrier lagoon. The facies successions demonstrate that cycle II consists of a tide-dominated delta system that is partly analogous to the modern Rajang Delta and Lupar Embayment of southern Sarawak. Fluvio-tidal channel and tide-dominated delta successions represent periods of river-fed progradation. Wave-dominated shoreface and barrier lagoon facies successions represent depositional systems that developed during periods of transgression and/or delta lobe abandonment. Cycle II consists of several high-order sequences stacked together into two lower-order, c. 100–300 m thick fining-upwards, unconformity-bounded megasequences. This stratigraphic architecture reflects a combination of hinterland denudation and long-term eustatic sea-level rise. These trends were interrupted by frequent, higher-order relative sea-level falls, which were a result of movement along the West Balingian Line fault zone. Variations in the thickness of megasequences between the three oilfields reflect fluctuations in tectonically driven subsidence rates. This exerted a fundamental control on the reservoir architecture, zonation and correlation and provides a basis for comparing field behaviour.

The emergence of Miocene reefs in South China Sea and its resilient adaptability under varying eustatic, climatic and oceanographic conditions

“…The paleoshoreline could have been oriented in a trend that is perpendicular to the general NE-SW direction of the platforms, which is congruent to previous estimations of a NW-SE direction of ancient coastlines in this area with the offshore basins deepening towards the north and NE (e.g. 30,43,44 ). Modelled paleogeographic locales of the coastal plain ( Fig.…”

“…During the Oligo-Miocene transitional period, prolonged subsidence and extensional normal fault systems were ubiquitous in the southern Sundaland following regional crustal stretching and extreme thinning in the SCS 2 . Because the balance between deposition and erosion is predominantly influenced by hydraulic velocity and sediment flux 34 , under moderate velocities and exuberant sediment supply, as in the case of the present study location (e.g., 29,30 ), along with the subsequently created accommodation space and the onset of rapid sea level rise could have resulted in the progradation of siliciclastic material along coastlines in the form of deltas with developed sand bars and linear sand ridges ( Fig. 5A).…”

“…A few studies have focused on the sedimentological aspects of prominent paleodeltas in this region using well data, outcrop descriptions that could be considered as equivalents to offshore geology and by considering regional models (e.g. 30 ). Our findings confirm and precisely highlight the presence and classification of at least two paleodeltas by observing the growth patterns of Middle Miocene carbonate platforms that we demonstrated to have evolved on a substratum organized by deltaic sand bodies and during growth, inadvertently mimicked the underlying strata The conceptualized evolution of a large Oligo-Miocene delta that formed under conditions of exuberant sediment supply, prolonged subsidence and accelerated sea level rise that facilitated the rapid progradation of siliciclastic material to form well-developed tidal deltaic sand bars and linear sand ridges.…”

“…29 ), changes in subsurface sedimentology of clastic sequences that predate the carbonate platforms (e.g. 30 ) and paleobathymetries ( Fig. 2) (e.g.…”

“…Concurrently, in addition to all the aforesaid tectonic and climatic changes in Southeast Asia, especially in the southern South China Sea region, large deltas rapidly prograded into the surrounding deep basins at the Oligo-Miocene boundary 2,17,28 . The exact paleogeography of these Paleogene-Neogene deltas, however, is only partly known because of the limited amount of data available 29,30 and because tectonic movements could have overprinted the depositional geometries.…”