New Insight Into Berau Sub-Basin North East Borneo: Basin Evolution and Tectonostratigraphy and Their Implication to New Exploration Play Concept

Abstract

Understanding the evolution of the basin and tectonostratigraphy is the key role to reveal all geological aspects and potential hydrocarbon resources. Northeast Borneo has many hydrocarbon resources especially in Mahakam delta. However, Berau sub-basin remains unclear due to lack of G&G data. This paper presents a new concept of tectonostratigraphy and basin evolution based on subsurface and surface data integrated with thin section as well as radiolaria analysis to determine the age of such basin. Present-day aerogravity data shows that Berau sub-basin has two depocenters trending N-S and E-W and is bordered by Mangkalihat High (MKH) in the south and Rajang Embaluh Group (REG) in the west area. The metamorphic belt in REG area was formed in Early Jurassic (190 Ma), meanwhile in MKH, the ophiolite sequence was formed during Middle-Late Jurassic based on the presence of Holocrptocanium sp. in chert interbedded with mudstone. Based on the analysis, Berau sub-basin experienced subduction to obduction during Early Jurassic to Late Jurassic. In Cretaceous, Berau sub-basin is filled with conglomerate, shale and quartz sandstone of Telen and Benggara Fm. that has provenance from MKH and REG area. In Paleogene, major breakup unconformity can be seen on the seismic section and spread across the basin overlaid by shale with tuff of Eocene-Oligocene Sembakung Fm. The deposition of Sembakung Fm is controlled by extensional regime caused by subduction rollback in NW Borneo. The carbonate sequence has dominated this area in Late Oligocene to Early Miocene. Following the collision of Kuching high in Middle -Late Miocene, the deposition was dominated by deltaic sediment due to regional regression phase. In Plio-Pleistocene period, Berau sub-basin consists of carbonate and deltaic sediment from Domaring and Sajau Fm. In this time structural reactivation and inversion due to transpressional system with SE-NW pattern had controlled Berau sub-basin. Based on the evolution of Berau sub-basin, four hydrocarbon plays are identified in this paper, Mesozoic Play especially in Telen Fm, Paleogene Carbonate Play in Tabbalar & Birang Fm, Middle Miocene Play especially in Latih Fm and Plio-Pleistocene Play in Sajau Fm and Labanan Fm. Working petroleum system in the basin manifested by many oil seeps that can be found in surface and postmortem of several wells data shows commercial to sub-commercial and abundant oil and gas show.

Mesozoic-Cenozoic Stratigraphy and Tectonic Development of the Southern Great Tarakan Basin, Northeast Borneo, Indonesia

“…The existence of an inversion structure is caused by reactivation of the existing Paleogene structure, and the inversion causes Neogene sediments to experience uplift followed by erosion. There are two main strike-slip systems defined as the North Mangkalihat Fault Zone (NMFZ) and Latih Fault Zone (LFZ) (Krisnabudhi et al, 2020). The NMFZ extends from Sangkulirang Bay to the western part of the Berau Sub-basin, while the LFZ extends from the Berau delta to the northern part of the Tarakan Subbasin.…”

“…The existence of radiolarian fossil Holocryptocanium sp. indicates that the deep-marine sediments were deposited during the Middle Jurassic-Early Cretaceous (Krisnabudhi et al, 2020). In southwest Borneo, the presence of chert and radiolaria in the Meratus Mountains also has a Middle Jurassic-Early Cretaceous age (Wakita, 2000).…”

“…In addition to their complex tectonic and stratigraphic histories, the Muara and Berau sub-basins have a high hydrocarbon potential (Wilson and Evans, 2002;Doust and Noble, 2008;Krisnabudhi et al, 2020), which is supported by a large amount of oil seepage in the Berau Sub-basin (Wight et al, 1993), which tends to point north (Situmorang, and Burhan, 1995). The accumulation of oil seepage around the contractional structure indicates that the petroleum system has performed admirably (Macgregor, 1992).…”

“…The analysis and interpretation of the residual anomaly gravity map (Wijayanti et al, 2014;Maulin et al, 2021) reveals two major depocentres, the N-S and W-E pattern in the west and east of the Berau depocentre. According to recent studies, the two depocentres are separated by the NW-SE trending structure known as the North Mangkalihat Fault Zone (NMFZ) and the Latih Fault Zone (LFZ) (Krisnabudhi et al, 2020).…”

“…The identification of Paleogene to Neogene sediments in the south, on the other hand, refers to the stratigraphy of the northern area. The southern zone has a high stratigraphic complexity in terms of lithology, age, and geological structure (Situmorang and Burhan, 1995; Krisnabudhi et al, 2020).…”