Far-Field Tectonics, Structural Evolution and Depositional System of NW Borneo

Balaguru, Allagu; Lukie, Terrence
Exploration Malaysia, Talisman Energy, Kuala Lumpur, Malaysia.

The Miocene to recent regressive fluvio-deltaic systems of NW Borneo have been progressively deformed and overlie the Oligocene Crocker accretionary complexes. The Oligocene strata comprise slightly metamorphosed, highly deformed deep-water turbidite sediments (Stage II). The Miocene section, which has an unconformable relationship with the underlying section, can be divided into three deltaic complexes that generally young from east to west; in younging order, the Meligan, Champion and Baram Delta Systems. A significant Middle Miocene unconformity (also known as Deep Regional unconformity) (MMU/DRU) separates the Meligan Delta (Stage III) from the overlying middle to late Miocene Champion Delta (Stage IV-ABC). The Baram Delta succession (Stage IV-DEFG) is the youngest of the three deltaic systems and is separated from the older Champion Delta sequence by the late Miocene Shallow Regional Unconformity (SRU). This prominent unconformity in Sabah coincides with significant regional uplift and erosion. Published data from onshore and offshore NW Sabah define three tectonic provinces; an inverted, an extensional, and a compressional province. These three provinces have previously been termed neotectonic provinces due to the associated present day tectonic activity.

New geological mapping, detailed field studies and a reinterpretation of existing seismic data suggest that the region consists of west-vergent fold-thrust belts formed in the Early Miocene with syn- and post-deposition of the large Meligan, Champion and Baram Delta Systems on an active margin in NW Borneo. Integrated evaluation indicates that the NW Borneo Delta province evolved during the Early Miocene to present day from a foreland basin to a shelf margin. Multiple phases of compressional folding and faulting events have affected the region causing uplift of the hinterland (large deltaic progradational events) and inversion of gravity-related faults. Most folds are detached, buried, thrust-cored anticlines that ‘young' towards west. The prodelta shale was progressively buried by the prograding delta front sediments, becoming overpressured and mobilizing during Pliocene, further complicating the deformation style. This indepth integrated evaluation provides new insight into the tectonic evolution of rapidly prograding Tertiary delta systems and reveals how the compressional tectonics have migrated basinward as the delta system prograded.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012