The origin of the 'circular basins' of Sabah, Malaysia

Abstract

Surface mapping, dating and radar image study of strata in southern Sabah (northern Borneo) have made it possible to revise the stratigraphy and reinterpret the structure and tectonic evolution of the area. Early Miocene regional unconformity may be equivalent to the Deep Regional Unconformity recognised offshore, below which the succession can be resolved into an Eocene accretionary complex age overlying an ophiolitic basement, and an upper Paleogene deep-water succession which formed in a forearc. The Paleogene deposits underwent syn-depositional deformation, including the development of extensive melanges, all of which lie below the unconformity. Localised limestones were deposited followed after a period of uplift and erosion in the Early Miocene, followed by an influx of clastic sediments deposited in delta and pro-deltaic environments in the Middle Miocene. These deltaic to shallow marine deposits form two coarsening-upward successions, mapped as the Tanjong and Kapilit Formations. The total thickness of these two formations remaining in the southern Sabah Basin amounts to 6,000 m, about half of previous estimates. The Early Miocene unconformity is interpreted to be the result of deformation and uplift following underthrusting of continental crust of the South China Sea which terminated Paleogene subduction beneath North Borneo. Renewed subsidence led to the development of a major Miocene depocentre above the older forearc accretionary complex. A new tectonic model is proposed for southern Sabah whereby a major transpressional deformation probably occurred during the Late Pliocene and the Tanjong. and KapilitFormations were deformed into broad NW-SE-trending synclines separated by narrow anticlines. The anticlines are sub-parallel to major faults and associated with high angle reverse faults, and positive flower structures. Secondary fold-faults formed oblique to the major faults. The structural style suggests that the NW-SE trending faults acted as major left-lateral transpressional zones and possibly produced largescale contractional duplexes. The faults may in part be reactivated basement structures. This deformation uplifted the area and is termed here the Meliau Orogeny. Renewed extension during the Quaternary caused some sequence repetition and widened the original synclines. The 'subcircular-to• elliptical-shaped basins' of the Meliau, Malibau and Tidung areas are structurally controlled synclines and interpreted as remnants of a single large basin, deformed in the NW-SE trending transpressional fault zones.

Transverse segmentation of the Baram-Balabac Basin, NW Borneo: refining the model of Borneo's tectonic evolution

“…At a minimum, these zones probably reflect reactivation of older, deep structural elements that are favourably aligned with imposed tectonic stress. The Meliau Orogeny, marked by localized Late Miocene to Pliocene inversion and development of the SRU in the Baram-Balabac Basin, has been attributed to transpression along NW-SEtrending strike-slip faults (Balaguru et al 2003), suggesting these faults do link up in some manner. Neotectonic considerations support the concept of island-scale transverse segmentation.…”

“…Pliocene inversion, including fold reactivation and uplift, is recorded in several of the large fields in the Baram-Balabac Basin, Samarang, Champion, Seria and SW Ampa (Sandel 1996;Morley et al 2003;Carrillat et al 2008) and resulted in several local unconformities. Late Miocene to Pliocene inversion has been attributed to NW-SE strike-slip and transpressional faulting during an event termed the Meliau Orogeny (Balaguru et al 2003;Balaguru & Hall 2008). The present-day state of stress in the inboard area of Brunei, with the maximum horizontal stress orientated NW-SE, suggests tectonic compression and shortening ).…”

Nature and demise of the Proto-South China Sea

“…The Crocker Formation in western Sabah is unconformably overlain by the Lower Miocene shallow marine Meligan Formation (Wilson & Wong, 1964) and Kudat Formation. To the east of the Crocker Mountains during the Middle and Late Miocene there was subsidence and deposition of a thick succession of fluvio-marine deposits (Noad, 1998;Balaguru et al, 2003;Balaguru & Nichols, 2004) in the Central Sabah Basin (Hutchison, 1992) whose remnants are now found in the circular basins of eastern Sabah (Tongkul, 1993;Clennell, 1996;Balaguru et al, 2003;Tongkul & Chang, 2003).…”

“…The collision caused emergence of much of Sabah and the present central highlands of northern Borneo, with folding and thrusting of both basement and cover. However, by the end of the Early Miocene much of present-day Sabah was below or close to sea level (Noad, 1998;Balaguru et al, 2003;Hall et al, 2008) with probably a low elevated range of hills at the position of the Crocker Mountains. Because there are few Neogene rocks in western Sabah this is uncertain, but in Brunei and Sarawak Neogene rocks are preserved and the shelf edge moved broadly northwestwards from the Middle Miocene onwards (e.g.…”

Strike‐slip reactivation of segmented normal faults: Implications for basin structure and fluid flow

“…Although strike-slip reactivation is reported in the literature (e.g. Aris, Coiffait, & Guiraud, 1998;Balaguru, Nichols, & Hall, 2003;Ducea, Kidder, Chesley, & Saleeby, 2009;Faure, Tremblay, Malo, & Angelier, 2006;Firth et al, 2015;Hartz & Andresen, 1995;Jankowski & Probulski, 2011;Kim, 1996;Turner, Liu, & Cosgrove, 2011), detailed descriptions of the strike-slip reactivation of normal faults (Van Noten et al, 2013) and the associated effects of reactivation on along-strike transfer zones (Barton, Evans, Bristow, Freshney, & Kirby, 1998;Kelly, McGurk, Peacock, & Sanderson, 1999 Massironi, 2007) are scarce. Thus, an understanding of key features and typical structures produced during strike-slip reactivation of normal faults is currently lacking.…”