Geology of Sabah PDF

GEOLOGY OF SABAH Geology, Stratigraphy & Tectonic Evolution Regional Geology and Petroleum Resources of Malaysia and SEA QCB4013 BY DR. MOHD SUHAILI ISMAIL  INTRODUCTION Oldest unit - Crystalline Basement rocks...

GEOLOGY OF SABAH Geology, Stratigraphy & Tectonic Evolution Regional Geology and Petroleum Resources of Malaysia and SEA QCB4013 BY DR. MOHD SUHAILI ISMAIL  INTRODUCTION Oldest unit - Crystalline Basement rocks comprises of granitic and metamorphic rocks in the Darvel Bay and Segama areas Triassic–Jurassic Dominant unit - Crocker and Trusmadi Formation consisting of deep-water sandstones with minor shales and argillaceous beds highly deformed Eocene to early Miocene interpreted as an accretionary prism formed during subduction of the proto– South China Sea beneath Sabah (van Hattum et al., 2006).  INTRODUCTION Sabah Orogeny  created the early Miocene Top-Crocker unconformity  followed by the deposition of neritic and fluvial formations, preserved in eastern Sabah (Hutchison, 2005; Hall, 2013). Since there is no report which discuss the overall geology of whole Sabah, the geology is thus describe according to area.  Western & North Sabah Consisting of sedimentary and igneous rocks of Early Cretaceous to Pliocene in age with subordinate metamorphic rocks. Rocks has undergone several episodes of deformation: – earliest episode of deformation was responsible for the deformation and uplift of the basement rock (chert-spilite formation), – probably occurred during Late Cretaceous to Early Eocene – thought to have controlled the development of an elongate basin trending approximately N-S and E-W in Western and Northern Sabah respectively – Basin later became the site for the deposition of Middle Eocene to Early Miocene sediments of the Crocker, Trusmadi and Kudat formations.  Western & North Sabah Sedimentary rocks:  dominantly of sandstones and shales with subordinate cherts, limestones and conglomerates. Igneous rocks  serpentinites, basalts/spilites, agglomerates, gabbros, dolerites, andesites, granodiorites and adamellites. Metamorphic rocks  mainly hornblende schists and gneisses.  Western & North Sabah Oldest dated sedimentary rocks are radiolarian cherts of Early Cretaceous age (Basir & Sanudin. 1988). – Thinly bedded cherts, closely associated with basaltic/spilitic type of basaltic igneous rocks. – Also closely associated with basalt and spilite are ultrabasic rocks (serpentinites/peridotites) intrusive rocks (dolerites) and metamorphic rocks (hornblende schists and gneiss). – This association of rock types, which resembles an ophiolite series, is interpreted to represent an oceanic crust of Mesozoic age, and forms the basement rock of this region. – Lying unconformably on this basement rock are sedimentary rocks of Eocene to Early Miocene age represented by the Crocker, Trusmadi and Kudat Formations.  Western & North Sabah Crocker and Trusmadi Formations – occur mostly in Western Sabah, – are mostly deep-water flysch sediments characterised by rhythmic alternation of sandstone and shale beds, Kudat Formation – occurs in Northern Sabah – mostly shallow water sediments – characterised by interbedded carbonaceous sandstones and shales with lenses of Eocene-Early Miocene biohermal limestones. Western & North Sabah  Western & North Sabah Bongaya Formation – Shallow water deposits consisting of sandstones, shales, limestone and conglomerates – Upper Miocene age – Lie unconformably on the basement rock, Crocker and Kudat Formations in Northern Sabah. – This deposit is in turn overlain unconformably by shallow water sediments of theTimohing Formation of Pliocene -Pleistocene in age on Balambangan Island. Igneous rocks, both intrusives (Mt. Kinabalu plutonics) and extrusive (Sirar Island volcanics), were formed during Miocene-Pliocene times.  Crocker Formation Turbidites (probably reach a thickness of 1,000 m) Interbedded sandstone and shale deposited in a deepwater basin (submarine fan) during the latest Eocene (37 Ma) through to the earliest Miocene (21 Ma). Crocker Range runs NNE to SSW and is deformed by a series of high- angle reverse faults dipping south or south-east; Reverse faults probably formed during the Miocene, and the soft shale layers have often acted as slip planes for the faults and deformation.  Crocker Formation Tongkul - divided the turbidites into the lower sandstone unit (several hundreds of metres thick) and the upper shale unit (about 100m thick). Lower sandstone unit – is an alternation of thick grey sandstone beds and relatively thin shale beds. – sandstone is quartz rich, and the individual beds range from tens of centimetres to a few metres thick Upper shale unit has much thinner sandstone layers and occurs as a cap rock of grey or red shale. Crocker turbidites are also exposed on islands offshore KK, and extend offshore western Sabah below the Miocene-Quaternary deltaic sediments  Crocker Formation The Crocker Formation turbidites sit on the Eocene Trusmadi Formation (thick dark shale beds interbedded with thin sandstone layers). The relationship between the two formations is probably an unconformity. The basement rock of this part of Sabah is an ophiolite mélange (ocean-floor subduction rocks), probably of Cretaceous age. Crocker Formation  NORTH SABAH The northern part of Sabah, consisting of sedimentary and igneous rocks of Early Cretaceous to Pliocene age Has experienced three major episodes of deformation associated with NW-SE and N-S oriented compressions. The earliest episode deformed and uplifted an oceanic basement (Chert-Spilite Formation) to form an elongate basin, trending approximately NE-SW, during the Late Cretaceous to Early Eocene. – This elongate basin became the site for the deposition of middle Eocene to Early Miocene quartzose sediments of the Crocker and Kudat formations, sourced from continental basement towards the southwest and north, respectively.  Kudat Peninsula Kudat Peninsula comprises of four formations, the – Ophiolitic Basement, – Crocker Formation and – Kudat Formation, and the – mélange unit. Kudat Peninsula is dominantly made up of Kudat Formation, a relatively deep to shallow water sediments (Rahim et al., 2017; Lunt & Madon, 2017). The Gomantong, Sikuati and Tajau Members of Kudat Formation are made up of interbedded sandstone and mudstone.  Kudat Peninsular Gomantong Member – referred to as the Upper Unit of Kudat Formation by Tongkul (2006), – possibly describing this unit as the youngest member. – consists of interbedded medium to fine-grained sandstone and mudstone, predominantly sandstone layer – The sandstone bed is characterized by sedimentary structures such as parallel lamination, ripple marks, convolute structure, and water structure  Kudat Peninsular Sikuati Member – made up of interbedded fine-grained sandstone and mudstone with abundance of sedimentary structures such as parallel lamination, cross lamination and wavy lamination. Tajau Member – Comprises of thick sandstone bed interbeds with thin mudstone layer which formed the northern Kudat terrane, – Early to Middle Eocene calcareous nannofossils (Rahim et al., 2017).  Kudat Peninsular Mélange unit – is found in a few localities mostly in the northern part of the peninsula. – mélange appears within a strip zone, bounded by major faults situated in between Tajau Member and Sikuati Member. – It is made up of an intensely deformed mixture of the ophiolitic basement rock (Clennell, 1991) and presence in the form of knockers and lens-shaped phacoid structures (Chang et al.,2019). – Blocks of rocks that were identified in the mélange are serpentinite, chert, and red mudstone.  Kudat Peninsula A knocker is defined as a complex outcrop showing random bedding orientation where each side have different reading, resulted in difficulties to obtain the accurate measurement and it is usually associated with a mélange. The knocker found on the peninsula is a boulder of chaotic unit comprising ofr ed chert, green chert and red mudstone, originated from the basement rock that had been uplifted to the surface. This unit is highly deformed characterized by folds and refolded folds as shown in Figure 4. This mélange strip is found in a faulted zone of strike-slip fault, indicated by the slickenside surface of serpentinite showing dextral sense of movement Presence of Cyclicargolithus floridanus (NN6) and other associated nannofossils in the mudstone of the mélange unit is dated Middle Miocene in age.  Kudat Peninsular Interbedded sandstone and mudstone of Gomantong, Sikuati and Tajau Members. All outcrop numbering mentioned in this paper is based on the map in Figure 1. A) and B) have thick beds of sandstone interbed with thin mudstone layer and hows a highly folded beds cross-cut by a normal fault. C) massive sandstone and mudstone beds with wavy boundary D) sharp straight boundary. These sandstone beds are filled with sedimentary structures such as parallel lamination, cross-lamination, and wavy lamination. C) freshly cut outcrop exposed in Pantai Sikuati. The strata are slightly folded on the north side of the outcrop showing the presence of a fold limb. E) and F) exposed at the shoreface in Kg. Raja Laut and Tanjung Simpang Mengayau respectively. Thick sandstone layer with thin mudstone interbed. Sedimentary structures observed in sandstone of Gomantong and Sikuati Members. A) Flame structures in the thick sandstone layer; B) Parallel, wavy and cross lamination occurred in the sandstone layers.; C) Parallel and cross lamination; D) Parallel and wavy lamination structures in sandstone beds in Sikuati Member  GEOLOGY of SOUTHWEST SABAH Weston to Sipitang in southwest Sabah Area consists of Temburong Formation, Crocker Formation, Meligan Formation and Liang Formation. Temburong Formation underlying the Crocker Formation in terms of stratigraphic sequence position which has been considered otherwise. This means that the position of stratigraphic sequence of Temburong Formation which was previously considered to be above the Crocker Formation is now being interpreted below the Crocker Formation The Temburong Formation and Crocker Formation are both dated as Upper Eocene to Lower Miocene while the Meligan Formation is Middle Miocene to Upper Miocene and Liang Formation is Pliocene  GEOLOGY of SOUTHWEST SABAH Wilson (1964) - Temburong Formation is part of Crocker Formation based on the similarity of lithology units in the two formations. Temburong Formation interfingering with the Crocker Formation. Previous studies showed the occurrence of Planktonic foraminera in Temburong formation aged Upper Oligocene-Lower Miocene (Junaidi et.al) For Crocker Fm, present of foraminifera planktonik Globigerinoides sp. in Tenom age similar to Temburong Fm (Muhd Nur Ismail, 2014)  GEOLOGY of SOUTHWEST SABAH Meligan Formation with high composition of quartz in southwest Sabah (Sanudin & Baba, 2007). Meligan Formation is Middle Miocene to Upper Miocene age (based on formainifera occurrences.(Lee et al., 2004). Meligan Formation is overlay by Liang Formation with angular unconformity (Hutchison, 2005). Liang Formation is of Pliocene age.  EASTERN SABAH Chaotically disrupted rock units cropped out over approx. 12,000 sq km – Consider as one of the largest mélange (olistostrome) terrane in the world – Lithology mainly mud-matrix olistostrome and broken formations, include tuff and tuffaceous layers. – Broken formations known variously as Kuamut, Garinono, Ayer and Kalabakan formations – Olistostrome were formed by slumping into a deep marine basin. Explosive volcanism accompanied the olistostrome deposition as indicated by large amount of tuffaceous material in the Kuamut, Garinono and especially in the Ayer Formation in the Dent Peninsular.  EASTERN SABAH Olistostrome deposits and older rock units were uplifted in the early Middle Miocene The uplifted Crystalline Basement and ophiolitic Chert-Spilite Formation probably acted as a barrier ridge separating the NE Sabah Basin from the SE Sabah Basin. Formation of Central Sabah Sub-basin (of the NE Sabah Basin) and Northern Tarakan Sub-basin (of the SE Sabah Basin) Northern Tarakan Sub-basin – Tanjong and Kapilit formations – Exposed in circular, sub-circular and synclinal basins. – Mainly deltaic shallow marine clastics  EASTERN SABAH Oldest rocks (Mesozoic) is located in the eastern part of Sabah (Semporna and Dent Peninsula), is part of a basement complex comprising of various types of igneous and metamorphic rocks. Volcanic activity began in the Early Miocene to Pleistocene in Semporna and Dent Peninsula Occurrences of volcanic rocks in Semporna area are believed to be south-west onshore continuation of the Sulu Arc from Zamboanga which formed by the subduction of the Celebes Sea  EASTERN SABAH Volcanic activity – NE Sabah & SE Sabah – Indicated by tuffaceous and volcanoclastics of the Segama Group of rocks in the Dent Peninsular and the Kalumpang Formation in the Semporna area. A tectonic event: late Middle to early Late Miocene. – Uplifted and erosion of the Tanjong formation and equivalent units as well as older units which resulted in another cycle of deltaic to shallow marine sediment filling in a new depocenter that is the Sandakan Sub-basin in eastern Sabah. – Contains the Dent Groups of sediments – mainly clastics with minor carbonates. – Sebahat, Ganduman and Togopi formations  EASTERN SABAH ELSEWHERE – Remnants of the younger cycle sedimentation in both NE Sabah and SE Sabah basins include the Sandakan Formation, Bongaya Fm, Simengaris Fm, Umas-Umas Fm and Balung Formation. Plio-Pleistocene sediments – Mostly limestones, calcareous sandstone, conglomerate, carbon shale, occur in coastal areas – Togopi and Wallace fm.  Tectonic Evolution of Sabah Sabah lies at an important junction between the Eurasian, Indo-Australian, Pacific and Philippines Sea plates. It also occupies a central position between three marginal basins: the Sulu, Celebes and South China Seas.  Tectonic Evolution of Sabah Main tectonic elements of Sabah – a major fold-thrust belt trending northeast in the west (NW Borneo Trend) and bending to the east and southeast towards the north and eastern part (Sulu Trend) of Sabah. – this arcuate belt consists of a deep-marine Eocene-Oligocene accretionary complex. The Early Miocene deformation – interpreted to mark a major tectonic event, causing formation of the mélanges, major uplift and erosion which produced the Base Miocene Unconformity. – this was followed by a change in depositional environment from deepwater to a shallow deltaic.  Tectonic Evolution NW-SE rifting of the Sulu Sea (Late Early Miocene) – interpreted to have rejuvenated the Central Sabah Basin with regional extension and subsidence, and initiated rift basins as part of the formation of the Sulu Sea in a back arc setting. Collision of the Cagayan Arc and Palawan micro-continental block (Middle Miocene) – caused another Middle Miocene Unconformity and has been noted to mark the Deep Regional Unconformity in Sabah. Late Miocene tectonic event marks another major folding and uplift which can be correlated as the Shallow Regional Unconformity of this region. – Latest tectonic event was probably caused by strike-slip faulting and transpressional fault movement which continued during the Pliocene to present day.  Tectonic Evolution Pre-Cenozoic a. Presence of granitic and metamorphic rocks of possible continental origin (Reinhard and Wenk, 1951; Leong, 1974) associated with the ophiolitic complex. b. Interpretation of gravity data has led to the suggestion that normal continental basement lies beneath the ophiolite (Holt, 1998; Milsom and Holt, 2001); c. Most of the metamorphic rocks would have had a basic protolith (Hall and Wilson, 2000). d. Granitic rocks, which are of very small volume (Hutchison et al., 2000), could represent arc plutonic rocks intruded into an older ophiolitic basement.  Tectonic Evolution Paleocene to Eocene Sedimentation a. Rajang Group is a widespread association of Late Cretaceous to Eocene deep water mudstones and turbiditic sandstones which include the Sapulut, Trusmadi and East Crocker formations. b. All are thought to have been deposited in the large NE-SW trending Crocker Basin and all are highly deformed with tight isoclinal folds and thrusts (Hutchison, 1996). c. The Palaeogene was therefore a period of continued deposition of deep marine turbidites. d. The strongly deformed turbiditic Rajang Group is interpreted as a part of an accretionary prism related to southeasterly subduction of the proto-South China Sea in the NW Borneo.  Tectonic Evolution Late Eocene Uplift a. An unconformity within the succession of Palaeogene turbidites between the Middle and Upper Eocene is inferred by Rangin et al. (1990) on the evidence of reworking of nannofossils. b. Hutchison (1996) also argues that the West Crocker Formation includes detritus from uplifted and eroded Rajang Group and East Crocker Formation rocks.  Hutchison (1996) refer to this uplift as the ‘Sarawak orogeny’ and suggest it was probably driven by collision along the northern Borneo margin at this time. c. The unconformity is generally difficult to recognize in outcrop in Sabah because of similarities in lithologies either side of it and the strong Neogene deformation. In general, the contact is obscure..  Tectonic Evolution Late Eocene - Miocene a. Uplifting and erosion of the Rajang Group accretionary complex provided a source of sediment for the Borneo trough to the NW and also to the SE where material was deposited in a deep water setting as the West Crocker, Labang and Kulapis formations. b. The fold-thrust belt of the West Crocker Formation, which is well exposed in western Sabah, represents the accretionary complex related to continued southeasterly subduction of the proto-South China Sea in the NW Borneo. c. The Labang and Kulapis formations exposed in eastern Sabah represent deposition of deep-water clastics in a forearc basin setting from the Late Eocene through to the Late Oligocene. d. During the Oligocene there was widespread regional subsidence. Outcrops of Labang/Kulapis Formation typically show abundant syn-depositional and syn- diagenetic extensional faults that suggest active growth faulting associated with this subsidence.  Tectonic Evolution Early Miocene Deformation (22-20 Ma) a. Early Miocene was a period of progressive tectonic deformation in the forearc region during subduction and widespread mélange development in Sabah. b. Inclusion of Labang Formation sandstone and mudstone clasts in the Gomantong Limestone demonstrates that uplift and deformation started by the Early Miocene, between approximately 22 and 20 Ma (Balaguru et al., 2003) c. Deformation continued for several million years, with the Gomantong Limestone forming on structural highs during relatively quiescent times in the Early Miocene. d. Unconformity separates the deformed and lithified melange unit of the Kuamut, Garinono, or Ayer formations from the less tectonised strata (Balaguru, 2001, 2003). e. Early Miocene (22-20 Ma) deformation is interpreted to mark a major tectonic event, causing formation of the mélanges, major uplift and erosion, which produced the Base Miocene Unconformity (BMU or Pre-DRU). f. This tectonic event is related to subduction and collision of the Dangerous Ground Continental Block to the NW Borneo and referred as the ‘Sabah Orogeny’ (Hutchison, 1996). g. This was followed by a change in depositional environment from deep-water to a shallow deltaic setting (Balaguru, 2001; Balaguru et al., 2003; Van Hattam, 2005). The associated major uplift and erosion provided sediment supply to the deltaic to shallow marine Middle to Upper Miocene successions of the Meligan and Tanjong Deltas.  Tectonic Evolution Early Miocene Deformation (22-20 Ma) a. Early Miocene was a period of progressive tectonic deformation in the forearc region during subduction and widespread mélange development in Sabah. b. Inclusion of Labang Formation sandstone and mudstone clasts in the Gomantong Limestone demonstrates that uplift and deformation started by the Early Miocene, between approximately 22 and 20 Ma (Balaguru et al., 2003) c. Deformation continued for several million years, with the Gomantong Limestone forming on structural highs during relatively quiescent times in the Early Miocene. d. Unconformity separates the deformed and lithified melange unit of the Kuamut, Garinono, or Ayer formations from the less tectonised strata (Balaguru, 2001, 2003).  Tectonic Evolution Early Miocene Deformation (22 – 20 Ma) a. The Early Miocene deformation is interpreted to mark a major tectonic event, causing formation of the mélanges, major uplift and erosion, which produced the Base Miocene Unconformity (BMU or Pre-DRU). b. Related to subduction and collision of the Dangerous Ground Continental Block to the NW Borneo and referred as the ‘Sabah Orogeny’ (Hutchison, 1996). c. Followed by a change in depositional environment from deep-water to a shallow deltaic setting (Balaguru, 2001; Balaguru et al., 2003; Van Hattam, 2005). d. The associated major uplift and erosion provided sediment supply to the deltaic to shallow marine Middle to Upper Miocene successions of the Meligan and Tanjong Deltas.  Tectonic Evolution Early Miocene Limestone Development a. Limestone outcrops in southern Sabah are correlated with the Early Miocene (Burdigalian) Gomantong Limestone Formation, which contains clasts of the Labang Formation (Noad, 1998). b. This suggests widespread uplift followed by carbonate sedimentation throughout the central and eastern Sabah. c. This change in depositional environment is also recognized offshore NW Sabah. d. In eastern Sabah the Gomantong Limestone outcrops in a ENE-WSW-trending belt stretching at least 200 km, which suggests that this may have been a zone of uplift along which localised carbonate sedimentation occurred, isolated from any clastic sediment influx from the west.  Tectonic Evolution Late Early Miocene to Middle Miocene Clastic Sedimentation a. End of early Miocene deformation is marked by the onset of Tanjong, Meligan or Kudat Formation clastic deposition, the oldest dates for which are late Burdigalian (18-16 Ma). b. Absence of widespread synsedimentary deformation in the Tanjong Formation suggests that it was deposited during a period of relative tectonic quiescence, which lasted through the deposition of late Middle Miocene (12-10 Ma) or younger strata. c. Continued subsidence created a cumulative thickness of at least 6,000 m. The Middle Miocene subsidence in the central Sabah Basin is possibly related to coeval development of the Sulu Sea Basin in a back-arc setting (Nichols et al., 1990) or regional thermal subsidence (Ismail et al., 1995). d. Facies trends in the Tanjong, Kalabakan and Kapilit formations indicate that detritus eroded from uplifted strata of the Rajang and Kinabatangan groups in the west and was deposited in a deltaic to shallow marine system which prograded towards the northeast. e. All the Neogene ‘circular basins’ of eastern Sabah were part of a single NE-SW trending shallow basin.  Tectonic Evolution Middle Miocene Deformation and Clastic Sedimentation a. Arc-continent collision in the northern Borneo between the Cagayan Arc and Palawan Continental Block (Rangin, 1991) created another Middle Miocene Unconformity (MMU, 15.5 Ma) which marks the Deep Regional Unconformity (DRU) in onshore and offshore Sabah. b. This deformation had stopped the extension and caused inversion of the early Middle Miocene sediments and continued with post-rift sedimentation. c. There had been continued subsidence after this tectonic event, which continued to deposit the thick prograding post-rift sediments. d. Progradation of a large delta (Champion and Kapilit deltas) resumed during the time following a very similar pattern to the underlying Meligan and Tanjong deltas.  Tectonic Evolution Late Miocene Deformation and Uplift a. The Late Miocene (SRU, 8.6 Ma) tectonic event marks another major folding and uplift which can be correlated as the Shallow Regional Unconformity (SRU) of this region (Levell, 1987). b. The Kinabalu emplacement (10-8 Ma) event plausibly contributed to uplift and supply of sediments. c. This was followed by development of the Baram Delta which prograded to NW Sabah, and Kinabatangan Delta prograded to NE Sabah d. The Late Pliocene tectonic event caused by NW-SE trending strike-slip faulting and transpressional fault movement in this region resulted in major structural inversion and uplift. This event is here termed the Meliau Orogeny (Balaguru et al., 2003). e. All the Miocene outliers in central Sabah were part of a single shallow basin. f. The present outcrop pattern of the Miocene strata is the product of regional strike-slip and transpressional tectonics and inversion during the Late Miocene (8.6 Ma) onwards and probably lasted until the latest Pliocene.  Tectonic Evolution Late Miocene Deformation and Uplift a. The transpressional movement along the major strike-slip faults in this region would better explain the structural development in these areas and is possibly related to propagation of deformation from Sulawesi towards NW Sabah. b. The Late Pliocene strike-slip deformation is regionally significant and occurred at a similar time as important deformation in NE Kalimantan, Sulawesi and NW Sabah. c. This transpressional movement is interpreted to be the cause of the major orogenic deformation, uplift and final structural development in Sabah region and possibly continued to the present day. Thank you  Tectonic Evolution of Sabah Tectonic evolution in Sabah occurred since Early Tertiary. There were several regional tectonic events. The regional tectonic events resulted in diverse structural trend and depositional framework of Sabah. At least three major episodes were linked to NW-SE compression coinciding with the ongoing subduction of the proto-South China Sea during the Late Eocene, Early Miocene and Middle Miocene. The Late Eocene tectonic deformation is characterized by folding and thrusting of basement rock and older paleogene sediments. The Paleogene regional tectonic setting of Sabah seems to be very complex, with southeasterly subduction in the NW Borneo, and extension in the SE in the Celebes Sea and Makassar Strait. The Early Miocene deformation is interpreted to mark a major tectonic event, causing formation of the mélanges, major uplift and erosion which produced the Base Miocene Unconformity. This was followed by a change in depositional environment from deepwater to a shallow deltaic.  The Kuamut Formation has been linked to sedimentation on the flanks of an accretionary wedge in Late Oligocene times (Balaguru et al., 2003; Balaguru and Hall, 2009; Hall, 2013, Fig. 3) but as noted above this is actually an Early Miocene formation, and as Leong (1974) described in detail (op.cit., p. 180–183) it is an extensional mélange or olistostrome deposit. It is a unit devoid of shearing or compressional features, deposited within fault bounded basins This extensional phase is associated with intra-arc rifting of the Sulu Arc from the Cagayan Arc offshore east Sabah in the eastern Sulu Sea (Tongkul, 1991; Hutchison, 1992, 2005 Fig. 99, Hall, 2013). The Late Miocene uplift of the Western Cordillera of Sabah has removed much Early Miocene stratigraphic record but on its flanks the Stage III sequence drilled offshore by about a dozen wells, is dominated by claystone and lacks either reworked or transported bioclasts, in contrast to the very sandy Late Oligocene Kudat Formation outcrops just 20 km away.  Tectonic Evolution Below the Early Miocene unconformity lies ophiolitic basement, which is overlain by an accretionary complex of Eocene age and a late Paleogene deep water succession which formed in a fore-arc basin. The late Paleogene deposits underwent syn-depositional deformation, including the development of extensive melanges, all of which can be demonstrated to lie below the unconformity in this area Some localised limestone deposition occurred during a period of uplift and erosion in the Early Miocene, following which there was an influx of clastic sediments deposited in delta and pro-deltaic environments in the Middle Miocene. These deltaic to shallow marine deposits are now recognised as forming two coarsening-upward successions, mapped as the Tanjong and Kapilit Formations. The total thickness of these two formations in the Central Sabah Basin amounts to 6000 m, only half of the previous estimates, although the total stratigraphic thickness of Cenozoic clastic strata in Sabah may be more than 20,000 m.