QCB4013 Lecture 6 Sarawak PDF

GEOLOGY OF SARAWAK Geology, Stratigraphy & Tectonic Evolution Regional Geology and Petroleum Resources of Malaysia and SEA QCB4013 BY DR. MOHD SUHAILI ISMAIL  INTRODUCTION – STRUCTURE AND STRATIGRAPHY OF SARAWAK Sa...

GEOLOGY OF SARAWAK Geology, Stratigraphy & Tectonic Evolution Regional Geology and Petroleum Resources of Malaysia and SEA QCB4013 BY DR. MOHD SUHAILI ISMAIL  INTRODUCTION – STRUCTURE AND STRATIGRAPHY OF SARAWAK Sarawak can be divided into three tectonostratigraphic zones according to their geological history (Haile, 1974). Miri Zone. Sibu Zone Kuching Zone The zones represent decreasing stratigraphic towards the east. In westernmost Sarawak, the Kuching Zone is believed to be the peripheral part of the continental basement of Borneo, the West Borneo Basement, which extends into Kalimantan. Paleozoic and Mesozoic rocks crop out mostly in this part of Sarawak.  INTRODUCTION – STRUCTURE AND STRATIGRAPHY OF SARAWAK Oldest rocks (pre-Late Carboniferous) believed to be phyllites and schists of the Kerait Schist and Tuang Formation. – In many places, these rocks are covered by thick succession of Tertiary continental strata. Central and northern Sarawak, rocks are almost exclusively Late Mesozoic and Cenozoic age. Sibu zone: essentially formed by Upper Cretaceous to Upper Eocene deepwater deep sediments of the Rajang Group. Sediments of the Rajang Group have been deformed into a fold and thrust belt referred to as the Rajang Fold-Thrust Belt. Miri Zone is underlain by Upper Eocene to Recent strata. INTRODUCTION Generalised stratigraphy of Sarawak  MIRI ZONE most northerly Underlain by Upper Eocene strata dominated by Oligocene-Miocene shallow marine shelf sediments that were deposited upon older continental crust crop out in central Sarawak. Sedimentary rock formation include Tatau Formation, Nyalau Formation, Setap Formation,Lupar Formation, Belaga Formation, Buan Formation. Chrono-stratigraphic Table of major formations in Miri Zone The Upper Cretaceous to Upper Eocene Rajang Group (flysch) forms the Sibu Zone and underlies the Miri Zone The Sarawak Orogeny caused low- grade metamorphism and strong folding characterized by steep dips of the Rajang Group. The overlying formations (molasse) are much less deformed, and un- metamorphosed, except in localized shear zones. Modified after Hutchison (2005, Figure 22).  TATAU FORMATION Middle Eocene to Oligocene clastic sediments of approximately 2500m thick Ransi Member (oldest unit ) Exposed in Tatau area at Ransi Hill and Tutong Hill Made up of 20 – 30m moderately thick bedded (1 – 2m) sandy conglomerate and sandstone with very thin bedded, light to dark grey shale. Made up of 3 lithofacies: – Thick-bedded, coarse-grained conglomerate in the lower part – Thin to medium-bedded coarse-grained, bioturbated sandstone in middle part – Medium-grained, cross-bedded sandstone in the upper part  TATAU FORMATION  Lower contact with the underlying Belaga Formation is an angular unconformity  Grades upward into the rest of Tatau Formation  Rest unconformably on the Balaga Formation  BUAN FORMATION – Predominantly shaly – Contains thin beds of siltstone and fine to medium grained sandstone  NYALAU FORMATION  Oligocene - Miocene  Hard fine to medium grained sandstones alternating with shale  Overlies Buan Formation  Coal beds encountered in the formation  Sandstone have cross-bedding and show ripples  Burrows – Ophiomorpha common  Shallow marine to estuarine, shallow littoral to inner neritic  Thickness 5000m  Conformably overlain by Sibuti Formation in the east  Interfingering with shaly Setap Shale in the northeast  SIBUTI FORMATION  Occurrences in central and north Sarawak  Clay and shale with subordinate siltstone and limestone  Inner neritic and shallow environment (present of ripples)  SETAP SHALE  Thick extensive monotonous succession of shale with subordinate thin sandstone beds and a few thin lenses of limestone  Common lithologies consists of grey shale, mudstone, sandstone and a few limestone  Inner neritic and shallow environment (present of ripples)  Change to very sandy Lambir formation in north Sarawak  Can also be found in Central zone  1600m thick  BALINGIAN FORMATION  Thick sequence of sandstone, pebbly sandstone, fossiliferous mudstone with abundant coal and lignite.  Estuarine to lagoonal  In Central zone, Balingian rest unconformably on Lambir Formation and also unconformable overlain by Begrih Formation.  In north zone, Lambir Formation is overlain by Miri Formation  Miri Formation – mainly argillaceous in the lower part, sandstone dominance in upper part.  BEGRIH FORMATION  Mainly fluviatile and non-marine.  Contain abandoned channel deposits  Conformably overlain by Liang Formation  Liang Formation: succession of clay and sand with abundant lignite and some tuff  Coastal plain to shallow marine  Tatau-Mersing Line Boundary between Miri Zone and Sibu Zone Structurally complex zone consists of Palaeocene to Eocene ophiolitic rocks including spilite, basalt, tuff and radiolarian chert The Line also represents a major unconformity between the Belaga, Mulu and Kelalan formations (Rajang Group) and the overlying Upper Eocene-Recent sediments of Miri Zone. The Late Eocene unconformity represents a major phase of tectonism that deformed the deep marine rocks of the Rajang Fold-Thrust Belt. A major thrust fault zone or terrane suture  SIBU ZONE  Rocks are almost Upper Cretaceous to Upper Eocene age  Rocks of the Rajang Group underlie the Sibu Zone  Lupar, Belaga and part of Danau Formation are part of the Rajang Group  Rajang Group:  Deformed into Rajang Fold-Thrust Belt: rocks are intensely folded, thrust and low grade metamorphosed.  SIBU ZONE BELAGA FORMATION – thick shale-sandstone turbidite sequences deposited upon oceanic crust during the Late Cretaceous and ended in the Eocene by the Sarawak Orogeny – the oldest formation at the base of the Rajang Group – Highly deformed, steeply dipping – rocks were uplifted in Late to Middle Eocene time. – Surrounded by young formation: Tatau and Nyalau formations  BELAGA FORMATION Balaga turbdite was formed as a result of being compressed, uplifted and sheared when Sundaland and Luconia blocks collided Collision led to the subduction of the Rajang Sea beneath the south Borneo Block that uplifted the Balaga Formation  Lupar Line Boundary between Sibu Zone and Kuching Zone Part of the southwestern boundary of the Rajang Group is faulted along the Lupar Line, juxtaposing the Rajang group rocks against a zone of Melange termed the Lubok Antu Melang Rajang group divided into Lupar and Belaga Formation by the Lupar Line Lubok Antu Melange: comprises of blocks of chert, sandstones,shale, limestone, gabbro, basalt and serpentinite ina sheared, cleavely clay matrix. Interpreted as a tectonic melange formed during Eocene.  LUPAR LINE – Lubok Antu Melange is overlain by the flysch-like deep sea sediments (Lupar Formation) that are interbedded with pillow basalt and intruded by gabbro. – Lupar Formation: Overlain by the basal member of the Balaga Formation. Foraminiferal evidence suggest the age as Upper Cretaceous.  KUCHING ZONE located to the southwestern part of Sarawak Palaeozoic and Early Mesozoic rocks consists of Jurassic – Cretaceous shelf deposits, molasses and related non-marine deposits on the edge of the West Borneo Basement Complex. – Upper Carboniferous-Triassic marine limestone in the central region south of Kuching. – In close asscociation with the limestone are basic to intermediate volcanic rocks (Late Triassic) – Limestones overlain by Jurassic-Cretaceus mainly siliclastic sequences – Cretaceous granitoids intrude the Cretaceous and older rocks – All rocks above are overlain unconformably by mixed terresttrial – marine siliclastic rocks of Late Cretaceous to Middle Miocene  WEST BORNEO BASEMENT most southerly zone composed of Carboniferous – Permian basement rocks intruded by Cretaceous volcanic and plutonic rocks Oldest rocks are Middle-Upper Carboniferous to Permian mica-schist, hornfels and metaquartzites. Intrusion by Middle Jurassic to Late Cretaceous plutonic suites comprising quartz diorite, tonalite, granite, some gabbro, diorite and norite with K-Ar ages (75-115 Ma) (Late to Early Cretaceous)  WEST BORNEO BASEMENT The West Borneo Basement is the northern edge of Sundaland separated by the Rajang Sea from the Miri Zone which was the southern edge of the Luconia Microcontinent. The Luconia Block moved southwards to collide with the West Borneo Basement during Late Mesozoic to Early Cenozoic (James, 1984) time. The collision of the two continental blocks led to the uplifting of the deep sea sediments of the Sibu Zone to expose the deep sea turbiditic sequence of the Belaga Formation. Basement forms the Schwaner Mountains, appears to extend eastwards to underlie the Barito and Kutei basins and northwards beneath the Tertiary Melawi and Ketungau basins within the Kuching Zone.  TECTONIC EVOLUTION Before the advent of plate tectonic theory, tectonic evolution of Sarawak was interpreted in the context of the geosynclinal theory (Haile,1969). – Deepwater turbiditic rocks in the Sibu zone was interpreted as “eugeosynclinal deposits – Upper Eocene-Recent neritic coastal sediments of Miri zone as miogeosynclinal deposits – Geosynclinal concepts have been replaced by plate tectonic theory  TECTONIC EVOLUTION Pre-Tertiary tectonic development of Sarawak can be traced back in time in the context of the breakup of Gondwanaland and evolution of the Tethys Ocean West Borneo Basement – may have been contiguous with the East Malaya Block which is part of the Sundaland craton Late Carboniferous to Early Permian – Shallow marine sedimentation (Terbat Formation) – West Borneo Basement still attached to Gondwanaland  TECTONIC EVOLUTION WBB separated by the Rajang Sea from the Miri Zone Miri Zone is the southern edge of the Luconia microcontinent Luconia block move southwards to collide with WBB during Late Mesozoic to Early Cenozoic  TECTONIC EVOLUTION Middle Permian –Early Triassic Sedimentation interrupted by suturing of East Malaya to Cathaysia After the interruption, sedimentation of continental to shallow marine deposits (Sadong Formation) Widespread andesitic to basaltic lavas and pyroclastics (Serian Volcanics) Marine sedimentation continued into Jurassic and Cretaceous associated with basic volcanism (Bau Limestone and Kedadom and Pedawan formations) – Early – Middle Cretaceous Deposition interrupted by folding, – Late Cretaceous Deposition of Pedawan Formation ended with folding and igneous activity  TECTONIC EVOLUTION Late Cretaceous – Deep marine turbidite (Belaga Formation) sedimentation occurred in a remnant ocean basin Maybe associated with a subduction zone existed along the Lupar valley called (Lupar Line) – Similar turbiditic rocks occur in the inner Baram-Tinjar area (NE Sarawak) as Mulu and Kelalan formations. – By late cretaceous western Sarawak was already uplifted resulted in continental sedimentation (Kayan Fm) which continued into Miocene with deposition of Silantek and Plateau Sandstone. Tectonic Evolution  TECTONIC EVOLUTION Late Mesozoic to Early Cenozoic evolution is a manifestation of subduction and collision processes at the northern margin of western Borneo associated with closure of the Rajang Sea. Kuching and Sibu zones – interpreted as Mesozoic-early Cenozoic crustal material added to the West Borneo Basement. Miri Zone represents the onshore extension of Sarawak Basin that developed during Late Eocene on the uplifted active continental margin formed the Kuching and Sibu zones. THANK YOU