Northwest Borneo Research Articles

Deep structural controls on the distribution of carbonate reservoirs and overburden heterogeneity in Central Luconia province, offshore Borneo revealed by 3D anisotropic inversion of regional controlled-source electromagnetic and magnetotelluric profile data

Understanding the deep structural controls on reservoir distribution and overburden heterogeneity is important for near-field exploration and green-field development of the Miocene to Holocene carbonate buildups in Central Luconia province in offshore northwest Borneo, Malaysia. Data from 59 stations along an approximately 180 km long controlled-source electromagnetic (CSEM) and magnetotelluric (MT) survey line with three segments recorded using different CSEM transmitter-towing directions were available. We applied three-dimensional (3D) anisotropic resistivity inversion with cross-gradient constraint and verified the resulting models using resistivity logs from nearby wells and the acoustic basement interpreted from seismic data. Our anisotropic resistivity models reveal a fragmented carbonate-rich zone atop a segmented basement comprising electrically resistive horsts coinciding with the northerly Mega-platform, Central and Southern Field Highs, separated by steep conductive zones coinciding with the West, East, and Southeast Troughs previously interpreted from seismic data. The structural highs correlate with the spatial distribution of the known carbonate buildups implying a genetic link. The carbonate bodies are overlain and underlain by persistent layers (C2 and C3) of low resistivity and high anisotropy, which we interpret as indicating compressional deformation or detachment zones. Overburden layer C2 (whose base coincides with the top of a key sedimentary package, Cycle V in seismic data) is thinnest over the East Trough and is discontinuous at the eastern margin of the West Trough, which are locations where drilled wells did not find hydrocarbons implying that the seal rocks are inefficient or breached at those localities. We used these observations to refine the existing seismic-based interpretation of carbonate play-types along our transect indicating how 3D joint CSEM-MT imaging can potentially contribute to derisking or optimizing future exploration and/or development work in this province.

Rapid Climate Links Between High Northern Latitudes and Tropical Southeast Asia Over the Last 40 ka

AbstractThe climate response of tropical Southeast Asia to abrupt climate change originating from high northern latitudes remains poorly understood. Here, marine sediments recovered from the Northwest Borneo Trough are analyzed to trace variations in terrigenous material composition associated with sea level and palaeoflood activities over the past 40 ka. We describe for the first time the influence of sea level change on terrigenous deposition from a tropical island with small mountainous rivers surrounded by narrow continental shelves and the coupling between North Atlantic dynamics and climate feedbacks in tropical Southeast Asia during the Dansgaard‐Oeschger stadials. This study demonstrates that climate oscillations occurring at high northern latitudes can be transmitted to tropical Southeast Asia through the functions of sea level, the East Asian winter monsoon and the Intertropical Convergence Zone. Such information is fundamental to correctly assessing future sea level rise and flood risks in tropical Southeast Asia.

Seismic-electromagnetic projection attribute: Application in integrating seismic quantitative interpretation and 3D controlled-source electromagnetic-magnetotelluric broadband data inversion for robust ranking and sweet spotting of hydrocarbon prospects in offshore northwest Borneo

We introduce a new seismic-electromagnetic (EM) projection (SEMP) attribute to improve the characterization of pay sands by integrating seismic P impedance and S impedance with electrical resistivity measurements leveraging on the high sensitivity of resistivity to fluid saturation and the capability of seismic data to delineate thin beds. Porosity is predicted using an extended elastic impedance (EEI) approach to reduce the risk of encountering SEMP anomalies related to low porosity. First, we determine the seismic-EM integration concept using well logs from a well that encountered hydrocarbons in a deepwater fold belt in offshore Borneo. The SEMP logs supported by the EEI log successfully delineate the pay zones in the well. Second, we extend the approach in three dimensions and evaluate its effectiveness using large-size seismic controlled-source EM (CSEM) and magnetotelluric (MT) data from the same area. The seismic data are inverted to produce P- and S-impedance volumes. EEI volume calibrated to total porosity also is produced. We then perform 3D anisotropic cross-gradient joint CSEM and MT inversion of a large-size survey comprising 647 receivers with receiver spacing of 1.5–3 km at prospect to regional scale. The SEMP volumes computed using the seismic and CSEM-MT inversion results are then interpreted with the EEI volume to identify possible geobodies of pay sand. Resistive geobodies with low porosity are assigned higher risks because they are likely due to compaction rather than hydrocarbon presence, whereas geobodies with high porosity are assigned lower risks and identified as potential sweet spots. The geobodies need to be corroborated with independent geologic studies to mature them into exploration prospects and assess their associated risk and potential. Although a vertical transverse isotropy approximation is used in our CSEM-MT study, the SEMP concept also is applicable to cases considering tilted transverse isotropy or arbitrary anisotropy where available and operational for such large-size exploration data.

Diversity and Distribution of the Benthic Foraminifera on the Brunei Shelf (Northwest Borneo): Effect of Seawater Depth

The marine benthic diversity of the Palawan/North Borneo ecoregion is poorly known, despite its implied unique high species richness within the Coral Triangle. The present study investigated the diversity and distribution of benthic foraminifera on the Brunei shelf. The objectives were to determine the species composition of sediment samples collected from 11 sites, extending ~70 km from the Brunei coastline and along a depth gradient of 10–200 m. We retrieved a total of 99 species, belonging to 31 families and 56 genera, out of which 52 species represented new records for Brunei and probably the ecoregion. Using presence/absence data, analyses were also performed to compare species diversity patterns (species richness, occupancy, taxonomic distinctness) and species assemblage similarity across the sites. For further insight into the relationship between distribution and depth-associated environmental conditions, we undertook stable isotope analyses of selected species of Rotaliida, Miliolida, and Lagenida. Oxygen isotope values were positively correlated with depth and species distribution, confirming cooler temperatures at greater depth. The carbon isotope data revealed species differences relating to habitat and food source specificity and a biomineralization effect. Close to one-third of the species were recorded from single sites, and species richness and taxonomic distinctness increased with depth and were greatest at the second deepest site (144 m). Together, these findings suggest data underrepresentation of diversity, habitat disturbance in shallower water, and species specialization (adaptation) in deeper water. Importantly, assemblage similarity suggests the occurrence of at least three marine biotopes on the Brunei shelf (10–40 m, 40–150 m, and >150 m). This study contributes significantly to our understanding of the local and regional patterns of foraminiferal diversity and distribution.

Continuance Intention to Use Online Learning Platform during COVID-19 Pandemic: Perspective from Young Customers of Higher Learning Institutions In Northwest Borneo Island (Sarawak)

Continuance Intention to Use Online Learning Platform during COVID-19 Pandemic: Perspective from Young Customers of Higher Learning Institutions In Northwest Borneo Island (Sarawak)

Using Large-Size Three-Dimensional Marine Electromagnetic Data for the Efficient Combined Investigation of Natural Hydrogen and Hydrocarbon Gas Reservoirs: A Geologically Consistent and Process-Oriented Approach with Implications for Carbon Footprint Reduction

The recycling or burial of carbon dioxide in depleted petroleum reservoirs and re-imagining exploration strategies that focus on hydrogen reservoirs (with any associated hydrocarbon gas as the upside potential) are a necessity in today’s environmental and geopolitical climate. Given that geologic hydrogen and hydrocarbon gases may occur in the same or different reservoirs, there will be gains in efficiency when searching for both resources together since they share some commonalities, but there is no geophysical workflow available yet for this purpose. Three-dimensional (3D) marine controlled-source electromagnetic (CSEM) and magnetotelluric (MT) methods provide valuable information on rock-and-fluid variations in the subsurface and can be used to investigate hydrogen and hydrocarbon reservoirs, source rocks, and the migration pathways of contrasting resistivity relative to the host rock. In this paper, a process-oriented CSEM-MT workflow is proposed for the efficient combined investigation of reservoir hydrocarbon and hydrogen within a play-based exploration and production framework that emphasizes carbon footprint reduction. It has the following challenging elements: finding the right basin (and block), selecting the right prospect, drilling the right well, and exploiting the opportunities for sustainability and CO2 recycling or burial in the appropriate reservoirs. Recent methodological developments that integrate 3D CSEM-MT imaging into the appropriate structural constraints to derive the geologically robust models necessary for resolving these challenges and their extension to reservoir monitoring are described. Instructive case studies are revisited, showing how 3D CSEM-MT models facilitate the interpretation of resistivity information in terms of the key elements of geological prospect evaluation (presence of source rocks, migration and charge, reservoir rock, and trap and seal) and understanding how deep geological processes control the distribution and charging of potential hydrocarbon, geothermal, and hydrogen reservoirs. In particular, evidence is provided that deep crustal resistivity imaging can map serpentinized ultramafic rocks (possible source rocks for hydrogen) in offshore northwest Borneo and can be combined with seismic reflection data to map vertical fluid migration pathways and their barrier (or seal), as exemplified by the subhorizontal detachment zones in Eocene shale in the Mexican Ridges fold belt of the southwest of the Gulf of Mexico, raising the possibility of using integrated geophysical methods to map hydrogen kitchens in different terrains. The methodological advancements and new combined investigative workflow provide a way for improved resource mapping and monitoring and, hence, a technology that could play a critical role in helping the world reach net-zero emissions by 2050.

Biogeochemical and physical drivers of hypoxia in a tropical embayment (Brunei Bay)

Dissolved oxygen is an ecologically critical variable with the prevalence of hypoxia one of the key global anthropogenic issues. A study was carried out to understand the causes of low dissolved oxygen in Brunei Bay, northwest Borneo. Hypoxia was widespread in bottom waters in the monsoonal dry season with dissolved oxygen < 2mg/L throughout the coastal zone. This was a result of riverine nutrient input primarily from the Padas river driving excess primary production and its subsequent sinking into stratified bottom water where its decomposition consumed oxygen. Despite higher riverine nutrient input in the wet season hypoxia was less extensive due to the combination of turbidity reducing coastal primary production, the intrusion of oxygen-rich water from the South China Sea into offshore bottom layer waters and horizontal flushing increase advection of phytoplankton biomass out of the bay. Future investigation of hypoxia in shallow tropical regions therefore needs to consider the role of monsoonal season.

A Discussion on the relationship between prominent unconformities on the SCS shelf margins and the end of seafloor spreading in the South China Sea

In an effort to reconcile different data sources (seafloor spreading, seismic and gravity images, well calibrations, outcrop studies) in the South China Sea (SCS), we reviewed the unconformity records, in particular in the context with the shut-off of seafloor spreading in the SCS. With respect to the start of spreading, there is a consensus: ca. 34-41 Ma. Recent data infer an end of spreading, near to the magnetic Anomaly 5 = ca. 15.5 Ma (Langhian age). In Northwest Borneo, it is suggested that this event is coeval with the Deep Regional Unconformity (DRU) in Sabah and Brunei, and the Mid-Miocene Unconformity (MMU) in Sarawak. The MMU is also recognized in offshore Vietnam and Palawan, on the Western and Southeastern margins of the SCS, respectively. The MMU/DRU may constitute the border between active margin and passive margin deposits within the marine SCS sub-basins. The progradation of clastic shelves post-MMU/DRU may have hampered growth of bioherms whilst creating prolific sandstone reservoir sequences offshore Northwest Borneo and Vietnam.

Genetic structure and population history of a peat swamp forest tree species, Shorea albida (Dipterocarpaceae), in Brunei Darussalam.

Southeast Asia supports high biodiversity, in a mosaic of forest types formed by the expansion and contraction of habitats through past climate changes. Among the region's forest types, the geographical distribution of peat swamp forests has fluctuated intensely over the past 120,000 years. Most peat swamp forests in Southeast Asia are found in coastal regions and formed within the last 7,000 years after a decline in sea level. However, some peat swamps were initiated earlier on substrates of slightly higher elevation, and these peat swamps might have been refugia for peat swamp species in the last glacial period and the high sea level period. We assessed genetic diversity, genetic structure and divergence time of current genetic groups for Shorea albida in Brunei, an endemic tree species of Bornean peat swamp forests, using 18 microsatellite markers. Genetic diversity was not lower than has been found in other Shorea species, possibly because of the high density of S. albida in Brunei. Although overall genetic divergence between populations was low, two populations (Ingei and Labi Road 3) were distinct from the other populations. Analysis using DIYABC estimated that three genetic groups (Ingei, Labi Road 3 and others) diverged simultaneously from their ancestral population, whose effective size was very small, about 7,500 years ago, corresponding to a recent sea level peak in the Belait-Baram river basin. In that high sea level period, some higher-elevation lands remained, and peat formation had already started in this region. We propose that the current genetic structure of S. albida in Brunei was formed from small refugial populations that survived the period of higher sea level in these higher-elevation areas. Because of their relatively high genetic diversity, Brunei's S. albida populations should become an important genetic resource for the recovery of genetically healthy populations in other parts of northwest Borneo.

Dayaks in a Ledger: A Bornean Labor History and an Oil Town's Indigenous Workers

AbstractThis article delineates a hitherto eclipsed labor history of the Northwest Borneo oilfields. In 2018, Brunei Shell Petroleum (BSP) in an unprecedented move, released to Brunei's national archive two labor registers of the British Malayan Petroleum Company (BMPC-renamed BSP in 1958), with entries dating between the 1940s and 1950s. These registers provided a rare glimpse of the workers who were recruited to the Brunei oilfields as labor, a category distinct from staff. As BMPC labor they worked to rehabilitate the company town and the oilfields that were destroyed during the Second World War by the Japanese army and allied bombing in the British protectorate of Brunei. Like colonial records that amassed information for the control and rule of colonized subjects, each entry in BMPC's ledger meticulously noted the date of engagement, place of employment, wages, work history, as well as some biographical information about its workers. Inadvertently, these entries also revealed modes of worker resistance and assertions of agency, thus providing a glimpse of the hidden transcripts of a labor history shaped by the policies of BMPC in this colonial outpost. My article draws on these two BMPC labor registers to trace a micro-spatial history of “Dayak” labor in the emergent Borneo oilfields. Often obscured in historical records, the registers made visible the ways in which Indigenous workers negotiated and resisted the company's control of its labor force. I explore Dayak labor recruitment within the context of the 1880s-1941 when state borders irrevocably shifted and regional economies were increasingly drawn into a global market. In doing so, I chart migrant labor routes across varied regional economies in Northwest Borneo, BMPC's management of a multiethnic labor force, and company workers' agency.

A review of the family Cymothoidae (Isopoda: Cymothooidea) infesting marine fishes from Malaysian waters, with new host and geographical records.

A checklist of parasitic cymothoids from Malaysian waters is presented based on available literature and material collected from 2010 to 2020. Most of the collected specimens were recorded from waters of Terengganu, east coast of Peninsular Malaysia (facing the South China Sea), whereas literature records were included from Sarawak, along the Miri coast of northwest Borneo. The checklist comprises 19 species in ten genera, seven of which are new records from Malaysia: Anilocra nemipteri Bruce, 1987; Ceratothoa barracuda Martin, Bruce & Nowak, 2015; Ceratothoa carinata (Bianconi, 1869); Cymothoa epimerica Avdeev, 1979; Elthusa sigani Bruce, 1990; Joryma engraulidis (Barnard, 1936) and Renocila richardsonae Williams & Bunkley-Williams, 1992. Eight new host records are based on collected specimens: Anilocra nemipteri was dorsally attached on Nemipterus nemurus (Bleeker, 1857), Nemipterus nematophorus (Bleeker, 1854), Nemipterus tambuloides (Bleeker, 1853) and Nemipterus thosaporni Russell, 1991 (family Nemipteridae); Ceratothoa carinata was found in the buccal cavity of Decapterus macrosoma Bleeker, 1851 (family Carangidae); Cymothoa eremita (Brunnich, 1783) was attached in the buccal cavity of Nemipterus tambuloides (Bleeker, 1853) and Nemipterus furcosus (Valenciennes, 1830); Elthusa sigani was found attached on the gills of Pterois russelli Bennett, 1831 (family Scorpaenidae), and Renocila richardsonae was attached on the caudal fin of Upeneus japonicus (Houttuyn, 1782) (family Mullidae). All cymothoid species listed here are known to have a Central Indo-Pacific distribution, with some ranging as far as the Western Indian Ocean. A cymothoid-host association is here listed from 28 fish families, with the most commonly reported from Carangidae (pompanos, jack mackerels, runners, scads), Engraulidae (anchovies), and Leiognathidae (ponyfishes, slipmouths). This paper is the first comprehensive review of both verified literature records and deposited specimens. A key for the family of Cymothoidae in Malaysian waters is given.

Late Oligocene-Early Miocene Palynological Succession From Marginal Marine Deposits, Nyalau Formation, Bintulu Sarawak: Palynostratigraphy, Paleovegetation And Paleoclimate Significance

Palynological analysis was conducted on one hundred and twenty-four samples collected from ten sedimentary outcrops in Sangan, Tatau, Bintulu and Similajau areas of central Sarawak. These outcrops form part of the Oligocene-Miocene marginal marine successions of the Nyalau Formation. Rich palynomorph assemblages were recovered from the samples and they provide well-preserved palynological record for the Oligocene-Miocene boundary in the onshore of northwest Borneo. Three distinct palynological zones were identified based on changes in pollen assemblages. The three zones are informally named FT-I, FT-II and FT-III. The FT-I zone is characterized by high frequency of Florschuetzia trilobata with common Florschuetzia semilobata including sporadic Meyeripollis naharkotensis. High percentage of F. trilobata and sporadic occurrence of F. semilobata are typical of the FT-II zone. Another important characteristic for this zone is characterized by common to abundant Casuarina type pollen while M. naharkotensis is virtually absent. The FT-III zone is marked by the presence of Florschuetzia levipoli. The zone is also characterized by abundant F. trilobata including regular occurrence of F. semilobata with common montane elements represented by Pinus, Picea, Alnus, Ephedra and Tsuga. All the identified zones record regular occurrence of Gramineae throughout with strong variation in diversity and frequency of peat swamp taxa represented by Blumeodendron type, Calophyllum type, Stemonurus type Calamus type and Dactylocladus type. The mangrove element such as Rhizophora type exhibits gradual increased in number throughout the FT-I and FT-II zone and showing reduced abundance in FT-III zone. These three zones are correlatable to the Late Oligocene to Early Miocene palynostratigraphy of the Cycle I and Cycle II in the Sarawak Basin. The palynological successions from these areas suggest a typical wet climate with intermittent seasonally dry conditions throughout the Late Oligocene - Early Miocene. This is evident from the regular occurrence of grass pollen i.e., Gramineae/Poaceae with common rain forest and peatswamp elements. This is supported by the common to high frequency of mangrove pollen notably Rhizophora type (Zonocostites ramonae). The Early Miocene may have experienced occasional super wet climatic conditions where rain forest pollen assemblages were prevalent including intermittent acme of Casuarina type pollen.

Deepwater fold-thrust belt contraction driven by mixed deformation components

The formation of fold-thrust belts is driven by compressive stresses caused by crustal tectonics, gravity, or a combination of both. The formation mechanism of a single compressive stress component has been thoroughly investigated by laboratory experiments and field observations. It is yet less well established how fold-thrust systems deform under multiple compressional stresses. The formation of the deepwater fold-thrust belt on the northwest Borneo margin has been previously explained by compressive gravity-driven stresses in the south and crustal-driven tectonics in the north. This study focuses on the transition zone between the gravity-driven south and crustal-driven north, and investigates the structural diversity around this transition using 3D seismic-reflection data. Structural interpretation results reveal two structural provinces distinct in deformation styles and structural kinematics within the deepwater fold-thrust belt. Folds and thrusts in each structural province reflect deformation stresses that occurred at different times with different orientation. Structural features in each structural province developed independently and were preserved largely without mixing in the fold-thrust belt, except for an interference zone of ca. 15 km in width. The fold-thrust belt can be interpreted to have formed by a multi-directional compressive stress system and exhibits greater structural heterogeneity than deformation caused by a single-component compressive stress system. Particular deformation characteristics and fault activity in the interference zone reflect a complex disparate compressive stress relationship.

Seismostratigraphic and sedimentological characterization of deepwater channel systems on the NW Borneo margin: Sediment sources and structurally-controlled routing system

• Late Miocene folding in deepwater NW Borneo influenced submarine channel development. • The Champion sediment-supply system comprised in its onshore part multiple rivers. • The paleo-Padas River was one of the primary rivers supplying lithic-rich sediment. • Variation in catchment-area geology influenced deepwater sediment composition. The northwest (NW) Borneo margin is one of the geologically most complex regions of Southeast Asia characterized by a steep slope gradient and an extensive deepwater fold and thrust belt. This area is economically important because of large-volume hydrocarbon accumulations in the deep-marine sandstones in fold and thrust anticlines. Although much attention has been paid to the distribution of deepwater reservoir rocks, the provenance of these rocks and compositional variations are yet not fully understood. In this study we present geomorphological and petrological analyses of Late Miocene deepwater channel deposits that form important reservoirs in the region. Our results reveal the presence of a northwest-trending deepwater channel system displaying morphological variations induced by syn -sedimentary structural development. Petrological analyses of core samples show a predominant lithic-rich rock composition in the reservoir sandstones, suggesting sediment supply from a lithic-rich Crocker Formation hinterland, probably through a paleo-Padas River. This rock composition differs from the quartz-rich rock composition of an adjacent contemporaneous deepwater reservoir mainly comprising reworked quartz-rich Meligan sandstones. The observed petrological differences are interpreted to reflect a Late Miocene multi-source sediment supply system that drained offshore different NW Borneo hinterland areas. Offshore, sediment transport to and across the slope was dominantly margin-perpendicular, linear or of low sinuosity, in the deepwater locally affected by faulting and folding. This study provides new insights into the complexity of sediment routing systems along continental margins, highlighting the influences of the configuration of the sediment supply system and tectonics on deepwater sedimentation.

Use of structure-guided 3D controlled-source electromagnetic inversion to map karst features in carbonates in offshore northwest Borneo

Fractured and/or karstic carbonates (FKCs) in the subsurface are commonly associated with significant drilling risk or reservoir effectiveness issues. Understanding the distribution of karsts will help avoid drilling into possible voids and also reassess risks associated with reservoir effectiveness. A 2020 3D seismic acquisition in offshore northwest Borneo provided data for identifying new carbonate prospects and an opportunity to revisit a 2010 marine controlled-source electromagnetic (CSEM) survey that was not designed specifically for FKC mapping but can serve to test new inversion capability for imaging karsted carbonate bodies. A 3D CSEM data were used to detect and characterize the nature (i.e., fractured and/or karsted) of carbonate prospects mapped using 3D seismic data. In one approach, structure tensors computed from these seismic data were used to constrain the 3D CSEM inversion on the Azure cloud platform. In another approach, cross gradients between vertical and horizontal resistivities were used as a structural guide obviating the need for seismic data. The resulting anisotropic resistivity models were validated using resistivity logs from a nearby well; the resistivity results matched the well-logs satisfactorily, providing geologic justification to interpret the presence of karst features in the resistivity volumes. Lateral boundary of the carbonate prospects was mapped based on the resistivity characteristic, in seismic- and nonseismic-guided structure-coupled inversion. Resistivity-depth cross section of the area revealed the presence of resistivity discontinuity at the seismic-inferred boundary of the main carbonate prospect. Also, resistivity depth slices of the models clearly demonstrated that the areal distribution of low and high resistive zones can be mapped and useful deductions such as the presence of FKC and basement characteristics can be made using the 3D inversion of the CSEM data.

Diversity of Fisheries in Sarawak, Northwest Borneo: Present Status and Conservation Issues

Information on fisheries resources in East Malaysia is scarce and poorly known. The current review aims to compile a checklist of fisheries resources in the Northwest Borneo (Sarawak, Malaysia) from available published literature, address the resources' present status, and suggest future monitoring needs for selected critical species. The study also aims to determine several Sarawak land-use issues that are in flux and responsible for habitat degradation. Five hundred sixty-four species belonging to 123 families and 32 orders were recorded from Sarawak waters. Freshwater fish species comprised 48.0% of the total, followed by a marine (36.6%), marine-euryhaline (12.9%), and brackish water (2.5%) species. Of this, Cyprinidae was the most dominant group accounting for the greatest number of species (82 species), followed by Balitoridae (34 species), Bagridae (21 species) and Penaeidae (21 species). Therefore, available fisheries resources should be managed carefully as 48 species (9.0%) are currently vulnerable to extinction. Furthermore, the presence of 20 alien species in Sarawak water bodies also requires attention from the authorities due to the potential disruption of aquatic ecological balance. Changing land use issues in Sarawak such as forest degradation, agricultural expansion, peatland deforestation and conversion, logging, destruction of mangrove forests, and construction of hydroelectric power dams and flood mitigation channels pose significant challenges to fishery management in Sarawak. Our study documents the priority of fishery monitoring and conservation in Sarawak water bodies to ensure sustainable management of fisheries resources.

Okalianecopinata sp. nov. (Insecta, Coleoptera, Elmidae) from Gunung Mulu National Park in Sarawak (Malaysia).

Okalianecopinatasp. nov., from Sarawak, northwest Borneo, Malaysia, is described and illustrated along with an identification key. The standard barcoding fragment of the mitochondrial gene coding for cytochrome c oxidase subunit I (COI) was used together with morphological characters to delimit the taxonomic boundaries of the two known species, which live in shallow streams flowing through dense primary forests in limestone areas in Pahang (West Malaysia) and Sarawak (East Malaysia). The majority of all examined Okalia are flightless. Morphological distinguishing characters are the length of the granulated fifth elytral interval, the elytral and pronotal punctation, the aedeagal morphology, and the distal portion of the ovipositor.

Genetic diversity of Aedes albopictus (Skuse) in Sarawak, Malaysia and other regions of the world

AbstractThis study inferred the genetic diversity and dispersal pattern of Aedes albopictus, for the first time from various populations in Sarawak, the largest Malaysian state situated in northwest Borneo Island. A set of sequences of 120 Ae. albopictus from Sarawak aligned as 633 characters of the cytochrome c oxidase subunit I (COI) revealed 22 haplotypes (A1–A22), of which A1 was the most widespread haplotype. The overall haplotype and nucleotide diversities were 0.65014 and 0.00176, respectively, with no significant genetic differentiation and high gene flow (Nm = 1.07). The genetic distances among the populations ranged from 0 to 0.0227. In the global dataset, sequence alignment of Ae. albopictus from Sarawak and other regions of the world revealed 72 haplotypes. Based on uniquely shared haplotypes, Ae. albopictus in Sarawak has a close affinity with those from Southeast Asian and Oceania regions.

Geochemistry and paleogeography of the Rajang Group, Northwest Borneo, Malaysia

The Late Cretaceous to Late Eocene Rajang Group in Borneo is one of the world's largest deep-sea sedimentary fans. The volume of the Rajang Group cannot be explained by erosion of the Schwaner Mountains in SW Borneo and the Malay Peninsula. To identify other contributing sources, this study examined the provenance history of the Rajang Group and the overlying Tatau Formation. A combination of bulk rock geochemistry, zircon morphological analysis and U–Pb geochronology is used to better constrain the provenance of the Rajang Group. Bulk rock Nd data, supported by detrital zircon data indicates that a late Mesozoic magmatic belt include the Schwaner Mountains was an important source before the Paleocene, after which sediment supply was dominated by older crustal sources, consistent with the Malay Peninsula. The increased contribution from older crustal material is considered to be the consequence of collapse of the magmatic arc and collision between Australian microcontinental fragment(s) and the southern margin of Sundaland. Paleocene river systems that flowed through the Malay Peninsula, transported large amounts of sediments to the marine basins including the deep-sea Rajang Group. A strong signal of sediment recycling for the Tatau Formation indicates uplift and denudation of lower Rajang Group in Late Eocene.

Crustal architecture and evolution of the southwestern South China Sea: Implications to continental breakup

The South China Sea (SCS) is a marginal basin characterized by propagating breakup and subsequent seafloor spreading during the Cenozoic. Our study investigates the crustal architecture and tectonic evolution of the Xisha Islands - Northwest Borneo conjugate margins using a 1000 km long seismic profile and two shorter seismic lines. This system is characterized by wide margins showing a succession of rift basins with thinned continental crust, associated with large extensional detachment faults soling on top of the lower crust. In relation with crustal extension, several syn-rift sequences have been identified. The lower syn-rift unit (syn-rift I) shows well expressed wedge-shape growth strata. The upper one (syn-rift II) presents a more uniform thickness, and is slightly offset by normal faults dipping toward the depocenters. To illustrate the evolution of the southwestern SCS margins during continental breakup, we restore two conjugate sections near the oceanic magnetic anomaly C5En (18.8 Ma). The conjugate COT presents an asymmetrical hyper-extension architecture in cross sections, with the southern margin being the lower plate margin. In map view, the spatial variation of crustal structures illustrates a bayonet shape characterized by an initial N–S extension coeval with the first phase of seafloor spreading in the east sub-basin in the SCS. The extension direction changed shortly later (circa 23Ma) to NW-SE opening in the southwest sub-basin in relation to a ridge jump. We suggest that variable extension direction is linked to changes in the compressional tectonic regime along Borneo and Palawan.