East Sabah Research Articles

Assessment of genetic diversity within eucheumatoid cultivars in east Sabah, Malaysia

Studies have shown that cultivars of the carrageenophytes Kappaphycus and Eucheuma are clones of a limited number of strains originally domesticated from wild populations. For the development and selection of new cultivars, it is important that a comprehensive record of available variants exists. This study was conducted to provide up-to-date analysis and compilation of the current state of cultivars as the last list of cultivars was compiled nearly a decade ago. The present study analyzed the cox2–3 spacer and cox1 (1356 bp) genetic diversity of cultivars collected from 2019 to 2020 from the east coast of Sabah where the seaweed farms are concentrated. These data were compared with cultivars reported from 2010 to 2012 to assess changes, if any, to the gene pool of farmed eucheumatoid in Malaysia. Kappaphycus alvarezii, K. striatus, and K. malesianus are currently cultivated while Eucheuma denticulatum is no longer an important cultivar compared to a decade ago, probably due to its lower price. Analysis of the cox2–3 spacer revealed a new haplotype, LBT10, and, by including published GenBank data, a further four previously unnamed haplotypes were recognized from Sabah. This study confirms that there is a limited gene pool within cultivars in Malaysia and suggests the need for new or genetically diverse cultivars which can adapt to a changing environment, to ensure a more sustainable carrageenan industry.

Marine litter pollution on coral reefs of Darvel Bay (East Sabah, Malaysia)

Marine litter is recognized as an increasing component of marine ecosystem pollution. In this baseline study, we document the magnitude, types, sources, and potential impacts of litter on six coral reefs in East Sabah. We applied a simplified classification of litter to extract abundance data from video transects. The average density was 10.7 items per 100 m2. Plastics represent 91% and the remaining 9% were metal, glass, and wood. Most (~70%) plastics are single-use items derived from dumping. Discarded fishing gear accounts for ~25%. Litter pollution increases closer to urban developments, with Sakar reef having higher densities (51 items per 100 m2), and higher Clean Coast Index (CCI = 10.2, dirty) and higher Plastic Abundance Index (PAI = 4.68) scores. This method could and should be readily integrated into ongoing monitoring programs to support assessments of the extent and magnitude of marine litter pollution on reefs worldwide.

Assessment Of Tsunami Hazard In Sabah – Level Of Threat, Constraints And Future Work

The coastal areas of Sabah are exposed to far-field earthquake-induced tsunamis that could be generated along the trenches of Manila, Negros, Sulu, Cotabato, Sangihe and North Sulawesi. Tsunami simulation models from these trenches indicated that tsunami waves can reach the coast of Sabah between 40 and 120 minutes with tsunami wave heights reaching up to 3 m near the coast. The level of tsunami threat is high in southeast Sabah due to its narrow continental shelf and proximity to tsunami source in the North Sulawesi Trench. The level of tsunami threat is moderate in north and east Sabah due to their proximity to tsunami source in the Sulu Trench. The level of tsunami threat is low in west Sabah due to its distant location to tsunami source from the Manila Trench. While tsunamis cannot be prevented, its impact on human life and property can be reduced through proper assessment of its threat using tsunami simulation models. Unfortunately, constraints remain in producing a reliable tsunami inundation models due to the lack of high-resolution topography and bathymetry data in Sabah and surrounding seas. It would be helpful if such data can be acquired by the relevant government agencies, at least first, in high threat-level areas, such as Tawau and Semporna districts. In order to properly plan mitigation measures tsunami risk mapping should be intensified in high threat-level areas. The locations of settlements (including water villages), population concentrations, types of buildings and houses, road system, drainage system, harbours, jetties and vegetations (including mangroves) need to be mapped in great detail. Based on the detailed tsunami risk map, targeted vulnerable communities could be given continuous and intensive education and awareness on basic tsunami science and tsunami hazard preparedness.

Late Middle Miocene volcanism in Northwest Borneo, Southeast Asia: Implications for tectonics, paleoclimate and stratigraphic marker

Explosive volcanic events often produce pyroclastic materials that can be recognized from the geological record. These discrete pyroclastics form regional marker beds. Here we report the occurrence of a tephra layer interbedded within very thick coal beds near Mukah, Sarawak, Borneo. Traceable for tens of kilometers in the Mukah area of Sarawak, this tephra layer can be considered as regional stratigraphic marker with precise chronostratigraphic control. Systematic sedimentological, mineralogical, geochemical and zircon UPb geochronological studies have revealed a major effusive volcanic event during the latest Middle Miocene, presumably contemporaneous and/or related to a magmatic event of an earlier phase of the Mt. Kinabalu pluton or magmatism in West Sarawak or East Sabah. The volcanic event had promoted catastrophic flooding of coastal swamps and fall-out from the ash clouds that formed a regionally monotonous tephra layer across the Serravallian- Tortonian boundary. In conjunction with the regional occurrences of trap rocks, structural trends and known tectonic events, we constrained the regional depositional environments, and climate. The tephra layer was deposited in a coastal plain-swamp,- seasonal, shallow, high-moderate energy, fluvial channel-lacustrine environmental setting, wherein atmospheric fallout and eroded material from regoliths formed over older basement and volcanic rocks of the hinterland which were mixed to produce the tephra layer. This tephra layer is sandwiched between the very thick coal beds. A pre-existent volcanic chamber that was active for a long time, also experienced periodic explosive activity from probably the same magma chamber and conduit and including a major explosive activity that recycled early-formed crystals and felsic magma (rhyolite-dacite) during the major effusive event are also recognized. Our findings provide robust evidence for the prevalence of intensive chemical weathering under a wet-humid climate, and relative tectonic quiescence before the major effusive event, and the existence of vast, monotonously gently-sloping coastal plains and luxuriant vegetation akin to the present.

Diagenetic history of late Oligocene-early Miocene carbonates in East Sabah, Malaysia

Limestones are particularly susceptible to drastic early diagenesis modifications, mainly cementation and dissolution. During the early Miocene, a major tectonic deformation has caused a widespread of uplift in Sabah. This has resulted change in depositional environment from deep to shallow marine, which favours the deposition of Gomantong Limestone. This study aims to investigate the diagenetic history of Gomantong Limestone in East Sabah. Thorough understanding of the diagenetic processes may provide data to unravel the tectonic activities which affected the reservoir quality of the carbonates. Combining the data from comprehensive petrographic analysis, and Scanning Electron Microscopy (SEM) of 30 samples, two main cements type were identified. These are microcrystalline cement and Mg-calcite cement of granular and blocky mosaics which are dominantly seen in all samples. The sequence of diagenesis events are determined as (1) micritization; (2) grain scale compaction; (3) cementation (pore-filling); (4) mechanical compaction and cementation infilling fractures and (5) chemical compaction. These diagenetic events are interpreted as reflection of changes in diagenetic environment from shallow marine to deep burial. The massive cementation in the Gomantong Limestone has resulted into a poor reservoir quality.

Evaluating land use and aboveground biomass dynamics in an oil palm–dominated landscape in Borneo using optical remote sensing

The focus of this study is to assess the efficacy of using optical remote sensing (RS) in evaluating disparities in forest composition and aboveground biomass (AGB). The research was carried out in the East Sabah region, Malaysia, which constitutes a disturbance gradient ranging from pristine old growth forests to forests that have experienced varying levels of disturbances. Additionally, a significant proportion of the area consists of oil palm plantations. In accordance with local laws, riparian forest (RF) zones have been retained within oil palm plantations and other forest types. The RS imagery was used to assess forest stand structure and AGB. Band reflectance, vegetation indicators, and gray-level co-occurrence matrix (GLCM) consistency fea- tures were used as predictor variables in regression analysis. Results indicate that the spectral variables were limited in their effectiveness in differentiating between forest types and in cal- culating biomass. However, GLCM based variables illustrated strong correlations with the forest stand structures as well as with the biomass of the various forest types in the study area. The present study provides new insights into the efficacy of texture examination methods in differ- entiating between various land-use types (including small, isolated forest zones such as RFs) as well as their AGB stocks. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JRS.8.083695)

Status of Coral Reef Communities on Two Carbonate Platforms (Tun Sakaran Marine Park, East Sabah, Malaysia)

This study concerns three sites, located on carbonate platforms, east Sabah: Gaya West, Gaya East, and Mantabuan. At each site, the dominant coral shapes and their health were recorded (lagoons and outer slopes). Densities of echinoderms, Tridacna, and nudibranchs were recorded while fish density was estimated. Generally, the coral vitality is low (≤50% living corals). Massive corals dominate all sites, except the Gaya West-outer slope where coral coverage and diversity are the highest. On the Mantabuan-mesh reef, a diverse Acropora assemblage dominates the landscape. On the reef flat of Gaya East, monospecific circa 10 meter coral patches occur. Primary producers are scarce on all sites. Sea urchins, dominated by Diadema, are abundant on the Gaya East-reef flat and the Gaya West-mesh reef. Sea stars and holothurids are the most prevalent in Gaya West-outer slope, although they remain scarce. Crinoids are only abundant in Mantabuan. Stegastes damselfish highly characterizes the sites of Gaya East (reef flat and inner slope) and the Mantabuan-mesh reef. On the Mantabuan-outer slope, parrotfish and other fishes are plentiful. No sign of eutrophication has been detected and natural hypersedimentation and/or eventual ancient bleaching events appear to be the direct principal causes of coral death or coral degradation.

The Madai-Baturong Limestone in eastern Sabah and its new interpretation as a seamount

The shallow marine Lower Cretaceous Madai-Baturong Limestone of east Sabah is surrounded by deep water ophiolitic rocks such as cherts, turbiditic greywackes and spilitic basalts belonging to the Chert-Spilite Formation. A new interpretation that it is a seamount carbonate is proposed because of: the extreme purity of the carbonates and the lack of terrigenous detrital inputs into the limestone, its intimate relationship with the surrounding typical deep water ophiolitic rocks, and its large size and yet limited lateral extend. The development of fissures filled with younger Upper Cretaceous limestone breccias with volcanic input in its matrix enclosing blocks of the older limestone indicating exposure and erosion of the top of the limestone which must have remained near the paleosea-Ievellends further support to the hypothesis. The smaller limestone bodies interbedded with the Chert-Spilite Formation rocks could be blocks which have slumped off the topographically higher seamounts into the deeper parts surrounding them.

Sequence stratigraphy of the Middle Miocene-Pliocene southern offshore Sandakan Basin, East Sabah

A sequence stratigraphic study was performed in the southern offshore Sandakan Basin with the aim of deriving a workable chronostratigraphic scheme and identifying plays, including stratigraphic traps. The data set includes 1800 km of high quality 1990 seismic and 8 wells. The study area can be divided into a structurally complex landward northern province and a relatively undisturbed basinward southern province. Three chronostratigraphic units were identified, each bounded by Type 1 third-order sequence boundaries. Each unit consists ofthird to fourth-order sequences which can be correlated from landward coastal plain facies to basinward bathyal facies. Unit 1 (Middle Miocene-early Upper Miocene) is characterised by moderate progradation, moderate aggradation; Unit 2 (middle Upper Miocene) by high progradation, low aggradation; and Unit 3 Oate Upper Miocene-Pliocene) by high aggradation, low progradation. . The positions of the prominent shelf edges in Unit 1, Unit 2 and lower Unit 3 indicate a southeastward progradation from Middle to Upper Miocene. Pliocene progradation was probably eastwards as suggested by N-S growth faults in the northeastern part of the study area, and is interpreted to have occurred within a ramp setting, as prominent shelf edges are lacking. The study led to the recognition of two play-types in the southern province, both associated with lowstand systems tract sediments. The fIrst is a slope fan play in Unit 1. The second is a basin floor fan play in Unit 2. Comparison of the locally derived onlap chart and the global onlap chart of Haq et al. (1987) highlighted some differences. The main difference is major Upper Miocene progradation in the study area versus Upper Miocene aggradation in the global chart, testifying to the importance of the interplay of local tectonics and sedimentation in the Sandakan Basin.

The origin and tectonic significance of mélanges in Eastern Sabah, Malaysia

Extensive chaotically disrupted rock bodies are found across Sabah in diverse tectonic settings. These units, which include broken formations, a dismembered arc-ophiolite complex and mud-matrix mélanges were formed by a combination of sedimentary, tectonic and diapiric processes. The mélanges of the eastern part of Sabah are considered to be related to basin initiation in an intra-arc setting, and are not related directly to subduction-accretion processes. The East Sabah mélanges are composed predominantly of deep water clastic sediments, deposited in the Central Sabah Basin, mixed with varying amounts of exotic ophiolitic material. The sedimentary clasts have a variety of well-developed “soft-sediment” deformation structures. These are in part inherited into the mélange from syn-sedimentary deformation, and in part generated during the mélange-forming events. The mélanges are not metamorphosed, and vitrinite reflectance data suggest that except for a few localities, a maximum temperature of less than 120°C was attained in the matrix. The ophiolitic blocks commonly have tectonic shearing fabrics associated with low temperature metamorphism. These metamorphic fabrics are incompatible with the deformation mechanisms in the sedimentary clasts and the mud matrix, and are interpreted as being inherited from shear in the ocean floor environment (e.g. fracture zones) or associated with ophiolite obduction. The similarity in clast type, deformation history and general structure also suggest that all the mélanges of the east of Sabah were formed in a series of related events during late Early Miocene and earliest Middle Miocene time. It is postulated that these events, which triggered sedimentary, diapiric and tectonic mélange-forming processes, are related to the coeval onset of extension and sea floor spreading in the southeastern Sulu Sea.

The Maliau Basin, Sabah: Geology and tectonic setting

A field survey of the eastern half of the Maliau Basin established the presence of several good quality coal seams in the dominant mudstone sequence of the Early to Middle Miocene Tanjung Formation. Although volumetrically minor, the several metres thick sublitharenite beds dominate the landscape forming high waterfalls, concen­ tric cuesta and other ridges with dipslopes inclined into the basin. Sandstone channel fills are common. Sedimentary current indicators including current ripple marks, tabular and trough cross beds, and lineation of carbonised plant fragments indicate that the Il).ajority of currents was towards northeast. The presence of coal, dominant mudstone, marine body and trace fossils suggest that the Tanjung Formation developed in low-energy environ­ ment, probably in wide tidal flats. Except for one locality exposing open folds, the beds dip uniformly and gently inward forming an eccentric basinal structure associated with normal faulting. These phenomena could have only been caused by gravitational subsi­ dence without tectonic compression. The northern boundary strike ridge intercepts internal strike ridges at oblique angles. This pattern and the off-centre position of the youngest beds suggest that the Maliau Basin during the deposition of the Tanjung Formation became progressively narrower while its depocentre migrated towards the south rim. The structural basins contairiingthe Tanjung Formation and time-equivalent Kapilit Formation are arranged in northeast and southeast rows; the Maliau basin occupying the junction of these two directions. Geologically the Maliau Basin is the landward extension of the Tarakan Trough and is at least partially floored by melange rocks of the Kinabalu Suture Zone. Subsidence ofthis basin and other early-middle Miocene basins of east Sabah began when the East Sabah Terrane stopped drifting south and isostatic readjustment sank the denser ophiolitic basement of the suture zone.

Accretion Tectonics in Sabah: Kinabalu Suture and East Sabah accreted terrane

Accretion Tectonics in Sabah: Kinabalu Suture and East Sabah accreted terrane