The lack of preserved basement results in uncertain placements of many terranes in Southeast Asia.Here,we flag the first evidence of the oldest basement in Indonesian Borneo,which can help locate terranes in Borneo on...The lack of preserved basement results in uncertain placements of many terranes in Southeast Asia.Here,we flag the first evidence of the oldest basement in Indonesian Borneo,which can help locate terranes in Borneo on the northern margin of Gondwana in the early Paleozoic and explain the regional tectonic setting of the island.Two schist samples from the Embuoi Complex in the Semitau Block,Northwest Kalimantan yielded zircon U-Pb dates of 453.3±1.9 Ma and 462.4±2.6 Ma,respectively,representing the formation time of the protolith.Petrographic,internal structural and high Th/U ratios of zircons indicate that the protolith of schists is of magmatic origin.The zircons haveεHf(t)values of−4.1 to+1.1 and Hf model ages of 1.37–1.69 Ga,indicating they were derived from a mixed source of juvenile crust with old components.By comparison of zircon age distribution,two-stage Hf model ages andεHf(t)variations of the early Paleozoic igneous rocks from Semitau with those of South China,Tengchong–Baoshan,and Indochina,the Semitau Block was most likely a part of or placed next to the Indochina Block of northern Gondwana during the early Paleozoic.Such a similar tectono-magmatic pattern on northern Gondwana formed a prolonged early Paleozoic arc-related belt associated with subduction of the Proto-Tethyan Ocean.展开更多
Winter coastal upwelling off northwest Borneo in the South China Sea （SCS） is investigated by using satellite data, climatological temperature and salinity fields and reanalysis data. The upwelling forms in Decem- b...Winter coastal upwelling off northwest Borneo in the South China Sea （SCS） is investigated by using satellite data, climatological temperature and salinity fields and reanalysis data. The upwelling forms in Decem- ber, matures in January, starts to decay in February and almost disappears in March. Both Ekman trans- port induced by the alongshore winter monsoon and Ekman pumping due to orographic wind stress curl are favorable for the upwelling. Transport estimates demonstrate that the month-to-month variability of Ekman transport and Ekman pumping are both consistent with that of winter coastal upwelling, but Ek- man transport is two times larger than Ekman pumping in January and February. Under the influence of E1 Nino-Southern Oscillation （ENSO）, the upwelling shows remarkable interannual variability： during winter of El Nino （La Nina） years, an anticyclonic （a cyclonic） wind anomaly is established in the SCS, which behaves a northeasterly （southwesterly） anomaly and a positive （negative） wind stress curl anomaly off the north- west Borneo coast, enhancing （reducing） the upwelling and causing anomalous surface cooling （warming） and higher （lower） chlorophyll concentration. The sea surface temperature anomaly （SSTA） associated with ENSO off the northwest Borneo coast has an opposite phase to that off southeast Vietnam, resulting in a SSTA seesaw pattern in the southern SCS in winter.展开更多
A new record of the rhacophorid frog, Theloderma licin is reported from Gunung Serambu, in the Bau region of western Sarawak, East Malaysia, which comprises the first published record of the species from the Sundaic i...A new record of the rhacophorid frog, Theloderma licin is reported from Gunung Serambu, in the Bau region of western Sarawak, East Malaysia, which comprises the first published record of the species from the Sundaic island of Borneo. The species was previously known from the Malay Peninsula （southern Peninsular Thailand and Peninsular Malaysia）. Species of Theloderma are widespread in mainland and insular Southeast Asia, their arboreal habits perhaps contributing to our perception of rarity.展开更多
The Southwest Borneo(SW Borneo)block belongs to Sundaland and is the oldest continental fragment of Borneo that is believed to derive from the Gondwana land.The U-Pb isotopic dating ages of 113 detrital zircons from s...The Southwest Borneo(SW Borneo)block belongs to Sundaland and is the oldest continental fragment of Borneo that is believed to derive from the Gondwana land.The U-Pb isotopic dating ages of 113 detrital zircons from sandstones of the Ketapang Complex in SW Borneo range from 3298 Ma to 78 Ma,and show six major age populations:2476-2344 Ma,2016-1831 Ma,1296-759 Ma,455-406 Ma,262-210 Ma,and 187-78 Ma.The youngest age of these detrital zircons is 78 Ma,indicating that the maximum depositional age of the sandstones is Campanian.Permian-Late Cretaceous detrital zircons are interpreted as having been derived from the nearby Schwaner Mountains and the Permian-Triassic tin belt granitoids in Southeast Asia(SE Asia).Archean-Carboniferous detrital zircons have a continental Gondwana provenance,with their age spectra similar to those of northwestern Australia,indicating that these zircons could be derived from the orogenic belts and cratons in northwestern and central Australia.The provenance of these detrital zircons in this study indicates the SW Borneo block was located on the northwestern margin of Australia during the Paleozoic,in the region of the Banda Embayment.SW Borneo rifted from Australia and moved northward in the Early Jurassic,and this block was added to Sundaland in the Early Cretaceous.The Luconia-Dangerous Grounds continental fragment derived from East Asia collided with SW Borneo after subduction in the Cretaceous,which induced the widespread magmatism in the Schwaner Mountains in SW Borneo.展开更多
Based on the volume magnetic susceptibility and specific gravity measurements and mineral and lithologic identification results for 540 samples,the rock type,density,and magnetic susceptibility of rocks from northern ...Based on the volume magnetic susceptibility and specific gravity measurements and mineral and lithologic identification results for 540 samples,the rock type,density,and magnetic susceptibility of rocks from northern Borneo were analyzed,and the applicability of gravity and magnetic data to the lithologic identification of the Mesozoic strata in the southern South China Sea was assessed accordingly.The results show that there are 3 types and 25 subtypes of rocks in northern Borneo,mainly intermediate-mafic igneous rocks and exogenous clastic sedimentary rocks,with small amounts of endogenous sedimentary rocks,felsic igneous rocks,and metamorphic rocks.The rocks that are very strongly-strongly magnetic and have high-medium densities are mostly igneous rocks,tuffaceous sandstones,and their metamorphic equivalents.The rocks that are weakly magnetic-non-magnetic and have medium-very low densities are mostly conglomerates,sandstones,siltstones,mudstones,and coal.The rocks that are weakly magnetic-diamagnetic and have highmedium densities are mostly limestones and siliceous rocks.The Cenozoic rocks are characterized by low densities and medium susceptibilities;the Mesozoic rocks are characterized by medium densities and medium-high susceptibilities;and the pre-Mesozoic rocks are characterized by high densities and low magnetism.Based on these results and the distribution characteristics of the various rock types,it was found that the pre-Mesozoic rocks produce weak regional gravity anomalies;the Mesozoic sedimentary rocks produce negative regional gravity anomalies;whereas the Mesozoic igneous rocks produce positive regional gravity anomalies;and the Cenozoic igneous rocks produce positive regional gravity anomalies.The regional high magnetic anomalies in the southern part of the South China Sea originate from the Mesozoic mafic igneous rocks and their metamorphic equivalents;and the regional medium magnetic anomalies may be produced by the felsic igneous rocks and their metamorphic equivalents.Accordingly,the identification of the Mesozoic lithology in the southern South China Sea shows that the Mesozoic sedimentary rocks are distributed over a large area of the southern South China Sea.Thus,it is concluded that the Mesozoic strata in this area have the potential for oil and gas exploration.展开更多
This work details the simulation of tsunami waves generated by seaquakes in the Manila Trench and their effect on fixed oil and gas jacket platforms in waters offshore North Borneo. For this study, a four-leg living q...This work details the simulation of tsunami waves generated by seaquakes in the Manila Trench and their effect on fixed oil and gas jacket platforms in waters offshore North Borneo. For this study, a four-leg living quarter jacket platform located in a water depth of 63 m is modelled in SACS v5.3. Malaysia has traditionally been perceived to be safe from the hazards of earthquakes and tsunamis. Local design practices tend to neglect tsunami waves and include no such provisions. In 2004, a 9.3Mw seaquake occurred off the northwest coast of Aceh, which generated tsunami waves that caused destruction in Malaysia totalling US$ 25 million and 68 deaths. This event prompted an awareness of the need to study the reliability of fixed offshore platforms scattered throughout Malaysian waters. In this paper, we present a review of research on the seismicity of the Manila Trench, which is perceived to be high risk for Southeast Asia. From the tsunami numerical model TUNA-M2, we extract computer-simulated tsunami waves at prescribed grid points in the vicinity of the platforms in the region. Using wave heights as input, we simulate the tsunami using SACS v5.3 structural analysis software of offshore platforms, which is widely accepted by the industry. We employ the nonlinear solitary wave theory in our tsunami loading calculations for the platforms, and formulate a platform-specific risk quantification system. We then perform an intensive structural sensitivity analysis and derive a corresponding platform-specific risk rating model.展开更多
A new record of the homalopsid snake, Gerarda prevostiana is presented from a mangrove-dominated patch in the vicinity of Kampung Bako, Sarawak, East Malaysia, and this comprises the first published record from the Su...A new record of the homalopsid snake, Gerarda prevostiana is presented from a mangrove-dominated patch in the vicinity of Kampung Bako, Sarawak, East Malaysia, and this comprises the first published record from the Sundaic Island of Borneo. A possible second locality for the species is a ca. 6.68 km site to its northeast, Kampung Buntal, based on an unlocated museum specimen. The species is widespread in mainland Southeast Asia, with additional records to the west （the Indian Subcontinent） and east （the Philippines Archipelago）, but was previously unrecorded from the islands of the Sundas. The secretive habits of the species, including the occupancy of mud lobster （Thalassinia spp.） mounds in mostly inaccessible, swampy habitats may be a reason for its perceived rarity and few published records.展开更多
Dietary data on Ansonia latidisca, the little known Bornean Rainbow Toad, are presented, through an investigation of a population at Gunung Penrissen, Sarawak, Malaysia(north-western Borneo), at elevations between 1,...Dietary data on Ansonia latidisca, the little known Bornean Rainbow Toad, are presented, through an investigation of a population at Gunung Penrissen, Sarawak, Malaysia(north-western Borneo), at elevations between 1,100–1,229 m asl. Standard sampling techniques, including visual encounter surveys, were employed and individuals encountered stomach-flushed, ma rked, a nd released. The volume of food ingested by adults, apart from large females, did not vary monthly, and there was no significant difference between wet and dry periods, the dominance index between the two periods showing no significant difference, indicating that seasonal variation does not affect the dietary constitution of the species across months. The mean longest prey was recovered from a female in March, during the end of the wet season. Larger individuals did not consume larger prey in the species, although larger females did harvest the largest insects, and as may be expected, had fewer prey items in their stomachs at the time. Males fed on fewer prey items than females, the adult male diet predominantly comprised of members of the Hymenoptera, including formicids(ants), as indicated by percentage frequency of occurrence of 78.69, while for adult females, equivalent figure was 90.70. Coleopterans(beetles) were found secondary in importance(48.8% in females, 5.85% in males), the rest categorized as tertiary. Plant items(including bryophytes) had a high frequency of occurrence(23.3% in females, 4.64% in males). Females examined in the month of July had voluminous stomach contents, and may have eaten more to increase fat reserves for breeding in the upcoming wet season. Since the diet of all size classes consisted of hymenopterans(ants) and coleopterans, the study species is here considered to have a narrow food preference, and consequently, is a dietary specialist.展开更多
New bioactive 13-epi-neoverrucosane diterpenoid,5β-acetoxy-13-epi-neoverrucosanic acid(1)along with three known secondary metabolites,13-epi-neoverrucosan-5β-ol(2),chelodane(3)and(E)-β-farnesene(4)were isolated fro...New bioactive 13-epi-neoverrucosane diterpenoid,5β-acetoxy-13-epi-neoverrucosanic acid(1)along with three known secondary metabolites,13-epi-neoverrucosan-5β-ol(2),chelodane(3)and(E)-β-farnesene(4)were isolated from the MeOH extract of east Malaysia’s liverwort Pleurozia subinfata.The chemical structure of new compound was elucidated by the analyses of its spectroscopic data(FTIR,NMR and HR-ESI-MS).These epi-neoverrucosane-type compounds seem to be notable chemosystematic markers for P.subinfata in Borneo.Compound 3 was widespread in marine sponges however this is the frst record for 3 to be found in liverwort.These metabolites were tested for their antifungal potentials against selected fungi from the marine environment.Compound 1 exhibited efective antifungal activity against Lagenidium thermophilum.展开更多
Tropidophorus micropus van Lidth de Jeude, 1905, described from the upper Mahakkam River, Kalimantan, Indonesia, is here redescribed, based on new material from upper Baleh, Sarawak, East Malaysia（Borneo）, collected...Tropidophorus micropus van Lidth de Jeude, 1905, described from the upper Mahakkam River, Kalimantan, Indonesia, is here redescribed, based on new material from upper Baleh, Sarawak, East Malaysia（Borneo）, collected after over 100 years. The new locality is ca. 94 km to the north of the type locality, and comprises a new national record.展开更多
The South China,Indochina,and Borneo margins surrounding the South China Sea contain long-lived arcs that became inactive at approximately 85 Ma,even though an embayment of oceanic crust(the‘Proto-South China Sea’)r...The South China,Indochina,and Borneo margins surrounding the South China Sea contain long-lived arcs that became inactive at approximately 85 Ma,even though an embayment of oceanic crust(the‘Proto-South China Sea’)remained in the intervening region.This oceanic crust eventually subducted in the Cenozoic below Borneo and the Cagayan arc,while the modern South China Sea opened in its wake.To investigate the enigmatic cessation of Mesozoic subduction below South China and Borneo,we studied a fragment of oceanic crust and overlying trench-fill sediments that accreted to NW Borneo during the final stages of Paleo-Pacific subduction.Based on radiolarian biostratigraphy of cherts overlying the pillow basalts and detrital zircon geochronology of the trench-fill,we constrained the minimum age of the oceanic crust during accretion to 40 Ma.This shows that subduction cessation was not related to ridge subduction.Geochemical analysis of pillow basalts revealed an enriched mid-ocean ridge basalt signature comparable to oceanic plateaus.Using paleomagnetism,we show that this fragment of oceanic crust was not part of the Izanagi Plate but was part of a plate(the‘Pontus’Plate)separated from the Izanagi Plate by a subduction zone.Based on the minimum 40 Ma age of the oceanic crust and its geochemistry,we suggest that Mesozoic subduction below South China and Borneo stopped when an oceanic plateau entered the trench,while the eastern plate margin with the Izanagi Plate remained active.We show how our findings offer opportunities to restore plate configurations of the Panthalassa-Tethys junction region.展开更多
Overpressure prediction for exploratory drilling has become robust in most basins with increasing well control,high-quality seismic datasets,and proactive real-time overpressure monitoring while drilling.However,accur...Overpressure prediction for exploratory drilling has become robust in most basins with increasing well control,high-quality seismic datasets,and proactive real-time overpressure monitoring while drilling.However,accurate overpressure prediction remains challenging in offshore Northwest Borneo despite several decades of drilling experience.This paper focuses on two exploration wells drilled by Brunei Shell Petroleum 40 years apart that faced similar challenges with overpressure prediction and well control.An integrated lookback study is attempted using seismic and well-log data to explore the causes of the unsatisfactory Pore Pressure Prediction(PPP)outcome in pre-drill and real-time operation settings for thesewells.Our study indicates that the misprediction of overpressures is due to real differences in shale pressure(basis of pre-drill work and monitoring)and sand pressure(source of drill kick and well control chal-lenges)due to large-scale vertical leak or expulsion of deep-seated fluids into pre-compacted normally pressured overlying sediments in several regions through a mix of shear and tensile failure mechanisms.Such migrated fluids inflate the sand pressure in the normally compacted shallower sequences with the shale pressure remaining low.A predictive framework for upward fluid expulsion was attempted but found impracticable due to complex spatial and temporal variations in the horizontal stress field responsible for such leakage.As such,it is proposed that these migratory overpressures are essentially'unpredictable'from conventional PPP workflows viewed in the broad bucket of compaction disequi-librium(undercompaction)and fluid expansion(unloading)mechanisms.Further study is recommended to understand if such migrated overpressures in the sand can produce a discernible and predictable geophysical or petrophysical signature in the abutting normally compacted shales.The study highlights the possibility of large lateral variability in the sand overpressure within the same stratigraphic unit in regions with complex tectonostratigraphic evolution like Northwest Borneo.展开更多
Weathering products of silicate rocks are particularly useful for evaluating the continental chemical weathering on the Earth's surface and its mechanism.Clay mineralogy and major-element geochemistry of surface s...Weathering products of silicate rocks are particularly useful for evaluating the continental chemical weathering on the Earth's surface and its mechanism.Clay mineralogy and major-element geochemistry of surface sediment samples collected in major rivers of Malay Peninsula and North Borneo in the tropical Southeast Asian region are used to study the present chemical weathering process and its controlling factors of tropical regions.The results indicate that the clay mineral assemblage in Malay Peninsula consists dominantly of kaolinite(average 80%) and minor illite(average 17%),almost without chlorite and smectite,whereas in North Borneo it consists mainly of illite and chlorite,with minor amounts of kaolinite(average 14%) and no smectite.Total contents of illite and chlorite in both Northwest and Northeast Borneo are 84% and 87%,respectively.Major-element geochemical results of both bulk and clay-fraction sediments show intensive chemical weathering degree for both areas.Relatively,the chemical weathering degree is gradually strengthened from Northeast Borneo,Northwest Borneo,to Malay Peninsula,and it is extremely intensive in Malay Peninsula.Our results indicate that,in the tropical Southeast Asian region exampled by Malay Peninsula and Borneo,climatic condition of tropical warm temperature and East Asian monsoon rainfall is the first-order controlling factor on the chemical weathering,resulting in intensive chemical weathering throughout tropical areas,and tectonic activity and lithology of parent rocks are subordinate factors,which still have an important impact on the weathering products,forming completely different clay mineral assemblages between Malay Peninsula and Borneo.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41802243,41772232 and 42161144007)the fund from the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources(Grant No.J1901-27)+1 种基金the Outlay Research Fund of the Institute of Geology,Chinese Academy of Geological Sciences(Grant No.J2008)the China Geological Survey Program(Grant Nos.DD20190358,DD20221646 and DD20190001).This study is a contribution to International Geoscience Programme(IGCP)project 662“Orogenic architecture and crustal growth from accretion to collision.”We thank two anonymous reviewers for their helpful suggestions and constructive comments that helped us to improve this manuscript.
文摘The lack of preserved basement results in uncertain placements of many terranes in Southeast Asia.Here,we flag the first evidence of the oldest basement in Indonesian Borneo,which can help locate terranes in Borneo on the northern margin of Gondwana in the early Paleozoic and explain the regional tectonic setting of the island.Two schist samples from the Embuoi Complex in the Semitau Block,Northwest Kalimantan yielded zircon U-Pb dates of 453.3±1.9 Ma and 462.4±2.6 Ma,respectively,representing the formation time of the protolith.Petrographic,internal structural and high Th/U ratios of zircons indicate that the protolith of schists is of magmatic origin.The zircons haveεHf(t)values of−4.1 to+1.1 and Hf model ages of 1.37–1.69 Ga,indicating they were derived from a mixed source of juvenile crust with old components.By comparison of zircon age distribution,two-stage Hf model ages andεHf(t)variations of the early Paleozoic igneous rocks from Semitau with those of South China,Tengchong–Baoshan,and Indochina,the Semitau Block was most likely a part of or placed next to the Indochina Block of northern Gondwana during the early Paleozoic.Such a similar tectono-magmatic pattern on northern Gondwana formed a prolonged early Paleozoic arc-related belt associated with subduction of the Proto-Tethyan Ocean.
基金The National Natural Science Foundation of China under contract No.91128212the National Natural Science Foundation of China under contract No.41306024+3 种基金the National Basic Research Program of China under contract No.2013CB430301the National Science Fund of China for Distinguished Young Scholars(NSFDYS)under contract No.41125019the Project of Global Change and Air-Sea Interaction under con-tract No.GASI-03-01-03-03the Basic Research Program of Second Institute of Oceanography,State Oceanic Administration of China under contract No.JT1301
文摘Winter coastal upwelling off northwest Borneo in the South China Sea （SCS） is investigated by using satellite data, climatological temperature and salinity fields and reanalysis data. The upwelling forms in Decem- ber, matures in January, starts to decay in February and almost disappears in March. Both Ekman trans- port induced by the alongshore winter monsoon and Ekman pumping due to orographic wind stress curl are favorable for the upwelling. Transport estimates demonstrate that the month-to-month variability of Ekman transport and Ekman pumping are both consistent with that of winter coastal upwelling, but Ek- man transport is two times larger than Ekman pumping in January and February. Under the influence of E1 Nino-Southern Oscillation （ENSO）, the upwelling shows remarkable interannual variability： during winter of El Nino （La Nina） years, an anticyclonic （a cyclonic） wind anomaly is established in the SCS, which behaves a northeasterly （southwesterly） anomaly and a positive （negative） wind stress curl anomaly off the north- west Borneo coast, enhancing （reducing） the upwelling and causing anomalous surface cooling （warming） and higher （lower） chlorophyll concentration. The sea surface temperature anomaly （SSTA） associated with ENSO off the northwest Borneo coast has an opposite phase to that off southeast Vietnam, resulting in a SSTA seesaw pattern in the southern SCS in winter.
基金the Sarawak Forest Department for issuance of a research permit(No.NCCD.907.4.4 Jld.VII–106)the Fundamental Research grant[No.FRGS/07(04)787/2010(68)] from the Ministry of Higher Education for support of our research on the herpetofauna of Sarawak
文摘A new record of the rhacophorid frog, Theloderma licin is reported from Gunung Serambu, in the Bau region of western Sarawak, East Malaysia, which comprises the first published record of the species from the Sundaic island of Borneo. The species was previously known from the Malay Peninsula （southern Peninsular Thailand and Peninsular Malaysia）. Species of Theloderma are widespread in mainland and insular Southeast Asia, their arboreal habits perhaps contributing to our perception of rarity.
基金Supported by the National Natural Science Foundation of China(Nos.41803038,41903005)the Guangxi Natural Science Foundation(No.2018GXNSFAA138193)the China Postdoctoral Science Foundation(No.2019M662458)。
文摘The Southwest Borneo(SW Borneo)block belongs to Sundaland and is the oldest continental fragment of Borneo that is believed to derive from the Gondwana land.The U-Pb isotopic dating ages of 113 detrital zircons from sandstones of the Ketapang Complex in SW Borneo range from 3298 Ma to 78 Ma,and show six major age populations:2476-2344 Ma,2016-1831 Ma,1296-759 Ma,455-406 Ma,262-210 Ma,and 187-78 Ma.The youngest age of these detrital zircons is 78 Ma,indicating that the maximum depositional age of the sandstones is Campanian.Permian-Late Cretaceous detrital zircons are interpreted as having been derived from the nearby Schwaner Mountains and the Permian-Triassic tin belt granitoids in Southeast Asia(SE Asia).Archean-Carboniferous detrital zircons have a continental Gondwana provenance,with their age spectra similar to those of northwestern Australia,indicating that these zircons could be derived from the orogenic belts and cratons in northwestern and central Australia.The provenance of these detrital zircons in this study indicates the SW Borneo block was located on the northwestern margin of Australia during the Paleozoic,in the region of the Banda Embayment.SW Borneo rifted from Australia and moved northward in the Early Jurassic,and this block was added to Sundaland in the Early Cretaceous.The Luconia-Dangerous Grounds continental fragment derived from East Asia collided with SW Borneo after subduction in the Cretaceous,which induced the widespread magmatism in the Schwaner Mountains in SW Borneo.
基金supported by the National Major Science and Technology Project of the Ministry of Science and Technology of China(2016ZX05026-004-001)the Major Program of the National Natural Science Foundation of China(41790453)+1 种基金the Natural Science Foundation of Jilin Province(20170101001JC)the Supported by Graduate Innovation Fund of Jilin University(101832020CX200)。
文摘Based on the volume magnetic susceptibility and specific gravity measurements and mineral and lithologic identification results for 540 samples,the rock type,density,and magnetic susceptibility of rocks from northern Borneo were analyzed,and the applicability of gravity and magnetic data to the lithologic identification of the Mesozoic strata in the southern South China Sea was assessed accordingly.The results show that there are 3 types and 25 subtypes of rocks in northern Borneo,mainly intermediate-mafic igneous rocks and exogenous clastic sedimentary rocks,with small amounts of endogenous sedimentary rocks,felsic igneous rocks,and metamorphic rocks.The rocks that are very strongly-strongly magnetic and have high-medium densities are mostly igneous rocks,tuffaceous sandstones,and their metamorphic equivalents.The rocks that are weakly magnetic-non-magnetic and have medium-very low densities are mostly conglomerates,sandstones,siltstones,mudstones,and coal.The rocks that are weakly magnetic-diamagnetic and have highmedium densities are mostly limestones and siliceous rocks.The Cenozoic rocks are characterized by low densities and medium susceptibilities;the Mesozoic rocks are characterized by medium densities and medium-high susceptibilities;and the pre-Mesozoic rocks are characterized by high densities and low magnetism.Based on these results and the distribution characteristics of the various rock types,it was found that the pre-Mesozoic rocks produce weak regional gravity anomalies;the Mesozoic sedimentary rocks produce negative regional gravity anomalies;whereas the Mesozoic igneous rocks produce positive regional gravity anomalies;and the Cenozoic igneous rocks produce positive regional gravity anomalies.The regional high magnetic anomalies in the southern part of the South China Sea originate from the Mesozoic mafic igneous rocks and their metamorphic equivalents;and the regional medium magnetic anomalies may be produced by the felsic igneous rocks and their metamorphic equivalents.Accordingly,the identification of the Mesozoic lithology in the southern South China Sea shows that the Mesozoic sedimentary rocks are distributed over a large area of the southern South China Sea.Thus,it is concluded that the Mesozoic strata in this area have the potential for oil and gas exploration.
基金Universiti Teknologi PETRONAS Research Grant(No.0153B2-A44)
文摘This work details the simulation of tsunami waves generated by seaquakes in the Manila Trench and their effect on fixed oil and gas jacket platforms in waters offshore North Borneo. For this study, a four-leg living quarter jacket platform located in a water depth of 63 m is modelled in SACS v5.3. Malaysia has traditionally been perceived to be safe from the hazards of earthquakes and tsunamis. Local design practices tend to neglect tsunami waves and include no such provisions. In 2004, a 9.3Mw seaquake occurred off the northwest coast of Aceh, which generated tsunami waves that caused destruction in Malaysia totalling US$ 25 million and 68 deaths. This event prompted an awareness of the need to study the reliability of fixed offshore platforms scattered throughout Malaysian waters. In this paper, we present a review of research on the seismicity of the Manila Trench, which is perceived to be high risk for Southeast Asia. From the tsunami numerical model TUNA-M2, we extract computer-simulated tsunami waves at prescribed grid points in the vicinity of the platforms in the region. Using wave heights as input, we simulate the tsunami using SACS v5.3 structural analysis software of offshore platforms, which is widely accepted by the industry. We employ the nonlinear solitary wave theory in our tsunami loading calculations for the platforms, and formulate a platform-specific risk quantification system. We then perform an intensive structural sensitivity analysis and derive a corresponding platform-specific risk rating model.
基金the Sarawak Forest Department for issuance of a research permit(No.NCCD.907.4.4 Jld.7–39)a Fundamental Research Grant[Grant No:FRGS/07(04)787/2010(68)]from the Ministry of Higher Education of Malaysia for supporting our study on the herpetofauna of Sarawak.Y.M.
文摘A new record of the homalopsid snake, Gerarda prevostiana is presented from a mangrove-dominated patch in the vicinity of Kampung Bako, Sarawak, East Malaysia, and this comprises the first published record from the Sundaic Island of Borneo. A possible second locality for the species is a ca. 6.68 km site to its northeast, Kampung Buntal, based on an unlocated museum specimen. The species is widespread in mainland Southeast Asia, with additional records to the west （the Indian Subcontinent） and east （the Philippines Archipelago）, but was previously unrecorded from the islands of the Sundas. The secretive habits of the species, including the occupancy of mud lobster （Thalassinia spp.） mounds in mostly inaccessible, swampy habitats may be a reason for its perceived rarity and few published records.
基金supported by a Fundamental Research Grant, FRGS/07(04)787/2010(68) from the Ministry of Higher Education, Government of MalaysiaThe Rufford Small Grants Foundation。
文摘Dietary data on Ansonia latidisca, the little known Bornean Rainbow Toad, are presented, through an investigation of a population at Gunung Penrissen, Sarawak, Malaysia(north-western Borneo), at elevations between 1,100–1,229 m asl. Standard sampling techniques, including visual encounter surveys, were employed and individuals encountered stomach-flushed, ma rked, a nd released. The volume of food ingested by adults, apart from large females, did not vary monthly, and there was no significant difference between wet and dry periods, the dominance index between the two periods showing no significant difference, indicating that seasonal variation does not affect the dietary constitution of the species across months. The mean longest prey was recovered from a female in March, during the end of the wet season. Larger individuals did not consume larger prey in the species, although larger females did harvest the largest insects, and as may be expected, had fewer prey items in their stomachs at the time. Males fed on fewer prey items than females, the adult male diet predominantly comprised of members of the Hymenoptera, including formicids(ants), as indicated by percentage frequency of occurrence of 78.69, while for adult females, equivalent figure was 90.70. Coleopterans(beetles) were found secondary in importance(48.8% in females, 5.85% in males), the rest categorized as tertiary. Plant items(including bryophytes) had a high frequency of occurrence(23.3% in females, 4.64% in males). Females examined in the month of July had voluminous stomach contents, and may have eaten more to increase fat reserves for breeding in the upcoming wet season. Since the diet of all size classes consisted of hymenopterans(ants) and coleopterans, the study species is here considered to have a narrow food preference, and consequently, is a dietary specialist.
基金supported by SaBC Grant[No.GL0070]and UMS Grant[SBK0258-SG-2016].
文摘New bioactive 13-epi-neoverrucosane diterpenoid,5β-acetoxy-13-epi-neoverrucosanic acid(1)along with three known secondary metabolites,13-epi-neoverrucosan-5β-ol(2),chelodane(3)and(E)-β-farnesene(4)were isolated from the MeOH extract of east Malaysia’s liverwort Pleurozia subinfata.The chemical structure of new compound was elucidated by the analyses of its spectroscopic data(FTIR,NMR and HR-ESI-MS).These epi-neoverrucosane-type compounds seem to be notable chemosystematic markers for P.subinfata in Borneo.Compound 3 was widespread in marine sponges however this is the frst record for 3 to be found in liverwort.These metabolites were tested for their antifungal potentials against selected fungi from the marine environment.Compound 1 exhibited efective antifungal activity against Lagenidium thermophilum.
基金funded by Sarawak Energy Berhad,under the Hydropower Environmental Sustainability Program(grant no.GL(I01)SEB/2014/02[03])
文摘Tropidophorus micropus van Lidth de Jeude, 1905, described from the upper Mahakkam River, Kalimantan, Indonesia, is here redescribed, based on new material from upper Baleh, Sarawak, East Malaysia（Borneo）, collected after over 100 years. The new locality is ca. 94 km to the north of the type locality, and comprises a new national record.
基金SHAvdL and DJJvH were funded by NWO Vici grant 865.17.001 to DJJvH.LC acknowledges funding from the National Natural Science Foundation of China(grant 42106073)Open Fund of the State Key Laboratory of Marine Geology(Tongji University)(grant MGK202107).
文摘The South China,Indochina,and Borneo margins surrounding the South China Sea contain long-lived arcs that became inactive at approximately 85 Ma,even though an embayment of oceanic crust(the‘Proto-South China Sea’)remained in the intervening region.This oceanic crust eventually subducted in the Cenozoic below Borneo and the Cagayan arc,while the modern South China Sea opened in its wake.To investigate the enigmatic cessation of Mesozoic subduction below South China and Borneo,we studied a fragment of oceanic crust and overlying trench-fill sediments that accreted to NW Borneo during the final stages of Paleo-Pacific subduction.Based on radiolarian biostratigraphy of cherts overlying the pillow basalts and detrital zircon geochronology of the trench-fill,we constrained the minimum age of the oceanic crust during accretion to 40 Ma.This shows that subduction cessation was not related to ridge subduction.Geochemical analysis of pillow basalts revealed an enriched mid-ocean ridge basalt signature comparable to oceanic plateaus.Using paleomagnetism,we show that this fragment of oceanic crust was not part of the Izanagi Plate but was part of a plate(the‘Pontus’Plate)separated from the Izanagi Plate by a subduction zone.Based on the minimum 40 Ma age of the oceanic crust and its geochemistry,we suggest that Mesozoic subduction below South China and Borneo stopped when an oceanic plateau entered the trench,while the eastern plate margin with the Izanagi Plate remained active.We show how our findings offer opportunities to restore plate configurations of the Panthalassa-Tethys junction region.
文摘Overpressure prediction for exploratory drilling has become robust in most basins with increasing well control,high-quality seismic datasets,and proactive real-time overpressure monitoring while drilling.However,accurate overpressure prediction remains challenging in offshore Northwest Borneo despite several decades of drilling experience.This paper focuses on two exploration wells drilled by Brunei Shell Petroleum 40 years apart that faced similar challenges with overpressure prediction and well control.An integrated lookback study is attempted using seismic and well-log data to explore the causes of the unsatisfactory Pore Pressure Prediction(PPP)outcome in pre-drill and real-time operation settings for thesewells.Our study indicates that the misprediction of overpressures is due to real differences in shale pressure(basis of pre-drill work and monitoring)and sand pressure(source of drill kick and well control chal-lenges)due to large-scale vertical leak or expulsion of deep-seated fluids into pre-compacted normally pressured overlying sediments in several regions through a mix of shear and tensile failure mechanisms.Such migrated fluids inflate the sand pressure in the normally compacted shallower sequences with the shale pressure remaining low.A predictive framework for upward fluid expulsion was attempted but found impracticable due to complex spatial and temporal variations in the horizontal stress field responsible for such leakage.As such,it is proposed that these migratory overpressures are essentially'unpredictable'from conventional PPP workflows viewed in the broad bucket of compaction disequi-librium(undercompaction)and fluid expansion(unloading)mechanisms.Further study is recommended to understand if such migrated overpressures in the sand can produce a discernible and predictable geophysical or petrophysical signature in the abutting normally compacted shales.The study highlights the possibility of large lateral variability in the sand overpressure within the same stratigraphic unit in regions with complex tectonostratigraphic evolution like Northwest Borneo.
基金supported by National Natural Science Foundation of China (Grant Nos. 40925008,40876024,and 40776027)National Basic Research Program of China (Grant No. 2007CB815906)+1 种基金Shanghai Shuguang Program (Grant No. 07SG23)Shanghai Subject Chief Scientist Program (Grant No. 10XD1406300)
文摘Weathering products of silicate rocks are particularly useful for evaluating the continental chemical weathering on the Earth's surface and its mechanism.Clay mineralogy and major-element geochemistry of surface sediment samples collected in major rivers of Malay Peninsula and North Borneo in the tropical Southeast Asian region are used to study the present chemical weathering process and its controlling factors of tropical regions.The results indicate that the clay mineral assemblage in Malay Peninsula consists dominantly of kaolinite(average 80%) and minor illite(average 17%),almost without chlorite and smectite,whereas in North Borneo it consists mainly of illite and chlorite,with minor amounts of kaolinite(average 14%) and no smectite.Total contents of illite and chlorite in both Northwest and Northeast Borneo are 84% and 87%,respectively.Major-element geochemical results of both bulk and clay-fraction sediments show intensive chemical weathering degree for both areas.Relatively,the chemical weathering degree is gradually strengthened from Northeast Borneo,Northwest Borneo,to Malay Peninsula,and it is extremely intensive in Malay Peninsula.Our results indicate that,in the tropical Southeast Asian region exampled by Malay Peninsula and Borneo,climatic condition of tropical warm temperature and East Asian monsoon rainfall is the first-order controlling factor on the chemical weathering,resulting in intensive chemical weathering throughout tropical areas,and tectonic activity and lithology of parent rocks are subordinate factors,which still have an important impact on the weathering products,forming completely different clay mineral assemblages between Malay Peninsula and Borneo.
