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We study the basement configuration in the slow-spreading Eurasia Basin, Arctic Ocean. Two multichannel seismic (MCS) profiles, which we acquired during ice-free conditions with a 3600 m long streamer, image the transition from the North Barents Sea Margin into the southern Eurasia Basin. The seismic lines resolve the up to 5000 m thick sedimentary section, as well as the crustal architecture of the southern Eurasia Basin along 120 km and 170 km, respectively. The seismic data show large faulted and rotated basement blocks. Gravity modeling indicates a thin basement with a thickness of 1–3 km and a density of 2.8*10 3  kg/m 3 between the base of the sediments and the top of the mantle, which indicates exhumed and serpentinized mantle. The Gakkel spreading ridge, located in northern prolongation of the seismic lines is characterized by an amagmatic or sparsely magmatic segment. From the structural similarity between the basement close to the ultra-slow spreading ridge and our study area, we conclude that the basement in the Eurasia Basin is predominantly formed by exhumed and serpentinized mantle, with magmatic additions. An initial strike-slip movement of the Lomonosov Ridge along the North Barents Sea Margin and subsequent near-orthogonal opening of the Nansen Basin is supposed to have brought mantle material to the surface, which was serpentinized during this process. Continuous spreading thinned the serpentinized mantle and subsequent normal faulting produced distinct basement blocks. We propose that mantle exhumation has likely been active since the opening of the Eurasia Basin. [ABSTRACT FROM AUTHOR]

The identification of oceanic crust at rifted margins plays a crucial role in academic research understanding rifting mechanisms and the architecture of continent–ocean boundaries, and is also important for hydrocarbon exploration extending into deeper water. In this paper, we provide a workflow for the determination of the crustal nature in the Mozambique Channel, east of Davie Ridge, by presenting a compilation of several geophysical attributes of oceanic crust at divergent margins. Previous reconstructions locate the Davie Ridge at the trace of a transform fault, along which Madagascar drifted to the south during the breakup of Gondwana. This implies a sharp transition from continental to oceanic crust seaward of Davie Ridge. Using new multichannel seismic profiles offshore northern Mozambique, we are able to identify distinct portions of stretched basement east of Davie Ridge. Two phases of deformation affecting the basement are observed, with the initial phase resulting in the formation of rotated fault blocks bounded by listric faults. Half-grabens are filled with wedge-shaped, syn-extensional sediments overlain by a prominent unconformity that northward merges with the top of highly reflective, mildly deformed basement, interpreted as oceanic crust. The second phase of deformation is associated with wrench faulting and probably correlates with the southward drift of Madagascar, which implies that the preceding phase affected basement generated or modified prior to the opening of the West Somali Basin. We conclude that the basement is unlikely to consist of normal oceanic crust and suggest that the first extensional phase corresponds to rifting between Madagascar and Africa. We find evidence for a wide area affected by strike–slip deformation, in contrast to the earlier proposed major single transform fault in the vicinity of Davie Ridge and suggest that the Mozambique Channel area to the north of Madagascar may be classified as an oblique rather than sheared margin. [ABSTRACT FROM AUTHOR]

A reconnaissance study of potential hydrocarbon source rocks of Paleozoic to Cenozoic age from the highly remote New Siberian Islands Archipelago (Russian Arctic) was carried out. 101 samples were collected from outcrops representing the principal Paleozoic-Cenozoic units across the entire archipelago. Organic petrological and geochemical analyses (vitrinite reflectance measurements, Rock-Eval pyrolysis, GC-MS) were undertaken in order to screen the maturity, quality and quantity of the organic matter in the outcrop samples. The lithology varies from continental sedimentary rocks with coal particles to shallow marine carbonates and deep marine black shales. Several organic-rich intervals were identified in the Upper Paleozoic to Lower Cenozoic succession. Lower Devonian shales were found to have the highest source rock potential of all Paleozoic units. Middle Carboniferous-Permian and Triassic units appear to have a good potential for natural gas formation. Late Mesozoic (Cretaceous) and Cenozoic low-rank coals, lignites, and coal-bearing sandstones also display a potential for gas generation. Kerogen type III (humic, gas-prone) dominates in most of the samples, and indicates deposition in lacustrine to coastal paleoenvironments. Most of the samples (except some of Cretaceous and Paleogene age) reached oil window maturities, whereas the Devonian to Carboniferous units shared a maturity mainly within the gas window. [ABSTRACT FROM AUTHOR]

Seismic reflection data imaging conjugate crustal sections at the South China Sea margins result in a conceptual model for rift-evolution at conjugate magma-poor margins in time and space. The wide Early Cenozoic South China Sea rift preserves the initial rift architecture at the distal margins. Most distinct are regular undulations in the crust–mantle boundary. Individual rift basins are bounded to crustal blocks by listric normal faults on either side. Moho uplifts are distinct beneath major rift basins, while the Moho is downbended beneath crustal blocks, with a wavelength of undulations in the crust–mantle boundary that approximately equals the thickness of the continental crust. Most of the basin-bounding faults sole out within the middle crust. At the distal margins, detachment faults are located at a mid-crustal level where a weak zone decouples crust and mantle lithosphere during rifting. The lower crust in contrast is interpreted as being strong. Only in the region within about 50 km from the Continent–Ocean Transition (COT) we suggest that normal faults reach the mantle, enabling potentially a coupling between the crust and the mantle. Here, at the proximal margins detachment fault dip either seaward or landward. This may indicate the presence of exhumed mantle bordering the continental margins. Post-rift shallow-water platform carbonates indicate a delay in subsidence during rifting in the South China Sea. We propose that this is an inherent process in highly extended continental margins and a common origin may be the influx of warm asthenospheric material into initially cool sub-lithospheric mantle. On a crustal-scale largely symmetric process predominate in the initial rifting stage. At the future COT either of the rift basin-bounding faults subsequently penetrates the entire crust, resulting in asymmetry at this location. However, asymmetric deformation which is controlled by large scale detachment faulting is confined to narrow areas and does not result in a margin-wide simple-shear model. Rather considerable along-margin variations are suggested resulting in alternating “upper and lower plate” margins. [ABSTRACT FROM AUTHOR]

The attenuated continental crust of the Dangerous Grounds is located in the southeastern part of the South China Sea. It was affected by unconformities as identified by several authors ( Cullen et al., 2010; Hinz and Schlüter, 1985; Hutchison, 2010; Hutchison and Vijayan, 2010 ). In the northeastern Dangerous Grounds, a prominent reflector in seismic data is associated with the top of a widespread Oligocene to Early Miocene (18–20 Ma) carbonate platform. This reflector and the underlying carbonates can be used to constrain the timing of the unconformities and the rifting history of the Dangerous Grounds. By carefully interpreting seismic reflection lines we trace the platform carbonates based upon their appearance in the seismic image. This platform is continuous in the Palawan–Borneo trough and gets patchy toward the Dangerous Grounds. In the Dangerous Grounds the image of this key reflector changes and here it merely forms the top of a clastic layer. Carbonates remain abundant but mainly as isolated reefs that grew on top of tilted fault blocks. In the southwestern Dangerous Grounds the prominent unconformity sealing the tectonic activity is known as the Middle Miocene Unconformity. This in fact is an Early Miocene unconformity, which represents a sequence boundary in the Borneo–Palawan trough and in various parts of the Dangerous Grounds, while in other parts of the Dangerous Grounds, it represents a major angular unconformity. The unconformity characteristics supplemented with tentative ages indicate that Luconia and the southern Dangerous Grounds were sub-aerial during the Early Miocene, while the Reed Bank, the northern Dangerous Grounds and parts of the central Dangerous Grounds were mostly submerged except for some islands concentrated on the western edge of the Borneo–Palawan trough. This trough is interpreted as a foreland basin where the flexural forebulge provided shallow marine conditions that promoted reef growth. As the carbonate deposition migrated from the Borneo–Palawan trough toward the Dangerous Grounds we suggest that the flexural forebulge provided shallow water conditions for further reef growth on the eastern Dangerous Grounds. [ABSTRACT FROM AUTHOR]

Abstract: We interpret two-dimensional seismic reflection data from the Rovuma Delta basin deep-water fold-and-thrust belts. Two major arcuate complexes with different architecture and extent are identified. While in the northern Palma arcuate complex a multitude of steep, east-dipping thrust-related fold anticlines formed above a single main detachment, in the southern Mocimboa arcuate complex multiple detachments resulted in the formation of thrust duplexes. In between the two arcuate domains, only few thrust-related fold anticlines developed. Our interpretation of the Rovuma basin is a linked system of up-dip extension and down-dip compression that is mainly driven by gravity tectonics. Sediment loading and a hinterland uplift due to the development of the East African Rift System since the Oligocene is proposed as origin of the delta. It is shown that the main, seaward-dipping detachment in Early Cenozoic strata is likely under-compacted and overpressured shale. Conversely, shale diapirism is questionable since the shape and location of such structures in the fold-and-thrust-belts appear simply indicating steeply dipping imbricated folds, rooted by a near vertical thrust. We suggest that mainly a different rheology and thickness and thus efficiency of the shale detachment across the delta resulted in different morphologies and geometries of the deep-water fold-and-thrust-belts. [Copyright &y& Elsevier]

Abstract: Regional seismic reflection and potential field data document the South Atlantic's break-up history, between 39°S and 19°S, from the Early Cretaceous onwards. Previous maps of distribution of volcanics along the margin showed volcanics along the whole African margin based on extrapolation of data. Based on previously unpublished marine geophysical data, we found the southernmost 460 km long margin segment to be lacking huge volumes of break-up related volcanic effusives. Northwards, break-up was accompanied by the emplacement of huge volumes of volcanic material, prominently featured in seismic sections as huge wedge-shaped seaward dipping reflectors (SDRs). Detailed mapping of offsets (left- and right-stepping) and variations in structural character of the volcanics reveal the segmentation along and the break-up history of the margin. Several superimposed SDR sequences, suggesting episodicity of volcanic emplacement (divided by periods of erosion and sedimentation), are distinct along southerly lines, losing prominence northwards. A main outcome of our study is that this passive margin is not continuously of the volcanic type and that the change from a non-volcanic to a volcanic margin occurs abruptly. We define four distinct First-order Segments along the 2400 km section of the southwestern African margin covered by our seismic data. From south to north these First-order Segments are: Magma-poor Segment I; Segment II with enormous SDRs volumes; decreasing SDRs volumes in Segment III; Segment IV again with enormous volcanic output, likely influenced by Walvis Ridge volcanism. Most important is that there is no systematic increase in the volumes of the effusives towards the Tristan da Cunha hot-spot. Rather there is an alternating pattern in the SDRs' volumes and widths. The boundary between the volcanic and magma-poor margin segments in the southernmost study area is sharp (10s of km), which we propose is reflected in magnetic anomaly data as well. We suggest that this variability along the margin is mainly due to a change in stretching/rifting character from oblique during the early stages of breakup to conventional seafloor spreading from Chron M4 (∼130 Ma) onwards. [Copyright &y& Elsevier]

Abstract: The link between the deformation of southern and central Palawan Island, Philippines and the deformation of the adjacent offshore wedge is investigated. The wedge is a continuation of the Palawan fold and thrust belt and bounds the Borneo–Palawan Trough to the Dangerous Grounds and to Palawan Island. Key parameters for the understanding of the formation and development of this wedge are two limestone formations: The Oligocene to Middle Miocene Nido limestone and the Upper Miocene to Lower Pliocene Tabon limestone. The initiation of the thrust belt formation is constrained by the Nido limestone, which was deposited from shortly before the breakup of the eastern South China Sea (∼35Ma) until the Early Miocene. Age data available from wells offshore central Palawan gives an age of Early Miocene close to the base of the Nido limestone. While cropping out onshore north Palawan, these limestones were overthrusted by the wedge in southern and central Palawan. Seismic images show gently east dipping carbonates below the wedge. The seismic data show that these limestones are only mildly affected by the wedge formation. The end of the wedge development can be constrained by the Tabon limestone. With an age of ∼9 to ∼4Ma, this limestone sequence overlies unconformably the offshore wedge. A detailed biostratigraphic correlation of the Tabon limestone along the southwest Palawan shelf, using well data, combined with multichannel seismic data and investigations onshore southern and central Palawan, shows a time- and space-transgressive development of these limestones. They are progressively younging towards the west. We propose that the formation of the Tabon limestone is directly linked with the development of the wedge that tectonically controls the formation of this carbonate platform. This constrains the time for the final phase of the formation of the Palawan thrust belt. After the final compressional phase and wedge formation in the lower Early Pliocene the wedge underwent a phase of subsidence. Based upon the detailed correlation of these limestones we propose that the wedge did not form in the southern Palawan area prior to ∼18Ma. Using the sealing Tabon limestone as time constraint we suggest that the development of the wedge in the south Palawan area started in the lower Middle Miocene (∼15Ma) and continued developing towards the west until the upper Late Miocene to Early Pliocene (∼5Ma). After the wedge propagation stopped, the wedge front collapsed in several places due to gravitational sliding. Southern and central Palawan were uplifted above sea level during a second phase of compression in the Late Pliocene. Onshore outcrops give indications to a working spleothem since ∼1.2Ma. [Copyright &y& Elsevier]

Abstract: Traditionally active rifts are thought to evolve in response to thermal upwelling of the asthenosphere, whereas passive rifts develop in response to lithospheric extension driven by far-field stresses. Depending on the volumes of extension-related magmatism two end-member passive margin types, either volcanic or magma-poor are defined. Volcanic rifted margins evolve by extension accompanied by extensive extrusive magmatism over short time periods during breakup, manifested in reflection seismic data as seaward dipping reflectors. These margins are commonly related to mantle plumes; however, in the past years this has been questioned. Magma-poor rifted margins in contrast show wide domains of extended crust with wide-ranging extensional features as rotated faults blocks and detachment surfaces near the base of the continental crust, but limited magmatism that in addition seems to be systematically delayed to post-breakup. In this study three unique rifted margins are presented: The Laptev Sea margin in the Arctic Ocean, where the active Arctic mid-oceanic ridge meets continental lithosphere at a high angle, the South China Sea that may represent an intermediary form of continental extension between the end member extremes, and the southernmost South Atlantic with well expressed conjugate volcanic rifted margins, which are traditionally interpreted as result of a mantle plume, the Tristan da Cunha hot-spot. The accurate timing of the events when continental rifting initiated and stopped, and when subsequent sea-floor spreading began is crucial to refine models of margin development. Therefore, a detailed description of rift-onset and breakup unconformities is presented for the three continental margins that evolved in the Early Cretaceous, the Paleocene and the Oligocene, respectively. The investigation reveals that a major controlling mode of deep, hot-spot related mantle processes on the rift evolution and rift-related magmatism cannot be observed. Instead, it is suggested that passive margin evolution is controlled by several lithosphere-scale processes and parameters, including the mode of rift propagation and propagation barriers. [Copyright &y& Elsevier]

Abstract: We interpret a more than 500km long composite multi-channel seismic reflection profile across the entire Dangerous Grounds, the South China Sea. Five tectonostratigraphic units are determined, together with seven sequence boundaries. Detailed analysis of extensional features, based on measurements of fault heaves, revealed two major phases of extension, separated by a distinct unconformity, which likely correspond with the beginning of sea-floor spreading in the South China Sea. Early extension occurred during continental rifting (Late Cretaceous–Early Oligocene), and resulted in formation of half-grabens and rotated blocks, controlled by a deeply rooted detachment system. Extension continued in our study area during the drifting phase of the East Subbasin of the South China Sea (Late Oligocene–Early Miocene) until the subsequent opening of the Southwest Subbasin at about 25Ma, but its intensity decreased markedly thereafter. Deeply rooted detachment systems evolved possibly during this second phase of extension at the continent–ocean transition area. From a coincidence of the lowermost reflections and Moho depth as derived from gravity inversion we tentatively interpret the flattened part of this detachment system as the crust–mantle boundary. It is suggested that the Dangerous Grounds reflect a magma-poor rift system at the initial stage of mantle unroofing. We suggest that a widespread carbonate platform developed across the Dangerous Grounds, concurrent with the period of seafloor spreading in the Southwest Subbasin of the South China Sea. Fault-related stretching factors (β f ) along the line show discrepancies with the whole crustal stretching factors (β c ). The continental crust of the Dangerous Grounds may have experienced nonuniform thinning. [Copyright &y& Elsevier]

Abstract: Multichannel reflection seismic data from the southern South China Sea, refraction and gravity modelling were used to investigate the compressional sedimentary structures of the collision-prone continental margin off NW Borneo. An elongated imbricate deepwater fan, the toe Thrust Zone bounds the Northwest Borneo Trough to the southeast. The faults separating the individual imbricates cut through post-Early Miocene sediments and curve down to a carbonate platform at the top of the subsiding continental Dangerous Grounds platform that forms the major detachment surface. The age of deformation migrates outward toward the front of the wedge. We propose crustal shortening mechanisms as the main reason for the formation of the imbricate fan. At the location of the in the past defined Lower Tertiary Thrust Sheet tectonostratigraphic province a high velocity body was found but with a much smaller extend than the previously defined structure. The high velocity structure may be interpreted either as carbonates that limit the transfer of seismic energy into the sedimentary layers beneath or as Paleogene Crocker sediments dissected by remnants of a proto-South China Sea oceanic crust that were overthrust onto a southward migrating attenuated continental block of the Dangerous Grounds during plate convergence. [Copyright &y& Elsevier]

Abstract: It is well established that the Argentine passive margin is of the rifted volcanic margin type. This classification is based primarily on the presence of a buried volcanic wedge beneath the continental slope, manifested by seismic data as a seaward dipping reflector sequence (SDRS). Here, we investigate the deep structure of the Argentine volcanic margin at 44°S over 200 km from the shelf to the deep oceanic Argentine Basin. We use wide-angle reflection/refraction seismic data to perform a joint travel time inversion for refracted and reflected travel times. The resulting P-wave velocity-depth model confirms the typical volcanic margin structure. An underplated body is resolved as distinctive high seismic velocity (v p up to 7.5 km/s) feature in the lower crust in the prolongation of a seaward dipping reflector sequence. A remarkable result is that a second, isolated body of high seismic velocity (v p up to 7.3 km/s) exists landward of the first high-velocity feature. The centres of both bodies are 60 km apart. The high-velocity lower-crustal bodies likely were emplaced during transient magmatic–volcanic events accompanying the late rifting and initial drifting stages. The lateral variability of the lower crust may be an expression of a multiple rifting process in the sense that the South Atlantic rift evolved by instantaneous breakup of longer continental margin segments. These segments are confined by transfer zones that acted as rift propagation barriers. A lower-crustal reflector was detected at 3 to 5 km above the modern Moho and probably represents the lower boundary of stretched continental crust. With this finding we suggest that the continent–ocean boundary is situated 70 km more seaward than in previous interpretations. [Copyright &y& Elsevier]

Shallow gas, here defined as free gas that is trapped in unconsolidated, deltaic and shallow marine siliciclastic sediments of Plio-Pleistocene age, is found within the topmost 1000 m of sediment in the southern North Sea. Shallow amplitude anomalies in seismic reflection data are likely due to the presence of gas. The most prominent and easy-to-recognize indicators are high-amplitude anomalies, or “bright spots”, that are widespread within the southern North Sea. Gas from shallow reservoirs is currently produced offshore The Netherlands. In this study, we determine whether there are analogous shallow gas accumulations within the German North Sea. Therefore, we screened 2D and 3D multichannel seismic data for shallow amplitude anomalies. Several clusters of bright spots are identified above salt domes that closely resemble the economic deposits known in the Dutch sector in both size and their characteristic multilayered shape. Three of these potential gas accumulations, occurring in combination with additional hydrocarbon indicators such as seismic attenuation and velocity push-downs, are investigated in detail and compared to shallow gas fields from offshore The Netherlands. Amplitude anomalies indicate gas seepage on the seafloor that may contribute to the atmospheric methane budget and may have an impact on offshore infrastructure. [ABSTRACT FROM AUTHOR]

The continental breakup which gave way to the formation of the oceanic South China Sea (SCS) basin began in the latest Cretaceous in the northeastern SCS and propagated in southern and western direction over a long period of time, possibly more than 40 m.y. The seafloor spreading history of the South China Sea has been interpreted in different ways in the past and the debate over the correct timing of the major tectonic events continues. We review the different models that have been published and present a revised interpretation of seafloor spreading anomalies based on three datasets with documented high quality which cover all of the SCS but the northernmost and southernmost parts. We can precisely date the onset of seafloor spreading in the central part of the SCS at 32 Ma. After a ridge jump at 25 Ma spreading also began in the southwestern sub-basin and spreading ended at 20.5 Ma in the entire basin, followed by a phase of magmatic seamount formation mainly along the abandoned spreading ridge. Spreading rates vary from 56 mm/yr in the early stages to 72 mm/yr after the ridge jump to 80 mm/yr in the southwestern sub-basin. We find indications for a stepwise propagation of the seafloor spreading from northeast to southwest in segments bounded by major fracture zones. Seafloor spreading ended abruptly probably because the subduction zone along the eastern and southern boundary of the SCS (of which today the Manila Trench remains) was blocked by collision with a continental fragment, possibly the northern part of Palawan or a part of the Dangerous Grounds. [ABSTRACT FROM AUTHOR]

Abstract: Based on new multi-channel seismic data, swath bathymetry, and sediment echosounder data we present a model for the interaction between strike-slip faulting and forearc basin evolution off north-western Sumatra between 2°N and 7°N. We examined seismic sequences and sea floor morphology of the Simeulue- and Aceh forearc basins and the adjacent outer arc high. We found that strike-slip faulting has controlled the forearc basin evolution since the Late Miocene. The Mentawai Fault Zone extends up to the north of Simeulue Island and was most probably connected farther northwards to the Sumatran Fault Zone until the end of the Miocene. Since then, this northern branch jumped westwards, initiating the West Andaman Fault in the Aceh area. The connection to the Mentawai Fault Zone is a left-hand step-over. In this transpressional setting the Tuba Ridge developed. We found a right-lateral strike-slip fault running from the conjunction of the West Andaman Fault and the Tuba Ridge in SSW-direction crossing the outer arc high. As a result, extrusion formed a marginal basin north of Simeulue Island which is tilted eastwards by uplift along a thrust fault in the west. The shift of strike-slip movement in the Aceh segment is accompanied by a relocation of the depocenter of the Aceh Basin to the northwest, forming one major Neogene unconformity. The Simeulue Basin bears two major Neogene unconformities, documenting that differences in subsidence evolution along the northern Sumatran margin are linked to both forearc-evolution related to subduction processes and to deformation along major strike-slip faults. [Copyright &y& Elsevier]

Chang et al. introduce some new lines of evidence for an end of seafloor spreading in the South China Sea not before 15 Ma. However, we find strong indications that their interpretation is not conclusive. The origin of the East Taiwan Ophiolite from the SCS as assumed by Chang et al. is not in agreement with recent studies which find continental crust in the deep-water domain of the northeastern South China Sea. The age dating of the East Taiwan Ophiolite is based on one single K–Ar age of questionable accuracy. The calculation of Te-derived ages leaves a thermal rejuvenation of the oceanic crust in the South China Sea by post-spreading volcanism out of consideration. Biostratigraphically determined ages of sediments recovered directly above igneous crust of the South China Sea during IODP 349 drilling expedition are inconclusive so far. The final key to unlocking the spreading history of the SCS will be the Ar–Ar age dating of the basaltic rocks recovered during IODP Expedition 349. [ABSTRACT FROM AUTHOR]

Deep seismic data and plate kinematic reconstructions help understand the mechanisms of rifting and opening of new oceans, basic principles of plate tectonic cycles. In this study, available deep wide-angle seismic velocity models from the Atlantic margins are reviewed and plate reconstructions used to define conjugate model pairs. The main objective was to study the question of how magma-rich and magma-poor margins develop and the role of inheritance in the break-up. We also studied the question of the mechanism of formation and the origin of transform marginal plateaus, which are typically found at the border of two ocean basins of different ages and are mostly characterized by at least one volcanic phase during their formation. The results of the study include the comparison of crustal thickness, oceanic plate thickness and the influence of volcanism along the Atlantic margins. The conjugate profiles image different degrees of asymmetry of the Atlantic Margin rifts. Marginal plateaus might form when rifting stops at barriers leading to the accumulation of heat in the mantle and increased volcanism directly before or after halting of the rifting. • Deep seismic velocity models, plate kinematic reconstructions and geological information are used. • Rifting styles and volcanic influence along the Atlantic Margins are studied. • Zones of exhumed and serpentinized upper mantle had been discovered only at magma-poor margins. • At magma-rich margins the volume of magma is largest close to transfer zones and decreases in the direction of rifting. • Sheared margins are often associated with transform marginal plateaus, which have undergone at least one volcanic phase. [ABSTRACT FROM AUTHOR]

Using recently gathered onland structural and 2D/3D offshore seismic data in south and central Palawan (Philippines), this paper presents a new perspective in unraveling the Cenozoic tectonic history of the southeastern margin of the South China Sea. South and central Palawan are dominated by Mesozoic ophiolites (Palawan Ophiolite), distinct from the primarily continental composition of the north. These ophiolites are emplaced over syn-rift Eocene turbidites (Panas Formation) along thrust structures best preserved in the ophiolite–turbidite contact as well as within the ophiolites. Thrusting is sealed by Early Miocene (∼20 Ma) sediments of the Pagasa Formation (Isugod Formation onland), constraining the younger limit of ophiolite emplacement at end Late Oligocene (∼23 Ma). The onset of ophiolite emplacement at end Eocene is constrained by thrust-related metamorphism of the Eocene turbidites, and post-emplacement underthrusting of Late Oligocene – Early Miocene Nido Limestone. This carbonate underthrusting at end Early Miocene (∼16 Ma) is marked by the deformation of a seismic unit corresponding to the earliest members of the Early – Middle Miocene Pagasa Formation. Within this formation, a tectonic wedge was built within Middle Miocene (from ∼16 Ma to ∼12 Ma), forming a thrust-fold belt called the Pagasa Wedge. Wedge deformation is truncated by the regionally-observed Middle Miocene Unconformity (MMU ∼12 Ma). A localized, post-kinematic extension affects thrust-fold structures, the MMU, and Late Miocene to Early Pliocene carbonates ( e.g . Tabon Limestone). This structural set-up suggests a continuous convergent regime affecting the southeastern margin of the South China Sea between end Eocene to end Middle Miocene. The ensuing structures including juxtaposed carbonates, turbidites and shallow marine clastics within thrust-fold belts have become ideal environments for hydrocarbon generation and accumulation. Best developed in the Northwest Borneo Trough area, the intensity of thrust-fold deformation decreases towards the northeast into offshore southwest Palawan. [ABSTRACT FROM AUTHOR]

Abstract: The coupled simple-shear/pure-shear model (CSSPSM) with broad application for studying the evolution of continental extensional sedimentary basins was proposed by Kusznir and co-workers. It can be used to determine the geometry of sedimentary basins and their crustal structure by integration of the rheological, thermal and isostatic response of lithosphere to various loads caused by lithosphere extension. We developed a MATLAB code, MODBAS, to model extensional sedimentary basin formation based on the CSSPSM. The validity of the code was tested with a single listric fault model and a multiple-fault model. The application of the code in the Pearl River Mouth Basin (PRMB) on the northern margin of the South China Sea demonstrates (1) the effective elastic thickness of the lithosphere beneath the PRMB is very low (<5km), which may support the idea of a very weak continental crust beneath the northern margin of the South China Sea; and (2) there are significant misfits between predicted and observed basements beneath the two high-standing areas on the profile, which was interpreted as an indication of substantial dynamic support from small-scale mantle convection. [Copyright &y& Elsevier]

The Olga Basin is a Paleozoic and Mesozoic sedimentary basin in the northern Barents Sea. Gas seepage at the basin's margins indicate active but so far poorly understood petroleum systems. Despite the consensus that late Cenozoic uplift and erosion must have strongly influenced petroleum systems in this region, the amount of erosion is controversially discussed. To decipher the influence of erosion, we studied petroleum generation from potential Paleozoic and Mesozoic source rocks based on two basin and petroleum systems models. Three scenarios were calculated for each model with Cenozoic erosion amounts of 500 m, 1000 m and 1800 m, respectively. Petroleum has been generated in all scenarios from the Carboniferous to Triassic source rocks, but Jurassic or younger source rocks remain immature even for the highest amount of erosion. Maturity estimates from bound gas measurements of seafloor sediments in the Olga Basin indicate that the migrated gas originates from an oil window mature source rock (vitrinite reflectance between 0.65% and 1.1%), which fits well to the calculated maturity of Upper Permian to Triassic potential source rocks. Our petroleum systems modelling data indicate that main hydrocarbon generation from a Carboniferous source rock occurred during the Triassic and generation from Upper Permian to Mid-Triassic source rocks occurred during the Cretaceous to Mid-Paleogene period. Different erosion scenarios had no influence on petroleum generation from a Carboniferous source rock, whereas modelled decreasing erosion from 1800 m to 500 m suppresses petroleum generation from Triassic source rocks by c. 60%. Petroleum might have charged closure structures at different stratigraphic levels (Carboniferous-Jurassic) mapped in the northeastern Barents Sea. Gas seepage, indicated by enhanced bound gas concentrations and the occurrence of pockmarks and flares, at the basin's margins can be explained by subcropping Jurassic shales to the south and intense faulting to the north. • Lower and Middle Triassic source rocks are the main sources for petroleum. • The Hekkingen (Agardhfjellet) Formation is immature in the northern Barents Sea. • Seeps along the basin's margin can be sourced from Triassic or older source rocks. [ABSTRACT FROM AUTHOR]