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1.
Following the discovery of asphalt volcanism in the Campeche Knolls a research cruise was carried out in 2006 to unravel the nature of the asphalt deposits at Chapopote. The novel results support the concept that the asphalt deposits at the seafloor in 3000 m of water depth originate from the seepage of heavy petroleum with a density slightly greater than water. The released petroleum forms characteristic flow structures at the seafloor with surfaces that are ‘ropy’ or ‘rough’ similar to magmatic lava flows. The surface structures indicate that the viscosity of the heavy petroleum rapidly increases after extrusion due to loss of volatiles. Consequently, the heavy petroleum forms the observed asphalt deposit and solidifies. Detailed survey with a remotely operated vehicle revealed that the asphalts are subject to sequential alterations: e.g. volume reduction leading to the formation of visible cracks in the asphalt surface, followed by fragmentation of the entire deposit. While relatively fresh asphalt samples were gooey and sticky, older, fragmented pieces were found to be brittle without residual stickiness. Furthermore, there is evidence for petroleum seepage from below the asphalt deposits, leading to local up-doming and, sometimes, to whip-shaped extrusions. Extensive mapping by TV-guided tools of Chapopote Asphalt Volcano indicates that the main asphalt deposits occur at the south-western rim that borders a central, crater-like depression. The most recent asphalt deposit at Chapopote is the main asphalt field covering an area of ∼2000 m2. Asphalt volcanism is distinct from oil and gas seepage previously described in the Gulf of Mexico and elsewhere because it is characterized by episodic intrusions of semi-solid hydrocarbons that spread laterally over a substantial area and produce structures with significant vertical relief. As Chapopote occurs at the crest of a salt structure it is inferred that asphalt volcanism is a secondary result of salt tectonism.  相似文献   

2.
尖峰北盆地位于南海北部大陆边缘南部,是一个新生代沉积盆地。盆地发育了A、B、C、D、E5套地震层序;盆地内地质构造复杂,断裂发育,平面上断裂展布方向主要有NE向、近EW向和NW向三组,断裂可分为正断层及平移断层,以正断层为主。古新世—始新世为盆地形成时期即断陷阶段,盆地内部充填了大量河湖相沉积。渐新世—中中新世为盆地发展期即坳陷阶段,盆地沉积类型由陆相逐步过渡到海陆过渡相和海相。中中新世末期,盆地相对隆升,部分地区遭受剥蚀。晚中新世—全新世为区域沉降阶段,盆地及其围区以稳定的浅海-半深海相沉积为主。盆地早期河湖相、三角洲相沉积分布范围较广,最大沉积厚度超过4500m,具有一定的生烃能力;盆地储盖条件良好,油气运移条件良好;尖峰北盆地具备较好的油气潜力。  相似文献   

3.
Host sediments may exert a significant influence on the formation of gas hydrate reservoirs. However, this issue has been largely neglected in the literature. In this study, we investigated the types, characteristics and the depositional model of the fine-grained gas hydrate-bearing sediments in the northeastern margin of the South China Sea by integrating core visual observations and logging-while-drilling downhole logs. The gas hydrate-bearing sediments consist dominantly of muddy sediments formed in the inter-canyon ridges of the upper continental slope, including hemipelagites, debrites (mud with breccia) and fine-grained turbidites. Cold-seep carbonates and associated slumping talus, muddy breccia debrites, as well as coarse-grained turbidites, may locally occur. Four classes and six sub-classes of log facies were defined by cluster analysis. Core-log correlation indicates that gas hydrates are majorly distributed in fine-grained sediments with high resistivity and low acoustic transit time (AC) log responses, which are easily differentiated from the fine-grained background sediments of high gamma-ray (GR), high AC, and low resistivity log values, and the seep carbonates characterized by low GR, high resistivity, high density, low AC and low porosity log values. The primary host sediments consist of fine-grained hemipelagic sediments formed by deposition from the nepheloid layers of river material and from the microfossils in seawater column. Most of the hemipelagic sediments, however, might have been extensively modified by slumping and associated gravity flow processes and were re-deposited in the forms of debrites and turbidites. Locally developed seep carbonates associated with gas hydrate dissociation and leakage provided additional sources for the gravity flow sediments.  相似文献   

4.
Central Luconia is a geological province of the Sarawak Basin, offshore NW Borneo, characterised by extensive development of Miocene to Recent carbonate build-ups. In the subsurface, many of these build-ups are reservoirs for hydrocarbons. This study focuses on shelf-wide stratigraphic architecture, from which implications are drawn for the stratigraphic-sealing potential of the deltaic clastics. A stratigraphic model is proposed whereby clastic sediments surrounding the carbonate build-ups are interpreted as stacked low-relief deltas deposited in response to high-frequency oscillation of the sea level. The deltas are shown to have frequently prograded beyond carbonate build-ups. As a result of interaction between eustacy and deposition, deltaic topsets are juxtaposed against carbonate build-ups, providing migration routes for hydrocarbons. Most of the carbonate reservoirs are consequently underfilled, with hydrocarbon columns limited to the youngest onlapping stratigraphic sequence.  相似文献   

5.
Blanca fan is a submarine fan composed of Miocene volcaniclastic strata. Parts of the fan system are exposed on Santa Cruz and Santa Rosa Islands, and possibly correlative strata crop out on San Miguel and Santa Catalina Islands. The Blanca fan and underlying breccia reflect regional transcurrent faulting in the California Continental Borderland and development of a system of rapidly subsiding basins and uplifted linear ridges during early and middle Miocene time. Erosion of uplifted crystalline basement rocks followed by the onset of silicic volcanism created linear sediment sources for the alluvial and submarine fans, respectively.  相似文献   

6.
Detailed measurements of bubble composition, dissolved gas concentrations, and plume dynamics were conducted during a 9-month period at a very intense, shallow (22-m water depth) marine hydrocarbon seep in the Santa Barbara Channel, California. Methane, carbon dioxide, and heavier hydrocarbons were lost from rising seep bubbles, while nitrogen and oxygen were gained. Within the rising seawater bubble plume, dissolved methane concentrations were more than 4 orders of magnitude greater than atmospheric equilibrium concentrations. Strong upwelling flows were observed and bubble-rise times were ~40 s, demonstrating the rapid exchange of gases within the bubble plume.  相似文献   

7.
Blanca fan is a submarine fan composed of Miocene volcaniclastic strata. Parts of the fan system are exposed on Santa Cruz and Santa Rosa Islands, and possibly correlative strata crop out on San Miguel and Santa Catalina Islands. The Blanca fan and underlying breccia reflect regional transcurrent faulting in the California Continental Borderland and development of a system of rapidly subsiding basins and uplifted linear ridges during early and middle Miocene time. Erosion of uplifted crystalline basement rocks followed by the onset of silicic volcanism created linear sediment sources for the alluvial and submarine fans, respectively. Margin setting represents fan and/or source area  相似文献   

8.
Mud volcanoes are cold seeps, in which the escape of gas and fluids associated with mud creates 3-D bottom structures that enhance the spatial heterogeneity and potentially alter the functioning of the benthic ecosystems. We investigated a complex system of mud volcanoes of the Mediterranean Sea characterised by the presence of different structures (i.e., isolated domes, domes surrounded by moats, clustered domes, and ridges) displaying different levels of seepage. We hypothesize that the combined effects of seafloor heterogeneity (i.e., different 3-D structures as revealed by detailed topographic analysis), fluid emissions and trophic characteristics of these systems can influence the structural and functional biodiversity of meiofauna (with special focus on the nematodes). We found that sediments affected by intensive seepage displayed the lowest faunal abundances and number of higher taxa. However, mud volcanoes without emissions, but characterized by a high structural complexity (such as the ridges), were associated with the highest meiofaunal abundances and number of higher taxa. Mud volcanoes hosted also a remarkable abundance of rare taxa specifically associated with these structures (e.g., acarians, cumaceans, tanaids, cladocerans and hydroids) and absent in slope sediments (used as a control). Each mud-volcano area displayed a different nematode species composition. Overall 76 nematode species (from a total of 235) were exclusively associated with mud-volcano structures, whilst 29 were exclusively encountered in slope sediments. We conclude that the presence of mud volcanoes, for their contribution to increase spatial heterogeneity and for the extreme conditions associated with gas emissions, promotes higher levels of beta diversity, thus enhancing the regional (gamma) benthic diversity. These findings provide new insights on the factors controlling meiobenthic biodiversity in mud volcanoes and clues for future action of conservation of the biodiversity specifically associated with these habitats.  相似文献   

9.
A. Zabanbark 《Oceanology》2006,46(4):557-563
With respect of its structure, the Gulf of Mexico basin is heterogeneous. The following individual basins and subbasins can be distinguished; (1) Mississippi-Louisiana; (2) Gulf Coast within the boundaries of Texas and New Mexico; (3) Mexican Gulf Coast and adjacent system of foredeeps; (4) Yucatan subbasin; (5) Cuba-Bahamas system of foredeeps. Regional seismic studies reveal a close relationship between salt movements and sedimentation. Salt bodies represent excellent cap rocks for hydrocarbon fluids. Anticline folds termed “turtle” structures forming a system of belts appear in the deep parts of the gulf. These structures host large reserves of hydrocarbons, which are concentrated in the Paleogene-Miocene turbidite reservoirs with a porosity approximately 30% overlain by excellent cap rocks (salt, clay) with permeability exceeding 3 darcy. Three productive zones are defined: (1) the folds of the Mississippi River fan; (2) the Perdido belt of anticline folds; (3) Florida. The Paleogene and Miocene-Pliocene-Pleistocene sediments developed on the continental slopes of the Gulf of Mexico basin are the areas most promising with respect to hydrocarbon deposits. On January 1, 2006, the offshore oil production was 53 million tons and the gas production 40 billion cubic meters. Total prospective oil and gas reserves are estimated to be 5.5 billion tons and 4.7 trillion cubic meters, of which over 50% of oil and 1/3 of gas are expected to be discovered on the continental slope.  相似文献   

10.
Methane concentrations in some sediment cores from the Kodiak Shelf and adjacent continental slope increase with depth by three or four orders of magnitude and exceed the solubility in water at ambient conditions. Acoustic anomalies in seismic-reflection records imply that methane-rich sediment is widespread. Molecular composition of hydrocarbon gases and isotopic composition of methane indicate gas formation by shallow biogenic processes. Stratigraphic positions of acoustic anomalies in Quaternary glacial and posttransgressive sediments suggest that these units are likely sources of gas. A seep along the extension of a fault may be gas venting from a deeper thermogenic source.  相似文献   

11.
The petroleum system of the Kunsan Basin in the Northern South Yellow Sea Basin is not well known, compared to other continental rift basins in the Yellow Sea, despite its substantial hydrocarbon potential. Restoration of two depth-converted seismic profiles across the Central Subbasin in the southern Kunsan Basin shows that extension was interrupted by inversions in the Late Oligocene-Middle Miocene that created anticlinal structures. One-dimensional basin modeling of the IIH-1Xa well suggests that hydrocarbon expulsion in the northeastern margin of the depocenter of the Central Subbasin peaked in the Early Oligocene, predating the inversions. Hydrocarbon generation at the dummy well location in the depocenter of the subbasin began in the Late Paleocene. Most source rocks in the depocenter passed the main expulsion phase except for the shallowest source rocks. Hydrocarbons generated from the depocenter are likely to have migrated southward toward the anticlinal structure and faults away from the traps along the northern and northeastern margins of the depocenter because the basin-fill strata are dipping north. Faulting that continued during the rift phase (∼ Middle Miocene) of the subbasin probably acted as conduits for the escape of hydrocarbons. Thus, the anticlinal structure and associated faults to the south of the dummy well may trap hydrocarbons that have been charged from the shallow source rocks in the depocenter since the Middle Miocene.  相似文献   

12.
Over the past several years, a number of hydrocarbon reservoirs have been discovered in the deepwater area of Qiongdongnan Basin, northwestern South China Sea. These oil/gas fields demonstrate that the...  相似文献   

13.
The Shabwa Basin is the northeastern extension of the Marib-Al Jawf-Shabwa system of Mesozoic grabens, located onshore in the Republic of Yemen. An evaporitic sequence with an estimated maximum depositional thickness of 300 metres was deposited during the Tithonian. It is designated the Sabatayn Formation and exerts significant control on most of the play elements in the principal hydrocarbon play systems anticipated in the northeastern part of the basin. Migration of hydrocarbons from pre-salt source rocks into intra-and post-salt reservoirs is restricted by the evaporites. Localised heat flow perturbations introduced by the salt, increase the maturity of post-salt source rocks. Post and intra-salt reservoirs are structured by listric faulting on a salt detachment, salt pillowing due to post-depositional loading, by local salt dissolution and by late folding due to gravity sliding of the post-salt section on a salt detachment. Early dissolution and reprecipitation of salt is responsible for occlusion of porosity in intra-salt clastic reservoirs.  相似文献   

14.
An evaluation of the petroleum generating potential of onshore Eocene-Miocene sequences of Western Sabah, Malaysia was performed based on organic petrological and geochemical methods. The sequences analysed are the Belait, Meligan, Temburong and West Crocker formations of western Sabah. The Belait Formation which is Stage IV equivalent in the offshore represents one of the major source rock/reservoirs of the petroleum-bearing Sabah Basin. The Eocene-Early Miocene West Crocker and Temburong formations are deepwater turbidites whilst the Miocene Meligan and Belait formations are shallow marine fluvio-deltaic deposits. The vitrinite reflectance and pyrolysis Tmax values show that the Belait samples are generally immature for hydrocarbon generation, whereas the Meligan, Temburong and West Crocker samples are in the mature to late maturity stage of hydrocarbon generation. The overall bulk source rock properties of the Belait and Meligan show fair to good petroleum source rock potential with TOC more than 1 wt %, hydrocarbon yield in the range of 400–1300 ppm and moderately high HI for many of the samples. Most of the samples representing the Temburong and West Crocker formations have TOC less than 1 wt% and have no to fair hydrocarbon generating potential. Interestingly, the samples collected in the West Crocker Formation characterized by slump deposits (MTD) have TOC>2 and possess good to excellent hydrocarbon generating potential. The organic matter present in all of the studied formations is mainly of terrigenous origin based on the abundance of woody plant materials observed under the microscope. Consequently, the analysed sequences are predominantly gas prone, dominated by Type III and Type III-IV kerogen except for minor occurrence of mixed oil-gas prone Type II-III kerogen in the Belait Formation and in the slump mass transport deposits (MTD) of the West Crocker Formation.  相似文献   

15.
Four specimens of the thyasirid Conchocele bisecta (Conrad) and one small specimen of the vesicomyid Hubertschenckia ezoensis (Yokoyama), each with a drill hole made by a naticid gastropod, were found at a cold‐seep site in the upper Eocene Poronai Formation of Hokkaido. This is apparently the oldest record not only of drill holes, but also of predation scars, in a cold‐seep fauna. In addition, drilled vesicomyids are known from several Miocene cold‐seep sites in Japan. We suggest that the Eocene and Miocene chemoautotrophic bivalves were drilled only in the shallow‐water settings preferred by most naticids. The lack of drill holes in Oligocene chemoautotrophic bivalves in the northwestern USA suggests that this innovation, which allowed naticids to prey upon highly toxic bivalves, first appeared in the western Pacific during the Eocene.  相似文献   

16.
Surprisingly few natural hydrocarbon seeps have been identified in Australia's offshore basins despite studies spanning thirty years. Early studies of natural hydrocarbon seepage around the Australian margin were generally based on the geochemical analysis of stranded bitumens, water column geochemical ‘sniffer’ sampling, synthetic aperture radar or airborne laser fluorosensor. Later studies involved the integration of these remote sensing and geochemical techniques with multi-channel and shallow seismic. A review of these earlier studies indicates that many seepage interpretations need to be re-evaluated and that previous data sets, when placed in a global context, often represent normal background hydrocarbon levels. Low Recent burial and subsidence rates are not favourable for high rates of seepage. There are also difficulties in proving seepage on high energy, shallow carbonate shelves, where seabed features may be rapidly re-worked and modern marine signatures are overprinted on authigenic seep carbonates. Thus, the relatively few sites of proven natural hydrocarbon seepage in Australia's offshore sedimentary basins can be reconciled relative to their geological occurrences and the dominantly passive margin setting. Active thermogenic methane seepage on the Yampi Shelf, the only proven documented occurrence in Australia, is driven by deposition of a thick Late Tertiary carbonate succession and Late Miocene tectonic reactivation. Therefore, to increase the success of detecting and correctly interpreting natural hydrocarbon seepage, data need to be analysed and integrated within the context of the local geological setting, and with an understanding of what is observed globally.  相似文献   

17.
Erosional shelf ridges in the mid-eastern Yellow Sea   总被引：1，自引：0，他引：1  
In the mid-eastern Yellow Sea, closely spaced high-resolution seismic profiles and a 44-m-long sediment core (YSDP-104) were analyzed to reveal the internal structures and stratigraphy of the shelf ridges currently shaped by tidal currents. Three depositional sequences (sequences I, II and III in descending order) can be recognized. Sequence III, the substratum of the ridges, consists of coarse-grained sediments in the lower part (non-marine deposits) and tide-influenced muddy sediments in the upper part (probable transgressive to highstand systems tract). Sequence II represents internal ridge sediments, similar in character to sequence III, but is demarcated by an undulatory ridge topography. According to radiocarbon dating of marine muds, these sequences range in age from 47,000 to 28,000 years B.P., representing two cycles of short-term sea-level fluctuations during oxygen isotope stage 3. Sequence I consists mostly of late-Holocene transgressive sand veneer on the ridge surface. It also includes minor amounts of early-Holocene muddy sediments occasionally underlying the sand. Most of the ridges are presently undergoing erosion by tidal currents, forming widespread sand dunes on the entire surface.  相似文献   

18.
In the mid-eastern Yellow Sea, closely spaced high-resolution seismic profiles and a 44-m-long sediment core (YSDP-104) were analyzed to reveal the internal structures and stratigraphy of the shelf ridges currently shaped by tidal currents. Three depositional sequences (sequences I, II and III in descending order) can be recognized. Sequence III, the substratum of the ridges, consists of coarse-grained sediments in the lower part (non-marine deposits) and tide-influenced muddy sediments in the upper part (probable transgressive to highstand systems tract). Sequence II represents internal ridge sediments, similar in character to sequence III, but is demarcated by an undulatory ridge topography. According to radiocarbon dating of marine muds, these sequences range in age from 47,000 to 28,000 years B.P., representing two cycles of short-term sea-level fluctuations during oxygen isotope stage 3. Sequence I consists mostly of late-Holocene transgressive sand veneer on the ridge surface. It also includes minor amounts of early-Holocene muddy sediments occasionally underlying the sand. Most of the ridges are presently undergoing erosion by tidal currents, forming widespread sand dunes on the entire surface.  相似文献   

19.
Geochemical characteristics of organic matter in the profiles of Dukla, Silesian, Sub-Silesian and Skole units of the Polish Outer Carpathians and of the Palaeozoic–Mesozoic basement in the Dębica-Rzeszów-Leżajsk-Sanok area were established based on Rock-Eval, vitrinite reflectance, isotopic and biomarker analyses of 485 rock samples. The Oligocene Menilite beds have the best hydrocarbon potential of all investigated formations within the Dukla, Silesian, and Skole units. The Ordovician, Silurian, Lower Devonian and locally Middle Jurassic strata of the Palaeozoic–Mesozoic basement are potential source rocks for oil and gas accumulated in Palaeozoic and Mesozoic reservoirs. Thirty one natural gas samples from sandstone reservoirs of the Lower Cretaceous-Lower Miocene strata within the Outer Carpathian sequence and eight from sandstone and carbonate reservoirs of the Palaeozoic–Mesozoic basement were analysed for molecular and isotopic compositions to determine their origin. Natural gases accumulated both in the Outer Carpathian and the Palaeozoic–Mesozoic basement reservoirs are genetically related to thermogenic and microbial processes. Thermogenic gaseous hydrocarbons that accumulated in the Dukla and Silesian units were generated from the Menilite beds. Thermogenic gaseous hydrocarbons that accumulated in the Sub-Silesian Unit most probably migrated from the Silesian Unit. Initial, and probably also secondary microbial methane component has been generated during microbial carbon dioxide reduction within the Oligocene Menilite beds in the Dukla Unit and Oligocene-Lower Miocene Krosno beds in the Silesian Unit. Natural gases that accumulated in traps within the Middle Devonian, Mississippian, Upper Jurassic, and Upper Cretaceous reservoirs of the Palaeozoic–Mesozoic basement were mainly generated during thermogenic processes and only sporadically from initial microbial processes. The thermogenic gases were generated from kerogen of the Ordovician-Silurian and Middle Jurassic strata. The microbial methane component occurs in a few fields of the Dukla and Silesian units and in the two accumulations in the Middle Devonian reservoirs of the Palaeozoic–Mesozoic basement.  相似文献   

20.
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.  相似文献   

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