Evolution and petroleum geology of Amlia and Amukta intra-arc summit basins, Aleutian Ridge

Amlia and Amukta Basins are the largest of many intra-arc basins formed in late Cenozoic time along the crest of the Aleutian Arc. Both basins are grabens filled with 2–5 km of arc-derived sediment. A complex system of normal faults deformed the basinal strata. Although initial deposits of late Micocene age may be non-marine in origin, by early Pliocene time, most of the basinfill consisted of pelagic and hemipelagic debris and terrigenous turbidite deposits derived from wavebase and subaerial erosion of the arc's crestal areas. Late Cenozoic volcanism along the arc commenced during or shortly after initial subsidence and greatly contributed to active deposition in Amlia and Amukta Basins.Two groups of normal faults occur: major boundary faults common to both basins and ‘intra-basin’ faults that arise primarily from arc-parallel extension of the arc. The most significant boundary fault, Amlia-Amukta fault, is a south-dipping growth fault striking parallel to the trend of the arc. Displacement across this fault forms a large half-graben that is separated into the two depocentres of Amlia and Amukta Basins by the formation of a late Cenozoic volcanic centre, Seguam Island. Faults of the second group reflect regional deformation of the arc and offset the basement floor as well as the overlying basinal section. Intra-basin faults in Amlia Basin are predominantly aligned normal to the trend of the arc, thereby indicating arc-parallel extension. Those in Amukta basin are aligned in multiple orientations and probably indicate a more complex mechanism of faulting. Displacement across intra-basin faults is attributed to tectonic subsidence of the massif, aided by depositional loading within the basins. In addition, most intra-basin faults are listric and are associated with high growth rates.Although, the hydrocarbon potential of Amlia and Amukta Basins is difficult to assess based on existing data, regional considerations imply that an adequate thermal history conducive to hydrocarbon generation has prevailed during the past 6-5 my. The possibility for source rocks existing in the lower sections of the basins is suggested by exposures of middle and upper Miocene carbonaceous mudstone on nearby Atka Island and the implication that euxinic conditions may have prevailed during the initial formation of the basins. Large structures have evolved to trap migrating hydrocarbons, but questions remain concerning the preservation of primary porosity in a sedimentary section rich in reactive volcaniclastic debris.     

Barbados: maturation,source rock potential and burial history within a Cenozoic accretionary complex

A number of diagenetic properties were studied in sedimentary rocks exposed along a 25 km across-strike transect on Barbados, the crest of the Barbados accretionary complex. The island of Barbados consists of three structural levels: a lower (mostly Eocene or undated) basal complex composed of quartzose turbidites, hemipelagites and melange; an intermediate level (Eocene to Miocene) of nappes composed mostly of calcareous pelagite; and a Pleistocene coral cap. Diagenetic studies concentrated on the basal complex although preliminary data from the nappes are also presented. The following subjects were studied: (1) clay mineralogy (% illite interlayers in mixed-layer clays); (2) vitrinite reflectance; (3) organic type and maturation, by Rock-Eval pyrolysis; (4) thermal alteration index of spores and pollen; (5) dry bulk density; (6) silica mineralogy. Taken together, the data can be interpreted to indicate maximum temperatures attained during diagenesis of less than 80°C. Based on a uniform palaeogeothermal gradient of 15°C km^?1, and a temperature at the sediment/water interface of 10°C, maximum burial depths of basement complex rocks were about 2–5 km. Minimum possible burial depths are < 1 km. No across-strike changes in maturation are observed indicating that these trench-associated rocks were uplifted uniformly. Mudstones are typically rich in total organic carbon (> 1 %), and are immature. Organic matter was derived mostly from terrigenous or oxidized sources (type III kerogens), although some marine planktonic sources are indicated locally (type II kerogens). Organic matter is therefore primarily gas-prone.     

The petroleum geology of the Unst Basin, North Sea

The Unst Basin is situated in the northern North Sea between the East Shetland Basin and the Shetland Isles. The basin is essentially a three-armed, Permo-Triassic fault-controlled basin containing up to 3600 m of red-beds. This is overlain by a westerly thickening Jurassic and early Cretaceous sequence, the stratigraphy of which is very similar to that of the East Shetland Basin. In particular, the Brent Group (140 m), Humber Group (685 m) and Cromer Knoll Group (300 m) are well represented.As a result of Laramide uplift of the area, the thick Upper Cretaceous and Palaeocene strata of the East Shetland Basin are absent from the Unst Basin. This uplift resulted in substantial erosion within the Unst Basin providing the major source for Palaeocene sands in the Viking Graben and the Faeroes Basin. Late Palaeocene and younger Tertiary strata transgress westwards across this erosion surface.Petroleum exploration within the basin culminated in the drilling of two exploration wells. These wells encountered potential reservoir and source rocks in the Jurassic section. However, geochemical analyses indicate these source rocks are immature for hydrocarbon generation within the Unst Basin. It is concluded that the Unst Basin has a low petroleum potential.     

Comparative petroleum systems analysis of the interior basins of Turkey: Implications for petroleum potential

The interior basins of Turkey remain effectively unexplored and their petroleum systems are poorly understood. This paper presents a comparative summary of the geological evolution, petroleum potential and prospectivity of the Central (Tuz Gölü, Sivas and Çankırı) and East Anatolian (Muş-Hınıs, Pasinler-Horasan and Tercan-Aşkale) basins using geological, seismic, geochemical and petrophysical data, and a series of quantitative basin models. The studied basins are ranked on the basis of source effectiveness, reservoir quality, seal efficiency, and the timing of hydrocarbon expulsion and migration relative to trap formation. A qualitative risk assessment, based on the elements of the petroleum system, is used to evaluate the likelihood of hydrocarbon discovery in each of the basins. This study shows that the chance of hydrocarbon discovery in the East Anatolian basins is unlikely-very unlikely and Tuz Gölü, Sivas and Çankırı basins are equally likely/unlikely-unlikely, likely and unlikely, respectively. Heavy oil and minor gas associated with two mature petroleum systems were discovered in the Tuz Gölü basin. Various trap forming mechanisms such as salt tectonics and Middle Eocene compression, accompanied by the effective sealing capacity of the Eocene evaporites favor the hydrocarbon exploration potential of the Tuz Gölü basin. The highest exploration risk in the Tuz Gölü basin arises from the poor quality sandstone reservoirs. The biggest risk factor in the Eastern Anatolian basins is insufficient thermal maturity, despite the presence of good quality source rocks. The Sivas basin is one of the most promising interior basins of Turkey due to the presence of multiple mature petroleum systems and high quality reservoirs. There is a high chance of accumulation of multi-phase hydrocarbons in the Eocene and Miocene traps. The major problem in the Sivas basin is the lack of an efficient seal rock. The Çankırı basin contains all of the necessary elements of an ideal petroleum system except the presence of an organic-rich source rock. Thus, the chance of hydrocarbon discovery in the Çankırı basin is low.     

Quantitative estimation of petroleum prospect outcome probabilities: an overview of procedures

Estimation of prospect outcome probabilities in numerical form should be a central objective for petroleum geologists. Most numerical estimates of outcome probabilities represent subjective guesses. While the effectiveness of subjective procedures is difficult to gauge, several postmortem analyses suggest that subjective procedures are ineffective. Objective procedures for estimating outcome probabilities should yield much improved estimates. Objective procedures require that geological, geophysical and production data be organized so that geological and geophysical characteristics of prospects interpreted before they were drilled can be compared systematically with outcomes of prospects after they have been drilled. An example application that involves well data and an example application that involves seismic data demonstrate that objective procedures are simple in principle, but require organization of information in a form suitable for computation of frequencies, on which objective estimates of probabilities can be based.     

Geochemical assessment of the Colombian oils based on bulk petroleum properties and biomarker parameters

This geochemical survey defines the typical features of representative oils from the major Colombian basins, and proposes a classification scheme useful for hydrocarbon exploration. This work is based on properties of whole oils such as API gravity, sulfur, vanadium and nickel concentrations, and gas chromatography fingerprints. The framework is completed by inclusion of biomarker parameters derived from GCMS and GCMSMS analysis.Oils from the basins of the Middle Magdalena Valley, Upper Magdalena Valley, Sinú - San Jacinto, Putumayo-Caguan, Lower Magdalena Valley and Catatumbo were assessed. Conclusions were drawn regarding possible sources of origin, oil families, degree of thermal evolution, biodegradation, mixing and refreshing, and inferences regarding exploration implications.The oils from the Middle Magdalena Valley and Upper Magdalena Valley (intermontane basins) and Putumayo (foreland basin), except those from the Caguan area, are oils with similar characteristics. In these three cases the oils are probably coming from source rocks intervals deposited in a marine Cretaceous platform, with variable carbonate/siliciclastic features. In these basins there are no oils derived from Tertiary source rocks.In Sinú-San Jacinto and Lower Magdalena Valley basins the main proportions of oils comes from very proximal environments, probably deltaic type, of Tertiary age with a minor proportion of oils coming from Cretaceous source rocks of marine anoxic environment (the only marine Cretaceous oils discovered so far in the Sinú-San Jacinto and Lower Magdalena Valley basins).The oils from Eastern Foothills of the Eastern Cordillera, look to be derived mainly from proximal Cretaceous source rocks with some mixing of oils derived from Tertiary strata. In the Catatumbo basin there are oils derived mainly from Cretaceous source rocks and some from Tertiary source rocks.Regarding the processes after entrapment, in all of the basins, the biodegradation effects were observed in varying degrees. These processes are dominant toward more quiescent regions, beyond the areas with more tectonic activity, far from the foothills of the Eastern Cordillera. Instead, close to the Eastern Cordillera are more common the paleobiodegradation processes due to reburial of younger molasses. The effects of mixing or refreshing are remarkable close to the Eastern Cordillera foothills in Llanos, Middle Magdalena Valley, and Upper Magdalena Valley basins.     

石油污染对莫桑比克罗非鱼血清酶活性的影响

本文通过分析莫桑比克罗非鱼血清酶活性的变化,研究石油对鱼类的致毒效应.试验结果表明,石油污染能升高血清谷草转氨酶、乳酸脱氢酶和碱性磷酸酶活性,石油对莫桑比克罗非鱼血清酶活性产生作用的浓度阈值为0.05mg/dm3.分析鱼类血清酶活性的变化,可以为诊断石油污染提供科学依据.     

现代海底热液硫化物的成矿序列和指示意义——以印度洋中脊为例

与快速扩张的洋中脊相比,主要由超慢速-慢速扩张洋脊组成的印度洋中脊具有独特的热液硫化物成矿模式.运用高精度矿相显微镜、XRD、电子探针和ICP-AES/MS等测试手段,对印度洋中脊的热液硫化物矿床样品开展了矿物成分、结构构造、地球化学等各方面分析.结果表明,来自中印度洋脊(CIR)艾德蒙德(Edmond)热液区的硫化物A主要由黄铁矿、白铁矿以及黄铜矿构成,其成矿期次可划分为白铁矿-黄铁矿阶段(Ⅰ)、闪锌矿-黄铜矿阶段(Ⅱ)以及后期石英阶段(Ⅲ),成矿流体温度经历了低-高-低的变化;同样来自于艾德蒙德热液区的硫化物B主要矿物成分为黄铁矿、白铁矿和硬石膏,成矿期次划分为硬石膏-白铁矿-黄铁矿阶段(Ⅰ)和胶状黄铁矿-石英(Ⅱ) 2个阶段,流体温度经历了低-高的变化;与之相比,来自西南印度洋脊(SWIR)龙旂热液区的硫化物C主要由纤铁矿、黄铜矿、黄铁矿和白铁矿组成,成矿期次划分为纤铁矿-白铁矿-黄铁矿阶段(Ⅰ)和闪锌矿-黄铜矿(Ⅱ)阶段,后期闪锌矿、黄铜矿的出现反映热液流体温度发生了升高.地球化学特征表明,印度洋中脊的热液硫化物总体为富Fe型,并相对富集Co和Ni元素,而Zn和Cu元素的含量相对较低.此外,取自艾德蒙德热液区的硫化物与EPR 21°N热液硫化物组成非常相似,而与慢速扩张脊TAG相比,Pb、Zn、Ag和Sr元素含量较高,Cu和Fe元素含量则较低.     

Fault linkage patterns and their control on the formation of the petroleum systems of the Erlian Basin, Eastern China

Fault linkage patterns in rift basins are very common. While the process of fault linkage may be very short, it changes sedimentation patterns before and after linkage and controls the development of half-grabens. The propagation and growth of boundary faults can be divided into a simple fault propagation pattern and a fault growth-linkage pattern. Based on structural style, sedimentation patterns and oil-source correlations in the Erlian Basin, three types of grabens and petroleum systems can be identified. The Abei graben is controlled by a single boundary fault and forms an independent petroleum system. The Saihantala graben is controlled by several linked faults, which also has an independent petroleum system. The Wuliyasitai Depression controlled by two boundary fault segments which results in two petroleum systems. As not all half-grabens develop one petroleum system; they may, therefore, have two or more systems. The relay ramps between fault segments before linkage are the locations of deposition of sands and conglomerates, and consequently, are the focus areas for stratigraphic–lithologic trap exploration.     

Hydrocarbon test in lower-layer atmosphere to predict deep-sea petroleum or hydrate in the Okinawa Trough: an example

INTRODUCTIONItisaverypossiblenewmethodforustopredictdeep seapetroleumorhydratebymeansoftestinglighthydrocarbonandanalyzingCisotopicoflower layeratmosphericsamplesnearseasurface Thismethodisbasedonthetheoryofoilandgasmicro seepages,whichsuggeststhatsomegasessuchasCH4,CO2 etc .(Cheng ,1 999;Daietal.,1 994 ;Daietal.,1 995;Teder,1 985;Jonesetal.,1 985;Fangetal.,2 0 0 0 ;Guo ,1 995;Gongetal.,2 0 0 2 ;Huangetal.,1 998) ,willcontinuallymigrateupwardsintofracturesandporosityofrocks ,seabedse…     

Geochemistry,origin, and accumulation of petroleum in the Eocene Wenchang Formation reservoirs in Pearl River Mouth Basin,South China Sea: A case study of HZ25-7 oil field

The Pearl River Mouth Basin in the South China Sea has accumulated >2 km of Eocene sediments in its deep basin, and has become the exploration focus due to the recent discoveries of the HZ25-7 oil field in the Eocene Wenchang (E₂w) Formation. In this study, the geochemical characteristics of potential source rocks and petroleum in the HZ25-7 oil field are investigated and the possible origins and accumulation models developed. The analytical results reveal two sets of potential source rocks, E₂w and Enping (E₂e) formations developed in the study area. The semi-deep-to-deep lacustrine E₂w source rocks are characterized by relatively low C₂₉ steranes, low C₁₉/C₂₃ tricyclic terpane (<0.6), low C₂₄ tetracyclic terpane/C₃₀ hopane (<0.1), low trans-trans-trans-bicadinane (T)/C₃₀ hopane (most <2.0), and high C₃₀ 4-methyl sterane/ΣC₂₉ sterane (>0.2) ratios. In contrast, the shallow lacustrine and deltaic swamp-plain E₂e source rocks are characterized by relatively high C₂₉ steranes, high C₁₉/C₂₃ tricyclic terpane (>0.6), high C₂₄ tetracyclic terpane/C₃₀ hopane (>0.1), variable yet overall high T/C₃₀ hopane, and low C₃₀ 4-methyl sterane/ΣC₂₉ sterane (<0.2) ratios. The relatively low C₁₉/C₂₃ tricyclic terpane ratios (mean value: 0.39), low C₂₄ tetracyclic terpane/C₃₀ hopane ratios (mean value: 0.07), high C₃₀ 4-methyl sterane/ΣC₂₉ sterane ratios (mean value: 1.14), and relatively high C₂₇ regular sterane content of petroleum in the HZ25-7 oil field indicate that the petroleum most likely originated from the E₂w Formation mudstone in the Huizhou Depression. One stage of continuous charging is identified in the HZ25-7 oil field; oil injection is from 16 Ma to present and peak filling occurs after 12 Ma. Thin sandstone beds with relatively good connectivity and physical properties (porosity and permeability) in the E₂w Formation are favorable conduits for the lateral migration of petroleum. This petroleum accumulation pattern implies that the E₂w Formation on the western and southern margins of the Huizhou Depression are favorable for petroleum accumulation because they are located in a migration pathway. Thus exploration should focus in these areas in the future.     

Impact of strong easterly trade winds on carbonate petroleum exploration - Relationships developed from Caicos Platform,southeastern Bahamas

Brisk, persistent easterly trade wind influences define Holocene patterns of carbonate sedimentation across the Caicos Platform (southeastern Bahamas). Resultant predictive sedimentary facies models based on trade wind influences are more widely applicable to the exploration for subsurface carbonate plays than are existing models based on the northern Bahamas facies patterns, which are characterized by gentle trade winds and strong platform-margin-related oceanic processes (swells and tidal currents). The Caicos Platform relationships may be more applicable because many ancient shallow carbonate depositional environments were within the trade wind belts and commonly within broad intracratonic seas that were little influenced by oceanic processes.The grainstone-dominated Caicos Platform exhibits reservoir potential over much of its surface, in contrast to northern Bahamian platforms, where oceanic tidal currents or swells and gentle easterly trade winds confine higher energy environments with reservoir potential to platform margins. Strong easterly trade winds across Caicos Platform promote widespread Holocene platform-interior oolitic, skeletal and grapestone grainstone bodies on this platform. Orientations of ooid sand bodies vary depending on preexisting topography, water depth and bottom energy. Shallow subtidal ooid sand shoals orient parallel to these winds. Ooid sands developed along older shorelines orient parallel to the shorelines but prograde perpendicular into these winds. Deeper platform-interior oolitic sands exist as widespread, sheet-like deposits. These trade winds allow reefs and ooids to coexist in many settings, permit isolated linear reefs to flourish on certain leeward platform margins, and promote effective off-bank transport of carbonate sands that create onlapping grainstone wedges. These relationships are very applicable to the rock record.Strong trade wind influences, such as seen on Caicos Platform, better explain the occurrence of Cretaceous reef and/or oolitic grainstone reservoirs developed well in from platform margins (Fairway Field in East Texas; Black Lake Field in Louisiana) than do existing northern Bahamian models. Depositional models based on conditions in the northern Bahamian models would predict low-energy facies in these platform-interior settings. A trade-wind-driven depositional model, characterized by strong persistent easterlies, also better explains the origin of the onlapping wedge of skeletal grainstones at Poza Rica oilfield in Mexico.The Caicos Platform easterly trade-wind-driven depositional model should generally apply to any ancient shallow carbonate environment that developed 5–22° north or south of the paleoequator, whether or not a platform margin was near by. Future carbonate exploration or exploitation should always factor in not only geological age, but also physiographic, latitudinal and climatic setting at a global and local scale.     

Progressive deformation of an evaporite-bearing accretionary complex: SeaMARC I,SeaBeam and piston-core observations from the Mediterranean Ridge

The Mediterranean Ridge is an arcuate ridge of deformed sediment caught up in the convergent plate margin between the African plate and the Aegean. An intensive campaign of SeaMARC I and SeaBeam surveys followed by piston coring has been conducted along the contact between undeformed turbidites of the Sirte Abyssal Plain and folded and faulted sediments of the Mediterranean Ridge. Along the outer edge of the Ridge, surficial sediments have been deformed into sinusoidal ridges and troughs (wavelengths 0.5–2 km, amplitude 20–150 m), which we interpret as folds. In plan view, the ridge and the trough fabric parallels the NW-SE trending regional contours, suggesting that the folds formed in response to compression orthogonal to the Mediterranean Ridge. The outermost ridge is shedding a debris apron out onto the abyssal plain, implying that uplift and deformation are ongoing. We show that the geometry of the outermost folds can be produced by elastic bending of a packet of 5–10 relatively strong layers, each 10–20 m thick, interbedded between weaker layers; we equate the strong layers with gypsum beds in the Messinian upper evaporites. Folding the seafloor from a flat layer into the observed ridge and trough topography would shorten the layer by less than 2%. Two percent shortening (equals two percent thickening) is insufficient to create the observed relief of the Mediterranean Ridge even if the entire sediment column down to basement were involved; we infer that additional shortening/thickening is accommodated by thrust faulting above a decollement at the top of the Messinian salt layer. At distances > 15 km from the deformation front and more than 500 m from the abyssal plain, sharp-edged, fine-grained side-scan lineations with very little vertical relief cut across the kilometer-scale ridge and trough topography. These fine-grained lineations fall in two groups trending N/S to NNE/SSW and ~ENE. We interpret these lineaments as traces of conjugate strike-slip faults formed in the same compressional regime which formed the NW/SE trending folds. The onset of strike-slip faulting may coincide with the cessation of imbricate thrust fan development above the initial salt-controlled decollement surface. The following characteristics of the Mediterranean Ridge are attributed to the presence of evaporites in the incoming sedimentary section: (1) initial deformation by folding rather than thrust faulting; (2) narrow taper; (3) rapid rate of outward growth; (4) karstification.     

Modeling an atypical petroleum system: A case study of hydrocarbon generation,migration and accumulation related to igneous intrusions in the Neuquen Basin,Argentina

In the Altiplanicie del Payún area (Neuquen Basin, Argentina), immature source rock sections intruded by up to 600 m thick Tertiary laccoliths show full spectrum maturity aureoles over hundreds of meters from the contacts. Commercial oil accumulations (20–33°API) and oil shows are located along the entire column, both in sandstone/carbonate and fractured igneous reservoirs. A challenging numerical model that included the emplacement of the intrusive bodies, with extreme temperature ranges and unusually short calculation time steps, has been done with the aim to better understand hydrocarbon generation and migration processes related to these thermal anomalies.     

马里亚纳海沟挑战者深渊初期多金属氧化物的 矿物学、地球化学特征及其成因环境研究

对大洋27航次在西太平洋马里亚纳海沟挑战者深渊获取的3个多金属氧化物样品进行了X射线矿物衍射分析、穆斯堡尔谱分析及地球化学元素分析,研究其矿物、地球化学特征差异。结果表明,所取样品处于多金属氧化物发育的初始阶段,具有独特的矿物地球化学特征:(1)相较于太平洋CC区及中太平洋海盆获取的多金属结核样品,本研究样品的矿物组成中含有异常高的石英、斜长石以及黏土矿物,而水羟锰矿和钙锰矿含量较低。(2)样品中铁相矿物主要为正方针铁矿(91.6%),另含少量纤铁矿(8.4%),推测是纤铁矿向更加稳定的正方针铁矿衍变的结果。(3)由于样品中深海黏土组分以及氧化物核心物质的混入,加上吸附金属氧化物时间较短,导致SiO₂和Al₂O₃含量均高于正常结核,而Fe、Mn、Cu、Co、Ni等其余金属元素含量较低。(4)由于形成时间较短,样品中稀土元素含量相对较低,ΣREE仅约为0.4×10^-3(一般太平洋CC区及中太平洋结核中稀土含量均大于1.0×10^-3);加之海水氧化还原作用的降低以及研究区海底热液活动的影响,Ce元素未表现出多金属结核中常见的正异常。     

Oil migration through preferential petroleum migration pathway (PPMP) and polycyclic faults: A case study from the Shijiutuo Uplift,Bohai Bay basin,China

The Shijiutuo uplift is an oil enriched uplift in the offshore Bohai Bay Basin. Petroleum migration is a key factor for oil enrichment in Neogene reservoirs far away from the hydrocarbon kitchen. In this article, an integration of geological, geophysical and geochemical analyses are employed to investigate the petroleum migration and accumulation on the Shijiutuo uplift. Hydrocarbons in the QHD32-6 and QHD33 oilfields are mainly originated from the third (E₂s₃) and first (E₂s₁) member of the Shahejie Formation. The shallow traps have significant contributions of late-stage E₂s₁-derived oil. Lateral petroleum migration is a major mechanism forming large oilfields on the Shijiutuo uplift. The large oilfields have multiple hydrocarbon kitchens, multiple source rocks, and numerous preferential petroleum migration pathways (PPMPs). Once petroleum arrives at the structural highs on the Shijiutuo uplift through the Guantao Formation (N₁g) carrier-beds, neotectonic faults cutting through Guantao (N₁g) and Minghuazhen (N₁m^L) formations could serve as effective conduits for vertical petroleum migration. Neotectonic faults have experienced polycyclic fault activities. Fluid inclusions indicate episodic hydrocarbon charging. Crude oils display duplex properties of biodegradation and non-biodegradation, which is strong evidence for multiple and episodic oil charging on the Shijiutuo uplift. Finally, episodic petroleum charging along polycyclic neotectonic faults causes the late-stage E₂s₁-derived oils to occur in the shallow reservoirs.     

Bait-attending fauna of the Kermadec Trench, SW Pacific Ocean: Evidence for an ecotone across the abyssal-hadal transition zone

The bait-attending fauna of the abyssal-hadal transition zone of the Kermadec Trench, SW Pacific Ocean (4329-7966 m), was investigated using a baited camera and a trap lander. The abyssal stations (4329-6007 m) revealed a typical scavenging fish community comprising macrourids and synaphobranchid eels, as well as natantian decapods. At the hadal depths of 7199 and 7561 m, the endemic liparid Notoliparis kermadecensis was observed aggregating at the bait reaching surprisingly high numbers of 5 and 13, respectively. A total of 3183 invertebrate samples were collected (mean deployment time=16 h) of which 97.8% were of the order Amphipoda (nine families, 16 species). Ten of the amphipod species represent new distributional records for the Kermadec Trench and the New Zealand Exclusive Economic Zone; this includes the shallowest known record of the endemic hadal amphipod Hirondellea dubia (6000, 6007 m). Using amphipods to statistically examine the compositional change across the abyssal-hadal boundary, an ecotone between depths <6007 and >6890 m was found, indicating that there is an ecologically distinct bait-attending fauna in this trench.     

Transition from frontal accretion to underplating in a part of the Nankai Trough Accretionary Complex off Shikoku (SW Japan) and extensional features on the lower trench slope

Migrated multichannel seismic reflection profiles and bathymetry from a 200 × 120 km area of the Nankai Trough inner slope reveal three physiographic-tectonic domains on the lowermost slope. Linear ridges demarking laterally-continuous hangingwall anticlines above ramps in a relatively simple imbricate stack of trench turbidites characterize the western domain. An imbricate fan underlies a relatively flat structural terrace in the east. Between these two domains lies a compound knoll (Minami Muroto Knoll) some 40 km long, opposite which the thrust front pushes some 10 km further seaward than is the case in the domains to east and west. In the western ‘linear-ridge’ domain previous DSDP drilling penetrated turbiditic trench fill uplifted in the lowermost thrust-fold terrace above a decollement within the underthrusting Shikoku Basin (oceanic plate) sequence. The Shikoku Basin sequence in the western domain is divided into an upper, poorly reflective, hemipelagic claystone unit and a lower, strongly reflective, unit comprising Pliocene turbidites. The lower unit is traceable intact up to c.20 km landward below the lower trench slope and in the better resolved profiles the decollement lies along the base of the claystone unit. A similar decollement within the Shikoku Basin sequence in the eastern domain is traceable up to c.22 km landward. A critical seismic record crossing the western part of Minami-Muroto Knoll shows that the decollement is traceable only 8 km landward to a point, under the steep slope at the front of the knoll, landward of which the subducting Shikoku basin sequence is apparently thickened by as much as twice. This thickening, occuring as it does immediately along-strike from a simple imbricate fan to the east of the knoll and a relatively simple imbricate stack to the west (both evidently involving no strata from the lower Shikoku Basin unit) we ascribe to underplating by formation of duplexes of Shikoku Basin strata. Strike-parallel extension, akin to that postulated for high structural levels in certain thrust belts, is caused by uplift of the knoll as a result either of the underplating, or segmentation of the subducting oceanic crust, or both: a normal fault throws to the west off the west flank of the knoll. It bounds a transverse, trough-like, slope-basin with at least 900 m of fill. Upslope from the knoll broadly slope-parallel normal faults cut, and pond, recent slope sediments. The most impressive is a listric growth fault which dips trenchward. Alternative explanations for these involve extensional collapse of this part of the prism resulting from the subduction of a topographic high, or a zone of selective underplating below the trenchward portion of Minami Murato Knoll.     

Water quality and thermal regime of the Motueka River: Influences of land cover,geology and position in the catchment

We examined the effects of land use, geology, and longitudinal position within the river network on water quality and thermal regime at 23 sites within the Motueka River catchment. The concentrations of suspended solids, nitrate nitrogen, total nitrogen, Escherichia coli, and Campylobacter were higher at sites draining pastoral and horticultural land than in similar‐sized native or plantation forest streams. Average daily mean temperature and minimum temperature in summer and maximum winter temperature were higher in unshaded pastoral and horticultural streams than at native forest sites. Differences in water quality and thermal regime were also observed among sites with contrasting geology. Conductivity, pH, and minimum winter temperatures were highest at sites draining marble terrain. In contrast, longitudinal patterns in water quality and temperature regime along the 120‐km length of the river were relatively weak, although longitudinal patterns in amplitude of daily temperature fluctuation matched theoretical predictions. In this study, differences in land use appeared to have the strongest influence on most water quality and thermal variables examined. However, geology was an important factor explaining variation in certain variables (e.g., pH and conductivity). Longitudinal patterns in water quality and temperature were relatively weak and in many instances were linked with longitudinal patterns in land use and geology rather than catchment location alone.     

Mechanisms of petroleum accumulation in the Bozhong sub-basin, Bohai Bay Basin, China. Part 1: Origin and occurrence of crude oils

The origin of the fourteen major oil fields in the Bozhong sub-basin, Bohai Bay basin was studied based on the results of Rock-Eval pyrolysis on more than 700 samples and biomarker analysis on 61 source rock samples and 87 oil samples. The three possible source rock intervals have different biomarker assemblages and were deposited in different environments. The third member of the Oligocene Dongying Formation (E₃d₃, 32.8–30.3 Ma in age) is characterized mainly by high C₁₉/C₂₃ tricyclic terpane (>0.75), high C₂₄ tetracyclic terpane/C₂₆ tricyclic terpane (>2.5), low gammacerane/αβ C₃₀ hopane (<0.15) and low 4-methyl steranes/ΣC₂₉ steranes (<0.15) ratios, and was deposited in sub-oxic to anoxic environments with significant terrigenous organic matter input. The first (E₂s₁, 35.8–32.8 Ma) and third (E₂s₃, 43.0–38.0 Ma) members of the Eocene Shahejie Formation have low C₁₉/C₂₃ tricyclic terpane and low C₂₄ tetracyclic terpane/C₂₆ tricyclic terpane ratios and were deposited in anoxic environments with minor terrestrial organic matter input, but have different abundances of 4-methyl steranes and gammacerane. The hydrocarbon-generating potential and biomarker associations of these three source rock intervals were controlled by tectonic evolution of the sub-basin and climate changes. Three oil families derived from E₂s₃, E₂s₁ and E₃d, respectively, and three types of mixed oils have been identified. All large oil fields in the Bozhong sub-basin display considerable heterogeneities in biomarker compositions and originated from more than one source rock interval, which suggests that mixing of oils derived from multiple source rock intervals or multiple generative kitchens, and/or focusing of oils originated from a large area of a generative kitchen, is essential for the formation of large oil fields in the Bozhong sub-basin. E₂s₃- and E₂s₁-derived oils experienced relatively long-distance lateral migration and accumulated in traps away from the generative kitchen. E₃d₃-derived oils had migrated short distances and accumulated in traps closer to the generative kitchen. Such a petroleum distribution pattern has important implications for future exploration. There is considerable exploration potential for Dongying-derived oils in the Bozhong sub-basin, and traps close to or within the generative kitchens have better chance to contain oils generated from the Dongying Formation.