Mechanisms of collapse of the cretaceous helvetiafjellet formation at Kvalvågen,eastern Spitsbergen

Coastal cliffs at Kvalvågen, eastern Spitsbergen, expose palaeolandslide blocks and related slope failure features that record local collapse of an otherwise undisturbed succession of paralic sediments. The collapse occurred along a shallow sloping shelf at the edge of an epicontinental sea in the Early Cretaceous. The event was coincident with a rise in relative sea level along a coast that had just previously experienced a major paralic regression across a muddy marine environment. The low relief environment in which the slope failure structures formed, as well as the timing of the collapse raise questions regarding the cause of the topographic instability and the possible influence of sea level changes or tectonic activity. These outcrops have been previously interpreted as the collapse of a deltaic system triggered by local seismic activity or collapse of a shelf break in the headwall regions of submarine canyons. This paper presents new structural and stratigraphic data that refine and adjust the previous interpretations through the evaluation of a variety of possible mechanisms for collapse based on the new data. Our data suggest that active delta deposition was not occurring at Kvalvågen at the time of collapse and that the collapse was likely due to allogenic forcing. Despite the possible influence of pore fluids and rheological controls on the collapse, we find that the geometry and kinematics of landslide slip planes, synsedimentary folds, and other slope failure related features require over-steepened topography and that these are most consistent with westward-directed collapse off of a north striking escarpment with elevated topography on the east side. Fault exposures, a large contrast in palaeo-elevation, and liquifaction features support previous interpretations of a tectonic cause for the collapse and suggest that this topographic feature may have been a fault or fold scarp. This study demonstrates the importance of combining stratigraphic and sedimentological data with structural data and kinematic analysis in the interpretation of sedimentary processes.     

Origin of transverse folds in an extensional growth-fault setting: Evidence from an extensive seismic volume in the western Gulf of Mexico

Growth faults in gravity-driven extensional provinces are dominated by coast-parallel trends, but coast-perpendicular (transverse) trends are far less documented. The Clemente–Tomas fault in the inner Texas shelf has corrugations that are transverse to the fault and that plunge downdip. A large (8500 km²), high-quality, 3D seismic survey allows a uniquely encompassing perspective into hanging-wall deformation above this corrugated fault surface. Synextensional strata in the hanging wall are folded into alternating transverse ridges and synclines, typically spaced 10 km apart. Forward modelling in dip profiles of an extensional fault having three ramps produces ramp basin-rollover pairs that compare with the seismically revealed ridges and synclines. As they translated down the undulose fault plane, ramp basins and rollovers were juxtaposed along strike, forming the hanging-wall ridges and synclines observed offshore Texas. Fault-surface corrugations correlate broadly with footwall structure. We infer that corrugations on the Clemente–Tomas fault formed by evacuation of an allochthonous salt canopy emplaced in the late Eocene to early Oligocene. Early salt evacuation (Oligocene) created an undulose topography that influenced incipient Clemente-Tomas fault segments as they merged to form an inherently undulose fault. Late salt evacuation (early Miocene) further deformed this fault surface.     

梨树断陷断陷期小宽断裂带构造应力场数值模拟

在小宽断裂带构造解析基础之上,根据地质资料以及前人提供的岩石物理学参数建立了梨树断陷区的二维地质和数值模型。进行了构造应力场数值模拟,分析了梨树断陷小宽断裂带断陷期小宽断裂带断陷期在沙河子期(K1sh)、营城期(K1yc)、登楼库期(K1d)的构造应力场特征。模拟结果显示：(1)沙河子期在左旋走滑应力状态下,小宽断裂带处于近NE—SW方向的拉张应力状态,剪应力在沿着断裂带SW—NE走向逐渐减小; (2)营城期在右旋走滑的应力状态下,小宽断裂带处于近NW—SE向的拉张力状态,剪应力最大值位于断裂带的最中间部位;(3)登楼库期在左旋走滑的应力状态下,断裂带处于SWW—NEE向的张拉应力状态,剪应力最大值位于断裂带西南段。     

New insights into the carbonate karstic fault system and reservoir formation in the Southern Tahe area of the Tarim Basin

As worldwide hydrocarbon exploration has extended from shallowly to deeply buried strata, reservoir quality has attracted substantial and persistent interest in petroleum geology. In particular, deeply buried strata (>5500 m) in the Tarim Basin have attracted considerable attention because carbonate reservoirs that have experienced fracture or dissolution have also been shown to demonstrate considerable hydrocarbon potential. Therefore, it is necessary to determine how these reservoirs are developed and distributed in detail from both scientific and practical standpoints.In this paper, we address this issue using a case study in the southern Tahe area, which is contained within the largest Palaeozoic marine oilfield in China. In the northern Tahe area, mega-paleokarst systems developed in the Ordovician strata; however, the reservoir quality in the southern part of the Tahe area is relatively poor because it is covered by insoluble formations during karstification. Observations of cores and analyses of images of well logging demonstrate that these reservoirs are dominated by caves, vugs and fractures that have developed near faults. We speculate that the faults penetrating insoluble formations represent the main dissolution passages that originally developed these karstic fault systems. Additionally, we analyse a series of outcrops, seismic data, and structures to characterize the spatial geometry of these major faults and their surrounding fractures in detail. Most of these are strike-slip faults, and their subsequent reservoirs can be divided into three categories based on their development, including dendritic, sandwich and slab reservoirs. Recent studies demonstrate that karstic fault reservoirs are most common traps in the study area. Although various types of carbonate karstic fault reservoirs are represented in this region, the dendritic karstic fault reservoir is the most hydrocarbon-rich.Guided by these initial results, 108 wells were drilled from 2013 to 2014, producing 485 thousand tons of oil and yielding success ratios greater than 89%. The average production of dendritic reservoirs is 37.4 tons per day (t/d), while those of sandwich and slab types are 20.2 t/d and 14.0 t/d, respectively. These results represent significant references for future hydrocarbon exploration and the development of similar deeply buried karstic fault reservoirs in the Tarim Basin and elsewhere.     

莱州湾地区郯庐断裂带的构造特征及其新生代演化

郯庐断裂带中段分东西两支从莱州湾进入渤海,在莱州湾地区的构造特征与演化历史一直鲜为人知。通过对横穿研究区的两条地震测线的解释和分析,揭示了该区郯庐断裂带中段在研究区的构造差异,研究表明郯庐断裂带东西两支在该研究区表现出不同的断裂性质,西支断裂表现为正断层,东支断裂表现为走滑断层。郯庐断裂是本研究区的主控断裂,通过对本地区地层形态及其组合、断层的剖面形态和空间展布规律的深入研究,揭示了郯庐断裂带在莱州湾地区新生代以来的构造演化历史:古新世—始新世的伸展阶段、渐新世—中新世早期的挤压和右行走滑阶段、中新世中晚期至今的稳定发展阶段,这几个不同时期的演化阶段主要受太平洋板块运动的方向和速度变化的控制。     

平湖油气田主断裂西部烃源评价及油源对比

平湖油气田主力含油气区位于平湖主断裂以东区域,油源主要来源于东部生烃凹陷的半封闭海湾暗色泥岩和煤层.公司于2011年11月在主断裂西部钻了一口探井XY井,目的是为探测主断裂西部含油气情况,扩大油气储量.结果钻遇油气层12m,测试获日产气14.66×104m3,日产油107.8 m3,取得了一定突破.为进一步评价西部含油气规模,钻后进行了油源对比研究,认为西部的油气主要是东部运移聚集的结果,西部源岩也有一定贡献.西部有形成一定规模油气藏的潜力.     

琼东南盆地深水区东区凹陷带结构构造及其演化特征

琼东南盆地深水区东区凹陷带,即松南—宝岛—长昌凹陷,位于琼东南盆地中央坳陷东端。在大量地震资料解释的基础上,对38条主要断层进行了详细分析。获得以下认识:(1)琼东南盆地深水区东区凹陷带平面上表现为近EW向展布的平行四边形,剖面结构表现为自西向东由半地堑—不对称的地堑—半地堑有规律变化。(2)琼东南盆地深水区东区凹陷带断裂系统可划分控制凹陷边界断层、控制洼陷沉积中心断层和调节性断层3类。(3)琼东南盆地深水区东区凹陷带古近纪时期受到太平洋板块俯冲和南海海盆扩张的双重影响,构造应力场发生NW—SE→SN转变。构造演化可划分为3个阶段:~32 Ma,应力场以区域性NW—SE向伸展为主,断裂系统以NE—SW向为主,控制凹陷边界;32~26 Ma,以南海海盆近SN向拉张应力场为主,断裂系统以NWW—SEE向为主,断层活动控制凹陷沉积中心;26~ Ma,区域性伸展与南海海盆扩张应力均逐渐减弱,NE—SW向和NWW—SEE向断裂继承性发育。(4)琼东南盆地深水区东区凹陷带内部主要断层在渐新统崖城组和陵水组沉积时期活动速率快,地形高差大、沉积水体深、沉积厚度大,控制了崖城组和陵水组的大规模沉积,有利于烃源岩的发育。圈闭以受断层控制的断鼻和断块为主,长昌主洼凹中隆起带发育2个最为理想的构造圈闭。     

斑岩Cu-(Mo-Au)矿床的成矿构造环境及勘查意义

斑岩矿床是重要的矿床勘查目标。斑岩矿床的成矿构造环境研究有助于确定斑岩矿床的战略勘查方向。斑岩矿床形成的成矿构造环境包括板块汇聚边缘、大陆转换板块边界、陆内造山环境和非造山环境。本文重点对斑岩矿床在汇聚边缘和大陆转换板块边界的成矿构造环境及其勘查意义进行初步总结。构造变化对斑岩矿床的形成起到触发作用。微弱和中等程度的转换挤压应力最有利于岩浆的集聚、上升和就位。岩浆侵入可以是在广阔的转换挤压断层带内或在其周围局部呈引张的地区集中出现。对于斑岩矿床战略勘查方向而言,应注意研究区域走滑断层与侵入体的关系,加强对地表浅部喷气蚀变的识别。在我国西南地区已勘查发现的5个斑岩成矿带中,应注意沿区域走滑断裂构造方向开展找矿。从成矿构造环境与哀牢山-红河构造带对比来看,鲜水河-小江断裂带可能是西南地区新的斑岩矿床勘查区。     

The influence of differential sedimentary loading and compaction on the development of a deltaic rollover

Three-dimensional seismic data and wireline logs from the western Niger Delta were analyzed to reveal the sedimentary and tectonic history of a major deltaic growth-fault depocenter comprising a kilometer-scale rollover anticline. The seismic units of the rollover show a non-uniform thickness distribution with their respective maximum near the main bounding growth-fault on the landward side of the system. This wedge-shaped sediment-storage architecture ultimately reflects the non-uniform creation of accommodation space in the study area that was controlled by 1) the differential compaction of the hanging-wall and footwall strata, 2) the lateral variation of fault-induced tectonic subsidence above the listric master fault, and possibly 3) local subsidence related to the subsurface movement of mobile shale reacting to loading and buoyancy. A sequential three-dimensional decompaction of the interpreted deltaic rollover units allowed to reconstruct and measure the compaction development of the rollover succession through time, documenting that sediment compaction contributed per depositional interval to between 25 and 35% of the generation of depositional space subsequently filled by deltaic sediments. The incremental decompaction of sedimentary units was further used to quantify the cumulative amount of accommodation space at and around the studied rollover that was created by fault movement, shale withdrawal, regional tectonic subsidence, isostasy and changes in sea level. If data on the regional subsidence and eustasy are available, the contribution of these basinwide controls to the generation of depositional space can be subtracted from the cumulative accommodation balance, which ultimately quantifies the amount of space for sediments to accumulate created by fault movement or shale withdrawal. This observation is important in that it implies that background knowledge on subsidence, stratigraphic age and sea-level changes allows to reconstruct and quantify fault movement in syn-tectonic deltaic growth successions, and this solely based on hanging-wall isopach trends independent of footwall information.     

Anomalous hydrogen emissions from the San Andreas fault observed at the Cienega Winery,central California

We began continuous monitoring of H₂ concentration in soil along the San Andreas and Calaveras faults in central California in December 1980, using small H₂/O₂ fuel-cell sensors. Ten monitoring stations deployed to date have shown that anomalous H₂ emissions take place occasionally in addition to diurnal changes. Among the ten sites, the Cienega Winery site has produced data that are characterized by very small diurnal changes, a stable baseline, and remarkably distinct spike-like H₂ anomalies since its installation in July 1982. A major peak appeared on 1–10 November 1982, and another on 3 April 1983, and a medium peak on 1 November 1983. The occurrences of these peaks coincided with periods of very low seismicity within a radius of 50 km from the site. In order to methodically assess how these peaks are related to earthquakes, three H₂ degassing models were examined. A plausible correlational pattern was obtained by using a model that (1) adopts a hemicircular spreading pattern of H₂ along an incipient fracture plane from the hypocenter of an earthquake, (2) relies on the FeO–H₂O reaction for H₂ generation, and (3) relates the accumulated amount of H₂ to the mass of serpentinization of underlying ophiolitic rocks; the mass was tentatively assumed to be proportional to the seismic energy of the earthquake.