The Laptev Sea Rift

In north-eastern Siberia the active mid-ocean Gakkel Ridge interacts with the continental shelf of the Laptev Sea. Extension has affected the shelf since at least the Early Tertiary and has resulted in the formation of a complex horst and graben system. We present new seismic data from the Laptev Sea including deep seismic soundings.The most prominent rift basin is the Ust' Lena Rift with a minimum E–W width of 300 km at latitude 75°N and a Cenozoic infill up to 13 km in thickness. The asymmetric shape of the basin and conclusive evidence for a detachment imply a simple-shear geometry. The suggested rift model combines a ramp and flat geometry for the detachment with ductile stretching beneath the detachment. A major west-dipping, hingeline, listric fault separates the Ust' Lena Rift from the Laptev Horst.The 100–150 km wide Laptev Horst is subdivided into three units by narrow rift grabens. Another prominent rift graben is the Anisin Basin, which is located in the northern shelf area.Though the Laptev Sea Rift formed in interaction with an active mid-oceanic ridge, there are indications that the Laptev Sea rift is of the ‘passive rift’ type. The rift was developed east of a SW–NE trending transfer zone which links the Gakkel Ridge to the Laptev Sea Rift.     

Mesozoic rift to post-rift tectonostratigraphy of the Sverdrup Basin,Canadian Arctic

Jurassic-Cretaceous rift successions and basin geometries of the Sverdrup Basin are reconstructed from a review and integration of stratigraphy, igneous records, outcrop maps, and subsurface data. The rift onset unconformity is in the Lower Jurassic portion of the Heiberg Group (approximately 200–190 Ma). Facies transgress from early syn-rift sandstones of the King Christian Formation to marine mudstones of the Jameson Bay Formation. The syn-rift succession of marine mudstones in the basin centre, Jameson Bay to Deer Bay formations, ranges from Early Jurassic (Pleinsbachian) to Early Cretaceous (Valanginian). Early post-rift deposits of the lower Isachsen Formation are truncated by the sub-Hauterivian unconformity, which is interpreted as a break up unconformity at approximately 135–130 Ma. Cessation of rift subsidence allowed for late post-rift sandstone deposits of the Isachsen Formation to be distributed across the entire basin. Marine deposition to form mudstone of the Christopher Formation throughout the Canadian Arctic Islands and outside of the rift basin records establishment of a broad marine shelf during post-rift thermal subsidence at the start of a passive margin stage. The onset of the High Arctic Large Igneous Province at approximately 130 Ma appears to coincide with the breakup unconformity, and it is quite typical that magma-poor rifted margins have mainly post-rift igneous rocks. We extend the magma-poor characterization where rifting is driven by lithospheric extension, to speculatively consider that the records from Sverdrup Basin are consistent with tectonic models of retro-arc extension and intra-continental rifting that have previously been proposed for the Amerasia Basin under the Arctic Ocean.     

Incidence of flexural gravitational waves on the line of contact of two floating ice plates of different thickness

We analyze the influence of a rift in an ice field on the propagation of flexural gravitational waves in a basin of finite constant depth. The ice cover is simulated by two floating semiinfinite elastic plates of different thickness. We studied the dependence of the amplitude coefficients of reflection and transmission of waves incident on the rift on the frequency of running waves, the thickness of ice on both sides of the rift, and the type of contact boundary conditions at the rift. Translated by Peter V. Malyshev and Dmitry, V. Malyshev     

The Gulf of Suez—northern Red Sea neogene rift: a quantitive basin analysis

Subsidence analysis (backstripping) was carried out on a series of wells from the Gulf of Suez and northern Red Sea region of Egypt in order to examine the interplay between tectonic events, basin subsidence, sedimentation and sea level changes in a young, developing ocean basin and continental margin. Using constraints on chronostratigraphy and paleodepth from various sources combined with stratigraphic and structural information from industry wells and other geophysical sources it has been possible to compile the data necessary to perform geohistory analyses throughout the region.Major subsidence due to crustal thinning began ∼25 Ma with sedimentation initially occurring in isolated sub-basins. These earliest sediments record the transition from continental to marine depositional environments. Subsequently during early and middle Miocene times subsidence was rapid and uniform along and across the entire rift basin. Open marine sedimentation occurred across all structural regimes. The mid-Clysmic tectonic event (16.5 Ma) resulted in structural rearrangement of the rift basin and uplift of the rift shoulders. Rapid subsidence continued as global sea level fell, producing a series of prograding, siliciclastic fan-deltas at the rift margins. At ∼15.5 Ma, opening of the Suez rift was terminated, tectonic subsidence decreased dramatically in the southern rift and ceased entirely in the northern rift. Tensional plate motion probably was transferred from the Gulf of Suez to sinistral strike-slip movement on the Dead Sea transform at this time. The quiescence in subsidence combined with a lowered global sea level resulted in the deposition of a thick (up to 4 km) series of evaporites within the central trough of the rift from the middle to latest Miocene. The accumulation of such a thick sequence of sediments during a phase of decreased tectonic subsidence is interpreted as a ‘filling-in’ of the rift topography which developed during the earlier period of rapid subsidence and rift-shoulder uplift and continued compaction.A rapid global sea level rise concomitant with a subsequent pulse of increased tectonic activity in the latest Miocene—earliest Pliocene returned the rift to dominantly marine conditions.     

A seismic reflection study of the External Calabrian Arc in the northern Ionian Sea (eastern Mediterranean)

The External Calabrian Arc is located off the convex side of the Calabro-Peloritanian Arc in the northern Ionian Sea. A systematic reflection seismic survey indicates that it is made of different structural elements whose characters seem consistent with an active accretionary margin. The main structures are the Crotone-Spartivento slope (comparable to an inner trench slope) and the intermediate depressions (comparable to a trench area). Internal to these elements, the Crotone-Spartivento basin may represent a fore-arc basin. This partly outcrops in Calabria and its structure suggests that the accretionary margin developed at least since middle-upper Miocene.Subduction processes do not affect a true oceanic crust, because of the great thickness of sediments covering the whole eastern Mediterranean. Hence some peculiar features occur in the system. as the cobblestone topography, or are lacking, as a typical and continuous trench zone.In the areas with cobblestone topography we distinguish a Calabrian Ridge sensu stricto from a Calabrian Ridge sensu lato. The former is a N-S trending swell, external to the supposed trench zone, interpreted as a sedimentary outer-arc ridge produced by rather surficial tectonic accumulation of sediments further chaoticized by gravitative mechanisms. The Ridge s.l. is a very wide area with low relief and little or no seismic penetration. Tectonization seems gentler than in the Ridge s.s. and structural axes seem to possess different orientations. These areas are interpreted as due to a widespread surficial chaoticization above presumed decollement layers occurring within the sedimentary column of the Ionian bathyal plain.The pattern of deformations of the Calabrian Ridge seems consistent with the Calabro-Peloritanian Arc actively overriding the eastern Mediterranean, with a resultant direction of movement essentially towards the East.     

Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set

In 2001 and 2002, Australia acquired an integrated geophysical data set over the deep-water continental margin of East Antarctica from west of Enderby Land to offshore from Prydz Bay. The data include approximately 7700 km of high-quality, deep-seismic data with coincident gravity, magnetic and bathymetry data, and 37 non-reversed refraction stations using expendable sonobuoys. Integration of these data with similar quality data recorded by Japan in 1999 allows a new regional interpretation of this sector of the Antarctic margin. This part of the Antarctic continental margin formed during the breakup of the eastern margin of India and East Antarctica, which culminated with the onset of seafloor spreading in the Valanginian. The geology of the Antarctic margin and the adjacent oceanic crust can be divided into distinct east and west sectors by an interpreted crustal boundary at approximately 58° E. Across this boundary, the continent–ocean boundary (COB), defined as the inboard edge of unequivocal oceanic crust, steps outboard from west to east by about 100 km. Structure in the sector west of 58° E is largely controlled by the mixed rift-transform setting. The edge of the onshore Archaean–Proterozoic Napier Complex is downfaulted oceanwards near the shelf edge by at least 6 km and these rocks are interpreted to underlie a rift basin beneath the continental slope. The thickness of rift and pre-rift rocks cannot be accurately determined with the available data, but they appear to be relatively thin. The margin is overlain by a blanket of post-rift sedimentary rocks that are up to 6 km thick beneath the lower continental slope. The COB in this sector is interpreted from the seismic reflection data and potential field modelling to coincide with the base of a basement depression at 8.0–8.5 s two-way time, approximately 170 km oceanwards of the shelf-edge bounding fault system. Oceanic crust in this sector is highly variable in character, from rugged with a relief of more than 1 km over distances of 10–20 km, to rugose with low-amplitude relief set on a long-wavelength undulating basement. The crustal velocity profile appears unusual, with velocities of 7.6–7.95 km s⁻¹ being recorded at several stations at a depth that gives a thickness of crust of only 4 km. If these velocities are from mantle, then the thin crust may be due to the presence of fracture zones. Alternatively, the velocities may be coming from a lower crust that has been heavily altered by the intrusion of mantle rocks. The sector east of 58° E has formed in a normal rifted margin setting, with complexities in the east from the underlying structure of the N–S trending Palaeozoic Lambert Graben. The Napier Complex is downfaulted to depths of 8–10 km beneath the upper continental slope, and the margin rift basin is more than 300 km wide. As in the western sector, the rift-stage rocks are probably relatively thin. This part of the margin is blanketed by post-rift sediments that are up to about 8 km thick. The interpreted COB in the eastern sector is the most prominent boundary in deep water, and typically coincides with a prominent oceanwards step-up in the basement level of up to 1 km. As in the west, the interpretation of this boundary is supported by potential field modelling. The oceanic crust adjacent to the COB in this sector has a highly distinctive character, commonly with (1) a smooth upper surface underlain by short, seaward-dipping flows; (2) a transparent upper crustal layer; (3) a lower crust dominated by dipping high-amplitude reflections that probably reflect intruded or altered shears; (4) a strong reflection Moho, confirmed by seismic refraction modelling; and (5) prominent landward-dipping upper mantle reflections on several adjacent lines. A similar style of oceanic crust is also found in contemporaneous ocean basins that developed between Greater India and Australia–Antarctica west of Bruce Rise on the Antarctic margin, and along the Cuvier margin of northwest Australia.     

南太平洋地区盆地形成演化和油气资源潜力分析

本文从南太平洋地区区域构造演化出发,开展盆地类型划分和石油地质条件分析,了解不同类型盆地的油气成藏特征,并分析油气分布规律和资源潜力,以期对未来油气勘探开发国际合作选区提供借鉴。研究表明:（1）南太平洋地区经历了亨特-鲍恩造山运动、澳大利亚板块与南极洲板块分离、塔斯曼海扩张及珊瑚海扩张、巴布亚新几内亚地区的洋壳俯冲和弧-陆碰撞作用,最终形成了澳大利亚东部南缘和海域及新西兰地区以裂谷盆地为主、澳大利亚东部内陆以克拉通盆地为主的包括晚二叠世-三叠纪前陆盆地、古近纪-新近纪前陆盆地、古近纪-现今弧前盆地和弧后盆地6种盆地类型;（2）澳大利亚内陆南缘和东部海域以及新西兰地区裂谷盆地分布广泛,裂谷盆地油气最为富集,但内陆和海域有所差异,内陆南缘裂谷盆地油气资源丰富且石油与天然气的比值约为2:1,而东部海域裂谷盆地因油气成藏条件差,尚无油气发现;（3）根据盆地的剩余可采储量和远景资源量对南太平洋地区的资源潜力进行分析,认为白垩纪-古近纪裂谷盆地和古近纪-新近纪前陆盆地油气资源潜力最大,并优选出吉普斯兰（Gippsland）、塔拉纳基（Taranaki）和巴布亚（Papua）3个有利盆地。     

Seismic stratigraphic framework and depositional sequences in the Santos Basin,Brazil

The Santos Basin, situated offshore southern Brazil, is one of nine marginal rift basins in the equatorial South Atlantic. It formed by the collapse of a thermal dome in the late Jurassic and by subsequent rifting and opening of the South Atlantic in the early Cretaceous. Rifting was accompanied by immense volcanic outpouring seen at the surface today throughout the onshore Paraná Basin and thought to underlie the entire Santos Basin, and the adjacent São Paulo Plateau. Vulcanism was followed by subsidence of up to 10 km from Aptian to Recent time, and a coastal hingeline coincides with the Serra do Mar uplift. The basin depocentre, which is 700 km long, is bounded to the north and south by basement and volcanic highs, respectively. A restricted water circulation in the ocean basin, which prevailed up to the Santonian stage, has important repercussions for the hydrocarbon potential of the area. The nine genetically related basins have collective reserves of ≈ 5 billion barrels of oil and associated gas. A stratigraphic framework, based largely on seismic data, has been erected for the Santos Basin. Seven regional unconformities, or ‘R’ reflections, can be traced throughout the basin and form the boundaries for seismic sequences. Isopaching the seismic sequences defines the principal depositional units in the basin and also shows how the basin depocentre shifted with time. Limited well control has enabled the seismic sequences to be correlated with litho-environmental sequences which more fully reflect the geological evolution and provide a working exploration model. Finally, an attempt has been made to recognize and map seismic facies within the seismic sequences and to predict the lithofacies in areas away from well control     

Structure of the basins of the White Sea rift systems

For the first time, the structure of the sedimentary basins of the Late Proterozoic rift system in the White Sea is characterized based on a set of new marine geological geophysical data such as the results of the common depth point seismic method, gravity and magnetic data, and seismoacoustics. The main tectonic structures in the topography of the heterogeneous basement within the basin of the White Sea are distinguished and described. A structural tectonic scheme of the basement surface is presented. The thicknesses of the sediments are estimated and the stratigraphic confinement of the seismic units recognized is done.     

Distribution of crustal extension and regional basin architecture of the Albertine rift system, East Africa

By applying a kinematic and flexural model for the extensional deformation of the lithosphere, and using a recently available EROS Data Center topography DEM of Africa in conjunction with new and previous gravity data from Lakes Albert, Edward and George, we have determined the distribution, amplitude, and style of deformation responsible for the formation of the Albertine rift system, East Africa. Further, we have been able to approximate the three-dimensional architecture of the Albertine rift basin by analyzing a series of profiles across and along the rift system for which we also estimate the flexural strength of the rifted continental lithosphere and its along-strike variation. Previous modeling studies of the Lake Albert basin either overestimated the flexural strength of the extended lithosphere and/or underestimated the crustal extension. The single most important factor that compromised the success of these modeling efforts was the assumption that crustal extension was limited to the present-day distribution of the rift lakes. The style of deformation appears to have changed with time, beginning with a regionally distributed brittle deformation across the region that lead progressively to the preferential growth and development of the major border faults and antithetic/synthetic faults within the collapsed hangingwall block. Minor fault reactivation within the footwall block appears to be related to the release of bending stresses associated by the flexural uplift of the rift flank topography. By simultaneously matching the observed and modeled topography and free-air gravity across the Albertine rift system, we have determined a cumulative extension ranging from 6 to 16 km with the maximum extension occurring in the central and northern segments of the basin. Crustal extension is not constrained to the lake proper, but extends significantly to the east within the hangingwall block. Effective elastic thickness, T_e, varies between 24 and 30 km and is unrelated to either the amount of extension or the maximum sediment thickness. The variation of T_e relates possibly to small changes in crustal thickness, heterogeneities in crustal composition, and/or variations in radiogenic crustal heat production. Maximum sediment thickness is predicted to be 4.6 km and occurs within the central region of Lake Albert. Low bulk sediment densities, correlating with the location of major lake deltas, may be indicative of present-day sediment overpressures. Our results show that basin geometry is strongly dependent on the cumulative (and distribution) of lithospheric extension and the flexural rigidity of the lithosphere. Thus, in order to determine the total amount of extension responsible for the formation of a basin system, it is necessary to independently constrain the flexural strength of the lithosphere both during and after extension. Conversely, in order to determine the rigidity of extended lithosphere using the stratigraphy and/or geometry of rift basins and passive margins, it is necessary to independently constrain the cumulative extension of the lithosphere.     

台西盆地新生代构造的演化

于１９８６－１９９１年，应用地震地质方法，对台湾海峡的地震地层和地质构造进行调查，采用地震剖面资料，结合区域地质特征，对台西盆地的构造演估进行研究，认为该盆地由厦澎坳陷，乌丘屿坳陷，新竹坳陷和台湾坳陷等组成，其构造演化经历了中生代末－中始新世初始张裂，晚始新世一渐新世全面断裂，中新世构造调整，以及中新世末以来挤压－收缩－封闭等阶段，现今已成为残留陆缘裂谷盆地，是陆缘裂谷从产生到衰亡的一个典型实例。     

南黄海盆地构造特征及油气地质意义

南黄海盆地发育于前南华纪变质基底之上,是一个大型叠合盆地,经历了多期成盆和多期构造改造,形成了海相盆地和中新生代断陷盆地叠合改造型残留盆地。盆地演化历经南华纪—早、中三叠世海相地层发育期、晚白垩世—古近纪箕状断陷发育期和新近纪—第四纪坳陷发育期,为一典型地台—断陷—坳陷多层结构的复合型盆地。通过对地震资料解释、区域地质构造特征分析,综合烃源条件和后期保存条件,探讨了南黄海盆地油气远景。     

辽河盆地大民屯凹陷流体压力特征

大民屯凹陷是辽河断陷内4个下第三系凹陷之一。在综合利用钻井、试井及地震等资料的基础上，系统研究并论述了大民屯凹陷流体压力特征。基于57口井的声波测井资料，凹陷内泥岩压力特征可区分为正常压力、异常压力或强超压等类型；根据152口井391个点的压力测试数据，凹陷内产油层段的压力梯度多接近于1；利用公式法模拟计算了47条地震剖面的流体压力、剩余压力及压力系数的分布特征，凹陷内剖面压力系统自上而下一般由正常压力、弱超压和强超压3部分组成。此外，还根据流体压力演化的基本原理及钻井、岩性与试井等实际资料，模拟恢复了大民屯凹陷的压力演化史，其可划分为超压原始积累、超压部分释放及超压再积聚3个阶段。总体上，大民屯凹陷的超压强度低于渤海湾盆地其他地区的超压强度。     

Characteristics of seismic reflections in central region of the South China Sea and their geological significance

I~IOXThe speCiality in gootectonic position and complicity in origin and evolution of the sleuth China Sea (SCS) has aroused particular attention of the geoscientists at home and abroad. The central region, which consists of continental slope, island slope and a deep-sea basin, is an importantarea for the study of the mechanism of origin and evolution of the SCS. In addition to the surveysof bathemetry, gravity and magnetism, seismic surveys have been carried out by domestic andforeign in…     

Deep Crustal Structure of the Continental Margin off the Explora Escarpment and in the Lazarev Sea, East Antarctica

This study presents the results of a seismic refraction experiment that was carried out off Dronning Maud Land (East Antarctica) along the Explora Escarpment (14° W–12° W) and close to Astrid Ridge (6°E). Oceanic crust of about 10 km thickness is observed northwest of the Explora Escarpment. Stretched continental crust, observed southeast of the escarpment, is most likely intruded by volcanic material at all crustal levels. Seismic velocities of 7.0–7.4 km/s are modelled for the lower crust. The northern boundary of this high velocity body coincides approximately with the Explora Escarpment. The upper crystalline crust is overlain by a 4-km thick and 70-km wide wedge of volcanic material: the Explora Wedge. Seismic velocities for the oceanic crust north of the Explora Escarpment are in good agreement with global studies. The oceanic crust in the region of the Lazarev Sea is also up to 10-km thick. The lower crystalline crust shows seismic velocities of up to 7.4 km/s. This, together with the larger crustal thickness might point to higher mantle temperatures during the formation of the oceanic crust. The more southerly rifted continental crust is up to 25-km thick, and also has seismic velocities of 7.4 km/s in the lower crystalline crust. This section is interpreted to consist of stretched continental crust, which is heavily intruded by volcanic material up to approximately 8-km depth. Multichannel seismic data indicate that, in this region, two volcanic wedges are present. The wedges are interpreted to have evolved during different time/rift periods. The wedges have a total width of at least 180 km in the Lazarev Sea. Our results support previous findings that the continental margin off Dronning Maud Land between ≈2°E and ≈13°E had a complex and long-lived rift history. Both continental margins can be classified as rifted volcanic continental margins that were formed during break-up of Gondwana.     

Tectonic and sedimentary processes along the ultraslow Knipovich spreading ridge

2D multichannel seismic data and bathymetric records from the glaciated western Svalbard margin and the rift valley region of the ultraslow, and oblique-spreading, Knipovich Ridge are in this study interpreted to infer differences in seafloor spreading mechanisms and to identify sedimentary processes. Our results show that the rift flank geometry, the rift valley elevation and the active magmatism are closely linked. The inferred magmatic segments of the Knipovich Ridge exhibit high and steep rift flanks, whereas the rift flank heights of the proposed tectonic-dominated segments are lower and less steep. In addition, we observe significant rift flank asymmetry across the rift valley which can be partly explained by subsidence due to sediment loading. The identification of a huge sedimentary wedge on the western rift flank suggests that the oldest parts of these sediments have been transported from the western Svalbard margin and across the rift valley. However, we suggest that most of these sediments are glacimarine/hemipelagic sediments which have been deposited in the time period after the rift valley flanks had developed sufficiently to cut off the direct transport routes from the western Svalbard margin. We also observe thick current depositions on the western side, suggesting a strong along-slope influence of the West Spitsbergen Current during the Plio–Pleistocene time period.     

莫桑比克盆地构造演化与沉积充填特征

在阅读相关文献资料的基础上,分析了莫桑比克盆地的区域性幕式构造演化,并进一步总结归纳了其沉积充填特征。研究显示该盆地为东非边缘陆内裂谷盆地,以晚侏罗世破裂不整合面为界划分为断陷期及坳陷期,断陷期为陆相湖盆沉积充填,进入坳陷期后逐渐从海陆过渡相向浅海相和深水相演变。晚白垩世末和渐新世末两次构造抬升,使得盆地沉积环境及物源供应发生明显改变,也逐渐从深水相向滨浅海相或三角洲相演变。     

Depositional processes and stratigraphic architecture within a coarse-grained rift-margin turbidite system: The Wollaston Forland Group,east Greenland

The Wollaston Forland Basin, NE Greenland, is a half-graben with a Middle Jurassic to Lower Cretaceous basin-fill. In this outcrop study we investigate the facies, architectural elements, depositional environments and sediment delivery systems of the deep marine syn-rift succession. Coarse-grained sand and gravel, as well as large boulders, were emplaced by rock-falls, debris flows and turbulent flows sourced from the immediate footwall. The bulk of these sediments were point-sourced and accumulated in a system of coalescing fans that formed a clastic wedge along the boundary fault system. In addition, this clastic wedge was supplied by a sand-rich turbidite system that is interpreted to have entered the basin axially, possibly via a prominent relay ramp within the main fault system. The proximal part of the clastic wedge consists of a steeply dipping, conformable succession of thick-bedded deposits from gravity flows that transformed down-slope from laminar to turbulent flow behaviour. Pervasive scour-and-fill features are observed at the base of the depositional slope of the clastic wedge, c. 5 km into the basin. These scour-fills are interpreted to have formed from high-density turbulent flows that were forced to decelerate and likely became subject to a hydraulic jump, forming plunge pools at the base of slope. The distal part of the wedge represents a basin plain environment and is characterised by a series of crude fining upward successions that are interpreted to reflect changes in the rate of accommodation generation and sediment supply, following from periodic increases in fault activity. This study demonstrates how rift basin physiography directly influences the behaviour of gravity flows. Conceptual models for the stratigraphic response to periodic fault activity, and the transformation and deposition of coarse-grained gravity flows in a deep water basin with strong contrasts in slope gradients, are presented and discussed.     

Three-dimensional facies architecture analysis using sequence stratigraphy and seismic sedimentology: Example from the Paleogene Dongying Formation in the BZ3-1 block of the Bozhong Sag,Bohai Bay Basin,China

The Bohai Bay Basin is a classic non-marine rift basin in eastern China. The Paleogene Dongying sequences are the main hydrocarbon-bearing stratigraphic unit in the basin. Using three-dimensional (3-D) seismic data and one well control in the BZ3-1 Block in the western slope of the Bozhong Sag, we analyzed 3-D facies architectures of the Dongying sequences. The Dongying Formation, a second-order sequence, can be subdivided into four third-order sequences (from base to top: SQ1, SQ2, SQ3, and SQ4). The facies architecture was analyzed by using the seismic sedimentology approach based on 3-D seismic data. Sediment of the Dongying sequences was derived from the northern Shijiutuo Uplift via four major configurations of incised valleys, namely “V”, “U”, “W”, and composite shaped incised valleys. Seismic stratal slices reveal branching and converging characteristics of the channels from upstream to downstream. On the basis of an integrated analysis of well log, core data, seismic facies based on multi-seismic attributes, three sedimentary facies (e.g., “delta”, “fan-delta”, and “shore” or “shallow lacustrine” facies) have been recognized. The four types of incised valleys and their evolution control the sedimentary systems in the sedimentation area. The numbers and sizes of the fans are controlled by the sedimentary systems at various scales. Incised valley-fill and deltaic sand bodies are excellent hydrocarbon reservoirs and potentially good exploration targets for the study area. The reservoir quality of sequences SQ1, SQ2, and SQ3 become better gradually from base to top. The proposed sediment dispersal patterns may aid in the prediction of potential reservoir distribution. This study also demonstrates that facies architecture analysis using sequence stratigraphy and seismic sedimentology may serve as an effective approach for constructing 3D facies models for petroleum exploration in areas lacking of well or outcrop data.     

Lithospheric structure below the eastern Arabian Sea and adjoining West Coast of India based on integrated analysis of gravity and seismic data

Four uniformly spaced regional gravity traverses and the available seismic data across the western continental margin of India, starting from the western Indian shield extending into the deep oceanic areas of the eastern Arabian Sea, have been utilized to delineate the lithospheric structure. The seismically constrained gravity models along these four traverses suggest that the crustal structure below the northern part of the margin within the Deccan Volcanic Province (DVP) is significantly different from the margin outside the DVP. The lithosphere thickness, in general, varies from 110–120 km in the central and southern part of the margin to as much as 85–90 km below the Deccan Plateau and Cambay rift basin in the north. The Eastern basin is characterised by thinned rift stage continental crust which extends as far as Laxmi basin in the north and the Laccadive ridge in the south. At the ocean–continent transition (OCT), crustal density differences between the Laxmi ridge and the Laxmi basin are not sufficient to distinguish continental as against an oceanic crust through gravity modeling. However, 5-6 km thick oceanic crust below the Laxmi basin is a consistent gravity option. Significantly, the models indicate the presence of a high density layer of 3.0 g/cm³ in the lower crust in almost whole of the northern part of the region between the Laxmi ridge and the pericontinental northwest shield region in the DVP, and also below Laccadive ridge in the southern part. The Laxmi ridge is underlain by continental crust upto a depth of 11 km and a thick high density material (3.0 g/cm³) between 11–26 km. The Pratap ridge is indicated as a shallow basement high in the upper part of the crust formed during rifting. The 15 –17 km thick oceanic crust below Laccadive ridge is seen further thickened by high density underplated material down to Moho depths of 24–25 km which indicate formation of the ridge along Reunion hotspot trace.