Neotectonics of the Somogy hills (Part II): Evidence from seismic sections

The Somogy hills are located in the Pannonian Basin, south of Lake Balaton, Hungary, above several important tectonic zones. Analysis of industrial seismic lines shows that the pre-Late Miocene substratum is deformed by several thrust faults and a transpressive flower structure. Basement is composed of slices of various Palaeo-Mesozoic rocks, overlain by sometimes preserved Paleogene, thick Early Miocene deposits. Middle Miocene, partly overlying a post-thrusting unconformity, partly affected by the thrusts, is also present. Late Miocene thick basin-fill forms onlapping strata above a gentle paleo-topography, and it is also folded into broad anticlines and synclines. These folds are thought to be born of blind fault reactivation of older thrusts. Topography follows the reactivated fold pattern, especially in the central-western part of the study area.

The map pattern of basement structures shows an eastern area, where NE–SW striking thrusts, folds and steep normal faults dominate, and a western one, where E–W striking thrusts and folds dominate. Folds in Late Neogene are also parallel to these directions. A NE–SW striking linear normal fault and associated N–S faults cut the highest reflectors. The NE–SW fault is probably a left-lateral master fault acting during–after Late Miocene. Gravity anomaly and Pleistocene surface uplift maps show a very good correlation to the mapped structures. All these observations suggest that the main Early Miocene shortening was renewed during the Middle and Late Miocene, and may still persist.

Two types of deformational pattern may explain the structural and topographic features. A NW–SE shortening creates right-lateral slip along E–W faults, and overthrusts on NE–SW striking ones. Another, NNE–SSW shortening creates thrusting and uplift along E–W striking faults and transtensive left-lateral slip along NE–SW striking ones. Traces of both deformation patterns can be found in Quaternary exposures and they seem to be consistent with the present day stress orientations of the Pannonian Basin, too. The alternation of stress fields and multiple reactivation of the older fault sets is thought to be caused by the northwards translation and counter-clockwise rotation of Adria and the continental extrusion generated by this convergence.     

Tectonic Control of the Triassic Santa Maria Supersequence of the Paraná Basin, Southernmost Brazil, and its Correlation to the Waterberg Basin, Namibia

The Middle and Late Triassic Santa Maria Basin, exposed in southernmost Brazil, and Waterberg Basin, in Namibia, are herein interpreted as part of en échelon small basins in southern West Gondwana. The main structures are the Waterberg-Omaruru Fault which can be connected to a NW-strike anastomosed fault zone in Brazil. Based on field structural and stratigraphic analysis two populations of NW-strike fractures, named A-type and B-type, are recognized. A-type fractures (Az = 280°-290°) occur in the Sanga do Cabral Supersequence, underlying units of Santa Maria Basin, as extension of the Waterberg-Omaruru Fault during the Early Triassic. B-type fractures (Az = 295°-345°) are observed in all studied stratigraphic units, from the Triassic Sanga do Cabral Supersequence to the Early Cretaceous Botucatu/Serra Geral formations. Based on the structural analysis we propose that NNE-SSW extension reactivated structures of the Damara Belt, Namibia, with a propagation towards Rio Grande do Sul State forming an anastomosing normal fault system and related-rift basin by Early-Middle Triassic time. The A-type fractures were preferentially active by this phase and the B-type ones are interpreted as secondary link segments within the anastomosing system. During the Gondwana break-up and South Atlantic opening (rift to proto-oceanic phase, Aptian) the B-type fractures were reactivated as normal faults by N50°E-S50°W extension.     

Structure and tectonics along the inner edge of a foreland basin: The Hunter Coalfield in the northern Sydney Basin,New South Wales

From the early Late Permian onwards, the northeastern part of the Sydney Basin, New South Wales, (encompassing the Hunter Coalfield) developed as a foreland basin to the rising New England Orogen lying to the east and northeast. Structurally, Permian rocks in the Hunter Coalfield lie in the frontal part of a foreland fold‐thrust belt that propagated westwards from the adjacent New England Orogen. Thrust faults and folds are common in the inner part of the Sydney Basin. Small‐scale thrusts are restricted to individual stratigraphic units (with a major ‘upper decollement horizon’ occurring in the mechanically weak Mulbring Siltstone), but major thrusts are inferred to sole into a floor thrust at a poorly constrained depth of approximately 3 km. Folds appear to have formed mainly as hangingwall anticlines above these splaying thrust faults. Other folds formed as flat‐topped anticlines developed above ramps in that floor thrust, as intervening synclines ahead of such ramp anticlines, or as decollement folds. These contractional structures were overprinted by extensional faults developed during compressional deformation or afterwards during post‐thrusting relaxation and/or subsequent extension. The southern part of the Hunter Coalfield (and the Newcastle Coalfield to the east) occupies a structural recess in the western margin of the New England Orogen and its offshore continuation, the Currarong Orogen. Rocks in this recess underwent a two‐stage deformation history. West‐northwest‐trending stage one structures such as the southern part of the Hunter Thrust and the Hunter River Transverse Zone (a reactivated syndepositional transfer fault) developed in response to maximum regional compression from the east‐northeast. These were followed by stage two folds and thrusts oriented north‐south and developed from maximum compression oriented east‐west. The Hunter Thrust itself was folded by these later folds, and the Hunter River Transverse Zone underwent strike‐slip reactivation.     

Structural evolution of a normal fault array in the Gambier Embayment,offshore Otway Basin,South Australia: insights from 3D seismic data

This study was undertaken to determine the structural evolution of a normal fault array using detailed kinematic analysis of normal fault tip propagation and linkage, adding to the growing pool of research on normal fault growth. In addition, we aim to provide further insight into the evolution of the offshore Otway Basin, Australia. We use three-dimensional (3D) seismic reflection data to analyse the temporal and spatial evolution of a Late Cretaceous–Cenozoic age normal fault array located in the Gambier Embayment of the offshore Otway Basin, South Australia. The seismic reflection data cover a NW–SE-oriented normal fault array consisting of six faults, which have grown from the linkage of numerous, smaller segments. This fault array overlies and has partial dip-linkage to E–W-striking, basement-involved faults that formed during the initial Tithonian–Barremian rifting event in the Otway Basin. Fault displacement analysis suggests four key stages in the post-Cenomanian growth history of the upper array: (1) nucleation of the majority of faults resulting from resumed crustal extension during the early Late Cretaceous; (2) an intra-Late Cretaceous period of general fault dormancy, with the nucleation of only one newly formed fault; (3) latest Cretaceous nucleation of another newly formed fault and further growth of all other faults; and (4) continued growth of all faults, leading to the formation of the Cenozoic Gambier Sub-basin in the Otway Basin. Our analysis also demonstrates that Late Cretaceous faults, which are located above and dip-link to basement-involved faults, display earlier nucleation and greater overall throw and length, compared with those which do not link to basement-involved faults. This is likely attributed to increased rift-related stress concentrations in cover sediments above the upper tips of basement faults. This study improves our understanding of the geological evolution of the presently under-explored Gambier Embayment, offshore Otway Basin, South Australia by documenting the segmented growth style of a Late Cretaceous normal fault array that is located over, and interacts with, a reactivated basement framework.     

Structural interpretation and hydrocarbon potential of Balkassar oil field,eastern Potwar,Pakistan, using seismic 2D data and petrophysical analysis

The Balkassar oil field is situated in the eastern Potwar sub-basin, lies on the southern flank of Soan syncline in Himalayan collisional regime. The area represents Indo-Pak and Eurasian blocks of Precambrian to recent time. Thrusting and folding of Himalayan, Indo-Pak plate movement and Salt Range uplift form the structural trap in Balkassar sub-surface (Balkassar anticline). On the basis of information from eleven seismic 2D lines and wells data six reflectors well data, four faults were identified and marked. The structural trend is northeast southwest. Interpretation of seismic 2D data reveals that the study area has undergone intense deformation as a consequence of development of thrusts and backthrusts.The Balkassar anticline is bounded by two thrust faults one from southeast and the other from northwest. Time and depth contour models shows that anticline limbs at north-western side are steep as compared to south-eastern limbs. Seismic interpretation indicates the presence of well-developed anticline bounded by three faults in the cover sequence and one fault in basement and thus the structure may act as a trap for hydrocarbons. The petrophysical analysis of Balkassar-OXY-1 well shows about 83.1% hydrocarbons saturation in the reservoir rocks, hence this study suggest that Balkassar Oilfield has potential to produce hydrocarbons.     

Geological evolution and structural style of the Palaeozoic Tafilalt sub‐basin,eastern Anti‐Atlas (Morocco,North Africa)

The Tafilalt is one of a number of generally unexplored sub‐basins in the eastern Anti‐Atlas of Morocco, all of which probably underwent a similar tectono‐stratigraphic evolution during the Palaeozoic Era. Analysis of over 1000 km of 2‐D seismic reflection profiles, with the interpretation of ten regional seismic sections and five isopach and isobath maps, suggests a multi‐phase deformation history for the Palaeozoic‐aged Tafilalt sub‐basins. Extensional phases were probably initiated in the Cambrian, followed by uniform thermal subsidence up to at least the end of the Silurian. Major extension and subsidence did not begin prior to Middle/Upper Devonian times. Extensional movements on the major faults bounding the basin to the north and to the south took place in synchronisation with Upper Devonian sedimentation, which provides the thickest part of the sedimentary sequence in the basin. The onset of the compressional phase in Carboniferous times is indicated by reflectors in the Carboniferous sequence progressively onlapping onto the Upper Devonian sequence. This period of compression developed folds and faults in the Upper Palaeozoic‐aged strata, producing a structural style characteristic of thin‐skinned fold and thrust belts. The Late Palaeozoic units are detached over a regional décollement with a northward tectonic vergence. The folds have been formed by the process of fault‐propagation folding related to the thrust imbricates that ramp up‐section from the décollement. Copyright © 2007 John Wiley & Sons, Ltd.     

Modelling cover deformation and decoupling during inversion,using the Mid-Polish Trough as a case study

Seismic sections across the NW part of the Polish Basin show that thrust faults developed in the sedimentary units above the Zechstein evaporite layer during basin inversion. These cover thrust faults have formed above the basement footwall. Based on the evolution of the basin, a series of scaled analogue models was carried out to study interaction between a basement fault and cover sediments during basin extension and inversion. During model extension, a set of normal faults originated in the sand cover above the basement fault area. The distribution and geometry of these faults were dependent on the thickness of a ductile layer and pre-extension sand layer, synkinematic deposition, the amount of model extension, as well as on the presence of a ductile layer between the cover and basement. Footwall cover was faulted away from the basement only in cases where a large amount of model extension and hanging-wall subsidence were not balanced by synkinematic deposition. Model inversion reactivated major cover faults located above the basement fault tip as reverse faults, whereas other extensional faults were either rotated or activated only in their upper segments, evolving into sub-horizontal thrusts. New normal or reverse faults originated in the footwall cover in models which contained a very thin pre-extension sand layer above the ductile layer. This was also the case in the highly extended and shortened model in which synkinematic hanging-wall subsidence was not balanced by sand deposition during model extension. Model results show that inversion along the basement fault results in shortening of the cover units and formation of thrust faults. This scenario happens only when the cover units are decoupled from the basement by a ductile layer. Given this, we argue that the thrusts in the sedimentary infill of the Polish Basin, which are decoupled from the basement tectonics by Zechstein evaporites, developed due to the inversion of the basement faults during the Late Cretaceous-Early Tertiary.     

Late Cenozoic transtensional fault belt discovered on the boundary of the Awati Sag in the northwestern Tarim Basin

Late Cenozoic transtensional fault belt was discovered on Shajingzi fault belt, NW boundary of the Awati Sag in the northwestern Tarim Basin. And numerous Quaternary normal faults were discovered on Aqia and Tumuxiuke fault belts, SW boundary of Awati. This discovery reveals Quaternary normal fault activity in the Tarim Basin for the first time. It is also a new discovery in the southern flank of Tianshan Mountains. Shajingzi transtensional fault belt is made up of numerous, small normal faults. Horizontally, the normal faults are arranged in right-step, en echelon patterns along the preexisting Shajingzi basement fault, forming a sinistral transtensional normal fault belt. In profile, they cut through the Paleozoic to the mid-Quaternary and combine to form negative flower structures. The Late Cenozoic normal faults on the SW boundary of Awati Sag were distributed mainly in the uplift side of the preexisting Aqia and Tumuxiuke basement-involved faults, and combined to form small horst and graben structures in profile. Based on the intensive seismic interpretation, careful fault mapping, and growth index analysis, we conclude that the normal fault activity of Shajingzi transtensional fault belt began from Late Pliocene and ceased in Late Pleistocene (mid-Quaternary). And the normal faulting on the SW boundary of Awati Sag began from the very beginning of Quaternary and ceased in Pleistocene. The normal faulting on Awati’s SW boundary began a little later than those on the NW boundary. The origin of Shajingzi transtensional normal fault belt was due to the left-lateral strike-slip occurred in the southern flank of Tianshan, and then, due to the eastward escape of the Awati block, a tensional stress developed the normal faults on its SW boundary.     

陡倾逆断层形成机制——以塔里木盆地色力布亚断层为例

中国西部盆地多发育陡倾逆冲断层,但对其成因仍未取得统一认识。色力布亚断裂带位于塔里木盆地的西部,是一条典型的陡倾逆冲断层,为研究陡倾断层的成因提供了很好的实例。根据最新地震剖面与地层分析认为,色力布亚断裂上部倾角约为65°,经两期构造运动形成,第一期是加里东晚期运动-海西早期运动（362~439 Ma）,第二期为喜马拉雅中期运动（5.3~23.3 Ma）;正是断层的多期活动形成了上部的陡倾断层,即先存缓倾逆断层的活动改变了局部应力场,使最大主应力轴由水平变倾斜,随之产生的库伦断裂倾角变陡,并伴生反冲逆断层。同时利用数字砂箱模拟结果验证了上述推断。      

Polyphase late Palaeozoic deformation in the southeastern foreland and northwestern Piedmont of the Alabama Appalachians

Late Palaeozoic deformation in the southern Appalachians is believed to be related to the collisional events that formed Pangaea. The Appalachian foreland fold and thrust belt in Alabama is a region of thin-skinned deformed Palaeozoic sedimentary rocks ranging in age from Early Cambrian to Late Carboniferous, bounded to the northwest by relatively undeformed rocks of the Appalachian Plateau and to the southeast by crystalline thrust sheets containing metasedimentary and metaigneous rocks ranging in age from late Precambrian to Early Devonian. A late Palaeozoic kinematic sequence derived for a part of this region indicates complex spatial and temporal relationships between folding, thrusting, and tectonic level of décollement. Earliest recognized (Carboniferous(?) or younger) compressional deformation in the foreland, observable within the southernmost thrust sheets in the foreland, is a set of large-scale, tight to isoclinal upright folds which preceded thrafing, and may represent the initial wave of compression in the foreland. Stage 2 involved emplacement of low-angle far-traveled thrust sheets which cut Lower Carboniferous rocks and cut progressively to lower tectonic levels to the southwest, terminating with arrival onto the foreland rocks of a low-grade crystalline nappe. Stage 3 involved redeformation of the stage 2 nappe pile by large-scale upright folds oriented approximately parallel to the former thrusts and believed to be related to ramping or imbrication from a deeper décollement in the foreland rocks below. Stage 4 involved renewed low-angle thrusting within the Piedmont rocks, emplacement of a high-grade metamorphic thrust sheet, and decapitation of stage 3 folds. Stage 5 is represented by large-scale cross-folding at a high angle to previous thrust boundaries and fold phases, and may be related to ramping or imbrication on deep décollements within the now mostly buried Ouachita orogen thrust belt to the southwest. Superposed upon these folds are stage 6 high-angle thrust faults with Appalachian trends representing the youngest (Late Carboniferous or younger, structures in the kinematic sequence.     

Structural controls on the evolution of the Kutai Basin,East Kalimantan

The Kutai Basin formed in the middle Eocene as a result of extension linked to the opening of the Makassar Straits and Philippine Sea. Seismic profiles across the northern margin of the Kutai Basin show inverted middle Eocene half-graben oriented NNE–SSW and N–S. Field observations, geophysical data and computer modelling elucidate the evolution of one such inversion fold. NW–SE and NE–SW trending fractures and vein sets in the Cretaceous basement have been reactivated during the Tertiary. Offset of middle Eocene carbonate horizons and rapid syn-tectonic thickening of Upper Oligocene sediments on seismic sections indicate Late Oligocene extension on NW–SE trending en-echelon extensional faults. Early middle Miocene (N7–N8) inversion was concentrated on east-facing half-graben and asymmetric inversion anticlines are found on both northern and southern margins of the basin. Slicken-fibre measurements indicate a shortening direction oriented 290°–310°. NE–SW faults were reactivated with a dominantly dextral transpressional sense of displacement. Faults oriented NW–SE were reactivated with both sinistral and dextral senses of movement, leading to the offset of fold axes above basement faults. The presence of dominantly WNW vergent thrusts indicates likely compression from the ESE. Initial extension during the middle Eocene was accommodated on NNE–SSW, N–S and NE–SW trending faults. Renewed extension on NW–SE trending faults during the late Oligocene occurred under a different kinematic regime, indicating a rotation of the extension direction by between 45° and 90°. Miocene collisions with the margins of northern and eastern Sundaland triggered the punctuated inversion of the basin. Inversion was concentrated in the weak continental crust underlying both the Kutai Basin and various Tertiary basins in Sulawesi whereas the stronger oceanic crust, or attenuated continental crust, underlying the Makassar Straits, acted as a passive conduit for compressional stresses.     

3D seismic analysis of gravity-driven and basement influenced normal fault growth in the deepwater Otway Basin,Australia

We use three-dimensional (3D) seismic reflection data to analyse the structural style and growth of a normal fault array located at the present-day shelf-edge break and into the deepwater province of the Otway Basin, southern Australia. The Otway Basin is a Late Jurassic to Cenozoic, rift-to-passive margin basin. The seismic reflection data images a NW-SE (128–308) striking, normal fault array, located within Upper Cretaceous clastic sediments and which consists of ten fault segments. The fault array contains two hard-linked fault assemblages, separated by only 2 km in the dip direction. The gravity-driven, down-dip fault assemblage is entirely contained within the 3D seismic survey, is located over a basement plateau and displays growth commencing and terminating during the Campanian-Maastrichtian, with up to 1.45 km of accumulated throw (vertical displacement). The up-dip normal fault assemblage penetrates deeper than the base of the seismic survey, but is interpreted to be partially linked along strike at depth to major basement-involved normal faults that can be observed on regional 2D seismic lines. This fault assemblage displays growth initiating in the Turonian-Santonian and has accumulated up to 1.74 km of throw.Our detailed analysis of the 3D seismic data constraints post-Cenomanian fault growth of both fault assemblages into four evolutionary stages: [1] Turonian-Santonian basement reactivation during crustal extension between Australia and Antarctica. This either caused the upward propagation of basement-involved normal faults or the nucleation of a vertically isolated normal fault array in shallow cover sediments directly above the reactivated basement-involved faults; [2] continued Campanian-Maastrichtian crustal extension and sediment loading eventually created gravitational instability on the basement plateau, nucleating a second, vertically isolated normal fault array in the cover sediments; [3] eventual hard-linkage of fault segments in both fault arrays to form two along-strike, NW-SE striking fault assemblages, and; [4] termination of fault growth in the latest Maastrichtian. We document high variability of throw along-strike and down-dip for both fault assemblages, thereby providing evidence for lateral and vertical segment linkage. Our results highlight the complexities involved in the growth of both gravity-driven normal fault arrays (such as those present in the Niger Delta and Gulf of Mexico) and basement-linked normal fault arrays (such as those present in the North Sea and Suez Rift) with the interaction of an underlying and reactivating basement framework. This study provides an excellent example of spatial variability in growth of two normal fault assemblages over relatively short spatial scales (∼2 km separation down-dip).     

鄂尔多斯盆地南缘寒武纪同沉积伸展断裂系统及其成因机制分析

由于复杂的构造叠加及严重的覆盖,人们对鄂尔多斯盆地早古生代深部结构的研究仍很薄弱。本文主要通过地震数据处理和解释,结合野外地质调查,发现在寒武纪时期,盆地的南缘发育了一套北东向和近东西向的正断裂系统。作者对这套断裂系统的平面及剖面特征进行了详细的描述和分析,并结合区域地质背景探讨了其成因机制,结果表明该套断裂系统主要是由于先存的元古宙北东向基底断层在寒武纪时期发生了继承性活动而形成,同时在断裂系统的局部区段派生出了东西向展布的小规模新生断层。这套断裂系统的发现可能对鄂尔多斯盆地南缘在寒武纪的演化认识及油气勘探具有一定的启示意义。     

Platform margins, reef facies, and microbial carbonates; a comparison of Devonian reef complexes in the Canning Basin, Western Australia, and the Guilin region, South China

Devonian reef complexes were well developed in Western Australia and South China, but no detailed direct comparison has been made between reef building in the two regions. The regions differ in several respects, including tectonic, stratigraphic and palaeoceanographic–palaeogeographic settings, and the reef building styles reflect minor differences in reef builders and reef facies. Similarities and differences between the two reef complexes provide insights into the characteristics of platform margins, reef facies and microbial carbonates of both regions. Here we present a comparison of platform margin types from different stratigraphic positions in the Late Devonian reef complex of the Canning Basin, Western Australia and Middle and Late Devonian margin to marginal slope successions in Guilin, South China. Comparisons are integrated into a review of the reefal stratigraphy of both regions. Reef facies, reef complex architecture, temporal reef builder associations, 2nd order stratigraphy and platform cyclicity in the two regions were generally similar where the successions overlap temporally. However, carbonate deposition began earlier in South China. Carbonate complexes were also more widespread in South China and represent a thicker succession overall. Platforms in the Canning Basin grew directly on Precambrian crystalline basement or early Palaeozoic sedimentary rocks, but in South China, carbonate complexes developed conformably on older Devonian siliciclastic strata. Pre-Frasnian reef facies in South China had more abundant skeletal frameworks than in Canning Basin reefs of equivalent age, and Famennian shoaling margins containing various microbial reefs may have been more common and probably more diverse in South China. However, Late Devonian platform margin types have been documented more completely in the Canning Basin. Deep intra-platform troughs (deep depressions containing non-carbonate pelagic sediments — Nandan-type successions) that developed along syndepositional faults characterize Devonian carbonate platforms in South China, but have no equivalent on the Lennard Shelf, Canning Basin where inter-reef areas were more shallow. The South China platform-to-depression pattern was generally continuous from the Lower to Upper Devonian, indicating that many pre-Devonian tectonic features continued to exercise considerable effect through deposition. Localized, fault-controlled subsidence was an important factor in both regions, but similarities in 2nd order aggradation–progradation cycles suggest that eustasy was also an important control on the larger scale stratigraphic development of both regions.     

Spatial Characteristics and Controlling Factors of the Strike‐slip Fault Zones in the Northern Slope of Tazhong Uplift,Tarim Basin: Insight from 3D Seismic Data

The detailed characteristics of the Paleozoic strike-slip fault zones developed in the northern slope of Tazhong uplift are closely related to hydrocarbon explorations. In this study, five major strike-slip fault zones that cut through the Cambrian-Middle Devonian units are identified, by using 3D seismic data. Each of the strike-slip fault zones is characterized by two styles of deformation, namely deeper strike-slip faults and shallower en-echelon faults. By counting the reverse separation of the horizon along the deeper faults, activity intensity on the deeper strike-slip faults in the south is stronger than that on the northern ones. The angle between the strike of the shallower en-echelon normal faults and the principal displacement zone(PDZ) below them is likely to have a tendency to decrease slightly from the south to the north, which may indicate that activity intensity on the shallower southern en-echelon faults is stronger than that on the northern ones. Comparing the reverse separation along the deeper faults and the fault throw of the shallower faults, activity intensity of the Fault zone S1 is similar across different layers, while the activity intensity of the southern faults is larger than that of the northern ones. It is obvious that both the activity intensity of the same layer in different fault zones and different layers in the same fault zone have a macro characteristic in that the southern faults show stronger activity intensity than the northern ones. The Late Ordovician décollement layer developed in the Tazhong area and the peripheral tectonic events of the Tarim Basin have been considered two main factors in the differential deformation characteristics of the strike-slip fault zones in the northern slope of Tazhong uplift. They controlled the differences in the multi-level and multi-stage deformations of the strike-slip faults, respectively. In particular, peripheral tectonic events of the Tarim Basin were the dynamic source of the formatting and evolution of the strike-slip fault zones, and good candidates to accommodate the differential activity intensity of these faults.     

Influence of syn-sedimentary faults on orogenic structure: examples from the Neoproterozoic–Mesozoic east Siberian passive margin

The east margin of the Siberian craton is a typical passive margin with a thick succession of sedimentary rocks ranging in age from Mesoproterozoic to Tertiary. Several zones with distinct structural styles are recognized and reflect an eastward-migrating depocenter. Mesozoic orogeny was preceded by several Mesoproterozoic to Paleozoic tectonic events. In the South Verkhoyansk, the most intense pre-Mesozoic event, 1000–950 Ma rifting, affected the margin of the Siberian craton and formed half-graben basins, bounded by listric normal faults. Neoproterozoic compressional structures occurred locally, whereas extensional structures, related to latest Neoproterozoic–early Paleozoic rifting events, have yet to be identified. Devonian rifting is recognized throughout the eastern margin of the Siberian craton and is represented by numerous normal faults and local half-graben basins.Estimated shortening associated with Mesozoic compression shows that the inner parts of ancient rifts are now hidden beneath late Paleozoic–Mesozoic siliciclastics of the Verkhoyansk Complex and that only the outer parts are exposed in frontal ranges of the Verkhoyansk thrust-and-fold belt. Mesoproterozoic to Paleozoic structures had various impacts on the Mesozoic compressional structures. Rifting at 1000–950 Ma formed extensional detachment and normal faults that were reactivated as thrusts characteristic of the Verkhoyansk foreland. Younger Neoproterozoic compressional structures do not display any evidence for Mesozoic reactivation. Several initially east-dipping Late Devonian normal faults were passively rotated during Mesozoic orogenesis and are now recognized as west-dipping thrusts, but without significant reactivation displacement along fault surfaces.     

Structures associated with inversion of the Donbas Foldbelt (Ukraine and Russia)

The Donbas Foldbelt is part of the Prypiat–Dnieper–Donets intracratonic rift basin (Belarus–Ukraine–southern Russia) that developed in Late Devonian times and was reactivated in Early Carboniferous. To the southeast, the Donbas Foldbelt joins the contiguous, deformed Karpinsky Swell. Basin “inversions” led first to the uplift of the Palaeozoic series (mainly Carboniferous but also syn-rift Devonian strata in the southwesternmost part of the Donbas Foldbelt, which are deeply buried in the other parts of the rift system), and later to the formation of the fold-and-thrust belt. The general structural trend of the Donbas Foldbelt, formed mainly during rifting, is WNW–ESE. This is the strike of the main rift-related fault zones and also of the close to tight “Main Anticline” of the Donbas Foldbelt that developed along the previous rift axis. The Main Anticline is structurally unique in the Donbas Foldbelt and its formation was initiated in Permian times, during a period of (trans) tensional reactivation, during which active salt movements occurred. A relief inversion of the basin also took place at this time with a pronounced uplift of the southern margin of the basin and the adjacent Ukrainian Shield. Subsequently, Cimmerian and Alpine phases of tectonic inversion of the Donbas Foldbelt led to the development of flat and shallow thrusts commonly associated with folds into the basin. A fan-shaped deformation pattern is recognised in the field, with south-to southeast-vergent compressive structures, south of the Main Anticline, and north- to northwest-vergent ones, north of it. These compressive structures are clearly superimposed onto the WNW–ESE structural grain of the initial rift basin. Shortening structures that characterise the tectonic inversion of the basin are (regionally) orientated NW–SE and N–S. Because of the obliquity of the compressive trends relative to the WNW–ESE strike of inherited structures (major preexisting normal faults and the Main Anticline), in addition to reverse displacements, right lateral movements occurred along the main boundary fault zones and along the faulted hinge of the Main Anticline. The existence of preexisting structures is also thought to be responsible for local deviations in contractional trends (that are E–W in the southwesternmost part of the basin).     

塔里木盆地南部塘古孜巴斯坳陷发现晚新生代伸展构造

通过认真、系统的地震资料解释,在塔里木盆地南部的塘古孜巴斯坳陷及周缘首次发现晚新生代正断层。在塘古孜巴斯坳陷内部发现的晚新生代正断层走向为北西-南东向,剖面上组合成地堑或堑-垒构造,与巴楚隆起东北缘所发育的晚新生代正断层相似。塘古孜巴斯坳陷西北缘发现的两条晚新生代正断层走向为北东-南西,剖面组合成一地堑构造,与阿瓦提凹陷西北缘沙井子断裂带上发育的晚新生代张扭性正断层带走向一致,但不具备张扭性变形特征。正断层形成于上新世晚期(约3 Ma),持续演化至更新世早期(约2 Ma)。正断层的活动时间也与阿瓦提凹陷周缘的晚新生代正断层一致。它们形成于一个区域性弱伸展构造应力场内,代表印度-亚洲碰撞远程效应下,塔里木盆地脉式挤压(-冲断)过程中的一个构造间歇期。     

Growth of normal faults in multilayer sequences: A 3D seismic case study from the Egersund Basin,Norwegian North Sea

We investigate the structural style and evolution of a salt-influenced, extensional fault array in the Egersund Basin (Norwegian North Sea) through analysis of 3D reflection seismic and well data. Analysis of fault geometry/morphology, throw distribution and syn-kinematic strata reveal an intricate but systematic style of displacement and growth, suggesting an evolution of (1) initial syn-sedimentary fault growth contemporaneous with salt mobilization initiated during the Late Triassic, (2) cessation of fault activity and burial of the stagnant fault tips, and (3) subsequent nucleation of new faults in the cover above contemporaneous salt re-mobilization initiated during the Late Cretaceous, with downward propagation and linkage with faults. Stage 3 was apparently largely controlled by salt mobilization in response to basin inversion, as reactivated faults are located where the underlying salt is thick, while the non-reactivated faults are found where salt is depleted. Based on the 3D-throw analyses, we conclude that a combination of basement faulting and salt (re-) mobilization is the driving mechanisms behind fault activation and reactivation. Even though the sub- and supra-salt faults are mainly geometrically decoupled through the salt, a kinematic coupling must have existed as sub-salt faults still affected nucleation and localization of the cover faults.     

Review of the chronostratigraphic charts in the Sinú-San Jacinto basin based on new seismic stratigraphic interpretations

Disperse and punctual studies; absence of integration of data ranging from local to regional focus; interpretations based only on lithostratigraphic features; and interpretation of data premised on an allochthonous origin of the Caribbean plate, are some of factors that increase the confusion and uncertainty in understanding the Sinú-San Jacinto Basin. The sedimentary record of Upper Cretaceous to Eocene has been traditionally interpreted as the record of deep-water settings. However, recently these sediments have been related to shallow marine and deltaic settings. Second problematic point is about the deposition environment of the Oligocene to Late Miocene succession. Some studies suggest canyons, turbidites and sediments deposited in deep-water settings. However, recent studies propose deltaic and shallow marine settings. The last stratigraphic problem is related to the controversial fluvial vs. shallow marine interpretations of the Pliocene sediments. Based upon seismic stratigraphic analysis in recent and reprocessed 2D seismic data, integrated with well data, we propose chronostratigraphic charts for the northern, central and southern zones of the Sinú-San Jacinto Basin. Twenty seismic facies based on amplitude, continuity, frequency and geometry of seismic reflectors and twelve seismic sequences were recognized. The seismic stratigraphic analysis in this study suggests that the sediments of Upper Cretaceous to Paleocene/Eocene were associated to continental to shallow marine settings. Lagoons, coastal plain and carbonate platform dominated during this period. The Oligocene to Middle Miocene record was characterized by deep-water deposition, whereas the Late Miocene to recent sedimentation was characterized by falling base level, characterized by deltaic and fluvial deposits. Five syn-rift sequences with wedge-shaped geometry were identified in this study. Three Triassic to Jurassic syn-rift sequences were characterized by seismic facies typical of fluvial to lacustrine and flood plain sedimentation. Two Cretaceous to Paleocene syn-rift sequences were characterized by seismic facies related to lagoons to coastal plain settings. Normal high-angle faults with a northeast-southwest direction related to rifting processes controlled the development of these sequences. The sheet-drape post-rift section was characterized by passive margin settings in the northern part of the Sinú-San Jacinto Basin and by diachronic tectonic inversion of older normal faults during Cenozoic, predominantly in the central and southern zones. The stratigraphic record related to the Mesozoic to Early Cenozoic rifting; the shallow marine sedimentation during Eocene and the tectono-stratigraphic continuity across the northern Colombia and northwestern Venezuela is coherent and well explained by the in situ origin of the Caribbean plate and is not explained by the “allochthonous” model.