processes of forearc and accretionary complex formation during arc continent collision in the southern ural mountains the southern ural mountains of russia contain a well preserved well exposed paleozoic accretionary wedge and forearc that can be readily compared to those in active arc continent collision zones the early convergent history in the southern ural mountains is marked by the generation of boninite bearing arc tholeiites in the magnitogorsk forearc followed by arc tholeiite to calc alkaline volcanism with the entry of the east european craton continental crust in the subduction zone volcanism waned and stopped and high pressure metamorphism of its leading edge took place the arrival of the full thickness of the continental crust at the subduction zone is marked by increased sedimentation in the forearc basin and deposition of arc derived volcaniclastic turbidites across the subducting slab these together with offscraped continental material the exhumed high pressure rocks and a lherzolite massif formed an accretionary wedge a broad melange zone containing ultramafic fragments separates the forearc basement from the accretionary wedge and marks the damage zone that developed along the backstop region shallow water carbonates deposited unconformably on top of the mildly deformed arc record the end of the collision and the collapse of the arc

a new cordaitean pollen cone and pollen grains in situ from the early permian of hexi corridor and its geotectonic significance a new species of cordaitean pollen cone is described and diagnosed from early permian strata in gansu province northwestern china the gross morphology and well preserved features of the species named cordaianthus yongchangensis z x wang et b n sun sp nov have been studied in detail the current fossil has helically arranged bracts and secondary fertile shoots the bract longer and wider than in other known fossils diverges at approximately 90 from the axis the secondary fertile shoots are obovate with scales on individual shoots and fertile scales concentrated near the apex of the secondary fertile shoots more than five pollen sacs are clustered on the fertile scales which number 8 13 as the current species differs from any known species in the fossil records it is considered as a new species of cordaianthus the species with its microstructure of bracts and scales in situ pollen sacs and pollen grains provides important clues on the evolution of cordaitopsida based on the known reproductive organs of cordaitean plants we discovered that the current fossil with its wide bracts that protect the helically arranged secondary fertile shoots is similar to modern conifer cones suggesting that the current fossil is an evolutionally advanced species in comparisons with cordaitean fossils the leaves of cordaitean plants from the alt alashan terrane during the early permian presented mixed leaf features of specimens from the ncb north china block and scb south china block in conclusion the alt was already located between the ncb and scb in the early permian c 2016 elsevier b v all rights reserved

syn rift evolution of the pripyat trough constraints from structural and stratigraphic modelling the pripyat trough is a late devonian rift basin it forms part of the larger pripyat dniepr donets rift system which has a length in excess of 800 km and separates the ukrainian shield from the voronezh massif the pripyat trough contains a well resolved stratigraphic sub division within the syn rift basin fill sequence which allows the duration and rate of rifting to be determined using 2 d forward and reverse structural and stratigraphic modelling the analysis shows that rifting was extremely rapid sequential decompaction and flattening of 2 d cross sections has been applied to six syn rift time horizons between top upper devonian 364 ma and top middle devonian 377 ma and used to quantify the syn rift development of basin cross sectional area in time the evolution of basin cross sectional area shows that some initial rifting had occurred prior to the middle frasnian 369 ma however most rifting occurred in the famennian 367 364 ma forward syn rift modelling using the flexural cantilever model of rift basin formation has also been applied to quantify the magnitude of extension within the pripyat trough in time forward syn rift models are constrained by the intra syn rift flattened and decompacted cross sections and the observed evolution of the cross sectional area most rapid rift basin formation is shown to have occurred in the famennian with over 66 of basin cross sectional area forming in less than 5 myr and with approximately 80 or more of total extension occurring in less than 3 myr this period of most rapid extension during the famennian coincides with the most active period of volcanicity total devonian extension across the pripyat trough is estimated to be of the order of 11 14 km with a maximum stretching factor of approximately 1 12 extensional strain rates are estimated to be of the order of 0 8 10 15 s 1

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

tectonic variation in the dniepr donets basin from automated modelling of backstripped subsidence curves abstract the multiphase rift evolution of the dniepr donets dd basin is analysed by 1d backstripping and tectonic modelling of 66 stratigraphic sections mostly from well data distributed throughout the basin the backstripping results illustrate strong temporal and lateral variations in tectonic subsidence it is minor during an inceptive pre rift phase givetian early frasnian 380 8 370 ma and does not show clear spatial correlations within the dd basin framework the main rift phase frasnian famennian 370 362 5 ma corresponds to an acceleration in subsidence rates with tectonic subsidence up to 1500 m along the basin axis displaying a slight increase from the northwest to the southeast strong lateral variations perpendicular to the basin axis reflect the effects of major basin border faults a rift phase in the visean 345 340 ma is characterised by relatively minor subsidence up to about 500 m except for some wells in the southeast following a stage of extremely low rates of deposition in the earliest carboniferous the end of this rift phase can be taken to mark the onset of convex subsidence patterns in the later carboniferous and permian typical in shape of post rift thermal subsidence but significantly increasing in magnitude from northwest to southeast in the basin this trend shows no one to one relationship with late devonian syn rift subsidence the tectonic subsidence curves have been modelled using lithospheric stretching assumptions allowing different stretching factors for the crustal and sub crustal lithosphere and the incorporation of finite and multiple stretching phases a numerical technique was developed that automatically finds best fit stretching parameters for part or all of the tectonic subsidence data given the specification of onset and duration of the various rifting events maps of the 1d modelling results display intrabasinal variations in terms of timing and magnitude of rifting the results indicate that the observed spatial and temporal variations of tectonic subsidence in the dd basin specifically the increasing ratio of carboniferous to late devonian subsidence from northwest to southeast cannot be explained by either a uniform or depth dependent stretching model adopting only a single frasnian famennian rift phase a two phase model in which a significant part of carboniferous tectonic subsidence is related to visean rift activity strongly dominated by sub crustal lithospheric attenuation provides a satisfactory fit to the data although the tectonic implications of such a model are not easily reconcilable by independent constraints a semi quantitative investigation of the possible role of withdrawal of underlying devonian salt during the carboniferous to produce additional post devonian rift phase sediment accommodation space suggests that the effects of such a mechanism could be significant but that they are unlikely to preclude the necessity of the visean rifting event to explain the carboniferous basin evolution

36cl in ground water of the mazowsze basin poland abstract groundwater samples from the oligocene aquifer of the mazowsze artesian basin have been analysed for 36cl using the eth psi ams facility results of measurements and their hydrogeological interpretation are presented

quaternary normal and reverse faulting and the state of stress in the central andes of south peru field studies in the andes of southern peru show that in the high andes and pacific lowlands quaternary and recent faults are normal this extensional tectonics postdates compressional deformations of pliocene early quaternary age in the sub andes the observed deformations are compressional they affect early quaternary deposits some of the faults separate quaternary deposits from the bedrock and thus are clearly of tectonic origin and not landslide effects striations on the fault planes indicate n s trending extension in the high andes and pacific lowlands the total amount of crustal stretching is small probably of the order of 1 during the last 1 2 m y in the sub andes folds and faults affecting neogene and early quaternary deposits result from n s shortening nevertheless it is supposed that this n s shortening is of early quaternary age the present day compression probably strikes e w judging from focal mechanisms in the sub andes of central peru southern bolivia and northwest argentina data from structural analysis of faults and from earthquake focal mechanisms allow us to surmise the state of stress in the andes of southern peru the high andes and pacific lowlands subjected to n s trending extension are bounded by two zones of e w trending compression the sub andes to the east and the contact between the convergent nazca and south america plates to the west in our model the maximum horizontal compressive stress trajectory hmax is roughly parallel with the e w convergence between the two plates hmax corresponds to 1 in the sub andes and to 2 in the high andes the latter situation is caused by the elevated mass of the high andes where zz the vertical stress is inferred to be 1 thus the third principal stress axis being orthogonal to the other two axes it is oriented n s allowing extension to occur in that direction on the other hand in the sub andes zz is 3 and horizontal e w shortening occurs the state of stress in the andean continental crust above the 30 dipping slab appears to be different from that in the andes of central peru situated above the flat subducting segment in this region compressional deformantion affect a wider part of the cordillera

a new geodynamical thermal model of rift evolution with application to the dnieper donets basin ukraine abstract a model of the lithosphere incorporating both dynamic and thermal processes has been developed by solving a coupled system of differential equations governing stress and temperature in a 2 d block structured geophysical medium designed to study the roles of tectonic and geothermal factors in continental rift formation and evolution the model incorporates syn sedimentary and or erosional faulting of an upper crustal layer and allows the thermal regime of the lithosphere to be calculated through time the method has been applied to the formation and evolution of the northwest dnieper donets basin ddb along one regional profile controlled by seismic and other geophysical and subsurface data the results are compared with those published earlier for the same profile using different methods of modelling the rift and early post rift development of the region the final basement geometry at the end of the rifting stage predicted by the new model satisfactorily corresponds with geological data and is qualitatively similar to that predicted by the previously published models however the new results imply an important role for an active mechanism during rifting that generates greater mantle thinning than crustal thinning and elevated temperatures in the upper mantle beneath the rift

tectonic subsidence modelling of the polish basin in the light of new data on crustal structure and magnitude of inversion abstract the polish basin pb is one of a set of basins developed on the paleozoic platform of western europe in the late paleozoic between the variscan orogen and the east european craton eec its main depocentral axis the mid polish trough mpt was active during most of the basin development as a maximum subsidence zone with almost uninterrupted sedimentation the present base of the permian in the mpt ranges in depth from ca 3000 to 3500 m near the baltic coast to up to 8000 m to the southeast the mpt lies parallel and adjacent to the edge of the eec and appears to be related to a distinct structural zone within the crust the tornquist teisseyre zone ttz subsidence of the mpt can be explained in terms of crustal extension transtension and related lithosphere cooling coupled with the structural predetermination of the underlying ttz tectonic subsidence analysis of the preserved and reconstructed stratigraphic record suggests the occurrence of a late permian early triassic rifting phase however there is a deficit of geologically observable extensional features faulting of this age implying an important relationship between this phase of apparent basin subsidence and earlier post variscan late carboniferous early permian tectonism the match between crustal structure implied by basin modelling studies and available deep seismic sounding dds data is not always clear this is probably related to the heterogeneous basement which comprises the outer zone of the variscan belt in the southwest eec crust in the northeast and a complex of caledonian reworked precambrian crustal blocks in the central part of the basin changes to crustal architecture as a result of alpine tectonics may also play a role increased tectonic subsidence rates during oxfordian kimmeridgian times late jurassic correlate with intensified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin in contrast accelerating tectonic subsidence beginning in the cenomanian is a precursor of compressional deformations in the basin that culminated in alpine related basin inversion during the latest late cretaceous and earliest tertiary taking inversion into account the maximum depth of the base zechstein structural surface at the end of the cretaceous is estimated to have been as much as 5000 m near the baltic sea to more than 10 000 m in the southeasternmost part of the basin because of the erosion of these sediments however constraints on cretaceous subsidence and in turn the magnitude and exact timing of late cretaceous paleogene inversion are poor

crustal scale pop up structure in cratonic lithosphere dobre deep seismic reflection study of the donbas fold belt ukraine the dobre project investigated the interplay of geologic and geodynamic processes that controlled the evolution of the donbas fold belt ukraine as an example of an inverted intracratonic rift basin a deep seismic reflection profile provides an excellent image of the structure of the donbas fold belt which is the uplifted and compressionally deformed part of the late paleozoic pripyat dniepr donets basin both the effects of rifting and those of later structural inversion are recognized in the seismic and geologic data the interpretation of the reflection data shows that the inversion of the donbas fold belt occurred at the crustal scale as a mega pop up which involved a major detachment fault through the entire crust and an associated back thrust the dobreflection image provides a simple concept of intracratortic basin inversion the crustal pop up being uplifted and internally deformed the association of such a structure with inverted intracratonic basins such as the donbas fold belt implies brittle deformation of relatively cold crust

on the origin of the southern permian basin central europe abstract a detailed study of the structural and stratigraphic evolution of the southern permian basin during latest carboniferous to early jurassic times supported by quantitative subsidence analyses and forward basin modelling for 25 wells leads us to modify the conventional model for the rotliegend zechstein development of this basin the late permian early jurassic tectonic subsidence curves are typical for a permian to early triassic extensional stage that is followed by thermal subsidence however a purely extensional model is extremely problematic because active faulting during this time is minor and generally hard to document using inverse techniques to model the subsidence curves we quantitatively show that a significant component of late permian and triassic tectonic subsidence can be explained by thermal relaxation of early permian lithospheric thinning and by delayed infilling of paleo topographic depressions that developed during the early permian in this interpretation stephanian autunian wrenching resulted in thermal destabilisation of the lithosphere deep fracturing of the crust disruption and erosion of its sedimentary cover and regional uplift of the area of the future southern permian basin upon termination of wrench tectonics and associated volcanism towards the end of the autunian the southern permian basin began to subside in response to thermal contraction of the lithosphere the evolving basin was isolated from the world oceans and had subsided possibly up to some 700 m below their level at the beginning of upper rotliegend sedimentation after catastrophic flooding of this paleo topographic depression at the beginning of the zechstein changing sea level sedimentation and subsidence rates remained essentially in balance although the effects of triassic rifting overprinted parts of the southern permian basin its overall subsidence pattern persisted well into the jurassic in contrast to the remainder of the southern permian basin permian and triassic crustal extension contributed significantly to the subsidence of the polish trough

the formation of the south eastern part of the dniepr donets basin 2 d forward and reverse modelling taking into account post rift redeposition of syn rift salt abstract forward and reverse modelling of structure and stratigraphy has been used to investigate the syn rift late devonian and early post rift carboniferous evolution of the south eastern part of the dniepr donets basin ddb modelling was carried out with and without taking into consideration the withdrawal and surface extrusion of devonian salt during the formation of salt diapirs the great thickness of carboniferous deposits can be explained by the superimposed actions of three processes post rift thermal subsidence withdrawal of devonian salt from the mother layer during phases of salt diapir activity and regional subsidence of the east european platform the effects of other tectonic and or non tectonic processes are not required forward syn rift modelling using the flexural cantilever model of sedimentary basin formation predicts the total syn rift extension across the southeastern ddb to be approximately 65 km with a maximum stretching factor of 2 4 shallowing of the moho during the syn rift phase is estimated to be 15 km the present day moho after thermal subsidence and basin fill is predicted to be 4 6 km shallower than surrounding regions in the axial zone of the south eastern ddb the thickness of the devonian syn rift sequence may have reached 7 5 km by the end of the rift stage this is 3 3 5 km more than at present the thicknesses reduction is due to the outflow of devonian salt during post rift periods of halokinetic activity in the early visean the middle serpukhovian and in the early permian the withdrawal of salt from the mother layer produced additional accommodation space and up to 1 5 1 7 km of the total eventual thickness of the carboniferous sedimentary succession can be explained as a result of this

style and timing of salt tectonics in the dniepr donets basin ukraine implications for triggering and driving mechanisms of salt movement in sedimentary basins abstract the ukrainian dniepr donets basin ddb is a late palaeozoic intracratonic rift basin with sedimentary thicknesses up to 19 km displaying the effects of salt tectonics during its entire history of formation from late devonian rifting to the tertiary hundreds of concordant and discordant salt structures formed during this time it is demonstrated in this paper that the variety of styles of salt structure formation in the ddb provide important constraints on understanding the triggering and driving mechanisms of salt kinematics in sedimentary basins in general salt movement in the ddb began during the devonian syn rift phase of basin development and exerted controls on the later distribution of salt structures though the geometry of basement faults is not directly responsible for the regular spacing of salt structures post rift salt movements in the ddb occurred episodically episodes of salt movement were triggered by tectonic events specifically two extensional events during the carboniferous an extensional reactivation at the end of carboniferous earliest permian and a compressional event at the end of the cretaceous extensional events that induced salt movement were thick skinned i e basement involved in deformation rather than thin skinned most overburden deformation related to salt movements is ductile regardless of sedimentary bulk lithology and degree of diagenesis while the deformation of sedimentary cover in areas where salt is absent is mainly brittle this implies that the presence of salt changes the predominant mode of deformation of overlying sedimentary rocks episodes of salt movement lasted longer than the periods of active tectonics that initiated them buoyancy erosion and differential loading all played a role in driving halokinesis once tectonic forces had pushed the salt overburden system into disequilibrium among these factors erosion of overburden above growing salt structures acted as a key self renewing force for development of salt diapirs very high sedimentation rates related to high post rift tectonic subsidence rates particularly during the carboniferous were able to bury diapirs and to load salt bodies such that buoyancy erosion and differential loading forces eventually became insufficient to continue driving diapirism until the system was perturbed by an ensuing tectonic event in contrast some salt anticlines and diapirs developed continuously during the entire mesozoic because of much reduced tectonic subsidence rates and sedimentation supply during this time however a lower permian salt series and overhangs of buried diapirs played an important role in preventing overburden piercing and fracturing during the mesozoic and specifically during the late cretaceous salt diapirism phase

basement influence on foreland thrust and fold belt development an example from the southern urals abstract the reactivation of two sets of pre existing basement faults provided strong control on the geometric and kinematic evolution of the paleozoic south urals foreland thrust and fold belt pre existing basement faults oriented subparallel to the uralide structural grain were related to several stages of precambrian deformation reactivation focused the deformation along these earlier faults resulting in the subsequent incorporation of crystalline basement thrust sheets in the thrust belt at an early stage of its evolution pre existing basement faults oriented subperpendicular to the developing thrust belt structural grain were related to aulacogens in the archean crystalline basement that were filled by variable thickness of riphean aged sediments these influenced the localisation and development of numerous structures in the thrust belt that caused along strike structural changes related to lateral ramps recognition of these features and their influence on the geometric and kinematic evolution of the south urals foreland thrust and fold belt are important for understanding seismic reflection fabrics in the south urals thrust belt and for potential field 3 d geological and kinematic modelling

aulacogens and aulacogeosynclines regularities in setting and evolution abstract aulacogens and aulacogeosynclinal zones represent intra continental palaeorifts and inverted palaeorifts they were formed in the process of the break up of continents during the late proterozoic inversion of such basins occurred variably during the baikalian caledonian hercynian and alpine orogenic cycles in response to the build up of intraplate compressional stresses emanating from orogenic belts aulacogens were first recognized on the stable russian platform where they correspond to linear graben type depressions filled with proterozoic sediments often buried beneath a thick cover of palaeozoic and younger sediments some aulacogens have experienced a short period of reactivation during the palaeozoic aulacogeosynclines differ from the genetically related aulacogens by their greater dimensions and the amount of lithospheric extension that can go to the extent of opening of small ocean basins consequently they are characterized by a greater degree of destruction of the continental crust the depth of subsidence and the complexity of their post rift development which commonly terminates with their compressional deformation giving rise to the development of intracontinental linear folded and thrusted structures frequently associated with low grade metamorphism and small intrusions many ancient platforms are characterized by aulacogens metaplatforms are dissected by aulacogens and aulacogeosynclines whereas geosynclinal troughs are the precursors of geosynclinal mobil belts aulacogens aulacogeosynclines and geosynclinal troughs represent a group of negative linear structures which are characterized by an increasing degree of crustal destruction during rifting processes and increasing mobility during lithospheric contraction

structural features and evolution of the dniepr donets basin ukraine from regional seismic reflection profiles abstract a set of regional multichannel seismic reflection profiles crossing the dniepr donets dd basin in ukraine 100 200 km long and with a spacing of 10 15 km along strike illuminates the structure of the whole sedimentary cover the rift filled with pre and syn rift devonian sequences and overlain with post rift carboniferous permian mesozoic and palaeogene fill is clearly seen on all sections a basement layer previously identified as a riphean rift succession by refraction seismic studies constitutes in the main strata of the devonian and early carboniferous successions the structure of the rift is characterised by large scale rotational fault blocks and half grabens carried by basin parallel to normal marginal faults or by major horst blocks the total thickness of the devonian and younger succession is up to 19 km in the study area post rift carboniferous and mesozoic sediments cover the rift flanks and increase in thickness towards the rift axis and to the southeast the cumulative thickness of the carboniferous succession alone reaches 11 km with the maximum depth of their base at about 15 km major post rift tectonic events took place at the end of early visean in the middle of serpukhovian in permian times and between the mesozoic and cenozoic tectonic reactivations during carboniferous and early permian times were most pronounced in the southeastern part of the dd basin while they were least pronounced in the northwestern part of the basin merging with the pripyat trough where they are barely observed the most active development of salt structures and stocks corresponds with the periods of tectonic reactivation

neogene paleostress changes in the basin and range a case study at hoover dam nevada arizona at hoover dam 40 km southeast of las vegas nevada well exposed highly faulted miocene rocks provide an excellent opportunity to study the paleostress history of a very small area within a region where previous geologic studies indicate clockwise rotation of paleostress and a nearness to a major strike slip fault zone boundary within 0 5 km3 of rock the sense of slip was determined on almost 500 separate faults the fault slip data show internal consistency with respect to lithology size of faults and location within the small area with respect to fault slip however the data represent an in homogeneous mixture of primarily strike slip and dip slip motions from this mixture it is possible to resolve two distinct stress fields with directions of extension that differ by 60 each stress field corresponds to a mixture of strike slip and dip slip faults and thus the orientations of 1 and 2 are not tightly constrained if however the data are first separated into strike slip and dip slip faulting modes and subsequently searched for sub populations that correspond to contrasting paleostress orientations the computations yield tightly constrained tensors that illustrate two distinct stress fields with subhorizontal 3 axes that trend n50 e and n75 w the 1 and 2 axes permutate in two vertical planes that strike n40 w and n15 e because 1 and 2 are close in value relative to 3 these relationships suggest that strike slip and dip slip faulting belong to the same tectonic regime qualitative observations of polyphase slip fault fault offsets and fault bedding geometric relationships when evaluated in the context of changes in 3 orientation and permutations of 1 and 2 provide a basis for a two stage late cenozoic structural evolution at hoover dam these stages are 1 strike slip faulting partly pre tilt and dip slip faulting and associated stratal tilting and 2 mostly post tilt complexly interrelated strike slip oblique slip and dip slip faulting the qualitative evaluations indicate that strike slip and dip slip faulting alternated in time during the second stage of deformation and may have done so during the first these mixed mode movements probably represent stress oscillations in time and space rather than discrete stress reorganizations in contrast the two different orientations of 3 either represent a major clockwise rotation of the stress field or a major counterclockwise rotation of the rocks during the faulting history each alternative is consistent with regional geologic relationships and the choice of which is correct cannot be made within the small area that was studied

petroleum geology of the black sea abstract the black sea comprises two extensional basins formed in a back arc setting above the northward subducting tethys ocean close to the southern margin of eurasia the two basins coalesced late in their post rift phases in the pliocene forming the present single depocentre the western black sea was initiated in the aptian when a part of the moesian platform now the western pontides of turkey began to rift and move away to the south east the eastern black sea probably formed by separation of the mid black sea high from the shatsky ridge during the palaeocene to eocene subsequent to rifting the basins were the sites of mainly deep water deposition only during the late miocene was there a major sea level fall leading to the development of a relatively shallow lake most of the margins of the black sea have been extensively modified by late eocene to recent compression associated with closure of the tethys ocean gas chromatography mass spectrometry and carbon isotope analysis of petroleum and rock extracts suggest that most petroleum occurrences around the black sea can be explained by generation from an oil prone source rock of most probably late eocene age although a wider age range is possible in the basin centres burial history modelling and source kitchen mapping indicate that this unit is currently generating both oil and gas in the post rift basin a palaeozoic source rock may have generated gas condensate in the gulf of odessa in bulgarian waters the main plays are associated with the development of an eocene foreland basin kamchia trough and in extensional structures related to western black sea rifting the latter continue into the romanian shelf where there is also potential in rollover anticlines due to gravity sliding of neogene sediments in the gulf of odessa gas condensate has been discovered in several compressional anticlines and there is potential in older extensional structures small gas and oil discoveries around the sea of azov point to further potential offshore around the central azov high in offshore russia and georgia there are large culminations on the shatsky ridge but these are mainly in deep water and may have poor reservoirs there are small compressional structures off the northern turkish coast related to the pontide deformation these may include eocene turbidite reservoirs the extensional fault blocks of the andrusov ridge mid black sea high are seen as having the best potential for large hydrocarbon volumes but in 2200 m of water

variscan tectonics in the holy cross mountains poland and the role of structural inheritance during alpine tectonics abstract the present study was carried out in the holy cross mountains hcm of south central poland and includes computation of palaeostresses following angelier s method and field structural analysis the palaeozoic basement of the hcm comprises two tectonic units separated by the major wnw ese striking holy cross fault hcf fold analysis indicates a n s to nne ssw direction of variscan shortening micro structures and fold analysis from upper devonian rocks further reveal 1 a brittle tectonic event due to a nw se compression preceding folding that could be related to pre late carboniferous tectonics due to block transport within the tornquist teisseyre zone ttz and 2 polyphase variscan folding comprising a an early stage of n s shortening marked by north verging ramps b a main folding event and axial cleavage formation involving n s to nne ssw shortening and c a late stage of shortening deforming older folds and cleavage a mainly extensional tectonic regime dominated from the permian until the cretaceous during which time the hcf was reactivated as a normal fault large nw se faults bordering the mid polish trough mpt developed subsequent tectonic inversion of the mpt resulted in basin uplift mid polish swell mps palaeostress computations from mesozoic strata suggest a ne sw direction for the main maastrichtian paleocene shortening phase in addition to two minor brittle events resulting from n s and e w compression analysis of local folds in the mesozoic cover indicates a causal relationship with the maastrichtian paleocene reactivation of older faults in particular en echelon folds in the radomsko elevation suggest a sinistral reactivation of the palaeozoic hcf folds in the southwestern part of the hcm argue for reactivation in the reverse mode of a nw se trending fault bordering the mps that originated in the mesozoic in palaeozoic strata post variscan brittle deformation and micro fault reactivation are attributed to the tectonic events of maastrichtian paleocene age reactivation of n s fractures is demonstrated in the rzepka quarry where fractures in devonian dolomites are filled by calcite probably formed during a late variscan event and by younger late permian early triassic sediments they were subsequently reactivated as dextral strike slip faults during the ne sw maastrichtian paleocene compression

crustal scale structure and evolution of an arc continent collision zone in the southern urals russia the outcropping geology of the southern urals contains a well preserved accretionary complex related to the paleozoic collision that took place between the magnitogorsk arc and the former east european craton the crustal scale structure of the accretionary complex has been determined from outcropping field geology that is integrated with three reflection seismic profiles the reflection profiles show the accretionary complex to be highly reflective allowing direct comparison of many reflections with surface geological features we interpret the accretionary complex to be a thrust stack that is composed of shallowly subducted continental shelf and rise material syncollisional sediments derived from the arc deeply subducted high pressure gneisses that are intercalated with eclogites and blueschist and at the highest structural level ophiolite complexes it is bound at the base by a thrust and at the rear by a highly deformed zone the main uralian fault adjacent to the backstop the magnitogorsk arc deposition of the late devonian volcaniclastic sediments of the zilair formation appears to be related to collision uplift and erosion of the arc possibly following the arrival of the full thickness of the east european craton continental crust at the subduction zone with the arrival of the continental crust at the subduction zone offscraping and underplating of paleozoic slope and platform material took place at the base of the accretionary complex uplift of the arc was followed by its collapse and the unconformable deposition of lower carboniferous shallow water carbonates on top of it a time lag of 10 15 myr occurred between the high pressure metamorphism and the subsequent arrival of the east european craton at the subduction zone

magmatism and the geodynamics of rifting of the pripyat dnieper donets rift east european platform abstract the distribution of volcanism in the late devonian pripyat dnieper donets rift within the east european platform based upon the results of deep drilling indicates that pre existing basement structures and the major rift bounding faults played an important role in channelling the magmas towards the surface major and trace element and sr nd isotopic studies of the most primitive basic and ultrabasic magmas combined with estimates of the amount of extension 1 1 to 1 3 strongly suggest that magmatism was triggered by the upwelling of a thermally and geochemically anomalous mantle plume from the deep mantle during the late frasnian the peak of the magmatism occurred in the famennian coincident with the maximum amount of lithospheric extension magmatism rifting and domal basement uplife were contemporaneous at several localities within the eep suggesting that the thermal and geodynamic evolution of the platform could have been influenced by a cluster of mantle plumes during the late devonian

a model of palaeozoic obduction and exhumation of high pressure low temperature rocks in the southern urals abstract a new evolutionary geodynamic model of devonian continental subduction and exhumation of high pressure low temperature metamorphic rocks in the southern urals is proposed based on the results of physical modelling geological and geophysical data and on the comparison of this belt with other orogens the model includes the following principal phases 1 closure of the western uralian ocean by eastward intraoceanic subduction associated with the magnitogorsk volcanic arc 2 subduction of the european continental margin causing failure of the overriding plate in the arc area along a fault dipping eastward under the arc 3 subduction into the mantle of the fore arc block together with the underlying continental crust and sedimentary layer the sedimentary cover as well as the crustal and mantle fragments of this block are scraped off and accreted in front of and under the arc the continental crust shielded from the hot mantle by the fore arc block subducts to depths of more than 150 km remaining at a relatively low temperature the crust then fails at depths of several tens of kilometres 4 the subducted crustal slice starts to rapidly rise and intrude the interplate zone scraping and pushing up the sediments and slivers of the oceanic fore arc block previously dragged down to different depths 5 exhumation of the rising high pressure low temperature rocks within the uraltau dome separating the subduction accretionary complex from the magnitogorsk arc the eastern border of the uraltau dome coincides with the main uralian fault this fault represents a complex suture zone which at the stage of deep crustal subduction was associated with a major thrust subduction fault and at the exhumation stage with a major normal fault corresponding to the upper surface of the rising crustal sedimentary body

paleostress characterization of the wallachian phase in its type area southeastern carpathians romania abstract the wallachian phase is defined in the east carpathians a convex to the east mountain belt in romania as a tectonic event occurring between pliocene and quaternary times this event formed folds and minor thrusts structures that are usually located in internal parts of the somewhat older fold and thrust belt structure this location contrasts with the location one would predict from their recent age and contrasts with the older cretaceous middle tortonian piggyback thrust mode of propagation in the southeastern carpathians this late overstep sequence of thrusting resulted from a modification in the stress field our data indicate that the direction of compression changed from nw se to n s during middle tortonian time this is further supported by stratigraphic dating of structures and thereby paleostresses indicating that the wallachian episode was not a brief event at the pliocene quaternary boundary but lasted from middle tortonian to early pleistocene

tectonic paleostress fields and structural evolution of the nw caucasus fold and thrust belt from late cretaceous to quaternary abstract the nw caucasus fold and thrust belt essentially corresponds to the inverted western flysch zone of the great caucasus mountains a deep basin that developed from late jurassic to eocene times between the scythian plate to the north and the transcaucasian terranes to the south the shatsky ridge sw of the nw caucasus zone the flysch basin was strongly affected by compression in late eocene times when the characteristic wnw trending folds and thrusts of the nw caucasus belt developed some authors regard the main compressive deformation as miocene in age by means of remote sensing analysis we elucidate the geometry of major structures in the belt wnw trending south vergent thrusts and folds and major vertical and transverse nne ssw to ne sw deep fault zones the later structures are interpreted as ancient faults that were active during the development of the flysch basin paleostress investigations reveal seven main tectonic episodes in the evolution of the nw caucasus since late cretaceous combining structural interpretation remote sensing analysis and paleostress field reconstruction we propose a model for the structural evolution of the belt during the late cretaceous paleocene the western caucasus zone was under transtensional regime with an e w to ne sw trending 3 that generated oblique normal movements along nne ssw transverse faults and wnw ese margins of the flysch basin this tectonism could correspond to rifting related to the formation of the eastern black sea basin at the paleocene eocene boundary a transpressional event with an e w to nw se trending 1 developed and the nne ssw to ne sw trending faults could have been inverted this event could correspond to an attenuation in the eastern black sea basin formation or to the incipient accretion of the transcaucasian terranes during the eocene another e w to nw se oblique extension transtensional event affected the flysch basin that could be related to a known rifting phase in the eastern black sea basin strong nne ssw to ne sw compression characterises late eocene tectonism the fold and thrust belt developed at this time as a result of the direct collision of the shatsky ridge with the scythian plate a ne sw extension followed the late eocene event related to basin development around the newly formed fold belt a wnw ese oblique contraction affected the belt during the early miocene as the result of arabian plate convergence with the caucasian system the latest inferred event is a compressional regime with nnw sse trending 1 that is affecting the nw caucasus belt from sarmatian times until the present under this oblique compression the belt has deformed as in a dextral shear zone and the thrust surfaces have acquired lenticular shapes this study highlights the occurrence of oblique movements in the nw caucasus area prior to and after the dominant late eocene compression from the late cretaceous until the eocene the structural development of the nw caucasus was closely related to the evolution of the eastern black sea basin from the late eocene until quaternary times it was rather related to the arabia eurasia plate convergence

paleostress field reconstruction and revised tectonic history of the donbas fold and thrust belt ukraine and russia 1 in the wnw ese donbas fold belt df inversion of 3500 microtectonic data collected at 135 sites in proterozoic devonian carboniferous and cretaceous competent rocks allowed reconstruction of 123 local stress states accordingly four successive paleostress fields reveal the tectonic evolution of the df at the numerous sites that have been affected by polyphase tectonics the chronology between local paleostress states also paleostress fields was established using classical criteria crosscutting striae pre or post folding stress states stratigraphic control the oldest event is an extensional stress field with nne ssw 3 it corresponds to the rifting phases that generated the basin in devonian times and its early visean reactivation later the df was affected by a transtension with nw se 3 characterizing early permian tectonism including the development of the main anticline of the df and the pronounced uplift of its southern margin and ukrainian shield two paleostress fields characterize the cretaceous paleocene inversion of the df which was accompanied by folding and thrusting both are compressional in type but differ by the trend of 1 which was first nw se and subsequently n s the discrete paleostress history of the df allows a revised interpretation of its tectonic evolution with significant implications for understanding the geodynamic evolution of the southern margin of the east european craton

structures associated with inversion of the donbas foldbelt ukraine and russia abstract 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

sedimentary cycles and paleogeography of the dnieper donets basin during the late visean serpukhovian based on multiscale analysis of well logs abstract an integrated approach combining the available geological geophysical information was employed to construct a series of paleogeographic maps of the northwestern part of the dnieper donets basin ddb during the late visean serpukhovian early carboniferous the major source of information consists of well log data the basin fill shows a pattern of stacked transgressive regressive units of different order correlations on the scale of the basin are based on biostratigraphy seismics cyclostratigraphic subdivisions and correlations of the successions throughout the basin the cyclicity has a multifold character short shallowing upward transgressive regressive t r cycles characterized by the presence of hydrocarbons productive horizons cover a time span of the order of 500 ka long cycles include 4 to 6 short t r cycles they seem to be correlatable to western europe and probably to north america the long cycles form part of higher order stacking patterns indicative of still longer cycles considering the variable thickness of the cycles throughout the basin tectonics must have influenced the character of the series in addition to glacio eustatic sea level fluctuations the paleogeographical development of the basin shows axial deposition during the late visean likely related to late stage rifting related subsidence of a central graben followed by basin wide subsidence related to thermal subsidence during the serpukhovian

evolution of the southern margin of the donbas ukraine from devonian to early carboniferous times a devonian early carboniferous succession comprising thick clastic and carbonate sediments with interbedded volcanics was examined along the southern margin of the donbas fold belt ukraine following initial rifting and subsidence a continental fluvial lacustrine succession was established this first phase of synrift activity eifelian was accompanied by the extrusion of basalts in late givetian early famennian times half graben development was pronounced and a series of e w trending half grabens were formed along with coeval volcanic activity subsequent basin subsidence led to the establishment of a broad marine carbonate platform across the region late famennian tournaisian early visean renewed uplift led to partial exposure and karstification of the platform this was accompanied by trachyte intrusion and extrusion the overlying chert rich unit was probably deposited under lacustrine conditions although a shelf environment has also been suggested renewed tectonic activity along the main basin bounding fault resulted in the synsedimentary deformation of this unit