release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

evolution of geothermal systems around the red sea the current thermal regime around the red sea was initiated by a mantle plume beneath ethiopia eretria yemen and sw of saudi arabia at about 31 ma before the present the evolution of the geothermal systems around the red sea is coeval to the initial onset of volcanism over the separated land masses eritrea ethiopia djibouti yemen saudi arabia and egypt at 14 ma the entire tectono magmatic activities around the red sea gave rise to several geothermal provinces over the continents surrounding the red sea represented by thermal springs and fumaroles at several locations in eretria djibouti ethiopia yemen and saudi arabia these countries have the potential to develop these resources like ethiopia to mitigate co2 emissions in countries like saudi arabia and to enhance the gdp gross domestic product of the economically backward countries the geothermal resources have the potential to make these countries energy independent in future

fault reactivation and structural inversion backarc and intraplate compressive deformations example of the eastern sunda shelf indonesia the tectonic evolution of the eastern sunda platform in indonesia is revealed by the study of seismic profiles and comprises three general tectonic periods during the cenozoic extension with graben infill from the paleogene to the early miocene a tectonically quiet period with only broad subsidence and a middle miocene recent period of folding inversion and thrusting these structures reveal changes in the intraplate stress field which was controlled by the changes in the boundary conditions of the plates collisions on the northern and eastern sides and interplate coupling southward along the java subduction zone inversions often occurred without reactivation of pre existing normal fault planes at the upper levels of these faults the factors controlling these deformations are discussed with special interest placed on the conditions for the potential reactivation of cohesionless normal faults inversion and reactivations were mostly controlled by the orientation of the pre existing fault planes in relation with the regional stress field and by the tectonic stress regime in a strike slip regime effective principal stresses 1 and 3 horizontal with 1 2 3 the optimum conditions for reactivation in isotropic rocks are pre existing faults that strike close to the potential two vertical conjugate failure planes the same mechanical properties as for pre existing fault prevail in such conditions strike slip movements and reverse strike slip movements and associated en echelon folds were generally observed in a compressive regime 1 and 2 horizontal with 1 2 3 typical steeply dipping normal faults are difficult to reactivate by slip movements we suggest that reverse slip movements occurred in the deeper levels of faults and were accommodated by flexure above the pre existing fault planes and the inversion of grabens the strongly inverted grabens are those whose orientation is perpendicular to the regional compression nevertheless with strong regional shortening large uplifts and thrust faults were observed with reactivation in the form of reverse or reverse strike slip movements along pre existing steeply dipping normal fault planes

marine geologic evidence for a levantine sinai plate a new piece of the mediterranean puzzle marine geophysical data recorded offshore egypt illustrate the presence of an active fault belt trending n145 e that obliquely transects the eastern nile deep sea fan this belt more than 150 km long consists of a series of linear transtensive faults with an apparent right lateral horizontal component these fault zones bound thick sediment filled grabens where linear salt ridges and diapirs represent likely messinian salt reactive response to regional transcurrent geodynamics we infer that this tectonic belt might correspond to an offshore extension of the gulf of suez rift system if our hypothesis is correct this fault belt might represent the western boundary of a levantine sinai microplate locked between the major arabia and africa plates and the anatolian aegean microplate

the tectonic development of the western margin of the gulf of elat aqaba rift abstract along the western coast of the gulf of elat a 30 km wide shear belt of subparallel faults trending n s to ne sw is developed this shear belt is observed mainly within the precambrian basement terrain sinistral movements on these faults have been recognized based on offsets of magmatic bodies and lithological contacts in rocks of precambrian age the cumulative displacement measured independently at several localities across the belt attains a total of 24 km early neogene volcanism in the form of long dikes trending nw se is known from the eastern desert of egypt of the gulf of suez and along the red sea coast of saudi arabia volcanic bodies of a similar pattern have been identified in eastern sinai these bodies mainly dolerites and basalts intruding mesozoic sediments are parallel to each other and to the gulf of suez they are tens to hundreds of kilometers long and spaced several tens of kilometers apart dating k ar of bodies in sinai saudi arabia and in the eastern desert of egypt suggest an age of 20 22 m y for this extensive volcanism all the dikes are sinistrally displaced by the individual faults of the eastern sinai shear belt the amount of movement recorded using the precambrian markers is identical to movement recorded by offsets of the early neogene dikes this proves that the total 24 km shear of this fault system postdates the 20 22 m y volcanic phase it is assumed that the recorded movements are part of the 105 110 km shear persumed to exist along the gulf of elat which is also younger than 20 22 m y preliminary results suggest that a similar amount of movement is observable along a shear zone developed on the eastern coast of the gulf of elat thus only some 60 km movement are taken up by faults in the gulf itself the evolving model suggests that 1 a the intrusion of very long basaltic dikes in a nw se direction on both sides of the red sea accompanied the initial stage of development of the red sea gulf of suez rift valley 2 b a basic change in the geotectonic regime occurs after the intrusion of this volcanic suite large scale horizontal movements are initiated being recorded as a 105 110 km sinistral movement along the arava jordan rift this movement implies a synchronous opening of the red sea

sedimentology of rift climax deep water systems lower rudeis formation hammam faraun fault block suez rift egypt abstract in most marine rift basins subsidence outpaces sedimentation during rift climax times typically this results in sediment starved hangingwall depocentres dominated by deep marine mudstones with subordinate local development of coarser clastics in the immediate hangingwall derived from restricted catchments on the immediate footwall scarp to highlight the spatial variability of rift climax facies and the controls upon them we have investigated the detailed three dimensional geometry and facies relationships of the extremely well exposed miocene rift climax lower rudeis formation in the immediate hangingwall to the thal fault zone suez rift egypt detailed sedimentological analyses allows the lower rudeis formation to be divided into two contemporaneous depositional systems 1 a laterally continuous slope system comprising hangingwall restricted interpretation of individual facies facies relationships and their spatial variability indicate that deposition in the immediate hangingwall to the thal fault occurred via a range of submarine concentrated density flows surge like turbidity flows mass wasting and hemipelagic processes major controls on the spatial variability and stratigraphic architecture of the depositional systems identified reflect the influence of the steep footwall physiography accommodation and drainage evolution associated with the growth of the thal fault the under filled nature of the hangingwall depocentre combined with the steep footwall gradient result in a steep fault controlled basin margin characterised by either slope bypass or erosion with limited coastal plain or shelf area sediment supply to the slope apron deposits is controlled in part by the evolution and size of small footwall drainage catchments in contrast the localized submarine fan is interpreted to have been fed by a larger antecedent drainage network the structural style of the immediate footwall is also believed to exert a control on facies development and stratigraphic evolution in particular fault scarp degradation is enhanced by fault propagation folding which creates basinward dipping bedding planes in the pre rift footwall strata that large pre rift blocks slide on

seismic study of the crust of the northern red sea and gulf of suez we report the results of fifteen expanding spread profiles esp s and a seismic wide angle reflection refraction une performed during march april 1986 in the gulf of suez and the egyptian part of the northern red sea area north of 25 n four 16 4 air guns were used as a sound source on board r v le suroit and a 96 channel 2 4 km long streamer was towed by a supply vessel the whity tide most of the profiles show good crustal reflection and refraction arrivals and often good moho arrivals obtained for a distance of 80 to 100 km we present the results of x t and p analysis obtained by a velocity inversion performed in the p plane and by ray tracing modeling of both the p and the x t sections the velocity models are computed for planar and linear gradient velocity layers the northernmost part of the red sea appears to be characterized by a continental type crust extremely thinned 4 lying at a mean depth of 7 8 km whereas the moho is at a mean 14 15 km depth the southern part shows a seismic velocity structure of an oceanic type except in the 40 km closest to the coastline in both parts seismic waves progressively get more attenuated with distance from the shore to the axial zone which is presently tectonically active the difference between the northern continental and southern oceanic zone is related to the termination of the levant fault the northern continental area appears to represent the termination of the levant fault as a zone of distributed deformation

geometry of propagating continental rifts reconstruction of past plate configurations through palinspastic restoration of continental margins1 4 requires a detailed knowledge of the geometries of horizontal continental extension extension is often restricted to discrete linear zones termed rifts5 6 and rift models that invoke propagating vertical dykes and cracks7 10 are useful for assessing the relative significance and timing of uplift subsidence and extension in the tectonic evolution of rift basins however many models do not adequately account for the observed asymmetry of rifts i describe here the general three dimensional character of young and aborted continental rifts which can be used to derive a structural model for the propagation of rifts in continental lithosphere the rifts become asymmetric as a consequence of the role played by low angle normal faults in the overall rift geometry

evaporite accumulation during the messinian salinity crisis the suez rift case 1 the mediterranean basin may have not always been connected to the atlantic ocean during the messinian salinity crisis 5 96 5 33 myr the mediterranean sea reduced progressively its connection with the global ocean by a complex combination of tectonic and glacio eustatic processes during this period deep erosion occurred on the margin and on the continent furthermore a large quantity of evaporites was deposited in the basins 1500 m the way by which the evaporites accumulated in the various sub basins has not been precisely determined here we demonstrate by quantitative analysis that a combination of several mediterranean sea level drawdown events associated with limited atlantic sea inflow and continuous river discharge can explain the quantity of evaporites in the mediterranean basins and the observation of an intermediate lowstand at 500 m using a paleogeographical reconstruction and a numerical model we show that the evaporites of the gulf of suez gos are a consequence of the threshold which disconnected the gos red sea from the eastern mediterranean at the end of the miocene

scaling properties of normal fault populations in the western corinth graben greece implications for fault growth in large strain settings abstract a variety of one dimensional and two dimensional map techniques of fractal analysis have been employed to investigate the scaling properties of the dominant wnw trending normal fault population of the western corinth graben in central greece to assess possible constraints on fault geometry during fault growth the data have been compiled separately from the northern and southern domains of the graben which have experienced differing amounts of finite strain based on power law distributions of the fault throw the applied extension is estimated at 30 and 22 for the northern and southern domains respectively however the fault spacing and fault length populations in both domains obey similar power law relationships these conclusions are also supported by maximum throw vs trace length data which demonstrate that the faults in the northern domain have systematically higher values for the slip to length ratios than those in the southern domain it is proposed that the corinth graben has reached fracture saturation that is the fault spacing stops evolving and displacement increases rather than faults lengthening to accommodate the increasing extension this growth process consistent with throw distributions along individual faults may be explained either in terms of a stress feedback mechanism or by the mechanical interaction between the wnw trending normal faults with a set of nne trending transverse faults

uplift and extension at the gulf of suez indications of induced mantle convection reconstruction of tectonic movements since the initiation of the gulf of suez rift indicates that there has been 25 27 km of extension the uplift bordering rift indicates that lithosphere heating greatly exceeds that producible by uniform lithosphere extension i propose that small scale convection induced by the rifting augments the heating introduced by extensional rifting and produces the broad uplifts flanking the rift

inherited discontinuities and neogene structure the gulf of suez and the northwestern edge of the red sea the gulf of suez and the northern red sea rifts are the result of intracontinental deformation during neogene times the initiation and the development of the rift are controlled by i four main trends offaults n1400 n1500 ns to n200 sub e w and n40 60 ii a zigzag faulting pattern iii two main tectonic events the first is characterized by strike slip displacements inducing the formation of antithetic tilted blocks the geometry of the blocks changes according to their orientation complex structures can result from the combination of several trends vertical movements are weak the second is characterized by synthetic normal movements forming a horst and graben pattern vertical displacements are important and induce the generation of the axial trough and uplift of the shoulders of the rift the zigzag pattern of the faults that govern the rift and the initial strike slip displacements cannot result from a simple extensional model but imply a reactivation of inherited discontinuities in the miocene stress system induced by the northern convergent boundaries of the african and arabic plates the major trends of faults that control the neogene structure have been active in this area since palaeozoic or even proterozoic times

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

structural trends in the northern red sea the northern red sea is underlain by a series of plio pleistocene sedimentary sequences that unconformably overlie evaporitic series of late miocene age a series of bathyal rifts and cogenetic diapirs trending approximately n s were recently discovered in that region between latitude 26 30 n and 28 n the rifts are up to 60 km long and 7 km wide and the diapirs commonly ascended along the rifts boundary faults the diapirs stem from the late miocene evaporites thus the discerned structural trends were developed during the plio pleistocene the encountered structural patterns deviate considerably from the nw se structural trends that prevail in the central red sea as well as in the faults that border the northern red sea and the gulf of suez the tectonic activity that formed the suez rift in the middle to late miocene was not rejuvenated there during the plio pleistocene and the new data indicate that the axis of the tectonic extension at the northern red sea jumped to show a northward orientation it is suggested that incipient spreading center extends from the red sea northward to the gulf of elat and the dead sea rift

segmentation and along strike asymmetry of the passive margin in socotra eastern gulf of aden are they controlled by detachment faults on the island of socotra the southern passive margin of the gulf of aden displays along its strike two different types of asymmetric structures western socotra is made up of a series of southward tilted blocks bounded by consistently northward dipping normal faults eastern socotra consists of a broad asymmetric anticline with a steep northern limb and a gently dipping southern limb a zone of ne sw striking strike slip and normal faults separates the two areas the overall structure is interpreted as representing two rift segments separated by a transfer zone the along strike juxtaposition of crustal scale asymmetric structures on the southern margin of the gulf of aden is complemented by the asymmetry of the conjugate margins on either side of the gulf whereas the western socotra margin is narrow and characterized by oceanward dipping normal faults the conjugate oman margin is broader and dominated by horsts and graben considering that asymmetric structures in the upper crust are often associated with synthetic shear zones at deeper ductile levels we propose that the western and eastern socotra margin segments were controlled at depth by two detachment faults with opposite dips and senses of shear the normal faults of western socotra would sole out into a top to the north ductile shear zone whereas the asymmetric anticline of eastern socotra would be associated with a top to the south detachment fault

lithospheric strength variations as a control on new plate boundaries examples from the northern red sea region abstract the complex plate boundary between arabia and africa at the northern end of the red sea includes the gulf of suez rift and the gulf of aqaba dead sea transform geologic evidence indicates that during the earliest phase of rifting the red sea propagated nnw towards the mediterranean sea creating the gulf of suez subsequently the majority of the relative movement between the plates shifted eastward to the dead sea transform we propose that an increase in the strength of the lithosphere across the mediterranean continental margin acted as a barrier to the propagation of the rift a new plate boundary the dead sea transform formed along a zone of minimum strength we present an analysis of lithospheric strength variations across the mediterranean continental margin the main factors controlling these variations are the geotherm crustal thickness and composition and sediment thickness the analysis predicts a characteristic strength profile at continental margins which consists of a marked increase in strength seaward of the hinge zone and a strength minimum landward of the hinge zone this strength profile also favors the creation of thin continental slivers such as the levant west of the dead sea transform and the continental promontory containing socotra island at the mouth of the gulf of aden calculations of strength variations based on changes of crustal thickness geotherm and sediment thickness can be extended to other geologic settings as well they can explain the location of rerifting events at intracratonic basins of backarc basins and of major continental strike slip zones

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

complex fault patterns transtension and structural segmentation of the lofoten ridge norwegian margin using digital mapping to link onshore and offshore geology an integrated onshore offshore study involving regional to outcrop scale fault analysis is used to develop a self consistent structural model for transtension along the lofoten ridge the lofoten vesteralen archipelago lva is a segmented basement high showing distinct lateral variations in trend deformational style and structural complexity this study investigates whether segmentation can be linked to differences in the obliquity of preexisting structures relative to plate movement vectors regional analysis of fault lineament patterns using geographic information systems gis reveals that the lva can be subdivided into a series of distinct lineament domains these domains are closely coincident with changes in ridge trend and variations in structure within offshore models derived from seismic reflection studies digital field mapping and spatial analysis of faulting in the north lofoten reveal that multimodal faulting is dominated by transtensional dip slip and oblique slip movements which are comparable to analogue models where the ridge axis is 30 oblique to regional extension the overall change in fault orientation fault geometry and deformation style are consistent with models for transtension where the ridge bounding structure becomes increasingly oblique to regional extension previously identified transfer zones simply reflect segment domain boundaries and are not reactivating basement structures this model is a possible analogue for other orthogonal and oblique rift structures on the norwegian and other margins

physical characteristics and evolutionary trends of continental rifts rifts may be defined as zones beneath which the entire lithosphere has ruptured in extension they are widespread and occur in a variety of tectonic settings and range up to 2 600 m y in age the object of this review is to highlight characteristic features of modern and ancient rifts to emphasize differences and similarities in order to help characterize evolutionary trends to identify physical conditions favorable for initiation as well as termination of rifting and to provide constraints for future modeling studies of rifting rifts are characterized on the basis of their structural geomorphic magmatic and geophysical features and the diverse character of these features and their evolutionary trends through time are discussed mechanisms of rifting are critically examined in terms of the physical characteristics and evolutionary trends of rifts and it is concluded that while simple models can give valuable insight into specific processes of rifting individual rifts can rarely if ever be characterized by well defined trends predicted by these models more data are required to clearly define evolutionary trends and the models require development to incorporate the effects of lithospheric heterogeneities and complex geologic histories

the cenozoic graben system of sardinia italy geodynamic evolution from new seismic and field data abstract a tectono sedimentary scenario for the southern sardinia italy cenozoic graben system is proposed using field observations and the interpretation of onshore and offshore seismic profiles the major structural events are tied to the general geodynamic evolution of the western central mediterranean thus the extensional late oligocene aquitanian event is a consequence of an apenninic westward subduction process associated with a volcanic arc 29 30 to 15 16 my which is particularly well exposed in sardinia deposition of sub aerial clastics was followed by transgression of the rift depression at the beginning of the aquitanian subduction terminated at the opening of the oceanic provencal basin and the rotation of sardinia corsica during burdigalian time 20 21 to 15 16 my the messinian compressional event ne sw oriented documented from microtectonic data strongly affected the oligo miocene basin the superimposed plio quaternary campidano graben which is probably related to the formation of the tyrrhenian basin contains more than 600 m of syntectonic deposits a change in polarity of the master faults bounding the oligo miocene rift created a central horst type twist zone separating two depocenters in the oristano and cagliari regions emplacement of large volcanic bodies and inversion of the basin during the messinian in cagliari area has reduced the areas with potential for hydrocarbon exploration the two remaining prospective zones are the oristano sub basin and the offshore south of cagliari where burial of lower miocene marine organic matter may have been sufficient to generate hydrocarbons potential reservoirs could be pre rift mesozoic or eocene strata but are mainly excellent miocene sands derived from erosion of the granitic basement in tilted blocks

the evolution of the suez rift a combination of stretching and secondary convection abstract different physical mechanisms have been put forward in order to explain the lithospheric evolution beneath a continental rift models of stretching of the lithosphere though giving good values for the trough subsidence could not satisfactorily account for other features of the rifts such as the rapid uplift of the rift shoulders in some cases however the idea that the thinning of the lithosphere is also accomplished by secondary convection phenomena is now receiving growing attention using a thermomechanical model dealing with a non newtonian crust and mantle moretti and froidevaux have suggested that the evolution of numerous continental rifts is the consequence of the combination of the upward propagation of an asthenospheric thermal anomaly and of an extensional regional stress the suez rift evolution examined by tectonic subsidence studies may be regarded as the result of an asthenospheric upwelling and of a short active initial lithospheric stretching phase

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

channel flow and the development of parallel dipping normal faults 1 in a series of numerical experiments arrays of parallel dipping normal faults formed only if the model contained a thin viscous layer sandwiched between the brittle faulted layer on top and a lower boundary that resisted vertical displacement with this particular vertical stratification parallel dipping faults developed even if the viscous layer had a shear stress free lower boundary condition this observation contradicts previous studies relating parallel dipping normal faults to consistent horizontal shear stress in the brittle layer we explain the formation of parallel dipping normal faults in our experiments through the properties of flow in a thin viscous channel and how this flow accommodates and delocalizes faulting in the brittle layer on top first for closely spaced normal faults an array of parallel dipping faults minimizes the viscous work rate dissipation in the viscous layer as it minimizes the distance between sources and sinks in the flow pattern second a thin layer of moderate viscosity leads to the required formation of closely spaced single faults a highly viscous substratum tends to reflect faults at the base of the brittle layer and hence promotes the formation of a local graben at each necking site in the brittle layer with lower viscosities a thick layer or a floating lower boundary condition usually leads to the formation of widely spaced core complexes in the brittle layer our scheme can explain varying dip polarity along strike which is observed in many rift systems and difficult to explain through consistent shear stress

longitudinal evolution of the suez rift structure egypt abstract a three dimensional study of the structure of the suez rift has been carried out using field and subsurface data in an attempt to determine the role of transverse faults and the longitudinal evolution of the rift as in most intracontinental rifts the structure of the gulf of suez area is governed by normal faults and tilted blocks whose crests constitute the main target of exploratory wells the fault pattern consists of two major sets of trends 1 1 longitudinal faults parallel to the rift axis and created in an extensional regime where 3 was trending ene wsw and 2 2 transverse faults with a n s to nne ssw dominant trend the transverse faults are inherited passive discontinuities while most of the longitudinal faults were created during neogene times in a purely extensional regime both sets were simultaneously active producing a zigzag pattern and rhombic shaped blocks the transverse faults can show horizontal strike slip components and act as relays between major normal faults although the suez rift appears as a simple narrow elongated trough dominated by two almost symmetrical shoulders its internal structure is asymmetrical cross profiles show that all the major blocks are tilted in the same direction however the tilt direction changes twice along the rift to the north and to the south of the rift the blocks are tilted eastward while in the central part they are tilted westward to the north the change of dip is accompan ed by a graben type twist zone without transverse faulting at least in the neogene series to the south the change of dip is accompanied by a more complex structure involving both a major transverse fault and a horst type twist zone in this latter case the transverse fault does not cut through the entire rift balanced cross sections established from subsurface data show that the tilt angle and the amount of extension increase from north to south while the width of the blocks decreases indicating a pole of opening close to the northern end of the gulf minimum values for the amount of opening range from 5 km in the north to about 20 km in the south

style and sequence of deformation during extensional fault propagation folding examples from the hammam faraun and el qaa fault blocks suez rift egypt kilometre scale fault parallel folds are identified adjacent to normal faults in the oligo miocene suez rift egypt and are interpreted to have formed in response to fault propagation folding above upward propagating blind faults the geometry scale and distribution of secondary structures within the folds and their cross cutting relationships with the master faults allow the style and sequence of deformation during fault propagation folding to be established and suggest that during the initial stages of folding the proto footwall underwent extension which was accommodated by layer parallel slip in encasing mudstone horizons and linked normal faulting and block rotation in carbonate and sandstone units the proto hanging wall also contains dominantly extensional normal faults although locally where the master fault had a convex into the footwall map view trace reverse faulting and fracturing occurred secondary structures adjacent to the master fault were not all active simultaneously but initiated and died at different stages during the evolution of the fault propagation fold the results of this study confirm many key predictions of numerical and physical analogue models but also highlight several important controls on the evolution of fault propagation folds in extensional settings which existing models cannot capture such as the influence of the map view trace of the propagating fault and lateral variations in cover stratigraphy lithology and strength on the style and magnitude of secondary deformation

crustal structure and the mechanism of extension in the northern red sea constraints from gravity anomalies gravity data from detailed marine surveys were used to investigate the density structure of the crust and upper mantle beneath the northern red sea a continental rift considered by many to be in the process of establishing a mid ocean ridge type spreading center a gravity and bathymetry profile across the sea near 27 n was analyzed in detail model constraints include single channel and multichannel seismic reflection lines coincident with the gravity profile which provide detailed information on sedimentary layers a series of esp seismic experiments centered nearly on the gravity line which constrain the sediment and crustal thickness and a series of 58 closely spaced heat flow measurements nearly coincident with the gravity line which closely constrain the mantle thermal structure and thus density variations within the mantle the calculated gravity anomalies based on the known crustal and mantle structure fail to match the observed data specifically the model anomalies become steadily more negative from the margins toward the center of the sea with the result that the calculated gravity is approximately 25 mgal more negative near the axis relative to the marginal areas than are the observed anomalies two possible solutions were investigated one is to introduce a lower crustal layer resulting from crustal underplating within what was originally considered to be the upper mantle beneath the marginal areas the other is to introduce an area of slightly denser crust resulting from intrusion of new mafic crustal material within the axial depression both solutions can reproduce the observed gravity anomalies within the red sea however the complete set of geophysical data and in particular the heat flow in the red sea and gravity and seismic refraction data on land suggests that the most satisfactory model is that the crust of the axial depression is denser than that of the marginal areas this implies that crustal extension in the northern red sea is presently occurring in large part by intrusion of new mafic material

control of extensional transfer zones on syntectonic and post tectonic sedimentation implications for hydrocarbon exploration the gulf of suez red sea rift system exhibits superb outcrop examples of extensional transfer zones and displays the control of these zones on syntectonic and post tectonic sedimentation hard and soft linkage transfer zones were identified at variable scales hard linkage transfer zones form inward and outward fault kinks whereas soft linkage transfer zones form relay ramps between overlapping rift parallel faults the two types of transfer zones invariably exerted fundamental control on the deposition of syn and post tectonic sediments flow direction of drainage systems and locations of sediment entry points as well as the intensity of erosion patterns of the structurally high sediment source areas this study highlights the close relationship between the transfer zones and hydrocarbon accumulations in clastic syntectonic reservoirs in rift basins

displacement and strain patterns of extensional orogens rock fabrics that result from displacement in extensional orogens provide a means of identifying geometric models responsible for extension of continental crust strain compatibility arguments indicate that a finite extension can be accommodated by displacements across 1 planar nonrotating faults or ductile shear zones 2 shear zones which rotate above a horizontal detachment the domino model or 3 shear zones which rotate as a result of a horizontally oriented pure shear stretching component the plastic model listric normal shear zone geometries may develop as the result of a depth dependent change in the pure shear component in the plastic model or the area loss component in the planar shear zone model within the geometric framework of these various models the effects of superposed simple shear pure shear extension and area change on the rock fabric are investigated these displacement components which may be superposed sequentially or simultaneously determine the state of finite strain associated with a given magnitude of tectonic extension the relationships between displacement and strain are expressed as graphs of foliation dip or strain ratio versus shear strain and as graphs of foliation dip or strain ratio versus tectonic extension the shear strain graphs illustrate the effects of the different displacement components on the rock fabric in a single shear zone whereas the tectonic extension graphs better illustrate these effects on the regional scale the shear strain and tectonic extension graphs can be used by field geologists 1 to determine tectonic extension across a region from measurements of strain ratio or orientation and fluctuation of foliation 2 to distinguish between possible extension models from field data and 3 to evaluate the influence of shear zone attitude and thickness upon the amount of displacement applications of these methods are illustrated for field areas in metamorphic core complexes of arizona and in the basin and range province of the north america cordillera

controversy over the great flood hypotheses in the black sea in light of geological paleontological and archaeological evidence abstract legends describing a great flood are found in the narratives of several world religions and the biblical account of noah s flood is the surviving heir to several versions of the ancient mesopotamian flood myth recently the story of the biblical deluge was connected to the black sea together with the suggestion that the story s pre mesopotamian origins might be found in the pontic basin ryan w b f pitman iii w c 1998 noah s flood the new scientific discoveries about the event that changed history simon and schuster new york based on the significance of this flood epic in the judeo christian tradition popular interest surged following publication of the idea currently two great flood scenarios have been proposed for the black sea 1 an early holocene event caused by catastrophic mediterranean inflow at 7 2 ky bp initial hypothesis of ryan et al 1997 an abrupt drowning of the black sea shelf marine geology 138 119 126 or 8 4 ky bp modified hypothesis of ryan et al 2003 catastrophic flooding of the black sea annual review of earth and planetary science 31 525 554 and 2 a late pleistocene event brought on by caspian influx between 16 and 13 ky bp chepalyga a l 2003 late glacial great flood in the black sea and caspian sea gsa annual meeting and exposition 2 5 november 2003 seattle usa p 460 both hypotheses claim that the massive inundations of the black sea basin and ensuing large scale environmental changes had a profound impact on prehistoric human societies of the surrounding areas and both propose that the event formed the basis for the biblical great flood legend this paper attempts to determine whether the preponderance of existing evidence sustains support for these great floods in the evolution of the black sea based upon established geological and paleontological data it finds that the late pleistocene inundation was intense and substantial whereas the early holocene sea level rise was not between 16 and 13 ky bp the late neoeuxinian lake the late pleistocene water body in the pontic basin pre dating the black sea increased rapidly from 14 to 50 m below the present level of the black sea then rose gradually to 20 m by about 11 ky bp at 11 10 ky bp the younger dryas it dropped to 50 m when the black sea re connected with the sea of marmara at about 9 5 ky bp inflowing mediterranean water increased the black sea level very gradually up to 20 m and in so doing it raised the salinity of the basin and brought in the first wave of mediterranean immigrants these data indicate no major drawdown of the black sea after the younger dryas and they do not provide evidence for any catastrophic flooding of the black sea in the early holocene in addition available archaeological and paleoenvironmental evidence from the pontic region reveal no recognizable changes in population dynamics between 14 and 6 ky bp that could be linked to an inundation of large magnitude dolukhanov p shilik k 2006 environment sea level changes and human migrations in the northern pontic area during late pleistocene and holocene times in yanko hombach v gilbert a s panin n dolukhanov p m eds the black sea flood question changes in coastline climate and human settlement springer dordrecht pp 297 318 stanko v n 2006 fluctuations in the level of the black sea and mesolithic settlement of the northern pontic area in yanko hombach v gilbert a s panin n dolukhanov p m eds the black sea flood question changes in coastline climate and human settlement springer dordrecht pp 371 385 more specifically mesolithic and early neolithic archaeological data in southeastern europe and ukraine give no indications of shifts in human subsistence or other behavior at the time of the proposed catastrophic flood in the early holocene anthony d 2006 pontic caspian mesolithic and early neolithic societies at the time of the black sea flood a small audience and small effects in yanko hombach v gilbert a s panin n dolukhanov p m eds the black sea flood question changes in coastline climate and human settlement springer dordrecht pp 345 370 dergachev and dolukhanov 2006 the neolithization of the north pontic area and the balkans in the context of the black sea floods in yanko hombach v gilbert a s panin n dolukhanov p m eds the black sea flood question changes in coastline climate and human settlement springer dordrecht pp 489 514

extension and rifting the zeit region gulf of suez abstract a field analysis of faults and fractures in the ras gharib ras gemsa region of the gulf of suez shows that the main late cenozoic extension occurred perpendicular to the rift axis three main types of dip slip normal faults successively developed as the tilt of blocks bounded by antithetic normal faults increased determinations of the amount of extension from structural data are compatible with estimates made using subsidence data through a simplified model of lithospheric stretching the uplift of rift shoulders is related in chronology and volume to the subsidence of the rift the geometry of fault patterns and directions of extension suggests that the late cenozoic total movement corresponds to a counterclockwise rotation of 4 5 of sinai relative to africa with a pole close to cairo