uplift and a possible moho offset across the dead sea transform abstract the east africa rifts and the red sea spreading center are characterized by uplifted shoulders and sunken median valleys the dead sea transform on the northern extension of the arabian african plate boundary has a similar morphological character despite its well documented strike slip motion to understand the rift morphology and the crustal structure beneath the transform we compiled a 320 km long gravity and topography profile perpendicular to the dead sea transform the gravity field and the topography in the region surrounding the profile are generally parallel to the trend of the dead sea transform justifying the two dimensional approximation of the analysis the gravity profile was modeled using constraints from seismic refraction borehole and surface geology data the observed gravity anomaly can be explained by the juxtaposition of two different sedimentary and crustal sections which have been offset by a 105 km left lateral displacement across the transform boundary suggesting a step in the depth to moho the existence of a significant density anomaly under the median valley is not required by the model the current elevation of the transform shoulders appears not to be compensated locally assuming a state of local isostasy prior to the development of the transform the magnitude of the uplift in the vicinity of the profile is estimated at 700 900 m with a half width of 100 125 km this topography uplift can be fitted equally well by models which assume either dynamic support or regional compensation it is suggested that if the source of the uplift is thermal it is located within the upper mantle since there is no requirement for a shallow density anomaly under the rift itself or in the crust nearby

episodic post rift subsidence of the united states atlantic continental margin sediment thickness paleobathymetry and chronostratigraphy from cost wells offshore from georgia and new jersey indicate periods of rapid subsidence superimposed on the slower thermal subsidence of the continental margin rapid subsidence occurred during the coniacian santonian the eocene and in the cost wells off new jersey since the end of early miocene once the maximum effects of water and sediment loading compaction and thermal cooling are removed the residual vertical movements caused by tectonic and sea level fluctuations can be analyzed because no global sea level change can account for all residual movements we propose that tectonism variously amplified by loading is responsible for the observed episodes of rapid subsidence synchroneity of subsidence with sea floor spreading changes in the north atlantic suggests a unified cause for these events recognition of episodic subsidence may have implications for fault timing petroleum potential and global sea level effects on passive margins

namurian uplift in australia and south america triggered the main gondwanan glaciation the permo carboniferous glacigenic sediment at the base of the gondwanan basins reflects the culmination1 2 of the glacial episode that started in australia and southern south america in the namurian after two local episodes in northern south america and adjacent africa in the visean and latest devonian3 fig 1 here we show that the start of each episode was associated with orogenic uplift of the bordering regions northern south america and adjacent africa in the latest devonian and visean and southern south america and eastern and central australia in the namurian all areas except southern south america in the namurian were at mid and not high latitudes thus we show that whereas the first order control of glaciation was the configuration of the continents and oceans during the closing of palaeo tethys orogenesis provided a second order control by the accumulation of ice about bordering uplifts during the three glacial episodes

age and significance of sequence boundaries on jurassic and early cretaceous rifted continental margins the age and significance of sequence boundaries on jurassic to early cretaceous rifted continental margins in three ocean basins have been documented the margins are the santos basin in the south atlantic the grand banks in the north atlantic and the beaufort sea in the arctic ocean large industry data bases were used for the interpretation of each area megasequence boundaries separate the major phases of basin evolution for example syn rift and post rift boundaries developed with an average periodicity of 49 m y sequence boundaries define the component parts of each megasequence and developed with a modal periodicity of 10 15 m y out of 27 total boundary ages most 16 are developed on just one margin only two possible age ranges overlap on all three margins ighty percent of the megasequence boundaries and 50 of the sequence boundaries show a direct causal connection with coeval faulting and or folding the rest of the boundaries appear as unstructured surfaces separating transgressive and or regressive sedimentary wedges and are interpreted to result from changes in the rate of basin subsidence sediment input and long term eustatic sea level these data do not support theories advocating synchronous worldwide boundary development resulting from periodic short term falls in global eustatic sea level only in like basins of the same age with identical subsidence and sediment input rates are boundaries likely to develop synchronously hence the concept of global synchroneity of sequence boundary development may well be an illusion creat d by the similarity in age of the majority of basins studied as a result of this study it seems wise discard the global approach to basin analysis

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

2003 mw6 8 chengkung earthquake and its related seismogenic structures abstract the mw 6 8 chengkung earthquake on december 10 2003 in eastern taiwan was associated with abundant aftershocks to explore the seismogenic mechanism and its causative fault system we relocated the aftershocks determined the focal mechanisms from p wave polarities and used the finite dimension source model method to identify the fault plane based on our results the earthquake can be divided into three seismic clusters one is located in the east of the southern longitudinal valley one on the chihshang fault and the other on the western side of the luyeh fault to the south both the seismic distribution and finite dimension source model method show that east dipping fault planes with thrust mechanisms coincide with previous studies based on background seismicity the third seismic cluster suggests thrust mechanism along west dipping fault plane that was not recognized by background seismicity this seismic cluster occurred along the central range fault previously proposed as active by geomorphic and geologic evidence

permian early mesozoic tectonism and continental margin formation in israel and its implications for the history of the eastern mediterranean summary the early mesozoic tectonic reorganization of the tethys region also affected the levant area here two processes were superimposed a the pattern of long wavelength vertical motions of the arabo nubian platform changed in the late permian when israel and nearby areas began to subside b rifting occurred in this subsiding area probably in several phases late anisian and ladinian carnian norian and liassic differential movements reached 2 3 km and magmatism occurred in the liassic and perhaps also in the triassic the tectonism was strongly felt up to 50 km landward of the present coast the crust was thinned and modified under the present continental margin and in the main rifts passive margin conditions were established in late liassic times over the previously faulted area later in the jurassic a carbonate shelf was constructed along this subsiding margin its basinward edge was 1 1 5 km high which shows that the adjacent se mediterranean was already a deep sea hence this basin and its passive margin are considered to have been shaped by the early mesozoic rifting which is recognized in israel the rifting process probably signifies oblique separation of the tauride block from the levant part of gondwana

early stage evolution of growth faults 3d seismic insights from the levant basin eastern mediterranean the geometry and kinematic evolution of small growth faults were analysed from a high resolution 3d seismic dataset located at the margins of the levant basin in the eastern mediterranean the 3d geometry segmentation history and throw distribution of one particular fault was reconstructed to evaluate and illustrate the changes in dimension and displacement distribution that occurred during the transition from purely blind propagation to propagation at the free surface the fault is considered to have grown by blind radial propagation of three main segments that hard linked prior to surface interaction the fault subsequently reached the seabed and continued to accrue displacement as a syn sedimentary fault most of the fault surface area formed during the blind propagation phase but most of the displacement was added during the syn sedimentary phase of the growth history with little increase in surface area the interaction of the fault with the free surface led to a change in the position of the point of maximum displacement as well as modifying the vertical throw distribution the amount of displacement added after this transition from blind fault to growth fault is discussed with respect to existing fault growth models

late tertiary paleodepth reconstruction of the levant margin off israel abstract paleodepth reconstructions of the late tertiary levant continental margin off israel using one and two dimensional quantitative basin analysis reveals several interesting phenomena in the evolution of the margin such as tilting events of the deep basin in north south and east west directions westward progradation of the continental shelf in the southern levant and the variation in style along the levant margin this variation may be the result from the decreasing influence of the nile to the north and the increasing influence of the nearby plate boundaries in general the bathymetry of the margin from the deep basin to the base of the slope has become shallower since base neogene this reflects the general filling of the eastern mediterranean at a time when the sediment supply from the continental margin exceeds the subsidence the paleodepth reconstruction also suggests the existence of a deep basin in pre messinian time which resembles the present one thus implying that the deposition of the evaporites during the messinian desiccation of the mediterranean sea occurred in a deep basin

folding of oceanic lithosphere folding of the lithosphere just south of the bay of bengal appears as 1 undulations in acoustic basement topography and 2 as linear geoid undulations in the seasat altimeter data from the seasat data we find that the east west trending folds have wavelengths ranging from 130 to 250 km and clustering about 190 km the horizontal gravity disturbances due to the folds range in amplitude from 15 to 50 mgal elastic models of oceanic lithosphere have in the past been used to demonstrate the implausibility of lithosphere buckling or folding in response to compression these elastic models typically predict that compressive stresses of about 5 gpa are required to buckle oceanic lithosphere with an age comparable to that of the northeastern indian ocean 40 70 ma these stresses exceed the strength of lithospheric rock we use an elastic plastic model to show that oceanic lithosphere of this age should have a net compressive strength equal to about 12 of the elastic buckling stress we further demonstrate that loads approaching the net compressive strength cause the lithosphere to fold with a wavelength about 200 km i e the wavelength observed from seasat our results reinforce earlier speculation that this folding may be related to the himalayan orogeny

intraplate stresses and dynamical aspects of rifted basins abstract intraplate stresses play a important role during the syn and post rift evolution of sedimentary basins deviations from long term thermal patterns of post rift subsidence as well as the development of unconformities within rifted basins reflect to a large extent the temporal fluctuations of the regional stress fields in the lithosphere it appears that incorporation of intraplate stresses in dynamical models for basin development together with a quantification of the role of petrological changes in the crust lithosphere system can explain some of the observed shortcomings of thermal models of post rift basin subsidence late neogene accelerations in tectonic subsidence in the deeper parts of rifted basins in the northern atlantic and mediterranean regions could reflect a change in the level of intraplate stress over large areas of the globe non thermal contributions to the subsidence record affect estimates of crustal extension and consequently influence the depth at which hydrocarbon source rocks enter the maturity window stress induced changes in basement topography have also important consequences for the budget of fluid flow in the deeper parts of the sediment fill of the rifted basins as well as on the dynamics of diapirism

constraints on the tectonic development of the eastern gulf of mexico provided by magnetic anomaly data boundaries between oceanic and transitional crust in the eastern gulf of mexico have been delineated using detailed accurately navigated high quality aeromagnetic data these data indicate that considerably more oceanic crust may be present than previously suggested by other geophysical data especially seismic reflection data the n s extent of oceanic crust substantially increases westward from approximately 280 km near 87 w to roughly 390 km near 90 w indicating the proximity 10 of the pole of rotation variations in the amount of oceanic crust together with discontinuities in the magnetic anomaly patterns interpreted as the traces of fossil transform faults or fracture zones have been used to obtain a rough estimate of the location of the pole of rotation 24 n 81 5 w for the seafloor spreading phase of opening the magnetic data have been used to develop a model for the opening of the gulf and to identify some geometrical relationships between its conjugate continental margins based upon the estimated pole position the eastern gulf is interpreted to have opened in an approximately nne ssw direction with the counterclockwise rotation of yucatan away from north america the seafloor spreading phase of movement accounts for about 25 of the counterclockwise motion of yucatan rotating the yucatan block clockwise by this amount to restore it to its predrift position places the campeche bank adjacent to the mississippi trough louisiana shelf further clockwise rotation of yucatan by an additional 30 35 about this pole restores extended crust to its original thickness and is consistent with rotations of yucatan predicted from paleomagnetic data from chiapas

neotectonic implications and regional stress field constraints on mud volcanoes in offshore southwestern taiwan abstract recently discovered numerous mud volcanoes mvs and mud diapirs mds in sw taiwan both onshore and offshore show eruption lineaments suspected to be related to neotectonic processes spatial and temporal distribution of the mvs eruption events shows an obvious switch of the lineament orientation from nne ne n s nw and e w trending in n s direction the mud volcanoes have experienced multi stage eruptions and should have occurred

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

the structural evolution of the messinian evaporites in the levantine basin abstract the levantine basin in the south eastern mediterranean sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load because the messinian evaporites are comparatively young the sediment load varies along the basin margin they are hardly tectonically overprinted and the geometry of the basin and the overburden is well defined in this study we analyse depositional phases of the evaporites and their structural evolution by means of high resolution multi channel seismic data the basinal evaporites have a maximum thickness of about 2 km precipitated during the messinian salinity crisis 5 3 5 9 ma ago the evaporite body is characterized by 5 transparent layers sequenced by four internal reflections we suggest that each of the internal reflection bands indicate a change of evaporite facies possibly interbedded clastic sediments which were deposited during temporal sea level rises all of these internal reflections are differently folded and distorted proving that the deformation was syn depositional thrust angles up to 14 are observed backstripping of the pliocene quaternary reveals that salt tectonic is mainly driven by the sediment load of the nile cone the direction of lateral salt displacement is mainly ssw nne and parallel to the bathymetric trend apparent rollback anticlines off israel result rather from differential subsidence than from lateral salt displacement in the south eastern basin margin the deposition of the isreali slump complex isc is coeval with the onset of salt tectonic faulting suggesting a causal link between slumping processes and salt tectonics the superposition of thin skinned tectonics and thick skinned tectonics becomes apparent in several locations the fold belt off the israeli mediterranean slope mainly results from active strike slip tectonics which becomes evident in faults which reach from the seafloor well below the base of the evaporites owing to the wrenching of the crustal segments which are bounded by deep rooted fault lines like the damietta latakia pelusium and shelf edge hinge line the setting is transpressional south of 32 n where the fault lines bend further towards the west this adds a component of thick skinned transpression to the generally thin skinned compressional regime in the basin above 1 5 km of evaporites a mud volcano is observed with the mud source seemingly within the evaporite layer at the eastern cyprus arc the convergence zone of the african and the anatolian plates deep rooted compression heavily deformed the base of the evaporites whereas at the eratosthenes seamount mainly superficial compression affecting the post messinian sediments and the top of the evaporites is observed

some consequences of compressional tectonics for extensional models of basin subsidence changes in intraplate stress levels have important consequences for the stratigraphy of rifted basins and provide a tectonic explanation for the generation of sequence boundaries late stage compressional phases during the post rift evolution of basins produce unconformities with offlap phases that increase in magnitude with the age of the rifted basin late stage compression has not only a strong bearing on the generation of unconformities but also induces significant downbending of the centre of a basin ignorance of the vertical motions of the lithosphere induced by late stage compression during post rift evolution can therefore give rise to substantial errors in the estimates of crustal extension derived from analysis of basement subsidence using stretching models consequently late stage compression can be of great significance in estimates of depth and timing of the hydrocarbon window inferred from extensional models of basin subsidence quantification of the subsidence induced by post rift compression has important implications for integrated models of basin subsidence and hydrocarbon generation

tectonic processes in offshore northern israel and the evolution of the carmel structure abstract the carmel structure in northern israel is an elevated tilted block that extends from the land into the continental shelf and divides the levant continental margin into two distinct provinces its axis trends at a high angle to the levant margin and deflects mesozoic and cenozoic sedimentary and basement rocks the carmel structure is probably older than the levant margin itself and has been through several phases of activity most of the multichannel seismic profiles in the offshore of northern israel were reprocessed through time migration and then interpreted the resultant maps combined with gravimetric magnetic and bathymetric maps show a complex tectonic picture of the carmel structure and its vicinity four evolutionary stages can be recognized in this area a early mesozoic rifting along the present levant margin we speculate that the carmel was at that time a triple junction a thick mesozoic volcanic and carbonatic section of more than 6500 m indicates rapid subsidence probably accompanied by normal faulting b folding along the nne axis this is probably part of the syrian arc compressional system which was active from the late cretaceous until the eocene normal faults of the previous stage were probably reactivated becoming reverse faults c left lateral strike slips faulting this formed a north west fault system which resulted in a clockwise rotation of segments of the fold axis and was active from the late miocene to early pliocene d a tensional tectonic regime prevails since the pliocene and is probably still active at present the well pronounced kishon graben which extends from land to the continental shelf was formed during this period the first two stages are of regional extent whereas the latter stages are the reslt of local modification of the regional stress fields

extensional tectonics and stratigraphy of hibernia oil field grand banks newfoundland the tectonic evolution of the grand banks involved several episodes of rifting and sequential development of the continental margin the dominant period of rifting and basin formation in the central grand banks was late callovian to aptian extensional failure of the central grand banks crust probably occurred along a shear zone that dipped gently to the west listric normal basin forming faults merge at depth with this detachment system the listric murre fault soles at 26 km 16 mi creating the very deep jeanne d arc basin cross basin transfer faults accommodated different amounts and rates of extension and resulted in the conspicuous offset pattern and funnel shaped geometry of the jeanne d arc basin the hibernia oil field is associated with one of these structural salients the stratigraphy of the jeanne d arc basin and the hibernia oil field is a direct response to this tectonic and structural framework large scale unconformity bounded sequences correspond to major plate reorganizations and zipper type opening of the atlantic ocean smaller scale adjustments to episodic extension are expressed in multiple stacking of depositional sequences the broad scale evolution of the synrift succession involved the early deposition of limestones and oil prone shales about 10 12 m y later rifting climaxed resulting in floods of coarse terrestrial material from the rift shoulders the characteristics of these depositional systems reflect a pervasive structural control affecting the distribution of facies tracts dip slip movement on basin bounding faults and c oss basin transfer fault trends were equally important a profound structural modification of the hibernia structure occurred in late barremian time when a major detachment developed within the basin fill this structural modification and associated antithetic and synthetic faulting in the hanging wall largely controlled reservoir distribution and the maturation migration and trapping of hydrocarbons

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

three dimensional vp and vs structural models associated with the active subduction and collision tectonics in the taiwan region summary 3 d vp and vs models for the crust and upper mantle beneath the taiwan area have been determined using selected high resolution earthquake data from an island wide seismic network and two local seismic arrays lateral structural variations in the upper crust as also evident from surface geology are responsible for the observed large traveltime residuals or station corrections prior shallow velocity information inferred from traveltime residuals and joint hypocentral determination jhd station corrections for the uppermost crust is essential to facilitate a reliable tomographic inversion a finite difference method that is efficient and accurate for a highly heterogeneous velocity structure is applied to calculate p and s wave traveltimes from the source to receiving stations all earthquakes in the taiwan central weather bureau s catalogue are then relocated using the resultant 3 d vp and vs models the depth of the moho varies significantly especially along the east west direction in the western coastal plain and western foothills the depth of the moho is around 35 km which deepens gradually eastward reaches a maximum depth of 55 km beneath the eastern central mountain range shallows up rapidly beneath the longitudinal valley and coastal range and merges with the thin philippine sea plate offshore of eastern taiwan in central taiwan the central mountain range is bounded to the east and west by two steeply westward dipping active faults from the upper crust to a depth of about 30 km therefore the uplifted and thickened central mountain range serves as a backstop for the converging eurasian and philippine sea plates the crust beneath the central mountain range is characterized by a brittle high velocity and seismically active upper crust 15 km and a ductile low velocity and aseismic mid to lower crust below 15 km most probably due to the high geothermal activity from the excess heat supplied from the hot upper mantle beneath the thin oceanic crust to the east from the surrounding hotter upper mantle beneath the thickened continental crust and from shear heating during active collision the collision zone in eastern taiwan is characterized by an active and steeply eastward dipping seismic zone along a region of low vp and high vp vs ratio near the taitung region in southeastern taiwan it transforms into an active westward steeply dipping seismic zone along a transition zone between the high vp and vs oceanic crust and the low vp and vs continental crust near hualien region in central eastern taiwan there is no apparent seismicity within many sedimentary basins imaged from the tomographic inversion however af ew basins are either bounded on one side by an active fault or are characterized by blind faults beneath the geometry of the subduction zone in northeastern taiwan can be clearly imaged from the relocated earthquake locations behind the subduction a region of low vp and high vp vs ratio at depths of 5 to 10 km can be identified beneath the tatun chilung volcano group indicating a potential magma reservoir two steeply dipping linear seismic zones in the volcano region may mark the upward escape paths of the magmatic materials in the region

polyphase rift evolution of the voring margin mid norway constraints from forward tectonostratigraphic modeling the mid norwegian voring margin bounding the northern atlantic underwent several rift episodes after the caledonian orogeny permo triassic extension concentrated at the eastern inner margin followed by jurassic cretaceous extension at the center of the margin finally more westward the last rift episode led to continental breakup in the earliest eocene although the general architecture of the margin may be clear the timing and distribution of particularly the oldest rift structures are poorly constrained we use two dimensional forward tectonostratigraphic modeling for better quantitative understanding of the tectonic evolution of the margin two regional profiles crossing the margin have been analyzed modeling of the two profiles integrates the basin shape and fill as well as the underlying crustal structure of the margin the modeling allows us 1 to quantify the distribution and timing of extension of subsequent rift episodes 2 to predict the basin and crustal architecture at deep levels and 3 to test different interpretations of the seismic data the level of lithospheric necking during basin formation is constrained by basement topography and moho depth and lies within the middle crust 20 km furthermore we investigate the migration of the rift axes and the elastic lithospheric strength during the different rift episodes locations of previous extension are not reactivated during renewed rifting instead renewed rifting occurs preferentially in regions where the lithosphere has experienced less extension

plate reorganization a cause of rapid late neogene subsidence and sedimentation around the north atlantic subsidence analysis of wells in the central north sea and labrador grand banks and oft the west greenland scotian shelf and united states atlantic margin shows distinct quantitative stratigraphic correlation patterns of circum north atlantic sites a significant departure from the overall decrease in subsidence for the pliocene occurs in many wells when the rate is found to have increased one or more orders of magnitude from oligocence miocene rates wells were selected along transects from shore to basin to find if relative basin position is influenced by differential basin subsidence although stratigraphic resolution is not detailed more basinward sites experienced up to four times larger subsidence rates in the late neogene than in the oligocene miocene with a peak in the pliocene wells at the basin edge experienced much less subsidence or showed uplift the observations are consistent with a rapid change of intraplate stress at the cause for this observed transition in neogene subsidence major reorganizations of spreading direction and rate occurred during the pliocene along the entire atlantic spreading system possibly in conjunction with more global changes in plate motions we propose that the associated changes in intraplate stress caused the excess margin subsidence relative uplift along basin edges is consistent with this mechanism of relative movement and may explain apparent eustatic changes in sea level

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

subsurface imaging taiger experiments and tectonic models of taiwan abstract the seismicity deformation rates and associated erosion in the taiwan region clearly demonstrate that plate tectonic and orogenic activities are at a high level major geologic units can be neatly placed in the plate tectonic context albeit critical mapping in specific areas is still needed but the key processes involved in the building of the island remain under discussion of the two plates in the vicinity of taiwan the philippine sea plate psp is oceanic in its origin while the eurasian plate eup is comprised partly of the asian continental lithosphere and partly of the transitional lithosphere of the south china sea basin it is unanimously agreed that the collision of psp and eu is the cause of the taiwan orogeny but several models of the underlying geological processes have been proposed each with its own evolutionary history and implied subsurface tectonics taiger taiwan integrated geodynamics research crustal and mantle imaging experiments recently made possible a new round of testing and elucidation the new seismic tomography resolved structures under and offshore of taiwan to a depth of about 200 km in the upper mantle the steeply east dipping high velocity anomalies from southern to central taiwan are clear but only the extreme southern part is associated with seismicity toward the north the seismicity disappears the crustal root under the central range is strongly asymmetrical using 7 5 km s as a guide the steep west dipping face on the east stands in sharp contrast to a gradual east dipping face on the west a smaller root exists under the coastal range or slightly to the east of it between these two roots lies a well delineated high velocity rise spanning the length from hualien to taitung the 3 d variations in crustal and mantle structures parallel to the trend of the island are closely correlated with the plate tectonic framework of taiwan the crust is thickest in the central taiwan collision zone and although it thins toward the south the crust is over 30 km thick over the subduction in the south in northern taiwan the northward subducting psp collides with taiwan and the crust thins under northern taiwan where the subducting indenter reaches 50 km in depth the low vp vs ratio of around 1 6 at a mid crustal depth of 25 km in the central range indicates that current temperatures could exceed 700 c the remarkable thickening of the crust under the central range its rapid uplift without significant seismicity its deep exhumation and its thermal state contribute to make it the core of orogenic activities on taiwan island the expanded network during the taiger deployment captured broadband seismic data yielding enhanced s splitting results with mainly sks skks data the polarization directions of the fast s waves follow very closely the structural trends of the island supporting the concept of a vertically coherent taiwan orogeny in the outer few hundred kilometers of the earth

intraplate stresses a new tectonic mechanism for fluctuations of relative sea level stress variations in the lithosphere of a few hundred bars can explain the major part of the seismostratigraphic record at passive margins and intracratonic basins however to induce apparent sea level fluctuations with magnitudes greater than 50 m changes in stress level of more than 1 kbar are required these must be related to major reorganizations at convergent plate boundaries fragmentation of plates or collision processes specific rapid falls in the vail et al curves can be associated quantitatively with particular plate tectonic reorganizations of lithospheric stress fields the seismostratigraphic record may provide a new source of information on paleo stress fields to be correlated with results of independent numerical modeling of intraplate stresses

episodic north america and pacific plate motions the north america plate motion for the period 20 0 m y is modeled by two absolute angular velocity vectors with a change occurring at about 9 m y the model incorporates new geologic constraints based on 1 the recognition of a discontinuity in north america plate motion at 9 m y 2 a reexamination of the iceland and yellowstone hotspot traces 3 improved delineation of the present north america pacific relative motion and 4 a revised history of pacific absolute motion the two stage model is consistent with several features of the late cenozoic geologic history of north america including geological observations relating to tectonism along a large portion of both the eastern and western boundaries of north america this plate model combined with a previously established pacific plate model makes specific predictions concerning the 15 0 m y history of the north america pacific plate boundary which compare favorably with the known history these models together resolve most of the discrepancies previously encountered between absolute and relative motion models of the two plates the implications of the north america plate model are the greatest for those events related to the 9 m y change in its motion among the geologic consequences of this change are rifting in the western united states intense compressional deformation along the northern caribbean plate boundary a hiatus in aleutian arc volcanic activity and a change in the orientation of the lesser antilles arc this picture reinforces the notion that the major plates behave rigidly and transmit stresses over great distances the predictive power of the model may help in interpreting the history of the north america plate boundary in those areas where clear observations are lacking an extra force needs to be applied to a plate to cause a change in plate motion by treating the plate as a rigid spherical shell overlying a uniformly viscous fluid we derive a simple class of forces sufficient to cause a given change in plate motion such force balance considerations indicate that an additional force applied in the northwest pacific region toward the northeast would result in the observed change in north america plate motion this force is surprisingly similar to that which apparently caused a large change in pacific plate motion about 5 m y later we propose that a common mantle process is responsible for both changes and is related to the ability of the northwest pacific subducted lithosphere to enter into the lower mantle

a global scale plate reorganization event at 105 100 ma abstract a major plate reorganization is postulated to have occurred at approximately 100 ma however this reorganization has received limited attention despite being associated with the most prominent suite of fracture zone bends on the planet and many other geological events we investigate tectonic events from the period 110 to 90 ma and show that the reorganization occurred between 105 and 100 ma was global in scale and affected all major plates seafloor evidence for plate motion changes is abundant during this period with either fracture zone bends or terminations preserved in all ocean basins long lived eastern gondwanaland subduction ended along a 7000 km long section of the margin while elsewhere around the proto pacific rim subduction continued and there is evidence that compressional stresses increased in the overriding plates thrusting in western north america transpression and basin inversion in eastern asia and development of the present day andean style margin along western south america occurred contemporaneous with the development of an extensional regime in eastern gondwanaland basin instability in africa and western europe further demonstrates that lithospheric stress regime changes were widespread at this time considering the timing of the reorganization and the nature of associated plate boundary changes we suggest that eastern gondwanaland subduction cessation is the most likely driving mechanism for the reorganization subduction is the dominant driver of plate motion and therefore this event had the potential to strongly modify the balance of driving forces acting on the plates in the southwestern proto pacific and neighboring plates whereby producing widespread changes in plate motion and continental lithospheric stress patterns we propose that major changes in ridge trench interaction triggered the cessation of subduction the progressive subduction of two closely spaced perpendicular mid ocean ridges at the eastern gondwanaland subduction zone to the east of australia and new zealand respectively resulted in very young crust entering the trench and we suggest that by 105 100 ma there was insufficient negative buoyancy to drive subduction finally we propose that the plume push force of the bouvet plume that erupted near the african antarctic south american triple junction contributed to plate motion changes in the southern atlantic region

a structural transect between the central north sea dome and the south swedish dome middle jurassic quaternary uplift subsidence reversal and exhumation across the eastern north sea basin

gulf of mexico plate reconstruction by palinspastic restoration of extended continental crust abstract a number of recently published gulf of mexico plate reconstructions are strikingly dissimilar there are no sea floor magnetic lineations and the sizes and shapes of the continental blocks are not well defined perhaps the only common feature of the several reconstructions is that they ignore the role of continental crust extension during rifting in this study total tectonic subsidence analysis was used to estimate the mount of crust extension in the gulf of mexico to determine its effects on the proposed plate reconstructions this involves the calculation and mapping of the sediment unloaded basement depth from observations of the basement depth water depth and sediment compaction properties the well known depth age relation for oceanic crust and a model for the subsidence of extended continental crust allowed within the limits of available data the identification and mapping of crust type and the amount of extension of transitional crust the zone of extended continental crust under the northern margin of the gulf is extraordinarily wide more than 800 km 500 mi in a cross section through east texas the zone of extended crust to the south is much narrower about 150 km 90 mi on the margin of the yucatan block palinspastic restoration shows that the total 950 km 590 mi of extended and thinned continental crust corresponds to 490 km 300 mi of continental crust of original thickness therefore 460 km 280 mi of crustal extension occurred during rifting and prior to ocean crust formation the 460 km 280 mi of extension along this cross section and the results of similar calculations on other cross sections must be accounted for properly when reconstructing the prerift configuration of the gulf of mexico end of article last page 525

intraplate stresses and the subsidence history of the sirte basin libya abstract results of quantitative analysis of subsidence data from 20 wells covering six major basement blocks from the sirte basin libya are presented following the late cretaceous onset of extension and associated collapse of the sirte arch the tectonic history post dating this event can be separated into four distinct phases 1 1 minor subsidence during the late cretaceous 2 2 differential fault tectonics and reactivation of basement faults during latest cretaceous to paleocene 3 3 regional uplift and subsidence during the eocene 4 4 minor subsidence during the early oligocene and early miocene a late cretaceous paleocene stretching phase of finite duration can explain the overall patterns of observed tectonic subsidence during the syn and post rift evolution of the sirte basin strong short term deviations from thermally induced long term subsidence observed during the eocene can be explained by intraplate compression and subsequent stress release related to changes in atlantic flowline geometry modelling of the observed tectonic subsidence for the sirte basin yields estimates of extension in excess of estimates inferred from displacements along high angle normal faults the effect of late stage intraplate compression on tectonic subsidence may cause part of the observed discrepancy between estimates of crustal extension

dense network intense seismicity and tectonics of taiwan abstract a temporary seismic network consisting of 295 land stations was deployed in 2009 in taiwan to monitor airgun sources during an onshore offshore experiment in taiwan we exploit the continuously recorded dataset to detect and map seismicity in the seismically very active taiwan by combining recent automatic detection and phase picking techniques we successfully generate an initial earthquake catalog of over 8400 events the hypodd algorithm is used to relocate and filter these events this network recorded smaller events than the permanent regional network because of the many stations around the high mountain ranges and the generally high station density along 6 lines the results based on the 2009 data generally reproduce the dominant seismicity features from many years of earthquake monitoring in taiwan in addition we map hitherto unknown dipping zones under the foothills and the central range that may correspond to seismogenic structures

segmentation of the levant continental margin eastern mediterranean 1 the levant continental margin is divided into two major segments by the carmel structure which extends from the dead sea fault into the eastern mediterranean new seismic reflection data over the unexplored northern segment are used for completing the structural framework of the levant area together with existing data south of it inclusive depth structural maps of the area were produced for the base pliocene and base messinian evaporites previous studies indicate that differences between the two segments are well expressed in the deep crustal structure the present study which focuses mainly on the shallow section shows that these differences are maintained throughout the accumulation of young sedimentary units and even in the bathymetry this preservation of segmentation both in the shallow and in the deep structure insinuates that the two segments were formed through different continental breakup processes which continue to dictate the style of sediment accumulation

thermo mechanical modelling of black sea basin de formation abstract we present the results of a thermo mechanical modelling study carried out to investigate the effect of pre rift rheology on subsequent basin de formation in the black sea area important differences are inferred for the bulk lithosphere structure and mechanical properties expressed in terms of different estimates for levels of necking in the western and eastern black sea respectively gravity data provide constraints on the mode of flexure in the black sea pointing to significant lateral variations in pre rift lithospheric strength these features strongly affect predictions for mesozoic cenozoic basin stratigraphy and have implications for the presence and development of rift shoulder topography on the margins of the black sea basins differences in lithosphere strength affect the mode of stress propagation from the basin margins into the central parts of the black sea basins during the post rift phase these post rift compressional stresses could be of key importance for long wavelength late neogene differential motions within the basins superimposed on vertical motions induced by rifting and subsequent sediment loading thermo mechanical modelling of integrated lithospheric strength points to a rapid increase of strength during the later stages of post rift evolution and the presence of relatively strong lithosphere in the centre of the basin these features predict preferential shortening induced by compressional activity of surrounding orogens to be primarily accommodated at the basins margins

geomorphic evolution of the malta escarpment and implications for the messinian evaporative drawdown in the eastern mediterranean sea abstract carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in numerous sites around the world their geomorphic evolution is poorly understood due to difficulties in assessing escarpment outcrops and the limited resolution achieved by geophysical techniques across their steep topographies the geomorphic evolution of carbonate escarpments in the mediterranean sea has been influenced by the messinian salinity crisis msc during the msc 5 97 5 33 ma the mediterranean sea became a saline basin due to a temporary restriction of the atlantic mediterranean seaway resulting in the deposition of more than one million cubic kilometres of salt the extent and relative chronology of the evaporative drawdown phases associated to the msc remain poorly constrained in this paper we combine geophysical and sedimentological data from the central mediterranean sea to reconstruct the geomorphic evolution of the malta escarpment and infer the extent and timing of evaporative drawdown in the eastern mediterranean sea during the msc we propose that during a msc base level fall fluvial erosion formed a dense network of canyons across the malta escarpment whilst coastal erosion developed extensive palaeoshorelines and shore platforms the drivers of geomorphic evolution of the malta escarpment after the msc include i canyon erosion by submarine gravity flows with the most recent activity taking place

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

initiation of gravitational collapse of an evaporite basin margin the messinian saline giant levant basin eastern mediterranean regional 2d and 3d seismic data from the levant basin reveal the updip extensional component of thin skinned gravity tectonics on this continental margin because of its youth 5 7 ma the earliest stages of deformation of this salt basin are preserved without the severe structural overprinting common on more mature giant salt tectonic systems extension detaches onto and within messinian evaporites up to 1800 m thick by structural restoration we reconstruct the tectonic evolution of the messinian evaporites using paleobathymetric constraints from wells and seismic profiles this analysis suggests that the mediterranean drawdown during the messinian salinity crisis was 800 m the 10 to 15 km wide extensional domain tracks the landward pinch out of the mobile messinian evaporites against an older late miocene scarp diachronous extension began in the center of the margin in the mid pliocene then spread northward in the late pliocene then finally southward in the early pleistocene extension continues today on many of the most landward faults extensional strain varies greatly along strike from 1 km to as much as 12 15 km comparing observations with four end member conceptual models we infer that both extension and seaward salt flow thinned the evaporite margin and its overburden both processes were triggered by a combination of uplift of the continental shoulder of the dead sea rift and subsidence in the mediterranean basin at least three factors controlled variations in extension 1 degree of tilting of the salt wedge related to the interplay of coastal uplift and basin subsidence 2 presence of pre messinian canyons overlain by landward salients of salt and 3 variations in evaporite facies and the proportion of siliciclastic admixture

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

magnetic anomalies over the central levant continental margin abstract the magnetic field over the central levant continental margin off northern israel and southern lebanon and the adjacent levant basin has two distinct trends mount carmel and its offshore continuation carmel nose which are the surface expression of a large subbottom structure that extends from the land area across the continental shelf to the continental slope form a dividing zone between the two magnetic trends south of the carmel structure the magnetic field trends east west while north of the carmel structure it trends northeast and north northeast several pronounced magnetic anomalies exist mainly north of the carmel structure the majority of which trend north northeast and northeast parallel and sub parallel to the trend of the magnetic field in this area some also trend northwest perpendicular to the trend of the magnetic field in several cases the magnetic anomalies indicate large lithological elements which continue from land to sea gravity and seismic refraction data show that the two magnetic domains north and south of the carmel structure are associated with areas of different crustal structure south of the carmel structure the continetal oceanic crustal transition zone is located beyond the continental margin at the base of the continental slope while north of the carmel structure it is located under the continental shelf near the shore on land there are also differences in the structure of the crust north and south of the carmel structure the crust being much thinner north of the structure than south of it we suggest that some of the large magnetic anomalies off the central levant were formed during the rifting phase of the eastern mediterranean

a midcrustal ramp fault structure beneath the taiwan tectonic wedge illuminated by the 2013 nantou earthquake series 1 taiwan s active mountain belt is a spotlight for orogenic studies and was first used to test the critical taper wedge mechanics the concept of an orogenic wedge above a shallow detachment surface has been highly influential on current understanding of orogenic processes in taiwan however the recent ml 6 2 and ml 6 5 2013 nantou reverse faulting earthquakes in central taiwan have nucleated below the proposed detachment indicating that active mountain building is occurring below the orogenic wedge we estimate the coseismic slip distributions and fault geometry using the uniform stress drop slip inversions the earthquakes occur on essentially the same 30 dipping fault plane ramping up from 20km depth near a cluster of 1999 chi chi earthquake aftershocks to the shallow detachment and the chi chi fault plane the fault could be a deep extension of a mature shallow fault or a newly developed deep ramp fault that is not reflected in the surface geology

mass balanced paleogeographic reconstructions paleogeography paleotopography and paleobathymetry of a closed erosion depositional system can be reconstructed by restoring sedimentary masses to elevated surfaces in a drainage basin based on the inverse of present erosion equations and adjusting for isostasy sea level changes sediment compaction and thermal subsidence the erosion deposition history of the northwestern gulf of mexico margin and its western central north american source area during the cenozoic is used to explore the sensitivity of mass balance reconstructions and changes in assumptions concerning erosion rate parameters and sea level

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

late tertiary seismic facies and structures of the levant passive margin off central israel eastern mediterranean abstract the late tertiary seismic facies and structures of the levant passive margin off central israel in the eastern mediterranean sea were studied by the interpretation of more than 3000 km of seismic reflection profiles most of them previously unpublished single channel profiles the neogene growth and evolution of this margin was influenced by the interaction of three main processes 1 the outbuilding and loading of the margin by the nile sediments since the pliocene 2 uplift and tectonic subsidence related to the tectonic activity along the dead sea transform and 3 the effect of the above processes on the thick messinian evaporites which caused many salt tectonic features including flowage piercement diapirs slumps and en echelon listric normal faults in the supra salt sediments we suggest that the study area may be divided into two segments north and south of caesarea these segments vary in their depositional environment the amount of sediment supply and load salt related features and tectonic activity we propose that the northern segment is affected by low sediment supply and by the continued uplift of the carmel structure and that this segment may even be a part of this structure the southern segment has been affected by the deposition and loading in the nile derived sediments since the pliocene three main depositional sequences were observed in the southern segment 1 sequence i early pliocene onlaps the top of the messinian evaporites representing a rise of sea level and renewed subsidence 2 sequence ii early pleistocene is lens shaped thinning to the north west and east and was derived during a relatively short time interval from the pre nile and 3 sequence iii since the pleistocene represents a major episode of continental shelf construction

tectonic tremor and lfes on a reverse fault in taiwan we compare low frequency earthquakes lfes from triggered and ambient tremor under the southern central range taiwan we apply the pagerank algorithm used by aguiar and beroza 2014 that exploits the repetitive nature of the lfes to find repeating lfes in both ambient and triggered tremor we use these repeaters to create lfe templates and find that the templates created from both tremor types are very similar to test their similarity we use both interchangeably and find that most of both the ambient and triggered tremor match the lfe templates created from either data set suggesting that lfes for both events have a common origin we locate the lfes by using local earthquake p wave and s wave information and find that lfes from triggered and ambient tremor locate to between 20 and 35 km on what we interpret as the deep extension of the chaochou lishan fault

post messinian evolution of the southeastern levant basin based on two dimensional stratigraphic simulation abstract the evolution of the southeastern levant basin following the messinian salinity crisis was interpreted using observations derived from seismic sections and well data and from output of a two dimensional forward stratigraphic simulation program sedpak the working assumption was that the thick evaporitic messinian sequence was generated in a shallow water albeit a topographically deep basin the sea level dropped at least 800 m below its present level and may have been as low as 1300 m the latter value representing the reconstructed depth of the top messinian in the deep part of the basin the top of the evaporitic sequence in that part of the basin was virtually horizontal at the end of the messinian crisis and thus may be used as a regional datum subsidence rates measured for the shelf and coastal plain of israel indicate a reduction of these rates for the pleistocene when compared to the pliocene during the pleistocene subsidence rates for the base slope increased and dictated the modern physiography of the margin earlier in the middle to late pliocene small scale salt movements occurred in the deep basin producing the fragmented and irregular shape of the m horizon the seismic event marking the top of the evaporitic sequence and deforming the overlying pliocene section the simulated rate of sediment supply indicates a constant increase over time for the pliocene and the pleistocene probably in response to an increased influx of nile derived along shelf sediment transport

seismic refraction profiles between cyprus and israel and their interpretation summary a long seismic refraction profile was carried out between southern israel and cyprus the seismic energy was generated by 33 sea shots each of 0 8 t explosives and was recorded by land stations in israel and cyprus and by ocean bottom seismographs deployed along the profile the results showed that the continental crust of southern israel thins towards the mediterranean underneath a northward thickening sedimentary cover cyprus is underlain by a 35 km thick continental crust thinning south wards and extending to mt eratosthenes between mt eratosthenes and the israel continental shelf the crystalline crust is composed of high velocity 6 5 km s 1 material and is about 8 km thick it is covered by 12 14 km of sediments and may represent a fossil oceanic crust

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

are the norwegian mountains compensated by a mantle thermal anomaly at depth article i nfo article history the norwegian mountains or scandes represent a long mountain range stretching from southern norway to the arctic and is characterised by a rugged topography and peaks up to 2 5 km high the origin of this mountain chain far away from any plate boundary remains a matter of passionate debates inside the geoscientific community hot mantle fingers originating from the iceland plume impacting the base of the scandinavian lithosphere and creating asthenospheric diapirs is one of the most accepted hypotheses for explaining cenozoic uplift in norway in order to test this hypothesis we conducted integrated gravity and thermal modelling we used the dense ngu gravity grid i e one measurement every 3 km and modelled the depth extent and the mass deficit associated to the compensating loads located below the southern scandes assuming that the density deficit below the scandes is purely thermal in origin thermal modelling allowed for testing the magnitude of the potentially associated temperature anomaly and its impact on surface heat flow recently acquired heat flow data were used in order to constrain the results from the thermal modelling the results of our integrated geophysical modelling rule out the possibility that the present day topography of the southern scandes is compensated by a deep seated asthenospheric diapir however our modelling does not exclude that thermal processes in the deep mantle could have initiated or assisted recent uplift of the southern scandes

a single stage megaflood at the termination of the messinian salinity crisis geophysical and modelling evidence from the eastern mediterranean basin abstract the messinian salinity crisis was an extraordinary event that resulted in the deposition of kilometre thick evaporite sequences in the mediterranean sea after the latter became disconnected from the world s oceans the return to fully and stable marine conditions at the end of the crisis is still subject to debate three main hypotheses based on geophysical and borehole data onshore outcrops and climate simulations have been put forward these include a single stage catastrophic flood a two step reflooding scenario and an overspill of paratethyan water followed by atlantic inflow in this study two research questions are addressed i which event marked the termination of the messinian salinity crisis ii what was the sea level in the eastern mediterranean sea during this event geophysical data from the western ionian basin are integrated with numerical simulations to infer that the termination of the crisis consisted of a single stage megaflood following a sea level drawdown of 1900 m this megaflood deposited an extensive sedimentary body with a chaotic to transparent seismic signature at the base of the malta escarpment fine well sorted sediments are predicted to have been deposited within the thicker sections of the flood deposit whereas a more variable distribution of coarser sediments is expected elsewhere the north western ionian basin hosts evidence of episodic post messinian salinity crisis slope instability events in the last 1 8 ma the largest of these emplaced a 200 km3 deposit and is associated with failure of the head of noto canyon offshore se sicily apart from unravelling the final phase of the messinian salinity crisis and the ensuing stratigraphic evolution of the western ionian basin our results are also relevant to better understand megafloods which are some of the most catastrophic geological processes on earth and mars

evidence for kilometre scale neogene exhumation driven by compressional deformation in the irish sea basin system simon p holford paul f green jonathan p turner gareth a williams richard r hillis david r tappin ian r duddy

crustal structure of the levant basin eastern mediterranean abstract a seismic refraction wide angle reflection experiment was undertaken in the levant basin eastern mediterranean two roughly east west profiles extend from the continental shelf of israel toward the levant basin the northern profile crosses the eratosthenes seamount and the southern profile crosses several distinct magnetic anomalies the marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources the results of this study strongly suggest the existence of oceanic crust under portions of the levant basin and continental crust under the eratosthenes seamount the seismic refraction data also indicate a large sedimentary sequence 10 14 km thick in the levant basin and below the levant continental margin assuming the crust is of cretaceous age this gives a fairly high sedimentation rate the sequence can be divided into several units a prominent unit is the 4 2 km s layer which is probably composed of the messinian evaporites overlying the evaporitic layer are layers composed of plio pleistocene sediments whose velocity is 2 0 km s the refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single layer oceanic crust takes place along the levant margin the transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual the northern profile north of the carmel structure presents a different structure the continental crust is much thinner there and the transition in the crustal structure is more rapid the crustal thinning begins under western galilee and terminates at the continental slope the results of the present study indicate that the levant basin is composed of distinct crustal units and that the levant continental margin is divided into at least two provinces of different crustal structure

paleogeographic evolution of early deep water gulf of mexico and margins jurassic to middle cretaceous comanchean the paleobathymetric configuration of the early gulf of mexico is inferred from 1 cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data 2 distribution of jurassic and cretaceous platform and basinal facies and 3 hindcasting of subsidence history in the central basin substantial paleogeographic ambiguity results from uncertainty about 1 kinematics and timing of late triassic to jurassic extensional opening of the gulf basin which probably involved major strike slip faulting 2 the magnitude of subsequent compressive deformation on the western and southern basin margins and 3 possible accretion of allochthonous terranes the initial sub sea level topographic depression created by crustal extension is manifested by the distribution of callovian pre marine salt and oxfordian basinal marine facies late jurassic sea floor spreading split the main salt body and created a central deep water 1 km trough from the oxfordian to early neocomian ramp like platform margins generally underwent net retreat except in the northern gulf where major clastic progradation took place carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the cretaceous these cretaceous carbonate margins exhibit a variety of architectural styles including 1 in the northwestern gulf two cycles of progradation coahuilan and comanchean terminated by drowning events 2 in the southwestern gulf a single cycle of progradation 3 continuous aggradation along the florida and campeche escarpments paleobathymetric relief across cretaceous carbonate margins ranges from high and steep to low relief to ramplike the close of comanchean drowning event greatly and permanently reduced the extent of circum gulf carbonate platforms and especially rimmed margins locations of cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust by the distribution of salt and by clastic progradation eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the gulf but other paleoenvironmental variables such as nutrient abundance are probably important as well

late tertiary subsidence history of the southern levant margin eastern mediterranean sea and its implications to the understanding of the messinian event the late tertiary subsidence history of the southern levant continental margin situated in the southeastern mediterranean sea was quantitatively analyzed paleodepth reconstruction across the margin off ashdod suggests the existence of a deep basin in pre messinian time which resembles the present one this implies that the deposition of the evaporites in the study area during the messinian desiccation of the mediterranean sea occurred in a deep basin the path of the tectonic subsidence of the basement since early tertiary is generally smooth as expected from the nature of the thermal subsidence the unconformity beneath the messinian indicates erosion of 50 200 m at the coastal plain in the pliocene the tectonic subsidence in the coastal plain and shelf area diverts from the expected thermal path and increases from 250 m to 450 m respectively in the quaternary the rate of tectonic subsidence nearly resumed the predicted thermal subsidence sedimentation and subsidence rates decrease but are still higher than those of the pre messinian we suggest that the evolution of the southern levant margin is most probably influenced by three main causes 1 the messinian event in late miocene 2 the deposition of large volumes of nile derived sediments since the pliocene and 3 the flexural response of the lithosphere to the load from the nile delta and or from the uplift of the judea mountains the western shoulder of the dead sea transform we interpret the latter to be the cause of the anomalous subsidence of the southern levant margin during the pliocene

3d seismic characterisation of an array of blind normal faults in the levant basin eastern mediterranean the geometry throw distribution and kinematics of an array of blind normal faults were investigated using a high resolution 3d seismic dataset located in the levant basin offshore israel to establish criteria allowing true blind faults to be distinguished from minor synsedimentary faults a detailed analysis of throw distribution on the fault planes shows that the displacement exhibits a crudely concentric pattern about a maximum region located centrally on a fault plane as expected for ideal blind faults however vertical displacement profiles do not exhibit classical linear or triangular profiles but are mostly flat topped or hybrid in type comparison of unrestricted blind faults to those that interacted with a mechanical boundary or another structure suggests that such interactions significantly modify the throw spatial distribution on a fault plane to distinguish small synsedimentary faults from blind faults we use a combination of three criteria to assess whether a fault grew by blind propagation 1 plunging upper tip region and complementary pattern in the throw contours 2 presence of upper tip propagation fold and 3 absence of stratigraphic evidence that the fault interacted with the free surface

seasat derived gravity constraints on stress and deformation in the northeastern indian ocean we use seasat derived gravity data to investigate crustal deformation in the ne indian ocean gravity highs reflecting crustal undulations vary in orientation from e w in the central indian basin to ne sw in the wharton basin the undulations vary in trend similarly to the variation of the maximum compression directions predicted by a plate driving force model cloetingh and wortel 1985 and are essentially restricted to the area of predicted compression for both principal horizontal stresses this agreement implies that the stress model describes the basic features of the deformation observed in the gravity as well as the seismicity the gravity data also provide insight into two enigmatic tectonic features the transition in the morphology of the 90 e ridge at 10 s from a continuous high to a complex blocky structure appears related to the deformation since undulations in the central indian basin can be projected eastward to blocks on the ridge the morphology formerly interpreted as a fossil feature may reflect the recent deformation the discrepancy between the trends of the southernmost 85 e ridge and the 90 e ridge previously thought to exclude similar hot spot track origins appears to result from treating a crustal undulation as part of the 85 e ridge earthquakes do not appear to be preferentially located with respect to the peaks and troughs of the undulations

is the lishan fault of taiwan active abstract the lishan fault has been characterized alternately as a major discontinuity in stratigraphy structures and metamorphism a ductile shear zone a tectonic suture or non existent in addition to being a geological boundary it also marks transitions in subsurface structures thus the seismicity to the west of the fault permeates through the upper and mid crust while beneath the central range it is noticeably less and largely concentrated in the upper 12 km a prominent west dipping conductive zone extends upward to meet the lishan fault also the eastward increase of crust thickness from 30 km in the taiwan strait quickens under the lishan fault to form a root of over 50 km under the central range in the past the small magnitude seismicity along the lishan fault has been noticed but is too diffuse for definitive association with the fault recent processing of aftershock records of the 1999 mw 7 6 chi chi earthquake using central weather bureau data and especially data from three post chi chi deployments of seismic stations across central taiwan yielded hypocenters that appear to link directly to the lishan structure the presence of a near 4 km long vertical seismic zone directly under the surface trace of the lishan fault indicates that it is an active structure from the surface down to about 35 km and the variety of focal mechanisms indicates that the fault motion can be complex and depth dependent

regional stress field of the indian plate we have calculated the regional stress field in the indian plate implementing dependence of slab pull and ridge push on the age of the oceanic lithosphere in the finite element procedure the high level of the calculated stress field order of a few kbar and the dominance of compression in the plate are consequences of the unique dynamic situation of the present day indian plate the calculated stress field explains the concentration of intraplate deformation in the region of the ninetyeast ridge and yields insight into the variations in stress directions in the australian continent

sequence stratigraphic analysis in deep water underfilled nw european passive margin basins sequence stratigraphic analysis is now carried out routinely on mesozoic cenozoic sedimentary basins with a view to understanding their post rift stratal geometries and predicting facies architecture the conventional method embodies two concepts the physical division of strata into unconformity bounded units and their genetic interpretation on the assumption that hierarchical changes in sea level represent the primary control on sedimentary architecture the genetic model is reflected in a complex descriptive terminology and derives from the development of the method in shallow water basins where the results of analyses typically accord with geological data constraints applied to deep water underfilled basins however the sea level assumption yields results that are unsatisfactory and in many cases misleading reflecting the influence of additional controls including tectonic movements deep sea currents and climate e g glaciation on stratal geometries and facies architecture this is illustrated by comparative analyses of examples from the deep water cenozoic basins of the nw european atlantic passive margin which contain a set of seismic megasequences bounded by unconformable to conformable surfaces correlative from shelf to slope to basinal settings the deep water successions contain regional locally diachronous submarine unconformities that were generated in response to changes in deep water current circulation and slope processes rather than subaerial erosion these bound aggradational contourite drifts that include upslope accretion against basin margins the deep water successions interfinger at two levels with seaward prograding shelf slope wedges that reflect differential tectonic movements involving coeval uplift and subsidence the youngest wedges formed in the last 4 ma and record seaward progradation of the margin by up to 100 km overprinting high amplitude variations in sea level and coeval with changes in deep ocean currents sediment supply by fluvial sources gave way in the pleistocene to direct glacial sediment supply to the slope in all these instances the stratal geometries and facies architecture cannot be attributed to a simple lowering of regional sea level but instead reflect a complex interplay of controlling factors including tectonic movements changes in sediment supply deep water current activity and climate in addition to sea level sequence stratigraphic analysis in such settings must recognise and evaluate alongslope downslope and vertical components of sediment supply

pleistocene development of the se nordic seas margin abstract throughout the pleistocene the sedimentary environment on the se nordic seas continental slope outer shelf off western norway has been strongly controlled by variability in the norwegian atlantic current nwac glaciations of the shelf areas and sea level changes acoustic and core data from the southern voring plateau show a pleistocene sequence characterised by hemipelagic sediments interfingered by diamictons on the upper slope the area of the 7 25 14 c ka bp storegga slide shows evidence of a long history of pleistocene mega slides during the last interglacial and most likely also during previous interglacials the slide region has been the locus of rapid deposition between water depths of 800 and 1200 m as a result of nwac winnowing along the upper slope the north sea fan region is strongly influenced by glacigenic debris flows gdfs deposited during glacial advances reaching the shelf edge when the norwegian channel was occupied by the norwegian channel ice stream it appears that gdf activity was initiated at ca marine isotope stage 12 interbedded between the debris flow sequences mega slide events such as the more and tampen slides have been identified during glaciations when the entire se nordic seas continental shelf was covered by extensive grounded ice sheets basal till were transported to the shelf edge from where subsequent mass movement occurred during late glaciation early deglaciation meltwater plumes were released at the time of disintegration of ice streams in the norwegian channel as is evidenced from the last deglaciation of the margin at ca 15 14 c ka bp the plume material was transported northwards by currents before rapidly deposited as a thick package within the storegga slide area and on the south voring plateau based on identification and dating of iceberg scourings glacial erosion surfaces and delta deposits on the shelf subsidence rates between 0 7 and 1 2 m ky have been calculated for the last ca 250 ka

extricating dynamic topography from subsidence patterns examples from eastern north america s passive margin abstract global sea level eustatic histories generated by backstripping stratigraphy are predicated upon the lithosphere having a well understood tectonic history however sub plate processes play a role in governing lithospheric vertical motions with timescales and amplitudes akin to eustasy which are difficult to predict we examine how stratigraphic and geophysical observations combined with simple isostatic models can be used to disentangle histories of sub plate support and eustasy we focus on the passive margin of eastern north america where a generally accepted history of eustasy has been estimated negative long wavelength free air gravity anomalies residual ocean age depth estimates fast upper mantle shear wave velocities and geodynamic models suggest that cenozoic evolution of this passive margin has been influenced by upper mantle drawdown we build on existing analyses to backstrip sixteen wells which combined with seismic data constrain timing and extent of cenozoic subsidence results indicate up to 1000 m of water loaded subsidence between 20 0 ma centered on the baltimore canyon trough seismic data from the trough shows neogene aggrading clinoforms there is little evidence for faulting or stratigraphic growth which indicates that neogene lithospheric strain rates were low amplitude and spatial extent of neogene subsidence are difficult to explain by glacio eustasy or glacio isostatic adjustment instead sub plate support calculated from conversion of shear wave velocities to temperature and isostatic calculations indicate that upper mantle drawdown was responsible for subsidence of the margin because mantle convection is vigorous such observations are expected throughout the stratigraphic archive

pliocene change in pacific plate motion the absolute motion of the pacific plate has been nearly constant during the past 15 myr but epp1 recognized that some change took place between 15 myr and the present and tentatively chose 1 myr for the time of the change cox and engebretson2 found a change in pacific absolute motion based on hotspot tracks and a change in pacific antarctic relative motion the pliocene deformation in california and the juan de fuca rotations led them to postulate a 5 myr age for the change the manner and timing of the change are explored more thoroughly here and we put the time for the change in motion of the pacific plate at between 5 and 3 2 myr basing the younger limit on the correlation of computed hotspot tracks with pacific and nazca hotspot traces the change may explain several observations on the neighbouring continental and oceanic plate boundaries including direct adjustments at the pacific spreading ridges a likely mechanism for the change is a large clockwise torque caused by acceleration of the sinking slab beneath the kurile trench where a fossil spreading ridge is inferred to have been subducted

displaced terranes and crustal evolution of the levant and the eastern mediterranean geophysical data from the levant and the eastern mediterranean suggest that this area can be divided into distinct crustal units of different origins for example a marked difference in crustal structure and structural style exists in the levant between samaria and judea south of the carmel structure and the galilee and lebanon north of it on the other hand several microcontinental fragments such as cyprus and the eratosthenes and anaximander seamounts are embedded within the oceanic crust of the eastern mediterranean the present location of these units has resulted from complex tectonic processes which were active during the mid paleozoic mesozoic evolution of this area during this period several crustal units were accreted to the northern margin of africa while others were detached away from it the crustal evolution of the eastern mediterranean and the levant is intimately linked with the closure of the paleo tethys the formation of the neo tethys and its subsequent closure

palaeocene uplift and eocene subsidence in the northern north sea basin from 2d forward and reverse stratigraphic modelling structural and stratigraphic basin modelling has been used to examine quantitatively the cretaceous and tertiary post rift subsidence history of the northern north sea basin following late jurassic extension 2d forward and reverse syn rift and post rift modelling has been used to determine the magnitude and timing of departures from the mckenzie post rift thermal subsidence trend for regional stratigraphic profiles in the outer moray firth the south viking graben and the north viking graben observed stratigraphy has been reverse post rift modelled using flexural backstripping combined with decompaction and reverse thermal subsidence calculations and forward modelled through the syn rift and post rift period using the flexural cantilever model of continental rift basin formation long term global eustasy has been included in the analysis only reliable palaeobathymetric markers such as erosion surfaces and coals have been used to constrain subsidence history both forward and reverse 2d modelling show that a palaeocene regional uplift followed by a rapid eocene subsidence must be superimposed on mckenzie post rift cretaceous and tertiary basement subsidence in order to generate the stratigraphy observed the magnitude of palaeocene uplift deduced from modelling was of the order of 375 m in the outer moray firth central north sea increasing to 525 m in the north viking graben northern north sea rapid early eocene subsidence was of the order of 160 310 m the most likely mechanism for regional palaeocene uplift and rapid eocene subsidence in the northern north sea was the palaeocene development of the iceland plume situated at a distance of 700 900 km from the study area in the early tertiary forward and reverse modelling predict axial bathymetries in the graben of up to 1300 m for the early cretaceous and 900 m for the upper cretaceous the large palaeobathymetries at the end of the cretaceous provided much of the accommodation space for tertiary sedimentation

neogene tectonic and stratigraphic events in the gulf of suez rift area egypt abstract the gulf of suez neogene syn rift section contains at least five datable intra basinal unconformities or stratigraphie hiatuses these events and associated changes in sedimentary sequences seen in the basin can be related to changes in suez rift subsidence miocene eustasy and the tectonic effects of adjacent red sea and dead sea rifting the first hiatus spans oligocene to earliest miocene time and separates syn rift from pre rift strata throughout the region this erosional event resulted from regional emergence during the oligocene and the initiation of suez rifting a second hiatus from 21 19 ma separates the poorly dated shallow marine nukhul formation of aquitanian to early burdigalian age from the overlying upper bathyal shales of the middle burdigalian to langhian nn3 5 rudeis formation this hiatus resulted from both a brief lowstand in early burdigalian sea level and increased suez rift related tectonism this event climaxed with the rapid tectonic subsidence that established deep marine conditions by 19 ma a third major event occurs within the rudeis at 17 ma nn4 n7 and marks the initiation of uplift of i he rift shoulders and margins and decelerated subsidence or even minor uplift in the axial trough hiatuses are seen over paleohighs e g tilted fault blocks whereas coarse elastics are deposited in more basinal areas in submarine fans and as turbidites a fourth unconformity at 14 ma separates the middle miocene kareem formation from overlying anhydrites and open marine shales of the belayim formation minor tectonic uplift throughout the suez region resulted from this event and a sill was established between the mediterranean and suez basins allowing cyclic anhydrite marl deposition from 14 to 11 ma this post kareem event may be the sedimentary response to initiation of movement along the dead sea aqaba transform a sharp drop in sea level at 11 ma restricted the suez basin even more and marked the initiation of massive halite precipitation in the central and southern suez well south of the sill area a final major neogene event occurs at the miocene pliocene boundary and is marked by a major unconformity caused by tectonic uplift this tectonic pulse is related to initiation of red sea sea floor spreading and acceleration of sinistral motion along the dead sea aqaba transform at 5 ma this event establishes the marine connection with the red sea and the sedimentary environments seen in the gulf of suez today

constrains on the origin and history of the eastern mediterranean basin abstract the basin formed along the northern passive margin of gondwanaland as a relict of the mesozoic neotethys in early mesozoic time though direct information from the basin itself is meagre the geology of its passive margins and the regional framework of the tethys evolution constrain the formation and history of the basin the eastern mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from early permian to middle jurassic times before pangaea s complete disintegration this led to the detachment of the eratosthenes and tauride blocks from the margins of the levant and herodotus basins respectively the latter merged in the northeast with the cyprus basin that extended along arabia s northern margin the main rifting probably occurred in the triassic leading to seafloor spreading in the herodotus and cyprus basins while along the levant margin important rifting also occurred in the jurassic during the initial rifting stages extension perpendicular to the levant margin was important but subsequently the tauride block drifted mainly northward the existence of the passive margins and slopes of the eastern mediterranean is documented at least from the end of the middle jurassic until then the basin was probably narrow 200 300 km but during the main phase of the africa laurasia separation it grew to twice its present width or more this scenario depends critically on the interpretation that the tauride block was originally located next to northeastern africa on the western side of the eratosthenes block plate convergence and consumption of the northern portion of the basin have taken place since mid cretaceous times but the active convergent boundary on its northern side formed only in the neogene by modification of earlier structures some intra plate deformation also took place especially in the neogene but it hardly changed the original configuration of the remaining portion of the basin