geometry mechanisms and significance of extensional folds from examples in the rocky mountain basin and range province u s a abstract geologic mapping and structural analysis in paleogene half graben of idaho and montana have revealed over 70 extensional folds that form orthogonal sets with mostly ne and se trending axes on a regional scale they parallel or lie perpendicular to the strikes of the largest normal faults transverse folds at a high angle to the fault and folds oblique to the fault comprise more than half of the folds and reflect the highly three dimensional nature of the bulk strain detailed geometric analysis of 15 folds in the salmon horse prairie and medicine lodge basins shows that they typically have an upright to steeply inclined bisecting surface an interlimb angle of 141 and a plunge of 19 based on our synthesis of the eight common mechanisms of extensional folding and their distinguishing characteristics we were able to determine how some of the investigated folds formed fault bend folding above both fault parallel and fault perpendicular bends in the underlying normal fault produced most of the folds in the study area but displacement gradients along normal faults fault drag isostatic adjustments and transtension were also factors in the deformation most of the compound folds which result from more than one mechanism of folding are oblique to all adjacent normal faults recognition of such extensional folds is critical because they might be misinterpreted as contractional structures they influence sediment thickness patterns and dispersal in rift basins and may control the migration and trapping of petroleum and groundwater resources

localisation of normal faults in multilayer sequences abstract existing conceptual growth models for faults in layered sequences suggest that faults first localise in strong and brittle layers and are later linked in weak and ductile layers we use the discrete element method for modelling the growth of a normal fault in a brittle ductile multilayer sequence the modelling reveals that faults in brittle ductile sequences at low confining pressure and high strength contrast localise first as mode i fractures in the brittle layers low amplitude monoclinal folding prior to failure is accommodated by ductile flow in the weak layers the initially vertically segmented fault arrays are later linked via shallow dipping faults in the weak layers faults localise therefore as geometrically and kinematically coherent arrays of fault segments in which abandoned fault tips or splays are a product of the strain localisation process and do not necessarily indicate linkage of initially isolated faults the modelling suggests that fault tip lines in layered sequences are more advanced in the strong layers compared with weak layers where the difference in propagation distance is most likely related to strength and or ductility contrast layer dependent variations in fault localisation rates generate fringed rather than smooth fault tip lines in multilayers

origin dimensions and distribution of remobilized carbonate deposits in a tectonically active zone eocene thebes formation sinai egypt abstract determination of the distribution and mechanism for carbonate dominated mass transport sediments is often compromised by the scale and access to exposures consequently many studies lack the resolution to capture the heterogeneity and dimensions of mass transport deposits this study documents the size shape and stratal assemblage of remobilized carbonates in the eocene thebes formation in the hammam faraun fault block hffb of western sinai revealing the complexities of carbonate mass transport deposits at sub seismic scale present day pseudo three dimensional exposure of the thebes formation in a large fault block formed during the opening of the gulf of suez allowed for lateral and down dip measurement of slope and basinal facies in the field and from photos remobilized facies were digitized in the photos and evaluated using image analysis software a technique with a wide range of applications to outcrop studies of sedimentary architecture debris flow deposits in the lower section of the thebes formation comprises clasts with differing fossil assemblages a relative sea level rise at the start of upper thebes formation deposition resulted in basinal sediments comprising periodic incursions of high density turbidite grainstones encased within a background of planktonic foraminiferal wackestones foraminiferal assemblages of remobilized facies imply multiple sources on the carbonate platform demonstrating the effect of short lived tectonism on slope instability and deposition of mass transport deposits the results of the study confirm that tectonism associated with the syrian arc fold belt which altered the style of basin sedimentation between egypt and syria persisted into the eocene at least as far south as wadi araba in the western desert and hammam faraun in sinai in addition the shape size and extent of the two dominant remobilized facies debris flows and grainstone turbidites are influenced by their mud rich versus grainy compositions

preliminary paleointensity measurements and detailed magnetic analyses of basalts from the skalamaelifell excursion southwest iceland among the many excursions reported in the late brunhes the skalamaelifell excursion recorded in 22 flows in three hills of assumed late wisconsin basalts in the active rift zone of the reykjanes peninsula is one of the most reliable it is characterized by a single well defined transitional direction d 260 i 16 paleointensity pi measurements using the thellier method as modified by coe in a vacuum with partial thermoremanent magnetization checks were made on six samples from the excursion flows for comparison 10 samples from the adjacent and probably nearly contemporaneous normally magnetized flows were also measured because of sample scarcity four of the excursion samples and seven of the normal samples had been already af demagnetized to 20 mt in iceland the samples however were chosen because of their high coercivity and lack of viscous remanent magnetization they retained 70 95 of their natural remanent magnetization nrm after 20 mt demagnetization and their remanence directions were stable during the 20 mt demagnetization and during 2 6 years of storage following it saturation magnetization js measurements suggest that the reason for the low nrm of the excursion samples was a paleofield one fourth to one tenth that of the normal basalts the mean pi from four excursion samples is 4 3 0 6 t whereas the mean pi of the five normal samples considered reliable is 30 9 t the quality of the nrm thermoremanent magnetization trm data correlated well with the reversibility of the js t curves the pi differences agree in general with those predicted by the nrm js data especially when comparing the means of the two groups which average the effects of different grain sizes a prior partial alternating field af demagnetization of one sample in each of two pairs from the same cores caused the pi to be underestimated by only 10 continuous af demagnetization during the nrm trm measurements of one sample in another pair that had nonlinear trm trm plots even in the undemagnetized sample caused the pi to be overestimated by 40 these results combined with other studies suggest that the effect of partial af demagnetization on high coercivity samples depends on when the demagnetization is done i e only prior to or during the nrm trm measurements and probably more importantly the thermochemical stability of the sample if correct this increases the usefulness for pi determinations of old hard to recollect partially demagnetized collections the very low pi of 4 t is similar to that found for excursions and transitions in iceland and other places however o its virtual geomagnetic pole lies 90 from a north south vertical plane through the sites which rules out a purely axisymmetric model for the excursion the low normal intensities are similar to those found in the chaine des puys france and elsewhere for the period 10 0000 50 000 years b p given its very low pi and a direction only 70 from complete reversal the skalamaelifell excursion is most likely the result of nondipole fields and an unusually weak dipole field such as that observed in france for the 10 000 year interval 35 000 45 000 years b p surrounding the laschamp excursion

tectonic and sedimentary evolution of the gulf of suez and the northwestern red sea abstract the structural pattern of the gulf of suez and red sea rift is inherited from the basement tectonics n140 faults clysmic direction parallel to the regional elongation of the rift are associated with submeridian aqaba direction and sub e w faults duwi direction that also play an important role in the rifting processes the pre rift sedimentary cover includes cretaceous and eocene platform deposits it was slightly deformed prior to rifting the syn rift sedimentary sequence comprises four major units groups a to d delimited by unconformities group a oligocene to early burdigalian continental to restricted subaquatic deposits group b burdigalian to middle miocene open marine sediments group c middle to upper miocene major evaporitic episode and group d plio pleistocene which returns to an open marine environment four majors stages of structuration are recorded an initial stage of compressive deformation direction of shortening close to nw se characterized by strike slip movements and associated drag folds early group a a tilted block stage late group a corresponding to the period of highest extensional rate a horst and graben stage group b resulting in the cutting out of the tilted blocks by numerous synthetic faults group b corresponds to the period of highest subsidence rate when a flexuration stage of the margin expressed by a centripetal evolution of the subsidence is associated with major periferal uplift

numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum 1 a hydrodynamic model incorporating a self consistent treatment of ocean self attraction and loading sal and a physically based parameterization of internal tide it drag is used to assess how accurately barotropic tides can be modeled without benefit of data and to explore tidal energetics in the last glacial maximum lgm m2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm rms in the open ocean this accuracy and agreement with atlimetric estimates of energy dissipation are achieved only when sal and it drag are included in the model solutions are sensitive to perturbations to bathymetry and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations the 100 m drop in sea level during the lgm results in significant changes in modeled m2 tides with some amplitudes in the north atlantic increasing by factors of 2 or more dissipation is also significantly changed by the drop in sea level if it drag estimated for the modern ocean is assumed dissipation increases by about 50 globally and almost triples in the deep ocean however it drag depends on ocean stratification which is poorly known for the lgm tests with modified it drag suggest that the tendency to a global increase in dissipation is a robust result but details are sensitive to stratification significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained

bedding plane slip in initial stages of fault related folding abstract frictional slip along bedding planes contributes to fault related folding of layered rocks we use numerical experiments to investigate the deformation of frictional bedding planes near dipping faults under layerparallel contraction and extension within the numerical experiments contraction boundary conditions produce asymmetric anticlines and extension produces asymmetric synclines the fold shape may be used to infer dip of the underlying fault in situations where the fault may not be observable additionally sense of slip along bedding planes may indicate proximity to the fault tip under uniform remote tectonic strain fault slip induces deformation in both the hangingwall and the footwall at depths as shallow as 1 km there is no significant difference between fold amplitudes in the hangingwall and the footwall this result is contrary to many kinematic models currently in use kinematic models of fault related folds commonly include the development of flat ramp and flat ramp flat fault geometries which may be attributed to initial ramp thrusting and later flat development our mechanical models show that fault flats may be produced from fault ramps due to slip along frictional bedding planes near the thrust fault tips our numerical experiments also evaluate joint initiation joints perpendicular to bedding are promoted in extensional environments we compare the results of the mechanical model to kinematic models of fault propagation folds and conclude that mechanical models offer important insights to better understand the folding process

a model for the structure and development of fault zones cross sections of fault zones commonly show two sub parallel slip surfaces which bound more or less deformed rock this characteristic geometry can be explained by a combination of 9tip line9 and 9asperity9 bifurcation processes fault tip line bifurcation is due to irregular tip line propagation resulting in leading edge segmentation fault overlap and eventual duplex formation asperity bifurcation removes a fault surface irregularity by the generation of a new slip surface which by passes the original slip surface repetitions of either or both bifurcation processes give rise to a fault zone with a complex and unpredictable internal geometry these processes are described mainly on the basis of observation of normal faults hut can be applied to other fault types fault zone thickening by bifurcation is intermittent rather than progressive and localised fault zone thinning may occur

fault relays bends and branch lines abstract branch lines between normal faults and their sub parallel splays mapped from 3d seismic reflection data show a range of forms from straight lines to closed loops the different geometries are interpreted as representing stages in the failure of relay zones and in the progressive replacement of fault tip lines with fault branch lines the geometries of these normal fault branch lines are similar to those for thrusts previously inferred from limited two dimensional data the orientation of the axis of a relay and its associated bends relative to a fault slip direction is identified as an important control on the structures developed within the relay neutral restraining and releasing bends can each occur on any fault type normal reverse and strike slip but data bias is a major factor in determining which bend geometry is most often observed with each fault type on normal faults the initial relay zone geometry controls the dominant branch line orientation and the same control is likely on branch lines associated with the other modes of faulting a review of the relay geometries and strains occurring with all three modes of faulting highlights the role of the orientation of the mechanical anisotropy of a bedded sequence relative to the orientations of fault surface and slip directions this relative orientation determines how the relay strain is accommodated and hence the degree of hard linkage and development of branch lines

structural geology and 4d evolution of a half graben new digital outcrop modelling techniques applied to the nukhul half graben suez rift egypt abstract lidar based digital outcrop mapping in conjunction with a new surface modelling approach specifically designed to deal with outcrop datasets is used to examine the evolution of a half graben scale normal fault array in the suez rift syn rift deposition in the nukhul half graben was controlled by the graben bounding nukhul fault the fault can be divided into four segments based on the strike of the fault the morphology of hangingwall strata and the variation in throw along strike the segments of the fault became geometrically linked within the first 2 5 m y of rifting as evidenced by the presence of early syn rift abu zenima formation strata at the segment linkage points fault perpendicular folds in the hangingwall related to along strike variations in throw associated with precursor fault segments persist for a further 1 8 m y after linkage of the segments suggesting that the fault remains kinematically segmented we suggest this occurs because of sudden changes in fault strike at the segment linkage points that inhibit earthquake rupture propagation or because displacement is geometrically inhibited at fault linkage points where the orientation of the intersection line of the segments is significantly different from the orientation of the slip vector on the fault system length throw plots and throw contour patterns for minor faults show that some faults initiated in pre rift strata whereas late east striking faults initiated in the syn rift basin fill the late initiating faults are spatially associated with the east striking baba markha fault which was active throughout the rift history but developed as a transfer fault between major block bounding fault systems around 6 7 ma after rift initiation

fault propagation folding in extensional settings examples of structural style and synrift sedimentary response from the suez rift sinai egypt field data from the oligocene miocene gulf of suez rift demonstrate that coeval growth faults folds and transfer zones exerted a major control on synrift stratigraphic sequence development growth folds in the suez rift are related to steeply dipping normal faults that propagated upward resulting in broad upward widening monoclines in overlying strata folding during fault propagation was accommodated by layer parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault the eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall this evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults whereas they diverge into broadly synclinal expanded sections away from the growth monocline continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments each successively younger sequence dipping basinward at a shallower angle than the previous one the resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults along strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low relief transfer zones data from other rift basins indicate that fault propagation folds are not unique to the gulf of suez

the steens mountain oregon geomagnetic polarity transition 2 field intensity variations and discussion of reversal models we carried out an extensive paleointensity study of the 15 5 0 3 m y miocene reversed to normal polarity transition recorded in lava flows from steens mountain south central oregon one hundred eighty five samples from the collection whose paleodirectional study is reported by mankinen et al this issue were chosen for paleointensity investigations because of their low viscosity index high curie point and reversibility or near reversibility of the strong field magnetization curve versus temperature application of the thellier stepwise double heating method was very successful yielding 157 usable paleointensity estimates corresponding to 73 distinct lava flows after grouping successive lava flows that did not differ significantly in direction and intensity we obtained 51 distinguishable complete field vectors of which 10 are reversed 28 are transitional and 13 are normal the record is complex quite unlike that predicted by simple flooding or standing nondipole field models it begins with an estimated several thousand years of reversed polarity with an average intensity of 31 5 8 5 t about one third lower than the expected miocene intensity this difference is interpreted as a long term reduction of the dipole moment prior to the reversal when site directions and intensities are considered truly transitional directions and intensities appear almost at the same time at the beginning of the transition and they disappear simultaneously at the end of the reversal large deviations in declination occur during this approximately 4500 1000 year transition period that are compatible with roughly similar average magnitudes of zonal and nonzonal field components at the site the transitional intensity is generally low with an average of 10 9 4 9 t for directions more than 45 away from the dipole field and a minimum of about 5 t the root mean square of the three field components x y and z are of the same order of magnitude for the transitional field and the historical nondipole field at the site latitude however a field intensity increase to pretransitional values occurs when the field temporarily reaches normal directions which suggests that dipolar structure could have been briefly regenerated during the transition in an aborted attempt to reestablish a stationary field changes in the field vector are progressive but jerky with at least two and possibly three large swings at astonishingly high rates each of those transitional geomagnetic impulses occurs when the field intensity is low less than 10 t and is followed by an interval of directional stasis during which the magnitude of the field increases greatly for the best documented geomagnetic impulse the rapid directional change corresponds to a vectorial intensity change of 6700 2700 nt yr 1 which is about 15 50 times larger than the maximum rate of change of the nondipole field observed during the last centuries the occurrence of geomagnetic impulses seems to support reversal models assuming an increase in the level of turbulence within the liquid core during transitions the record closes with an estimated several thousand years of normal polarity with an average intensity of 46 7 20 1 t agreeing with the expected miocene value however the occurrence of rather large and apparently rapid intensity fluctuations accompanied by little change in direction suggests that the newly reestablished dipole was still somewhat unstable

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

ground based and uav based photogrammetry a multi scale high resolution mapping tool for structural geology and paleoseismology this contribution reviews the use of modern 3d photo based surface reconstruction techniques for high fidelity surveys of trenches rock exposures and hand specimens to highlight their potential for paleoseismology and structural geology we outline the general approach to data acquisition and processing using ground based photographs acquired from standard dslr cameras and illustrate the use of similar processing approaches on imagery from unmanned aerial vehicles uavs it is shown that digital map and trench data can be acquired at ultra high resolution and in much shorter time intervals than would be normally achievable through conventional grid mapping the resulting point clouds and textured models are inherently multidimensional x y z point orientation colour texture archival and easily transformed into orthorectified photomosaics or digital elevation models dems we provide some examples for the use of such techniques in structural geology and paleoseismology while pointing the interested reader to free and commercial software packages for data processing visualization and 3d interpretation photogrammetric models serve to act as an ideal electronic repository for critical outcrops and observations similar to the electronic lab book approach employed in the biosciences this paper also highlights future possibilities for rapid semi automatic to automatic interpretation of the data and advances in technology

geometry and architecture of faults in a syn rift normal fault array the nukhul half graben suez rift egypt the geometry and architecture of a well exposed syn rift normal fault array in the suez rift is examined at pre rift level the nukhul fault consists of a single zone of intense deformation up to 10 m wide with a significant monocline in the hanging wall and much more limited folding in the footwall at syn rift level the fault zone is characterised by a single discrete fault zone less than 2 m wide with damage zone faults up to approximately 200 m into the hanging wall and with no significant monocline developed the evolution of the fault from a buried structure with associated fault propagation folding to a surface breaking structure with associated surface faulting has led to enhanced bedding parallel slip at lower levels that is absent at higher levels strain is enhanced at breached relay ramps and bends inherited from pre existing structures that were reactivated during rifting damage zone faults observed within the pre rift show ramp flat geometries associated with contrast in competency of the layers cut and commonly contain zones of scaly shale or clay smear damage zone faults within the syn rift are commonly very straight and may be discrete fault planes with no visible fault rock at the scale of observation or contain relatively thin and simple zones of scaly shale or gouge the geometric and architectural evolution of the fault array is interpreted to be the result of i the evolution from distributed trishear deformation during upward propagation of buried fault tips to surface faulting after faults breach the surface ii differences in deformation response between lithified pre rift units that display high competence contrasts during deformation and unlithified syn rift units that display low competence contrasts during deformation and iii the history of segmentation growth and linkage of the faults that make up the fault array this has important implications for fluid flow in fault zones

discrete element modelling of contractional fault propagation folding above rigid basement fault blocks many studies have shown that discrete blind faults at depth are commonly linked to more distributed deformation in particular folding at higher levels one category of fault related folds forced folds is common where there is a distinct mechanical contrast between faulted basement and sedimentary cover outcrop numerical and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation monoclines above discrete faults at depth with increasing displacement the folds are often cut by faults as they propagate upwards into the cover while the trishear kinematic model of fault propagation folding appears to approximately represent the geometric development of such structures comparatively little is known of the mechanical controls on their development here we present a 2d discrete element model of sedimentary cover deformation above a contractional fault in rigid basement the elements consist of a series of soft spheres that obey newton s equations of motion and initially interact with elastic forces under the influence of gravity particles are bonded until the separation between them exceeds a defined breaking strain at which time the bond breaks simulated by the transition from repulsive attractive forces to solely repulsive forces the model is used to investigate the influence of basement fault dip and sedimentary cover strength on the geometry of the folds developed and the rate of fault propagation in all cases an upward widening monocline occurs above the basement fault we find that shallow basement fault dips produce homogenous thickening of the monocline limb while steeper dips produce contemporaneous thinning and thickening within the monocline thinning and thickening within the monocline are accommodated by a combination of small scale faulting and folding with decreasing cover strength the zone of deformation becomes wider localization does not occur on a single fault and fold geometries resemble trishear fold profiles with low propagation to slip ratios p s 1 in contrast a stronger cover produces a narrower zone of deformation localization on a single fault and more rapid fault propagation similar to trishear fold profiles where p s 2 3 the fault propagates into the cover at approximately the same angle as the basement fault the model reproduces well many of the features observed in analogue modelling and reported from outcrop and seismic studies

some statistical properties of palaeomagnetic directions in icelandic lava flows summary this paper extends the efforts of kristjansson mcdougall to obtain a semi quantitative description of various long term 0 1 10 myr properties of the geomagnetic field in iceland due to the long time intervals between eruptions of the lavas recording the field local average and stochastic properties are emphasized rather than detailed aspects such as pole paths these properties can be represented by smooth functions of virtual pole latitude it is possible to describe both the frequency distribution of virtual poles in latitude and the estimated frequency of geomagnetic reversals by a simple process of random walk of the pole this is also in agreement with the observed long term symmetry of the reversal process and demonstrates that memory effects are unnecessary to account for the behaviour of the field the average transition time for the field isofthe order of 5 6000yr right handedness is a pervasive property of the field in iceland apparently increasing with age it is demonstrated that the size of palaeomagnetic collections in lava sequences has to be much larger than 20 units in order to yield consistent values of statistical parameters for mean palaeofield directions

an estimate of late pleistocene geomagnetic intensity variation from sulu sea sediments abstract sediments from site 769 of the ocean drilling program s leg 124 provide a record of geomagnetic intensity variation over the past 110 ky using continous shipboard measurements exclusively i estimate the variation in the geomagnetic field strength by employing low field magnetic susceptibility as a normalization parameter for the measured remanence intensity by calibrating the resultant relative paleointensity record against previously available holocene age estimates of absolute paleointensity i derive an estimate of virtual dipole moment since 110 ka the record obtained from these sulu sea sediments is strikingly like that previously obtained from sediments of a similar age in the mediterranean basin with distinct intervals of low intensity near 15 20 40 and 65 70 ka the sulu sediments also indicate a low intensity feature near 108 ka important differences in paleointensity estimates obtained from these different regions for the interval between 30 and 20 ka suggest that a relatively large non dipolar component of the geomagnetic field might have been present at that time

palaeointensities of the auckland geomagnetic excursions by the ltd dht shaw method we report new palaeointensity results concerning the auckland geomagnetic excursions using the double heating technique of the shaw method with low temperature demagnetisation ltd dht shaw method the excursional palaeodirections recorded in six volcanoes of the auckland volcanic field new zealand have been classified into three groups north down nd west up wu and south up su directions in the present study five to six consistent palaeointensities have been obtained from each of five volcanoes recording the auckland geomagnetic excursions the wiri 27 ka crater hill and puketutu volcanoes nd group yielded mean palaeointensities of 10 6 1 2 1 11 8 2 8 and 11 1 0 4t respectively the hampton park volcano 55 ka wu group gave 9 5 1 2t while the mclennan hills volcano su group gave 2 5 0 5t it is notable that consistent palaeointensities have been obtained from the three different volcanoes which have almost the same palaeodirections nd group possibly supporting the reliability of the palaeointensity data these five palaeointensities for the auckland geomagnetic excursions correspond to virtual dipole moments vdms of 0 6 2 1 10 22 am 2 whereas three mean palaeointensities obtained from the auckland volcanoes having non excursional palaeodirections are 13 1 40 0 t giving stronger vdms of 2 1 6 9 10 22 am 2 these results suggest that the dipole component of the geomagnetic field reduced to about 2 10 22 am 2 or less during the auckland geomagnetic excursions

high resolution record of displacement accumulation on an active normal fault implications for models of slip accumulation during repeated earthquakes the spatial and temporal accumulation of slip from multiple earthquake cycles on active faults is poorly understood here we describe a methodology that can determine the time period of observation necessary to reliably constrain fault behaviour using a high resolution longtimescale the last 17 kyr fault displacement dataset over the rangitaiki fault whakatane graben new zealand the fault linked at ca 300 ka bp and analysis of time periods within the last 17 kyr gives insight into steady state behaviour for time intervals as short as ca 2 kyr the maximum displacement rate observed on the rangitaiki fault is 3 6g1 1 mm yr k1 measured over 17 kyr displacement profiles of the last 9 ka of fault movement are similar to profiles showing the last 300 ka offault movement in contrast profiles determined for short time intervals 2 3 kyr are highly irregular and show points of zero displacement on the larger segments this indicates temporal and spatial variability in incremental displacement associated with surface rupturing slip events there is spatial variability in slip rates along fault segments with minima at locations of fault interaction or where fault linkage has occurred in the past this evidence suggests that some earthquakes appear to have been confined to specific segments whereas larger composite ruptures have involved the entire fault the short term variability in fault behaviour suggests that fault activity rates inferred from geodetic surveys or surface ruptures from a single earthquake may not adequately represent the longer term activity nor reflect its future behaviour different magnitude events may occur along the same fault segment with asperities preventing whole segment rupture for smaller magnitude events q 2006 elsevier ltd all rights reserved

influence of mechanical stratigraphy and initial stress state on the formation of two fault propagation folds abstract kinematic and mechanical modeling of the rip van winkle se new york usa and la zeta sw mendoza argentina anticlines illustrate the influence of mechanical stratigraphy and initial stress state on the kinematics of fault propagation folding in both anticlines faults nucleating at distinct stratigraphic levels open upward into triangular zones of folding folding intensity and finite strain attenuates with distance from the fault tip trishear reproduces the bulk geometry and finite strain of the relatively homogeneous limestone sequence of the rip van winkle anticline and predicts an initial location of the fault tip consistent with the field observations folding of the heterogeneous sedimentary section of la zeta anticline however cannot be simulated by the trishear model alone an additional mode of deformation involving transport of material from the backlimb into the hinge area and extension parallel to the direction of fault propagation is necessary to reproduce the geometry and finite strain of the anticline mechanical distinct element modeling dem of the anticlines indicates that their contrasting kinematics could have resulted from differences in mechanical stratigraphy and initial stress state folding of a homogenous normally consolidated assemblage initial horizontal to vertical stress ratio k o 1 is trishear like and resembles the rip van winkle anticline folding of a heterogenous layered such as la zeta over consolidated assemblage k o 1 departs from the trishear model and resembles la zeta anticline based on the dem simulations we postulate that the rip van winkle anticline formed at high depths high overburden loads and lithostatic stress conditions and that la zeta anticline formed at shallow depths after substantial uplift and erosion of the andean mountain front which induced over consolidation and high k o

internal structure and deformation of an accommodation zone in the northern part of the suez rift abstract detailed structural study of the eastern onshore part of the gharandal accommodation zone that separates the northern sw dipping and central ne dipping half grabens of the suez rift helped decipher the internal structure and deformation of accommodation zones of continental rifts this 60 km wide zone is affected by pure normal faulting the ne dipping faults of the northern half graben extend southward into the accommodation zone where they interfinger with sw dipping faults extending from the central half graben these two sets of rift parallel faults form several horsts and grabens in the accommodation zone areas dipping parallel to the northern or southern half grabens form several intermixing dip domains in the accommodation zone smaller scale accommodation of dip between these dip domains proceeds by the development of rift parallel folds twist zones in contrast to the southern accommodation zone of the suez rift the internal structure of the gharandal accommodation zone is believed to be representative of accommodation zones in regions a unaffected by prerift structures lying at high angles to the rift and b experiencing relatively small extension accommodation zones in areas having pre rift structures lying at high angle to the rift have relatively narrow width and are characterized by transverse strike slip faults strike slip movement on these faults is related to the torsional strain resulting from the opposite tilt directions and transport of fault blocks of adjacent half grabens

laser scanning and digital outcrop geology in the petroleum industry a review abstract the use of lidar light detection and ranging systems for modelling petroleum reservoir analogues has become increasingly popular over the past few years and there has been a proliferation of articles on the subject both on techniques and applications a review of the literature of recent years has been conducted focussing on the use of lidar data not only in petroleum geology related projects but also looking to the wider field of lidar usage to examine what other approaches may be of use to the petroleum geologist benefits of digital data acquisition are considered as well as a basic overview of data collection approaches use of a variety of attributes intensity colour dip azimuth co linearity co planarity among others is discussed as an aid to both manual and automated interpretation approaches integration of lidar data with other data types from traditional field data sedimentary logs for example and other digital data types such as multispectral and hyperspectral imagery and ground penetrating radar are discussed as a way of increasing the amount of information in the digital dataset the application of artificial intelligence approaches such as smart swarms and neural networks are considered as well as current developments in both hardware and software a variety of examples are given where lidar has been used in an innovative or interesting way showing the strength of this data acquisition approach when combined with appropriate interpretation and modelling techniques

transitional field behaviour from southern hemisphere lavas evidence for two stage reversals of the geodynamo palaeomagnetic records from australasian basalts provide a rare view of transitional field behaviour as seen from mid southern latitudes these data suggest that a geomagnetic reversal is accomplished in two steps separated by an interval of relative dynamo quiescence a potentially long lived field configuration developed early is observed to be the stepping stone from which both successful and unsuccessful reversal attempts are made several aborted attempts involving the same intermediate field geometry may precede an actual polarity transition

the accuracy of surface elevations in forward global barotropic and baroclinic tide models abstract this paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents both one layer and two layer simulations are performed as far as the authors are aware the two layer simulations and the simulations in a companion paper deep sea research ii 51 2004 3043 represent the first published global numerical solutions for baroclinic tides self consistent forward solutions for the global tide are achieved with a convergent iteration procedure for the self attraction and loading term energies are too large and elevation accuracies are poor unless substantial abyssal drag is present reasonably accurate tidal elevations can be obtained with a spatially uniform bulk drag c d or horizontal viscosity k h but only if these are inordinately large more plausible schemes concentrate drag over rough topography the topographic drag scheme used here is based on an exact analytical solution for arbitrary small amplitude terrain and supplemented by dimensional analysis to account for drag due to flow splitting and low level turbulence as well as that due to breaking of radiating waves the scheme is augmented by a multiplicative factor tuned to minimize elevation discrepancies with respect to the topex poseidon t p constrained got99 2 model the multiplicative factor may account for undersampled small spatial scales in bathymetric datasets an optimally tuned multi constituent one layer simulation has an rms elevation discrepancy of 9 54 cm with respect to got99 2 in waters deeper than 1000 m and over latitudes covered by t p 66 n to 66 s the surface elevation discrepancy decreases to 8 90 cm 92 percent of the height variance captured in the optimally tuned two layer solution the improvement in accuracy is not due to the direct surface elevation signature of internal tides which is of small amplitude but to a shift in the barotropic tide induced by baroclinicity elevations are also more accurate in the two layer model when pelagic tide gauges are used as the benchmark and when the t p constrained tpxo6 2 model is used as a benchmark in deep waters south of 66 s for antarctic diurnal tides the improvement in forward model elevation accuracy with baroclinicity is substantial the optimal multiplicative factor in the two layer case is nearly the same as in the one layer case against initial expectations that the explicit resolution of low mode conversion would allow less parameterized drag in the optimally tuned two layer m 2 solution local values of the ratio of temporally averaged squared upper layer speed to squared lower layer speed often exceed 10

middle late pleistocene relative palaeointensity of the geomagnetic field from lacustrine sediments lake chewaucan western united states summary detailed palaeomagnetic and rock magnetic studies of a 15 m succession of middlellate pleistocene lacustrine sediments from ancient lake chewaucan southern oregon western united states indicate that the remanence bearing grains are sufficiently uniform to be applicable to relative palaeointensity studies we have used arm sirm and x for normalization of the nrm all three parameters give essentially identical results in their relative stratigraphic variations which indicates that the normalizations efficiently remove the effects of variation in magnetic mineral concentration patterns in grain size variation as indicated by small scale quasi cyclic fluctuations in hysteresis parameters may be due to environmental changes such as lake level variation however these fluctuations are within the acceptable range of grain sizes for palaeointensity studies and cannot be correlated with any of the features of the normalized remanence record we therefore conclude that the large scale variations in the normalized remanence record are due to geomagnetic palaeointensity fluctuations parts of the normalized remanence record where firm chronological constraints exist may correlate with features of relative palaeointensity records from deep sea sediments our results also confirm the observation that low geomagnetic field intensities dominate during geomagnetic excursions further studies of relative palaeointensity of the geomagnetic field may enable the development of an independent time scale which would make possible the direct correlation of palaeoclimate records from deep sea and continental environments

digital outcrop models applications of terrestrial scanning lidar technology in stratigraphic modeling abstract laser ranging is extremely accurate and efficient terrestrial scanning lidar light detection and ranging applied to outcrop stratigraphic mapping enables researchers to capture laser range data at a rate of thousands of individual x y z and laser intensity points per second these data in conjunction with complementary remotely and directly sampled data are used to conduct high precision facies characterization and to construct 3d geological computer models outcrop data are presented here to explain our workflow and to discuss the construction of rock based 3d digital outcrop models doms reproducibility and quantification are the drivers of this methodology high resolution terrestrial lidar acquisition processing interpretation and visualization are discussed and applied to mapping of geological surfaces in three dimensions laser generated models offer scientists an unprecedented visualization medium in a quantitative 3d arena applications of this technology include constructing and visualizing complex 3d earth models from outcrops for improved reservoir modeling flow simulation in hydrocarbon and aquifer systems and property modeling to constrain forward seismic modeling

influence of mechanical stratigraphy on folding vs faulting abstract the competing processes of folding and faulting during shortening of a layered sequence are investigated using elastic plastic models in order to determine the influence of mechanical stratigraphy on the development of fold belts vs thrust belts the models consist of a strong middle layer and weaker decollement and cover layers the mechanical behaviour of each layer is determined by its plastic hardening modulus h and its elastic shear modulus g with bonded contacts fold amplification at low shortening strain relatively large h is greatest for a thin cover layer and a thick decollement layer at higher shortening strain h g the middle layer may reach its peak strength before the other layers causing it to become relatively weaker in shortening and causing fold amplification to be greatest for a thick middle layer free slip contacts between the layers enhance folding and fold amplification is greatest if the slip surfaces are roughly equally distributed throughout the sequence a relatively weak decollement layer enhances folding consistent with the fact that fold belts usually include a salt decollement layer dominant wavelengths increase with increasing strength contrasts between the layers and with increasing thicknesses of the decollement and strong layers

geomagnetic paleointensities from excursion sequences in lavas on oahu hawaii paleomagnetic data demonstrating three late tertiary excursions in the direction of the geomagnetic field recorded in sequences of basaltic lavas on the island of oahu hawaii were published by r r doell and g b dalrymple in 1973 we have determined geomagnetic paleointensities by the thelliers method for 14 lavas from the three sites during these experiments considerable difficulty was encountered because of the presence of titanomaghemite in many lavas and the contamination of natural remanent magnetization by lightning in many others moreover we often observed the production of spurious high temperature chemical remanent magnetization during the thellier experiments an analysis of this particularly troublesome problem is presented two of the sites showed low paleointensities associated with angular departures of the paleomagnetic field direction from that of a geocentric axial dipole which suggests that these excursions represent aborted reversals or fragments of reversals at the third site however the paleointensity did not become low as the field diverged this excursion may reflect the variation of a large nondipole source near hawaii

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

explicit tidal forcing in an ocean general circulation model 1 the eight dominant constituents of the semi diurnal and diurnal tides plus accurate phase information have been implemented in a global version of the modular ocean model version 4 developed by the geophysical fluid dynamics laboratory the simulated tidal signal in the southeast asian region has been validated with observations indicating that the amplitudes and phases are reasonably well reproduced by the model tidal currents play an essential role in transport and mixing processes in the indonesian seas and off the australian northwest shelf vertical tidal mixing introduces a distinct signal in the surface mixed layer and upper ocean temperature the results suggest that application of explicit tidal forcing in operational ocean general circulation models ogcms should become feasible in the near term future

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

extensional fault related folding northwestern red sea egypt the duwi and hamadat areas on the northwestern margin of the red sea rift system exhibit superb outcrop examples of kilometric scale extensional fault related folds in this area the nakheil and hamadat faults of the rift border fault system consist of a series of wnw and nw trending segments that link through breached relay ramps the fault hanging walls are characterised by a series of offset synclines with non linear axial traces sub parallel to the faults the synclines are doubly plunging and in the immediate hanging wall to the normal faults the strata dip sub parallel to the fault these folds result from along strike displacement variations on the individual fault segments together with extension related fault propagation folding as the faults propagated upwards through a highly anisotropic pre rift sedimentary section in the duwi area the axial traces of the synclines are offset and bend in the regions of relay ramps in the hamadat area the synclines associated with individual fault segments are separated by transverse hanging wall anticlines that formed where segment linkage occurred numerical simulations of extension related fault propagation folding using a trishear model produce geometries that closely match those of the duwi and hamadat folds the dimensions of these hanging wall synclines and their relationships to fault displacement variations indicate that they are formed by extensional fault propagation folding rather than by frictional drag along the fault surface

early evolution of an extensional monocline by a propagating normal fault 3d analysis from combined field study and numerical modeling abstract the nopolo structure is located along the eastern margin of the baja california peninsula and formed during the early stages 12 6 ma of development of the gulf of california the nopolo structure is an 15 km long series of two nw striking extensional monoclines produced by the upward propagation of normal faults where normal faults reach the surface the footwall contains undisturbed gently dipping strata whereas the hanging wall is a highly deformed zone that contains fractured and faulted steep to subvertical strata long narrow grabens with moderate to steep east dipping strata are present in the hanging wall of the main normal faults initial monoclinal folding over blind normal faults produced a minimum of 300 m of structural relief once the faults propagated to the surface they offset the monoclines 20 30 m before faulting ceased we use an elastic dislocation model to invert fault geometry from bedding orientations around the nopolo structure the data are best matched by a listric normal fault that soles out at 5 km depth the model suggests that the tip line of the fault was located 1 km below the surface prior to the breaching of the monocline because the offset along the main normal faults is minimal 20 m the nopolo structure is a unique example of an extensional faulted monocline and monocline system where faulting ended soon after the monoclines were breached and offset

normal fault growth displacement localisation and the evolution of normal fault populations the hammam faraun fault block suez rift egypt abstract fault segment linkage migration of the locus of fault activity and displacement localisation were important processes controlling the late oligocene recent evolution of the normal fault population of the hammam faraun fault block suez rift initial fault activity was distributed across the fault block on fault segments that had attained their final length within 1 2 my of rifting these initial segments then either grew by increasing displacement and linked to form longer segmented fault zones or died during a rift initiation phase that lasted 6 8 my following this rift initiation phase displacement became localised onto 25 km long border fault zones bounding the fault block and many of the early high displacement intra block fault zones died following displacement localisation onto the major faults bounding the fault block the locus of maximum displacement continued to migrate with post middle miocene displacement focused on the western margin of the fault block this migration of fault activity between major crustal scale normal faults can be viewed in terms of strain localisation at the rift scale the results from this study question conventional fault growth models based on final displacement distributions and highlight the sequential nature of faulting on major normal faults bounding domino style tilted fault blocks

the influence of structural lithic units in fault related folds seminoe mountains wyoming u s a abstract analysis of basement involved folds in the seminoe mountains south central wyoming reveals that lithological contrasts within the sedimentary section created a mechanical anisotropy that influenced both fault geometry and the relative rates of fault propagation and fault slip two structural lithic units are identified a competent lower unit and an overlying incompetent unit the upper unit is made up of moderate ductility rocks that were thinned ahead of the hurt creek fault offset formations in the upper unit have small relative stretch r values and are interpreted to have represented an impediment to fault growth in contrast fault propagation was rapid relative to fault slip in the competent rocks of the lower structural lithic unit which have a correspondingly higher relative stretch the black canyon fault is oriented at a low angle to bedding in the lower structural lithic unit and is layer parallel near the base of the upper unit the red spring fault is a thin skinned thrust fault and is interpreted to be linked to the black canyon fault to generate a triangle zone geometry similar structures can be identified elsewhere in the rocky mountain foreland and this configuration may represent a previously unrecognized indicator of low angle basement faults changes in the deformation style between structural lithic units must be reflected in changing fold form thus preventing the direct application of geometric and kinematic models that predict a uniform fold profile

oceanic tides from geosat altimetry direct tidal analysis of the altimetry from the geosat exact repeat mission s first year is used to derive estimates of the diurnal and semidiurnal oceanic tides the geoid is removed by collinear differences at 34 1 day separation and the orbit error is reduced by subtracting a slowly modulated 1 cycle revolution term a sequence of independent analyses at grid areas of 1 latitude 1 5 longitude using orthotide functions ensures complete definition of the diurnal and semidiurnal species global admittance maps for m2 and s2 within the latitudes 58 n and 59 s compare well with ground truth at 66 open ocean sites maps of differences between geosat and the naval surface weapons center model show important areas of the order of 10 15 cm the integral for the global power input from the moon gives 2 51 tw m2 0 44 tw s2 lower than many previous estimates but in agreement with figures deduced from a recent analysis of satellite orbits

experimental models of extensional forced folds we have used single layer and multilayer clay models to study the development of forced folds above normal faults our modeling results show that the deformation patterns associated with extensional forced folding depend on the dip of the underlying normal fault and the presence of layer parallel detachments in single layer clay models extensional forced folds are upward widening monoclines anticlinal axial surfaces dip in the same direction as underlying master normal faults and synclinal axial surfaces dip in the opposite direction of master normal faults most secondary faults are upward steepening normal faults if master normal faults are steeply dipping however many secondary normal faults become high angle reverse faults at shallow depths the propagation and linkage of secondary faults into through going normal faults terminates the development of extensional forced folds more folding occurs prior to fault linkage if the master normal fault is steeply dipping rather than gently dipping most dipping beds and secondary faults are preserved in the hanging walls of the through oing normal faults in multilayer clay models with layer parallel detachments extensional forced folds are also upward widening monoclines slip on the lowest detachment laterally transfers extension induced by normal faulting and forced folding from the master normal fault to the detachment edge slip on overlying detachments accommodates minor thickness changes associated with upward widening of the fold secondary faults include low angle normal faults near the anticlinal axial surface minor thrust faults near the synclinal axial surface and high angle normal faults above the detachment edge the model predicted deformation patterns are similar to those of extensional forced folds from the gulf of suez and offshore norway this similarity suggests that our modeling results apply to extensional forced folds and can provide guidelines for interpreting field well and seismic data

geometrical analysis of the refraction and segmentation of normal faults in periodically layered sequences normal faults contained in multilayers are often characterised by dip refraction which is generally attributed to differences in the mechanical properties of the layers sometimes leading to different modes of fracture because existing theoretical and numerical schemes are not yet capable of predicting the 3d geometries of normal faults through inclined multilayer sequences a simple geometric model is developed which predicts that such faults should show either strike refraction or fault segmentation or both from a purely geometrical point of view a continuous refracting normal fault will exhibit strike i e map view refraction in different lithologies if the intersection lineation of fault and bedding is inclined an alternative outcome of dip refraction in inclined multilayers is the formation of segmented faults exhibiting en echelon geometry the degree of fault segmentation should increase with increasing dip of bedding and a higher degree of segmentation is expected in less abundant lithologies strike changes and associated fault segmentation predicted by our geometrical model are tested using experimental analogue modelling the modelling reveals that normal faults refracting from pure dip slip predefined faults into an overlying sand cover will as predicted exhibit systematically stepping segments if the base of the cover is inclined

new age for the skalamaelifell excursion and identification of a global geomagnetic event in the late brunhes chron article ar 39 ar geochronology paleomagnetism sixteen lava flows sampled from isolated hills including skalamaelifell hill on the reykjanes peninsula in southwest iceland record excursional geomagnetic field directions that correspond to virtual geomagnetic poles vgps grouped at 12 s 250 e in the eastern pacific ocean the vgps are similar to those obtained in earlier studies of these lavas for which the name skalamaelifell excursion was previously assigned based on unspiked k ar dating of nine samples from six hills it has been accepted for more than two decades that the transitionally magnetized lavas reflect the 41 ka laschamp excursion however nine new 40 ar 39 ar incremental heating experiments on four of the transitionally magnetized lavas give an age of 91 13 ka moreover 238 u 230 th isochrons determined for two of these lava flows yield a weighted mean age of 96 10 ka 2 the weighted meanof the

new archeomagnetic secular variation data from central europe ii intensities abstract variations of the geomagnetic field during the past millennia can be obtained by investigating archeological material the spatial distribution of the available data across europe is rather uneven and only about 15 of the sites provide a full vector record of the geomagnetic field here we report 39 new reliable paleointensity data for sites from austria germany and switzerland with ages ranging between 1500 bce and 1900 ce for 31 of them directional information is available too paleointensities were determined with thellier type techniques with the multiple specimen domain state corrected paleointensity protocol or with both techniques corrections for anisotropy of thermoremanent magnetization were carried out for the structures showing small variations of only a few per cent in most cases cooling rate dependence was tested for 16 structures often strong alteration during the experiments was observed seven successful cooling rate corrections were applied which lowered the paleointensity values by about 10 values obtained from the multiple specimen technique are generally somewhat lower than those from the thellier experiments rock magnetic measurements revealed magnetite type minerals mostly in pseudo single domain range as main magnetic carrier but also high coercive mineral components like hematite or epsilon iron oxide are present the new data are mostly in good agreement with published paleointensities they support the presence of strong intensity variations around 800 ce and in the millennium bce the new full vector data reveal that the deep paleointensity minimum observed from german data around 850 bce is accompanied by large variations in direction with declinations up to 50

the gulf of suez northern red sea neogene rift a quantitive basin analysis abstract subsidence analysis backstripping was carried out on a series of wells from the gulf of suez and northern red sea region of egypt in order to examine the interplay between tectonic events basin subsidence sedimentation and sea level changes in a young developing ocean basin and continental margin using constraints on chronostratigraphy and paleodepth from various sources combined with stratigraphic and structural information from industry wells and other geophysical sources it has been possible to compile the data necessary to perform geohistory analyses throughout the region major subsidence due to crustal thinning began 25 ma with sedimentation initially occurring in isolated sub basins these earliest sediments record the transition from continental to marine depositional environments subsequently during early and middle miocene times subsidence was rapid and uniform along and across the entire rift basin open marine sedimentation occurred across all structural regimes the mid clysmic tectonic event 16 5 ma resulted in structural rearrangement of the rift basin and uplift of the rift shoulders rapid subsidence continued as global sea level fell producing a series of prograding siliciclastic fan deltas at the rift margins at 15 5 ma opening of the suez rift was terminated tectonic subsidence decreased dramatically in the southern rift and ceased entirely in the northern rift tensional plate motion probably was transferred from the gulf of suez to sinistral strike slip movement on the dead sea transform at this time the quiescence in subsidence combined with a lowered global sea level resulted in the deposition of a thick up to 4 km series of evaporites within the central trough of the rift from the middle to latest miocene the accumulation of such a thick sequence of sediments during a phase of decreased tectonic subsidence is interpreted as a filling in of the rift topography which developed during the earlier period of rapid subsidence and rift shoulder uplift and continued compaction a rapid global sea level rise concomitant with a subsequent pulse of increased tectonic activity in the latest miocene earliest pliocene returned the rift to dominantly marine conditions