refinements for footwall red bed diagenesis in the sediment hosted stratiform copper deposits model the emplacement of copper in sediment hosted stratiform copper deposits requires the circulation of a low temperature chloride rich brine in rift filling footwall red beds probably driven by meteoric recharge in adjacent highlands the descending oxygen rich meteoric water may become saline probably by leaching of footwall evaporites or possibly by mixing with brines draining down from contemporaneous evaporite pans and evolve toward a moderately oxidized brine as oxygen is consumed during the diagenetic reddening of the initially nonred coarse grained clastic rift sediments under these conditions the pore solution attains its maximum ability to leach and transport trace amounts of copper from the red beds sediment hosted stratiform copper deposits may form where the brine crosses a redox boundary into reduced sulfide rich gray beds with further consumption of oxygen during reddening the brine may become highly reduced and able to take iron into solution possibly explaining synsediment hosted stratiform copper iron oxide alterations and deposits the timing of copper deposition is clearly linked to the diagenetic reddening of immature footwall sediments in rift basins a process considered to extend over millions of years

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

petrology geochemistry and na metasomatism of triassic jurassic non marine clastic sediments in the newark hartford and deerfield rift basins northeastern usa many sandstones and associated siltstones and shales of the triassic jurassic newark supergroup in the newark hartford and deerfield rift basins are immature feldspathic alluvial and lacustrine closed basin deposits they were derived from felsic igneous and metamorphic continental blocks on the flanks of their depositional basins the provenance was dominantly calc alkaline basement rocks similar to the sierra nevada of california the physical and chemical environments of erosion and deposition were probably similar to those in moist pleistocene holocene alluvial basins and playas in the great basin of california and nevada new petrographic and geochemical data for 113 samples indicate that albite rich sandstones and shales of the stockton lockatong and passaic formations in the newark basin and in the portland and east berlin formations of the hartford basin and analcime rich shales up to 52 normative analcime of the lockatong formation have unusually high na2o contents 4 7 textural evidence indicates both sodium replacement in feldspars and formation of authigenic albite and analcime in these rocks by comparison with modem sediments derived from similar provenance using mixing models it is estimated that up to 4 na2o was diagenetically added to the detrital clastics trace metals co cr cu ni zn abundances were apparently enhanced by deposition from brines in the lockatong formation analcime deposition occurred in shales with al2o3 na2o sio2 0 46 this ratio is found only in sediments to which na has been added from salts brines source rocks and the weathering products derived from them may be considered as a closed system in which sodium was retained partly in solids as feldspar and part went into solution during weathering the dilute solution migrated into the depositional basin where evaporation yielded concentrated brine during semi arid to arid climate in the drier parts of 21 000 yr milankovitch cycles reaction of brine during diagenesis at near surface and or shallow depths 2 km with ca plagioclase k feldspar and layer silicates at estimated temperatures 50 c to 100 c and ph 7 9 yielded thermodynamically stable authigenic albite and analcime in the sodium metasomatised clastic sediments low activity of k precluded development of authigenic k feldspar however k from solution incorporated into muds and silts as smectites were transformed to illite some lockatong beds contain anomalously high p2o5 ce la y th and u in authigenic apatite or monazite suggestive of mobilization of these elements in diagenesis

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

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

gregarious behaviour among non avian theropods inferred from trackways a case study from the cretaceous cenomanian candeleros formation of patagonia argentina abstract gregarious behaviour among dinosaurs has been inferred from several lines of evidence monospecific bonebeds skeletal morphology phylogenetic inferences comparison with modern ecosystems and parallel trackways with particular characteristics but is relatively poorly documented for non avian theropods here we report five parallel theropod trackways of large track size average length of 28 cm in the cretaceous cenomanian candeleros formation from northwestern patagonia argentina the tracks are provisionally assigned to aff asianopodus pulvinicalx and considering the autopod morphology of the theropod taxa documented in the candeleros formation abelisaurid theropods are suggested as trackmakers the trackways possess similar stride speed estimation direction and preservational features and track show uniform depth and do not overlap physical barriers i e large fluvial channels or perennial lake that could influence the direction of the theropod trackmaker gaits were not recognized in the section taking into account these considerations a gregarious behaviour for the abelisaurid theropod trackmakers is proposed the tracks are preserved as shallow undertracks in a medium grained sandstone bed deposited in a floodplain setting the tracking surface is interpreted as the overlaying layer of muddy siltstone the occurrence of swelling clays and microbial mats in the track bearing level could have contributed to the substrate stabilization and their role in the preservation is discussed

intraplate deformation and basin formation during the tertiary within the northern iberian plate origin and evolution of the almazan basin the tertiary almazan basin was a topographic high during the mesozoic rifting at the northern part of the iberian plate it was bordered by two mesozoic basins 1 the castilian basin with a maximum thickness of more than 2000 m to the south and 2 the cameros basin with a maximum thickness of 9000 m to the north to the east the almazan basin is bordered by paleozoic rocks of the nw se trending aragonian range which underwent little subsidence during the mesozoic the two mesozoic basins show an e w direction during the tertiary nne ssw compression mainly late eocene early miocene both mesozoic basins were inverted and uplifted and the almazan basin with an overall synclinal geometry was filled with syn tectonic terrestrial sediments reaching a maximum thickness of 3500 m deformation during the tertiary was strongly controlled by preexisting structures both mesozoic extensional faults and reactivated variscan folds the depocenter of the tertiary basin migrated southward during the paleogene this migration is consistent with a piggyback transport of the whole basin northward due to the movement on the underlying crustal scale north verging cameros thrust the geometry and sedimentary evolution of the almazan thick skinned piggyback basin was controlled by the uplift associated with the main crustal scale thrust which was the main source area and was separated from the foreland basin since the early stages of filling late eocene this makes the main difference with thin skinned piggyback basins controlled by the foreland thrust belt and separated from the foreland basin only at their late stages

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

late palaeozoic hydrocarbon migration through the clair field west of shetland uk atlantic margin geochemical analysis of bitumen and hydrocarbon bearing fluid inclusions from the devonian carboniferous clair field indicates that the reservoirs contain a mixture of oils from different marine and lacustrine sources reconstruction of the clair field oil charge history using fluid inclusion petrography show that oil charging occurred at times of k feldspar quartz and calcite cementation temperature composition time data yielded from the integration of fluid inclusion microthermometry with high resolution ar ar dating date hydrocarbon bearing k feldspar overgrowths at 247 3 3 ma these data show that in order for oil to be trapped within primary fluid inclusions in k feldspar overgrowths hydrocarbon migration throughout the uk atlantic margin must have been taking place during the late palaeozoic and as such current industry oil play models based solely on oil charging from jurassic cretaceous marine sources are clearly incomplete and need revision apatite fission track analysis and vitrinite reflectance data were used to reconstruct thermal burial histories and assess potential oil generation from middle devonian lacustrine source rocks thermal history data from wells along the rona ridge adjacent to the clair field show that the palaeozoic section was heated to greater than 100 c at some time between 270 and 230 ma confirming that devonian source rocks were mature and expelling oil during the late palaeozoic at the time that authigenic k feldspar overgrowths were growing in the clair field

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

assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually determined fluorescence colours abstract the thermal maturity of oils extracted from inclusions and the fluorescence colours of oil bearing fluid inclusions have been measured in 36 sandstone samples from australasian oil fields the inclusion oils were analysed using an off line crushing technique followed by gc ms a maturity assessment was made for each inclusion oil using 25 molecular maturity ratios including a newly defined dimethyldibenzothiophene ratio dmdr each inclusion oil was placed in one of 4 maturity brackets approximately equivalent to early mid peak and post oil generation windows the fluorescence colours of oil inclusions were visually discriminated into blue white and yellow plus orange and their proportions estimated using point counting techniques sixteen samples have 85 of oil inclusions with blue fluorescence whilst other samples have more variable fluorescence colours one sample has 100 of oil inclusions with yellow plus orange fluorescence the results show that samples containing mainly blue fluorescing oil inclusions have thermal maturities anywhere within the oil window in particular the molecular geochemical data strongly suggests that oil inclusions with blue fluorescence can have relatively low maturities calculated reflectance

a model for the effect of illitization on porosity and quartz cementation of sandstones abstract quartz cementation is commonly the most important porosity reducing process in deeply buried quartzose sandstones on the norwegian continental shelf the quartz cement is mostly sourced from stylolites but silica may also be derived from illitization of kaolinite illitization can proceed at silica activities several times higher than quartz saturation whereas dissolution of quartz at stylolites is very sensitive to silica supersaturations and the illitization reaction may consequently stop or retard dissolution of quartz at stylolites since the illitization reaction does not cause a net porosity loss porosity loss due to precipitation of quartz cement is reduced or totally prevented over the depth temperature range where illitization takes place illitization affects albitizatio of k feldspar because both reactions consume k feldspar oil replacement during illitization may conceivably cause greater porosity loss than if oil were not present since oil emplacement might stop or retard illitization but not quartz cementation sourced from stylolites

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

rise closure and reactivation of the bicorb quesa evaporite diapir eastern prebetics spain the bicorb quesa diapir belongs to a complex system of evaporite diapirs located in the se iberian peninsula it was emplaced along the axis of a graben system flanked by two syn diapir growth basins filled by miocene sediments the miocene evolution of the diapir may be divided into three major phases an initial extensional phase during which the graben system formed and the diapir rose a second phase during which regional shortening closed the diapir and a third phase characterized by normal faulting during which diapirism was reactivated cutting the previously formed thrusts and folds this evolutionary trend demonstrates that diapirism was initiated and promoted by regional extension during the two extensional phases the diapir grew by reactive active and passive rise sedimentation during the reactive stage was characterized by strong basin subsidence sharp changes in sediment thicknesses and major coarse grained sediment input during the active stage the coeval basin fill sequence displays progressive angular unconformities gravitational deposits and subtle changes in thickness with the sediments unconformably overlying most of the earlier formed faults finally during the passive stage the sediments synchronous with diapir formation include abundant components from the extruding rocks and show gentler changes in thicknesses a progressive decrease in the input of coarse sediments and the deposition of mudstones and or lacustrine carbonates that clearly extend onto the faulted basin margins

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

siliceous islands in a carbonate sea modern and pleistocene spring fed wetlands in ngorongoro crater and oldupai gorge tanzania abstract a biogenic mechanism is proposed that produces a diagnostic geochemical signature of perennial spring fed wetlands in arid basins especially the saline and alkaline volcanic basins of east africa respiration by vegetation and decay of organic matter within marshes in ngorongoro crater tanzania locally increases aqueous equation the resulting lowered ph inhibits the precipitation of calcite and decreases the rate of silica dissolution steep geochemical gradients are produced these are represented mineralogically by siliceous biomineralization within the perennial marsh and carbonate precipitation in surrounding ephemeral wetlands mudflats and lacustrine environments as a test of this model of geochemical sedimentation the mineralogy of the early pleistocene siliceous earthy claystone of oldupai gorge is consistent with its interpretation as a paleo spring wetland deposit because such deposits are expressions of the paleo water table this approach has potential applications in many studies of basin paleohydrology paleoclimatology paleoecology and archaeology

emplacement of bitumen asphaltite veins in the neuquen basin argentina veins of solid bitumen asphaltite have been commercially exploited in the neuquen basin argentina for over 100 yr veins are up to 5 m wide and several kilometers in length over a region of 15 000 km2 these veins were emplaced in fractures both parallel and at high angles to bedding in close proximity to their source rocks in the vaca muerta and agrio formations late jurassic early cretaceous two or more phases of bitumen emplacement can be recognized in several localities structures bearing viscous oil are younger than structures having solid bitumen bitumen emplacement was vigorous and caused brecciation and spalling of the host rocks the bitumen was also viscous and supports rock debris ranging in size from sand grains up to meter scale slabs brecciation bedding parallel injection and wall rock impregnation suggest high fluid pressures during emplacement high fluid pressure may have been engendered by substantial hydrocarbon generation from rich source rocks in a low permeability sequence and probably caused the fractures into which the bitumen migrated the bedding parallel veins facilitated decollement during thrusting that took place during and after bitumen emplacement the timing of emplacement relative to thrusting and oil migration constrains bitumen emplacement to the eocene oligocene

alteration halos in the tordillos sediment hosted copper deposit of the neuquen basin argentina abstract the tordillos sediment hosted cu deposit is located in the north central sector of the huincul high structure in the neuquen basin argentina it is hosted in sedimentary rocks of the huincul formation an upper cretaceous redbed sequence deposited in a fluvial environment field mapping petrography and chemical analysis of the authigenic clay sulfate carbonate and sulfide minerals at tordillos have identified systematic variation in alteration and paragenesis with time and with respect to the main feeder zones the alteration associated with cu mineralization provides evidence of a multistage infiltration of fluids spatially associated with paleo hydrocarbon migration driven by tertiary tectonism early diagenesis formed hematite kaolinite and calcite1 that have been preserved in the reddish brown mudstones later influx of hydrocarbons and warm reduced formation waters from deeper reservoir rocks is associated with dissolution of early cements and clasts and precipitation of new minerals in the thickest paleo channels of the huincul formation dissolution of early cements hematite kaolinite calcite1 and barite1 and clasts locally increased the porosity of sandstones up to 24 and destroyed hematite that changed sandstones and conglomerates from red to yellowish grey bitumen impregnations are abundant along with calcite2 3 and 4 pyrite minor montmorillonite quartz overgrowth and coarse barite2 crystals with primary organic fluid inclusions at the contact with hydrocarbon tubes the mno enrichment of calcite in stages 3 and 4 reflects their precipitation under reduced conditions grey and greenish grey sandstones with montmorillonite v hematite smectite chlorite group minerals and pyrite respectively are exposed between the reddish brown mudstones and the yellowish grey sandstones and conglomerates the grey and greenish grey horizons are representative of abrupt changes in eh ph conditions between regional early oxidizing solutions responsible for the formation of early diagenetic redbeds and later infiltration of reducing fluids responsible for alteration of sedimentary rocks copper mineralization is located inside the altered sandstones and conglomerates zones forming halos surrounding vertical tubes containing bitumen these tubes are interpreted as the conduits through which migrated hydrocarbons formation waters and subsequent chloride and metal rich fluids in these places pyrite calcite and barite cements of the altered rocks have been dissolved and replaced by copper rich sulfides and then by late supergene cu minerals interconnection among stacked permeable paleo channels in the mid section of the huincul formation facilitated the migration of several generations of fluids during early diagenesis hydrocarbon up flow and exhumation of the neuquen group resulting in the development of alteration halos and cu mineralization that can be used both in outcrop and drill core during exploration for sediment hosted cu mineralization

large scale bleaching of red beds related to upward migration of hydrocarbons los chihuidos high neuquen basin argentina abstract the striking arrangement of colorful facies in the sandstones outcrops of the los chihuidos high argentina has been attributed to the surface expression of hydrocarbon induced alteration the huincul formation late cenomanian early turonian is part of the thick continental red bed dominated neuquen group which consists of meandering fluvial deposits developed in a foreland basin visual distinctions reveal four diagenetic facies red white gray and minor brown sandstones differences in the diagenetic mineralogy among sandstones facies are interpreted to depend on the degree of interaction with hydrocarbon bearing solutions and the relative position of the redox roll front developed during this process the red facies represents the original oxidized sandstone with hematite kaolinite quartz and albite overgrowths and calcite cement precipitated under oxidizing conditions during the regional burial diagenesis the white facies formed during the interaction of red beds with reduced fluids in presence of hydrocarbons or organic acids where clasts and cement were partially dissolved and iron was reduced to fe2 due to redox reactions and removed resulting in the sandstone decoloration and in a marked development of the secondary porosity minor montmorillonite replaced kaolinite and detrital feldspars and a poikilotopic calcite precipitated filling the pores the gray and the brown sandstone bound the redox front which is characterized by the presence of abundant clay minerals and oxide minerals enriched in vanadium and copper montmorillonite and secondary hematite are dominant in the more oxidized gray sandstones whereas interstratified chlorite montmorillonite is more abundant in the more reduced brown sandstones the coexistence of these minerals indicates metastable reducing oxidizing conditions at the redox front based on diagenetic characteristics tectonic framework maturation timing of source rocks and petroleum emplacement history hydrocarbons could have migrated into the huincul formation during the tertiary uplift but later erosion could have released the hydrocarbons and exhumed the reservoir this multi scale investigation of diagenetic features related to burial history and to structure controlled upflow of hydrocarbons in a succession of siliciclastic rocks enhances modeling of a regional scale redox system worldwide our study offers new insight into the application of authigenic minerals to trace hydrocarbon pathways along red beds and to evaluate the reservoir quality in the understanding the importance of fluid compositions mixing and fluid rock interaction along a major redox system

intraplate deformation in the nw iberian chain mesozoic extension and tertiary contractional inversion the iberian chain developed within the iberian plate during the palaeogene and early miocene as a result of convergence between the african and eurasian plates it is a fold and thrust belt which involves the hercynian basement and the mesozoic and cenozoic cover a generalized cross section of the nw part of the chain of 195 km length is presented mesozoic basins developed on the hercynian basement display thickness variations across normal faults that bounded them and that can be recognized in the field the tertiary contraction deformed and inverted the mesozoic basins and it is inferred to have produced a thrust sheet about 5 km thick in its frontal northeastern part which thickens to the sw the total tertiary shortening in the section is 66 6 km 26 the structure and the crustal shortening and thickening of the iberian chain are explained by a major upper crustal thrust system with simple flat and ramp geometry which may branch to the pyrenees or the betics this is combined with internal deformation of the thrust sheet the contribution of the iberian chain shortening to the convergence of the african and eurasian plates during the tertiary is about one half of that of the pyrenees and should be taken into account in any reconstruction of the kinematics of these plates

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

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

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

an isochemical model for formation of authigenic kaolinite k feldspar and illite in sediments abstract although thermodynamic calculations indicate a narrow range of conditions for coprecipitation of kaolinite and k feldspar coexistence of authigenic kaolinite and k feldspar is common in jurassic sandstones of the north sea this paper shows that the coexistence of authigenic k feldspar and kaolinite may indicate that this narrow range of conditions did prevail and that the system behaved as a closed system these conditions are presence of muscovite in the sediment pore waters supersaturated with respect to quartz and temperatures lower than 50 c at higher temperatures the authigenic kaolinite and authigenic k feldspar may react and form authigenic illite muscovite and quartz cement the direction of the isochemical reaction is thermodynamically determined by the degree of supersaturation with respect to quartz in the formation water published data on the degree of supersaturation with respect to quartz in formation waters suggest that the illitization of kaolinite may take place at temperatures as low as 50 c much lower than previously believed

mid crustal detachment in the betic system of southeast spain abstract the tertiary orogenic belts of eastern spain can be interpreted using the principles of thin skinned thrusting with a fundamental detachment at mid crustal level in the eastern betics the compression involves an oblique restacking of a stretched continental margin much of the shortening is transmitted on permian and triassic detachments which emerge as forward and back thrust duplexes an interpretation of the guadarrama range of central spain is presented in which significant shortening is shown on a mid crustal detachment propagating from the southeast it is suggested that this represents the external limit of a compressive system linked to the betics the pyrenees and eastern cantabrians are a separate tertiary compressive system again resulting from restacking of an extensional basin during the collision of iberia and france previous authors have proposed mid crustal detachment in the pyrenees observation of the geological map of the iberian ranges suggests a broadly similar structural origin may apply in which case the iberian ranges may represent the most external zone of a major pyrenean system again linked by a mid crustal detachment thus it is suggested that the whole of eastern spain is made up of two major compressive systems linked at mid crustal level

microcodium revisited root calcification products of terrestrial plants on carbonate rich substrates abstract microcodium is a problematic calcitic microfeature of many calcretes and calcareous paleosols in the cretaceous and tertiary continental and marine successions of the peri tethyan realm the main controversy about the microcodium structures is their origin and possible relation with calcified plant roots microcodium and rhizogenic root formed microfabrics were studied in calcrete profiles within the paleocene shallow marine carbonate succession in southwestern slovenia the prominent laminar calcrete horizons contain abundant calcite aggregates 150 m to 1 cm in size with perfectly preserved structural details of plant root tissues morphology and structure of these aggregates indicate that they formed through biologically controlled precipitation of calcium carbonate within the root cortical cells the morphologies intermediate between the typical microcodium aggregates composed of a single layer of individual elongate pyramidal or prismatic crystals of calcite measuring 100 500 m in length and 20 70 m in width and calcified roots with multilayer arrangement of isodiametric cells were observed and this supports previous rhizogenic interpretations of microcodium structures intermediate forms show that the typical microcodium aggregates formed through morphological transformation of the root tissue by growth of the calcite within the cortical cells which distorted the cell shape calcification of roots and the creation of microcodium structures can be explained as an effective nutrient acquiring mechanism used by certain types of terrestrial plants inhabiting nutrient poor calcareous substrates the widespread occurrence of microcodium in almost unaltered shallow marine limestones indicates that its formation took place during early stages of paleosol development probably reflecting specific types of vascular plants of a pioneer community that were able to colonize carbonate substrates during the early phases of subaerial exposure

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

open or closed geochemical systems during diagenesis in sedimentary basins constraints on mass transfer during diagenesis and the prediction of porosity in sandstone and carbonate reservoirs descriptions of mineralogy and textural relationships in sandstones and limestones have been used to establish a sequence of diagenetic events epigenesis involving mineral dissolution and precipitation which have been interpreted to have occurred during the burial history published epigenetic sequences commonly imply a geochemically open system with very significant changes in the bulk chemical composition of the sediments during burial near surface diagenetic reactions may be open involving significant changes in the sediment composition and formation of secondary porosity caused by high pore water flow rates of meteoric water or reactions with sea water near the sea floor calculations show that the bulk chemical composition of the sediments below the reach of high pore water flow rates of meteoric water or hydrothermal convection should remain nearly constant during progressive burial because of limited pore water flow mass transport between shales and sandstones is also limited because the pore water is in most cases buffered by the same minerals so that the concentration gradients are low recent studies show that silica released from clay mineral reactions in mudstones has been precipitated locally as small quartz crystals and not exported to adjacent sandstones if the geochemical constraints for mass transfer during burial diagenetic reactions are accepted the chemical reactions involved in diagenesis can be written as balanced equations this offers the possibility to make predictions about reservoir quality based on assumptions about primary sediment composition related to facies and provenance large scale changes in the bulk composition of sandstones and mudstones during burial diagenesis have been suggested but because such changes cannot be explained chemically and physically no predictions can be made burial diagenetic processes are in most cases not episodic but occur as slow adjustments to increased stress and temperature driving the sediments toward increased mechanical and thermodynamic stability as a result the porosity of a single lithology must decrease during progressive burial but each lithology has a different porosity curve this article discusses quantitative calculations and estimates that show clearly that burial diagenesis must represent geochemically nearly closed systems where mineral dissolution and precipitation must be balanced this provides a theoretical basis for the modeling and prediction of reservoir quality

stable isotope and fluid inclusion study of sediment hosted stratiform copper deposits from the neuquen basin argentina the los chihuidos and el porvenir deposits of the neuquen basin are examples of sediment hosted stratiform cu deposits generated by interaction of hydrocarbons and formation water with host red beds and metal charged basinal brines during early diagenesis of red beds precipitated hematite kaolinite at 60 c from meteoric water followed by calcite 1 13c 8 to 3 3 and barite 34s 4 1 with increasing temperature 75 85 c from an evolved surface fluid 18ofluids 0 9 to 2 7 during the tertiary andean orogeny hydrocarbons and formation water migrated and reacted with the red beds resulting in bleaching of the sandstone smectite fluid 18o 2 2 and d 73 7 chlorite smectite mixed layer minerals fluid 18o 6 9 and d 84 pyrite 34s 10 2 and calcite 2 13c 12 9 to 6 8 formed as by product of the redox reactions calcite 2 formed from low salinity fluids 0 4 to 5 9 wt nacl equiv at slightly higher temperatures 125 145 c at el porvenir and at los chihuidos deposit 80 105 c during subsequent uplift metal charged basinal brines flowed into the bleached sandstone and precipitated chalcopyrite bornite 34s 12 3 followed by chalcocite spionkopite 34s 64 to 4 1 calcites 3a 13c 19 to 10 1 and 3b 13c 31 4 to 9 5 that accompanied fe cu and cu sulfides respectively formed from saline fluids up to 21 3 wt nacl equiv at temperatures of 159 70 c the 18o values 5 6 to 11 4 of fluids in equilibrium with calcite 3a are similar to oilfield and basinal brines fluids in equilibrium with calcite 3 in los chihuidos and calcite 3b in el porvenir show much lighter 18o values 7 3 to 4 6 and 0 6 to 2 3 respectively which suggests the involvement of methane as the main reductant and possibly meteoric water interaction

palaeogene evolution of deformation in the northeastern iberian peninsula during the palaeogene alpine compression three units were differentiated in the studied area south of the ebro basin the catalan coastal range dominated by ne sw major basement faults with a sinistral movement the iberian range where the important basement faults have a nw se direction and a reverse movement often with a dextral component the linking zone between these two ranges where an e w dominant structural direction is marked by an array of folds and thrusts with a northward vergence in the mesozoic cover from the analysis of both these major structures and the small scale structures it can be deduced that the compression in the studied area has evolved from a nw se direction lower middle eocene to a n s direction and to a ne sw one uppermost oligocene the major structures are due to the n s compression later the stress field progressively changed to a distensive regime we suggest a relation between the compressive phases and the displacement direction of the iberian plate with reference to the european plate

geochemical constraints from formation water analyses from the north sea and the gulf coast basins on quartz feldspar and illite precipitation in reservoir rocks

the jurassic succession in west central argentina stratal patterns sequences and paleogeographic evolution abstract jurassic rocks in west central argentina are predominantly marine and marginal marine siliciclastics associated with prominent but volumetrically subordinate carbonates and evaporites facies developments were ruled by paleogeographic persistence within the southern infratropical latitude belt within 40 50 s and by siliciclastic derivation from the patagonian hinterland to the southwest minor volcanic and volcaniclastic supply arrived from the west out of a magmatic belt related to circum pacific convergence timing of the main marine flooding events and general correspondence with the high rank stratal packaging recorded in western north america suggest that global eustasy was also a factor in controlling the local stratigraphic record early jurassic sedimentation occurred within a series of semi isolated depocentres linked to fault bounded triassic troughs the sinemurian toarcian deposits record depocentre expansion and coalescence these trends were coeval with progressively more widespread marine invasions from the northwest and west leading to an elongate marine seaway which connected central patagonia with the pacific domain during the aalenian bajocian the region was subject to a more subdued tectonism and the foreland side of the basin became fringed by an extensive clastic embankment bathonian and early callovian were times when coarse clastics prograded into the basin while the marine embayment shrank as a result of stepwise forced regressions during late callovian to oxfordian globally rising sea level the depocentre witnessed the appearance of cosmopolitan invertebrates and a stratal pattern of basin widening and depositional underbalance that promoted cratonward onlap and inception of widespread carbonate deposition ooidal coralline carbonate development was terminated after a relatively sudden messinian style event that desiccated a large tract of the andean basin and favored massive precipitation of anhydrite in the course of the kimmeridgian the evaporite basin was largely flooded by siliciclastics and turned into a broad and featureless mudflat salina complex linked to a widespread erg and to an ephemeral drainage system by the tithonian at a period of peak oceanic stand marine connection was reinstated and recorded as the most widespread jurassic transgression across the neuquen aconcagua embayment shelfal deposition consisted of molluscs and ooid dominated carbonate terraces that grew in pulses tuned to eustatic fluctuations like in other prolific petroleum provinces around the world the tithonian basinal strata involve widespread euxinic deposits featuring unusually high organic content

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

mineralogical signature of hydrocarbon circulation in cretaceous red beds of the barda gonzalez area neuquen basin argentina the portezuelo formation is part of a red bed sequence in the neuquen basin assigned to the neuquen group lower cenomanian middle campanian in outcrops of the portezuelo formation in the barda gonzalez region iron oxide and hydroxide cements are only preserved in the less permeable claystone layers paleomigration of hydrocarbons and formation waters along the most permeable layers bleached the rocks due to partial to total dissolution of cements and grains and formation of several authigenic minerals 1 montmorillonite and pyrite in the medium to fine grained sandstones and mudstones and 2 multistage calcite and pyrite in the coarse grained sandstones and conglomerates the canyon diablo troilite of 24 4 to 60 values in pyrite point to microbial reduction of a sulfate precursor the oxidation of hydrocarbons and fluctuations in ph and carbon dioxide pressure caused by organic acids resulted in multiple stages of dissolution and precipitation of calcite calcite crystals host hydrocarbon bearing fluid inclusions pyrite with variable fluorescence color indicating that hydrocarbon composition changed with time the intermediate peedee belemnite 8 11 to 8 52 and 9 76 to 9 83 isotope composition of calcites may have resulted from mixtures of rich after the dissolution of local calcrete with poor from oxidizing hydrocarbons this contribution provides for the first time key information to predict the distribution of authigenic minerals in reservoir rocks in the basin and improves understanding of the diagenetic history of the portezuelo formation

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

model for hydrocarbon microseepage and related near surface alterations despite recent advances in surface and near surface geochemical methods there continues to be a need for improved understanding of the scientific basis relating these methods to petroleum deposits we have reviewed the literature pertinent to the several methods we have used and integrated that information with some 100 man years of our experience to contribute to that end evidence indicates that hydrocarbon micro seepage from reservoirs most probably involves buoyant colloidal size microbubbles of light hydrocarbons principally methane through the butanes ascending relatively rapidly through a water filled network of fractures joints and bedding planes bacterial consumption of these hydrocarbons creates carbon dioxide and hydrogen sulfide which may alter sediments producing detectable modifications in geomorphic seismic magnetic and radiometric properties we have used combinations of 1 airborne microwave sensing and laboratory analyses of soil gas hydrocarbons 2 shallow source aeromagnetic and soil magnetic susceptibility measurements 3 aerial and surface gamma ray measurements and 4 geomorphology to find productive oil and gas deposits results suggest that using these methods can substantially increase the probability of wildcat success and reduce finding costs in selected geologic settings however these surface methods cannot reveal depth size or quality of reservoirs or even if producible hydrocarbons will be found

hypersulfidic deep biosphere indicates extreme sulfur isotope fractionation during single step microbial sulfate reduction coexisting dissolved sulfide and sulfate from hypersulfidic interstitial waters of a 380 m long sediment core show a large isotopic difference of up to 72 caused by in situ microbial sulfate reduction this is considerably larger than the assumed biological maximum of 46 derived from laboratory studies with pure cultures of sulfate reducing bacteria similar high fractionations inferred from sedimentary metal sulfides have been previously explained by a multistage process involving sulfide reoxidation and disproportionation of sulfur intermediates our data show that extreme isotopic differences between sulfate and the reduced sulfur species can also be generated during microbial single step fractionation this result indicates that the sulfate reducing communities and or their cellular metabolic activities in the deep biosphere may differ from those observed in near surface sediments or the water column

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

seismic evidence of alpine crustal thickening and wedging from the western pyrenees to the cantabrian mountains north iberia 1 the alpine collision between the iberian and european plates resulted in a complex crustal structure beneath the northern iberian peninsula as revealed from a new set of seismic refraction wide angle reflection profiles the study area is characterized by two major e w ranges the cantabrian mountains and the pyrenees which are relayed to the south by the iberian chain important variations in crustal thickness and velocity distribution are found in a 560 km long e w transect in contrast to the typical 30 to 32 km thick european variscan crust of the western end of the profile a continuous alpine crustal root is evidenced from the cantabrian mountains to the central pyrenees with a moho depth of 46 48 km locally rising to 40 km depth in between beneath the basque cantabrian basin another outstanding feature is the inferred presence of high velocities of 6 40 6 75 km s at midcrustal depths which can be associated with portions of a lower crustal wedge from the northern european domain indenting the southern iberian crust during the alpine stage of compression this indentation produces the delamination of the iberian crust with northward underthrusting of its lower half and the consequent crustal thickening the indenting wedge has a discontinuous presence along the longitudinal section as it was controlled and or affected by n s to ne sw structures further evidence of the northward subduction of the iberian plate is provided by another profile toward the aquitaine basin while a n s profile across the iberian chain reveals an alpine midcrustal thickening beneath this belt with moho depths of 42 km

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

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget

the controls on the composition of biodegraded oils in the deep subsurface part ii geological controls on subsurface biodegradation fluxes and constraints on reservoir fluid property prediction the principal controls on the fluid properties of biodegraded oil systems have been determined by a combination of petroleum geochemistry numerical modeling of oil biodegradation in reservoirs and analysis of oil property data sets from a variety of geological settings petroleum biodegradation proceeds under anaerobic conditions in any reservoir that has a water leg and has not been heated to temperatures more than 80c in most reservoirs with low concentrations of aqueous sulfate methanogenic degradation is a primary mechanism of petroleum degradation whereas in waters containing abundant sulfate sulfate reduction and sulfide production may dominate net degradation of petroleum fractions in reservoirs is primarily controlled by the reservoir temperature the chemical compounds being degraded and relationships between the oil water contact owc area and oil volume the relative volumes of water leg to oil leg prior level of oil biodegradation and reservoir water salinity act as second order controls on the process typically degradation fluxes kilograms of petroleum destroyed per square meter of oil water contact area per year or kg petroleum m2 owc yr1 for fresh petroleum in clastic reservoirs are in the range of 103 104 kg petroleum m2 owc yr1 and increase with decreasing reservoir temperature from zero near 80c to a maximum flux at the owc of less than 103 kg petroleum m2 owc yr1 at a temperature less than 40c at very low reservoir temperatures and with severely degraded oils such as are seen in the near surface canadian tar sands at the present day the net degradation fluxes are much less than maximum values nutrient supply from the aquifer and adjacent shales mostly buffered by mineral dissolution probably provides the ultimate control on the range of degradation flux values oil compositional gradients and resulting oil viscosity variations are common on both reservoir thickness and field scales in biodegraded oil reservoirs and are a defining characteristic of heavy oil fields produced by crude oil biodegradation continuous vertical gradients in the oil columns document episodic degradation for many millions of years suggesting that the time scales of oil field degradation and petroleum charging are similar the flux temperature relationship we have derived coupled with typical reservoir charge histories defines the range of variation of fluid properties seen in many biodegraded oil provinces and identifies oil charge mixing of biodegraded and fresh oils and reservoir temperature history as the primary controls on fluid properties these flux temperature relationships are easily integrated into prospect charge modeling procedures sensitivity analyses show that the limiting factor in fluid property predictions using even this first level approach are ultimately constrained by the accuracy of current oil charge modeling estimates the absence today of any functional geochemical proxies for assessing oil residence time in oil fields and the substantial uncertainty in petroleum charging times estimated by forward basin modeling is a major obstacle to more accurate fluid property predictions that needs to be addressed