tectonic wedging blueschist metamorphism and exposure of blueschists are they compatible tectonic wedging is currently deforming rocks along the westernmarginofthecentralvalleyofcalifornia structuralrelations in the strata of the mesozoic great valley group fore arc basin indicatethatearlierphasesofwedgingwerecoevalwithsubduction and accretion of the franciscan complex to the west the presentday geometry of tectonic wedging is incompatible with blueschist metamorphism in the franciscan complex because the detachment for the wedge system would have prevented the transport of accretionary wedge materials to great depth we propose a sequence of tectonic events that reconciles these tectonic processes franciscan subduction and metamorphism began at 165 ma and great valley group deposition began in the tithonian shortening affected great valley group rocks in the hauterivian barremian and may havecoincidedwithagapinblueschistmetamorphisminthefranciscan major uplift of franciscan blueschist relative to the unmetamorphosed great valley group rocks began in the albian cenomanian this uplift was accommodated along an east dipping extensional fault system between the franciscan complex and the structurally overlying coast range ophiolite and great valley group movement on this fault system caused the western side of thefore arcbasintosubside resultinginuninterrupteddeposition ofgreatvalleygroupsedimentsfromthecenomaniantothecampanian maastrichtian the youngest exposed blueschists in the franciscan were metamorphosed at 80 90 ma uplift of blueschist relativetogreatvalleygrouprocksmusthavebeencompleteprior todevelopmentofthepresentstyleofeast vergenttectonicwedging this style of deformation probably began between the maastrichtian and paleocene resulting in exhumation and deformation of bothfranciscanandgreatvalleygrouprocks thedevelopmentof wedging was coincident in part with the shallowing of subduction dip and voluminous frontal accretion of the coastal belt of the franciscan

deformation paths in the shallow levels of an accretionary prism the eocene shimanto belt of southwest japan detailed structural analysis of coherent turbidites in a part of the eocene shimanto belt on the muroto peninsula shikoku island japan reveals a structural evolution that is typical of the shallow levels of accretionary prisms in style and sequence of deformational fabrics but anomalous in that it includes both a marked rotation in shortening direction and a major out of sequence thrust deformation throughout a history of progressive lithification and burial was dominated by subhorizontal shortening and seaward vergent shear structures evolved from predominantly mesoscale thrusts and folds to larger more brittle faults and finally to kilometer scale amplified fault bend folds with an associated pressure solution cleavage this structural progression is consistent with increasing strength of the rocks decreasing fluid pressures and increasing temperature and pressure as the sediments were dewatered lithified and accreted to the prism in contrast to this straightforward structural evolution the prism scale deformation of the eocene shimanto belt is difficult to reconcile with simple models of prism developmentthat assume orthogonal subduction and seaward stepping imbrication a 50 counterclockwise rotation in the shortening direction and a major out of sequence or intraprism thrust are recorded by two distinct structural domains in both the earliest structures are clastic dikes and faults indicative of north south shortening one domain is characterized by east striking regional scale folds and cleavage that are transected by an east northeast trending cleavage however the other is characterized by northeast striking folds and cleavage that are transected by a slightly more north striking cleavage the different deformation histories of the two do mains require that they be separated by a major intraprism fault this fault carries tectonic melange containing blocks of pillow basalt and chert indicating that it rooted in the decollement zone beneath the prism the tectonostratigraphy and deformation histories of the two domains suggest that both before and after the out of sequence fault developed higher structural levels of the prism experienced significant subhorizontal shortening whereas lower structural levels bypassed this zone of deformation

the weathering of micrometeorites from the transantarctic mountains abstract micrometeorites are cosmic dust particles recovered from the earth s surface that dominate the influx of extraterrestrial material accreting to our planet this paper provides the first in depth study of the weathering of micrometeorites within the antarctic environment that will allow primary and secondary features to be distinguished it is based on the analysis of 366 particles from larkman nunatak and 25 from the transantarctic mountain collection several important morphological categories of weathering effects were identified 1 irregular and faceted cavities 2 surface etch pits 3 infilled cavities 4 replaced silicate phases and 5 hydrated and replaced metal these features indicate that congruent dissolution of silicate phases in particular olivine is important in generating new pore space within particles comparison of the preservation of glass and olivine also indicates preferential dissolution of olivine by acidic solutions during low temperature aqueous alteration precipitation of new hydrous phases within cavities in particular ferrihydrite and jarosite results in pseudomorph textures within heavily altered particles glass in contrast is altered to palagonite gels and shows a sequential replacement indicative of varying water to rock ratios metal is variably replaced by fe oxyhydroxides and results in decreases in ni fe ratio in contrast sulphides within metal are largely preserved magnetite an essential component of micrometeorites formed during atmospheric entry is least altered by interaction with the terrestrial environment the extent of weathering in the studied micrometeorites is sensitive to differences in their primary mineralogy and varies significantly with particle type despite these differences we propose a weathering scale for micrometeorites based on both their degree of terrestrial alteration and the level of encrustation by secondary phases the compositions and textures of weathering products however suggest open system behaviour and variable water to rock ratios that imply climatic variation over the lifetime of the micrometeorite deposits

the classification of micrometeorites due to their small size the mineralogical and chemical properties of micrometeorites mms are not representative of their parent bodies on the centimeter to meter scales that are used to define parent body groups through the petrological study of meteorites identifying which groups of mm are derived from the same type of parent body is problematic and requires particles to be rigorously grouped on the basis of mineralogical textural and chemical properties that reflect the fundamental genetic differences between meteorite parent bodies albeit with minimal bias towards preconceived genetic models specifically the interpretation of mms requires a rigorous and meaningful classification scheme at present the classification of mms is however at best ambiguous a unified petrological chemical classification scheme is proposed in the current study and is based on observations of several thousand mms collected from antarctic ice

forced folding and fracturing induced by differential compaction during post depositional inflation of sandbodies insights from numerical modelling abstract three series of numerical models based on the discrete element method were constructed to simulate forced folding and fracturing triggered by postdepositional inflation of fluidised sandbody the models consist of numerous particles that have relatively low to high interparticle bonds to represent overburden sediments with a relatively low to high cohesion and cohesionless frictionless particles to represent fluidised sands the modelling results show that normal faults were produced due to the upward inflation of sand domes and the resulting flexed overburden when the cohesion of the host sediments is low opening voids were created as a result of strata collapse when the intrusion related normal faults terminated within the host sediments as blind faults conical fractures that are aligned along sandbody margins were produced which consist of closed lower segments with a reverse displacement and opening middle upper segments with a minor to zero shear component forced folds were generated in most models with a moderate to high cohesion resulting in differential compaction in the overlying sediments that can account for the formation of fold related fractures which are either shear hybrid or pure tensile depending on their structural positions the amplitude of forced folds is closely associated with both cohesion and thickness of sediments in the overburden whilst fold wavelength is mainly controlled by sediment cohesion based on the modelling results three types of preferential sites for the storage of injected sands were suggested which are believed to be instructive for subsurface sandbody detection and prediction this study demonstrates that differential compaction induced by sand inflation can play an important role in overburden folding and fracturing

emplacement of sandstone intrusions during contractional tectonics abstract sandstone injections are created by the forceful emplacement of remobilized sand in response to increases in overpressure however the contribution provided by horizontal compressive stress to the build up in overpressure and the resulting emplacement of sand injection complexes is still to be substantiated by robust field observations an opportunity to address this issue occurs in central california where a large volume of sandstone intrusions record regionally persistent supra lithostatic pore pressure detailed fieldwork allows sandstone filled thrusts to be recognized and for the first time permits us to demonstrate that some sandstone intrusions are linked to contractional deformation affecting the western border of the great valley basin fluidized sand was extensively injected along thrust surfaces and also fills local dilatant cavities linked to thrusting the main aims of this paper are to provide detailed descriptions of the newly recognized syn tectonic injections and describe detailed cross cutting relationships with earlier sandstone injection complexes in the study area finally an evolutionary model consisting of three phases of sand injection is provided in this model sand injection is linked to contractional tectonic episodes affecting the western side of the great valley basin during the early middle cenozoic this study demonstrates that sand injections driven by fluid overpressure may inject along thrusts and folds and thereby overcome stresses associated with regional contractional deformation it is shown that different generations of sand injection can develop in the same area under the control of different stress regimes linked to the evolving mountain chain

seismically active fold and thrust belt in the san joaquin valley central california structural analysis of late cenozoic folds along the western and southern margins of the san joaquin basin suggests that the folds are related to development of a fold and thrust belt rather than to wrench tectonics the folds have formed by the processes of fault bend folding and fault propagation folding which commonly occur in fold and thrust belts our structural interpretation attributes the seismically active coalinga and kettleman hills north dome anticlines to fault bend folding above a thrust fault s that steps up from a detachment within the franciscan assemblage to a detachment at the base of the great valley group this thrust does not reach the surface blind thrust and its slip is consumed in backthrusting and formation of subsurface folds under the san joaquin valley movement on the postulated thrust s would explain the cause of the may 2 1983 coalinga earthquake and the august 15 1985 avenal earthquake and would account for the lack of significant surface rupture or shallow subsurface faulting during both earthquakes well documented examples of fault bend and fault propagation folding also occur at wheeler ridge in the san emigdio mountains and at kettleman hills south dome deformation associated with fold and thrust belts can be extremely complicated considerable fault movement can occur without accompanying surface rupture or shallow level faulting conversely surface rupture can occur that has no direct relationship to fault slip at depth an example would be flexural slip folding wherein the slip planes reach the surface but do not root into any significant faults at depth consequently traditional geologic approaches to seismic risk evaluation which rely largely on surface data are subject to numerous pitfalls when applied to fold and thrust belts our interpretation of the structural style that developed in central california during the late cenozoic requires that the strain associated with the transpressive motion between the pacific and north american plates be resolved into normal and tangential components thrust faulting and folding normal to the plate boundary and strike slip faulting parallel to the plate boundary san andreas fault the thrust faults root in a deecollement at the brittle ductile transition zone above which shortening is associated with folding and thrust faulting and beneath which shortening in the lower crust is accommodated by ductile processes of tectonic thickening or incipient subduction

identifying soft sediment deformation in rocks abstract the correct identification of sedimentary folds and fabrics created during gravity driven deformation of unlithified successions from those tectonic structures formed during regional deformation is essential when interpreting geological histories preserved within the rock record this topic has become increasingly relevant over the past 40 years as improved seismic resolution and coverage have led to the realisation that significant portions of unlithified sediments along the continental margins undergo gravity driven deformation to create mass transport deposits mtd s the late pleistocene lisan formation exposed in the dead sea basin was chosen as a case study because it remains poorly lithified and structures developed within it are unequivocally related to soft sediment deformation ssd created when the succession underwent downslope directed movement this work tests various assertions previously used to deduce if structures were formed in unlithified sediments or during hard rock deformation hrd associated with subsequent tectonism within the lisan formation we describe veins developed along fractures and cleavage forming axial planar to folds that are structures previously assumed to be restricted to hrd in addition truncated folds incorporation of deformed fragile fragments into overlying sediment and cross cutting clastic dykes are all indicative of ssd the key diagnostic feature in establishing ssd is the sedimentary infill of irregular erosive surfaces that truncate underlying structures although compaction and diagenesis have not played a significant role in the case study caution should be exercised when examining structures preserved in the rock record as folds and fabrics originally created by ssd may be considerably enhanced and altered where significant overburden exists

distinguishing tectonically and gravity driven synsedimentary deformation structures along the apulian platform margin gargano promontory southern italy abstract the assessment of deformation types within the slope of a carbonate platform can be complicated by the possible interaction of rooted tectonically induced and superficial gravity driven structures an ideal case study to document and distinguish tectonically and gravity driven structures is provided by the cretaceous slope to basin carbonates exposed in the gargano promontory southern italy these carbonates formed adjacent to the apulian platform margin which was oriented approximately ne sw to nw se along the southern and northern edges of the promontory respectively slump related folds are characterised by axial planes typically oriented either sub parallel or at small angles to the strike of the inferred paleoslope in fact the strike of folds is roughly ne sw in the southern portion of the study area whereas it is nw se in the northern part correspondingly gravity driven normal and reverse faults strike sub parallel and at acute angles to the adjacent apulian paleoslope cretaceous tectonic faults in the slope to basin carbonates form two principal sets striking nw se and wnw ese the former set is made up of normal faults and the latter one includes mainly oblique slip normal faults neither normal nor oblique slip normal faults show any relationship with the geometry of the paleoslope the results obtained from this study may help the interpretation of subsurface data in those geological contexts in which the interplay of gravitational and tectonic processes is responsible for deformation

petrofacies of eocene sand injectites of the tumey giant injection complex california usa abstract the forearc succession of great valley group in central california provides some of the best examples of giant sand injection complexes in the world and is therefore considered valuable analogues for injectite systems in the subsurface several sand injection complexes are well described in the outcrop and subsurface however the petrographic characteristics of injectites are still poorly documented in this paper we present the results of an integrated study of field observations quantitative and qualitative sandstone petrography provenance and petrofacies analysis of the tumey giant injection complex tgic in order to understand its lithostratigraphy and petrological evolution and its impacts on reservoir petrofacies characteristics and fluid migration the tgic intrudes into a 450 m thick deep water succession of slope mudrocks and sandy channel fills of the kreyenhagen shale eocene forming an interconnected network of sandstone sills dykes and injection breccias the complex generated a horizontal and vertical plumbing system for fluid migration connecting isolated sandy channel fills among low permeability mudrocks the primary detrital composition diagenetic products microtextures and provenance signatures allowed for the definition and discrimination of depositional and intrusive petrofacies and their genetic relations petrofacies associations confirm that the gypsum cemented feldspathic litharenites from the kreyenhagen shale channel fills are the only source for the injection complex eodiagenetic compaction and extensive gypsum cementation reduced the primary porosity of the complex while telodiagenetic dissolution of autigenic constituents formed pervasive secondary porosity the underlying calcite cemented arkosic sandstones of the lodo and domengine formations acted as barriers for fluid flow aiding lateral fluid migration and overpressure buildup within the overlying kreyenhagen channel fills intense grain microfracturing occurred during sand remobilization and injection along with erosion of the host mudrocks this study has significance for the generation of reliable stratigraphic and petrological models for sand injection complex genesis and evolution that consequently can help the understanding and exploration of injectite complexes elsewhere

physical models of magmatic intrusion during thrusting to investigate how magma rises through the brittle upper crust in a context of compressional tectonics we have performed experiments on scaled physical models powdered silica having a cohesion of 300 pa and an angle of internal friction of 38 was used to represent brittle crust a vegetable oil with a newtonian viscosity of 10 2 paae sa t 50c was used to represent magma a moving piston shortened the models in a box while oil was injected steadily at the base on cooling to room temperature the oil solidified the resulting intrusions were thin sills dykes and laccoliths their shapes and emplacement modes depended on the ratio r between rates of shortening and injection from shapes and orientations of intrusions we infer that hydraulic fracturing was one mechanism of emplacement unconsolidated intrusions strongly influenced thrust formation on the basis of our experiments we suggest that magmas in orogenic belts can rise along thrust faults

impact ejecta at the paleocene eocene boundary extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of earth a rapid carbon cycle perturbation and global warming event about 56 million years ago at the paleocene eocene p e boundary the paleocene eocene thermal maximum was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep sea benthic organisms here we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine p e boundary sections on the atlantic margin distinct characteristics identify the spherules as microtektites and microkrystites indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the p e boundary

mid crustal emplacement and deformation of plutons in an andean style continental arc along the northern margin of the north china block and tectonic implications abstract outcrop mapping and thermobarometrical thermochronological and microstructural analyses in five late carboniferous early permian arc plutons in the northern north china block ncb indicate a transition of tectonic regime from arc perpendicular contraction to transpression and successive uplift and exhumation of the crustal rocks during magma emplacement and construction of the continental arc system the early emplaced daguangding and boluonuo plutons 324 302 ma display well developed penetrative moderately to steeply dipping magmatic foliations and high temperature sub solidus foliations that are parallel to host rock foliation near the contact widespread high temperature sub solidus foliations in these plutons indicate that they are syn tectonic with n s arc perpendicular shortening and record arc construction at a convergent continental margin however the late emplaced tianqiao and xianghuangqi wudaoyingzi plutons 288 274 ma display relatively weak magmatic fabrics at their margins and lack sub solidus foliations and pluton related ductile deformation of the contact host rocks these structural differences likely reflect a kinematic transition from early arc perpendicular contraction to late sinistral transpression during continental arc formation aluminum in hornblende barometry shows that their estimated emplacement depths decrease gradually from the late carboniferous 18 7 0 8 km to early permian 13 8 0 9 km indicating successive exhumation of the crustal rocks at an average rate of ca 123 mm ka over 40 million years of arc formation 40 ar 39 ar thermochronological results show that cooling of the continental crust was very slow 4 9 c ma during arc construction in the late carboniferous late permian but increased significantly during the late permian middle triassic after arc termination the mid crust of the northern ncb remained very hot 530 c during arc construction and emplacement of the arc batholiths combined with emplacement depth estimated by aluminum in hornblende barometry paleogeothermal gradients of 42 8 46 5 c km were estimated in mid to upper crustal levels 0 19 km hot mid crust and high mid upper crust geothermal gradients resulted from magmatic advection are likely the most important reasons for crust thickening and uplift during construction of andean style continental arcs and largely influenced the rheological behavior of continental crust

ocean drilling project hole 689b spherules and upper eocene microtektite and clinopyroxene bearing spherule strewn fields montanari et al 1993 reported a positive ir anomaly in the upper eocene sediments from ocean drilling program hole 689b on the maud rise southern ocean vonhof 1998 described microtektites and clinopyroxene bearing cpx spherules associated with the ir anomaly in hole 689b and suggested that they belong to the north american and equatorial pacific cpx strewn fields respectively we searched a suite of 27 samples taken through the spherule layer from hole 689b and we recovered 386 microtektites and 667 cpx spherules we studied the petrography of the microtektites and cpx spherules and determined the major element compositions of 31 microtektites and 14 cpx spherules using energy dispersive x ray analysis we also determined the minor element compositions of eight microtektites using instrumental neutron activation analysis we found that the peak abundance of cpx spherules is 2 cm below the peak abundance of the microtektites 128 7 m below sea floor which suggests that the cpx spherule layer may be slightly older 3 5 ka the microtektites are mostly spherical and are generally transparent and colorless they are similar to the north american microtektites in composition the biggest differences being their generally lower na2o and generally higher zr ba and ir up to 0 3 ppb contents we agree with vonhof 1998 that the hole 689b microtektites probably belong to the north american tektite strewn field we calculate that the number of microtektites 125 m cm2 at hole 689b is 52 this number is close to the concentration predicted by extrapolation of the trend of concentration vs distance from the chesapeake bay structure based on data from other north american microtektite bearing sites thus the north american strewn field may be at least four times larger than previously mapped the hole 689b cpx spherules range from translucent yellow to opaque black but most are opaque tan to dark brown they are generally spherical in shape and all are 125 m in diameter some contain ni rich spinels in addition to clinopyroxene microlites the cpx spherules are petrographically and compositionally similar to cpx spherules previously found in the northwestern atlantic ocean caribbean sea gulf of mexico equatorial pacific and eastern indian ocean the abundance and widespread geographic occurrence of these spherules suggest that the strewn field may be global in geographic extent assuming a global extent we estimate that there may be at least 25 billion metric tons of cpx spherules in the strewn field based on age size and geographic location we speculate that the 100 km diameter popigai crater in northern siberia may be the source of the cpx spherule layer

the facing of faults it is proposed that the usage of the term structural facing be extended to include fault structures fault facing is defined as the direction in a fault plane which is at right angles to the trace of the bedding and is directed towards the younger beds certain types of faulted structures are found to have diagnostic patterns of facing variation

granite magma migration and emplacement along thrusts this paper investigates the influence exerted by brittle tectonic structures in the emplacement of granite plutons in contractional settings we address both cases where contractional tectonics and magma intrusion are 1 coeval to study how active contractional tectonics controls the transport of magma and 2 diachronous to study the role of pre existing structures on the transport of magma in light of new experimental models we show that magma can rise along thrusts ramps and flats this phenomenon occurs for both low viscosity magma basalts to andesite and high viscosity magma dry granite the experimental results also allow the evaluation of the role played by magma viscosity in determining pluton geometries in addition a review of literature demonstrates a spatial and causal relationship between granites and thrusts and highlights the geometric control of magma pathways in the pluton final shape the abundance of subhorizontal and tabular granitic intrusions indicates that the location of inflating granitic sills along thrust flats can be common we argue that active and pre existing flats and ramps thrusts provide a preferential continuous planar anisotropy susceptible to become a granitic magma migration pathway

regional sand injectite architecture as a record of pore pressure evolution and sand redistribution in the shallow crust insights from the panoche giant injection complex california abstract observations on outcrop of a regionally developed sand injectite are used to infer and estimate the pore pressure conditions in the shallow crust that caused the fluidization and injection of tens of cubic kilometres of sand the estimated pore fluid pressures at the base of the injection complex at 1500 m burial depth below a regionally developed shale dominated seal are from 22 26 to 25 08 mpa which respectively correspond to 0 81 and 0 95 lithostatic pressure a theoretical basis for prediction of sand injection is defined and applied to the prediction of pore pressure at the time of sand injection the depth at which seal failure occurred and the density and granular content of the fluidized flow lateral variations in the style and abundance of sandstone intrusions are described and these all fit into a remarkably uniform tripartite division of parent units an intrusive complex and an extrusive complex a sill zone intrusions are dominated by sills occurs in a restricted stratigraphic interval 200 270 m thick location of the base of the sill zone is directly related to the thickness of the overburden and an isobaric surface at the time of sand injection the lithostatic equilibrium surface is defined at the base of the sill zone when the sills formed an extended period of supra lithostatic pressure occurred within the sill zone

sedimentary and structural controls on seismogenic slumping within mass transport deposits from the dead sea basin abstract comparatively little work has been undertaken on how sedimentary environments and facies changes can influence detailed structural development in slump sheets associated with mass transport deposits mtds the nature of downslope deformation at the leading edge of mtds is currently debated in terms of frontally emergent frontally confined and open toed models an opportunity to study and address these issues occurs within the dead sea basin where six individual slump sheets s1 s6 form mtds in the late pleistocene lisan formation all six slumps which are separated from one another by undeformed beds are traced towards the ne for up to 1 km and each shows a change in sedimentary facies from detrital rich in the sw to more aragonite rich in the ne the detrital rich facies is sourced predominantly from the rift margin 1 5 km further sw while the aragonite rich facies represents evaporitic precipitation in the hyper saline lake lisan the stacked system of mtds translates downslope towards the ne and follows a pre determined sequence controlled by the sedimentary facies each individual slump roots downwards into underlying detrital rich layers and displays a greater detrital content towards the sw which is marked by increasing folding while increasing aragonite content towards the ne is associated with more discrete thrusts the mtds thin downslope towards the ne until they pass laterally into undeformed beds at the toe the amount of contraction also reduces downslope from a maximum of 50 to

flow pattern within a permian submarine slump recorded by oblique folds and deformed fossils ulladulla south eastern australia the flow pattern within a slump in permian marine rocks of the southern sydney basin australia is recorded by folds and deformed fossils abundant brachiopod and bryzoan fossils in the slumped rocks are relatively undeformed but fossil crinoid stems have been deformed by relative rotation of individual ossicles measurement of the strain indicates that the deformation of the crinoids is consistent with flexural flow folding within the slump previous models assume that curved slump fold axes remain parallel to the enveloping bedding surface of a slump sheet detailed measurements of the orientation of slump folds in this study found fold axes to be oblique to bedding which is interpreted as a result of folds plunging downward towards the flanks of the slump or slump lobes in the present model fold axes are not generally parallel to the strike of the fold axial surface and this can explain differences between the orientations of slump fold axes and axial surfaces when these are used as directional indicators of slump movement

regional scale subsurface sand remobilization geometry and architecture an architectural hierarchy of clastic sills is recognized in the panoche giant injection complex in which staggered stepped with erosive top surfaces and multi layered geometries occur in that stratigraphic order upward genetic relationships between parent depositional sand bodies the sand injections a zone of hydraulic fracture and a palaeo sea floor are seen at a scale previously observed only by using seismic data sills and randomly oriented dykes intrude into a hydraulically fractured shale unit above and below which dykes predominate erosive surfaces scallops are identified on sills that along with smaller erosional features record low viscosity turbulent flow during sand injection sand extrusions occur where dykes reach the palaeo sea floor

reappraisal of hypothetical franciscan thrust wedging at coalinga implications for tectonic relations along the great valley flank of the california coast ranges 1 correlation of the character and orientation of seismic reflectors imaged on profiles across the coalinga anticline with known surface geology indicates that local franciscan thrust wedging favored for past geodynamic interpretations of the 1983 coalinga earthquake is an untenable hypothesis the inference that a subhorizontal detachment surface of simple shear is present beneath the anticline is consequently unnecessary and unlikely in view of the coherent areal pattern of wrench folding within the southern diablo range elsewhere along the structural front of the california coast ranges at the western flank of the great valley interpretations of similar thrust wedging based in part on analogy with supposed structural relations at coalinga are equally questionable in a wider context the seismogenic behavior of blind thrust and reverse faults in california cannot be interpreted with the invalid concept of thrust wedging at coalinga as a guiding template for geotectonic interpretations

multiple episodes of sand injection leading to accumulation and leakage of hydrocarbons along the san andreas san gregorio fault system california abstract the presence of sand injections has been shown to enhance the likelihood of hydrocarbon traps within siliciclastic successions through the development of large interconnected networks of sills and dykes sand injection complexes provide a volume of porous and permeable rocks within the low permeability host units overall the formation of sand injection complexes requires extensive fracturing and hydrofracturing which can be particularly pronounced when sand injections are coupled with brittle tectonic deformation in some circumstances this process may threaten the integrity of the reservoir top seal thereby preventing further hydrocarbon accumulation studying exceptional exposures along the coastal area of santa cruz in california we report evidence for top seal failure associated with injection episodes two distinct sand injection episodes are proposed the first event datable to the late miocene resulted in large volumes of sand being emplaced within the top seal units and was followed by accumulation of hydrocarbons within the newly injected sandstones later a series of brittle tectonic events associated with the san andreas san gregorio fault system caused remobilization and accumulation of sand along newly formed fault planes our case study documents this combination of pervasive brittle deformation and sandstone injection along fault structures which can ultimately disrupt the integrity of a host unit leading top seal failure and leakage of hydrocarbons

crumbs from the crust of vesta achondritic cosmic spherules from the south pole water well ten glass cosmic spherules cs from the south pole water well collection were analyzed by electron microprobe nine of them have fe mn and fe mg ratios in the range typical of chondrites one of them sp37 3 along with up to six other previously analyzed cs have nonchondritic fe mn and fe mg ratios that agree well with values typical of either basaltic howardite eucrite and diogenite hed meteorites or martian basalts but not of lunar samples sp37 3 also contains an anorthite relic grain anorthite has not previously been reported in cosmic spherules but is well known in hed meteorites the much greater frequency of heds among hand sized meteorites suggests but does not prove that hed precursors are more likely for the nonchondritic spherules we estimate that hed like micrometeorites constitute 0 5 0 4 of the total population of micrometeorites in the south pole water well a fraction that translates to a flux of 1 6 0 3 x 10 8 g hed micrometeorites m 2 y the ratio of hed like objects to carbonaceous objects is about 100 times less in micrometeorites than among hand size specimens we infer that the comparative mechanical weakness of carbonaceous precursor materials tends to encourage spherule formation

the west central florida inner shelf and coastal system a geologic conceptual overview and introduction to the special issue abstract this paper provides an overview for this special publication on the geologic framework of the inner shelf and coastal zone of west central florida this is a significant geologic setting in that it lies at the center of an ancient carbonate platform facing an enormous ramp that has exerted large scale control on coastal geomorphology the availability of sediments and the level of wave energy in order to understand the holocene geologic history of this depositional system a regional study defined by natural boundaries north end of a barrier island to the apex of a headland was undertaken by a group of government and university coastal geologists using a wide variety of laboratory and field techniques it is the purpose of this introductory paper to define the character of this coastal inner shelf system provide a historical geologic perspective and background of environmental information define the overall database present the collective objectives of this regional study and very briefly present the main aspects of each contribution specific conclusions are presented at the end of each paper composing this volume

terrestrial and marine records of climatic and environmental changes during the pliocene in subtropical florida pollen ostracode and benthic foraminifer assemblages deposited during sea level high stands in subtropical florida record a climate change during the period 4 5 1 0 ma before 3 5 ma open shelf marine faunas and pollen assemblages with abundant pinus quercus fagus carya and nonarboreal pollen were present indicating cooler conditions than today from 3 5 to 1 0 ma marine and terrestrial records indicate warmer conditions similar to those existing in south florida today combined with evidence for much warmer than modern conditions at high latitudes these data suggest that increased poleward oceanic heat transport possibly related to the emergence of the central american isthmus between 3 5 and 2 5 ma was a major influence on mid pliocene warmth

large scale fluid flow in the middle devonian presqu ile barrier western canada sedimentary basin saddle dolomite cements are regionally extensive in the middle devonian presqu9ile or keg river barrier and are spatially associated with mississippi valley type mineralization at pine point northwest territories from northeastern british columbia to pine point over a lateral distance of 400 km these dolomite cements show general trends of decreasing 87 sr 86 sr ratios 0 7106 to 0 7081 and homogenization temperatures 178 to 92 c with some increase in 18 o values 16 to 7 pdb these regional trends suggest that hotter and more radiogenic basinal fluids moved eastward updip along the presqu9ile barrier and mixed with cooler ambient formation waters these movements of basinal fluids were probably related to tectonic thrusting and compression sedimentary loading and tectonic uplift on the western margin of the western canada sedimentary basin which began to form during late jurassic to early cretaceous time and climaxed during the late cretaceous to paleocene the middle devonian presqu9ile barrier appears to have acted as a deeply buried regional conduit system that played an important role in focusing and channeling these basinal fluids these regional fluid flows appear to have been responsible for extensive burial dolomitization secondary migration of hydrocarbons and local mississippi valley type mineralization in the western canada sedimentary basin

mechanisms and controls on the formation of sand intrusions sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep water settings they also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments a variety of mechanisms have been cited as triggers for clastic intrusions these include seismicity induced liquefaction application of tectonic stresses excess pore fluid pressures generated by deposition related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body the formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures when the seal on an unconsolidated overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize the fluidized slurry can then inject along pre existing or new fractures to form clastic intrusions the scale and the geometry of an intrusive complex is governed by the stress state depth and pre existing joints or faults within the sedimentary succession as well as the nature of the host sediments for the simplest tectonic setting where the maximum stress in a basin is vertical gravitational loading small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface whereas at greater depth dykes and sills forming clastic intrusion networks are more typical a simple relationship is derived to calculate the maximum burial depth at which a dyke sill complex forms as a function of the source bed to sill height the bulk density of the surrounding sediments and the ratio of the vertical to horizontal effective stresses k 0 when applied to three examples of large scale dyke sill complexes developed within paleocene and eocene deep water reservoir sand bodies of the north sea maximum burial depths in a range of 375 to c 500 m 450 700 m and 550 850 m are estimated for intrusion of each of the three complexes

tectonic evolution of the jurassic cretaceous great valley forearc california implications for the franciscan thrust wedge hypothesis interpretation of seismic reflection data and restoration of depositional geometries of cretaceous forearc basin strata in the northwest great valley of california provide important controls on structural reconstructions of the western margin of the sacramento valley and northern coast ranges monoclinal eastward dips of great valley group strata and fault systems striking northwest southeast which are features proposed as evidence for a west dipping blind great valley franciscan sole thrust and related backthrusts instead are expressions of bedding geometry that resulted from folding of the paskenta and related synsedimentary normal faults depositional onlap and a major structural stratigraphic discontinuity the discontinuity separates east dipping aptian and younger great valley group strata from beds of lower great valley group and coast range ophiolite that were deformed and erosionally or structurally truncated by mid cretaceous time dip divergence imaged between the supracrop and subcrop of the discontinuity is not unique to the ancient great valley forearc but is also observed in modern forearc basins advocates of the franciscan thrust wedge model have also proposed that west dipping shingled patterns of seismic events imaged beneath the sacramento valley are imbricate thrust slices of the great valley group this hypothesis however is incompatible with borehole potential field and seismic refraction data that characterize the sacramento valley basement as ophiolitic seaward dipping reflections in the ophiolitic basement of the sacramento valley are analogous to layering developed in the oceanic crust of volcanic rifted margins or generated along midocean ridges thus late stage tectonic mechanisms are not required to interpret a forearc that owes much of its present day bedding architecture to processes coeval with deposition thickening of the great valley group stratigraphic section valanginian turonian in the hanging walls of the paskenta elder creek and cold fork fault zones combined with attenuation or complete omission of preextensional units including the coast range ophiolite and geometric evidence based on seismic reconstructions suggest that these faults are jurassic cretaceous normal faults that developed in a submarine setting down structure views of the great valley outcrop belt simplify otherwise complex map relations and portray the paskenta and related faults as half graben bounding faults that accommodated significant northwestward tectonic transport of hanging wall rocks it is significant that these faults sole into the coast range fault an enigmatic forearc structure that juxtaposes rocks of the franciscan complex blueschists with rocks of the coast range ophiolite and great valley group that have sustained only zeolite grade metamorphism discovery of jurassic cretaceous crustal scale extension in the great valley forearc suggests that a significant part of coast range fault related attenuation developed early in the history of the subduction complex

oriented clastic dike swarms as indicators of paleoslope an example from the upper cretaceous nanaimo group canada abstract an impressive oriented clastic dike swarm 165 dikes occurs within 3 25 m of strata of a submarine fan turbidite succession of the upper cretaceous nanaimo group british columbia the dikes are remarkably parallel in orientation are consistently subvertical and strike southwest slump fold vergence paleocurrent indicators and other evidence indicate that local paleoslope strike was northwest with a downslope direction to the southwest thus the clastic dikes strike downslope indicating that extension occurred perpendicular to the regional downslope direction not parallel as generally expected two possible models are proposed 1 rapid downslope compression caused by sudden loading perhaps due to slumping events or deposition of thick turbidity current beds this downslope compression caused minor extension perpendicular to the downslope direction resulting in small extensional joints that accommodated clastic injection from buried overpressured sands 2 chaotic sedimentary breccias laterally adjacent to the dike swarm formed as part of a large slumping event which created a local slump channel minor slumping into the main channel from the sides caused extension parallel to the channel margin slope and formation of the clastic dikes parallel to the channel margin but perpendicular to the regional slope oriented clastic dike swarms may represent a new type of paleoslope indicator but they may be created by a number of processes and should therefore be used only in conjunction with supporting evidence

style and magnitude of tectonic shortening normal to the san andreas fault across pyramid hills and kettleman hills south dome california a blind thrust zone and the overlying fold forming the kettleman hills south dome were produced by late cenozoic shortening normal to the san andreas fault west of kettleman hills toward the san andreas fault the region of pyramid hills experienced structural growth as early as late cretaceous time and growth accelerated in pliocene to holocene time these structures were imaged to a depth of 7 km by reprocessing a seismic reflection record section restored structural cross sections indicate a three stage growth history for kettleman hills south dome 1 late miocene reverse faulting 2 pliocene fault propagation type folding and 3 late pliocene to holocene tectonic wedge emplacement late pliocene to holocene structural growth at pyramid hills probably resulted from thrust emplacement of the franciscan complex a forward model demonstrates that tectonic wedging could account for post 2 5 ma deformation of pyramid hills and kettleman hills south dome horizontal shortening across pyramid hills and kettle man hills south dome normal to the san andreas fault since the cretaceous period is 3 7 km this figure does not include shortening within the basement adding shortening of our tectonic wedge model yields 7 9 km of shortening since cretaceous time post 2 5 ma shortening determined by our tectonic wedge model is 6 3 km the rate of post 2 5 ma shortening 2 5 mm yr when added to that on the west side of the san andreas fault is consistent with the values derived from plate motion models that describe the san andreas discrepancy

paleohydrogeology of the san joaquin basin california mass transport can have a significant effect on chemical diagenetic processes in sedimentary basins this paper presents results from the first part of a study that was designed to explore the role of an evolving hydrodynamic system in driving mass transport and chemical diagenesis using the san joaquin basin of california as a field area the authors use coupled hydrogeologic models to establish the paleohydrogeology thermal history and behavior of nonreactive solutes in the basin these models rely on extensive geological information and account for variable density fluid flow heat transport solute transport tectonic uplift sediment compaction and clay dehydration in the numerical simulations tectonic uplift and ocean regression led to large scale changes in fluid flow and composition by strengthening topography driven fluid flow and allowing deep influx of fresh ground water in the san joaquin basin sediment compaction due to rapid deposition created moderate overpressures leading to upward flow from depth the unusual distribution of salinity in the basin reflects influx of fresh ground water to depths of as much as 2 km and dilution of saline fluids by dehydration reactions at depths greater than approximately 2 5 km simulations projecting the future salinity of the basin show marine salinities persisting for moremore than 10 m y after ocean regression results also show a change from topography to compaction driven flow in the stevens sandstone at ca 5 ma that coincides with an observed change in the diagenetic sequence results of this investigation provide a framework for future hydrologic research exploring the link between fluid flow and diagenesis less

fluidization and injection in the deep water sandstones of the eocene alba formation uk north sea the nauchlan member of the late eocene alba formation uk north sea consists of a deep water channel fill that was extensively modified by post depositional sand remobilization and injection sandstone textures facies associations and the geometry of the channel fill were affected a suite of sand rich facies was produced by large scale fluidization and injection within the channel fill and above it these facies termed here unstratified facies are characterized by the absence of stratification surfaces and by discordant relationships with bedding in the adjacent succession they reflect variable degrees of disruption of the primary sedimentary structures caused by escaping pore fluid the velocity of which is estimated at least in the order of 0 1 ms 1 adjacent mudstones were severely disrupted by hydraulic fracturing and fragments of fractured mudstone were incorporated into the fluidized sand average porosity was decreased in the sandstones affected by fluidization two main phases of sand injection are inferred to occur at different burial depths a shallow burial phase below 100 m produced thin dykes with ptygmatic folds the second phase occurred at the boundary between eocene and oligocene 300 m burial depth and resulted in large scale tabular wing like dykes that project from the edges of the channel fill the significant pore fluid overpressure which was required to hydraulically fracture the thick mudstone seal and to fluidize the large volume of sand was likely to be built up by static liquefaction of the source sand and was possibly enhanced by hydrocarbon gas influx

geochemistry of cenozoic microtektites and clinopyroxene bearing spherules abstract we have determined the major and trace element compositions of 176 individual microtektites spherules from the australasian ivory coast and north american microtektite and clinopyroxene bearing cpx spherule layers trace element contents for up to 30 trace elements were determined by instrumental neutron activation analysis inaa and major element compositions were determined using energy dispersive x ray edx analysis in combination with a scanning electron microscope sem in addition petrographic data were obtained for the cpx spherules using the sem and edx this is the first trace element study of individual australasian microtektites and the data revealed the presence of a previously unrecognized group of australasian microtektites with high contents of ni up to 471 ppm in previous studies the high mg hmg australasian microtektites were thought to be related to the hmg australasian tektites but our trace element data suggest that the high ni hni australasian microtektites rather than the high mg microtektites are related to the high mg australasian tektites we find that cenozoic microtektites spherules from a given layer can be distinguished from microtektites spherules from other layers as a group but it is not always possible to determine which layer an individual microtektite spherule came from based only on trace element compositions the cpx spherules and most of the microtektites have cr co and ni contents that are higher than the average contents of these elements in the upper continental crust suggesting the presence of a meteoritic component the highest cr co and ni contents are found in the cpx spherules and low si cpx related microtektites unetched to slightly etched cpx spherules have ni cr and ni co ratios that generally lie along mixing curves between the average upper continental crust and chondrites the best fit appears to be with an ll chondrite the moderately to heavily etched cpx spherules have values that lie off the mixing curves in a direction that suggests ni loss probably as a result of solution of a ni rich phase olivine the ni rich australasian microtektites also have ni values that lie close to mixing curves between the average upper continental crust and chondrites however both the cpx spherules and hni australasian microtektites appear to have ir and to a lesser extent au contents that are much too low to have ni ir ratios similar to chondritic values we have no explanation for the low ir and au contents except to speculate that they may be the result of a complex fractionation process the ivory coast and north american microtektites do not have high enough siderophile element contents to reach any firm conclusions regarding the presence of or nature of a meteoritic component in them trace element compositions are consistent with derivation of the cenozoic microtektite spherule layers from upper continental crust the normal australasian microtektites appear to have been derived from a graywacke or lithic arenite with a range in clay and quartz content the source rock for the high mg australasian microtektites is not known but the hmg microtektites do not appear to be normal australasian microtektites that were simply contaminated by meteorites or ultramafic rocks the average ivory coast microtektite composition can be matched with a mixture of target rocks at the bosumtwi crater the average composition of the north american microtektites suggests an arkosic source rock but with graywacke and quartz rich end members however we could not match the composition of the north american microtektites with lithologies in impact breccias recovered from the chesapeake bay impact structure that is believed to be the source crater likewise we could not match the composition of the cpx spherules with mixtures of basement rocks and overlying sedimentary deposits for which compositional data are available at the popigai impact crater that may be the source crater for the cpx spherules this may be because the cpx spherules were derived in large part from clastic surface rocks sandstones and shales for which no compositional data are available

the flexural slip mechanism abstract detailed field studies of turbiditic sequences from south georgia south atlantic north devon england and cardigan bay wales show that flexural slip occurs on discrete movement horizons between rock packets in which the beds have welded contacts stair stepping displacements of sedimentary dykes and of early quartz veins show that the movement horizons generally have a decimetre to metre spacing and are marked by bedding parallel quartz veins these veins are from 1 mm to several cm thick and can be used to identify movement horizons in the absence of displaced markers they consist of several sheets of quartz fibres which each carry a slickenfibre lineation and which together preserve a record of the displacements on an individual surface complex slickenfibre patterns and departures from ideal behaviour in which slip occurs orthogonal to the fold hinge probably result from changes in slip vector on the limbs of growing non cylindrical folds movement horizons show many of the features associated with large scale thrusting such as ramps duplexes and imbricate structures and the shear sense given by fibre steps on these surfaces and by duplexes within stratigraphically restricted packages changes across fold hinges chevron folds are thought to develop mainly by flexural flow in the early stages with flexural slip becoming dominant later as the beds become lithified new slip surfaces are generated as the dip of the fold limbs increases

clastic dike swarms and the structural evolution of the foreland fold and thrust belt of the southern andes clastic dike swarms are intruded into a cenozoic foreland fold and thrust belt in southern chile the dike material consists of sandstone and conglomerate with clasts as much as 25 cm in diameter brecciated wall rocks are also found in the clastic matrix the dikes often exceed 50 cm in width and hundred of metres in length in outcrop and are oriented overwhelmingly transverse to fold axes and parallel to cross joints the dike swarms are concentrated near the toe of major thrusts where they are found injected into the hanging wall a regional axial planar spaced cleavage is developed in the clastic dikes and sills clearly postdating injection of clastic material dike injection postdates at least the initiation of extension fractures the cross joint set within the swarms the dike intrusions represent as much as 20 extension parallel to fold axes in addition to several percent extension represented regionally by the cross joints the structural features of the dike swarms and their geometric relationship to other structures suggest rapid single phase injection the arrival of the front edge of a thrust on an already highly overpressured sedimentary sequence would cause an instantaneous increase in the overburden pressure and therefore could result in injection of a dense slurry of wet coarse sediments along preexisting planes of weakness field relationships of mesoscopic structures suggest the following evolution cross joint development incipient cleavage development initiation of thrusting and buckling clastic dike injection regional spaced cleavage development and associated late stage tightening of folds

lightning induced volcanic spherules glass spherules have been documented in many geologic deposits and are formed during high temperature processes that include cloud to ground lightning strikes volcanic eruptions of low viscosity magmas and meteorite impacts this study reviews the known glass spherule forming processes and proposes for the first time a mechanism induced through the heat generated by volcanic lightning in eruptive columns and plumes laterally spreading clouds during explosive eruptions ash fall samples were collected from two eruptions where volcanic lightning was extensively documented the a d 2009 eruption of mount redoubt alaska usa and the 2010 eruption of eyjafjallajokull iceland these samples reveal individual glass spherules 50 mm in average diameter that compose 5 of the examined portion of the deposit textures include smooth hollow or cracked spherules as well as aggregates which suggest melting of ash particles as a result of proximity to the electrical discharge channel and subsequent re solidification of the particles into spherical morphologies the natural ash fall samples are compared with pseudo ash samples collected from high voltage insulator experiments in order to test our hypothesis that volcanic ash particles can be transformed into glass spherules through the heat generated by electrical discharge we refer to this new morphological classification of ash grains as lightning induced volcanic spherules and hypothesize that this texture not only provides direct physical evidence of lightning occurrence during explosive eruptions but will also increase settling velocities and reduce aggregation of these particles affecting ash transport dynamics

impact origin of the chesapeake bay structure and the source of the north american tektites seismic profiles drill core samples and gravity data suggest that a complex impact crater 35 5 million years old and 90 kilometers in diameter is buried beneath the lower chesapeake bay the breccia that fills the structure contains evidence of shock metamorphism including impact melt breccias and multiple sets of planar deformation features shock lamellae in quartz and feldspar the age of the crater and the composition of some breccia clasts are consistent with the chesapeake bay impact structure being the source of the north american tektites

neoarchean to paleoproterozoic continental growth in the southeastern margin of the north china craton geochemical zircon u pb and hf isotope evidence from the huoqiu complex abstract the huoqiu complex in the southeastern margin of the north china craton ncc is dominated by neoarchean gray gneisses amphibolites and voluminous metasediments here we report the occurrence of neoarchean to paleoproterozoic rocks from drill core samples the gneisses are similar to ttg tonalite trondhjemite granodiorite in composition and show close spatial association with amphibolites geochemical characteristics such as high sr y and la yb n with steep ree patterns and trace element modeling suggest that these rocks were generated by partial melting of hydrous meta basalts amphibolites at the base of a thickened mafic continental crust leaving a rutile bearing eclogite residue la mc icp ms u pb age data from magmatic zircon grains show protolith emplacement ages of 2 76 2 71 ga subsequently widespread migmatization took place at 1 91 1 82 ga generating voluminous migmatites and high k granites hf isotopic compositions of zircon grains from the amphibolite and gneiss show ehf t values of 2 4 15 5 and 3 0 1 5 respectively the tdm2 hf model ages of the gneisses range from 2 87 to 3 14 ga and are identical to the tdm1 hf ages of amphibolites 2 84 3 16 ga within analytical uncertainty suggesting that the gneisses formed by partial melting of amphibolite and attest to large scale reworking of the ancient continental crust during neoarchean the zircon grains from the granites define two groups with regard to their hf isotopic composition the older group 1916 42 ma has ehf t values and tdm2 hf ages of 10 5 2 4 and 2 40 3 20 ga respectively whereas the younger one 1823 41 ma shows a large variation in ehf t values ranging from 18 1 to 12 5 with tdm2 hf model ages of 1 70 3 59 ga a couple of zircon grains from the younger group display consistent u pb ages and tdm2 indicating accretion of juvenile crust from depleted mantle sources during 1 82 to 1 91 ga however the dominant hf isotope features are consistent with the reworking of preexisting continental crust we therefore infer that only limited accretion of juvenile crust occurred during this time and that the paleoproterozoic 1 82 to 1 91 ga tectonics in the southeastern margin of the ncc witnessed extensive reworking of older continental crust

a reappraisal of the early slip history of the san andreas fault central california usa the modern san andreas fault system california united states is widely considered to have formed in response to the initiation of pacific north american plate interaction ca 27 ma although there is general consensus on the magnitude and timing of neogene displacement along the san andreas system its paleogene history remains unresolved in particular 100 km of right lateral offset between mid cretaceous plutonic rocks of the northern salinian block and the western edge of sierra nevada basement remains unaccounted for after restoration of neogene displacement along strike slip faults of the san andreas system our detrital zircon data invalidate a key paleogene piercing point by demonstrating that displaced portions of the hypothesized middle eocene butano point of rocks submarine fan were never contiguous across the san andreas fault we instead show that the eocene provenance characteristics exhibited by northern salinian strata closely match those of the southern sierra nevada and northwestern mojave desert this implies that the northern salinian block was located at least 75 50 km farther south in eocene time than previously recognized our data require 1 pre 23 ma dextral slip along the san andreas fault in central california and or 2 slip along a predecessor fault that formed prior to pacific north american plate interaction this previously undocumented slip may indicate that significant pacific north american plate interaction propagated from the plate margin into the continental interior much earlier than conventionally believed alternatively late paleogene slip could predate the development of the modern plate boundary and represent inboard dextral strike slip displacement along the eastern margin of the salinian block similar to the deformation that occurs today along the strike slip sumatra fault system

the nature and significance of sand intrusions in a hydrocarbon rich fold and thrust belt eastern carpathians bend zone romania sand intrusions are commonly associated with hydrocarbon bearing clastic reservoirs and they can host a significant part of the reserves they modify the depositional sandbody architecture and can have an impact on the petroleum system elements their significance and complex architecture is difficult to assess in the subsurface due to limited resolution of seismic or core data outcrop analogues are key to better understand these complex reservoirs in the eastern carpathians bend zone the oligocene and lower miocene succession offer spectacular exposures of deep water siliciclastic rocks modified by remobilization and sand intrusion processes these rocks are also present in producing fields in this area sills can be as thick as the depositional sandstones c 4 m and sill dominated outcrops can provide a net gross net sandstone to shale ratio of about 35 50 we quantified their architecture in a study of the timing and mechanism of emplacement their relationship to regional tectonics and their impact on reservoir connectivity the intrusions are interpreted to be syn tectonic related to the major mid miocene compression in this part of the carpathian mountain belt the intrusions lead to a large increase in vertical and horizontal connectivity our results will help to improve reservoir characterization and production in these reservoirs

coseismic horizontal slip revealed by sheared clastic dikes in the dead sea basin despite the hazard caused by near surface destructive horizontal displacements during earthquakes field evidence for coseismic slip along horizontal discontinuities is exceptionally rare mainly due to the lack of adequate exposure and markers however within the seismically active dead sea basin the late pleistocene lisan formation contains vertical clastic dikes that are sheared laterally at maximum depths of 15 m and thereby provide unique profiles of such horizontal displacement in order to investigate how coseismic horizontal shearing is distributed near the surface we document an 1 m thick brittle shear zone consisting of up to 11 slip surfaces that can be traced for tens of meters in the lisan formation displacements along individual slip surfaces are up to 0 6 m and the total displacement across the shear zone is up to 2 0 m displacement profiles and gradients indicate that the brittle shear zone formed by simple shear and deformation was associated with slip partitioning and transfer between primary and secondary slip surfaces evidence for concurrent displacement along slip surfaces during a single event indicates that the brittle shear zone was formed during a coseismic event subsequent to 30 ka we consider the mechanical effect of seismic wave related transient stress which when added to the initial static effective stress may result in concurrent horizontal shear failure along detrital rich layers in the lisan formation the exceptional quality of exposures and markers enables us to document for the first time the details of near surface horizontal shearing and indicates that displacement along horizontal bedding planes is a viable mechanism to absorb coseismic deformation in well bedded near surface strata

integrated taphonomy of an avian death assemblage in marine sediments from the late pliocene of florida we integrate taphonomic data on vertebrate and invertebrate paleontology micropaleontology and palynology to explain the formation of a late pliocene death assemblage of marine birds and fish in the pinecrest sand gulf coastal florida stereonet plots of orientation data on over 1500 cormorant phalacrocoracidae phalacrocorax bones indicate that this fossil assemblage formed first from gradual accumulation of bone shell and sediments on a barrier island beach and second by rapid sedimentation in a quiet back beach setting associated with multiple episodes of breaching of the barrier this latter event resulted in the preservation of 137 partial and complete cormorant skeletons and thousands of isolated bones that show a high angle of dip and a preferred orientation to the northeast invertebrate fossils exhibit taphonomic signatures characteristic of high energy reworking with a large percentage of abraded shell fragments similar to beach deposits moreover these data indicate that more than a single depositional episode caused the formation of the deposits referred to as the bird layers palynological evidence supports this conclusion the pollen recovered from the deposits is highly abraded and broken and does not represent an in situ vegetational environment as compared to other deposits of this age in florida and georgia the large number of cormorant and other seabird and fish remains in the bird layers appears to have been caused by a series of toxic red tides that occurred on the gulf coast of florida these events today cause die offs of large flocks of cormorants and bottom dwelling fish similar to those recovered from the site palynological analysis of the sediments revealed abundant cysts of a dinoflagellate species known to produce toxic red tides the most likely cause of the death of the cormorants and other vertebrates at this site is a toxic bloom of a variety of pyrodinium bahamense the thecate form of the dinoflagellate cyst polysphaeridium zoharyi which has a stratigraphic range from the lower eocene to the holocene

multiple geometries and modes of fault propagation folding in the canadian thrust belt abstract a multitude of fold models have been proposed to explain the variety of fold geometries which develop in front of thrust faults detailed field fabric and photogrammetric studies of 4 fault cored asymmetrical folds in the thin skinned canadian thrust belt were used to test models of fault propagation folding fold geometries include combinations of angular and rounded fold surfaces highly contorted anticlinal hinge areas and minimal penetrative deformation or changes in bedding thickness interlimb angles generally decrease with increasing shortening indicating progressive fold tightening about fixed anticlinal hinges extensive flexural slip thrusting toward the anticlinal axes of angular folds suggests that kink folding in thin skinned thrust belts is aided by material transfer from both fold limbs into hinge areas fold geometries change dramatically along the strike of individual structures demonstrating the non uniqueness of fault propagation fold geometries no single mode of fault propagation folding can explain the diverse fold geometries seen in the canadian thrust belt this geometric variability can be ascribed to the complex interplay of multiple modes of folding in strata near the causal thrusts oblique shear and flexural slip in triangular shear zones distribute thrust displacements into both rounded and angular folds simultaneous angular folding of overlying strata commonly occurs by progressive kink folding where folds tighten by flexural slip on all fold limbs until the thrust breaks through the fold regional and local differences in the amount of pervasive top to the craton shear needed for progressive kink folding may be partially responsible for the variability of fault propagation fold geometries in thin and thick skinned orogens world wide

diverse pliocene quaternary tectonics in a transform environment san francisco bay region california the san francisco bay region occupies part of the diffuse transform boundary zone between the pacific and north american plates although dextral strike slip faulting is dominant the plate motion is expressed in a variety of ways some strike slip faults are parallel with the plate boundary but some are slightly oblique the major strike slip faults are zones in which an interplay occurs between strands some of which are en echelon this interplay may be responsible for some apparent pull apart basins and presumed normal faults along the calaveras fault zone in extensive areas between strike slip fault zones there are many compressional structures folds and reverse faults that are pliocene quaternary in age hence largely coeval with the strike slip faults some of the compressional structures are oblique to and others are parallel with the major strike slip faults we have divided the san francisco bay region into domains on the basis of the types orientations and relationships of structures or in one case lack of strong deformation each domain has responded in its own way to the regional northwest southeast dextral shear imposed by the relative plate motion in an attempt to understand the origin of various structures and the interrelationships among them we compared established models with our observations some observed geometric relationships agree quite well with classical coulomb anderson and simple shear models but others require further explanation models based on fault interaction seem to apply to certain cases for example the east bay hills domain which is between the left stepping calaveras and hayward rodgers creek fault zones is under compression resulting from interaction between the two strike slip zones

rise and emplacement of magma during horizontal shortening of the brittle crust insights from experimental modeling 1 magmatic activity tends to concentrate at plate margins at divergent margins extensional tectonics provide steep conduits for magma to reach the surface at rapidly convergent margins such as the andes one might imagine that horizontal compression prevents the rise of magma nevertheless volcanoes are also common in order to study the mechanisms by which magma rises in a compressional context we resorted to laboratory experiments in which a brittle crust was shortened while magma was intruding our model materials were 1 cohesive fine grained silica powder representing brittle crust and 2 molten low viscosity vegetable oil representing magma in general horizontal shortening and injection were coeval but independent processes thrust faults accommodated the shortening while overpressured oil formed hydraulic fractures in those experiments where there was no shortening injection resulted in a saucer shaped intrusive body in the other experiments where there was shortening oil formed a basal sill before rising along thrust faults once in place the sill lubricated the base of the model so that arcuate thrusts formed at the leading edge of a plateau uplift of the plateau promoted further intrusion of oil at depth in general the pattern of deformation and intrusion depended on the kinematic ratio r between rates of shortening and injection the lengths of the basal sill and plateau increased with decreasing r on the basis of these results we have reexamined two natural examples of magmatic complexes which were emplaced in compressional tectonic settings tromen volcano in argentina and the boulder batholith of montana

late eocene microtektites and radiolarian extinctions on barbados a late eocene microtektite layer has been found in three exposed sections on barbados west indies these microtektites and associated tektite fragments are compositionally similar to the north american tektites and thus like the caribbean and gulf of mexico microtektites may belong to the strewn field of north american microtektites which have been found in deep sea deposits from the caribbean sea across the pacific and into the northeastern indian ocean1 2 the north american layer has been reported to be approximately synchronous with several radiolarian extinctions3 4 and with an anomaly in iridium concentrations5 7 and it has been hypothesized that the microtektites the extinctions and the iridium anomaly are all related to an asteroid impact we report here that the radiolarian extinctions predate the microtektite layer and that the highest ir concentrations apparently coincide with the extinctions thus although the extinctions may be causally related to the ir anomaly the microtektites appear not to be

flexural slip folding in the meguma group nova scotia canada abstract flexural slip folding has been established for two anticlines in the meguma group nova scotia flexural slip postdates the main acadian episode of flexural flow fold growth and represents a late brittle ductile reactivation of the fold belt flexural slip structures are dominated by bedding parallel movement horizons but include a linked system of frontal and lateral ramps and conjugate movement horizons slip amount calculated from displacement of discordant quartz veins combined with vein spacing indicates an average local shear strain of approximately 0 5 however because flexural slip occurred when the fold limbs were steep the shear strain accounts for a small change in limb dip 4 8 variation of slip amount with spacing of movement horizons suggests progressive flexural slip was accommodated by continuous initiation of new movement horizons as well as continuing slip on existing movement horizons the presence of quartz veins along flexural slip structures together with evidence for ductile deformation coeval with flexural slip suggests that slip episodes were fluid assisted and intermittent separated by periods of ductile deformation and build up of fluid pressure flexural slip veins in the ovens anticline are auriferous and a flexural slip model may be appropriate for other similar meguma gold deposits thrust sheets up to 10 m thick occurring on a fold limb are interpreted to have originated in flat box fold hinges and to have been placed onto the steep limbs of the chevron folds during the flexural slip episode thrusting may have assisted the transformation of a box fold into a chevron

tectonic diapiric and sedimentary chaotic rocks of the rakhine coast western myanmar abstract the western margin of myanmar is the northern extension the active sunda india eurasia subduction zone coastal regions and offshore islands have remarkable exposures of chaotic rock terranes along wave cut terraces that allow characteristics of tectonic sedimentary and diapiric melanges to be recognized tectonic shear zones tectonic melanges contain fragments of cretaceous ophiolites chrome spinel bearing peridotites and radiolarian cherts that are in contact with thrust packets of eocene turbidite units broken formations the turbidites contain shale rich beds that have been sheared during soft sediment deformation sedimentary broken formations and are sandwiched between undeformed thick sandy beds these are mass transport deposits mtds that most likely formed during deposition of the initial detritus of the himalayan orogenic zone probably trench slope basins on the accretionary prism the ophiolitic and turbiditic thrust slices have been exhumed and are currently being intruded by active mud volcanoes that bring fragments of units up from depth to the surface forming diapiric melanges these diapiric melange bodies contain only small fragments

flexural slip during visco elastic buckle folding abstract flexural slip is considered as an important mechanism during folding and a general conceptual and qualitative understanding has been provided by various field studies however quantitative evidence of the importance of the flexural slip mechanism during fold evolution is sparse due to the lack of suitable strain markers in this study 2d finite element analysis is used to overcome these disadvantages and to simulate flexural slip during visco elastic buckle folding variations of single and multilayer layer fold configurations are investigated showing that flexural slip is most likely to occur in effective single layer buckle folds where slip occurs between contacts of competent layers based on effective single layer buckle folds the influence of the number of slip surfaces the degree of mechanical coupling based on the friction coefficient and layer thickness on the resulting slip distribution are investigated the results are in agreement with the conceptual flexural slip model and show that slip is initiated sequentially during the deformation history and is maximum along the central slip surface of the fold limb the cumulative amount of slip increases as the number of slip surfaces is increased for a lower degree of mechanical coupling increased slip results in different fold shapes such as box folds during buckling in comparison with laboratory experiments geometrical relationships and field observations the numerical modeling results show similar slip magnitudes it is concluded that flexural slip should represent a significant contribution during buckle folding affecting the resulting fold shape for increased amounts of slip

bed parallel slip identifying missing displacement in mass transport deposits abstract bed parallel slip bps where neighbouring beds slide past one another along bedding planes is notoriously difficult to identify without reference to pre existing features such as steep faults or dykes that act as markers to record bps offset while bps is intuitively thought to operate during downslope sliding of mass transport deposits mtds in sedimentary basins there is a conspicuous lack of supporting outcrop or seismic data to corroborate this and bps displacement may therefore have remained unaccounted for this study addresses this gap in knowledge by investigating late pleistocene mtds developed around the dead sea basin and provides the first detailed analysis of bps that pervades a gravity driven setting in particular we examine the role of bps that crosscuts earlier normal and reverse faults that act as markers to allow metre scale patterns of horizontal displacement to be identified in mtds the studied bps always forms with a consistent top to the east sense of offset that corresponds with gravity driven downslope movement towards the depo centre of the basin bps frequently develops adjacent to competent detrital rich beds and forms discrete glide planes with little or no visible deformation in sediments on either margin although detachment folds are occasionally developed above the slip plane and confirm directions of easterly movement early downslope dipping normal faults that are cut by later bps planes results in older over younger stratigraphic relationships across the bps surface together with sawtooth patterns where multiple bps planes have developed conversely early upslope dipping normal faults that are cut by bps create younger over older stratigraphic relationships combined with missing section and staircase patterns where multiple bps planes exist as bps in sub horizontal sequences does not have a vertical component of displacement it may be examined in terms of horizontal heave bps increases heave in upslope dipping normal faults whereas it reduces heave in downslope dipping normal faults and may even become negative where sections are repeated across sawtooth profiles in addition bps increases heave in upslope dipping reverse thrust faults and reduces heave across downslope dipping backthrusts although individual bps planes may have limited displacement the net consequence of multiple planes of bps that form in the shallow subsurface is to distort patterns and estimates of extension and contraction across fault zones in mtds

off scraping accretionary process under the subduction of young oceanic crust the shimanto belt of okinawa island ryukyu arc the eocene kayo formation exposed at the southwestern end of the shimanto belt in the ryukyu arc records the progressive development of off scraping accretion accompanied by increase in lithification and burial as well as synaccretionary thermal imprint the formation consists almost wholly of coherent trench turbidites supplied by axial currents detailed structural analysis has revealed that two successive deformation stages are recognized in the formation the early deformation stage 1 occurred by horizontal shortening related to the initial stage of off scraping accretion in this stage sands were water rich and nearly unlithified and the competence contrast between sandstone and shale was low the late deformation stage 2 is marked by the formation of seaward verging imbricate fold and thrust system within the accretionary wedge compared with stage 1 sands in stage 2 were more dewatered and lithified and the competence contrast between sandstone and shale increased in accordance with this deformation history structures caused by high pore fluid pressure indicate increased cohesion of sands during off scraping accretion studies of the vitrinite reflectance and the illite crystallinity clearly suggest that the formation became buried and suffered thermal imprint pressure solution cleavage developed as an axial planar to the stage 2 folds thermal imprint on the formation is characterized by high paleotemperatures at approximately 250 c 300 c in a region of the prehnite pumpellyite facies metamorphism this thermal event took place during and slightly after the stage 2 probably associated with subduction of a young and hot oceanic plate

sand injectites from source to emplacement an example from the miocene age frimmersdorf seam garzweiler open cast mine lower rhine embayment

tektites and microtektites key facts and inferences abstract tektites are generally small black rounded silicate glass bodies found scattered over several widely separated areas of the earth s surface called strewn fields four major tektite strewn fields are known 1 australasian 2 ivory coast 3 czechoslovakian and 4 north american tektites from these four strewn fields have been dated at 0 7 1 15 and 34 ma respectively most tektites are splash forms i e spheres teardrops dumbbells etc but some have undergone a second period of melting to produce ablated forms tektites with a blocky layered appearance are called muong nong types microtektites microscopic tektites belonging to the australasian ivory coast and north american strewn fields have been found in deep sea sediments the geographic occurrence and abundance of microtektites at each site have been used to determine the size and mass of each strewn field the australasian ivory coast and north american strewn fields contain 100 million 20 million and 1 billion tonnes of glass respectively although tektites resemble obsidian they can be distinguished from terrestrial volcanic glasses by their composition and petrography tektites for example are drier than volcanic glasses and have higher feo fe 2 o 3 ratios in addition tektites unlike volcanic glasses contain lechatelierite particles sio 2 glass and are devoid of primary crystallites although some authors favor a lunar volcanic origin most of the compositional and petrographic data indicate a terrestrial impact origin the major trace and isotopic compositions of tektites indicate that the parent material was a terrestrial sedimentary deposit and the presence of lechatelierite coesite and shocked relict inclusions favors an impact origin furthermore two tektite strewn fields have been associated with known impact craters and tektites from one strewn field have been found associated with impact ejecta unlike the cretaceous tertiary boundary layer microtektite layers are not associated with mass extinctions or iridium anomalies

supplementary cementitious materials the current widespread use of calcium silicate or aluminate hydrate binder systems in the construction industry finds its roots in the antique world where mixtures of calcined lime and finely ground reactive alumino silicate materials were pioneered and developed as competent inorganic binders architectural remains of the minoan civilization 2000 1500 bc on crete have shown evidence of the combined use of slaked lime and additions of finely ground potsherds to produce stronger and more durable lime mortars suitable for water proof renderings in baths cisterns and aqueducts spence and cook 1983 it is not clear when and where mortar technology evolved to incorporate volcanic pumice and ashes as a functional supplement a plausible site would be the akrotiri settlement at santorin greece where archeological indications of strong ties with the minoan culture were found and large quantities of suitable highly siliceous volcanic ash were present this so called santorin earth has been used as a pozzolan in the eastern mediterranean until recently kitsopoulos and dunham 1996 evidence of the deliberate use of this and other volcanic materials by the ancient greeks dates back to at least 500 400 bc as uncovered at the ancient city of kamiros rhodes efstathiadis 1978 idorn 1997 in the subsequent centuries the technological knowledge was spread to the mainland papayianni and stefanidou 2007 and was eventually adopted and improved by the romans mehta 1987 the roman alternatives for santorin earth were volcanic pumices or tuff found in neighboring territories the most famous ones found in pozzuoli naples hence the name pozzolan and in segni latium preference was given to natural pozzolan sources but crushed ceramic waste was frequently used when natural deposits were not locally available the exceptional lifetime and preservation condition of some of the most famous roman buildings such as the pantheon or the pont du