can a fractured caprock self heal 2015 elsevier b v the ability of geologic seals to prevent leakage of fluids injected into the deep subsurface is critical for mitigating risks associated with greenhouse gas sequestration and natural gas production fractures caused by tectonic or injection induced stresses create potential leakage pathways that may be further enhanced by mineral dissolution we present results from reactive flow experiments in fractured caprock dolomitic anhydrite where additional dissolution occurs in the rock matrix adjacent to the fracture surfaces preferential dissolution of anhydrite left a compacted layer of dolomite in the fractures at lower flow rate rock fluid reactions proceeded to near equilibrium within the fracture with preferential flow paths persisting over the 6 month duration of the experiment and a negligible change in permeability at higher flow rate permeability decreased by a dramatic two orders of magnitude this laboratory scale observation of self healing argues against the likelihood of runaway permeability growth in fractured porous caprock composed of minerals with different solubilities and reaction kinetics however scaling arguments suggest that at larger length scales this self healing process may be offset by the formation of dissolution channels our results have relevance beyond the greenhouse gas sequestration problem chemical disequilibrium at waste injection sites and in hydrothermal reservoirs will lead to reactive flows that may also significantly alter formation permeability

micromorphology of a welded sangamonian to wisconsinan age paleosol in southwestern wisconsin abstract micromorphological characteristics indicate that in southwestern wisconsin pedogenesis transgressed the sangamonian wisconsinan chronostratigraphic boundary in conjunction with colluvial and eolian sedimentation the use of micromorphology helps to distinguish between pedological colluvial and eolian components in the paleosol horizon sequence which can be difficult to resolve and interpret solely from field investigations and from other laboratory analyses results show that a basal loess mixed zone within the welded paleosol profile contains features that are the products of colluvial reworking processes we present micromorphology data which support stratigraphic relationships suggesting that colluvial processes were important in the formation of basal loess mixed zones in addition to other possible mixing processes such as pedoturbation and bioturbation

self driven mode switching of earthquake activity on a fault system theoretical results based on two different modeling approaches indicate that the seismic response of a fault system to steady tectonic loading can exhibit persisting fluctuations in the form of self driven switching of the response back and forth between two distinct modes of activity the first mode is associated with clusters of intense seismic activity including the largest possible earthquakes in the system and frequency size event statistics compatible with the characteristic earthquake distribution the second mode is characterized by relatively low moment release consisting only of small and intermediate size earthquakes and frequency size event statistics following a truncated power law the average duration of each activity mode scales with the time interval of a large earthquake cycle in the system the results are compatible with various long geologic paleoseismic and historical records the mode switching phenomenon may also exist in responses of other systems with many degrees of freedom and nonlinear dynamics 1999 elsevier science b v all rights reserved

reservoir characterization and facies prediction within the late cretaceous doe creek member valhalla field west central alberta canada oil resources at valhalla field of west central alberta canada are stratigraphically trapped within the upper cretaceous doe creek member of the kaskapau formation the reservoir is subdivided into four thin 1 10 m 3 33 ft cyclic alternations of offshore mudrock and shoreface sandstone that are designated the i 1 i i 1 and i 2 units the thickest and most widespread i sandstone is the primary reservoir optimum reservoir quality corresponds to coarser grain shoreface sandstone however reservoir quality may be diminished by postdepositional calcite cement commonly observed near the top of shoreface sandstones open hole well logs are used to predict depositional facies and calcite cement occurrence in wells that lack core control decreasing shale volume vsh and increasing deep resistivity values correspond to progressively shallower water deposits zones of calcite cemented shoreface sandstone greater than 0 5 m 1 6 ft thick are interpreted when the neutron porosity exceeds the density porosity by more than 7 facies distributions predicted for the i sandstone closely match trends of the sandstone gross pore volume and daily total fluid production and suggest that open hole well logs may be used to anticipate reservoir quality and continuity regional and local observations support previous interpretations that attribute the doe creek to forebulge erosion and southwestward sediment transport toward a foredeep where shoreface sandstones accumulated within a coastal embayment to the western interior seaway regionally the doe creek interval thins northeast of valhalla and is truncated beneath the k1 unconformity and shoreface sandstone bodies are encased within offshore mudrocks and detached from their contemporaneous shoreline locally at valhalla the doe creek reservoir progrades toward the southwest and is extensively and commonly uniformly burrowed by a relatively diverse assemblage of trace makers

melt viscosity temperature and transport processes troodos ophiolite cyprus abstract the lava section in the troodos ophiolite cyprus is chemically stratified and divided into a shallow lava sequence with low tio 2 content and a deeper lava sequence with high tio 2 content we calculate the viscosity at magmatic temperature based on major element chemistry of lavas in cyprus crustal study project ccsp holes cy 1 and 1a we find that typical shallow low ti lavas have a magmatic viscosity that is two to three orders of magnitude lower than that of the deeper high ti lavas this implies that after eruption on axis troodos low ti lavas would have been able to flow down the same slope faster and farther than high ti lavas the calculated lava viscosity increases systematically from the lava sediment interface to the bottom of the composite hole cy 1 1a this suggests that an efficient process of lava segregation by viscosity on the upper flanks of the paleo troodos rise may have been responsible for the chemical stratification in the troodos lava pile calculated magmatic temperature and molar mg mg fe or mg decrease systematically down section while sio 2 content increases correlation of mg in the lavas with mg in the underlying lower crustal plutonic rocks sampled by ccsp hole cy 4 shows that the shallow lavas came from a high temperature lower crustal magma reservoir which is now represented by high mg pyroxenite cumulates while the deeper lavas were erupted from a lower temperature mid crustal reservoir which is now represented by gabbroic cumulates with lower mg

constructional features of the troodos ophiolite and implications for the distribution of orebodies and the generation of oceanic crust the map pattern of the troodos ophiolite in cyprus is an expression of a simple elongate anticlinal structure the cross sectional form of the anticline can be described by a sinusoidal dip model on the northern flank of the anticline the thickness of various units number of gossans etc were measured along profiles at 2 5 km intervals normal to strike using existing maps supplemented by new observations profiles are approximately perpendicular to the spreading direction during crustal construction and uncertainties in unit thickness are smaller than the range of unit thicknesses data on the profiles were analyzed quantitatively by harmonic analysis using the fourier transform method the harmonic analysis discloses cyclic variation in the thickness of major units number of gossans etc that provides a link with the regular spacing of five groups of cu fe zn orebodies groups of orebodies occur preferentially where sheeted dikes are at a shallow crustal depth sheet and massive flows and dike

the effects of dolomitization on petrophysical properties and fracture distribution within rift related carbonates hammam faraun fault block suez rift egypt abstract petrographic and petrophysical data from different limestone lithofacies skeletal packstones matrix supported conglomerates and foraminiferal grainstones and their dolomitized equivalents within a slope carbonate succession eocene thebes formation of hammam faraun fault block suez rift egypt have been analyzed in order to link fracture distribution with mechanical and textural properties of these rocks two phases of dolomitization resulted in facies selective stratabound dolostones extending up to two and a half kilometers from the hammam faraun fault and massive dolostones in the vicinity of the fault 100 metres stratabound dolostones are characterized by up to 8 times lower porosity and 6 times higher frequency of fractures compared to the host limestones precursor lithofacies type has no significant effect on fracture frequency in the stratabound dolostones at a distance of 100 metres from the fault massive dolostones are present which have 0 5 times porosity of precursor limestones and lithofacies type exerts a stronger control on fracture frequency than the presence of dolomitization undolomitized vs dolomitized massive dolomitization corresponds to increased fracture intensity in conglomerates and grainstones but decreased fracture intensity in packstones this corresponds to a decrease of grain crystal size in conglomerates and grainstones and its increase in packstones after massive dolomitization since fractures may contribute significantly to the flow properties of a carbonate rock the work presented herein has significant applicability to hydrocarbon exploration and production from limestone and dolostone reservoirs particularly where matrix porosities are low

comparative micromorphology of two late pleistocene paleosols in the paris basin summary the micromorphology of two late pleistocene paleosols in the paris basin st pierre les elbeuf and bois du moulin were studied in order to characterize their pedogenic and sedimentary processes and to reconstruct and interpret the pedosedimentary history and climate of each profile the micromorphological observations of greatest interpretive value were the types of clayey and silty textural accumulations argillans and siltans pedality and porosity of lesser value were papules bioactivity and concretions during the last interglacial period on both profiles developed a sol brun lessive comparable to those developed during the holocene with the onset of cold conditions of the last glaciation the two differentiate pedologically and sedimentologically at elbeuf in the seine valley we observe colluviation of silts and the development of grey forest soils with strong textural degradation under cold and moderately dry local conditions at moulin on the plateau the grey forest phase is very weak and probably brief and is followed by a marked phase of churning and eluviation of silt conditions were wetter than in the valley such that the upland position protected the profile from colluvial truncation the advantages of micromorphology in interpreting pedo sedimentary sequences is discussed

desert loess versus glacial loess quartz silt formation source areas and sediment pathways in the formation of loess deposits abstract pathways are presented which show the proposed sequence of events involved in the formation of loess deposits both hypothetical deposits and those of central china hungary nigeria and tunisia these pathways illustrate the potential role of and inter relationships between a variety of silt generating mechanisms in the formation of loess using these pathways the existence of desert loess is discussed and it is concluded that this depends on how the terms glacial loess and desert loess are applied if desert loess is taken either to signify nonglacial mechanisms of silt production or to characterise the environment from which aeolian entrainment took place then desert loess is a very real and widely distributed deposit however if the term glacial loess is used to refer to the global climatic regime under which the loess deposit has formed rather than the geomorphic mechanisms responsible for silt generation then desert loess would not be an appropriate term for the classification of loess deposits it is suggested that classifying loess deposits with reference to the global climatic regime under which they accumulated would facilitate a greater understanding of the role of environmental conditions at all stages in the formation of loess deposits

pedogenic modification of loess significance for palaeoclimatic reconstructions abstract this review considers the role of pedogenic processes in modifying wind blown dust loess concentrating particularly on the ways that resulting properties may be interpreted as indicators of past climatic conditions and changes emphasis is placed on the sequences of palaeosols developed within loess deposits that are frequently regarded as some of the best terrestrial equivalents of marine sediment records of long term global climatic change a palaeosol is generally interpreted in terms of the broad pedogenic processes and environments assumed to be currently responsible for that type of soil forming at the present surface even the very presence of a palaeosol may have palaeoclimatic significance however in that it is often taken to indicate a period of relative land surface stability and warmer and or moister conditions between cold and or arid phases of loess accumulation in reality it may be more useful to consider many loess palaeosol sequences in terms of changing balances between pedogenesis and loess accumulation over geological time in most regions it seems that the balance swings towards pedogenesis during interglacials or interstadials when sediment supply and transport are limited and the climate is warmer and or wetter where accumulation rates are still appreciable during these soil forming intervals however the soils and palaeosols may be accretionary with surface build up keeping pace with pedogenesis welding may also occur where covering sediments are insufficiently thick to isolate an underlying palaeosol from the effects of pedogenesis active at a new land surface further complications occur due to reworking of palaeosols and syndepositional pedogenic alteration of loess units generally such pedocomplexes can only be deciphered if the different pedogenic geomorphic and sedimentary processes are identified and ordered within a pedosedimentary reconstruction a recent trend has been to treat some loess palaeosol sequences as quasi continuous time series particularly when comparing depth functions of climatic proxy properties such as magnetic susceptibility and grain size with marine and ice core isotope curves

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

short climatic oscillations in a western european loess sequence kesselt belgium this new study of the loess section at kesselt is focused mainly on the reconstruction of palaeoenvironments of the last glacial period in the belgian dutch region detailed grain size analyses in combination with the study of the palaeosols and periglacial structures indicate the occurrence of climatic cycles during loess deposition permafrost development coincided with enhanced deposition of relatively coarse loess and alternated with permafrost degradation decreased deposition of finer loess and tundra soil formation a newly designated palaeosol lafelt soil is described in detail particularly in terms of its micromorphological properties it is a luvisol and its chronostratigraphical position is still open to debate but radiocarbon dating places it in the weichselian middle pleniglacial 1998 john wiley sons ltd

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

micromorphological variation of the s 1 paleosol across northwest china abstract a micrornorphological approach based upon sets of closely spaced thin sections taken from three sites located along a climatic and depositional gradient has been utilised to reconstruct the sequence of pedogenic and sedimentary events leading to the development of the s1 paleosol in northwest china two main pedosedimentary stages related to regional changes in monsoonal controls are evident at each site although the resolution processes and resultant features vary in a manner reflecting differences in climate and rates of loess deposition around xining in the west where loess accumulation rates were high and pedogenic processes were restricted to shallow leaching and limited bioturbation by the low rainfall s 1 comprises two discrete weakly developed paleosol units separated by a less pedogenically altered layer of loess in contrast at sites farther away from the loess source area in the more humid southeast s 1 is a thinner welded and more pedogenically developed unit dominated by the effects of extensive leaching bioturbation and sometimes even clay translocation processes

rivers and loess the significance of long river transportation in the complex event sequence approach to loess deposit formation abstract rivers are essential for loess deposit formation river systems which relate directly to loess deposit formation include the danube and the rhine the mississippi and the missouri the thames and the medway the indus ganges and brahmaputra the dnepr don and volga the clutha mataura and rakaia new zealand rivers the yellow river rivers in south america siberian rivers flowing north the odra and the wisla between the mountains and the ice the syr darya and amu darya into the desert the contention is that rivers are not just important in major loess deposit formation they are mandatory necessary imperative obligatory essential indispensable requisite for a complete and satisfactory study of a loess deposit we need to know how the material is produced how it is transported and distributed across the landscape how intermediate deposits are formed how transportation provides the defining properties i e open structure collapsibility draping across the landscape and what may happen post deposition e g chernozemisation fragipan formation increased collapsibility etc if rivers are essential then it would appear that the british loess is probably alpine material delivered by the proto rhine and the polish loess is not derived from the ice sheet to the north but from the mountains to the south the lack of loess in canada is explained by the absence of suitable rivers the loess in russia and neighbouring countries can be classified as jefferson et al jefferson i f evstatiev d karastenev d mavlyanova n g smalley i j 2003b the engineering geology of loess and loess like deposits a commentary on the russian literature engineering geology 68 333 351 suggested on the basis of associated rivers a new deposit of glacial loess is recognised associated with the dnepr don and volga rivers the uswr loess the smalley leach smalley i j leach j a 1978 the origin and distribution of the loess in the danube basin and associated regions of east central europe a review sedimentary geology 21 1 26 available from www geo edu ro sgr mod downloads pdf smalley sedgeo 1978 pdf vision of the loess in the danube basin and east central europe is probably misconceived they assigned a great significance to glacial action and put loess in a northern band it appears that this proposed glacial influence is minimal and that the danube loess is essentially mountain loess derived from the alps the carpathians the sudeten mountains and other high regions the danube system is a classic example of a river controlling loess distribution

mid ocean ridge or marginal basin origin of the east taiwan ophiolite chemical and isotopic evidence the east taiwan ophiolite eto occurs as allochthonous fragments embedded in the plio pleistocene lichi melange in the coastal range of eastern taiwan it is probably the youngest among the known ophiolitic complexes of the world the overall geochemical and isotopic characteristics of the representative rock types are very oceanic and strongly argue for a mid ocean or marginal basin origin of the eto the best criteria include 1 major element compositions 2 ree distribution patterns 3 nd isotopic ratios some have nd 12 4 pb isotopic ratios and 5 the presence and nature of the red shale this conclusion is supported by previous studies of metamorphic evolution of the eto

pathways of dust input to the chinese loess plateau during the last glacial and interglacial periods abstract it has been established that loess deposited on the chinese loess plateau was derived from arid and semi arid regions in north and northwest china but the specific pathways of dust transport are still not proved in this study 32 loess palaeosol profiles of the last glacial and interglacial periods were measured for magnetic susceptibility in order to investigate the dust transport pathways of dust input to the loess plateau the magnetic susceptibility variations of the loess palaeosol deposits within the last glacial cycle can be correlated with marine oxygen isotope variations to estimate the ages of boundaries of the loess units and intercalated palaeosols the sedimentation rate of each depositional unit can be obtained by dividing the thickness by the time that it represents because sedimentation rates decrease downwind from the dust source the spatial distribution of dust sedimentation rates shows that northwest and west winds were the two most important agents for transport of dust to the loess plateau during the last glacial cycle the north and northeast winds played an almost negligible role in addition topography and dust from local sources strongly affected the dust accumulation rates at some measured sites

boron isotope systematics of a fossil hydrothermal system from the troodos ophiolite cyprus water rock interactions in the oceanic crust and subseafloor ore deposits abstract we determined concentrations and isotopic compositions of boron in a complete section of the hydrothermally altered cretaceous oceanic crust of the troodos ophiolite the boron content and 11 b value for each lithological section are pillow lava 3 8 206 8 g g 63 g g average 11 b 0 17 to 15 6 8 1 average sheeted dike complex 0 6 18 0 g g 4 0 g g average 11 b 3 3 to 10 6 6 0 average and plutonic complex 0 3 8 4 g g 1 7 g g average 11 b 1 7 to 18 5 4 5 average these boron contents are higher than the estimated original igneous values throughout the oceanic crust indicating uptake of boron from seawater and hydrothermal fluid at temperatures ranging from 50 c to 300 c although our boron data for the troodos ophiolite are generally consistent with those for the oman ophiolite of similar age the distinctly low 11 b values of the lower gabbro section in the troodos ophiolite 11 b depleted fluid at a very small water rock ratio the boron content of the bulk oceanic crust 12 3 g g estimated for the troodos ophiolite is relatively high as a result of strong boron enrichment in the pillow lava section which underwent prolonged seafloor weathering despite these differences the weighted average 11 b value of the bulk oceanic crust 7 6 is similar to that of the oman ophiolite 7 9 we also analyzed the boron isotope geochemistry of a subseafloor hydrothermal stockwork sulfide deposit in the troodos ophiolite to investigate its formation processes in contrast to the normal upper oceanic crust the 11 b values of the rocks below the ore body decrease with increasing depth and have large negative values 6 in the highly altered uppermost dike section these low 11 b values are coupled with high boron contents 2 5 17 g g and high and uniform 87 sr 86 sr ratios 0 7064 average and are unlikely to have resulted from interactions with fluids at a small water rock ratio these characteristics are better explained by interaction of ore forming hydrothermal fluids with oceanic crust that had previously been enriched in boron through hydrothermal alteration at low temperatures these observations demonstrate that boron and boron isotopes are useful for quantitative evaluation of fluid related processes with multiple stages including petrogenesis of hydrothermal ore deposits

the hozameen fault system and related coquihalla serpentine belt of southwestern british columbia the hozameen fault of southwestern british columbia is associated with the coquihalla serpentine belt and separates two distinct crustal units northeast of the fault are greenstones of the early t

distribution and genesis of calcitic pedofeatures within a rapidly aggrading loess paleosol sequence in china abstract the distribution of calcitic pedofeatures within part of a buried paleosol complex on gaolanshan mountain near lanzhou in the western semi arid part of the loess plateau of china is interpreted in terms of a pedosedimentary model controlled by changes in dominance of regional climatic monsoonal forces during periods of moderate loess accumulation rates and moisture availability accretionary pedogenesis was characterised by localised dissolution and redistribution of calcite and development of compound calcitic depletion concentration pedofeatures these took one of two forms i equigranular hypidiotopic calcitic coatings or infillings 100 350 m and calcitic depletion hypocoatings the reconstruction provides the basis for explaining the ubiquitous occurrence of high concentrations of sand size grains and nodules of calcite within weakly leached horizons of other paleosols in the western part of the loess plateau of china their presence reflects not only the influence of semi arid conditions prevailing during the main stable soil forming intervals but also preceding drier periods of accretionary pedogenesis associated with transitional changes in relative dominance of dry northwesterly winter monsoons responsible for the transport of the dust to that of moist southwesterly and southeasterly monsoons the study emphasises the general need for a pedosedimentary approach when attempting to interpret loess paleosol sequences

transport direction of peoria loess in nebraska and implications for loess sources on the central great plains abstract in the midwestern united states large rivers draining the laurentide ice sheet lis were the most important sources of peoria loess deposited during the last glaciation loess deposition near those rivers may have responded primarily to ice sheet dynamics rather than direct effects of climatic change in contrast it has been proposed that thick peoria loess on the central great plains was derived mainly from unglaciated landscapes northwest of the main loess deposits in this study transport directions inferred from more than 600 measurements of peoria loess thickness in nebraska are used to test the hypothesis that much of the peoria loess on the great plains is nonglaciogenic a strong northwest to southeast thickness trend indicates that most peoria loess in nebraska was transported from one or more unglaciated northwestern source areas rather than from glacially influenced river floodplains the missouri river draining the lis the platte river draining alpine glaciers and the elkhorn river unglaciated basin were secondary sources their contribution is not detectable beyond a distance of 40 60 km peoria loess deposition on the central great plains was largely a direct response to climatic change in the unglaciated source region

the late cretaceous palaeolatitude of the neotethyan spreading axis in the eastern mediterranean region abstract a compilation of available palaeomagnetic data from the troodos cyprus and baer bassit syria ophiolitic terranes of the eastern mediterranean tethyan orogenic belt is presented the ophiolites represent fragments of oceanic lithosphere generated at a neotethyan spreading axis in the late cretaceous although debate continues over the tectonic setting of this spreading axis and its position within the eastern mediterranean palaeogeography two types of model reconstructions have been proposed type 1 the ophiolites formed in a southerly neotethyan basin by spreading above an oceanic subduction zone the baer bassit ophiolite was then emplaced a relatively short distance tens of kilometers southwards on to the arabian continental margin leaving the troodos ophiolite isolated in an intra oceanic setting to the west and type 2 the ophiolites formed in a northerly neotethyan basin by spreading at a normal oceanic ridge with subsequent large scale thrusting hundreds of kilometers to the south of emplaced ophiolites over microcontinental fragments to reach their present positions palaeomagnetic determination of the palaeolatitude of the neotethyan spreading axis is therefore of considerable interest previous palaeomagnetic analyses have demonstrated the presence of significant and in some cases extreme relative tectonic rotations of a variety of origins in both ophiolites to allow palaeomagnetic data from these rotated units to be combined an inclination only formulation of the palaeomagnetic tilt test is employed this provides unequivocal evidence that both ophiolites retain pre deformational remanent magnetizations which are interpreted as original ocean floor magnetizations acquired close to the time of crustal formation in the late cretaceous the mean inclinations of 37 0 2 6 for the troodos terrane and 41 1 3 4 for the baer bassit terrane indicate respective palaeolatitudes for the spreading axes of 20 6 n 1 8 and 23 6 n 2 5 consistent with a late cretaceous position between the arabian and eurasian margins these data together with a well defined palaeolatitude of 25 5 n 4 5 for the eastern pontides previously reported in the literature provide constraints which must be incorporated in any successful tectonic reconstruction of the eastern mediterranean tethys the implications of these constraints for type 1 and 2 models are discussed using a series of plate tectonic cross sections constructed along a line extending northwards from the arabian continental margin in the absence of palaeomagnetic data from late cretaceous rocks of the eastern taurides however it is presently impossible to use these palaeolatitudinal constraints to resolve the root zone debate on a purely palaeomagnetic basis solutions which satisfy the constraints may be found for both types of model reconstruction additional published field based geological considerations however strongly support models in which the troodos and baer bassit and other southerly ophiolites were generated in a southern neotethyan basin rather than those involving generation in a northerly basin and subsequent large scale thrust displacement to the south

geochemistry and tectonic environment of basaltic rocks from the misis ophiolitic melange south turkey abstract the miocene misis tectonosedimentary melange was formed during the closing stages of the neotethys in what is now the adana basin of southern turkey a major part is characterized by large disorientated limestone blocks set in a predominantly volcanogenic matrix of bedded and chaotic units comprising basaltic pillow lavas associated hyaloclastites serpentinites and various acidic tuffs all the basaltic rocks are mildly metamorphosed zeolite facies variably vesicular and differentially altered to smectite chlorite fe oxides zeolites and carbonate petrographic and chemical data on the least altered pillow lavas indicate they were originally sparsely olivine plagioclase clinopyroxene phyric tholeiites and minor amphibole phyric basaltic andesites the basaltic clasts in the melange matrix are genetically related to the pillow lava sequences with the observed variation throughout the suite being governed by low pressure fractional crystallization as a group the basalts are characterized by low zr y 2 4 relatively high th yb 0 5 0 7 and la nb 1 5 2 5 ratios and moderate chondrite normalized light ree enrichment la yb n 3 patterns the basalts have a mildly enriched subduction related chemistry and were possibly formed initially in a back arc basin setting the supra subduction zone characteristics of the misis basaltic units are similar to other tethyan basalts in eastern mediterranean ophiolites

geochemistry and mineralogy of the late pleistocene loess palaeosol sequence in zlota near sandomierz poland implications for weathering sedimentary recycling and provenance abstract in order to determine the provenance of material the late pleistocene loess palaeosol sequence in zlota poland was analysed geochemically icp ms icp es and mineralogically qemscan investigating simultaneously the weathering signature and effect of sedimentary sorting a total number of 39 loess and soil samples were tested for the geochemical composition and 5 for the mineralogy the investigated samples compared to upper continental crust are enriched with elements such as si zr hf nb ta th u and rare earth elements especially the heavy rare earth elements related rather to felsic igneous rocks the enrichment of only two mafic elements ti and cr can be explained by heavy minerals admixture loess in zlota is strongly mixed and homogenized during transportation and or sedimentary recycling for each sample the uniform shape of the chondrite normalized rare earth elements patterns were found characterized by steep light rare elements lan smn 3 45 4 08 avg 3 81 constant negative eu anomalies eu eu 0 50 0 63 avg 0 56 and distinctly flat heavy rare earth elements gdn ybn 1 17 1 45 avg 1 28 the material is not significantly affected by chemical weathering and the post depositional modifications are not particularly important for the trace element composition both in loess and soils e g th u 3 1 4 65 avg 3 64 ce ce 0 96 1 09 avg 1 01 lan ybn 6 22 7 93 avg 6 94 the research reveals that relatively fresh felsic related parent material has been well mixed during transportation but post depositional alterations related only to the pedogenesis have not been intense enough to mask their chemical signature the investigated material has been probably originated in scandinavia likely norway but deflated directly from the glacial drift covering the terrain of poland

permeability and seismic velocity and their anisotropy across the alpine fault new zealand an insight from laboratory measurements on core from the deep fault drilling project phase 1 dfdp 1 the alpine fault a transpressional plate boundary between the australian and pacific plates is known to rupture quasi periodically with large magnitude earthquakes mw 8 the hydraulic and elastic properties of fault zones are thought to vary over the seismic cycle influencing the nature and style of earthquake rupture and associated processes we present a suite of laboratory permeability and p vp and s vs wave velocity measurements performed on fault lithologies recovered during the first phase of the deep fault drilling project dfdp 1 which sampled principal slip zone psz gouges cataclasites and fractured ultramylonites with all recovered lithologies overprinted by abundant secondary mineralization recording enhanced fluid rock interaction core material was tested in three orthogonal directions orientated relative to the down core axis and when present foliation measurements were conducted with pore pressure h2o held at 5 mpa over an effective pressure peff range of 5 105 mpa permeabilities and seismic velocities decrease with proximity to the psz with permeabilities ranging from 10 17 to 10 21 m2 and vp and vs ranging from 4400 5900 m s in the ultramylonites cataclasites and 3900 4200 m s at the psz in comparison with intact country rock protoliths the highly variable cataclastic structures and secondary phyllosilicates and carbonates have resulted in an overall reduction in permeability and seismic wave velocity as well as a reduction in anisotropy within the fault core these results concur with other similar studies on other mature tectonic faults in their interseismic period

diffusion in silicate minerals and glasses a data digest and guide to the literature the rates of diffusion of cations oxygen and hydrogen in silicates are of fundamental importance to a wide range of petrological and geochronological problems in order that the earth scientist may readily apply the available experimentally determined diffusion rates to such problems a compilation of data for diffusion in silicate minerals and glasses is presented along with a working guide for its use published data and experimental conditions are listed in tables and these are preceded by an outline of diffusion mechanisms terminology equations and units diffusion regimes factors controlling diffusion rates measurement techniques and diffusional behaviour

the pedosedimentary evolution and chronology of tortugas a late quaternary type site of the northern pampa argentina new micromorphological magnetic susceptibility geochemical and geochronological data have been collected from tortugas a key late quaternary type site of the northern pampa argentina thus enabling the detailed reconstruction of the pedogenic and sedimentary history of this loess paleosol sequence paleosols developed in the ceres formation and the overlying lower member of the tezanos pinto formation retain evidence for leaching bioturbation and particularly clay translocation processes being dominant both paleosols are truncated evidence for water sorting and sediment reworking as well as continued bioturbation and redistribution of carbonates suggests that intervening depositional phases were complex the previously recorded hypsithermal soil developed in the upper member of the tezanos pinto formation has similar characteristics to the buried paleosols yet does not appear to have been truncated at this site and is only covered by a thin layer of sediment san guillermo formation this latter unit has been pedogenically welded onto the hypsithermal soil thus creating the present day surface soil complex a series of optically stimulated luminescence dates from throughout the sequence provide a stratigraphically consistent chronological framework ca 1 150 ka for the pedosedimentary reconstruction yet conflict with the previously reported thermoluminescence based chronology for the site and region ca 1 90 ka

sedimentation and volcanism in a permian arc related basin southern new zealand an exceptionally well exposed ancient intra arc basin in the permian takitimu group of new zealand contains 14 km of interbedded primary volcanic and marine volcaniclastic rocks of basaltic to rhyodacitic composition these are the products of subaerial and submarine arc volcanism and closely associated turbidite sedimentation the takitimu oceanic arc basin setting formed a dynamic closed sedimentary system in which large volumes of volcaniclastic material generated at the arc was rapidly redeposited in marine basins flanking the eruptive centres volcanism probably included 1 moderate to deep water extrusion of lava and deposition of hyaloclastite 2 extrusive and explosive eruptions from shallow marine to marginally emergent volcanoes in or on the margin of the basin and 3 plinian and phreato plinian eruptions from more distant subaerial vents along the arc much of the newly erupted material was rapidly transported to the adjacent marine basin by debris flows slumping and sliding hemipelagic sedimentation predominated on the outer margin of the basin infrequently interrupted by deposition of ash from the most explosive arc volcanism and the arrival of extremely dilute turbidites turbidite sedimentation prevailed in the remainder of the basin producing a thick prograding volcaniclastic apron adjacent to the arc the volcaniclastic strata closely resemble classic turbidite deposits and show similar lateral facies variations to submarine fan deposits study of such sequences provides insight into poorly understood processes in modern arc related basins

temporal change in permeability of the rock estimated from repeated water injection experiments near the nojima fault in awaji island japan 1 three boreholes with depths of 500 800 and 1800 m were drilled near the nojima fault which is one of the 1995 hyogoken nanbu earthquake faults in order to research the structure and its temporal change of the active fault the water injection experiments were conducted from the 1800 m borehole in 1997 and 2000 then the discharge changes at the 800 m borehole were observed during the water injections considering the permeable zone near the fault as simple two dimensional layer with an uniform thickness we estimated the permeability of the permeable zone near the nojima fault from the discharge changes associated with the water injections it is found that the permeability of the permeable zone in 2000 became lower than that in 1997

reorganization of geological sciences and particularly of metamorphic geology by the advent of plate tectonics a personal view abstract plate tectonics having being formulated in geophysics in the 1960 s was introduced into and caused reorganization of geological sciences in about 1968 1975 an anticipated system of reorganized geology was formulated around 1970 by a few pioneering geologists with a strong background of global scale regional geology pre existing dutch school tectonics with an explicit uniformitarian tendency played an important role in the beginning development and acceptance of plate tectonic viewpoints global scale views in metamorphic geology that had begun prior to the advent of plate tectonics were developed into tectonic models of regional metamorphism as well as discussions of the p t t paths and of secular changes in the type of regional metamorphism

loess in italy genesis characteristics and occurrence abstract there is currently a renewed interest in loess genesis and occurrence in italy well known loess profiles in northern italy have been re examined and previously unknown loess deposits in central and southern italy have been reported this work combines a meta analysis of published data with new data presented here for the first time to provide the state of the art on the spatial distribution characteristics genesis and deposition ages of loess in italy a database of 98 soil horizons from 91 soil profiles was created and made available it stores information on soils formed from loess or containing layers that show admixture of loess soil data include the source of information the topographic geomorphological and geological setting kind of parent material and land use main soil horizon properties as described in the field soil classification particle size distribution and chemical data loess is reported from almost all regions of italy it is generally pedogenized throughout the entire loess body and forms the parent material of deep and complex soil profiles the thickness of the loess deposits varies from a few decimeters to a few meters pedogenesis and local reworking partially change the original loess characteristics in this study we propose a set of parameters that help recognizing loess in soils particle size distribution and sorting geomorphological setting pedostratigraphic position shape of the grains under optical and scanning electron microscope sem and soil micromorphological characteristics the ages of the loess deposits range between 70 ka bp and 18 ka bp there are also a number of samples that have been dated to the holocene the meta analysis suggests that climate is not the only driver of loess deposition in italy geomorphological instability and human disturbance as well as the influence of saharan dust most likely played major roles too this study demonstrates that loess is much more widespread in italy than previously estimated yet further research on the spatial and temporal distribution of loess deposition across the mediterranean region is needed to better understand its genesis sources and trajectories periods of enhanced loess formation and the role of loess deposits in ecosystem functioning and resilience

pedosedimentary reconstruction of a thick loess paleosol sequence near lanzhou in north central china abstract a 38 m well section near lanzhou at the semiarid western margin of the loess plateau china contained a continuous high resolution loess paleosol sequence spanning the last 130 000 yr depth functions of micromorphological features magnetic susceptibility calcium carbonate organic carbon and median grain size provide the basis for pedosedimentary and associated paleoenvironmental reconstructions of three paleosol complexes s1 sm and s0 each pedosedimentary stage reflects the interaction of changing intensities of controlling monsoonal forces three periods of reduced dust inputs and enhanced pedogenic activity notably bioturbation and weak leaching can be identified from within the s1 pedocomplex these soil forming intervals were separated by phases of varying land surface instability characterized by arid dust deposition semiarid accretionary pedogenesis water reworking and crust formation or even freeze thaw modification the sm pedocomplex represents an interval of relatively rapid dust accumulation with only minimal syndepositional modification and minor pedogenic alteration at ephemeral land surfaces the s0 pedocomplex is clearly more pedogenically developed although erosion reworking and mixing by water have partly homogenized the property depth functions

geochemistry and intrusive directions in sheeted dikes in the troodos ophiolite implications for mid ocean ridge spreading centers 1 sheeted dikes at mid ocean ridge volcanoes represent the link between deep magma production and storage processes and shallow processes such as volcanism and hydrothermal activity as such they are crucial for the interpretation of many observations at mid ocean ridges or other volcanoes with pronounced rift zones including topography hydrothermal systems petrology and geochemistry we carried out a structural magnetic and chemical investigation of a 4 10 km sheeted dike section in the troodos ophiolite cyprus on the basis of major and trace element geochemistry we distinguish dikes that may be correlated with the basal high ti series hts lavas from those of the overlying low ti series lts lavas all dikes studied are nearly parallel to each other with vertical or steeply dipping planes whose strike likely indicates the orientation of the spreading center anisotropy of magnetic susceptibility measurements suggests that the hts and lts dikes intrude in fundamentally different ways hts dikes reflect the intrusive behavior of dikes in the vicinity of a magma supply system and define ridge parallel intrusive sheets that radiate out from the magma chamber lts dikes show a bimodal orthogonal set of intrusive directions one shallow and one near vertical near lateral propagating dikes provide a means for delivery of magma into distant portions of a rift system and near vertical dike propagation directions are probably associated with feeder dikes to down rift surface flows our study suggests that the types of dike intrusive behavior in the troodos ophiolite may also be typical for normal mid ocean ridges or other major shield volcanoes with well developed rift zones

pedosedimentary development and palaeoenvironmental significance of the s1 palaeosol on the northeastern margin of the qinghai xizang tibetan plateau the s1 pedocomplex correlated to oxygen isotope stage 5 of the ocean cores has been traced west of the loess plateau on to the extreme northeastern margin of the qinghai xizang tibetan plateau in china detailed micromorphological analysis of closely spaced thinsections from the pedocomplex at this site provides the basis for reconstruction of the sequence of pedosedimentary processes and associated palaeoenvironmental changes occurring during this time interval the six pedosedimentary stages identified are interpreted in terms of temporal variations in depositional rates size of particles transported and availability of moisture for pedogenic alteration as determined by changing balances in dominance of winter and summer monsoonal forces two main soil forming intervals are identified the more extensive of the two in terms of resultant pedological features reflects pedogenic alteration at a relatively stable land surface under a semi arid climate during the later part of pedosedimentary stage 2 the other main period corresponds to pedosedimentary stages 4 and 5 when leaching and bioturbation processes were active at aggrading surfaces leading to development of an accretionary unit without clear differentiation of horizons pedosedimentary stages 1 3 and 6 were characterised mainly by rapid rates of coarse loess accumulation with synsedimentary modification restricted to surface slaking and crust formation and minor localised redistribution of calcite

geochemical characterization of the late pleistocene loess palaeosol sequence in tyszowce sokal plateau ridge se poland abstract the late pleistocene loess palaeosol sequence in tyszowce sokal plateau ridge se poland has been analysed for major elements si na k mg ca fe mn al ti and p in order to determine its chemical composition stratigraphy and degree of chemical weathering for the investigation a total number of 85 loess and soil samples were tested the vertical differentiation of chemical composition is strongly correlated with the variability of pedo and lithostratigraphic units the loess palaeosol sequence in tyszowce is geochemically distinct from other loess presented in the worldwide literature the profile is generally enriched with silica while other chemical elements are relatively depleted the contents of the major elements except si are lower in relation to the global average loess gal composition weathering indices such as chemical index of alteration cia or k al molar ratio and a cn k diagram imply weak to moderate weathering of the source material

stratigraphy and chronology of the periphery of the scandinavian ice sheet at the foot of the ukrainian carpathians abstract the article presents the results of research on the formation conditions and the age of glaciogenic deposits left by the scandinavian ice sheet in the eastern carpathian foreland in its part drained by the dniester river and its tributaries black sea basin these deposits till erratics glaciolacustrine and glaciofluvial sediments preserved only in some places and occurring in the range of altitudes defined by terrace vi early pleistocene and terrace v middle pleistocene are the southernmost traces of the ice sheet in europe they are underlain by fluvial deposits and overlain by loess deposits and locally occur as intraloess layers the following research methods were used geomorphological mapping sedimentological lithological micromorphological palaeopedological and palaeontological analyses as well as luminescence dating the obtained results allowed a reconstruction to be made of the main stages of morphogenesis and the style of the ice sheet advance at its maximum extent defined as the sambor phase the area was glaciated during mis 12 elsterian ii sanian 2 okanian as indicated by the occurrence of a complete middle upper pleistocene loess palaeosol sequence the oldest palaeosol s4 i e sokal mazovian zavadivka soil that developed directly on the glaciogenic deposits or loess l5 is correlated with the holsteinian likhvinian interglacial mis 11

tectono stratigraphic evolution of the early proterozoic wisconsin magmatic terranes of the penokean orogen the early proterozoic penokean orogen developed along the southern margin of the archean superior craton the orogen consists of a northern deformed continental margin prism overlying an archean basement and a southern assemblage of oceanic arcs the wisconsin magmatic terranes the south dipping niagara fault suture zone separates the south facing continental margin from the accreted arc terranes the suture zone contains a dismembered ophiolite the wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure the northern pembine wausau terrane contains a major succession of tholeiitic and calc alkaline volcanic rocks deposited in the interval 1860 1889 ma and a more restricted succession of calc alkaline volcanic rocks deposited about 1835 1845 ma granitoid rocks ranging in age from about 1870 to 1760 ma intrude the volcanic rocks the older succession was generated as island arcs and or closed back arc basins above the south dipping subducti

healing and sliding stability of simulated anhydrite fault gouge effects of water temperature and co2 abstract anhydrite bearing faults are currently of interest to 1 co2 storage sites capped by anhydrite caprocks such as those found in the north sea and 2 seismically active faults in evaporite formations such as the italian apennines in order to assess the likelihood of fault reactivation the mode of fault slip and or fault leakage it is important to understand the evolution of frictional strength during periods of no slip and upon reloading healing and relaxation behavior and of the velocity dependence of friction of anhydrite fault gouge therefore we performed slide hold slide experiments combined with a velocity stepping sequence using simulated anhydrite fault gouge 95 wt caso4 vacuum dry and water wet experiments were performed at temperatures ranging from 20 to 150 c and at an effective normal stress of 25 mpa we also performed tests using dry co2 water wetted co2 and co2 saturated water as pore fluid but only at 120 c if pore fluid was present a fluid pressure of 15 mpa was present vacuum dry samples exhibit similar frictional healing to samples containing lab air but healing is significantly enhanced in wet samples dry samples exhibit velocity weakening behavior at t 120 c and wet samples exhibit velocity strengthening behavior over the full temperature range the presence of co2 does not influence the healing behavior or the velocity dependence of friction samples containing water wetted co2 exhibit behavior similar to wet samples we infer that the healing in dry samples is controlled by plastic asperity creep dieterich type possibly through dislocation creep and or twinning in wet samples healing is inferred to be controlled by increases in contact area and cohesion by pressure solution using a pressure solution rate model to extrapolate healing by contact area growth indicates that the maximum re strengthening through such a mechanism will only take days to tens of days

the impact of natural and anthropogenic processes on the evolution of closed depressions in loess areas a multi proxy case study from naleczow plateau eastern poland abstract closed depressions are reported in loess landscapes in various parts of europe the anthropogenic and natural origin of closed depressions is highly debated in literature closed depressions are an important component of the landscape in loess areas of the lublin upland furthermore they perform the role of local closed sediment basins creating unique conditions for the preservation of soils and colluvial sediments along with the record of the evolution of the holocene landscape occurring under the influence of climate changes and human activity the study objective was to evaluate the contribution of natural and anthropogenic processes influencing the origin and evolution of closed depressions the naleczow plateau is composed of loess whose thickness varies from a few meters to 30 m 1761 closed depressions have been documented within the naleczow plateau 493 km 2 a detailed investigation was conducted within selected closed depression dissected by a deep and long road trench the studied form was 40 m long 26 m wide and 0 7 m deep the analyzed exposure 20 m long and 7 m high presents a cross section of the closed depression fieldwork and subsequent laboratory analyses were conducted morphological micromorphological microstructural geochemical physico chemical osl and 14 c dating archaeological and historical correlations were also performed the primary bottom and slopes of the studied depression are composed of loess in situ overlain by late glacial holocene fossil soil periglacial structures such as deformed ice wedge pseudomorphs cracks and lenses macro structures were documented in the loess and palaeosol at the bottom of the closed depression the depression is filled with neoholocene soil sediment sequences consisting of 2 layers of colluvial sediments separated by neoholocene subfossil soil they constitute a record of the two stages of cd infillings in the holocene connected with human agricultural activity lasting from the neolithic up to modern times a detailed analysis of the loess late glacial holocene fossil soil and holocene colluvial sediments made it possible to distinguish the stages of evolution of closed depression influenced by changing environmental conditions and human activity during the late glacial and holocene

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

ion exchange experiments and rbsr dating on celadonites from the troodos ophiolite cyprus abstract rb sr dating of celadonites from several geographic stratigraphic locations from the troodos ophiolite cyprus yield crystallization ages varying between 57 9 3 9 and 89 0 1 9 ma the oldest celadonite age 89 0 1 9 ma agrees well with the crystallization age of the troodos igneous complex suggesting that low temperature chemical exchange with seawater started immediately after formation of the ophiolite drillcore samples suggest a duration of low temperature alteration of ca 10 ma whereas outcrop samples yield much longer durations of 30 ma the exact reason for this discrepancy is not fully understood but may represent the difference in localized downwelling in different parts of the ophiolite or may be related to the extensive weathering of the upper extrusive suite additionally in nearly all cases rb sr age estimates are older than k ar age data from the same samples to evaluate the potential disturbances of rb sr isotope systematics from exchangeable interlayer and basal surface positions a series of ion exchange experiments was carried out these data show that significant amounts of rb and sr can be in exchangeable positions and therefore a fraction of the parent and daughter inventory of these clays is vulnerable to late stage chemical exchange however the overall agreement between the data of the whole mineral and ion exchanged clay separates suggests that the influence of this exchange on the rb sr isotopic system is minor the post crystallization chemical behavior of exchangeable k and ar was not evaluated but the loss of radiogenic argon from exchangeable sites could result in k ar ages younger than rb sr ages of the same sample

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

pliocene pedosedimentary cycles in the southern pampas argentina well developed bt horizons of five palaeosols p1 p5 have been recorded previously within a 20 m thick succession of pliocene siltstones and clayey siltstones in the southern part of the buenos aires province of argentina this paper reports a detailed field and micromorphological thin section investigation of a 6 m portion of the sequence encompassing p2 and p3 large scale faunal burrow infillings occur throughout other bioturbation features in the form of channel and spongy microstructures are mainly confined to the siltstones the intervening clayey siltstones bt horizons have been affected more by shrink swell disruption as evidenced by slickensides and a range of striated b fabrics in thin sections clay coatings indicative of illuvial accumulation of clay translocated in suspension from overlying a or e horizons occur in both the siltstones and clayey siltstones the types microstratigraphic associations and depth functions of features are interpreted in terms of changing interactions balances and dominances between sedimentary pedogenic and erosional processes over time thus providing the basis for the pedosedimentary reconstruction of landscape evolution in the region during part of the pliocene represented by the whole p1 p5 sequence 4 5 ma bp it is envisaged that this period was dominated by aeolian deposition although fluvial and mass movement processes probably led to reworking and redistribution of some of the materials overall rates of subaerial deposition however were not substantial pedogenic processes were active throughout the balance between sedimentation and pedogenesis varying over time in a cyclical fashion phases of reduced deposition and establishment of relatively stable land surfaces were marked by the development of argillic soil profiles with clearly defined eluvial and illuvial horizons intervening periods of more rapid accumulation of coarser material were characterized by accretionary soil development and welding of new pedological features on existing soils as the surface accreted first transforming existing eluvial horizons into bct ae horizons siltstones and then encouraging the syndepositional upward extension of these complex horizons the primary basis of the alternating units of siltstones bct ae horizons and clayey siltstones bt horizons lies in the cyclical change in size of particles deposited although pedogenic translocation processes enhanced these textural differences the underlying driving mechanism behind the pedosedimentary cycle can only be speculated upon although it is tempting to relate the sedimentation pattern to climatic fluctuations linked to glacial advances and retreats in the patagonian andes during the pliocene

patterns and processes of alteration in the lavas and dykes of the troodos ophiolite cyprus alteration patterns in the lavas and dykes of the troodos ophiolite cyprus record a complex history of axial hydrothermal alteration crustal aging and subsequent uplift and emplacement of the ophiolite field mapping shows that distribution of five alteration zones each with distinct mineralogical geochemical and hydrologie characteristics is influenced by igneous stratigraphy structure and the nature and thickness of the overlying sediments paragenetic sequences of secondary minerals indicate that alteration conditions changed progressively as the crust cooled and moved off axis along spreading axes low temperatures 50 c were maintained by the rapid flow of seawater in and out of the lavas and only minimal alteration took place in contrast lower water rock ratios and higher temperatures 200 c in the dykes promoted extensive seawater rock interaction although the sharp rise in temperature between the two regimes generally coincides with the lava dyke transition late stage intrusions or hydrothermal upwelling zones locally cause high temperature alteration to extend upward into the lavas as a segment of crust moved off axis temperatures remained low in the lavas and progressively decreased from 250 to 80 c in the dykes high permeability in the uppermost lavas led to the downward migration of an oxidative alteration front whose thickness and spatial distribution was dependent upon the rate and nature of sedimentation and thus the original seafloor morphology although field relations show that alteration has a consistent vertical pattern in troodos the alteration zones are not laterally continuous and the stratigraphie depth of their boundaries varies considerably

lost loesses rapid communication loesses form wide belts in front of previously glaciated areas their thicknesses may be considerable changing in eurasia from maximally a few metres in the west to a hundred metres or more in the east the eastern particularly chinese loesses are mostly unrelated to glaciations the periglacial loesses from china and elsewhere predominantly date from the last pleistocene glaciation relatively few comparable occurrences are known from earlier quaternary glaciations as it is difficult to imagine that the conditions in front of the land ice masses during the earlier glaciations differed fundamentally from those of the last one considerable quantities of loess must have disappeared this disappearance which is commonly ascribed to fluvial and eolian erosion is not easily explained as equivalent deposits that may have the older loesses as a source are practically absent a possible explanation might be that loess is recycled during successive glaciations some loess disappears during interglacials by erosion but this quantity is more than compensated by the formation of new silt particles the implication would be that the loess deposits increase in volume for each new glaciation

experimental postseismic recovery of fractured rocks assisted by calcite sealing postseismic recovery within fault damage zones involves slow healing of coseismic fractures leading to permeability reduction and strength increase with time to better understand this process experiments were performed by long term fluid percolation with calcite precipitation through predamaged quartz monzonite samples subjected to upper crustal conditions of stress and temperature this resulted in a p wave velocity recovery of 50 of its initial drop after 64 days in contrast the permeability remained more or less constant for the duration of the experiment microstructures fluid chemistry and x ray microtomography demonstrate that incipient calcite sealing and asperity dissolution are responsible for the p wave velocity recovery the permeability is unaffected because calcite precipitates outside of the main flow channels the highly nonparallel evolution of strength recovery and permeability suggests that fluid conduits within fault damage zones can remain open fluid conduits after an earthquake for much longer durations than suggested by the seismic monitoring of fault healing

fault zone healing effectiveness and the structural evolution of strike slip fault systems summary numerical simulations of long term crustal deformation reveal the important role that damage healing i e fault zone strengthening plays in the structural evolution of strike slip fault systems we explore the sensitivity of simulated fault zone structure and evolution patterns to reasonable variations in the healing rate parameters in a continuum damage rheology model healing effectiveness defined herein as a function of the healing rate parameters describes the post seismic healing process in terms of the characteristic inter seismic damage level expected along fault segments in our simulations healing effectiveness is shown to control thespatialextentofdamagezonesandthelong termgeometricalcomplexityofstrike slipfault systems in our 3 d simulations specifically simulations with highly effective healing form interseismically shallow fault cores bracketed by wide zones of off fault damage ineffective healing yields deeper fault cores that persist throughout the interseismic interval and narrower zones of off fault damage furthermore highly effective healing leads to a rapid evolution of an initially segmented fault system to a simpler through going fault while ineffective healing along a segmented fault preserves complexities such as stepovers and fault jogs healing effectiveness and its role in fault evolution in our model may be generalized to describe how heat fluid flow and stress conditions that contribute to fault zone healing affect fault zone structure and fault system evolution patterns

spreading induced faulting and fracturing of oceanic crust examples from the sheeted dyke complex of the troodos ophiolite cyprus

recycled loesses a micromorphological approach to the determination of local source areas of weichselian loess the article presents the results of micromorphological studies of selected neopleistocene loess palaeosol sequences broader studies of thin sections are presented for the polanow samborzecki zlota site they served as models for analysis for similar targeted observations in other sequences on their basis 3 groups of microfeatures litho pedo and cryogenic were described an additional group are pedogenic features clay concentrations selected fe and mn fe nodules as well as charcoals documented in non soil locations generally limited to loess macroscopically defined as primary an analysis of these features shows that these are redeposited pedogenic microfeatures occurring in a secondary location according to this genetic interpretation they can be identified as pedorelicts and possibly also as lithorelicts these features clearly show that the older pedogenically modified layers were involved in the formation of younger loesses these studies show that the younger loesses are partially built of older loess material

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

luvisols or cambisols micromorphological study of soil truncation in young morainic landscapes case study brodnica and chelmno lake districts north poland abstract eight soil profiles in brodnica lake district and chelmno lake district were described and sampled the profiles were divided into four pairs study areas dissimilar in lithology relief or land use each pair of profile contained soil located on the crest or upper slope exposed to erosion and back slope slightly exposed to erosion positions the relief of this area is inherited from the last vistulian glaciation and represents mostly flat and hummocky moraine plateau landscapes all investigated pedons have a b horizon five profiles have vertical contrasting texture and contain a significantly developed eluvial zone a and e horizons above b horizon in three cases pedons have a b c horizon sequence to date numerous studies have shown that the soils with a b c profiles developed on moraine tills should be treated as cambisols on existing soil agricultural maps these soils are also marked as cambisols the b horizons are enriched in the clay fraction and contain low amount of carbonates in comparison with the parent material all these criteria can be used to distinguish a cambic horizon but analysis of thin sections revealed the presence of significant amounts of clay and silt illuvial features the illuvial pedofeatures resulted in these horizons being classified as argic horizons bt these soils cannot be classified as cambisols which are characterized by absence of appreciable amounts of illuvial silt and clay instead the a b c profile forms represent truncated luvisols in which the material from eluvial horizons was entirely removed the soils described in this study occur in areas where soil erosion is common the upper part of slopes and crests in arable areas the illuvial origin of b horizons in truncated pedons a b c was also confirmed by the presence of eluvial horizons in nearby soils on the back slope position slightly or non exposed to erosion the results showed that accelerated erosion had a significant role in development of soil cover in agriculture moraine landscapes of brodnica and chelmno lake districts the micromorphological analysis confirmed that the loamy soils with the a b c profile developed on ground moraine tills should be classified as truncated eroded luvisols the b horizons of these soils have significant accumulation of clay and silt features the illuvial microforms are the relic feature of eluviation illuviation lessivage process the material from the eluvial horizons of luvisols was entirely removed this study is important to understand the influence of soil erosion processes on soil cover development in young glacial regions further investigations concerning formation and characteristic of a b c soils and appropriate classification of described pedons are very important for understanding the impact of accelerated erosion in young glacial landscapes

palaeoclimate sedimentation and soil development during the last glacial stage devensian heathrow airport london uk abstract the langley silt complex overlying the taplow terrace of the river thames at prospect park near heathrow airport west of london is described in terms of lithology carbonate content organic carbon content particle size characteristic macrostructure micromorphology and stratigraphic position the langley silts were deposited by wind or water in cold climate conditions and include evidence for the development of periglacial structures and for devensian lateglacial and holocene soil formation the langley silts rest upon a last interglacial ipswichian ois 5e soil developed in the taplow gravel deposited during the previous cold stage ois 6 during the early devensian and the dimlington stadial and younger dryas of the late devensian wind deposited the silts and during the middle devensian wind and surface wash built up a laminated silt and sand during the middle devensian seasonal dessication formed non sorted polygonal patterns as this laminated unit aggraded but this process ceased with the return to loess deposition in the late devensian argillic soil development occurred during the windermere interstadial only to be disrupted by ground ice processes during the succeeding younger dryas cold phase the site provides one of the most complete sedimentary sequences through the last glacial stage in britain and confirms recent interpretations of soil development and evidence for aeolian deposition in britain during the lateglacial

time dependent recovery of microcrack damage and seismic wave speeds in deformed limestone limestone samples were deformed up to 5 inelastic axial strain at an effective confining pressure peff 50 mpa in the cataclastic flow regime and subsequently maintained under constant static stress conditions either isostatic of triaxial for extended periods of time while elastic wave speeds and permeability were continuously monitored during deformation both seismic wave speeds and permeability decrease with increasing strain due to the growth of subvertical microcracks and inelastic porosity reduction during the static hold period under water saturated conditions the seismic wave speeds recovered gradually typically by around 5 relative to their initial value after 2 days while permeability remained constant the recovery in wave speed increases with increasing confining pressure but decreases with increasing applied differential stress the recovery is markedly lower when the samples are saturated with an inert fluid as opposed to water the evolution in wave speed is interpreted quantitatively in terms of microcrack density which shows that the post deformation recovery is associated with a decrease in effective microcrack length typically of the order to 10 after 2 days the proposed mechanism for the observed damage recovery is microcrack closure due to a combination of backsliding on wing cracks driven by time dependent friction and closure due to pressure solution at contacts between propping particles or asperities and microcrack walls the recovery rates observed in the experiments and the proposed underlying mechanisms are compatible with seismological observations of seismic wave speed recovery along faults following earthquakes

spatial and temporal variability in crystallization of celadonites within the troodos ophiolite cyprus implications for low temperature alteration of the oceanic crust celadonite a low temperature 30 c hydrothermal alteration mineral is a predominant fracture and void filling phase within the volcanic rocks of the troodos ophiolite the combined chemical and structural properties of celadonite i e high k2o and ar retentive along with its common occurrence provide a valuable tracer for studying the temporal and spatial variability of low temperature hydrothermal fluid circulation and alteration within this ancient oceanic crust some 54 new k ar age determinations of celadonites from various geographic and stratigraphic locations within the extrusive rocks of troodos yield crystallization ages ranging from 90 9 1 0 to 49 8 0 5 ma with the oldest in close agreement with the estimated 91 92 ma crystallization age of troodos igneous rocks the youngest age indicates that low temperature water rock chemical exchange continued for at least 40 m y after crustal formation this represents a 100 increase over previous estimates based on limited numbers of k ar dates of celadonite of the duration of low temperature mineral precipitation in troodos correlation between celadonite ages and field relationships suggests the following 1 there is no apparent relationship between celadonite crystallization and stratigraphic depth 2 celadonite crystallization occurs homogeneously on an outcrop scale with adjacent samples from a single flow unit yielding equivalent k ar ages 3 flow units with relatively high primary permeabilities e g pillows and breccias yield celadonites with younger k ar ages 4 celadonite precipitation at distinct locations occurred rapidly with little or no age difference between rim and core sections of single large deposits the above correlations suggest that low temperature hydrothermal fluid circulation and secondary mineral precipitation are controlled by the local alteration conditions such as intrinsic permeability degree of fracturing and water rock ratios and are independent of time and space integration of these local heterogeneities over the entire extrusive sequence suggests that the upper oceanic crust undergoes relatively homogeneous closure to hydrothermal fluid circulation no evidence is found to support a progressive upward sealing of the oceanic crust

a view into the cretaceous geomagnetic field from analysis of gabbros and submarine glasses the nature of the geomagnetic field during the cretaceous normal polarity superchron cns has been a matter of debate for several decades numerical geodynamo simulations predict higher intensities but comparable variability during times of few reversals than times with frequent reversals published geomagnetic paleointensity data from the cns are highly scattered suggesting that additional studies are required here we present new paleointensity results from 18 sites collected from the lower oceanic crust of the troodos ophiolite cyprus 92 1 ma old together with recently published data from the troodos upper crust we obtain three independent paleointensity time series these sequences reveal quasi cyclic variations of intensities about a mean value of 54 20 z am 2 providing insight into the fluctuating nature of the cretaceous magnetic field our data suggest the cns field was both weaker and more variable than predicted by geodynamo simulations the large amplitudes of these variations may explain the wide range of dipole moments previously determined from the cns 2007 elsevier b v all rights reserved

micromorphology of loess paleosol sequences a record of paleoenvironmental change abstract the record of paleoenvironmental change retained within thin sections from loess paleosol sequences is discussed with reference to case studies from western europe china and northwestern usa the paleoenvironmental significance of individual micromorphological features such as calcitic concentrations clay coatings and cryogenic structures are first evaluated and the value of recognising and interpreting microstratigraphic relationships of features in terms of paleoenvironmental change is illustrated recent developments have seen a greater emphasis on using micromorphology within a pedosedimentary approach whereby both pedogenic and sedimentary processes are taken into account when interpreting loess paleosol sequences this has led not only to the acquisition of important information on conditions during phases of enhanced loess accretion and periods of climatic transition but also to an increased awareness of spatial changes in processes and environmental controls during particular time periods micromorphologically based reconstructions have enabled the isolation of key stages of pedosedimentary development although absolute dating of stages is often limited by lack of age controls a novel approach aimed at addressing this limitation afforded by presence of datable tephra in microstratigraphic association with key micromorphological features is discussed

prehistoric dates of the most recent alpine fault earthquakes new zealand we use four methods to investigate the earthquake history over the past 600 yr of the central alpine fault new zealand trenches across the active fault trace at five locations identify two ruptures on the fault in the past 450 yr three other indirect indicators episodes of landsliding and aggradation dated either via 14 c or from forest establishment on the resulting surfaces and tree ring growth anomalies provide further evidence for these two earthquakes and a greater resolution in estimates of their timing and extent the most recent earthquake occurred in a d 1717 and the rupture extended over a section of fault between milford and the haupiri river a distance of 375 km about 1630 another earthquake occurred on the fault and this extended between at least the paringa and ahaura rivers 250 km regional episodes of landsliding and forest establishment provide evidence for a third earthquake at about 1460 over the same section of fault the pattern of earthquake recurrence is not regular but averages 200 yr and varies from 100 yr to at least 280 yr which is the lapsed time since the most recent rupture

progressive offset and surface deformation along a seismogenic blind thrust in the po plain foredeep southern alps northern italy here we present for the first time in the po plain foredeep northern italy the middle to late pleistocene growth history of an outcropping secondary fold and related faults whose progressive deformation over an intermediate time window 105 years is driven by an underlying seismogenic blind thrust we trenched and logged an outcropping decametric secondary anticline related to a deeper blind compressional structure which deforms fluvial sediments and an overlying loess paleosol sequence folded units were dated using radiocarbon and optically stimulated luminescence methods to the late pleistocene holocene and tentatively correlated with glacial interglacial phases occurring during the time interval from marine isotope stage 6 to the present a multistep retrodeformation of the fold allowed us to calculate uplift rates for this secondary and shallow anticline varying between 0 02 and 0 1 mm yr since circa 200 kyr trishear forward deformation modeling of the fold indicates that the amplification of the observed fold could be caused by two shallow thrusts formed through a break backward activation this generated a decametric surface fold whose most recent growth was associated with bending moment normal faulting in the crestal and forelimb region our observations demonstrate that near surface compressive tectonics can be caused by blind thrusting via a complex array of fault and folds upward strain propagation and generation of shallow low angle thrust and related folding seem to be mainly due to secondary fold related faulting according to an out of syncline thrusting mechanism

new on fault evidence for a great earthquake in a d 1717 central alpine fault new zealand the dextral reverse alpine fault is the major onshore plate boundary structure between the australian and pacific plates in new zealand no previous study of the central portion of the 200 km long central segment has provided on fault evidence for the most recent event mre using lidar light detection and ranging data coupled with field mapping we recognized the main trace of the alpine fault north of gaunt creek south island as a north striking fault scarp we enhanced a natural exposure that revealed evidence for repeated late holocene thrust fault movement the north northwest striking fault zone is characterized by a distinct 5 50 cm thick clay fault gouge layer juxtaposing hanging wall bedrock mylonites and cataclasites over unconsolidated late holocene footwall colluvium the bedrock is cut by a strath terrace and overlain by mid holocene ca 5400 calibrated 14 c yr b p alluvial terrace which has been faulted repeatedly and is conformably overlain by undeformed late holocene colluvium and alluvium an unfaulted peat at the base of the scarp is buried by post mre alluvium and yields a calibrated 2 radiocarbon age of a d 1710 1930 which dates the mre as post 1709 our data are consistent with sparse on fault data and validate earlier off fault records that suggest an a d 1717 mre the 1717 event had a moment magnitude of m w 8 1 0 1 based on the 380 km long surface rupture because the fault has not ruptured for 300 yr it is likely approaching the end of its seismic cycle and poses a significant seismic hazard to new zealand

isotopic and trace element composition of volcanic glasses from the akaki canyon cyprus implications for the origin of the troodos ophiolite abstract we report major elements k rb cs sr ba sc cr ni hf ta th and ree concentrations and isotopic compositions of sr nd pb and o of carefully handpicked volcanic glasses from the akaki river section of the troodos ophiolite complex on the basis of sr and o isotopic composition and fe 2 o 3 feo ratios nine of the ten glasses analyzed are considered to be fresh even with respect to those elements that are easily affected by alteration the glasses range in composition from basaltic andesite to dacite incompatible element concentrations in the mafic compositions are low 10 chondritic and the light ree are strongly depleted however the ratios of low field strength elements k rb cs sr th to high field strength elements ta hf ti and rare earth elements are higher than those in n morb nd isotopic compositions show a very small range with e nd t 80ma varying from 6 5 to 7 5 initial 87 sr 86 sr ratios range from 0 7033 to 0 7040 pb isotope ratios have a restricted range with 206 pb 204 pb 18 60 18 70 207 pb 204 pb 15 55 15 59 and 208 pb 204 pb 38 08 38 51 the oxygen isotopic composition for fresh glasses falls within the range reported for fresh mafic mantle derived volcanics with 18 o varying from 5 4 to 6 5 all geochemical characteristics of the troodos volcanic glasses are similar to those observed in supra subduction zone volcanics but we cannot distinguish between an early stage island arc or back arc origin for the troodos ophiolite on a geochemical basis only however considering our data and previously published geologic and geochemical data we suggest that the troodos ophiolite formed in the earliest stages of island arc development

pedosedimentary and climatic reconstruction of the last interglacial and early glacial loess paleosol sequence in south tadzhikistan abstract the thick loess paleosol sequences in tadzhikistan which indirectly record the environmental changes from the upper pliocene to the present day have been extensively described from a chronostratigraphical and archaeological point of view the genesis of the soil sedimentary complexes and their implications for palaeoenvironmental reconstruction in tadzhikistan however have been considered only relatively recently bronger a winter r derevjanko o aldag s 1993 loess paleosol sequences in tadjikistan as a palaeoclimatic record of the quaternary in central asia quaternary proceedings 4 69 81 lomov s p tursina t v zhou l p 1996 magnetic susceptibility of soils micromorphology and possible reconstructions of climate in soil micromorphology studies in soil diversity diagnostics dynamics 10th international working meeting on soil micromorphology moscow russia july 8 13 1996 p 145 the pedocomplex of last interglacial and early glacial age oxygen isotope stage 5 in the tagidjar and darai kalon sections near the town of khovaling is represented by three major stages of soil formation the soil characteristics have been micromorphologically analysed the distinction between primary and secondary carbonates is of major importance to understand the soil forming processes the relative distribution of needle fibre calcite nfc micritic infillings m hypocoatings chc coarse calcitic grains ccg and calcified root cells crc provides detailed insights into the environmental conditions prior during and following pedogenesis the abundance of coprolitic aggregates ca and pupal chambers gives a clear indication of the rate of biological activity which prevailed during the last two soil forming stages void pseudomorphs after gypsum crystals gypsum pseudomorphs are frequently observed beneath the cca horizons of the paleosols using the present day climate and soilscape as a reference base the obtained pedosedimentary events detected in the tadzhikistan sections provide a detailed palaeoenvironmental record indeed glacial and interglacial climates and soils respond to contemporaneous climatic schemes and soil forming processes which are still active in the region today the amount and the seasonal variability of precipitation mostly are at the origin of the variable soils formed during glacial and interglacial ages

troodos extrusive series of cyprus a comparison with oceanic crust the extrusive section on the northern flank of the troodos ophiolite is 1 000 to 1 500 m thick and consists of about 12 lithologic units of pillowed and massive lava and breccia some pillowed units which average 100 to 200 m in thickness vary systematically from lava tubes up to 6 m in diameter at the base through common pillows less than 1 m in diameter to small pillows and extrusive breccias at the top these assemblages appear to be individual volcanoes suggesting episodic volcanic accretion the upper 100 to 200 m of the section is pervasively altered and oxidized but fresh volcanic glass is preserved throughout most of the extrusive section the lavas are subdivided on geochemical evidence into a lower differentiated andesite to dacitic andesite series resembling evolved island arc tholeiites and an upper series of picrite mafic basalt and basaltic andesite very low in tio2 k2o p2o5 nb rb and ba the highly depleted basalt and basaltic andesite resemble lavas from ocean crust near island arcs lateral continuity of lithologic units interpreted as individual volcanoes and the relatively constant dips of the extrusive rocks suggest that tilting and rotation have not played major roles in the accretion process the occurrence of fractionated lavas at the base and primitive lavas at the top suggests a broad zone of accretion located above a subduction zone

genesis and relationship of macromorphology and micromorphology to contemporary hydrological conditions of a welded argixeroll from the palouse in idaho abstract soils formed in distal loess of the palouse region have welded profiles that make assessment of their genesis and pedostratigraphic relationships difficult these soils typically have a mollic cambic horizon sequence that is underlain by a well expressed albic e horizon and a strongly developed argillic horizon in this study we utilized hydrological monitoring combined with micromorphological analysis and new stratigraphic data to help establish the genesis of a representative argixeroll of the region and the relationship of its morphology to ancient and contemporary hydrological conditions monitoring results indicate that the argixeroll is seasonally episaturated for approximately 5 6 months per year ferrimanganiferous nodules segregations hypocoatings and depletion mottles are observed in thin section throughout the pedon but dominate within just above and below the present day e horizon measured soil eh is sufficiently low for fe and mn reduction to occur for 1 3 months during the period of episaturation suggesting that at least some of these redoximorphic features are likely to be contemporary other compound redoximorphic features are clearly relict however as they are coated by illuvial clay which is unaffected by fe mn redistribution processes thick illuvial clay coatings on interpedal fissures of the argillic horizon postdate pockets of holocene tephra within deeply bioturbated aggregates while other channel argillans in the same part of the pedon are clearly older this indicates that at least two distinct phases of clay accumulation have occurred the most recent being contemporaneous with loess aggradation during the holocene our results suggest that these welded profiles consist of a mollic cambic horizon sequence that has formed primarily in holocene loess and an albic argillic sequence that has formed in wisconsinan loess the modern day e horizon was initiated as the clay eluvial surface horizon of the regionally recognized washtucna paleosol that continued forming into the late wisconsinan cold phase and upon burial by holocene loess it has been transformed into an albic horizon and even enlarged as a result of redoximorphic processes associated with seasonal saturation

sedimentary and pedological processes in the upper pleistocene loess of northern italy the bagaggera sequence abstract the bagaggera sequence consists of two late pleistocene loesses superimposed on the top of middle pleistocene fluviatile sediments the lower loess includes at its base a mousterian archaeological level represented by artifacts dated by tl as 60 500 7500 bp and charcoal from hearths which mainly consists of boreal forest species at the top of the lower loess aurignacian artifacts occur which suggest a tentative date of 35 000 bp the sedimentary and pedological processes which lead to the formation of the sequence were reconstructed by means of mineral and textural analyses and thin section analysis and can be summarized as follows erosion and colluviation of the eemian soil at the base of the sequence during the early wurm isotopic substages 5 a c sedimentation of the lower loess deposits during the first pleniglacial period isotopic stage 4 a large number of coarse pedofeatures in this soil suggests that primary aeolian dust has been redistributed in place or for short distances by syngenetic slight pedogenesis and by water reworking as a result of alternating phases of wet and dry climate an alfisol characterized by strong clay illuviation developed in the lower loess during the hengelo arcy interstadial phase its top was affected by reworking and slight frost activity at the beginning of the second pleniglacial period isotopic stage 2 the upper loess was deposited in a drier environment during the second pleniglacial period isotopic stage 2 water reworking was less effective holocene weathering is expressed by clay illuviation and slight hydromorphism

glacial interglacial changes in dust deposition on the chinese loess plateau the chinese loess plateau clp contains an extensive record of aeolian deposition through multiple glacial interglacial cycles independent chronologies based on pedostratigraphy magnetic susceptibility radiocarbon and luminescence dating were developed for 79 sites and used to estimate aeolian mass accumulation rates mars for marine isotope stages 1 5 the regional median value of mar for stage 2 is 310 g m2 yr compared to an estimate of 65 g m2 yr for stage 5 estimated mars from individual sites for stage 2 are approximately 4 3 times greater than mars for stage 5 and 2 1 times greater than for stage 1 mar values at individual sites are consistently highest in the northwest and lowest in the southwest of the clp during all marine isotope stages mars estimated on sections through loess terraces are consistently higher than mar estimates at other sites indicating that local recycling of loess material from exposed river valley deposits has been significant throughout the last 130 kyr although the spatial and temporal patterns in mar are robust there are uncertainties about the magnitude of these changes due to a lack of bulk density measurements and uncertainties in the chronologies for individual sites b site and chronological biases in the sampling used to derive regional estimates and c the unquantified nature of human impact on accumulation rates during the late holocene nevertheless the records from the clp pose a number of challenges which could be addressed by numerical models of the palaeo dust cycle

thermal regime in the central alpine fault zone new zealand constraints from microstructures biotite chemistry and fluid inclusion data abstract the thermal state within plate boundary fault zones is likely to influence the dimensions of large co seismic fault ruptures and strain localisation in underlying mylonitic shear zones vein microstructures biotite chemistry and fluid inclusion data offer new insights into the thermal structure of the mylonitic shear zone down dip of the alpine fault the main pacific australian plate boundary structure through southern new zealand quartz veins within the fault rocks were formed and deformed at temperatures ranging from 500 c to immediately above that of the brittle viscous transition 325 c illustrating that fluids are present throughout the fault zone microthermometric data from primary mixed co 2 h 2 o fluid inclusions in boudin neck quartz carbonate veins indicate that these inclusions were trapped at temperatures of 325 15 c and pressures of c 40 mpa vein microstructures indicate that fluid temperatures were equal to rock temperatures assuming hydrostatic fluid pressure the veins were trapped at depths of 2 o co 2 fluids in the shallower crust of 500 kg m 3 biotite grains in the mylonites are a mixture of porphyroclastic grains with high r ti mg inherited from the parent alpine schist and smaller low r grains that recrystallised during mylonitisation particularly those that are found within syn mylonitic shear bands assuming a simple step function model approximating diffusive equilibration the changes in biotite chemistry indicate t during mylonitic deformation of 340 c according to the ti in biotite thermometer of henry et al 2005 a best fit uplift p t path to existing data and these new results indicate that the uplift path p t gradient of fault zone rocks above the brittle viscous transition is of the order of 40 c km 1 below the brittle viscous transition the uplift path p t gradient is 10 c km 1 the p t profile within the fault rocks is comparable to that in the immediate hanging wall alpine schist indicating there is no peak in the crustal isotherms in the fault hanging wall as was indicated by previous numerical models and analyses that did not consider data from the fault rocks themselves

a comparative analysis of potential biosignatures in basalt glass by fib tem abstract bulk analyses of fresh and altered subseafloor basalts have elucidated the large scale geochemical fluxes that result from water rock interactions which ultimately affect both seawater and mantle compositions but these analyses do not provide insights into the physical and chemical processes occurring on the scale of microorganisms micron sized tubules that may represent microbial boring into basalt glass are ubiquitous throughout the seafloor and can potentially be preserved over geological time these putative biosignatures give clues into the history of life on earth and may be significant for the search for life on other planets however their formation and mineralization are still poorly understood we have used a combination of focused ion beam fib milling and transmission electron microscopy tem to analyze the textural and geochemical characteristics of tubular alteration features from four basalt glass samples representing different sample locations collection depths and ages including one sample from the cretaceous troodos ophiolite high resolution tem imaging consistently identified platy layers of partially crystalline material infilling the tubules the lattice spacings and diffraction patterns showed that this material comprises a mix of two layer and three layer silicates closer inspection of the contact point between the tubules and the surrounding basalt glass commonly revealed a thin leached rim around the tubules electron energy loss spectroscopy mapping demonstrated that these rims are depleted in everything but si and o which implies that they are formed by a leaching process likely the incongruent dissolution of the glass during formation of the tubule the infilling material is depleted in ca and enriched in k and in most cases also enriched in fe which is consistent with their identification as fe bearing phyllosilicates these observations are consistent across the samples which implies that the processes that form and mineralize tubular glass alteration features are similar throughout the oceanic subsurface and through time

experimental decrepitation and re equilibration of fluid inclusions in synthetic quartz abstract strong discrepancies between densities of the fluids trapped in fluid inclusions f i and p tp couples deduced from other geological considerations are common so it was decided to test experimentally the possible f i re equilibrations when bringing the host crystal in p tp conditions different from trapping conditions runs were conducted on synthetic quartz in a gas apparatus and in a griggs solid medium apparatus the following modifications of the f i were observed 1 1 drastic shape changes of the primary f i and appearance of clusters or trails of small secondary inclusions sometimes related to a crack 2 2 lowering of the fluid densities such a re equilibration is a decrepitation phenomenon first hydraulic fracturing then sealing of the cracks with appearance of secondary inclusions when using the gas apparatus the new measured densities are in very good accordance with the nominal p tp conditions when using the solid medium apparatus the new densities are surprisingly low relative to the nominal p t conditions probably due to a strongly anisotropic stress state in the apparatus

postseismic pressure solution creep evidence and time dependent change from dynamic indenting experiments active faults in the earth s upper crust can slide either steadily by aseismic creep or abruptly causing earthquakes seismic and aseismic processes are closely related earthquakes are often followed by transient afterslip creep postseismic displacement rates progressively decrease with time over a period of years or decades so seismic fracturing activates the creep rate and various healing processes progressively reduce it this article presents pressure solution indenter experiments on halite calcite and plaster that show how fracturing and comminution processes induced by dynamic stress loading applied by dropping steel balls drastically accelerate the displacement rates accommodated by pressure solution creep by decreasing the dissolution contact area and the diffusive mass transfer distance along this contact however as fractures progressively heal and dissolution contacts flatten these effects disappear and the displacement rates slow down the time dependent change in indenter displacement after dynamic stress loading has been measured and is best fitted by power laws with exponents that change with time from 0 3 to 1 when healing is achieved natural postseismic afterslip displacement time relationships have been analyzed and also show a power law change with a power law exponent in the range of 0 25 0 4 it is proposed that the variation in power law exponent with time is related to the change in morphology of the dissolution contact that is fractured or comminuted during the dynamic event and is then progressively healed and smoothed in natural faults monitoring the power law parameters could give access to the characteristic healing time in the fault

stratigraphic architecture and fracture controlled dolomitization of the cretaceous khami and bangestan groups an outcrop case study zagros mountains iran this work has been carried out as part of a joint study between norsk hydro now statoil and nioc national iranian oil company

soil evolution and origin of landscape in a late quaternary tectonically mobile setting the po plain northern apennines border in lombardy italy abstract the interactions among quaternary paleo soil forming erosion re deposition and geomorphic processes at the origin of the present day landscape are discussed at three isolated tectonic reliefs of the southern po foredeep basin of lombardy san colombano casalpusterlengo and zorlesco reliefs italy these sites offer the possibility to combine different scales of geopedological geomorphological stratigraphic and structural observations to unravel the contribution of climate and tectonics to the quaternary geological evolution and to the origin of the landscape field surveys laboratory analyses and soil micromorphology were used to characterize the late quaternary pedogenic processes acting on different paleo surfaces in combination with the detailed study of seven selected soil profiles pedo stratigraphic correlations revealed that two alluvial loess paleosol sequences which originated from the late pleistocene to holocene glacial interglacial fluctuations are differently preserved throughout the present day hill landscape in situ paleosols allowed to localize the paleo topographic surfaces of geomorphic tectonic and sedimentary stabilization redeposited paleosols occurring systematically close to the main faults and or at the erosional bottom of paleo valleys allowed to mark the stages of tectonic instability the integrated approach contributed to unravel the composite nature and rank of the stratigraphic boundaries polycyclic loess soil aggradation characterized the stable paleo highs uplifted during different phases of active thrusting of the northernmost emilian arcs of the apennine while valley incision fluvial terracing soil truncation and redeposition occurred in the intervening structural lows in the san colombano hill area late pleistocene transtensional faulting induced changes of the drainage network and enhanced redeposition of paleosols in colluvial wedges on the hangingwalls along the fault scarps lgm loess was preserved above different dissected remnants of the paleo topography composing the hilltops these new constraints permit to refine the late quaternary tectono depositional history and landscape evolution at the southern margin of the po basin