stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

mixed brittle and viscous strain localization in pelagic sediments seaward of the hikurangi margin new zealand calcareous pelagic input sediments are present at several subduction zones and deform differently to their siliciclastic counterparts we investigate deformation in calcareous pelagic sediments drilled 20 km seaward of the hikurangi megathrust toe at site u1520 during iodp expeditions 372 and 375 clusters of normal faults and subhorizontal stylolites in the sediments indicate both brittle faulting and viscous pressure solution operated at 150 c where frictional possibly seismic slip likely predominates

experimental pressure solution in halite the effect of grain interphase boundary structure to investigate the mechanisms and kinetics of pressure solution we measured deformation at contacts between polished convex lenses of halite and polished flat lenses of either halite or fused silica in saturated brine at 50 2 0 2 c and fluid pressures of 0 1 mpa loads applied using small springs ranged from 0 1 4 2 n mean effective normal stresses within the contact zone ranged from 1 14 mpa the geometry and diametric growth rate of the contact spot neck growth and the rate at which the lenses approached one another convergence were monitored during deformation using transmitted and reflected light photomicrography time dependent convergence did not occur at measurable rates when two halite lenses were pressed together in saturated brine but did occur when halite and fused silica lenses were pressed together in brine convergence rates in the halite silica experiments were 0 01 0 05 m day although the initial deformation during loading involved elastic and plastic processes control experiments without brine showed no time dependent convergence indicating that dislocation creep did not contribute to the observed rates no undercutting or cataclasis was observed in any experiments residual fluid inclusions were formed along grain boundaries between two halite lenses loaded in brine indicating non zero wetting angles

self organization and nonlinear dynamics in sedimentary basins and discussion patterns of mineralization may develop during diagenesis that are not a direct reflection of sedimentary features or stresses and fluids imposed on the boundaries of a basin these patterns occur through the amplification of omnipresent non uniformities of textural or compositional variables amplification occurs through feedback involving the coupling of diagenetic processes the spatial scale of these patterns varies from microns to kilometres examples to be discussed include intracrystalline oscillatory zoning millimetre to metre scale differentiated layering and stylolites liesegang bands reaction front fingering pulsatile fluid release from overpressurized zones in deep basins and kilometre scale basin compartmentation

frictional viscous flow of phyllosilicate bearing fault rock microphysical model and implications for crustal strength profiles it is widely believed that around the brittle ductile transition crustal faults can be significantly weaker than predicted by conventional two mechanism brittle ductile strength envelopes factors contributing to this weakness include the polyphase nature of natural rocks foliation development and the action of fluid assisted processes such as pressure solution recently ring shear experiments using halite kaolinite mixtures as an analogue for phyllosilicaterich rocks for the first time showed frictional viscous behavior i e both normal stress and strain rate sensitive behavior involving the combined effects of pressure solution and phyllosilicates this behavior was accompanied by the development of a mylonitic microstructure a quantitative assessment of the implications of this for the strength of natural faults has hitherto been hampered by the absence of a microphysical model in this paper a microphysical model for shear deformation of foliated phyllosilicate bearing fault rock by pressure solution accommodated sliding along phyllosilicate foliae is developed the model predicts purely frictional behavior at low and high shear strain rates and frictional viscous behavior at intermediate shear strain rates the mechanical data on wet halite kaolinite gouge compare favorably with the model when applied to crustal materials the model predicts major weakening with respect to conventional brittle ductile strength envelopes in particular around the brittle ductile transition the predicted strength profiles suggest that in numerical models of crustal deformation the strength of high strain regions could be approximated by an apparent friction coefficient of 0 25 0 35 down to depths of 15 20 km

the early toarcian anoxia a synchronous event in the western tethys an approach by quantitative biochronology unitary associations applied on calcareous nannofossils during the early toarcian major paleoenvironnemental and paleoceanographical changes occurred leading to an oceanic anoxic event oae and to a perturbation of the carbon isotope cycle although the standard biochronology of the lower jurassic is essentially based upon ammonites in recent years biostratigraphy based on calcareous nannofossils and dinoflagellate cysts is increasingly used to date jurassic rocks however the precise dating and correlation of the early toarcian oae and of the associated 13c anomaly in different settings of the western tethys are still partly problematic and it is still unclear whether these events are synchronous or not in order to allow more accurate correlations of the organic rich levels recorded in the lower toarcian oae this account proposes a new biozonation based on a quantitative biochronology approach the unitary associations ua applied to calcareous nannofossils this study represents the first attempt to apply theuamethod to jurassic nannofossils the study incorporates eighteen sections distributed across western tethys and ranging from the pliensbachian to aalenian comprising 1220 samples and 72 calcareous nannofossil taxa the biograph savary j guex j 1999 discrete biochronological scales and unitary associations description of the biograph computer program memoires de geologie de lausanne 34 282pp and ua graph copyright hammer o guex and savary 2002 softwares provide a discrete biochronological framework based upon multi taxa concurrent range zones in the different sections the optimized dataset generates nine uas using the co occurrences of 56 taxa these uas are grouped into six unitary association zones ua z which constitute a robust biostratigraphic synthesis of all the observed or deduced biostratigraphic relationships between the analysed taxa the ua zonation proposed here is compared to classic calcareous nannofossil biozonations which are commonly used for the southern and the northern sides of tethys the biostratigraphic resolution of the ua zones varies from one nannofossil subzone or part of it to several subzones and can be related to the pattern of calcareous nannoplankton originations and extinctions during the studied time interval the late pliensbachian early toarcian interval corresponding to the ua z ii represents a major step in the jurassic nannoplankton radiation the recognized ua zones are also compared to the carbon isotopic negative excursion and tocmaximum in five sections of central italy germany and england with the aim of providing a more reliable correlation tool for the early toarcian oae and of the associated isotopic anomaly between the southern and northern part of western tethys the results of this work show that the toc maximum and 13c negative excursion correspond to the upper part of the ua z ii i e ua 3 in the sections analysed this suggests that the early toarcian oae was a synchronous event within the western tethys

provenance of albian cenomanian rocks of the methow and tyaughton basins southern british columbia a mid cretaceous link between north america and the insular terrane basin analysis of albian cenomanian rocks of the tyaughton and methow basins suggests that the two basins were filled by three principle petrofacies during a regionally significant contractional ev

water films at grain grain contacts debye huckel osmotic model of stress salinity and mineralogy dependence abstract water film diffusion is one of the mechanisms proposed to explain the deformation of rocks by pressure solution during geological processes in the upper crust this mechanism assumes that matter is dissolved inside the contact between two grains the resulting solutes are transported in the pore fluid through diffusion in an adsorbed water film the main problem of this theory is that it requires the presence of a water film that is believed to be stable under large deviatoric stresses inside the contact between two grains in this paper we show that the electrically charged surface of a mineral can attract counter ions from the pore and by the related change of osmotic pressure keep water within the contact this is due to the counter ions in the water film that increase the salinity in the film relative to that in the pore this lowers the free energy of water in the contact zone to a degree that balances the increase in free energy of water due to the elevated pressure in the film these notions are made more precise by combining the theory of the debye huckle double layer with equations of osmotic pressure the resulting d h o theory predicts the dependence of the water film thickness on stress across the contact composition of the pore fluid and the identity of the minerals involved

a constitutive model for layer development in shear zones near the brittle ductile transition 1 the microstructure of ductile shear zones differs from that of surrounding wall rocks in particular compositional layering is a hallmark of shear zones as layered rocks are weaker than their isotropic protolith when loaded in simple shear layering may hold the key to explain localization of ductile deformation onto ductile shear zones i propose here a constitutive model for layer development a two level mixing theory allows the strength of the aggregate to be estimated at intermediate degrees of layering a probabilistic failure model is introduced to control how layers develop in a deforming aggregate this model captures one of the initial mechanism of phase interconnection identified experimentally by holyoke and tullis 2006a 2006b fracturing of load bearing grains this model reproduces the strength evolution of these experiments and can now be applied to tectonic modeling

the effect of fluid composition salinity and acidity on subcritical crack growth in calcite crystals chemically activated processes of subcritical cracking in calcite control the time dependent strength of this mineral which is a major constituent of the earth s brittle upper crust here experimental data on subcritical crack growth are acquired with a double torsion apparatus to characterize the influence of fluid ph range 5 7 5 and ionic strength and species na2so4 nacl mgso4 and mgcl2 on the propagation of microcracks in calcite single crystals the effect of different ions on crack healing has also been investigated by decreasing the load on the crack for durations up to 30 min and allowing it to relax and close all solutions were saturated with caco3 the crack velocities reached during the experiments are in the range 10 9 10 2 m s and cover the range of subcritical to close to dynamic rupture propagation velocities results show that for calcite saturated solutions the energy necessary to fracture calcite is independent of ph as a consequence the effects of fluid salinity measured through its ionic strength or the variation of water activity have stronger effects on subcritical crack propagation in calcite than ph consequently when considering the geological sequestration of co2 into carbonate reservoirs the decrease of ph within the range of 5 7 5 due to co2 dissolution into water should not significantly alter the rate of fracturing of calcite increase in salinity caused by drying may lead to further reduction in cracking and consequently a decrease in brittle creep the healing of cracks is found to vary with the specific ions present

quantifying the partition between seismic and aseismic deformation along creeping and locked sections of the north anatolian fault turkey shallow aseismic creep is a key deformation component along plate boundaries that contributes to the energy budget during the seismic cycle several major active continental faults show spatial alternation of creeping and locked sections the present study focuses on the evaluation of the aseismic part of the total displacement along the north anatolian fault in turkey detailed microstructural analyses of finite strain were performed using various methods based on change of length or angle on six representative samples collected over 32 outcrops along locked and creeping sections of the fault chemical analyses were used to map mineral composition of fault rocks and to calculate relative volume changes associated with creep the relationship between finite strain and volume change allowed quantifying the evolution of the penetrative pressure solution cleavage mechanism of creep in volcanic and analogous creeping rocks finite strain measurements revealed two spatial scales of strain that correspond to the alternation of two types of shear zones with cleavages either oblique or sub parallel to the fault displacement using geodetic and geologic data cumulative aseismic displacement was calculated in the range 9 49 of the total 80 km displacement in the creping sections and was negligible in locked sections the large uncertainty in the kilometer width creeping sections was related to the difficulty of quantifying the high strain values associated with high shear displacement and for which measurement uncertainties are large a promising way to improve such quantification would be to develop reliable statistical analysis of cleavage orientation in the field

estuaries of the past and present a biofacies perspective abstract estuaries are complex sedimentary and ecological systems where controlling factors are variable largely depending on wave vs tidal dominance and fluvial processes paleoenvironmental reconstruction of their ancient counterparts in the form of coastal valley deposits in the subsurface or outcrop requires a multidisciplinary approach microfossils can play an integral part in identifying estuarine subenvironments foraminifera can be abundant in modern estuaries and resemble characteristics of brackish ichnofaunal communities in featuring low species diversity but high abundances of opportunistic species different feeding strategies and common infaunal species whereas sediment distribution is highly controlled by energy regimes foraminifera seem to respond to salinities and tidal exposure whereas individual taxa can widely range bathymetrically the combination of certain taxa becomes diagnostic for estuarine environments fossil marginal marine assemblages are dominated by agglutinated species due to taphonomic loss of the calcareous component that is often dominant in modern estuaries when comparisons between fossil and modern assemblages are undertaken it is advisable to compare with recent subsurface or remnant assemblages for a more accurate basis of paleoenvironmental interpretation more integrated research with detailed taphonomic observations is needed on ancient coastal valley deposits to find the paleoecological requirements of extinct taxa and their link to sedimentary facies and ichnofacies

cross strata and bedforms of probable transitional dune to upper stage plane bed origin from a late precambrian fluvial sandstone northern norway a late precambrian fluvial sandstone sequence in northern norway is dominated by large scale cross sets that show either lenticular or tabular geometries in the streamwise sections the lenticular sets interdigitate and in places show nearly symmetrical formsets the tabular sets are in places solitary but are mainly grouped in cosets in both cross set types the cross strata range from concave up to sigmoidal in shape with the latter variety comprising subhorizontal to gently inclined topset strata with parting lineation that merge uninterruptedly downflow into the steeper 10 2 foresets within the cross sets the geometry and dip azimuths of the foresets are conspicuously consistent although the concave up and sigmoidal strata commonly alternate downcurrent the cross strata characteristics suggest flood stage deposition from relatively high velocity steady currents heavily laden with suspended sand both cross set types are interpreted as representing bedforms generated by flow in the dune to upper stage plane bed transition the lenticular cross sets probably represent periodic dunes but it is far less clear whether the long bedforms represented by the tabular sets should be classified as dunes or rather as solitary to quasi periodic bars

sequence stratigraphic analysis and paleogeographic interpretation of the buntsandstein and muschelkalk facies permo triassic in the se iberian range e spain abstract the iberian ranges is an alpine structure trending nw se in central spain they first appeared as small intracratonic basins in the early permian and experienced different periods of extensional tectonics during the mesozoic and cenozoic controlled by ancient hercynian or older fracture systems and at least two periods of compressive inversion tectonics the permian and triassic of the se iberian ranges are of germanic type within the prevailing buntsandstein and muschelkalk facies eight formations are recognized pollen and spore assemblages and some ammonoid horizons allow for age assessments ranging from thuringian late permian to carnian late triassic two phases of sedimentation can be distinguished during the early extensional period the first phase rift phase led to the development of the lower buntsandstein facies bounded by two angular unconformities and subdivided into two depositional sequences ds 1 and ds 2 the lower one is dominated by alluvial fans deposited in half grabens and the upper one by sandy braided rivers in more symmetrical grabens the second phase thermal or flexural subsidence phase led to the deposition of the uppermost buntsanstein rot and muschelkalk facies mostly shallow marine carbonates subdivided into two depositional sequences ds 3 and ds 4 with well developed lowstand transgressive and highstand systems tracts lst tst and hst intervals the criteria for separating systems tracts and the interplay of tectonics eustatism and rate of sedimentation are discussed ds 3 and ds 4 broadly correspond to 2 1 and 2 2 third order cycles but their limits are about 3 4 m y younger this may be explained by local tectonic factors

structure of some lower old red sandstone conglomerates kincardineshire scotland deposition from late orogenic antecedent streams a thick succession of early lower old red sandstone ors conglomerates and subordinate sandstones are preserved in a small fault bounded basin in the ne midland valley of scotland the conglomerates associated with the northern margin of this basin are distinguished by a complex provenance which involved both reworking of existing gravels and addition of contemporary volcanic and plutonic detritus this may explain their characteristic bimodal texture deposition was in large probably permanent low sinuosity channels with evidence for both periods of uniform high stage flow and repeated flow stage fluctuations variable palaeoflows in the basal part of the succession suggest deposition on wet type alluvial fans supplied by feeder channels with a high sediment and water discharge the thickness of the succession the poorly developed cyclothems despite active syndepositional faulting evidence for rapid aggradation and the inferred scale of channel bars and coarsening upward units produced by bar migration suggest the basin may have been externally drained transverse antecedent streams are invoked to account for the structure of alluvium during the early devonian central scotland lay close to the boundary between regions suffering scandian orthogonal shortening and acadian strike slip shear the tectonic controls which governed the preservation of early lower ors sediments may have been largely uncoupled from those determining the supply and dispersal of the sediment

reconciling the roles of tectonism and climate in quaternary alluvial fan evolution tectonism and climate are the primary variables considered in conceptual models of alluvial fan evolution and basin fill architecture yet their roles and relative importance are far from resolved the madison range and madison river valley southwestern montana were affected during late quaternary time by varying degrees of tectonic activity as well as by climate change through multiple glaciations we are thus able to evaluate the impact of tectonism and climate on fan evolution two primary fan deposits were correlated along the range front they were deposited as proglacial outwash fans during glacial periods of increased sediment and water discharge during the present interglacial period these deposits were entrenched and secondary fans formed on lower fan areas temporal and stratigraphic relations indicate that climate was largely responsible for driving both fan aggradation and entrenchment in contrast stratigraphic relations between fan deposits and surface faults do not support a direct relation either spatial or temporal between local faulting and fan deposition because tectonism produces and maintains the relief necessary for fans to form its primary role is long term controlling the duration over which fan deposition may occur along a mountain front if quaternary alluvial fan evolution is representative of ancient alluvial fan evolution this study has important implications for interpreting primary controls on deposition of the ancient alluvial fan sequences

structural evolution of lake malaŵi africa over 2 000 km of seismic reflection profiles have been collected in lake mala i nyasa the southernmost of the east african rift lakes these studies reported here reveal a severely faulted lake floor bounded by rift structures of pliocene or greater age faults that penetrate the uppermost sedimentary units and numerous earthquakes1 attest to continuing activity in the rift inter basinal differences in fault spacing orientation and sedimentary thicknesses have led to a subdivision of lake mala i into four discrete structural provinces these provinces only now are linked by faults attributed to the most recent episodes of extension an evolutionary sequence of 1 initial block faulting and subsidence 2 fragmentation of fault blocks 3 uplift and 4 renewed subsidence and rotation of fault blocks is proposed for the central part of the mala i rift

the implications of fault zone transformation on aseismic creep example of the north anatolian fault turkey aseismic creep is observed at surface along several segments of the north anatolian right lateral active fault in turkey a major plate boundary between eurasia and anatolia identifying the mechanisms that control creep and their temporal and spatial change represents a major challenge for predicting the mechanical evolution of active faults the interplay between creep and earthquakes and the link between short term observations from geodesy and the long term fault zone evolution we combine geological observations laboratory analyses and imaging techniques shedding new light on the mechanism of fault creep along the north anatolian fault naf and its time dependent change a clear correlation is shown between shallow creep and near surface fault gouge composition locked segments of the naf are mostly composed of massive limestones without clay gouges whereas creeping segments comprise clay gouges that contain low friction minerals such fault gouges appear to result from a progressive change of initial volcanic host rocks during their deformation anastomosing cleavage develops during the first stage of displacement leading to layering oblique at first and then subparallel to the fault which accommodates part of the aseismic creep by pressure solution soluble minerals are dissolved leading to passive concentration of phyllosilicates in the gouges where alteration transformations by fluid flow produce low friction minerals at the same time damage zones are fractured and fractures are sealed by carbonates as a result these mineralogical and structural transformations weaken the gouge and strengthen the damage zone leading to the change from diffuse to localized seismic aseismic zones

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

lithostratigraphic and tectonic framework of jurassic and cretaceous intermontane sedimentary basins of south central british columbia1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia the south central intermontane belt of british columbia has a complex architecture comprising late paleozoic to mesozoic volcanic and plutonic arc magmatic suites marine and nonmarine clastic basins high grade metamorphic complexes and accretionary rocks jurassic and cretaceous clastic basins within this framework contain stratigraphy with hydrocarbon potential the geology is complicated by cretaceous to eocene deformation dismemberment and dislocation the eocene to neogene history of the southern intermontane belt is dominated by non arc volcanism followed by pleistocene to recent glaciation the volcanic and glacial cover makes this a difficult region to explore for resources much recent work has involved re evaluating the challenges that the overlying volcanic cover has historically presented to geophysical imaging of the sedimentary rocks in this region in light of technological advances in geophysical data collection and analysis this paper summarizes the lithological and stratigraphic fra

origin of the permian triassic iberian basin central eastern spain abstract the iberian basin was an intracratonic rift basin in central eastern spain developed since early permian times the basin boundary faults were normal listric faults controlling an asymmetric extension propagating northeast with time hercynian or older lineaments controlled the orientation of the iberian basin and extension was accommodated basically in the hanging wall block by the formation of secondary grabens and a central high the basin was related with the coeval ebro catalan and cuenca mancha basins and their connections are discussed subsidence curves show that the early permian early jurassic period of extension can be subdivided into three rifting episodes and a flexural one extension factor increases from 1 17 in the northwest to 1 29 near the mediterranean coast the increasing extension rate was accommodated by transfer faults trending nne ssw more important in the levante area the rift evolution is intermittent and seems to reflect distinct stress fields the collapse of the late hercynian orogen and related increased heat flux extension and rifting is the most probable origin of the iberian basin and related basins the origin of the catalan and the valencia prebetic basins is related to the southwards migration of the hesse burgundy rift along the eastern margin of the iberian microplate

dramatic effects of stress on metamorphic reactions thermodynamic calculations predict mineralogy from temperature and pressure and vice versa such calculations assume that stress is isotropic despite the fact that differential stresses prevail in earth resulting from large scale tectonics and or differences between fluid and rock pressures in porous rocks new calculations show that differential stress can have significant effects on thresholds for metamorphic reactions depending on the grain scale reaction pathways a differential stress may depending on the reaction pathway have an effect equivalent to a pressure difference on the order of assemblage volume reaction volume change differential stress the multiplying factor is typically 10 or more for example the onset of a garnet clinopyroxene breakdown reaction may be offset up or down by the equivalent of 500 mpa in pressure for a 50 mpa differential stress the effect is equivalent to a temperature difference on the order of assemblage volume reaction entropy change differential stress for example the onset of muscovite quartz breakdown may be offset up or down by the equivalent of 130 c for a 50 mpa differential stress much of earth is under differential stress so the new calculations invite a reappraisal of metamorphic mineralogy and microstructure indicating that new insights into stresses and fluid pressures on earth can be gained

the upper permian boniches conglomerates formation evolution from alluvial fan to fluvial system environments and accompanying tectonic and climatic controls in the southeast iberian ranges central spain the boniches conglomerates fm upper permian represents the first episode of sedimentation in the southeast border margin of the iberian basin central spain the iberian basin commenced development as a rift basin running mainly nw se during the early permian and underwent its first general extensional period during the late permian the boniches fm was deposited as a small segment less than 100 km long and 9 10 km wide of the iberian basin that extended in a northeast direction during this period detailed mapping and palaeocurrent analysis have shown that the boniches fm is of a curvilinear wedge shaped morphology sediments close to the southwest main faulted border are of a maximum thickness of 230 m clear lateral variation in thickness controlled by the activity of secondary transfer faults perpendicular to the main nw se axis may be observed this network of faults permitted the formation of blocks limited laterally by the transfer faults these blocks experienced subsidence and rotation against the elevated southwest footwall block which resulted in the isolation of reduced sub basins with different sedimentary characteristics based on facies and facies association the boniches fm is thought to have evolved vertically from two main alluvial fan systems in the lowest part of the formation into fluvial braided systems flowing southeast as expected no flow orientations towards the footwall block are observed during the first episodes of the refill this may be explained by erosion or simply a lack of sedimentation due to the gentle slope the change from alluvial fan to fluvial environments is interpreted as a relatively sudden tectonic reorganization of the whole segment favouring new longitudinal fluvial drainage from a transfer zone located to the northwest three different reorganization episodes clearly marked in the boniches fm as main boundary surfaces mbs separate four members subdivided into 4 5 levels 34 m thick each level consists of fining upward successions less than 1 m thick tectonics and climatic factors clearly controlled sedimentation tectonic activity was probably of greatest importance and was conditioned by the movement of the main nw se and ne sw transfer faults the role of climate in ancient conglomerate sediments has not been well established palaeogeographical mineralogical sedimentological and clast analyses suggest that the boniches fm was deposited under humid conditions by running water the differentiation between proper alluvial fans and fluvial environments during the transition period of the boniches fro is not clear since in many recent alluvial fans braided fluvial systems are associated with fans

natural dissolution of modern shallow water benthic foraminifera taphonomic effects on the palaeoecological record comparison of the living and dead assemblages of benthic foraminifera from the coastal areas of the skagerrak kattegat reveals that although there are considerable similarities in terms of the presence absence of species there are major differences in relative abundance at species level furthermore the relative abundance of calcareous tests in the living assemblages is considerably higher than that of the dead assemblages average values of 67 and 30 respectively since the environments are microtidal there is little transport of foraminiferal tests due to tidal currents so there are no introduced exotic species although there is local transport caused by waves and wave induced currents however the major taphonomic process appears to be dissolution of calcareous tests this is manifested through etching and breakage of test walls leading to complete decalcification which leaves a residue of organic linings of certain taxa e g ammonia beccarii and a marked increase in abundance of agglutinated tests in the dead assemblages although dissolution is normal in marsh settings throughout the world the skagerrak kattegat area is unusual in the intensity of dissolution in the subtidal zone whereas most of the calcareous species occur throughout the investigated depth range except marsh two of the subtidal agglutinate species eggerelloides scaberand ammotium cassis show upper depth limits consequently the agglutinated foraminifera are better indicators than calcareous foraminifera of upper depth limits in these shallow subtidal environments 1999 elsevier science b v all rights reserved

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

tectonic and climatic control of triassic sedimentation in the beryl basin northern north sea the beryl basin embayment occupies a central position along the viking graben of the northern north sea and has been a hydrocarbon play since the early 1970s detailed analysis reveals a complex half graben that was established during a rift phase of development that occurred in the early triassic teist formation after which a long period of thermal subsidence lomvi and lunde formations provided accommodation for in excess of 1000 m of sediment the teist formation sediments are complex they include shales sands and conglomerates and their superimposition on zechstein salts is indicative of both uplift and the development of a moderate relief they give way to the comparatively clean and occasionally pebbly sands of the lomvi formation for which an analysis of both bedding and texture suggests deposition by a westerly directed river system draining the hanging wall ramp the lunde formation records the spreading influence of a bajada playa complex and its eventual conversion to a more persistent lake the growing importance and eventual dominance of the succession by lacustrine sediments gives clear indication of a change in climate and this has been attributed to the rapid northward drift of pangea during the triassic period

strain localisation in bimineralic rocks experimental deformation of synthetic calcite anhydrite aggregates abstract deformation of synthetic calcite anhydrite aggregates to large shear strains up to 12 4 at 600 c 300 mpa confining pressure and a constant angular displacement rate corresponding to a shear strain rate of 10 3 s 1 resulted in the first experimental observation of strain localisation from initially homogeneous rocks in contrast to experiments on pure calcite and anhydrite which deformed homogeneously to large strains 5 all experiments on calcite anhydrite mixtures resulted in heterogeneous deformation at 1 and the formation of narrow localised bands in the microstructures at 4 in these bands the amount of strain is at least twice as large as in the rest of the sample and individual grains of the same phase cluster and align thereby forming microstructural layering similar to planar fabrics in natural mylonites a switch in deformation mechanism in anhydrite from dislocation creep to diffusion creep and or grain boundary sliding occurs simultaneously with strain localisation it is concluded that deformation induced heterogeneous phase distributions cause local strength differences initiating strain localisation in the calcite anhydrite mixtures the study suggests that the presence of two phases in combination with a change in deformation mechanism may be responsible for strain localisation in natural poly mineralic mylonites

triassic sediments of the inner moray firth scotland early rift deposits patterns of triassic sedimentation in the inner moray firth are examined in the light of a new model of continental rift sedimentation that has been developed in the tertiary to recent rifts of east africa the major tectonic control during the trias was the great glen fault to the northwest which can be shown to have been moving in dip slip fashion at this time the structure of the firth appears to have resembled the simple half graben that makes up the great east african rift system deposits both thicken and get finer towards the fault sediments found in off shore wells are dominated by laminated fine sand and silty clay with sporadic evaporites similar sequences are characteristic of or associated with ephemeral lakes in modern semi arid continental rift settings no alluvial fans have been detected close to the faulted margin again this is consistent with general patterns of sedimentation against boundary faults in the kenyan rift the coarsest sedimentary sequences in the moray firth are on the unfaulted margin to the south around burghead they consist of fluviatile lake shore and aeolian deposits the fluvial sediments show evidence of tectonically induced cycles of sedimentation which are interpreted in terms of waves of detritus working down the drainage system beds dominated by pebbly horizontal laminae and reminiscent of steep straight and shallow ephemeral streams alternate with troughed sands of deeper more sinuous but equally ephemeral rivers these are the coarsest sediments of the unfaulted margin of the basin however the lack of thick conglomerate sheets which are a feature of east african sequences at equivalent positions within the rift basin suggests only small scale fault activity and a relatively subdued topography during triassic times this is supported by evidence of extensive calichification during the rhaetic which produced a top trias marker horizon found throughout the inner moray firth

structures and textures in triassic braided stream conglomerates bunter pebble beds in the sherwood sandstone group north staffordshire england in the northern parts of the needwood and stafford eccleshall basins england the pebble beds of the sherwood sandstone group contain thick successions of texturally mature fluvial pebble cobble conglomerates which are organized into either horizontal or cross stratified sets the horizontally lying sets generally coarser grained and more poorly sorted than the cross bedded sets are usually disorganized and either matrix or clast supported although thin lenses of well sorted occasionally openwork units interpreted as falling stage phenomena are often present the cross stratified conglomerates have foresets exhibiting remarkable textural organization with a coarse bimodal sometimes matrix supported part grading upwards or being abruptly overlain by a finer well sorted occasionally openwork part and finally capped by sandstone these rhythmic textural changes are attributed partly to an avalanche process at high stage and partly to falling stage conditions the most common types of vertical association are thick successions of horizontally bedded conglomerates up to 20 m and sequences of an upwards coarsening nature 2 12 m in which cross stratified sets are overlain by flat lying sets the environment of deposition of the gravels is interpreted as one in which water depths at high stage were greater than depths in most modern braided stream plains proglacial or alluvial fan but shallower than depths associated with the pleistocene catastrophic floods from which texturally mature giant gravel bars have been recorded recent braided streams with relatively confined channels and considerable bar channel relief are better analogues in particular medial or mid channel bars with a two tier structure subaqueous and partly emergent portions may explain the upward coarsening sequences in which horizontally lying conglomerates overlie cross stratified conglomerates the thicker sequences of horizontally stratified conglomerates represent proximal longitudinal bar deposits sheets of pebbly sandstone and argillaceous sandstone lying between the conglomerates and commonly occurring towards the top of the succession largely represent deposition from sandwaves and dunes finer interbedded argillaceous sandstones siltstones and mudstones are interpreted as overbank and waning flood deposits basin forming tectonism of increasing intensity probably caused the initial coarsening upwards of the lower part of the succession whilst more stable tectonic conditions and decreasing relief on the margins of the basins and in the areas of provenance in the midlands and the hercynides account for the upwards fining of the upper part of the succession

generation of evenly spaced pressure solution seams during late diagenesis a kinetic theory stylolites and pressure solution seams can form during diagenesis of rocks subjected to stress through a feedback involving texture and pore fluid solute concentration this feedback destabilizes the state of uniform texture represented here only by porosity for simplicity a mathematical kinetic model that includes pressure solution diffusion and reprecipitation predicts the spontaneous generation even in initially uniform rocks of regions alternatingly in space more and less soluble a region that becomes more soluble also becomes simultaneously more porous the kinetic theory predicts that stylolites can form at roughly constant spacings this agrees with many field and petrographic observations bedding planes between beds that have initially different texture are shown by the theory to be the focus of a porosity instability that can lead to the formation of a stylolite and to the generation of more stylolites within each bed this prediction agrees with the observation that many stylolites have developed at bedding planes

experimental evidence for rock layering development by pressure solution natural deformation of rocks is commonly associated with development of mineralogical layering leading to irreversible transformations of their microstructure the mechanisms of such chemical differentiation processes during diagenesis tectonics metamorphism or fault differentiation remain poorly understood as they are difficult to reproduce experimentally due to the very slow kinetics involved this paper shows that development of differentiated layering similar to that observed in natural deformation is stress driven and can be obtained from indenter experiments samples of 1 gypsum plaster mixed with clay and 2 natural diatomite loosely interbedded with volcanic ash saturated with aqueous solutions in equilibrium were subjected to loading for several months at 40 c and 150 c respectively x ray microtomography and scanning electron microscopy observations show that layering develops by a self organized pressure solution process stress driven dissolution of the soluble minerals either gypsum or silica is initiated in the areas initially richer in insoluble species clay or volcanic ash as diffusive mass transfer along the interface between soluble and insoluble minerals is much faster than along the healed boundaries of the soluble minerals the passive concentration of the insoluble minerals amplifies the dissolution along layers oriented perpendicularly to the maximum compressive stress conversely in areas with an initial low content of insoluble minerals and clustered soluble minerals dissolution is slower consequently these areas are less deformed they host the re deposition of the soluble species and act as rigid objects that concentrate both stress and dissolution near their boundaries thus amplifying the differentiation and the development of layered microstructures

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

reply to the comment on first records of syn diagenetic non tectonic folding in quaternary thermogene travertines caused by hydrothermal incremental veining by billi et alii abstract in our previous paper billi et al 2017 using field geological observations u th dating and stable isotope analyses we studied two deposits of pleistocene thermogene travertines from tuscany in central italy we concluded our study 1 warning that the common stratigraphic concept of travertine being a sedimentary succession with age younging from bottom to top is not always correct 2 demonstrating that caco3 mineralization and veins can develop within the travertines after their formation with this syn diagenetic process being able to modify the continuous bottom up age evolution and 3 showing that this post depositional mineralization veining process can not only modify the temporal succession but also deform and change the initial depositional travertine structure and its petrophysical properties these conclusions could potentially make the interpretation of a travertine series more difficult than commonly thought alcicek et alii questioned our conclusions claiming that the travertine structures that we observed in tuscany and interpreted as post depositional features should have been interpreted in analogy to similar structures from travertines elsewhere as primary structures although we recognize as already thoroughly stated in billi et al 2017 that the travertine depositional post depositional processes generally require further studies we reaffirm the validity of our original interpretation at least for the structures analyzed in our previous paper we therefore counter all criticisms by alcicek et alii and conclude by indicating the way forward to further explore the depositional and post depositional processes of thermogene travertines

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

sedimentary processes vertical stratification sequences and geomorphology of the roaring river alluvial fan rocky mountain national park colorado abstract the roaring river alluvial fan formed on 15 july 1982 in rocky mountain national park colorado by a catastrophic flood that was generated by a dam failure the fan covers an area of 0 25 square km has a radial length of 0 7 km and is up to 14 m thick sedimentation occurred in three phases each producing a distinct fan lobe initial sedimentation was by a noncohesive sediment gravity flow which deposited two levees on the proximal boundaries of lobe i the levees consist of a poorly sorted mixture of logs sand pebbles cobbles and boulders the first two lobes were built primarily by sheetflooding which deposited imbricated boulders in trains behind obstacles that formed as jams between boulders or logs and upright trees horizontally laminated granule and sand sedimentation took place down fan from the boulders due to deceleration of the expanding sheetflood thin to medium interbedded sand and cobble pebble gravel couplets were deposited by sheetflooding on the third lobe gravel was transported as bedload by supercritical flow and deposited locally where antidunes broke sand was transported as suspended load and deposited where flood velocity locally decreased due to destruction of antidunes increased roughness or flow separation around the low amplitude gravel bed forms the flood rechannelized at the distal end of lobe iii due to constriction between the fan and the valley margin deposits in the upper rechannelized reaches consist of crudely bedded cobble and pebble gravel and interstratified pebble gravel and backset bedded sand deposition was by supercritical flow in the lower reaches planar cross bedded sandy pebble gravel and climbing ripple horizontal trough cross bedded and backset bedded sand were deposited by supercritical and subcritical flow the flood deposit was modified during waning flood stage and during the three years following the flood by noncatastrophic discharge events these events formed braided distributary channels by erosion into the top of the sheet flood deposits fan building took place mostly by catastrophic unconfined discharge whereas much of the present fan surface consists of braided channels that formed by erosion into the sheetflood deposits by noncatastrophic discharge

paleoenvironmental and chronological constraints on the mount tatlow succession british columbia first recognition of radiolarian and foraminiferal faunas in the intermontane cretaceous back arc basins of western canada1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia 2geological survey of canada contribution 20100279 the cretaceous succession at mount tatlow british columbia is a cornerstone of cordilleran stratigraphy preserving a mostly continuous record of upper lower cretaceous to lower upper cretaceous sedimentary strata the succession is capped by volcanic strata of the powell creek formation lithofacies assemblages within the mount tatlow succession reflect sedimentation in a deep water submarine fan system at the base of the section to overlying submarine fan and to pro deltaic deposition and finally to delta plain sedimentation at the top of the succession radiolarian and foraminifer fossils from the lower part of the mount tatlow section are the first recovered from the intermontane basins of british columbia and indicate a middle albian to cenomanian age most likely cenomanian the presence of these fossils indicates that open marine conditions existed locally in the basin at this time but the strongly altered and pyritized nature of the fauna suggests that a reducing environment fostered early diagenetic pyritization processes in the subsurface sediments detrital zircon populations collected from the succession are in agreement with the paleontological ages

cretaceous sedimentation and tectonics tyaughton methow basin southwestern british columbia the mesozoic tyaughton methow basin straddles the fraser yalakom pasayten straight creek fypsc strike slip fault zone between six tectono stratigraphic terranes in southwestern british columbia data from hauterivian cenomanian basin fill provide constraints for reconstruction of fault displacement and paleogeography the early cretaceous eastern margin of the basin was a region of uplifted jurassic plutons and active intermediate volcanism detritus shed southwestward from that margin was deposited as the marine jackass mountain group albian inner to mid fan facies of the jackass mountain group can be correlated across the yalakom fault suggesting 150 25 km of post albian dextral offset deposits of the jackass mountain group overlap the major strike slip zone fypsc if that zone represents the eastern boundary of the tectono stratigraphic terrane wrangellia then accretion of wrangellia to terranes to the east occurred before late early cretaceous time the western margin of the basin first b

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

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