geochemistry and sedimentology of the lower silurian longmaxi mudstone in southwestern china implications for depositional controls on organic matter accumulation abstract spatial and temporal changes of lithofacies and abundance of organic matter in mudstones control distribution of prospective unconventional petroleum reservoirs in a sedimentary basin lithofacies characterization is an essential prerequisite to understanding of organic matter accumulation depositional processes and water column chemistry this research combines geochemical analyses and detailed sedimentologic observations in order to investigate the depositional controls on organic matter abundance in the prolific black mudstone of the long 1 member of the lower silurian longmaxi formation in southwestern china six primary lithofacies deposited at variable marine water depths and under differing water column chemistry were identified from an 83 m long core based on microscopic observations of sediment texture and structure and biota and analyses of total organic carbon toc content mineralogy and trace element abundances our results show that toc content is well correlated to biogenic quartz content and the non detrital components of v u mo ni and cu suggesting the accumulation of organic matter in the studied mudstone was controlled by high paleoproductivity and anoxic water conditions the good correlations also suggest that the abundant organic matter was produced by algal blooms which are typically associated with radiolarian thrive because of the symbiotic relationship between algal and radiolarian the low mo toc ratios of the three lithofacies formed in deep anoxic environments were similar to the ratios of modern sediments deposited in anoxic euxinic environments suggesting moderate basin restriction during deposition the mudstone in the lower longmaxi formation may be part of the globally abundant organic rich mudstones of early silurian age whose depositional mechanism have yet to be fully explored the distribution of lithofacies in the studied interval shows an overall trend from deep water to shallow water depositional environments we developed a detailed depositional model to interpret the evolution of depositional environments of the lower longmaxi formation this study provides an example to how better characterize unconventional hydrocarbon systems through coupling of rigorous geochemical and sedimentological analysis

deposits from wave influenced turbidity currents pennsylvanian minturn formation colorado u s a turbidity currents generated nearshore have been suggested to be the source of some sandy marine event beds but in most cases the evidence is circumstantial such flows must commonly travel through a field of oscillatory flow caused by wind generated waves little is known however about the interactions between waves and turbidity currents we explore these interactions through detailed process oriented sedimentological analysis of sandstone event beds from the pennsylvanian minturn formation in north central colorado u s a the minturn formation exhibits a complex stratigraphic architecture of fan delta deposits that developed in association with high topographic relief in a tectonically active setting an 20 35 m thick unconformity bounded unit of prodelta deposits consists of dark green shale and turbidite like sandstone beds with tool marks produced by abundant plant debris some of the sandstone event beds most abundant at distal localities contain reverse to normal grading and sequences of sedimentary structures that indicate deposition from waxing to waning flows in contrast proximal deposits in some cases less than a kilometer away contain abundant beds with evidence for deposition by wave dominated combined flows including large scale hummocky cross stratification we interpret the majority of these event beds as a record of deposition from hyperpycnal flows i e turbidity currents generated directly from highly concentrated river plumes which accelerated and decelerated in response to a rising and falling flood discharge additional support for this interpretation includes the following 1 a variety of sole marks including flute and gutter casts as well as tool marks made by relatively large up to tens of centimeters across woody debris i e groove prod and chevron marks 2 consistent unimodal orientation of sole marks and abundant ripple cross stratification which indicate strong downslope directed flow 3 a well documented sedimentological framework for the formation of fan delta deposits adjacent to nearby highlands and 4 plant fossils typical of middle to high elevation habitats that are abundant in the turbidite beds but absent in underlying and overlying shoreline and marginal marine deposits which have a separate floral assemblage differences in grain sizes vertical stratification sequences and bed thicknesses between outcrops are interpreted to result from the spatial distribution of wave effects the time history of hyperpycnal flows and the interaction of these processes the latter varied both spatially and temporally and produced a wide range of bed types which are incorporated into a new conceptual model for storm influenced hyperpycnal flows

late ordovician shallow marine environments due to glacio eustatic regression scrach formation mid wales an ashgill to llandovery offshore marine sequence in mid wales is punctuated by a shallow marine sequence the scrach formation attributed to late ordovician glacio eustatic regression the base of the regressive sequence is gradational and suggests progressive fall in sealevel during mid hirnantian late ashgill time an abrupt top to the scrach formation marks a rapid sealevel rise probably within the persculptus zone late hirnantian interbedded lenticular thin sands and muds dominate the scrach formation and represent shallow shelf environments with evidence of nw directed tidal ebb flow and storm currents sporadic medium bedded sand sheets represent the strom events locally lenticular thick bedded sand units embedded in the fine facies probably represent barrier facies in an area of high clastic input the scrach formation thins se into the present ne striking myddfai steep belt this is underlain by ne striking faults that actively controlled late ordovician to early silurian sedimentation the faults probably defined an emergent but low relief coast during the glacial regression offshore to the nw the scrach passed into parallel laminated mudstones then across a fault influenced slope the present tywi lineament into coarse clastic sediments deposited by gravity flows

sedimentary dynamics of the kimmeridge clay tempests and earthquakes storms are suggested to be an important influence upon the formation of epicontinental black shales controlling both their distribution and facies types a variety of storm produced event beds are described from the kimmeridge clay of dorset these include horizons of graded rip up clasts silt laminae thin graded mud horizons and shell pavements biostratinomy and population dynamics indicate that the pavements represent brief benthic colonization events in a predominantly anaerobic dysaerobic environment differential near surface lithification has also affected the sediments leading to the formation of flow phenomena these include loop structures microfolding and brecciation earthquake induced fissuring also occurs at a number of horizons the kimmeridge clay shows well developed cyclically alternating organic rich shales and mudstones on a decimetre scale a feedback mechanism of storm induced benthic oxygenation and temperature stratified inhibition of storm mixing may account for the abrupt nature of the cyclicity subsidence and sedimentation rate were probably important factors controlling the thickness and organic richness of the sediments whilst the influence of storms was important in controlling the distribution and facies types of these important source rocks the model proposed for the kimmeridge clay may be of general application to many epicontinental black shales in the geological record

organic matter rich shales of china abstract organic matter rich shales are the main target rocks for unconventional oil and gas exploration and development across the world in china shale gas geological resources are estimated as approximately 110 1012 m3 with recoverable gas reserves of ca 20 1012 m3 recoverable shale oil reserves are estimated as ca 5 109 t a total 35 important organic matter rich shale units have been recognized from mesoproterozoic to cenozoic strata across the entire china these shales are categorized according to their origin under marine marine nonmarine transitional and lacustrine conditions shales of marine origin with ca 9 1012 m3 recoverable resources dominate china s potential in terms of total volume of organic carbon currently the most favorable marine shales for oil and gas exploration are found in the sichuan basin within the lower cambrian qiongzhusi formation and in the wufeng longmaxi formations of uppermost ordovician through lower silurian a fortuitous combination of of sea level variations of paleo productivity of tectonic activity causing development and migration of partially closed deep basin depocenters and of sediment accumulation rates controlled the extensive deposition and distribution of organic matter rich shales in these wufeng and longmaxi formations organic matter rich shales in marine nonmarine transitional facies associated with coal measures occur in north china within the carboniferous and permian and in south china within the permian these carboniferous permian organic matter rich shales are important source rocks for the gas fields in the ordos and sichuan basins abundant organic rich shales are also widely distributed within coal bearing clastics and coal measure shales of fluvial lacustrine and swamp facies in upper triassic to middle jurassic successions of many basins lacustrine organic rich shales were deposited during the permian through neogene in various freshwater to saline lake settings lacustrine organic matter rich shales are the main oil source rocks in the songliao bohai bay ordos and junggar basins lacustrine algae contributed to the rain of organic matter and the preservation of organic matter and distribution of organic rich shale was controlled by lake currents water depth and oxygen poor conditions with enhanced preservation when buried by turbidity currents algal blooms were partly induced by trace nutrients from volcanic ash falls in all of these lacustrine basins seawater intrusion into the freshwater lake of the songliao basin promoted some episodes of black shales saline lacustrine basins such as middle permian junggar basin contain organic rich dolomite mudstone that mainly formed during hot climate conditions when the lakes had high salinity and stratified water columns that deprived the bottom waters of oxygen thereby preserving massive amounts of organic matter laminated calcite rich mudstone in the saline lacustrine settings formed in more brackish waters under stable warm conditions and weak biological activity the modeling of the factors controlling the distribution of organic matter rich shales within china s basins is important for the exploration and development of unconventional oil and gas resources

no causal link between terrestrial ecosystem change and methane release during the end triassic mass extinction profound changes in both marine and terrestrial biota during the end triassic mass extinction event and associated successive carbon cycle perturbations across the triassic jurassic boundary t j 201 3 ma have primarily been attributed to volcanic emissions from the central atlantic magmatic province and or injection of methane here we present a new extended organic carbon isotope record from a cored t j boundary succession in the danish basin dated by high resolution palynostratigraphy and supplemented by a marine faunal record correlated with reference c isotope and biotic records from the uk it provides new evidence that the major biotic changes both on land and in the oceans commenced prior to the most prominent negative c isotope excursion if massive methane release was involved it did not trigger the end triassic mass extinction instead this negative c isotope excursion is contemporaneous with the onset of floral recovery on land whereas marine ecosystems remained perturbed the decoupling between ecosystem recovery on land and in the sea is more likely explained by long term flood basalt volcanism releasing both so2 and co2 with short and long term effects respectively

finite difference calculation of traveltimes in three dimensions the traveltimes of first arriving seismic rays through most velocity structures can be computed rapidly on a three dimensional numerical grid by finite difference extrapolation head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 11 percent are found between the results of this technique and ray tracing for a complex but smooth model this scheme has proven useful for earthquake location and shows promise as an inexpensive well behaved substitute for ray tracing in forward modeling and kirchhoff inversion applications

anoxic events during sedimentation of a palaeogene diatomite in denmark a diatomite about 60 m thick of late palaeocene early eocene age crops out in northern jutland denmark the diatomite is locally termed moler frustules of marine diatoms constitute c 65 by weight of the diatomite and clay minerals chiefly montmorillonite make up the remainder slight variations in the relative supply of diatom frustules and clay minerals are preserved undisturbed in laminated diatomite while lamination is partly destroyed by burrowing organisms in weakly laminated diatomite and obliterated by total bioturbation in structureless diatomite these three facies alternate throughout the sequence the presence or absence of infaunal burrowing organisms is interpreted as a record of the content of dissolved oxygen in the water above the sediment water interface and hence of the position of the redox potential discontinuity interspaced in the diatomite are 179 identifiable layers of volcanic ash these ash layers provide a means of precise lateral correlation they show that levels of laminated diatomite may be followed throughout the basin and therefore that changes between anoxic and oxic conditions occurred simultaneously across the area the laminated diatomites may consequently be interpreted as representing short term anoxic events of which twelve have been recognized

tempestite facies models for the epicontinental triassic carbonates of the betic cordillera southern spain this study focuses on storm deposits in the muschelkalk facies of the betic cordillera southern spain and interprets their deposition mechanisms three types of storm deposit are distinguished i pot gutter casts ii tempestite beds and iii storm winnowed deposits each deposit provides information about the carbonate platform environment in which it was deposited the tempestite models proposed are i the bypass zone tempestite model occurring in a muddy ramp at the epicontinental basin margin this model is characterized by potholes and gutters that form in a shoreline bypass zone during storms ii the gradient current tempestite model in which frequent tempestite beds are related to storm gradient currents thickness and grain size decrease towards the deep distal ramp and iii the winnowed deposit tempestite model whereby storm deposits are winnowed and deposited in the same environment with only short lateral transport having occurred this model evokes more restricted and shallower conditions lagoons or inland seas the distribution of all these deposits in the stratigraphic sections studied corroborate the eustatic third order cycle identified although the different features of the storm deposits and their positions in each section indicate a subsidence varying in time and space in the transgressive stage the margins of the epicontinental basin were a well developed ramp with potholes and gutters in contrast during the high sea level stage storm deposits generated tempestite beds or storm winnowed deposits in the different areas the epicontinental carbonate platform with ramp edges evolved into a complex depositional system of coastal and shallow marine environments with lagoons and restricted inland seas thus the epicontinental platform underwent substantial change from the late anisian to the late ladinian and this is reflected in its storm deposits

p and s velocity images of the lithosphere asthenosphere system in the central andes from local source tomographic inversion summary about 50 000 p and s arrival times and 25 000 values of t recorded at seismic arrays operated in the central andes between 20 s and 25 s in the time period from 1994 to 1997 have been used for locating more than 1500 deep and crustal earthquakes and creating 3 d p s velocity and qp models the study volume in the reference model is subdivided into three domains slab continental crust and mantle wedge a starting velocity distribution in each domain is set from a priori information in the crust it is based on the controlled sources seismic studies in slab and mantle wedge it is defined using relations between p and s velocities temperature and composition given by mineral physics each iteration of tomographic inversion consists of the following steps 1 absolute location of sources in 3 d velocity model using p and s arrival times 2 double difference relocation of the sources and 3 simultaneous determination of p and s velocity anomalies p and s station corrections and source parameters by inverting one matrix velocity parameters are computed in a mesh with the density of nodes proportional to the ray density with double sided nodes at the domain boundaries the next iteration is repeated with the updated velocity model and source parameters obtained at the previous step different tests aimed at checking the reliability of the obtained velocity models are presented in addition we present the results of inversion for vp and vp vs parameters which appear to be practically equivalent to vp and vs inversion a separate inversion for qp has been performed using the ray paths and source locations in the final velocity model the resulting vp vs and qp distributions show complicated essentially 3 d structure in the lithosphere and asthenosphere p and s velocities appear to be well correlated suggesting the important role of variations of composition temperature water content and degree of partial melting

changes in the bivalve assemblage of an early jurassic mudstone sequence the fjerritslev formation in the gassum 1 well denmark abstract in the gassum 1 well cores were cut at regular intervals through the lower jurassic fjerritslev formation in which the dominant lithologies are dark grey mudstone and silt streaked mudstone bivalves are found in most samples though generally in small numbers and form the basis of a palaeoecological study the proportions of epifaunal suspension feeders infaunal suspension feeders and infaunal deposit feeders changes through the sequence independent of the lithology and a development from a normal shale facies fauna to a restricted shale facies fauna is seen gassum 1 is located centrally in the danish basin and a restricted shale facies fauna is encountered here in the lower pliensbachian while contemporaneous comparable lithologies from more marginal localities have normal shale facies faunas the recorded change in the fauna composition in gassum 1 is therefore related to an increase in water depth the diversity of three benthic groups bivalves ostracods and foraminifera changes simultaneously through the sequence these biological changes are not reflected in the lithology which indicate some other source for the environmental change probably variations in the content of dissolved oxygen in the bottom water related to phases of increase in water depth the latter can be shown to correlate with some of the phases of eustatic rise of sea level recognized by hallam

a study of the seismogenic process beneath the south western foothills in taiwan in relation with the 2010 jiasian earthquake abstract a moderate earthquake occurred near the town of jiasian in kaohsiung county taiwan at 8 18 am local time on 4 march 2010 the epicenter was located about 60 km northeast of kaohsiung city about 70 aftershocks occurred during the same day in this study we invert a 3 d velocity structure beneath the southwestern part of taiwan furthermore we accurately determine the locations the focal mechanisms and the regional stress tensor from the inverted 3 d velocity model according to the results we can conclude 1 a low vp anomaly zone with a high vp vs ratio in the southwestern part of the research area may have been caused by the subducting oceanic lithosphere 2 a high vp anomaly zone with low vp vs ratio in the northeastern part of the research area demonstrates that there is an intervening continental sliver 3 based upon the inverted 3 d velocity model and the relocated seismicity we suppose that there might be a nw se trending blind fault which dips to the north 4 according to the results of the focal mechanisms of the jiasian earthquake sequence and the regional stress tensor inversion we can surmise that the possible blind fault may be a thrust fault with left lateral characteristic and 5 based upon the different tectonic process in this area we can conclude that the chishan transfer fault zone leads to a possible oblique slip fault locks and exhibit high seismic potential which caused the jiasian earthquake sequence

accurate fault mechanism determinations for a 1984 earthquake swarm at campi flegrei caldera italy during an unrest episode implications for volcanological research we have analyzed 42 microearthquakes 1 ml 3 that occurred at campi flegrei volcanic area during an intense swarm like activity more than 500 events in half a day in the last period of strong ground uplift 1982 1984 focal mechanisms of these earthquakes have been computed by a probability method which uses p wave polarity and s wave polarization data composite focal mechanisms for different groups of earthquakes have also been computed by the same technique results show a well defined fault plane in agreement with the elongation of the epicentral pattern the orientation and dip of this fault plane together with other observations about hypocenter locations and focal mechanisms of the whole seismicity accompanying the ground uplift episode suggest the presence of an elliptical fracture system at the caldera center this fracture system dipping toward the center of the caldera should represent the limit of the most recent caldera collapse which is also indicated by a negative bouguer gravity anomaly moreover an important differential feature among various groups of earthquakes has been shown namely a rotation up to about 30 of the strike of the compressive stress axis between the easternmost and the westernmost events the resulting pattern indicates that the axis is always oriented towards the town of pozzuoli which roughly represents the very center of the caldera and also the center of symmetry of the ground deformation these observations strongly suggest that earthquakes are generated by the variation of the stress field associated with the deformation along prefractured zones because of their greater weakeness this study provides then the first direct evidence that both seismicity and ground deformations have a common origin

facies internal structures and sequences of modern gironde derived muds on the aquitaine inner shelf france abstract seventy cores from the aquitaine continental shelf were examined using radiographic and grain size techniques in order to describe the sedimentary structures of the muddy deposits and to evaluate their depositional processes four lithofacies are identified in this fine grained deposit a homogeneous silty sand b interbedded homogeneous mud and sand c silty clayey mud and d mottled mud they show a logical pattern in relationship to the water depth and the distance from the coast primary structures are present particularly in the landward and central portion of the mud fields where the sediment is organized into sequences with a sharp based erosional contact overlain by a fining up succession centimetre to decimetre scale the beginning of each of these is characteristic of a high energy storm event which is common on this shelf the settling of suspended fine sediment corresponds to the flood estuarine discharge during quiet periods primary sedimentary structures decrease in the distal area where the muddy sediment is frequently reworked by infauna finally primary structures and their preservation depend on the relative magnitudes of surface waves storms infaunal mixing and fluvial sediment deposition rates i e floods

continental collision and basin opening in southern italy a new plate subduction in the tyrrhenian sea an analysis of the spatial distribution of the seismicity of the southern tyrrhenian sea is presented with the aim of putting constraints on the geometry of the complex benioff zone of this area by relocating the earthquakes that occurred in the period 1985 1990 the data set used in this analysis is based on information from ing isc and neis databases in order to ensure the quality of epi hypocentral locations we based our selection of earthquakes on both the available number of p and s readings at least eight p and two s pickings and the epicentral distances of the stations reporting the event 5 such a selection enabled us to obtain a catalogue of 450 well located events with focal depths of up to 500 km the seismogenetic volumes estimated from the distribution of hypocentres of the whole seismicity analysed were interpreted according to a recent geodynamic model proposed for this area this has led us to the hypothesis of an active nw se oriented subduction of the lithosphere generated and stressed by the opening of the tyrrhenian basin

glacially influenced sedimentation in the later proterozoic of the paraguay belt mato grosso brazil abstract late proterozoic probably early vendian 610 590 ma glaciogenic and turbiditic sediments and metasediments are present along the transitional zone between the amazonian craton to the northwest and the paraguay belt to the southeast in the cuiaba region mato grosso brazil a few exposures of diamictites are associated with conglomerates and graded pebbly sandstones on the cratonic fringe and pass southeastwards into fine grained sediments deposited in the deeper part of the probably marine basin in the paraguay belt these rocks have been affected by the brasiliano orogeny possibly around 570 ma they show increasing deformation and metamorphism from the craton towards the fold belt the sedimentation scheme proposed for the western border of the paraguay belt and the eastern edge of the amazonian craton involves three probably marine main depositional systems to the west on the craton the platform domain can be subdivided into a western inner shelf and an eastern outer shelf the deposits on the inner shelf subdomain show an alternation of dominant massive diamictites sandstones and fine grained sediments with few dropstones this diamictite association is tentatively interpreted as glaciomarine in origin in the outer shelf subdomain the massive diamictites are progressively replaced southeastwards by an association of massive diamictites stratified diamictites and fine grained sediments this diamictite association is interpreted as a whole as resedimented glacial debris deposited by subaqueous debris flows the slope domain located at the transition between craton and fold belt is characterized by strong reworking of the glaciomarine sediments by gravity flows responsible for a type of submarine fan deposition the coarse clastic facies which result from a reworking by rapid downslope transport of cohesive debris flows and gravity flows with high viscosity fill feeder channels in the upper fan eastward inside the belt a progressive sorting in the deeper portions of the fan is shown by the transition from diamictites massive gravels sandstone intercalations with occasional inverse and or normal grading debris flow turbidity current to normal graded finer sediments turbidity current sandstone and siltstone intercalations represent interchannel deposits formed by turbidity currents east of the slope well bedded fine grained sediments were generated by low density turbidity currents direct glacial influence is reduced to the presence of a few isolated clasts or dropstones two distinct upper proterozoic glaciogenic units are known in brazil the older and more widespread one dated at about 950 ma is located on the sao francisco craton and in the adjacent brasiliano fold belts the younger one 600 ma is restricted to the paraguay belt and the adjacent border of the amazonian craton in southern western gondwana late proterozoic glaciation is of mountain type and developed at latitudes of 60 on highs probably generated by pan african brasiliano rifting at the same time in its northern part a widespread ice sheet covered the west african craton

relationship between shallow and intermediate depth seismicity in the eastern aleutian subduction zone the transition from shallow interplate thrusting to intermediate depth seismicity is often poorly observed but critical for understanding the fate of the downgoing slab in order to better examine the transition 1448 earthquakes are relocated from data recorded by a regional seismic network in the eastern aleutian arc using an improved three dimensional velocity model and accurate ray tracing single event first motion solutions are determined from these rays for 31 slab events the interplate thrust zone is a planar fault zone dipping 10 15 at 25 35 km depth and is no more than 5 10 km wide most intermediate depth earthquakes are localized to a plane no wider than 5 km near the top of the descending plate fault plane solution orientations for these events vary by several tens of degrees in orientation although 73 show t axes aligned within 45 of the slab dip a parallel seismic zone 20 25 km deeper into the slab also shows down dip plunges of t axes for 3 of 5 solutions the fault plane solutions are poorly explained by plate bending or unbending about a neutral fiber hypocenters show that intermediate depth events are confined near the subducted oceanic crust supporting compositional rather than pure thermal control of intermediate depth seismicity one explanation is that the upper plane events are an indirect consequence of phase changes in subducted crust perhaps similar processes are important in producing earthquakes in the lower parallel zone

a new correlation of triassic jurassic boundary successions in nw europe nevada and peru and the central atlantic magmatic province a time line for the end triassic mass extinction abstract understanding the end triassic mass extinction event 201 36 ma requires a clear insight into the stratigraphy of boundary sections which allows for long distance correlations and correct distinction of the sequence of events however even after the ratification of a global stratotype section and point global correlations of tjb successions are hampered by the fact that many of the traditionally used fossil groups were severely affected by the crisis here a new correlation of key tjb successions in europe u s a and peru based on a combination of biotic palynology and ammonites geochemical 13 c org and radiometric u pb ages constraints is presented this new correlation has an impact on the causality and temporal development during the end triassic event it challenges the hitherto used standard correlation which has formed the basis for a hypothesis that the extinction was caused by more or less instantaneous release of large quantities of light carbon methane to the atmosphere with catastrophic global warming as a consequence the new correlation instead advocates a more prolonged scenario with a series of feedback mechanisms as it indicates that the bulk of the hitherto dated high titanium quartz normalized volcanism of the central atlantic magmatic province camp preceded or was contemporaneous to the onset of the mass extinction in addition the maximum phase of the mass extinction which affected both the terrestrial and marine ecosystems was associated with a major regression and repeated enhanced earthquake activity in europe a subsequent transgression resulted in the formation of hiati or condensed successions in many areas in europe later phases of volcanic activity of the camp producing low titanium quartz normalized and high iron quartz normalized basaltic rocks continued close to the first occurrence of jurassic ammonites and the defined tjb during this time the terrestrial ecosystem had begun to recover but the marine ecosystem remained disturbed

eustatically controlled sedimentation in the hettangian sinemurian early jurassic of poland and sweden in earliest jurassic times terrigenous continental and marginal marine deposition occurred in a large epeiric basin along the tornquist line in europe detailed sedimentological studies allow recognition of palaeoenvironmental fluctuations in space and time the main earliest jurassic transgressions occurred in the early hettangian early sinemurian mid sinemurian and latest sinemurian and formed bounding discontinuities transgressive surfaces of considerable correlative significance there is a step wise trend of increasing marine extension and influence during the early hettangian early sinemurian mid sinemurian and latest sinemurian earliest pliensbachian transgressions four sequences four transgressive systems tracts three highstand systems tracts and three levels regarded as equivalents of maximum flooding surfaces are distinguished in the case of type 2 sequences when incised valley fill deposits are not developed and regional erosion is less common it may be rather difficult to define the sequence boundaries which are often concealed within the amalgamated fluvial deposits occurring in the neighbouring parts of two adjacent sequences fluvial deltaic sediments terminate the highstand systems tracts and in this setting the transgressive systems tracts start with continental deposits prior to the transgressive surfaces generally an exact correlation can be achieved between the sequence stratigraphy of the northeast and northwest european lower jurassic and the eustatic curve proposed by epr assuming some changes proposed by a hallam the establishment of this correlation hopefully will stimulate future studies of the sequence stratigraphy of poorly dated siliciclastic deposits of marginal basins in this setting even minor changes in sea level may cause major changes in facies development over large areas

calculation of strong ground motion due to an extended earthquake source in a laterally varying structure abstract lateral heterogeneity of the crust combined with the complexity of an extended earthquake source may account for observations of strong ground motion not easily explained by simplified source models in a laterally homogeneous medium both the effects of an extended source and lateral heterogeneity can be examined using a forward modeling technique that combines distributed nonuniform slip on a fault plane with dynamic ray tracing in a three dimensional medium using this technique velocity seismograms are calculated at ranges less than 10 km for a finite source which occurs in a wedge shaped zone of low velocity this structure is chosen to approximate the structure of fault zones found in reflection and refraction surveys across active faults in california iterative paraxial ray tracing is used to solve the two point ray tracing problem the low velocity zone surrounding the fault causes arrivals in the laterally varying structure to be delayed and rays to leave the fault more closely to the fault normal at most locations examined the effect of the three dimensional structure on isochrone velocity is small compared to the effects on geometric spreading and radiation pattern because rays are bent substantially in the near source region the seismograms calculated for the laterally varying structure vary substantially in amplitude and polarity from seismograms calculated for the laterally homogeneous structure

significance of pot and gutter casts in a middle triassic carbonate platform betic cordillera southern spain pot casts and gutter casts are described for the first time in the lower part of the majanillos formation a middle triassic carbonate unit located in the external zones of the betic cordillera southern spain their identification as well as their relation to tempestites enables the better interpretation of the depositional environments and the shoreline to offshore facies transition on the anisian muddy carbonate ramp of the southern iberian massif the majanillos formation contains three members which become progressively more marly towards the top well preserved pot and gutter casts and thin intercalations of calcarenite which are interpreted as tempestites are abundant in the lowest member above the pot and gutter casts thicker calcarenite beds which locally contain hummocky cross stratification predominate bioturbated nodular limestones are prevalent at the top of the member the remaining succession which records a long term triassic transgressive cycle consists mostly of fine grained limestones deposited in very shallow marine environments calcarenitic sediments only accumulated within potholes and gutters in the nearshore they developed during storms when strong currents transported sediment to the outer shelf where it was deposited as tempestite beds pot and gutter casts characterize sedimentation in the bypass zone it is concluded that storm deposits provide important constraints for the interpretation of palaeobathymetry it is proposed that gutter casts display a trend of increasing width thickness ratios towards the outer shelf the identification of these structures in marine successions elsewhere should prove useful in the interpretation of depositional environments

record of continental to marine transition from the mesoproterozoic ampani basin central india an exercise of process based sedimentology in a structurally deformed basin abstract the mesoproterozoic ampani group of rocks a structurally deformed sedimentary package hosted within the bastar craton in central india was studied for process based facies and paleoenvironmental analyses outcrop mapping on 1 1500 scale deconvolution of deformation pattern and process based facies analyses have led to the identification of fifteen facies types clubbed under four facies associations a range of paleoenvironmental settings varying from continental fluvial to distal marine shelf is inferred deductive paleohydrology revealed poorly efficient dirty river character for the ampani river system with low water discharge however at times of catastrophic sheet floods release of sediments trapped at the river mouth in form of hyperpycnal underflows triggered formation of river mouth delta reworking of delta front sediment in wave dominated coastline resulted development of beach foreshore and shoreface proximal to distal variation in the relative proportion of bar and interbar products within the shoreface successions exposed at different studied sections is interpreted as signature of relative bathymetric variation the pro deltaic ampani shelf was storm infested tectonic perturbance in the basin hinterland in course of ampani sedimentation is inferred from occurrence of a disparately thick lobate high density flow deposit towards the top of shoreface succession and increase in feldspar content upward within the shoreface succession addition of detritus from a 1600 ma mesoproterozoic provenance in upper part of shoreface also strengthen the contention deconvolution of deformation pattern and delineation of environmental products ranging between continental and deep marine allowed us to infer the ampani sediment package as fining upward in character evolved in a transgressive mode

alluvial fan to storm dominated shelf transition in the mesoproterozoic singhora group chattisgarh supergroup central india abstract mesoproterozoic siliciclastic strata at the basal part of the singhora group central india provide an example of a pre vegetation alluvial fan and braid delta depositional system detailed process based facies and paleoenvironmental analysis have led to the identification of 15 facies types grouped under four different facies associations which record paleoenvironmental settings ranging between continental alluvial fan and distal marine shelf two formations investigated are the rehtikhol formation formed in a conglomeratic or coarse arenaceous alluvial fan braid plain and delta setting and the overlying saraipalli formation which preserved the sedimentation record of a storm infested inner to distal shelf setting the preponderance of granular and sandy sediment gravity flow products with subordinate rock fall deposits within the alluvial fan system together with a pervasive west northwesterly paleocurrent is suggestive of a gently sloping beveled source area in the east southeast distal to the inferred fan a braid plain system developed with the decrease in the depositional slope streams within the braid plain had widths up to several hundred meters the braid plain system at the margin of the marine basin developed a delta with the deposition of wave reworked fluvial dominated sediments the crest trends of wave generated bedforms within the inferred delta sediments depict the northeast southwest shoreline interpreted for the singhora sea the prodeltaic basinal part of the singhora braid delta was storm infested the inner shelf acted as a zone of throughput with high velocity storm flows eroding deep narrow scours gutter casts and is interpreted as a zone of bypass operation of geostrophic currents on the singhora shelf has been inferred from the directional relationship of gutters with the inferred orientation of the shoreline a proximal distal relationship has been established within the shelf products based on the relative dominance of erosional and depositional features the singhora alluvial fan and braid delta facies are arranged in a fining upward sequence denudation of the source area increasing bathymetry with relative rise in sea level or a combination of both is inferred both extrabasinal and intrabasinal forcings possibly contributed to the deepening upward trend

depositional controls on mudstone lithofacies in a basinal setting implications for the delivery of sedimentary organic matter deep water mudstones from ancient epicontinental settings are significant repositories for organic matter but the detailed temporal variations of and controls on the abundance and type of organic matter om is little studied using micro petrographic and geochemical data from late mississippian mudstones of the widmerpool gulf uk the processes that delivered fine grained sediment to this basin during a glacioeustatic sea level cycle are interpreted from detailed lithofacies analysis seven primary lithofacies are identified from core which show specific and systematic variations in total organic carbon toc content and bulk carbon isotope composition of organic material 13corg during sea level highstands thin bedded carbonate bearing mudstones are the dominant facies deposited contain up to 6 6 toc average 4 6 1 3 and have mean 13corg of 28 5 0 9 during phases of lower sea level thin bedded silt bearing clay rich mudstones with up to 4 1 toc average 2 3 0 8 mean 13corg 28 2 1 0 were interbedded with more organic lean graded silt bearing mudstones and sand bearing silt rich mudstones average toc 1 7 0 6 derived from turbidity currents the latter mean 13corg 26 2 0 7 are closely linked to significant proportions of terrestrial plant material while some rare plant debris and sand bearing mudstones produced from debris flows have more than 7 0 toc and 13corg 26 0 the 13c values of wood fragments ranged from 27 1 to 24 0 and therefore the 13corg is interpreted as a function of the ratio of marine and terrestrial organic matter more negative values in the carbonate bearing and the clay rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material the data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea level stages marine om was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial om was delivered by sediment density flows variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine om organic rich mudstones preserved in these marine basins are potential hydrocarbon source rocks especially as unconventional shale gas reservoirs detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source rock potential of basinal mudstones and of fine grained organic rich sediments in general

thin fine grained storm layers in a muddy shelf sequence an example from the lower jurassic in the stenlille 1 well denmark thin storm sand layers are a characteristic feature of many sandy shelf sequences while little evidence of storm layers is preserved in muddy shelf deposits where bioturbation is often total the present study shows that storm generated depositional processes governed sedimentation in a muddy shelf environment the studied sequence is dominated by blackish mudshale and silt streaked mudshale with thinner intervals of pale fine grained heterolithic sandstone it represents the lower jurassic fjerritslev formation in the eastern part of the danish basin and has been studied in four cores from the stenlille 1 well within the muddy outer shelf association four sedimentary facies and 14 types of laminae 0 5 10 mm thick may be distinguished most of the laminae share the characteristics of graded bedding erosive bases and occasional fading ripples with storm layers of sand grade the structures indicate that the mudshale laminae formed by settling of the suspension load carried by storm generated currents this kind of episodic deposition of fine grained storm layers may be common though rarely preserved in outer shelf environments

lower silurian distal shelf storm induced turbidites in the welsh borders sediments tool marks and trace fossils the upper llandovery hughley shales of shropshire are interpreted as storm induced distal shelf turbidites they comprise a sequence of calcareous sandstones interbedded with purple mudstones the trace fossils body fossils and palaeogeography indicate a deep shelf position for their deposition the thin sandstone units are interpreted as having been deposited from density current bedload and suspension storm surge ebb traction currents arising from intermittent major offshore storms are considered to have initiated the density currents a deepened storm wave base allowed transportation of fine sand in suspension out onto the distal shelf internally the resultant sands are differentiated from distal fan turbidites by multi directional bedload currents which are shown most clearly by spectacular tool marks on sandstone bases the tools are clearly identifiable in many cases as indigenous benthonic organisms such as horn corals coral colonies crinoids brachiopods and trilobites the sandstone beds were later colonized by burrowers and other track producing organisms the trace fossils include diplocraterion or corophioides palaeophycus skolithos chondrites scolicia rusophycus cruziana and diplichnires cruziana facies assemblage a new ichno species walcottia devilsdingli is established for small burrows with regular lateral appendage marks at certain points

3 d velocity structure of damavand volcano iran from local earthquake tomography damavand volcano is a large intraplate quaternary composite cone overlying the active fold and thrust belt of the central alborz mountains in northern iran in this study we present the first 3 d

distribution of10be and9be in the pacific ocean abstract the vertical distributions of10be and9be at three locations in the pacific 25 n 170 e 17 n 118 w 3 s 117 w are presented the results show that both isotopes exhibit nutrient like profiles from the surface to the bottom the increase for10be is two to threefold and that for9be is about fivefold while the inter station variations in surface water concentrations may reach a factor of two deep water values tend to be much more uniform averaging about 2000 atoms g for10be and 30 pm for9be a similar situation applies to the10be 9be ratio it varies approximately from 1 to 3 10 7 atom atom at shallow depths but tends toward a value close to 1 1 10 7 in the deep ocean the variation of10be 9be can be viewed as resulting from the fact that10be in a given parcel of water consists of two components recycled and primary the recycled component is that part of10be which has reached tracer equilibrium with9be as opposed to the primary component which upon entering the sea from the atmosphere has yet to equilibrate with9be through particle cycling and mixing processes it is estimated that 70 to nearly 100 of10be at the three stations are being recycled and the recycled beryllium bears an atomic ratio of10be 9be close to 1 10 7 the oceanic residence time of be is of the order of 1000 4000 years comparable to or slightly longer than the ocean mixing time

carbonate dissolution in mesozoic sand and claystones as a response to co2 exposure at 70 c and 20mpa abstract the response to co2 exposure of a variety of carbonate cemented rocks has been investigated using pressurised batch experiments conducted under simulated reservoir conditions 70 c and 20 mpa and with a durations of up to14 months calcite dolomite ankerite and siderite cement were present in the unreacted reservoir rocks and caprocks core plugs of the reservoir rocks were used in order to investigate the alterations in situ crushing of the caprock samples was necessary to maximise reactions within the relatively short duration of the laboratory experiments synthetic brines were constructed for each batch experiment to match the specific formation water composition known from the reservoir and caprock formations in each well chemical matched synthetic brines proved crucial in order to avoid reactions due to non equilibra of the fluids with the rock samples for example observations of the dissolution of anhydrite which were not associated with the co2 injection but rather caused by mismatched brines carbonate dissolution as a response to co2 injection was confirmed in all batch experiments by both petrographical observations and geochemical changes in the brines increased ca and mg concentrations after 1 month reaction with co2 and crushed caprocks are ascribed to calcite and dolomite dissolution respectively though not verified petrographically ankerite and possible siderite dissolution in the sandstone plugs are observed petrographically after 7 months reaction with co2 and are accompanied by increased fe and mn contents in the reacted fluids clear evidence for calcite dissolution in sandstone plugs is observed petrographically after 14 months of reaction with co2 and is associated with increased amounts of ca and mg in the reacted fluid dolomite in sandstones shows only minor dissolution features which are not clearly supported by increased mg content in the reacted fluid silicate dissolution cannot be demonstrated either by chemical changes in the fluids as si and al concentrations remain below the analytical detection limits nor by petrographical changes as partly dissolved feldspar grains and authigenic analcime are present in the sediments prior to the experiments it is noteworthy that authigenic k feldspar and authigenic albite in sandstones show no signs of dissolution and consequently seem to be stable under the experimental conditions

the campania lucania southern italy earthquake of 23 november 1980 abstract we present the main seismological results of our study of the campania lucania earthquake of 23 november 1980 a complete set of far field and local data has been analysed from long period body waves data we determine the fault plane solution 1 140 1 60 2 75 2 54 a depth of 15 km and calculate a seismic moment of 6 1025 dyne cm and a source duration of 6 s from data of a local network deployed immediately after the event we determine aftershock locations they are aligned in a direction nw se that fit extremely well with the focal solution determined above we can choose as fault plane the plane striking 140 and dipping at 60 and the event is a normal event with a large component of left lateral strike slip the source area evaluated from this aftershock distribution 14 km 40 km is quite suitable for an earthquake of a seismic moment of 6 1025 dyne cm

small scale 5 0 m vertical heterogeneity in mudstones implications for high resolution stratigraphy in siliciclastic mudstone successions 48 mudstone samples from the peterborough member oxford clay formation have been analysed to determine the small scale vertical and lateral lithofacies variability in this succession the samples were collected every 0 15 m from saxon and king9s dyke brickpits whittlesey peterborough uk over a short vertical interval 15 m the sampled interval spans the obductum to the grossouvrei subzones of the callovian upper jurassic lithofacies present were described using combined field logging optical and backscattered electron optical techniques the succession predominantly comprises silt rich mudstones with subordinate clay rich mudstones shell beds and shell pavements the individual units are variously composed of detrital clay quartz pyrite calcite with minor apatite kaolinite and glauconite in some units millimetre scale upward fining couplets are present elsewhere the original bedding structures have been destroyed by bioturbation comparison of successive thin sections reveals that upward coarsening is present on a metre scale and that shell enriched units are located close to the tops of these upward shoaling units comparison of samples collected laterally on a 0 01 1 0 m scale from the same level 3 0 m below the top of bed 14 indicates that there is lateral lithofacies variability the small scale 0 001 m couplets are interpreted to be beds deposited by waning flow currents significant breaks between these depositional events allowed a dysaerobic infauna to colonize the sediment the metre scale upward coarsening intervals which are capped by shell enriched units are interpreted to be parasequences the observed small scale lateral lithofacies variability is interpreted to be a product of small but significant vertical miscorrelation errors rather that systematic lateral facies changes these data suggest that producing reliable bed scale lateral correlations over distances of more than 1 km in this and successions like it will be very difficult

facies architecture and sequence development in a neoproterozoic carbonate ramp lakheri limestone member vindhyan supergroup central india abstract outcrop based study of high resolution sequence stratigraphy intra and interfacies sedimentologic clues in neoproterozoic lakheri limestone central india reveals definite signals for relative sea level variations and paleogeographic shifts between shallow beach shoreface and distal shelf depositional cycles in this carbonate formation are bound by unconformities or disconformities of ravinement origin on outcrop scale the unconformities are sharp and irregular and marked by definite depletion in 13 c values of limestones in the study area the entire lakheri limestone succession is divided into four depositional sequences bound by type i unconformities different variants of system tracts transgressive highstand and lowstand resulting from differences in paleogeographic locations basin floor physiography and variable rates of relative sea level change constitute the sequences developed on lakheri carbonate ramp a possible forcing of intrabasinal tectonics both extension and compression on meter to tens of meter thick lakheri sequences is inferred facies impersistence both along and across depositional strike of lakheri limestone is an additional complexity in depositional architecture of carbonate ramp sequence this possibly resulted from formation of depositional slope breaks through tectonic or depositional factors three dimensional reconstruction of lowstand wedge brings out the control of rugged physiography of the basin floor imparted through patchy biohermal growth on facies distribution in this neoproterozoic ramp succession

aftershocks of the campania lucania italy earthquake of 23 november 1980 abstract the result of a study of 1130 aftershocks of the 1980 campania lucania earthquake are presented the data were collected primarily with a dense array of portable smoked drum seismographs deployed in the epicentral region a few days after the main shock tests performed on subsets of the data to establish the location accuracy are described in detail and epicentral maps and cross sections are presented and discussed one hundred and sixty well constrained fault plane solutions using upward traveling rays are presented the distribution of aftershocks forms an elongate cloud which does not define a plane this is not because the events are poorly located a subset of events located with epicentral errors of less than 1 km and depth errors less than 2 km forms a similar cloud to the complete aftershock set the aftershock mechanisms are very varied some are similar to the main event but many differ profoundly these include events on shallow or vertical planes and thrust events the latter include some events which require contraction in the direction in which the main event indicates extension the aftershocks of all mechanisms are intermixed in space in such a way that no simple system of faults can explain them a model to explain the aftershocks and the lack of surface ruptures in the main event is offered it is proposed that the main shock cuts between two aseismic detachment surfaces and that the aftershocks are a consequence of the complicated deformation that such a geometry demands whatever interpretation is adopted the results are a challenge to the commonly accepted view that aftershocks even approximately define simple fault planes or that aftershock mechanisms replicate the mechanism of the main shock defects in interpretations of the main shock and aftershocks process arise largely from a lack of information about the geometry of structures at depth in the epicentral region suitable deep reflection profiles could help to resolve this problem

origin and morphosedimentary evolution of fine grained modern continental shelf deposits the gironde mud fields bay of biscay france the gironde mud fields are thin blankets 4 m that extend from the inner to mid shelf over a restricted area 600 km 2 and overlie palimpsest sands and gravels seaward of the modern gironde estuary south western france the bulk of the mud has accumulated over the last two millennia and reflects the complex interactions of 1 an increasing estuarine supply of suspended particulate matter 2 resuspension of substrate material by storm events and 3 biological mixing the combination of these processes has produced various features within the deposits related to 1 the water depth and distance from source of the fine grained material which are manifested as a proximal distal cross shelf trend from an area of alternating mud sedimentation temporary after large river flows with resuspension by storm events to an area of mud accumulation in deeper water where bioturbation predominates 2 expansions of the mud depocentres over time such that they become more remote from sources of coarser shelf sediment resulting in an upward fining trend the lithofacies of the gironde shelf mud fields exhibit a number of similarities to those of larger scale modern muddy shelves and ancient shallow water mudrocks this work provides a detailed description of a facies model for fine grained shelf sediments deposited under relatively constant sea level

latest miocene to earliest pliocene sedimentation and climate record derived from paleosinkhole fill deposits gray fossil site northeastern tennessee u s a abstract lacustrine sediments deposited within a paleosinkhole at the gray fossil site gfs in northeastern tennessee usa provide a latest miocene and earliest pliocene 4 5 7 ma record of sedimentation and paleoclimate the basal graded facies consists of mm to cm thick normally graded layers of primarily locally derived terrigenous silts and fine sands with low organic content which record storm flow influxes into a 40 m deep paleosinkhole lake the graded facies is overlain by the laminated facies which is characterized by mm thick non graded a b couplets of abundant macerated terrestrial organic matter and fine to coarse quartz sand a alternating with quartz and carbonate silt b isotopic evidence for establishment of either c4 dominated or mixed c3 c4 terrestrial ecosystems is not evident at this site 13 c values of bulk organic matter from the basal graded facies range from 24 to 26 pdb and decrease upsection to 28 to 30 in the organic rich laminated facies isotope values covary with changes in both total organic content toc 0 25 1 wt in graded facies 2 12 wt in laminated facies and in carbon nitrogen ratio c n 1 2 in graded facies 20 50 in laminated facies these upsection changes in sedimentary facies and organic geochemistry within the gfs are attributed to either 1 a climate shift characterized by increased precipitation and concomitant increased vegetation within the paleosinkhole watershed over time or 2 progressive shallowing and eutrophication of the paleosinkhole lake coupled with organic diagenesis within either the watershed or the paleosinkhole sediments in which there was isotopic discrimination associated with organic matter decomposition subaerial exposure of the paleosinkhole lake is recorded by paleosol development

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

recognition of facies bounding surfaces and stratigraphic patterns in foreland ramp successions an example from the upper devonian appalachian basin u s a abstract a detailed stratigraphic study of the upper devonian lock haven formation in the appalachian basin provides new interpretations applicable to understanding sedimentation and stratigraphic architecture in the foreland ramp setting the common occurrence of graded beds hummocky cross stratification and shell lags indicates that storm processes played an important role in deposition gradational based coarsening upward shoreface sequences of interbedded sandstone and mudstone formed during gradual fall in relative sea level in contrast sharp based regressive sequences consist of laminated sandstone facies overlying a submarine erosion surface that developed in response to more rapid fall in relative sea level transgressive sequences become finer grained upward from conglomerate lag which was deposited on a basal transgressive surface to heterolithic facies and mudstone facies a combination of eustasy and tectonic subsidence of the foreland ramp produced changes of relative sea level these fluctuations provided a means for transporting sand onto the ramp and for producing repetition of stratigraphic patterns in the lock haven formation the upper devonian clastic succession which includes both the lock haven formation and the catskill formation represents northwestward progradation of shoreline to nonmarine environments as sediment supply to the foreland ramp exceeded the rate of formation of accommodation compared to passive margin shelves thick fine grained successions such as the lock haven formation are more likely to form in foreland basins where tectonic subsidence provides a mechanism for creating accommodation sediment influx from uplifted areas and absence of a slope break on the foreland ramp results in a higher rate of fine grained clastic sedimentation than occurs on shelves of passive margins

a revised sea level curve for the early jurassic a comparison is undertaken of three different methods of eustatic sea level analysis 1 shallowing and deepening transgressive events inferred from the facies sequence 2 changes through time in the areal spread of epicontinental seas 3 seismic stratigraphy the results of these methods are compared mainly with reference to the lower jurassic new data are brought forward from several continents in a stage by stage study and it is concluded that thelias was characterized by interrupted sea level rise with no major regressions both the transgressions and regressions were relatively rapid with the major transgressions associated with widespread anoxic bottom waters estimates of the net amount of sea level rise through early jurassic time range from 75 m to 110 m

subduction system and flat slab beneath the eastern cordillera of colombia seismicity at the northern terminus of the nazca subduction is diffused over a wide area containing the puzzling seismic feature known as the bucaramanga nest we relocate about 5000 earthquakes recorded by the colombian national seismic network and produce the first 3 d velocity model of the area to define the geometry of the lithosphere subducting below the colombian andes we found lateral velocity heterogeneities and an abrupt offset of the wadati benioff zone at 5 n indicating that the nazca plate is segmented by an e w slab tear that separates a steeper nazca segment to the south from a flat subduction to the north the flat nazca slab extends eastward for about 400 km before dip increases to 50 beneath the eastern cordillera where it yields the bucaramanga nest we explain this puzzling locus of intermediate depth seismicity located beneath the eastern cordillera of colombia as due to a massive dehydration and eclogitization of a thickened oceanic crust we relate the flat subducting geometry to the entrance at the trench at ca 10 ma of a thick buoyant oceanic crust likely a volcanic ridge producing a high coupling with the overriding plate sub horizontal plate subduction is consistent with the abrupt disappearance of volcanism in the andes of south america at latitudes 5 n

low frequency events at vulcano aeolian islands italy abstract data from a digital three component seismic array in operation during summer 1987 and 1988 at vulcano aeolian islands southern tyrrhenian sea italy allow us to put experimental constraints on the seismic source of the shallower events connected to volcanic activity in the region spectral and wave polarization analyses based on the properties of the covariance matrix of the three component signals emphasize sharp similarities between different stations evidence is provided of a possibly very complex source which cannot be explained by a simple model

modern shallow water graded sand layers from storm surges bering shelf a mimic of bouma sequences and turbidite systems abstract a sequence of graded sand layers interbedded with mud extends offshore over 100 km from the yukon delta shoreline across the flat shallow 100 kin such shallow water graded layers off lobate deltas may be distinguished from similar deep water turbidites by 1 the predominance of trough cross lamination perhaps resulting from wave oscillation effects in the proximal part of the system and 2 gradation to common shallow marine fossils bioturbation and storm lag layers n distal areas

recognition and hydrologic significance of passive margin updip sequences an example from eocene coastal plain deposits u s a abstract sequence stratigraphic interpretations are extended to a passive margin updip setting using sedimentological observations from cores and well to well correlations in eocene coastal plain strata of south carolina in the succession studied formation contacts tend to follow sequence boundaries even as lithologies vary within individual sequences sequence boundaries at the base of the congaree formation and near the top of the tinker formation formed during relative sea level fall associated with second order global cycles these boundaries can be recognized clearly in both downdip and updip areas of the passive margin three other sequence boundaries which occur at the base and top of the warley hill formation and within the tinker formation are interpreted as formed during relative sea level fall associated with third order global cycles hydrostratigraphic units in the strata studied conform to depositional patterns that were controlled by changes in sea level and sediment influx sand of the gordon aquifer comprises a thick aggradational succession deposited predominantly in the nearshore shelf environment as accommodation increased during relative rise in sea level because of high rates of sedimentation in the proximal setting aggradational stacking of nearshore sands may be common to other updip marine strata in accommodation dominated regimes the overlying gordon confining unit consists of marine shelf clay and carbonate sediment deposited in response to maximum transgression during subsequent relative sea level fall accumulation of shoreface deposits produced a progradational succession that is represented by the lower part of the upper three runs aquifer unlike formation contacts boundaries between the clastic aquifers and confining units do not follow the third order sequence boundaries because of lithologic variations within the sequences an increasing degree of breaching through the gordon confining unit which results in downward contaminant migration into the gordon aquifer occurs in the updip direction because of nearly continuous sand deposition near the base of the interval studied contaminants migrate locally through the crouch branch confining unit because of erosional breaches formed by scour during sea level lowstand in this example and in other strata deposited in an updip passive margin setting the extent to which confining units are breached at sequence boundaries decreases in the downdip direction resulting in better protection of the adjacent aquifer

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

hybrid numerical modelling of t wave propagation application to the midplate experiment summary a hybrid method coupling a ray tracing method and a nite diierence approach is proposed for modelling t wave propagation from an underwater source to an on land seismic station the long range hydroacoustic wave eld estimated in the sofar channel by the maslov approach shows many triplications of propagation with an increasing number of caustics as the range increases ray tracing approaches lead to a straightforward analysis of the sofar propagation we nd that the duration and the amplitude of the hydroacoustic t waves generated by a source close to the sofar axis may be respectively eight times longer and almost seven times higher than the duration and the amplitude of hydroacoustic t waves generated by a source close to the sofar limits the nite diierence modelling handles the complex hydroacoustic seismic t wave conversion on atoll shores with an illustration of seismic t waves recorded during the midplate experiment in 1989 two diierent seismic stations fga on the fangataufa atoll and din on the mururoa atoll both in french polynesia have recorded the seismic t waves due to an underwater chemical blast at a distance greater than 900 km synthetic seismograms computed by our proposed hybrid method are close enough to the real data for quantitative interpretation we believe that the input model structure is accurate enough to allow such analysis of the seismic t waves the numerical simulation shows that the seismic t waves recorded at both stations are mainly composed of p phases and rayleigh phases the simulation shows that the seismic t wave duration is often linked to the source depth although other factors the continental slope or the distance between the top of the continental slope and the seismic station may also aiect the signal duration

high resolution sequence stratigraphy of a hettangian sinemurian paralic succession bornholm denmark sequence stratigraphic interpretation of paralic successions is complicated by the complex interfingering of marine and continental strata the successions may also include terrestrial extensions of marine parasequences and completely independent lacustrine parasequence analogues failure in recognizing the possible interbeddding of these two independent parasequence types may lead to construction of sequence stratigraphic schemes based on incompatible data sets we have studied a lower jurassic paralic section from the baltic island of bornholm situated in the tornquist zone which demarcates the transition from the stable precambrian baltic shield to the subsiding danish basin and danish polish trough the hettangian sinemurian sose bugt member ronne formation of bornholm includes lacustrine fluvial and restricted marine estuarine deposits reflecting the basin margin position biostatigraphic resolution is poor and a sequence stratigraphic interpretation of the paralic succession is far from straightforward a multidisciplinary approach including facies analysis recognition and lateral trading of key surfaces palynostratigraphy palynofacies coal petrography palaeopedology clay mineralogy and source rock geochemistry is applied in order to obtain a high degree of precision in the interpretation of the paralic facies in this way four sequences are recognized in the overall backstepping lacustrine to estuarine succession marine and marginal marine parasequences are distinguished from their purely lacustrine analogues and an internally consistent sequence stratigraphic scheme is proposed this is compared and tentatively correlated with fossiliferous marine sediments in the danish basin and with published eustatic cycle charts

storm surge ebb origin of hummocky cross stratified units of the andrews mountain member campito formation lower cambrian white inyo mountains eastern california the andrews mountain member of the campito formation consists of complexly interbedded and regionally metamorphosed feldspathic quartzites siltstones and mudstones of latest precambrian and early cambrian age extensive outcrops of the member occur in the white inyo mountains of eastern california the andrews mountain member accumulated in a shallow water offshore depositional system within the broadly subsiding cordilleran miogeocline the sedimentology of the member suggests that both storm and fairweather processes were involved in its formation the following idealized sequence of sedimentary structures is recognized within individual beds 1 an erosional base with localized flute and load casts 2 fine grained sands containing parallel and low angle cross lamination hummocky cross stratification rare penecontemporaneous deformation and internal channels and discontinuities 3 these free sands grade into silts and very fine sands containing climbing ripples wave current ripples flaser bedding and locally abundant bioturbation and 4 the uppermost portions of the bed grade into bioturbated muds with cruziana ichnofossil assemblages and local occurrences of linguoid symmetrical and interference ripples the sedimentary structures in these sequences reflect deposition by high energy storm events the flows generated by these events are interpreted to be the product of the ebb of large storm surges an inferred scenario of storm deposition can be reconstructed for the andrews mountain member shelf 1 initial erosion and suspension of fairweather sediments in response to long period storm waves 2 as a low pressure system moves onshore and dissipates a sediment charged return bottom flow is generated that flows across the shelf and further erodes and entrains material 3 fine sands are deposited as parallel laminated and hummocky cross stratified units as the competence and capacity of the flow decreases 4 attenuation of the surge leads to low flow regime deposition of climbing ripples and where deposition is within storm wave base wave current ripples and flaser bedding 5 with the resumption of fairweather conditions softbodied benthic communities recolonize muddy substrates which are locally reworked by tidal and oceanic currents rather than depositing sand sheets over extensive areas multiple storm surges are inferred to have moved sand incrementally across the andrews mountain member shelf thinning fining upward and thickening coarsening upward sequences may reflect changes in both the intensity of the flows and the proximity of a local sand source

separated earthquake location we present a practical method of locating earthquakes in laterally varying media the procedure has two distinct phases an estimation phase and an application phase in the estimation phase all existing arrival time residuals relative to some reference one dimensional velocity model for a region are used to estimate a set of path anomalies station corrections that vary as a function of source position this is done by sorting earthquakes into groups localized in space and applying a novel multiple event location algorithm this algorithm uses a pair of complementary projection operators to combine a priori information about the lateral structure that is indeterminate from the available data with the information that can be determined uniquely from the available data having estimated path anomalies as a function of source location we can generate a table of path anomalies that can be accessed and interpolated for future earthquake location this is the application phase of the method we have tested the method on synthetic data designed to study how well earthquakes can be located in the vicinity of the rupture zone of the 1984 morgan hill california earthquake we found precise absolute locations could be obtained provided the a priori information was specified appropriately distortion of relative locations occurred near large lateral velocity gradients and for groups of events spread over large areas because of the inadequacy of fitting a single set of path anomalies to the whole group

storm influenced inner shelf sand lobes in the caradoc ordovician of shropshire england abstract a sequence through the middle caradoc ordovician of shropshire shows the horderley sandstone with thick beds of hummocky cross stratified sandstone succeeded by the cheney longville flags consisting of interbedded mudstones siltstones and sandstones some of which also exhibit hummocky bedding in the upper formation the mudstones are commonly bioturbated but also have many wave rippled silty horizons the interbedded thick siltstones and sandstones all lack current ripples and appear to have been rapidly deposited as a result of storm episodes the siltstone and sandstone beds can be separated into two types type 1 beds are massive or faintly planar laminated and have good lateral continuity type 2 beds are lenticular coarser well laminated and have hummocky bedding the f rmer are believed to have been deposited from suspension and the latter from powerful bottom traction currents flowing offshore during storm surges two varieties of hummocky bedding have been recognized within the sequence the more usual type has laminae mantling a hummocky erosional topography a second variety confined to the cheney longville flags has laminae that accreted upwards from a planar base to produce undulating bedforms wavelength up to 3 m wave height up to 15 cm that have symmetrical internal laminae that are form concordant the bedforms resemble wave ripples in cross section but are about an order of magnitude larger than usual wave ripples in the cheney longville flags the argillaceous sediments and their fauna show virtually no change through 80 m of the succession the type 1 beds however increase in proportion upwards whereas the type 2 beds show two strong maxima because the overall environment apparently remained nearly constant and there is no evidence for progradation we interpret the two developments of type 2 beds as reflecting two localized lobes of sand carried offshore into an inner shelf environment by strong laterally restricted offshore currents analogous to but on a larger scale and more powerful than rip currents the independent upward increase in type 1 beds might reflect regional changes in paleogeography which caused a progressive exposure of the shoreface to an oceanic wave climate

three dimensional velocity structure and earthquake locations beneath the northern tien shan of kyrgyzstan central asia we used the arrival times of local earthquakes and quarry blasts recorded by the kyrgyzstan broadband network knet to obtain three dimensional 3 d p and s wave velocity models of the upper crust beneath an actively deforming mountain front and its associated foreland in the kyrgyz tien shan the continuous velocity models described by cubic b spline interpolation of the squared slowness over a regular 3 d grid were computed by simultaneous inversion of hypocenter and medium parameters exact ray tracing was done in the smooth 3 d medium by shooting rays from the sources to the stations by an analytical perturbation method based on the paraxial ray theory the deduced large sparse linear system was solved using the damped iterative least squares algorithm lsqr the stability and resolution of the result was qualitatively tested by two synthetic tests the spike test and the checkerboard resolution test we found that the models are well resolved up to a depth of 27 km for most parts of our image domain the p and s wave velocity models are consistent with each other and provide evidence for marked heterogeneity in the upper crustal structure beneath the northern tien shan at shallower depths 7 km the sediment filled foreland is imaged as a relatively lower velocity feature compared to the mountains which are cored by crystalline basement rocks in contrast at midcrustal depths the mountains are underlain by relatively lower velocity materials compared to the foreland a distinct contrast in velocity structure is also observed between the eastern and western parts of the kyrgyz range at midcrustal depths with the presence of relatively higher velocities toward the east the seismicity is concentrated near the traces of major active faults and extends deeper beneath the foreland compared to the mountains the regional compression in the tien shan is accommodated along a series of high angle reverse faults distributed throughout the orogenic system that extend from the surface down to midcrustal depths the range bounding fault zone can be identified by a sharp lateral gradient in seismic velocities with a pronounced southward dip combined with a zone of seismicity that also deepens to the south and reverse fault source mechanisms from moderate sized events a pronounced low velocity zone lvz is imaged in the p wave field at midcrustal depths beneath the western part of the kyrgyz range this lvz is presumably correlatable with reported high conductivity zones in this region that have been proposed to mark active fault zones along which fluid migration occurs the location of the lvz which is closely coincident with the depth of maximum earthquake generation might imply that it is a crustal decoupling zone at the brittle ductile transition

shallow water marl limestone alternations in the late jurassic of western france cycles storm event deposits or both abstract the contribution of event deposits to various basin fills can be very significant higher than 90 in some cases events may lead to the formation of marl limestone alternations which can also result from cyclic changes in sea level or climate for example the marl limestone alternations of the late jurassic of western france contain abundant coarse grained accumulations that resemble storm deposits described in other western european successions the detailed analysis of facies evolution and hierarchical high frequency stacking pattern of depositional sequences of the phare de chassiron section ile d oleron western france allows the controls on marl limestone formation to be defined this section contains nearshore and shallow marine mud deposits that were exposed to high energy events elementary small and medium scale depositional sequences are defined the stacking pattern and the duration of these sequences suggest an orbital control on sedimentation precession 20 ka cycles notably controlled the formation of elementary sequences that correspond to marl limestone alternations the deposition of marly or carbonate mud occurred in this storm dominated system because of muddy sea beds the gentle slope of the shelf and the great amount of particles in suspension which reduced water energy resulting from storms sediment supply was also sufficient to limit bioturbation and favour the preservation of numerous storm deposits the production of carbonate mud was localised on positive structures and partly controlled by milankovitch scale sea level cycles transport by storms of carbonate mud to the adjacent marly depressions during high carbonate production periods led to the formation of calcareous beds marl limestone alternations in the late jurassic of western france therefore result from the combined effects of cyclic changes in carbonate production and high energy episodic events

toarcian black shales in the dutch central graben record of energetic variable depositional conditions during an oceanic anoxic event the wrong figure was printed in place of figure 4 in the february 2012 issue of jsr p 114 please

three dimensional inversion of regional p and s arrival times in the east aleutians and sources of subduction zone gravity highs free air gravity highs over forearcs represent a large fraction of the power in the earth s anomalous field yet their origin remains uncertain seismic velocities as indicators of density are estimated here as a means to compare the relative importance of upper plate sources for the gravity high with sources in the downgoing plate p and s arrival times for local earthquakes recorded by a seismic network in the eastern aleutians are inverted for three dimensional velocity structure between the volcanic arc and the downgoing plate a three dimensional ray tracing scheme is used to invert the 7974 p and 6764 s arrivals for seismic velocities and hypocenters of 635 events one dimensional inversions show that station p residuals are systematically 0 25 0 5 s positive at stations 0 30 km north of the aleutian volcanic arc indicating slow material while residuals at stations 10 30 km south of the arc are 0 1 0 25 s negative both features are explained in three dimensional inversions by velocity variations at depths less than 25 35 km tests using a one dimensional or a two dimensional slab starting model show that below 100 km depth velocities are poorly determined and trade off almost completely with hypocenters for earthquakes at these depths the locations of forearc velocity highs in the crust of the upper plate correspond to the location of the gravity high between the trench and volcanic arc free air anomalies calculated from the three dimensional velocity inversion result match observed gravity for a linear density velocity relationship between 0 1 and 0 3 mg m 3 km s 1 when a 50 km thick slab is included with a density of 0 055 0 005 mg m 3 values outside these ranges do not match the observed gravity the slab alone contributes one third to one half of the total 75 150 mgal amplitude of the gravity high but predicts a high that is much broader than is observed the inclusion of upper plate velocity anomalies predicts the correct width of the anomaly 100 150 km where the anomaly is most positive because the forearc gravity high is continuous along the entire aleutian arc and is found in most arcs globally high upper plate forearc velocities are suspected to be a common feature of the upper plate of most subduction zones the forearc mass excesses appear to be sustained by upward regional flexure of the upper plate that partly balances the depression of the lower plate at the trench thus elevating high density and high velocity material thus a part of the downward flexure of the subducting plate is regionally compensated by shallow positive mass anomalies in the upper plate and the strength of the upper plate helps generate the forearc gravity highs

discriminating ecological and evolutionary controls during the ediacaran cambrian transition trace fossils from the soltanieh formation of northern iran abstract the nature of the cambrian explosion one of the most critical events in earth history has been a major topic of discussion the trend of increasing morphological complexity and taxonomic diversity of trace fossils within this interval has been used as evidence of the true evolutionary nature of the cambrian explosion however the distribution of trace fossils is controlled by a complex interplay between evolutionary and ecological constraints the pre trilobite soltanieh formation of northern iran displays a significant vertical facies recurrence allowing comparison of identical environments through time therefore its study provides a test case for evaluating the role of evolutionary and ecological controls on lower cambrian trace fossil distribution an integrated study of sedimentary facies small shelly fossil zones sequence stratigraphy and distribution of associated trace fossils indicates a complex interplay of these two sets of factors the distribution and preservation of diagnostic early cambrian trace fossils in the lower shale member of the soltanieh formation is very likely to have been controlled by facies especially within storm generated siltstone shale intercalations providing better preservation potential for interfacial trace fossils therefore delaying the stratigraphic occurrence of treptichnus pedum in contrast evolutionary innovations exerted the primary control on trace fossil distribution in the upper shale member where the vertical distribution of trace fossils strongly matches that observed worldwide this result suggests that although trace fossils provide a valid means of global correlation placing trace fossil assemblages within a paleoenvironmental and sequence stratigraphic framework is a prerequisite of any sound evaluation of the evolutionary and biostratigraphic implications of trace fossils

azimuthal distortion of the seismic focal sphere application to earthquakes in subduction abstract new broadband seismographs enable us to analyse in more detail mantle waves perturbed by the complexity of the medium around the source we propose to apply ray tracing for complex media around the source and more efficient ray tracing for a spherically symmetric earth through the mantle up to the stations we show on synthetic examples that the complexity around the source may indeed modify considerably the seismograms we analyse theoretical teleseismic waveforms and relate modulation of the amplitude to the medium s structure around the source for the example of the romanian earthquake of 30 may 1990 we analyse three seismograms which were not modelled correctly with a spherically symmetric earth model by adding some near surface interfaces we were able to improve the fit between observed and computed seismograms the deduced hypothetical model which may not be the only possible model is in agreement with proposed published models in the area

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

ray tracing for earthquake location in laterally heterogeneous media we propose a technique for the fast solution of ray tracing in three dimensional laterally heterogeneous media analytical solutions for both ray tracing and paraxial ray tracing for a medium with an arbitrary gradient of the square of slowness are used to develop a systematic procedure to construct exact solutions complex heterogeneous media are divided into tetrahedral finite elements inside which the square of the slowness has a simple linear distribution arbitrarily complex media may be studied by judicious choice of the elements we develop appropriate boundary conditions for interfaces with zeroth or first order velocity discontinuities two point ray tracing is performed by a newton method based on paraxial ray theory with a few iterations the ray trajectories through the source and the observer are calculated with the same overall speed as with ray bending the paraxial method has the additional advantage that it can be used to identify caustics and to separate travel time branches we used the previously described method to replace the ray tracing algorithm of the hypo71 program probably the most commonly used earthquake location program the ray tracing routine may be easily modified to adapt it to other earthquake location environments with the modified hypo71 program we relocated the aftershock sequence of the november 23 1980 irpinia italy earthquake the introduction of a low velocity zone proposed by different authors shifts aftershock locations to the ne this horizontal displacement of hypocenters is not very sensitive to the thickness of the low velocity zone

measurements of storm generated bottom stresses on the continental shelf large values of bottom friction velocity u and roughness length z0 determined from burst averaged speed data taken on the continental shelf in outer norton sound alaska with the geoprobe tripod during a storm in september 1977 are correlated with extremely large values of near bottom concentration of total suspended particulate matter tsm combined wind driven and tidal currents exceeding 30 cm s at 1 m above the bottom and intense oscillatory bottom currents with maxima above 45 cm s were associated with the largest measured values of tsm at 2 m above the sea floor the values of u and z0 obtained from the law of the wall velocity depth relationship are diminished substantially throughout the storm period average reduction of 44 when the turbulence reducing effects of the vertical concentration gradient of tsm are considered the form of the latter correction was adapted from smith and mclean 1977a values of the mean u computed from the theory of grant and madsen 1979 which predicts an enhanced shear stress due to nonlinear wave current interactions compare favorably with the u values determined from the measured velocity profiles the measured values of z0 however are considerably larger than any of the estimates based on 1 the actual scales of the physical roughness elements 2 the apparent roughness of grant and madsen 1979 or 3 the thickness of the bed load layer as formulated by smith and mclean 1977a