sandwave migration in monterey submarine canyon central california abstract repeated high resolution multibeam bathymetric surveys from 2002 through 2006 at the head of the monterey submarine canyon reveal a sandwave field along the canyon axis between 20 and 250 m water depth these sandwaves range in wavelength from 20 to 70 m and 1 to 3 m in height a quantitative measure was devised to determine the direction of sandwave migration based on the asymmetry of their profiles despite appreciable spatial variation the sandwaves were found to migrate in a predominantly down canyon direction regardless of season and tidal phases a yearlong adcp measurement at 250 m water depth showed that intermittent internal tidal oscillations dominated the high speed canyon currents 50 80 cm s which are not correlated with the spring neap tidal cycle observed currents of 50 cm s or higher were predominantly down canyon applying a simple empirical model flows of such magnitudes were shown to be able to generate sandwaves of a size similar to the observed ones

coarse grained sediment waves in hyperpycnal clinoform systems miocene of the austral foreland basin argentina in this paper we present an outcrop example of coarse grained sediment waves generated by hyperpycnal discharges at the toe of miocene clinoform systems exposed in the northeast atlantic coast of tierra del fuego argentina an individual set of these sediment waves is formed during the waxing and waning phases of the hyperpycnal discharge during the waxing phase accumulation of coarse grained sediments with generation and migration of dune bedforms occurs at the base of the clinoforms these deposits show transitions of tractive sedimentary structures with evidence of bedload transport and a continuous reworking by the overpassing hyperpycnal flow the continued erosion and reworking during the waxing phase affect mainly the top and the stoss side of the dunes resulting in isolated lenses having upcurrent aggradation structures during the waning phase these isolated lenses are covered by fine grained heterolithic strata that are thicker on the stoss side than on the lee side constituting a differential draping the pulsating and sustained character of the hyperpyc nal flows and the steep depositional slope clinoforms controlled the stacking pattern of the coarse grained sediment waves during successive hyperpycnal events in this way small scale coarse grained sediment waves with wavelengths of 10 40 m and up to 5 m amplitude and a stacking pattern showing an up current growth are generated by high density hyperpycnal flows on slopes having steep gradients

stratigraphic record of basin development within the san andreas fault system late cenozoic fish creek vallecito basin southern california the fish creek vallecito basin contains a 5 5 km thick section of late miocene to early pleistocene sedimentary rocks exposed in the hanging wall of the west salton detachment fault these deposits preserve a high fidelity record of late cenozoic subsidence and basin filling that resulted from deformation in the san andreas fault system of southern california existing and new paleomagnetic data combined with new u pb zircon ages of two tuffs high in the section show that the section ranges in age from ca 8 0 0 4 ma at the base to ca 0 95 ma at the top geohistory analysis reveals 1 moderate subsidence 0 46 mm yr from ca 8 0 to 4 5 ma 2 rapid subsidence 2 1 mm yr from 4 5 to 3 1 ma 3 moderate subsidence 0 40 mm yr from 3 1 to 0 95 ma and 4 rapid uplift and erosion that has exhumed the section since ca 1 ma onset of sedimentation at ca 8 0 0 4 ma records earliest extension or transtension in the area possibly related to localization of the pacific north america plate boundary in the salton trough and gulf of california alternatively marine incursion at 6 3 ma may be the earliest record of plate boundary deformation in the gulf of california salton trough region a thick interval higher in the section records progradation of the colorado river delta into and across the basin starting ca 4 9 ma progradation continued during an abrupt increase in subsidence rate at 4 5 ma and fluvial deltaic conditions persisted for 1 4 m y during the rapid subsidence phase indicating that delta progradation was driven by a large increase in rate of sediment input from the colorado river uplift and inversion of the basin starting ca 1 0 ma record initiation of strike slip faults that define the modern phase of dextral wrench tectonics in the western salton trough

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

morphological expression of bedforms formed by supercritical sediment density flows on four fjord lake deltas of the south eastern canadian shield eastern canada high resolution swath bathymetry data collected in fjord lakes pentecote walker and pasteur eastern quebec canada allowed imaging in great detail the deltas of four rivers in order to understand the factors controlling the formation and downslope evolution of bedforms present on their slopes the morphometry and morphology of 199 bedforms reflect the behaviour of sediment density flows the shape of the bedforms mostly crescentic and the relationships between their morphological properties indicate that they were formed by supercritical density flows and that they are cyclic steps the crescentic shape suggests an upslope migration while the aspect ratios and increasing wavelengths with distance from the shore and decreasing slopes are compatible with a cyclic step origin at the rollover point the acceleration of the density flows on steep slopes produces tightly spaced hydraulic jumps and favours short wavelength and symmetrical bedforms further downslope decreasing slopes and increasing specific discharge increase the wavelength and asymmetry of the bedforms the wavelength and asymmetry are increased because density flows require longer distances to become supercritical again on lower slopes after each successive hydraulic jump bedform morphometry and morphology are used to reconstruct density flow behaviour downslope froude numbers are high near the rollover point and gradually decrease downslope as the slope becomes gentler conversely the specific discharge and flow depth are low near the rollover point and gradually increase downslope as the flow either erodes sediments or becomes more dilute due to sediment deposition and water entrainment the supercritical density flows are believed to be triggered mainly by hyperpycnal flows but some evidence of delta front slope failures is also observed the differences in delta morphology and bedform development between the four deltas are linked to basin morphology and watershed hydrology but also mainly to the fjord heritage of the lakes that allowed the focusing of sediment at the delta front

the hydraulic autogenesis of distinct cyclicity in delta foreset bedding flume experiments abstract we report the experimental discovery of autogenic cyclicity in delta foreset bedding that arises simply from steady water and sediment input under particular hydraulic characteristics this autogenesis is intrinsic to froude supercritical flow associated with a train of upstream migrating hydraulic jumps that delineate cyclic steps upstream migration of hydraulic jumps is associated with discrete packages of sediment accumulation on the foreset slope this synchronism originates from the periodic alternation between supercritical and subcritical flow states on the delta topset just upstream of the shoreline i e the topset foreset break of the delta the alternation in turn depends on the distance from the topset foreset break to the nearest hydraulic jump immediately upstream when the hydraulic jump is still in close proximity to the river mouth delta shore it reworks existing topset deposits and perhaps upper foreset deposits as well as it migrates upstream reworked sediment is then entrained into the subcritical flow between the shore and the hydraulic jump which then emplaces this fine suspended sediment onto the foreset slope as the hydraulic jump moves sufficiently far upstream of the mouth the topset flow becomes supercritical with a flow velocity sufficient to transport fine sediment offshore beyond the foreset under these conditions the sediment emplaced on the foreset tends to be coarser material deposited via avalanching or proximal deposition from suspension the details of this selective sedimentation vary according to the material in the topset bed near the mouth that is available for entrainment into the subcritical flow regardless of the details however distinct cyclic sedimentation of the delta foreset can be sustained as long as the inflow conditions of water and sediment dictate the formation of cyclic steps on the alluvial bed of the topset such hydraulic autogenesis accounts for a set of stratigraphic features that are common in ancient gilbert deltas

mid holocene serpulid build ups in an estuarine environment buenos aires province argentina abstract a bed with several serpulid build ups is described from a holocene outcrop at quequen grande river argentina the tubes were dated at 6360 80 years bp the morphology and size parameters of the serpulids were compared to different species of serpulids from the literature and tubes of ficopomatus enigmaticus hydroides dianthus and hydroides plateni from argentinean waters in spite of the fact that today only f enigmaticus constructs build ups in argentine brackish environments the fossil tubes could not be assigned to this species but instead they show close similarities to those of the two species of hydroides the sequence is interpreted as having originated from a brackish environment at present neither the endemic h plateni nor any other species of hydroides construct build ups in brackish waters of southern south america this suggests that suitable environments to construct aggregates were more widespread than today or that the invasion of f enigmaticus replaced hydroides alternatively various causes may have acted jointly

rates of late cenozoic tectonism in the vallecito fish creek basin western imperial valley california the kinetics of continental rifting are recorded in the late neogene sediments of the western imperial valley california the gulf of california opened in its present form about 4 m y ago capturing the colorado river some 5 km of deltaic and fluvial sediments accumulated in the vallecito fish creek area during the interval 4 3 0 9 m y ago initial sedimentation rates were 5 5 mm yr 1 which diminished in an exponential fashion to 0 5 mm yr 1 when isostatic adjustments are accounted for this implies tectonic subsidence rates of 1 5 mm yr 1 decreasing systematically to 0 1 mm yr 1 after 0 9 m y ago right lateral shearing along the elsinore fault zone cut across the basin causing it to be tilted and uplifted at a mean rate of 5 9 mm yr 1 the basin was concurrently rotated as a unit 35 clockwise the dissected pediments and badlands that now characterize the area were formed and eroded in the past 0 9 m y

mineralogy of the sulphide deposits at sulitjelma northern norway abstract the pyritic vms deposits at sulitjelma northern norway have been regionally metamorphosed at amphibolite facies during the caledonide orogen the deposits contain a wide diversity of sulphide sulphosalt and related minerals which are systematically discussed with reference to their occurrence paragenesis and mineral chemistry most of these minerals are however rare to absent within the massive deposits which are dominantly composed of pyrite with subordinate chalcopyrite sphalerite and pyrrhotite galena arsenopyrite cubanite molybdenite stannite and tetrahedrite occur in minor amounts syn metamorphic mobilisation has however resulted in the redistribution of a range of elements including cu pb sb as ni and au these elements have been reconcentrated into mobilised segregations where they have crystallised under retrograde conditions into a range of discrete phases ore mobilisation which took place along tectonically controlled pathways is however of a highly localised nature with a considerable range in mineral textures and parageneses observed in different samples typical associations within these mobilisates include a range of cu pb sb and cu pb as sulphosalts including bournonite meneghinite seligmannite and jordanite breithauptite nisbite costibite arsenopyrite and gudmundite co existing galena is characterised by elevated concentrations of ag bi and se argentian tetrahedrite 9 17 wt ag the chief ag carrier in the deposits as well as other ag bearing phases including pyrargyrite hessite and empressite are strongly enriched in the mobilisates gold as electrum 50 75 wt au and more rarely as aurostibite is also relatively enriched in the mobilisate samples over those from more massive parts of the deposits a further range of minerals including native antimony native arsenic allargentum dyscrasite argentite mckinstryite jalpaite and native silver occur as low temperature breakdown products of earlier formed minerals preserved textures do not contradict a model involving more than a one phase of mobilisation during the metamorphic evolution

chronology of miocene pliocene deposits at split mountain gorge southern california a record of regional tectonics and colorado river evolution late miocene to early pliocene deposits at split mountain gorge california preserve a record of basinal response to changes in regional tectonics paleogeography and evolution of the colorado river the base of the elephant trees formation magnetostratigraphically dated as 8 1 0 4 ma provides the earliest well dated record of extension in the southwestern salton trough the oldest marine sediments are ca 6 3 ma the nearly synchronous timing of marine incursion in the salton trough and northern gulf of california region supports a model for localization of pacifi c north america plate motion in the gulf ca 6 ma the fi rst appearance of colorado river sand at the miocene pliocene boundary 5 33 ma suggests rapid propagation of the river to the salton trough and supports a lake spillover hypothesis for initiation of the lower colorado river

erosion and deposition by supercritical density flows during channel avulsion and backfilling field examples from coarse grained deepwater channel levee complexes sandino forearc basin southern central america abstract erosion and deposition by supercritical density flows can strongly impact the facies distribution and architecture of submarine fans field examples from coarse grained channel levee complexes from the sandino forearc basin southern central america show that cyclic step and antidune deposits represent common sedimentary facies of these depositional systems and relate to the different stages of avulsion bypass levee construction and channel backfilling during channel avulsion large scale scour fill complexes 18 to 29 m deep 18 to 25 m wide 60 to 120 m long were incised by supercritical density flows the multi storey infill of the large scale scour fill complexes comprises amalgamated massive normally coarse tail graded or widely spaced subhorizontally stratified conglomerates and pebbly sandstones interpreted as deposits of the hydraulic jump zone of cyclic steps the large scale scour fill complexes can be distinguished from small scale channel fills based on the preservation of a steep upper margin and a coarse grained infill comprising mainly amalgamated hydraulic jump zone deposits channel fills include repeated successions deposited by cyclic steps with superimposed antidunes the deposits of the hydraulic jump zone of cyclic steps comprise regularly spaced scours 0 2 to 2 6 m deep 0 8 to 23 m long infilled by intraclast rich conglomerates or pebbly sandstones displaying normal coarse tail grading or backsets these deposits are laterally and vertically associated with subhorizontally stratified low angle cross stratified or sinusoidally stratified sandstones and pebbly sandstones which were deposited by antidunes on the stoss side of the cyclic steps during flow re acceleration the field examples indicate that so called spaced stratified deposits may commonly represent antidune deposits with varying stratification styles controlled by the aggradation rate grain size distribution and amalgamation the deposits of small scale cyclic steps with superimposed antidunes form fining upwards successions with decreasing antidune wavelengths indicating waning flows such cyclic step antidune successions form the characteristic basal infill of mid fan channels and are inferred to be related to successive supercritical high density turbidity flows triggered by retrogressive slope failures

palaeozoic oolitic ironstone of the french armorican massif a chemical and structural trap for orogenic base metal as sb au mineralisation during hercynian strike slip deformation in the saint aubin des ch teaux quarry armorican hercynian belt western france an epigenetic hydrothermal alteration affects an oolitic ironstone layer intercalated within the lower ordovician gres armoricain formation the hydrothermal overprint produced pervasive and massive sulphidation with stratoid pyritised lenticular bodies within the oolitic ironstone layer these sulphide lenses are spatially associated with strike slip faults and extend laterally from them after the massive sulphidation stage fe as stage 1 subsequent fracturing allowed the deposition of base metals stage 2 and pb sb au stage 3 parageneses in veins the dominant brittle structures are vertical extension veins conjugate shear veins and strike slip faults of various orders all these structures are filled with the same paragenetic sequence deformation analysis allows the identification of structures that developed incrementally via right lateral simple shear compatible with bulk strain affecting the central armorican domain each increment corresponds to a fracture set filled with specific parageneses successive hydrothermal pulses reflect clockwise rotation of the horizontal shortening direction geothermometry on chlorite and arsenopyrite shows an input of hot hydrothermal fluids maximum of 390 350 c during the main sulphide stage 1 the subsequent stages present a marked temperature drop 300 275 c lead isotopes suggest that the lead source is similar for all hydrothermal stages and corresponds to the underlying neo proterozoic basement lead isotope data relative ages of deformation and comparison with neighbouring deposits suggest that large scale fluid pulses occurred during the whole hercynian orogeny rather than pulses restricted to the late hercynian period the vicinity of the hercynian internal domain appears as a key control for deformation and fluid flow in the oolitic ironstones which acted as a chemical and structural trap for the hydrothermal fluids the epigenetic mineralisation of saint aubin des ch teaux appears to be very similar to epigenetic sulphidation described in banded iron formation hosted gold deposits

the battle is not to the strong serpulid reefs in the lagoon of orbetello tuscany italy abstract two serpulid species build reefs in the lagoon of orbetello a poly hyperhaline coastal pond hydroides dianthus verrill and ficopomatus enigmaticus fauvel the latter species reached higher densities and built the most conspicuous reefs notwithstanding that the former species had tubes with better biomechanical properties size thickness bulk density and porosity

le district a antimoine or durico beirao portugal evolution paragenetique et geochimique implications metallogeniques the veins of this hercynian district occur within the epimetamorphic series of the durico beirao anticlinorium along the edges of a straight carboniferous syncline a comparative paragenetic study microprobe analyses of arsenopyrite and sphalerite and a preliminary fluide inclusion study improve the knowledge to the metallogenic process pure or ag bearing gold is concentrated in the veins during all metallogenic process in the different stages with arsenopyrite pyrite or jamesonite or berthieritestibnite i or galena fuloppite pyrargyrite stibnite ii carbonates late hydrothermal remobilization stage or sboxides weathering the presence of discrete w sn minerals in the first stage of the sb au veins supports the possibility of a genetic link with the w sn deposits related to nearby granites the pb zn ag veins located in the south eastern margin of the district present epithermal characters and are probably more recent the durico beirao district can thus be compared to other hercynian metallogenic provinces french massif central central marocco considered as examples of geochemical interference between pb and sb by metallogenic superimposition as consequences for exploration these results suggest a southward extension of the sb au district and the presence of ag rich gold in the pb zn stage

experiments on upstream migrating submarine knickpoints abstract laboratory studies are commonly used to improve our understanding of physical processes that are very difficult or almost impossible to investigate in their natural settings erosion impacts on large scale submarine morphology are good examples we present the results of a preliminary laboratory study focused on submarine knickpoints which are bed depressions bounded by steep walls upstream and a gentle slope downstream originated by the passage of a turbidity current over an erodible bed eight experiments using different materials were performed in a facility capable of running continuous turbidity currents the sediments used in these experiments were kaolin clay two different silica flours and fine sand silica flours and fine sand were each used as single sediments in four experiments the other four experiments were performed using a mixture of these sediment types the bed deposit was formed by a net depositional turbidity current the total sediment concentration by volume in the experiments was 5 in one experiment and 10 in the other seven the discharge ranged from 0 009 to 0 055 l s each experiment started with an initial slope in the channel bed of 15 8 53 as the experiments progressed the bed deposit inside the flume built up knickpoints were observed in four of the eight experiments knickpoints formed under a wide variety of conditions they were found when one material or a combination of materials was used in the tests and when the turbidity current was partially and totally distributed over the channel measured width of the bed depressions ranged from 2 to 4 cm length ranged from 3 to 6 cm and the estimated maximum depth was close to 0 5 cm calculations of the speed of upstream migration indicate values in the vicinity of 0 5 mm s upscaled geometric dimensions based on these laboratory experiments fairly reproduce bed depressions observed on a field scale in earlier studies these laboratory observations suggest that the body of the turbidity current is responsible for the upstream migration of the knickpoint

genesis of the wolverine volcanic sediment hosted massive sulfide deposit finlayson lake district yukon canada mineralogical mineral chemical fluid inclusion and sulfur isotope evidence the wolverine deposit is a high grade 6 2 mt at 12 7 zn 1 3 cu 1 6 pb 370 9 g t ag and 1 8 g t au volcanic and sedimentary rock hosted massive sulfide deposit in the finlayson lake area yukon territory the area has the potential to become an important mining camp and currently contains more than 30 million tons mt of massive sulfide ore in five deposits a succession of metamorphosed early mississippian felsic volcanic and sedimentary rocks that are interpreted to have formed on the margin of an ensialic back arc ocean basin between the yukon tanana terrane and the ancestral north american craton hosts the wolverine deposit the massive sulfide ore occurs at a single horizon that marks a significant change in the character of the volcanism from quartz and feldspar phyric rhyolite of the footwall to aphyric rhyolite and chemical sedimentary exhalative rock of the hanging wall the deposit consists of two discrete zn pb ag massive sulfide lenses situated at the same stratigraphic level connected by strata bound semimassive replacement style zn pb ag mineralization copper rich massive sulfide commonly replaces the zn pb ag massive sulfide at the base of the lenses and in the footwall replacement zones beneath the massive mineralization several zones of sulfide stringer veins and chlorite sericite carbonate alteration occur within permeable footwall volcaniclastic rocks alteration minerals preferentially associated with massive sulfide mineralization include ba rich phengitic mica biotite mg rich chlorite and siderite microthermometric measurements of fluid inclusions in the massive sulfide bodies and accompanying stringer zones indicate formation at temperatures of 235 to 353 c primary aqueous liquid rich fluid inclusions in hydrothermal quartz from quartz sulfide stringer veins contain low salinity fluids 2 1 8 5 wt nacl equiv mean 6 0 there is no evidence of fluid boiling in the inclusions and based on the average fluid salinity and temperature of homogenization mineralization took place under a minimum water depth of 1 000 m in situ analyses of 34sv cdt in sulfide minerals from massive sulfide lenses means 0 8 and sulfide stringer veins mean 12 0 display a bimodal distribution lower 34s values characterize sulfides near the top of the lenses versus higher more positive values in underlying veins may reflect different processes of reduction of seawater sulfate sulfur in sulfides from the tops of the lenses was likely derived mainly from bacterial reduction of seawater sulfate whereas sulfur in the stringer veins and at the base of the lenses was mainly from inorganic reduction of seawater sulfate sulfide minerals precipitated both on the sea floor and in the subsea floor from hydrothermal fluids that vented from multiple mounds the presence of black shales and the strongly positive sulfur isotope compositions of the sulfides provide evidence that the ambient bottom water in the basin in which the wolverine deposit formed was likely anoxic this environment may have contributed to the preservation of the sulfide mounds based on its tectonic setting host rock types local geologic setting metal grades age and source s of sulfur the wolverine deposit best exemplifies the volcanic sediment hosted massive sulfide vshms class of syngenetic massive sulfide deposits in the district

upslope migrating bedforms in a proglacial sandur delta cyclic steps from river derived underflows abstract backstepping cross strata on steep foresets of a gilbert type proglacial fluviodeltaic system are ascribed to cyclic steps and other associated supercritical bedforms they provide insight into how sandur river flows transition into the marine realm these sedimentary structures are located on steep foresets up to 17 with corresponding top lying flat based topsets in an upper pleistocene delta on the north shore of the gulf of st lawrence quebec canada packages of backstepping cross strata of sand and gravel lying in the lower part of the delta front outcrop are organized in 10 20 m spaced pseudo foresets with a mean slope of 11 12 seawards backstepping strata include frequent internal erosion surfaces that onlap upslope on pseudo foresets and are interpreted as cyclic steps narrow deep and asymmetrical scours and upslope climbing cross beds are interpreted as chutes and pools and antidunes respectively very shallow 15 m depositional paleo bathymetry is inferred from the preservation of the delta brink the well organized stratal pattern in cyclic step to antidune deposits indicates relatively steady and uniform flow patterns there is insufficient distance for a headscarp large enough to transform to the volume of observed accreted sands or for a flow transformation from a gravitational collapse to net depositional cyclic steps these deposits are sandier than the topsets beds and are thus not derived from them but rather correspond to topset erosional surfaces the development of cyclic steps from hyperpycnal flows was likely enhanced by tidal drawdown processes the resulting sediment laden supercritical flows plunged inertially and evolved into an underflow that generated the cyclic steps on the upper foresets the cyclic steps have a high aspect ratio and represent an end member of coarse grained sediment deposited on steep slopes in contrast to low gradient low aspect ratio muddy deposits

early pleistocene initiation of the san felipe fault zone sw salton trough during reorganization of the san andreas fault system structural and stratigraphic analyses along the western margin of the salton trough show that the san andreas fault system was reorganized in early pleistocene time from a system dominated by two fault zones the san andreas fault and the west salton detachment fault to a network of dextral faults that include the san andreas and at least four dextral faults to the southwest the san felipe fault zone one of these dextral faults has 5 8 2 8 km of right separation and consists of three principal faults in the peninsular ranges these are the san felipe fault in the wnw sunset fault in the middle and fish creek mountains fault in the ese they form a left stepping array and bound domains in which the sunset conglomerate the older west salton detachment fault and cretaceous mylonitic rocks below the detachment are folded about wnw trending folds a complex flower structure within the left stepovers probably produced this fault parallel folding because all the rocks within stepovers of the san felipe fault zone from cretaceous to pleistocene are deformed about wnw trending folds and record broadly similar shortening strains we infer a quaternary age of deformation parts of the san felipe fault zone cut latest pleistocene to holocene surficial deposits and the fault zone is likely active evidence for early pleistocene initiation of the san felipe fault zone is preserved in conglomerate ne of the sunset fault poorly sorted angular boulder conglomerate and pebbly sandstone of the sunset conglomerate are 600 m thick and lie in angular unconformity on the pliocene palm spring group the conglomerate coarsens upward and toward the fault and is dominated by plutonic clasts derived from sw of it conglomerate beds contain up to 10 sandstone clasts recycled from older basin fill and accumulated in proximal to medial alluvial fans that were shed to the ne from uplifted rocks along the then active sunset fault based on lithologic stratigraphic structural and compositional similarities we correlate the sunset conglomerate to the pleistocene ocotillo formation clasts of recycled sandstone record erosion of detachment related basin fill that predates the san felipe fault and once covered the vallecito and fish creek mountains these crystalline cored mountain ranges first emerged from beneath basin fill during early slip above the nascent san felipe fault ca 1 1 1 3 ma later the san felipe fault zone cut upward folded cut across and deactivated the west salton detachment fault within a 9 km wide contractional bend and pair of left steps areas that accumulated sediment within this step over zone between ca 1 1 and ca 0 6 ma are currently being inverted and folded initiation of the san felipe fault in early pleistocene time was a significant event in the reorganization of the southern san andreas fault system the quaternary dextral faults broadened the plate boundary zone south westward from roughly 25 km during coeval slip on the san andreas fault and west salton detachment fault to 50 70 km and mark a change in the dominant structural style from transtension to distributed dextral faulting south of the big bend

sphalerite geobarometry and arsenopyrite geothermometry applied to metamorphosed sulfide ores in the swedish caledonides metamorphosed massive sulfide deposits in the swedish caledonides were investigated using sphalerite geobarometry and arsenopyrite geothermometry the sphalerite investigations yield pressure estimates of 3 to 5 kb for six deposits from host rocks of greenschist lower amphibolite facies a bimodal fes distribution is apparent for the chlorite grade deposits whereas the fes distribution in biotite grade deposits is unimodal the arsenopyrite geothermometry is apparently sensitive to high contents 0 2 wt of either of the trace elements co and ni and possibly also of sb temperature estimates for six deposits from the chlorite zone of greenschist facies yield 371 degrees or 45 degrees c whereas one deposit from the biotite zone gives a temperature of 422 degrees or 25 degrees c the pressure and temperature data obtained for the deposits correspond excellently with the metamorphic grade of the host rocks thus sphalerite geobarometry and arsenopyrite geothermometry can be applied successfully to metamorphosed sulfide orebodies if attention is paid to textural relationships and minor element distribution in the minerals investigated

ore mineralogy of the applachian caledonian stratabound sulfide deposits abstract the diverse ore mineralogies of more than 100 stratabound sulfide deposits that occur along the length of the appalachian caledonian orogen have been tabulated the minerals reflect the varying cu zn pb ratios that have been used as a means to separate the ore deposits into six distinct types following the igcp project 60 guidelines the ore deposits each containing at least one million metric tons of ore are typical of massive sulfide deposits throughout the world and provide a basis for contrasting and comparing this orogen with others differing grades of metamorphism have significantly modified the ore mineral grain sizes and textures but do not seem to have effectively influenced the number or variety of mineral species present

mineral chemistry study of progressive metamorphism in calcareous schists from ankarvattnet swedish caledonides abstract the composition of muscovite chlorite and biotite has been studied in a low grade calcareous phyllite metagreywacke sequence blasjo phyllite in the seve koli nappe complex at ankarvattnet swedish caledonides the b0 lattice constant of muscovite is shown to be a good measure of the mg fe2 content i e the phengite content in muscovite according to the following equation b0 8 992 0 358rm or d 060 3 31 1 499 0 060 rm where rm mole prop 2fe2o3 feo mgo in the chlorite zone the b0 values are mostly controlled by the rock composition thus obliterating the effect of metamorphic conditions in the limiting assemblages of the biotite zone muscovite is continuously de phengitizated and na enriched with increasing grade furthermore the element distribution of mg and fe among coexisting phengite and chlorite is controlled by metamorphic grade temperature the appearance of biotite is found to be due to the following continuous reaction phengitic muscovite chlorite less phengitic more paragonitic muscovite al enriched chlorite biotite quartz water biotite quartz water

cyclic steps review and aggradation based classification abstract cyclic steps are a type of upper flow regime bedform consisting of trains of upstream and upslope migrating bed undulations the overriding flow is characterised by a series of hydraulic jumps occurring in the troughs of the undulations cyclic steps form in open channel flows such as rivers and comprise a common bedform in subaqueous density flows in oceans lakes and reservoirs cyclic steps are associated with alternating froude subcritical and froude supercritical flow on respectively the stoss side and lee side of individual bedforms the transition between these flow states is embodied by the hydraulic jump in the trough of the bedform leading to the permanent or quasi permanent morphology of cyclic steps over the past decade numerous studies affirmed the dominant role of cyclic steps in generating bed undulations in modern and ancient glacial outwash fluvial delta and turbidite environments as reviewed here cyclic steps were previously discriminated as net depositional climbing transportational and net erosional falling in different parts of sedimentary systems the following cyclic step descriptors with distinct depositional signatures are proposed fully depositional partially depositional transportational partially erosional and fully erosional partially depositional cyclic steps are most common they are associated with backset bedded sets high aggradation rate and nested scours filled with massive to backset bedded deposits low aggradation rate the new classification can be used as a predictive tool in the reconstruction of modern and ancient sedimentary successions using repeat bathymetry seismic reflection or outcrop data it is applied in three turbidite case studies classical deep sea system small scale delta slope and line sourced carbonate slope

modern polychaete reefs in western mediterranean lagoons ficopomatus enigmaticus fauvel in the albufera of menorca balearic islands abstract the calcareous serpulid worm ficopomatus enigmaticus fauvel is prominent in the coastal lagoon of the albufera of menorca where it encrusts hard substrates its bioconstructions differ in shape depending on location substratum and water level this worm occurs along the entire littoral area forming a continuous layer up to 3 m thick on the bottom of the lagoon they develop as micro atolls in the shallowest areas and patch reefs over 2 m height and 4 m in diameter encrusting molluscan shells boulders and small rock outcroppings although the worm needs a hard substratum for fixation growth over molluscan shells can result in a spread out worm reef overlying a muddy substrate fluctuations in water level causes death of the emergent parts of the reef although these are easily recolonized when the environmental conditions change the best physico chemical conditions for the development of ficopomatus on these islands seem to be in the albufera of menorca where it attains an annual production in dry weight of 21 269 kg m 2 yr 1 the environmental conditions present are 9 6 27 2 c temperature 9 5 30 0 salinity 1 75 3 75 meq 1 1 alkalinity and 36 202 oxygen saturation of annual oscillation the rapid and spectacular growth of these bioconstructions that occurs in the coastal lagoon can cause change in the ecological dynamics the lagoon can be progressively filled up by reefs and skeletal debris of serpulids and associated benthic organisms

lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows from cyclic steps to humpback dunes abstract the preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record although these bedforms are known from a variety of depositional environments this field based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps chutes and pools antidunes and humpback dunes from three dimensional outcrops the well exposed middle pleistocene successions from northern germany comprise glacilacustrine ice contact subaqueous fan and glacial lake outburst flood deposits the studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high energy depositional environments such as fluvial settings coarse grained deltas or turbidite systems deposits of cyclic steps occur within the glacial lake outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets cyclic steps formed due to acceleration and flow thinning when the glacial lake outburst flood spilled over a push moraine ridge these bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes and pools and antidunes the subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms which are interpreted as deposits of aggrading stationary antidunes which require quasi steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation humpback dunes are characterised by downflow divergent cross stratification displaying differentiation into topsets foresets and bottomsets and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common the absence of planar parallel stratification in all studied successions suggests that the formation of these bedforms is suppressed in flows characterised by hydraulic jumps under highly aggradational conditions the large scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the initial supercritical flows which was strongly affected by the occurrence of hydraulic jumps small scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge bed topography and pulsating unstable flows

asymmetrical inversely graded upstream migrating cyclic steps in marine settings late miocene early pliocene fish creek vallecito basin southern california abstract cyclic steps are ubiquitous in modern sedimentary environments yet their recognition remains sparse in the rock record here we interpret three sets of undulating backsets 1 to 3 recognized in the late miocene early pliocene latrania formation in the anza borrego desert the fish creek vallecito basin southern california usa as the first cm to dm scale outcrop record of cyclic steps based on asymmetrical cross sections upstream migration and inversely graded laminae upstream migration and asymmetrical cross sections of backsets and concomitant backset laminae are attributed to supercritical to subcritical flow transitions through weak hydraulic jumps which are composed of i thin tens of centimetres and slower reported as flow velocities of 0 45 to 1 45 m s 1 with mean value of 0 89 m s 1 subcritical represented by internal froude numbers fr of 0 67 to 0 99 with mean value of fr 0 84 turbidity currents on the stoss sides and ii thin tens of centimetres and faster reported as of 0 99 to 4 03 m s 1 with mean value of 2 24 m s 1 supercritical represented by fr of 1 84 to 3 07 with mean value of fr 2 42 turbidity flows on the lee sides the inversely graded laminae in the troughs of backsets are 2 to 5 cm thick and consist of two discrete divisions i 1 to 2 cm thick lower finer grained divisions made up of parallel laminated siltstones overlain by very fine to fine grained sandstones and ii 2 to 3 cm thick upper divisions composed of medium to coarse grained sandstones with sporadic occurrence of subrounded pebbles these inversely graded laminae are related to stratified collisional and or frictional traction carpets under conditions of high fall out rates due to the poor preservation potential of cyclic steps the rock record of cyclic steps is generally considered to be rare the present outcrop based study presents a detailed analysis of sedimentary facies growth patterns and flow dynamics of marine cyclic steps thereby contributing to better understand architectural styles and lithological properties of cyclic steps in the geological record

supercritical and subcritical turbidity currents and their deposits a synthesis common facies models of turbidite deposits are based on idealized sequences of turbidite units which are assumed to reflect the depositional processes of a decelerating turbidity current we show how suites of turbidite units i e distinct turbidite facies associations that are easily described from core and outcrop may characterize the entire range of large scale dynamics of turbidity currents enabling estimates of their densimetric froude number fr subcritical versus supercritical and suspension fall out rate stratified versus nonstratified flows the linking of facies associations with large scale flow dynamics resolves process facies links that were hitherto unresolved by the common turbidite facies models

miocene pliocene exhumation along the west salton detachment fault southern california from u th he thermochronometry of apatite and zircon 1 the salton trough is the northernmost segment of the active gulf of california oblique rift system the main rift related structure in the western salton trough is the low angle west salton detachment fault wsdf footwall and hanging wall apatite and zircon u th he ages record a significant contrast in thermal history across the wsdf confirming pliocene normal slip along the fault apatite u th he ages record rapid exhumational cooling from 5 to 2 ma consistent with the timing of accelerated tectonic subsidence recorded in wsdf hanging wall sedimentary strata and consistent with the initiation age of dextral plate boundary slip on the southern san andreas fault in the salton trough our results indicate that the wsdf caused at least 2 3 4 km of exhumation and 8 10 km of approximately e directed horizontal extension since 5 ma slip rate of the wsdf at yaqui ridge was likely in the range of 2 3 5 km ma from 7 to 2 ma the wsdf may have been active well before 5 ma middle miocene apatite u th he ages from samples at high elevations have steep age elevation gradients and suggest that exhumation may have initiated by 12 ma about when subduction ceased along a large segment of the baja california margin and consistent with the age of onset of extension in northeastern baja california

backset lamination produced by supercritical backwash flows at the beachface shoreface transition of a storm dominated gravelly beach middle pleistocene central italy abstract bedforms and resulting sedimentary structures of interpreted upper flow regime origin are fairly common in various ancient and modern depositional settings yet outcrop examples of shallow water strata dominated by sedimentary structures arising from such flow conditions are rarely documented this outcrop based study presents the first detailed analysis of mid pleistocene beachface shoreface strata containing sedimentary structures interpreted to have been formed by storm generated backwash flows during the transition in flow regime from supercritical to subcritical here we propose that moving down the steep beachface backwash flows rapidly accelerated and became thinner experienced abrupt deceleration and flow thickening passing through an erosional hydraulic jump in the trough at the toe of the beachface and then waned to thicker and subcritical conditions just downflow of the hydraulic jump in this frame landward dipping backset laminae deposited on the downflow side of the trough evolved into thinner upper stage plane parallel laminae further downstream the transition from the proximal to the distal upper shoreface records a significant increase of preserved wave ripples and burrowed intervals in concert with a progressive decrease in thickness and grain size of individual sets of plane parallel laminae and increase of gravel filled gutter casts

an examination of froude supercritical flows and cyclic steps on a subaqueous lacustrine delta lake chelan washington u s a density driven submarine flows including turbidity currents play an important role in the transfer of sediment into deep water these bottom hugging flows often produce flow transverse bedforms along their path a sedimentological and geophysical survey of the stehekin river delta in lake chelan washington reveals a downslope elongate field of bedforms on the delta foreset associated with hyperpycnal discharges of the stehekin river an analysis of the bedform morphologies delta geometry and density contrast between lake and river water suggests that these hyperpycnal flows are froude supercritical the bedforms are likely cyclic steps flow transverse bedforms that are bounded by stable hydraulic jumps between alternating subcritical and supercritical flow regimes the ability to examine the three dimensional bed configuration produced by natural density driven flows adds valuable information to the body of experimental work focused on the behavior of cyclic steps in flumes

supercritical flow structures on a late carboniferous delta front sedimentologic and paleoclimatic significance deposits of fluvial systems in highly seasonal tropical climates possess unique architectural and facies characters owing to a flood prone regime alternating with lengthy periods of ineffective discharge distally linked deltaic successions should also feature distinctive attributes with great potential to preserve the stratigraphic evidence of exceptional discharge events we describe late carboniferous delta front valley confined sandstones from the pennine basin uk originally deposited at paleoequatorial latitudes during final assembly of the pangean megacontinent and characterized by giant sedimentary structures with repetitively sigmoidal geometry facies traits indicate geologically instantaneous deposition of a large sediment volume from a density current at sustained supercritical flow conditions leading to aggradation of cyclic steps recently identified bedforms developing in high energy flows and of which this is the first complete outcrop example the lack of unconformable erosional surfaces and absence of different associated facies point to a single aggradational event during which the structures attained dimensions comparable to those indicated by seismic data sets from which they are remotely detected on modern seafloors cyclic step formation in a deltaic setting suggests that pangean megamonsoons could have triggered hydrologic events capable of imprinting sedimentologic signatures on shallow marine deposits

large scale scours formed by supercritical turbidity currents along the full length of a submarine canyon northeast south china sea abstract high resolution multibeam bathymetric and seismic data enables a detailed morphological investigation of a submarine canyon west penghu canyon on the northeastern south china sea margin where twenty three 23 scours are observed along the canyon thalweg these scours form narrow topographic depressions in plan view and show asymmetrical morphologies in cross section the identified scours can be further divided into two groups types a and b based on their sizes and relative locations they are separated by a slope break at a water depth of 2850 m type a scours s1 s18 occur upslope from the slope break whereas type b scours s19 s23 lie downslope from this same break the scours are interpreted as net erosional cyclic steps associated with turbidity currents flowing through the west penghu canyon the currents that form type a scours reflect higher v q and el compared to the currents forming type b scours a change in slope gradient and loss of lateral confinement are proposed to control the change from type a to type b scours furthermore coriolis force influences the flow direction of turbidity currents leading to the preferential development and larger incision depths of scours towards the southwestern flank of the west penghu canyon our results contribute to a better understanding on the origin of scours in submarine canyons across the world