u pb dating of zircon and 40ar 39ar dating of biotite at bingham utah uranium lead dating of zircon and 40ar 39ar dating of biotite provide a new estimate of the age of the bingham hydrothermal system the u pb age of zircon from the last chance monzonite establishes the age of crystallization of this intrusion at 38 55 0 19 ma 2 mswd 2 08 the oldest hydrothermal event in the monzonite is dated at 38 40 0 16 ma and is based on a 40ar 39ar determination plateau age of primary igneous biotite this age is indistinguishable from the u pb zircon age of emplacement of the monzonite petrographic and fluid inclusion data show that the biotite bearing sample was propylitically altered at 400 c which would reset the 40ar 39ar age within 115 ka thus the concordance of the biotite age with the intrusion age of the monzonite suggests that propylitic alteration was essentially contemporaneous with monzonite emplacement the 40ar 39ar ages from three hydrothermal biotites sampled within the 0 35 percent cu isopleth in the monzonite overlap within uncertainty and indicate that potassic alteration in monzonite occurred at 37 57 0 11 ma the youngest hydrothermal activity is identified from a biotite sample 37 07 0 21 ma correlation age in potassically altered quartz monzonite porphyry within the central mos2 zone hydrothermal biotite within the bingham deposit was produced over a time period of approximately 0 50 0 32 ma

subaqueous sand flow cross strata abstract subaqueous sand flow cross strata are formed by the flowage of sand down the slipfaces of submerged bedforms and isolated steps such cross strata make up the great bulk of the foreset deposits of shallow stream megaripples and bars characteristics of sand flow cross strata that form in fine to medium sand on subaqueous slipfaces less than 2 m high include steep dip angles generally 27 34 little if any curvature in dip cross sections distinct segregation of grain types downward coarsening along the cross stratum and generally upward coarsening inverse grading across the cross stratum loose gram packing absence of interbedded grainfall or other deposits small range of cross stratum thickness within a set increasing cross stratum thickness with increasing slipface heigh and great width lateral extent relative to cross stratum thickness and slipface height in coarse subaqueous sand the sand flow cross strata tend to be narrower more lenticular in horizontal sections flume experiments suggest that each cross stratum is produced by one in a series of intermittent sand flows and that the avalanching is generally not closely controlled by bedforms that spill over the brink of the slipface subaqueous cross strata that formed in fine to medium sand on relatively low slipfaces typically differ from eolian cross strata that formed under similar conditions grainfall deposits are less common on subaqueous slipfaces probably because avalanching tends to be more nearly continuous there than on eolian slipfaces another difference is that subaqueous sand flow cross strata tend to be wider more extensive laterally than eolian ones in part because avalanching tends to be more nearly continuous on subaqueous slipfaces and in part because submerged sand is even less cohesive than dry eolian sand

origin dimensions and distribution of remobilized carbonate deposits in a tectonically active zone eocene thebes formation sinai egypt abstract determination of the distribution and mechanism for carbonate dominated mass transport sediments is often compromised by the scale and access to exposures consequently many studies lack the resolution to capture the heterogeneity and dimensions of mass transport deposits this study documents the size shape and stratal assemblage of remobilized carbonates in the eocene thebes formation in the hammam faraun fault block hffb of western sinai revealing the complexities of carbonate mass transport deposits at sub seismic scale present day pseudo three dimensional exposure of the thebes formation in a large fault block formed during the opening of the gulf of suez allowed for lateral and down dip measurement of slope and basinal facies in the field and from photos remobilized facies were digitized in the photos and evaluated using image analysis software a technique with a wide range of applications to outcrop studies of sedimentary architecture debris flow deposits in the lower section of the thebes formation comprises clasts with differing fossil assemblages a relative sea level rise at the start of upper thebes formation deposition resulted in basinal sediments comprising periodic incursions of high density turbidite grainstones encased within a background of planktonic foraminiferal wackestones foraminiferal assemblages of remobilized facies imply multiple sources on the carbonate platform demonstrating the effect of short lived tectonism on slope instability and deposition of mass transport deposits the results of the study confirm that tectonism associated with the syrian arc fold belt which altered the style of basin sedimentation between egypt and syria persisted into the eocene at least as far south as wadi araba in the western desert and hammam faraun in sinai in addition the shape size and extent of the two dominant remobilized facies debris flows and grainstone turbidites are influenced by their mud rich versus grainy compositions

the udo tuff cone cheju island south korea transformation of pyroclastic fall into debris fall and grain flow on a steep volcanic cone slope the udo tuff cone of cheju island south korea is a middle pleistocene basalt tuff cone that has formed by early surtseyan type eruptions and later drier hydroclastic eruptions the tuff cone comprises steep 20 30 and planar beds of lapillistone lapilli tuff and tuff that can be grouped into seven sedimentary facies a g facies a and b comprise continuous to lenticular layers of grain supported and openwork lapillistone that are inversely graded and coarsen downslope they suggest emplacement by grain flows that are maintained by gravity induced stress and grain collisions facies c includes poorly sorted crudely bedded and locally inversely graded lapilli tuff also suggestive of rapid deposition from highly concentrated grain flows facies d includes thinly stratified and mantle bedded tuff that was probably deposited by fallout of wind borne ash other facies include massive lapilli tuff facies e chaotic lapilli tuff facies f and cross bedded tuffaceous sandstone facies g that were deposited by resedimentation processes such as debris flow slide slump and stream flow respectively the grain flows that produced facies a b and c are interpreted to have originated from falling pyroclasts which initially generated highly dispersed saltating avalanches in which momentum was transferred by the particles themselves this transport mechanism is similar to that of debris fall as the slope gradient was too low to maintain a highly dispersed flow the debris fall decelerated and contracted due to a decrease in dispersive pressure the mode of momentum transfer changed to one of collision because contraction of the debris fall resulted in an increase in particle concentration this transport mechanism is similar to that of common grain flows grain segregation occurred in several ways initial segregation of ash from lapilli occurred due to their differing terminal fall velocities and their contrasting degrees of sliding friction with the bed percolation of ash into interstices of lapilli during flow kinematic sieving augmented further segregation of ash from lapilli the latter process along with a dispersive pressure effect gave rise to vertical inverse size grading downdip inverse grading was produced by particle overpassing

sorting in grain flows at the lee side of dunes abstract sediment sorting at the lee side of ripples dunes and bars has already been recognized long ago a predictive model of the sorting is necessary but unavailable for implementation in sediment transport models for sediment mixtures relevant processes in sedimentological and physical literature are reviewed and compared to the sparse data of sediment sorting a synthesis is given of the most important variables governing the sorting processes for the benefit of future experimentation and modelling these variables are the sorting standard deviation skewness and bimodality of the sediment mixture delivered to the brink point the height of the dune or bar relative to the average grain size of the mixture the velocity of the flow above the brink point relative to the settling velocity for all grain size fractions and the frequency of the grain flows in addition the initiation mechanism and frequency of the grain flows affect the pattern and effectiveness of sorting

high velocity ring shear tests on sand ring shear tests on sand materials have been carried out to show whether there is a change in the behaviour of these materials at high shearing rates and normal stresses this question is relevant to the problem of the mobility of large rock avalanches sturzstroms but is also of more general academic interest a ring shear apparatus of unusual although simple design has been constructed capable of achieving circumferential velocities of 2 m s at normal stresses of up to 200 kpa tests were carried out on two types of coarse sand wet or dry sand rock flour mixtures and polystyrene beads perfect frictional behaviour was observed in all the tests uninfluenced by either velocity or normal stress over the entire range of these variables change in frictional behaviour due to high rate of shearing therefore cannot be used to explain the high observed mobility of sturzstroms des essais de cisaillement circulaire par torsion ont ete effectes afin de decouvrir si un changement ait lieu dans le comportem

high cu grades in porphyry cu deposits and their relationship to emplacement depth of magmatic sources observations at several porphyry cu deposits indicate that in those formed above source magma chambers emplaced to relatively shallow levels roofs 3 4 km deep zones of higher cu grade are associated with the oldest intrusions of a central porphyry cluster abundant early a type quartz veins secondary feldspar alteration and usually high fe fe cu low s fe cu sulfide oxide mineral assemblages in deposits for which source magma chambers were deeper roofs 5 km porphyries closest in age to ore are spatially less directly related to mineralization in these higher cu grades in early mineralization comprise swarms of veinlets with alteration halos that include sericite as well as secondary feldspar and biotite sulfide oxide assemblages are usually of lower fe fe cu and higher s fe cu these differences in deposit characteristics appear to correspond with a change from two phase chloride bearing aqueous fluids that would exsolve from magma at shallow depths to one phase fluids deeper

copper deposition during quartz dissolution by cooling magmatic hydrothermal fluids the bingham porphyry abstract scanning electron microscope cathodoluminescence imaging is used to map successive generations of fluid inclusions in texturally complex quartz veinlets representing the main stage of ore metal introduction into the porphyry cu au mo deposit at bingham utah following conventional fluid inclusion microthermometry laser ablation inductively coupled plasma mass spectrometry la icpms is applied to quantify copper and other major and trace element concentrations in the evolving fluid with the aim of identifying the ore forming processes textures visible in cathodoluminescence consistently show that the bulk of vein quartz q1 characterized by bright luminescence crystallized early in the vein history cu fe sulfides are precipitated later in these veins in a microfracture network finally filled with a second generation of dull luminescing q2 quartz mapping of brine and vapor inclusion assemblages in these successive quartz generations in combination with la icpms microanalysis shows that the fluids trapped before and after cu fe sulfide precipitation are very similar with respect to their major and minor element composition except for copper copper concentrations in inclusions associated with ore formation drop by two orders of magnitude in a tight pressure temperature interval between 21 and 14 mpa and 425 350 c several hundred degrees below the temperature of fluid exsolution from the magma copper deposition occurs within a limited p t region in which sulfide solubility shows strong normal temperature dependence while quartz solubility is retrograde this permits copper sulfide deposition while secondary vein permeability is generated by quartz dissolution the brittle to ductile transition of the quartz feldspar rich host rocks occurs in the same temperature range which further enhances vein reactivation and promotes cooling and expansion of fluids ascending across the transition from lithostatic to hydrostatic conditions

morphometric analysis of slipface processes of an aeolian dune implications for grain flow dynamics grain flows are an integral part of sand dune migration they are a direct response to the local windregime and reflect complex interactions between localized over steepening of a dune slipface andcomplex turbulent airflow on the lee slope grain flows are primarily responsible for delivering sediment to the base of a dune thus driving slipface advancement yet there are few constraints on their morphological and spatial characteristics or the amount of sediment that is redistributed bythese flows using a combination of high resolution terrestrial laser scanning and video recordings four distinct grain flow types are identified based on morphology and area on a dune slipface grainflow morphologies range from small superficial flows to larger flows that affect greater portions of the slipface moving significant amounts of sediment detailed field observations are presented of the dynamics of lee slopes including measurements of the initiation location thickness magnitude and frequency statistics of grain flows as well as volume estimates of redistributed sediment for each grain flow observed high resolution laser scans enable accurate quantification of bulk sediment transfer from individual grain flows and can be used to study grain flows in a variety of environments a categorization of grain flow morphologies is presented that links styles of flows with wind strength and direction turbulent airflow sediment deposition and environment

can dispersive pressure cause inverse grading in grain flows grain flows in the collisional regime are self regulated in such a way that dispersive pressure at every level tends to balance static pressure and so cannot promote the upward segregation of large particles in a steady flow le roux adds new insights to this analysis by pointing out that dispersive and static pressures would not balance in unsteady flows when shear strain rate increases in a grain flow dispersive pressure which is positively correlated to shear strain rate increases too and the gradient of dispersive pressure becomes higher than the gradient of static pressure as a consequence the grain flow expands thus lowering the dispersive pressure until the two gradients reequilibrate during the

evolution of hydrothermal fluid characteristics at the santa rita new mexico porphyry copper deposit mineralogic and fluid inclusion investigations conducted in the laboratory combined with in situ observations of temporal relationships among geologic features demonstrate that systematic changes in hydrothermal fluid characteristics occurred with time during evolution of mineralization and alteration of the granodiorite stock at the santa rita porphyry copper deposit the earliest fluids to circulate are recorded in potassically altered orthoclase and biotite stable veins as vapor rich h 2 o co 2 inclusions and hypersaline 30 70 equiv wt nacl or kcl inclusions which homogenize over a wide temperature range from 240 degrees to greater than 800 degrees c the high salinity fluid inclusions are complex chloride brines with significant concentrations of sodium potassium copper iron and sulfur but sulfide minerals are not associated with the early potassic assemblage produced by this fluid oxygen isotope ratios of quartz in the orthoclase and biotite stable veins are identical to phenocryst quartz in the intrusion 8 2ppm later solutions circulated through newly formed fractures and older reopened veins and are recorded in low salinity less than 15 equiv wt nacl fluid inclusions which homogenize primarily in the temperature range of 220 degrees to 360 degrees c these hydrothermal fluids formed two distinct alteration assemblages as they reacted with potassically altered rock chlorite is the dominant silicate gangue mineral of the earlier chalcopyrite bearing orthoclase and clay stable assemblages and sericite characterizes the later phyllic alteration assemblage with quartz and pyrite oxygen isotope ratios of quartz of the later assemblages 8 6 10 4ppm are heavier than quartz of the earlier potassic assemblages it is concluded that the earliest hydrothermal fluids to circulate within the stock localizing the orebody at santa rita could have been derived by phase separations of fluids exsolved from crystallizing magma into condensed hypersaline liquids and h 2 o co 2 vapors as these fluids moved through fractures potassic alteration of rock occurred without concomitant deposition of sulfides later solutions of dominantly meteoric origin progressively formed hypogene copper mineralization associated with chlorite stable alteration and then phyllic alteration

the bingham canyon porphyry cu mo au deposit i sequence of intrusions vein formation and sulfide deposition the bingham canyon porphyry copper gold molybdenum deposit is one of the largest and highest grade porphyry orebodies in the world this study focused on the northwest side of the deposit where quartz mon zonite porphyry qmp the first and largest porphyry intrusion hosts the bulk of the high grade copper gold ore 1 0 cu 1 0 ppm au the north northeast trending high grade zone had pre mining dimensions of 1 500 m strike 300 m vertical and 500 m width and contained more than 500 million tonnes mt of ore associated with potassic alteration and abundant quartz veins the lack of superimposed sericitic alteration yielded ideal exposures in which to study the early high temperature stages of ore formation a style of mineralization that in many porphyry deposits represents the major period of copper introduction we mapped multiple porphyry dikes in the sequence 1 qmp 2 latite porphyry lp 3 biotite porphyry bp 4 quartz latite porphyry breccia qlpbx and 5 quartz latite porphyry qlp porphyry dikes faults and quartz veins are steeply dipping and have two dominant orientations north northeast and northwest striking dikes have a north northeast strike but they thicken and develop northwest trending apophyses and host high grade copper gold zones at intersections with northwest faults indicating that magmatic hydrothermal fluids were focused by these structural intersections each porphyry intrusion was accompanied by a similar sequence of veins potassic alteration and sulfides biotite veinlets were followed by fractures with early dark micaceous edm halos of sericite k feldspar biotite andalusite and local corundum containing disseminated bornite chalcopyrite gold edm halos are cut by multiple generations of a quartz veins representing the main cu au ore forming event postdating all intrusions are quartz molybdenite veins followed by quartz sericite pyrite veins cathodoluminescence cl petrography identified distinct a quartz veinlets consisting of dark luminescing quartz filling fractures and dissolution vugs in earlier a quartz veins and adjacent porphyry wall rock these veinlets contain abundant bornite and chalcopyrite and minor k feldspar and are closely linked in time to the introduction of the bulk of the copper and gold although a similar sequence of veins was repeated on emplacement of all porphyry intrusions the vein density and intensity of potassic alteration declined with time the youngest porphyry qlp is mostly weakly mineralized and locally unaltered these observations indicate that magmatic hydrothermal fluids underwent a similar physiochemical evolution during and immediately following emplacement of each of several porphyry dikes the relationship between edm veins and a quartz veins requires that the flux of magmatic fluid from the magma chamber occurred in an episodic manner as opposed to a continuous discharge vein truncation relationships coupled with abrupt changes in copper gold grades sulfide ratios and potassic alteration intensity at porphyry intrusive contacts indicate that the mass of introduced copper and gold decreased significantly during successive porphyry intrusive hydrothermal cycles presumably due to depletion of metals and volatiles in the underlying magma chamber

geometrical mechanism of inverse grading in grain flow deposits an experimental revelation abstract the grain flow has so far been defined with reference to the distinctive sediment support mechanism the dispersive pressure the role of sediment support mechanism however is required in a multiphase flow to prevent the gravitational settling of the particles through the driving medium during the flow in a single phase flow of non cohesive grains no such secondary mechanism is required to counteract the gravitational pull the driving force of the flow so the definition of grain flow needs a critical revision this in turn involves proper understanding of the grain flow mechanism so that the relation between the process and the product can be properly established the most distinctive feature often demonstrated by a grain flow deposit is the particle size segregation which leads to the development of inverse grading the available explanations for this phenomenon find theoretical constraints in the present study an attempt was made to understand the mechanism of single phase non cohesive granular flow of different flow regime and the particle segregation pattern in the resultant deposit through laboratory simulation the experimental observations revealed that no sustained granular flow sets in on a slope deviating much from the limiting value of the angle of repose of the granular material a persistent simple shear flow develops on slopes of this critical value each of the grains rolls in response to simple shearing if the shear stress attains a critical value theoretically the larger grains can even climb up the adjacent smaller ones towards the down slope direction in reality however high angle climb is not very common the larger grains preferably roll over the smaller grains when the common tangent becomes almost horizontal or makes a very low angle with the direction of flow and by this process gradually reaches the upper surface of the flow causing the development of inverse grading the upper surface of the resultant deposit remains parallel to the sloping substratum these properties readily distinguish this variety of granular flow from the other natural flows and the flow may thus be assigned the distinct status of grain flow

clay mineralogy of phyllic and intermediate argillic alteration at bingham utah the earliest alteration mineral zones in the porphyry cu mo au ore deposit at bingham utah include the outermost propylitic and inner potassic alteration of igneous rocks innermost phyllic and intermediate argillic alteration is superimposed on propylitic and potassic alteration petrographic x ray diffraction and electron microprobe analyses are used to characterize the clay mineralogy of phyllic and intermediate argillic alteration phyllic alteration affects monzonite near the contact with the quartz monzonite porphyry in the southwest and northeast portions of the deposit and consists primarily of veins and vein selvages of illite interstratified with an average of 7 percent smectite r 3 ordering the veins and selvages also contain small amounts of smectite and kaolinite the illite smectite interstratification is a mixture of 1m and 2m polytypes structural formulas for the illite show less k and al and more si than muscovite octahedral mg and both a tetrahhedral and an octahedral layer charge the kubler crystallinity index and smectite content increase systematically as particle size decreases consistent with an increase in smectite in the interstratification in the smaller size fractions intermediate argillic alteration consists of smectite illite and kaolinite that occur primarily as a replacement of plagioclase phenocrysts a few veins of intermediate argillic minerals are present in the quartz monzonite porphyry illite is interstratified with an average of 6 percent smectite r 3 ordering but a few samples contain a regular interstratification of illite with 40 to 50 percent smectite r1 ordering the smectite replacing plagioclase is montmorillonite and smectite that occurs in one vein is beidellite statistical trends in intermediate argillic alteration mineralogy within the quartz monzonite porphyry show that illite and kaolinite abundances increase generally upward and toward the northeast smectite abundance increases generally downward and toward the southwest in a cross section near the center of the deposit abundances of kaolinite and illite decrease as abundance of smectite increases with increasing depth the occurrence of interstratified illite smectite averaging 6 to 7 percent smectite together with discreet smectite suggest formation near 200 c a temperature difference between phyllic and intermediate argillic alteration could not be resolved from the mineralogy temperature estimates from fluid inclusions for phyllic alteration at other porphyry copper deposits generally range from 200 to 350 c the activity ratio of na k for the fluid calculated from na k in illite averages 5 0 for a phyllic vein that crosscuts propylitic alteration 1 4 for a phyllic vein that crosscuts potassic alteration and 2 8 for intermediate argillic alteration superimposed on potassic alteration log f h 2 o f hf of the hydrothermal fluid computed from the fluorine content of illite averages 6 1 for a phyllic vein that crosscuts propylitic alteration 5 8 for a phyllic vein that crosscuts potassic alteration and 5 7 for intermediate argillic alteration log f h 2 o f hf of fluids forming late stage biotite is about 5 0 intermediate argillic alteration could not be correlated with sulfides in the quartz monzonite porphyry an increase in illite upward and toward the northeast may correlate with massive sulfides in sediments recently discovered in that region

sediments and processes on a small stream flow dominated devonian alluvial fan shetland islands abstract the main conglomerate type of a small devonian alluvial fan in shetland northern britain is an inverse to normally graded framework supported gravel the sedimentological details of these beds and fundamental considerations of the mechanics of movement of highly concentrated flows suggests that neither debris flow nor grain flow were responsible for the deposition of these conglomerates on the contrary these inverse to normally graded conglomerates were deposited by water as thick gravel sheets with little topographic relief but broadly analogous to longitudinal bars they were deposited under high aggradation conditions first on the rising and then on the falling flood the high concentration of material in transport on the rising and peak flood was responsible for the polymodal and unstratified nature of the conglomerates as the flood waned normal grading was developed and a preferred horizontal fabric was produced under low concentrations of sediment other conglomerate types comparatively of lesser importance were deposited from highly concentrated clast dispersions and are notably richer in matrix and locally possess inverse grading the hydrological environment was one of flashy discharges of short duration but of high velocity flow was dissipated rapidly perhaps due to extreme water loss this example from the devonian of shetland provides an interesting alternative to the mass transport dominated fan models currently in vogue

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

endeavour 26 north a porphyry copper gold deposit in the late ordovician shoshonitic goonumbla volcanic complex new south wales australia endeavour 26 north is the largest of 12 pipelike porphyry cu au deposits found near parkes in central west new south wales within the late ordovician goonumbla volcanic complex the dominant volcanic rocks of the complex the goonumbla volcanics are latitic flows and volcanic breccias which are overlain by the trachytic wombin volcanics the volcanic rocks are characterized by high k 2 o and high k 2 o na 2 o ratios which are typical of the shoshonite association as well as an enrichment in large ion lithophile elements and a low concentration of high field strength elements the nelungaloo volcanics form an early ordovician nonshoshonitic volcanic substrate to the complex which initially developed in a submarine and subsequently subaerial setting the 87 sr 66 sr epsilon nd and pb isotope data indicate the magmas were derived from mantle sources the shoshonitic magmas may be products of high pressure fractionation in the subcontinental lithosphere the porphyry deposits are associated with a gravity low which is taken to reflect a subvolcanic chamber beneath the center of the complex all deposits are located within a pronounced circular feature in the aeromagnetic data that is interpreted as the margin of a collapsed caldera dioritic to monzonitic stocks which in part define the caldera rim represent a resurgent phase of magmatism the endeavour 31 stock which was part of this phase is ringed by six porphyry cu au deposits including endeavour 26 north the deposits are centered on fingerlike quartz monzonite porphyries which cut the endeavour 31 stock at depth geochemical anomalies of cu and zn in the bedrock define the size of the alteration system associated with the stock in part the distribution of the cu au deposits is controlled by the endeavour lineament in comparison to most other volcanic and intrusive rocks of the goonumbla volcanic complex the endeavour

inverse grading resulting from coarse sediment transport lag inverse grading in turbidites is conventionally ascribed to dispersive pressure caused by mutual collisions among grains within a traction carpet or grain flow the shearing traction carpet is supposed to become stratified with particle size increasing upward freezing of this traction carpet yields an inversely graded layer an alternative mechanism proposed here emerges from the fact that coarse sediment fractions are transported more slowly than fine fractions in a turbidity current a sufficiently heterogeneous mix of sediment sizes should undergo streamwise size segregation as the coarsest fractions lag behind if deposition begins before the coarsest fraction that will reach a particular station has arrived the lower part of the resulting deposit should be inversely graded a similar mechanism may produce inversely graded intervals in pyroclastic flow deposits because the head of a turbidity current typically travels only about 0 83 as fast as flow velocity in the body a short distance behind the head the coarsest grains able to keep up with the front of the flow are those having transport velocity v sed nearly equal 0 83 u body if coarser size fractions are available they will arrive later than the head permitting the development of inverse grading the proposed mechanism will not operate when the coarsest size fraction travels as fast as or faster than the head of the flow or when onset of deposition is delayed until after the coarsest size fraction has arrived assuming a logarithmic velocity profile below the maximum velocity streamline transport velocity can be calculated for particular sizes of suspended sediment and expressed as a fraction of flow velocity an upper limit for flow strength shear velocity can then be derived from the fall velocity of the coarsest grains at the base of an inversely graded interval u 4 w init where deposition of an inversely graded turbidite began immediately after passage of the head of the current u nearly equal 4 w init

hummocky cross stratification like structures in deep sea turbidites upper cretaceous basque basins western pyrenees france by mulder et al 2009 sedimentology 56 997 1015 discussion

sodium calcium metasomatism chemical temporal and spatial relationships at the yerington nevada porphyry copper deposit tilting associated with extensional tectonics has exposed 1 800 m of continuous palcovertical relief through the jurassic age yerington porphyry copper deposit the rarely observed root zones of a porphyry system are characterized at yerington by sodium calcium metasomatism the principal hydrothermal reactions involve the replacement of primary k feldspar by oligoclase and of primary biotite by actinolite copper has been removed sodic calcic alteration developed at deep intrusive contacts nearly simultaneously with potassic alteration and copper mineralization at shallow intrusive contacts the reactions accompanying potassic alteration are the reverse of those accompanying sodic calcic alteration plagioclase reacted to form k feldspar hornblende reacted to form biotite the potassic and sodic calcic alteration couplet principally accompanied each of two separate intrusive events 1 luhr hill granite stock and associated porphyry dikes and 2 walker river granite porphyry dikes the younger walker river intrusion was emplaced at slightly deeper levels than the older luhr hill complex vertically stacked and partially superimposed alteration and mineralization patterns resulted from differences in depth and in timing of emplacement at lower temperatures late sodic alteration was superimposed on early sodic calcic alteration at deeper levels in the system whereas late quartz sericite pyrite alteration was superimposed on potassic alteration at higher levels sodic alteration is characterized by the replacement of k feldspar by albite and of biotite by chlorite copper deposited during potassic alteration was remobilized the transition to lower temperature alteration is associated only with the walker river intrusion the hydrothermal system associated with the emplacement of the luhr hill complex had not evolved to lower temperature assemblages prior to emplacement of the walker river dikes phase equilibria and geologic reconstruction of depth of emplacement suggest that temperatures during early sodic calcic alteration were limited to the range of 360 degrees to 480 degrees c at pressures between 300 and 800 bars late sodic alteration took place at similar pressures but at temperatures less than 360 degrees c nearly simultaneous development of potassic and sodic calcic alteration resulted from the flow of fluids away from intrusions at shallow levels potassic alteration and from the flow of fluids toward intrusions at deeper levels sodic calcic alteration because k na and na ca activity ratios of a fluid in equilibrium with granitic rocks decrease with decreasing temperature cooling of high temperature fluids can generate potassic alteration and heating of fluids to high temperatures can generate sodic or sodic calcic alteration

grain size sorting in grainflows at the lee side of deltas the sorting of sediment mixtures at the lee slope of deltas at the angle of repose is studied with experiments in a narrow deep flume with subaqueous gilbert type deltas using varied flow conditions and different sediment mixtures sediment deposition and sorting on the lee slope of the delta is the result of i grains falling from suspension that is initiated at the top of the delta ii kinematic sieving on the lee slope iii grainflows in which protruding large grains are dragged downslope by subsequent grainflows the result is a fining upward vertical sorting in the delta systematic variations in the trend depend on the delta height the migration celerity of the delta front and the flow conditions above the delta top the dependence on delta height and migration celerity is explained by the sorting processes in the grainflows and the dependence on flow conditions above the delta top is explained by suspension of fine sediment and settling on the lee side and toe of the delta large differences in sorting trends were found between various sediment mixtures the relevance of these results with respect to sorting in dunes and bars in rivers and laboratory flumes is discussed and the elements for a future vertical sorting model are suggested

can dispersive pressure cause inverse grading in grain flows discussion the concept of dispersive pressure was originally proposed by bagnold 1954 who showed experimentally that sheared granular material develops a dispersive pressure that is proportional to the shear stress and the particle concentration legros 2002 presented a theoretical analysis suggesting that dispersive pressure cannot account for the inverse grading commonly observed in grain flows modified grain flows or traction carpets contrary to what has been accepted for decades by many sedimentologists he pointed out that if the dispersive pressure in a sheared granular mass increases and exceeds the applied normal stress or static pressure the net upward force acting upon the bed causes it to expand as has in fact been observed in experiments bed expansion immediately causes a decrease in particle concentration and consequently in dispersive pressure until the latter balances the static pressure and expansion stops if the dispersive pressure becomes less than the static pressure the net downward force acting upon the granular bed causes compaction thus increasing the particle concentration and dispersive pressure this is an important concept enhancing our understanding of an as yet poorly understood process however legros 2002 went further to state that the dispersive pressure must always equal the applied normal shear stress at every level emphasis mine through the shearing granular bed this implies that the whole sheared bed is in constant equilibrium which is probably not the case in this discussion a modified process is proposed that accounts for the bipartite traction carpet structure proposed by sohn 1997 traction carpets are moving layers of highly concentrated bedload material developed beneath and driven by an overlying turbulent flow dzulynski and sanders 1962 sohn 1997 on the basis of numerical analyses computer simulations field measurements and experimental studies bagnold 1955 1963 hanes and bowen 1985 wan

formation of inversely graded basal layers in ignimbrites by progressive aggradation a model for the formation of coarse depleted inversely graded basal layers in ignimbrites is presented it is proposed that the deposit forms by progressive aggradation of sediment below the flow and that the basal layer at any place is deposited from the leading part of the flow sinking of large lithics within the flow produces a normal grading which is reversed in the basal deposit by the caterpillar like motion of the flow large pumices rise to the top of the flow and migrate to the head where many are pushed aside and accumulate in levees pumices which deposit from the head are mostly re entrained into the flow due to their buoyancy but exceptionally some may be trapped at the base of the aggrading deposit we describe concentrations of large pumices in the basal layer of small volume ignimbrites which give support to this model the model is an alternative to the traditional hypothesis which assumes that coarse depleted inversely graded basal layers in ignimbrites are the result of the upward migration of large particles out of the basal layer in a flow which later freezes en masse

experiments on the flow behaviour of granular materials at high velocity in an open channel a series of laboratory flume experiments has been conducted to investigate the flow behaviour of dry sand at high velocities the first incentive for this experimental programme was an attempt to explain the high mobility of apparently dry masses of rapidly moving broken rock during rock avalanches sturzstroms test velocities of over 5 m s and most other parameters of the tests were found to be dimensionally similar to those for a typical rock avalanche yet the conclusion was negative even the most rapid of the experiments indicated flow behaviour which is in conformity with the constant volume uniform coulomb friction relationship as applicable to slow shearing this conclusion was confirmed independently both by direct measurements of base friction and mean density of the flows and by detailed observations of flow uniformity acceleration and velocity profiles the surprising mobility of st umlrzstroms therefore requires a different explanation une serie de tests a canaux a ete entreprise dans le

on traction carpet sedimentation traction carpets are highly concentrated bedload layers that are developed beneath and driven by turbulent overlying flows they have a convex up velocity profile and comprise a lower frictional and an upper collisional region the frictional region having a particle concentration more than 80 of the packed bed is characterized by nearly continuous grain contacts low strain rate and hampered grain segregation on the other hand the collisional region has a particle concentration between 15 and 80 of the packed bed and is characterized by active grain collisions and higher strain rate deposition from the traction carpets occurs via progressive aggradation of the bed rather than via en masse freezing while the downward grain flux from the overlying flow maintains them the thickness of a traction carpet stratum is therefore determined by the cumulative amount of sediment settled during the lifespan of a traction carpet and can be much larger than the thickness of a moving traction carpet inverse grading can be produced in the collisional region by the vertical gradient of dispersive pressure which is related to nonuniform distribution of particles when a thick frictional region develops however the inverse size distribution in the collisional region is poorly recorded in the deposits depositional features of traction carpet strata are therefore determined by the duration of a traction carpet and the thickness ratio of collisional to frictional regions the thickness ratio is further controlled by the applied shear stress sediment fallout rate and grain size generally a collisional region is better developed beneath a highly competent and coarse grained gravelly flow whereas a thick frictional region is developed beneath a heavily sediment laden fine grained sandy flow this explains the more common occurrence of inverse grading in coarse grained deposits

an experimental study of subaquaeous slipface deposition abstract a flume study indicates that grainflow on slipfaces accounts for most cross strata formed in unidirectional shallow water flows the slipfaces studied were on small megaripples and delta like steps 0 06 0 28 m high during intermittent avalanching at relatively low flow velocities periods between avalanches were marked by grainfall onto the slipface the intensity of which was greatest near the brink of the slipface and increased with current velocity nearly all grainfall deposits however were incorporated into subsequent grainflows grain flow cross strata were made up of relatively distinct layers at least near the base of the slipface continuous avalanching at high flow velocity was marked by a steady stream of grains forming more poorly defined cross strata although the fundamental cause of grain flow is the gradual buildup of sediment on the upper slipface to the angle of initial yield four other processes were recognized as promoting avalanching 1 migration of superimposed bedforms to the brink 2 generation of turbulent pulses upstream of the brink 3 lee eddy impingement on the lower slipface and 4 extension of the lee eddy above the brink the lee eddy proved very significant in slipface processes by redistributing grainfall sediments and both promoting and impeding grainflow regression analyses showed that the slipface advance per avalanche sa is strongly correlated with the slipface height h expressed approximately by sa 0 060h in addition sa is a direct function of the rate of slipface advance vb the relationship among sa h and vb can be expressed as sa h 0 0385 1 0 134 min cm vb 1 cross strata dip angles between 28 and 34 show no systematic relation to h and vb but dip angles greater than 34 occurred only when both h and vb were small and dip angles less than 28 occurred only when both h and vb were large

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

tsunami deposits in a super large wave flume abstract understanding the process of sediment transport under tsunami inundation is essential to providing credible information about potential tsunamis from tsunami deposits in this study a super large wave flume 205 m long and 3 4 m wide was used to investigate the hydraulic process of tsunami inundation and sedimentary features of the resulting tsunami deposit a uniformly sloping topography 1 50 with a sand dune 0 2 m high was built in the flume and the topography change induced by a solitary wave was measured the maximum wave height at the shoreline was 0 6 m and the horizontal velocity reached up to 3 5 m s resulting in a sediment concentration of up to 5 by volume the inundation and return flow completely eroded the dune and caused deposition which showed landward and seaward thinning and fining the vertical distribution of grain size and density in the inundation flow indicated upward fining and an upward decrease in density and the deposits showed inverse grading at the base in addition to normal grading therefore the inverse grading was attributed to the depositional process instead of the vertical distribution of grain size in the flow such as via a traction carpet the inundation flow was classified into two phases the first phase flow which appeared at the front of the inundation flow was governed by the wave speed at the shoreline the second phase flow which occurred near the dune was controlled by the difference in wave levels in front of and behind the dune the deposits caused by the first phase flow near the inundation limit were constant regardless of the presence of the dune indicating that the effect of the dune on the deposits was limited in the nearshore region the deposits near the inundation limit showing rapid fining and different chemical compositions were carried by muddy foam floating on the water surface the sediment supply from offshore to onshore over the dune was small and the erosion of the sand dune accounted for 36 of the onshore deposits the offshore deposits were mainly caused by wave motion and the contribution of the onshore sediment brought by the return flow was small 24 however the return flow had a large effect on the sedimentary structure of the offshore deposits such as seaward fining our results will help to examine the physical processes resulting in the empirically established common sedimentary characteristics of tsunami deposits and will provide a detailed data set to validate sediment transport models used in numerical simulations

heterozoan carbonate deposition on a steep basement escarpment late miocene almeria south east spain heterozoan temperate water carbonates mixed with varying amounts of terrigenous grains and muddy matrix azagador limestone accumulated on and at the toe of an inherited escarpment during the late tortonian early messinian late miocene at the western margin of the almeria nijar basin in south east spain the escarpment was the eastern end of an uplifting antiform created by compressive folding of triassic rocks of the betic basement channelized coralline algal bryozoan rudstone to coarse grained packstone together with matrix supported conglomerate are the dominant lithofacies in the higher outcrops comprising the deposits on the slope these sediments mainly fill small canyon shaped half graben depressions formed by normal faults active before during and after carbonate sedimentation roughly bedded and roughly laminated coralline algal bryozoan rudstone to coarse grained packstone are the main lithofacies forming an apron of four small kilometre scale lobes at the toe of the south eastern side of the escarpment almeria area channelized and roughly bedded coralline algal bryozoan rudstone to coarse grained packstone conglomerates packstone and sandy silt accumulated in a small channel lobe system at the toe of the north eastern side of the escarpment las balsas area carbonate particles and terrigenous grains were sourced from shallow water settings and displaced downslope by sediment density flows that preferentially followed the canyon shaped depressions roughly laminated rudstone to packstone formed by grain flows on the initially very steep slope whereas the rest of the carbonate lithofacies were deposited by high density turbidite currents the steep escarpment and related break in slope at the toe favoured hydraulic jumps and the subsequent deposition of coarse grained low transport efficiency skeletal dominated sediment in the apron lobes accelerated uplift of the basement caused a relative sea level fall resulting in the formation of outer ramp carbonates on the apron lobes which were in turn overlain by lower messinian coral reefs this is the first known example of a base of slope apron within temperate water carbonate systems this article is protected by copyright all rights reserved

aeolian slipface dynamics and grainflow morphologies on earth and mars abstract in 2015 an active dune field on mars was visited up close by the curiosity rover in gale crater providing the first high resolution ground images of fine scale windblown features not previously resolved from orbital based imagery for the first time these images allow for direct comparison with terrestrial aeolian dynamics and provide critical ground truth data to bridge the gap between model predictions and satellite observations the image data from the slipface on the namib dune within the bagnold dune field shows grainflow morphologies that are similar to dunes on earth quantitative estimates of flow thickness based on shadow length are presented for the grainflows on the namib dune slipface and compared to grainflow characteristics measured by terrestrial laser scans from the maspalomas dune field located in gran canaria spain using observations from maspalomas to support interpretations of martian slipface dynamics we discuss implications for the local wind regime style of grainflow seasonal activity and dune migration the presence of multiple large magnitude grainflows on the namib slipface suggests an active aeolian environment capable of delivering enough sediment to the slipface to initiate these flows and transport sediment to the bottom of the lee slope however the thinness of grainflows on the namib dune the formation of smaller grainflows directly below the dune brink and limited grainfall suggest a lower wind energy environment at least for the most recent slipface activity large actively migrating stoss ripples obliquely oriented to the dune crest regularly deposit sediment on to the upper slipface and may be a mechanism in which larger grainflow occur during seemingly low energy wind events this mechanism of sediment delivery may also explain the existence of a variety of slipface morphologies both young and old which are otherwise quickly erased on earth due to sediment redistribution and grainfall

subaqueous grain flows at the head of carmel submarine canyon california abstract the head of carmel submarine canyon lies in 15 m of water about 200 m off a coarse sand beach in the southeast corner of carmel bay california very coarse sand is the predominate material on the beach adjacent shelf and upper canyon head slopes while silt and clay cover the surface below a water depth of about 35 m along a shore normal transect median grain size decreases between the beach and canyon rim but increases down the upper canyon head slope on angle of repose slopes in the upper canyon head downslope coarsening deposits which are everywhere there is active sand movement are similar to a type of sediment gravity flow deposit formed by grain flows sand avalanches using three sand fractions that were dyed different fluorescent colors scuba divers generated sand avalanches that produced deposits similar to the natural deposits the dyed sand deposits which extended as far as 25 m below the initiation point were inversely graded and increased in grain size downslope inverse grading was well developed within two m of the initiation point though the thicknesses of the three layers varied in a nonsystematic manner both across and down slope the minor amount of native material found within the dyed sand layers showed hat entrainment of the underlying sand was minimal

palaeoproterozoic fluvio aeolian deposits from the lower gulcheru formation cuddapah basin india abstract an analysis of facies was done to understand the depositional environment and the palaeoclimate of the sedimentary succession from the lower part of the palaeoproterozoic 2 0 ga gulcheru formation exposed along the southwestern margin of the cuddapah basin twelve distinct sedimentary facies were identified and grouped into three main facies associations wadi fan ephemeral fluvial and aeolian identification of the fluvial and the aeolian facies allowed a more elaborate interpretation of the depositional environment and its palaeoclimate facies characteristics indicated that the sediments in the beginning were deposited in a dominantly aeolian realm under warm and semiarid climatic condition translatent strata pin stripe lamination zibars high index granule ripples sand sheet deposits grainflow cross strata and grainfall laminae asymptotically down lapping cross strata often with erosional lower bounding surface and massive sand bodies with bimodal fabric the unambiguous evidences of aeolian depositional regime led to this conclusion however the aeolian regime was often punctuated temporarily by fluvial input from ephemeral streams during sudden rainstorm depending upon the size character and availability of sediments relief difference and the sediment water ratio cohesionless debris flow hyperconcentrated flood flow and sheetflood deposits were formed near the basin margin whereas coarse load braided channel deposits were laid further inside the basin ephemeral lakes ponds were formed due to stagnation of floodwater in normally dry interdune lows overbank interdune sediments were deposited in those ephemeral lakes ponds amongst the aeolian facies translatent strata and sand sheet dominate in the west whereas massive beds and dunes with well developed slipfaces dominate in the eastern part the spatial distribution of the aeolian bedforms suggests development of erg apron to the west and dune field erg to the east the aeolian sediments identified in the gulcheru formation may be considered to be amongst the oldest palaeoproterozoic aeolian sediments of the world