core based evidence for sandy slump and sandy debris flow facies in the pliocene and pleistocene of the gulf of mexico implications for submarine fan models examination of nearly 3 500 feet of conventional core from pliocene and pleistocene deep water reservoirs cored in 25 wells in 8 different areas covering the eastern central and western gulf of mexico reveals that the reservoirs are predominantly composed of mass transport deposits mainly sandy slumps and sandy debris flows 60 100 of cored intervals bottom current reworked sands are common 10 50 of importance to existing submarine fan models is that turbidities are extremely rare 1 of all cores sedimentary features indicative of slump and debris flow origin include sand units with sharp upper contacts slump folds discordant steeply dipping layers up to 60 degrees glide planes shear zones brecciated clasts rafted mudstone clasts planar clast fabric inverse grading of clasts and moderate to high matrix content 5 20 these reservoirs have been interpreted by others to represent turbidite dominated basin floor fans and slope fans of the often used sequence stratigraphic model however our core data do not show a dominance of turbidities sandy debris flows exhibit a variety of log motifs e g blocky fining up and coarsening up due to changes in concentration of midstone clasts and a variety of internal seismic facies e g parallel continuous irregular discontinuous chaotic discontinuous and lateral pinch out perhaps due to changes in stacking patternsmore of debris flows and slumps classic submarine fan models commonly advocated for these reservoirs may not be appropriate we propose a slump and debris flow dominated slope model in which sea floor topography and depositional freezing i e plastic flows control sand distribution and geometry contrary to popular belief sandy debris flows can be thick areally extensive and excellent reservoirs less

mass transport processes on amazon cone western equatorial atlantic three large mass transport deposits occur on the upper to middle amazon cone these slump debris flow complexes have been mapped from 3 5 khz echograms and cover approximately 75 000 sq km or about 10 of the cone the debris flows traveled down slopes with gradients as low as 1 90 to 1 165 0 3 to 0 6 for distances up to 300 km these deposits average 10 to 50 m in thickness and the total amount of sediments displaced may exceed 3 800 cu km the upslope parts of these complexes generally consist of hummocky slump or slide deposits which are commonly bounded by scarps of varying relief downslope from this zone of removal the deposits consist of thin the occurrence of such widespread mass movements on the amazon cone indicates that mass transport is probably an important sedimentation process on deep sea fans however most studies and models of modern deep sea fans have minimized or ignored the potential importance of mass transport processes in fan development we suggest that in the future both ancient and modern deep sea fans be more closely examined for mass transport deposits so that the importance of this process to overall fan development can be more accurately assessed

the downstream gradation of particle sizes in the squamish river british columbia the exponential downstream decline in particle size predicted by sternberg 1875 is examined within a highly active alpine fluvial environment the gravel bed squamish river in southwestern british columbia transect survey procedures for sampling within the coarse alluvial gravels are described in detail downstream trends for various particle size statistics plotted with distance from a major sediment source are considered according to two scenarios evaluation of overall trends indicates that the downstream expression derived by sternberg 1875 is not the most appropriate rather curves are better described by power functions this reflects a very rapid decline in particle size immediately downstream of the major sediment source secondly evaluation of downstream trends in relation to channel planform determines that exponential functions with different coefficients describe adequately relations within individual planform reaches there is insufficient evidence to suggest which of these two scenarios may be appropriate several lines of evidence suggest that the trends found are more the result of selective sediment transport phenomena than of abrasion a condition attributed to channel competence within a system dominated by sediment supply conditions

longitudinal changes in the size and shape of stream bed material evidence of variable transport conditions summary the pattern of downstream changes in particle size and shape is used to identify dominant transport conditions in a basin with two main lithologies having distinct spatial distributions grain size decreases exponentially and roundness increases geometrically in the sandstone group but shale particles show no such changes largely because shale is supplied discontinuously below headwater reaches where abrasion is no longer at its most effective particle flatness varies more consistently between the lithological groups an initial increase being followed by a geometric decrease discs and blades are the dominant zingg shapes reflecting the influence of bedrock structure and preferential transport three process regimes are identified in which different processes are dominant abrasion and size sorting in the headwater area shape and size sorting in the middle reaches sorting and breakage towards the downstream end of the stream underlying the general tendencies are discontinuities related to tributary inflow the main effects being to increase grain size and flatness below junctions

interpretation of channelized architecture using three dimensional photo real models pennsylvanian deep water deposits at big rock quarry arkansas abstract mapping geological details and interpreting three dimensional geometries in a highly heterogeneous outcrop such as the exposure at big rock quarry has been a continuous challenge especially because high vertical cliffs make access to most of the rocks difficult for direct geological observations previous interpretations of facies architecture were derived from gamma ray profiles a core and measurements made on two dimensional photomosaics this paper represents the first attempt of three dimensional interpretation of the geometry and facies pattern of the jackfork nested channel complex deposited at the base of slope examination of the photo real model of the outcrop with assigned lithologies allowed extraction of accurate 3 d qualitative as well as quantitative channel dimensions geometric information this facilitated interpretation and reconstruction of the submarine channel complex architecture making possible correlations of strata exposed on the two sides of the quarry most of the exposed vertically and laterally stacked channels are large aggradational with well defined axial regions overlain by matrix supported breccia which grades upward into amalgamated sandstones the thickness of the sandstone decreases toward the southeastern end of the quarry where more shale is present the channel infill consists of thin bedded sandstones interlayered with shale which overlain the breccia the upper part of the quarry is made up of smaller lateral migrating channels significant channel width and thickness variation can be recognized at outcrop scale thirty eight identified channels are characterized by a relatively low aspect ratio 4 1 to 32 1 with channel dimensions ranging from 25 m to 314 m wide and 2 m 24 m deep bed thickness distributions of various facies show that the sandstone comprises a significant proportion 83 of the total channel thickness while shale and breccia represent about 8 and 17 respectively this yields a high net to gross ratio of more than 80 compared to previous reconstructions our 3 d photo real model is more accurate and it can be used to calibrate simulation of processes in deep water environments

the bouma division a and the possible duration of turbidity currents abstract experimental data arnott and hand 1989 combined with theoretical arguments suggest that the transition in a turbidite from division a to division b occurs at a deposition rate of unsupported grains of about 6 7 10 4 m s 1 in the case of fine medium quartz sand a second rate may be calculated from properties measured at the transition from division b to division c allen 1971b these rates together permit an estimate to be made of the order of magnitude of the duration of deposition from a turbidity current the calculated order of a few tens of minutes for a mio pliocene turbidite described and interpreted hydraulically by komar 1985 is in broad agreement with his independent estimate based on the sequenc of sedimentary structures

experimental evidence for the origin of two kinds of inclusions in diamonds from the deep mantle abstract the conditions of origin for the type iii inclusions in diamonds from brazil hutchison thesis 1997 and the napx en inclusion from china wang and sueno miner j 18 1996 9 16 were experimentally determined using a split sphere anvil apparatus ussa 2000 the type iii inclusions formed at a minimum pressure and temperature of 25 gpa and 2000 c while the origin of the napx en inclusion was close to 23 gpa and 1900 c both determinations suggest that the temperature at the corresponding depths is about 300 c higher than predicted by most geotherms for a convecting mantle without a thermal boundary layer at 660 km both kinds of inclusions required rapid single stage transport by carbonate melt to the earth s surface which is consistent with the depths of origin for this melt greater than 660 km the unusual composition of the napx en inclusion is the result of metasomatism by carbonate melt enriched in na k and mg and depleted in si and al since this melt is not kimberlitic in composition exchange of material between the melt and the mantle was necessary for the melt to become kimberlitic by the time it reached the surface the resulting metasomatism taking place over a long period of time could cause major changes in the mineral and chemical composition and the structure of the earth s mantle and thus play an important role in its evolution

hydraulic controls of grain size distributions of bedload gravels in oak creek oregon usa grain size distributions of gravels transported as bedload in oak creek oregon show systematic variations with changing flow discharges at low discharges the gravel distributions are nearly symmetrical and gaussian as discharges increase the distributions become more skewed and follow the ideal rosin distribution the patterns of variations are established by goodness of fit comparisons between the measured and theoretical distributions and by q mode factor analysis two end members are obtained in the factor analysis having respectively almost perfect gaussian and rosin distributions and the percentages of the two end members within individual samples vary systematically with discharge transformation from gaussian to rosin distribution with increasing discharge may be explained by processes of selective entrainment of grains from a bed of mixed sizes samples of bed material in oak creek follow the rosin distribution at high discharges the transported bedload approaches the grain sizes of that bed material source and mimics its rosin distribution random selection processes must be more important to grain entrainment at lower discharges so that the resulting gaussian distributions of transported bedload reflect similar distributions of bed stresses exerted by the stream flow the results from oak creek demonstrate that the competence of the flow is reflected in the entire distribution of transported gravel sizes a sequence of layers of fluvial gravels modern or ancient might show systematic variations between coarse rosin and finer grained gaussian distributions and these could be used to infer frequencies of various discharges and to establish a relationship to the source sediment with further study analyses of changing bedload grain size distributions and their transport rates will lead to a better understanding of downstream variations in grain sizes of bed sediments and how their distributions reflect the progressive development of textural maturity

enstatite jadeite join and its role in the earth s mantle phase relations on the enstatite jadeite join were experimentally determined at solidus temperatures and 90 152 kb and at 1400 2050 c 175 219 kb with a split sphere anvil apparatus ussa 2000 new findings include immiscibility in garnet and determination of the stability of naalsio4 calcium ferrite structure with stishovite a thermodynamic model for the enstatite jadeite join was developed to calculate a complete phase diagram for the join at 500 2500 c and 0 270 kb the results indicate that the two major discontinuities in the earth s mantle at 400 and 670 km depths could correspond respectively to the formation and the breakdown of garnet with a pyroxene composition a model for a chondritic upper mantle is proposed in which large scale chemical and mineral layering was produced by fractionation of liquidus phases in a magma ocean solidification was completed at 400 km depth by crystallization of sodium enriched residual melts which produced a pyroxene layer at 300 400 km depths

comparison of depositional elements of an ancient and a modern submarine fan complex early pennsylvanian jackfork and late pleistocene mississippi fans normark urged that all future meaningful deep sea fan comparisons be confined to key depositional elements common to most turbidite systems these elements should include basin size tectonic and eustatic setting and depositional process indicators a test case for elemental comparisons between two widely studied fan complexes is presented and evaluated the lower pennsylvanian morrowan jackfork submarine fan complex extends from central arkansas to northeast texas sequence analysis suggests that the jackfork is composed of four to seven depositional episodes and occupies the floor of a deep basin bordered to the north and east by a passive carbonate siliciclastic shelf margin and to the south and east by a northward advancing orogenic belt the jackfork apparently unrestricted to the west and southwest the mississippi submarine fan complex extends from the submerged continental shelf of southern louisiana to the abyssal depths between yucatan and florida the fan complex is primarily pleistocene in age with the present morphologic fan being late wisconsinian the mississippi fan is composed of 17 depositional episodes it occupies the floor of a deep basin bordered on the north and west by quiescent halokinetic siliciclastic shelf margins and to the east and south by passive carbonate margins elemental comparisons between themore mississippi fan and a palynspastically restored jackfork fan complex suggest that both are quite similar even though the mississippi fan is up to three times larger in some categories comparative study of key depositional elements facilities a more complete understanding of both modern and ancient submarine fans less

mineral inclusions in diamonds associations and chemical distinctions around the 670 km discontinuity three new mineral associations have been discovered within diamonds from the juina district of brazil these include a previously unrecorded na al mg fe sio3 phase associated with ferropericlase and the tetragonal almandine pyrope phase tapp also reported are an association of corundum with aluminous pyroxene and an olivine composition phase associated with ferropericlase the minerals in each association often occurred within the same diamonds in addition to being recovered from individual diamonds in different combinations high pressure experimental data indicate that these associations formed at different depths within a region ca 60 km on either side of the upper mantle lower mantle boundary mineral compositions show that for the regions sampled the deep transition zone and lower mantle are chemically distinct and inhomogeneous importantly in the shallow lower mantle al is not solely accommodated within perovskite structured mg fe sio3 as some recent experimental studies have suggested

do gravel bed river size distributions record channel network structure 1 bed load sediment particles supplied to channels by hillslopes are reduced in size by abrasion during downstream transport the branching structure of the channel network creates a distribution of downstream travel distances to a given reach of river and thus may strongly influence the grain size distribution of the long term bed load flux through that reach here we investigate this hypothesis using mass conservation and the sternberg exponential decay equation for particle abrasion to predict bed material variability at multiple scales for both natural and artificial drainage networks we assume that over a sufficiently long timescale no net deposition occurs and that grains less than 2 mm are swept away in suspension we find that abrasion during fluvial transport has a surprisingly small effect on the bed load sediment grain size distribution for the simple case of spatially uniform supply of poorly sorted hillslope sediments this occurs because at any point in the channel network local resupply offsets the size reduction of material transported from upstream thus river bed material may essentially mirror the coarse component of the size distribution of hillslope sediment supply furthermore there is a predictable distance downstream at which the bed load grain size distribution reaches a steady state in the absence of net deposition due to selective transport large scale variability in bed material such as downstream fining must then be due primarily to spatial gradients in hillslope sediment production and transport characteristics a second key finding is that average bed load flux will tend to stabilize at a constant value independent of upstream drainage area once the rate of silt production by bed load abrasion per unit travel distance is equal to the rate of coarse sediment supply per unit channel length q bed load flux equilibrates over a distance that scales with the inverse of the fining coefficient in the abrasion rate law and can be approximated simply as q 3 thus the efficiency of particle abrasion sets a fundamental length scale shorter for weaker rocks and longer for harder rocks which controls the expression in the river bed of variability in sediment supply we explore the role of the abrasion length scale in modulating the influence of sediment supply variability in a number of channel network contexts including individual tributary junctions a sequence of tributary inputs along a main stem channel and variable basin shapes and network architecture as expressed by the width function these findings highlight the need for both data and theory that can be used to predict the grain size distributions supplied to channels by hillslopes

duplex like structures in submarine fan channels ouachita mountains arkansas submarine fan channel sequences of the jackfork formation lower pennsylvanian at degray dam section in the ouachita mountains arkansas contain discrete units 10 75 cm thick with moderately dipping 25 40 sigmoidal imbricate slices adjacent units with opposing imbricate slices are common the sigmoidal structures are similar in geometry to a tectonic feature known as a duplex a tectonic origin of sigmoidal structures however seems unlikely because opposing directions of imbrication in adjacent units would require an unrealistic tectonic movement history for the area we propose that the jackfork sigmoidal structures were formed by a process kinematically similar to that responsible for generating duplex structures unlike tectonic duplexes however the sigmoidal structures were formed by soft sediment deformation of sand and mud layers as high energy sediment gravity flows glided over these layers sediment gravity flows responsible for forming the sigmoidal deformation were probably generated by slumping of adjacent channel walls dip direction of sigmoidal slices is perpendicular to channel axes thus recognition of sigmoidal deformation structures may be useful in inferring the trend of channels in ancient submarine fan complexes

experimental study of abrasion and its role in producing downstream fining in gravel bed rivers abstract previous experimental studies on abrasion of gravel showed diminution rates much lower than those typical of gravel bed rivers this might be one reason many studies of downstream fining in rivers stress hydraulic sorting as the dominant fining mechanism previous experiments however did not replicate well the particle to particle impact between the bed load gravels and bed gravels in rivers on alluvial fans during floods the purpose of this study was to reexamine the effect of abrasion on downstream fining to determine if abrasion is responsible for longitudinal changes in gravel size in rivers on alluvial fans a rotating drum with three interior vanes was used to produce repeated collisions among test gravel particles in water the drum was only partially filled with water in order to simulate the impact velocity of particle collisions during a flood the test particles were slightly weathered andesite and chert taken from the bed of the watarase river japan experiments were conducted using three unisize grains l 7 0 128 mm to 6 5 91 mm m 5 5 45 mm to 5 0 32 mm s 4 0 16 mm to 3 5 11 mm and mixtures of two different sizes from the three size classes there are six principal results from the experiments 1 test gravel particles break frequently and decrease in weight rapidly 2 abrasion of chert produces mostly gravel while andesite produces mostly sand and silt 3 l size chert cobbles decrease in weight rapidly as a result of being broken into smaller pieces while andesite cobbles break so rarely that their weight decreases very slowly 4 s size andesite pebbles decrease in weight more rapidly than chert 5 abrasion depends strongly on the presence of different sizes because smaller fragments are crushed by larger gravel particles 6 diminution coefficients of andesite and chert obtained from the experiment are in the range of 10 3 10 1 km 1 diminution coefficients from this experiment are one to two orders of magnitude larger than those from previous experiments on abrasion this is mainly because of the larger impact velocities in this experiment diminution coefficients from the experiment are also consistent with those obtained from many japanese rivers on alluvial fans 10 2 10 1 km 1 this result suggests that downstream fining of river bed gravel on alluvial fans can be explained by abrasion

an integrated chemo and sequence stratigraphic framework of the early pennsylvanian deepwater outcrops near kirby arkansas usa and its implications on remnant basin tectonics abstract the jackfork group in arkansas u s a is a major training ground for academics students and petroleum industry geoscientists interested in deep water exploration and development several superb outcrop sections are exposed and over the years numerous papers have been published on these rocks the kirby sections in western arkansas provide a unique opportunity to build a complete and continuous sequence stratigraphic framework for early pennsylvanian time in the ancient ouachita basin there are 25 outcrops including 12 roadcuts on highway 27 and 13 measured sections in the baumgartner quarry all the measurements and interpretations on the outcrops were integrated with previous work using modern concepts of deepwater turbidite geology including 1 regional tectonic and sequence stratigraphic framework of the stanley group jackfork group and johns valley shale in the ouachita basin 2 deepwater outcrop characterization and correlation from the degray lake section dierks section and big rock quarry which are on the trend of the depositional fairway 3 chemostrata data from key shale layers which are considered as potential correlative condensed sections twenty five key shale samples from kirby degray and dierks sections have been tested using inductively coupled plasma and mass spectrometry icp ms tests an additional 525 samples were later collected for handheld x ray fluorescence xrf tests for both major and trace elements results of sequence and chemostrata analysis indicate that the entire kirby sections consist of at least three 3rd order sequences from the bottom of the jackfork group to the middle of the johns valley group and over ten 4th order sequences caused by a combined effect of tectonic uplift eustatic sea level change mixed sediment provenance and shifting of depositional fairways when the ouachita basin was transitioning from a passive margin to a remnant marine basin rare earth and trace element results are compared with known tectonic data to further pinpoint the tectonic environment of the ouachita basin during early pennsylvanian time which is dominantly a continental arc setting

elasticity of a majorite pyrope solid solution the elastic properties of a solid solution consisting of 59 mole percent pyropic garnet and 41 mg sub 4 si sub 4 o sub 12 majorite a high pressure form of pyroxene have been measured by brillouin spectroscopy under ambient conditions values of the adiabatic bulk modulus k sub s 164 plus minus 15 gpa and shear modulus g 89 4 plus minus 3 7 gpa are similar to those for low pressure aluminosilicate garnets the enstatite majorite reaction is characterized by a large 49 increase in k sub s and a much smaller 13 increase in g the properties of low pressure garnets suggest that the contrast in shear moduli for this reaction is probably larger in ca rich systems taken at face value the stp properties of these phases imply that large quantities of ca rich clinopyroxene are needed in order to satisfy seismologically determined shear modulus gradients in the transition zone this suggestion is however subject to considerable uncertainties in the pressure and temperature derivatives of elastic properties for mantle minerals and the velocity structure of the transition zone

reinterpretation of depositional processes in a classic flysch sequence pennsylvanian jackfork group ouachita mountains arkansas and oklahoma discussion the pennsylvanian jackfork group in the ouachita mountains of arkansas and oklahoma has conventionally been interpreted by many workers including us as a classic flysch sequence dominated by turbidites in a submarine fan setting however normal size grading and bouma sequences indicative of turbidite deposition are essentially absent in these sandstone beds they appear massive i e structureless in outcrop but when slabbed reveal diagnostic internal features these beds exhibit sharp and irregular upper bedding contacts inverse size grading floating mudstone clasts a planar clast fabric lateral pinch out geometries moderate to high detrital matrix up to 25 sigmoidal deformation duplex structures and contorted layers all these features indicate sand mplacement by debris flows mass flows and slumps mud matrix in these sandstones was sufficient to provide cohesive strength to the flow discrete units of current ripples and horizontal laminae have been interpreted to represent traction processes associated with bottom current reworking the dominance of sandy debris flow and slump deposits nearly 70 at degray spillway section and bottom current reworked deposits 40 at kiamichi mountain section and the lack of turbidites in the jackfork group have led us to propose a slope setting our rejection of a submarine fan setting has important implications for predicting sand body geometry and continuity because deposits of fluidal turbidity currents in fans are laterally more continuous than those of plastic debris flows and slumps on slopes a turbidite dominated fan model would predict an outer fan environment with laterally continuous sheetlike sandstones for the jackfork group in southern oklahoma and western arkansas whereas a debris flow slump model would predict predominantly a slope environment with disconne ted sandstone bodies for the same area

determination of offset across the northern margin of the wichita uplift southwest oklahoma the wichita uplift represents a tectonic element within the ancestral rocky mountains a series of basement involved uplifts and associated basins within the foreland of the ouachita orogen contrasting tectonic models for the evolution of the wichita uplift are evaluated by i analyzing the suite of structures within the frontal fault zone which separates the uplift from the adjoining anadarko basin and ii undertaking a palinspastic restoration of houton group late ordovician devonian thickness trends between the basin and the frontal fault zone to estimate the magnitude and sense of offset across the principal uplift bounding faults cross sections from uplift to basin show basement involved thrusts and folds similar to those recognized within the laramide late cretaceous tertiary foreland of the rocky mountains structural patterns in map view possess elements that have been previously interpreted as resulting from reverse slip and or left slip on the uplift bounding faults palinspastic restoration of isopach patterns between the frontal fault zone and anadarko basin indicates that offset across the frontal faults may be explained by oblique slip left reverse slip on the uplift bounding faults the component of left slip is nearly an order off magnitude less than proposed in some previous models of carboniferous tectonism within the foreland of the ouachita orogen

downstream variation in grain size along an alpine river analysis of controls and processes downstream variation in bed material size was studied along a 115 km reach of the piave river eastern alps italy this river drains a region producing high sediment yields and has a braided pattern along half of its length during the last century the river system has been affected by several human impacts hydroelectric dams diversions gravel mining which have strongly altered flow regime and sediment dynamics the aim of the study is to analyse the changes of bed material size in the downstream direction and to explain these changes in the light of both natural and anthropogenic factors surface material was sampled at 35 sites using the grid by number method the collected data give a detailed picture of the downstream variation in sediment size which is characterised by a complex pattern rather than by a simple decreasing trend an explanation of this variation was found through identification of discontinuities significant steps in the downstream trend and factors which can determine changes in sediment texture both natural lateral sediment sources and anthropogenic factors e g barrages are significant in this river system and they provide an explanation for most of the observed discontinuities seven out of eight discontinuities few tributaries disrupt downstream fining while as expected the barrages produce important changes in sediment texture fining processes were investigated in the lower part of the study reach where the lateral sediment sources and the barrages have minor effects on the bed material exponential models provide acceptable explanations of the downstream variations and give fining coefficients equal to 0 027 and 0 028 km 1 respectively for d50 and d84 evidence suggests that both abrasion and sorting are important in determining the downstream fining observed but it is likely that sorting is the dominant process

elasticity of majorite and a majorite pyrope solid solution to high pressure implications for the transition zone 1 high seismic velocity gradients in the transition zone have been attributed to large pressure derivatives of the elastic moduli of transition zone minerals such as majorite garnet here we present brillouin scattering measurements of the elasticity of polycrystalline mg majorite mj100 mg4si4o12 and a mj50py50 majorite pyrope solid solution to pressures similar to those at the top of the transition zone 15 1 1 gpa and 12 8 1 gpa respectively the pressure derivatives of the adiabatic bulk ks and shear moduli of both mj50py50 and mj100 are 4 2 3 and 1 4 2 respectively and are equal to those of pyrope within the experimental uncertainties we conclude that neither the adiabatic compression of majorite garnet nor any other likely transition zone phase is able to produce the high velocity gradients observed seismically high velocity gradients are consistent with gradual transformations between minerals with very different elastic properties the transformation of 25 or more of clinopyroxene into majorite above 520 km and the formation of ca silicate perovskite below 520 km could produce the observed seismic gradients

jackfork group southeastern oklahoma new gas play in the ouachita overthrust recent discovery of natural gas in sandstones of the jackfork group of southeastern oklahoma has led to revised interpretations of hydrocarbon potential in the ouachita thrust province of eastern oklahoma jackfork reservoirs consist of fine to very fine grained submarine fan lobe sandstones with low matrix permeability and porosity production is dependent upon natural fractures enhanced in most cases by artificial stimulation individual wells have produced at rates of 1 3 5 7 mcf footnote per day and possess estimated reserves in the range of 2 0 7 6 gcf footnote hyperbolic decline suggests gas contribution from the matrix possibly due to the presence of microfractures drilling has concentrated on two subsidiary thrust blocks in the hanging wall of the ti alley thrust southern latimer county however recent outcrop petrographic and sedimentological analyses have shown that traditional depositional models of the jackfork are overly limited and that potential jackfork reservoirs exist across a broad area to the south of the current play such analyses have revealed the existence of thick medium coarse grained channel sequences at a number of localities in the lynn mountain syncline similar sequences may also exist well to the south in the boktukola syncline where thick sand intervals have been identified petrographic study of samples from the lynn mountain syncline suggests that channel sequences may have significantly higher reservoir quality than is found in productive jackfork sandstones to the north traditional assumptions pos ulating low regional hydrocarbon potential for the jackfork therefore stand in need of revision

elastic moduli of jadeite enstatite majorite 1 the adiabatic bulk ks and shear g moduli of a polycrystalline majorite garnet solid solution with composition na0 92mg2 08 mg0 02al1 06si0 92 si3o12 were measured at ambient conditions by brillouin spectroscopy ks and g were found to be 171 6 3 5 gpa and 103 5 2 0 gpa respectively assuming a linear dependence of the elastic moduli on composition for the mg2si2o6 enstatite majorite en mj naalsi2o6 jadeite majorite jd mj join the calculated ks and g of the fictive jd mj end member are 178 and 125 gpa respectively at ambient conditions the shear velocity change associated with the pyroxene to majorite transition increases dramatically with increasing na content in the system in contrast there is virtually no shear velocity increase associated with the pyroxene to majorite transition in mgsio3 if this relationship holds at high pressures and temperatures it suggests that for mineral assemblages containing an abundance of large radius cations such as ca and na the pyroxene garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone

subsurface structure of the eastern arkoma basin analysis of 425 km of seismic reflection data in the eastern arkoma basin reveals a structure and history quite different from those previously reported for the arkoma basin the eastern arkoma basin has three structural styles that formed in the following chronological order deep steep normal faults shallow listric normal faults and thrust faults the origin of the structural styles and the paleozoic history of the eastern arkoma basin may be summarized as follows late proterozoic or early cambrian rifting was followed by deposition of cambrian through upper mississippian strata on a passive plate margin the mississippian pennsylvanian boundary marks a time of major down to the south normal faulting with coincident folding of the footwall blocks and truncation of t e faulted and folded terrain by a pre morrowan mississippian pennsylvanian unconformity the unconformity slopes southward and steepens locally across the erosionally truncated footwall blocks during the pennsylvanian down to the south listric normal faults cut the atokan and morrowan sections and merged with but did not displace the steeper segments of the sub morrowan unconformity surface folds north of the ross creek thrust are rollover anticlines overlying these listric normal faults major deformation in the eastern arkoma basin terminated with emplacement of the ross creek thrust in the late pennsylvanian

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

sound velocities and elastic properties of fe bearing wadsleyite and ringwoodite the sound velocities and single crystal elastic moduli of phase wadsleyite and phase ringwoodite of mg fe 2sio4 with fe fe mg ratios of 0 075 and 0 09 respectively have been determined at ambient conditions by brillouin spectroscopy both compressional and shear wave aggregate velocities decrease with increasing fe content in both phases but the magnitude of this decrease is different for the two phases the adiabatic bulk modulus ks of fe bearing mg2sio4 ks 170 2 gpa is indistinguishable from that of the mg end member within experimental uncertainty whereas ks of mg fe 2sio4 increases rapidly with increasing iron content the shear moduli of both phases decrease with increasing fe content our measurements indicate that the velocity and impedance contrasts between olivine and mg fe 2sio4 are independent of fe content for mg rich compositions but the contrast for the mg fe 2sio4 transition increases significantly with increasing fe content the new data support a previous estimate of 40 10 for the olivine content of the upper mantle and suggest that less than 50 mg fe 2sio4 is sufficient to account for the observed impedance contrasts at depths of both 410 km and 520 km unless the effect of fe on elastic properties is accounted for it is difficult to account for both the 410 and 520 km discontinuities with a single olivine content

seismic velocity gradients in the upper mantle the radial velocity gradients for p and s waves in the upper mantle are of considerable interest for petrological studies of the upper mantle but are difficult to constrain directly comparison of three different styles of velocity model constructed within a common parametrisation to give a good fit to the travel times of p and s waves to 30 provide a useful framework for constructing bounds on the radial gradients for depths from 250 1000km a somewhat subjective set of bounds are suggested for the velocity gradients and velocity contrasts at the major discontinuities in an average mantle one of the most significant factors affecting the estimation of radial gradients is the presence of small scale heterogeneity in the mantle modest heterogeneity around 1 percent perturbations on scale lengths of about 300km can give rise to horizontal velocity gradients which can overwhelm the radial gradients in the shallower parts of the mantle and still be a quarter of the size of the radial gradients at greater depths however such scales of heterogeneity are unlikely to simulate the presence of additional upper mantle discontinuities for ray paths travelling near vertical

a simple model of the 1982 83 californian el nino steric height steric height anomaly sea level and sea level anomaly show that the 1940 41 and the 1982 83 californian el nino events were resonant responses of the california current to the expansion and intensification of the aleutian low and decrease in strength of the north pacific high in both cases the subsurface anomalies were dynamically produced by onshore transport of subarctic water and a downward tilt of the inshore thermocline sea surface temperature anomalies however resulted from thermodynamic as well as dynamic processes most previous californian el nino or anti el nino events probably were resonant or anti resonant responses of the seasonal cycle of the california current to anomalous large scale atmospheric forcing

grain size along two gravel bed rivers statistical variation spatial pattern and sedimentary links a new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel bed rivers in northeastern british columbia canada a preliminary assessment of grain size variability establishes a basis for examination of the spatial pattern of grain size change standard anova techniques are inappropriate because individual samples have unequal variances and are not normally distributed alternative tests for homoscedasticity and comparison of means are therefore utilized within site between sample variability is not significant the grain size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled in both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining textural variations along the two rivers studied here are complex and show negligible overall fining in over 100 km this is the consequence of a large number of tributary inputs and non alluvial sediment sources which are the legacy of late pleistocene glaciation the identification of lateral sources like these is fundamental for understanding textural changes within rivers the sedimentary link a channel reach between significant lateral sediment inputs provides a means of isolating fluvial maturation processes abrasion and sorting from contingent lateral inputs strong fining trends are apparent in most links and classification of grain size measurements according to their location within particular links greatly improves the statistical explanation of textural variation identification of sedimentary links provides a means of applying models of fluvial fining processes so isolation of link networks will aid the development of basin scale models of textural variation 1998 john wiley sons ltd

carbonate debris flows cow head group western newfoundland abstract the cow head group is an allochthonous cambro ordovician sequence of deep water limestone conglomerates mudstones to grainstones minor quartz sandstones siltstones and shales platy clast conglomerates and boulder rich megaconglomerates as much as 100 m thick exhibit features similar to those described for subaerial debris flows that is flat sharp bases with only minor evidence for erosion poorly developed clast fabric with tilting of platy clasts at right angles to the flow direction boulders floating within flows or projecting above the tops of flows irregular flow tops indicating primary relief above the sea floor and tapered flow margins snouts snout geometry and the extent of boulder projection both allow calculation of debris static strength these results combined with measured flow thickness permit calculation of minimum and maximum paleoslope gradients original debris static strengths were in the range of 103 to 105 dynes cm2 similar to the observed range in subaerial flows calculations yield bottom gradients of l l 8 but independent field data suggest that the paleoslope dip was on the order of only a few degrees this constraint suggests that debris strength was substantially reduced during flow probably by excess pore fluid pressures thus permitting flow on very gentle slopes the paleoslope orientations used in this study are substantially different from those previously published by hubert et at 1977

deposition of ungraded muds from high density non turbulent turbidity currents turbidity current deposits of mud have recently been found up to 10m in thickness resulting from single depositional events1 2 turbidites 1 5 m thick from the madeira abyssal plain3 4 display long segments with little vertical change of grain size5 6 this suggests that the currents froze in some way making them unable to sort sediment here we suggest that a decline in flow speed of these currents led to a concentration gradient in silt close to the bed that was sufficiently steep to stratify the flow a concentration gradient of 18 kg m 3 over 1 5 m height gives a layer richardson number above the critical value of 0 25 for damping of turbulence we propose that with turbulence severely damped a dense suspension of fine material consolidates like a static suspension while continuing to flow downslope the current changes from a fully turbulent flow to a decelerating flow with suppressed turbulence and increasing density in the latter state interparticle forces prevent differential settling of the coarser grains

traction carpet stratification in turbidites fact or fiction abstract the spaced stratification that characterizes some thick deep water sandstones consists of a stack of layers 5 10 cm thick that are inversely graded at their base and structureless at their top these layers have been attributed to deposition from a succession of collapsed inertia layers traction carpets prior to collapse each layer was believed to have been maintained by shear from the overriding turbidity current this depositional model is based on the mistaken assumption that the distribution of shear stress in such a traction carpet is indistinguishable from the distribution of shear stress in a grain flow on a steep slope instead shear stress in an externally sheared traction carpet should be approximately constant from the top to the base of the layer and deposition sho ld be a gradual process leaving no record of sequentially active inertia layers inertia layers that do form under large turbidity currents are probably never as thick as 5 10 cm based on available data from shear cell experiments instead inertia layers are probably about 1 cm thick similar to the thickness of the inversely graded basal part of each layer in field examples of spaced stratification the rest of each inversely graded stratum probably forms due to rapid fallout from suspension the basal inversely graded 1 cm is believed to record strong shear that may accompany impingement on the bed of large turbulent eddies hence spaced stratification may not be a structure produced beneath steady flows but may record strong y fluctuating hydrodynamic conditions and vigorous burst sweep cycles in large turbidity currents

effects of flood abrasion of the carpathian alluvial gravels abstract floods occurred in the drainage basins of two large mountain tributaries of the vistula the sola and the skawa in 1996 1997 and 2001 this paper shows changes in petrographical composition of gravel bars and characteristics of clasts in both rivers after the episodes of flood transport the drainage basins of both rivers lie within the carpathian mountains in their southern headwater parts and the in the o wiecim depression belonging to the foreland in the northern part the sola and skawa are gravel bed rivers which transport mostly sandstone and conglomerate gravels derived from erosion of flysch rocks both drainage basins share many characteristic features the main difference being their hydrotechnical infrastructure the sola is regulated by three dams and the discharge below the dams is artificially controlled there is no dam in the skawa and its discharges are natural petrographical composition of gravels roundness shape and size of clasts were studied in 12 sites in the sola valley and in 11 sites in the skawa valley after each flood more than 5000 clasts were studied in total granulometrical characteristics of the sediments changed markedly after the floods both increase and decrease in mean size of largest clasts in gravel bars were observed the results point to the important role played by the tributaries which control the characteristics of clasts in the main rivers in the foreland lateral supply is not so important because the bedrock consists of argillaceous rocks which do not produce gravels the processes observed there include selection of material and changes in its composition caused by the presence of dams conglomerates are the least resistant to flood transport among gravel components the most resistant are quartz clasts but they are present only in the finest size classes the most persistent characteristic of the clasts is their shape the influence of the dams on clasts characteristics contrary to expectations is only slight it is visible only in the greater proportion of quartz clasts in the alluvium of the sola where the dams are present

submarine fan sedimentation ouachita mountains arkansas and oklahoma abstract more than 10 000 m 32 800 ft of interbedded sandstones and shales comprise the upper mississippian and lower pennsylvanian flysch succession stanley jackfork johns valley atoka in the ouachita mountains of arkansas and oklahoma deposited primarily by turbidity current and hemipelagic processes in bathyal and abyssal water depths these strata formed major submarine fan complexes that prograded in a westward direction along the axis of an elongate remnant ocean basin that was associated with the collision and suturing of the north american and african south american plates a longitudinal fan system is visualized as the depositional framework for these strata which were deposited in a setting analagous to the modern bengal fan of the indian ocean facies analysis of the jackfork formation indicates that inner fan deposits are present in the vicinity of little rock arkansas middle fan channel and interchannel deposits occur at degray dam and friendship arkansas and outer fan depositional lobe deposits are present in southeastern oklahoma boulder bearing units olistostromes often with exotic clasts were shed laterally into the ouachita basin they occur throughout the flysch succession and in all fan environments i e inner middle and outer this relationship may serve as a useful criterion for recognizing analogous longitudinal fan systems in the rock record

composition of the upper mantle geophysical tests of two petrological models the elastic properties of candidate mantle phases are used to test the viability of olivine rich pyrolitic and cao al 2o 3 rich eclogitic assemblages for the mantle high temperature adiabats for each phase of interest are constructed and compared to mantle seismic properties both pyrolitic and eclogitic assemblages satisfy the seismic properties between 200 and 400 km between 400 and 670 km depth an eclogitic assemblage yields a superior match to velocities and velocity gradients the 400 km seismic discontinuity may represent a chemical boundary between pyrolite and picritic eclogite piclogite or phase transformations in the olivine orthopyroxene components of a piclogitic assemblage containing about 16 olivine high velocity gradients in the transition zone may be explained by the transformation of ca rich cpx to majorite garnet seismic properties at the top of the lower mantle are consistent with pyrolite piclogite or perovskite implying that the 670 km discontinuity may be a chemical boundary

transformation of enstatite diopside jadeite pyroxenes to garnet the high pressure stability of enstatite en diopside di jadeite jd pyroxenes has been investigated experimentally with a split sphere anvil apparatus ussa 2000 on the enstatite pyrope join the compositions of garnet coexisting with enstatite were determined at 100 165 kbar and 1450 1850 c the results indicate complete solubility between enstatite and pyrope in the system cao mgo al2o3 sio2 cmas the compositions of coexisting pyroxenes and garnet were determined at 100 165 kbar and 1250 1750 c at 157 kbar 1650 c garnet with the composition en79di21 mol forms on the en di join in the system na2o mgo al2o3 sio2 nmas the compositions of coexisting pyroxenes and garnet were determined at 60 160 kbar and 1200 1850 c on the en jd join the first garnet has the composition en48jd52 at 135 kbar 1650 c and en53jd47 at 140 kbar 1500 c on the di jd join the first garnet with the composition di63jd37 forms around 170 kbar 1650 c in the en di jd system the first appearance of garnet with the composition en42di9jd49 is estimated at 133 kbar 1650 c the new pyroxene with the composition namg0 5si2 5o6 napx transforms to garnet at 154 kbar 1650 c the experimental results indicate that the transformation of a twopyroxene assemblage to garnet and residual pyroxene in the en di jd system could occur at pressures consistent with the 400 km seismic discontinuity and in a pressure interval of 0 3 kbar

the eclogite garnetite transformation in the morb h2o system abstract to decipher phase relations of oceanic crust in the coldest slab at the mantle transition zone multi anvil experiments were conducted in the morb h 2 o system at pressures of 10 19 gpa and temperatures of 700 1500 c garnet and stishovite were recognized in all run charges above 15 gpa garnet drastically increases nasi na 2 msi 5 o 12 component m ca mg fe 2 jadeite occurs instead of omphacite na k hollandite containing 7 mol naalsi 3 o 8 and ca perovskite with 60 mol catio 3 were observed at p 17 gpa with decomposition of omphacite and increase of modal ratio of garnet there is a sharp increase of density at 440 km the density increase due to appearance of ca perovskite at 570 km is estimated approximately 100 km shallower than that of previous estimation

paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in huangshui valley the northeastern tibetan plateau china abstract gravel deposits on fluvial terraces contain a wealth of information about the paleofluvial system in this study flow direction and provenance were determined by systematic counts of more than 2000 clasts of imbricated gravel deposits in the xining region northeastern tibetan plateau china these gravel deposits range in age from the modern huangshui riverbed to miocene aged deposits overlain by eolian sediments our major objectives were not only to collect first hand field data on the fluvial gravel sediments of the xining region but also to the reconstruct the evolution of the fluvial system these data may offer valuable information about uplift of the northeastern tibetan plateau during the late cenozoic era reconstructed flow directions of the higher and lower gravel deposits imply that the river underwent a flow reversal of approximately 130 180 in addition the lithological compositions in the higher gravel deposits differ significantly from the lower terraces suggesting that the source areas changed at the same time eolian stratigraphy overlying the gravel deposits and paleomagnetic age determination indicate that this change occurred sometime between 1 55 ma and 1 2 ma we suggest that tectonic activity could explain the dramatic changes in flow direction and lithological composition during this time period therefore this study provides a new scenario of fluvial response to tectonic uplift a reversal of flow direction in addition field observation and statistical analyses reveal a strong relationship between rock type size and roundness of clasts

is the turbidite facies association scheme valid for interpreting ancient submarine fan environments although turbidite facies reflect only processes of deposition turbidite facies associations are routinely used to identify ancient submarine fan subenvironments e g upper fan channel lobe etc the assumption that process of deposition also reflects environment of deposition may not be valid for the following reasons 1 mutti and ricci lucchi9s facies association scheme for submarine fans has been developed exclusively from ancient turbidite sequences however the true relationship between such turbidite facies associations and related fan subenvironments has not been confirmed from modern fans 2 individual channel levee systems of many modern submarine fans are in many cases large enough to contain the entire ancient fan systems on which these facies associations are based 3 large channel levee systems comparable to those of modern fans have not been recognized in outcrops consequently the validity of turbidite facies associations for interpreting ancient submarine fan subenvironments must be considered tenuous until confirmed in modern fans

which tributaries disrupt downstream fining along gravel bed rivers tributaries and other lateral sediment sources can have a significant impact on river bed sediment texture and in turn on channel form sufficiently voluminous or distinct sediment inputs redefine the mainstem grain size distribution punctuating downstream maturation and isolating a sequence of discrete sedimentary links within these links fining processes usually dominate such that models of sorting and abrasion when applied to individual links provide reasonable predictions of grain size change links represent the fundamental natural unit within which fining models can be tested developed and applied identification of significant lateral sources is therefore important yet beyond vague references to relative tributary size sediment load and sediment calibre no criteria exist for the a priori discrimination of such sources in this paper a procedure for identifying significant lateral tributary sources without the benefit of grain size information is outlined a high resolution characterisation of bed material texture along two canadian gravel bed rivers facilitated classification of all their perennial tributaries as either significant or insignificant three absolute tributary basin parameters and their relative counterparts chosen to reflect the likely controls on tributary significance are then used to develop a discriminant function which isolates a large proportion of significant tributaries while minimising incorrect classifications examination of consistently misclassified anomalous tributaries reveals the importance of lateral source spacing and of inconsistencies in the geomorphic history of the contributing basins in turn a general tributary categorisation procedure is suggested which includes a logistic regression model for attaching probability statements to individual classifications the generality of the discriminant and logistic functions cannot be assessed because of the lack of other suitable data sets

comments on sequence stratigraphy of an argillaceous deepwater basin plain succession vischkuil formation permian karoo basin south africa from van der merwe flint and hodgson marine and petroleum geology 2010 27 321 333

submarine fan environment inferred from turbidite thickness distributions recent studies of turbidite bed thickness distributions have demonstrated power law as well as log normal statistical distributions the different distributions may reflect different fan processes and environments and therefore could be used as a quantitative method to help identify those environments including those devoid of sequential patterns the cumulative distributions of well known turbidite deposits spanning a range of interpreted fan subenvironments are used to illustrate the potential correlation between cumulative distribution and environments assuming that power law distributions may for some systems be the primary input signal one dimensional modelling allows semi quantitative characterization of the effects of different fan processes such as erosion and bed amalgamation environments indicative of different fan processes may be characterized based on the degree to which processes have acted as a filter to modify the assumed power law distribution systematically this model of the effect of fan processes on the power law distribution is used to help to account for bed thickness distributions observed in several field sites

comment on a paper by zou et al 2017 entitled an integrated chemo and sequence stratigraphic framework of the early pennsylvanian deepwater outcrops near kirby arkansas usa and its implications on remnant basin tectonics