mud capped dredge pits an experiment of opportunity for characterizing cohesive sediment transport and slope stability in the northern gulf of mexico abstract mud capped dredge pits mcdps defined as sand borrow sites from paleo river channels with cohesive sediment capped walls are used for northern gulf of mexico ngom coastal restoration projects due to lower cost than more distal restoration resources mcdp evolution including infilling and pit wall slope stability is poorly understood in relation to sandy borrow areas we present and interpret bathymetric data from sandy point mcdp which was constructed in 2012 about 20 km northwest of southwest pass the most active mississippi river distributary in water depths of 11 m repeat bathymetric surveys show the pit is infilling 54 cm or volumetrically 200 000 m3 per year which is on the same order as seasonal scale and an order of magnitude higher than the decadal scale vertical accretion rates observed seaward of southwest pass this infilling rate is higher than predicted based solely on excavated volume when compared with other dredge pits in sandy substrate sediment starved settings mcdp infill is volumetrically dominated by far field here defined as river plume or shelf bed resuspension sediment with only 9 of pit infill from pit wall failure geomorphic comparison of sandy point mcdp walls with southwest pass mudflow gully walls shows that the mcdp is oversteepened relative to natural depression features in this setting the convergence of mcdp and mudflow gully gradients towards a common value 4 5 may represent an angle of repose in lieu of decadal scale forcings findings from this experiment of opportunity show that mcdps 1 are effective sediment traps 2 have steep but relatively laterally stable walls 3 do not represent significant risk to infrastructure in a 3 year time scale and 4 are predicted to infill within about 2 decades provided a proximal sediment source exists

high pressure methane and carbon dioxide sorption on coal and shale samples from the parana basin brazil abstract an experimental study has been conducted to assess the potential for coalbed methane production and carbon dioxide storage in coals carbonaceous shales and source rocks in the parana basin in brazil high pressure sorption tests with methane and carbon dioxide were performed on coal and carbonaceous shales from the santa terezinha coalfield and samples from two principal petroleum source rocks measured excess sorption capacities ranged from 0 03 to 0 47 mmol g for methane and 0 14 to 0 81 mmol g for carbon dioxide showing a decrease with decreasing organic matter content linear regression lines for methane sorption capacity vs toc extrapolated to approximately zero whereas for carbon dioxide the intercept of the regression line indicated a residual sorption capacity of 0 2 mmol g on the mineral matter present day gas contents of coals collected from the first cbm well in the santa terezinha coalfield correspond to 13 38 of the measured maximum sorption capacities carbon dioxide sorption capacities exceed methane sorption capacities by a factor of 1 9 to 6 9 for these coals free sorption capacities of the under saturated coals in combination with preferential sorption of carbon dioxide could favour co 2 enhanced methane recovery and co 2 storage in coals and shales of the study area based upon the calculated coal reserves gas contents and measured sorption capacities a total storage potential of 15 4 gt co 2 was estimated for an area of 20 40 km 2 in the santa terezinha coal field assuming a combined co 2 enhanced coalbed methane ecbm production and co 2 storage operation to fully evaluate the potential for carbon dioxide storage and coalbed methane production further studies are required to assess producibility of methane and efficiency of long term co 2 storage in the study area

measuring flow velocity and sediment transport with an acoustic doppler current profiler an acoustic doppler current profiler adcp measures three dimensional velocity profiles within the water column using the doppler shift principle whilst the bottom tracking function and acoustic backscatter can be used to measure bed load velocity and estimate suspended sediment concentration the adcp offers many advantages over traditional single point current meters and sediment samplers including deployment from a moving launch a single instrument for both velocity and sediment transport measurements profiles of three dimensional velocity and suspended sediment and the ability to map an entire flow field limitations of adcps include a large sampling diameter close to the bed coarse measurement of vertical velocity fragmented bottom track records a poor understanding of the relation between bottom tracking and the mechanisms of sediment transport and sensitivity of the acoustic backscatter to particle size

impact of geological complexity of the fruitland formation on combined co2 enhanced recovery sequestration at san juan basin pilot site abstract in this study we present well log and 3d seismic interpretations of a coalbed methane reservoir in the late cretaceous fruitland formation in the area surrounding the southwest regional partnership on carbon sequestration s san juan basin carbon sequestration pilot site in new mexico usa the interpretation incorporated geophysical logs from 38 wells located in a 23 km 2 area surrounding the pilot site which lies near the southern edge of the high rate fruitland coal production fairway located along the axis of the san juan basin log interpretations revealed three coal bearing zones upper middle and lower within the fruitland formation that are approximately 7 4 7 and 8 5 m 23 15 5 and 28 ft thick respectively the interpretations indicate that each of these coal zones is split by a parting into upper and lower beds making a total of six mappable coal beds in the area surrounding the co 2 injection well the combined thickness of the upper two coal beds in the upper coal zone varies between 3 5 and 4 8 m 11 5 to 15 7 ft and that of the middle beds from 2 to 4 3 m 6 6 to 14 1 ft thick the thickness of the individual coal beds in the lower coal zone varies from about 2 7 to 4 25 m 9 to 14 ft for the upper bed and from about 3 to 5 5 m 10 to 18 ft for the basal coal bed partings separating the upper and lower coal beds in each zone are on average about 2 m 7 ft in the upper and middle zones and about 1 m 3 5 ft in the lower zone seismic response of the upper middle and lower coal zones was interpreted and correlated through the 23 km 2 area the stratigraphic complexity of this coalbed methane reservoir is also accompanied by considerable structural disharmony between the three coal zones the reservoir complexity revealed in this study may account for lower than expected co 2 injectivity and preferential injection into the lower coal zone during the pilot test

swelling induced volumetric strains internal to a stressed coal associated with co2 sorption abstract it is generally accepted that typical coalbed gases methane and carbon dioxide are sorbed both adsorbed and absorbed in the coal matrix causing it to swell and resulting in local stress and strain variations in a coalbed confined under overburden pressure the swelling interactions of gases within the coal matrix and the resultant changes in the permeability sorption gas flow mechanics in the reservoir and stress state of the coal can impact a number of reservoir related factors these include effective production of coalbed methane degasification of future mining areas by drilling horizontal and vertical degasification wells injection of co2 as an enhanced coalbed methane recovery technique and concurrent co2 sequestration such information can also provide an understanding of the mechanisms behind gas outbursts in underground coal mines the spatio temporal volumetric strains in a consolidated pittsburgh seam coal sample were evaluated while both confining pressure and carbon dioxide co2 pore pressure were increased to keep a constant positive effective stress on the sample the changes internal to the sample were evaluated by maps of density and atomic number determined by dual energy x ray computed tomography x ray ct early time images as soon as co2 was introduced were also used to calculate the macroporosity in the coal sample scanning electron microscopy sem and photographic images of the polished section of the coal sample at x ray ct image location were used to identify the microlithotypes and microstructures the co2 sorption associated swelling and volumetric strains in consolidated coal under constant effective stress are heterogeneous processes depending on the lithotypes present in the time scale of the experiment vitrite showed the highest degree of swelling due to dissolution of co2 while the clay kaolinite and inertite region was compressed in response the volumetric strains associated with swelling and compression were between 15 depending on the location although the effective stress on the sample was constant it varied within the sample as a result of the internal stresses created by gas sorption related structural changes sem images and porosity calculations revealed that the kaolinite and inertite bearing layer was highly porous which enabled the fastest co2 uptake and the highest degree of compression

a reevaluation of the enigmatic permian synapsid watongia and of its stratigraphic significance the enigmatic synapsid watongia initially described on the basis of fragmentary remains from the chickasha formation of oklahoma as an early therapsid a gorgonopsian is redescribed and is shown to represent the largest known varanopid synapsid its assignment to the varanodontinae varanopidae synapsida is supported by several diagnostic features including a strongly recurved marginal dentition with both posterior and anterior unserrated cutting edges quadratojugal with two discrete superficial rami a large lateral tuberosity on the postorbital short deep excavations on the neural arches and a broad short radiale the presence in watongia of a posterolateral process of the frontal precludes therapsid or sphenacodontid affinities the previously described preparietal that provided the strongest evidence of therapsid affinities for watongia is shown to be based on misinterpreted skull fragments that were incorrectly assembled the presence of a varanopid in the chickasha formation is consiste

no gap in the middle permian record of terrestrial vertebrates during the permian tetrapods showed a major transition from basal synapsid dominated faunas in the first half to therapsid dominated faunas in the second the transition was significant in marking the beginning of richer and more complex communities a precursor to modern terrestrial ecosystems this changeover may have been gradual or abrupt but its study has been complicated by the postulated occurrence of a substantial hiatus in the fossil record termed olson9s gap which obscured the nature of the turnover new evidence from redating of key tetrapod bearing units of the american southwest and european russia confirms that there is no gap in the fossil record of permian tetrapods indeed evidence for substantial sampling bias in the permian tetrapod fossil record as a whole is queried

dynamics of bedforms in the lower mississippi river abstract the size and roughness characteristics of dunes in the mississippi river are not predicted well by experimental and theoretical relations even though intensive flow measurements were made in the study area although dunes increase in scale with increasing discharge of water and sediment the development of multiple dune sizes and nonuniform flow obscure the relationship of dune geometry to synoptic hydraulic variables some nonuniformity is caused by the development of large bed undulations from kinematic waves that can deform into compound dunes but most of it is related to flow convergence and divergence in pools and riffles varying flow geometry with increasing stage and reach controlled relations between flow and energy loss even though changes of bedform size are not found to lag the flow changes because sand transport is large a considerable volume of sediment is required to initiate and propagate the largest compound dunes this means that they might be profiled in different stages of growth and have a varying effect on the flow during their evolution spatially and temporally

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

hydrodynamic sorting and transport of terrestrially derived organic carbon in sediments of the mississippi and atchafalaya rivers abstract over the course of two years four cruises were conducted at varying levels of discharge in the lower mississippi and atchafalaya rivers mr and ar where grab samples were collected from sand and mud dominated sediments the tetramethylammonium hydroxide tmah thermochemolysis method was used to determine sources of terrestrially derived organic carbon oc in these two sediment types to examine the effects of hydrodynamic sorting on lignin sources in river sediments average lignin concentrations in the lower mr were 1 4 1 1 mg goc 1 at english turn et and 10 4 27 4 mg goc 1 at venice using these concentrations annual lignin fluxes to the gulf of mexico from tidal and estuarine mud remobilization at et and venice were 3 1 2 5 10 5 kg and 11 4 30 0 10 5 kg respectively much of the lignin derived materials in muddy sediments appeared to be derived from non woody grass like sources which should decay more quickly than the woody materials typically found in the sandy deposits the average total oc 1 93 0 47 of english turn sands yields an annual flux of 0 34 0 09 10 9 kg lignin flux in the english turn sands 3 6 2 6 mg gc 1 using the numbers above would be 12 2 9 4 10 5 kg the extensive amounts of sand sized woody materials coffee grinds found in the sandy sediments in both the ar and mr are likely derived from woody plant materials this is the first time it has been demonstrated that sandy sediments in the mr provide an equally important pathway compared to muds for the transport of terrestrially derived organic matter to the northern gulf of mexico using the ar average oc in sand 1 16 0 72 we estimated an annual flux of oc to the shelf of 0 13 0 07 10 9 kg lignin flux for ar sands was estimated to be 12 4 12 1 10 5 kg despite the high error associated with these numbers we observe for the first time that the flux of lignin in sandy sediments in the ar to the northern gulf of mexico is comparable to that found in the mr these results further support the likelihood of grain size related hydrodynamic sorting of terrestrially derived organic carbon in the lower mississippi and atchafalaya rivers suggesting that there is a distinct sandy sediment organic fraction contributed by major rivers to the global carbon cycle

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

characterization of the co2 fluid adsorption in coal as a function of pressure using neutron scattering techniques sans and usans abstract small angle neutron scattering techniques have been applied to investigate the phase behavior of co2 injected into coal and possible changes in the coal pore structure that may result from this injection three coals were selected for this study the seelyville coal from the illinois basin ro 0 53 baralaba coal from the bowen basin ro 0 67 and bulli 4 coal from the sydney basin ro 1 42 the coals were selected from different depths to represent the range of the underground co2 conditions from subcritical to supercritical which may be realized in the deep subsurface environment the experiments were conducted in a high pressure cell and co2 was injected under a range of pressure conditions including those corresponding to in situ hydrostatic subsurface conditions for each coal our experiments indicate that the porous matrix of all coals remains essentially unchanged after exposure to co2 at pressures up to 200 bar 1 bar 105 pa each coal responds differently to the co2 exposure and this response appears to be different in pores of various sizes within the same coal for the seelyville coal at reservoir conditions 16 c 50 bar co2 condenses from a gas into liquid which leads to increased average fluid density in the pores pore with sizes r 1 105 r 1 104 a pore 0 489 g cm3 as well as in small pores with size between 30 and 300 a pore 0 671 g cm3 these values are by a factor of three to four higher than the density of bulk co2 co2 under similar thermodynamic conditions co2 0 15 g cm3 at the same time in the intermediate size pores with r 1000 a the average fluid density is similar to the density of bulk fluid which indicates that adsorption does not occur in these pores at in situ conditions for the baralaba coal 35 oc 100 bar the average fluid density of co2 in all pores is lower than that of the bulk fluid pore co2 0 6 neutron scattering from the bulli 4 coal did not show any significant variation with pressure a phenomenon which we assign to the extremely small amount of porosity of this coal in the pore size range between 35 and 100 000 a

comparison of high pressure co2 sorption isotherms on central appalachian and san juan basin coals accurate estimation of carbon dioxide co2 sorption capacity of coal is important for planning the co2 sequestration efforts in this work we investigated sorption and swelling behavior of several eastern and western us coal samples from the central appalachian basin and from san juan basin the co2 sorption isotherms have been completed at 55 c for as received and dried samples the role of mineral components in coal the coal swelling the effects of temperature and moisture and the error propagation have been analyzed changes in void volume due to dewatering and other factors such as temporary caging of carbon dioxide molecules in coal matrix were identified among the main factors affecting accuracy of the carbon dioxide sorption isotherms the helium void volume in the sample cells was measured before and after the sorption isotherm experiments and was used to build the volume corrected data plots

eastern mississippi delta late wisconsin unconformity overlying transgressive facies sea level and subsidence abstract analysis of 92 engineering core logs located in the balize sector of the eastern mississippi delta focuses on the late wisconsin unconformity and lithofacies of strata lying immediately below and above this stratigraphic horizon this major sequence boundary is a key feature used to correlate strata across shelf and slope to the basin observations emphasize lithofacies distributions of the latest pleistocene sediments underlying the unconformity the late pleistocene to early holocene transgressive facies and the immediately overlying deltaic deposits maps and a cross section compiled with this information highlight the critical relation between lithofacies distributions and late wisconsin sea level oscillations core analysis reveals that the transgressive facies comprises distinct environments of deposition offshore to onshore findings identify criteria to determine the approximate position of the shoreline at the late wisconsin maximum sea level lowstand and at the extent of early holocene maximum marine inundation in the balize complex mapping of lithologies along the late wisconsin unconformity serves to improve correlation of sediment facies with changes in acoustic response along high resolution seismic profiles an estimate of long term averaged land subsidence suggests lowering of at least 1 mm year near the shelfedge during the past 18 000 years this mapping also refines sea level response models for the mississippi delta including criteria to locate key paleogeographic features such as shelfedges and maximum flooding surfaces in other recent marine deltas and in older stacked deltaic sequences

bed load discharge coefficient using dimensional analysis the bed load discharge coefficient for the case of two dimensional flow over dunes is expressed in terms of bed form geometry and the sand size of the bed material experiments are conducted in a rectangular flume using artifical dunes and a flow visualization method to measure the flow separation length from which the bed load coefficients were determined the results show that the bed load coefficient is affected significantly by sand grain size only when the dunes are flat when dunes are steep the value of the bed load coefficient is affected mainly by the dune steepness application of the bed load coefficient results in some improvement of estimating bed load

fracture and 3d seismic interpretations of the fruitland formation and cover strata implications for co2 retention and tracer movement san juan basin pilot test abstract this study presents data on faults and fractures in the fruitland formation and its cover strata at a carbon sequestration pilot site in the high rate fruitland coal fairway in the northeastern san juan basin the study incorporates satellite imagery fracture detection and shear wave anisotropy logs and 3d seismic to identify potential issues that could impact long term reservoir integrity co2 flow and retention the properties of fracture networks within the reservoir and sealing strata are important to understand in carbon sequestration and enhanced recovery efforts fracture networks exert significant control on the ability of a reservoir to retain co2 for long thousand year time frames with minimal leakage local structural complexity at the pilot site resulted in tracer migration patterns that differed from predictions based on regional descriptions of fracture and cleat orientations measured in areas several miles from the site perfluorocarbon pfc tracer breakthrough in the production stream of nearby producing wells for example occurred first in a well to the east in a direction close to the presumed butt cleat trend rather than in a well at equal distance along what had been assumed to be the more permeable face cleat trend the study reveals local tectonic complexity not suggested by well log derived structure maps of the area and suggests that fractures and faults disrupt the local fruitland coal reservoir and the overlying kirtland shale primary seal

co2 sequestration potential of charqueadas coal field in brazil abstract although coal is not the primary source of energy in brazil there is growing interest to evaluate the potential of coal from the south of the country for various activities the i2b coal seam in the charqueadas coal field has been considered a target for enhanced coal bed methane production and co 2 sequestration a detailed experimental study of the samples from this seam was conducted at the netl with assistance from the pontificia universidade catolica do rio grande do sul such properties as sorption capacity internal structure of the samples porosity and permeability were of primary interest in this characterization study the samples used were low rank coals high volatile bituminous and sub bituminous obtained from the i2b seam it was observed that the temperature effect on adsorption capacity correlates negatively with as received water and mineral content langmuir co 2 adsorption capacity of the coal samples ranged 0 61 2 09 mmol g the upper i2b seam appears to be overall more heterogeneous and less permeable than the lower i2b seam the lower seam coal appears to have a large amount of micro fractures that do not close even at 11 mpa of confining pressure

morphological evolution of a mud capped dredge pit on the louisiana shelf nonlinear infilling and continuing consolidation abstract buried sandy paleo river channels on the continental shelf can be accessed through dredging for the restoration of beaches and barrier islands which are under the threat of land loss and rising sea levels however our knowledge on post dredging evolution of paleo river channels is still very limited in this study we focus on infilling rate sediment acoustic characteristics slope change and surficial morphology all of which have implications for the management of seafloor oil and gas infrastructure bathymetric data collected during nine bathymetric surveys over 13 years were used to study the long term changes of the peveto channel dredge pit which is 5 km offshore of holly beach in western louisiana usa this pit was constructed in 2003 and was completely infilled in or before 2016 initial pit infilling rates began at 214 cm year from 2003 to 2004 and then rapidly decreased to an average rate of only 33 cm year from 2006 to 2016 this corresponds volumetrically to 418 753 and 80 816 m3 year for the same intervals pit wall margins displayed small lateral migration moving

poisson s ratio values for rocks abstract compared to other basic mechanical properties of rocks poisson s ratio is an elastic constant of which the significance is generally underrated yet in rock mechanics there is a considerable number of diverse areas which require a prior knowledge or estimation of the value of poisson s ratio this paper examines the values and applications of poisson s ratio in rock mechanics following an historical account of the initial controversy whether it was a material constant or not the effects of poisson s ratio in the elastic deformation of materials intact rocks and rock masses are briefly reviewed also the reported values of poisson s ratio for some elements materials and minerals are compiled while typical ranges of values are presented for some rocks and granular soils finally poisson s ratio classifications are recommended for isotropic intact rocks

the reptile macroleter first vertebrate evidence for correlation of upper permian continental strata of north america and russia the spectacular evolutionary history of terrestrial vertebrates is uncharacteristically poorly documented between the paleozoic subequatorial exposures of the permo carboniferous of north america and europe and the much higher latitude upper permian deposits of central russia and southern africa we report here that the discovery of the reptile macroleter in oklahoma provides the first direct vertebrate evidence of biochronological correlation between continental sediments from the upper permian of north america and russia the presence of the reptile macroleter a member of a major group of upper permian amniotes known previously only from central russia in north america improves dramatically our understanding of this early phase of amniote evolution and also provides evidence of terrestrial tetrapod faunal interchange between north america and russia in late permian time

discussion and reply the reptile macroleter first vertebrate evidence for correlation of upper permian continental strata of north america and russia discussion reisz and laurin 2001 1 documented the presence of the reptile macroleter in the chickasha formation of oklahoma and concluded that the chickasha formation belongs to the guadalupian and that it is equivalent in age to the late kazanian or early tatarian of the russian platform p

modelling permeability for coal reservoirs a review of analytical models and testing data abstract as with other reservoir types permeability is a key controlling factor for gas migration in coalbed methane reservoirs the absolute permeability of coal reservoirs changes significantly during gas production often initially decreasing but then increasing as the reservoir pressure and gas content is drawn down it has also been observed to decrease markedly during co2 injection to enhance coalbed methane recovery in order to predict gas migration models for coal permeability must represent the mechanisms leading to these observed behaviours the permeability of coal reservoirs behaves in a similar fashion to other fractured reservoirs with respect to effective stress decreasing exponentially as the effective stress increases however a unique effect of coal is that it shrinks with gas desorption and swells with adsorption within the reservoir this swelling shrinkage strain leads to a geomechanical response changing the effective stress and thus the permeability modelling coal permeability incorporating the impacts from both effective stress and coal swelling shrinkage dates back about 25 years since then a number of permeability models have been developed in recent years this topic has seen a great deal of activity with a growing body of research on coal permeability behaviour and model development this article presents a review of coal permeability and the approaches to modelling its behaviour as an important part of this the field and laboratory data used to test the models are reviewed in detail this article also aims to identify some potential areas for future work

a review of the guadalupian middle permian global tetrapod fossil record abstract until recently the guadalupian middle permian tetrapod fossil record was known almost exclusively from the karoo basin of south africa and the cis urals region of russia limiting progress towards understanding global middle permian tetrapod biogeography recent work has shed light on several new or under explored guadalupian tetrapod bearing basins and we review and synthesize these findings here we also review changes to the international and russian guadalupian time scales and present updated biostratigraphic correlations for all of the basins discussed in general there are few tetrapod genera or species shared between mid permian basins a pattern starkly different from the generic cosmopolitanism seen during lopingian late permian times the parana basin of brazil has produced a unique fauna that combines typical south african and russian clades suggesting a pathway for faunal interchange between the northern and southern portions of pangea the dashankou fauna of china yields basal therapsids that suggest a northern pangean origin for this clade the sundyr assemblage of russia preserves a latest guadalupian fauna that seems to illustrate patterns of faunal turnover across the guadalupian lopingian boundary continued field work in the lesser known mid permian strata will facilitate testing hypotheses about the transition between early and middle permian faunas the end guadalupian extinction event pangean tetrapod biogeography and the origins of widespread late permian clades

the first half of tetrapod evolution sampling proxies and fossil record quality abstract the first half of tetrapod evolution witnessed substantial diversification of the clade and several major turnovers and mass extinctions in the time since their origin more than 380 myr ago to the beginning of the middle jurassic 175 myr ago tetrapods apparently diversified fitfully reaching their highest level in the middle permian and showing major diversity declines in the late moscovian early permian wordian lower wuchiapingian end permian lower anisian lower ladinian late triassic lower norian to upper rhaetian end triassic and early jurassic upper sinemurian lower pliensbachian of these diversity drops only the end permian and end triassic correspond to recognised mass extinctions and the late moscovian and early norian drops to other previously identified environmental crises the remainder could be real extinction or turnover events or partially artefacts of biased sampling there are strong correlations between formation counts and tetrapod palaeodiversity suggesting a sampling component in the raw data but the covariation is not uniform through the whole time span being poor from devonian to middle permian and better from late permian to early jurassic there is limited evidence for covariation between the tetrapod palaeodiversity time series and other putative sampling metrics such as specimen completeness numbers of publications map areas gap bounded sedimentary units rock volumes formations and fossil collections modelling by multiple correlations shows that formation count is generally the best explanatory model either on its own or combined with other sampling time series however it is not clear that formation count is independent of the palaeodiversity time series because rises and falls in both signals could reflect variations in original diversity or in preservation or in sampling

bedform transport rates for the lowermost mississippi river 1 new methods of data collection and processing are developed to provide quantitative reach scale measurements of bedform transport mass within the tidally influenced mississippi river a multibeam swath profiler was used to collect daily bathymetry over a range of water discharges and bed elevation changes induced by dune migration are measured these values are coupled with bulk physical properties of the bed sediment to constrain mass flux and annual bedform transport is estimated at 2 2 x 10 6 metric tons mt the total annual sand flux from the mississippi river calculated by combining measured bedform transport rates and suspended sediment flux is estimated to be 20 x 10 6 mt survey data also provide information about the spatial distribution of dunes across the channel bottom straight reach segments are commonly mantled by dunes for the entire cross section while bends are typically areas of focused scour devoid of bedforms presumably any sediments associated with migrating dunes are propelled into suspension within bends before redepositing in the subsequent straight reach movement via suspension is therefore an important component for the downriver transport of bed materials in the lower mississippi river

heleosuchus an enigmatic diapsid reptile from the late permian or early triassic of southern africa the primitive diapsid reptile heleosuchus griesbachi from the late permian or early triassic of southern africa is redescribed on the basis of a new cast made from the type specimen few diagnostic features of the skeleton are preserved making it difficult to establish specific affinities no characters are known that are uniquely shared with archosauromorphs in common with lepidosauromorphs but in contrast with stem diapsids cervical vertebrae 3 5 are shorter than the anterior trunk vertebrae and the transverse processes are relatively short heleosuchus may be a member of the eosuchia or an otherwise unrecognized lineage of primitive lepidosauromorphs the possibility that this specimen shows thyroid fenestration of the pelvis and a shortened and or hooked fifth metatarsal cannot be unequivocally established

degradation of the plaquemines sub delta and relative sea level in eastern mississippi deltaic coast during late holocene abstract the stratigraphic architecture of plaquemines sub delta lobe is identified from sedimentary cores and sub bottom seismic data collected at lower breton sound louisiana usa four lithofacies were identified in cores from bottom to top 1 organic poor mud 2 organic poor silty sand 3 massive mud 4 organic rich peat and root rich soft mud overall the lithofacies displays a typical progradational deltaic deposit at bottom with upward coarsening feature and then an upward fining deposit overlying on top stratigraphic position of the organic rich peat facies indicates that it is formed after the fluvial sediment source moves away from this region and it is recognized as a termination of progradation of the plaquemines sub delta dated peat samples show that sub delta progradation stops between 876 and 1384 yr ad during which a 20 70 cm relative sea level rise is detected the geological framework reported in this study provides critical information for future modeling on river diversions the stratigraphic architecture underlying lower breton sound implicates that top three facies of root rich soft mud organic rich peat and massive mud are likely to be eroded away before the development of new crevasse splay or sub delta when sediment diversion is in operation the deeper organic poor silty sand lithofacies however can serve as a firm foundation to build new land

model for calculating bed load transport of sediment a bed load transport model based on the mechanics of sediment moving by saltation yields predicted values of bed load flux as a function of boundary shear stress grain diameter and density the parameters required to calculate bed load transport particle velocity bed load sediment concentration and the height of the bed load layer can all be determined from our model which computes sequences of trajectories of individual saltating grains as well as the concentration of moving grains that the flow can support the latter is related to the momentum the accelerating grains extract from the flow predicted curves of bed load transport vs boundary shear stress agree well with transport data collected by gilbert meyer peter iet al n and the waterways experimental station measured shear stress was corrected for pressure drag when bed forms were present comparison of predicted bed load transport with common bed load equations reveals considerable similarity among the relationships the best agreement with the data is produced by relationships in which the transport rate vanishes as the shear stress approaches the critical shields number as in our model and yalin s equation

sediment infilling and geomorphological change of a mud capped raccoon island dredge pit near ship shoal of louisiana shelf abstract to restore degraded barrier shorelines of the mississippi river delta of coastal louisiana sand is dredged from high quality borrow areas on the adjacent continental shelf this dredging process generally creates a topographic low that facilitates the rapid capture of sediments our understanding of sedimentary processes and influences on seabed morphologic evolution is still limited in this study raccoon island dredge pit in a paleo river channel on the louisiana shelf was studied via multiple bathymetric surveys physical parameters include pit geometry and topographic change from post dredging and infilling sediment sources were analyzed raccoon island pit was 100 filled up less than six years after dredging the average infilling rate in the raccoon island pit was 1 10 m year from 2013 to 2018 during the surveying period the pit wall slope decreased by 6 8 within two years the sediment infilling process in the raccoon island pit was likely under the combined influence of topography wind driven currents storm waves and the dynamic atchafalaya river dispersal system the atchafalaya river reached high discharge in 2016 which likely contributed to a surprisingly high sediment infilling rate at raccoon island pit between 2015 and 2018 raccoon island pit is in a mixed texture environment in which the sandy pit was fully filled with mud mud is useful for marsh restoration but is not considered a quality resource for barrier island or beach restoration thus the raccoon island pit is not regarded as a renewable resource for future barrier island restoration

permian tetrapod extinction events abstract four substantial tetrapod extinctions have been identified during the permian but only one of these is an apparent mass extinction analyses of global compilations of the family level diversity of permian tetrapods have been confounded by incorrect and compiled correlations instead analyzing diversity patterns at the genus level in best sections identifies only one apparent mass extinction of permian tetrapods much evolutionary turnover took place among tetrapods during the latter part of the early permian and had been identified as a single mass extinction at the artinskian kungurian boundary however the only stratigraphically dense tetrapod record of the late early permian from the southwestern usa indicates a succession of extinctions spread out from redtankian through littlecrontonian kungurian time not a single mass extinction olson s gap remains a hiatus in the global record of permian tetrapods equivalent to part of the kungurian roadian across the gap eupelycosaur dominated assemblages were replaced by therapsid dominated assemblages but the claim that this is associated with a mass extinction olson s extinction has been based on compressing all of the extinctions of the redtankian littlecrotonian and olson s gap into one event recognition of olson s gap does not preclude the possibility of an extinction at the early middle permian boundary olson s extinction however the gap in the tetrapod fossil record makes it impossible to establish the magnitude precise timing and structure of the extinctions that took place across olson s gap the only permian mass extinction of tetrapods is the dinocephalian extinction event during the gamkan near the end of the guadalupian which saw the total extinction of dinocephalians and major diversity drop in therocephalians in the karoo basin of south africa this extinction is the loss of at least 64 of generic diversity the changeover from dinocephalian assemblages to assemblages without dinocephalians in other parts of permian pangea suggests that the dinocephalian extinction event was a global event the late permian tetrapod extinctions are older than the end permian marine extinctions furthermore the magnitude of the diversity drop and ecological severity of the end permian tetrapod extinctions have been greatly overstated best sections analysis in the karoo basin indicates a stepwise late permian tetrapod extinction during deposition of the upper dicynodon assemblage zone that took at least 250 000 and perhaps more than a million years the culmination of this stepwise extinction across the highest occurrence of dicynodon boundary of platbergian and lootsbergian land vertebrate faunachrons is a loss of genera not much above an inferred background extinction rate of permian tetrapod genera and resembles the amount of turnover seen at several other boundaries of permian and triassic land vertebrate faunachrons the case for coeval land plant insect and tetrapod extinctions during the permian is a weak one the first coeval marine and nonmarine mass extinctions of the phanerozoic were likely the end guadalupian extinction climate change notably greenhouse climates may have driven permian tetrapod extinctions but that hypothesized relationship needs better documentation

the response of subaqueous dunes to floods in sand and gravel bed reaches of the dutch rhine the branches of the river rhine in the netherlands characterized by a sand gravel bed in the upstream part and a sand bed in the downstream part of the river system show migrating dunes especially during floods in the last 20 years these dunes have been studied extensively high resolution echo sounding measurements of these dunes made with single and multibeam equipment were analysed for three different sections of the rhine river system during several floods this analysis was done to quantify the growth decay and migration rates of the dunes during floods in addition the migrating dunes were used to calculate bedload transport rates with dune tracking the results of dune growth and decay and migration rate are shown to be very different for the various sections during the various floods and these differences are related to differences in grain size of the bed and to differences in the distribution of discharge over the main channel and the floodplain the relations are used to show that the growth and migration rate of dunes and the calculated bedload transport rates during the rising stage of a flood wave can be predicted from the mobility of the bed material with simple power relations

estuarine controls on fine grained sediment storage in the lower mississippi and atchafalaya rivers observations of the lower mississippi river channel in 1999 2003 with side scan and subbottom seismic profilers multibeam bathymetry core radiotracers 7be 137cs 210pb and 234th and water column profiles of fluid and suspended sediment properties are utilized to constrain the timing location and intensity of the seasonal storage of fine grained sediments in the estuarine channel reach below venice louisiana unlike earlier studies that suggested little or no estuarine sedimentation was taking place in the river the present study demonstrates that the river channel above the head of passes seasonally stores as much as 10 of the annual suspended sediment discharge during periods of falling to low mississippi water discharge associated with salt stratification in the channel thalweg mud deposits are up to 3 2 m thick with 7be derived sediment deposition rates of up to 8 9 mm day water column profiling and 234th 7be ratios suggest that 1 particles are transported and settled mainly as flocs and 2 riverine flocs are settling through the strong salt wedge halocline and are protected from re erosion by the salt stratification with onset of the spring freshet and the corresponding seaward retreat of the saltwater wedge the entire volume of fine grained material stored in the lower river except in low freshet years is remobilized and transported to the gulf of mexico in the turbid freshwater plume this tidal hysteresis strongly influences the timing of sediment supply to the ocean high turbidities in the shelf plume during rising water discharge spikes of 1 to 2 week duration are the product of local channel floor remobilization as well as increased supply from the drainage basin pulsed resupply of sediments and the pore water products of early diagenesis potentially have major implications for issues such as continental margin carbon budgets and coastal eutrophication companion surveys conducted in the lowermost 12 km reach of the atchafalaya distributary of the mississippi show no evidence of saltwater wedge intrusion at low discharge or seasonal fine grained sediment storage likely due to the shallow 7 m river mouth sill that impedes the upstream movement of gulf water