the shoreline distribution and degradation of tilapia carcasses salton sea california taphonomic implications abstract the salton sea is a hypersaline closed lake system in southern california usa episodic fish kills led to bloating and floating fish bodies that were driven onto the shoreline by wind shear the documented taphonomic destruction of the stranded fish carcasses includes the distribution of the fish parts after desiccation and disarticulation mainly by wave induced transport with possible minor component of wind transport on the upper shoreface carcass decay is divided into five taphonomic categories 1 through 5 category 1 represents whole pliable fish recently washed onto the shoreline while category 5 incorporates longer term destruction into ultimately single isolated skeletal elements high water strand line deposits are delineated by the presence of categories 3 through 5 mixtures the general trend in 2012 was observed to be considerable bone disarticulation away from the shoreline because categories 1 and 2 were present in the swash zone the influx of fresh fish carcasses recharged the shoreline during 2013 the absence of new 1 and 2 categories arriving to the shoreline enhanced wave action to further break down categories 3 and 4 ultimately into category 5 in addition isolated bone elements segregate according to density differences typically on low gradient beaches wave and wave induced current action coupled with beach topography controls distribution of the various fish bones as an actualistic model the salton sea implies that shore parallel complete to partial fish carcass concentrations are more shoreward and isolated skeletal elements more distal

bar dynamics in a sandy braided river insights from sediment numerical simulations abstract bar dynamics in sandy braided rivers are keys to better understand the morphological processes of braided rivers and sediment distributions limited by insufficient quantitative information and satellite images that only show the larger scale morphology and do not reveal the sand bars in the deeper channels most previous studies have qualitatively assessed bar dynamics but the ways in which the hydraulic parameters of sandy braided rivers control bar dynamics remains poorly understood here we present sediment numerical simulations on sandy braided rivers to investigate the quantitative controls of river parameters on bar dynamics three bar dynamic forms downstream migration lateral variations and bar tail elongation are observed unit bars are prone to downstream migration following formation and the migration rate shows a deceasing trend during braided river evolution this gradually decreasing migration rate is proven to be strongly connected to the decreasing flow velocity of braided channels that confine bar growth the lateral variation in bar dynamics exhibits narrowing migration and widening of sectional morphologies we suggest that braided channel curvature dominantly controls lateral sediment transportation around the bar and thus results in several lateral variation forms of bars the bar tail elongation difference between the two sides of the bar is associated with bar asymmetry strong bar asymmetry can make apparent differences in bar tail elongation

green river laminites does the playa lake model really invalidate the stratified lake model proponents of the playa lake model have proposed deposition of most of the green river formation microlaminated carbonates including oil shales in lakes that were not perennially stratified meromictic however there is a variety of evidence favoring a meromictic depositional environment 1 close similarity of much of the lamination to varves in modern meromictic lakes 2 evidence that hydrologic events favoring development of meromixis chemical stratification occurred prior to deposition of major accumulations of oil shale 3 mutually exclusive distribution of fossil nekton especially fish and normal lacustrine benthos including mollusks and 4 analogy with a quaternary playa that became a meromictic lake following increased inflow the playa lake model is untenable for the typical fish bearing kerogen rich microlaminated sediments these laminites were probably deposited in a large ectogenic meromictic lake a chemically stratified lake that formed when increased fresh water inflow drowned a saline playa complex

fish taphonomy and environmental inference in paleolimnology abstract the contribution of fish studies to palaeoecology generally takes the form of 1 inference from analogies in modern fish faunas and 2 fish taphonomy the pattern of death and dispersal of bones 1 modern fish faunas and associated organisms provide taxonomic ecological or functional analogues for interpretation of ancient limiting factors and behaviors these inferences presume taxonomic conservatism they also presume functional relationships between morphological form and feeding mode or habitat they become weak with increased geologic age or phyletic distance between ancient subject and modern anaogue 2 fish taphonomy may contribute information about limnology community composition life history mortality depositional environment and preservation taphonomic reconstruction of ecology and preservation depends on the applicability of analogous processes in modern ecology and l limnology in aquatic taphonomy temperature is the most important factor in determining the fate of a carcass above about 16 c depending on depth and pressure most carcasses are made buoyant by bacterial decay gases and are transported to the surface where they may decay further and fall piecemeal into deepwater environments or drift to beach environments where wave energy disarticulates abrades and scatters the bones below about 16 c most carcasses remain on the bottom until buried they may be disturbed by scavengers depending on oxygen concentration in the hypolimnion

taphonomic variations in eocene fish bearing varves at horsefly british columbia reveal 10 000 years of environmental change the eocene horsefly locality in british columbia has yielded many fossil fishes insects and plants its varved sediments make it ideal for study of temporal changes in environment and fish morphology several intervals of diatomaceous varves indicate a deep stratified lake setting earlier studies focused on morphological and taphonomic change during the 700 year h2 interval and morphological change during the 10 000 year h3 interval the present study uses taphonomy as an index for environmental change during the ten millennia represented by h3 comparing taphonomic changes with the morphologic changes found earlier the h3 interval records deposition in deep water indicated by dominance of the fish genera amyzon and eohiodon quiet water conditions are indicated by minimal fin disarticulation hypoxia at the time of fish death is confirmed by open mouths of most fish specimens while cool water on the lake floor prevented full flotation of fish carcasses water depth temperature and oxygenation fl

the significance of mid channel bars in an active meandering river mid channel bars are common on many active meandering gravel bed rivers but specific information on timescales of development and on the occurrence of bars is lacking data from the river dane in cheshire nw england are presented here which indicate that a sequence of formation from accumulations of coarse gravel on the centre of riffles through to attachment of bars to floodplains is common and takes a period of 5 15 years the sedimentological and vegetation changes through the sequence are described and the ro1e of flow events is discussed about 10 of bends in this meandering reach contain mid channel bars at any time bars develop in steeper sections of the channel and downstream of sharp corners and rapidly eroding apices many of the bars are caused by excessive erosion of the banks which overwidens the channel in the longer term the bars become incorporated in the developing meanders

nh _4 in pegmatitic feldspars from the southern black hills south dakota trace amounts of ammonium ion 0 7 mol nh 4 substitution have been identified from the infrared spectra of alkali feldspars from pegmatites occurring in the southern black hills district south dakota the spectroscopic data indicate that the ammonium is structurally bound most likely in the m site of the microcline these results indicate that ammonium was likely a component of metamorphic fluids present during anatexis of metasedimentary rocks in the southern black hills district

nitrogen in rock occurrences and biogeochemical implications 1 there is a growing interest in the role of bedrock in global nitrogen cycling and potential for increased ecosystem sensitivity to human impacts in terrains with elevated background nitrogen concentrations nitrogen bearing rocks are globally distributed and comprise a potentially large pool of nitrogen in nutrient cycling that is frequently neglected because of a lack of routine analytical methods for quantification nitrogen in rock originates as organically bound nitrogen associated with sediment or in thermal waters representing a mixture of sedimentary mantle and meteoric sources of nitrogen rock nitrogen concentrations range from trace levels 200 mg n kg 1 in granites to ecologically significant concentrations exceeding 1000 mg n kg 1 in some sedimentary and metasedimentary rocks nitrate deposits accumulated in arid and semi arid regions are also a large potential pool nitrogen in rock has a potentially significant impact on localized nitrogen cycles elevated nitrogen concentrations in water and soil have been attributed to weathering of bedrock nitrogen in some environments nitrogen released from bedrock may contribute to nitrogen saturation of terrestrial ecosystems more nitrogen available than required by biota nitrogen saturation results in leaching of nitrate to surface and groundwaters and where soils are formed from ammonium rich bedrock the oxidation of ammonium to nitrate may result in soil acidification inhibiting revegetation in certain ecosystems collectively studies presented in this article reveal that geologic nitrogen may be a large and reactive pool with potential for amplification of human impacts on nitrogen cycling in terrestrial and aquatic ecosystems

human impact on land ocean sediment transfer by the world s rivers abstract land ocean transfer of sediment by rivers is a key pathway for material transfer on earth contemporary data on the sediment loads of rivers provide clear evidence of significant recent changes in the sediment fluxes of several rivers in response to human impact the key drivers of increased sediment loads include land clearance for agriculture and other facets of land surface disturbance including logging activity and mining although programmes for soil conservation and sediment control can result in reduced sediment loads the trapping of sediment by dams represents the dominant cause of reduced loads this influence is currently assuming increasing importance at the global scale any attempt to link these drivers to changes in the global land ocean sediment flux must take account of the aggregation and buffering effects that operate in larger basins which can cause damping and even removal of signals of increasing flux within the upstream basin and complicate the link between upstream and downstream response to human impact further work is required to provide a precise quantitative assessment of the human impact on global land ocean sediment fluxes and the net effect of increasing and decreasing fluxes particular attention must be paid to the temporal perspective and the variation of impact trajectories in different areas of the globe and for river basins of different sizes

analysis of the impacts of dikes on flood stages in the middle mississippi river abstractthe us army corps of engineers has constructed numerous river engineering structures in and along the middle mississippi river river training and bank stabilization measures include pile dikes stone dikes bendway weirs chevrons and revetments concerns have long been voiced about the effects of these structures on flood stages recent debate concerning the scientific basis for these concerns has been invigorated by specific gauge analysis that appears to show a rising trend in flood stages over the past 150 years this paper attempts to advance the debate by providing an objective review of the specific gauge analysis technique that explains how the method should be performed and the results interpreted identifies strengths and limitations examines the uncertainties associated with application to the middle mississippi river given the available data and reassesses the conclusions that can and cannot reasonably be drawn regarding the impacts of dikes and levees on flood stages based on spe

nitrogen in future biosphere studies this article suggests a theme for future nitrogen studies involving the functioning and evolution of the biosphere together with certain aspects of human biology it is hoped that this theme could be developed into a multi authored book at some point in the future although numerous new case studies may be required the biosphere can be considered to be a single interactive system comprised of numerous component parts including the atmosphere rain rivers lakes oceans continental ecosystems marine ecosystems soils and sediments in order to study the internal complexity of each of the components and the relationships that exist between them one can choose a common theme the author believes that nitrogen is a good prospect because of its ubiquitous nature and complex chemistry the burial of sedimentary volatiles in the continental crust has contributed to the long term chemical evolution of the exterior environments of the earth the most marked effects notably the accumulation of atmospheric oxygen have been due to the burial of reduced carbon an understanding of the passage of sedimentary volatiles through the crust will provide important constraints on the evolution of the biosphere and may lead to a more meaningful comparative planetology carbon is difficult to trace through crustal processes because its high temperature form graphite is incompatible with the crystal structures of silicate minerals however the high temperature form of sedimentary nitrogen ammonium readily enters into potassic minerals and it can be easily traced through crustal processes herein the fate of sedimentary nitrogen is traced from wet sediments through metamorphic rocks into granites and other crustal melts without the trapping of nitrogen in the crust and the liberation of oxygen that is a consequence of biological nitrogen fixation the n2 o2 of the atmosphere may have been about 82 9 to 16 3 and the total atmospheric pressure about 1 2 atm most of the changes in the oxygen content is due to dilution by nitrogen with only about 5 of the present atmospheric oxygen being a consequence of nitrogen fixation the ancient continental surfaces would have been volcanic deserts containing little 1 ppm or no nitrogen today nitrogen rich soils support continental ecosystems one can use nitrogen as a window to speculate on the colonisation of the continents by land plants herein nitrogen fixation by legumes is considered in detail and by drawing analogies with the present day the author speculates on the colonisation of the continents by land plants having speculated on the co evolution of the atmosphere soils and continental ecosystems one can place a human being in the centre of a tropical forest and begin to examine how they relate to the modern biosphere the chosen example is the metabolism of plant protein and the roles of glutamate dehydrogenase gdh vitamin b2 and flavin mononucleotide fmn the realisation of this theme would imply numerous new case studies notably those concerning the continental crust where nitrogen studies were linked to mineralogy petrology and other geochemical tracers including sr o al and k and where the short range order of 15n were taken into consideration

a new longitudinal approach to assess hydrologic connectivity embanked floodplain inundation along the lower mississippi river hydrologic connectivity is fundamental to understanding floodplain processes along meandering river corridors this study contributes to understanding hydrologic connectivity by utilizing a high resolution light detection and ranging dem with a new gis based approach for identifying the precise elevation of flood stage the method created a high resolution longitudinal channel bank profile enabling a detailed examination of embanked floodplain hydrologic connectivity a simple channel cross section approach is likely to result in a large underestimation of floodplain inundation and hydrologic connectivity along meandering river floodplains because of differences in the elevation of the natural levee surface relative to floodplain bottoms and the considerable variability in the elevation of the channel bank profile there is a large disparity in discharge duration associated with floodplain inundation in comparison to river channel bank inundation a discharge duration of 10 is associated with inundation of 87 of the floodplain surface whereas only 53 of the channel bank profile is overtopped an apparent threshold in inundation occurs as the discharge duration decreases below about 35 while a duration of 25 results in very little of the channel bank being overtopped it inundates 50 of the floodplain surface floodplain borrow pits which are created in association with dike construction represent a constant anthropogenic influence on the lower mississippi embanked floodplain morphology and are inundated by low discharge magnitudes the results of the investigation shed new light on the topic of hydrologic connectivity for an important embanked fluvial system that has previously received little attention concerning its physical floodplain processes copyright 2013 john wiley sons ltd

the diffusion behavior of hydrogen in plagioclase feldspar at 800 1000 c implications for re equilibration of hydroxyl in volcanic phenocrysts to use structural hydroxyl oh concentrations preserved in volcanic phenocrysts to constrain magmatic water contents prior to eruption it is first necessary to understand the diffusive behavior of hydrogen in plagioclase in this study diffusion coefficients for a natural oh bearing plagioclase feldspar ab 66 an 31 or 3 are determined from a series of integrated loss heating experiments performed at 800 1000 c and 1 atm under air nitrogen gas and a co 2 h 2 mixture at the fmq oxygen buffer hydrogen diffusion is found to be isotropic within analytical error using a one dimensional diffusive loss model for an infinite slab the diffusion behavior for hydrogen in plagioclase is described by the diffusion parameters log d 0 1 62 0 31 m 2 s and e a 266 77 kj mol and log d 0 0 97 0 35 m 2 s and e a 278 90 kj mol for experiments only conducted under nitrogen gas nearly complete 83 97 loss of oh from the andesine was achieved in 900 and 1000 c heating series except for the 900 c fmq buffer experiment in which only 64 of the total oh was lost after 21 6 days of cumulative heating the diffusion rates of hydrogen in the plagioclase after 800 1000 c are similar to interpolated diffusion rates for sodium diffusion in an 30 feldspar implying that na and h both diffuse via frenkel defects involving the large cation sites and interstitial ions the diffusion coefficient d values for hydrogen in plagioclase are lower than most reported diffusion data for hydrogen in nominally anhydrous minerals and are most similar to d reported for pure forsterite unaffected by iron redox reactions based on the hydrogen diffusion parameters in this study a 1 mm spherical plagioclase phenocryst experiencing dehydration under lowered water activity during ascent and eruption at 800 c retains 50 of its initial oh concentration after 34 days at 900 and 1000 c a 1 mm phenocryst retains 50 of its initial oh concentration after only 1 3 days and 0 25 day respectively oh concentrations in plagioclase are therefore most indicative of magmatic water contents during the latest stages of ascent and eruption

palaeontological and sedimentological observations on nonmarine lameta formation upper cretaceous of maharashtra india their palaeoecological and palaeoenvironmental significance abstract the lameta formation upper cretaceous is exposed in parts of central and western india as detached outcrops and covers an area of nearly 5000 km 2 it generally rests on precambrian and gondwana rocks and is invariably capped by deccan trap volcanic flows in the nand and dongargaon areas of the chandrapur and nagpur districts of maharashtra the lameta formation covers more than 400 km 2 attains a thickness of 20 m and is richly fossiliferous the palaeontological and sedimentological observations strongly indicate alluvial limnic environment for the deposition of the lameta sediments under semi arid conditions different lithofacies representing channel overbank paludal and lacustrine subenvironments have been identified the biota represents terrestrial semiaquatic and aquatic communities and is represented by dinosaurs fishes crocodiles chelonia gastropods ostracodes charophytes coniferales and angiosperms the biota appears to be mainly controlled by the different lithofacies thereby suggesting strong palaeoecological and taphonomical control over their occurrence records of mass death of clupeids have been observed in many layers within the lacustrine clays a nesting site of sauropods has been found near pavna along with evidence of site fidelity a clutch with small oblong shaped eggs of avian like affinity has been also unearthed from this nesting site the lameta sediments were deposited in a freshwater environment that provided the preferred ecological niche for large scale breeding and nesting of sauropods

fish otoliths in superficial sediments of the mediterranean sea abstract otoliths represent a significant biogenic carbonate component in marine sediments that may provide valuable information for paleoenvironmental and biogeographic reconstructions in spite of their importance relatively little is still known about the taxonomic composition abundance and early taphonomic characteristics of recent otolith death assemblages which would add to their value to interpret situations in the geological record here we present data on the distribution of fish otoliths from bottom sediments collected in the central mediterranean sea ranging in depth from 51 to 3300 m the preservation of otoliths ranges from fresh semi translucent white specimens to dull coloured dark ones although whitish specimens are predominant across all the samples this diversity in lustre and colour and at times texture reflects the degree of early taphonomic processes undergone by these aragonitic bodies post mortem under submarine conditions never being exposed to diagenetic processes on land in general a correlation with depth is observed with best preservation observed in otoliths sampled at depths

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

taphonomic analysis of fish in rift lacustrine systems environmental indicators and implications for fish speciation abstract two rift basin lacustrine successions cacheuta and los rastros formations in the middle triassic of argentina were studied to test two different hypotheses 1 fish taphonomy is useful as an indicator of environmental conditions for these two paleolakes and 2 fish taphonomy is useful for understanding environmental effects on speciation the fish fossils are found in two lacustrine deposits as isolated and disarticulated scales and cranial bones clumps and stringers of scales articulated body segments and complete specimens four taphofacies are defined for cacheuta specimens ca a to ca d and three taphofacies are defined for los rastros fish assemblages lr a to lr c a principal components analysis was performed with the taphonomic features supporting the seven taphofacies defined a taphonomic model is proposed that characterizes a lacustrine deltaic environment developed in the rift basin and identifies three sub environments each one with its particular fossil assemblages the fish assemblages in the los rastros formation suggest that the fishes preserved in delta front and turbidity current deposits lr b and lr c taphofacies were allochthonous to the lake and probably inhabited the delta plains and affluent fluvial system in contrast the isolated fish remains preserved in open lake deposits lr a taphofacies likely represent both autochthonous and or allochthonous specimens in the cacheuta formation articulated and isolated fish remains preserved in open lake deposits ca a and ca d tafofacies might represent autochthonous lacustrine specimens based on the good preservation of the material the fish remains preserved in underflow and turbidity current deposits ca b and ca c taphofacies were allochthonous to the lake and probably inhabited the delta plain and affluent fluvial system the fish taphonomic study of two different rift basin lacustrine successions allows test of the two proposed hypotheses fish taphonomy was useful as an indicator of environmental conditions beacuse the differences in fish preservation allowed differentiation of the sub environments and reconstruction of the environmental conditions and dynamics of the rift lake basins also fish taphonomy was useful for understanding environmental effects on speciation by characterizing the environments and dynamics that promote the development of new fish species recognizing fish inhabited environments and identifying the generalist and specialist species

paleolimnology and taphonomy of some fish deposits in fossil and uinta lakes of the eocene green river formation utah and wyoming abstract in four sections in the lacustrine eocene green river formation in utah lake uinta fish are preserved on carbonate mudflats along high energy carbonate shorelines in the littoral zone and in deeper profundal areas scattered bones and scales are found throughout dropped from disintegrating floating carcasses gar scales typify shallow water deposits partly due to habitat preference beach concentrations of greatly abraded bones and scales grade offshore into storm lag layers and lenses which grade to loosely packed horizons or patches of unworn remains littoral fish fossils range from dropped bones to good skeletons with much floating lifting and scavenging preservation improves away from the waterline not only into deep and cold profundal waters where the carcasses are protected from scavenging by anoxia and prevented from floating by temperature and pressure but also onto mudflats where stranding and burial of carcasses can also protect them a section through an isolated part of the green river formation in wyoming fossil lake also ranged from profundal to littoral with minor emergence dropped body parts were found throughout but preservation quality of the best specimens improved with presumed depth the beds with the best specimens seem to have accumulated at the bottom of a deep stratified warm monomictic lake our lake uinta sections were generally shallower and suggest more fluctuations in water level but this is not relevant to broad paleolimnological interpretations because they represent marginal zones which are necessarily more sensitive to changes in depth overall fish fossils are especially informative in deeper waters where sedimentary distinctions fail

a new terrestrial plant rich fossil lagerstatte from the middle cenomanian late cretaceous of the apennine carbonate platform magliano vetere southern italy depositional and palaeoenvironmental settings abstract we describe a new terrestrial plant rich fossil lagerstatte discovered at magliano vetere campania region s italy in the middle cenomanian of the apennine carbonate platform the deposit 1 42 m thick is made up of a thin bedded interlayering of evenly laminated dolomicrites lenticular dolorudites and carbonaceous seams which contain well preserved remains of terrestrial plants yielding cuticles and minor fishes this study focuses on plant remains to provide systematical taphonomical and palaeoenvironmental considerations nevertheless a preliminary analysis carried out on fossil fishes has led to the identification of pycnodontids and teleosts the fossil lagerstatte retains sterile foliage bearing shoots with epidermal features belonging to the genus frenelopsis of the extinct conifer family of the cheirolepidiaceae plant remains possibly represent a stable biotope as floral composition displays no variation along the deposit nevertheless episodes of harsh environmental conditions occurred as demonstrated by a fish mortality event and ca sulphate evaporite precipitation taphonomical considerations and sedimentological evidence from the encasing sediments suggest a parautochthonous deposition of fossil plants in a supratidal intertidal mudflat including a salt marsh that was characterised by a restricted sea water circulation deposition of primary dolomite and episodical wildfires the presence of xeromorphic features in frenelopsis from magliano vetere could represent an adaptation to haline environment which was subjected to microtephra supply from a distant orogenic volcanism the facies evolution of the studied fossil lagerstatte records a rapid regressive and a following slower transgressive trend and constitutes the lowermost portion of a 20 m thick interval characterised by several dolomitic plattenkalk up to 1 50 m thick which are separated by cyclically stacked peritidal limestones we infer that 1 the 20 m thick plattenkalk bearing interval represents a sequence boundary zone in the stratigraphical record of the middle cenomanian apcp 2 frenelopsis thrived at the verge of an arid semiarid climatical phase during a major pulse of relative sea level fall

human modifications to the sediment regime of the lower mississippi river flood plain the mississippi river is one of the most regulated rivers in the world human modifications constructed mainly after 1920 include dams and reservoirs artificial levees dikes concrete revetments and a series of channel cutoffs this paper examines some of the effects of these modifications on the channel and sediment budget of the river in particular the changes to the thalweg profile and the size of channel bars are examined in detail it is concluded that prior to the 1930s when major modifications were introduced the lower mississippi river was an aggrading meandering river the role of the flood plain has also changed prior to modifications the flood plain was the major sediment source as the result of bank caving today the flood plain provides only a minor amount of sediment it can be shown that major degradation to the channel including the growth of channel bars has occurred as a result of these engineered modifications the data also indicates that the different geomorphic regions respond to modifications in different ways

hydrous species in feldspars a reassessment based on ftir and sims recent interest in hydrogen incorporation in feldspars has been driven by the potential of this common mineral species to record magmatic water contents accurate measurement of h concentrations in feldspars by fourier transform infrared ftir spectroscopy is hampered by the need to collect polarized spectra in three mutually perpendicular directions which can be impractical for crystals characterized by small dimensions polysynthetic twinning and or chemical zoning sims is an attractive alternative to ftir offering high spatial resolution high precision and the feasibility of attaining low detection limits in this study we compare ftir and sims data for 19 feldspars including plagioclase anorthoclase sanidine microcline and orthoclase we present adjustments to previously published ftir data on some of these samples our new sims and ftir data are well correlated and we demonstrate the feasibility of quantitatively measuring h concentrations as low as 1 2 ppmw h 2o using sims combination of the new data together with re evaluation of the nmr calibration of johnson and rossman 2003 indicates that the ir absorption coefficients for hydrous species in feldspar increase with decreasing frequency of their o h absorptions in accord with theory we derive new molar integral ir absorption coefficients i for feldspars with the following hydrous species as defined by johnson and rossman 2003 type i and ii h 2o microcline and orthoclase i 120 470 11 360 l mol 1 h 2o cm 2 type iib oh sanidine i 150 000 15 000 l mol 1 h 2o cm 2 type iia oh plagioclase and anorthoclase i 202 600 20 260 l mol 1 h 2o cm 2 these absorption coefficients depend on critical assumptions with regards to sims matrix effects if accurate one important implication is that the h concentrations of plagioclase crystals estimated in the literature are too high by up to a factor of two requiring revision of previously estimated plagioclase melt h partitioning coefficients

dynamics of 30 large channel bars in the lower mississippi river in response to river engineering from 1985 to 2015 abstract channel bars are a major depositional feature in alluvial rivers and their morphodynamics has been investigated intensively in the past several decades however relatively less is known about how channel bars in alluvial rivers respond to river engineering and regulations in this study we assessed 30 yr morphologic changes of 30 large emerged bars located in a 223 km reach of the highly regulated lower mississippi river from vicksburg mississippi to the mississippi atchafalaya river diversion landsat imagery and river stage data between 1985 and 2015 were utilized to characterize bar morphologic features and quantify decadal changes based on bar surface areas estimated with the satellite images at different river stages a rating curve was developed for each of the 30 bars to determine their volumes results from this study show that the highly regulated river reach favored the growth of mid channel and attached bars while more than half of the point bars showed degradation currently the mid channel and attached bars accounted for 38 and 34 of the total volume of the 30 bars the average volume of a single mid channel bar is over two times that of an attached bar and over four times that of a point bar overall in the past three decades the total volume of the studied 30 bars increased by 110 118 000 m 3 41 total dike length in a dike field was found mostly contributing to the bar volume increase currently the emerged volume of the 30 bars was estimated approximately 378 183 000 m 3 the total bar volume is equivalent to 530 million metric tons of coarse sand based on an average measured bulk density of 1 4 t m 3 for the bar sediment the findings show that these bars are large sediment reservoirs

a survey of hydrous species and concentrations in igneous feldspars the hydrous components in 85 feldspars from various igneous environments spanning the range of naturally occurring compositions were examined with infrared spectroscopy the feldspars contain structural oh 0 512 ppm h 2o h 2o 0 1350 ppm h 2o and nh 4 0 1500 ppm nh 4 groups as well as fluid inclusions and alteration products although composition and structure do influence the type of hydrous species that can be incorporated into a particular feldspar mineral the concentration of these species is not controlled by major element composition coarse perthitic microclines have a heterogeneous distribution of hydrous species and contain h 2o or nh 4 in k rich lamellae and fluid inclusions in na rich areas the structural oh in plagioclase feldspars is not associated with twin boundaries or exsolution lamellae all of the possible structural hydrous species are found in pegmatite feldspars whereas volcanic feldspars contain only structural oh the variation in oh concentration within a given feldspar composition suggests that fluids in the geologic environment play a role in determining the hydrogen concentration of each sample the vast majority of plutonic feldspars have undergone partial or total equilibration with meteoric fluids during low temperature 400 150 c hydrothermal exchange obliterating any structural hydrogen and creating substantial concentrations of fluid inclusions up to 4000 ppm h 2o in the exchanged regions the amount of water stored as fluid inclusions within feldspars in the upper crust 1 10 19 kg is small compared to the 1 35 10 21 kg of water in the oceans but is roughly equivalent to the reservoir of water stored in hydrous minerals in the upper crust

toward a model for open and closed basin deposition in ancient lacustrine sequences the newark supergroup triassic jurassic eastern north america abstract climate and tectonics have a profound influence on the lacustrine sedimentary record because they affect hydrologic systems in depositional basins lakes in hydrologically closed basins tend to fluctuate in depth producing transgressive regressive sequences sometimes associated with evaporites lakes in hydrologically open basins tend to have stable shorelines producing thick sedimentary deposits that lack transgressive regressive sequences and evaporites in addition some lakes fluctuate between open and closed producing transgressive regressive sequences in which deep water sediments were deposited when the lake was overflowing and shallow water sediments capped by subaerial exposure surfaces were deposited when the basin was closed lacustrine deposits in the northern part of the newark supergroup consist of cyclic transgressive regressive sequences locally containing evaporites they are interpreted as deposits of hydrologically closed basins which occasionally became open at lake high stand in the southern part of the newark supergroup many of the lacustrine sequences are thicker lack evaporites and some contain coal and siderite these features suggest deposition in hydrologically open basins fluvial paleocurrents in at least one southern basin suggest through flow and open basin deposition thin lacustrine sequences interpreted as perennial floodplain lake deposits are associated with these fluvial systems and may also indicate open basin conditions

taphonomy of lacustrine fish fossils of the parnaiba basin northeastern brazil spatial and causative relations of konservat lagerstatten in west gondwana during jurassic cretaceous abstract fossil bonanzas called konservat lagerstatten provide geological windows to the ecology of ancient life communities these deposits often occur as cluster of fossil localities with similar geographic locations geological ages and facies as the fossils were generally preserved during special periods and large scale events in earth history within environments with exceptional taphonomic conditions this work applied petrological and geochemical analyses to evaluate the taphonomic pathway of a konservat lagerstatten in the muzinho shale upper jurassic lower cretaceous of the parnaiba basin northeastern brazil these lacustrine deposits include interbedded limestones and fossiliferous black shales deposited in anoxic non euxinic and saline environment black shales contain articulated skeletons of fish fossils characterised by three dimensional preservation of the skeletal tissue the polytypical assemblage includes diverse ontogenetic stages and is concentrated in a specific stratigraphic level mass mortality was triggered by anoxia probably established by stratified water column high c flux and thermocline demise the specimens are encased in kerogen bearing siliciclastic laminae and cementstone microfacies both microbially induced the fossils were cemented by eodiagenetic poikilotopic calcite that filled the skeletal articulation including bone trabeculae and voids originally filled by bone marrow the short distance similar fossil assemblages ages and coincident palaeoenvironments suggest that muzinho shale parnaiba basin and crato formation araripe basin compose a cluster of exceptional preservation in west gondwana lava flows and outgassing related to the central atlantic magmatic province camp resulted in the subaereal exposure of volcanic plains acid rains and subsequent co2 greenhouse crisis camp magmatism was especially voluminous in northern brazilian basins enhancing nutrient rich waters and lacustrine eutrophication due to intensified chemical weathering in this area probably other konservat lagerstatten remain unreported in west gondwana despite similar causative events the individual taphonomic pathways of muzinho shale and crato formation are very different suggesting that in these cases local phenomena affected authigenesis and diagenesis

a review of sediment diversion in the mississippi river deltaic plain abstract one of the proposed methods for restoring the disappearing mississippi delta is sediment diversion which uses channels and structures to divert water and sediment from the mississippi and atchafalaya rivers into adjacent basins this study presents a comprehensive review of geological and physical aspects of sediment dynamics in the mississippi river deltaic plain mrdp with special reference to diversion studies over the past two decades we synthesize these studies present the current understanding of sediment diversions in the context of sediment dynamics identify multiple key knowledge gaps and make recommendations for future studies to maximize net land building in the mrdp management strategies should be focused on a enhancing river sediment delivery both mud and sand b increasing sediment retention in receiving basins and c minimizing erosion in bays and estuaries compared with extensive studies of land building there have been relatively fewer studies of erosional processes a heterogeneous coastal geological framework cohesive sediment erodibility and subsidence together play complicated yet critical roles in future sediment dynamics in bays and estuaries of the mrdp sediment retention rates are highly sensitive to spatial and temporal scales types of sediments and delivery season sediment diversions to seaward receiving basins provide more surge protection but tend to have lower sediment retention due to active coastal processes structures and devices that improve sediment retention trap sediments dissipate waves and build living shorelines should be explored and cost to benefit analysis is needed long term planning should consider more landward diversions strategic community relocation and nonlinear response of the complex sedimentary system of the mrdp

fossil marine actinopterygian fishes from the kaskapau formation upper cretaceous turonian near watino alberta turonian fossil marine fishes occur at several localities near watino alberta in sandstones and in shale concretions of the vimy member kaskapau formation the actinopterygian fossils in the san

an approximation of the sediment budget of the lower mississippi river prior to major human modification a sediment budget is constructed for the lower mississippi river prior to the introduction of most human modifications components of the budget are derived from historical data including mississippi river commission hydrographic survey maps for the period from 1877 to 1924 a quantitative estimate of major sediment sources sinks and storage locations in the lower mississippi valley suggest that the most important sediment source was from bank caving and that at least 50 per cent more sediment was deposited in short term channel storage than in longer term overbank storage the budget indicates that the proportion of sediment transported as bedload was significantly greater than previously estimated the magnitude and variability of these sediment budget components are discussed the results of the study suggest that prior to modifications the river was aggrading over much of its length

tertiary lacustrine sediments from sentinel butte north dakota and the sedimentary record of ectogenic meromixis abstract about 10 meters of probable oligocene or miocene lacustrine sediments which crop out on top of sentinel butte in western north dakota consist mostly of greenish gray zeolitic mudstone interbedded with relatively thin layers of dolomite limestone and chalcedony the dolomite layers are several centimeters thick and are mostly dolomicrite with laminae or lenses of arkosic sand and pellets they probably formed by deposition of protodolomite in shallow closed saline lakes the limestone layers are up to 30 centimeters thick their basal portions contain varve couplets of micrite and organic matter graded bedding in micrite laminae and concentration of aeolian silt in organic laminae suggest that deposition of carbonate took place during a relatively brief portion of each year pres rvation of varves fossil fish and coprolites in the limestone imply deposition in a meromictic lake in contrast poor preservation of fish and bioturbation in the upper parts of two limestone beds record transition to holomictic conditions some variations in varve thickness appear rhythmic and possibly related to the sunspot cycle several asymmetric cycles of contrasting carbonate facies ideally consisting of massive dolomite overlying clay and underlying laminated limestone imply that the ancient lake in which the sequence was deposited underwent several episodes of shrinkage and closure during which its salinity increased followed by expansion accompanied by abrupt development of ectogenic meromixis changes in authigenic mineralogy and upward increase in thickness of limestone beds relative to dolomite beds record a long term trend toward freshening of basinal hydrology models involving ectogenic meromixis can explain intimate associations of evaporitic facies with varved sediments in other sedimentary sequences and may be applicable to some precambrian iron formations

the stratigraphy and paleoenvironment of a lycoptera bed site in eastern inner mongolia china correlation with the fossiliferous lower cretaceous strata in western liaoning abstract the stratigraphy and the fossil assemblage of a lower cretaceous lycoptera bed of the xinganling group in naketa arongqi area inner mongolia china are described and the paleoenvironment is discussed as it relates to the jehol biota the naketa fossil bed belongs to the lower part of volcanic sedimentary jiufengshan formation and preserves a typical eel eosestheria ephemeropsis trisetalis lycoptera davidi faunal assemblage which indicates a strong affiliation to the jehol biota of western liaoning china the fossil bed was deposited in a shallow to semi deep lacustrine setting with occurrence of oil shale facies and this is different from the lycoptera bed of the yixian formation and more similar to the overlying jiufotang formation in western liaoning a layer of volcanic tuffite within the fossil bed is dated as 121 6 0 47 ma using the zircon u pb isotopic dating method this age is contemporary with the age of the base of jehol biota producing jiufotang formation in western liaoning thereby supporting the biostratigraphic correlation however the genus lycoptera is almost entirely absent in western liaoning with only one species in the jiufotang formation where the dominant fish genus is jinanichthys therefore lycoptera in the great xing an mountain areas appears to have a longer record than in western liaoning which likely indicates that the fish fauna changed earlier in western liaoning and this observation supports the hypothesis that the yanliao area was the diversification center of some cretaceous new groups in ne asia preliminary analysis of the taphonomy and the geology indicates that the mass mortality of fish at the naketa site may not be related to volcanism additional taphonomic investigations would allow a better understanding of the early cretaceous aquatic paleoecology and paleoenvironment in the volcanic rifting regions the great xing an mountain area is a new opportunity for expanding the research on the jehol biota beyond the core localities in western liaoning

taphonomy of lacustrine shoreline fish part conglomerates in the late triassic age lockatong formation collegeville pennsylvania usa toward the recognition of catastrophic fish kills in the rock record abstract fish parts bones and scale elements preserved in sandstones and conglomerates characterize an uncommon type of lacustrine strandline setting identified in the triassic lockatong formation of the newark supergroup the triassic fish part sandstones and conglomerates are composed of disarticulated skeletal remains and formed during the lake expansion phase diverse mudstone clast types derived from the underlying lowstand playa deposits integrated into the younger transgressive shoreline sequence that contains disarticulated fish parts we propose that the salton sea california usa is a modern hypersaline lacustrine environmental analog for the deposition of fish remains on the salton sea high wind events cause mass fish kills forming a modern shoreline dominated by barnacles and fish remains using modern day observations from fish kills in the salton sea california usa we suggest that the following taphonomic scenario mass kills of triassic fish species took place during deposition of the lacustrine lockatong formation high wind events caused overturning of the lake waters either depleting oxygen or toxically poisoning the fish after death bacterial decomposition bloated the fish by generated gas in tissues causing the fish carcasses to float the decomposing fish carcasses were driven shoreward by wind and wave action and deposited on the shoreline and possibly scavenged by phytosaurs following soft tissue decay the disarticulated remains were reworked into normally graded beds composed of intraclasts and fish part elements the intermixing of intraformational clasts and fish parts reflects the impact of storms on the lacustrine shoreline during the expansion phase of the van houten cycle short period milankovich frequency cycles that consist of three recorded phases of lake rise to fall recorded in various facies stackings

sand as a stable and sustainable resource for nourishing the mississippi river delta dams have starved the lower mississippi river of sediment over recent decades suggesting that the drowning of the delta is inevitable analysis of the rivers suspended sediment load and morphodynamic modelling suggest that the amount of sand essential for land building has not significantly decreased since dam construction with sand remaining available for several centuries

an anoxic event at the albian cenomanian boundary the fish scale marker bed northern alberta canada abstract the fish scale marker bed fsmb of the shaftesbury formation which marks the albian cenomanian boundary is a regional stratigraphic marker in the western interior of canada at the outcrop studied on the smoky river in northwestern alberta three major shale units can be distinguished in the fsmb and contiguous strata the lowermost shale unit 1 is bioturbated and contains high diversity dinoflagellate and moderate diversity foraminiferal assemblages it has dominantly type iii terrestrial organic matter om and low total organic carbon content toc the unit was deposited in an open marine neritic environment of normal salinity the fsmb unit 2 represents a zone of condensed bioclastic accumulation composed of abundant fish remains the dinoflagellate species diversity is drastically reduced in this unit and it lacks benthonic foraminifera and bioturbation unit 2 is characterized by mainly type ii marine om and high toc values unit 2a contains rippled sandstone related to either a shallowing or to deeper water currents a fish hash conglomerate making up unit 2b can alternatively be interpreted as a bioclastic condensed and winnowed deposit or as a transgressive lag unit 2c consists of black platy shale with abundant fish remains and represents a minor marine trangression during the deposition of fsmb when the bottom waters were dominantly anoxic collectively the features of unit 2 suggest deposition under a stratified water column with moderate productivity of planktonic and nektonic organisms in the upper oxygenated layers but with anoxic bottom waters unit 3 overlying the fsmb consists of blocky shale with reduced concentration of fish remains due to increased rate sedimentation during its deposition the organic rich sediment of unit 3 was progressively diluted by clastic material and there was an increase in the dissolved oxygen content of the bottom waters the anoxic event at the fsmb is related to a relative rise in sea level and possibly to the mixing of waters different salinities and temperatures from the arctic ocean and the gulf of mexico in the western interior seaway

terrestrial biota in coastal marine deposits fossil lagerstatten in the pennsylvanian of kansas usa abstract the fossil animal assemblages of three pennsylvanian marine lagerstatten of kansas are compared detailed taphonomic investigations and comparison of total fossil assemblages are the most reliable for palaeoenvironment interpretation functional morphology taxonomic uniformitarianism behavior absence of marine fossils for freshwater and palaeogeography are weak criteria of a hypothesis of freshwater depositional environment based on the assumption that closely related taxa have similar environment preferences functions and behaviors in general invertebrates being less mobile are better indicators of their general environment than vertebrates terrestrial vertebrates can dominate the fossil vertebrate assemblage of a clearly marine depositional palaeoenvironment as long as acceptable indicators of palaeozoic freshwater environment are not found the hypothesis of freshwater environment cannot stand the test only easily falsified by the discovery of marine fossils fishes may indicate marine connectedness not necessarily a marine depositional environment

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

geomorphological explanation of the long profile of the lower mississippi river abstract concavity in the long profile of rivers has traditionally been explained through the concept of grade in which the slope declines downstream as a response to changing discharge bed material size and sediment transport applying this concept to particular river systems has however proved problematic the long profile reflects spatially distributed form process feedbacks between all aspects of channel morphology operating at a range of poorly defined time and space scales and in the presence of natural controls in many river systems process form dynamics are further complicated by engineering interventions which add additional extrinsic controls and constrain the range of intrinsic dynamics in this paper the 1974 75 long profile of the lower mississippi river is examined at three scales the regional the reach and the sub reach pool crossing scales a combination of curve fitting zonation algorithms and empirical classification techniques are used to show that although the long profile of the lower mississippi river is concave at the largest scale the profile is characterised by discontinuities shorter trends and zonal variations in the amplitude and wavelength of pool crossing morphology these characteristics are a response to morphological and bed material changes relating to a range of physical geological tectonic tributary input and engineering controls despite its apparent simplicity and correspondence to a graded condition the long profile of the lower mississippi river is actually a complex and scale dependent morphological property at best the concave river profile is therefore a property which emerges from several scales of process form interaction at worst it is no more than an artefact arising from the application of over simplified curve fitting techniques disclosure of the nature of the long profile thus requires the application of a variety of analytical techniques as well as geomorphological explanations which are themselves scale dependent and which consider the interaction of natural processes and the history of engineering intervention

dam impacts on the changjiang yangtze river sediment discharge to the sea the past 55 years and after the three gorges dam 1 in 5 recent years 2000 2004 the changjiang yangtze river has discharged past datong 600 km from the river mouth an average of 250 million tons mt of sediment per year a decrease of more than 40 since the 1950s and 1960s whereas water discharge at datong has increased slightly water and sediment discharge data from the upper middle and lower reaches of the river suggest that the reduction of the changjiang sediment load has occurred in two phases between 1950 and 2002 following the closure of the danjiangkou reservoir on the hanjiang tributary in 1968 and following the installation of numerous dams and water soil conservation works in the jialingjijang catchment after 1985 as the three gorges dam tgd started operating in 2003 the changjiang entered a third phase of sediment reduction with annual sediment loads at datong less than 200 mt yr upon completion of the three gorges dam tgd in 2009 the sediment load at datong will decrease to 210 mt yr for the first 20 years then will recover to 230 mt yr during 2030 2060 and will reach 310 mt yr during 2060 2110 from the sediment budget and sediment erosion data for the changjiang subaqueous delta it can be assumed that the delta will be eroded extensively during the first five decades after tgd operation and then will approach a balance during the next five decades as sediment discharging from tgd again increases