branched aliphatic alkanes with quaternary substituted carbon atoms in modern and ancient geologic samples a pseudohomologous series of branched aliphatic alkanes with a quaternary substituted carbon atom baqcs specifically 2 2 dimethylalkanes and 3 3 and 5 5 diethylalkanes were identified in warm 65 c deep sea hydrothermal waters and late cretaceous black shales 5 5 diethylalkanes were also observed in modern and holocene marine shelf sediments and in shales spanning the last 800 million years of the geological record the carbon number distribution of baqcs indicates a biological origin these compounds were observed but not identified in previous studies of 2 0 billion to 2 2 billion year old metasediments and were commonly misidentified in other sediment samples indicating that baqcs are widespread in the geological record the source organisms of baqcs are unknown but their paleobiogeographic distribution suggests that they have an affinity for sulfides and might be nonphotosynthetic sulfide oxidizers

concretionary methane seep carbonates and associated microbial communities in black sea sediments abstract gas seeps in the euxinic northwestern black sea provide an excellent opportunity to study anaerobic methane based ecosystems with minimum interference from oxygen dependent processes an integrated approach using fluorescence and electron microscopy fluorescence in situ hybridization lipid biomarkers stable isotopes 13c and petrography revealed insight into the anatomy of concretionary methane derived carbonates currently forming within the sediment around seeps some of the carbonate concretions have been found to be surrounded by microbial mats the mats harbour colonies of sulphate reducing bacteria dss group and archaea anme 1 putative players in the anaerobic oxidation of methane isotopically depleted lipid biomarkers indicate an uptake of methane carbon into the biomass of the mat biota microbial metabolism sustains the precipitation of concretionary carbonates significantly depleted in 13c the concretions consist of rectangularly orientated rod to dumbbell shaped crystal aggregates made of fibrous high mg calcite the sulphate reducing bacteria exhibit intracellular storage inclusions and magnetosomes with greigite fe3s4 indicating that iron cycling is involved in the metabolism of the microbial population transfer of fe3 into the cells is apparently mediated by abundant extracellular vesicles resembling known bacterial siderophore vesicles marinobactine in size 20 to 100 nm and structure

a new distinct mechanism of river bank erosion in a forested catchment abstract it has been thought that the two main processes responsible for river bank retreat are the removal of particles or layers of material by flow erosion or sloughing and collapse by slumping a third process involving the development of a subsurface cavity after washout of gravels which is succeeded by slow subsidence of a segment of the former channel bank has been identified at a site in the new forest southern england the process was monitored over a 9 month period and was observed to be assisted by the hydrological effects of a dam of coarse woody debris across the channel as these dams occur frequently the process is likely to have occurred elsewhere along channels in forested areas

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

variability in sulfur isotope records of phanerozoic seawater sulfate the s of seawater sulfate reflects processes operating at the nexus of sulfur carbon and oxygen cycles however knowledge of past seawater sulfate s values must be derived from proxy materials that are impacted differently by depositional and post depositional processes we produced new timeseries estimates for the s value of seawater sulfate by combining 6710 published data from three sedimentary archives marine barite evaporites and carbonate associated sulfate with updated age constraints on the deposits robust features in multiple records capture temporal trends in the s value of seawater and its interplay with other phanerozoic geochemical and stratigraphic trends however high frequency discordances indicate that each record is differentially prone to depositional biases and diagenetic overprints the amount of noise quantified from the variograms of each record increases with age for all s proxies indicating that post depositional processes obscure detailed knowledge of seawater sulfate s s value deeper in time

methane derived carbonate conduits from the late aptian of salinac marne bleues vocontian basin france petrology and biosignatures abstract peculiar carbonate bodies occur in distinct marl layers of the marnes bleues formation aptian albian vocontian basin southern france the carbonate conduits exhibit pipe or sausage like forms and a central channel their sizes range between 30 and 60 cm in length and 5 10 cm in diameter the conduit carbonates consist of automicrite authigenically formed within the sediment millimeter sized aggregates of framboidal pyrite are abundant within the conduit automicrites probably representing former colonies of sulfate reducing bacteria the central channel reflects former pathways of reduced fluids in the carbonate conduit ni enrichments at the margins of the central cavity are may be due to the activity of methane related metabolism as ni is an important bio element for respective microbes light stable carbon isotope ratios of the conduit automicrites 25 86 to 23 10 vpdb point to carbonate precipitation linked to anaerobic oxidation of methane aom while less depleted stable carbon isotope ratios of microspar in marginal zones of the central opening 8 96 vpdb are in line with microbial sulfate reduction a methane related origin of the conduit carbonates is confirmed by the presence of authigenic lipid biomarkers tentatively sourced by archaea most of which are characterized by strong 13 c depletions 13 c values down to 104 the presence of organically bound sulfur is well in line with microbial sulfate reduction isorenieratane potentially point to the presence of brown pigmented green sulfur bacteria the methane was probably sourced by older oae black shales which are known to contain isotopically 13 c heavy biomarkers of archaea as reported elsewhere

groundwater discharge along a channelized coastal plain stream in the coastal plain of the southeastern usa streams have commonly been artificially channelized for flood control and agricultural drainage however groundwater discharge along such streams has received relatively little attention using a combination of stream and spring flow measurements spring temperature measurements temperature profiling along the stream bed and geologic mapping we delineated zones of diffuse and focused discharge along little bayou creek a channelized first order perennial stream in western kentucky seasonal variability in groundwater discharge mimics hydraulic head fluctuations in a nearby monitoring well and spring discharge fluctuations elsewhere in the region and is likely to reflect seasonal variability in recharge diffuse discharge occurs where the stream is incised into the semi confined regional gravel aquifer which is comprised of the mounds gravel focused discharge occurs upstream where the channel appears to have intersected preferential pathways within the confining unit seasonal fluctuations in discharge from individual springs are repressed where piping results in bank collapse thereby focused discharge can contribute to the morphological evolution of the stream channel

deep to shallow lacustrine evaporites in the libros gypsum southern teruel basin miocene ne spain an occurrence of pelletal gypsum rhythmites abstract a number of non marine evaporite units composed of primary gypsum were deposited in saline lakes that developed in the southern teruel basin ne spain during the miocene in the basin depocentre a continuum of lacustrine evaporite lithofacies influenced by the activity of organisms is displayed the libros gypsum was deposited in a deep lake in which water stratification became unstable with progressive shoaling rhythmites composed of laminae of pelletal gypsum and laminae of very fine lenticular gypsum crystals mixed with siliceous microorganisms formed in addition to gypsum turbidites intraformational gypsum breccias and slump structures the pelletal laminae originated from the faecal activity of animals crustaceans ingesting gypsum crystallites in the lake water during episodes of maximum evaporation whereas the laminae of very fine lenticular gypsum mixed with microorganisms accumulated during episodes of relative dilution in the wide marginal zones of the basin the libros gypsum unit consists of massive to thin bedded bioturbated gypsum and thin bedded clotted gypsum which formed in intermediate to very shallow palustrine water depths the bioturbated gypsum lithofacies were produced by the action of diverse organisms presumably worms and coleopterans and chironomid larvae to a lesser extent the massive lithofacies precipitated in very shallow water and the thin bedded lithofacies formed in shallow to deeper settings the thin bedded clotted gypsum is a relatively deep facies that may have diverse origins e g bioturbation compaction disruption of soft sediments and early diagenesis there is a well developed metre scale cyclicity in the marginal lake sequences which is not observed in the inner lake deposits this suggests a depth control in the various lacustrine subenvironments to record cyclic evaporitic processes the isotopic composition of the gypsum indicates early sulphate reducing bacterial activity in the bottom of the lake and suggests that the sulphate was derived from the chemical recycling of triassic evaporites of the country rocks

methane related microbial gypsum calcitization in stromatolites of a marine evaporative setting munder formation upper jurassic hils syncline north germany fossil stromatolites may reveal information about their hydrochemical palaeoenvironment provided that assignment to a specific microbial community and a corresponding biogeochemical mechanism of formation can be made tithonian stromatolites of the munder formation at thuste north germany have traditionally been considered as formed by intertidal cyanobacterial communities however thin sections of the stromatolites show elongated angular traces of former gypsum crystals in a dense arrangement but no algal or cyanobacterial filament traces moreover high fe 2 and mn 2 contents oxygen isotope and sulphur isotope ratios of carbonate bound sulphates and sulphurized hydrocarbon biomarkers of the stromatolitic carbonate indicate that caco3 precipitation occurred near the oxic anoxic interface as a result of intensive bacterial sulphur cycling rather than photosynthetic activity furthermore anaerobic oxidation of methane by archaea may have driven caco3 precipitation in deeper parts of the biofilm community as reflected by high concentrations of squalane with a strongly negative d 13 c in conjunction with evaporite pseudomorphs showing extremely low d 13 ccarb ratios consequently the thuste stromatolites are now interpreted as having initially formed by gypsum impregnation of biofilms subsequently early mg calcitic calcitization within the biofilms occurred because of combined bacterial iron manganese and sulphate reduction with an increasing contribution of anaerobic oxidation of methane with depth this model plausibly explains the prominent preservation of signals derived from oxygen independent metabolic pathways whereas virtually no geochemical record exists for an aerobic community that may nevertheless have prevailed at the stromatolite surface photic zone stromatolites with a prominent signal of anaerobic oxidation of methane may be common in and indicative of oxygen depleted sulphate bearing environments with high rates of methane production conditions that possibly were fulfilled at the archaean to proterozoic transition

modification of meander migration by bank failures meander migration and planform evolution depend on the resistance to erosion of the floodplain materials to date research to quantify meandering river adjustment has largely focused on resistance to erosion properties that vary horizontally this paper evaluates the combined effect of horizontal and vertical floodplain material heterogeneity on meander migration by simulating fluvial erosion and cantilever and planar bank mass failure processes responsible for bank retreat the impact of stream bank failures on meander migration is conceptualized in our rvr meander model through a bank armoring factor associated with the dynamics of slump blocks produced by cantilever and planar failures simulation periods smaller than the time to cutoff are considered such that all planform complexity is caused by bank erosion processes and floodplain heterogeneity and not by cutoff dynamics cantilever failure continuously affects meander migration because it is primarily controlled by the fluvial erosion at the bank toe hence it impacts migration rates and meander shapes through the horizontal and vertical distribution of erodibility of floodplain materials planar failures are more episodic however in floodplain areas characterized by less cohesive materials they can affect meander evolution in a sustained way and produce preferential migration patterns model results show that besides the hydrodynamics bed morphology and horizontal floodplain heterogeneity floodplain stratigraphy can significantly affect meander evolution both in terms of migration rates and planform shapes specifically downstream meander migration can either increase or decrease with respect to the case of a homogeneous floodplain lateral migration generally decreases as result of bank protection due to slump blocks and the effect on bend skewness depends on the location and volumes of failed bank material caused by cantilever and planar failures along the bends with possible achievement of downstream bend skewness under certain conditions

organic matter preservation in the carbonate matrix of a recent microbial mat is there a mat seal effect abstract phototrophic mats microbial mats with a phototrophic top layer are complex systems in terms of microbial diversity biogeochemical cycles and organic matter om turnover it has been proposed that these mats were a predominant life form in proterozoic shallow water settings prior to the emergence of bioturbating organisms in the ediacaran cambrian transition for most of the precambrian microbial mats were not only quantitative important carbon fixing systems but also influenced the transfer and transformation of om before it entered the geosphere the profound alteration of compound inventories during transit through microbial mats implying substantial consequences for om preservation in the proterozoic was recently proposed as a mat seal effect pawlowska et al 2012 geology 41 103 106 to obtain a better understanding of the early diagenetic fate of primary produced om in microbial mats we studied a recent calcifying mat from a hypersaline lake in kiritimati which showed in the deeper mat layers a maximum 14 c carbonate age of 1500 years we particularly focused on om entrapped in the carbonate matrix because of the better potential of such biomineral encapsulated om to reach the geosphere before degradation and remineralization our data indicate that selective preservation is important in phototrophic mats while a diagenetic transformation of lipid fatty acids fas was evident their fatty acyl derived hydrocarbon moieties were not introduced into protokerogen which was instead mainly comprised of cyanobacterial and or algal biomacromolecules our data support the proposed major impact of the mat seal effect on om turnover and preservation i e the suppression of biosignatures derived from the upper mat layers while signals of heterotrophic microbes thriving in deeper mat layers become preferentially preserved e g high hopane sterane ratios this mechanism may have broad consequences for the interpretation of biomarkers from proterozoic shelf environments because biosignatures of phototrophic mat dwellers as well as planktonic signals may have become heavily biased by the production and turnover of om in microbial mat systems

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

modeling 100 000 year climate fluctuations in pre pleistocene time series a number of pre pleistocene climate records exhibit significant fluctuations at the 100 000 year 100 ky eccentricity period before the time of such fluctuations in global ice volume the origin of these fluctuations has been obscure results reported here from a modeling study suggest that such a response can occur over low latitude land areas involved in monsoon fluctuations the twice yearly passage of the sun across the equator and the seasonal timing of perihelion interact to increase both 100 ky and 400 ky power in the modeled temperature field the magnitude of the temperature response is sufficiently large to leave an imprint on the geologic record and simulated fluctuations resemble those found in records of triassic lake levels

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

taphonomy and palaeoecology of high stress benthic associations from the upper jurassic of asturias northern spain abstract the late kimmeridgian terenes formation exposed on the coast of asturias northern spain displays a complex pattern of directed changes of grain size carbonate content and skeletal concentrations in its upper part here investigated the formation represents a protected shelf lagoon in which four major facies types are distinguished the nanogyra virgula mudstone 1 and the corbulomima concentrations 2 are characterized by concentrations of small bivalves the carbonate mudstone 3 contains pseudomorphs after gypsum crystals and thin crusts of gypsum occasionally in connection with thin microbial layers finally the silty to fine sandy marlstone and micrite and marly silt 4 is highly bioturbated and contains a moderately diverse benthic macrofauna these facies indicate a generally quiet environment punctuated by brief episodes of high water energy two low diversity macrobenthic assemblages can be recognized each of them strongly dominated by a single bivalve taxon the nanogyra virgula assemblage exhibits a higher diversity than the near monospecific corbulomima assemblage the former lived in well aerated waters of slightly reduced salinity and the latter in dysoxic waters of more strongly reduced salinity the environmental stress responsible for the extremely low species richness and evenness is thought to be multifactorial produced by reduced salinity dysoxic conditions and a soft substrate and resulted in simple food chains the eurytopic opportunist corbulomima was the only element of the shelly macrobenthos that was able to thrive in the shelf lagoon under these conditions it occurs in countless mm to cm thick pavements and shell beds which show evidence of winnowing influence of weak currents and occasionally of distal storms as can be deduced from the orientation pattern of shells these rhythmic corbulomima concentrations are explained as reflecting small scale climatic fluctuations between wetter stormier conditions leading to mixing of the water masses and enabling colonization of the lagoonal floor by the bivalve and drier more tranquil conditions the latter resulted in a stratified water mass and anoxia at the bottom superimposed on this rhythmic alternation are three higher orders of cycles which are partly climatic controlled partly reflect changes in relative sea level

calcite cementation during bacterial manganese iron and sulphate reduction in jurassic shallow marine carbonates faunally restricted argillaceous wackestones from the middle jurassic of eastern england contain evidence of early diagenetic skeletal aragonite dissolution and stabilization of the carbonate matrix closely followed by precipitation of zoned calcite cements and precipitation of pyrite distinctive cathodoluminescence and trace element trends through the authigenic calcites their negative 13c compositions and the location of pyrite in the paragenetic sequence indicate that calcite precipitation took place during sequential bacterial mn fe and sulphate reduction calcite 18o values are compatible with cementation from essentially marine pore fluids although compositions vary owing to minor contamination with 18o depleted late cements mg and sr concentrations in the calcites are lower than those in recent marine calcite cements this may be a result of kinetic factors associated with the shallow burial cementation microenvironments bicarbonate for sustained precipitation of the authigenic calcites was derived largely from aragonite remobilization augmented by that produced through anaerobic organic matter oxidation in the metal and sulphate reduction environments aragonite dissolution is thought to have been induced by acidity generated during aerobic bacterial oxidation of organic matter distinction of post oxic metal reduction and anoxic sulphate reduction diagenetic environments in modern carbonate sediments is uncommon outside pelagic settings and early bacterially mediated diagenesis in modern platform carbonates is associated with extensive carbonate dissolution high detrital fe contents of the jurassic sediments and their restricted depositional environment were probably the critical factors promoting early cementation these precipitates constitute a unique example of calcite authigenesis in shallow water limestones during bacterial mn and fe reduction

hyporheic flow as a potential geomorphic agent in the evolution of channel morphology in a gravel bed river abstract morphologic and hydrologic properties of head cut gullies formed in meandering bends of a gravel bed river in northern japan were examined to investigate their topographic development head cut gullies had incised to 2 m below the floodplain surface and had perennial seepage outflows because no surface runoff was observed across the meandering necks we hypothesized that hyporheic flow erosion cutting into the down river edge of the meandering necks is one factor for the development of head cut gullies several topographic features caused by sapping and piping erosion were observed within the head cut gullies a tracer experiment and examination of the water table water chemistry and water table responses in wells on the floodplain and within the head cut gully revealed that significant preferential hyporheic flow occurred between coarse cobble and fine sediment layers of the floodplain materials during a storm event water tables around the head cut gully quickly responded to changes in the water table of the stream channel this result also suggests that hyporheic flow occurred across the meandering bends hyporheic flow around the head cut gullies had higher hydraulic conductivities and preferential flow paths that may relate to buried beds of paleochannels an erosion model suggests that it is unlikely that hyporheic flow alone had enough energy to account for all the soil erosion thus a combination of hyporheic flow sapping erosion and channel erosion bank erosion appeared to contribute to the formation of the head cut gullies hyporheic flow is an important component in the geomorphic evolution of channels and the floodplain in a gravel bed river

influence of seepage undercutting on the stability of root reinforced streambanks several mechanisms contribute to streambank failure including fluvial toe undercutting reduced soil shear strength by increased soil pore water pressure and seepage erosion recent research has suggested that seepage erosion of noncohesive soil layers undercutting the banks may play an equivalent role in streambank failure to increased soil pore water pressure however this past research has primarily been limited to laboratory studies of non vegetated banks the objective of this research was to utilize the bank stability and toe erosion model bstem in order to determine the importance of seepage undercutting relative to bank shear strength bank angle soil pore water pressure and root reinforcement the bstem simulated two streambanks little topashaw creek and goodwin creek in northern mississippi simulations included three bank angles 70 to 90 four pore water pressure distributions unsaturated two partially saturated cases and fully saturated six distances of undercutting 0 to 40 cm and 13 different vegetation conditions root cohesions from 0 0 to 15 0 kpa a relative sensitivity analysis suggested that bstem was approximately three to four times more sensitive to water table position than root cohesion or depth of seepage undercutting seepage undercutting becomes a prominent bank failure mechanism on unsaturated to partially saturated streambanks with root reinforcement even with undercutting distances as small as 20 cm consideration of seepage undercutting is less important under conditions of partially to fully saturated soil pore water conditions the distance at which instability by undercutting became equivalent to instability by increased soil pore water pressure decreased as root reinforcement increased with values typically ranging between 20 and 40 cm at little topashaw creek and between 20 and 55 cm at goodwin creek this research depicts the baseline conditions at which seepage undercutting of vegetated streambanks needs to be considered for bank stability analyses copyright 2008 john wiley sons ltd

soil pipe collapses in a loess pasture of goodwin creek watershed mississippi role of soil properties and past land use little is known about the association of soil pipe collapse features with soil properties or land use history three loess covered catchments in northern mississippi usa were characterized to investigate these relationships soil pipe collapses were characterized for their size type feature and spatial location along with soil properties across the three catchments although mapped as the same soil one of the catchments did not contain pipe collapse features while the other two had 29 4 and 15 4 pipe collapses per hectare these loess soils contained fragipan layers that are suspected of perching water thereby initiating the piping processes pipe collapses associated with subsurface flow paths were not always consistent with surface topography the surface layer tended to be non erodible while layers below even the upper fragipan layers were susceptible to erosion by pipeflow soil properties of the lowest fragipan layer were highly variable but tended to prevent further downward erosion of soil pipes and thus formed a lower boundary for gullies middle to lower landscape positions in one of the piped catchments contained anthropic soils that were highly erodible these anthropic soils were previously gullies that were filled in in the 1950s when forested areas assumed to have been established when land was previously converted from crop to forest land were converted to pasture three decades after this land use change from forest to pasture pipe collapses became evident in contrast the adjacent catchment that does not exhibit pipe collapse features experienced severe sheet and rill erosion prior to the 1930s while in cotton production the surface horizons above the lower fragipan layer were completely removed during this period thus the top soil layer that tends to form a bridge above soil pipes in the more erodible subsoil layers was removed this study showed that knowledge of soil characteristics or topography alone do not explain the distribution of soil pipe collapses as past land use can play a definitive role copyright 2015 john wiley sons ltd

modeling seepage erosion and bank retreat in a composite river bank in large alluvial river courses where bank failure is prominent seepage erosion may be a significant contributor that is often overlooked seepage erosion typically occurs simultaneously with fluvial erosion and other mass failure processes during the recession period of hydrographs in this study a functional relationship between seepage erosion rate and its controlling variables was developed using lysimeter experiments this experimental relationship was used to formulate a mathematical seepage model that predicts the daily seepage erosion rate for a composite river bank soils collected from the brahmaputra river banks were repacked in lysimeters with horizontal stratification similar to the actual bank stratification a total of 71 lysimeter experiments were conducted with various combinations of the controlling variables the results indicate that the seepage gradient has a dominating effect on the time taken in developing undercuts that lead to the bank collapse increase in the number of silt layers in the bank profile increased the time to collapse significantly in situ bank erosion measurements were taken to validate the performance of a bank erosion model for the middle reaches of the brahmaputra river in india the model predictions of seepage erosion rate showed a close agreement with the in situ bank retreat measurements

sediment detachment and transport processes associated with internal erosion of soil pipes subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping the development of perched water tables in duplex soils fosters lateral flow that can result in seepage at the surface of hillslopes and or formation of soil pipes by internal erosion of lateral preferential flow paths continued internal erosion of soil pipes can lead to gullies dam and levee failures however the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented this paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes

mid chain branched mono and dimethyl alkanes in hot spring cyanobacterial mats a direct biogenic source for branched alkanes in ancient sediments hot spring cyanobacterial mats from yellowstone national park u s a and the orakei korako thermal area new zealand have been found to contain suites of monomethyl alkanes compounds frequently reported in cultured and natural populations of cyanobacteria the complete range of possible structural isomers for mid chain branching for c17 c18 and c16 c18 alkanes occurs in the two mats respectively several c19 dimethyl and c20 multibranched alkanes were also observed as major hydrocarbons of the orakei korako mat the recognition of series of mid chain branched alkanes in modern cyanobacterial mats suggests that their occurrence in ancient sediments may reflect direct biogenic contributions rather than formation by diagenetic processes

pseudomorphs after evaporitic minerals interbedded with 2 2 ga stromatolites of the yerrida basin western australia origin and significance widespread quartz pseudomorphs after evaporitic minerals are interbedded with stromatolites in 2 2 ga sedimentary rocks in the yerrida rift basin of western australia these deposits preserve diverse original crystal morphologies that grew displacively either as individuals or as clusters within stromatolitic horizons and associated fine grained siliciclastic beds the stromatolites were deposited in shallow marine restricted environments although evaporitic minerals are largely replaced by quartz their crystal shapes include lenticular rosette needle and nodular forms suggesting that they formed from calcium sulfate rich brines textures suggest that replacement by quartz occurred during early alteration of the sediments original calcium sulfate minerals such as gypsum or anhydrite are indicated by the morphologies of the pseudomorphs this concept is supported by anhydrite inclusions in the quartz crystals that form the pseudomorphs and this finding indicates that calcium sulfate existed in early proterozoic sedimentary environments

late diagenetic calcitization of anhydrite from the mississippian of saskatchewan western canada mississippian nodular anhydrites beneath an unconformity in the subsurface of southern saskatchewan are locally replaced by calcite pyrite and celestite triassic clastics above the unconformity are green rather than red and a usually developed subunconformity alteration zone where carbonates are dolomitized and porosity is filled with anhydrite is absent the unconformity lacks karstic features unlike in the usa and probably formed in a hyperarid climate mississippian anhydrites near the unconformity are not preferentially dissolved nor were they extensively hydrated anhydrite calcitization occurred only after the unconformity was shallowly buried by redbeds and it probably involved sulphate reducing bacteria hydrogen sulphide generated by bacteria reduced redbed pigments the replacement calcite contains pseudomorphs and relicts of anhydrite and pseudomorphs of secondary gypsum these indicate calcitization occurred only after original mississippian gypsum was altered to anhydrite and this in turn was partially converted back to secondary gypsum beneath the unconformity replacement occurred concurrently with the formation elsewhere of the dolomitized zone beneath the unconformity sulphur isotopic ratios of replacement pyrite are depleted relative to mississippian sulphate values consistent with the activities of sulphate reducing bacteria carbon isotopic ratios of replacive calcites however do not support this interpretation and are identical to those of mississippian limestones simple replacement of sulphate by pore water bicarbonate in equilibrium with host limestones is unlikely because protons generated during the reaction should have created acidic conditions in which calcite would have dissolved a full explanation of the calcitization remains elusive but may involve replacement occurring in an active groundwater system and or bacterial sulphate reduction occurring upstream of the site of calcitization

how do disconnected macropores in sloping soils facilitate preferential flow runoff from hillslopes is generated by processes such as infiltration excess and saturation overland flow subsurface stormflow and subsurface return flow preferential flow through macropores can affect any one of these runoff generation processes field studies at the hitachi ohta experimental watershed in japan have noted that self organization processes may manifest the connectivity of such subsurface flow paths particularly via macropores from hillslopes to stream channels it is well established from soil physics principles that the connectivity of macropore networks depends on soil wetness and this has been shown experimentally at hitachi ohta where subsurface flow and streamflow respond to thresholds of wetness numerical solutions to the three dimensional richards equation are derived for a sloping soil block containing a population of disconnected macropores of various sizes shapes and orientations solutions for the case of steady water flux applied to the surface of the soil block are evaluated to determine the conditions where the disconnected macropores become active in the flow process results show that subsurface flow is directed through the preferential flow network in the saturated portion of the soil but bypasses the macropores in the drier regions the preferential flow network expands as the degree of saturation increases the expanding network of active macropores leads to less resistance to overall flow in the domain and access to increased volumes of the flow domain although the individual macropores are disconnected it is argued that large localized hydraulic gradients can potentially lead to preferred zones of subsurface erosion in addition to the importance of these findings related to stormflow generation in catchments they add support to the concept of self organization of subsurface flow systems in soils copyright 2010 john wiley sons ltd

assessment of river bank erosion in southern minnesota rivers post european settlement article i nfo river bank erosion is one of the major sources of sediment for many rivers around the world with the cur rent emphasis on developing total maximum daily loads tmdls for impaired waters in the united states there is heightened interest in quantifying background sediment levels in rivers in this study we assessed variations in river bank erosion over time using a combination of 1855 public land survey system plats aerial photographs from 1938 to 2009 and light detection and ranging lidar data from 2005 to 2009 for sediment impaired rivers in southern minnesota results showed that bank erosion was episodic making comparisons of erosion rates from dissimilar time intervals unreliable for comparable time intervals average river bank retreat rates 0 51 m yr 1 from 1855 to 1938 vs 0 37 m yr 1 from 1938 to 2009 were statistically similar t 2 13 p 0 14 suggesting that bank erosion rates have remained stable since european settlement comparisons over shorter time intervals of 1938 1971 and 1971 2009 also showed similar statistical trends t 0 76 p 0 45 with average river bank retreat rates of 0 57 and 0 50 m yr 1 respectively however additional 145 observations of bank retreat were found in the period 1971 2009 relative to 1938 1971 in dicating that the number of actively eroding river banks may have increased over time contrary to assump tions made in the literature bank erosion measurements using lidar data showed a poor relationship r 2

lipid biomarkers preserved in hydrate associated authigenic carbonate rocks of the gulf of mexico anaerobic oxidation of methane aom is common in ocean margin sediments where it is mediated by consortia of archaea and bacteria and can result in the formation of authigenic carbonate including extensive carbonate crusts previous work indicates that aom is associated with gulf of mexico hydrocarbon seeps and is mediated by similar organisms as identified in other settings however biological investigations have not been done on the associated 13c depleted carbonates here we show that 13c depleted archaeal and bacterial biomarkers are abundant in gulf of mexico authigenic carbonate rocks revealing that aom mediating organisms are closely associated with carbonate authigenesis moreover the rocks share general characteristics of the background soft sedimentary archaeal and bacterial community inferred from biomarker analysis suggesting that the organisms associated with carbonate authigenesis are the same as those that live elsewhere in the hydrocarbon seep environment this provides further evidence that aom by archaea and sulfate reducing bacteria can result in the sequestration of significant quantities of methane derived carbon in carbonate rocks

coupling between sulfur recycling and syndepositional carbonate dissolution evidence from oxygen and sulfur isotope composition of pore water sulfate south florida platform u s a sulfur cycling in fe poor organic rich shelf carbonates known to have rapid rates of so4 2 reduction remains poorly studied despite the volumetric significance of shelf deposits in modern and ancient carbon budgets we investigated sulfur cycling in modern carbonates of the florida platform from end member depositional environments muddy sands from the atlantic reef tract and finer grained mudbank and island flank deposits from florida bay relations between pore water chemistry so4 2 co2 ca 2 cl and oxygen and sulfur stable isotope compositions of so4 2 require direct coupling between sulfur redox cycling and syndepositional carbonate dissolution oxygen isotope compositions of pore water sulfate were remarkably shifted away from the established value for marine so4 2 9 5 despite near normal so4 2 cl ratios chemical evolution was least in reef tract pore waters and greatest in florida bay relative to overlying seawater mudbank sediments exhibited sulfate depletion with 18oso4 and 34sso4 values both increasing by about 7 more bioturbated island flank sediments colonized by thalassia grass had a 5 increase in 18oso4 variable 34sso4 values 17 7 to 23 3 and exceptionally high ca 2 cl ratios the large excess of ca 2 up to 1 7 mm requires a much larger acid source than the amounts derived from utilization of dissolved o2 0 3 mm and small degrees of net so4 2 reduction 0 5 mm reduced a conceptual model was constructed using chemical and isotopic data on natural pore waters and on sulfate isotope fractionation factors obtained from sediment incubation experiments the model outputs show that pore water compositions can be explained by a redox cycle where microbial so4 2 reduction is followed by very efficient h2s oxidation thus maintaining virtually invariant so4 2 cl ratios the enhanced o2 transport may be driven by associated marine grass rhizome systems and microbial communities established in bioturbated sediments the net result of the cycle is that the rate of sulfide oxidation which is largely balanced by the rate of microbial sulfate reduction is stoichiometrically related to the rate of carbonate dissolution this is consistent with previously reported rates of carbonate dissolution 400 mol cm2 yr and average rates of sulfate reduction 200 mol cm2 yr from the florida platform and a 2 1 stoichiometry

spatial distribution of pipe collapses in goodwin creek watershed mississippi the internal erosion of soil pipes can induce pipe collapses that affect soil erosion processes and landform evolution the objective of this study was to determine the spatial distribution of pipe collapses in agricultural fields of goodwin creek watershed ground survey was carried out to detect pipe collapses and the location size and surface elevation was measured with differential gps a total of 143 of the 145 pipe collapses were found in cropland and the density was approximately 0 58 collapses per hectare the spatial distribution of pipe collapses was not uniform as pipe collapses were concentrated in the flat alluvial plains where the land use was dominated by cropland one of the four parcels had 90 of the pipe collapses with a density of 7 7 collapses per hectare the mean depth area and volume of these pipe collapses were 0 12 m 0 34 m2 and 0 02 m3 respectively and all these properties exhibited a skewed distribution the drainage area slope gradient equation which has been widely used for erosion phenomenon prediction did not represent pipe collapses in this study as the coefficient of determination was 0 01 this is clear evidence that subsurface flow is not represented by surface topographic characteristics the pipe collapses were found to intercept runoff thereby reducing the slope length factor by 6 and the drainage area by 7 both of these factors can reduce the sheet and rill erosion however the increased subsurface flow could enhance ephemeral gully erosion published 2012 this article is a u s government work and is in the public domain in the usa

an early jurassic deep water stromatolitic bioherm related to possible methane seepage los molles formation neuquen argentina an assemblage of microbial stromatolites and worm tubes makes up a limestone bioherm 15 m thick and 60 m in diameter enclosed in marls and dark shales of the early jurassic los molles formation neuquen basin argentina the los molles formation is a basinal unit consisting primarily of shales silts and sandstone turbidites deposited after the first general marine transgression in the basin below storm wave base in relatively deep water poorly oxygenated conditions the bioherm is composed of stacked stromatolites 1 4 m in diameter and 1 2 m thick they initially grew horizontally tabular stromatolites or vertically columnar stromatolites and later became domal equidimensional to asymmetric structures they often display vertical and overturned flanks each stromatolite consists of micritic laminae alternating with early botryoidal cements which make up the bulk of the structure calcareous worm tubes are embedded in peloidal micrite associated with the stromatolites the growth of the assemblage was uninterrupted by terrigenous input the diagenetic sequence indicates evolution from marine phreatic to burial environments isotopic values for micrite worm tubes early botryoidal cements and spar cements yield very negative 13c values down to 33 and negative 16o values down to 11 these depleted values indicate precipitation in very anomalous conditions in the jurassic ocean under the influence of methane rich fluids these characteristics suggest that the stromatolitic bioherm formed in relation to methane seeps in the seafloor of the neuquen basin it is suggested that the structure grew within the photic zone although a chemosynthetic component cannot be excluded minimum depositional depth has been estimated at 50 m and could be up to 100 m the vent fluids would have migrated through shallowly buried early rift faults which bound underlying depocenters infilled with continental clastic and volcanic rocks the origin of these fluids could be related to magmatic activity which resulted in accumulation of the syn rift volcanics alternatively the structure could indicate seepage related to the presence of hydrocarbon accumulations in the syn rift succession during the jurassic the importance of which is being gradually acknowledged in the petroleum system of the neuquen basin

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

numerically predicting seepage gradient forces and erosion sensitivity to soil hydraulic properties summary research has suggested that streambank seepage can be an important mechanism of bank instability however limited information is available on the level of soil characterization necessary to accurately predict seepage gradient forces and erosion the objective of this research was to quantify the expected range of predicted seepage gradients for various degrees of site characterization uncertainty analysis on seepage gradient predictions was performed relative to variability in soil hydraulic properties a two dimensional unsaturated saturated groundwater flow model was used to simulate a homogeneous soil layer for sand and loamy sand soils packed at various bulk densities qb a pedotransfer function rosetta designed to estimate unsaturated hydraulic properties from surrogate soil data i e texture and bulk density was used to derive the saturated hydraulic conductivity ks and water retention parameters for various levels of site information i e only textural class percent sand silt and clay ssc ssc and qb and ssc qb and ks statistical distributions were derived for each soil hydraulic parameter and monte carlo simulations were performed to generate distributions of maximum seepage gradient the deviation in predicted seepage gradient was calculated using assumed baseline conditions ranges in predicted soil hydraulic parameters and maximum seepage gradients were considerably reduced when using ssc as compared to soil texture therefore at a minimum soil samples should be taken for particle size analysis for qb between 1450 and 1500 kg m 3

cold seep deposits of beauvoisin oxfordian southeastern france and marmorito miocene northern italy microbially induced authigenic carbonates the relation of two well known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study archaea are found to be associated with the formation of oxfordian seep carbonates from beauvoisin and with a miocene limestone from marmorito tube worm limestone carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative 13ccarbonate values respectively highly positive values 15 reflect the use of 13c enriched co2 produced by methanogenesis low 13c values of the marmorito carbonates 30 indicate the oxidation of seepage derived hydrocarbons likewise the 13c content of specific tail to tail linked isoprenoids biomarkers for archaea was found to be strikingly depleted in these samples as low as 115 the isotopic signatures corroborate that archaea were involved in the cycling of seepage derived organic carbon at the ancient localities another miocene limestone marmorito limestone shows a strong imprint of methanotrophic bacteria as indicated by 13c values of carbonate as low as 40 and biomarker evidence epifluorescence microscopy and field emission scanning electron microscopy revealed that bacterial biofilms were involved in carbonate aggregation in addition to lucinid bivalves previously reported from both localities we infer that sponges from beauvoisin and tube worms from marmorito depended on chemosynthesis as well low 13c values of nodules related to sponge taphonomy 27 indicate that sponges might have been linked to an enhanced hydrocarbon oxidation tube worm fossils from marmorito closely resemble chemosynthetic pogonophoran tube worms from recent cold seeps and are embedded in isotopically light carbonate 13c 30

stromatolitic fabric of authigenic carbonate crusts result of anaerobic methane oxidation at cold seeps in 4 850 m water depth methane seepage leads to mg calcite and aragonite precipitation at a depth of 4 850 m on the aleutian accretionary margin stromatolitic and oncoid growth structures imply encrustation of microorganisms microbial mats in the host sediment with a unique growth direction downward into the sediment forming crust shaped lithologies biomarker investigations of the residue after carbonate dissolution show strong enrichments in crocetane and archaeol which contain extremely low 13c values this indicates the presence of methane consuming archaea and 13c values of 42 to 51 pdb indicate that methane is the carbon source for the carbonate crusts thus it appears that stromatolitic encrustations of methanotrophic anaerobic archaea probably occurs in a consortium with sulphate reducing bacteria and that carbonate precipitation proceeds downward into the sediment where ascending cold fluids provide a methane source strontium and oxygen isotope analyses as well as 14c ages of the carbonates suggest that the fluids come from deep within the sediment and that carbonate precipitation began about 3 000 years ago

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

case study two dimensional model simulation of channel migration processes in west jordan river utah the paper presents the application of a two dimensional depth averaged numerical model to simulate the lateral migration processes of a meandering reach in the west jordan river in the state of utah a new bank erosion model was developed and then integrated with a depth averaged two dimensional hydrodynamic model the rate of bank erosion is determined by bed degradation lateral erosion and bank failure because bank material in the west jordan river is stratified with layers of cohesive and noncohesive materials a specific bank erosion model was developed to consider stratified layers in the bank surface this bank erosion model distinguishes itself from other models by relating bank erosion rate with not only flow but also sediment transport near the bank additionally bank height slope and thickness of two layers in the bank surface were considered when calculating the rate of bank erosion the developed model was then applied to simulate the processes of meandering migration in the study reach

synsedimentary versus metamorphic control of s o and sr isotopic compositions in gypsum evaporites from the cameros basin spain abstract sulfate 34s and 18o and sr isotope compositions are presented for berriasian upper jurassic gypsum evaporites from the cameros basin a continental basin in the iberian ranges of northern spain solute sources to the ephemeral lakes in which the evaporites formed are dominated by weathering of sediments containing older keuper marine evaporites and granitic metamorphic variscan basement strontium isotopic ratios of the continental evaporites 87sr 86sr 0 707882 to 0 707933 are elevated compared to the keuper source 87sr 86sr 0 707605 to 0 707799 most likely reflecting a radiogenic component from basement lithologies sulfate 34s in the continental evaporites at around 18 2 v cdt is higher than any possible mixture of solutes to the basin the degree of 34s enrichment is small 3 7 and is most likely the result of partial bacterial reduction of lake water sulfate the same process would also enrich sulfate in 18o but by only 1 evaporite sulfate 18o at around 21 7 v smow is in fact enriched by 10 relative to sulfate sources to the basin this large effect is most likely the result of re equilibration of oxygen isotopes during low grade metamorphism of the basinal sequence sulfur and strontium isotopes in the evaporites remained internally buffered and thus unchanged during metamorphism while oxygen isotopes were open to exchange with aqueous fluid and or interbedded carbonates that constituted a large exchangeable oxygen reservoir the potential of sulfate oxygen to undergo isotopic exchange at elevated temperatures must be taken into account when interpreting the significance of evaporite sulfate oxygen data from units that have undergone deep burial or low grade metamorphism

climate and tectonic influences on continental erosion of tropical south america 0 13 ma is tectonic uplift or climate change the primary driving force behind continent scale erosion here we examine these two hypotheses for tropical south america by comparing a high resolution record of terrigenous sediment accumulation rates from the western tropical atlantic ocean with continental tectonic reconstructions and both low latitude and high latitude climate indices that span the past 13 m y over the full record terrigenous sedimentation rates most closely follow lowland aridity as recorded by abundance ratios of terrigenous oxide minerals an indication that basin integrated climate is an important control of erosion step like transitions in the flux and composition of terrigenous material near 8 and 4 5 ma however follow dated tectonic events which suggests progressive expansion of the drainage basin into less humid or less vegetated regions that were more prone to erosion on long time scales high latitude climate variability and sea level as recorded by 1 8 o do not closely track terrigenous sedimentation we conclude that regional climate change provides a mechanism for long term erosion of tropical south america tectonics plays a significant but secondary role in this area perhaps by shaping the drainage basin to include regions in which the climate is more favorable to erosion

piping process genesis and network characterization through a pedological and geophysical approach abstract piping is a soil erosion process initiated by concentrated subsurface water flow which can develop in both natural and anthropogenic landscapes and causes various environmental impacts the piping process acts as a relief modifier leading to soil subsidence on a short time scale this paper aims to provide a more comprehensive characterization of the piping process in a tropical forested area of brazil first we sought to understand and examine the subsurface environment of the soil using field description and soil sampling for chemical and physical analyses ph cec bulk density total porosity flocculation degree based on this information we performed geophysical tests using direct current resistivity method dc resistivity with six lines of electrical resistivity tomography ert to map the pipes and check the connection between subsurface tunnels data on the basic properties of the soil aided our interpretation of the geophysical results and the genesis of the piping process the soil of the study area presented horizons in which textural variations accompanied changes in total porosity bulk density and flocculation degree the dc resistivity method efficiently detected the pipes resistive zones of values 4000 o m and high contrast with adjacent zones and revealed the connection and continuity of the pipe network while various factors may contribute to the subsurface erosive process in the study area the decisive factor triggering the process seems to be the presence of a permeable layer that lies just above the impermeable layer which may stop water infiltration and facilitate the lateral water movement

piping sapping erosion ii identification diagnosis although erosion of streambanks and other shorelines by emergent seepage is widespread this erosion mechanism termed piping or sapping has not been recognized as important to the overall erosion process the mechanism is complex and interactions with other bank and shore processes tend to mask the effects of piping sapping direct evidence water emerging from a soil face and carrying away soil particles is rarely encountered several types of indirect evidence are presented and illustrated in this paper including cavities formed by piping deposits of dislocated particles below piping zones blind gullies staining produced by persistent seepage outflow and particular types of localized failures slab toppling block shearing and tensile falls caused by undercutting due to piping sapping the interactions of this erosion mechanism with other erosion deposition processes are described the purpose of this paper is to facilitate identification and evaluation of piping sapping erosion particularly

near bank impacts of river stage control a gently sloping subaqueous bench is the topographical phenomenon resulting from the retention of pools to allow navigation in controlled stage streams bench formation has been observed at many sites on the ohio illinois and kanawha rivers they are the result of bank failure and erosion processes including seepage induced erosion localized failure of undermined layers reworking of failed soils by waves and erosion by current forces benches are prevalent along alluvial banks composed of layered soils and are covered by a shallow water zone that is ecologically significant this article summarizes the research to date on the bench phenomenon and draws inferences for future work in bank protection and development of riverine ecosystems

methane derived carbonates and authigenic pyrite from the northwestern black sea abstract methane seeps in the northwestern black sea are accompanied by carbonate and pyrite precipitates sediments were sampled at locations on the romanian 120 m depth and ukrainian 180 200 m depth shelf and slope layered carbonate crusts are formed of i carbonate cemented siliciclastic sediment containing dreissenoid bivalves ii microcrystalline high mg calcite or aragonite and iii aragonitic cement the dreissena sediment is subrecent and was deposited during the freshwater phase of the black sea it has been affected by seepage of methane rich fluids which induced intergranular precipitation of authigenic carbonates the microcrystalline carbonates exhibit an intense autofluorescence high mg calcite contains 11 14 mol mgco3 the aragonitic cement 8300 9500 ppm sr forms either isopachous layers or botryoids microbial filaments about 10 20 m in diameter and up to 900 m in length are preserved within and on carbonate crusts the carbonates are depleted in 13c microcrystalline carbonate ranges from 27 to 41 pdb and botryoidal aragonite ranges from 26 to 38 pdb the 13c depletion indicates that the carbonates predominantly derive from the microbial oxidation of methane carbonate deposits do not project up into the oxic water column they are restricted to the anoxic water column and to anoxic sediments revealing the crucial role of anaerobic methane oxidation for carbonate precipitation 14c contents give apparent radiocarbon ages of 20 640 180 a bp for a sample of botryoidal aragonite and 19 110 180 a bp for a sample of microcrystalline carbonate compatible with minimum ages of carbon derived from a fossil hydrocarbon source the 18o values of methane derived carbonates show a narrow range from 1 2 to 0 2 pdb 87sr 86sr ratios of microcrystalline carbonate mean 0 70927 and aragonitic cement mean 0 70918 are indistinguishable from ambient seawater mean 0 70917 and thus indicate a shallow sr source higher 87sr 86sr ratios of the dreissena sediment mean 0 71005 are probably caused by sr derived from detrital mica carbonates are accompanied by blocks and crusts composed of pyrite the framboidal sulphide exhibits a palisade like fabric with framboids arranged to parallel pillars sulphur isotopic ratios 34s ranging from 16 8 to 19 7 cdt indicate that the sulphur derives not from the 34s depleted h2s of the water column or the uppermost sediment layers most likely pyrite formed in the lacustrine sediments after the first incursion of mediterranean seawater

structure and distribution of branched aliphatic alkanes with quaternary carbon atoms in cenomanian and turonian black shales of pasquia hills saskatchewan canada abstract twelve pseudohomologous series of branched alkanes with one or two quaternary carbon atoms baqcs c14 c33 range are present in the extractable organic matter of cenomanian and turonian black shales of pasquia hills saskatchewan canada five of these pseudohomologous series are also observed in a holocene sample from the russian arctic three of the pseudohomologous series were identified by kenig et al pnas 100 2003 12554 12558 as 3 3 and 5 5 diethylalkanes deas and 2 2 dimethylalkanes dmas the nine other pseudohomologous series of baqcs are tentatively identified on the basis of their characteristic mass spectral fragmentation and retention indices as 3 3 dimethylalkanes dmas 3 ethyl 3 methyl and 5 ethyl 5 methylalkanes 9 9 7 7 and 6 6 diethylalkanes deas 3 3 3 3 and 5 5 5 5 tetraethylalkanes and 5 butyl 5 ethylalkanes pseudohomologous series of branched alkanes with tertiary carbon atoms such as monomethyl and monoethylalkanes are also present in the same carbon number range all these pseudohomologous families share the particularity of including isomers with exclusively odd or exclusively even carbon numbers clearly indicating a biosynthetic origin baqcs such as 5 5 deas 3 3 deas and 3 ethyl 3 methylalkanes seem to be widespread in sediments and sedimentary rocks ranging from modern to 2 1 billion years a xenobiotic source for baqcs can be excluded at this point baqcs seem to have a very low biodegradability in part explaining their widespread occurrence in ancient sediments

multiple pulses of neogene compressive deformation in the ayacucho intermontane basin andes of central peru strata of the neogene ayacucho intermontane basin central peru can be subdivided into three tectonostratigraphic units the larampuquio volcanics consisting largely of intermediate lavas and coarse conglomerates of similar lithology the unconformably overlying huanta formation consisting of a lower part formed predominantly of lacustrine and volcaniclastic sedimentary rocks and an upper part composed largely of intermediate lavas tuffs and conglomerates and the unconformably overlying ayacucho formation consisting of complexly interfingering volcaniclastic sedimentary rocks silicic tuffs and lavas of intermediate to silicic composition radiometric ages of 17 3 0 2 m y and 18 3 0 6 m y have been obtained on tuffs from the upper and lower parts of the larampuquio volcanics determinations on 2 rocks from the lower member of the huanta formation indicate an age of 11 4 0 5 m y and a rock from the upper member is dated at 9 3 0 3 m y b p units of the ayacucho formation yield ages showing that it was deposited between 7 7 and 6 m y ago the intervening molinoyocc and puchcas volcanics were erupted between 9 9 and 7 4 m y ago these units may postdate the huanta formation or may be associated in part with the huanta and in part with the ayacucho formation coarse conglomerates of the larampuquio volcanics represent debris eroded from highlands uplifted during the first and most intense pulse of the late cenozoic quechuan phase of andean compressive tectonism that began in the early miocene folding of the larampuquio volcanics may have taken place during this or a subsequent pulse of compression a marked unconformity between the huanta and ayacucho formations demonstrates a period of deformation between 8 5 and 9 5 m y ago compression also was active during at least part of the deposition of the ayacucho formation as shown by inter fingering wedges of coarse clastic debris along the northeastern margin of the basin and by angular unconformities within the formation folded rocks of the ayacucho formation and its equivalents to the west are overlain by undeformed volcanic units dated at 3 8 0 4 m y b p and 5 5 m y b p bracketing a well defined pulse of deformation slightly younger than 6 m y these subsequent episodes of compressive deformation represent recurrent pulses of the quechuan phase folding related to these late quechuan pulses is restricted in the andes to northwest trending belts corresponding to reactivated fault zones in the pre neogene substratum a system of north trending dikes in the huachocolpa district 70 km west of ayacucho suggests relaxation of compression in the pliocene and compression of quaternary age has been recognized in the huancayo area 170 km northwest of ayacucho taken together with the first pulse of quechuan deformation in the early and middle miocene these data indicate at least four pulses of crustal compression during the late cenozoic separated by periods during which compressional stresses were at least partly relaxed and at times possibly replaced by extension

instability of sandbars in grand canyon the glen canyon dam located in the northeastern corner of arizona is operated to satisfy peak power demands of neighboring states the discharge regime of the dam is such that the river stage in the colorado river downstream of the dam varies diurnally as much as 4 m in some sections it is alleged that these fluctuations of the river stage are responsible for the destruction of sandbars and as a result the loss of the extant biomass and the reduction of recreational facilities in this paper an analysis is developed to determine the equilibrium slope below which slope failures mass wasting bank failures due to seepage of bank stored water would be unlikely the sediments enclosed by the equilibrium seepage slope range 11 14 for the sediments downstream of the glen canyon dam and the maximum slope angle range from 26 to 32 is subjected to ongoing aggradation and erosion field data from ground surveys support the analysis described in this paper

on slope instability induced by seepage erosion this paper is focused on seepage erosion causing liquefaction processes and rapid slope failures one case history which occurred along an old fluvial terrace in the po plain northern italy is

abundance and geochemical significance of c2n dialkylalkanes and highly branched c3n alkanes in diverse meso and neoproterozoic sediments several series of branched alkanes with quaternary carbon centers have been detected by gc ms in the saturated hydrocarbon fractions of neoproterozoic sedimentary rocks associated with fossilised microbial mats officer basin south australia and of shallow water carbonates spitsbergen east greenland and baffin island canada a series of 5 5 diethylalkanes was predominant in most of these sediments and was typically accompanied by related series in lower abundance which based on mass spectral characteristics are tentatively assigned as 6 6 diethylalkanes 5 butyl 5 ethylalkanes and 6 butyl 6 ethylalkanes each series displays strong odd or even carbon number preferences several of the sediments contained additional series of structurally undefined c3n alkanes notable for very negative retention time factors which become more negative with increasing molecular weight indicating that branching increases with each c3 addition the strongly sequential carbon preference of the respective c2n and c3n branched alkane series and a predominantly light 13c signature of the 5 5 diethylalkanes cf co occurring n alkanes are consistent with an origin from organisms with a distinct physiology and or carbon source the relatively wide occurrence and high abundance of these branched alkanes in proterozoic sediments containing benthic microbial mats suggests a relationship with specific paleoenvironmental conditions for example strong water column redox gradients that may have been more prevalent than in the phanerozoic