morphology and environment of cold water coral carbonate mounds on the nw european margin cold water coral carbonate mounds owing their presence mainly to the framework building coral lophelia pertusa and the activity of associated organisms are common along the european margin with their spatial distribution allowing them to be divided into a number of mound provinces variation in mound attributes are explored via a series of case studies on mound provinces that have been the most intensely investigated belgica hovland pelagia logachev and norwegian mounds morphological variation between mound provinces is discussed under the premise that mound morphology is an expression of the environmental conditions under which mounds are initiated and grow cold water coral carbonate mounds can be divided into those exhibiting inherited morphologies where mound morphology reflects the morphology of the colonised features and developed morphology where the mounds assume their own gross morphology mainly reflecting dominant hydrodynamic controls finer scale surface morphological features mainly reflecting biological growth forms are also discussed

channel arrangements and depositional styles in the sao lourenco fluvial megafan brazilian pantanal wetland abstract the brazilian pantanal is an extensive lowland tropical basin characterized by the presence of fluvial megafans and seasonally inundated savanna floodplain wetlands with an area of about 16 000 km 2 the sao lourenco is the second largest megafan in the pantanal three distinct fluvial channel styles that formed at different times during the late quaternary are found here a geomorphological and sedimentary assessment of these depositional patterns provides valuable insight on the environmental context of their evolution new optically stimulated luminescence data indicate that the upper five meters of sediment in the sao lourenco megafan has been accumulating since the late pleistocene ancient fan lobes located in upper and intermediate fan settings consist of medium and coarse grained fluvial sands and exhibit well preserved distributary braided paleochannels on their surfaces as the megafan evolved through time pleistocene lobes were incised by a prominent valley filled with holocene aged meander belt deposits which consist of silts interbedded with very fine sands and clays currently the incised valley is a zone of sediment bypass modern deposition occurs along the distal toe of the megafan system where lobes characterized by distributary channel levee ridges are widespread these features formed by progradation of avulsion belts into a broad swampy floodbasin which caused the lower portion of the meander belt to be abandoned the significant differences observed in intra fan morphology appear to be linked to the variability in effective precipitation fan lobes deposited with braided distributary channels occurred under relatively dry conditions in the late pleistocene by contrast aggradational meander belt deposits and lobes with distributary channel levee ridges formed during fluctuating precipitation conditions of the holocene when the pantanal emerged from deglacial aridity modern lobes form under heavy seasonal flooding and deposition occurs in response to very rapid and common avulsion events these results have implications for interpreting the complexity of megafan facies in similar continental basins

productivity controlled cold water coral growth periods during the last glacial off mauritania abstract article history received 17 june 2010received in revised form 29 october 2010accepted 11 december 2010available online 21 december 2010communicated by g j de langekeywords lopheliacold water coralscarbonate moundsbanda mound provincenw africaprimary productivity cold water corals are widely distributed along the atlantic continental margin with varying growth patternsinrelationtotheirspeci cenvironment here weinvestigatethelong termdevelopmentofcold watercoralsthat once thrived on a low latitude 17 40 n cold water coral mound in the banda mound province offmauritania duringthelastglacial interglacialcycle u thdatesobtained from20specimensofthecold watercoral lophelia pertusa revealed three distinct periods of coral growth during the last glacial at 65 to 57 kyr bp 45 to 32 kyr bp and 14 kyr bp thus comprising the cool periods of marine isotopic stages mis 2 4 thesecoral growth periods occur during periods of increased productivity in the region emphasizing thatproductivity seems to be the major steering factor for coral growth off mauritania which is one of the majorupwelling regions in the world this pattern differs from the well studied coral mounds off ireland where thecurrent regime predominantly in uences the prosperity of the cold water corals moreover coral growth offireland takes place during rather warm interglacial and interstadial periods whereas off mauritania coralgrowth is restricted to glacial and stadial periods however the on mound sedimentation patterns offmauritania largely resemble the observations reported from the irish mounds the bulk of the preservedsediments derives from periods of coral growth whereas during periods without corals hardly any netsedimentation or mound growth took place 2011 elsevier b v all rights reserved

137cs and 210pb derived sediment accumulation rates and their role in the long term development of the mkuze river floodplain south africa abstract wetlands are well known to act as sinks for sediment and chemicals in the landscape within the mkuze river floodplain in northern kwazulu natal south africa deposition of clastic sediment occurs predominantly in close proximity to the river channel resulting in the formation of levees over time this leads to channel avulsion a process that may be accelerated by the activities of hippopotami whose trails create hydraulically favourable pathways sedimentation rates determined using the isotopes 210pb and 137cs indicate that the mkuze river floodplain is a relatively rapidly aggrading system that should experience frequent avulsion with average short term rates in the order of 0 25 to 0 50 cm y sediments on the floodplain are also an important sink for solutes which concentrate in the groundwater and precipitate out because of evapotranspiration over long timescales chemical sedimentation affects the landscape by influencing salinity vegetation distribution hydrological flows and local topography the mkuze river floodplain is an actively evolving system which continues to aggrade as a result of the combination of clastic and chemical sedimentation in a region characterised by a strong annual water deficit temporal patterns of clastic and chemical sedimentation are likely to exert influence on the long term development of wetland systems elsewhere in southern africa this study the first on sediment accretion rates using 210pb and 137cs dating for a southern african wetland demonstrates that radioisotopic methods are an important tool that can be applied toward fully understanding wetland formation evolution and functioning in the region

seabed image acquisition and survey design for cold water coral mound characterisation abstract cold water coral cwc habitats are commonly regarded as hotspots of biodiversity in the deep sea however a standardised approach to monitoring the effects of climate change anthropogenic impact and natural variability through video surveying on these habitats is poorly established this study is the first attempt at standardising a cost effective video survey design specific to small cwc mounds in order to accurately determine the proportion of facies across their surface the piddington mound of the moira mounds porcupine seabight offshore ireland has been entirely imaged by downward facing video in 2011 and 2015 the 2011 video data is navigated into a full mound georeferenced video mosaic a quadrat based manual classification of this video mosaic at 0 25 m2 resolution shows the exact proportion of facies abundance across the mound surface the minimum number of random downward facing images from the mound are determined to accurately characterise mound surface facies proportions this minimum sample size is used to test the effectiveness of various common survey designs for rov video based habitat investigations single pass video lines are not representative of the mound surface whilst gridded survey designs yield best results similar to 100 mound coverage the minimum sample size and manual classification are applied to the 2015 video data to show a 19 mound surface facies change over 4 years at 0 25 m2 resolution the proportion of live coral facies show little change while coral rubble facies show most change this highlights an inconsistency between temporally separated data sets and implies that in 20 years the mound surface may almost entirely change

giant carbonate mud mounds in the southern rockall trough seismic profiles sidescan sonar data bottom photography and sampling proved for the first time that there are giant carbonate mounds bioherms in the rockall trough the pelagia mounds on the northern porcupine bank are relatively isolated whereas most of the logachev mounds on the southeast rockall bank form a field of closely spaced contiguous mounds they are all found on the upper slope at depths between about 500 and 1200 m and as a result of this study about 500 have been mapped they have a variety of shapes and the larger ones are very steep sided up to 350 m high and 2 km wide at the base sediment samples show that the mounds consist of pale coloured muds mainly aragonite usually with live and or dead cold water corals at the seafloor and with buried dead corals coral thickets appear to be detected as a brush like signature on high resolution profiles and as a speckled pattern on high resolution sidescan sonar records shelly sands are found on the seabed between the mounds currents in the mound areas are strong enough to transport sands along slope as medium sized sand waves and to prevent pelagic deposition thus providing surfaces for initial coral settlement by the winnowing of fines to leave glacial dropstones and exposed rocks these observations show that the poleward directed upper slope current of the eastern north atlantic extends further south than hitherto known and that there is a southwesterly directed current on rockall bank there are waves on the logachev mounds with a wavelength of about 20 30 m that are thought to be moulded in carbonate muds by across slope directed internal tidal currents and or cascading currents mounds develop above erosional surfaces seen on seismic data the huge amount of carbonate mud seems to be produced by the rapid growth and breakdown of cold water corals living in a very favourable environment intermediate nepheloid layers formed upstream by the strong currents may provide the food source for the deep water suspension feeders conditions for giant mound growth require an ideal balance between current speed and sedimentation rate among other factors no evidence for the suggested link to methane seepage has been found so far

pliocene and quaternary depositional model of the algarve margin contourite drifts gulf of cadiz sw iberia seismic architecture tectonic control and paleoceanographic insights abstract the contourite drifts off southwest iberia that formed as a result of the interaction of the mediterranean outflow water mow with the continental middle slope were studied in the algarve margin using multichannel reflection seismic lines oil wells piston cores and a bathymetric compilation of four datasets the seismostratigraphic interpretation of a dense array of oil industry seismic and stratigraphic correlation allowed the identification of five seismic units of early pliocene through holocene in the faro and albufeira drifts and four correlative seismic units in the lagos and sagres drifts and three in the portimao drift a three phased evolutionary model for the contourite formation is proposed firstly a precursory phase of pliocene age made up of sheeted drifts represents an initial phase of deposition under bottom current activity that is correlated with the first stages of an enhanced mow at about 3 5 ma secondly the building up phase of early pleistocene age is related to a strengthening of the mow close to the onset of the northern hemisphere glaciations at about 2 6 ma during which were deposited low mounded drifts thirdly the growing phase from middle pleistocene through holocene suggests the presence of a stronger mow since the beginning of the middle pleistocene transition at about 1 3 1 0 ma accounting for the deposition of mounded drifts and formation of the alvares cabral moat seismostratigraphic interpretation and isochron maps allowed for the establishment of the main oceanographic climatic morphologic and tectonic factors that controlled the drifts deposition i the pliocene and quaternary mow circulation forced by climate changes ii the sea bottom topography inherited from the late miocene mainly shaped by the portimao lagos and bartolomeu dias canyons system iii the interaction between along slope and down slope processes since the pliocene and iv pliocene quaternary fault activity and diapirism

paleoenvironmental reconstruction of challenger mound initiation in the porcupine seabight ne atlantic the understanding of the paleoenvironment during initiation and early development of deep cold water coral carbonate mounds in the ne atlantic is currently a focus of international research the integrated ocean drilling program iodp expedition 307 drilled the 155 m high challenger mound in the porcupine seabight sw off ireland in order to investigate for the first time sediments from the base of a giant carbonate mound in this study we focus in high resolution on 12 m of sediments from site 1317 encompassing the mound base the mound initiation and start up phase coincide with the intensification of the northern hemisphere glaciation inhg at around 2 7 ma further carbonate mound development seems to be strongly dependent on rapid changes in paleoceanographic and climatic conditions at the pliocene pleistocene boundary especially characterized and caused by the interaction of intermediate water masses the mediterranean outflow water mow the eastern north atlantic water enaw and the influence of southern component water scw this study is based on well established proxies such as 18o and 13c of planktonic globigerina bulloides and benthic foraminifera fontbotia wuellerstorfi discanomalina coronata lobatula lobatula lobatula antarctica and planulina ariminensis as well as grain size parameters to identify the paleoenvironmental and paleoecological setting favourable for the initial coral colonization on the mound stable oxygen and carbon isotope records of benthic foraminiferal species indicate that l lobatula provides a reliable isotopic signature for paleoenvironmental reconstructions in particular 18o values of l lobatula indicate that initial mound growth started in a glacial mode with moderate excursions in 18o values carbon isotope values of d coronata are significantly offset compared to other epibenthic species this offset may be related to vital effects bottom water temperatures calculated using standard equations based on 18o of foraminiferal tests range between 7 and 11 c consistent with the known temperature range conducive for cold water coral growth and development bottom currents transporting intermediate water masses of southern origin mediterranean and bay of biscay enhanced at 2 6 ma supporting first coral settlements with the inhg the benthic 13c and the sortable silt records indicate that the early pleistocene hydrodynamic regime was characterized by weaker current intensities associated with vertical movements of mow or its replacement by scw at intermediate depth after these sluggish phases enhanced mow flow dominated again and led to stronger current intensities and most probably sediment erosion on challenger mound erosion in combination with early diagenetic oxidation processes overprinted the sediment layers as indicated by dissolved coral skeletons the increase in ca content and sediment density minimum 13cplanktonic values as well as the occurrence of gypsum and pyrite implying a careful evaluation of original and overprinted geochemical signals we conclude that the challenger mound development was already influenced by short term variability of water masses from southern origin and possible erosional events comparable to the late pleistocene setting

sedimentological regimes for turbidity currents depth averaged theory turbidity currents are one of the most significant means by which sediment is moved from the continents into the deep ocean their properties are interesting both as elements of the global sediment cycle and due to their role in contributing to the formation of deep water oil and gas reservoirs one of the simplest models of the dynamics of turbidity current flow was introduced three decades ago and is based on depth averaging of the fluid mechanical equations governing the turbulent gravity driven flow of relatively dilute turbidity currents we examine the sedimentological regimes of a simplified version of this model focusing on the role of the richardson number ri dimensionless inertia and rouse number ro dimensionless sedimentation velocity in determining whether a current is net depositional or net erosional we find that for large rouse numbers the currents are strongly net depositional due to the disappearance of local equilibria between erosion and deposition at lower rouse numbers the richardson number also plays a role in determining the degree of erosion vs deposition the currents become more erosive at lower values of the product ro ri due to the effect of clear water entrainment at higher values of this product the turbulence becomes insufficient to maintain the sediment in suspension as first pointed out by knapp and bagnold we speculate on the potential for two layer solutions in this insufficiently turbulent regime which would comprise substantial bedload flow with an overlying turbidity current

cold water coral mounds on the pen duick escarpment gulf of cadiz the microsystems project approach here we present a case study of three cold water coral mounds in a juvenile growth stage on top of the pen duick escarpment in the gulf of cadiz alpha beta and gamma mounds although cold water corals are a common feature on the adjacent cliffs mud volcanoes and open slope no actual living cold water coral has been observed this multidisciplinary and integrated study comprises geophysical sedimentological and bio geochemical data and aims to present a holistic view on the interaction of both environmental and geological drivers in cold water coral mound development in the gulf of cadiz coring data evidences past or present methane seepage near the pen duick escarpment several sources and pathways are proposed among which a stratigraphic migration through uplifted miocene series underneath the escarpment the dominant morphology of the escarpment has influenced the local hydrodynamics within the course of the pliocene as documented by the emplacement of a sediment drift predominantly during post middle pleistocene glacial episodes favourable conditions were present for mound growth an additional advantage for mound formation near the top of pen duick escarpment is presented by seepage related carbonate crusts which might have offered a suitable substrate for coral settling the spatially and temporally variable character and burial stage of the observed open reef frameworks formed by cold water coral rubble provides a possible model for the transition from cold water coral reef patches towards juvenile mound these rubble graveyards not only act as sediment trap but also as micro habitat for a wide range of organisms the presence of a fluctuating sulphate methane transition zone has an important effect on early diagenetic processes affecting both geochemical and physical characteristics transforming the buried reef into a solid mound nevertheless the responsible seepage fluxes seem to be locally variable as such the origin and evolution of the cold water coral mounds on top of the pen duick escarpment is probably more than any other ne atlantic cold water coral mound province located on the crossroads of environmental hydrodynamic and geological seepage pathways

the moira mounds small cold water coral mounds in the porcupine seabight ne atlantic part b evaluating the impact of sediment dynamics through high resolution rov borne bathymetric mapping large cold water coral carbonate mounds are well known from several locations along the north east atlantic continental margin with these mound structures which can measure up to 350 m in height often smaller mounds are found in the same hydrodynamic settings this paper illustrates the importance of local sediment dynamics on the morphology and development of small sized mounds the moira mounds in the belgica mound province porcupine seabight sw of ireland through rov borne microbathymetry and video data the data set illustrates the sedimentary setting of small mounds in the porcupine seabight gives new insights in the sedimentary processes acting around the small mounds and sheds more light on the interaction between hydrodynamics sedimentation and erosion cold water coral mound initiation and mound growth the high resolution bathymetry over the moira mounds reveals the presence of several well delineated zones each characterized by typical sedimentary structures bearing witness of active sediment transport the most important ones are 1 regular e w directed sediment waves 2 irregular overgrown sediment waves and 3 furrows and ridges associated with straight crested sediment waves the moira mounds appear as small mounded features subcircular in shape measuring 30 50 m across and up to 5 m tall the evolution of the moira mounds can be explained by the interaction between cold water coral growth and sediment baffling through a positive feedback mechanism however it is suggested that the small mound build ups represent nowadays rather a way of mound formation under stressed conditions due to high sediment fluxes than an initial phase of extensive mound growth

environmental boundary conditions of cold water coral mound growth over the last 3 million years in the porcupine seabight northeast atlantic iodp expedition 307 made it for the first time possible to investigate the entire body of a cold water coral carbonate mound here we provide new insights into the long term history of challenger mound on the european continental margin off ireland this study is based on age determinations 230th u 87sr 86sr and geochemical signals mg li and ba ca measured in the scleractinian cold water coral lophelia pertusa from iodp site 1317 in the porcupine seabight the paleoceanographic reconstructions reveal that coral growth in the porcupine seabight was restricted to specific oceanographic conditions such as enhanced export of primary production and bottom water temperatures bwt between 8 10 c related to the water mass stratification of the mediterranean outflow water mow and eastern north atlantic water enaw the geochemical signals from the coral skeletons can be explained by the close interaction between cold water coral growth sea surface productivity and the surrounding water masses the boundary layer between mow and enaw enhanced sea surface productivity and the build up of a stable water mass stratification between enaw and mow caused enhanced nutrient supply at intermediate water depths and facilitated a steady mound growth between 3 0 2 1 ma with the decrease in sea surface productivity and related reduced export productivity the food supply was insufficient for rapid coral mound growth between 1 7 1 ma during the late pleistocene over the last 0 5 myr mound growth was restricted to interglacial periods during glacials the water mass boundary between enaw mow probably was below the mound summit and hence food supply was not sufficient for corals to grow

quaternary fluvial systems of tropics major issues and status of research abstract fluvial systems in tropical regions are not only the lifeline for modern civilizations there but also form an important continental archive for reconstructing quaternary palaeoclimates and palaeoenvironments tropical rivers drain through a variety of geological and geomorphological settings across the world and have been studied for their hydrology sediment transport characteristics facies models stratigraphic development and flood hazards this paper presents an overview of the research on tropical rivers globally and identifies major gaps and unanswered research questions as a part of the igcp 582 on tropical rivers the participants of this project are continuing to tackle many of these issues the collection of papers in this special issue is an outcome of this activity and presents new data on processes and alluvial stratigraphy of the tropical rivers from china india south america and northern australia

gas hydrate crystals may help build reefs during a recent cruise in the porcupine basin off southwest ireland we discovered two extensive and hitherto largely unsuspected deep water reef provinces including a giant cluster of hundreds of buried mounds the ring shapes of many reefs suggest that they are caused by an axial fluid expulsion at the sea bed a transient flow well confined in space and time we are exploring various hypotheses but a stimulating avenue for research is opened by a glacially controlled growth pulse and subsequent decay of a shallow layer of gas hydrates as a methane buffer and probably indirectly as a ground for overlying biological communities

late quaternary sedimentary dynamics in western amazonia implications for the origin of open vegetation forest contrasts abstract this work investigated the evolution of sedimentary environments during the latest quaternary and their influence on the paradoxical occurrence of open vegetation patches in sharp contact with the amazonian forest the approach integrated pre existing geological and floristic data from lowlands in the brazilian amazonia with remote sensing imagery including multispectral optical images tm etm and aster phased array l band synthetic aperture radar palsar insar c band srtm dems and high resolution images obtained from google earth the detection of an abundance of paleomorphologies provided evidence of a scenario in which constant environmental shifts were linked to the evolution of fluvial and megafan depositional systems in all studied areas the open vegetation patches are not random but associated with sedimentary deposits representative of environments either deactivated during the holocene or presently in the process of deactivation sedimentary evolution would have determined the distribution of wetlands and terra firme in many areas of the amazonian lowlands and would have a major impact on the development of open vegetated patches within the modern rainforest subsiding areas were filled up with megafan deposits and many fluvial tributaries were rearranged on the landscape the close relationship between vegetation and the physical environment suggests that sedimentary history related to the evolution of depositional settings during the latest quaternary played a major role in the distribution of flooded and non flooded areas of the amazonian lowlands with a direct impact on the distribution of modern floristic patterns as the depositional sites were abandoned and their sedimentary deposits were exposed to the surface they became sites suitable for vegetation growth first of herbaceous species and then of forest although climate fluctuations might have been involved fault reactivation appears to have been the main cause of changes in depositional dynamics through time a process that had an immediate effect on the development of large open vegetation patches intermingled with the amazonian rainforest

the okavango fan and the classification of subaerial fan systems abstract controversy exists over the classification of fluvially formed subaerial fans authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers the okavango fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers the fan is a large 150 km radial axis shallowly sloping 0 00036 highly vegetated subaerial fan which can be subdivided into four subenvironments these are 1 the entry corridor or panhandle characterized by single and anastomosing meander belts 2 the upper fan characterized by meander belts diverging from the fan apex comprising peat confined meandering channels with interchannel swamps forming thick peats 3 the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with however little chance of peat preservation and 4 the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre existing aeolian and lacustrine deposits with the recognition of this new fan type the spectrum of subaerial fan types can be expressed in terms of 1 debris flow dominated fans of which the death valley fans are a member 2 braided river dominated fans of which the kosi fan is a member and 3 low sinuosity meandering losimean river dominated fans of which the okavango fan is a member this spectrum can be expressed in terms of variation in slope maximum size and percentage of surface vegetation but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface comparable ancient examples of the three fan types are recognizable many of which provide intermediates between the ideal end members debris flow dominated and braid dominated fan types are known from throughout earth history however the losimean fan type because of its reliance on confining vegetation may only have developed after the devonian period the spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows processes associated with braided rivers or processes associated with meandering and low sinuosity rivers

avulsion flow path selection on rivers in foreland basins river avulsions help distribute sediment across the floodplain and the frequency and flow path selected by each avulsion determines flooding and sedimentation patterns however rivers avulse infrequently making it difficult to quantify flow path behavior and test hypotheses posed by experimental and numerical studies we used google earth engine to create a novel data set of 55 avulsions that occurred from a d 1984 to 2014 in the andean and himalayan foreland basins on each avulsion we measure hop length the displacement of the avulsion across the floodplain orthogonal to the parent channel and avulsion length the length of the parent channel reach without controlling for external factors such as climate or geology we find that both hop length and avulsion length scale with parent channel belt width avulsion channels tend to hop 2 5 channel belt widths away from their parent channel and avulsion length is 13 4 parent channel belt widths we use these data to test between end member scenarios where flow paths are randomly selected or steered by floodplain topography observed avulsions are inconsistent with flow path predictions derived from a directed random walk model and a scaling analysis of alluvial ridge size shows that hop lengths are set by alluvial ridge widths these results suggest that avulsion flow path selection in the andean and himalayan basins is driven by alluvial ridge topography which promotes evenly spaced or compensational channel sand bodies over decadal time scales these data and results are important for understanding controls on avulsion flow path selection and how avulsion processes are represented in the stratigraphic record of foreland basins

the holocene occurrence of cold water corals in the ne atlantic implications for coral carbonate mound evolution abstract u series dating of constructional cold water corals is a powerful tool to reconstruct the evolution of corals on carbonate mounds here we have investigated the time framework of corals such as lophelia pertusa and madrepora oculata on five different mound settings of the eastern north atlantic on rockall bank and in porcupine seabight sampled at variable depth and location 610 880 m water depth we have found that the past 11 ka reflect a period generally favourable for coral development we further determined local mound growth rates and identified mound surface erosion framework collapse during times of active coral framework construction local vertical mound growth rates vary between less than 5 cm ka 1 and up to 220 cm ka 1 we interpret rates exceeding 15 cm ka 1 as representative of densely populated coral reefs during times of reduced or absent coral development mound evolution rates are by far smaller 0 to 1 the time resolution achieved here furthermore provides first evidence for reduced coral ecosystem activity at 1 8 2 0 ka 4 2 4 8 ka and between 6 and 8 2 ka within the holocene that may be related to climate driven changes of the coral growth environments during glacial periods coral growth in those areas seems apparently extremely reduced or is even absent on mounds

quaternary of the pantanal west central brazil abstract the pantanal is a tectonic depression located at the left margin of the upper paraguay river the paraguay is the trunk river of an alluvial depositional tract composed by several large marginal alluvial fans the taquari fan being the largest one the present landscape is a complex tropical wetland characterized by month long floods every year with geomorphic features derived from the present conditions and others inherited from successive pleistocene and holocene climates some areas containing ponds are landscape relicts generated by eolian deflation during the last glacial maximum many ponds closed depressions isolated from the superficial waters by vegetated crescent ridges of fine sands were interpreted as salt pans bordered by lunette sand dunes initiation of the modern wetland has occurred during the pleistocene holocene transition with the change to a more humid climate and the individualization of lacustrine systems active tectonics has been playing an important role in the development of the pantanal landscape nowadays the paraguay river meanders in a large flood plain with extensive swamp surfaces being structurally constrained by faults in the west border of the basin sedimentation within the pantanal wetland is also affected by tectonic activity especially along faults associated with the transbrasiliano lineament

upstream and downstream controls of recent avulsions on the taquari megafan pantanal south western brazil avulsion the natural relocation of a river is a key process in the evolution of subaerial fans river floodplains and deltas the causes of avulsion are poorly understood which is partly due to the scarcity of field studies of present avulsions at present two avulsions are occurring on the middle and lower taquari megafan pantanal basin south western brazil here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes the middle fan avulsion started in 1997 1998 is a result of upstream control overbank aggradation was caused by the variable input of sandy sediment into the system which caused channel belt superelevation and also created an easily erodible subsurface favouring bank retreat crevassing and scour of deep floodplain channels the sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage the lower fan avulsion started c 1990 results from interplay of upstream and downstream controls the latter being related to the local base level the paraguay river floodplain at the toe of the fan channel and overbank aggradation on the lower fan was influenced by fan sub lobe progradation and channel backfilling fan sub lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel avulsions are commonly supposed to be preferentially triggered by high magnitude floods when there is considerable channel belt superelevation however both avulsions studied by us were triggered by small to average floods with modest channel belt superelevation we conclude that flood magnitude and channel belt superelevation have been overrated as causes of avulsion and demonstrate additional causes that influence the growth of crevasses into avulsions

quantification of a distributive fluvial system the salt wash dfs of the morrison formation sw u s a abstract recent analysis of modern aggradational continental sedimentary basins reveals that sedimentation patterns are dominated by distributive fluvial systems dfss the salt wash member of the late jurassic morrison formation has previously been described as a fan shaped fluvial system this study characterizes facies variations across the salt wash dfs to quantitatively test predicted trends in conceptual dfs models notable proximal to distal trends include a change in total thickness of the fluvial succession from 174 m to 40 m and an average grain size from coarse sand to silt while the percentage of sand decreased from 70 in the proximal region to 8 in the distal region the proportion of amalgamated channel belt deposits decreased from 67 to 0 while floodplain facies and lacustrine deposits increase 38 to 94 and 0 1 to 7 respectively a downstream decrease in average channel belt thickness 15 m to 3 8 m from thickest to thinnest and average story thickness 7 7 m to 2 3 m from thickest to thinnest is also recorded significant downstream changes in deposit architecture were also noted with proximal regions dominated by stacked channel belt deposits with a high degree of amalgamation distal deposits are dominated by floodplain muds and sheet sandstones and sparse ribbon channels with little to no amalgamation of channel deposits this study provides quantified information for an ancient dfss with the aim of providing a dataset that can be used for objective comparison between different dfss as well as providing numerical data to aid resource exploration and modelling efforts

river avulsions on the taquari megafan pantanal wetland brazil abstract the pantanal wetland is located in a tectonically active interior sedimentary basin in west central brazil the south flowing paraguay river is the trunk river of an alluvial constructional landform comprising several large alluvial fans the largest one of which is the taquari megafan the taquari river flows in two distinct geomorphologic zones within the megafan entrenched on sediments of pleistocene fan lobes the taquari river flows in a 3 to 5 km wide meander belt in the upper fan where avulsion is hindered by entrenchment downstream of the intersection point stream discharge progressively decreases and the taquari river becomes narrow and shallow toward the paraguay river plain within the distributary fan lobe the channel levee sandy complex is topographically higher than the adjacent floodplains and avulsion is a natural consequence of crevasses in the natural levees many channel avulsions have occurred during the last decades and documented cases show that significant channel changes may take place in a few years beginning with crevassing in 1988 and ending with the abandonment of the former channel in 1998 the river completely changed course in the lower fan presently a major avulsion is occurring in the upper portion of the growing fan lobe where many crevasses have appeared in the natural levees with associated splays onto the floodbasin new anastomosed channels have formed north of the taquari river but downstream of them the flow is unconfined and the water spreads into natural floodbasins this avulsion is still in process and allows observation of channel evolution the geomorphic features produced the sedimentary processes involved and resulting effects if the new channels do not rejoin the main channel the river mouth may abandon its present master channel and shift to a position a hundred kilometers north from its present position a large volume of sediment has been transferred to the floodbasin with progradation of crevasse splay deposits over fine overbank sediments many geomorphic features recognizable in satellite and radar images clearly show that avulsion has occurred many times before in the taquari river avulsion belt deposits and former diverted channels testify to ancient avulsion events within the fan lobe and show that progradation of splays onto the floodbasin is the most important infilling process within the taquari distributary fan lobe the avulsion process in the lower taquari river has accelerated in the last 30 years along with the magnitude of flooding pasture and intensive agriculture in the catchment area has increased the sediment supply to the wetland but larger floods are also a consequence of higher rainfall since 1973 avulsion and floods have been a cause of great concern among the local population and landowners before human intervention in attempting to control floods however a better understanding of the avulsive river system is needed especially because a major navigation project including the channelization of the paraguay river was recently proposed

spatial and temporal evolution of an avulsion on the taquari river distributive fluvial system from satellite image analysis avulsion processes have been observed and analyzed using field based studies however they have rarely been analyzed through use of satellite imagery even though such an approach allows documentation of spatial and temporal variations of the resulting deposits in order to document changes that are occurring at the caronal avulsion on the taquari river brazil a time series of landsat imagery from 1985 to present 2010 was compiled as of july 2010 the imagery shows that the avulsion is not yet complete with discharge being routed to both the parent channel and the avulsion channel in the floodbasin the avulsion was initiated as flow was diverted from the parent channel to the floodbasin through two small crevasses allowing the development and evolution of splays with a single splay stabilizing only since 1999 the avulsion area is marked by the growth of new splays the formation of an avulsion belt and progradation of avulsion deposits into the floodbasin the parent channel downstream of the avulsion site has experienced decreasing width through time associated with the higher volumes of water and sediment being captured by the avulsion channel because this avulsion is not yet complete we expect more morphological changes to occur as the avulsion belt evolves into the primary channel rapid sedimentation caused by this avulsion and the 24 year time series of imagery that captured this change allowed us to construct a 3d block representing the evolution of depositional environments associated with avulsion using time in the vertical dimension thus we could represent the evolution of geomorphological patterns including floodbasin proximal levee distal levee and channel deposits and project their distributions through time this block of evolving sedimentary settings can be used as a guide for future sedimentologic studies by offering visual clues regarding the way which depositional systems track avulsion initiated changes

carbonate budget of a cold water coral mound challenger mound iodp exp 307 abstract cold water coral ecosystems represent a worldwide distributed carbonate factory which is so far not considered in global carbonate budget estimations the herein presented study evaluates the carbonate budget of a complete cold water coral mound sequence from challenger mound belgica mound province porcupine seabight sw offshore ireland drilled during iodp expedition 307 reaching back to the late pliocene versus background sediment derived calcite dominated carbonate cores from adjacent drift deposits were examined for comparison studies challenger mound which developed in a fast growth phase unit m1 2 7 to 1 6 ma and a slower growth phase or mound decline unit m2 0 8 ma until today separated by a so called mound crisis displays increased carbonate accumulation rates for both phases 17 3 g cm 2 ka for unit m1 and 5 7 g cm 2 ka for unit m2 compared to adjacent drift deposits but only about 33 to 40 wt of the carbonate is derived from corals bulk sedimentation rates of on and off mound deposits suggest a decline of challenger mound since the onset of drift deposition in the area about 1 2 ma ago yet total carbonate accumulation rates as well as hemipelagic background sediment derived carbonate accumulation rates from challenger mound unit m2 still exceed the carbonate accumulation rates of the adjacent drift deposits the selective enrichment of background sediment derived carbonate by a factor of 2 0 in a cwc mound is herein observed for the first time this might be caused by the different hydrodynamic behaviour and slower settlement of marine fluff rich in calcareous detritus compared to siliciclastic sediments and its effective baffling by the coral framework and or the active catch of the calcareous plankton by the corals the carbonate accumulation rates of challenger mound are about 4 to 12 of the carbonate accumulation rates of tropical shallow water reefs but exceeds the carbonate accumulation rates of continental slopes by a factor of 3 9 to 11 8 the carbonate production for the entire belgica mound province is estimated with 3 2 10 3 t a for unit m1 and 1 0 10 3 t a for unit m2

genesis and morphology of cold water coral ridges in a unidirectional current regime abstract cold water coral ridges with waveform morphology are commonly observed in mound surfaces in the northeast atlantic ocean and interpreted as sediment waves overgrown by corals this work documents the first cold water coral ridges that are waveform but lack sand dune cores these coral ridges are situated at the base of the miami terrace in the straits of florida depths of 630 to 870 m they are entirely biogenic in origin and are unrelated to antecedent topography five lines of evidence based on 27 km2 of high resolution geophysical oceanographic and ground truthing data support this interpretation first the waveform coral ridges are aligned perpendicular to a southward flowing bottom current and juxtaposed to an active sand dune field devoid of corals both the coral ridges and sand dunes are asymmetric in profile with respect to the current however the ridges have their steep sides facing the current whereas the dunes exhibit a steep leeside second the coral ridge matrix consists of very fine sand to mud particles with no bedload sand transport on the ridge flanks or troughs in contrast active sand ripples superimpose the juxtaposed sand dunes indicating that coarse sand is transported via traction in this domain third bedload sand transport occurs in linear streaks at the shallowest part of the surveyed area these streaks orthogonally crosscut some coral ridges but coral colonies are not aligned along these streaks instead the bedload sand smothers the coral colonies and thereby segments the ridges fourth the sand dune and coral ridge acoustic responses are different below the dunes there is no sub bottom reflection due to energy attenuation in contrast a continuous reflection below the coral ridges proves the absence of attenuating sand cores fifth this continuous sub bottom reflection is not correlated with the coral ridge topography indicating that antecedent topography does not control the waveform morphology and spatial distribution of the ridges the differences in depositional profiles sediment dynamics and features as well as acoustic facies between the coral ridges and the juxtaposed dunes show that the coral ridges are entirely bioconstructional and not a veneer of corals covering paleo sand dunes this field of biogenic ridges at the miami terrace and the distribution of sand streaks as well as active sand dunes provide new insights how the lateral variability of current velocities and sediment transport conditions control the morphology distribution and genesis of cold water coral features

kosi megafan historical records geomorphology and the recent avulsion of the kosi river abstract it has been proposed that the kosi river continuously migrated 113 km westward across the surface of the megafan over the last two centuries examination of a number of old maps published between 1760 and 1960 shows that during most of this period the kosi river occupied a position slightly east of the megafan axis the apparent channel movement shown in these maps is oscillating in nature and not unidirectional instead of encountering deposits left behind by a sweeping braided kosi like stream a preliminary study of the uppermost 2 5 m succession in the north central part of the megafan reveals overwhelming dominance of meandering stream deposits assuming the existing notion of kosi river migration the rate of deposition averaged over 100 200 years for the uppermost 5 10 m of megafan deposits works out to be unusually high 50 mm y all these observations question the soundness of the hypothesis of rapid westward migration of the kosi river over the last two centuries the existing facies model for the uppermost 8 10 m of the megafan deposits also appears untenable the three dimensional geometry of the kosi megafan is similar to those of typical alluvial fans but with much gentler gradient 0 05 0 01 and with larger area 10 000 km 2 based mainly on the patterns of paleo and modern channels recognised in the satellite images three major accretionary lobes can be identified on the kosi megafan relative age of the lobes determined from the truncating relationship of the paleochannels indicates a random shift of the trunk channel forming these lobes similar multilobate form and evidences of random switching of the loci of lobe aggradation are also found to be common in the tista and taquari megafans the factors known to favour avulsion and the results of the recent simulation studies of alluvial deposits are inconsistent with the notion of unidirectional shift of the channels for more than 100 km across the entire megafan surface this study suggests that the relocation of the kosi river in the past was through random nodal avulsion rather than systematic unidirectional shift the recent avulsion of the kosi channel by a large distance to the east follows this expected pattern further study and age dating is required for a comprehensive understanding of the depositional dynamics of the megafan and the pattern of channel movement on it future flood predictions and disaster management plans should be based on such comprehensive understanding

the west melilla cold water coral mounds eastern alboran sea morphological characterization and environmental context a new mound field the west melilla mounds interpreted as being cold water coral mounds has been recently unveiled along the upper slope of the mediterranean moroccan continental margin a few kilometers west of the cape tres forcas this study is based on the integration of high resolution geophysical data swath bathymetry parametric sub bottom profiler ctd casts acoustic doppler current profiler adcp rov video and seafloor sampling acquired during the topomed gassis 2011 and melcor 2012 cruises up to 103 mounds organized in two main clusters have been recognized in a depth range of 299 590 m displaying a high density of 5 mounds km2 mounds 1 48 m high above the surrounding seafloor and on average 260 m wide are actually buried by a 1 12 m thick fine grained sediment blanket seismic data suggest that the west melilla mounds grew throughout the early pleistocene holocene settling on erosive unconformities and mass movement deposits during the last glacial interglacial transition the west melilla mounds may have suffered a drastic change of the local sedimentary regime during the late holocene and unable to stand increasing depositional rates were progressively buried at the present day temperature and salinity values on the west melilla mounds suggest a plausible oceanographic setting suitable for live cwcs nonetheless more data is required to groundtruth the west melilla mounds and better constrain the interplay of sedimentary and oceanographic factors during the evolution of the west melilla mounds

cold water coral banks and submarine landslides a review this paper aims to review the relation between cold water coral bank development and submarine landslides both are common features on continental margins but so far it has not been reviewed which effect if at all they may have upon each other indirect and direct relations between coral banks and landslides are evaluated here based on four case studies the magellan mound province in the porcupine seabight where fossil coral banks appear partly on top of a buried slide deposit the sula ridge reef complex and the storegga landslide both off mid norway and the mauritania coral bank province associated with the mauritanian slide complex for each of these locations positive and negative relationships between both features are discussed based on available datasets locally submarine landslides might directly favour coral bank development by creating substratum where corals can settle on enhancing turbulence due to abrupt seabed morphological variations and in some cases causing fluid seepage in turn some of these processes may contribute to increased food availability and lower sedimentation rates landslides can also affect coral bank development by direct erosion of the coral banks and by the instantaneous increase of turbidity which may smother the corals on the other hand coral banks might have a stabilising function and delay or stop the headwall retrogradation of submarine landslides although local relationships can be deduced from these case studies no general and direct relationship exists between submarine landslides and cold water coral banks

river systems and their sediment flux indo gangetic plains northern bihar india river systems of part of the himalayan foreland northern bihar plains india are described in terms of their channel morphology hydrology and suspended sediment characteristics a simple classification of the river systems based mainly on the source area characteristics is proposed i mountain fed ii foothills fed iii plains fed and iv mixed fed rivers distinct differences are noted between these classes of river systems most rivers show evidence of channel movement mainly by avulsion but cut offs also occur locally the mountain fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains fed rivers have relatively low discharge and high suspended sediment concentration the foothill fed rivers have moderate values of discharge and suspended sediment concentration the mountain fed rivers have built megafans of large extent whereas the foothills fed and plains fed rivers have formed muddy interfan areas semi quantitative estimates of water and sediment flux suggest that about 99 9 of the mass transfer into the plains is water with the remaining 0 1 being sediment and that 10 s of the latter 0 01 of the total is retained in the basin the remainder being transferred to the bengal fan

deep sea survey for the detection of methane at the santa maria di leuca cold water coral mounds ionian sea south italy abstract the santa maria di leuca cold water coral cwc province northern ionian sea was investigated for the first time to detect eventual occurrence of methane anomalies as a possible indication of hydrocarbon seepage stimulating the coral growth most coral mounds have developed in correspondence with tectonic scarps and faults orthogonal to the southern margin and trending nw se which could be potential sites of gas escape a visual and instrumental inspection was performed by using a new deep sea probe equipped with video cameras sonar ctd methane sensors and a water sampler eight areas were explored by 10 surveys depths ranging from 380 to 1100 m for a total of more than 26 h of continuous video and instrumental recording sediments were also sampled by gravity corers and analysed in laboratory the images allowed to assess distribution abundance and geometry of the colonies most of which are developed on morphological highs often characterised by tectonic scarps all data indicate however the lack of a significant occurrence of methane both in seawater and sediments no direct or indirect expressions of gas seepage were recognised on the seabed weak methane anomalies were detected only in seawater at the base of some fault linked scarps where more reducing conditions and bacterial methanogenesis are possibly enhanced by less water circulation the faults are not fluid bearing as previously suggested by high resolution geophysical signatures the development of the coral colonies thus cannot be attributed to seeping fluids but to a favourable physiographic position with exposure to nutrient rich currents

pleistocene geochemical stratigraphy of the borehole 1317e iodp expedition 307 in porcupine seabight sw of ireland applications to palaeoceanography and palaeoclimate of the coral mound development stable isotopes and element compositions of the fine grained matrix were measured for iodp expedition 307 hole u1317e drilled from the summit of challenger mound in porcupine seabight northeast atlantic to explore the palaeoceanographic and palaeoclimatic background to development of the deep water coral mound the 155 m long mound section was divided into two units by an unconformity at 23 6 mbsf unit m1 2 6 1 7 ma and unit m2 1 0 0 5 ma results from 519 specimens show a difference in 13c value between unit m1 0 6 to 5 0 and unit m2 1 0 to 1 0 but such a distinct difference was not seen in 18o values 1 0 2 5 caco3 content 40 60 wt sr ca ratio 2 0 8 0 mmol mol 1 and mg ca ratio 10 0 20 0 mmol mol 1 through the mound positive 18o and negative 13c shifts at the mound base are consistent with the oceanographic changes in the northeast atlantic at the beginning of the quaternary the positive 13c regression in unit m2 suggests a linkage to the mid pleistocene intensified glaciation in the northern hemisphere warm mediterranean upper core water of mediterranean outflow water eastern north atlantic water and cold labrador sea water of north atlantic deep water are key oceanographic features that cause spikes and shifts in stable isotope and element composition however the stable isotope values of the sediment matrix could not primarily record the glacial interglacial eustatic temperature change but indirectly indicate current regimes of the intermediate oceanic layer where the coral mound grew similarly elemental ratios and caco3 content may not represent the productivity and temperature of surface sea water respectively but superpose the fractions from both surface and bottom water it is concluded that palaeoceanographic change coupled to the pleistocene glacial interglacial cycles is a key control on the geochemical stratigraphy of the matrix sediments of the carbonate mound developed in porcupine seabight copyright 2011 john wiley sons ltd

high resolution bathymetry of the eastern slope of the porcupine seabight the topography of the eastern margin of the porcupine seabight was surveyed in june 2000 utilizing swath bathymetry the survey was carried out during rv polarstern cruise ant xvii 4 as part of the geomound project the main objective was to map and investigate the seafloor topography of this region the investigated area contains a variability of morphological features such as deep sea channels and giant mounds the survey was planned and realized on the basis of existing data so as to guarantee the complete coverage of the margin in order to achieve a resolution of the final digital terrain model dtm that meets the project demands data processing was adjusted accordingly the grid spacing of the dtm was set to 50 m and an accuracy better than 1 of the water depth was achieved for 96 of the soundings

fault associated seabed mounds carbonate knolls off western ireland and north west australia abstract groups of seabed mounds suspected to be modern carbonate knolls or bioherms have been located on reflection seismic data in the porcupine basin off western ireland and in the vulcan sub basin off north west australia the size of these mounds is impressive often being over 1 km across and over 100 m high in the porcupine basin they occur in water depths of 650 1000 m whereas in the vulcan sub basin they occur in water depths of 200 350 m shallow seabed coring in the porcupine basin has provided data on the age lithological composition and hydrocarbon concentrations in the upper 3 m layer of sediment both on and off the mounds in both basins the mounds occur close to faults which may provide conduits for upward migrating hydrocarbons the seepage of hydrocarbons is suspected to have caused local eutrophication or fertilization by providing nutrients to bacteria which in turn are part of the food chain for higher organisms the dominant organism in the porcupine basin examples appears to be the deep water coral lophelia sp whereas in the vulcan sub basin the mounds appear to be halimeda dominated

therese mound a case study of coral bank development in the belgica mound province porcupine seabight high resolution seismic profiles swath bathymetry side scan sonar data and video imageries are analysed in this detailed study of five carbonate mounds from the belgica mound province with special emphasis on the well surveyed therese mound the selected mounds are located in the deepest part of the belgica mound province at water depths of 950 m seismic data illustrate that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime sigmoidal sediment bodies create local slope breaks on the most recent local erosional surface which act as the mound base no preferential mound substratum is observed neither is there any indication for deep geological controls on coral bank development seismic evidence suggests that the start up of the coral bank development was shortly after a major erosional event of late pliocene quaternary age the coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current regime the summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes deposition of the encased drift sequence has been influenced by the coral bank topography sediment waves are formed besides the coral banks and are the most pronounced bedforms these seabed structures are probably induced by bottom current up to 1 m s large sediment waves are colonised by living corals and might represent the initial phase of coral bank development the biological facies distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral populations toward the lower flanks the data suggest that the development of the coral banks in this area is clearly an interaction between biological growth processes and drift deposition both influenced by the local topography and current regime

the 2 6 ma depositional sequence from the challenger cold water coral carbonate mound iodp exp 307 sediment contributors and hydrodynamic palaeo environments during iodp expedition 307 the first complete sequence through a cold water coral carbonate mound a bio geological seafloor feature created through successive stages of cold water coral mediated sediment accumulation was successfully acquired the full recovery of the challenger mound one of the large ca 155 m high coral carbonate mounds along the ne atlantic continental margin belgica mound province eastern porcupine seabight facilitates for the first time the study of the entire development of a coral carbonate mound and hence allows the identification of the environmental conditions driving and maintaining the entire build up of these remarkable seafloor habitats in this study the different sediment contributors to the challenger mound are identified and assessed throughout its entire 2 6 ma long development high resolution siliciclastic particle size end member modelling and its ground truthing xrd quartz sand surface microtextures indicate the influence of an all dominant contour current system operating in variable energetic modes for most of the sediment accumulation history of the challenger mound only local short distance current controlled sediment re dispersal is evidenced while iceberg rafting is identified as an important depositional mechanism throughout the whole mound development period furthermore evidence for icebergs repeatedly reaching the eastern porcupine seabight continental margin even in the early stages of northern hemisphere glacial expansion is preserved in the mound sequence supporting the existing coral stratigraphy the challenger mound depositional sequence reveals a two phase development separated by a significant hiatus the lower mound phase m1 2 6 1 7 ma indicates a semi continuous steadily changing fast accumulating current controlled depositional environment the condensed upper mound phase m2 998 1 5 ka bears witness of a distinct shift to a more glacially influenced low accumulation environment most likely resulting from a reduced capacity to deposit and or preserve sediments cold water coral density at the site of deposition is assumed to play an essential role in sediment deposition and preservation on challenger mound it enabled the preservation of a unique higher resolution record in the lower m1 sequence in the otherwise erosive non depositional early pleistocene environment along the nw european continental margin the potential of coral carbonate mounds as intermediate water depth continental margin plio pleistocene palaeo archives is thereby showcased

impact of bottom water currents on benthic foraminiferal assemblages in a cold water coral environment the moira mounds ne atlantic abstract strong bottom currents play a key role in cold water coral environments by shaping their morphology and providing the necessary food for the corals to thrive this study investigates the differences between living and dead benthic foraminiferal assemblages in such environments more precisely on the moira mounds ne atlantic a specific focus is to understand the role of currents and their influence on the taphonomy of benthic foraminiferal assemblages here we analyze high resolution sediment grain size distributions coupled with benthic foraminiferal assemblage composition to assess how much deep sea bottom currents affect benthic foraminiferal assemblages we suggest that the dead benthic foraminiferal assemblage consists of a reworked glacial fauna associated with contemporary species reworked glacial species elphidium excavatum sigmoilopsis schlumbergeri are the most abundant dominant species that are present almost exclusively in the living assemblage alabaminella weddellensis nonionella iridea trifarina spp are associated with high phytodetritus input possibly as a response to the later phase of the north east atlantic spring bloom dead assemblages are further characterized by the scarcity of organic walled agglutinated foraminifera in comparison to living assemblages sediment grain size distributions show that the downslope moira mounds consist of well sorted fine sand typical of contourite deposits in the area grain size distributions and the average shannon diversity of living and dead foraminiferal assemblages indicate that the coral cover offers a sheltered environment baffling eroded sediment and preventing post mortem transport of dead foraminifera we conclude that cold water coral environments provide a valuable paleoenvironmental archive by trapping sediment in an otherwise non depositional system

basement reactivation in a sub andean foreland flexural bulge the pantanal wetland sw brazil the role of sub andean foreland peripheral bulges in controlling sedimentary sequence deposition and quaternary geomorphology is discussed in the case of the pantanal wetland sw brazil this shallow 0 5 km and wide 200 km depression was formed because of uplift and flexural extension in the brittle upper crust which mechanically reactivated the neoproterozoic paraguai fold thrust belt depth to the basement and structural information within the pantanal wetland were obtained from gravity reflection seismics drill hole and digital topography data the upper part of the basin is filled with pliocene quaternary unlithified sands the age of the oldest sediments is unknown and normal faults are mostly observed on the western border of the basin a two dimensional flexural model composed of a semi infinite thin elastic plate for the brazilian shield lithosphere with an effective elastic thickness of 125 150 km its western edge at 67 5 w under the altiplano and loaded on a free end by the andes topography predicts the forebulge to be presently located over the pantanal wetland flexural modeling was constrained using gravity data extending from the pacific ocean to the east of the pantanal wetland the width of the bulge is 700 km and its amplitude is 310 m the total amount of extension and subsidence observed in the pantanal basin is interpreted as due to a cumulative strain since late oligocene when the brazilian shield started its westward migration together with compression and uplift of the central andes the main phase of the wetland subsidence is very likely related to the last compressional pulse in the andes during the upper pliocene lower pleistocene 2 5 ma as inferred from field study of fault kinematics of the central andes

large deep water coral banks in the porcupine basin southwest of ireland the porcupine basin southwest of ireland was one of the earliest sites from where the deep water corals lophelia sp and madrepora sp were recovered these deep water corals have since been found all along the atlantic margins of europe in water depths ranging from 50 to more than 2000 m recent geophysical studies have demonstrated the mound building potential of deep water corals available data indicate that three major provinces of coral bank occurrences can be identified in the porcupine basin 1 high relief surface mounds which have a dimension of 1 by 5 km and a height up to 200 m hovland mounds flanked to the north by 2 a swarm of buried mounds somewhat smaller up to 90 m and with more irregular shapes than those recognised in area 1 magellan mounds and 3 outcropping or buried conical mounds single or in elongated clusters up to 150 m high occurring on the southeastern slope of the basin belgica mounds as far as can be inferred from shallow cores the surface lithology predominantly consists of an upper layer rich in foraminiferal sand and terrigenous silty clay with intercalations of biogenic rubble the banks host a remarkable number of colonies of living and dead lophelia pertusa and madrepora oculata the living and dead assemblages are underlain by a significant layer of coral debris in a muddy matrix deep water coral debris together with a living association of the same species covers the surface of the belgica and hovland mounds which may suggest that these corals have played a significant role in the development of the mound structures the capacity for mound formation by scleractinian corals in the aphotic zone has been known for some time examples are found at different locations along the shelves and the continental margins of the north atlantic the role of the corals in these deep water build ups is still a point of debate though the genesis and initial control of mound settings in this basin might be related to hydrocarbon seeps it appears that the major development of the porcupine coral banks in recent geological times has most likely been controlled by oceanic circulation and dynamics in water masses and nutrient supply

deglacial upslope shift of ne atlantic intermediate waters controlled slope erosion and cold water coral mound formation porcupine seabight irish margin abstract turbulent bottom currents significantly influence the formation of cold water coral mounds and sedimentation processes on continental slopes combining records from coral mounds and adjacent slope sediments therefore provide an unprecedented palaeo archive to understand past variations of intermediate water mass dynamics here we present coral ages from coral mounds of the belgica province porcupine seabight ne atlantic which indicate a non synchronous holocene re activation in mound formation suggested by a temporal offset of 2 7 kyr between the deep start 11 3 ka bp at 950 m depth and shallow start 8 6 ka bp at 700 m depth mounds a similar depth dependent pattern is revealed in the slope sediments close to these mounds that become progressively younger from 22 1 ka bp at 990 m to 12 2 ka bp at 740 m depth based on core top ages we suggest that the observed changes are the consequence of enhanced bottom water hydrodynamics caused by internal waves associated to the re invigoration of the mediterranean outflow water mow and the development of a transition zone tz between the mow and the overlying eastern north atlantic water enaw which established during the last deglacial these highly energetic conditions induced erosion adjacent to the belgica mounds and supported the re initiation of mound formation by increasing food and sediment fluxes the striking depth dependent patterns are likely linked to a shift of the enaw mow tz moving the level of maximum energy 250 m upslope since the onset of the last deglaciation

the enya mounds a lost mound drift competition the genesis and evolution of cold water coral banks along the northeastern atlantic margin is known to be influenced by several factors among which the palaeotopography and nature of the coral settling surface the presence of bottom currents and sediment supply in this paper a case study is presented of the enya mound cluster located in the southernmost tip of the belgica mound province west of ireland below this mound cluster seismic stratigraphy revealed a yet unmapped local unconformity rd1b being part of a composite erosion event rd1 as such from the late miocene to late pliocene at least two erosional events have incised the margin ending with the final rd1a moundbase unconformity acting as a base for the enya mounds during the quaternary the mounds became outgrown and were covered by a mounded contourite drift in addition they are closely associated with a cluster of seabed pockmarks the bottom current regime which became active since the middle pleistocene has certainly influenced the fate of this mound cluster the occurrence of the pockmarks seems to be related to relatively recent fluid migration processes however leaving an open question if any previous seepage phases were involved in the growth or initiation of the coral banks

shifting of the kosi river northern india the kosi river shifts laterally over the himalaya foreland plain by continual minor cutoffs and bank cutting and by episodic major shifts across watersheds by moving into and then out of preexisting adjacent less actively aggrading streams migration is unidirectional because after a channel is filled to instability floodwater will drain preferentially into a new adjacent low rather than across it to the next watershed or back to the last abandoned channel major shifts seem stochastic and autocyclic they do not correlate with the many severe quakes and floods that undoubtedly helped prime the system for shifts

morphological adjustment of the qingshuigou channel on the yellow river delta and factors controlling its avulsion abstract the avulsion time scale of channels on the yellow river delta yrd is about a decade due to the large sediment load and rapid channel aggradation and progradation nevertheless the qingshuigou channel has been maintained for about four decades since 1976 this channel provides an ideal opportunity to study channel evolution following avulsion and to examine different avulsion criteria in this study we analyzed the geomorphic adjustment of the lower qingshuigou channel during 1976 2015 and calculated normalized gradient advantage and superelevation at the channel to estimate how close the channel was to avulsion results showed that channel evolution processes may be divided into four phases i 1976 1980 rapid aggradation ii 1980 1985 channel widening and enlargement iii 1985 1996 main channel aggradation and shrinkage and iv 1996 2015 main channel incision and deepening evolution phases i ii and iii are similar to the avulsion cycle observed in natural and experimental fluvial systems the calculated values of normalized gradient advantage and superelevation in early 1990s exceeded the critical values suggested by previous studies implying that the channel was prone to avulsion nevertheless avulsion was prevented mainly due to limited overbank flows constriction from artificial dikes and slowed channel extension as a result of reduced sediment load the evolution of the qingshuigou channel confirms previous arguments that superelevation and gradient advantage are not sufficient for avulsion and multiple factors should be considered including flood frequency lateral mobility sediment diameter and human interruptions

statistical estimation of the position of an apex application to the geological record abstract knowing the position of an apex of a distributive depositional system can provide important spatial constraints on paleogeographic reconstructions and thus can greatly help facies predictions at both a system and a basin scale to date predicting the position of an apex of a sedimentary system is often limited to generalized statements based on facies mapping and qualitative analyses of paleocurrent readings this paper presents a user friendly quantitative methodology based on the von mises distribution and uses the method of maximum likelihood to obtain an estimated apex and associated confidence regions for a dataset the methodology presented has been applied to two modern distributive fluvial systems dfss the taquari dfs situated in southwestern brazil and the gilbert dfs situated in northwestern queensland australia the position of each apex is known for the two systems thus allowing the accuracy of the methodology to be tested a range of datasets within which the amount and spatial distribution of localities were selected independently was analyzed the predicted apices came within encouraging proximity of the true apices ranging in distance from 2 7 km to 40 3 km 1 6 to 23 4 of the total dfs length away with accuracy generally increasing with increasing dataset size and proximity to the apex data collected from the late jurassic salt wash dfs were also analyzed using the code results have helped to give better geographical constraints on the system and apex location as well as on the southern margin of the morrison depositional basin although tested on modern and outcrop based datasets from dfs the methodology can be applied to any dataset subsurface or surface in which dispersion occurs from a point source thus unlocking the potential for better paleogeographic constraint on a broad range of sedimentary environments such as deltas and submarine fans

high resolution facies zonation within a cold water coral mound the case of the piddington mound porcupine seabight ne atlantic abstract framework forming cold water corals cwc s such as lophelia pertusa and madrepora oculata generate positive topographic features on the seabed called cwc mounds in the north east atlantic cwc mounds have been studied in detail and reveal heterogeneous spatial on mound organisation of coral patches many of these studies are limited by a paucity of remotely sensed and video imagery at an appropriate resolution and coverage this study is the first attempt to video mosaic an entire cwc mound the piddington mound of the moira mounds porcupine seabight irish margin the mosaic is divided into 18 980 0 25 m 2 cells with a manual classification applied to each within a geographic information system gis geospatial analysis shows that cell distribution is not random but clustered significantly across the mound surface these clusters of cells make up a ring like facies pattern a model for the processes that lead to this facies pattern is suggested based on contemporary environmental controls parallels to shallow water reef atolls are also drawn which subsequently has implications for interpreting fossil coral outcrops

influence of landscape evolution on the distribution of floristic patterns in northern amazonia revealed by δ13c data the amazonian lowlands include large patches of open vegetation which contrast sharply with the rainforest and the origin of these patches has been debated this study focuses on a large area of open vegetation in northern brazil where d 13 c and in some instances c n analyses of the organic matter preserved in late quaternary sediments were used to achieve floristic reconstructions over time the main goal was to determine when the modern open vegetation started to develop in this area the variability in d 13 c data derived from nine cores ranges from 32 2 to 19 6 but with nearly 60 of data above 26 5 the most enriched values were detected only in ecotone and open vegetated areas the development of open vegetation communities was asynchronous varying between estimated ages of 6400 and 3000 cal a bp this suggests that the origin of the studied patches of open vegetation might be linked to sedimentary dynamics of a late quaternary megafan system as sedimentation ended this vegetation type became established over the megafan surface in addition the data presented here show that the presence of c4 plants must be used carefully as a proxy to interpret dry paleoclimatic episodes in amazonian areas copyright 2012 john wiley sons ltd

the moira mounds small cold water coral banks in the porcupine seabight ne atlantic part a an early stage growth phase for future coral carbonate mounds this paper presents a comprehensive overview of the moira mounds in the porcupine seabight combining a review of currently published material with new data and interpretations the moira mounds are circular to ovoid shaped individual or clustered coral banks referred to as scleractinian spaced cluster macroreefs located in the belgica carbonate mound province porcupine seabight west of ireland they are up to 10 m high and 20 to 35 m in diameter for the first time a map showing the complete extent and location of the moira mounds is published revealing 256 examples grouped into four areas mainly between 800 and 1100 m water depth rov groundtruthing revealed the importance of bedload sand transport in moira mound formation and development processes through sediment entrapment by coral frameworks lophelia pertusa and madrepora oculata new estimated growth rates for the moira mounds are comparable to those measured for much larger irish coral carbonate mounds but an order of magnitude lower than rates from comparably sized reefs offshore norway as well as the framework corals 26 macrobenthic invertebrate species were identified from a single box core that were similar to those communities found in adjacent off mound habitats it is proposed that the moira mounds are an example of the early stage growth phase of nearby giant coral carbonate mounds and represent a westward extension of the zone of active cold water coral mound growth and therefore a deepening of the zone of cold water coral growth over recent climate cycles

controls on synorogenic alluvial fan architecture beartooth conglomerate palaeocene wyoming and montana late palaeocene uplift of the beartooth range in northwestern wyoming and southwestern montana generated the beartooth conglomerate along the eastern and northeastern flanks of the range systematic unroofing sequences and intraformational unconformities folds and faults in the conglomerate attest to deposition during uplift along the eastern flank at least three ancient alluvial fan systems and a braidplain system can be distinguished on the bases of petrofacies and lithofacies the two southern fans consist of 700 m of sedimentary clast conglomerate and subordinate sandstone dominated by hyperconcentratedflow and stream flow facies the next fan to the north is dominated by plutonic and metamorphic clasts and contains abundant mud matrix supported debris flow facies as well as stream flow facies the northernmost depositional system consists of arkosic channellized fluvial conglomerate and sandstone overbank mudstone and crevasse splay sandstone units palaeocurrent data indicate eastward dispersal away from the beartooth range outstanding exposure of the beartooth conglomerate allows facies to be mapped on lateral photographic mosaics a seven fold hierarchy of bounding surfaces and enclosed lithosomes exists in the beartooth conglomerate first through fourth order surfaces are analogous to first through fourth order surfaces that recently have been documented in sandy fluvial facies with one exception sediment gravity flows are bounded by first order surfaces fifth order surfaces are either erosional e g lateral migration of fanhead trench or accretionary e g aggradation of fan surface during backfilling of trench and construction of lobes on lower fan during entrenchment on upper fan some fifth order surfaces coincide with intraformational angular unconformities and are thus the result of long term fanhead entrenchment following uplift of the upper part of the fan sixth order surfaces bound individual fan packages that are several hundred metres thick and 10 km2 in area the enclosed sixth order lithosomes are distinguishable in terms of petrofacies and lithofacies a single seventh order surface bounds the entire beartooth conglomerate lower order lithosomes are produced by intrinsic processes of fan construction fifth order lithosomes can be attributed to both extrinsic and intrinsic controls sixth and seventh order lithosomes are generated by extrinsic controls

chronology and controls of avulsion along a mixed bedrock alluvial river tooth stephen rodnight h duller g a t mccarthy t s 2006 chronology and controls of avulsion along a mixed bedrock alluvial river geological society of america bulletin 119 3 pp 452 461 rae2008

growth history of a cold water coral covered carbonate mound galway mound porcupine seabight ne atlantic abstract during the past decade knowledge about the ecology and the environment of giant carbonate mounds has been growing continuously however still little is known about their growth dynamics three gravity cores from galway mound belgica mound province in the porcupine seabight off ireland were investigated for their sedimentological geophysical and geochemical properties to get insight into the long term development of this cold water coral covered carbonate mound these data were supplemented by radiometric age determinations on planktonic foraminifera and coral skeletons the records from three different settings on galway mound reveal a coherent growth history that in general is similar to what is known from other carbonate mounds at the irish margin however whereas other cores are often disturbed by numerous and not correlateable hiatuses galway mound in contrast appears to be characterised by only one major hiatus representing a time gap of 250 kyr several mechanisms are discussed in this study as possible causes for the observed stratigraphic record at galway mound the most likely explanation is that the hiatus has its origin in a major mass wasting event on an instable possibly glacial unit that could have acted as a slip plane the overall late quaternary growth history of galway mound fits well into existing cyclical mound development models pointing to galway mound being an actively growing mound coral bank stage at present

holocene stratigraphic evolution of saline lakes in nhecolandia southern pantanal wetlands brazil nhecol ndia is a fossil lobe of the taquari river megafan and a prominent geomorphic subunit of the pantanal wetlands because of the presence of 10 000 small lakes we investigated the stratigraphic records of three saline lakes from nhecol ndia to explore their potential as quaternary hydroclimate archives radiocarbon data indicate that accumulation at two lakes was approximately continuous in the late holocene and chemostratigraphic variability suggests sensitivity to environmental change with multicentennial resolution a basal sandy unit and an upper muddy unit comprise the shallow stratigraphy of each lake a pronounced change in depositional environment from freshwater wetlands to saline lakes at 3300 3200 cal yr bp best explains the lithofacies transition ephemeral freshwater wetlands formed on the abandoned megafan lobe which was molded by deflation in the arid early holocene wind scouring of the megafan lobe generated topographically closed depressions with complex marginal sand ridges which allowed permanent lakes to evolve when rainfall increased in the late holocene the lakes became highly saline and alkaline after 910 cal yr bp which influences biogeochemistry and aquatic ecology the results hold implications for understanding the response of the southern pantanal to climate change as well as the development of pans in tropical megafan settings

seismic evidence of current controlled sedimentation in the belgica mound province upper porcupine slope southwest of ireland the porcupine seabight is an embayment that takes a particular position in the ne atlantic slope sonographs a few current measurements and hydrodynamic modelling suggest the presence of a strong northward flowing bottom current locally enhanced by internal tides affecting the eastern slope of the seabight at this location a province of coral banks is described expressed as mounds lined up in along slope trending ridges in this paper very high resolution single channel seismic profiles are used to evaluate to what extent the bottom currents influenced the deposition of the sediments surrounding the mounds throughout the late cenozoic three seismostratigraphic units p1 p2 and p3 can be identified in the belgica mound area separated by two margin wide discontinuities rd2 and rd1 within unit p1 probably early to middle miocene upslope migrating sediment waves are observed suggesting strong bottom currents were already active in the miocene after an early middle miocene erosion event represented by reflector rd2 an acoustically transparent layer unit p2 of as yet unknown lithology was deposited in the studied area a second margin wide erosional event marked by the late pliocene rd1 reflector removed a large part of unit p2 and has cut deeply into unit p1 subsequently the belgica mounds were constructed spectacularly fast on topographic irregularities on the rd1 paleobathymetry the onlap within the quaternary unit p3 which surrounds these mounds suggests that the mounds were already present before the deposition of p3 and were big enough to affect the intensity of the currents around them furthermore the channels and the mounds are together with the complex oceanographic regime the key morphological elements responsible for the shaping of a contourite system in the belgica mound area during the quaternary one drift body is formed by an inferred south north directed current with a drift levee and associated channel located on its western side between this channel and the mounds large scale sediment waves suggest an intensified bottom current running along the foot of the steep flanks of the mounds the belgica mounds are embedded in another drift body here an interaction of bottom and turbidity currents is suggested creating short turbidite channels at the southern and northern flanks of the mounds locally small confined drifts can be observed where unit p3 is deposited in a narrow passage made by the paleobathymetry of rd1 and the mounds

holocene avulsion styles and sedimentation patterns of the saskatchewan river cumberland marshes canada abstract this paper describes the styles and sedimentation patterns of holocene avulsions of the saskatchewan river at the cumberland marshes predating the most recent 1870 s avulsion holocene avulsions involved two major styles 1 progradation of lacustrine deltas and splay complexes and 2 local reoccupation or appropriation of preavulsive channels most avulsions were progradational and occurred in floodplain lakes occupying floodbasin areas between elevated alluvial ridges the two most recent avulsions old channel and 1870 s diverted mainly into inundated peatland progradational avulsions were accompanied by deposition of avulsion belt sediments associated with multiple channel networks the characteristics of avulsion belt deposits include 1 sediments dominated by poorly sorted silt and very fine sand 2 lateral continuity in transverse and longitudinal directions with subhorizontal upper and lower boundaries 3 predominantly nonerosional contacts with underlying sediments 4 coarsening upward successions 5 consistent radiocarbon dates for the tops of preavulsive substrates and 6 occurrence beneath levee and overbank deposits of the associated major channel belt indicating that avulsion belt deposition occurs prior to the development of a new master channel the width of ancient avulsion belts reaches 18 km with typical thicknesses of 2 3 m avulsion belt deposition accompanied by many small channels was followed by flow reversion to a few larger channels and eventually to one single channel accompanied by deposition of levee and channel deposits reoccupational avulsions were not accompanied by deposition of widespread avulsion belt sediments and led mainly to the modification of pre existing channel belts the sedimentation patterns of holocene avulsions of the saskatchewan river reveal that avulsion belt sediments represent major components of the floodplain deposits supporting the model developed from observations of the 1870 s avulsion

new insights on coral mound development from groundtruthed high resolution rov mounted multibeam imaging abstract currents play a vital role in sustaining and developing deep water benthic habitats by mobilising food and nutrients to otherwise relatively barren parts of the seabed where sediment supply is significant it can have a major influence on the development and morphology of these habitats this study examines a segment of the belgica mound province ne atlantic to better constrain the processes affecting a small sized cold water coral cwc mound habitat and conversely the hydrodynamic influence of cwc mounds on their own morphological development and surroundings here we utilise rov mounted multibeam rov video data and sediment samples to investigate current processes mound morphology density and development detailed mapping shows that the area may have the highest density of coral mounds recorded so far with three distinct mound types defined based on size morphology and the presence and degree of distinct scour features a residual current of 36 40 cm s 1 is estimated while large scour features suggest low frequency high magnitude events these 3 mound types are i smaller mounds with no scour ii mounds with scour in one to two distinct directions and iii larger mounds with mound encircling scour the differing mound types likely had a staggered initiation where younger mounds preferentially developed near clusters of pre existing mounds given the high density of these small cwc mounds we support the hypothesis that over time this clustering may eventually lead to these mounds coalescing into larger coral mound features

contrasting fluvial styles of the paraguay river in the northwestern border of the pantanal wetland brazil abstract the upper paraguay drainage basin is situated mainly in west central brazil near the bolivian border flowing from north to south the paraguay is the trunk river of an alluvial depositional tract characterized by complex geomorphologic zonation that resulted from an intricate geologic evolution since the late pleistocene this paper focuses on the geomorphology of the paraguay river at the northwestern border of the pantanal wetland where two broad geomorphologic zones were distinguished north from the pantanal wetland the paraguay river flows in an aggradational fluvial plain 5 km wide and incised into older alluvial deposits the river exhibits a meandering style over most of its course but sinuosity drops from 2 2 to 1 1 near the northwest border of the pantanal wetland where the river has been forming the paraguay fluvial megafan since the late pleistocene the river deflects 90 eastward at the entrance into the pantanal changing its fluvial style because of a progressive loss of confinement downstream of the point where the river reaches lowland plains the river becomes more sinuous adopts a distributary pattern within the wetland and brings about the creation of the modern depositional lobe characterized by higher topographic gradient and active sedimentation likely linked to increased accommodation space allowing progradation fluvial discharge diminishes in the pantanal wetland because of channel overbank flow during the rainy season and frequent levee crevassing avulsion belts and channel levee complex are preserved on the floodplain as relict forms south of the convergence of the two main channels that define the taiama island a loss of gradient marks the base of the depositional lobe further downstream the paraguay river returns to a meandering fluvial style but crossing a large fluvial plain populated by hundreds of small lakes and seasonally flooded that characterizes the pantanal wetland

avulsion mechanisms on the okavango fan botswana the control of a fluvial system by vegetation a study of the avulsion of a major distributory channel on the alluvial fan 22 000 km2 in area of the okavango river in northern botswana has revealed that channels serve as arterial systems distributing water which sustains large areas of permanent swamp the channels are vegetatively confined a primary channel defined here as a channel which receives water and sediment directly from the fan apex aggrades vertically as a result of bedload deposition the rate of aggradation increases downchannel and may exceed 5 cm yr 1 in the distal reaches rapid aggradation is associated with a decline in flow velocity this initiates a series of feedback mechanisms involving invasion of the channel by aquatic plants which trap floating plant debris further reducing flow rate and causing the channel water surface to become elevated thereby increasing rate of water loss from the channel accelerating blockage and aggradation the channel ultimately fails enhanced water loss from the channel promotes the growth of flanking swamp vegetation which confines the failing channel increased flow through the swamp erodes pre existing hippopotamus trails producing a secondary channel system which overlaps but does not connect directly to the failing reach of the primary channel the region of failure of the primary channel migrates upstream accompanied by headward propagation of the secondary channel system the swamp distal to the failed primary channel dessicates and is destroyed by peat fires secondary channels are stable and not prone to blockage comparison with avulsions described in other river systems indicates that the influence of plants in the okavango river system is exceptionally strong

carbonate mound development in contrasting settings on the irish margin cold water coral carbonate mounds formed by framework building cold water corals are found in several mound provinces on the irish margin differences in cold water coral mound development rates and sediment composition between mounds at the southwest rockall trough margin and the galway mound in the porcupine seabight are investigated variations in sediment composition in the two mound provinces are related to the local environmental conditions and sediment sources mound accumulation rates are possibly higher at the galway mound probably due to a higher influx of hemipelagic fine grained non carbonate sediments in both cold water coral mound areas mound growth has been continuous for the last ca 11 000 years before this period several hiatuses and unconformities exist in the mound record the most recent unconformity can be correlated across multiple mounds and mound provinces at the irish margin on the basis of apparent age on the southwest rockall trough margin these hiatuses unconformities are associated with post depositional aragonite dissolution in and lithification of certain intervals while at galway mound no lithification occurs this study revealed that the influx and types of material transported to cold water coral mounds may have a direct impact on the carbonate mound accumulation rate and on post depositional processes significantly the logachev mounds on the sw rockall trough margin accumulate slower but because they contain lithified layers are less susceptible to erosion this net effect may account for their larger size compared to the belgica mounds

high resolution bathymetry and acoustic geophysical data from santa maria di leuca cold water coral province northern ionian sea apulian continental slope abstract a total of 800 km 2 of multibeam echo sounder coverage roughly 800 km of chirp sonar data and 18 km of side scan sonar profiles 100 500 khz were acquired a few km offshore santa maria di leuca south eastern italy from 200 m to 1300 m water depth the explored area belongs to the upper slope of the gently south eastward dipping apulian continental margin northern ionian sea acoustic datasets were collected by three different oceanographic expeditions where evidence of living cold water coral cwc colonies were documented by previous surveys and samples high resolution multibeam bathymetry indicated an extensive rough seafloor with an irregular faulted upper surface to the west reflecting large scale tectonic control on the margin and a highly disrupted upper slope formed by prominent downslope mass movements to the north a broad area in the east was influenced by mass transport deposition which resulted in a very complex hummocky seafloor mainly shaped by detached block like features and failure related bedforms i e low scarps downslope lineations and compressional ridges from the shallow seismic stratigraphic data failure events appeared to be multiple and recurrent and chaotic reflectors both buried and exposed at the seafloor affected most of the investigated area drift sedimentation was also recognised along a central large ridge resulting in an interplay between contour currents and downslope turbidity currents the spatial distribution of the cwc reefs was inferred from the acoustic facies interpretation based on video images and ground truthed by sediment samples it appeared that 1 within the investigated area living coral frameworks were located along large topographic highs facing the main flow of the bottom currents where hard and firm substrata and or failure related sediment bedforms occurred 2 cwc mainly settled on clustered and isolated mound like features tens to a few hundreds of metres long and no more than 25 m high and were located between 600 and 900 m water depth within the broad area affected by downslope mass transport deposits such mound like morphologies could thus be interpreted as a result of sediment accreted by coral growth with the consequent sediment trapping on small scale positive seafloor irregularities formed by different types of pleistocene exposed mass transport deposits their burial prevented by bottom currents

do norwegian deep water coral reefs rely on seeping fluids hundreds of large coral reefs up to 45 m high exist a on the continental shelf and b on morainic threshold ridges in fjords of northern mid and southwest norway they occur in water depths between 400 and 40 m and contain a large variety of megafauna the most common frame building coral is lophelia pertusa l the oldest reef found to date is 8600 calendar years old determined by radiocarbon dating of buried lophelia skeleton even though many of these reefs have been known to science for over 200 years there is as yet no viable and unifying hypothesis to explain their existence in deep cool waters other than perhaps the hydraulic theory presented by the author in 1990 it states that primary producers mainly bacteria are locally formed and concentrated at reef locations due to seepage of light hydrocarbons mainly methane on the continental shelf and nutrient rich groundwater in the fjords the hydraulic theory is supported by the following topographic reflection seismic and geochemical indicators for the continental shelf reefs a seaward dipping sedimentary permeable strata enhanced acoustic seismic reflectors adjacent pockmark craters locally elevated light hydrocarbon sediment content locally elevated seawater methane content for the fjord reefs b threshold morainic substratum rather than adjacent hardrock substratum sub surface dipping sedimentary layers h2s smell of near surface sediment samples these indicators or reef associated observations have been documented by german british and norwegian researchers over the last 10 15 years however all the listed indicators do not necessarily occur at each of the respective shelf and fjord reef locations simultaneously

textural analyses of sidescan sonar imagery from two mound provinces in the porcupine seabight large mound structures have been discovered in the porcupine seabight northeast atlantic at a depth of 500 1200 m associated with the growth of cold water deep sea coral species such as lophelia pertusa l or madrepora oculata l during the training through research cruise in 1997 high resolution oretech sidescan sonar data were acquired over two provinces of these structures this article focuses on the presentation and quantitative interpretation of representative sections of these sidescan data from areas around the belgica and hovland mounds several image analysis tools were used but texture analysis based on grey level co occurrence matrices gave the best results entropy and homogeneity indices were calculated and the resulting images made it possible to discriminate between different seabed features on a quantitative basis mounds moats and background sediments could be delineated accurately and the image textures could be linked to the actual seafloor appearance through core descriptions and deep towed video data a major difference was found in the acoustic returns from the two provinces studied the belgica province shows much rougher textures this is due to an actual difference in seabed roughness caused by a difference in bottom currents and sediment dynamics in the two areas the combined effect of the northward directed north atlantic slope current and superimposed internal waves and tides appears to be much stronger in the belgica province the reported difference in current strength might well influence the growth of the deep water coral species in both areas

grounding pleistocene icebergs shape recent deep water coral reefs the widespread view that scleractinian corals in cold and deep waters of high latitudes are slow growing organisms that do not form reefs is challenged by the discovery of a huge coral reef over 13 km in length 10 to 35 m in height and up to 300 m in width formed by the coral lophelia pertusa in water depths of 270 to 310 m at 64 n on the sula ridge mid norwegian shelf cruises in 1994 1995 and manned submersible operations in may 1997 provide data and observations from which the structure and development of the sula ridge coral reef have been determined the fennoscandian icesheet retreated from the mid norwegian shelf prior to 12 000 years before present and modern oceanographic conditions were established at 8000 years before present coral growth since that time has resulted in a large deep water shelf reef for which recent stable isotopic studies have demonstrated high growth rates for these azooxanthellate cold water corals information on the geometry of deep water coral reefs and their environmental controls is still fragmentary controversial and raises issues of conservation in this area of active fishing and oil exploration this paper reports on the discovery of what is probably one of the largest deep water coral reefs existing in the northeast atlantic and indicates that its siting is due to post glacial structures iceberg plough marks events the second storegga slide and local conditions on the seafloor surprisingly reef accumulation rates on the sula ridge are comparable with those measured on tropical coral reefs

the imprint of methane seepage on the geochemical record and early diagenetic processes in cold water coral mounds on pen duick escarpment gulf of cadiz abstract the diagenetic history and biogeochemical processes in three cold water coral mounds located in close proximity to each other on pen duick escarpment in the gulf of cadiz were examined the influence of ascending methane rich fluids from underlying sediment strata delineated two mound groups alpha and beta mound showed evidence for the presence of a sulfate methane transition zone smtz at shallow depth whereas gamma mound appeared to lack a shallow smtz in the methane influenced alpha and beta mound upward diffusion of hydrogen sulfide from the shallow smtz caused extensive pyritization of reactive iron phases as indicated by values for the degree of pyritization 0 7 this secondary pyritization overprinted the sulfur isotope composition of sulfides formed during organoclastic sulfate reduction the almost complete consumption of reactive iron phases by upward diffusing sulfide limited dissimilatory iron reduction to the top layer in these mounds while organic matter in the pyritized zones below was primarily degraded by organoclastic sulfate reduction hydrogen sulfide produced during sulfate reduction coupled to the anaerobic oxidation of methane aom diffused upward and induced aragonite dissolution as evidenced in strongly corroded corals in alpha mound this mound has been affected by strong fluctuations in the depth of the smtz as observed by distinct layers with abundant diagenetic high mg calcite with a 13 c depleted carbon isotope composition in the non methane influenced gamma mound low sulfate reduction rates elevated concentrations of dissolved iron and solid phase iron speciation indicated that organic matter mineralization was driven by dissimilatory iron reduction and organoclastic sulfate reduction coupled to oxidative sulfur cycling the latter process led to 34 s depletion in pyrite of up to 70 relative to pore water sulfate