the formation and evolution of the barrier islands of inhaca and bazaruto mozambique abstract the barrier islands of inhaca and bazaruto are related to the extensive coastal dune system of the mozambican coastal plain south east africa optically stimulated luminescence osl dating of key stratigraphic units indicates that accretion of sediment within these systems is episodic both islands appear to have been initiated as spits extending from structural offsets in the coastline superposition of significant quantities of sediment upon these spits during subsequent sea level highstands formed the core of the islands which were anchored and protected by beachrock and aeolianite formation at least two distinct dune building phases occurred during marine oxygen isotope stage mis 5 tentatively attributed to marine transgressions during sub stages 5e and 5c although some localized reactivation of dune surfaces occurred prior to the holocene large quantities of sediment were not deposited on either island during the low sea levels associated with mis 2 significant dune building and sediment reworking occurred immediately prior to and during the holocene though it is not clear whether these processes were continuous or episodic significant erosion of the eastern shoreline of bazaruto suggests that it is far less stable than inhaca and may suffer further large scale erosion a model is presented for the formation of barrier islands along the mozambican coastal plain

land sea interaction and morphogenesis of coastal foredunes a modeling case study from the southern baltic sea coast abstract coastal foredunes are developed as a result of the interplay of multi scale land sea processes basic driving mechanisms of coastal foredune morphogenesis as well as natural processes and factors involved in shaping the foredune geometry are quantitatively studied in this paper by a numerical model aeolian sediment transport and vegetation growth on the subaerial part of a beach is simulated by a cellular automata ca approach while the sediment budget in the subaqueous zone serving as a sediment source sink for the foredune ridges is estimated in a process based model the coupled model is applied to a 1 km long section of a barrier coast swina gate in the southern baltic sea for a 61 year 1951 2012 hindcast of its foredune development general consistency is shown between the observational data and simulation results indicating that the formation of an established coastal foredune results from a balance between wind wave impacts and vegetation growth driven by an effective onshore wind and a boundary sediment supply small scale dunes develop on the backshore and migrate landward they are then trapped in a narrow strip characterized by a large density gradient of vegetation cover which separates the hydrodynamically active zone and the vegetated zone continuous accumulation of sediment in this strip induces the development of a foredune ridge according to the simulations the formation of an established coastal foredune has to meet three preconditions 1 an effective onshore aeolian transport 2 a net onshore or lateral sediment supply and 3 a climate favoring vegetation growth the formation of a new foredune ridge in front of an already existing foredune is determined by a combination of the sediment supply rate the extreme wind wave event frequency and the vegetation growth rate simulation results demonstrate a remarkable variability in foredune development even along a small 1 km coast section implying that the medium to long term land sea interaction and foredune morphogenesis is quite sensitive to boundary conditions and various processes acting on multi temporal and spatial scales

tracking shoreline evolution in central cyclades greece using beachrocks beachrocks represent a significant paleo environmental proxy because they can record both the vertical and the horizontal evolution of the shoreline they have often been used to assess holocene shoreline evolution and crustally induced relative sea level rsl changes in the mediterranean sea in this paper we used submerged beachrocks from paros and naxos islands aegean sea greece to reconstruct the shoreline modification and provide new insights on the rsl evolution in central cyclades paros and naxos islands are of great importance in terms of archaeological evidence of coastal occupation however the evolution of their coastlines was seldom explored in this study we coupled detailed underwater surveys analysis of aerial photogrammetry microstratigraphic analysis and luminescence dating to study beachrock outcrops found down to about 6 m below the present sea level we then spatially and chronologically constrained some major palaeogeographical changes of a number of coastal sectors of the two islands furthermore the multiple analyses of beachrocks sediment coring and archaeological data suggested that rsl rose by at least 3 8 m in the last 4 0 ka and that rsl variation in the last 2 0 ka did not exceed 2 m with respect to the present mean sea level

an integrated model of extrusive sand injectites in cohesionless sediments clastic injection and surface expression of subsurface sediment remobilization is a phenomenon which is becoming increasingly recognized however understanding of the physical mechanisms that control these features remains limited dominated by inference from outcrop and seismic studies here this limitation is addressed through a set of experiments focused on the development and evolution of fluidization features in non cohesive bedded sequences fluidization and the onset of piping are shown to occur progressively through a sequence of discrete phases with initial void formation development of infiltration horizons rupture and finally pipe formation critically the style of piping the stability of piping and the temporal evolution of venting are shown to exhibit considerable variability in particular pipes may either be stable or very mobile migrating laterally over large distances these produce deposits that are typically interpreted in outcrop as being the product of en masse liquefaction rather than localized dynamic fluidization these differing elements are synthesized to produce a model of sand extrudites in addition the implications of this model are explored

experiments on piping in sandy gravels tests on internally unstable sandy gravels show that a significant proportion of the sand content is washed out by piping at hydraulic gradients far lower than the critical gradient given by a classical theory the probable explanation is that a major part of the overburden load is carried on a framework of gravel particles leaving the sand under relatively small pressures by contrast piping of the sand from stable sandy gravels occurs at approximately the full theoretical gradient the tests broadly confirm kenney s criterion for the internal stability of granular materials des essais realises sur des graves sableuses a instabilite interne importante montrent qu une proportion non negligeable du sable est lessivee pour des gradients hydrauliques bien inferieurs au gradient critique donne par les theories classiques l explication la plus probable est que la majeure partie de la surcharge des couches subjacentes est transmise au reseau des particules graveleuses le sable n etant alors plus soumis qu

latest pleistocene and holocene dune construction at the north eastern edge of the rub al khali united arab emirates abstract optical dating of two dune pro les developed in linear dunes in ras alkhaimah united arab emirates has been used to establish the timing and rateof dune accretion one section at awa was over 17 m high while that at idhnwas over 40 m high the awa dune appears to have accumulated very rapidly 10 000 years ago with a vertical accumulation rate of about 3ae3mka 1 theidhn dune appears to have accumulated over the past 1000 years with 20 m ofsediment accumulating in a time period of about 270 years the awa dunemay have accumulated in response to the transgression of the persian gulf byrising sea levels in late pleistocene and holocene times the idhn dune mayhave accumulated rapidly because of intensi ed human activity a short livedclimatic event or because it may periodically be reactivated after erosion by uvial action at its base keywords linear dune optical dating rub al khali sand accumulation introductionthere remains some uncertainty surrounding thestyle and timing of deposition of large aeoliandunes with authors supporting both gradual andpunctuated models of dune development for adiscussion see thomas 1997 this divergence ofopinion results from both the general absence ofdating control within dunes in most studies anddif culties in gaining exposures within some ofthe larger dune bedforms the purpose of thispaper is to establish a chronology of dunedevelopment for two thick 10 m dune sectionsexcavated within large complex linear dunesfrom within the rub al khali near ras alkhaimah in the north of the united arabemirates fig 1 the sites were selected becauseof the availability of thick fresh sections inrecently excavated moist sand with an area of around 600 000 km

the structure and geomorphology of the dashgil mud volcano azerbaijan the large scale and small scale 10 m structure and geomorphology of the active dashgil mud volcano in central azerbaijan have been studied through historical records it is known that this mud volcano has major eruptions every 6 32 years the activity observed during two field trips in 1995 consisted of low energy venting and debouching of mud water oil and gas from three mud pools salses and about 20 individual cones gryphons located on the summit plateau of the mud volcano besides the bubbling mud pools ranging from 30 to 75 m across and the cones ranging from 0 8 to 3 m height a 200 m long string of about 10 sinter mounds was found on the summit plateau the internal structure of the mud volcano and the processes responsible for the observed dashgil geomorphology are discussed assuming the dashgil mud volcano to be continuously active with an average methane production similar to that observed in 1995 between the rare major eruptions we have conservatively estimated the dashgil mud volcano to produce an annual amount of at least 800 sm3 standard cubic metres of gas mainly methane which is emitted directly into the atmosphere this estimate indicates that the natural contribution of atmospheric greenhouse radiatively active gases from the world s terrestrial and submarine mud volcanoes is highly significant

the geomorphologic evolution of the wilderness dune cordons south africa abstract the wilderness dune cordons consist of steep sided ridges up to 207 m high separated by coastal lakes they probably formed during the sea level highstands of the pleistocene interglacials three major dune cordons are developed there is an additional huge coalesced mass of older fossil dunes landward of these cordons forming hills up to 340 m high in places lying on the coastal platform 150 260 m generally locally 210 260 m the dunesand reaches thicknesses in excess of 300 m the cordons form by accretion of transgressive dunefields and large compound imbricate parabolic dunes an individual cordon can result from numerous phases of dune formation during periods of sea level highstand the dunes of the present interglacial are mostly accreting on top of the seaward cordon which was initiated during the last interglacial during the complex sea level history there have been numerous phases of dune building followed by coastal erosion that formed seacliffs in the dune cordons in some areas almost all the cordon was subsequently eroded away these fossil seacliffs form large steep seaward facing slopes parallel to the present coastline and form a major element in the morphology of the cordons trailing arms of parabolic dunes form another major topographic element oriented at 15 30 to the shoreline river erosion has altered the cordon morphology in places the geomorphology of the cordons is thus a function primarily of dune cordon construction accentuated by coastal erosion in the form of cliff cutting secondarily of dune morphology and thirdly of fluvial erosion the evolution of the cordons can be dated tentatively using palaeontologic stratigraphic and sediment dynamic data the seaward cordon formed during the eem and holocene a fairly reliable dating the middle cordon probably formed between 200 500 ka and the landward cordon probably formed between 600 900 ka the coalesced dune deposits lie inland of the cordons and are thus older this would place the minimum age of the younger coalesced dune deposits in the middle pleistocene about 1000 ka early miocene fossil plant remains in the knysna lignites which underlie the older coalesced dunes indicate their maximum possible age westerly winds dominated in the area for the past few million years

experimental studies of the fluidization of layered sediments and the formation of fluid escape structures experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non fluidizing top layer before the base layer can fluidize the weight of the overlying material must be balanced and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer this static layer allows the top layer to lift away from the base layer which is then free to fluidize a water filled crack forms below the static layer and as this grows instability causes the static layer and top layer to bend and conical voids to form below the antiformal sections rupture occurs at the apex of the water void allowing the underlying water and fluidizing material to burst out through the top layer the fluidized base layer material then flows through the rupture until all of this material except that in the static layer is deposited above the previously overlying layer and a stable fluidization system results the top layer material is bent upwards around the rupture and the resulting pillar type escape structure is preserved if flow then ceases the vigour of the burst out is greatest when the base layer material has a grain size 15 of the top layer material if the base layer grain size is less than 8 of the top layer then base layer material will pass through the top layer pore spaces without forming an escape structure if cohesive material is present escape structures form when a layer of fine grained cohesive material overlies a layer of cohesionless material at low flow rates small pipes with scattered angular bends pierce the top layer and base layer material passes through them the base layer material is ejected on to the top layer and builds up around the mouth of each pipe to form constructional structures sand volcanoes this is in contrast to the cohesionless experiments where the weight of material being deposited on the top layer caused an ejecta filled depression to form around the rupture if flow then ceases both the pipes and the sand volcanoes are preserved at high flow rates where the base layer fluidizes the top cohesive layer becomes fragmented small fragments circulate within the fluidizing base layer and are preserved as floating clasts large fragments sink to the bottom of the fluidizing base layer erosion of the bottom surface of these larger fragments causes this surface to become convex downward the experimentally derived structures are similar to pillar type structures observed in the field and the processes described can be used to investigate the development of these structures fluidization experiments also demonstrate the genesis of dish structures and the cohesive behaviour can be applied to the deformation of these structures after initial formation

fluid flow in and around a mud volcano field seaward of the barbados accretionary wedge results from manon cruise a field of mud diapirs and mud volcanoes situated in the barbados trench at 13 50 n and extending along an old oceanic fracture zone mercurus was investigated during the manon cruise using both surface ship and nautile submersible sampling and measurements the entire zone from 13 50 n up to 14 20 n has an anomalously high heat flow which implies that fluids are drained into it from a segment of the accretionary wedge a few hundred kilometers wide two structures interpreted as diatremes atalante and cyclops expell large amounts of water and methane we propose that they were formed from the release of a light fluid when gas hydrates were dissociated in the sediment as the result of the circulation of warm fluid in the area however they expell only a small fraction of the incoming fluid implying that disperse flow is the dominant mode of expulsion in this area the chemoautotrophic communities on the surface of the structures rely mostly on sulfides submersible observations temperature measurements in the sediment and the chemistry of the pore fluid indicate that convection of seawater occurs within the first few meters of sediment through high permeability channels such as cemented carbonate conduits we propose that this convection is driven by the density difference between the pore fluid and seawater but fresh water released by the dissolution of shallow hydrates may also contribute this shallow convection may be a frequent process in cold seep environments

the formation of shadow dunes abstract an investigation of the modification of airflow by a discrete semi circular roughness element in this case vegetation the resulting flow structure and the formation of pyramidal shaped shadow dunes is presented two erect pioneer sand dune grasses festuca littoralis and ammophila arenaria were used in the experiments which were conducted in both the field and a wind tunnel for a range of wind velocities 4 20 m sec 1 the three dimensional flow structure about the vegetation is dominated by horizontal separation characterized by symmetrically opposed reversing vortices which form within a triangular wake a vertical separation envelope is also formed over the vegetation pyramidal shadow dunes are formed within this flow structure when aeolian sand transport occurs shadow dune height is dependent on element basal width and repose angle of the sand shadow dune length is dependent on element basal width and wind velocity the results are extrapolated to include all semi porous to non porous semicircular discrete roughness elements the role of shadow dune formation in the development of foredunes and related environments is examined

understanding late quaternary change at the land ocean interface a synthesis of the evolution of the wilderness coastline south africa coastal barrier systems have been widely used to understand the responses of coastal margins to fluctuating pleistocene sea levels what has become apparent particularly with the development of robust chronological frameworks is that gaps in terrestrial barrier sedimentary records are not uncommon and that they most likely reflect phases of barrier construction on the now submerged continental shelf thus understanding the land ocean interface through time is critical to fully appreciate the quaternary archives contained within the barriers and their associated back barrier deposits this study uses offshore and lakefloor back barrier seismic profiling from the south african south coast at wilderness to link the sub aerially exposed barrier stratigraphy to the currently submerged geological and sedimentological record a total of eight separate submerged aeolian units are identified at water depths of up to 130 m below mean sea level their approximate ages are constrained with reference to the eustatic sea level record and the deepest units are consistent with the estimated magnitude of sea level lowering during the last glacial maximum lgm on the south african coastline as previously assumed aeolian sedimentation tracked the shoreline onto the continental shelf during the late pleistocene during sea level regressions both the incision of fluvial channels and the deposition of back barrier systems occurred across the continental shelf during late low stand early transgression periods landward shoreface migration occurred pre existing channel incisions were infilled and pre existing barriers were truncated rapid transgression however allowed the preservation of some back barrier deposits possibly aided by protection from antecedent topography as sea level neared the present day elevation erosion of the mid shelf sediments resulted in the development of a holocene sediment wedge which was augmented by holocene fluvial sediment supply the holocene sand wedge is preserved in the back barrier lakes and was deposited during the holocene highstand inundation overlying middle to late holocene terrestrial muds reflect the deposition of river borne mud onto the shelf these results clearly demonstrate that within transgressive regressive sea level cycles accommodation space for barriers is controlled by antecedent drainage systems and gradients on the adjacent inner continental shelf

fluid flow through active mud dome mound culebra offshore nicoya peninsula costa rica evidence from heat flow surveying mud extrusion is frequently observed as a dewatering phenomenon in compressional tectonic settings such as subduction zones along the middle american trench several of these features have been recently discovered this paper presents a heat flow study of actively venting mound culebra offshore nicoya peninsula and is complemented by data from geophysical surveys and coring the mud diapir is characterised by methane emission and authigenic carbonate formation at its crest and is composed of overconsolidated scaly clays and clast bearing muds compared with the conductive background heat flow the flux through the mud dome is elevated by 10 20 mw m2 possibly related to advection of heat by fluids rising from greater depth decreased chlorinity in the pore waters from gravity cores may support a deep seated fluid origin geothermal measurements across the mound and temperature measurements made with outriggers on gravity corers were corrected for the effects of thermal refraction forced by the topography of the mound corrected values roughly correlate with the topography suggesting advection of heat by fluids rising through the mound thereby generating the prominent methane anomaly over the dome and nurturing vent biota however elevated values occur also to the southeast of the mound we believe that the overconsolidated clays and carbonates on the crest form an almost impermeable lid fluids rising from depth underneath the dome are therefore partially channelled towards the flanks of the mound

fluid methane and energy flux in an active margin gas hydrate province offshore costa rica joint analysis of seafloor temperature data borehole temperature measurements and observations that constrain the position of the top and base of the gas hydrate zone ghz at sites on the non accretionary costa rican margin provide quantitative constraints on the flux of energy fluid and methane through the sediments on the overriding plate a comparison of borehole temperature data obtained in the trench at the toe of the deformed sedimentary wedge and at a midslope location indicates that the thermal regimes are perturbed by appreciable advective flux at 1 km oceanward 19 mm yr 1 and 1 4 km landward 5 7 mm yr 1 of the deformation front this observation is loosely consistent with models that predict the most rapid dewatering and highest rates of fluid expulsion within a few kilometers of the deformation front using data that constrain the thickness of the ghz at three sites on the forearc we estimate methane and fluid flux rates through application of a one dimensional analytical model that constrains the nature of the plumbing system for the gas hydrate reservoir our results indicate a two fold decrease in methane flux between a site located 400 m from the toe of the wedge and a site 12 km from the toe an intermediate site located 1 4 km from the toe of the wedge has a thick ghz extends to at least 340 365 m below seafloor that requires a very high methane supply rate 345 mol m 2 kyr 1 for a mass flux of 5 mm yr 1 we conclude that this site has the most two dimensional fluid flux regime with fluids being fed into the zone laterally by conduits and fractures and vertically by expulsion during compaction of underthrusting sediments

present day dune environment dynamics on the coast of the świna gate sandbar polish west coast abstract in present day polish coastal dunes development heavy storms and human activity play a significant role natural or almost natural dune processes and accumulation of the coast is observed only in a few places such as the wina gate sandbar also called barrier as far as the spit number and morphology of the youngest ridges is concerned they are different in the western the middle and the eastern part in the western part ridges are smaller and closer to each other thus depressions between them are narrower moreover beach is widely covered by small hillocks in the middle part ridges are higher but narrower likewise depressions between them are wider the beach is wide and covered by large numbers of plants and dune hillocks in the eastern part dunes are also high but tend to be narrow with steep seaside slope having the most frequent occurrence depressions and beach are narrow the number of plants is not considerable compared with other parts since 1997 an increase of the new dune ridge on the still developing beach has been observed each year the beach is becoming wider and covered by larger number of plants plants lead to the development of new dunes and increase of the sandbar the new foredune ridge consists of several hillocks joined into irregular ridge this new first ridge is also shaped by storm waves but still becomes a real ridge this development may be caused by continuous sand supply and by very strong north and west winds a lot of different dune psammophyties on the beach are in favour of sand fixing on the increasing beach far from the first ridge only on part of spit with a tendency to erosion accumulation of the dunes is not to be observed additionally human activity stops aeolian accumulation and plant growth on the beach

coastal paleo environment and sea level change at macassa bay southern mozambique since c 6600 cal bp changes in holocene coastal paleo environment and sea level variations have been recorded in estuary sediments from macassa bay southern mozambique methods include analysis of fossil diatoms sediment stratigraphy mineral magnetic properties stable carbon and nitrogen isotope composition and carbon and nitrogen content the chronology based on six ams c 14 dates suggests a basal age of the sediment core of c 6600 cal bp calibrated years before present the multi proxy dataset implies two phases when the site was experiencing marine conditions and tentative sea level high stands 1 between c 6600 6300 cal bp which is contemporary with the last phase of the global transgression and the holocene climatic optimum and 2 between c 4700 1000 cal bp a period when sea level curves from the region suggest occasional minor sea level high stands between these phases c 6300 4700 cal bp the environment within the macassa bay estuary was less influenced by marine processes and studied proxies indicate a freshwater phase associated with relatively low sea levels after c 1000 cal bp a terrestrial environment prevailed at the site probably as a result of a combined effect of sea level lowering and high accumulation of organic peat within the estuary c 2011 elsevier ltd and inqua all rights reserved

optical dating of aeolian dynamism on the west african sahelian margin abstract the sahelian margin of west africa is widely recognised as an area of recent environmental catastrophe and human suffering arising from food shortage and land degradation associated with prolonged drought the propensity of this region to suffer drought has been related using environmental data collected during the period of instrumental records to a combination of low mean annual rainfall levels and a high degree of rainfall variability which relates to sea surface temperature anomalies in the adjacent tropical atlantic ocean despite the significant environmental and human consequences of such droughts there is a paucity of long term environmental data for the west african sahel aeolian dune reactivations in this area are a potentially highly useful environmental archive of past periods of extended drought conditions which may have resulted in localised or widespread dune reactivation here we describe the initial results from an ongoing programme of research which seeks to develop a detailed record of past dune reactivations in mali we find evidence for repeated holocene dune reactivation events and a significant number of reactivations which commenced at the time of onset of the last major drought cycle in the early 1970s we obtain ages as young as 20 30 years for some significant dune units thickness up to 1 m and describe the results of experiments which test the performance of our dating exercise we specifically test for the significance of preheat temperature on single aliquot regeneration sar equivalent dose determinations and recycling ratios neither are found vary significantly as a function of preheating optical dating of sand sized quartz could provide a useful tool for palaeogeographical mapping of ancient and historical dune reactivations in this region and elsewhere

optical dating of young coastal dunes on a decadal time scale we explore the use of quartz optically stimulated luminescence osl dating for reconstructing coastal evolution on a time scale of decades to a few hundred years samples are taken from the accretionary south west coast of texel a barrier island just offshore of the northern netherlands the ages of dune ridges are known from historical sources an excellent chronology with a decadal accuracy exists for the past 260 years osl ages of less than 10 years on the youngest samples indicate that the osl signal of the quartz grains is very well zeroed prior to deposition and burial osl ages of five samples from a 250 year old dune ridge are indistinguishable and the osl ages on 17 out of 20 samples are in excellent agreement with the well known independent age controls our results highlight the potential of osl dating for high resolution reconstruction of coastal evolution over the past few centuries

the influence of microbial mats on the formation of sand volcanoes and mounds in the red sea coastal plain south jeddah saudi arabia abstract extensive areas covered by microbial mats have been found in the upper intertidal flats and supratidal pools in the red sea coastal plain of south jeddah saudi arabia numerous microbially controlled sediment surface morphologies are evident such as flat cohesive mats that commonly pass into mats with wrinkles reticulates and tufts together with erosion pockets and mat chips these microbial mats form cohesive surface layers that lead to biostabilization of the sediment surface fluidization of the underlying sediments is due to tidal influences and pressurized gas escape from decay and photosynthesis of microbial mats and causes deformation and rupture of the cohesive surface mat layer via vertical and sub vertical pipes extrusion of fluidized sediments and water through these pipes leads to redeposition of sediment grains above the surface mat layer to form sand volcanoes and mounds most of the sand volcanoes present in the intertidal flats and supratidal pools show a symmetrical morphology whereas in tidal channels asymmetrical forms are more common extrusion of underlying sediments through several adjacent vents leads to coalescence of sand volcanoes to form sand mounds in this study sand volcanoes are also compared with other cone like features from the red sea such as gas domes and crab mounds this comparison should help in differentiating similar cone like features associated with microbial mats in the rock record

beachrock formation in low latitudes implications for coastal evolutionary models abstract beachrock is present in many parts of the world particularly on low latitude coastlines its formation during stillstands or minor regressions in subtropical areas involves cementation of clastic grains and thus prevents grain transport in the littoral zone during later transgression or regression existing short and medium term conceptual and numerical models of coastal evolution fail to take into account this effective reduction of littoral sand supply and the effects of the beachrock itself on shoreline development in the short term reduction of sediment supply through beachrock formation during transgression should enhance landward translation of the shoreline conversely the beachrock itself may afford a degree of protection from erosion in the medium to long term beach rock formation during multiple pleistocene transgressions and regressions in areas which lack significant sediment input from land drainage systems may have caused a long term reduction in sediment volume during the course of the pleistocene this assumes that beachrock formation is not matched by its destruction through physical and bioerosion and chemical weathering preservation of coastal facies is greatly enhanced by beachrock formation which may promote overstepping and drowning of strandline facies during transgression or preferential preservation during regression precise records of sea level fluctuations may be preserved by beachrock formation a situation rendered almost impossible in other areas due to littoral transport of mobile sediment in the widespread areas in low latitudes where it occurs beachrock formation may be an important element in models of horizontal shoreline displacement and coastal evolution

evidence of episodic fluid gas and sediment venting on the northern gulf of mexico continental slope surficial sediments and sea floor features of the northern gulf of mexico continental slope record dramatic episodic venting and slower seepage of formation fluids brines crude oil gases and fine grained sediments faults activated by massive sediment input during periods of plio pleistocene falling to low sea levels accompanied by compensating salt movement provide avenues of vertical transport to the continental slope surface many of these faults cut thick sedimentary sequences that frequently contain geopressured zones which provide the driving force for fluid and gas expulsion flux rate and fluid characteristics are interpreted as important determinants of modern sea floor geology and biology qualitatively under conditions of rapid flux of sediment rich fluids mud volcanoes up to 1 km wide and 50 m high and extensive sheets of extruded mud result these sediments contain old and displaced microfaunas muds are frequently extruded with large volumes of crude oil and gas both biogenic and thermogenic in water depths greater than approximately 500 m rapid to moderate vertical flux of hydrocarbon gases and fluids results in the construction of relief features composed of gas hydrates ejected mud and authigenic carbonates areas with near surface hydrates frequently support complex chemosynthetic communities with associated hardgrounds containing calcareous remains of mussels clams and associated gastropods slow flux seeps promotes the formation of 13 c depleted carbonate hardgrounds stacked carbonate slabs and moundlike carbonate buildups frequently 20 m relief barite along with carbonate has been found in areas where rapid flux of sediment carrying fluids has waned in the recent past and mineral rich brines are now being ejected crests chimneys and cones of these minerals are found in such settings both recent numerical simulations of fluid release from geopressured zones and direct observations at the sea floor support a pattern of episodic venting short term episodes of venting are probably regulated by fault movement perhaps controlled by local salt adjustment destabilization of gas hydrates by oceanographic processes also causes short term episodic gas expulsion these events occur with interannual to intra annual frequencies longer gas hydrate stabilization destabilization cycles in continental margin settings are forced by hydrostatic loading and unloading at the frequency of sea level change radiometric dating suggests that other long term episodes of venting and major venting expulsion events are also probably modulated by sea level change time scales of thousands of years in response to low stand sedimentary loading results of this summary of vent seep related phenomena suggest that sediment input from the shelf margin associated with cyclic plio pleistocene falling to low sea level periods followed by major listic fault and salt adjustments to a new sediment load have activated venting seepage throughout this period and perhaps longer

photonic dating of holocene back barrier coastal dunes northern north carolina usa abstract we have made the first application of luminescence sediment dating methods to coastal dunes from the barrier island system in north carolina as part of a larger study of the timing of activation and stabilization of coastal dunes of northern north carolina and southern virginia that employed ground penetrating radar trenching 14c dating and analysis of soils we applied photonic dating to seven samples from four sites jockeys ridge nags head woods penney hill and run hill we used fine sand sized potassium feldspar from the four samples with sufficient feldspar concentrations and quartz from all samples we applied the multi aliquot infrared stimulated luminescence thermal transfer correction additive dose add and the late light subtraction add methods to the feldspars we applied the single aliquot regenerative dose sar method with 470 nm stimulation to the quartz feldspar thermal transfer age estimates from 5 46 a year to 823 56 a 1 o are typically

seismic architecture stratigraphy and evolution of a subtropical marine embayment maputo bay mozambique abstract the seismic stratigraphy architecture and evolution of a large subtropical embayment maputo bay southern mozambique is described nine seismic units are documented and show repeated phases of incised valley formation and transgressive infilling trangressive infilling alternates between the classic wave dominated transgressive succession of fluvial and central estuarine bay deposits and the filling by intertidal flat and tidal bedforms developed during stages of inlet restriction and shallowing associated with barrier growth at stillstand intervals imprinted on the succession are several key facets of subtropical stratigraphy hurricane generated erosional surfaces and beachrock horizons the upper stratigraphy comprises the highstand bayhead delta a prograding feature constructed by several flood events in comparison with literature from other similar systems such as lagoons coastal lakes and estuaries a generic three stage stratigraphic model of large marine embayments is proposed that includes incision during glaciations transgressive infilling during deglaciations and shallowing during the stillstand episodes of the recent deglaciation

in situ cone penetration tests at the active dashgil mud volcano azerbaijan evidence for excess fluid pressure updoming and possible future violent eruption active mud volcanism is a global phenomenon that represents a natural hazard by self igniting eruptions and the continuous emission of methane gas in both marine and continental settings mud domes are often found in compressional tectonic settings such as the caucasus orogenic wedge dashgil mud volcano the most prominent of 200 features in azerbaijan has erupted vigorously in historic times for several years we have observed variations in the activity of dashgil dome including transients in methane flux build up of extrusive mud cones on the main feature and flexural polygonal cracks adjacent to the main crater lake and new mud cones in spring 2007 we carried out in situ cptu cone penetration testing with pore pressure measurement experiments in the crestal area of dashgil our data suggest that the central portion of the crater lake which hosts the conduit for gas and possible mud ascent shows both low sediment shear strength 5 20 kpa and excess pore fluid pressures between 15 and 30 kpa supra hydrostatic at 1 m sub bottom depth in situ cone resistance as a measure for undrained shear strength is as low as 150 kpa in the conduit whereas the mud is found rather stiff in all other testing locations 300 700 kpa probably a result of deeply buried shales of the maikop formation parts of which now liquefy and ascend pore pressure is low in the centre of the conduit probably because of rapidly migrating gas it increases to 30 kpa at the lake bottom and deep flank then decreases upslope on the lake flank and reaches hydrostatic values at the crater rim from the overpressured region beneath the fluid filled crest of dashgil dome combined with the other observations we suspect to currently witness an ongoing period of updoming the presence of sintered mudstones from explosive eruptions in 1908 and 1928 and most likely before suggests that a similar violent activity may occur in the near future

late quaternary sea level change in south africa abstract a late quaternary sea level curve for south africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations available evidence suggests that sea level in south africa broadly follows that described from the caribbean but that deviations occur during sea level highstands during the last interglaciation oxygen isotope stage 5 and the late holocene coastal emergence produced higher sea levels in south africa than those identified in the caribbean during the same time intervals this is tentatively ascribed to predicted lithospheric deformation in continental margin settings

9000 years of sea level change along the southern african coastline abstract beachrocks are good indicators of sea level stillstands on microtidal coastlines and data for this sea level curve is mainly based on dating a series of holocene beachrocks and planation episodes on the southeast african coastline sea level reached its present level along the southern african coastline at ca 6500 bp sea level then rose depositing a series of beachrocks at an elevation of 2 75 m this mid holocene sea level highstand persisted for a period of 2500 years with a 3 5 m stillstand dated at 4480 bp being the highest sea level reached during the holocene in post holocene sea level optimum times a regression occurred lowering sea level to its present level at 3880 bp and down to 2 m at approximately 3000 bp subsequently sea level rose to 1 5 m at 1610 bp and attained its present level at about 900 bp the mid holocene sea level highstand appears to have resulted from a combination of isostatic emergence and the steric expansion of seawater relating to warmer ocean temperatures associated with the holocene hypsithermal event on the eastern agulhas bank

the distribution of carbonate eolianite abstract carbonate eolianite forms distinctive coastal landforms on many mid latitude continents and islands numerous studies of extensive continental and smaller island deposits in both hemispheres have shown the eolianites are predominantly pleistocene in age the coorong coastal plain of south australia contains the world s longest record of eolianite deposition revealing that major phases of carbonate accumulation occurred during interglacial and some interstadial sea level highstands throughout the quaternary similarly the well studied eolianite islands of bermuda and the bahamas record a close match between dune accretion and sea level highstands since the middle pleistocene several other eolianite deposits appear to have formed at least partially during glacial periods the glacial age deposits are eolian reworked relict shelf or coastal sediments or remnants of former highly mobile coastal dunes sourced from low sea level shorelines the distribution and bioclastic composition of large scale eolianite deposits suggests carbonate production on shallow shelves and banks is the ultimate control on the formation of eolianite the bulk of the carbonate comprising those eolianites is heterozoan being produced where there is low terrigenous sediment input in dominantly temperate cool water and subtropical carbonate provinces quaternary cyclical movements of sea level have also controlled the form and rate of coastal carbonate deposition with repeated pulses of sedimentation during highstands forming laterally coalesced vertically stacked or composite dune successions major unconformities within the deposits are marked by paleosols which record hiatuses in coastal sedimentation in several regions major eolianite units overlie coastal deposits of terrigenous sediment those successions suggest that the trend towards aridity and reduction in the supply of terrigenous sediment to shelves during the quaternary has enhanced the production of carbonate and the deposition of eolianite

marine geology of the sodwana bay shelf southeast africa abstract the geostrophic current controlled northern zululand shelf displays a unique assemblage of interesting physical sedimentological and biological phenomena the shelf in this area is extremely narrow 3 km and is characterised by submarine canyons coral reefs and steep gradients on the continental slope three submarine canyons occur in the study area and are classified as mature or youthful phase canyons depending on the degree to which they breach the shelf these canyons originated as mass wasting features which were exploited by palaeo drainage during sea level regressions shelf lithology is dominated by a series of coast parallel patch coral reefs which have colonised beachrock and aeolianite sequences that extend semi continuously from 5 to 95 m and delineate late pleistocene palaeocoastline events the unconsolidated sediment on the shelf is either shelf sand mainly terrigenous quartz grains or bioclastic sediment large scale subaqueous dunes commonly form in the unconsolidated sediment on the outer shelf due to the agulhas current flow these dunes occur as two distinct fields at depths of 35 to 70 m the major sediment transport direction is towards the south but occasional bedload parting zones exist where the bedform migration direction changes from south to north

multiphase late quaternary aeolian sediment accumulation in western south africa timing and relationship to palaeoclimatic changes inferred from the marine record abstract extensive aeolian deposits exist along the western margin of south africa from cape town through to the namib sand sea and represent a significant palaeoenvironmental archive recording millennial scale patterns of regional and hemispheric environmental change to establish the timing of dune development this study applies optically stimulated luminescence osl dating techniques to the aeolian features of the west coast in total 35 samples were obtained from six dune cores along a north south transect extending from elands bay 32 26 s 18 14 e to kleinsee 29 14 s 16 59 e ages from these dunes exhibit five distinct peaks suggesting phases of activity deposition at 4 5 16 24 30 33 43 49 and 63 73 ka the spatial and temporal extent of the data have allowed for correlations to be made with evidence from marine cores from the southeast atlantic and a more coherent regional environmental history to be developed results suggest that 1 environmental changes in this region are strongly linked to variations in wind strength and atmospheric circulation systems during the late quaternary and 2 luminescence ages from aeolian deposits cannot necessarily be equated with periods of increased aridity with other factors such as wind strength and sediment supply being of critical importance

aeolianite and barrier dune construction spanning the last two glacial interglacial cycles from the southern cape coast south africa the southern cape region of south africa has extensive coastal aeolianites and barrier dunes whilst previously reported limited knowledge of their age has precluded an understanding of their relationship with the climatic and sea level fluctuations that have taken place during the late quaternary sedimentological and geomorphological studies combined with an optical dating programme reveal aeolianite development and barrier dune construction spanning at least the last two glacial interglacial cycles aeolianite deposition has occurred on the southern cape coast at ca 67 80 88 90 104 128 160 189 and 200 ka before the present using this and other published data coupled with a better understanding of late quaternary sea level fluctuations and palaeocoastline configurations it is concluded that these depositional phases appear to be controlled by interglacial and subsequent interstadial sea level high stands these marine transgressions and regressions allowed onshore carbonate rich sediment movement and subsequent aeolian reworking to occur at similar points in the landscape on a number of occasions the lack of carbonates in more recent dunes oxygen isotope stages 1 2 and 4 5 is attributed not to leaching but to changes to carbonate production in the sediment source area caused by increased terrigenous material and or changes in the balance between the warm agulhas and nutrient rich benguela ocean currents

climatic and sea level controls on late quaternary eolian activity on the agulhas plain south africa abstract located at the interface between the temperate westerly and sub tropical climate systems south africa s winter rainfall zone wrz is a key location in understanding late quaternary atmospheric circulation dynamics inactive eolian deposits in the wrz comprising pan fringing lunette and coastal dunes were investigated to establish their depositional ages and utility as paleoenvironmental indicators the resulting optical luminescence chronology reveals episodic lunette accretion at 60 000 45 000 yr 12 000 13 000 yr 2800 2600 yr 1200 yr and episodes of lunette and coastal dune accretion on the agulhas plain are temporally distinct reflecting differing fundamental controls on their activity comparisons to previously published data also reveal that the lunettes differ in age from more ancient coastal eolianites lunette deposition is asynchronous between locations reflecting the topographic and hydrological setting of the individual pans in near coastal settings with limited surface recharge lunette accretion appears to be at least partially controlled by sea level induced changes in groundwater levels those pans with more significant surface recharge particularly from fluvial systems may produce less ambiguous paleoenvironmental records with pan status more strongly reflecting regional hydrological conditions lunette orientation is indicative of strong westerly winds during both the pleistocene and holocene lunette accretion would have been promoted by reduced on shore moisture transport during the summer months enhancing rainfall seasonality such conditions would have been promoted by increased continentality as the agulhas bank was exposed during low sea level stands

correlated transient fluid pulsing and seismic tremor in the costa rica subduction zone continuous measurements of fluid flow were made over a six month period across the nicoya peninsula costa rica pacific convergent margin utilizing osmotically driven fluid flow meters designed to quantify both inflow and outflow rates on the order of 10 5 to 3 cm d significant transience in flow was observed through the surface of the forearc three periods of correlated flow signals were seen on the subduction forearc among three instruments located in the out of sequence thrust oost zone over along margin strike distances of 30 km amplitudes of ground velocity recorded on collocated ocean bottom seismometers obs increase during the three correlated flow events the seismic signal has frequency characteristics that resemble volcanic and non volcanic tremor we hypothesize that repeated plate boundary slow slip events potentially originating at the up dip limit of the seismogenic zone generate the observed signals within the toe of the forearc we propose a model in which the poro elastic stress strain field around a series of creep dislocations simultaneously forces flow through fracture networks in the forearc and oceanic basement rocks and induces diffuse flow through the shallow sediments the former generates the seismic tremor like noise recorded by the obss and the latter generates the flow transients recorded by the fluid flow meters we suggest that high sensitivity fluid flow meters can be utilized to detect transient tectonic strain events in offshore environments where traditional geodetic techniques lack resolution or are not possible d 2005 elsevier b v all rights reserved

holocene lakes from ramlat as sab atayn yemen illustrate the impact of monsoon activity in southern arabia abstract paleoecology and paleohydrology of the ramlat as sab atayn southern arabia are reconstructed from a comparative study including sedimentology mineralogy stable isotope ratios of carbonates and palynology of lacustrine sediments recovered from the al hawa depression the section dates from 8700 to 7200 yr b p and records an early phase of flooding followed by distinct lacustrine development from 7800 to 7200 yr b p coeval with maximum activity of the indian monsoon comparison of the pollen record with modern pollen deposition suggests that regional vegetation was then already of desert type and was related to strong seasonal trade winds

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

miocene tubular concretions in east coast basin new zealand analogue for the subsurface plumbing of cold seeps the uplifted accretionary prism of east coast basin in hikurangi margin north island new zealand exposes late miocene slope mudrocks whangaehu mudstone 10 carbonate in coastal cliffs north of cape turnagain that contain conspicuous tubular carbonate concretions 50 85 carbonate supporting near central conduits pipe and bulbous morphologies dominate ranging in exposed length up to 5 m and up to 1 m in diameter the concretions were formed by the precipitation of micritic dolomite and calcite cement within the host mudstone at shallow burial depths 100 m 13c values of the cement range from 22 to 13 pdb and are interpreted to reflect carbonate precipitation from either the extensive anaerobic oxidation of methane aom and or mixing of microbial methane and methanogenic co2 aom is confirmed by lipid biomarker evidence indicating that methane oxidation occurred in the sediments at the time of carbonate precipitation the mixed dolomite calcite mineralogies and the trend of 13c in the tubular concretions from strongly negative to strongly positive values are interpreted to reflect methane oxidation from the onset of ascent through to the end of a migration event depleted and enriched 18o values suggest an evolved fluid source influenced by the dissociation of gas hydrates collectively our results indicate that the tubular concretions within the upper slope mudstones delineate parts of the subsurface plumbing network of a cold seep system on the late miocene paleo hikurangi margin in which the fluids were sourced from ascending methane the intermediate location of the whangaehu concretions between older early miocene seep carbonates to the west and modern ones offshore to the east indicates a progressive eastwards shift with time of a long lived if only periodically active seep system the concretionary plumbing features at whangaehu provide a conceptual model for subsurface fluid pathways and seep related processes beneath the modern hikurangi margin seabed and possibly also for other modern and ancient cold seep carbonate systems

luminescence dating of interglacial coastal depositional systems recent developments and future avenues of research abstract luminescence dating offers new opportunities to explore the evolution of quaternary marine coastal facies and landforms this review highlights the main advances in luminescence geochronology of interglacial coastal sediments through the analysis of 547 luminescence ages most of which were published during the last decade the majority of these reported luminescence investigations have been carried out along passive margin coasts since the turn of the century the discovery of a normalization procedure known as single aliquot regeneration sar has drastically reduced data scatter and improved precision with the consequence that quartz sar optically stimulated luminescence osl has become the dating protocol of choice for the last interglacial lig period a more complex technique known as thermally transferred osl tt osl is presumably proposed for dating older interglacials of the mid pleistocene and beyond feldspar luminescence is increasingly being applied to dating pleistocene sea level high stands due to a much higher dose saturation level than quartz osl the use of feldspar irsl infrared stimulated luminescence is limited by the occurrence of variable but ubiquitous anomalous fading af following the advent of af correction methods several middle pleistocene sites have been amenable to dating albeit with significant related uncertainties recently new protocols involving the measurement of post ir irsl at elevated temperatures have yielded relatively coherent ages for interglacial sediments up to ca 300 ka quartz osl tt osl af corrected irsl and post ir irsl ages are generally correlated with periods of sea level high stands a few ages are reported from the early and middle part of the middle pleistocene as mis11 9 and more commonly mis7 high stands are documented in strongly uplifting active margin coasts however by far the most obvious age peak corresponds to the end of the lig the mis5e shoreline is probably the most studied and luminescence dated coastal feature of all as the chronology of the sea level markers is crucial to assess global eustatic sea level variations through the course of the last interglacial nevertheless the observed abundance of young 100 120 ka luminescence ages for presumed mis5e sediments may underline methodological issues and or reflect the higher preservation potential of late regressive sequences on the other hand the occurrence of geographically distant reports of mis5a high stand might reflect a true eustatic origin for this event age analysis supports the impression of general reliability of luminescence for the timing of former sea level high stands there is a clear need to address issues in dose rate variability in the phenomenology of fading in feldspar and in the behaviour of luminescence growth with dose both in laboratory and natural conditions these could be addressed and properly evaluated by dating different minerals as multiple or single grains with consequent variable internal dose rates more robust practices in the application of luminescence dating techniques could eventually constrain the age uncertainties to no better than 2 3 therefore the strength of luminescence as a dating tool is more in terms of its extended age range and the ubiquity of datable material

sedimentological characteristics and morphology of the aeolian sand dunes in the eastern part of the uae a case study from ar rub al khali abstract the umm az zimul al wijan area is located in the southeastern part of the uae and covers about 1600 km 2 it is bounded to the east by the oman mountains and to the south and west by the extensive dune area of ar rub al khali field investigation revealed the common occurrence of parallel to sub parallel sand ridges with a general east west orientation also present but less frequent are barchan barchanoid and star dunes interdune areas are classified into four types that include dolomite mixed ancient sabkha and ophiolitic rock fragments mixed sand sheet and ophiolitic rock fragments and recent sabkha the textural characteristics of the sand forming the dunes are unimodal with a modal class in fine sand size moderately to very well sorted positively skewed and mesokurtic quartz grains are mainly subrounded to subangular the similarity in roundness properties in different dune types in the eastern province of the uae seems not to be influenced by dune form based on the heavy mineral suites and the angularity of quartz grains it is believed that the sand sediments are mostly derived from the ultrabasic rocks forming the ophiolitic sequence of the oman mountains acidic rocks of iran and from the coastal area

a 160 000 year record of dune development and atmospheric circulation in southern arabia aeolian deposits in the wahiba sands sultanate of oman reveal patterns of atmospheric circulation over the past 160 000 years luminescence dating indicates a correlation of dune activity with periods of low global sea level and decreased monsoon intensity evidence from dune orientation and sedimentary structures shows exclusively northbound transport of sand during times of high latitude glaciation these results are in contrast to the current paleocirculation model that assumes an increase of northwesterly winds because of a southward shift of the intertropical convergence zone our results indicate that the circulation pattern during glacial times was comparable to that of the present

optically stimulated luminescence dating of a danish eemian coastal marine deposit a test of accuracy abstract it is difficult to test convincingly luminescence dating techniques beyond the range of 14c and yet this is essential if claims that optically stimulated luminescence dating using quartz can reach back to beyond 105 years are to be given credence one possible approach is to use coastal marine sand identified as eemian by an examination of the palaeoecology the eemian period in northern europe is considered to last from 132 to 116 ka marine samples are likely to be linked most closely to at least part of this period and modern coastal sands are known to be well bleached thus from a luminescence dating perspective eemian marine sand can be considered to be of known age and it is very likely to be well bleached we have examined such a known age deposit on the east coast of jutland consisting of about 10 m of fine sand grading up from silty clays and clays in the lower part of the section this material is confidently expected to have been deposited during the very late saalian and early mid eemian 133 125 ka we report on the ages of 25 samples associated with this profile the observed overall precision is compared with the calculated precision on individual ages and the mean value of all the ages is compared with the expected mean of 130 ka

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

an experimental setup for fluid venting in unconsolidated sediments new insights to fluid mechanics and structures abstract focused outflow of water at the seafloor termed seepage or fluid venting is a widely recognized global phenomenon in an effort to better understand the mechanisms by which fluid flow related structures form we performed laboratory seepage experiments using samples representing a broad range of grain sizes and hydraulic conductivities 10e 3 to 10e 7 m s detailed observations led to the recognition of a typical often repeated progression of fluid flow structures that form during processes of increasing and decreasing hydraulic gradients the development of fluid flow structures like macro pores conduits and pipes is strongly dependant upon cohesion but is unrelated to grain size variations from sample to sample partial liquefaction leads to permanent changes in the grain fabric and to an increase in hydraulic conductivity our observations explain the longevity of seep sites and systematic relationships between hydraulic gradients grain fabric appearance and hydraulic conductivity that could be used to estimate flow rates based on structural findings

new quartz sar osl ages from the stranded beach dune sequence in south east south australia a sequence of stranded coastal barriers in south east south australia preserves a record of sea level variations over the past 800 ka huntley et al quat sci rev 12 1993a 1 quat sci rev 13 1994a 201 attempted to test thermoluminescence tl dating methods and found good agreement between quartz tl ages with independent ages for these dunes we investigate the accuracy of the single aliquot regenerative dose sar procedure radiat meas 32 2000 57 over an extended age range of 0 250 ka by comparing sar osl ages determined on quartz extracts from these dunes with the existing chronology we show that robe ii range is 60 ka and that robe iii is 100 ka old not surprisingly the osl ages increase monotonically from the robe ii range to the west naracoorte range for the younger dunes 240 ka the sar osl ages agree with the expected ages within 1 errors whereas for the older dunes the sar ages are consistent with independent ages within 2 error limits we consider these results to be very promising and lend support to the large number of quartz sar osl ages being presented in the literature where such comparisons with independent chronology are not usually possible

the evolution of coastal barrier systems a case study of the middle late pleistocene wilderness barriers south africa abstract barrier systems contain lengthy but complex records of long term environmental fluctuations the wilderness embayment south africa contains a system of shore parallel barriers reaching up to 200 m above modern sea level this study reports the results of chronological topographical both on and off shore sedimentological and micromorphological analyses within the wilderness embayment sixty one new luminescence ages from sixteen sites in unconsolidated dunes and three separate barriers are presented which when combined with previously published luminescence ages from the area provide a high resolution chronological framework for the emplacement and evolution of the barrier system the preserved barriers have been constructed within at least the last two glacial interglacial cycles with notable phases between 241 221 ka 159 143 ka 130 120 ka 92 87 ka and post 6 ka multiple phases of barrier construction occurred during sea level highstands with sediment deposition on each individual barrier occurring over at least two interglacials holocene evolution of the system sheds light on earlier events with dune preservation occurring only during early regression from the mid holocene highstand tectonic stability at wilderness allowed glacio eustatically formed shorelines to occupy similar positions on multiple occasions this in conjunction with a relatively humid climate and a well vegetated landscape enabled deflated sediment from beaches to form dunes which stacked upon each other to form an extensive and complex vertical accretionary sequence repeated erosion and recycling of pre existing barriers as well as barrier construction on what is currently the off shore platform during still stands in sea level regressional cycles when sea levels dropped below ca 50 m from the present day has added to the complexity of the preserved terrestrial barrier record the wilderness barrier system contrasts with barriers developed elsewhere in the world where higher rates of crustal uplift have allowed preservation of a more complete and more widely spaced palaeorecord this research also shows the utility of integrating off shore topography as revealed by bathymetry with terrestrial topographic data for the better understanding of the evolution of palaeo coastlines and the preserved dune record found on present day coastal plains local variation in the topography of the continental shelf at wilderness has generated spatial and temporal complexity within the sedimentary records of individual barriers as well as having a significant influence on preservation

the age of the koputaroa dunes southwest north island new zealand abstract four recent dune phases have previously been identified in the manawatu and horowhenua regions of southwest north island new zealand the oldest of these dune phases the koputaroa dunes occur over a restricted area near the town of levin previous estimates of the age of these dunes have largely been based upon the occurrence of aokautere ash an airfall member of the kawakawa tephra ca 22 14 c ka b p interbedded within the dune sands nine samples of koputaroa dune sand were collected from five sites and dated using infrared stimulated luminescence irsl the results suggest that the dunes were originally deposited at or before 40 50 ka and that they were then re mobilised in the period from 24 to 10 ka these periods of dune activity are compared with records of loess deposition in wanganui basin aeolian influx of quartz in taranaki and dust flux in the vostok ice core

evolution of an incised valley coastal plain estuary under low sediment supply a give up estuary the literature on incised river valley sedimentology is dominated by studies of sediment rich systems in which the valley has been filled during and or shortly after drowning in contrast the holocene evolution of the kosi lagoon south africa an incised coastal plain river valley took place under very low sedimentation rates which have produced a distinctive stratigraphy and contemporary sedimentary environments the findings are based on a synthesis of the results of studies of seismic stratigraphy sediment distribution morphodynamics and geomorphology barrier migration was prevented by a high pre holocene dune barrier against which holocene coastal deposits accumulated in an aggradational sequence holocene evolution of the back barrier involved i drowning of the incised valley ii wave induced modification of the back barrier shoreline leading to segmentation during the highstand and iii marine sedimentation adjacent to the tidal inlet segmentation has divided the estuary into a series of geochemically and sedimentologically distinctive basins connected by channels in the estuarine barriers the seismic stratigraphy of the back barrier essentially lacks a transgressive systems tract shoreline modification and deposition having been accomplished during the highstand the lack of historical geomorphological change suggests that the system has achieved morphological equilibrium with ambient energy conditions and low sediment supply this study presents a classification for estuarine incised valley fills based on the balance between sea level rise and sedimentation in which kosi represents a give up estuary where much of the relict incised channel form is drowned and preserved it exhibits a fundamentally different set of evolutionary processes and stratigraphic sequences to those of the better known incised valley systems in which sedimentation either keeps pace with sea level keep up estuaries or occurs after initial drowning catch up estuaries

seasonal control on coastal dune morphostratigraphy under a monsoon climate mui ne dunefield se vietnam abstract having developed in the later quaternary period the mui ne dunefield representing the upper most portion of a major coastal barrier complex in se vietnam formed by wind regimes associated with the asian monsoon climate the barrier complex is 100 km long and higher than 150 m in elevation but despite its large dimensions research on its geomorphological and geological characterization is limited several active dune fields extend 2 10 km landwards from the coast while the rest of the barrier surface is stabilized we applied ground penetrating radar gpr and quartz optically stimulated luminescence osl dating to the transverse dunes of the mui ne dunefield to characterize the morphostratigraphy and recent aeolian sedimentation history currently the dunes have a relief of typically 5 10 m and a wavelength of 50 100 m they are driven by the northeasterly winter monsoon winds and reversed with minor relief in response to the southwesterly summer monsoon gpr profiles and osl ages define three morphostratigraphic units the modern holocene and pleistocene dune units the gpr data of the modern dune unit is dominated by a series of steep reflections that dip exclusively towards the west reflecting the winter monsoon and is punctuated by reactivation surfaces evidence for the wind reversal is not preserved in the sediment successions but is represented by reactivation surfaces thus a subunit bounded by the reactivation surfaces defines annual deposition the preservation potential of a subunit varies with the migration rate of the transverse dune and in the fastest migrating dunes approximately one subunit was preserved every year 1 1 0 6 subunit yr the modern dunes are generally younger than 100 years and have migrated wsw at net rates of 0 6 2 5 m yr the holocene dune unit is as thick as the modern unit although it spans a period ten times longer reflecting the lower preservation potential of the transverse dunes as sedimentary records due to erosion associated with their migration the rate of dune migration suggests that an aeolian contribution of coastal sands has occurred following the sea level highstand of the middle holocene accounting for the extent of the active dunefields this mode of the barrier accumulation is considered as an analogue for earlier highstand events however the dunefields only cover a fraction of the entire barrier it is thus inferred that barrier formation occurred over a long period probably encompassing several glacial interglacial cycles sand accumulation during the lowstand either by transport of sand from the subaerially exposed shelf and or reworking of sand emplaced during the prior highstand may contribute significantly to the barrier development

luminescence based dune chronologies in southern africa analysis and interpretation of dune database records across the subcontinent abstract over 600 luminescence ages have to date been published from southern africa s continental dunefields and isolated dunes providing a rich record of aeolian system dynamics during the late quaternary the majority of records come from sites within the five linear dune dominated dunefields of the kalahari with lesser representation of other major dune areas including the namib and west coast dunefields and of other dune types including lunettes and transverse forms dune database records are analysed not only in terms of the evidence they provide for late quaternary environmental changes over the last 190 ka the purpose for which most ages have been produced but in terms of the analytical techniques used data quality and data presentation as these all impact on how dune luminescence ages have been or should be interpreted as a tool for palaeoenvironmental and dune development studies it is concluded that even despite the number of dated dune records from southern africa there is a marked spatial unevenness within and between dunefields in the data available for assessing dune depositional ages and conditions however this is not a situation that can simply be improved upon by adding more and more ages to the full set of records it is both necessary to appreciate the spatial differences in dune sensitivities to activation and relationships to potential changes in hydrological and other activity controls and to establish better tools and approaches for analysing a rich but presently environmentally ambiguous record of dune accumulation

temporal patterns of arid humid transitions in the south eastern arabian peninsula based on optical dating abstract the rub al khali aeolian system of the arabian peninsula is the world s largest erg while the region is presently hyper arid evidence for multiple past humid periods has been documented in previous studies radiocarbon dating of lacustrine travertine and palaeogroundwater deposits suggests that the climate was humid at 10 6 and 35 25 ka these phases have been associated with summer rainfall increases occurring in tandem with an intensification and northward migration of the monsoon system during northern hemisphere precessional maxima published optical dating studies have focused on preserved sand dune and aeolianite deposits to establish ages for the intervening arid phases here we present a summary of this work and additional optical dating results for samples of aeolian sediment from a deep drill core which provides insights into the style of barchan dune accretion in the liwa region of the united arab emirates the large dune accreted rapidly during the mid late holocene the results suggest that the transitions from humid to arid conditions and resulting accumulation of aeolian sediment in the form of large bedforms occurred abruptly at around 6 ka further aeolian sedimentation has not been constant since that time with initial gradual dune growth followed by rapid vertical accretion and possible termination of accumulation around c 2 ka

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

the nature and possible origin of mega dunes in liwa ar rub al khali uae abstract the liwa area is located in the south central part of the uae along the northeastern upwind margin of the ar rub al khali sand sea and covers about 3694 km 2 it has one type of dunes a mega barchan that is compound and complex in form characterized by the superimposition of smaller dunes due to the giant size of barchans interdune areas appear as closed depressions that vary in shape from irregular elongate triangular to circular or semi circular these depressions are mostly covered with small barchans or sabkha deposits with patches of gypcrete in their upper parts scattered flat top mounds are also observed in interdune areas the size of dunes in liwa is directly controlled by quaternary climatic changes multiple generations are superimposed on one another separated by calcretic horizons the climate during dune formation alternated between relatively arid to humid the dune sands are unimodal with a modal class of fine sand moderately to very well sorted and near symmetrical and mesokurtic quartz grains are mainly subrounded to subangular based on the heavy mineral suites the sand came mostly from the ultrabasic rocks that form the ophiolitic sequence of the oman mountains the acidic rocks of iran and from the arabian shield

sluggish and steady focussed flows through fine grained sediments the methane derived cylindrical concretions of the tertiary piedmont basin nw italy abstract in the cenozoic succession of the tertiary piedmont basin nw italy a wide array of methane derived carbonate rocks including both seafloor and sub seafloor products have been reported in the last decades the most intriguing features are cylindrical concretions more than 1 m long and around 10 cm across that were found within fine grained sediments of messinian age in their original stratigraphic position crossing the bedding planes at high angles these concretions result from cementation of the host muddy sediments by intergranular dolomite microcrystals and lack any evidence of exposure at the sea floor their c and o stable isotope signature suggests that dolomite precipitation was induced by anaerobic oxidation of methane possibly sourced by gas hydrate destabilization such cylindrical morphologies are interpreted as the result of carbonate precipitation and cementation of the sediments around fluid conduits and record a relatively long period of steady sluggish flux of methane rich fluids that opened their way rising up through fine grained unconsolidated sediments they formed immediately below the sea floor in a narrow horizon bracketed between the sulphate methane interface and the oxic anoxic interface cylindrical concretions represent only the highest part of pipes through which methane rich fluids flowed up the deeper part of the conduits conversely left no trace in the stratigraphic record because of the lack of chemical microbiological conditions favourable for carbonate precipitation

formation of danube delta beach ridge plains and signatures in morphology abstract danube delta as most of the large deltas favours complex interactions between river sediment supply and marine dispersing forces which create complex configurations with concurrent morphologies i e river versus wave influenced or processes accretion versus erosion and even distinct landscapes for the same accretionary features strandplains with low monotonous beach ridges or covered by transgressive dunefields beach ridge plains brps are a common feature of the wave influenced deltaic lobes that are created by juxtaposition of succesive berms on the prograding sandy coasts with different shapes and sizes depending on the accretionary mechanisms and the accomodation space this study reports the formation and dynamics of danube delta brps based on numerical age determination osl and ams of the paleoshorelines topographic and geophysical gpr surveys and stratigraphic records by cores a chronological framework is established for all deltaic brps which points to the importance of formation timespan and growth rate as a consequence of sediment supply on the resultant morphology varying inter site from small brp formation time

optically stimulated luminescence osl dating of loessic sediments and cemented scree in northwest england optically stimulated luminescence osl dates are reported for silts and very fine sands believed to be loessic sediments from northwest england at three sites loessic sediments were initially interpreted as primary aeolian deposits and at two other sites as loess incorporated into the matrix of cemented scree however the results of osl dating indicate a more complex pattern of accumulation than originally hypothesized and have prompted reconsideration of these materials whatever the process es and underlying cause s it is evident that significant amounts of soil erosion occurred on the limestone uplands earlier than previously thought all but one of the ages fall entirely within the holocene period and suggest that these deposits contain reworked rather than primary loess four of the five sites are characterized by non gaussian dose distributions and consequently equivalent doses have been estimated using a range of appropriate age models the implications of differences in the ages derived f

response of wave dominated and mixed energy barriers to storms wave dominated and mixed energy barriers are extremely dynamic landforms responding to processes operating over a spectrum of time scales ranging from daily to monthly fluctuations related to storm and post storm conditions to century to millennium scale evolution driven by relative sea level change two types of storms are of particular relevance warm core tropical and cold core extratropical cyclones both are responsible for generating very large waves highly energetic surf zone dynamics and sediment transport elevated inshore water levels and extensive morphological responses all cyclones are affected by climate change which governs their frequency intensity and tracks barrier storm response is primarily governed by maximum storm runup and barrier morphology as conceptualised in abby sallenger s storm impact scale model sallenger 2000 this model defines four storm impact regimes and includes erosive as well as accretionary responses on the erosion side the swash regime drives bar and berm flattening the collision regime is marked by dune scarping and beach lowe the overwash regime leads to dune scouring and channel incision and the inundation regime may result in barrier destruction on the deposition side storm berms and beach ridges may form and accrete in the swash and collision regimes localised vertical beach and barrier accretion are associated with the collision and overwash regimes and washover deposition takes place in the overwash and inundation regimes site specific factors play a key role in moderating the morphological response and include storm characteristics type duration and track longshore sediment supply upwelling downwelling currents coastal setting and inner shelf topography the response of a barrier to a tropical or extratropical cyclone can however not be considered in isolation and has to be appreciated in a longer temporal context involving morphological preconditioning due to antecedent wave and water level conditions additionally a simple process response approach of the cause and effect type is inappropriate and a more complex conceptual framework involving thresholds feedbacks resilience and vulnerability will need to be adopted a useful way to visualise and conceptualise more complex storm behaviours and the longer term vulnerability of barriers is the resilience trajectory which maps out the changes in barrier geometry elevation and width over various time scales from weeks to years or even longer and under varying forcing conditions including changes in storminess and sea level rise an increased understanding of barrier response to storms and sequences of storms is required to better quantify long term barrier response to climate change high resolution and comprehensive decadal records of barrier response to storms are a prerequisite to achieve this ambition linking site specific coastal settings hydrodynamic drivers and morphological responses and allowing the recognition of recovery and impact dominated phases the enhanced insights in barrier response to extreme events must then be incorporated into improved coastal response models to help predict the impacts of future climate change on wave dominated and mixed energy barriers around the world 2013 elsevier b v

soft sediment deformation structures in nw germany caused by late pleistocene seismicity new data on seismically triggered soft sediment deformation structures in pleniglacial to late glacial alluvial fan and aeolian sand sheet deposits of the upper senne area link this soft sediment deformation directly to earthquakes generated along the osning thrust which is one of the major fault systems in central europe soft sediment deformation structures include a complex fault and fold pattern clastic dikes sand volcanoes sills irregular intrusive sedimentary bodies flame structures and ball and pillow structures the style of soft sediment deformation will be discussed with respect to brittle failure liquefaction and fluidization processes and was controlled by 1 the magnitude of the earthquake and 2 the permeability tensile strength and flexural resistance of the alluvial and aeolian sediments it is the first time in northern germany that fluidization and liquefaction features can be directly related to a fault the occurrence of seismicity in the late pleistocene and in the seventeenth century indicates ongoing crustal movements along the osning thrust and sheds new light on the seismic activity of northern germany the late pleistocene earthquake probably occurred between 15 9 1 6 and 13 1 1 5 ka the association of soft sediment deformation structures implies that it had a magnitude of at least 5 5

the late cenozoic evolution of coastal water bodies in northern kwazulu natal south africa abstract three large coastal water bodies st lucia sibaya and kosi of markedly different contemporary morphology occur on the eastern margin of the northern kwazulu natal coastal plain south africa this paper examines their late cenozoic evolution and investigates the controls on their evolution that have produced the observed differences in morphology all three systems origins were due to mio pliocene low sea level still stands allowing rivers to scour channels into cretaceous and palaeocene sedimentary sequences during the last interglacial oxygen isotope stage 5e sea level was approximately 5 m above present level and the morphology of the three systems was similar an offshore barrier archipelago partially isolated a back barrier environment that comprised intertidal sand flats localised reefs and tidal channels the area around bazaruto island mozambique provides a modern analogy river rejuvenation and associated incision up to and during the last glacial maximum 16 000 18 000 bp caused a minimum of 40 m scour which is still reflected in the bathymetry of lake sibaya and kosi accumulation of barrier sands partly against pre existing interglacial barrier remnants during the holocene marine transgression 16 000 4500 bp ramsay p j 1995 9000 years of sea level change along the south african coastline quaternary int 27 1 5 was responsible for lagoon isolation although the extent and nature of separation from the sea varies markedly between the systems the northern part of lake st lucia was closed from the sea during the late holocene probably during a sea level fall from a holocene high stand of ca 3 m at 3000 bp the kosi system had a late pleistocene to early holocene outlet situated at bhanga nek lake nhlange but this inlet mouth closed approximately at 3000 bp the present mouth was established by 1600 bp lagoonal conditions within lake sibaya terminated ca 5000 bp when coastal barrier dune formation caused complete impoundment and enabled the lake water level to rise to 20 m above mean sea level lake st lucia s large catchment has meant that fluvial sediment input has kept pace with the holocene transgression whereas the localised drainage associated with sibaya and kosi has resulted in a negligible fluvial sediment input allowing for deep lacustrine conditions to develop lagoonal segmentation is present to some extent in each system as a result of mobile coastal sediments and their reworking by short period wind waves the differential stages of lagoonal segmentation in the three systems can be explained by a the presence of cohesive sediment and bedrock around st lucia which reduce shoreline mobility and b the great water depths in sibaya compared to kosi which require longer periods of infilling before segmentation is complete

fossil seep structures of the monterey bay region and tectonic structural controls on fluid flow in an active transform margin abstract the subsurface plumbing system of ancient seeps of hydrocarbon rich gases and fluids is partially preserved by seep deposits in miocene rocks of the coast ranges and on the seafloor of the monterey bay region in central california the fossil seep related deposits are of two types authigenic carbonates and intrusions of oil saturated sandstones both types occur in fractured and faulted siliceous mudstone and porcelanite layers of the organic rich miocene santa cruz mudstone they are associated with tectonic structures indicating deformation and are located in the proximity of faults the morphology of the seep carbonates is characterized by strong asymmetries and by holes pipes and other types of fluid conduits with orientations parallel to the directions of the local fracture and fault sets thus suggesting structural control over pathways of fluid migration the dominant direction of the conduits in the seep carbonates and of the intrusive dikes northeast southwest differs from the dominant orientation of the tectonic structures of the san andreas fault system northwest southeast previous interpretations of these ancient seep related deposits suggested that lateral changes of the thickness of the cenozoic marine host sediments favored fluid migration from basin depocenters located offshore toward basin margins different driving forces for fluids have been hypothesized including hydrocarbon generation differential compaction and tectonic compression most of the fossil seeps are located on structural highs of the basement and adjacent to offshore basins that form elongated depressions oriented northwest southeast previously unidentified structures that offset the basement along northeast southwest trends cross setting faults paralleling the orientations of the conduits of the seep carbonates and the dikes of oil saturated sandstones were also recognized tectonic deformation block rotations documented by local clockwise rotations of paleomagnetic directions in the coastal ranges and cross faults were probably produced during the late miocene and pliocene to accommodate the shear stress between conjugate faults during eastward shifting of the activity of the san andreas fault system comparison with previous studies on ancient seep deposits regional geology and offshore tectonic data suggest that the fluids that sourced the seeps were driven by episodes of inverse tectonics during which previously extensional depositional basins were involved in episodes of tectonic compression tectonic deformation created cross faults in rotated blocks which could have acted as important conduits for the flow of hydrocarbon rich fluids and gases and fostered the injection of liquefied sands

vast fields of hydrocarbon derived carbonate chimneys related to the accretionary wedge olistostrome of the gulf of cadiz we report the first discovery and sampling of vast fields of hydrocarbon derived carbonate chimneys along the gulf of cadiz continental slope at depths between 500 and 1200 m a large variety of carbonate chimneys more than 200 samples were recovered from four different areas named the diasom tasyo gbf guadalquivir basin and esf east moroccan fields observations from an underwater camera revealed a spectacular high density of pipe like chimneys some of them longer than 2 m lying over the sea floor and some protruding from muddy sediment local fissures and alignment of isolated chimneys were also observed suggesting that their distribution is controlled by fault planes chimneys collected show a wide range of morphological types spiral cylindrical conical mushroom like and mounded with numerous nodule protuberances and ramified fluid channelways the chimneys are mainly composed of authigenic carbonates ankerite fe bearing dolomite and calcite with abundance of iron oxides forming agglomerates of pseudo pyrite framboids n 18 o isotopic values vary from 0 7 to 5 5x whereas n 13 c values indicate that chimney carbonates are moderately depleted in 13 c ranging from 346x to 320x pdb interpreted as formed from a mixture of deep thermogenic hydrocarbons and shallow biogenic methane these vast fields of carbonate chimneys imply new considerations on the importance of hydrocarbon fluid venting in the gulf of cadiz and moreover on the active role of the olistostrome accretionary wedge of the gibraltar arc b 2003 elsevier science b v all rights reserved

porosity and packing of holocene river dune and beach sands the porosity and packing of 174 samples of surficial and shallowly buried to 17 m unconsolidated holocene sands medium to coarse grained were determined by point counting the upper surface of thin sections of epoxy impregnated samples in reflected light average depositional porosity for 124 surficial sands from beaches river point bars and braid bars and eolian dunes respectively is 47 48 and 49 the porosity values range between 40 and 58 beach sands exhibit an average packing value ci contact index of 0 79 fluvial sands an average ci of 0 91 and eolian sands an average ci of 1 02 beach sands typically contain 5 5 oversized pores river sands 3 8 oversized pores and eolian dune sands 4 0 oversized pores most oversized pores are depositional packing defects although trapped air bubbles are common in some beach sands extrapolation of our data for buried samples indicates depositional oversized pores are destroyed at a depth of less than 100 m average porosity is 46 for eolian ripple strata 50 for grain fall strata and 51 for grain flow strata differences in packing are significant for grain flow versus grain fall strata and for ripple versus grain flow strata for samples of similar grain size porosity is more uniform within individual beds from a river and a beach than among different beds at the same localities porosity of ancient sandstones from a particular bed or facies may be as uniform as sampled holocene sands unless cements having patchy distribution such as carbonate or anhydrite are present compaction associated with burial to 17 m is minor packing is tighter but our technique of measuring porosity is not sensitive enough to show any decrease in porosity changes in packing and porosity upon burial to common hydrocarbon reservoir depths will depend on individual histories of cementation compaction and secondary porosity development however if only physical compaction of quartzose river dune and beach sands takes place porosity would approach a limiting value of 26 and ci would approach 5 5

evidence for dune reactivation from gpr profiles on the maputaland coastal plain south africa the maputaland area of northeastern south africa is characterized by extensive dune fields which developed during polyphase reworking of regional aeolian cover sand from the mid pleistocene to the holocene extended parabolic dunes many preserved only as wind rift trailing limbs as well as areas of sinuous crested dunes hummocky dune systems and the high composite accretionary coastal barrier dune cordon are the dominant dune forms there are few natural sections exposing the stratigraphic succession and unequivocal relative age relationships between dune systems are uncommon a ground penetrating radar gpr survey of dunes and representative aeolian sand stratigraphic units was undertaken in order to investigate the internal structure of the different dune forms and identify stratigraphic relationships between buried sedimentary units the gpr profiles revealed that the trailing limbs of almost all the parabolic dunes that were surveyed comprise stacked sand units separated by low angle reflections interpreted as bounding surfaces which accumulated through polyphase vertical accretion most extended parabolic dunes are aligned north south and the upper parts of the dunes are characterized by inclined reflections in gpr profile interpreted as large scale sets of cross stratification with apparent dips toward the west a hummocky dune revealed cross stratified aeolian sand superimposed on a truncated dune form and probably formed through deflation of pre existing dunes using 100 mhz and 200 mhz antennae it is clear that gpr is capable of imaging very fine sedimentary structures and buried erosional surfaces in the homogeneous aeolian sand of maputaland at some of the sites investigated the buried sand units identified were sampled by hand augering for infrared stimulated luminescence dating the age determinations on these samples suggest that vertical accretion of up to 7 m of sand occurred intermittently over variable time scales up to 25 000 years on some parabolic dune limbs during the late pleistocene in some complex dunefields adjacent dunes were mobilized at different times suggesting that remobilization was localized the implications of the complex internal structure and vertical accretion of extended parabolic dunes are discussed in the context of changes in vegetation cover and water table due to seasonal and short term cyclical climate variations as well as long term climate change patterns during the last glacial cycle and the holocene

the luminescence chronology of dune development on the maputaland coastal plain southeast africa abstract geomorphological and lithostratigraphic mapping of dune systems on the maputaland coastal plain of northeastern kwazulu natal province south africa has defined the relative age relationships between the complex pattern of quaternary parabolic and hummocky dunes sand megaridges and the composite coastal barrier dune cordon here infra red stimulated luminescence irsl ages are presented in the context of regional stratigraphic relationships and serve to bracket the period of accumulation of the main dune systems the luminescence ages challenge the widely held belief that the north south aligned dune pattern reflects a coastward younging sequence the framework of ages highlights the spatial variations in dune mobilization and long accretion history on some dune forms weathered dune and interdune wetland sediments spanning from prior to marine isotope stages mis 11 and up to mis 7 underlie the coastal plain at least two generations of decalcified aeolianite of mis 5 and 4 form the core of the complex coastal barrier dune on the coastal plain frequent sand mobilization events during mis 3 2 resulted in the development of discrete complexes of highly extended northward directed parabolic dune systems and reworking of the crest of the central sand megaridge the luminescence dated dune mobilization history brackets the period of formation of interdune and lacustrine peat and diatomite deposits during the holocene marine transgression at least four laterally extensive complex transverse ridges of coalesced ascending parabolic dunes accreted against the aeolianite core of the coastal barrier polyphase dune formation and remobilization is discussed in the context of the regional groundwater and vegetation responses to global climatic changes wind regimes and glacio eustatic sea level fluctuations

optically stimulated luminescence dating of young sediments a review optically stimulated luminescence osl dating of young 1000 years sediments is used increasingly in a wide variety of late holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition this paper provides a summary of the basic principles of osl dating outlines the problems specific to the dating of young material and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits the overall reliability of this new generation of osl ages is examined by comparing where possible osl ages with independent age control it is concluded that the osl ages are accurate in that there is no evidence for systematic over or under estimation it is our conclusion that osl dating should be regarded as a reliable chronological tool for determining the time of deposition of water lain sediments from the coastal zone and aeolian deposits from both coastal and inland environments our conclusion is supported by the growing popularity of osl dating in geomorphology and geology

how wet is wet precipitation constraints on late quaternary climate in the southern arabian peninsula it is generally recognized that the southern arabian peninsula has had two wet periods in the late quaternary to quantify wet a 28 000 year old capillary surface associated with a paleowater table was mapped and used as a surrogate for the water table in a ground water model analysis of this model suggests 1 4 mm year 1 of recharge is necessary to support the water table at the mapped elevations during the wet period climatic relations between rainfall and recharge in arid areas infer that annual rainfall during this wet period was approximately 200 50 mm year 1 or approximately five times the present rate

complex flow patterns through hydrate ridge and their impact on seep biota our recent measurements of long term fluid flux rates and output fluid chemistry at seep sites on hydrate ridge cascadia suggest that the mechanisms driving fluid flow in gas hydrate bearing forearc settings may be significantly more complex than previously thought temporal changes in the polarity and magnitude of flow and in seep fluid chemistry were observed the nature of flow appears to generate a strong response in the chemosynthetic seep community ecology we document here 1 the frequency and range of temporal variability in flow rates 2 the relatively rapid changes in outflow composition 3 strong outflow of seawater like fluids 4 the association of calyptogena sp clams with oscillatory and inflow settings and 5 microbial mat communities associated with strong advection of altered fluids these results suggest that a reappraisal may be required of the nature of the hydrologic system and its effect on related processes such as benthic seep community ecology and biogeochemical cycles

morphology dynamics and internal stratification of some established foredunes in southeast australia abstract foredunes are shore parallel dunes formed by aeolian deposition within vegetation modern established foredunes are classified into five morphologic stages and the morphologies and processes of each is described stage 1 foredunes are well vegetated symmetric stable ridges characterised by stoss face and crest deposition stage 2 foredunes display minor erosional patches 75 90 vegetation cover and slight lateral variation in deposition and erosion stage 3 foredunes are hummocky have a 45 75 vegetation cover range and display various scales of blowouts concave stoss faces and steeper lee faces stage 4 foredunes are characterised by large scale erosional features such as blowouts sand sheets and high asymmetry stage 5 foredunes comprise poorly vegetated remnant knobs each stage is characterised by a set of erosional and depositional processes which produce generally distinctive sets of cross strata sedimentary structures within examples of each foredune stage are examined stage 1 and 2 foredunes are dominated by simple large scale convex continuous strata stage 3 and 4 foredunes display increasingly variable sets of cross strata and a greater degree of planar and trough cross stratification wave cut scarps blowout structures and very steep lee slope bedding may be preserved the internal sedimentary structures presented here form the basis of a facies model for foredunes

removal of methane through hydrological microbial and geochemical processes in the shallow sediments of pockmarks along eastern vestnesa ridge svalbard the recent discovery of methane seeps in the arctic region requires a better understanding of the fate of methane in marine sediments if we are to understand the contributions of methane to arctic ecosystems and climate change to this goal we analyze pore water data from five sites along eastern vestnesa ridge a sediment drift off north west svalbard to quantify the consumption of dissolved methane across the sulfate methane transition zone which are 3 5 m below seafloor from the investigated sites we use transport reaction models to quantify the hydrology as well as the carbon mass balance in the sediments pore water profiles and our model results demonstrate that hydrological microbial and geochemical processes reactions efficiently remove methane carbon from fluid over different time scales we interpret the nonsteady state behavior of the first 50 70 cm of our pore water profiles from the active sites as an annual scale downward fluid flow due to a seepage related pressure imbalance such downward flow supplies sulfate which enhances methane consumption through anaerobic oxidation of methane aom within this depth range our steady state modeling confirms the efficiency of aom in consuming dissolved methane in the upper 0 8 1 2 m of sediments based on the phosphate profiles we estimate that aom at the active pockmarks may have been operating for the last two to four centuries precipitation of authigenic carbonate removes more than a quarter of the dissolved inorganic carbon produced by aom and fixes it as authigenic carbonate in the sediments a process that sequestrates methane carbon over geological time

fluid flow or mud eruptions sediment temperature distributions on hakon mosby mud volcano sw barents sea slope hakon mosby mud volcano is located on the sw barents sea slope at a water depth of approximately 1250 m in situ temperature measurements using gravity corers equipped with autonomous temperature loggers and a short temperature lance operated by an rov were collected during three cruises between 2003 and 2006 revealing an exceptionally high level of activity and a complex thermal structure of the mud volcano simple analytical models were applied to the measured data to estimate rates of specific discharge and to test the hypothesis of episodic mud eruptions strongly curved profiles from 4 to 16 m below the seafloor suggest fluid flow at rates from 1 m year close to the limits of the central area to more than 4 m year approaching the geometrical center at the limits of the central area the profiles show distinct maxima at sediment depths of about 10 to 15 m which are interpreted as the result of lateral flow repeated measurements at shallow depths along a transect crossing the central area revealed a persistent pattern of temperature gradients while changes in the absolute values point to temporal variability temperatures gradients of more than 40 c m within the upper half meter of the sediments close to the geometrical center suggest even higher rates of specific discharge than estimated from the deeper profiles these high rates of fluid flow are most likely accompanied by frequent mud eruptions of small volume and limited local extent

late holocene sea level changes and paleoclimate recorded in lake lungue southern mozambique abstract we report on late holocene paleoenvironmental and sea level changes in southern mozambique based on analysis of diatom stratigraphy mineral magnetic susceptibility saturation isothermal remnant magnetization sirm and organic carbon content in a sediment core from lake lungue located ca 30 km north of xai xai city in the limpopo river floodplain eleven radiocarbon dates performed on terrestrial shells allowed establishment of an age depth model high content of brackish marine taxa especially diploneis suborbicularis and navicula yarrensis suggests that the lake lungue basin was part of the indian ocean coastal zone between ca 740 and 910 ce suggesting higher relative sea level during this phase a similar diatom distribution in older parts of the sequence of unknown age indicates that the site was connected to the indian ocean also at some stage prior to 740 ce between ca 910 and 1130 ce the basin was under a combined effect of sporadic marine water influx and limpopo river actions a freshwater lake was established sometime between 1130 and 1360 ce when the basin became less affected by marine influences due to lower sea levels instead the lake system was more influenced by limpopo river meandering dynamics and flooding events and eventually isolated into a more or less independent lake ecosystem where diatom diversity most likely responded to lake levels fluctuations driven by shifts in relative humidity and rainfall amounts within the floodplain and also from upstream sources during this phase high abundance of freshwater planktonic species i e aulacoseira granulata and a ambigua indicates high lake levels and wetter conditions dated to ca 1360 1560 ce from 1560 ce until present the lake has been subject to drier conditions and higher evaporation as indicated by lower lake levels reported by a decline in freshwater planktonic taxa and increase in brackish taxa e g amphora robusta

the response of the water table in coastal aeolian systems to changes in sea level abstract the water table in some aeolian systems is a control on the type and rate of accumulation and defines the depth to which deflation will occur in the formation of regional bounding surfaces at the basinal scale over time the elevation of the water table may be a function of climate tectonism and or sea level the latter invokes the hypothesis that the water table underlying an arid coastal sand sea without significant recharge adjusts to changes in sea level for tens to hundreds of kilometers inland the simplest physical and mathematical model for this hypothesis states that the water table re equilibrates as an inland directed diffusion wave to each increment of change in sea level model simulations incorporating a range of hydraulic parameters and periods of sea level cycles demonstrate scenarios ranging from one in which the continental water table is essentially unaffected by sea level to one in which the water table exactly mimics the sea level curve using a realistic set of mid range parameters the model produces a suite of water table curves that evolve from the coast to inland because of a diminishing amplitude for all cycles a loss of more minor cycles and a time lag the resulting stratigraphic record from the coast to more inland positions shows a diminishing number of recorded events a thinning of the section removal of previously preserved strata during lowstands and the appearance of new stratigraphic units far inland most of these characteristics are compatible with those of the jurassic page sandstone in regional cross sections in northern arizona and southern utah but are difficult to distinguish from the effects of tectonism

luminescence dating of quaternary sediments recent advances duller geoffrey 2004 luminescence dating of quaternary sediments recent advances journal of quaternary science 19 2 pp 183 192 rae2008

hydrogeology and its effect on slope stability along the coastal aquifer of nice france abstract along the ligurian continental margin off nice western mediterranean a considerable portion of the sediments is affected by pore pressure transients resulting from groundwater charging by the nearby river var and also from leaching clay mineral bearing deposits which results in sensitive weak clays in 1979 the area suffered a tsunamigenic landslide that generated several casualties and material damage to the coastal zone the seafloor presently shows evidence for soft sediment deformation and pore water freshening in this paper we present the first comprehensive in situ pore pressure data set collected over space and time between 2006 and 2009 in a landslide prone area using piezometers ifremer brest france and dynamic cone penetrometers ff cptu marum bremen germany as well as a simple modelling approach we illuminate what governing factors control strength and pore pressure in marine slope sediments affected by the var aquifer our results attest i a strong link between pore pressure transients and local precipitation over a period of 11 months ii overpressure at levels where groundwater flow occurs coarse intervals containing sand and gravel and iii fluidised fractures and channels that indicate high pore pressures at least temporarily in essence seepage and repeated pore pressure fluctuations weaken the sediment effectively so that it cannot be ruled out that the currently stable portion adjacent to nice airport may fail in the near future

coastal barrier dune construction during sea level highstands in mis 3 and 5a on tottori coast line japan abstract the southern coast of japan sea exhibits a number of late pleistocene coastal barrier dunes where the sediment record potentially provides important evidence for the palaeoenvironmental history of east asia the lack of direct dating of these barrier dunes however has veiled relationships between dune deposition sea level and other controlling factors quartz single aliquot regenerative optically stimulated luminescence osl dating was applied to the late pleistocene barrier dune at the tottori coast southern central japan sea we investigated a borehole drilled in a continuous ground penetrating radar gpr profile of the dune and an outcrop excavation where there has been recognised a sedimentary succession exposed of the pleistocene dune sand palaeosol daisen kurayoshi pumice dkp tephra palaeosol and holocene dune sand in ascending order the gradual transition from the pleistocene dune sand to palaeosol indicates a termination of the late pleistocene dune activity five osl ages from the uppermost pleistocene dune overlap within the period 48 2 51 4 ka which confirms that both deposition and termination of the dune occurred in early to mid marine isotope stage mis 3 another osl age from the lower section was 77 7 6 1 ka and indicates an earlier depositional stage in late mis 5a these reveal that the coastal dune deposition occurred in relation to the sea level highstands it would appear that a sea level of c 50 m relative to the present was the threshold for the dune activation morphology and sediment distribution of the modern shelf off the tottori coast suggest that the sea level lower than 50 m leads to increasingly unfavourable conditions for coastal dune activity due to longer sediment transport distances and decreased sediment supply these results have implications for the late pleistocene barrier dune along the southern japan sea coast and suggest that other dunes correlated with tottori based on the dkp tephra possibly would also have experienced a similar termination in relation to the sea level fall from mid mis 3 results also demonstrate that the depositional setting of the late pleistocene dunes was different from those constructed in the holocene due to the lower interstadial sea level highstands and resultant longer distance to the shore during mis 3 and 5a as a result the pleistocene dune exhibits less pronounced stratification and in finer grain size than the outer holocene dune ridge where sand is directly fed from the shore the grain size of the inner holocene dune ridge in contrast is almost identical to the pleistocene dune suggesting that the inner ridge partly consists of sand reworked from the pleistocene dune

u th systematics and ages of authigenic carbonates from hydrate ridge cascadia margin recorders of fluid flow variations uranium u concentrations and activity ratios 234u of authigenic carbonates are sensitive recorders of different fluid compositions at submarine seeps of hydrocarbon rich fluids cold seeps at hydrate ridge off the coast of oregon usa the low u concentrations mean 1 3 0 4 g g and high 234u values 165 317 of gas hydrate carbonates reflect the influence of sedimentary pore water indicating that these carbonates were formed under reducing conditions below or at the seafloor their 230th 234u ages span a time interval from 0 8 to 6 4 ka and cluster around 1 2 and 4 7 ka in contrast chemoherm carbonates precipitate from marine bottom water marked by relatively high u concentrations mean 5 2 0 8 g g and a mean 234u ratio of 166 3 their u isotopes reflect the 234u ratios of the bottom water being enriched in 234u relative to normal seawater simple mass balance calculations based on u concentrations and their corresponding 234u ratios reveal a contribution of about 11 of sedimentary pore water to the bottom water from the u pore water flux and the reconstructed u pore water concentration a mean flow rate of about 147 68 cm a can be estimated 230th 234u ages of chemoherm carbonates range from 7 3 to 267 6 ka 230th 234u ages of two chemoherms alvin and se knoll chemoherm correspond to time intervals of low sealevel stands in marine isotope stages mis 2 4 5 6 7 and 8 this observation indicates that fluid flow at cold seep sites sensitively reflects pressure changes of the hydraulic head in the sediments the 18o pdb ratios of the chemoherm carbonates support the hypothesis of precipitation during glacial times deviations of the chemoherm 18o values from the marine 18o record can be interpreted as to reflect temporally and spatially varying bottom water and or vent fluid temperatures during carbonate precipitation between 2 6 and 8 6 c

luminescence dating of holocene sedimentary deposits on romo a barrier island in the wadden sea denmark this study presents an optically stimulated luminescence osl based chronology for the evolution of the barrier island romo and related back barrier lagoon deposits in the danish wadden sea the chronology is constructed using 78 quartz osl ages obtained using a single aliquot regenerative dose sar protocol samples were retrieved from seven sediment cores each up to 25 m long taken from locations on the island and within the back barrier lagoon the reliability of the osl results is assessed using preheat plateaus thermal transfer tests and dose recovery measurements and by comparison with independent age control the osl ages compare favourably with three 14c age estimates and range between 220 20 and 15 800 1200 years romo appears to have developed as a progradational barrier system and the island appeared for the first time approximately 8000 years ago it then gradually expanded towards the west north and south as a result of an abundant sediment supply luminescence dating is concluded t

a numerical approach for approximating the historical morphology of wave dominated coasts a case study of the pomeranian bight southern baltic sea abstract comparison between historical maps from the 1900s 1980s and a modern map from the 2000s of the pomeranian bight at the southern baltic sea indicates that a major part of the coastline has been suffering continuous erosion this also holds for a major part of other coasts on a global scale quantifying coastal geomorphological changes on a decadal to centennial temporal scale thus needs to be intensified for coastal protection activities and integrated coastal zone management this study applies an estimation of sediment mass balance including the investigation of sediment source to sink transport in the case of absent historical survey data a numerical approach namely the dynamic equilibrium shore model desm is developed to approximate the historical morphology and to estimate sediment budget of wave dominated coasts based on the information of historical coastline configuration derived from maps a high resolution modern digital elevation model dem and relative sea level change the basic concept of the model is a dynamic equilibrium of the coastal cross shore profiles adapting to sediment mass balancing of a semi enclosed coastal area in which the unknown parameters of the cross shore profile shapes are calculated by numerical iterations the model is applied at the pomeranian bight in order to validate its capability in reflecting the pattern of bed level change and estimating sediment mass volume two tests of the model are conducted in approximating historical dems in 1980s and ca 1900 the changes of approximated dems from past to present are then respectively compared with the ones derived from a nautical sea chart in 1980s and the ones produced by a complex morphodynamic model that uses the approximated dem at ca 1900 as a starting point to hindcast the coastal morphological evolution of the research area the deposition erosion patterns along the coastline are consistent in both comparisons the pre conditions and limitations of the model are discussed in detail the model proposed here can serve as a useful tool for coastal morphological studies and potential applications for the future projection of coastal morphogenesis