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

impact of halite dissolution subsidence on quaternary fluvial terrace development case study of the huerva river ebro basin ne spain abstract this paper analyses the control of evaporite dissolution subsidence on the evolution of the lower 30 km long reach of the huerva river up to its confluence with the ebro river in the study area the huerva river flows across different interfingered lithofacies of the subhorizontally lying ebro basin fill 1 shales and sandstones upstream of cadrete 2 evaporites dominated by gypsum between cadrete and cuarte 3 gypsum with glauberite and halite units in the subsurface downstream of cuarte the halite shows a marked downvalley increase in thickness twelve terrace levels and seven pediment levels correlative to some of the terraces have been mapped in the studied area upstream of cadrete the terrace deposits with a relatively constant thickness less than 4 m and overlying unsoluble bedrock remain undeformed between cadrete and cuarte the deposits of some terraces show local thickening 60 m thick terrace alluvium that fills a 5 km long trough generated by synsedimentary subsidence phenomena caused primarily by the interstratal dissolution of halite the older terraces t1 to t4 show slight thickening 18 m and locally truncate paleocollapse structures ascribed to the interstratal karstification of halite beds the intermediate terraces t5 to t7 correspond to degradation surfaces that grade downstream of cuarte into aggradation flights underlain by the abruptly thickened deposits that fill this 5 km long dissolution trough subsidence migrated episodically downstream during the generation of these terraces and the subsidence aggradation rate was probably large enough to induce a base level drop and knickpoint migration upstream generating strath terraces with convergent longitudinal profiles the sedimentological changes that show the thickened terrace deposits in the subsidence area high proportion of overbank fines 60 including palustrine facies gravel channels with lower width depth ratio multiple fining upward cycles decrease in the calibre of the channel gravels indicate a change in the channel pattern from braided to meandering due to the lowering of the valley slope in the reach affected by subsidence some of the anomalous features of the lower terraces t8 to t12 attributable to dissolution subsidence include 1 steepening of the t8 terrace profile 2 change of the t10 terrace from degradational to aggradational downstream cuarte and 3 thickening recorded beneath the t11 terrace surface

lithological anomalies in a relict coastal dune geophysical and paleoenvironmental markers 1 ground exposures of migration surfaces slipfaces of a relict holocene coastal dune along the southeastern baltic sea coast provide an ideal opportunity for establishing the causes of prominent reflections on geophysical profiles high amplitude reflections on high resolution ground penetrating radar gpr images correlate well with two major lithological anomalies 1 paleosols developed on dune slipfaces and 2 slipfaces consisting of heavy mineral concentrations hmcs paleosols serve as indicators of dune stability represent datable chronostratigraphic surfaces and help reconstruct dune paleo morphology hmcs have substantially higher magnetic susceptibility values than background quartz rich sands and where they are well developed can be also used for spatial correlation based on their occurrence at the study site these enriched horizons likely represent periods of increased wind activity storminess multiple hmcs upwind of paleosol p1 800 670 cal years bp likely reflect periods of intensified wind activity along the southeast baltic region during the medieval warm period

the sedimentary structure of linear sand dunes linear sand dunes dunes that extend parallel to each other rather than in star like or crescentic forms are the most abundant type of desert sand dune1 but because their development and their internal structure are poorly understood they are rarely recognized in the rock record2 models of linear dune development2 3 4 5 6 have not been able to take into account the sub surface structure of existing dunes but have relied instead either on the extrapolation of short term measurements of winds and sediment transport or on observations of near surface internal sedimentary structures from such studies it has not been clear if linear dunes can migrate laterally2 7 8 here we present images produced by ground penetrating radar showing the three dimensional sedimentary structure of a linear dune in the namib sand sea where some of the world s largest linear dunes are situated these profiles show clear evidence for lateral migration in a linear dune moreover the migration of a sinuous crest line along the dune produces divergent sets of cross stratification which can become stacked as the dune height increases and large linear dunes can support superimposed dunes that produce stacked sets of trough cross stratification these clear structural signatures of linear dunes should facilitate their recognition in geological records

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

playa lake basins on the southern high plains of texas and new mexico part i hydrologic geomorphic and geologic evidence for their development playa lake basins of the southern high plains texas and new mexico may originate wherever water periodically can collect in a surficial depression they expand however by hydrologic and geomorphic processes including 1 dissolution of lithologic carbonates by infiltrating water 2 transport downward of fine grained clastic and organic material by the infiltrating ground water leading to continuing processes of oxidation and carbonate dissolution in the subsurface and 3 eolian removal of clastic material from the floor of playa lakes which at some sites appears to have deepened playa depressions evidence for largely hydrologic processes of playa basin development on the southern high plains includes 1 a geographic occurrence restricted to relatively flat areas of the high plains surface that have poorly developed fluvial drainage and which are underlain by generally unsaturated clastic and calcrete beds 2 a tendency to occur where water collects and infiltrates as along ephemeral streams and lineations suggestive of fracture systems and 3 hydrologic geochemical petrographic and bore hole data which suggest that recharge to the high plains aquifer is principally from playa lakes that various geochemical changes including carbonate dissolution and enhancement of secondary porosity occur as water moves downward through the unsaturated zone beneath playa lakes and that calcrete beds often are missing or significantly dissolved beneath playa floors

aeolian system responses to global change challenges of scale process and temporal integration aeolian sediment systems are extensive components of the earth s surface not just in today s active desert environments but in coastal locations and as presently stable loess and peri desert ergs all these systems are subject to potentially significant 21st century changes in dynamics due to global warming impacts on atmospheric circulation sediment moisture and vegetation cover but do we know enough in the critical areas of science to allow robust models of likely future dynamics to be developed since the establishment of modern aeolian science research has largely taken two divergent routes 1 small scale investigations of the processes of wind shear sediment entrainment and transportation and 2 landform and landscape analyses with bedform systems described and relationships to circulation explained an intermediate sedimentological route has generated attempts towards a more integrated understanding of system behaviour at a range of scales four recent developments provide the potential for more robust multiscale integrations of aeolian system behaviour these are 1 advances in empirical measurement that allow wind power and sediment flux relations to be better described 2 modelling of dune and dust dynamics and interactions with key controls 3 monitoring systems that allow high resolution observations of sediment flux variations to be recognized and aeolian deposit structures to be understood and 4 chronometric advances that permit the assessment of the frequency and drivers of dune system activity in the past we explore and analyse these methodological advances and their potential contribution to the multiscale integrations that are essential for better informed predictions of future global aeolian system dynamics considering whether the integration of these advances in reductionist and holistic elements of aeolian science represent an example of the effective application of the principles of earth system science copyright 2008 john wiley sons ltd

gpr in sediments advice on data collection basic processing and interpretation a good practice guide within sedimentological studies ground penetrating radar gpr is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non destructive method the purpose of this paper is to provide an introduction to the collection processing and interpretation of gpr data so that future sedimentary studies can be improved with gpr equipment now being lightweight robust and portable proper data collection and survey design methods need to be followed in order to acquire high resolution subsurface digital data various factors are discussed including reflection profiling velocity soundings test surveys topography logistics data quality and extreme environments basic data processing and visualization are then reviewed followed by a discussion on gpr interpretation strategies including a background to radar stratigraphy for the sedimentary geologist or geomorphologist gpr offers unique data of the shallow subsurface including stratigraphy geometry architecture and structure

sedimentology diagenesis and ichnology of cretaceous and palaeogene calcretes and palustrine carbonates from uruguay abstract the cretaceous mercedes formation and paleogene queguay formation deposits cropping out in w and s uruguay comprise two terrestrial limestone units that are very rich in trace fossils the study of these units permits to propose a sedimentological model for palustrine limestones and calcretes in which the distribution of different types of trace fossils is considered the study units include three main types of deposit lacustrine limestones palustrine limestones and calcretes the lacustrine limestones are relatively homogeneous and contain gastropods charophytes and ostracods but no trace fossils they were deposited in a relatively more perennial lacustrine environment the palustrine limestones include four different facies desiccated mudstones nodular limestones granular limestones and gravel sheets the desiccated mudstones indicate a lesser degree of pedogenic modification and the granular limestones a higher degree the gravel sheets are an indication of the reworking of previous limestones deposits during low lakewater levels most of the palustrine limestones except the gravel sheets contain the same bioclasts as the lacustrine limestones plus a variety of trace fossils such as rebuffoichnus sciuttoi fictovichnus gobiensis and different ichnospecies of celliforma the calcretes are either massive groundwater or laminar the massive calcretes are sandy limestones made up of a carbonate matrix and cements the laminar calcretes root mats which contain alveolar septal structures occur as centimetre thick layers and can be seen in all types of deposit they contain the same trace fossil association as the palustrine limestones the massive calcretes are poorer in such fossils the distribution of trace fossils in these environments is under strong facies control and provides good evidence of subaerial exposure and semi arid climates all the limestones are partially replaced and cemented by opal and quartz but in all cases the primary structure is preserved silicification occurred under groundwater meteoric conditions overall the limestones facies calcretes palustrine and lacustrine and their lateral distribution likely reflect the existence of wetland environments in semiarid to sub humid climates these climatic conditions were interrupted by a period of increased precipitations probably the early eocene climatic optimum

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

rodent community change at the pliocene pleistocene transition in southwestern kansas and identification of the microtus immigration event on the central great plains abstract a dense fossil rodent database and new paleomagnetic data from the meade basin of southwestern kansas document the transition from a pliocene community characterized by cricetids of southern aspect and archaic arvicolids with rooted molars to a pleistocene community with cricetids of temperate aspect and arvicolids with ever growing molars this new information suggests a revised date for the blancan irvingtonian north american land mammal age boundary between 2 06 and 1 95 ma coincident with the extinction of the sigmodon minor lineage and the immigration of microtus carbon and oxygen isotope compositions of paleosol carbonates indicate the faunal changes occurred during the final expansion of c 4 grasses in the great plains to modern abundance and a strong cooling trend reflecting the end of the early pliocene warm interval and onset of northern hemisphere glaciation although extinctions balance originations through the study period pulses of enhanced extinction and origination occurring near the pliocene pleistocene boundary strongly suggest environmental change as the likely forcing mechanism for rodent community compositional shifts the meade basin rodent sequence provides the most complete history of any terrestrial vertebrate group in north america for this period of time

three dimensional reverse time migration of ground penetrating radar signals three dimensional 3d ground penetrating radar gpr systems and 3d seismic imaging techniques have been developing fast and evolving rapidly in the last decade ray based migration methods have been successfully applied to processing 3d gpr signals based on the similarity between electromagnetic and seismic waves however reverse time migration rtm of 3d gpr signals has not been well studied in the past in this paper we present a 3d rtm based on maxwell s equations for 3d gpr surveys migration recovers the true subsurface structure from a distorted and unfocused time profile and suppresses common electromagnetic clutter and noise rtm based on maxwell s equations can consider conductivity directly and compensate for the attenuation within a high conductivity zone compared with 2d rtm 3d rtm back propagates both in line and cross line signals simultaneously and can include complex 3d permittivity and conductivity models we have integrated a parallel finite difference time domain fdtd algorithm based on a hybrid mpi and openmp scheme to reduce the computational cost of 3d problems the 3d rtm experiments on an anomaly of em shape and a realistic sand dune model demonstrate the effective recovery of 3d subsurface structures

combining ground penetrating radar surveys and optical dating to determine dune migration in namibia ground penetrating radar gpr profiles across a complex linear dune in the namib sand sea have been used to image sets of cross stratification and their bounding surfaces a combination of radar facies analysis and radar stratigraphy has been used to interpret the radar profiles and define a relative chronology thick sets of cross stratification indicate when the dune was most active whereas thin sets of cross stratification are interpreted to indicate the increased prevalence of wind reversals and lower rates of dune migration with bounding surfaces formed during periods of stabilization non deposition or erosion a drilling and dating campaign was designed on the basis of the dune stratigraphy as defined by the gpr survey sampling was targeted at large sets of cross stratification formed when the dunes were most active and avoiding bounding surfaces formed when the dune was stable or even eroded the results from optical dating give ages between 0 34 0 02 ka and 1 57 0 07 ka indicating a time averaged dune migration rate of 0 12 m a 1 over the past 1600 years

geomorphic and tectonic forcing of late cenozoic warping of the colorado piedmont late cenozoic warping of the colorado piedmont involved interplay of tectonic forcing river erosion and isostatic response to erosion modeled erosional isostasy closely replicates the observed pattern of deformation but accounts for only about half its magnitude the remainder reflects tectonic rock uplift that increases southward across the piedmont likely reflecting proximity to the northward propagating rio grande rift this differential uplift triggered differential erosion concentrated on southern piedmont river systems particularly the arkansas river which led in turn to differential isostatic rock uplift focused on the arkansas drainage covariation of tectonic uplift erosion and isostatic compensation across the piedmont reflects a positive feedback between uplift induced erosion and erosion induced isostasy which has progressed to the point that isostatic uplift is approximately equal to the initial tectonic forcing

building of shore oblique transverse dune ridges revealed by ground penetrating radar and optical dating over the last 500 years on tottori coast japan sea abstract coastal dunes provide valuable information on the past aeolian activity better characterization of internal dune structures and their chronology potentially can greatly improve the interpretation of past environmental changes ground penetrating radar gpr and optically stimulated luminescence osl dating was applied to two transverse dune ridges which are arranged obliquely to the shoreline on the tottori coast japan sea data shows that the inner ridge has a core of pleistocene dune draped with holocene sand while the outer ridge consists only of holocene sand the holocene dune is generally dominated by landward migration but the outer ridge shows a clear seaward accretion during the 18th century ad osl dating showed concordant results with radar stratigraphy and topographic changes since ad 1932 revealed by maps from this we were able to present the first detailed report of the multi decadal to centennial scale dune formation for the last 500 years in east asia contemporaneous with the little ice age during which many european coastal and inland dunes were activated in east asia it is thought that the winter monsoon plays an important role for aeolian processes the seaward migration during the 18th century reflects a decrease in wind capacity which restricted sand transport nearshore being related to decline in winter monsoon revealed by chinese historical documents in contrast two remarkable events of landward accretion occurred in ad 1580 1640 and around ad 1840 respectively corresponding to periods of increased dust fall in china which suggest enhanced winter monsoon the zone of maximum sedimentation shifted through time from the inner to outer ridges and also towards the seaward end of the shore oblique dune ridge reflecting an expansion of the dune field caused by shoreline progradation these suggest that the effective combination of gpr and osl dating was critical in detailed characterization of the complicated depositional pattern of the transverse dune ridge and thus in reconstruction of the past aeolian activity

first evidence for onshore marine isotope stage 3 aeolianite formation on the southern cape coastline of south africa abstract the southern cape coast of south africa boasts an impressive suite of plio pleistocene aeolian dune deposits aeolianite previous research has shown that in this region onshore dune accumulation was generally focused around interglacial sea level highstands with the locus of coastal dune accumulation shifting onto the adjacent continental shelf during glacial sea level lowstands here using new luminescence dating results we present the first evidence for preserved onshore glacial age dunes specifically on the robberg peninsula a rocky headland 28 km east of knysna two phases of aeolianite formation are identified corresponding to early 45 60 ka and late 35 30 ka marine isotope stage mis 3 subsequently during the holocene all substantive dune accumulation occurred between 10 2 and 7 0 ka forming cliff fronting dunes and filling the limited accommodation space on the headland including an archaeological rock shelter combining these ages with bathymetric data we infer that this distinct onshore glacial age aeolianite record reflects 1 restricted accommodation space during sea level highstands 2 a regional narrowing of the continental shelf and 3 liberation of sediments lying on a prominent 45 to 60 m offshore terrace which would have been exposed during mis 3 this demonstrates that despite broad regional scale trends in the timing of coastal aeolian activity driven by commonalities in relative sea level trends and climate distinct local variations in late quaternary coastal evolution can be identified this is ascribed to local controls on preservation accommodation space and sediment supply shoreline position and antecedent offshore sediment supplies such findings may have wider implications for interpretations of site context resource availability at several notable coastal archaeological sites and more broadly suggest that local offshore or onshore geologic contexts can at times assume greater influence on a preserved coastal aeolianite record than the regional scale trends in sea level and climate

chlorine partitioning between a basaltic melt and h2o co2 fluids at mount etna abstract partitioning experiments between a basaltic melt from mt etna and a low density hydrous fluid or vapor containing h 2 o or h 2 o co 2 were performed at 1200 1260 c at pressures between 1 and 200 mpa either near the nickel nickel oxide nno buffer or at two log units above it nno 2 and with different chloride concentrations most of the experiments were done at chloride brine undersaturated conditions although at the highest cl concentrations explored brine saturation might have been reached the average partition coefficients d cl fluid melt over the range of cl concentrations were derived on a weight basis by plotting the calculated concentrations of cl in the fluid phase versus the measured ones in the melt for h 2 o cl experiments in which the cl concentration in the melt was 0 4 wt a negative dependence between d cl f m and pressure is observed d cl fluid melt in h 2 o cl bearing experiments ranges between 11 14 at 1 and 25 mpa to 6 at 200 mpa at nno and between 4 at 50 mpa and 13 at 100 mpa at nno 2 addition of co 2 at nno yields lower partition coefficients than in co 2 free conditions over the pressure range investigated the negative pressure dependence observed for h 2 o cl experiments disappears when co 2 is present in the system overall once co 2 is introduced in the system cl fugacity in the silicate melt tends to increase thus resulting in a decrease of d cl f m application to mt etna shows that the composition of the volcanic plume in terms of cl records very shallow pressures of magma equilibration with its exsolved fluid

calcrete and palustrine assemblages on a distal alluvial floodplain a response to local subsidence miocene of the duero basin spain abstract in the upper miocene of the eastern duero basin two carbonate units cu 1 and cu 2 display a lateral transition from distal alluvial floodplain red mudstones to calcrete and an upwards transition from calcrete to palustrine facies the carbonate content in the calcrete increases upwards as shown in sequences from red or reddish brown mudstones with diffuse calcification to nodular calcrete facies to massive calcretes the palustrine facies display a broad range of textures related to the degree of exposure peloidal intraclast textures formed during the most prolonged phases of exposure and are those most commonly seen in the palustrine facies the transition from calcrete to palustrine facies occurs in two ways 1 as an indurated limestone level with mixed features of calcrete and palustrine facies and 2 a well delimited boundary between the two facies which show very similar characteristics in the vicinity of this boundary the 13cpdb and 18opdb values of the calcretes are similar to those of the palustrine facies this is because their genesis was related to groundwaters which inherited the isotopic signature of meteoric waters good covariance between 13c and 18o palustrine values r 0 78 is typical of lakes in semi arid regions with long water residence times in closed basins the calcrete palustrine association records a progressive decrease in the terrigenous supply and a continuous elevation of the groundwater table until it intersected with the surface to create a pond the rise in the groundwater table resulted from local subsidence that was not compensated by terrigenous supply leading to a lowering of the floodplain changes in the thickness of palustrine facies from central to marginal pond areas with ubiquitous exposure features suggest that the pond was progressively filled up by bio chemical carbonate precipitation balancing the available space created by subsidence this maintained the shallow character of the pond deposits

cenozoic paleoclimate on land in north america abstract paleotemperature and paleoprecipitation over the past 40 m yr can be inferred from the degree of chemical weathering and depth of carbonate nodules in paleosols of oregon montana and nebraska paleosol records show that late eocene 35 ma middle miocene 16 ma late miocene 7 ma and early pliocene 4 ma warm climatic episodes were also times of a wet climate in oregon montana and nebraska oregon and nebraska were humid during warm wet times but montana was no wetter than subhumid within the rain shadow of intermontane basins global warm wet paleoclimatic spikes steepened rather than flattened geographic gradients of rocky mountain rain shadows long lived mountain barriers created dusty dry basins with sedimentation rates high enough to preserve milankovitch scale 100 41 kyr global paleoclimatic variation in some sequences of paleosols greenhouse warm wet climates indicated by paleosols were also peaks of diversity for north american plants and animals and coincided with advance

diversity dynamics of the late cenozoic rodent community from south western kansas the influence of historical processes on community structure this study used the dense late cenozoic rodent record of south western kansas to test for an equilibrium in species richness through millions of years identify and clarify historical influences on species richness determine the relative contribution of immigration speciation and local extinction to species originations at the community level and calculate background extinction rates to compare with modern species losses due to anthropogenic activities the meade basin rodent community has been in equilibrium with an average of about 17 species for almost 5 million years no speciation events were identified in the meade basin rodent record although speciation ultimately contributes to the regional species pool local speciation events contributed little to community structure extinctions and immigrations continued through the study period with elevated bouts of turnover correlated with global cooling events and lowered sea level associated with the beringian land bridge turnover was generated primarily by stochastic climatic agents at several temporal scales possibly including rapid and devastating regional volcanic ashfalls none of the extinction rates recorded in the meade basin system rivals extinction levels in modern species due to anthropogenic activities

integration of channel and floodplain suites ii vertical relations of alluvial paleosols abstract extrachannel sediments of the lower eocene willwood formation which were subdivided into different pedofacies or developmental stages exhibit two well developed orders of pedofacies sequences over which a grosser scale cyclicity is superposed simple sequences with thicknesses measured in meters are comprised of one or more soil profiles that are bounded above and below by pedogenically unmodified crevasse splay deposits on a larger scale compound pedofacies sequences are tens of meters thick and consist of several simple sequences sandwiched between channel sandstones between these sandbodies pedogenic maturity of the multistorey paleosols progressively increases and then decreases upwards in response to episodic avulsion formation of both compound and simple pedofacies seq ences was largely controlled by local patterns of deposition and erosion that produced vertical variability in both rate of sediment accumulation and parent material because paleosol maturity also reflects the effects of extrabasinal factors a pedofacies megasequence which is hundreds of meters thick developed in response to changes in tectonic activity through willwood time comparison between willwood deposits in the northern and central parts of the bighorn basin also reveals that areally differing sediment accumulation rates and thereby basin subsidence rates can be interpreted from large scale pedofacies sequences consequently paleosols are useful in determining changes in relative rates of sediment accumulation that are controlled by both intrabasinal and extrabasinal factors

investigation of large scale washover of a small barrier system on the southeast australian coast using ground penetrating radar abstract prehistoric depositional signatures for large scale washover involving marine inundation events such as storms and tsunami have been the subject of considerable research over the last 15 years much of this research has focused on the identification of sandsheets in back barrier environments as depositional records for extreme washover events all these deposits must have a sediment source and by their nature the most likely source of sediment for washover into back barrier environments is the barrier itself this study identifies an erosional signature for large scale washover from a small coastal barrier on the southeast australian coast a distinct lens of marine sand up to 90 cm thick confined vertically by peat is found in the upper fill of a closed freshwater back barrier lagoon sequence this sand lens is attributed to a large scale washover event during the last 800 years and was possibly deposited by a tsunami the hypothesis for this study was that any event that breached the dune system must have caused considerable geomorphic change to the dunes and hence may have left an erosional signature ground penetrating radar transects of the system show an erosional contact between a series of truncated pre event dunes and several small overlying post event dunes this study outlines a relatively simple non invasive method for the identification of an erosional signature for prehistoric large scale washovers caused by storm surge exceptionally large waves or tsunami

crayfish burrows from late jurassic late cretaceous continental deposits of patagonia argentina their palaeoecological palaeoclimatic and palaeobiogeographical significance abstract the trace fossil loloichnus baqueroensis igen and isp nov from late jurassic late cretaceous continental deposits of patagonia argentina includes thickly lined mostly passively filled and y branched burrows other important features of this ichnofossil are the inner surface texture of lining showing transversal elongated and adjacent grooves and less commonly the pelletal filling of burrows l baqueroensis is recorded from the bajo grande bajo tigre punta del barco and laguna palacios formations which were deposited in different volcaniclastic environments of the deseado massif and san jorge basin geological provinces respectively the described burrows are found in many levels of palaeosols developed in reworked piroclastic deposits where they are the main component of the ichnofabrics in association with meniscate and thinly lined burrows and a diffuse and complex boxwork of small diameter burrows root traces are also present and in many cases occur inside l baqueroensis considering general morphology surface texture filling types palaeoenvironments in which they occur and comparisons with extant and fossil decapod burrows the likely trace makers of l baqueroensis were crayfishes decapoda astacidea probably parastacidae the producers of l baqueroensis inhabited soils where their burrows probably reached the water table and contained roots that were used for feeding considering climatic preferences of extant parastacids it is proposed a temperate climate for central patagonia during the deposition of the studied units the widespread presence of crayfishes during late jurassic late cretaceous times in central patagonia supports the monophyletic origin of this group during the triassic and suggests that the present restricted geographic distribution in southern south america is a relict of a broader one

osl dating and gpr mapping of palaeotsunami inundation a 4000 year history of indian ocean tsunamis as recorded in sri lanka to evaluate and mitigate tsunami hazard as long as possible records of inundations and dates of past events are needed coastal sediments deposited by tsunamis tsunamites can potentially provide this information however of the three key elements needed for reconstruction of palaeotsunamis identification of sediments dating and finding the inundation distance the latter remains the most difficult the existing methods for estimating the extent of a palaeotsunami inundation rely on extensive excavation which is not always possible here by analysing tsunamites from sri lanka identified using sedimentological and paleontological characteristics we show that their internal dielectric properties differ significantly from surrounding sediments the significant difference in the value of dielectric constant of the otherwise almost indistinguishable sediments is due to higher water content of tsunamites the contrasts were found to be sharp and not to erode over thousands of years they cause sizeable electromagnetic wave reflections from tsunamite sediments which permit the use of ground penetrating radar gpr to trace their extent and morphology in this study of the 2004 boxing day indian ocean tsunami we use gpr in two locations in sri lanka to trace four identified major palaeotsunami deposits for at least 400 m inland investigation inland was constrained by inaccessible security zones the subsurface extent of tsunamites not available without extensive excavation provides a good proxy for inundation the deposits were dated using the established method of optically stimulated luminescence osl this dating partly corroborated by available historical records and independent studies contributes to the global picture of tsunami hazard in the indian ocean the proposed method of combined gpr osl based reconstruction of palaeotsunami deposits enables estimates of inundation recurrence and therefore tsunami hazard for any sandy coast with identifiable tsunamite deposits the method could be also used for anchoring and synchronizing chronologies of ancient civilisations adjacent to the ocean shores

reconstruction of holocene coastal progradation on the east coast of korea based on osl dating and gpr surveys of beach foredune ridges coastal dunefields along the east coast of korea have long been thought to have originated from beach ridges that prograded during the holocene but there has been little chronological evidence based on absolute dating in this paper we use optically stimulated luminescence osl dating and ground penetrating radar gpr surveys to reconstruct the coastal progradation of anin dunefield in the gangneung area on the east coast of korea gpr profiles and sedimentological analyses of four beach foredune ridges reveal that the ridges are composed mainly of beach deposits showing seaward dipping and horizontal laminae capped by eolian sands with landward dipping laminae the beach deposits are in places underlain by fluvial sands with gravels coupled with data from osl dating we interpret these results to mean that the fluvial sands and rounded cobbles were deposited in the study area during the last glacial period between the mid holocene 6 5 kyr and c 3 5 3 0 kyr the transgression rate of the sea

a pedotype approach to latest cretaceous and earliest tertiary paleosols in eastern montana a pedotype approach to the study of paleosols emphasizes individual profiles it is an alternative approach to the study of geosols which are laterally extensive suites of paleosols or pedofacies which are pedogenically distinctive sedimentary facies this is the first pedotype study of paleosols across the cretaceous tertiary boundary in eastern montana pedotypes allow assessment of sedimentation and fossilization the sequence of paleosols across the cretaceous tertiary boundary at bug creek is one of high temporal resolution because most available geological time can be accounted for by differing degree of development inferred for each pedotype paleosols at bug creek include pedotypes that preserve plant fossils well but were unfavorable for preservation of fossil vertebrates pedotypes also allow reassessment of ecosystem change despite indications of catastrophe at the cretaceous tertiary boundary the array of paleocene and cretaceous pedotypes are not strikingly different the upper cretaceous hell creek formation includes pedotypes interpreted as gleyed alfisols inceptisols and entisols probably formed under seasonally water logged forest and mean annual rainfall of the order of 900 1200 mm most paleosols of the lower paleocene tullock formation were histosols but some can be interpreted as gleyed inceptisols and entisols probably formed under bald cypress swamps in a humid climate with 1200 mm mean annual rainfall broadly comparable pedotypes were present before and after the cretaceous tertiary boundary although paleocene flood plain forest lived in paleosols chemically a little more oligotrophic than cretaceous paleosols this modest difference supports the idea that change to coaly facies in the earliest paleocene was a local shift in sedimentary environment such local changes do not begin to account for profound disruption in specific composition of plant and animal communities at the cretaceous tertiary boundary in eastern montana

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

seasonal wetland carbonate sequences and dynamic catenas a re appraisal of palustrine limestones abstract palustrine carbonate cyclothems are compared directly to well documented peritidal carbonate cyclothems in the case of the latter the trend of increasing degree of exposure seen vertically through a cyclothem has been interpreted as due to the aggradation of the sediment surface relative to the semi diurnal tidal regime palustrine cyclothems also show similar increases in the degree of exposure and this is interpreted as the effect of sediment aggradation in a seasonal wetland regime the resulting changes in the drainage characteristic revealed in a palustrinc cyclothem reflect a type of seasonally variable catenary relationship referred to here as a dynamic catena this model explains the key features of palustrine cyclothems and suggests the importance of seasonal wetland environments in ancient continental settings

erosional and depositional characteristics of regional overwash deposits caused by multiple hurricanes regional scale washover deposits along the florida gulf and atlantic coasts induced by multiple hurricanes in 2004 and 2005 were studied through coring trenching ground penetrating radar imaging aerial photography and prestorm and poststorm beach profile surveys erosional and depositional characteristics in different barrier island sub environments including dune field interior wetland and back barrier bay were examined over the eroded dune fields the washover deposits are characterized by an extensive horizontal basal erosional surface truncating the old dune deposits and horizontal to slightly landward dipping stratification over the marshes in the barrier island interior the washover deposits are characterized by steep tabular bedding with no erosion at the bottom overwash into the back barrier bay produced the thickest deposits characterized by steep prograding sigmoidal bedding no significant erosional feature was observed at the bottom washover deposits within the dense interior mangrove swamp demonstrate both normal and reversed graded bedding the washover deposits caused by hurricanes frances 2004 and jeanne 2004 along the southern florida atlantic coast barrier islands are substantially different from those along the northern florida barrier islands caused by ivan 2004 and dennis 2005 in terms of regional extension erosional features and sedimentary structures these differences are controlled by different overall barrier island morphology vegetation type and density and sediment properties the homogeneity of sediment along the northern florida coast makes distinguishing between washover deposits from ivan and dennis difficult in contrast along the atlantic coast barrier islands the two overwash events as demonstrated by two phases of graded bedding of the bimodal sediments are easily distinguishable

geomorphic development of the canadian river valley texas panhandle an example of regional salt dissolution and subsidence development of the canadian river valley in the texas panhandle resulted mostly from regional subsidence following dissolution of permian bedded salts salts of the clear fork glorieta san andres and seven rivers formations have undergone dissolution along the margins of the palo duro dalhart and anadarko basins the canadian river valley follows a zone of subsidence for

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

geomorphic and sedimentary response of rivers to tectonic deformation a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings abstract rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting as such recognition of tectonic tilting effects on rivers and their resultant sediments can be a useful tool for identifying the often cryptic warping associated with incipient and smaller scale epeirogenic deformation in both modern and ancient settings tectonic warping may result in either longitudinal parallel to floodplain orientation or lateral normal to floodplain orientation tilting of alluvial river profiles alluvial rivers may respond to deformation of longitudinal profile by 1 deflection around zones of uplift and into zones of subsidence 2 aggradation in backtilted and degradation in foretilted reaches 3 compensation of slope alteration by shifts in channel pattern 4 increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches and 5 increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches lateral tilting causes down tilt avulsion of streams where tilt rates are high and steady down tilt migration combing where tilt rates are lower each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures or where non tectonic causes cannot be invoked however caution must be exercised when using these effects as criteria for past or current tectonic warping as these effects may be caused by non tectonic factors these non tectonic causes must be eliminated before tectonic interpretations are made

palustrine sedimentation in an episodically subsiding basin the miocene of the northern teruel graben spain lacustrine deposits form most of the sedimentary record accumulated throughout the miocene in the northern part of the teruel graben a landlocked basin situated in ne spain three main stratigraphic units units i iii spanning late vallesian to late turolian in age are distinguished in the area the two former units comprise mainly carbonate lacustrine deposits that were deposited in a palustrine or a more permanent but shallow lacustrine setting the latter being related mainly to periods of lake expansion under more humid and cooler climatic conditions in contrast deposition of unit iii characterised by gypsiferous lacustrine sediments in central parts of the basin reflects the influence of source rocks of evaporitic nature upper triassic formations that were emplaced by diapiric uplift in the eastern margin during the middle turolian carbonate lake sediments belonging to units i and ii consist of four main lithofacies associations a distal alluvial lake margin deposits b lacustrine carbonates and pedogenically modified lacustrine carbonates c carbonate fill channels and d organic rich marlstone and carbonate marshes lithofacies association a shows typically a sequential arrangement formed from bottom to top of red mudstone carbonate palaeosols and biomicrite beds sequence type 1a these sequences are interpreted as a result of slow but continuous aggradation of the floodplain areas and subsequent rise of the water table probably reflecting equilibrium between subsidence and sedimentation lithofacies association b consisting of biomicrite beds passing upward into palaeosols sequence type 1b is thought to be caused by marked pulses of tectonic subsidence that created the accommodation space required for fast development of a carbonate lake carbonate fill channels showing erosive lower surfaces dig out on previous channels marsh deposits and or lacustrine carbonates exhibit well developed prismatic structure at their bed tops the sequential arrangement suggests similar tectonic constrains than the envisaged for lithofacies 1b the comparison of depositional styles of the lake systems with the palaeoclimatic evolutionary pattern of the basin throughout the miocene indicates that the combined effect of tectonism climate and source rock played a major role in the stratigraphic framework of the basin during this period

playa lake basins on the southern high plains of texas and new mexico part ii a hydrologic model and mass balance arguments for their development hydrologic geologic geomorphic and mass balance data suggest that most of the 30 000 playa lake basins on the southern high plains have developed by a combination of dissolution of caliche and piping of surface material into the unsaturated zone rather than by eolian processes as has generally been stated a conceptual model suggests that particulate organic material much of which is sorbed on smectite clays is carried downward from the surface into the unsaturated zone by recharging water the organic material is oxidized to co 2 which dissolves in the water forms carbonic acid and dissolves lithologic carbonates because organic material is transported and oxidized deep in the unsaturated zone co 2 concentrations are much higher at depth than in the soil zone and recharging water remains thermodynamically subsaturated with respect to carbonates and thus able to dissolve them throughout the unsaturated zone dissolution promotes lithologic instability leading to piping and eluviation of material within the unsaturated zone playa basins expand laterally as recharge is concentrated at the edge of the playa floor because of lowered permeability in the center that results from accumulation of clays and other fine sediment mass balance calculations of gas liquid and solid fluxes beneath a playa basin suggest that sufficient mass is transported to account for the volume of the depression particulate flux is estimated by relating it to the co 2 flux out of the unsaturated zone solute flux is estimated from the difference between input values from the playa lake water and that observed in ground water gas flux is measured directly from gas samples at specific depths below the surface

groundwater dependent ecology of the shoreline of the subtropical lake st lucia estuary the ecology of the st lucia estuary in south africa is of unique international importance during droughts the estuary experiences high salinities with values above that of seawater ion poor groundwater flowing into the estuary from prominent sand aquifers along its eastern shoreline forms low salinity habitats for salt sensitive biota during droughts plants and animals can take refuge in the groundwater discharge zone until the condition in the estuary regains tolerable salinity simulations of the groundwater discharge indicate that the flow can persist during droughts over at least a decade and be of great important for the resilience of the estuary anthropogenic activities have reduced the river inflow and made the st lucia estuary more sensitive to droughts the groundwater has thereby become increasingly important for the estuary s ecology protection of the groundwater discharge along the shoreline itself and actions to increase the groundwater recharge are therefore important management tasks

the structure and development of foredunes on a locally prograding coast insights from ground penetrating radar surveys norfolk uk the internal structure of coastal foredunes from three sites along the north norfolk coast has been investigated using ground penetrating radar gpr which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non destructive or geophysical technique combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution the radar profiles show the internal structures which include foreslope accretion trough cut and fill roll over and beach deposits foredune ridges contain large sets of low angle cross stratification from dune foreslope accretion with trough shaped structures from cut and fill on the crest and rearslope foreslope accretion indicates sand supply from the beach to the foreslope while troughs on the dune crest and rearslope are attributed to reworking by offshore winds bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement radar sequence boundaries within dunes have been traced below the water table passing into beach erosion surfaces these are believed to result from storm activity which erodes the upper beach and dunes in one example at brancaster a dune scarp and erosion surface may be correlated with erosion in the 1950s possibly the 1953 storm results suggest that dune ridge development is intimately linked to changes in the shoreline with dune development associated with coastal progradation while dunes are eroded during storms and where beaches are eroding a stable coast provides more time for dune development resulting in higher foredune ridges a model for coastal dune evolution is presented which illustrates stages of dune development in response to beach evolution and sand supply in contrast to many other coastal dune fields where the prevailing wind is onshore on the north norfolk coast the prevailing wind is directed along the coast and offshore which reduces the landward migration of sand dunes

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

sand incursion into temperate lithuania and tropical the bahamas maritime vegetation georadar visualization of target rich aeolian lithosomes abstract interaction of windblown sand with maritime vegetation either as dune migration or episodic grain transport is a common phenomenon along many sandy coasts vegetation introduces antecedent surface roughness especially when scaled to the landform height but its role may be concealed if overwhelmed by aeolian incursion and burial where field observations and cores lack detail for characterizing this complex process ground penetrating radar gpr offers continuous visualization of aeolian sequences along the curonian spit lithuania dune reactivation phases resulted in massive invasion of siliciclastic sand triggered by natural perturbations and land clearance massive 30 m high dunes entombed mature pine oak and alder stands and this process is ongoing mid frequency 200 mhz georadar surveys reveal landward dipping lateral accretion surfaces interrupted by high amplitude point source anomalies produced by recently buried trees in tropical regions dense vegetation and potential for rapid lithification of carbonate sand results in more complex internal structures along the windward coast of san salvador island the bahamas a massive dune has buried several generations of maritime scrubland resulting in highly chaotic reflection pattern and high target density on a nearby little exuma island numerous reentrants in aeolianites promoted formation of blowouts and incursion of windblown sand 10 25 m into a silver thatch palm forest high frequency 800 mhz gpr images resolve diffractions from trunks and roots buried by 2 m of oolitic sand basal refection morphology helps differentiate the irregular dune beachrock surface from a smooth palm frond mat aside from detecting and mapping buried vegetation geophysical images capture its effect on sediment accumulation this has the potential for differentiating its effect from other discordant structures within dunes clasts dissolution voids trunk molds burrows and cultural remains

geomorphological and sedimentological features in quaternary fluvial systems affected by solution induced subsidence ebro basin ne spain abstract the quaternary evolution and the morpho sedimentary features of some of the most important rivers in spain ebro and tagus rivers among others have been controlled by subsidence due to alluvial karstification of the evaporitic bedrock the subsidence mechanism may range from catastrophic collapse to slow sagging of the alluvium by passive bending in the ebro basin the mechanisms and processes involved in karstic subsidence were studied through the analysis of present day closed depressions as well as through old subsidence depressions palaeocollapses and solution induced basins and associated deformations recorded in the quaternary alluvial sediments the gallego ebro river system is presented as a case study of channel adjustments and geomorphic and sedimentary evolution of fluvial systems in dissolution induced subsidence areas in this fluvial system evaporite dissolution during particular quaternary time intervals namely early and middle pleistocene have lead to the development of a solution induced basin approximately 30 km long by 8 km wide filled by quaternary deposits with a total thickness in excess of 190 m the main river response to balance the subsidence in the alluvial plain was aggradation in the central reach of the subsiding area and degradation both in the upstream reach and in the valley sides where alluvial fans and covered pediments may prograde over the fluvial sediments the main sinking areas are recognized in the sedimentary record by anomalous thickenings in the alluvial deposits and fine grained sediments deposited in backswamp and ponded areas