facies distribution and sedimentary processes on the modern baram delta implications for the reservoir sandstones of nw borneo the baram delta has been classified as wave dominated and as a modern analogue for the prolific tertiary sandstone reservoirs in the baram delta province of nw borneo however the delta s facies distribution and sedimentary processes indicate that sedimentation is presently occurring only on the large mouth bar and that the baram is more properly categorised as a mixed wave and tide influenced delta more than half of the surface area of the mouth bar is dominated by tidal currents and covered with tidally deposited sediments because a relatively large tidal prism controls the nearshore hydrodynamics conversely the widespread tertiary shoreface reservoir sandstones are clearly wave dominant and tidal signatures are absent consequently the baram delta is not an appropriate analogue for most shoreface reservoir sandstones in nw borneo

the orange river southern africa an extreme example of a wave dominated sediment dispersal system in the south atlantic ocean sediments delivered to the south atlantic ocean by the orange river are fractionated and dispersed northwards and westwards by a vigorous longshore drift system and a number of ocean currents gravels are accreted to the coastline for a distance 300 km north from the orange river mouth sands are transported alongshore for 700 km but are in places along this transport path returned onshore by coastal winds to form the main namib sand sea and other smaller dune fields mud is more widely dispersed westwards northwards and southwards probably by slow moving ocean scale currents into basins on the shelf and onto the continental shelf edge this dispersal system operating since at least eocene times is believed to have originated during a time when there was a late cretaceous early cenozoic uplift of southern africa which resulted in 1 intensification of the existing southerly wind system 2 incision of the orange river which coupled with a shift in climate resulted in a coarsening of its sediment load delivered to the coast 3 a broad weakly subsiding or mildly uplifting inner continental shelf with little accommodation space for the sediment load of the incising orange river

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

landscape evolution during the late quaternary at the doce river mouth espirito santo state southeastern brazil article the sedimentary deposits of the deltaicplain of the doce and barra seca rivers southeastern brazil were studied by faciesanalysis pollenrecords 13 c c n analysis and ams 14 c dating today thisdeltaicplain isdominated by beach ridges and sandy terraces occupied by arboreal and herbaceous vegetation between 47 500 and 29 400 cal yr b p a deltaic system was developed in response mainly to eustatic sea level fall although the studied stratigraphic succession is compatible with the trend of global sea level fall the earlier sea level sug gested by the topographic position of these deltaic deposits was above the one expected during the mis3 stage a tectonic uplift likely occurred during the late quaternary and raised these deposits the post glacial sea level rise caused a marine incursion with invasion of embayments and broad valleys and it favored the evolution of an estuary with wide tidal mud flats occupied by mangroves between 7400 and 5100 cal yr b p the high river sand supply and or the relative sea level fall in the late holocene led to seaward and downward translation of the shoreline during normal forced regression producing progradational deposits with shrinkage of mangrove stands and expansion of marshes colonized by herbaceous vegetation therefore the stratigraphic architecture and evolution of the doce river deltaic plain suggest that fluvial sediment supply and relative sea level fluctuations related to quaternary global climatic changes and local tectonism exerted major controls on sedimentation through the variation of accommodation space and base level changes

millennial to secular time scale impacts of climate and sea level changes on mangroves from the doce river delta southeastern brazil this work integrates geomorphological sedimentological and palynological data with radiocarbon dating as well as 13c 15n and c n from sedimentary organic matter to provide a model of mangrove dynamics during the evolution of a wave dominated delta in southeastern brazil mangrove dynamics are analyzed within the context of millennial and secular climatic and sea level changes tidal flats positioned at highest limit of the intertidal zone along the edge of a lagoon sheltered by beach ridges were occupied by wetlands represented by mangrove and herbaceous vegetation during the mid holocene high sea level after considering the relative sea level fall and relatively higher fluvial sediment discharge during the last 6350 years progradation took place along this shoreline resulting in extensive beach ridge deposits that overlie transgressive muds this process led to loss of mangrove area similar dynamics were repeated at 3043 cal yr bp although in a relatively more distal i e seaward posi

periodic mudflat progradation northeastern coast of south america a hypothesis abstract the guiana coast of northeastern south america backed by mangrove swamps and fronted by migrating mudflats and associated subtidal mudbanks has developed during the holocene as a prograding mud wedge from amazon derived sediment a hypothesis is offered for the periodic stabilization of shifting mudflats a process that has been recognized previously as the mechanism for initiation of new land growth the hypothesis assumes that solar semiannual and 18 6 yr tidal components allow abnormal exposures of coastal mudflats and conditions that are favorable for establishment of avicennia mangroves once colonized mangrove roots displace muds upward thus decreasing the frequency of tidal inundation and increasing the ability of vegetation to trap and hold muds based on estimated ates of root growth and forecasted tide records for the coast of surinam land elevation will increase by 25 cm in 10 yr and frequency of tidal inundation above 2 45 m 8 0 ft will decrease from 106 to 2 per year during the same period

a review of wave dominated clastic shoreline deposits abstract barrier islands beaches wave dominated deltas and chenier plains probably form more than one fifth of present coasts and constitute an even larger proportion of the subsiding lowland coasts likely to be preserved in the stratigraphic record the geometry vertical sequences and composition of their deposits are the result of 1 shoreline behaviour whether transgressive regressive or stable 2 physical processes particularly the relative intensities of waves and tides 3 climate 4 global tectonic setting and 5 topography of underlying deposits published interpretations indicate that equivalent deposits are abundant in the geological record sandstones are mostly quartzose cemented by carbonates and quartz and have sheet or linear geometries ancient deposits can provide evidence of palaeogeography and some are economically significant particularly as hydrocarbon reservoir rocks four end member sedimentation models are proposed for the interpretation of ancient deposits 1 transgressive sheet sands associated with deltas 2 non deltaic transgressive sheet sands 3 regressive sheet sands and 4 linear sand bodies probable depositional settings geometries characteristics of deposits and palaeocurrent patterns are discussed

early diagenesis of biogenic silica in the amazon delta alteration authigenic clay formation and storage deltaic environments are commonly assumed to be relatively minor sites of biogenic silica burial because of the small quantities of opaline silica detected by most operational analytical techniques rapid conversion of biogenic silica into authigenic silicates is also often discounted as a significant control on oceanic silica budgets a variety of evidence for extensive early diagenetic alteration of biogenic silica in rapidly accumulating amazon delta sediments indicates that both of these general assumptions are unjustified apparent lack of significant biogenic silica storage in deltaic environments particularly in the tropics may be largely an artifact of operational definitions that do not include early diagenetic products of biogenic silica biogenic silica particles buried in suboxic amazon delta deposits can be unaltered partially dissolved covered with aluminosilicate or metal rich coatings or completely reconstituted into authigenic k fe rich aluminosilicate minerals pore water k mg f si and solid phase distributions direct observations of particles laboratory experiments and depositional context indicate that authigenic clays form rapidly 1 yr in the seasonally reworked surface layer 0 5 2 m of the delta topset and are disseminated during sediment remobilization fe al oxide rich debris derived from the tropical drainage basin is an abundant reactant and thus the supply of biogenic silica is a major control on the amount of clay formed the mild 1 na2co3 alkaline leach procedure commonly used to estimate biogenic silica was modified to include an initial mild leach step with 0 1n hcl to remove metal oxide coatings and to activate poorly crystalline authigenic phases for alkaline dissolution well crystallized clays are not significantly affected by this modification nor is bulk amazon river bed sediment the two step procedure indicates that 90 of the biogenic silica originally present in deposits is converted to clay or otherwise altered raising the effective quantity of biogenic silica stored from 33 to 296 mol si g 1 1 8 sio2 biogenic si stored in the delta increases away from the river mouth across shelf and along the dispersal system where primary production is highest the k si ratio of labile authigenic material is 0 19 mol mol 1 far higher than amazon river suspended matter 0 07 mol mol 1 diagenetic models indicate formation rates in the mobile sediment layer of 2 8 mol k g 1 yr 1 16 mol si g 1 yr 1 inclusion of authigenic alteration products of biogenic silica in estimates of reactive si burial increases the deltaic storage of riverine si to 22 of the amazon river input the rapid formation of aluminosilicates from biogenic sio2 seawater solutes and remobilized fe al oxides represents a form of reverse weathering rapid reverse weathering reactions in tropical muds and deltaic deposits the largest sediment depocenters on earth confirms the general importance of these processes in oceanic elemental cycles

alongshore sediment bypassing as a control on river mouth morphodynamics river mouths shoreline locations where fluvial and coastal sediments are partitioned via erosion trapping and redistribution are responsible for the ultimate sedimentary architecture of deltas and because of their dynamic nature also pose great management and engineering challenges to investigate the interaction between fluvial and littoral processes at wave dominated river mouths we modeled their morphologic evolution using the coupled hydrodynamic and morphodynamic model delft3d swan model experiments replicate alongshore migration of river mouths river mouth spit development and eventual spit breaching suggesting that these are emergent phenomena that can develop even under constant fluvial and wave conditions furthermore we find that sediment bypassing of a river mouth develops though feedbacks between waves and river mouth morphology resulting in either continuous bypassing pathways or episodic bar bypassing pathways model results demonstrate that waves refracting into the river mouth bar create a zone of low alongshore sediment transport updrift of the river mouth which reduces sediment bypassing sediment bypassing in turn controls the river mouth migration rate and the size of the river mouth spit as a result an intermediate amount of river discharge maximizes river mouth migration the fraction of alongshore sediment bypassing can be predicted from the balance between the jet and the wave momentum flux quantitative comparisons show a match between our modeled predictions of river mouth bypassing and migration rates observed in natural settings

physical processes and fine grained sediment dynamics coast of surinam south america abstract the prograding holocene mud wedge between the amazon and orinoco rivers in the trade wind belt of northeastern south america provides a modern day example of muds accumulating under moderate wave energy conditions gigantic shore attached mudbanks 10 km 20 km composed partly of thixotropic fluid mud gel front this coast every 30 60 km to form a buffer to wave attack and a temporary storage for fine grained sediments this mesotidal coast tide range 2 0 m with gentle offshore slope 0 0006 allows the exposure twice a day of extensive tidal flat deposits which are backed by mangrove swamps on a well developed chenier plain complex field experiments were conducted in surinam du ing 1975 and 1977 to provide new information on process form relationships in this interesting but unusual muddy environment simultaneous measurements of waves currents tide elevation suspended sediment concentration and variations in mud density show that soft intertidal and subtidal muds are suspended at both tide and wave frequency suspended sediment concentrations typically exceed 1 000 mg l at the surface as incoming solitary like waves partially disperse fluid mud into overlying water on a falling or rising tide redeposition of mud may occur near time of high tide the strong attenuation of shallow water waves by these muds provides conditions that are favorable for further sedimentation high concentrations of suspended fluid mud together with solitary like waves from the northeast throughout the year can lead to extraordinarily high net sediment transport rates in the nearshore zone calculations based on solitary wave theory and on data obtained from this study indicate that 15 65 106 m3 of mud can move along shore each year without involving breaking waves the concept of radiation stress and a nearshore circulation cell or bedload transport farther offshore outside the zone of wave dominance wind driven currents and the guiana current combine to transport muds to the northwest consistent with the observed direction of mudflat migration

sediment accumulation in a modern epicontinental shelf setting the yellow sea sediment accumulation in the yellow sea epicontinental shelf environment is investigated on 100 yr and 1000 yr time scales using 210pb and 14c geochronologies the distribution of modern 210pb accumulation rates in the yellow sea reveals that the loci of modern huanghe sediment accumulation are the topset 1 2 mm yr foreset 4 9 mm yr and proximal bottomset deposits 2 4 mm yr of the shandong subaqueous delta which extends south from the shandong peninsula 210pb rates in the distal bottomset deposits of the subaqueous delta in the central and southern yellow sea are generally low 0 3 0 9 mm yr a sediment budget demonstrates that between 9 15 of the annual huanghe discharge is accumulating in the yellow sea about two thirds of this sediment is accumulating in the topset foreset and proximal bottomset deposits of the shandong subaqueous delta with the remaining third accumulating as widespread distal bottomset deposits 14c age dates of subaqueous delta sediments indicate that the thick 40m clinoform structure formed predominantly between 6200 and 4060 yrs b p at rates approaching 20 mm yr observations in the yellow sea as well as on the amazon and ganges brahmaputra shelves demonstrate that subaqueous deltaic stratigraphy is the general rule where major rivers enter energetic shelves whether epicontinental or pericontinental the development of extensive bottomset deposits may be restricted to epicontinental shelf environments and may be diagnostic of sedimentation in this type of setting

wave influence in the construction shaping and destruction of river deltas a review abstract waves are an important agent in the construction shaping and destruction of river deltas notwithstanding the commonality of waves in oceans and seas wave influence on deltas varies considerably depending on the coastal morphology and nearshore bathymetry although there have been advances in understanding the way waves approaching a delta shape its shoreline much still remains to be known of the interactions between waves and river deltas deltas are built essentially from sediments supplied by rivers sand sized and coarser sediments may also be derived from nearby abandoned delta lobes or from older relict nearshore deposits transported by wave reworking and longshore currents alternatively delta erosion by waves can also release sediment that is redistributed alongshore or that accumulates offshore the extent to which bedload is supplied to and sequestered in or lost by deltas through waves and longshore transport strongly depends on interactions between waves and fluvial discharge at the river mouth these interactions and the mutual adjustments they engender are not only important in the overall balance between delta retreat progradation or aggradation but also in processes such as avulsion and channel switching as well as in the eventual survival of a delta in the face of sea level rise where waves are important fluvial liquid discharge is high and sediment supply is rich in bedload two important aspects are the blocking of waves and longshore currents by strong river discharge and the formation of bars at the river mouth field studies of the complex interactive processes prevailing where river flows encounter waves are however non existent and numerical modelling though promising hampered by scale constraints and the difficulty of replicating them and generating mouth bars in the presence of longshore currents this interaction influences the seaward extent of the delta mouth protuberance and its stability this protuberance then forming the regional shoreline template to which waves and longshore currents adjust longshore currents can redistribute wave reworked mouth bar deposits emplaced during strong river flow transport may be either divergent from the mouth or may be regionally unidirectional but wherein the symmetry of some deltas probably rare may be maintained by a strong river blocking effect on transport from the updrift flank the mouth protuberance may be such as to foster transport reversal counter drift at the delta margins that contributes to sediment sequestering within the delta these interactions largely contribute in shaping delta shorelines and together with the abundance of sediment supply and grain size determine the resultant wave formed shoreline barrier types which include spits more or less closely spaced beach ridges and barrier islands and cheniers in situations of punctuated progradation or retreat where several distributary mouths occur pronounced longshore variability in wave processes and wave induced sediment transport may ensue resulting in multiple drift cells that assure the retention of sand and coarse grained sediments within the delta waves can also be an important agent in the reworking and retreat of mud rich deltas that generally conform in morphology to the river dominated such as the mississippi or tide dominated such as the ganges brahmaputra or chao phraya types resulting in the episodic formation of sandy cheniers and beach ridges although sea level rise is likely to lead to enhanced wave reworking of deltas the possible prevalence of aggradation in lieu of progradation channel switching and avulsion and washover processes may contribute to the disorganization of waves and longshore transport fostering deltaic sequestering of sand and coarser sized sediment and delta survival the weakening of river discharges resulting from human activities will invariably lead however to enhanced wave reworking of deltas and to deltaic sediment redistribution by longshore currents the massive swing towards significant reductions in fluvial sediment supply today may signify the ultimate demise of many deltas in the coming decades through a process of delta shoreline straightening by waves in addition to accelerated sinking these various foregoing aspects of the relationship between waves and river deltas are reviewed here across a range of timescales and new interaction concepts proposed using numerous examples of deltas in the world and on the basis of case studies conceptual studies and numerical modelling studies in the literature spanning more than forty years

seasonal interannual and mesoscale variability of the black sea upper layer circulation derived from altimeter data 1 topex poseidon and ers altimeter data comprising the period from may 1992 to may 1999 are assimilated into a shallow water model for providing a dynamically consistent interpretation of the sea surface height variations and estimation of the temporal and spatial characteristics of the upper layer circulation in the black sea these 7 year long observations offer a new capability for interpretation of major transient and quasi permanent features of the upper layer circulation the instantaneous flow fields involve a complex eddy dominated system with different types of structural organizations in which the eddies and the gyres of the interior cyclonic cell interact continuously among themselves and with meanders and filaments of the rim current the circulation possesses a distinct seasonal cycle whose major characteristic features repeat every year with some year to year variability an organized two gyre winter circulation system disintegrates gradually into a series of interconnecting eddies in the summer and autumn months which are also characterized by more pronounced and complex mesoscale activity in the peripheral flow system our analyses suggest a revised schematic circulation picture of the major quasi permanent and recurrent elements of the black sea

stratigraphy and holocene evolution of a regressive barrier in south brazil abstract the paranagua coastal plain is a 600 km 2 barrier system located in south brazil 25 30 s and is largely made up of pleistocene and holocene beach ridges sea level history in the area is characterized by a gradual 3 5 m sea level fall in the last 5000 years several reverse circulation drill logs from the pleistocene and holocene sectors allowed for the definition of a general morphostratigraphic model of the coastal plain which proposes the staking of at least two generations of marine deposits upon continental and paleo estuarine sediments analysis of shallow vibro cores and exposures along back barrier creeks indicates the existence of four transgressive estuarine estuarine channel overwash and flood tidal delta and three regressive beachface nearshore and upper shoreface sedimentary facies in the holocene section of the coastal plain the morphostratigraphy suggests that barrier emplacement took place at the last stages of the post glacial marine transgression when the back barrier estuary was squeezed in between the pleistocene and holocene barriers holocene barrier progradation was significant in both the shore normal and longshore direction and was apparently very swift in the last thousand years corresponding to a period when sea level fell by 1 5 m and when about half of the present barrier volume was accumulated higher progradation rates are ascribed to the arrival of sediment yielded by an active littoral drift system which appears to have eroded large extents of several holocene barriers along 100 km of coastline

composite sedimentary record of falling stages of pleistocene glacio eustatic cycles in a shelf setting crotone basin south italy abstract a thick pleistocene shelf and nearshore cyclical succession was deposited in the s mauro sub basin of the crotone basin southern italy the regressive units of the cycles are mostly represented by coastal siliciclastic and bioclastic prograding wedges showing a clinoform geometry these are separated by blanket like deposits of high lateral persistence recording major transgressive episodes the aim of this paper is 1 to describe facies patterns and depositional setting of two prograding wedges particularly focussing on their polycyclic internal architecture 2 to analyze these units within a sequence stratigraphic framework and 3 to speculate on the possible origin of the small scale cyclicity the two wedges analyzed in this paper consist of a number of shingles individual shingles consist of two physically connected units 1 a relatively thin package of sigmoid clinoforms grading into 2 a volumetrically dominant package of oblique tangential clinoforms with toplap terminations the shingles are bounded by seaward dipping surfaces with sigmoid clinoform geometry which are ravinement surfaces updip passing into conformable flooding surfaces downdip the wedges are thus organized into high frequency small scale sequences each comprising transgressive highstand and falling stage systems tracts as a whole individual prograding wedges are interpreted as forced regressive units as the shoreline was subject to an overall shift basinwards and downwards along a low angle trajectory in spite of the repeated minor relative sea level rises tectonic subsidence and particularly the syndepositional growth of gentle synclines are thought to have been the key factors allowing the preservation of these forced regressive units progradation of the wedges took place in a high energy wave climate characterized by high frequency of storms and very efficient alongshore redistribution of sediments recurrent storm driven offshore currents led to intense reworking of sediments on the topset platform and gravity spreading on the foreset slope of the prograding wedges well oxygenated conditions over the shelf due to intensified storm activity during glacial periods may have enhanced the rate of production of skeletal foramol type carbonates it can reasonably be assumed that progradation took place from a line source and that the sand bodies are to be regarded as coastal prograding bodies in spite of active syndepositional tectonics the cycles can be correlated to pleistocene high amplitude sea level oscillations the older of the two wedges can be correlated through bio magnetostratigraphy to the major climatic transition which occurred from the marine oxygen isotope stage 25 to 24 22 rio et al 1996 the younger probably developed during the sea level fall that ended with substage 18 2 as suggested by sequence and bio stratigraphic data the prograding wedges are thus interpreted to record long lived sea level falls of fourth order cycles due to the particular depositional setting we are inclined to exclude authigenic mechanisms in the origin of small scale cyclicity although the concomitance and interaction of different controlling factors may be taken into account it is tempting to ascribe this cyclicity to minor eustatic changes punctuating long lived erratic falling stages possibly accompanied by climate driven fluctuations of sediment supply shelf perched and shelf edge prograding units consisting of foramol type carbonates are apparently a common falling stage to lowstand depositional feature in the mediterranean area during the late pliocene and pleistocene

sedimentary facies and stratigraphy of a last interglacial coastal barrier in south brazil shoreline sedimentation during the last interglacial highstand on the rio grande do sul coastal plain southern brazil is represented by a sandy barrier that extends almost uninterrupted for hundreds of kilometers along the coast facies analyses of high quality exposures in several sandpits situated in the northern part of the coastal plain provided an opportunity to examine the stratigraphic nature of these deposits based on distinct assemblages of physical and biogenic sedimentary structures the vertical sequence of facies reveals a regressive prograded barrier with vegetated coastal dune sands overlying beach and shallow marine sediments progradation was probably promoted by abundant supplies of nearshore sand during the highstand and early fall of sea level forced regression associated with the last interglacial period around 125 ka as indicated by elevations of ophiomorpha burrows the maximum level reached by the sea was around 7 m above the present sea level paleocurrent data suggest that in the studied area shoreline orientation hydrodynamics and sediment transport during the last interglacial highstand were similar to present day conditions

the influence of amazon derived mud banks on the morphology of sandy headland bound beaches in cayenne french guiana a short to long term perspective abstract the 1600 km long south american coast between the amazon and the orinoco deltas has a prograded muddy shoreline comprised of sandy cheniers the 15 km long bedrock coast of cayenne french guiana differs from the rest of this fluctuating alluvial coast in that it comprises several headland bound fringing sandy barriers that have experienced limited progradation and do not behave as cheniers that migrate landward over a muddy base the limited progradation of these barriers is probably due to blanketing of fluvial sand by the cover of amazon mud on the inner shelf which precludes shoreward reworking to supply the beach and barrier systems aerial photographs satellite images and recent field observations show that alternations between mud bank phases when amazon derived mud banks migrating northwestwards attain the cayenne area and interbank phases characterised by relative scarcity of mud result in marked spatial and temporal variations in beach dynamics and morphology these include periodic alternations in longshore drift that lead to a rare form of total or partial beach rotation that does not result as is generally reported for nonmud bank affected beaches from seasonal variations in deepwater wave approach directions these beach morphological changes have been defined in terms of a simple four stage conceptual model comprising bank interbank and transitional phases in extreme bank phases the mud banks responsible for muddy coastal progradation on the amazon orinoco coast may directly weld onto the beaches for periods ranging from months to years leading to a rare example at the world scale wherein the dynamics of ocean facing beaches are completely muted under the protective cover of mud that may become rapidly colonised by mangroves the observations also suggest that these changes do not affect the medium term order of tens of years beach sand budgets mud welding onto the beaches may however sequester at short time scales order of months to years sand eroded from the beaches subsequent mud erosion leads to release of this sand and its restitution to the beach sand budget

depositional facies of a mud shoreface in suriname south america a mud analogue to sandy shallow marine deposits abstract immense volumes of argillaceous muds are being deposited along the world s longest continuous mud coastline which faces the open equatorial atlantic not only are these muds deposited in an environment normally associated with sand deposits but just as in sandstones sedimentary structures within these muds record the dynamic processes that deposited them this study investigates a 100 km long portion of the suriname coast utilizing cores bathymetric surveys and field observations from nearshore and innershelf environments using terminology borrowed from sand coastlines the innershelf nearshore of suriname is divided into transition zone shoreface foreshore and backshore the transition zone consists of a mix of offshore sands and shoreface muds shoreface and foreshore are subdivided into bank and interbank zones these zones are transitory because mud banks which make up the bank zones migrate westwardly mud banks are up to 5 m high 50 to 60 km long 10 to 20 km wide and oriented at oblique angles to the coastline these banks generally consist of fluid muds which are so fluid that they interact with surface waves causing them to be altered and damped banks are attached to the shoreline and commonly produce progradation of the coastline substrate within the interbank zone is more consolidat d than within the mud banks because of lack of wave dampening wave energies are relatively high within the interbank zone producing erosion of the shoreface and shoreline sand beaches are generally formed within the erosional interbank shoreline the vertical sedimentary sequence within the shoreface muds is a record of bank migration and other sedimentary processes present wave and current energies are recorded by scour and fill features discontinuity features micro cross laminations lenticular laminations and parallel to subparallel laminations laminations appear to be created by boundary layer shearing within fluid muds which are above wave base and made mobile by wave generated shore parallel currents large scale evidence for migration of the mud banks is westward dipping acoustical reflectors within the banks these reflectors which are over a kilometer apart mark the boundaries of annual migration events biogenic structures are generally absent within the fluid bank muds but are present within the more consolid ted interbank zone and associated with discontinuity features which are buried interbank surfaces migration and vertical stacking of mud banks are recorded by vertical sequences of massive and laminated muds which were deposited by mud banks and discontinuity features which were formed by interbank zones the coastal deposits of suriname are a mud analogue to nearshore and innershelf sand deposits transition zones of both mud and sand systems reflect a transition from offshore to shoreface processes and sediments both mud and sand shoreface foreshore systems reflect sediment input and wave current and tidal processes that act on them mud banks of suriname resemble linear sand ridges on the continental shelf of the eastern u s a in shape oblique orientation to the coastline and orientation with respect to dominant direction of transport processes the sequence of massive and laminated muds with discontinuity features resembles laminated to burrowed sequences found in ancient and recent nearshore and shallow marine sands

evidence for a transgressive barrier within a regressive strandplain system implications for complex coastal response to environmental change clastic depositional strandplain systems have the potential to record changes in the primary drivers of coastal evolution climate sea level and the frequency of major meteorological and oceanographic events this study seeks to use one such record from a southern brazilian strandplain to highlight the potentially complex nature of coastal sedimentological response to small changes in these drivers following a 2 to 4 m highstand at ca 5 8 ka in southern brazil falling sea level reworked shelf sediment onshore forcing coastal progradation smoothing the irregular coastline and forming the 5 km wide pinheira strandplain composed of ca 500 successive beach and dune ridges sediment cores grab samples and 11 km of ground penetrating radar profiles reveal that the strandplain sequence is composed of well sorted fine to very fine quartz sand since the mid holocene highstand the shoreline prograded at a rate of ca 1 to 2 m yr 1 through the deposition of a 4 to 6 m thick shoreface unit a 1 to 3 m thick foreshore unit containing ubiquitous ridge and runnel facies and an uppermost beach and foredune unit however the discovery of a linear 100 m wide barrier ridge with associated washover units a 3 to 4 m deep lagoon and 250 m wide tidal inlet within the strandplain sequence reveals a period of shoreline transgression at 3 3 to 2 8 ka during the otherwise regressive developmental history of the plain the protected nature of pinheira largely buffered it from changes in precipitation patterns wave energy and fluvial sediment supply during the time of its formation however multiple lines of evidence indicate that a change in the rate of relative sea level fall probably due to either steric or ice volume effects may have affected this coastline thus whereas these other potential drivers cannot be fully discounted this study provides insights into the complexity of decadal scale to millennial scale coastal response to likely variability in sea level change rates

episodic river flooding events revealed by palynological assemblages in jurassic deposits of the brent group north sea spore and pollen sporomorph assemblages from middle jurassic marine deposits of the brent group in the northern north sea are investigated to assess temporal and spatial variations in vegetation and depositional processes four wells were sampled for palynology from the penguins cluster and the don north east fields through the rannoch formation shoreface succession hyperpycnite deposits occur throughout but are concentrated within the lower part of the section these are expressed by sand prone beds displaying waxing and waning current motifs normally graded muddy beds and structureless mudstones hyperpycnal hypopycnal deposits resulting from episodic river flooding represent important sedimentary features as they may be preserved below fair weather wave base in more offshore settings and potentially be the only record of the former presence of a nearby river mouth the hyperpycnites typically contain abundant botryoccocus spp amorphous organic matter aom and hinterland sporomorph taxa with relatively few marine components compared to associated marine shoreface facies variations in palynofacies assemblages and botryococcus spp abundances indicate frequent river mouth avulsion ordination of samples using non metric multidimensional scaling nmds indicates that shoreface samples of the sampled wells are relatively distinct but hyperpycnite samples are highly similar regardless of their sampled well this suggests that depositional processes and spore pollen sources i e catchment zones were similar among hyperpycnite events across different wells abundant bisaccate pollen botryococcus spp and aom within interpreted hyperpycnites suggest sediment mixing along the fluvial drainage path during flooding events the terrestrial signature of hyperpycnite sporomorph assemblages demonstrates that underflows remained coherent as they descended the shoreface profile with little turbulent mixing with ambient marine waters sporomorph assemblages display few large changes through time suggesting vegetation on the adjacent coastal plain was relatively static through the studied interval

complex coastal change in response to autogenic basin infilling an example from a sub tropical holocene strandplain thick bay fill sequences that often culminate in strandplain development serve as important sedimentary archives of land ocean interaction although distinguishing between internal and external forcings is an ongoing challenge this study employs sediment cores ground penetrating radar surveys radiocarbon dates palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes notably a reduction in wave energy in response to coastal embayment infilling in coastal evolution and shoreline morphodynamics following a regional 2 to 4 m highstand at ca 5 8 ka the 75 km2 tijucas strandplain in southern brazil built from fluvial sediments deposited into a semi enclosed bay holocene regressive deposits are underlain by fluvial sands and a pleistocene transgressive regressive sequence and backed by a highstand barrier island the strandplain is immediately underlain by 5 to 16 m of seaward thickening fluvially derived holocene age basin fill mud several trends are observed from the landward oldest to the seaward youngest sections of the strandplain i the upper shoreface and foreshore become finer and thinner and shift from sand dominated to mud dominated ii beachface slopes decrease from 11 to ca 7 and iii progradation rates increase from 0 4 to 1 8 m yr 1 hydrodynamic modelling demonstrates a correlation between progressive shoaling of tijucas bay driven by sea level fall and sediment infilling and a decrease in onshore wave energy transport from 18 to 4 kw m 1 the combination of allogenic sediment supply falling relative sea level and geology and autogenic decrease in wave energy due to bay shoaling processes drove the development of a regressive system with characteristics that are rare if not unique in the holocene and rock records these findings demonstrate the complexities in architecture styles of highstand and regressive systems tracts furthermore this article highlights the diverse internal and external processes and feedbacks responsible for the development of these intricate marginal marine sedimentary systems

image distortion effects in sar subsurface imaging and a new iterative approach for refocusing and coregistration high resolution subsurface imaging and topography estimation in deserts is very useful in many applications such as oil field and ground water explorations and archaeological surveys to address this problem we previously developed a subsurface imaging interferometric synthetic aperture radar insar concept that can estimate the subsurface topography however the image resolution of such a system is rather limited by the current techniques available for sar focusing and insar image coregistration as the propagation effects and phase front distortion caused by the top layer are not accounted for in this paper we discuss different image aberrations that result from the top surface topography including geometric and defocusing distortion the issue created by subsurface caustics and their effect on sar imaging are discussed we then present a new approach to estimating and correcting such aberrations by using simulations and measurements it is shown that up to an order of magnitude improvement in the subsurface image resolution as well as significant improvement on subsurface interferogram coherence can be achieved the proposed approach is based on the application of a previously developed subsurface inversion algorithm and a newly developed fast subsurface insar simulator the results are verified numerically using 3 d simulations of different sand dune geometries and an experiment using scaled model measurements under laboratory conditions

littoral steering of deltaic channels abstract the typically single threaded channels on wave influenced deltas show striking differences in their orientations with some channels oriented into the incoming waves e g ombrone krishna and others oriented away from the waves e g godavari sao francisco understanding the controls on channel orientation is important as the channel location greatly influences deltaic morphology and sedimentology both subaerially and subaqueously here we explore channel orientation and consequent feedbacks with local shoreline dynamics using a plan form numerical model of delta evolution the model treats fluvial sediment delivery to a wave dominated coast in two ways 1 channels are assumed to prograde in a direction perpendicular to the local shoreline orientation and 2 a controlled fraction of littoral sediment transport can bypass the river mouth model results suggest that channels migrate downdrift when there is a significant net littoral transport and alongshore transport bypassing of the river mouth is limited in contrast river channels tend to orient themselves into the waves when fluvial sediment flux is relatively large causing the shoreline of the downdrift delta flank to attain the orientation of maximum potential sediment transport for the incoming wave climate using model results we develop a framework to estimate channel orientations for wave influenced deltas that shows good agreement with natural examples an increase in fluvial sediment input can cause a channel to reorient itself into incoming waves behavior observed for example in the ombrone delta in italy our results can inform paleoclimate studies by linking channel orientation to fluvial sediment flux and wave energy in particular our approach provides a means to quantify past wave directions which are notoriously difficult to constrain

relative sea level and climatic changes in the amazon littoral during the last 500 years abstract an integrated approach focused on sedimentology geochemistry palynology c and n isotopes and radiocarbon dating of a sediment core from an herbaceous plain not flooded by tides of the amapa littoral near the amazon river mouth allowed identification of two phases with marine and terrestrial influences mangroves occurred over tidal mud flats with marine influence between 5610 5470 and 470 310 cal yr bp the absence of mangrove vegetation since 470 310 cal yr was followed by the transition of brackish water organic matter to terrestrial c3 plants also the geochemical data indicate a decrease in sea water influence during this last time interval likely the displacement of mangrove forest to lower surfaces was caused by a relative sea level fall that may be associated with drier conditions with less rainfall during the second part of the last millennium as suggested by this work slight relative sea level fluctuations caused by regional or global climatic change may affect significantly the current mangrove area

a new mechanism for millennial scale positive precipitation anomalies over tropical south america abstract continental and marine paleoclimate archives from northwestern and northeastern south america recorded positive precipitation anomalies during heinrich stadials hs these anomalies have been classically attributed to enhanced austral summer monsoon precipitation however the lack of marine paleoclimate records off eastern south america as well as inconsistencies between southeastern south american continental and marine records hamper a comprehensive understanding of the mechanism responsible for sub tropical south american hydroclimate response to hs here we investigate piston core m125 95 3 collected off eastern south america 10 94 s and simulate south american hs conditions with a high resolution version of an atmosphere ocean general circulation model further meridional changes in precipitation over sub tropical south america were assessed with a thorough compilation of previously available marine paleorecords our ln ti ca and ln fe k data show increases during hs6 younger dryas it is the first core off eastern south america and the southernmost from the atlantic continental margin of south america that unequivocally records hs related positive precipitation anomalies based on our new data model results and the compilation of available marine records we propose a new mechanism for the positive precipitation anomalies over tropical south america during hs the new mechanism involves austral summer precipitation increases only over eastern south america while the rest of tropical south america experienced precipitation increases during the winter challenging the widely held assumption of a strengthened monsoon south american precipitation changes were triggered by dynamic and thermodynamic processes including a stronger moisture supply from the equatorial north atlantic tropical south atlantic in austral winter summer

an introduction to the geological significance of sediment transport and accumulation on the amazon continental shelf in order to understand the formative processes and resulting stratigraphy on the amazon shelf and adjacent shoreline of amapa geological investigations were undertaken as part of a multidisciplinary amazon shelf sediment study amasseds the design of the study provided results of a multifaceted nature integrated with observations in other disciplines focused on sedimentary processes representative of fluctuating conditions on several time scales and broadly distributed on the shelf including regions not investigated in the past on short time scales most muddy sediment is transported northwest of the river mouth from there it moves seaward as fluid mud to cause rapid accumulation of foreset beds and moves northwestward to prograde the northernmost amapa shoreline and to supply sediment to the guianas fluid muds cover the shelf as far northward as 3 5 n and allow strong tides to propagate to shore where tidal currents cause most of the amapa shoreline to undergo erosion today averaged over decades and centuries about half of the amazon sediment discharge accumulates on the adjacent shelf and another significant fraction one sixth leads to accretion of the northernmost amapa shoreline and northwestward bypassing of sediment the remaining sediment is hypothesized to be trapped in deltaplain deposits of the lower amazon river system the foreset region and shoreline represent the two common loci of sediment accumulation that alternate their predominance on time scales of millennia and lead to a two stage progradation of coastal plain and subaqueous deltaic deposits this muddy regressive sedimentation during high sea level is replaced by formation of erosional sand layers during low sea level and transgressive conditions future research in the study area should address important considerations that were delineated by the present study including mechanisms of shoreline accretion the holocene history recorded in topset and coastal plain strata the role in local sedimentation played by the large shoal extending from cabo norte and the entrapment of amazon sediment by the delta plain

ranging performance of satellite laser altimeters topographic mapping of the earth moon and planets can be accomplished with high resolution and accuracy using satellite laser altimeters these systems employ nanosecond laser pulses and microradian beam divergences to achieve submetre vertical range resolution from orbital altitudes of several hundred kilometres in this paper the authors develop detailed expressions for the range and pulsewidth measurement accuracies and use the results to evaluate the ranging performances of several satellite laser altimeters currently under development by nasa for launch during the next decade the analysis includes the effects of the target surface characteristics spacecraft pointing jitter and waveform digitizer characteristics the results show that ranging accuracy is critically dependent on the pointing accuracy and stability of the altimeter especially over high relief terrain where surface slopes are large at typical orbital altitudes of several hundred kilometres single shot accuracies of a few centimetres can be achieved only when the pointing jitter is on the order of 10 mu rad or less

microbial biomarkers support organic carbon transport from methane rich amazon wetlands to the shelf and deep sea fan during recent and glacial climate conditions abstract we have investigated the delivery of terrestrial organic carbon oc to the amazon shelf and deep sea fan based on soil marker bacteriohopanepolyols bhps adenosylhopane and related compounds and branched glycerol dialkyl glycerol tetraethers gdgts as well as on 14c dating of bulk organic matter the microbial biomarker records show persistent burial of terrestrial oc evidenced by almost constant and high bit values 0 6 and soil marker bhp concentration 80 230 g g toc total oc on the late holocene shelf and even higher bit values 0 8 0 9 but lower and more variable soil marker bhp concentration 40 100 g g toc on the past glacial deep sea fan radiocarbon data show that oc on the shelf is 3 4 kyr older than corresponding bivalve shells emphasizing the presence of old carbon in this setting we observe comparable and unexpectedly invariant bhp composition in both marine sediment records with a remarkably high relative abundance of c 35 amino bhps including compounds specific for aerobic methane oxidation on the shelf avg 50 of all bhps and the fan avg 40 notably these marine bhp signatures are strikingly similar to those of a methane producing floodplain area in one of the amazonian wetland varzea regions the observation indicates that bhps in the marine sediments may have initially been produced within wetland regions of the amazon basin and may therefore document persistent export from terrestrial wetland regions with subsequent re working in the marine environment both during recent and past glacial climate conditions

channel curvature effects on estuarine circulation in a highly stratified tropical estuary the sao francisco river estuary brazil abstract the effects of the channel curvature on estuarine circulation were assessed in the sao francisco river estuary this estuary is a deltaic front system with a highly stratified salinity distribution the assessment was based on field experiments where currents and salinity and temperature were monitored during a semi diurnal tidal cycle in two cross sections with distinct curvatures radii of 2 and 8 km the least squares method was used to determine the mean velocity residual velocity and the tidal velocity amplitude and phase for the m2 harmonic the results for the m2 harmonic were compared to an analytical solution that considers a simplified momentum balance between barotropic pressure gradient and bottom friction the model skill for these two results was 0 44 and 0 63 for sections a and b respectively the differences between these results indicate that there are other dynamically influential forces for the longitudinal momentum balance besides those included in the analytical solution the baroclinic pressure gradient presented values two orders of magnitude greater than the bottom friction demonstrating the dynamic importance of this force although centrifugal acceleration is a component of the lateral momentum balance it also plays a role in the distribution of longitudinal currents in the cross section displacing the maximum currents towards the exit of the curve in addition to the channel curvature effect the influence of the bathymetry was also observed on the tidal amplitude in the cross sections and on the depth averaged residual longitudinal velocities along the sections with the highest average speed in the shallowest areas of each section

transition from marine to fluvial dominated sediment supply at shoalhaven prograded barrier southeastern australia abstract prograded barriers are depositional coastal landforms which have the potential to reveal changes in the primary drivers of coastal evolution within their varied morphology beach ridges and intervening swales preserve paleoenvironmental records of coastal processes relative sea level and storm events optically stimulated luminescence osl dating of quartz grains airborne lidar derived morphology and sediment texture and mineralogy reveal four different periods of morpho sedimentary progradation history in the shoalhaven barrier system in southeastern australia the barrier is composed of approximately 40 ridges that occupy an area of 15 2 km2 comprising an estimated sand volume of approximately 88 000 000 m3 above mean sea level osl dating of ten samples taken from a 940 m long transect across the holocene system indicated that the barrier prograded at a slow rate of approximately 0 12 m yr from 6130 330 to 2400 130 years ago and subsequently at a higher rate of 0 22 m yr until 600 130 years ago more recently an increase in historical accumulation and progradation rates has favoured development of an anomalously high foredune fronting the system with the formation of lower ridges in the past two centuries increasing angularity and feldspar content observed via scanning electron microscope sem and determined using x ray diffraction xrd analysis respectively imply a transition in sediment supply progradation has been sustained through delivery and reworking of marine sediments from offshore following the marine transgression subsequently augmented by fluvial sands discharged to the coast by the shoalhaven river the adjustment in progradational rates and sediment provenance influenced the morphology and spacing of individual ridges and the regressive system as a whole average progradation rates for the shoalhaven barrier revised from those previously reported using radiocarbon dating are considered lower than most of barriers studied in similar coastal environments around australia indicating the different ways that similar progradation systems have evolved

the m2 tide on the amazon shelf as part of a multidisciplinary amazon shelf sediment study amasseds moored and shipboard current measurements made over the amazon shelf during 1990 1991 have been analyzed to determine the dominant semidiurnal tidal constituent the m2 these results have been combined with coastal sea level data from within the amazon and para rivers the adjacent shelf and with satellite derived tidal elevation data from off the shelf to provide a more complete description of the m2 tide in this complex river shelf system near the amazon river mouth the m2 tide propagates across the shelf and through the mouth as a damped progressive wave with its amplitude decreasing and phase increasing upriver over the adjacent shelf north of cabo norte the m2 tide approaches a damped standing wave with large amplitudes greater than 1 5 m near the coast due to near resonance within the coastal embayment formed by the cabo norte shoal to the south and cabo cassipore to the north the observed m2 tidal currents are nearly rectilinear and oriented primarily across the local isobaths comparisons between tidal observations in both the north channel and the cabo norte cabo cassipore embayment and a simple variable width channel tidal model indicate that 1 most of the m2 tidal energy dissipation occurs over the mid and inner shelf in water depths less than 20 m and 2 fluid muds found there cause a significant reduction of order 50 in the effective bottom friction felt by the m2 tide the approximate resonant period of the cabo norte cabo cassipore embayment is 11 9 hours and at resonance the average energy dissipation per forcing period is roughly 2 2 times the average mechanical energy in the embayment this damping rate is large enough that the tidal amplification is rather insensitive to forcing frequency so that the response of the embayment to forcing over the semidiurnal band should be essentially the same the vertical structure of the m2 tidal current is examined at one outer shelf site located in 65 m water depth the observed semimajor axis increases logarithmically with height above bottom within the lowest 1 2 m and reaches a maximum in excess of 0 5 m s at approximately 11 m above bottom the mean ellipticity is small less than 0 1 and positive indicating clockwise rotation of a nearly rectilinear current and the semimajor axis is oriented within 10 of the local cross isobath direction the m2 phase increases with height above bottom with flood at the bottom leading flood at the surface by about 1 hour a simple local homogeneous tidal model with time and space dependent eddy viscosity simulates the observed near bottom velocity reasonably well however the model suggests that stratification above the lowest few meters may significantly affect the tidal boundary layer structure at this site the m2 energy flux onto the amazon shelf and into the amazon and para rivers has been estimated using current and surface elevation data and the best fit variable width channel model results the net m2 energy flux into the mouths of the amazon and para rivers is 0 47 1010w and 0 19 1010w respectively a net m2 energy flux of about 3 3 1010w occurs onto the shelf between the north channel of the amazon river and cabo cassipore this stretch of the amazon shelf accounts for about 1 3 of the global dissipation of the m2 tide

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

the amazon influenced muddy coast of south america a review of mud bank shoreline interactions the 1500 km long coast of south america between the amazon and the orinoco river mouths is the world s muddiest this is due to the huge suspended sediment discharge of the amazon river 106 754 tons yr 1 9 part of which is transported alongshore as mud banks mud bank formation is controlled by the physical oceanography of the continental shelf seaward of the amazon river mouth an initial seafloor storage area for much of the suspended sediment discharged from the river in this area rapid and sustained fluid mud concentration and trapping are associated with fresh water salt water interaction and estuarine front activity on the shelf due to the enormous amazon water discharge ca 173 000 m3 s 1 at obidos 900 km upstream of the mouth fluid mud is transported shoreward and then along the coasts of the guianas by a complex interaction of wave and tidal forcing and wind generated coastal currents the mud banks which may number up to 15 or more at any time are up to 5 m thick 10 to 60 km long and 20 to 30 km wide and each may contain the equivalent mass of the annual mud supply of the amazon as the banks migrate alongshore their interaction with waves results in complex and markedly fluctuating shorelines that are associated with space and time varying depositional bank phases and erosional inter bank phases bank zones are protected from wave attack as a result of wave energy dampening by mud and undergo significant albeit temporary coastal accretion accompanied by rapid mangrove colonization the dampening of waves in bank areas as they propagate onshore is accompanied by the shoreward recycling of mud commonly in the form of individual mud bars these bars progressively undergo desiccation and consolidation and thus constitute a major pathway for rapid and massive colonization by mangroves erosion by waves propagating across relatively mud deficient shoreface zones in inter bank areas can lead to muddy shoreline retreat rates of tens of metres to several kilometres over a few months to a few years accompanied by massive removal of mangroves notwithstanding the higher incident wave energy on inter bank shores inter bank shorefaces are permanently muddy due to the pervasive influence of the amazon muddy discharge inter bank and transitional bank to inter bank phases are associated with both periodic sandy chenier formation and extreme forms of rotation of rare headland bound sandy beaches the high mud supply from the amazon has been the overarching geological control on the quaternary evolution of the northeastern south american coast having led to the growth of a muddy shelf clinoform at the mouth of the amazon and more or less important progradation throughout this coast net progradation reflects an imbalance in favour of deposition during each mud bank inter bank cycle the high mud supply has presumably blanketed shelf sand deposited by smaller rivers during eustatic lowstand phases the shelf clinoform structure at the mouth of the amazon and the muddy coastal progradation throughout the coast of the guianas and into venezuela provide analogues of the geological record on muddy shorefaces

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

evolution of coastal sandy aquifer system in kalpitiya peninsula sri lanka sedimentological and geochemical approach the study on the evolution of groundwater sources has arisen because of growing concern about deterioration of groundwater resources due to overexploitation the chemical nature of a coastal aquifer depends on the initial composition of aquifer media internal geochemical processes and external chemical inputs therefore geochemical characteristics of an aquifer can be used as indicative components on elaborating the origin of aquifer media and its evolutionary processes this study was aimed at understanding the evolution of quaternary coastal aquifers of the kalpitya area sri lanka by studying groundwater quality and aquifer media the textural mineralogical and chemical characteristics of aquifer media and chemical nature of groundwater of the area imply that the aquifer media may not have been derived from marine processes and paleo coastal formations of the western coast but are indicative of a fluvial origin due to past strong fluvial processes fluviatile sand depositions had taken place initially and with the gradual sea level rise deposits were transported sorted and then re deposited to form barrier islands parallel to the coast these have evolved to the present state during the quaternary period intermittent climatic changes caused several changes in the depositional pattern of the aquifer material and the chemical nature of the aquifer present day groundwater geochemistry indicates an evolution of a fresh water aquifer with relics of ionic constituents showing paleo geochemical processes that were active during the evolution in addition anthropogenic activities have also significantly altered the geochemical nature of groundwater in the present aquifer system

early permian sediment provenance and paleogeographic reconstructions in southeastern gondwana using detrital zircon geochronology northern perth basin western australia abstract the perth basin western australia forms part of a north trending belt of intracratonic rift basins that initiated in southeastern gondwana in the late paleozoic existing provenance studies have highlighted the dominance of proterozoic zircons derived from southerly terranes such as the albany fraser orogen leeuwin complex and more distant provinces in east antarctica with limited input from the adjacent archean western australian craton new u pb geochronology data were acquired using a sensitive high resolution ion microprobe shrimp ii on detrital zircons from lower permian formations exposed in the northeastern perth basin in contrast to previous studies archean zircons showing fine oscillatory zoning dominate the age spectra with up to 90 grains ranging between 3 0 and 2 6 ga indicating that granitic parent rocks of the adjacent craton were a major sediment source during the early permian a minor paleoproterozoic age population from the gascoyne complex of the capricorn orogen was likely transported southward and dispersed in the basin by a combination of longshore drift and tidal currents meso and neoproterozoic detritus became prominent only from the middle artinskian and may relate to the establishment of large northward flowing river systems draining the albany fraser province the prydz leeuwin belt and or the wilkes land in east antarctica this study shows that integrating depositional processes and stratigraphic evolution of sedimentary formations with provenance analysis can enhance reconstruction of dispersal pathways to and within basins

the amazon river plume during amasseds spatial characteristics and salinity variability the amazon river discharge forms a plume of low salinity water that extends offshore and northwestward over the north brazilian shelf observations acquired as part of a multidisciplinary amazon shelf sediment study amasseds are used to characterize the spatial structure and temporal variability of the amazon plume four shipboard conductivity temperature depth ctd surveys spanning the shelf from 1 s to 5 n during rising march 1990 maximum may 1990 falling august 1989 and minimum november 1991 discharge show the amazon plume is typically 3 to 10 m thick and 80 to over 200 km wide northwest of the river mouth the plume is often characterized by a wedge of low salinity water adjacent to the coast and a separate tongue of low salinity water extending offshore over the middle to outer shelf a bottom front separating the low salinity plume water from oceanic water is consistently located between the 10 and 20 m isobaths a moored array deployed about 300 km northwest of the river mouth from february to june 1990 included inner and midshelf moorings in 18 and 65 m of water on which temperature conductivity measurements were made the moored observations reveal salinity variations within the amazon plume of over 10 psu on timescales of days to weeks this variability includes intermittent events in which plume water pools up in the vicinity of the river mouth and the plume width can exceed 200 km these accumulation events are apparently due to wind events with a southeastward component which impede or block the normally northwestward freshwater transport the resulting bulges in the plume are then released northwestward when the wind reverses volume budgets indicate the amazon plume entrains roughly twice the river discharge between the river mouth at the equator and 3 n estimates of gradient richardson numbers from the moorings suggest entrainment due to the strong semidiurnal tidal currents occurs where the plume intersects the bottom and over the outer portion of the plume where salinities approach oceanic values

neotectonic evolution of the brazilian northeastern continental margin based on sedimentary facies and ichnology abstract quaternary post barreiras sediments are widespread along brazil s passive margin these deposits are well exposed in the onshore paraiba basin which is one of the rift basins formed during the pangean continental breakup in this area the post barreiras sediments consist of sandstones with abundant soft sediment deformation structures related to seismicity contemporaneous with deposition the trace fossils thalassinoides and psilonichnus are found up to 38 m above modern sea level in sandstones dated between 60 0 1 4 and 15 1 1 8 ka the integration of ichnological and sedimentary facies suggests nearshore paleoenvironments such deposits could not be related to eustatic sea level rise as this time coincides with the last glaciation hence an uplift of 0 63 mm yr or 1 97 mm yr if sea level was 80 m lower in the last glaciation would have been required to ascend the post barreiras sediments several meters above the present day sea level during the last 60 ka this would suggest that the post rift stage of the south american eastern passive margin may have experienced tectonic reactivation more intense than generally recognized although more complete data are still needed the information presented herein may play an important role in studies aiming to decipher the quaternary evolution of this passive margin

man s influence on the erosion and transport of sediment by asian rivers the yellow river huanghe example during the holocene sediment input from the yellow river to the yellow sea and adjacent areas has amounted to about 3000 km 3 detailed records from river gauging stations over the past 70 yrs together with estimates based on earlier historic records suggest that the river has contributed 2300 km 3 of sediment during the last 2300 yrs an average discharge of 1 km 3 yr 1 x 10 9 t yr prior to extensive agricultural use of the loess plateau in northern china beginning about 200 bc therefore the river s load must have been about 0 1 km 3 yr an order of magnitude lower than that at present a broad delta 20 m below sea level suggests that early holocene rates were higher than the pre agricultural average and therefore that middle holocene loads were low

regional controls on geomorphology hydrology and ecosystem integrity in the orinoco delta venezuela interacting river discharge tidal oscillation and tropical rainfall across the 22 000 km2 orinoco delta plain support diverse fresh and brackish water ecosystems to develop environmental baseline information for this largely unpopulated region we evaluate major coastal plain shallow marine and river systems of northeastern south america which serves to identify principal sources and controls of water and sediment flow into through and out of the orinoco delta the regional analysis includes a summary of the geology hydrodynamics sediment dynamics and geomorphic characteristics of the orinoco drainage basin river and delta system because the amazon river is a major source of sediment deposited along the orinoco coast we summarize amazon water and sediment input to the northeastern south american littoral zone we investigate sediment dynamics and geomorphology of the guiana coast where marine processes and holocene history are similar to the orinoco coast major factors controlling orinoco delta water and sediment dynamics include the pronounced annual flood discharge the uneven distribution of water and sediment discharge across the delta plain discharge of large volumes of water with low sediment concentrations through the rio grande and araguao distributaries water and sediment dynamics associated with the guayana littoral current along the northeastern south american coast inflow of large volumes of amazon sediment to the orinoco coast development of a fresh water plume seaward of boca grande disruption of the guayana current by trinidad boca de serpientes and gulf of paria and the constriction at boca de serpientes

quaternary fault control on the coastal sedimentation and morphology of the sao francisco coastal plain brazil abstract the role of neotectonic faulting in shaping topography and controlling sediment deposition has been increasingly documented along the stable continental margin of south america but the level of the present day tectonic stability of this margin is still a matter of debate this paper presents an investigation of the effects of quaternary fault reactivation on the sao francisco coastal plain sfcp this feature is a 56 km long progradational coastal plain located in the sergipe alagoas basin along the continental margin of brazil the sfcp is bounded on the west by a system of normal faults striking n s to ne sw the horst that bounds this plain is capped by the miocene barreiras formation and quaternary debris flow and fluvial deposits whereas the graben is filled with braided stream deposits and sandy beach ridge sediments the faulting contributed to the generation of accommodation space for the deposition of coastal sediments on the plain these processes started with the reactivation of cretaceous faults during the miocene during the quaternary fault reactivation and associated soft sediment deformation occurred between 82 and 8 3 ka with minor pulses between 1700 and 60 cal yr bp several faults along this margin are tectonically active and may represent the onshore continuation of gravitational collapses that have been documented offshore along the continental shelf and slope

longshore transport on the northeastern brazilian coast and implications to the location of large scale accumulative and erosive zones an overview using the average directions of the principal wavefronts that approach the northeastern brazilian coast which are coincident with the directions of the prevailing winds a wave climate model was defined for approximately 3000 km of coast by construction wave refraction diagrams a resulting sediment transport model that was obtained by numerical modeling starting with refraction diagrams taking into account the wave approach angles and their heights permitted the reproduction on a regional scale of the sediment dispersion pattern several drift cells were identified the limits of which were based on alterations in the direction or intensity of potential net longshore drift although also dependent on other factors such as the supply of fluvial sediments to the coastal zone and to wind activity the coastal sections that present progradation erosion or non deposition can be reasonably explained in a first order approximation by these variations as a generalization geomorphic drift indicator match patterns of regional scale sediment dispersal

subsurface valleys and geoarcheology of the eastern sahara revealed by shuttle radar the shuttle imaging radar sir a carried on the space shuttle columbia in november 1981 penetrated the extremely dry selima sand sheet dunes and drift sand of the eastern sahara revealing previously unknown buried valleys geologic structures and possible stone age occupation sites radar responses from bedrock and gravel surfaces beneath windblown sand several centimeters to possibly meters thick delineate sand and alluvium filled valleys some nearly as wide as the nile valley and perhaps as old as middle tertiary the now vanished major river systems that carved these large valleys probably accomplished most of the erosional stripping of this extraordinarily flat hyperarid region underfit and incised dry wadis many superimposed on the large valleys represent erosion by intermittent running water probably during quaternary pluvials stone age artifacts associated with soils in the alluvium suggest that areas near the wadis may have been sites of early human occupation the presence of old drainage networks beneath the sand sheet provides a geologic explanation for the locations of many playas and present day oases which have been centers of episodic human habitation radar penetration of dry sand and soils varies with the wavelength of the incident signals 24 centimeters for the sir a system incidence angle and the electrical properties of the materials which are largely determined by moisture content the calculated depth of radar penetration of dry sand and granules based on laboratory measurements of the electrical properties of samples from the selima sand sheet is at least 5 meters recent september 1982 field studies in egypt verified sir a signal penetration depths of at least 1 meter in the selima sand sheet and in drift sand and 2 or more meters in sand dunes

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

a 21 000 cal years paleoclimatic record from caco lake northern brazil evidence from sedimentary and pollen analyses abstract sedimentological studies including seismic profiles mineralogy and organic geochemistry on two cores from the center and margin of caco lake maranhao state northern brazil revealed variable climatic and environmental conditions during the last 21 cal kyr bp between 21 and 17 cal kyr bp during the late glacial maximum regional climate was predominantly dry interrupted by short humid phases as reflected by a succession of very thin layers of sand and organic matter the late pleistocene climate was relatively wet as is suggested by rapid lake level rise and forest expansion the late pleistocene humid climate differed significantly from present conditions we suggest that late glacial humid conditions were the consequence of intensification of the inter tropical convergence zone or shifts of its position resulting in antarctic cold front occurrences the abrupt climatic changes during this period were marked by siderite deposition into caco lake which appears to be related to regional hydrologic changes linked to global northern hemisphere events the holocene was characterized by lower moisture availability and a distinct dry period until 7 cal kyr bp in response to south american insolation conditions

an approximation to short term evolution and sediment transport pathways along the littoral of cadiz bay sw spain this work presents the results of a beach monitoring program carried out in the bay of cadiz sw spain which consists of urban natural and nourished beaches in the present study 24 topographic profiles have been monthly monitored during the 1996 1998 period in order to draw the morphodynamic behavior of this coast and the general characterization of short term coastal trends this way total volumetric budgets have been calculated for each beach profile in order to group beaches in different erosive accreting sectors studied beaches recorded both erosion and accretion the greatest accretionary trends have been observed at aguadulce la costilla and rota beaches with values ranging from 30 to 70 m3 m the largest erosion episodes have been recorded in the southernmost end of valdelagrana spit with values over 50 m3 m and in rota and vistahermosa after nourishment works main erosion and accretion pathways have been related to the existence of natural and human structures which blocked the longshore drift suggesting the existence of littoral cells

single and multipolarimetric p band sar tomography of subsurface ice structure in this paper first results concerning the characterization of the subsurface of ice sheets and glaciers through single and multipolarization synthetic aperture radar sar tomography tomosar are illustrated to this aim the processing of data acquired in the framework of the european space agency icesar 2012 campaign is discussed icesar 2012 was conceived so as to support the secondary objectives of the future earth explorer mission biomass which will be a sar instrument with media penetration capabilities due to the use of the p band frequency in this regard a tomographic study of ice was motivated by the fact that cryospheric remote sensing is of fundamental importance in order to understand more in depth the morphology and the dynamic processes regulating ice sheets the main objective of the tomographic experiment of the campaign herein discussed was indeed to assess the capability of p band sar to retrieve any information about ice subsurface structure imaging has been achieved through tomosar techniques applied to airborne multibaseline data acquired in the southwest of greenland different imaging approaches are compared and the main results achieved are presented it is found that scattering in the upper layers of glacial subsurface can be achieved up to an extent of about 20 60 m conditional on the different types of glaciological zone observed moreover clear morphological structures have been found beneath the ice surface at one of the investigated sites

re evaluating the paleogeography of the river dominated and wave influenced ferron notom delta southern central utah an integration of detailed facies architecture and paleocurrent analysis abstract this study re evaluates the paleogeography of a river dominated and wave influenced deltaic system in a single parasequence 6a of the cretaceous ferron sandstone south central utah which was previously interpreted as a typical asymmetric delta the conceptual asymmetric delta model of bhattacharya and giosan 2003 has been widely applied to interpret ancient deltaic systems however reconstructed paleogeographies relying on this conceptual model are commonly not scaled to the architectural elements which could possibly lead to inaccurate interpretations especially when data are relatively sparse the extensively exposed ferron sandstone outcrops provide an opportunity to demonstrate how detailed facies architecture work can be integrated with regional facies relationships to elucidate a properly scaled paleogeography seven facies associations fa are identified in parasequence 6a and are arranged into two distinctively different successions the river dominated succession consists of prodelta distal delta front proximal delta front and terminal distributary channel fa while the wave and storm dominated succession comprises offshore shelf lower shoreface and upper shoreface fa the river dominated succession is muddier and less bioturbated than the wave and storm dominated succession facies architecture analysis shows that the river dominated proximal delta front facies consists of mouth bar and terminal distributary channel elements that are not seen in the wave and storm dominated facies the scales of mouth bars and terminal distributary channels suggest that they are rather small features compared with the river dominated delta lobe which is incompatible with the simple bar elongation asymmetric delta model presented by li et al 2011 instead parasequence 6a is interpreted to be a valley fed river dominated symmetric delta protected from waves by an updrift barrier system which is analogous to the modern mongky river delta on the west coast of madagascar the progressive change in orientation of west directed mouth bars to north directed and east directed lobes around the periphery of the river dominated delta indicates a highly radial lafourche type delta moving away from the protection of the barrier system there is a gradual change from highly river dominated facies to increasingly wave and storm influenced facies toward the southeast due to the entrenched nature of the feeder river associated with an incised valley system the parasequence 6a delta was bifurcation dominated rather than avulsion dominated this study shows that it is critical to integrate detailed facies architecture analysis in order to reconstruct properly scaled paleogeographies and hypothesizes that stable bifurcation dominated deltas should be more common than avulsion dominated deltas in a lowstand delta system due to the entrenched nature of the feeding trunk river which inhibits avulsion

morphology and dynamic sedimentology of the eastern nile delta shelf coleman j m roberts h h murray s p and salama m 1981 morphology and dynamic sedimentology of the eastern nile delta shelf mar geol 42 301 326 some 13 000 km of bathymetry and overlapping side scan sonar data were collected over a 4450 km2 area of the eastern nile river shelf these data coupled with more detailed surveys of selected areas including bottom sampling and current measurements contribute to the understanding of shelf morphology lithofacies relationships and sediment transport processes four morphologic zones were defined zone 1 smooth bottomed flocculated clays and silty clays extending from the shore line 40 km seaward to the 25 m contour zone 2 a sand belt 5 20 km wide extending eastward from the damietta mouth and curving toward the coast at the boundary of the study area dominant bottom features were migratory bedforms of various dimensions superimposed on linear sand ridges zone 3 smooth clay to silty clay bottom topography punctuated with distinct algal mounds the mounds up to 10 m relief are composed of living coralline algae which contribute coarse debris to the surrounding sediments zone 4 mud diapirs and shelf edge slumps characterize this distal part of the shelf and the upper slope sand on the inner shelf is actively migrating and probably does not represent a relict deposit the damietta distributary causes a large scale perturbation in the mean easterly drift along the egyptian coast unusually strong currents capable of transporting and reworking large volumes of sand are associated with an eddy trapped behind this feature the directionality of these currents and the curvature of the eddy axis correspond well to the distribution pattern of sand on the inner shelf

coastal response to late stage transgression and sea level highstand coastal morphologic features associated with past shoreline transgressions and sealevel highstands can provide insight into the rates and processes associated with coastal response to the modern global rise in sea level along the eastern and southern brazilian coasts of south america 6000 years of sea level fall have preserved late stage transgressive and sea level highstand features 1 4 m above present mean sea level and several kilome ters landward of modern shorelines gps with real time kinematics data ground penetrating radar stratigraphy and radiocarbon dating within a 2 3 km wide river associated strandplain in central santa catarina southern brazil uncovered a diverse set of late stage transgressive and highstand deposits here the highstand took the forms of 1 an exposed bedrock coast in areas of high wave energy and low sediment supply 2 a 3 8 m high transgressive barrier ridge where landward barrier migration was prohibited by the presence of shallow bedrock and 3 a complete barrier island complex containing a 5 2 m high barrier ridge washover deposits a paleo inlet and a backbarrier lowland formed in a protected cove with ample sediment supply from small local streams and the erosion of upland sediments similar signatures of the mid holocene highstand can be traced across all coastal brazilian states this study presents the fi rst complete compilation of the diversity of these sedimentary sequences they are broadly classifi ed here as exposed bedrock coasts type a back barrier deposits type b transgressive barrier ridges type c and barrier island complexes type d according to localized conditions of upland migration potential wave exposure and sediment supply these brazilian systems present a paradigm for understanding future coastal response to climate change and accelerated sea level rise the recognition of a minimum threshold sea level rise rate of 2 mm yr 1 above which transgression proceeded too rapidly for the formation of these stable accretionary shoreline features demonstrates the nonlinearity of coastal response to sea level change and the site specifi city of conditions associated with the formation of each highstand deposit type even within a single small embayment demonstrates the non uniformity of that response

distribution of discontinuous mudstone beds within wave dominated shallow marine deposits star point sandstone and blackhawk formation eastern utah deposits of wave dominated shorelines are typically considered to act as relatively simple hydrocarbon reservoirs and are commonly modeled as tanks of sand however important heterogeneities that can act as barriers to fluid flow occur at the parasequence bedset and bed scales especially in viscous oil or low permeability oil fields heterogeneities at the parasequence and bedset scales have been well studied but discontinuous mudstone beds occurring within the shoreface have received little attention the book cliffs and wasatch plateau are among the best exposed and best studied deposits of wave dominated shallow marine systems in the world two parasequences within these outcrops have been studied in detail to investigate the distributions of intrashoreface shales and to propose models for the controls on their distribution a data set consisting of 30 km 18 6 mi of virtual outcrops derived from oblique helicopter mounted light detection and ranging lidar scanning with supporting stratigraphic sections makes it possible to collect a large quantity of accurate geometric data of depositional elements from inaccessible cliffs nine hundred and twenty one discontinuous mudstone beds were measured these occur as ellipses with long axes oriented normal to the paleoshoreline lengths and widths of these mudstone beds exhibit a lognormal distribution with means of 21 9 and 13 8 m 71 9 and 45 3 ft respectively within the shoreface succession the number of mudstone beds increases downward whereas size does not vary significantly with stratigraphic height an average of 100 m 328 ft cumulative length of shale exists per 100 m 328 ft of horizontal outcrop this increases threefold near both wave dominated deltas and bedset boundaries that reflect minor sea level fluctuations during progradation

controls on quaternary coastal evolution of the east northeastern coast of brazil roles of sea level history trade winds and climate abstract east northeastern brazil has a wave dominated micro to meso tidal coast lying entirely within the southern atlantic trade wind belt integration of geologic mapping radiocarbon dating and vibracoring data shows that the quaternary coastal evolution of this area was controlled by three major factors 1 sea level history 2 trade winds and 3 climate change sea level history along the east northeastern coast of brazil relative sea level has fallen approximately 5 m during the last 5000 y correlation of this sea level history with the evolution of beach ridge lagoonal and coastal plain deposits shows that 1 sea level rise favours the formation of barrier island lagoonal systems and the construction of intralagoonal deltas 2 sea level lowering is not conductive to barrier island formation rather lagoons and bays become emergent and beach ridge plains rapidly prograde trade winds sediment dispersal systems along the coastal zone of east northeastern brazil have been highly persistent since pleistocene time as deduced from beach ridge orientation this persistence results from the fact that sediment dispersal in wave dominated settings is ultimately controlled by atmospheric circulation which for the east northeastern coast of brazil is associated with the south atlantic high pressure cell the remarkable stability of this cell through time has allowed the accumulation of extensive beach ridge plains at the longshore drift sinks located along the coast climate change effects of quaternary climate changes on coastal sedimentation are twofold climate changes may affect rainfall patterns thus exerting an important control on coastal dune development along the coast of northeastern brazil active coastal dunes are only present in those areas in which at least four consecutive dry months occur during the year mapping of these areas has shown that dune development during the holocene has been episodic these episodes being probably controlled by variations in rainfall patterns associated with climate changes secondly despite its overall stability the position of the high pressure cell has experienced small shifts in position during the holocene in response to climate changes changes in wind direction associated with these shifts have induced modifications in the coastal dispersion system which are recorded in the strandplains as small truncations in the beach ridge alignments these results have important implications in understanding accumulation of ancient sandstone shoreline sequences

distribution of fluid muds on the amazon continental shelf abstract a comprehensive study of suspended sediment transport on the amazon shelf was conducted as part of the amasseds project a multidisciplinary amazon shelf sediment study to understand the link between physical processes and the fate of amazon river sediment a small instrumented tripod was used to measure the fluid flow and suspended sediment characteristics throughout the water column on varying time scales e g semidiurnal fortnightly seasonal dense nearbed suspensions or fluid muds suspended sediment concentration 10 g l on the order of a few meters in thickness were found on the inner and middle shelf covering an area ranging from 5 700 km2 during falling and low river discharge to 10 000 km2 during rising and high discharge fluid muds generally observed in the region of bottom salinity fronts extend across the topset beds to the foreset beds during rising and high discharge salinity and temperature anomalies frequently observed in fluid muds imply that often the muds do not result from erosion and resuspension from the seabed but from trapping processes at the bottom salinity front and transport across the shelf the vertical structure of fluid mud varies in space and tune variability close to the river mouth is predominantly fortnightly related to the location and structure of the bottom salinity front on the open shelf the variability appears to be related to seasonal differences in river and sediment discharge and the location of the bottom salinity front the total suspended sediment inventory on the shelf during the season of high discharge is approximately equal to the annual sediment discharge from the river 1 2 109 tons yr and 90 of that inventory is within fluid mud suspended sediment transport on the shelf is dominated by fluid mud

a multi proxy evidence for the transition from estuarine mangroves to deltaic freshwater marshes southeastern brazil due to climatic and sea level changes during the late holocene abstract the present study investigates a paleo estuary at the doce river delta southeastern brazil through a multi proxy approach that links palynology diatoms sedimentology and geochemistry analyses i e total c total n 13 c and 15 n these analyses temporally synchronized with five radiocarbon ages revealed environmental changes from marine to continental over the last 7550 years the studied sedimentary succession recorded the upward transition from estuarine channel until 7550 cal yr bp to estuarine central basin 7550 to 5250 cal yr bp deposits the latter containing increased mangrove vegetation marine and marine brackish water diatoms the range of geochemical values 13 c 30 10 15 n 2 8 and c n 4 40 also indicate marine estuarine organic matter and c 3 terrestrial plants to that time interval a following period recorded two phases lake ria 5250 to 400 cal yr bp and fluvial channel 400 cal yr bp until modern age during this stage mangroves were replaced by trees shrubs and herbs grasses due to the disconnection with the marine realm as a result the corresponding sediments contain only organic matter sourced from freshwater and c 3 terrestrial plants 13 c 29 26 15 n 0 8 and c n 10 45 the equilibrium between fluvial sediment supply and relative sea level changes during the holocene controlled the morphologic and vegetation changes in the studied littoral the estuary became established during the early holocene as a resulted of a eustatic sea level rise when the fluvial sediment supply to the coast was relatively lower due to a dry period however during the late holocene the climatic force was more significant to the development of coastal morphology due to a wet period that caused an increase in sandy sediment supply to coastal system then the increase of fluvial discharge associated to a relative sea level fall caused a marine regression and shrinkage of mangroves during the late holocene the evaluation of mangrove dynamics according to climatic and sea level changes mainly during the late holocene is essential for the understanding of their survival ability under future scenarios with a probable accelerated sea level rise and intensification of extreme climatic events in southeastern brazil for the next century

onlap offlap and the origin of unconformity bounded depositional sequences christie blick n 1991 onlap ofttap and the origin of unconformity bounded depositional sequences mar geol 97 35 56 unconformity bounded depositional sequences represent the fundamental building blocks of sedimentary successions they are typically characterized by onlap at the base and by offlap at the top and they tend to be markedly asymmetrical with onlap accounting for a larger part of any cycle of sedimentation than offlap offlap cannot be attributed solely to erosional truncation but instead implies that sequence boundaries develop over a finite interval of time depositional sequences are commonly associated with a cyclic arrangement of facies but transgressive regressive cycles are out of phase with respect to sequence boundaries which in down dip locations are both overlain and underlain by progradational deposits and hence form during times of regression of the shoreline these observations are used to develop some ideas about the origin of unconformity bounded sequences with reference to the inter related roles of changes in depositional base level and sediment supply in particular it is shown than onlap and offlap are due to lateral migration of a line of critical bypassing defined so as to incorporate the effects of sediment loading and compaction as well as the rate of change of elevation with respect to sea level downward shifts in onlap may be achieved by either an increase in the rate of eustatic fall or a decrease in the rate of tectonic subsidence and it is premature to assume that eustatic and tectonic controls on sea level may be distinguished solely on the basis of the frequency of depositional cyclicity small shifts in the position of onlap can also be produced by changes in sediment supply and more attention needs to be paid to the influence of sediment supply in the development of minor boundaries unconformities related to eustatic fluctuations are thought to correspond approximately to times of relatively rapid sea level fall inflection points but questions remain about the existence of possible leads and lags of up to cycle and hence about the degree to which sequence boundaries of eustatic origin may vary in age both within a given basin and from one basin to another

structure and dynamics of fluid muds on the amazon continental shelf thick layers of fluid mud occur in strong tidal flows over the inner portion of the amazon continental shelf in regions of strong salinity fronts associated with the plume discharged from the amazon river detailed shipboard profile measurements obtained in this region during a multidisciplinary amazon shelf sediment study amasseds provide an unprecedented opportunity to examine the structure and dynamics of fluid muds under natural conditions the analysis focuses on flows in which the motion is fully turbulent and suspended sediment dominates the stratification under these conditions a comparison of measurements and one dimensional model calculations indicates that vertical transport is controlled by suppression of turbulent mixing at gradient richardson numbers near 1 4 this constraint produces a distinctive vertical structure and leads to an upper bound on the total amount of suspended sediment that may be carried in a turbulent suspension by a tidal flow

the deltaic nature of amazon shelf sedimentation despite the annual discharge of more than a billion tons of sediment by the amazon river the sedimentary environment near the river mouth has little subaerial expression and thus does not meet the classic definition of a delta the river mouth however is not an estuary either these observations raise a major question as to what type of sedimentary environment the amazon river mouth represents seismic stratigraphy has been examined on the continental shelf at the mouth of the amazon river using high frequency 3 5 khz seismic records from about 6 000 km of ship track these records demonstrate three regions 1 the amazon river has built a subaqueous feature which stretches for hundreds of kilometres offshore and alongshore from its mouth the feature is prograding seaward and accreting upward and it contains fine scale stratification typical of classic deltas the feature forming at the mouth of the amazon is a subaqueous delta it differs from classic deltas primarily in its lack of subaerial expression subaqueous deltas such as the amazon represent the general case of a major river entering an energetic oceanic regime

intra parasequence architecture of an interpreted asymmetrical wave dominated delta although modern wave dominated shorelines exhibit complex geomorphologies their ancient counterparts are typically described in terms of shoreface shelf parasequences with a simple internal architecture this discrepancy can lead to poor discrimination between and incorrect identification of different types of wave dominated shoreline in the stratigraphic record documented in this paper are the variability in facies characteristics high resolution stratigraphic architecture and interpreted palaeo geomorphology within a single parasequence that is interpreted to record the advance of an ancient asymmetrical wave dominated delta the standardville ab1 parasequence of the aberdeen member blackhawk formation is exposed in the book cliffs of central utah usa this parasequence and four others in the aberdeen member record the eastward progradation of north south trending wave dominated shorelines within the standardville ab1 parasequence distal wave dominated shoreface shelf deposits in the eastern part of the study area are overlain across a downlap surface by southward prograding fluvial dominated delta front deposits which have previously been assigned to a separate stranded lowstand parasequence formed by a significant allogenic change in relative sea level high resolution stratigraphic analysis of these deposits reveals that they are instead more likely to record a single episode of shoreline progradation characterized by alternating periods of normal regressive and forced regressive shoreline trajectory because of minor cyclical fluctuations in relative sea level interpreted normal regressive shoreline trajectories within the wave dominated shoreface shelf deposits are marked by aggradational stacking of bedsets bounded by non depositional discontinuity surfaces interpreted forced regressive shoreline trajectories in the same deposits are characterized by shallow incision of fluvial distributary channels and strongly progradational stacking of bedsets bounded by erosional discontinuity surfaces that record enhanced wave base scour fluvial dominated delta front deposits most probably record the regression of a lobate delta parallel to the regional shoreline into an embayment that was sheltered from wave influence wave dominated shoreface shelf and fluvial dominated delta front deposits occur within the same parasequence and their interpretation as the respective updrift and downdrift flanks of a single asymmetrical wave dominated delta that periodically shifted its position provides the most straightforward explanation of the distribution and relative orientation of these two deposit types

topographic mapping from interferometric synthetic aperture radar observations interferometric synthetic aperture radar observations provide a means for obtaining high resolution topographic terrain maps from data acquired simultaneously at two slightly displaced antennas calculation of the three dimensional coordinates of all the points in a radar image can be made from the combination of along track slant range and interferometer fringe measurements thus the result compensates for the layover exhibited by conventional radar maps and removes the false targets generated by multiple signal paths to a given object in the scene we have derived a topographic map of a portion of the san francisco bay area utilizing data that were recorded by a radar system mounted on a nasa cv990 aircraft and processed by a general purpose digital computer this map displays the height above sea level of a region approximately 11 km by 10 km in size sampled on an 11 m pixel grid uncertainties in the estimated height result from imprecise knowledge of the observational geometry radar bandwidth limitations and finite signal to noise ratios for our system each factor contributed approximately 3 4 m to a relative rms error of about 6 m additional global errors of the order of 10 m can result from inaccurate monitoring of aircraft attitude the statistical variation of the height measurements from the ocean portion of the map which we can presume to be quite flat is 2 10 m rms which is consistent with the theoretical estimate comparison of our results with u s geological survey contour maps indicates a high degree of correlation between the two sets of altitude data

stoss side mud drapes deposits of interdune pond margins arcuate mud drapes have been observed in an interdune area in southern tunisia they are believed to have been formed by deposition from ponded water around aeolian dunes during flood events they are preferentially preserved on the stoss side of the dunes as a result of subsequent dune migration and exhibit extensive evidence of animal tracks they are useful in illustrating dune interdune dynamics and recording the type of animals present

variations of sediment texture on the amazon continental shelf abstract grain size distribution on the continental shelf adjacent to the amazon river reveals three detrital sedimentary deposits an outer shelf sand deposit 1 5 3 0 well sorted negatively skewed an inner shelf mud deposit 6 9 poorly sorted positively skewed and a corridor extending from the river mouth across the inner shelf in which mud is interbedded with sand modern mud covers most of the inner shelf and surface sediment does not reveal along shelf or across shelf sorting of discrete particles size sorting of particle aggregates floccules fecal pellets may occur at the time of deposition but is difficult to evaluate a lack of shoreward fining reverse grading c ntradicts the sedimentation model of gibbs 1976 the model most consistent with textural observations is that of a modern subaqueous delta prograding over a relict basal sand the outer shelf sand modern sand in surface sediment is restricted to the corridor extending from the river mouth across the inner shelf ambient physical processes are not competent to transport this sand along shelf subsurface sand layers within the inner shelf mud deposit i e outside the corridor are similar in texture to surficial sand in the corridor of interbedded mud and sand these observations may suggest that the location and or size of the corridor has changed with time

new insights to high resolution stratigraphy on the amazon continental shelf abstract the surficial stratigraphy upper 20 m of the amazon subaqueous delta has been well documented but the high resolution record of underlying strata was unknown prior to this study a geopulse seismic system was utilized to obtain new information about the preservation potential of sedimentary deposits on the amazon shelf widespread distribution of methane gas was documented on the inner shelf and prevented deep penetration of the seismic signal on the outer shelf high resolution

seasonal changes in beach morphology along the sheltered coastline of perth western australia abstract seasonal change in beach morphology is traditionally ascribed to a variation in the incident wave energy level with calm conditions in summer resulting in wide beaches with pronounced subaerial berms and energetic conditions in winter causing narrow beaches with nearshore bar morphology the coastline of perth western australia is characterised by a large seasonal variation in the incident wave height and local beaches exhibit a distinct seasonal change in morphology however these morphological changes are better explained by a seasonal reversal in the littoral drift direction than by variations in the incident wave energy conditions in summer when northward sediment transport prevails due to sea breeze activity beaches located south of coastal structures headlands or rocky outcrops become wider due to the accumulation of sediment against the obstacle these beaches will subsequently erode in winter during storms when the longshore sediment transport is toward the south in contrast beaches located north of obstacles will become narrower during summer and wider during winter the usefulness of the dimensionless fall velocity h b w s t where hb is the breaker height ws is the sediment fall velocity and t is the wave period as a predictor of presence absence of bar morphology and beach type was investigated it was found that fluctuates around the threshold of bar formation 1 5 2 over a variety of time scales daily weekly and seasonally these temporal variations in in conjunction with the relatively low wave energy level that characterises the coast negates the development of beach and nearshore morphology that is in equilibrium with the hydrodynamic conditions as a result bar occurrence and beach type can not be readily predicted using along the perth coast

late pleistocene holocene evolution of the doce river delta southeastern brazil implications for the understanding of wave influenced deltas abstract brazil s coast displays many wave influenced deltas that are still incompletely understood despite their significance for reconstructing the history of late pleistocene holocene sea level changes in this region and the potential to advance in the knowledge of wave influenced deltas among them the doce river delta is the most expressive given its larger geographic extension the present work shows that this is a wave influenced delta that evolved within the context of late pleistocene holocene sea level fluctuations rather than a mid holocene lagoonal delta as proposed elsewhere the delta had an initial progradation at an osl age of 132 7 9 1 ka after the marine isotope stage mis 5e which was followed by major progradation between 45 775 49 391 and 29 678 29 226 cal yr bp beach ridges spits formed during these phases were in part destroyed during an ensuing transgression between 8161 7933 and 4974 4850 cal yr bp the central delta remained dominated by fluvial processes which kept pace with the rising sea level due to relatively high rainfall in the doce river drainage basin the doce river delta started to grow again after the late holocene transgression a process still on going at the present time during this evolution the doce river was deflected northward and then southward a process that did not result in any significant facies change when the updrift and downdrift sides of the river s mouth are compared such a pattern is in disagreement with previously proposed asymmetry index models for wave influenced deltas which predict an uneven distribution of sandy or muddy rich deposits in the updrift and downdrift sides of the river s mouth respectively several other deltas along the brazilian coast also display facies configuration similar to the doce river delta or have patterns opposed to those proposed by the asymmetry index models based on these analogs it can be stated that the geometries and facies patterns of wave dominated deltas are not determined simply by the interplay of fluvial and marine processes instead they can be strongly influenced by the fluvial influx sea level changes and or tectonic reactivations as it appears to be the case of brazilian wave influenced deltas including the doce river delta such a conclusion calls for a word of caution when applying processes based facies models to reconstruct wave influenced deltas in the sedimentary record

mapping of sand layer thickness in deserts using sar interferometry this paper presents an interferometric synthetic aperture radar insar system to map the bedrock topography underneath the sand in deserts and arid areas this is anticipated to greatly increase the efficiency of oil field and ground water exploration as well as environmental and archaeological studies the proposed system consists of two insar subsystems one operating at ka band to map the sand topography and the other operates in the vhf band to map the subsurface topography the different issues associated with insar processing for subsurface mapping are discussed it is shown that conventional insar processing produces unacceptable error in height estimation since it does not account for the refraction and the different propagation velocity in the sand thus a new inversion algorithm is developed which can be used to accurately estimate the bedrock topography for arbitrary sand and bedrock geometries a sensitivity analysis is then presented to show the effect of the different systematic and random errors the inversion algorithm is verified experimentally for flat sand case using a scaled model that was implemented in the lab

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

low sediment accumulation rates and erosion on the middle and outer nile delta shelf off egypt abstract the nile delta and its contiguous continental margin seaward of egypt form the major sediment repository on the north african margin together they constitute an integral depositional system man has increasingly modified the delta since pre dynastic time but most extensively this century by the emplacement of two dams across the nile at aswan in upper egypt sediment once transported by the nile river to the coast is now almost cut off and it is postulated that changes induced by man are likely to impact on sedimentation in distal sectors beyond the coast and inner continental shelf continued anthropogenic modification of the delta is expected to result in the increased erosion of the surficial sediment cover of the middle and outer nile delta shelf eddy flow patterns mapped by others show the interrelation of bottom currents on the mid and inner shelf thus in designing engineering projects on the nile delta and sinai margin it would be useful to monitor depositional changes seaward of the inner shelf

lowermost amazon river morphology and shallow seismic characteristics abstract the riverbed morphology of the lowermost amazon river was characterized by high resolution acoustic profiling in 21 areas this technique has been used for the first time in this area and allowed the discovery of a variety of reflectors which delineate areas either of sediment transport or of deposition on an older river bottom records obtained with the pinger system made it possible to distinguish three main kinds of reflectors both surface and sub bottom 1 flat 2 wavy and 3 irregular reflection patterns which can be interpreted as strata deposited in a variable mostly high energy setting or reworked structures of initially flat or wavy strata that have been changed mapping of these different reflectors shows that they are not randomly distributed the constant association of a given reflector with a particular morphological setting is indicative of its lithological significance supported by riverbed sampling and erosional depositional processes depositional areas are characterized by transparent units consisting of soft silt overlying a highly reflective sub bottom related to old substrates alter do chao or barreiras formation this may result from inundation and incision caused by quaternary sea level changes previously eroded areas are covered by a wavy layer consisting of very fine to fine sand unit fs which can change locally to medium coarse sand unit ms reflectors are more abundant downstream a minimum of 3 units were indicated by seismic records and could be related to sea level fluctuations and changes in the river discharge moreover the detection of fault scarps interpreted to result from neotectonic activity shows that neotectonic features can be important locally and should not be ignored as a possible reason for modern river instability the dynamic setting of the lowermost amazon area results in patterns of deposition and erosion probably controlled by complex interactions of fluvial and oceanic processes the effect of the gurupa arch may result in a zone of sediment bypass in the central part and a zone of increased deposition in the distal downstream part

origin of amazon mudbanks along the northeastern coast of south america abstract seismic profiles sediment cores and water column measurements were collected along the northeastern coast of brazil to examine the origin of mudbanks in the amazon coastal mud belt these 10 60 km long shore attached features previously had been observed to migrate along the 1200 km coast of the guianas in response to wave forcing chirp 3 5 khz seismic profiles of the shoreface and inner shelf located two mudbanks updrift of the previous eastern limit in french guiana 210 pb geochronology shows that these two banks are migrating to the northwest over a relict mud surface in 5 20 m water depth the mudbanks are 3 4 m thick and are translating over a modern shoreface mud wedge deposited by previous mudbank passage in

determination of controls on holocene barrier progradation through application of osl dating the ilha comprida barrier example southeastern brazil abstract barrier development during the holocene is studied using the example of the ilha comprida southeastern brazil aerial photos facies analysis and optically stimulated luminescence dating are used to define the barrier emergence and evolution optically stimulated luminescence ages and facies successions indicate that the ilha comprida probably began as a holocene transgressive barrier island 6000 years ago just before the last relative sea level maximum since then the barrier has progradated through the addition of curved beach ridges based on beach ridge alignments six units of growth are identified with two growth directions transverse and longitudinal rates of progradation with transverse growth vary from 0 13 to 4 6 m year rates of longitudinal growth to ne range from 5 2 to 30 m year variation in coastal progradation rates and sediment retention during the last 6000 years is compared with climate physiography and relative sea level changes the physiography represented by pre cenozoic hills is the major control on sediment retention and alternation between longitudinal and transverse growth climate variations such as the little ice age event apparently control the formation of ridges types beach ridges foredunes and blowouts these results allow the use of the ilha comprida barrier as an example to analyze the major controls on barriers progradation

mangrove vegetation changes on holocene terraces of the doce river southeastern brazil article i nfo high resolution sedimentological geochemical and pollen analysis on sediment core from the coastal plain of the doce river southeastern brazil revealed changes in the depositional system and vegetation caused by combined action of oscillations in relative sea level rsl and sedimentary supply during the holocene two main phases were discerned using sedimentary features 13 c 15 n total organic carbon toc total ni trogen n c n and cluster analysis of pollen data temporally synchronized with radiocarbon age dating the data indicates the presence of a lagoon system surrounded by a tidal plain colonized by mangroves and its sedimentary organic matter sourced from c4 plants between 8050 and 7115 cal yr bp however during the mid and late holocene the mangroves shrank and freshwater vegetation expanded c3 plants proba bly due to a marine regression during this phase the development of a lacustrine environment was followed by the colonization of herbs trees and shrubs the continuous sediment infilling into the lake allowed the ex pansion of a herbaceous plain as seen today this geomorphologic and vegetation evolution is in agreement with the mid holocene rsl maximum above present rsl and subsequent fall to the present time

stratigraphic evidence of changes in amazon shelf sedimentation during the late holocene abstract late holocene sedimentation on the amazon shelf was investigated using a combination of seismic sedimentological and geochronological methods piston cores collected in the subaqueous delta region during a multidisciplinary amazon shelf sediment study amasseds penetrated a regionally traceable 1 25 10 4 km 2 seismic discontinuity which corresponds to a dense relict mud reflector overlain by acoustically transparent sediment distinct offsets in profiles of wet bulk density p wave velocity and 210 pb activity are noted in cores at the reflector horizon unconformity signifying a past change in sedimentation conditions on the shelf bulk sediment 14 c dating indicates net depositional conditions for the subaqueous delta from 1800 yr b p to 700 yr b p and a net erosional phase from about 700 yr b p to 100 yr ago sedimentological evidence of the erosional phase includes lag deposits and burrows present at the unconformity surface in piston cores the deposits above and below the unconformity are similar with respect to grain size parameters and sedimentary structures suggesting that environmental conditions during the two depositional periods were similar according to 14 c dates of coastal deposits the shoreline of amapa state brazil served as a major depocenter of amazon mud during the erosional phase on the shelf 210 pb geochronology indicates that the most recent phase of sediment accumulation in the study area commenced about 100 yr ago resulting in rapid progradation of topset deposits and burial of relict strata in the present environment oceanographic and meteorologic processes cause along shelf variations in sediment dispersal and depositional patterns and about 1400 km 2 of the erosional relict deposits are still exposed at the seabed the short time scales over which amazon shelf strata respond to changes in the physical environment preclude the influence of relative sea level cyclicity on recent sedimentation patterns during the late holocene sedimentation and strata formation on the amazon shelf are linked to fluvial oceanographic and meteorologic processes that affect sediment supply deposition and erosion

flexural deformation due to amazon fan loading a feedback mechanism affecting sediment delivery to margins the uplift associated with the peripheral bulge engendered by sediment loads such as the amazon fan may provide a potential tectonic feedback mechanism that affects both coastal and fluvial depositional processes for example topographic and geologic maps of the brazilian margin document the existence of a drainage divide affecting coastal river networks that is spatially coincident with the location of the peripheral bulge predicted by our flexural modeling of the fan load while regions in close proximity to the fan load are depressed regions farther from the load are lifted i e peripheral bulge by 25 50 m which is sufficient to cause subaerial exposure of large portions of the shelf and modification of existing fluvial drainage networks furthermore our modeling results suggest that the development of the peripheral bulge may have deflected the sediment laden waters of the amazon river progressively southward through time this prediction is consistent with the existence of canyons off the amapa coast north of the present day amazon canyon and with the distribution of amazon fan sediments both of which suggest that the proto amazon river delivered sediment farther north along the coast however changing the location of sediment input into a basin also changes the shape of the cumulative sediment load and thus the resultant deformation this feedback between sediment loading and the peripheral bulge uplift modifies the spatial and temporal history of sediment delivery to the margin and provides a viable way to change base level without having to invoke glacial eustasy the efficiency of this feedback is dependent on the flexural wavelength and thus the strength of the lithosphere at the time of loading and the relative position of the sediment load with respect to the continental margin

internal architecture of mixed sand and gravel beach ridges miquelon langlade barrier nw atlantic abstract the internal architecture of a beach ridge system can provide clues into the processes involved in its formation detailed investigation of the mixed sand and gravel beach ridge plain on the miquelon langlade barrier northwest atlantic ocean south of newfoundland provides a better understanding of such sedimentary systems in terms of internal architecture depositional processes and driving mechanisms investigations of this regressive paraglacial barrier included the topographic rtk gps and ground penetrating radar 100 to 500 mhz antennae data collection orthophotographs and optically stimulated luminescence osl dating the miquelon langlade beach ridge plain is composed of two opposing progradational systems reflecting contrasting eastward and westward hydrodynamic exposures four ridge sets each with concave planform shapes define the 500 1400 m wide eastward prograding plain along the sheltered eastern coast two ridge sets with linear and fan shaped planforms define the 200 500 m wide south westward prograding plain along the energetic western coast beach ridge units overlay a basal sedimentary unit that disrupted incoming wave energy and altered the planform morphology of the prograding plain the internal architecture pattern of individual beach ridges are characterized by sigmoidal configurations with seaward dipping beds 2 3 4 7 true dip angles it is proposed that these wave built facies are deposited as beach berms likely by fair weather waves the elevations of these facies are determined by the sea level elevation and the swash height of constructive waves during their formation beach ridges are overlain by either peat resulting from the flooding of topographically low lying areas or by aeolian sand deposits of varying heights and morphologies relict foredunes despite the differences in wave exposure along each coast the sedimentary composition and internal architecture of the two progradational systems are broadly similar bed dip angles of the individual beach ridges differ by only 1 2 steeper along the exposed westward facing coast overall the miquelon langlade beach ridge plain highlights the primary influences of wave exposure inherited topography and proximal sediment sources from erosion of moraines on coastal progradational patterns

asymmetry in holocene river deltas patterns controls and stratigraphic effects abstract understanding controls on sediment distribution in river deltas is paramount to predicting facies relationships and stratal architecture most classifications of deltas have focused on subaerial plan morphology as a simplistic function of river tide and wave energy new work however is revealing the importance of subaqueous deposits and in particular shore parallel sediment redistribution in the shaping of delta planform delta asymmetry has emerged as an important characteristic reflective of patterns of alongshore sediment dispersal asymmetry has been described from onshore and offshore environments from several different types of modern deltas but aspects of asymmetry have not been fully documented and the degree to which these patterns are recorded in deltaic strata is not yet known this study is a comprehensive literature review of sediment distributions in modern deltas focusing on studies with high resolution geomorphic geophysical and geochronological datasets we reviewed 27 deltas using over 100 papers primarily from the past 15 20 years morphological facies and stratigraphic aspects were analyzed across the entire spectrum of deposits from the delta apex to the most distal muds of the prodelta we define quantifiable indices of asymmetry describing upcurrent vs downcurrent distribution of sediment volume sediment area sediment caliber and distributary channels most deltas are asymmetrical to some degree with respect to one or more of these parameters many deltas are increasingly skewed toward the downcurrent side from proximal to distal sub environments i e delta plain delta front prodelta some deltas are skewed toward the upcurrent side in one sub environment and toward the downcurrent side in another sub environment sand is preferentially deposited on the downcurrent side of most deltas but distributary channels tend to develop toward the upcurrent side the highest sand mud ratios are often on the upcurrent side in the lower delta plain but in the delta front these ratios are highest on the downcurrent side these complex patterns of asymmetry reflect different combinations of controls including discharge partitioning lobe abandonment and localized transgression plume deflection by coastal currents dominance of longshore current direction variable subsidence and other factors these processes may result in upcurrent downcurrent variations in clinoform geometry rates of progradation and stratal lapping relationships asymmetry has multiple aspects manifestations and controls even within a single delta but the long term preservation potential of these patterns likely varies depending on depositional setting and shoreline trajectory studies of ancient deltas will be better informed by recognizing the wide variety of controls on sediment distribution and avoiding the tendency toward a single model of delta asymmetry

rates and mechanisms of shoreface progradation and retreat downdrift of the amazon river mouth field surveys of the 350 km shoreline adjacent to the amazon river mouth reveal three distinct types erosional mud accretionary sand and accretionary mud formation of these zones is controlled by the delivery of amazon suspended sediment mediated by the hydrodynamic regime erosional mud shorelines extend from rio araguari near the amazon river mouth northwestward 280 km to 3 5 n near cabo cassipore shoreface 5 m water depth retreat annually yields 1 4 106 tons of fine grained sediment deposited during an earlier phase of shoreface progradation sandbodies up to 5 m thick overlie erosional mud shorefaces for 10 30 km downdrift of small rivers the sand is supplied from these rivers and released by shoreline retreat of the river mouth areas amazon river sand is restricted in the coastal zone from its mouth north to the cabo norte shoal area where it mixes with sand carried by rio araguari from the guiana highlands north of 3 5 n mud aggradation and progradation is taking place on underconsolidated low gradient tidal flats backed by mangrove swamps 210pb and 14c geochronology of vibracores from the mudflats indicate that sediment accumulation is rapid 0 24 2 0 cm yr landward of the 2 m isobath supplied from a thick 50 150 cm seasonal surface layer shoreface progradation is episodic separated by decadal hiatuses fine grained suspended sediment flux from the amazon and minor amounts of sand and mud from the local rivers supply sediment to the mudflats shore normal tidal currents and solitary waves rework the surface mud layer preferentially transporting available sand landward into the mangrove fringe and producing very fine grained accumulation on the tidal flat 10 12 mean grain size lateral accretion of features 10 100 km long termed mudcapes produces tens of kilometers of seaward coastal plain addition along the northern coast similar features are identified downdrift along the guianas coast as far as the orinoco river 1600 km the northern amapa shoreface deposits are a locus of modern sediment accumulation which progrades over subaqueous deltaic strata

wave controls on deltaic shoreline channel morphodynamics insights from a coupled model it is widely recognized that waves inhibit river mouth progradation and reduce the avulsion timescale of deltaic channels nevertheless those effects may not apply to downdrift deflected channels in this study we developed a coupled model to explore the effects of wave climate asymmetry and alongshore sediment bypassing on shoreline channel morphodynamics the shoreline position and channel trajectory are simulated using a shoreline module which drives the evolution of the river profile in a channel module by updating the position of river mouth boundary whereas the channel module provides the sediment load to river mouth for the shoreline module the numerical results show that regional alongshore sediment transport driven by an asymmetric wave climate can enhance the progradation of deltaic channels if sediment bypassing of the river mouth is limited which is different from the common assumption that waves inhibit delta progradation as such waves can have a trade off effect on river mouth progradation that can further influence riverbed aggradation and channel avulsion this trade off effect of waves is dictated by the net alongshore sediment transport sediment bypassing at the river mouth and wave diffusivity based on the numerical results we further propose a dimensionless parameter that includes fluvial and alongshore sediment supply relative to wave diffusivity to predict the progradation and aggradation rates and avulsion timescale of deltaic channels the improved understanding of progradation aggradation and avulsion timescale of deltaic channels has important implications for engineering and predicting deltaic wetland creation particularly under changing water and sediment input to deltaic systems