arid and humid phases in southern spain during the last 4000 years the zonar lake record cordoba a multiproxy study of sediment cores from zonar lake 37 29 00 n 4 41 22 w 300 m a s l supported by 11 14c ams dates provides the first high resolution centennial scale reconstruction of past h

remote continental forcing of phytoplankton biogeochemistry observations across the caribbean atlantic front 1 a persistent front in large part generated by the confluence of western tropical north atlantic wtna surface waters with the massive freshwater plumes of the orinoco and amazon rivers separates waters of the caribbean sea from those of the adjacent wtna we characterized physical and biogeochemical properties across this front in order to elucidate the processes leading to enhanced near surface phytoplankton biomass within the front although chlorophyll content of the water column to either side of the front is similar phytoplankton in waters within this caribbean atlantic front resides for the most part above the pycnocline and sustains large production rates in comparison with the lower rates of deep sub pycnocline wtna phytoplankton nitrogen budgets indicate that a substantial fraction of the production within the front may arise from biological nutrient recycling while the deeper wtna communities rely to a greater extent on nutrients from below the nutricline

backwash and swash oriented current crescents indicators of beach slope current direction and environment abstract backwash and swash oriented current crescents which are confined to the swash zone of beach environments are reported with their detailed morphology and formation mechanism from the siliciclastic fine sandy beaches of sagar island and lower long sand two tidal islands of the ganga estuary northeast india morphologically the swash oriented arms of these current crescents are shorter and less prominent than the backwash oriented arms the shorter arms open landward whereas the longer arms open seaward they generally form around obstacles like armoured mud balls polychaete tubes tussocks etc which are partially set in a scour implying greater anchoring or a semipermanent nature these current crescents occur on fine to very find sandy beaches mz 2 9 to 3 1 with a beach slopes of 1 50 to 1 90 1 4 0 7 they are very commonly associated with current lineations the arms of crescents parallel current lineations and are at right angles to the shoreline in contrast ordinary backwash oriented current crescents form on steeper beach slopes 1 9 to 1 25 6 3 in fine to medium sand mz 1 8 to 2 they occur around tiny obstacles which are easily swept away by wave swash and backwash

cementation characteristics and age of beachrocks in a fresh water environment lake iznik nw turkey abstract this paper focuses on the cement characteristics and optical luminescence age of late pleistocene holocene beachrock exposed on the southeast shore of freshwater lake iznik in northwest turkey based on field observations various spectroscopic analyses and optical dating results the studied beachrock is a poorly sorted coastal conglomerate composed mostly of gravels derived from surrounding volcanic rocks and marbles as well as quartz and carbonate grains we identified different types of cements dominated by micritic envelopes bladed isopachous aragonite rims void fills radial aggregates and meniscus bridges implying no single origin cementation characteristics indicate that marine like cement micro fabrics may occur in freshwater lake environments where the lake water chemistry favors carbonate precipitation osl data revealed the existence of older beachrock dating back to 20 2 ka together with younger holocene age beachrock of between 5 6 and 2 4 ka this suggests that younger beachrocks have been superimposed on older cemented carbonates through the removal of carbonates by wave motion splash and spray during lower lake level conditions

upper ocean temperature response to hurricane felix as measured by the bermuda testbed mooring hurricane felix passed over the bermuda testbed mooring on 15 august 1995 providing a unique opportunity to observe the response of the upper ocean to a hurricane in the vicinity of bermuda felix was a particularly large hurricane with hurricane force winds over a diameter of about 300 400 km and tropical storm force winds over a diameter of about 650 800 km felix moved northwestward at about 25 km h21 with the eye passing about 65 km southwest of the mooring on 15 august peak winds reached about 135 km h21 at the mooring complementary satellite sea surface temperature maps show that a swath of cooler water by about 3 58 4 08c was left in the wake of felix with the mooring in the center of the wake prior to the passage of felix the mooring site was undergoing strong heating and stratification however this trend was dramatically interrupted by the passage of the hurricane as felix passed the mooring large inertial currents speeds of 100 cm s 21 at 25 m were generated within the upper layer the e folding decay timescale of the inertial currents was about 9 days the mixed layer depth was about 15 m before the arrival of felix and deepened to about 45 m within three days after felix s passage the temperature at 25 m decreased by approximately 3 5 8 4 08c large amplitude temperature oscillations 1 58c near the inertial period inertial pumping effect were set up by the hurricane in the seasonal thermocline resulting in vertical displacements of isotherms of approximately 15 m at 60 70 m comparative scale analyses of the upper ocean responses to hurricane felix and hurricane gloria 1985 indicate that they have several similarities

observations of the response of thermocline currents to a hurricane abstract in september 1985 the eye of hurricane gloria passed within about 100 km of a current meter mooring in the western north atlantic data from this mooring provide a clear view of the vertical structure of the near inertial wake in the main thermocline the response at 159 m was strong 25 cm s 1 amplitude and lasted about 18 days at greater depths the response was weaker and more irregular the phase of the near inertial currents increased with depth consistent with the downward spreading of enemy the total phase change across the thermocline reached about a half cycle seven days after the hurricane s passage indicating a large vertical scale of the response the observations are briefly compared with other time series measurements on the continental margin and with models

upper ocean thermal structure and the western north pacific category 5 typhoons part i ocean features and the category 5 typhoons intensification abstract category 5 cyclones are the most intense and devastating cyclones on earth with increasing observations of category 5 cyclones such as hurricane katrina 2005 rita 2005 mitch 1998 and supertyphoon maemi 2003 found to intensify on warm ocean features i e regions of positive sea surface height anomalies detected by satellite altimeters there is great interest in investigating the role ocean features play in the intensification of category 5 cyclones based on 13 yr of satellite altimetry data in situ and climatological upper ocean thermal structure data best track typhoon data of the u s joint typhoon warning center together with an ocean mixed layer model 30 western north pacific category 5 typhoons that occurred during the typhoon season from 1993 to 2005 are systematically examined in this study two different types of situations are found the first type is the situation found in the western north pacific south eddy zone sez 21 26 n 127 170 e and the kuroshio 21 30

fossil assemblages associated with submerged beachrock beds as indicators of environmental changes in terrigenous sediments examples from the gelasian early pleistocene of rhodes greece the lower pleistocene kritika member of the rhodes formation is composed of predominantly siliciclastic deposits that are sometimes intercalated with hardbottoms formed by drowning of former beachrock beds a wide variety of sclerobionts occur in this environment very different from the poorest soft bottom populations occurring in other levels of the kritika member the most characteristic abundant and frequently diverse are the encrusting forms coralline algae bivalves serpulid worms and bryozoans numerous other groups of sessile and vagile organisms are associated with these crust forming communities a number of skeletal organisms sometimes including zooxanthellate coral colonies formed small carbonate buildups on top of several beachrock beds boring organisms also occur evidence for a two step deepening succession over the previously formed beachrock is provided by palaeontological and sedimentological data the rapidly cemented sandy conglomeratic beds were first colonised by a relatively shallow water around 20 m biocoenosis of mostly encrusting organisms another association with encrusting and erect organisms was later established in a deeper environment 20 40 m a comparison with holocene beachrock occurring on the coast of rhodes was also undertaken their submerged part provided habitat for poorer but similar biotas to those occurring in the kritika member the lower pleistocene beachrock and associated organogenic fossil assemblages indicate repeated drowning episodes during deposition of the kritika member and provide help in sequence stratigraphic interpretations of these siliciclastic deposits notably they can be used as indicators of relative sea level changes

forced stage response to a moving hurricane abstract the upper ocean s response to three hurricanes norbert 1984 josephine 1984 and gloria 1985 is examined using field observations and a numerical ocean model our goal is to describe the physical processes that determine the structure and amplitude of hurricane driven upper ocean currents all three of these northern hemisphere hurricanes produced a rightward biased response of the mixed layer current and transport this asymmetry arises because the wind stress vector rotates clockwise on the right side of the track and remains nearly parallel with the inertially rotating mixed layer current during most of the hurricane passage the maximum observed mixed layer current varied from 0 8 m s 1 in response to josephine which was a large but comparatively weak hurricane to 1 7 m s 1 in response to gloria which was very large and also intense these cases have been simulated with a three dimensional numerical model that includes a treatment of wind driven vertical mixing within the primitive

beach cement incipient caco 3 cemented beachrock development in the upper intertidal zone north uist scotland abstract beachrock has only rarely been observed previously along high latitude coasts on several beaches on north uist nw scotland at over 57 n there is evidence of small scale beach cementation an area of beach cement at the back of traigh ear as well as unconsolidated sands from the beach and the adjacent traigh hornais have been studied using sem xrd and petrographical thin sections to throw light on the nature and causes of cementation unconsolidated sands from both beaches are similar in grain sizes shape and mineralogy but traigh ear grains commonly possess abundant cover of high mg calcite the beach cement on traigh ear exhibits low porosity with abundant micritic and aragonitic cements showing no evidence of vadose cementation along with traces of microorganisms these findings contrast with the vadose low mg calcite cements commonly reported from temperate zone beachrocks

biological mediation of stochastic peritidal carbonate accumulation exponential thickness frequencies of peritidal carbonate units in the lower ordovician kindblade and west spring creek formations at ardmore oklahoma are readily interpreted in a context of probabilities of upsection transition from one lithology to another these largely reflect poisson random processes of deposition from suspended load traction load and microbialitic accumulation although grainy to muddy particulate and cyanobacterial elements exhibit nearly equal ranges of unit thickness carbonate generation and or entrapment via algally mediated processes was less likely to lapse and therefore led to lower probability of transition to some other sediment type the mean thickness of microbially bound units is roughly double those from the physical transport and deposition of particulate material greater persistence of algal accumulation probably related to intrinsically higher biologically induced rates of carbonate precipitation and or binding by cyanobacteria stratigraphic intervals between successive occurrences of suspended load traction load and microbial units are also closely approximated by exponential frequency distributions for which regression slopes define probabilities of upsection recurrence of a particular sediment type values for grainy and algal carbonates are similar and are nearly twice that of muddy suspended load units although biological processes resulted in significantly lower transition probabilities for thrombolitic bioherms and cryptalgal laminites spatial dominance of carbonate mud across the region led to higher rates of stratigraphic recurrence and a volumetric dominance of muddy lithologies in the ardmore sequence poissonian distributions of unit stratigraphic duration and recurrence suggest a significant component of haphazard variation in the type and amount of accumulated carbonate sediment if deposition was influenced by extrabasinal forcing such control must have been nearly random in both secular and spatial dimensions of water depth change stratigraphic durations and recurrences in this sequence more closely reflect the inherently stochastic nature of carbonate accumulation in epicratonic platformal settings than any influence of rhythmic eustatic forcing

upper quaternary coastal palaeoenvironments and palaeosea levels in las canteras beach gran canaria canary islands spain abstract las canteras beach outcrops are vestiges of palaeoenvironments that represent changes in sea level and or climate conditions using broad sedimentological mineralogical geochemical and dating studies three different palaeoenvironmental facies were distinguished 1 the lower facies was defined as beachrock formed by decametric calcarenite layers dipping 8 5 seaward and composed mainly of sand grains and two generations of isopachous low magnesium calcite lmc cement in a context of lower holocene interglacial stage 6600 30 cal years bp rising sea level and coastal progradation 2 during the middle holocene about 6600 30 cal years bp a coastal progradation phase and or lower sea level might lead to land emersion and soil development with an abundance of terrestrial gastropods 3 the upper holocene

beachrock cementation in alexandria egypt beachrock is found in the intertidal and sublittoral zones along the mediterranean coast of alexandria egypt it occurs as beds or patches and shows several stages of cementation and hardness the seaward dip of the beachrock is similar to that of the slope of the foreshore the fabric shows micrite and fringe cement types aragonite was not identified in the beachrock at alexandria the average concentrations of ca mg sr fe and mn in the beachrock are similar to those of the beach deposits the process of beachrock cementation in alexandria is rather recent and typically marine

ocean response to a hurricane part i observations abstract the response of the ocean to hurricanes was investigated using aircraft deployable expendable current profilers axcp the goals were to observe and separate the surface wave and surface mixed layer sml velocities under the storms and to map the across track and along track velocity and temperature response in the mixed layer and thermocline custom instrumentation was prepared including slower failing axcps and the axcp equipment was installed on noaa wp 3d aircraft research flights were made into two 1984 hurricanes norbert in the eastern pacific off baja california 19 n 109 w and josephine off the east coast of the united states 29 n 72 w thirty one probes were deployed in each hurricane and about half the axcps provided temperature and velocity profiles most velocity profiles exhibited strong surface wave contributions slablike velocities in the sml strong shears beneath the sml and only weak flows in the upper thermocline separation of the surface gravity wave velociti

low salinity pools at barbados west indies their origin frequency and variability a vertical array of conductivity temperature recorders moored off the west coast of barbados west indies from may 1996 to november 1997 revealed a heterogeneous and variable salinity pattern punctuated by five pools of low salinity water 34 5 practical salinity units psu entering the region a typical pool extended to 30 m depth and lasted 25 days although one pool extended to 47 m and lasted 94 days water samples taken from a pool in may 1997 have radium 228 226 activity ratios of 1 consistent with previous measurements in barbados of water that originated in the amazon river mixing zone the amazon water likely was translated to barbados in rings spawned from the north brazil current analysis of sea height anomaly and residual derived from the topex poseidon satellite supports this conclusion and reveals that contrary to previous studies rings are shed throughout the year mostly during spring the pools of low salinity water and their associated velocities dramatically changed the already variable flow in our study area we believe the complex salinity and flow we observed represented the disorganized remnants of north brazil current rings that were at or near the ends of their lives the changes we observed in the velocity and water structure are interesting in their own right as evidence of the barbados region as a mixing zone and for their influence on recruitment of larval fishes to the reef along the island s west coast

variations in character and preservation potential of vegetation induced obstacle marks in the variable discharge burdekin river of north queensland australia abstract vegetation induced obstacle marks are described from dalrymple bend in the burdekin river of queensland australia and their preservation potential is discussed the bend is divided into a sand and gravel covered lower bar and a vegetated upper bar obstacle marks comprising an erosional scour and a depositional sediment tail are recognised on the lower bar and the lower margin of the upper bar two types of obstacle marks are dominant in the lower part of the lower bar sediment tail dominated obstacle marks associated with inclined trees of melaleuca argentea silver leaved paperbark and comparatively small obstacle marks around stranded driftwood obstacle marks in the upper part of the lower bar are formed around grass clumps armoured with mud and gravel at the lower margin of the upper bar scours and gravelly sediment tails are recognised around mature tall trees in these cases the scour is 4 m in width and covered with alternating beds of fine sand and mud among the obstacle marks described sediment tail dominated obstacle marks around groves of m argentea have the highest preservation potential obstacle marks in the lower margin of the upper bar are also considered to have high preservation potential obstacle marks around stranded driftwood have the lowest preservation potential obstacle marks around grass clumps survive more than 1 year but their long term preservation potential is nonetheless low implications for the stratigraphic record are also discussed

ams 14c ages and petrological features for solidified fractures with carbonates at coastal outcrops of yakushima island japan this paper describes the petrological features and the ages of rock fractures filled mainly with carbonates at coastal outcrops of yakushima island japan microscopic observation and geochemical analysis were used to investigate the petrological features and the compositions of the fracture fillings in addition ams 14c dating was also performed to estimate the ages of them microscopic study indicated that the fracture fillings contain not only cementing materials but also lithic fragments from host rock and bioclasts sem observation showed that the cements exhibit the characteristic textures of beachrocks the cements were identified as mg calcite from xrd analysis it was also observed from geochemical analysis that there were at least two stages of precipitation within the fractures in addition ams 14c dating for seventeen samples of fracture fillings showed that the ages range from 2 460 to 5 130 years bp which is found to be younger than that of the uplifted coral at yakushima island approximately 5 300 5 600 years bp the results suggest that the fractures were solidified after the coral was uplifted

diagenesis of quaternary bahamian beachrock petrographic and isotopic evidence abstract carbonate beachrock is a common feature on many beaches of san salvador island bahamas these well indurated slabs of cemented beach sand are jointed normal and parallel to the shoreline and slope gently seaward constituent sediment grains are identical to those of adjacent unlithified beach sands beachrock exposed along the northern western and southern coastline of the island is commonly characterized by aragonite needle cement micritized grains and micritic envelopes which are features of early marine phreatic diagenesis these beachrocks have whole rock 13c values of 4 75 pdb and 18o values of 0 75 pdb which are identical to carbon and oxygen isotopic compositions of isolated aragonite needle cement and unlithified beach sand inclusion of recent artifacts in the rock indicates that these deposits are holocene beachrock from one locality on the western side of the island is covered with a calcrete crust indicating prolonged subaerial exposure and vadose weathering associated with the formation of organic rich soils petrographic features include low mg calcite cement evidence of neomorphism of aragonitic cement and micritic rims to low mg calcite random needle fiber calcite calcified filaments and micritic networks whole rock 13c values of these beachrocks range from 3 66 to 6 85 and 18o from 2 16 to 3 68 the wide range of 13c values in these samples is probably a function of the relative proportions of meteoric vadose to meteoric and or marine phreatic cements in individual samples isolated meteoric phreatic cements are only slightly enriched in the light isotopes relative to marine cements whereas meteoric vadose cements are significantly lighter the diagenetic features suggest the beachrock passed through marine phreatic to meteoric phreatic and meteoric vadose diagenetic environments this diagenetic sequence commonly forms in response to sea level lowering evidence of deposition in a shoreline environment and prolonged residence in meteoric phreatic and meteoric vadose environments suggests that these beachrocks may be late pleistocene

kinetic control of morphology composition and mineralogy of abiotic sedimentary carbonates abstract conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid my ca ratios and crystal morphology crystal composition and carbonate mineralogy resulting in the formation of meteoric equant low magnesium calcite and marine acicular high magnesium calcite and aragonite problematically calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals and aragonite may coexist with calcite in either environment commonly however a systematic relation exists between crystal morphology composition mineralogy and rates of reactant supply to growing crystal surfaces for example equant rather than acicular crystals of calcite form in modern deep and or cold marine meteoric phreatic and deep burial settings where the degree of carbonate saturation and or rates of fluid flow are low in areas of higher saturation and or fluid flow such as in warm shallow marine and meteoric vadose environments acicular calcite may predominate this relation is also seen in systems in which aragonite and calcite form in intimate association aragonite precipitation is favored when rates of reactant supply are high calcite forms when rates are low such relations suggest that crystal morphology composition and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants principally carbonate ions at growth sites precipitating phases are the ones which can best accommodate such excess reactants ambient mg ca ratios only indirectly control the nature of inorganically precipitated carbonate phases

development of a foraminifera based transfer function in the basque marshes n spain implications for sea level studies in the bay of biscay abstract in order to reconstruct former sea level we have developed a foraminifera based transfer function using three models based on a modern dataset of 59 samples and 23 species obtained from four basque marshes in northern spain the relationship between observed and foraminifera predicted elevation illustrated the strong performance of the transfer function r 2 jack ranges from 0 74 to 0 81 these results indicated that precise reconstructions of former sea levels are possible error ranges from 0 11 to 0 19 m the transfer function was used to calibrate the foraminiferal assemblages collected from a 50 cm salt marsh core we placed the foraminifera based reconstructions into a temporal framework using 137 cs pb concentrations and 210 pb derived sediment accumulation rates the resulting relative sea level curve is in good agreement with regional tide gauge data both instrumental data and microfossil records suggest a rate of relative sea level rise of approximately 2 mm yr 1 for the 20th century

holocene evolution on galician coast nw spain an example of paraglacial dynamics abstract the recent evolution and the present coastal dynamic in middle atlantic latitudes as the coast of galicia can be considered in a paraglacial context the fossilization of eemian coastal landforms by deposits developed under cold conditions followed by a paraglacial environment during the holocene transgression the characteristics of the different types of deposits and the rising sea level curve controlled the evolution of the coastline showing the co existence of bluff retreat and continental sedimentation

prolonged el nino conditions in 2014 2015 and the rapid intensification of hurricane patricia in the eastern pacific hurricane patricia was the most intense tropical cyclone on record in the eastern north pacific or atlantic reaching a peak intensity of 95 m s 1 only 30 h after attaining hurricane status 33 m s 1 here it is shown that exceptionally warm sea surface temperatures ssts a deeper than normal thermocline and strong near surface salinity stratification all aided patricia s rapid intensification combining to increase its potential intensity by 1 14 m s 1 anomalous surface warming and thermocline deepening along patricia s track were driven by prolonged el nino conditions during 2014 2015 and punctuated by the buildup to the extreme el nino of 2015 2016 in the region where patricia intensified sst was 1 5 c higher and sea surface height was 10 cm higher compared to conditions during the last extreme el nino in 1997 emphasizing the extraordinary nature of the 2015 anomalies

beachrock formation on the coast of gokceada island and its relation to the active tectonics of the region northern aegean sea turkey abstract there are beachrock formations in 5 different sections of the south coast of gokceada turkey s largest aegean island these beachrocks form two different groups in terms of layering characteristics 18o and 13c stable isotope compositions consecutive cementation structures and 14c dating the west group beachrocks to the west were dated to 4010 5830 bp while the east group beachrocks were dated to 620 2390 bp the beachrock formations in both groups are separated by the ne sw trending ugurlu fault the ugurlu fault is a right lateral strike slip with reverse component oblique fault and is an active fault within the north anatolian fault zone in the period between the formation of the two beachrock groups 2390 4010 bp an earthquake was responsible for the destruction of gokceada yenibademli mound and the development of two generations of beachrock

stable isotopic composition of carbonate cemented recent beachrock along the mediterranean and the red sea coasts of egypt abstract recent beachrocks on the mediterranean and the red sea coasts of egypt have been studies in the mediterranean beachrock skeletal particles mainly molluscan fragments are the most abundant grain type comprising approximately 60 of the framework grains intraclasts make up the remaining 40 in contrast the red sea beachrocks are dominantly composed of igneous and metamorphic crystalline basement rock fragments that range in dimension from large boulders in proximal parts of the fan to gravels sands and silts in the distal parts high energy conditions as well as the presence of relatively coarse high porous and permeable sediments ensure that adequate volumes of supersaturated water are able to move through the pore system to accomplish the cementation process textural study light and sem microscope on samples from both localities reveals that high mg calcite cements occur as thick to thin bladed isopachous crusts which sometimes occlude all pore spaces aragonite cements are also present as thin circumgranular acicular crusts however some samples along the red sea coast contain high mg calcite displaying scalenohedral crystal forms the isotopic composition of these beachrock cements generally show high values of 18 o and 13 c in the mediterranean beachrock cements the 18 o and 13 c values range from 0 4 to 1 2 and from 1 0 to 2 1 pdb respectively whereas the 18 o and 13 c values of red sea beachrock cements range from 0 1 to 1 2 and from 2 1 to 4 5 pdb respectively the oxygen and carbon isotopes together with the texture and mineralogical composition of these cements are good indicators of the conditions of primary cementation and reflect the gross of stable isotopic and chemical composition of marine water

beachrocks from the island of la palma canary islands spain beachrocks on la palma island developed on platform forming lavas of the cumbre vieja volcano some of these lavas are related to the 1585 puerto naos 1677 and 1971 echentive eruptions radiocarbon dating of the charco verde beachrock gives a conventional age of 33 330 8 490 bp while that at playa chica beach gives a calibrated age of 14 940 8 525 bp the beachrocks up to 1 5 m thick and some tens of metres wide consist of several decimetre thick horizons dipping 2 15 seaward petrographically they can be classified as rudstones and arenites with volcanic clasts as their main component the original porosity of the beachrocks was intergranular and occasionally intragranular and was partially occluded by cementation and locally by internal sediments the main cements are fibrous aragonite and micrite high magnesium calcite hmc spar aragonite peloidal hmc and microbotryoidal hmc are scarce the elemental geochemistry of these cements is consistent with a marine origin whereas the isotopic geochemistry indicates precipitation from marine waters slightly modified by meteoric waters the evolution of beach deposits and especially the beachrocks in la palma island follows three stages 1 beach deposition 2 beachrock formation and 3 beach retrogradation and or erosion the studied beachrocks prompt us to make some important considerations 1 the mean tidal range in the canary islands has not varied over the last thousand years 2 the position of the beachrocks at the present day sea level would require a combination of eustatic and isostatic movements to keep the sea level stable at the present level over the last thousand years 3 volcanic activity supplies the sediment that forms the beaches 4 a dry warm climate with a very low rainfall below 250 mm year and a high insolation rate 6 11 h day favours and favoured cement precipitation and beachrock formation by increasing the water temperature in the intertidal zone and in the inner part of the beaches 5 the presence of beachrocks in the la palma beaches prevents the total disappearance of the beaches 2003 elsevier science b v all rights reserved

beachrock occurrence characteristics formation mechanisms and impacts beachrocks are hard coastal sedimentary formations consisting of various beach sediments lithified through the precipitation of carbonate cements the objectives of this contribution are to a collate and review information on the reported occurrences characteristics and formation mechanisms of beachrocks and b consider their impacts on the coastal zone the analysis of the available information has shown that a beachrock formation is a global and diachronic phenomenon and b the great majority of beachrocks are found in tropical subtropical and low temperate latitude microtidal coasts the cementing agents of beachrocks are composed predominantly of the metastable carbonate phases high magnesian calcite hmc and aragonite ar appearing in a diverse crystalline morphology it has been suggested that cement precipitation in the coastal environment is controlled by i the physicochemical conditions ii the presence of organic compounds and microbes iii the magnitude and distribution of the wave energy along the coast and iv the textural characteristics of the constituent sediments various theories have been proposed to explain beachrock formation itself linking the phenomenon to either physicochemical or biological processes these theories however do not seem to be of universal validity and acceptance as each is able to explain only some of the reported occurrences the presence of beachrocks appears to affect beach morphodynamics by i locking the beach profile ii modifying the nearshore hydrodynamics iii changing the porous character of the beach and thus its response to wave forcing and iv differential bed erosion at the margins of the beachrock outcrops that can alter significantly the long and particularly the cross shore sediment transport therefore although relict submerged beachrock outcrops may provide some coastal protection by reducing the wave energy impinging onto the coastline modern beachrocks may promote offshore loss of unconsolidated beach sediments and buried beachrock outcropping finally the presence of beachrocks may have also significant ecological impacts as the indigenous mobile substrate fauna and flora of the beach is replaced by hard substrate benthic assemblages which are commonly arranged in hydrodynamically controlled zones

beachrock morphology and genesis on a paraglacial beach abstract beachrock is present in deep stable sections of a mixed sand and gravel beach at whitepark bay 55 o 14 n on the paraglacial coast of northern ireland the beachrock was revealed following progressive and extreme beach erosion during two particularly stormy winters 2013 14 and 2014 15 it occurs as large up to 1 m diameter 0 2 m thick rounded disc shaped concretions in which original beach bedding structures are preserved both sand and gravel beach facies are cemented the cements are similar to those of tropical beachrocks and comprise an initial thin micrite rim and subsequent grain rims of aragonitic needles the cementation is attributed to saturation of beach groundwater with calcium carbonate sourced from adjacent cretaceous chalk outcrop in cliffs behind the beach and dunes the micrite rims suggest microbial activity in the initial cementation possibly by scavenging from chalk and skeletal carbonate grains subsequent aragonite rims were formed through degassing of co 2 aided by tidal water level fluctuations despite similar cementation processes to low latitude beachrocks only isolated concretions occur rather than extensive shore parallel outcrops conditions necessary for cementation and ultimately preservation in this cold temperate and paraglacial setting include long term beach stability a carbonate source in this case adjacent chalk cliffs and stream sapping and tidal water level fluctuations bacterial activity may initiate calcite precipitation following extreme storms and with progressive shoreline retreat prompted by rising sea levels increased reporting of cold water beachrocks is to be expected as formerly stable sections of beaches are exposed to wave action

beachrock a tool for reconstructing relative sea level in the far field abstract today s understanding of sea level change developed through a combination of process based physical modelling and observational data observational data of sea level change derives from coral reefs in the far field of the former ice sheets where a geographically variable relative sea level signal is expected as a response of the earth to ocean loading given this variability and the limited geographical distribution of coral reefs there is a need to explore other non coral based sea level markers to further understand sea level change and for example to fingerprint melt water here we present beachrock as a coastal deposit suitable for relative sea level rsl observations in the far field beachrock is an intertidal deposit forming in the zone where carbonate saturated meteoric and marine water mix and p co 2 decreases we provide the conceptual framework for beachrock analysis and describe techniques suitable for analysing and dating the deposit the approach is standardised by outlining the sediment characteristics in terms of rsl indicative meaning and indicative range and is tested against published data a study conducted on coasts of the mediterranean sea exemplifies the utility of beachrock for rsl reconstruction it is shown that the precision of the reconstruction is derived from the combined uncertainty of age and tidal amplitude or tidal range the uncertainty can be reduced to half the tidal amplitude when a deposit can be ascribed to the upper or lower intertidal zone beachrock based data benefit from the lack of non quantifiable error terms such as post depositional compaction due to the instantaneous formation and high preservation potential of the deposit this underlines the high precision of beachrock based rsl reconstruction which is a prime requirement for testing and extending coral based records

formation exposure and evolution of a high latitude beachrock in the intertidal zone of the corrubedo complex ria de arousa galicia nw spain abstract the presence of beachrocks is noted on the galician shoreline at 41 n a latitude at which this phenomenon is rarely found the present study focuses on the petrological characterization and sedimentological evolution of a beachrock that was exhumed during an exceptional storm in the winter of 2001 in the intertidal zone of a high energy beach the cemented material comprises medium to coarse mixed siliciclastic carbonate sands unlike tropical beachrocks the cement consists of epitaxial low mg calcite presenting varied morphologies and textures acicular and bladed coatings and pore linings pore fillings of sparitic calcite and meniscus style cements seawater dominantly wave action plus marine and meteoric mixed waters are invoked as the main generative fluids beachrock formation and evolution are approached from a morphodynamic viewpoint considering four progressive stages 1 initial cementation in the intertidal zone 2 exposure and modelling by wave action 3 colonization and hardening and 4 disintegration preservation and burial finally the morphodynamic significance climatic implications and occurrence of this type of cementation along the north and northwest shoreline of spain are discussed

organic matter sources for tidal marsh sediment over the past two millennia in the minho river estuary nw iberian peninsula abstract environmental changes during the last 2 millennia in the minho river tidal marsh nw portugal spain border were reconstructed changes in the sources of organic matter om delivered to the marsh were evaluated from elemental isotopic and molecular composition using a 1 m sediment core carbon isotopic composition 13 c and organic carbon to total nitrogen ratio c org n provided valuable information concerning the origin of the om these parameters indicated a major input from land plants reaching a maximum at 1100 1200 and 1750 1850 ad these periods match with major flood events in the nw of the iberian peninsula as reported by several authors a significant reduction in the terrestrial signature occurred at 6 4 cm ca 1960 1985 ad which is contemporaneous with the construction of several major dams on the minho river the distribution of selected lipid biomarkers including n alkanes n fatty acids and n alkan 2 ones and specific parameters derived from the molecular distributions were useful for refining bulk geochemical results long chain n alkanes with an odd number of carbons are indicators of soil and vascular plant derived terrestrial om and were dominant throughout the core in addition a greater contribution of plankton derived lipids was observed in the sections corresponding to ca 1960 1985 ad 6 4 cm and ca 100 200 ad 96 94 cm although different degradation rates for individual compounds might have partly affected biomarker assemblages the variations could be attributed to a sharp decrease in the freshwater contribution to the minho river estuary dam construction and a possible marine highstand respectively in addition several parameters suggested changes in land use including deforestation and farming and probably the effects of mining exploitation during the roman occupation of the area

cryptic intertidal microbialites in beachrock heron island great barrier reef implications for the origin of microcrystalline beachrock cement microbialites with microcolumnar growth morphology occur on the surfaces of solution enlarged crypts in modern beachrock an heron island great barrier reef australia the microbialites consist predominantly of felted aragonite but blocky mg calcite and fringes of acicular aragonite also occur a variety of microbial bodies and filaments occur within and on the surface of the microbialites although most heron beachrock is cemented by isopachous fringes of acicular aragonite irregular micritic cement is common adjacent to the microbialites the micritic cement consists predominantly of felted aragonite and contains microbial filaments and organic matter similar to those in the microbialites both the microbialite and the micritic cement are interpreted to be biologically induced although physico chemical models including co2 degassing and evaporation are commonly held to be sufficient to promote the formation of beachrock the similarity of heron cryptic beachrock microbialite with micritic beachrock cements supports the contention that some beachrock cements are biologically induced additionally the primary difference between fringes of acicular aragonite and the felts of aragonite in microbialites appears to be that the former nucleated on a well defined surface of organic matter whereas the latter nucleated within a framework of organic matter that contained irregularly disposed nucleation sites hence aragonite fringe cements may also be localized and or induced by films of organic matter c 1999 elsevier science b v all rights reserved

cathodoluminescence of carbonate cemented holocene beachrock from the togo coastline west africa an approach to early diagenesis carbonate cemented holocene beachrock outcrops sporadically along more than 100 km of the togo and benin coasts the sands are siliciclastic with subsidiary carbonate skeletal fragments and intraclasts 14c radiometric dating indicates the sand deposits have formed within the last 5000 years beachrock has been indurated in phreatic environments undergoing afterwards several stages of burial and subaerial exposure cathodoluminescence cl proved a useful tool in unravelling the intricate cementation of this beachrock which can be subdivided into three stages firstly magnesian calcite was precipitated in a marine phreatic active zone very dull orange and very dull blue colours emitted in isopachous rims of needle like crystals and peloidal micrite cl1 fabric reveal different eh and ph precipitating conditions in this environment secondly bright yellow orange luminescing acicular and equant spar cement cl2 fabric is interpreted to have formed in a mixed water phreatic zone the third stage of cementation occurred dominantly in the landward part of the beachrock and accompanied neomorphism of the earlier marine cements the resultant cl3 fabric dull blue medium orange luminescing equant spar is typical of continental fresh water phreatic zones the progression from marine to fresh water pore fillings accompanied sand bar progradation during a stable sea level stage ultimately there was erosion stage of the sand bar deposits which led to subaerial exposure and partial erosion of the beachrock recognition of the effects of repeated shoreline progradation during the early diagenesis of this holocene beachrock indicates the potential value of diagenetic studies in aiding recognition of marine regressions and transgressions in the geological record

marine vadose beachrock cementation by cryptocrystalline magnesian calcite maui hawaii abstract active precipitation of high magnesian cryptocrystalline calcite cement 15 5 mole mgco3 in the intertidal zone on the north shore of maui hawaii results in formation of an extensive beachrock exposure at hookipa park framework grains in the beachrock are coarse algal molluscan and intraclast bearing sands meniscus fabric is dominant in the cement indicating that most lithification occurs in the vadose zone the cryptocrystalline cement is generally brownish gold in color but very thin clear isopachous fringes of microcrystalline calcite surround darker cryptocrystalline cement especially in upper horizons of the beachrock peloidal texture is scarce in the cement but is present in a few samples silt and fine sand sized skeletal fragments have been trapped in he evolving cement resulting in cement supported fabric hollow rims of microcrystalline calcite occupy some pore spaces these hollow rims may have precipitated at the air water interface of bubbles that formed in pores and they may therefore be additional evidence of cementation in the vadose zone interstitial water samples from wells that penetrate portions of the beachrock and unconsolidated beach sands reveal temporal chemical variations that suggest the importance of co2 degassing in the formation of beachrock cement when chemical and tidal cycles fluctuate with the same period pco2 values in pore water of the intertidal zone generally bear a direct relationship to tidal stand increasing values of pco2 most often occur during semi daily rising tides and decreasing values of pco2 occur during falling tides saturation ratios with respect to calcite vary in direct proportion to pco2 saturation levels generally increase during rising tides and decrease during falling tides t ese data suggest that co2 degassing during falling tides results in precipitation of calcite cement from pore water of the beach

cement fabrics and optical luminescence ages of beachrock north cyprus implications for holocene sea level changes abstract caco 3 cemented beachrocks are widely found along the northern coast of cyprus in this study we aim to discuss the cementation history of beachrocks at ten particular sites within the context of holocene sea level changes cement fabrics petrographic and geochemical characteristics and optically stimulated luminescence ages of buried quartz grains were studied the seaward inclined 5 10 parallel stratified beds are composed mostly of sandstone alternating with conglomerate ooids benthic and planktic foraminifera bioclasts of red algae echinoid spines and gastropods make up a significant proportion of the cemented beds with caco 3 content ranging between 37 and 65 poorly sorted grains are bonded by four distinct cements circumgranular micritic coatings sparry calcite infillings pore fills and meniscus bridges this consecutive nature of cementation is typical of a marine phreatic and meteoric vadose environment when the sea level was lower than present but had a tendency to increase during middle to late holocene osl ages ranging from 5 4 ka to 0 38 ka indicate that the deposition and ensuing cementation of the quartz grains occurred during two main stages younger beds dated between 2 3 ka and 0 38 ka and older beds from 2 3 ka to 5 4 ka a period devoid of beachrock formation was attested between 3 5 ka and 2 3 ka

holocene sea level fluctuations and coastal evolution in the central algarve southern portugal in armacao de pera bay southern portugal environmental changes during the holocene can be interpreted based on the morphological and sedimentological similarities between older geomorphic features cemented beach and dune rocks and present coastal features using knowledge of the present beach and dune processes we propose a two step model for the evolution of armacao de pera bay first during the rapid sea level rise between about 8 800 and 6 600 yr cal bp the bay changed from a positive to a negative budget littoral cell and transgressive dunes formed favoured by drought conditions at about 5 000 yr cal bp during a sea level maximum beach width was less than the critical fetch and dunes stabilized and underwent cementation during the wetter atlantic climatic event the second phase of dune accumulation started at about 3 200 yr cal bp due to a regression of sea level during which the bay changed back to a positive budget littoral cell in which beach width was greater than the critical fetch currently the beach width is less than the critical fetch dunes are inactive and the sedimentary budget is negative due to sediment storage in local river systems

electrical resistivity tomography mapping of beachrocks application to the island of thassos n greece electrical resistivity tomography ert technique is widely used in mapping subsurface electrical properties in this study ert was used to map a beachrock outcrop extended both inland under beach sediments and seawards on and under seafloor sediments mapping of beachrock is considered important because it can help evaluate the lateral and vertical extend of the formation fast and reliable mapping of beachrocks may contribute in several applications like engineering and construction coastal management recreational reformation as well as scientific approaches like coastal evolution research and palaeo environmental studies the outcome of the survey was the mapping of the formation with centimeter precision especially towards the sea special processing was applied to the data in order to constrain the inversion procedure to include the known sea water layer

upper ocean response to hurricane gonzalo 2014 salinity effects revealed by targeted and sustained underwater glider observations during october 2014 hurricane gonzalo traveled within 85 km from the location of an underwater glider situated north of puerto rico observations collected before during and after the passage of this hurricane were analyzed to improve our understanding of the upper ocean response to hurricane winds the main finding in this study is that salinity potentially played an important role on changes observed in the upper ocean a near surface barrier layer likely suppressed the hurricane induced upper ocean cooling leading to smaller than expected temperature changes poststorm observations also revealed a partial recovery of the ocean to prestorm conditions 11 days after the hurricane comparison with a coupled ocean atmosphere hurricane model indicates that model observations discrepancies are largely linked to salinity effects described results presented in this study emphasize the value of underwater glider observations for improving our knowledge of how the ocean responds to tropical cyclone winds and for tropical cyclone intensification studies and forecasts

current crescents formed by marine algae valonia sp a new record of obstacle marks lacking preservation of obstacles obstacle marks formed around non permanent tools commonly occur on the beach faces of lower long sand island and sagar island two tidal islands in the ganga river estuary india the marine globose algae valonia sp which bloom profusely in the waters of the bay of bengal during winter are deposited on beach faces after being carried by wave swash and then act as impermeable obstacles in the path of wave backwash this creates around the globose algal bodies u shaped or crescentic marks 2 3 cm in width with arms 1 3 cm in length the globose vesicles are soon broken up by external forces or by forces of surface tension leaving crescentic marks around a circular filamentous impression the crescents always open toward the direction of wave backwash these structures may prove useful not only for interpreting the palaeoslope and palaeocurrent directions but also for recognizing the palaeoecology

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

experimental modelling of beachrock cementation under microbial influence a laboratory model has been developed which reproduces natural conditions of beachrock formation these conditions include the porosity of beach sand tidal movements alternation of phreatic and vadose conditions temperature evaporation illumination and water composition seawater with a control of the following parameters salinity ca mg co2 ph caco3 saturation the conditions of two beachrocks from the red sea egypt and shark bay australia have been simulated and the influence of the micro organism population undetermined sampled in these beachrocks was observed for 3 4 months in the experiments inoculated with micro organisms biomineralization produced characteristic crystals of various forms from 1 to 20 m in size the precipitates resemble the micritic cements of natural beachrocks on the contrary precipitation was much less developed in the control experiments under nearly sterile conditions these results confirm the importance of microbial activity during beachrock formation the first micritic cement which seems to control cementation and produce the initial consolidation is formed under a strong microbial influence in or near a biofilm covering the grain surface the presence of this micritic cement is necessary for the development of the subsequent prismatic cement which probably results from an abiotic precipitation during higher fluid circulation

current crescents from the herreria formation lower cambrian of northern spain current crescents are well preserved on the upper surfaces of quartzite beds in the lower cambrian herreria formation of the cantabrian mountains in northern spain within a sequence of nearshore deposits the current crescents are interpreted as having formed by flow separation of wave backwash around obstacles on a beach the obstacles are not preserved and are inferred to have been perishable organic material such as stranded algae or jellyfish which subsequently decayed

causes and evolution of the southeastern tropical atlantic warm event in early 2016 a strong warm event occurred in the southeastern tropical atlantic ocean off angola and namibia in january and february 2016 with sea surface temperature anomalies reaching 3 c in contrast to classical benguela nino events the analysis of various direct observations indicates that the warming was not predominantly forced by an equatorial kelvin wave exciting a coastally trapped wave but instead resulted from a combination of local processes that are related to 1 a weakening of the alongshore i e mainly southerly winds and 2 enhanced freshwater input through local precipitation and river discharge consistent with the weakened winds we find a reduction in latent heat loss from the ocean and a poleward surface current anomaly the surface freshening which is detected in satellite observations of sea surface salinity caused a very shallow mixed layer and enhanced upper ocean stratification this is supported by the analysis of the velocity structure of the angola current at 11 s which shows that at the time of the event subsurface velocities were directed northward while surface velocities were directed southward the shallow layer of warm and fresh surface water was thus advected poleward by the surface current in addition a reduction of the local upwelling and the formation of a barrier layer that inhibits the entrainment of cool subsurface waters into the surface mixed layer might have contributed to the warm surface anomaly the sudden termination of the warm event was accompanied by a re intensification of southerly winds in march

a morphological model of the beach profile integrating wave and tidal influences abstract meso and macrotidal beaches constitute a significant proportion of the world s beaches however by far they have been less studied and understood than tideless beaches even though in recent times several local studies have addressed this problem few attempts to model tidal beaches exist a morphological model capable of predicting the beach profile behaviour under different wave and tide conditions is proposed it is based on the concept of the two section equilibrium beach profile and has been validated with field and laboratory data this is achieved by means of two parameters the modal tidal range and the dimensionless fall velocity tide is considered a local variable whose principal effect is the lengthening of the intertidal profile the greater the tidal range the wider the intertidal profile here defined as the surf profile the dimensionless fall velocity defines the transition from dissipative to reflective situations in beaches of any given tidal range wave height is the controlling parameter in seasonal beach changes as the wave height decreases the beach profile changes from erosive to accumulative these morphological changes in the surf and shoaling sections of the profile occur in the opposite direction whilst in the surf profile the slope of the upper part of this section becomes steeper and the concavity of whole section increases in the shoaling profile the upper part flattens resulting in a less concave section in this transition the slope break between surf and shoaling profiles here defined as the discontinuity point becomes smoother and difficult to identify the main morphological parameter of the model xo describes the length of the surf profile this parameter is capable of expressing slightly different variability in micro meso and macrotidal beaches in microtidal beaches the length of the surf profile decreases proportionally to the dimensionless fall velocity in meso and macrotidal beaches xo decreases from the dissipative to the intermediate state but increases from intermediate to reflective this results from the flattening of the lower part of the surf profile in the reflective case where a small change in tidal range generates a high stretching of the surf profile this beach morphological model is presented as a framework to understand the first order behaviour of beaches under the action of waves and tides this becomes a useful and easy to apply tool in coastal management and prediction of equilibrium beach profile under diverse conditions

rock topography causes spatial variation in the wave current and beach response to sea breeze activity we hypothesized that beach profiles that are perched on natural rock structures would be better protected from waves and currents than profiles that are not fronted by rock in southwest western australia many beaches such as at yanchep are perched on quaternary limestone yanchep lagoon is fronted by a low crested limestone reef that partially encloses a coastal lagoon the spatial variation of waves and currents around the rock structures were quantified during the sea breeze cycle at locations 1 offshore 2 20 m seaward of the reef 3 inside the lagoon and 4 in the surf zone the spatial variation in the beach profile response was measured at two beach profiles 1 the exposed profile that was not fronted directly seaward by outcropping limestone and 2 the sheltered profile which was fronted seaward by submerged limestone at 2 m water depth and that was near the lagoon exit at the end of the limestone reef the sheltered profile had greater volume changes during the cycle of the sea breeze whilst the exposed profile recovered more by overnight accretion when wind decreased the lagoonal current drove the strong response of the sheltered profile and may have contributed to the lack of overnight recovery of the beach together with the seaward rock formation impeding onshore sediment transport the different direction and speed responses of bottom currents in the surf zone fronting the two profiles reflected the local variation in geology the influence of the jet exiting the lagoon and wave refraction around the reef that was measured with gps drifters and wave ray tracing using xbeach major spatial variation in waves currents and beachface behavior at this perched beach shows the importance of the local geological setting

first record of beachrock on black sea coast of turkey implications for late holocene sea level fluctuations abstract we present new data on the diagenetic characteristics subsurface nature and radiocarbon ages of beachrock from the thracian black sea coast of turkey indicative of sea level changes and climatic conditions favoring lithification of beach sands between 5 4 ka and 3 5 ka cal bp micrite coatings and succeeding meniscus cements typify diagenetic history and suggest a two stage cementation over this timeframe the early cements are typical of upper intertidal zone when the sea level was likely similar to that of today the ensuing intergranular bridges refer to an approximate 2 m decline in sea level favoring downward percolation of meteoric waters related to subaerial exposure marked by a reduction in mg concentration and dissolution pits on early cement coatings formation of beachrock during this bimillennial period could be associated with relatively drier conditions promoting the precipitation of connective cements

the corrubedo beach lagoon complex galicia spain dynamics sediments and recent evolution of a mesotidal coastal embayment abstract the corrubedo beach lagoon complex is situated in an embayment on the northwestern coast of spain the 4 1 m tidal range and southwesterly winds are the main agents of sediment transportation the sediments are hybrid arenites siliciclastic bioclastic with carbonate percentages ranging from 27 36 to 54 10 silt clay and organic matter occur in minor amounts repeated mapping and sampling of the beach tidal channels salt marshes and active and vegetated dunes recorded the vertical facies associations and their temporal evolution two peat layers at 0 6 and 1 7 m below the present day marsh have yielded ages of 2280 60 yrs b p and 1045 125 yrs b p respectively the possible causes of the relative sea level rise are discussed

hurricane forced upwelling and chlorophyll a enhancement within cold core cyclones in the gulf of mexico 1 clear skies subsequent to hurricane ivan s passage across the gulf of mexico in september 2004 provided a unique opportunity to investigate upper ocean responses to a major hurricane oceanic cyclonic circulation was rapidly intensified by the hurricane s wind field 59 62 m s 1 maximizing upwelling and surface cooling 3 7 c in two large areas along ivan s track upward isothermal displacements of 50 65 m computed from wind stress and sea surface height changes caused rapid ventilation of thermoclines and nutriclines leading to phytoplankton blooms with peak concentrations 3 4 days later wind speed changes along ivan s track demonstrated that the cool waters 20 26 c provided immediate negative feedback to the hurricane s intensity although our study focused on a relatively small ocean area it revealed that mesoscale cyclones in addition to warm anticyclones may play an important role in producing along track hurricane intensity changes

rapid beachrock cementation on a south african beach linking morphodynamics and cement style rapid cementation 5 years of beachrock is reported from the wave dominated microtidal coastline of durban south africa the beachrock is developing at mean sea level on a steep 10 30 reflective beach prone to periodic erosion by high energy wave action the most recent erosional event resulted in retrogradation of the beach by up to 10 m landward of the beachrock outcrop discussed in this study transmitted light microscopy and scanning electron micrographs show the precipitation of two dominant cement types which are linked to the beachface morphodynamics during the accreted beach phase when the locus of beachrock formation lay well landward of the beachface in the undersaturated upper intertidal to supra tidal backbeach meniscus cements were precipitated following a period of erosion associated with a landward shift of the beachface the incipient beachrock was then exposed to saturated conditions which promoted growth of acicular cements contemporary beachrock cementation occurred very rapidly 5 years between significant erosional events the observed cement textures record short term beach progradation and retrogradation but are similar to those typically associated with longer term regression and transgression

silica cemented beachrock from lake taupo north island new zealand abstract beachrocks on the north coast of lake taupo are composed of volcanic grains and diatoms that are bound together by isopachous meniscus or pore filling amorphous silica cements the littoral sediments were originally stabilized by epilithic and chasmolithic filamentous microbes that bound neighboring grains together the amorphous silica cement was precipitated from silica rich geothermal fluids that originated from warm water plumes that form in the northern part of lake taupo where hot spring waters flow into the lake and move along the shoreline water from the warm water plumes that is washed onshore by prevailing winds and currents then percolates down through the beach sands and gravels precipitation of amorphous silica triggered by cooling of the mixed spring and lake water is preferentially focused on the epilithic and chasmolithic filamentous microbes which act as templates for silica nucleation and precipitation

identification of the main driving mechanisms in the evolution of a small coastal wetland traba galicia nw spain since its origin 5700 cal yr bp this paper examines the interdependence among the different forcing factors in the evolution of the traba coastal wetland galicia nw spain based on lithofacies and diatom analyses of three cores reaching the basement according to radiocarbon data the wetland originated 5700 cal yr bp a time when similar systems on the atlantic coast of the iberian peninsula were formed diatom assemblage data allow the estimation of the sea level position at 5700 cal yr bp at least 7 m below present day mean sea level attenuation of the sea level rise at that time was a major driving mechanism that permitted the establishment of an incipient beach dune complex causing water logging in the traba basin however the location of this incipient wetland on a basement high which prevented an open connection to the sea made topographic inheritance the main forcing factor in the subsequent evolution of the wetland thus traba was never a coastal lagoon system as it has sometimes been defined the maximum permeability of the beach dune complex enclosing the wetland was recorded after its origin until 2900 cal yr bp when increased stormy conditions affected the galician shelf waters since then the evolution of the wetland has been mainly controlled by more local factors especially the continental sediment supply changes in land use in the basin have accelerated the infilling of the water body since the 19th century this rapid infilling makes the whole system more prone to total encroachment in the short term rather than to sea drowning palaeoenvironmental analyses showing the main trends in the long term evolution of coastal wetlands can be of key importance in any management decisions aimed at preserving these kinds of sensitive coastal environments