inorganic isotopic and organic composition of high chloride water from wells in a coastal southern california aquifer abstract chloride concentrations were as high as 230 mg l in water from the surface discharge of long screened production wells in pleasant valley calif about 100 km nw of los angeles wells with the higher cl concentrations were near faults that bound the valley depending on well construction high cl water from different sources may enter a well at different depths for example cl concentration in the upper part of some wells completed in overlying aquifers influenced by irrigation return were as high as 220 mg l and cl concentrations in water sampled within wells at depths greater than 450 m were as high as 500 mg l these high cl waters mix within the well during pumping and produce the water sampled at the surface discharge changes in the major ion minor ion trace element and 34s and 13c isotopic composition of water in wells with depth were consistent with changes resulting from so4 reduction precipitation of calcite and cation exchange the chemical and isotopic composition of high cl water from deep wells trends towards the composition of oil field production water from the study area chloride concentrations in oil field production water present at depths 150 m beneath freshwater aquifers were 2200 mg l and cl concentrations in underlying marine rock were as high as 4400 mg l high cl concentrations in water from deeper parts of wells were associated with dissolved organic c composed primarily of hydrophobic neutral compounds believed to be similar to those associated with petroleum in underlying deposits these compounds would not be apparent using traditional sampling techniques and would not be detected using analytical methods intended to measure contamination

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

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

hotspots mantle plumes flood basalts and true polar wander persistent long lived stationary sites of excessive mantle melting are called hotspots hotspots leave volcanic trails on lithospheric plates passing across them the global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions through the orientations and age distributions of volcanic trails left by these melting anomalies hotspots appear to be maintained by whole mantle convection in the form of upward flow through narrow plumes evidence suggests that plumes are deflected little by horizontal flow of the upper mantle mantle plumes are largely thermal features and arise from a thermal boundary layer most likely the mantle layer just above the core mantle boundary experiments and theory show that gravitational instability drives flow beginning with the formation of diapirs such a diapir will grow as it rises fed by flow through the trailing conduit and entrainment of surrounding mantle the structure thus develops a large spherical plume head and a long narrow tail on arrival at the base of the lithosphere the plume head flattens and melts by decompression producing enormous quantities of magma which erupt in a short period these are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks the plume supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core generated axial dipole paleomagnetic reference frame comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole mantle motion relative to the earth s spin axis this is termed true polar wander and has amounted to some 12 since early tertiary time the direction and magnitude of true polar wander have varied sporadically through the mesozoic probably in response to major changes in plate motions particularly subduction zone location that change the planet s moments of inertia

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

origin of groundwater salinity and hydrogeochemical processes in a confined coastal aquifer case of the rhone delta southern france the rhone delta south of france camargue 750 km2 is a coastal saline wetland located along the mediterranean sea the confined aquifer of this delta shows high values of electrical conductivity rising from the north 4 ms cm to the shoreline 58 ms cm this work aims to identify the origin of groundwater salinity and the geochemical processes occurring in this coastal confined aquifer according to the degree of salinity a natural tracing approach is considered using monthly sampling in 8 piezometers for chemical and isotopic analyses 18o 2h 13ctdic ionic and isotopic ratios demonstrate that strong salinities are due to a simple mixing between mediterranean seawater and freshwater seawater contribution reaches up to 98 at 8 km from the shoreline seawater intrusion induces a particular groundwater chemistry which varies with the degree of seawater contribution 1 in the less saline part of the aquifer seawater contribution 20 the intrusion induces so4 reduction which is confirmed by highly depleted 13ctdic values up to 19 the 13ctdic also reveals that methanogenesis processes may occur in the most reductive part of the aquifer due to so4 reduction the intrusion induces a shift in carbonate equilibrium leading to supersaturation with respect to dolomite and or magnesian calcite thus carbonate precipitation may occur in the area strongly influenced by seawater

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

evolution of saline waters and brines in the benue trough nigeria abstract hydrogeochemical assessment of 40 saline waters and brines from 20 locations within the lower southern and middle regions of the benue trough nigeria are presented and discussed in terms of genesis of the primary salinity and subsequent hydrochemical evolution the total dissolved ions range from 5263 to 88 800 mg l and 5148 to 47 145 mg l in the lower and middle region respectively the saline waters and brines are characteristically na cl type enriched in ca and sr on the one hand and depleted in mg and so 4 on the other relative to the seawater evaporation trend ionic ratios na cl br systematic and divalent cations suggest two likely sources of primary salinity a fossil seawater source and dissolution of halite however water rock interaction involving mg uptake by clay minerals and possibly dolomitization during diagenesis appear to be responsible for further modification of the primary chemistry a conceptualized hydrogeological flow model for the brines is presented

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

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

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

hot spotting in the pacific combining the geometry of plate tectonics and the computational advantage of digital sea floor topography provides a new method for locating plumes rising from the earth s deep mantle and for tracing the history of plate motions

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

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

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

geology and geochronology of the line islands geological and geophysical studies along the entire length of the line islands were undertaken in order to test the hot spot model for the origin of this major linear island chain volcanic rocks were recovered in 21 dredge hauls and fossiliferous sedimentary rocks were recovered in 19 dredge hauls volcanic rocks from the line islands are alkalic basalts and hawaiites in addition a tholeiitic basalt and a phonolite have been recovered from the central part of the line chain microprobe analyses of groundmass augite in the alkalic basalts indicate that they contain high tio2 1 0 4 0 wt and al2o3 3 4 9 1 wt and are of alkaline to peralkaline affinities major element compositions of the line islands volcanic rocks are very comparable to hawaiian volcanic rocks trace element and rare earth element analyses also indicate that the rocks are typical of oceanic island alkalic lavas the line islands lavas are very much unlike typical mid ocean ridge or fracture zone basalts dating of these rocks by 40ar 39ar k ar and paleontological methods combined with deep sea drilling project data from sites 165 315 and 316 and previously dated dredged rocks provide ages of volcanic events at 20 localities along the chain from 18 n to 9 s a distance of almost 4000 km all of these dates define mid cretaceous to late eocene edifice or ridge building volcanic events eocene volcanic events took place from 15 n to 9 s and late cretaceous events took place from 18 n to 9 s in the southern line islands both cretaceous and eocene events took place on the same edifice or ridge indicating recurrent volcanism at a single locality the irregular distribution of atolls in the chain the fact that late cretaceous reefs flourished along a distance of approximately 2500 km in the central and southern line islands and the observation that spatially closely related seamounts exhibit different subsidence histories are interpreted as indicating that large segments of the chain have not followed a t1 2 related subsidence path magnetic surveys of 11 seamounts show that four of the seamounts from the central line chain give virtual geomagnetic poles which fall well to the north of virtual geomagnetic poles of cretaceous seamounts these four poles agree with other paleomagnetic data of middle late eocene early oligocene age from the pacific one of these four seamounts yielded a 40ar 39ar total fusion age of 39 ma because the poles of all four seamounts fall into a tight group we infer that they are probably of middle late eocene age to early oligocene age the other three seamounts as well as one seamont from the line islands analyzed previously all give virtual geomagnetic poles which agree with late cretaceous paleomagnetic data from the pacific of these four seamounts three give late cretaceous 40ar 39ar ages ranging from 71 to 85 ma another in the southern line islands is interpreted on paleontological evidence to be of late cretaceous age the origin of the line islands has been ascribed by previous workers to the effects of a single hot spot and to the action of four hot spots the single hot spot model cannot account for all of the volcanic edifices in the line islands although it does explain a general age progression of 9 6 0 4 cm yr from north to south along the chain derived from a number of dated edifices the four hot spot model accounts for more of the dated volcanic edifices but still does not explain all of the available data the petrologic data argue against a mid ocean ridge or transform fault origin proposed by earlier workers the complex volcanic province represented by the line islands remains a challenge to existing models for the origin of midplate volcanism in the pacific an atoll drilling program which could determine edifice building histories paleolatitudes of seamount formation and subsidence rates and patterns in the line islands is needed

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

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