fluoride occurrence in publicly supplied drinking water in estonia a study was undertaken to examine the content and spatial distribution of fluoride in drinking water water samples 735 from public water systems covering all estonian territory were analysed using spadns method in order to specify the natural source of fluoride the chemistry data from five aquifer systems utilised for water supply were included into the study fluoride concentrations in tap water to a great extent ranged from 0 01 to 6 95 mg l drinking water in southern estonia where terrigenous middle devonian aquifer system is exploited has a fluoride concentration lower than recommended level 0 5 mg l thus promoting susceptibility to dental caries the western part of the country is supplied by water with excess fluoride content 1 5 6 9 mg l groundwater abstracted for drinking purposes originates from ordovician and silurian carbonate rocks the content of fluoride in silurian ordovician aquifer system is associated with the groundwater abstraction depth and the main controlling factors of dissolved fluoride are the ph value and the chemical type of water

extreme winds and waves in the aftermath of a neoproterozoic glaciation the most severe excursions in the earth s climatic history are thought to be associated with proterozoic glaciations according to the snowball earth hypothesis the marinoan glaciation which ended about 635 million years ago involved global or nearly global ice cover at the termination of this glacial period rapid melting of continental ice sheets must have caused a large rise in sea level here we show that sediments deposited during this sea level rise contain remarkable structures that we interpret as giant wave ripples these structures occur at homologous stratigraphic levels in australia brazil canada namibia and svalbard our hydrodynamic analysis of these structures suggests maximum wave periods of 21 to 30 seconds significantly longer than those typical for today s oceans the reconstructed wave conditions could only have been generated under sustained high wind velocities exceeding 20 metres per second in fetch unlimited ocean basins we propose that these extraordinary wind and wave conditions were characteristic of the climatic transit and provide observational targets for atmospheric circulation models

depositional facies of high energy beach to offshore sequence comparison with low energy sequence a study of the nearshore zone and continental shelf of a high energy coast was made in the ventura port hueneme area of california during the summer of 1974 to investigate depositional facies characteristics and compare them with similar facies from a low energy coastal setting analysis of box cores can cores and vibracores permits recognition of three principal zones 1 nearshore facies backshore to 9 m water depth made up primarily of parallel ripple and cross bedded clean sand bioturbation is only locally significant 2 transition facies 9 to 18 m water depth a zone of fine sand and silty sand characterized by an increase in biogenic over physical sedimentary structures that are commonly preserved as laminated to burrowed beds wave ripple bedding and parallel lamination are important structures in this facies 3 offshore facies 18 m water depth sandy silt is the primary texture and bioturbation is the dominant sedimentary structure remnant parallel lamination is the only physical sedimentary structure present comparison of the results of this study with a previous description of a low energy beach to offshore sequence at sapelo island georgia indicates that the two areas do not differ greatly in their facies or overall vertical sequence of sedimentary structures the principal difference is in the thickness of the three facies the california facies are significantly thicker than their georgia counterparts this difference is in direct response to the role of higher wave energy on the california coast

holocene development of the belize barrier reef previously knowledge of the holocene development of the belize barrier reef bbr the largest reef system in the atlantic ocean was limited to one location carrie bow cay we present new data from 11 rotary drill cores taken at 9 locations and 36 radiometric ages that indicate that the bbr was established from 8 26 to 6 68 ky bp on pleistocene reef limestones presumably deposited during oxygen isotope stage 5 the nonsynchronous start of holocene reef growth was a consequence of variation in elevation of antecedent topography largely controlled by underlying nne trending structures from north to south pleistocene elevation decreases along these structural trends probably reflecting differential subsidence and variations in karst topography reef anatomy is characterized by three facies in order of decreasing abundance these facies are represented by corals mainly acropora palmata and members of the montastraea annularis group by unconsolidated sand and rubble and by well cemented coral grainstones rudstones holocene reef accumulation rates average 3 25 m ky the degree of reef consolidation is negatively correlated with holocene thicknesses indicating that slowly growing reefs are better cemented than fast growing ones we present a holocene sea level curve for belize based on 36 dates from this study and 33 dates from our previous studies in the area

effects of biological activity on the entrainment of marine sediments nowell a r m jumars p a and eckman j e 1981 effects of biological activity on the entrainment of marine sediments mar geol 42 133 153 the effects of animal tracks and fecal pellet production on the critical entrainment velocity of marine sediments were examined experimentally laboratory measurements in a free surface seawater flume were made using three sediment sizes effects of three species of polychaetes and two species of bivalves were tested boundary shear velocity was calculated from the mean velocity profile in the logarithmic region of the boundary layer measurements were made with a hot film anemometer tracking doubled the boundary roughness and decreased the critical entrainment velocity by 20 ambient or free sediments were more easily entrained than fecal mounds which were restrained from movement by mucous adhesion between the fecal coils isolated pellets such as those egested by amphicteis scaphobranchiata transported readily as bedload over a cohesive sediment surface

storm deposits and storm generated coarse carbonate breccias on a pelagic outer shelf south east basin france uppermost jurassic limestones of the south east basin france are organized into four facies associations that were deposited in four distinct zones 1 peritidal lagoonal limestones 2 bioclastic and reefal limestones 3 pelagic lime mudstones 4 lime mudstones calcarenites coarse breccias calcarenite deposits of zone 4 exhibit sedimentary structures that are diagnostic of deposition under wave induced combined flow in subzone 4a both vertical and lateral transitions from lime mudstone calcarenite to breccia indicate in situ brecciation under wave cyclic loading breccias were produced by heterogeneous liquefaction of material previously deposited on the sea floor deposits in subzone 4a record relatively long periods 400 kyr of sedimentation below wave base alternating with periods of deposition under wave induced currents and periods of in situ deformation in this zone storm waves were attenuated by wave sediment interaction and wave energy was absorbed by the deformation of soft sediment with reference to present day wave attenuation water depths in this zone ranged between 50 and 80 m landwards of the attenuation zone in zone 3 storm waves were reduced to fair weather wave heights storm wave base was not horizontal and became shallower landwards as a consequence water depth and wave energy were not linearly related on a small area of the seaward edge of subzone 4a cobbles were removed by traction currents and redeposited in subzone 4b there they formed a 100 m thick wedge which prograded over 3 km and was built up by the stacking of 5 to 20 m thick cross stratified sets of coarse breccia this wedge records the transport and redeposition of cobbles by a high velocity unidirectional component of a combined flow the increase in flow velocity in a restricted area is proposed to result from flow concentration in a channel like structure of the downwelling in the gulf formed by the basin in more distal subzone 4c the hydrodynamic effect of wave induced currents was quasi permanent and brecciation by wave sediment interaction occurred only episodically this indicates that seawards of the attenuation zone hydrodynamic storm wave base was deeper than mechanical storm wave base uppermost jurassic carbonates were deposited and soft sediment deformed on a hurricane dominated ramp of very gentle slope and characterized by a zone of storm wave degeneration located seawards of a zone of sedimentation below wave base

rip currents mega cusps and eroding dunes abstract dune erosion is shown to occur at the embayment of beach mega cusps o 200 m alongshore that are associated with rip currents the beach is the narrowest at the embayment of the mega cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune to undercut the dune and to cause dune erosion field measurements of dune beach and rip current morphology are acquired along an 18 km shoreline in southern monterey bay california this section of the bay consists of a sandy shoreline backed by extensive dunes rising to heights exceeding 40 m there is a large increase in wave height going from small wave heights in the shadow of a headland to the center of the bay where convergence of waves owing to refraction over the monterey bay submarine canyon results in larger wave heights the large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale the strongly refracted waves and narrow bay aperture result in near normal wave incidence resulting in well developed persistent rip currents along the entire shoreline the alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95 confidence the alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95 confidence therefore it is concluded the mega cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega cusp

factors controlling the rate of caco3 precipitation on great bahama bank measurements by langdon et al 2000 in the man made mesocosm coral reef at biosphere 2 s ocean reveal a strong dependence of calcification rate on the degree of supersaturation of caco 3 in seawater a similar trend was previously encountered on the bahama banks where halimeda and other calcifiers are likely responsible for aragonite precipitation broecker and takahashi 1966 in this paper we compare these two sets of results and conclude that the dependence on saturation state is significant but less strong in the bahamas however it must be kept in mind that to some extent the reduction in caco 3 precipitation on the bahama banks may be due to impact of higher salinity on the growth of the calcifying algae however if as many sedimentologists are convinced the precipitation of caco 3 on the bahama banks is inorganic macintyre and reid 1992 milliman et al 1993 then the comparison of the bahamas and biosphere 2 results for dependence of calcification rate on saturation state is telling us something quite different

on the dependence of sea surface roughness on wave development abstract the aerodynamic roughness of the sea surface z0 is investigated using data from lake ontario from the north sea near the dutch coast and from an exposed site in the atlantic ocean off the coast of nova scotia scaling z0 by rms wave height gives consistent results for all three datasets except where wave heights in the atlantic ocean are dominated by swell the normalized roughness depends strongly on wave age younger waves traveling slower than the wind are rougher than mature waves alternatively the roughness may be normalized using the friction velocity u of the wind stress again young waves are rougher than mature waves this contradicts some recent deductions in the literature but the contradiction arises from attempts to describe z0 in laboratory tanks and in the field with a single simple parameterization here it is demonstrated that laboratory waves are inappropriate for direct comparison with field data being much smoother than their field equivalents in the open ocea

δ18o and marion plateau backstripping combining two approaches to constrain late middle miocene eustatic amplitude d 18 obenthic values from leg 194 ocean drilling program sites 1192 and 1195 drilled on the marion plateau were combined with deep sea values to reconstruct the magnitude range of the late middle miocene sea level fall 13 6 11 4 ma in parallel an estimate for the late middle miocene sea level fall was calculated from the stratigraphic relationship identified during leg 194 and the structural relief of carbonate platforms that form the marion plateau corrections for thermal subsidence induced by late cretaceous rifting flexural sediment loading and sediment compaction were taken into account the response of the lithosphere to sediment loading was considered for a range of effective elastic thicknesses 10 te 40 km by overlapping the sea level range of both the deep sea isotopes and the results from the backstripping analysis we demonstrate that the amplitude of the late middle miocene sea level fall was 45 68 m 56 5 6 11 5 m including an estimate for sea level variation using the d 18 obenthic results from the subtropical marion plateau the range of sea level fall is tightly constrained between 45 and 55 m 50 0 6 5 0 m this result is the first precise quantitative estimate for the amplitude of the late middle miocene eustatic fall that sidesteps the errors inherent in using benthic foraminifera assemblages to predict paleo water depth the estimate also includes an error analysis for the flexural response of the lithosphere to both water and sediment loads our result implies that the extent of ice buildup in the miocene was larger than previously estimated and conversely that the amount of cooling associated with this event was less important

subsurface thermal environment and groundwater flow around tokyo bay japan previous studies and borehole temperature measurements suggest that subsurface temperature distribution on the west side of tokyo bay from tokyo to yokohama is higher than that of the east side chiba side to understand the groundwater flow and other factors which may contribute to the subsurface temperature discrepancy such as geological setting in the study area groundwater temperature profiles were measured in 119 boreholes around the tokyo bay from 2002 to 2007 the data were analyzed and compared with previous studies horizontal distribution of subsurface temperature at the depths of 50 and 100 m was made to show the distribution of thermal regime a cross section across the bay of tokyo was made to see the isothermal lines and distribution of hydraulic heads in a vertical perspective these results show that the highest subsurface temperature zone is in the tokyo area along the river valley subsurface temperature at the depth of 50 and 100 m below sea level in the western part of the bay is comparatively higher than its eastern side at the same elevation and distance from the bay this fact suggests that there is a regional groundwater flow system in the area and it is strongly affected by the geological structure particularly buried valley systems of the bay during the paleo tokyo river and the topographical driving force which is the result of the different elevation of recharge areas groundwater discharge is concentrated along the buried valley of paleo tokyo river

measurements of wave attenuation due to a soft bottom the swamp experiment the sea wave attenuation measurement program swamp was designed to provide measurements of the attenuation of waves as they travel from deep water to relatively shallow water off the mississippi delta the soft bottom was suspected of causing strong attenuation in the area this effect has now been measured a wave staff and electromagnetic current meter were used to estimate directional wave spectra at the cognac platform in 312 m 1025 feet of water and at platform vv in south pass block 27 in 19 m 63 feet of water in addition measurements of vertical bottom motion were made at platform vv seven storm periods from sepember 1979 to february 1981 were studied the directional spectral comparisons showed that the theoretically calculated refraction and shoaling can explain the changes in the spectra when the wave height is low however as the wave height increases a nonlinear attenuation mechanism becomes increasingly strong the attenuation is a strong function of deep water wave height and a weak function of wave frequency the bottom motion measurements showed that the bottom moved downward with small amplitude under wave crests

reconstruction of paleo wave conditions during the late pleistocene from marine terrace deposits monterey bay california the santa cruz coastal terrace fringes much of the northern monterey bay region california it consists mainly of a regressive sequence of high energy barred nearshore marine sediments deposited during the last sangamonian highstand of sea level this sequence can be sub divided into several depth dependent facies on the basis of paleo current data and vertical sequence of sedimentary structures these include a lower shoreface facies deposited in 10 16 m water depth an upper shoreface facies including both a storm dominated assemblage and a surf zone assemblage deposited in 0 10 m water depth and a foreshore facies deposited in the swash zone up to 3 5 m above high tide the magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo wave heights using a variety of criteria e g critical threshold equations breaker depths berm heights in addition the climate and paleogeography during the deposition of these sediments were essentially the same as today allowing the use of present day wave statistics to estimate the frequency of these storm events the largest storms formed offshore flowing currents e g rip wind forced and possibly storm surge ebb currents that resulted in the deposition of approximately 30 of the sediments seaward of the surf zone however the magnitude and frequency of these events are unknown the remaining 70 of the sediment beyond the surf zone was deposited in response to smaller storm waves which were on the average at least 1 6 m high such waves presently occur no more than 15 of the time sediments deposited during fairweather conditions i e the remaining 85 of the time have a low preservation potential and are generally not preserved in this facies in contrast surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably 2 2 m such waves presently occur up to 92 of the time sediments within the swash zone were deposited by waves up to 3 m high the largest of which presently occur approximately 2 of the time most of the sediments were deposited by storms of intermediate magnitude and frequency different facies however appear to preferentially record events of different recurrence intervals in particular surf zone sediments were deposited under relatively small storm and post storm conditions whereas sediments deposited farther offshore record increasingly larger less frequent storm events relatively rare events e g the 100 or 1000 yr events do not appear to have significantly affected sedimentation in these nearshore environments

new instrumentation for the investigation of sediment suspension processes in the shallow marine environment abstract an instrumentation system has been developed that continuously measures flow velocity water depth and suspended sediment concentration profiles in the nearshore zone the system consists of four components 1 an array of electronic sensors including an electromagnetic current meter a surface piercing resistance wave gauge and a five element array of optical back scatterance sensors 2 a signal processing electronics unit 3 a guyed mast support structure and 4 a data acquisition system the small size of the sensors and their response characteristics make the array suitable for monitoring sediment transport to within a few centimeters of the bed under moderately large breaking waves 2 m results from an experiment on an exposed ocean beach on the coast of washington u s a indicate that sand suspension events of long duration 15 40 sec relative to the period of incident waves contribute a significant quantity of sand to the total littoral drift work is now in progress to modify the system for self contained operation on the continental shelf field investigations with the modified system will focus on the acquisition of a data set to test the validity of the suspended sediment distribution equation

magnitude and frequency of extra tropical north atlantic cyclones a chronology from cliff top storm deposits cliff top storm deposits ctsds are known to occur on cliffs at elevations of up to 50 m above sea level at exposed sites on the deep water coasts of the british isles eye witness accounts and time series field mapping of ctsds demonstrate their formation over the historical period and their continued modification during major storms with ctsds burying a range of modern human derived debris older deposits show surface lichen growth and weathering effects that relate to the relative age of ctsds over longer time spans buried sand and peat deposits provide dates on phases of ctsd emplacement and mobilisation and so provide an indication of the frequency and timing of the most severe storms two adjacent sites in shetland provide a combination of 14c dates on peat buried beneath storm deposited boulders 14c dates on marine shells buried inside ctsd boulder ridges and optically stimulated luminescence osl ages on sands intercalated with storm derived boulders although the precision is low this evidence identifies phases of exceptional storm activity spanning approximately 400 550 700 1050 1300 1900 and since 1950 ad by the very nature of cliff top erosion and deposition these records are fragmentary yet the timeline of major storms recorded in the shetland cliffs matches fairly well with the more general record of storminess in the north atlantic derived from the sea salt record in the gisp2 ice core as such ctsds represent an overlooked archive of storm sedimentation with the potential to elucidate local storm chronologies as well as informing debate surrounding the palaeo tempestology and impact of major cyclones and hurricanes

sedimentary patterns and geometries of the bahamian outer carbonate ramp miocene lower pliocene great bahama bank core logging and high resolution seismic data from odp leg 166 were used to analyse deposits of the neogene miocene lower pliocene bahamian outer carbonate ramp ramp sediments are cyclic alternations of light and dark grey wackestones packstones with interbedded calciturbidite packages and minor slumps cyclicity was driven by high frequency sea level changes light grey layers containing shallow water bioclasts were formed when the ramp exported material whereas the dark grey layers are dominantly pelagic calciturbidites are arranged into mounded lobes with feeder channels internal bedding of the lobes shows a north directed shingling as a result of the asymmetrical growth of these bodies calciturbidite packages occur below and above sequence boundaries indicating that turbidite shedding occurred during third order sea level highstands and lowstands highstand turbidites contain shallow water components such as green algal debris and epiphytic foraminifera whereas lowstand turbidites are dominated by abraded bioclastic detritus gravity flow depocentres shifted from an outer ramp position during the early miocene to a basin floor setting during the late miocene to early pliocene this change was triggered by an intensification of the strength of bottom currents during the tortonian which was also responsible for shaping the convex morphology of the outer ramp the miocene and lower pliocene of the leeward flank of great bahama bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps the contrast between its sedimentary patterns and the well known upper pliocene quaternary slope facies associations of the flat topped great bahama bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base of slope successions

post miocene diagenetic and eustatic history of enewetak atoll model and data comparison the post miocene diagenetic and eustatic history of enewetak atoll was investigated using a one dimensional forward model comparison of model and data suggests that the post miocene history of enewetak atoll was dominated by multiple episodes of meteoric phreatic diagenesis attendant with high frequency 10 sup 4 to 10 sup 5 yr fluctuations in sea level and a subsidence rate of 39 0 m m y sensitivity testing indicates that subaerial erosion results in the preservation of additional subaerial unconformities because stratigraphic shortening permits a succeeding sea level rise to flood the exposure surface and deposit sediment whereas without subaerial erosion this sea level rise would be recorded as a paleophreatic lens model results indicate that less then 10 of lapsed time is recorded by sediment deposition during periods of high frequency changes in sea level incompleteness of the stratigraphic record suggest that magnetostratigraphy may give erroneous ages for shallow marine carbonate sequences deposited during times of high frequency changes in sea level and frequent magnetic polarity reversals

yangtze offshore china highly laminated sediments from the transition zone between subaqueous delta and the continental shelf abstract this study examines the deposition of highly laminated muddy sediment in vibrocores recovered from a depth of 40 55 m of water and located 120 km east of the yangtze river mouth x radiographs show numerous sharp based sedimentary rhythmics with nearly parallel and undulated laminations interbedded with silty lenses and interbeds the laminated sediment varies from clayey silt to silty clay ams radiocarbon dates on well preserved bivalves are primarily younger than 5500 y bp indicating the formation of the laminated sediment under the present sea level conditions macro and microfossils in the sediments are consistent with the modern offshore sedimentary setting the laminated sediment originated from the yangtze estuary but the sedimentation processes were not deltaic the highly laminated sediment that lies below the normal wave base of 10 m was deposited on the seaward margin of the yangtze subaqueous delta closely associated with submarine tidal and storm generated currents

wave climate coastal sediment budget and shoreline changes for the danube delta abstract since its formation approximately 12 000 years ago the coastal zone of the danube delta experienced alternating periods of accretion and erosion related to the natural process of lobe abandonment caused by river avulsion over the last 150 years the effects of human interventions modified these natural trends regulation of the danube river e g the iron gates barrages facilitating navigation and controlling river discharge construction and extension of the sulina entrance jetties and dredging of the sulina mouth bar for navigational purposes are examples of human interventions that influenced and still influence the actual state of the danube delta coastal zone most importantly these interventions diminished the quantity of sediments reaching the coast and consequently led to a severe retreat of the shoreline especially in the sulina sf gheorghe coastal sector to investigate and quantify the recent sediment budget and associated shoreline changes along the danube delta coastal zone we constructed a hindcast of the wave climate the alongshore transport capacity and the resulting sediment budget using a numerical coastline model on a local scale it was found that overwash plays an important role i e the observed evolution of sahalin spit island shows a cross shore landward migration that is much larger than could be explained by the calculated alongshore sediment transport gradients on a delta scale however the resulting alongshore sediment transport gradients and associated sediment budgets comply very well with the observations confirming the dominant role of wave induced alongshore transport and giving confidence in our predictions regarding the shoreline position for the next 25 and 50 years the results of this study indicate the potential for broader applicability of the model to other deltas especially those in wave dominated settings

multi scale variability of beach profiles at duck a wavelet analysis beach profiles have been observed to change over a range of spatial and temporal scales however techniques for quantifying this variability have not been fully established in this paper a wavelet technique is introduced as a method to study the multi scale variability of beach profiles the beach profile data comprising a 22 year time series surveyed at the us army corps of civil engineers field research facility frf at duck are analysed using the adapted maximal overlap discrete wavelet transform amodwt the analysis successfully identifies strong local features in the variability of beach profiles in time and space separately that cannot be isolated by traditional statistical methods the analysis of spatial wavelet variances provides a new means of investigating the depth of closure analysis of variances by temporal scales shows that the combined effects of several temporal scales with one or two dominant scales can be seen at particular points across profiles whilst the dominant temporal scales are different at different portions of the profiles the method allows for the extremely nonstationary behaviour of beach profile to be analysed into separate frequency bands that can facilitate the interpretation of morphological changes in terms of physical processes

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

bathymetric expression of the fitzroy river palaeochannel northeast australia response of a major river to sea level change on a semi rimmed mixed siliciclastic carbonate shelf abstract palaeo river channels record the response of alluvial and estuarine depositional environments to sea level change and are also important geological indicators of former subaerial unconformities earlier studies have characterised lowstand palaeochannels on the central great barrier reef gbr shelf of northeastern australia reporting channel entrenchment shelf aggradation and topographic control of rivers by the outer shelf reef barrier we report the bathymetric expression of a palaeochannel corresponding to the last glacial lowstand path of the fitzroy river a high sediment yield river in the southern gbr during regression and lowstand the fitzroy river palaeochannel entrenched into the low gradient middle shelf and may have begun to incise the steeper outer shelf between the exposed reef platforms the wide spacing of outer shelf reefs and the continuous seabed slope may have enabled the palaeo fitzroy to maintain connection with the lowstand shoreline without becoming trapped behind shelf edge reefs the palaeochannel now forms a prominent depression across the middle and outer shelf evidently the sloping inter reefal seabed of the southern gbr coupled with tidal processes and wave exposure has limited shelf aggradation since the transgression this finding provides evidence that modern bathymetry can reflect palaeochannel location on the gbr shelf our results offer new insights into the evolution of the southern gbr shelf and show that no single existing model is able to adequately explain the behaviour of lowstand palaeochannels on rimmed siliciclastic carbonate shelves

firmgrounds key surfaces in the recognition of parasequences in the aptian lower greensand group isle of wight southern england aptian lower greensand group exposures in the cliffs of the isle of wight southern england display a consistent coarsening up cyclicity on the scale of centimetres to tens of metres that reflects the bed bed set parasequence parasequence set and sequence hierarchy these coarsening up cycles are most commonly recognized at the scale of parasequences 20 cm to 10 m thick genetically related groups of which form parasequence sets both parasequences and parasequence sets contain the succession of biofacies that culminate in firmground development numerous episodes of erosion deposition and colonization are recorded reflecting multiple erosion bypass events the increase in mean grain size through each cycle is reflected by changes in physical sedimentary structures ichnofauna or bioturbational fabric fossil fauna and diagenesis interbedded mudstones siltstones and sandstones in the lower beds of each cycle display a variety of structures ranging from low angle hummocky or tabular cross strata sandstone filled erosional gutters and planar lamination the cleaner sandstones found in the upper parts to each cycle are often completely bioturbated with only rare stratification and pebble plant debris filled scours preserved bioturbational fabrics change upward through each cycle from small subhorizontal mud or sandstone filled burrows to large branching clay filled or cemented burrow systems the top surface of each cycle is marked by a fossil epifauna indicative of firm to hard substrate conditions concentrations of bivalves brachiopods bryozoa crinoids and corals are preferentially cemented by iron oxide carbonate or phosphate such cements were early and thus utilized by firm or hard substrate dwellers this fossiliferous cemented sandstone is overlain by a flooding surface marked by the mudstone and silt rich sandstones at the base of the next cycle together the fauna and ichnofauna in each cycle represent the gradual development of firm substrate conditions culminating in the diverse firmground fauna preserved at the top of each cycle the fauna and changing substrate conditions reflect the hiatuses developed during successive episodes of marine flooding high species diversity is matched by complex patterns of taphonomic feedback in the mature firmground faunas that mark major flooding surfaces increasing faunal maturity allows recognition of a hierarchy of hiatuses this hierarchy is analogous to the parasequence parasequence set division the stratigraphic condensation of firmgrounds can be used to empirically define the condensed section the thickness of sediment between firmgrounds being a function of sediment supply and water depth accommodation space

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

longshore current profiles and lateral mixing across the surf zone of a barred nearshore greenwood b and sherman d j 1986 longshore current profiles and lateral mixing across the surf zone of a barred nearshore coastal eng 10 149 168 longshore currents were measured during a storm in a barred surf zone in the great lakes mean beach slope was 0 015 with three bars ranging up to 0 5 m in height comparisons with theoretical predictions revealed the effects of the bars on the horizontal structure of these currents and the degree of lateral mixing 1 perturbations in currents are localized spatially hut increase with bar relief 2 currents are lower and higher respectively in the outer and inner surf zone than expected for a plane beach the predictions of longuet higgins 1972 provide a reasonable approximation where relief is low 3 in the inner surf zone a plane beach solution suggests bars increase lateral mixing p 1 0 by increasing the velocity gradients 4 the barred slope model of ebersole and dalrymple 1981 most closely resembles the prototype 5 use of planar beach equivalents for p or n in models for barred beaches results in under prediction of the appropriate eddy viscosity

evidence for an albian hudson arm connection between the cretaceous western interior seaway of north america and the labrador sea numerous researchers have alluded to the existence of a cretaceous hudson arm connection between the labrador sea and the western interior seaway of north america however the evidence for this marine connection has been circumstantial in this paper we present sedimentary geochemical data that indicate a marine influence in the albian mattagami formation of the moose river basin james bay lowlands ontario the facies associations between dinoflagellate bearing laminated mudstones fluvial sandstones and early pyrite mineralization are interpreted to indicate deposition in the central basin of an estuary we use the facies association between the estuarine fill and coeval kaolinitic paleosols in the moose river basin and in similar deposits in quebec and labrador to reconstruct a southern shoreline of the albian hudson arm to the cretaceous western interior seaway we suggest that development of the hudson arm connection between the labrador sea and the cretaceous western interior seaway may be related to a regional extensional regime associated with rifting between labrador and greenland and the passage of eastern north america over cretaceous hotspots

holocene cemented beach deposits in belize abstract two types of cemented beach deposits occur on reef islands off the coast of belize these are 1 intertidal beachrock that is dominantly cemented by marine aragonite and high magnesium calcite cements and 2 supratidal cayrock that is cemented mainly by vadose low magnesium calcite cements besides differences in position relative to present sea level and resulting early diagenesic features beachrock and cayrock can be distinguished on the basis of differences in composition texture geographical position and age whereas the composition of beachrock is similar to that of the adjacent marginal reef sediments cayrock is enriched in benthic foraminifera intertidal beachrock is moderately to well sorted and well cemented while supratidal cayrock is very well sorted poorly cemented and friable beachrock occurs preferentially on windward beaches of sand shingle gays on the middle and southern barrier reefs and on the isolated platforms glovers and lighthouse reefs cayrock only occurs on larger mangrove sand gays of the isolated platforms turneffe islands lighthouse reef and the northern barrier reef 14c dating of ten whole rock and mollusk shell samples produced calibrated dates between ad 345 and ad 1435 for beachrock and between bc 1085 and ad 1190 for cayrock the large scale distribution of beachrock in belize supports the contention that physical processes such as water agitation rather than biological processes control beachrock formation and distribution only on windward sides of cays that are close to the reef crest where large amounts of seawater flush the beaches considerable amounts of cements can be precipitated to produce beachrock cayrock forms due to cementation in the vadose zone and is only preserved on larger stable mangrove sand cays

an estimate of albian sea level amplitudes and its implication for the duration of stratigraphic hiatuses abstract carbonate platform tops are reliable but incomplete recorders of past sea level fluctuations as they are riddled with hiatuses of various durations basinal sections represent a more complete record but fail to register regressive transgressive events with small to moderate amplitudes we seek to avoid these problems by combining information on past sea level fluctuations from coeval platform top slope and basinal sections the outcome of this study is a semiquantitative albian sea level curve from the southern tethyan margin in oman in subaerial exposure surfaces the northern oman margin recorded 4 high amplitude 50 m 6 intermediate amplitude 30 m and 26 low amplitude 10 m regressive transgressive cycles hiatuses that cap the platform top depositional sequences might account for between 30 to 70 of the cycle duration the resulting platform top depositional sequences have frequencies in the order of 230 20 kyr i e they are in the time range of orbital eccentricity cycles it appears that at least some of these albian regressive transgressive cycles were rapid and punctuated as opposed to sinus shaped milankovitchian sea level oscillations

sedimentology of rocky shorelines 3 hydrodynamics of megaclast emplacement and transport on a shore platform oahu hawaii abstract megaclasts of well cemented coralgal limestone have been emplaced onto a shore platform by large waves on the north shore of oahu hi emplacement and movements of the largest ca 96 ton megaclast have been dated using aerial photographs hydrodynamic forces at the low submerged shoreline cliff are computed using design wave characteristics based on linear wave theory and experimental results considering the local wave climate and near shore bottom topography force exerted by a tsunami has been estimated based on the 1946 aleutian tsunami the computed forces are evaluated in terms of the initial fracturing along a given failure plane that is required in order for the detachment to occur the analysis shows that tsunami as well as large swell waves are capable of quarrying the megaclast provided that sufficient initial fracturing is present dislodgement and emplacement most likely occurred in a sequence during impact of a single wave on the shoreline cliff swell waves however are seldom capable of emplacing large blocks onto the platform due to their rapid disintegration after breaking so that most blocks quarried from the cliff edge fall back onto the submarine terrace emplacement of large boulders seems to require extreme sea waves with periods longer than storms or north pacific swells usually produce transport mechanisms on the shore platform vary depending on megaclast shape sliding is a common mechanism of transport for larger and irregular megaclasts whereas somewhat smaller and platy megaclasts are occasionally found in overturned positions

an ocean facing aptian albian carbonte margin oman a high energy aptian albian platform margin in northern oman fronted onto an open oceanic basin making the area a valuable analogue for coeval guyot margins most similar aged carbonate margins described in the literature faced either intracratonic or minor oceanic basins the studied margin is characterized by a stabilized outer rim which although it did not rise discernibly above the adjacent lagoonal deposits flanked a steep upper slope 32 40 basinwards with a relief of at least 30 m two main facies provided the rigidity of the outer margin lithocodium boundstones that constituted up to 50 of the rock volume and marine fibrous cements that occluded up to 35 of primary pore space in contrast coral rudist patches and other shelly sessile benthos were distributed irregularly and the rudist bioherms of the outer margin were often disrupted with shells being transported and redeposited the inner margin is characterized by wedge shaped storm layers that radiate from the platform top lagoonwards where they interdigitate with carbonate sands and small rudist bioherms polygenetic discontinuity surfaces that bear evidence of both marine hardground and subaerial exposure stages are prominent features of the margin throughout the latest aptian to middle albian the platform succession recorded some 30 relative sea level falls of which seven reached amplitudes of many tens of metres these seven high amplitude falls in sea level are recorded across the entire south eastern portion of the arabian craton and are probably of eustatic origin