early cambrian wave formed shoreline deposits the hardeberga formation bornholm denmark during the early cambrian the danish island bornholm was situated on the northern edge of the continent baltica with palaeolatitudes of about 35 s an early cambrian terreneuvian transgression inundated large areas of baltica including bornholm creating shallow marine and coastline environments during this period wave formed shoreline sediments the vik member hardeberga formation were deposited on bornholm and are presently exposed at stroby quarry the sediments consist of fine and medium grained quartz cemented arenites in association with a few silt rich mudstones the presence of well preserved subaqueous dunes and wave ripples indicates deposition in a wave dominated upper shoreface littoral zone environment and the presence of interference ripples indicates that the littoral zone environment experienced water level fluctuations due to tides and or changing meteorological conditions discoidal structures medusoids are present in the quarry but due to the relative poor preservation of their fine scale structures it is difficult to determine if the discoids represent true medusae imprints or inorganic structures the preservation of the shallow water bedforms as well as the possible medusae imprints is related to either the formation of thin mud layers formed during a period of calm water when winds blew offshore for a longer period or to the growth of bacterial mats the orientation of the wave formed bedforms indicates a local palaeoshoreline trending ne sw and facing a large ocean to the north

biological remains geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the holocene lakes from north sahara abstract a detailed reconstruction of the holocene palaeoenvironments and palaeohydrology is presented for wwamp and lacustrine calcareous sediments which lie in closed depressions along the northern margin of the great western erg algeria it is based on a multidisciplinary approach using numerous techniques the chronological framework is established on the basis of 23 14 c dates on inorganic calcite and mollusc shells ranging from ca 9300 to 3000 yr b p and on an isolated 14 c age of ca 10 900 yr b p the significance of various environmental markers is discussed biological remains are abundant and diversified about 150 taxa including diatoms chrysophytes charophytes ostracods molluscs and foraminifera they provide information on the water chemistry total salinity ionic ratio ph and partial pressure of carbon dioxide and on the habitats water depth development of aquatic plants ephemerality etc emphasis is given to the total salinity individual organisms and palaeobiological assemblages are ordered as a function of their salt requirements and tolerances calibration based on modern diatom samples allows a tentative estimate of the palaeosalinities which range from fresh to marine like and even hypersaline waters attention is drawn to the possible colonization of marine organisms in continental basins without any connection with the sea stable isotope analyses have been carried out on both inorganic and biogenic mollusc and ostracod shells charophyte gyronites carbonates the 18 o contents demonstrate wide changes in the hydrological balance fluctuations in 13 c contents inform on water mixing residence time and on the importance of biological effects on total dissolved inorganic carbon geochemical analyses were performed on inorganic calcite and on ostracod shells high contents in fe and mn indicate reducing environments during stages of high salinity sr ca and mg ca are used as salinity indicators zn mg ratios suggest that the major water supply was the aquifer of the great western erg today down to about 50 m rather than surface waters from the atlas mountains salinities resulted from the balance between inputs from the water table evaporation rate leaching of pre existing salt crusts and seepage through the lake bottom a reconstruction of the evolution of the palaeosystems through time and space has been attempted with special attention to the instability of the water and ionic balances for different time scales short term fluctuations occurring during a single hydrological cycle annual or seasonal are deduced from the apparent discrepancies between the various indicators found in a given sample long term 10 2 10 3 years changes confirm the existence of a climatic phase being wetter than today from at least ca 9300 and may be from ca 10 900 yr b p to 3000 yr b p for the first time the salinity deduced from diatoms and the 18 o content of the water deduced from that of the carbonate at 25 c are used simultaneously to model the hydrological history of the basins and to estimate the relative humidity of the atmosphere during the holocene major environmental trends recorded from ca 9300 to 3000 yr b p do not show a clear synchronims between the different profiles studied therefore they cannot be interpreted in terms of palaeoclimate but instead demonstrate the importance of local hydrology in the evolution of closed basins associated with groundwater a common situation in arid and semi arid zones

two dimensional boundary fitted circulation model in spherical coordinates a two dimensional vertically averaged unsteady circulation model using a nonorthogonal boundary fitted technique was developed in spherical coordinates for predicting sea level and currents in estuarine and shelf waters both the dependent and independent variables are transformed into a curvilinear coordinate system the governing equations are solved by a semiimplicit method in which the elevations are solved implicitly and the vertically averaged velocities are solved explicitly the model employs a space staggered grid system and a three level time discretization truncation errors are second order both in space and time the model was tested against analytic solutions for a standing wave in a closed basin tidal circulation in a simple rectangular channel with an irregular grid system and various degrees of rotation and tidal flow in an annular section channel with quadratic bottom topography the model was also tested against steady state wind induced setup in a closed irregular basin with cons

a three dimensional model of the m2 s2 n2 k1 and o1 tides in the celtic and irish seas abstract a three dimensional model using various parameterizations of eddy viscosity covering the celtic and irish sea region is used to examine the spatial distributions of the m2 s2 n2 k1 and o1 tidal elevations and phases computed cotidal charts and comparisons with observations from shore based and offshore gauges show good agreement comparisons are also made with a standard two dimensional model in shallow water regions the three dimensional model shows significantly less damping than the two dimensional model with an associated improvement in accuracy a detailed examination of differences between computed and observed tidal currents at over thirty locations having three or more current meters in the vertical show that the model can accurately reproduce the tidal current and its vertical profile in the eastern irish sea the region furthest from the model s open boundary good agreement with observations is obtained although in the deeper channel to the south of this the model over predicts current magnitude

little ice age aridity in the north american great plains a high resolution reconstruction of salinity fluctuations from devils lake north dakota usa the little ice age was an interval between about ad 1500 and 1850 characterized by advancing glaciers in mountainous regions of europe and western north america however it is unclear whether this cool moist period was truly global in extent or how it was manifested in other regions with different climatic controls a high resolution reconstruction of salinity fluctuations in devils lake north dakota based on fossil diatoms ostracode shell geochemistry and bulk carbonate geochemistry indicates that saline conditions prevailed throughout much of the recent past these results suggest an arid climate in the northern great plains throughout the little ice age and that during this interval climatic gradients between the great plains and regions to both the east and west may have been quite steep

ichnology and paleoecology of offshore siliciclastic deposits in the cardium formation turonian alberta canada the raven river member of the cardium formation upper cretaceous turonian was deposited in a storm dominated offshore setting in the western interior seaway of north america the ichnology of this unit can provide a useful model for further investigation of shelfal deposits a two fold approach to the ichnology has been utilized in this study first lithofacies are delineated which encompass the degree of bioturbation as part of the rock s sedimentary texture in addition ichnofossil assemblages are established which represent recurring groups of ichnogenera lithofacies comprise several coarsening upward sequences of sandstone and mudstone in which bioturbation tends to decrease upwards mudstone units represent deposition below fairweather wave base in a quiet water setting while sandstone beds are the result of storm generated deposition the sequence shows a punctuated aggradation of shelfal sediments in a storm dominated environment ichnofossil assemblages show a differentiation into pre and post storm ichnogenera with textural changes playing a minor role in assembly composition ichnogenera present include asterosoma bergaueria conichnus cylindrichnus chondrites helminthopsis ophiomorpha palaeophycus planolites rhizocorallium rosselia skolithos teichichnus thalassinoides terebellina and zoophycos

palaeolimnological approaches to climate change with special regard to the biological record abstract lakes systems respond physically chemically and biologically to changes in climate and these responses are registered in many various ways in lake sediment records this paper focuses principally on the biological record and describes recent research that aims to reconstruct i past variability in effective moisture and ii past variability in temperature changes in effective moisture are manifested especially by changes in lake water level in closed lake basins water level change can cause significant changes in water salinity that is registered in sediments by changes in the composition of fossil assemblages especially diatoms in open freshwater lake basins changes in water level are best reconstructed from the aquatic macrofossil record and potentially from the ratio of open water to littoral species of cladocera ostracods and diatoms the most promising biological method for reconstructing past temperature is chironomid analysis and a range of new chironomid temperature transfer functions are being developed however biological responses to changing temperature are usually indirect as a result of temperature effects on water column stratification nutrient cycling and alkalinity generation and in most cases a correct interpretation of the climatic significance of changes in the fossil record requires an understanding of the processes that are operating in the water column a multi proxy whole lake approach is advocated as the best way forward not only as a means of reconstructing past climate but also as a means of assessing the impact of climate change on lake systems

tidal flushing and eddy shedding in mount hope bay and narragansett bay an application of fvcom 1 the tidal motion in mt hope bay mhb and narragansett bay nb is simulated using the unstructured grid finite volume coastal ocean model fvcom with an accurate geometric representation of irregular coastlines and islands and sufficiently high horizontal resolution in narrow channels fvcom provides an accurate simulation of the tidal wave in the bays and also resolves the strong tidal flushing processes in the narrow channels of mhb nb eddy shedding is predicted on the lee side of these channels due to current separation during both flood and ebb tides there is a significant interaction in the tidal flushing process between mhb nb channel and mhb sakonnet river sr channel as a result the phase of water transport in the mhb sr channel leads the mhb nb channel by 90 the residual flow field in the mhb and nb features multiple eddies formed around headlands convex and concave coastline regions islands channel exits and river mouths the formation of these eddies is mainly due to the current separation either at the tip of the coastlines or asymmetric tidal flushing in narrow channels or passages process oriented modeling experiments show that horizontal resolution plays a critical role in resolving the asymmetric tidal flushing process through narrow passages with a horizontal resolution of 50 m fvcom reproduces the eddy field that is in good agreement in the intensity and spatial scale with the current measurement data

early cambrian teichichnus dominated ichnofabrics and palaeoenvironmental analysis of the caerfai group southwest wales uk abstract the early cambrian caerfai group of pembrokeshire in southwest wales yields an intensely bioturbated teichichnus dominated ichnofabric and provides evidence for the early evolution of infaunal organisms three units of the caerfai group comprise the focus of this study in sections exposed at caerfai bay in the st non s sandstone few primary sedimentary structures are observed bedding being predominantly massive with subordinate parallel and current ripple cross lamination the topmost st non s sandstone contains common soft sediment deformation phenomena and collectively deposition is believed to have taken place in the proximal subaqueous reaches of a steep fronted delta system teichichnus is the dominant trace with subordinate planolites palaeophycus and possible rhizocorallium the overlying caerfai bay shales were deposited from mass flows with evidence of downslope creep suggesting deposition on a steep delta front sandstone debrites are common as are tuffaceous beds with evidence of reworking by bottom currents sandstone and tuff event beds contain common skolithos and arenicolites with less frequent planolites interbedded mudstones contain infrequent teichichnus the caerfai bay shales coarsen and thicken upwards into the caerbwdy sandstone debrite sandstone beds dominate and bed thickening upsection indicates progradation of the delta system the dominant trace fossil within the unit is teichichnus which is constrained to the top few centimetres of individual sandstone beds less common are planolites and palaeophycus the size and abundance of teichichnus in the caerfai group are similar to or exceed those in contemporaneous sections in avalonia and baltica local environmental factors were probably the primary control on trace fossil distribution substrate and salinity are proposed as the main influences on ichnodiversity and size in the caerfai group teichichnus is most abundant in the st non s sandstone where the proximal reaches of the delta experienced reduced salinity and possibly higher oxygen levels burrow diameter progressively decreases upsection and bioturbation becomes less pervasive in subsequent units of the caerfai group this indicates that by the cambrian stage 2 significant advances into reduced salinity environments had occurred along with the dispersal of the teichichnus producer throughout the avalonia baltica seaway correlation within avalonia indicates that a transgression in the cambrian stage 2 initiated the deposition of the caerfai group marking the onset of the welsh basin

the ichnogenus rhizocorallium classification trace makers palaeoenvironments and evolution rhizocorallium is one of the oldest known trace fossils with wide distribution through the phanerozoic and all over the world originally introduced from the epicontinental triassic of central germany its high morphological lability gave reason for the subsequent erection of about twenty ichnospecies the study of newly collected material from the type area and many specimens from various collections permits the conclusion that rhizocorallium jenense and rhizocorallium commune are the only valid ichnospecies of rhizocorallium the type ichnospecies r jenense is a comparatively small inclined and heavily scratched firmground burrow with passive fill while r commune consists of extensive more or less horizontal burrows with occasionally scratched marginal tubes and an actively filled spreite between the tubes the faecal pellets coprulus oblongus are typically associated with r commune morphological variations of r commune are captured in ichnosubspecies and varieties of this ichnospecies and can aid a refined reconstruction of palaeoenvironments a review of more than 180 records from the literature reveals the common confusion of both ichnospecies which has consequences for the application of rhizocorallium in facies interpretations the end members of both ichnospecies may be linked by transitional forms which suggests the same kind of trace maker polychaetes are the most likely producers of marine rhizocorallium based on their long ranging occurrence morphological features appearance of faecal pellets associated soft body remains and modern analogues r commune occurs from early cambrian to holocene while r jenense just appears after the end permian mass extinction probably as a consequence of an adapted firmground burrowing lifestyle of its producer fluvial r jenense are probably produced by mayfly larvae in homology to marine polychaete burrows a consequent application of the newly established classification scheme allows for a more rigorous application of rhizocorallium in the reconstruction of palaeoenvironments thus palaeozoic and mesozoic r commune are restricted to the cruziana ichnofacies of shallow marine environments while in cenozoic time similar forms are also found in deep marine deposits r jenense on the other hand is a constituent of the widespread glossifungites ichnofacies and aside from continental environments occurs in peritidal to deep marine deposits several studies have demonstrated the value of rhizocorallium for interpreting sequence stratigraphical surfaces current directions and fluctuations in salinity and oxygen

application of three dimensional boundary fitted circulation model to providence river a three dimensional boundary fitted circulation model by muin and spaulding in 1996b was applied to simulate tidal and wind driven flow in upper narragansett bay and the providence and seekonk rivers the model employs a split mode solution technique the exterior mode vertically averaged was solved using a semiimplicit method the interior mode vertical structure was solved explicitly except for the vertical diffusion term that is implicit the vertical eddy viscosity was calculated from a one equation turbulence model model predicted tidal currents for the principal constituents were in good agreement with field observations the im d2 dominated the tidal currents accounting for 80 of the total tidal energy a combination of bottom friction coefficient of 0 0025 and constant 0 3 in the mixing length formulation of the turbulence model provided the best fit to the available observations the model predicted a cooscillating wave pattern with the im d2 water elevation about three hours out of phase with the current an approximate one hour phase difference between the currents in the deep dredged channel and the shallow water on either side was predicted wind driven flow was simulated under constant wind forcing of 0 01 n m ua 0 1 dyne cm along and across the river axis the steady state flow patterns are consistent with observations showing flows against the wind direction in the dredged channel the model predicted steady state currents in the dredged channel have maximum values of 3 4 cm s for winds along the channel axis and 1 cm s for winds across the channel axis

abundant and diverse early paleozoic infauna indicated by the stratigraphic record marine benthic animals have lived within the sediment since the late precambrian an abundant early paleozoic infauna is indicated by bioturbated zones and diversity of deposit feeder and suspension feeder trace fossil genera burrow depths extended tens of centimetres below the sediment water interface trace fossil evidence of an abundant early paleozoic infauna conflicts with evidence from the shelled fauna which lacks infauna this requires reinterpretation of early paleozoic community structure and raises new questions about interactions between early paleozoic soft bodied and skeletonized animals

a late quaternary palaeolimnological record from jamaica based on trace element chemistry of ostracod shells abstract the trace element chemistry of ostracod shells provides one of the most promising methods for palaeolinmological reconstruction in this paper molar sr ca and mg ca ratios in shells of the ostracod cypretta brevisaepta furtos 1934 were used to reconstruct the late quaternary palaeolimnology of wallywash great pond a small freshwater coastal lake in jamaica analyses of modern jamaican ostracods were undertaken to establish molar distribution coefficients kd d m s for this species k d sr 0 306 0 069 k d mg 0 0142 0 0088 these values were used to reconstruct past levels of sr ca water and mg ca water for a 9 23 m lake sediment core from wallywash great pond the results were coupled with previously published stable isotope 18 o and 13 c determinations on fine grained calcite to reconstruct the salinity palaeohydrology and palaeoproductivity of the lake over the last 125 ka b p 10 3 calendar years before present three major highstands with slightly elevated salinity occurred during marine isotope stage 5 under elevated sea level and a humid climate the lake dried out 93 5 ka b p as sea level felll and the climate became drier it refilled around 10 7 ka b p three separate highstands during the holocene were sustained by humid conditions and high relative sea level although there were small increases in salinity during the holocene when sea level was close to the deepest part of the lake significant saltwater intrusion appears to have been prevented by freshwater discharge from inland throughout the late quaternary the salinity of the great pond showed low absolute variations from 0 3 to 0 6 o the long term trends in lake level reflect both orbitally induced changes in insolation and eustatic sea level water level fluctuations during the holocene however reflect climatic changes on the millennial timescale rather than orbital forcing or sea level change

tiering in suspension feeding communities on soft substrata throughout the phanerozoic tiering of benthic marine suspension feeding communities on soft substrata has varied throughout the phanerozoic epifaunal tiering was most developed during the middle and late paleozoic and the triassic to jurassic with large scale reductions in tiering occurring during the permian triassic extinctions and after the jurassic infaunal tiering reached its highest level of organization after the paleozoic

on extracting tidal current profiles from vertically integrated two dimensional hydrodynamic models a numerically accurate and computationally efficient method is developed for extracting tidal current profiles from vertically integrated two dimensional models the method can incorporate an arbitrary profile of eddy viscosity and determines tidal current profiles satisfying a no slip condition at the sea bed comparisons with observations and current profiles computed with full three dimensional models confirm the accuracy of the method bottom boundary layer thicknesses determined from these current profiles clearly show regions of the european continental shelf where the bottom boundary layer extends to the sea surface the boundary between these regions and other areas where the bottom layer is less than the water depth corresponds quite closely to the known position of tidal fronts

palaeoenvironmental and ecological interpretation of the trace fossil rhizocorallium based on contained iron framoboids upper devonian south china the trace fossil rhizocorallium commune is abundant in shallow marine deposits of the upper devonian frasnian tuqiaozi formation in ganxi sichuan province south china it consists of u shaped spreite burrows developed more or less parallel or slightly inclined to the bedding of marly limestone four types of iron framboids mostly oxygenated from pyrite framboids were found within the rhizocorallium burrow including 1 smooth sheathed spherical 2 prismatic 3 octahedral and 4 pyritohedral submicron crystals chemically the submicron crystals mainly consist of iron sulphur oxygen and carbon the iron framboids represent the stage of evolution of their original pyrite framboids from irregular morphologies and spherical framboids to octahedral and pyritohedral habits due to the activity of sulphate reducing bacteria no similar framboids were observed outside rhizocorallium therefore it is likely that sulphate reducing bacteria colonised the rhizocorallium spreite and marginal tube within a dysoxic environment with increasing degree of oxygenation of pore water the pyrite framboids were partly oxygenated into iron framboids and by exceptional circumstances preserved the original morphology of the crystals furthermore it is proposed that the investigated rhizocorallium was constructed by its trace maker for gardening with multifunctional purpose where different microbial colonies were planted and cultured in the marginal tube and spreite on the mutual basis of food supply and redox conditions these features indicate that a combined deposit feeding and gardening model may apply for the construction of rhizocorallium commune from the devonian of ganxi the responsible trace maker probably was a worm like organism such as a polychaete

diagnostic and prognostic numerical circulation studies of the south atlantic bight some of the results from a series of diagnostic and prognostic numerical simulations of the circulation in the south atlantic bight sab are described the numerical model developed for the study is a three dimensional primitive equation time dependent coordinate model with an imbedded turbulent closure submodel which should yield realistic ekman surface and bottom layers an implicit numerical scheme in the vertical direction and a mode splitting technique in time are adopted for computational efficiency a significant portion of the paper is concerned with realistic specification of initial conditions for temperature and salinity surface forcing and lateral open boundary conditions the latter are determined by a simple diagnostic geostrophic and ekman dynamics model which provides dynamically consistent temperature salinity and velocity boundary conditions it appears from an exaination of the numerical simulations that the full model yields results that share many features in common with our general understanding of the circulation of the south atlantic bight the region includes shallow shelf waters as well as deeper water dominated by the gulf stream data for synoptic skill assessment however are not available

holocene palaeolimnology of kajemamm oasis northern nigeria an isotopic study of ostracodes bulk carbonate and organic carbon a high resolution 5500 year palaeolimnological record from kajemarum oasis a closed basin in the manga grasslands of northern nigeria provides evidence of environmental change in subsaharan africa during the holocene palaeohydrological variations mainly changes in the balance between precipitation and evaporation are recorded by stable oxygen isotope ratios in bulk carbonate and ostracod calcite and by the sr ca ratio in ostracode shells variations in the carbon isotope ratios in carbonates indicate changes in primary productivity in the lake whereas the carbon isotope composition of organic carbon reflects ecophysiological processes within the lake and its surrounding catchment results indicate that there have been marked environmental changes in the manga grasslands over the last 5500 years a more variable climate set in around 1500 cal a bp a prolonged drought between 1200 and 1000 cal a bp with reduced aquatic productivity was followed by a switch to a wetter but still unstable climate moist conditions prevailed during the little ice age the results indicate that drought has affected the sahel episodically over the last 1500 years and is not solely a twentieth century phenomenon

biological and sedimentary facies of australian salt lakes abstract four main types of salt lakes are recognized in australian 1 large playa lakes 2 small closed lakes or pans 3 crater lakes and 4 coastal lakes not connected to the sea basically all have an nacl chemistry biological and sedimentary facies characteristic of these salt lakes can be arranged into three basic groups which relate to particular phases in lake regimes these phases are 1 wet phases of ephemeral shallow lakes 2 dry lakes and 3 deep water lakes all elements of the salt lake biota with fossilizable remains are discussed with a detailed account of the palaeo ecological information they offer elements of the nonaquatic biota associated with salt lake sediments are also analysed sedimentary features of australian salt lakes pertinent to palaeoecology are discussed in the context of their association with the biota using numerous illustrations the distribution of the biota on lake floors for example its concentration in particular areas of the lake or its destruction during particular episodes such as lake filling and drying is mentioned in the context of recognizing different facies three major lake regime phases are presented with emphasis on the biological and sedimentary facies which characterize them the paper concludes with a brief discussion of the relevance of recognizing particular salt lake facies and changes in lake histories for the study of palaeoclimates and for mineral and oil exploration

a model of passive settlement by planktonic larvae onto bottoms of differing roughness a simple one dimensional advection diffusion model was developed lhat predicts rates of settlement by larvae transported passively within turbulent boundary layers onto bottoms of differing roughness the model describes depth limited boundary layers and considers variation in boundary shear velocity larval fall velocity and the height and areal density of bottom roughness features larvae were allowed to settle onto the bottom but not onto roughness features the model predicts that rates of settlement should increase monotonically with areal density of roughness features relatively flat bottoms should experience rates of settlement 2 4 times higher than bottoms with low densities of roughness features but l 2 orders of magnitude lower than bottoms with relatively high densities of roughness whereas roughness density defines the direction of differences in settlement expected the degree of difference is also affected by the height of roughness features and the ratio of larval fall velocity to shear velocity the dispersal of marine benthic organisms of many species occurs through the water column via larval transport or by the swimming or drift of adults factors affecting settlement on the bottom by potential colonists thus have been the focus of considerable study laboratory and field studies show that larvae and adults exhibit complex behaviors and are capable of distinguishing among potential settlement sites based on diverse cues meadows and campbell 1972 gray 1974 crisp 1984 woodin 1986 hydrodynamic processes also exert important influences on dispersal and settlement patterns of oceanic circulation affect broad scale zoogeographic distributions ekman 1967 scheltema 1974 produce tidal to interannual fluctuations in larval recruitment shanks 1986 roughgarden et al 1988 and can accumulate lar

the ichnogenus teichichnus seilacher 1955 the ichnotaxonomy of the phanerozoic trace fossil teichichnus seilacher 1955 is revised and its ethology producers and environmental affiliation are re evaluated newly studied material reveals that teichichnus is a sub vertical spreite burrow with an arcuate shape containing stacked laminae and a passively filled terminal causative burrow funnel like extension of the terminal causative burrow and wall ornamentation may occur high variation of burrow morphology is common and has resulted in the erection of 18 ichnospecies of which only four are herein regarded as valid teichichnus rectus t zigzag t patens and t duplex these ichnospecies are characterised by their overall burrow shape spreite morphology and more subordinate occurrence of branching and sculpture as recommended ichnotaxobases combined modes of feeding become evident including deposit and suspension feeding suggesting that teichichnus is a dwelling trace rather than a feeding trace aside from the classical interpretation of polychaetes as producers many features accord with an interpretation of dwelling echiurans and holothurians this interpretation may apply for many post palaeozoic t rectus and t zigzag whereas t duplex and partly t patens are likely produced by arthropods i e trilobites and crustaceans bivalves are also considered for producing teichichnus like traces teichichnus is a marine trace fossil with predominance in shallow marine environments low diversity and high density occurrences of teichichnus characterise marginal marine paralic environments with reduced salinity i e brackish water and oxygen i e dysoxia whereas in shoreface and offshore settings teichichnus occurs in association with many other ichnotaxa and in low density deep marine occurrences of teichichnus are comparably sparse and isolated records may indicate dysoxic bottom conditions

middle and late holocene dune reactivation in the nebraska sand hills usa a combination of optical dating of aeolian sand and radiocarbon dating of palaeosols and interdune sediments has allowed some refinements to the chronostratigraphy of the nebraska sand hills our results directly confirm previous inferences that multiple phases of aeolian deposition including megabarchan dune reactivation occurred within the sand hills during the middle and late holocene optical dates on stratified aeolian barchan dune sediments from two localities provide ages ranging from c 6 ka to 300 years ago weakly developed palaeosols intercalated within the dune sediments and other forms of post depositional modification indicate periods of relative stability and reduced dune mobilization optical dates on the upper 12 15 m of two dune exposures indicate repeated possibly regionally correlative reactivations which occurred between c 400 500 and 200 300 years ago comparison of late holocene aeolian activity with local and regional palaeoclimatic proxy records suggests that dune reacti

spatial variations of holocene climatic change in the yellowstone region abstract the paleoecologic record of the northern rocky mountains shows considerable spatial variability which has been difficult to explain as a unified response to large scale changes in effective moisture or temperature through time comparison of past and present climatic patterns suggests that the spatial heterogeneity in the fossil record arises from a local response to the effects of greater summer solar radiation during the early holocene solar radiation directly determines evapotranspiration and indirectly controls the strength of the summer monsoon and the eastern pacific subtropical high pressure system the yellowstone region provides an example of an area where the indirect effects of solar radiation are manifest by the juxtaposition of two contrasting climatic regimes today and where these regimes were amplified during the early holocene fossil pollen data suggest that central and southern yellowstone the summer dry area became drier in the early holocene while northern yellowstone the summer wet area became wetter the boundary between regimes however is controlled by topography and has not changed significantly in the holocene the spatial variations of holocene vegetation and climatic changes in the northern rocky mountains may therefore be explained as a trade off between strengthened monsoonal circulation and a stronger subtropical high in the early holocene and the relative importance of these precipitation regimes on a topographically complex landscape

holocene eolian activity in the minot dune field north dakota stabilized eolian sand is common over much of the great plains region of the united states and canada including a subhumid area of 1500 km2 near minot north dakota eolian landforms consist of sand sheets and northwest trending parabolic dunes dunes and sand sheets in the minot field are presently stabilized by a cover of prairie grasses or oak woodland stratigraphic studies and accelerator mass spectrometry radiocarbon dating of paleosols indicate at least two periods of eolian sand movement in the late holocene pedologic data suggest that all of the dune field has experienced late holocene dune activity though not all parts of the dune field may have been active simultaneously similar immobile element ti zr la ce concentrations support the interpretation that eolian sands are derived from local glaciofluvial and glaciolacustrine sediments however glaciolacustrine and glaciofluvial source sediments have high ca concentrations from carbonate minerals whereas dune sands are depleted in ca

paleosalinity from trace metals in fossil ostracodes compared with observational records at devils lake north dakota usa abstract the chemistry of closed basin lakes responds directly to the hydrologic budget through evaporative concentration of dissolved salts and the sediments of these basins contain several excellent fossil and geochemical proxies for past changes in water chemistry and salinity the trace metal content of ostracode shells among the most promising of these paleosalinity methods is further explored in this study of mg and sr partitioning in candona rawsoni a widespread ostracode of the north american great plains the molar distribution coefficients kd mg and kd sr for this species k d mg ca caco 3 0 004 mg 2 ca 2 h 2 o 9 68 10 5 t c k d sr sr ca caco 3 sr 2 ca 2 h 2 oz 0 406 are determined from laboratory experiments in which c rawsoni are cultured under controlled temperatures and salinities our formulation of kd mg contains a correction term for excess mg that is incorporated into the shell during early calcification the accuracy of the distribution coefficients is tested against field collections of live ostracodes from a suite of 12 dakota lakes the kd inferred values for mg2 ca2 h2o and sr2 ca2 h2o are in close accord with the same ratios measured in the lakes a comparison of ostracode reconstructed and historically measured salinities for devils lake north dakota shows good agreement within the salinity range preferred by c rawsoni 1 10 0 although salinity excursions beyond this optimum are poorly represented in the sedimentary record in most lakes salinity is more readily inferred from mg ca h2o than sr ca h2o because sr solubility is a complex function of several carbonate phases as shown for devils lake sr ca h2o may not vary systematically with the salinity of some brines

substrate control of lower cambrian trace fossils from bornholm denmark abstract a ten meter thick sequence within the lower cambrian succession from snogebaek harbour to broens odde bornholm contains abundant trace fossils throughout the systematics of some of the ichnogenera are briefly discussed in particular buthotrephis and a new form of diplocraterion the trace fossils can be subdivided into four associations the skolithos diplocraterion rhizocorallium and teichichnus buthotrephis associations the recurrence of these associations can be correlated with changes in substrate in particular the diplocraterion association in the middle and upper part of the broens odde member exposed here occurs only in storm deposits

review of recent developments in tidal hydrodynamic modeling i spectral models in this paper we present a brief overview with a comprehensive set of references to recently published papers for detail of a range of techniques used in tidal hydrodynamic modeling and recent progress in the field although the paper aims to introduce the topic to someone new to the area the main emphasis is on new developments in near coastal shallow sea tidal modeling and consequently we concentrate on three dimensional modeling which has progressed significantly in recent years the paper gives a brief account of methods used to discretize the hydrodynamic equations in the horizontal namely finite difference finite element and boundary fitted coordinates and through time the representation of tidal current structure in a three dimensional model using a spectral method in the vertical is also described in this method the subgrid scale vertical diffusion of momentum which has a major influence on tidal current profiles is parameterized using a flow dependent eddy viscosity recent work on

patterns of holocene environmental change in the midwestern united states abstract four pollen sequences along a transect from north central iowa to southeast wisconsin reveal the distribution of prairie and forest during the holocene and test the use of pollen isopolls in locating the holocene prairie forest border prairie was dominant in central iowa and climate was drier than present from about 8000 to 3000 yr b p during the driest part of this period in central iowa 6500 5500 yr b p mesic forest prevailed in eastern iowa and wisconsin suggesting conditions wetter than at present prairie replaced the mesic forest about 5400 yr b p in eastern iowa but did not extend much farther east mesic forests were replaced in southern wisconsin and northern illinois about 5400 yr b p by xeric oak forests this change from mesic to xeric conditions at 5400 yr b p was widespread and suggests that the intrusion of drier pacific air was blocked by maritime tropical air from the gulf of mexico until the late holocene in this area

numerical simulations of the tidal and wind driven circulation in narragansett bay abstract a three dimensional numerical hydrodynamic model was used to study the tides and certain aspects of the wind forced flow in narragansett bay the governing equations are solved using the galerkin spectral method in the vertical and explicit finite differences in the horizontal and time a split mode formulation is used to minimize computational time simulations of the m 2 tide gave average errors of less than 2 in amplitude and 2 in phase when compared with observations at 12 tidal height stations within the bay an investigation of the bay s response to steady spatially uniform wind forcing indicated that the non linear interaction between the tidal and wind induced motions strongly affected the predicted steady state current pattern calculation of the steady state wind induced transports showed that a significant exchange exists between the west passage east passage and sakonnet river the dependence of the exchange on the wind magnitude and direction and on the choice of vertical eddy viscosity was investigated a comparison between modeled results and measurements of current at three locations in the bay indicated that the model is capable of reproducing some of the features of the wind induced flow

on improving the bed stress formulation in storm surge models a method of improving the representation of bottom stress in storm surge models an enhanced bed stress model is tested using a fine mesh model of the celtic and irish seas and is compared with results from a conventional two dimensional model the approach uses a convolution method to determine the bed stress rather than relating it directly to the depth mean current as in a conventional storm surge model for the region considered comparisons of surge elevations computed with both models and observations show only a slight improvement of surge elevation in the near coastal region with the enhanced bed stress model however spatial distributions of bed stresses from the two models do exhibit significant differences which are important in considering sediment movement paths during major storms the magnitude and direction of the bed stress vectors computed from the enhanced bed stress model are in excellent agreement with calculations using a full three dimensional model of the area this suggests that the enhanced bed stress model can compute a bed stress that is not significantly different from that in a full three dimensional model at a fraction of the computational cost

the response of the irish sea to boundary and wind forcing results from a three dimensional hydrodynamic model a three dimensional nonlinear hydrodynamic model of the irish sea is used to examine the response of the region to forcing along its open boundary and wind stress over the area frictional dissipation at the bed is parameterized with a quadratic law of bottom friction which can take account of enhanced frictional effects due to wind wave current interaction a standard finite difference grid is used in the horizontal with an expansion of functions through the vertical giving a continuous current profile from sea surface to seabed the model has a grid resolution of the order of 3 km and hence can resolve some features of the nearshore region the model is forced with m2 tidal input along its open boundary and time invariant wind fields corresponding initially to spatially uniform northerly and westerly wind stresses of 1 n m2 and subsequently to a west east gradient wind changing from 1 n m2 to 1 n m2 going from west to east and a north south gradient wind changing from 1 n m2 to 1 n m2 going from north to south the response to open boundary forcing through both elevations and currents is also examined and the influence of the effects of enhanced bottom friction due to wind waves is also briefly considered