coprolites from a brackish ecosystem in the pennsylvanian joggins formation nova scotia canada and their palaeoecological implications abstract the joggins fossil cliffs unesco world heritage site contains a wealth of terrestrial and aquatic fossils from the late carboniferous pennsylvanian period fossils from the aquatic realm have historically been under studied at joggins and the brackish ecosystem they represent is poorly understood globally we used coprolites which are abundant in the limestones of the joggins formation to broaden our knowledge of the aquatic ecosystem and help reconstruct the food web coprolites were studied in hand sample and with standard transmitted light microscopy to determine morphology and contents cathodoluminescence was used to examine coprolite microfabrics to interpret the degree of post depositional alteration specimens range in size from 1 to 10 cm in length and were divided into six broad groups based on size and shape in order of most to least abundant small equant cylindrical heteropolar macrospiral large irregular and amphipolar spiral where possible specimens were identified to ichnospecies the host rock limestone and large quantities indicate that at least most perhaps all coprolites originated from fish with some potentially originating from amphibious tetrapods bone fragments and or coated grains were found in the majority of samples however their relative abundance differs between morphotypes small equant coprolites contained the most coated grains and fewest bones and heteropolar macrospiral coprolites contained the most bones and almost no coated grains specific species identification of bones was not possible the mineralogy of the coprolites is phosphatic specifically carbonate fluorapatite suggesting that the fish producing these coprolites were carnivorous and that there was a lack of coprolites generated by herbivores based on our findings of coprolite morphology and contents and what is currently known about the biotic environment we introduce a hypothetical trophic pyramid with rhizodonts at the apex producing the largest coprolites and smaller fish species responsible for the small equant shaped coprolites at the secondary consumer level this research provides a foundation for further studies on coprolites and other bromalites for a deeper understanding of brackish ecosystems where fish diversified further into fresh water during the palaeozoic

fire ecology of the carboniferous tropical zone abstract fossil charcoal fusain indicating the occurrence of wildfire is common in the carboniferous rocks of north america and europe during the carboniferous these regions lay on the southern margins of the laurasian continent and within the tropical zone this study examines the facies distribution and botanical identity of charcoal in order to investigate the influence of fire on carboniferous tropical ecology new data from charcoal bearing units in eastern canada poland and the british isles are presented and synthesised with previously published data of charcoal occurrence tournaisian visean charcoal bearing strata were deposited in volcanic lacustrine alluvial plain and coastal marine environments in these deposits charred floras are dominated by pro gymnospermous plants whilst uncharred compressed or permineralised floras are dominated by lycopsids uncharred lycopsid remains were probably derived from wetland communities growing close to the depocentres whilst charred gymnospermous remains may have been sourced from well drained extrabasinal settings based on the vertical distribution of charcoal layers in annually laminated lacustrine deposits it is estimated that fires occurred with high frequency approximately every 3 35 years palaeoclimatic analysis indicates that southern laurasia at this time was subject to a seasonal monsoonal tropical climate such environments today are characterised by tropical savannas with high fire frequencies and early carboniferous fire prone gymnospermous plant communities may have represented a comparable vegetation biome namurian stephanian charcoal bearing strata were deposited in alluvial plain coastal plain and coastal marine environments channelised sandstone units interpreted as river channel deposits contain charcoal derived from cordaitaleans and conifers this assemblage records fires in extrabasinal coniferopsid forests mudstone units containing coals are interpreted as the deposits of floodbasins and peat mires hollow uncharred lepidodendrid stumps occur in this facies and contain lepidodendrid charcoal in the stump bases and lepidodendrid pteridosperm coniferopsid and sphenopsid charcoal outside the stumps this assemblage records fires in wetland lepidodendrid dominated forests lepidodendrid trunks comprising of a spongy parenchymatous core surrounded by dense periderm became hollowed out during fire events an estimate of fire frequency based on the vertical spacing of charcoal layers in coals implies that fires occurred every 105 1085 years in the peat mires palaeoclimatic analysis indicates that southern laurasia was subject to a humid tropical climate during the late carboniferous such environments today are characterised by tropical rainforests where fires occur rarely and late carboniferous communities may have represented a comparable biome

attempted predation on early paleozoic cornulitids abstract cornulitids appeared in the middle ordovician and the earliest repairs to their shells are reported from the upper ordovician katian of baltica and north america hirnantian shell repair is common in the silurian sheinwoodian unattached cornulitid cornulites cellulosus from the baltica and is interpreted here as a result of failed predation scalloped divoted and embayed type of shell repairs occur in three species of cornulites the species with the most repairs c cellulosus yielded a shell repair frequency of 20 7 with 29 specimens there are probable antipredatory adaptations such as spines and extremely thick vesicular walls in the morphology of silurian cornulitids the morphological and ecological evolution of cornulitids could thus have been partially driven by predation

residual circulation in shallow estuaries 1 highly stratified narrow estuaries long wave theory and simple turbulence closures have been used to show that three distinct types of circulation highly stratified weakly stratified and partially mixed arise in narrow shallow estuaries from the finite amplitude of the tide and the interaction of stratification with vertical mixing each type has a different dominant process causing the vertical exchange of salt and fresh water on the flood and each gives rise to a characteristic residual circulation the tidal circulation in highly stratified shallow estuaries described herein is the result of a finite amplitude internal motion driven by the barotropic tide shear instabilities at the interface are the major vertical exchange mechanism the residual circulation is caused primarily by ebb flood asymmetry in interface position and thickness a model based on our theoretical analysis shows that the interface thickness on flood is much less than the depth of flow up to a critical tidal amplitude at which the two layer flow is destroyed and correctly predicts the tidal amplitude of the neap spring transition in the columbia river estuary tidal frequency internal wave motion is not found in weakly stratified and partially mixed estuaries because of the reduced tidal shear shear instabilities are weak or absent and the residual circulation assumes a very different character as described in part 2

storm impacts on hydrodynamics and suspended sediment fluxes in a microtidal back barrier estuary abstract recent major storms have piqued interest in understanding the responses of estuarine hydrodynamics and sediment transport to these events to that end flow velocity wave characteristics and suspended sediment concentration ssc were measured for 11 months at eight locations in chincoteague bay md va usa a shallow back barrier estuary daily breezes and episodic storms generated sediment resuspending waves and modified the flow velocity at all sites which occupied channel shoal and sheltered bay environments with different bed sediment characteristics despite comparable ssc during calm periods ssc at the channel locations was considerably greater than at the shoal sites during windy periods because of relatively more erodible bed sediment in the channels sediment fluxes were strongly wind modulated within the bay s main channel depth integrated unit width sediment flux increased nonlinearly with increasing wind speed when averaged over all sites about 35 of the flux occurred during windy periods wind speed greater than 6 m s 1 which represented just 15 of the deployment time at channel sites the net water and sediment fluxes were opposite to the direction of the wind forcing while at shoal sites the fluxes generally were aligned with the wind implying complex channel shoal dynamics yearly sediment fluxes exceed previous estimates of sediment delivery to the entirety of chincoteague bay these observations illustrate the dynamic sedimentary processes occurring within microtidal back barrier lagoons and highlight the importance of storm events in the hydrodynamics and overall sediment budgets of these systems

diffusion kinetics of lutetium in diopside and the effect of thermal metamorphism on lu hf systematics in clinopyroxene abstract we report new experimental data for lu diffusion in diopside from 1150 to 1250 c at 1 bar pressure and oxygen fugacity corresponding to the iron wustite buffer the primary experimental dataset defines the following arrhenius relation for lu diffusion parallel to the b crystallographic axis d lu b 1 37 1 2 10 13 exp 208 7 15 2 kj mol 1 rt m 2 s where t is in kelvin we find that lu diffusion in diopside is significantly faster than that of hf which could lead to spurious lu hf ages via decoupling of 176lu from 176hf if the system was subjected to protracted periods of high temperature the extent to which lu hf ages are compromised during initial cooling depends on the peak temperature grain size cooling rate and the nature of lu partitioning between clinopyroxene and its surrounding phase s however in geologically realistic scenarios the effects of diffusion on lu hf ages during initial cooling do not produce lu hf ages that differ from the age corresponding to the closure temperature of hf by more than a few million years lu hf systematics in clinopyroxene are far more susceptible to diffusion during reheating events that occur after radiogenic 176hf has already accumulated in the host phase for a given thermal pulse the lu hf age varies as a function of grain size temperature the timing and duration of reheating and the partitioning of lu between clinopyroxene and its surrounding phase s the data collected and numerical model developed in this study have been used to simulate the effect of thermal metamorphism on the internal lu hf systematics of the eucrites millbillillie and piplia kalan although our model results do not offer a comprehensive solution to the apparent pre solar lu hf ages observed in many ancient meteorites we argue that the 4 9 ga pyroxene whole rock lu hf ages of these specific samples are at least partially if not primarily due to diffusive loss of lu from the constituent minerals to a partial melt phase during high temperature metamorphism

osmium isotopic homogeneity in the ck carbonaceous chondrites abstract variable proportions of isotopically diverse presolar components are known to account for nucleosynthetic isotopic anomalies for a variety of elements e g ca ti cr ni sr zr mo ru pd ba nd and sm in both bulk chondrites and achondrites however although large os isotopic anomalies have been measured in acid leachates and residues of unequilibrated chondrites bulk chondrites of various groups iron meteorites and pallasites exhibit os isotopic compositions that are indistinguishable from terrestrial or bulk solar isotopic abundances since the magnitude of nucleosynthetic anomalies is typically largest in the carbonaceous chondrites this study reports high precision os isotopic compositions and highly siderophile element hse concentrations for ten ck chondrites the isotope dilution concentration data for hse and high precision os isotope ratios were determined on the same digestion aliquots to precisely correct for radiogenic contributions to 186os and 187os while acid leached bulk unequilibrated carbonaceous chondrites show deficits of s process os components to the same extent as revealed by unequilibrated enstatite ordinary and rumuruti chondrites equilibrated bulk ck chondrites exhibit no resolvable os isotopic anomalies these observations support the idea that acid resistant carbon rich presolar grains such as silicon carbide sic or graphite are major carriers for nucleosynthetic isotopic anomalies of os the destruction of these presolar grains which are omnipresent in unequilibrated meteorites must have occurred during aqueous alteration and thermal metamorphism early in the ck chondrite parent body history the dispersal of ck chondrites along the iiiab iron meteorite isochron on a 187os 188os versus 187re 188os diagram with re os ratios from 0 032 to 0 083 in combination with the observed redistribution of other hse e g pt pd highlights the influence of parent body processes overprinted by effects of recent terrestrial alteration under the oxidizing conditions prevalent on the ck parent body evident from high abundances of magnetite and limited fe ni metal in ck chondrites these parent body processes made all isotopically anomalous os originally hosted in reduced presolar grains accessible the absence of os isotopic anomalies in ordinary enstatite and now also carbonaceous chondrites implies that the carriers of s and r process os must have been effectively homogenized across the region of chondrite formation and possibly even the entire solar protoplanetary nebula as suggested by the os isotopic compositions of iron meteorites and non anomalous ureilites except for a limited number of ureilites the relative proportions of presolar s and r process carriers of os and other elements such as w in chondrites and most other planetary bodies must have remained constant during all subsequent nebular and planetary processes which appears not to have been the case for other siderophile elements including mo ru and pd the existence of mo ru pd and other siderophile element isotopic anomalies thus appears to be in part controlled by the chemical properties of these elements e g volatility their host phase s e g sic graphite metal sulfides and the nature of the nebular or planetary processes experienced in the early solar system

the application of sequence stratigraphy to upper carboniferous fluvio deltaic strata of the onshore uk and ireland implications for the southern north sea stratigraphical correlations and fades interpretations of upper carboniferous fluvio deltaic strata have been based traditionally on cyclothems bound by marine flooding surfaces marine bands the recent recognition of major regionally extensive erosional unconformities exxon style sequence boundaries within selected cyclothems questions their validity as units of genetically related strata u sing examples from the carboniferous of the onshore uk and ireland we present sedimentological criteria for the recognition of sequence boundaries placing particular emphasis on the regional context of these surfaces sequence boundaries comprise widespread deeply eroded surfaces at the base of major fluvial sandstone complexes and laterally equivalent palaeosols developed on interfluves at the margins of the fluvial complexes these sequence boundaries define units of genetically related strata sequences which contain other key surfaces of time stratigraphic significance including marine bands and regionally extensive coals the recognition of key surfaces enables the construction of a high resolution stratigraphic framework within which coeval facies relationships can be interpreted sequence boundaries can be correlated between individual basins in the onshore uk by reference to their position in relation to a particular marine band for example the sequence boundary at the base of the farewell rock in the south wales basin can be correlated with that at the base of the rough rock in the pennine basin northern england since both these sandstone bodies are directly overlain by the subcrenatum marine band interbasinal correlations of this nature imply that potential fluvial sandstone reservoirs within major incised valley fills in the upper carboniferous strata of the southern north sea can be predicted by correlation with the onshore uk the stratigraphical framework can be extended and tested using core and well log data particularly spectral gamma ray data which are able to identify key sequence stratigraphic surfaces

shear instability in a highly stratified estuary abstract shear instability is found to be the principal mechanism of vertical exchange within the pycnocline of a salt wedge estuary a field program involving high resolution velocity and density measurements as well as high frequency acoustic imagery allowed direct comparison of instantaneous richardson number distributions to the occurrence of shear instability the theoretical stability threshold of 0 25 is consistent with the measurements based on estimates of gradients that contain the mean as well as fluctuations due to internal waves an effective stability threshold based on mean gradients is found to be approximately one third reflecting a significant contribution of internal wave shear the integral effect of the mixing process is to homogenize the gradients of velocity and density producing linear profiles of these quantities across the pycnocline a turbulent prandtl number of unity is suggested by the vertical distributions of velocity and density during periods of active vertical mixin

invertebrate trace fossils and agglutinated foraminifera as indicators of marine influence within the classic carboniferous section at joggins nova scotia canada the sea cliffs at joggins nova scotia are the most extensive and continuous carboniferous section in eastern north america although the section has been considered to have formed within a nonmarine depositional basin paleobiological information indicates that parts of the section were deposited in brackish water the occurrence of a trace fossil assemblage which includes cochlichnus kouphichnium and treptichnus is part of an assemblage of biogenic structures that apparently reflects paleodeposition within fluvial systems that may have experienced distal marine influences presence of agglutinated foraminifera characteristic of brackish water environments supports this interpretation this information provides new evidence of brackish water conditions at joggins such as those now being widely recognized in other carboniferous coal bearing sections

quantification of electron microprobe compositional maps of rock thin sections an optimized method and examples quantification of discrete pressure temperature domains in deformed chlorite white mica bearing metapelites was undertaken on mineral compositions derived by two dimensional microprobe compositional mapping of selected areas of rock thin sections in order to achieve compositional information at sufficient analytical precision spatial resolution and sample coverage within a typical analysis time of 1 day an optimization of measurement methods was necessary the method presented here allows collection of raw counts for eight different element concentrations at an analytical precision of 1 2 wt x ray intensity multiplane maps one map per measured chemical element are translated into concentration multiplane maps utilizing selected conventionally measured spot analyses combined with the castaing approximation for each mineral as this step requires identification of the different minerals present in the mapped area a statistical clustering technique to identify different groups of composition was developed guided by simple petrographic inspection of the thin section to delineate the important minerals in the mapped area finally the compositions of each pixel are translated into a mineral structural formula thus yielding a new kind of image with a high content of petrological information the reliability of the mineral composition images was emphasized by carrying out precision tests on the analytical data the possible use of chemical maps to infer the p t deformation history of metamorphic rocks is illustrated with two samples from the spitzbergen and the sambagawa blueschist facies belts in both samples a strong correlation between structures and chemistry is observed qualitative estimates of p t conditions from the si content of mica and chlorite are in good agreement with their location in microstructures that formed at different times therefore the combination of chemical maps with microstructural observations is a very powerful approach to understand both the evolution of complex metamorphic rocks and the control by deformation of mineral reactivity

evolution of atchafalaya lacustrine deltas south central louisiana abstract the entrenched pleistocene holocene mississippi alluvial valley was cut during the last low sea level stand and alluviation of the entrenched valley occurred during the holocene sea level rise regional gulf coast structures salt domes and faults have strongly influenced the morphology of the valley valley paleotopography has controlled depositional patterns and locations of major river courses as well as partially isolated large interdistributary basins within the alluvial deltaic plain interdistributary basin formation is further enhanced by distributary channel progradation switching and abandonment in conjunction with compactional subsidence of the alluvial plain surface geomorphology and sediment cores from the atchafalaya basin louisiana revealed that this basin has alternately accumulated fine grained organic rich sediments and terrigenous clastic dominated meander belt and lacustrine deposits basin subsidence and the presence of an active distributary channel in the basin are major determinants of the lithology of the sedimentary fill prograding lacustrine deltas of the atchafalaya river are the primary mechanism for filling the atchafalaya basin these upward coarsening deltas are relatively thin 3 m but are areally extensive tens to hundreds of kilometers and because they occur so frequently during the infilling process they account for a significant volume of the basin sequence the atchafalaya basin sequence documents lacustrine deltaic episodes dating from the early holocene maringouin and teche deltas to the present atchafalaya delta continued development of the atchafalaya river will rework portions of the backswamp and lacustrine deposits into meander belt deposits upon complete filling of the atchafalaya basin sediment will mostly bypass the basin and become deposited in the marine delta in atchafalaya bay

high resolution sequence stratigraphy of the late namurian in the widmerpool gulf east midlands uk abstract analysis of facies stacking patterns and stratal surfaces within late namurian deltas of the widmerpool gulf has revealed 10 high frequency fourth order depositional sequences sequence correlation is based on the characteristic marine band fauna of their condensed sections in many instances sequence boundaries are difficult to recognize unless there is clearly demonstrable lowstand incision consequently it is often difficult to separate late highstand from falling stage progradation with any degree of confidence sequence thickness variations and the dominance of particular stratal surfaces and systems tracts were controlled by a longer period third order cycle of relative sea level rise and fall during the marsdenian yeadonian major fluvio deltaic sand bodies in the widmerpool gulf were formed by distributary channel progradation e g chatsworth grit during the late highstand and or falling stage systems tracts and by the filling of incised valleys e g ashover grit and rough rock following marked sea level falls channel belt and valley fill orientation was initially influenced by differential compaction but this influence decreased during the late namurian the recognition of incised valley fills within the late namurian has implications for estimating the magnitudes and periodicities of carboniferous relative sea level change

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

structure variability and salt flux in a strongly forced salt wedge estuary this researchwas funded by national science foundation grant oce 0452054 ralston also received partial support from the penzance endowed fund in support of assistant scientists and the john f and dorothy h magee fund in support of scientific staff at woods hole oceanographic institution

comment on the paper of gierlowski kordesch and cassle the spirorbis problem revisited sedimentology and biology of microconchids in marine nonmarine transitions earth science reviews 148 2015 209 227 abstract gierlowski kordesch and cassle 2015 earth science reviews 148 209 227 interpreted microconchids extinct tentaculitoid encrusters as strictly marine rejecting the previous conclusions that these organisms occupied a variety of habitats ranging from marine to non marine we argue that due to misunderstanding of previous statements concerning the affinity of microconchids the authors used an actualistic approach and incorrectly compared microconchids with modern phoronids which led to oversimplifications and misinterpretations also their idea that microconchids as supposedly strictly marine organisms were preserved in non marine settings only because of transport by storm surges and tsunamis is unsupported on paleontological grounds these errors led to mistaken conclusions about microconchid paleoecology that must be discussed in order to avoid an erroneous interpretation of microconchid paleoenvironments

temporal and spatial variability of vertical salt flux in a highly stratified estuary 1 the temporal and spatial variability of vertical salt flux in the fraser river estuary british columbia was investigated observationally using several different direct and indirect indicators of buoyancy flux data were collected from the estuary using shipboard instrumentation primarily an acoustic doppler current profiler and a towed conductivity temperature depth unit direct estimates of buoyancy flux were made from along channel control volume analyses and from measurements of overturn scales the spatial and temporal evolution of the salt wedge structure through a tidal cycle was evaluated using the results of these buoyancy flux calculations as well as gradient richardson number froude number and stratification profiles observations indicate that buoyancy flux is driven primarily by interfacial stress and not bottom stress as is common in many estuaries vertical salt flux as opposed to seaward advection of high salinity fluid was found to be the dominant mechanism responsible for removal of salt from the estuarine channel during each daily tidal cycle buoyancy flux was highly variable in time and space however with vertical salt flux during ebb tides on the order of 2 to 3 times greater than that estimated during floods this is due to an increase in the vertical shear of horizontal velocity and a sharp increase in stratification which was observed during early ebb enhanced mixing was observed spatially within a region dominated by a channel constriction in which the channel narrows by approximately 25

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

on nonhydrostatic coastal model simulations of shear instabilities in a stratified shear flow at high reynolds number the nonhydrostatic surface and terrain following coastal model nhwave is utilized to simulate a continually forced stratified shear flow in a straight channel which is a generic problem to test the existing nonhydrostatic coastal models capability in resolving shear instabilities in the field scale the resolved shear instabilities in the shear layer has a reynolds number of about 1 4 106 which is comparable to field observed value using the standard smagorinsky closure with a grid size close to the ozmidov length scale simulation results show that the resolved energy cascade exceeds 1 order of magnitude and the evolution and turbulent mixing characteristics are predicted well two different approaches are used to estimate the turbulent dissipation rate namely using the resolved turbulent energy spectrum and the parameterized subgrid turbulent dissipation rate and the predicted results provide the upper and lower bounds that encompass the measured values model results show significantly higher turbulence in braids of shear instabilities which is similar to field observations while both the subgrid turbulent dissipation rate and resolved vorticity field can be used as surrogates for measured high acoustic backscatter signals simulation results also reveal that the surface velocity divergence convergence is an effective identifier for the front of the density current and the shear instabilities to guide future numerical studies in more realistic domains an evaluation on the effects of different grid resolutions and subgrid viscosity on the resolved flow field and subgrid dissipation rate are discussed

estimating carboniferous sea level fluctuations from gondwanan ice extent the magnitude of carboniferous sea level fluctuations is not well known but the estimates are important for constraining cyclothem models in this paper we apply area volume relations developed for quaternary ice sheets to estimate the glacio eustatic component of sea level fluctuations in the carboniferous utilizing the best estimate of gondwanan ice area at the time of its greatest extent we arrive at a figure of 60 15 m for the isostasy corrected glacio eustatic component this value is nearer the lower limit of sea level estimates for cyclothem fluctuations from other sources

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

simulating the wave induced response of a submerged wave energy converter using a non hydrostatic wave flow model abstract with the increasing interest in wave energy and when moving towards commercial scale wave energy projects a detailed understanding of the interactions between single and arrays of wave energy converters wecs with the ambient wave and flow field becomes imperative for both design and operational purposes as well as assessment of their environmental impacts this work presents a new numerical approach to simulate the nonlinear evolution of the waves and their interactions with a submerged wave energy converter at the scale of a realistic coastal region the numerical approach is based on the non hydrostatic framework and implemented in the open source swash model which provides an efficient tool to simulate the nonlinear evolution of waves over realistic coastal bathymetries here we present a numerical extension to the non hydrostatic approach to account for interactions between waves and a submerged point absorber and to capture the response of such a wave energy device model results are compared with an analytical solution based on potential flow theory a cfd simulation and experimental data to validate its capabilities in simulating the wave wec interactions for both linear and nonlinear wave conditions overall the results of this validation demonstrate that the model captures the wave structure interactions and the body response with satisfactory accuracy notably the results also indicate that a coarse vertical resolution was sufficient to capture these dynamics making the model sufficiently computationally efficient to simulate the interaction of waves and wecs over large scales as a consequence this new modelling approach should provide a promising new alternative to simulate the interactions between nonlinear wave fields and submerged point absorbers at the scale of a realistic coastal region

efremovka 101 1 a cai with ultrarefractory ree patterns and enormous enrichments of sc zr and y in fassaite and perovskite inclusion 101 1 from the cv3 carbonaceous chondrite efremovka is a compact type a ca al rich inclusion cai highly enriched in ultrarefractory ur oxides it is the first complete cai with a ur rare earth element ree pattern found in a cv3 chondrite the inclusion is petrographically complex and was formed in a multistage process it consists of several lithologically unrelated units the core contains abundant y and zr perovskite sc and zr rich fassaite and metallic feni enclosed in melilite all mineral species except spinel in all lithological units exhibit the same basic ur ree pattern four different populations of perovskites are distinguished by different y zr ratios a few of the perovskites have y zr ratios similar to those obtained from crystal liquid fractionation experiments perovskites from the other three populations have either chondritic lower than chondritic y zr ratios or extremely low zr contents ca isotopic ratios differ among three perovskites from different populations demonstrating a variety of sources and formational processes most fassaites crystallized in situ through reaction between the cai liquid and preexisting perovskites this process induced redistribution of zr y sc and v between perovskite and fassaite thus overprinting the original abundances in perovskite fassaite reaction rims around feni metals are also encountered they are enriched in v which was gained from the metal through oxidation of v in metal during fassaite crystallization the relative abundances of zr y and sc in perovskites are complementary to the abundances of these elements in sc and zr fassaite indicating subsolidus partitioning of these elements between the two phases perovskites are enriched in y and depleted in sc and zr in comparison to fassaites the core contains two complete captured cais several sinuous fragments and fine grained polygonal refractory fragments an assemblage of andradite wollastonite hedenbergite and pure metallic iron is encoun tered as enclaves in the interior of some sinuous fragments metallic fe and wollastonite formed by reduction of preexisting andradite and hedenbergite nebular alteration products upon inclusion in the highly reduced cai melt numerous spinel clusters and framboids with varying v2o3 and cr2o3 concentrations are enclosed in individual melilite crystals in the host cai and captured cais the rim sequence of the host consists of six layers from the inside outward a feo poor spinel b sc bearing fassaite c al diopside d al and ca bearing olivine e pure diopside and f ca poor olivine like the constituents of the cai core all mineral layers of the rim sequence except spinel have the same ur ree pattern however the total ree abundances decrease systematically by 1 order of magnitude from layer 2 to layer 6 this feature strongly suggests formation of the rim sequence by successive condensation from a unique reservoir enriched in ur elements and excludes formation by flash heating petrography mineral chemistry ree refractory lithophile element abundances and ca isotopic compositions demonstrate the complex multistage formation history of a cai that on the surface looks like a regular type a inclusion copyright 2002 elsevier science ltd

palaeosols in westphalian coal bearing and red bed sequences central and northern england westphalian a c coal bearing strata and red beds in the pennine basin of central and northern england contain a wide variety of palaeosols in coal bearing facies associations alluvial gley semi gley organic and rare well drained palaeosols reflect the predominance of poor drainage conditions during deposition in red beds more evolved ferruginous and ferallitic palaeosols testify to free drainage conditions during deposition catenary relationships can be inferred between most of the palaeosols in both facies associations providing further information on the palaeogeomorphology of the depositional systems and assisting in the understanding of the environments and conditions of coal seam formation

unusual features of sediment supply dominated transgressive regressive sequences paleogene clastic wedges se pyrenean foreland basin spain abstract the paleogene marine to nonmarine succession in the southeastern pyrenean foreland basin consists of a series of 3rd order 3 5 m y transgressive to regressive sequences that can be related directly to the stacking and southward displacement of successive basement cover thrust sheets the regressive limbs of the 3rd order clastic wedges are coeval with thrust movement with maximum subsidence developing towards peak regression this relationship between sedimentation and tectonics is sediment supply driven one of these 3rd order wedges which was produced by the montserrat and sant llorenc del munt fan delta systems demonstrates how such steep sloped coarse grained high sediment supply systems generate a hierarchy of transgressive regressive architectures striking features of this rapidly subsiding supply dominated basin margin in addition to the tectonics wedge architecture relationship include the nonperiodic character of the contained high frequency sequences the unusual thickness and landward thickening geometry of transgressive systems tracts a tendency for misfit between alluvial fan and shorezone sectors of sequences a lack of marked incision associated with the tops of coarse grained regressive phases of sequences most of the features are symptomatic of high subsidence rates and very high sediment supply the last feature suggestive of few major relative falls of sea level is also consistent with continuous rapid subsidence however it should be remembered that lack of incision may be a poor indicator for lack of base level fall in a setting where the steepness of alluvial slopes exceeds the slope of the coeval shelf

the role of phosphates for the lu hf chronology of meteorites abstract the 176lu 176hf isotopic system is widely used for dating and tracing cosmochemical and geological processes but still suffers from two uncertainties first lu hf isochrons for some early solar system materials have excess slope of unknown origin that should not be expected for meteorites with ages precisely determined with other isotopic chronometers this observation translates to an apparent lu decay constant higher than the one calculated by comparing ages obtained with various dating methods on terrestrial samples second unlike the well constrained sm nd value to within 2 for the chondritic uniform reservoir chur the lu hf ratios in chondrites vary up to 18 when considering all chondrites adding uncertainty to the lu hf chur value in order to better understand the lu hf systematics of chondrites we analyzed mineral fractions from the richardton h5 chondrite to construct an internal lu hf isochron and set up a numerical model to investigate the effect of preferential diffusion of lu compared to hf from phosphate the phase with the highest lu hf ratio in chondrites to other minerals the isochron yields an age of 4647 210 million years myr using the accepted 176lu decay constant of 1 867 0 008 10 11 yr 1 combining this study with the phosphate fractions measured in a previous study yields a slope of 0 08855 0 00072 translating to a 176lu decay constant of 1 862 0 016 10 11 yr 1 using the pb pb age previously obtained in agreement with the accepted value the large variation of the lu hf phosphates combined with observations in the present study identify phosphates as the key in perturbing lu hf dating and generating the isochron slope discrepancy this is critical as apatite has substantially higher diffusion rates of rare earth elements than most silicate minerals that comprise stony meteorites results of numerical modeling depending of temperature peak size of the grains and duration of the metamorphic event show that diffusion processes in phosphate can produce an apparently older lu hf isochron while this effect will remain negligible in perturbing the sm nd chronology our results suggest that only type 3 chondrites with the lowest metamorphic grade and large minerals with minimal diffusive effects are suitable for determination of the lu hf chur values and the lu decay constant respectively

thulium anomalies and rare earth element patterns in meteorites and earth nebular fractionation and the nugget effect this study reports the bulk rare earth element rees la lu compositions of 41 chondrites including 32 falls and 9 finds from carbonaceous ci cm co and cv enstatite eh and el and ordinary h l and ll groups as well as 2 enstatite achondrites aubrite the measurements were done in dynamic mode using multi collector inductively coupled plasma mass spectrometers mc icpms allowing precise quantification of mono isotopic rees pr tb ho and tm the ci chondrite normalized ree patterns lan lun a proxy for fractionation of light vs heavy rees and eu anomalies in ordinary and enstatite chondrites show more scatter in more metamorphosed petrologic types 4 6 than in unequilibrated types 1 3 chondrites this is due to parent body redistribution of the rees in various carrier phases during metamorphism a model is presented that predicts the dispersion of elemental and isotopic ratios due to the nugget effect when the analyzed sample mass is limited and elements are concentrated in minor grains the dispersion in ree patterns of equilibrated ordinary chondrites is reproduced well by this model considering that rees are concentrated in 200 lm size phosphates which have high lan lun ratios and negative eu anomalies terrestrial rocks and samples from ordinary and enstatite chondrites display negative tm anomalies of 4 5 relative to ci chondrites in contrast cm co and cv except allende show no significant tm anomalies allende cv chondrite shows large excess tm 10 these anomalies are similar to those found in group ii refractory inclusions in meteorites but of much smaller magnitude the presence of tm anomalies in meteorites and terrestrial rocks suggests that either i the material in the inner part of the solar system was formed from a gas reservoir that had been depleted in refractory dust and carried positive tm anomalies or ii ci chondrites are enriched in refractory dust and are not representative of solar composition for refractory elements a new reference composition relevant to inner solar system bodies ci is calculated by subtracting 0 15 of group ii refractory inclusions to ci the observed tm anomalies in ordinary and enstatite chondrites and terrestrial rocks relative to carbonaceous chondrites indicate that material akin to carbonaceous chondrites must have represented a small fraction of the constituents of the earth tm anomalies may be correlated with ca isotopic fractionation in bulk planetary materials as they are both controlled by addition or removal of refractory material akin to fine grained group ii refractory inclusions

alternating braidplain and lacustrine deposition in a strike slip setting the pennsylvanian boss point formation of the cumberland basin maritime canada abstract the boss point formation was deposited in the cumberland basin of southeastern new brunswick and northern nova scotia during the early pennsylvanian the basin is bounded to the northwest and south by strike slip faults active during the pennsylvanian the boss point comprises two main fades associations sandy braidplain bfa and muddy lacustrine lfa the abrupt alternation of which allows 16 depositional megacycles to be defined the lfa forms units 50 m thick that rest sharply but nonerosively on braidplain sandstone in some instances the contact can be traced for over 12 km perpendicular to paleoflow commonly dunes and ripples are preserved in relief beneath lacustrine mudstone implying rapid but very low energy flooding of t e braidplain the bfa comprises multistory channel sandbodies 90 m thick separated from the underlying lfa by sixth order surfaces with up to 15 m of erosional relief the erosion surfaces are commonly overlain by spectacular mudstone breccias and boulders that reflect deep erosion and rotational slumping into channels cut into and sometimes right through lacustrine deposits bfa packages are internally partitioned by fifth order erosion surfaces into individual channel fill units commonly about 5 m thick the bfa is dominated by trough cross bedded fine to lower medium sandstone conglomerate pebbly sandstone and ripple laminated and planar laminated sandstone are minor components rare mud filled abandoned channels suggest a mean width and de th of 160 m and 4 8 m respectively the dominance of trough cross bedding suggests relatively deep channels whose banks may have been maintained by a dense vegetation cover repeated channel avulsion and flood related erosion resulted in a rock record dominated by deep channel and flood stage deposits bartop facies were rarely preserved channel dimensions lateral consistency of facies paucity of muddy channel plugs and regionally consistent paleoflow suggest deposition on a braidplain the distribution of conglomerates indicates a local gravel source area in the caledonia highlands to the northwest but much of the sand is likely to have been sourced far to the southwest the boss point falls into two sharply disjunct paleoflow domains one directed to the north and northeast and the other to the east and southeast separated by the harvey hopewell fault zone the absence of an adequate watershed between the two domains strongly suggests tectonic juxtaposition involving several tens of kilometers of sinistral offset

estuarine boundary layer mixing processes insights from dye experiments a series of dye releases in the hudson river estuary elucidated diapycnal mixing rates and temporal variability over tidal and fortnightly time scales dye was injected in the bottom boundary layer for each of four releases during different phases of the tide and of the spring neap cycle diapycnal mixing occurs primarily through entrainment that is driven by shear production in the bottom boundary layer on flood the dye extended vertically through the bottom mixed layer and its concentration decreased abruptly near the base of the pycnocline usually at a height corresponding to a velocity maximum boundary layer growth is consistent with a one dimensional stress driven entrainment model a model was developed for the vertical structure of the vertical eddy viscosity in the flood tide boundary layer that is proportional to u 2 n where u and n are the bottom friction velocity and buoyancy frequency above the boundary layer the model also predicts that the buoyancy flux averaged over the bottom boundary layer is equal to 0 06n u 2 or based on the structure of the boundary layer equal to 0 1nblu 2 where nbl is the buoyancy frequency across the flood tide boundary layer estimates of shear production and buoyancy flux indicate that the flux richardson number in the flood tide boundary layer is 0 1 0 18 consistent with the model indicating that the flux richardson number is between 0 1 and 0 14 during ebb the boundary layer was more stratified and its vertical extent was not as sharply delineated as in the flood during neap tide the rate of mixing during ebb was significantly weaker than on flood owing to reduced bottom stress and stabilization by stratification as tidal amplitude increased ebb mixing increased and more closely resembled the boundary layer entrainment process observed during the flood tidal straining modestly increased the entrainment rate during the flood and it restratified the boundary layer and inhibited mixing during the ebb

numerical modeling of an estuary a comprehensive skill assessment i numerical simulations of the hudson river estuary using a terrain following three dimensional model regional ocean modeling system roms are compared with an extensive set of time series and spatially resolved measurements over a 43 day period with large variations in tidal forcing and river discharge the model is particularly effective at reproducing the observed temporal variations in both the salinity and current structure including tidal spring neap and river discharge induced variability large observed variations in stratification between neap and spring tides are captured qualitatively and quantitatively by the model the observed structure and variations of the longitudinal salinity gradient are also well reproduced the most notable discrepancy between the model and the data is in the vertical salinity structure while the surface to bottom salinity difference is well reproduced the stratification in the model tends to extend all the way to the water surface whereas the observations indicate a distinct pycnocline and a surface mixed layer because the southern boundary condition is located near the mouth the estuary the salinity within the domain is particularly sensitive to the specification of salinity at the boundary a boundary condition for the horizontal salinity gradient based on the local value of salinity is developed to incorporate physical processes beyond the open boundary not resolved by the model model results are sensitive to the specification of the bottom roughness length and vertical stability functions insofar as they influence the intensity of vertical mixing the results only varied slightly between different turbulence closure methods of k e k and k kl

quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries abstract this numerical modeling study quantifies for the first time the contribution of various processes to estuarine circulation in periodically stratified tidal flow under the impact of a constant horizontal buoyancy gradient the one dimensional water column equations with periodic forcing are first cast into nondimensional form resulting in a multidimensional parameter space spanned by the modified inverse strouhal number and the modified horizontal richardson number as well as relative wind speed and wind direction and the residual runoff the along tide momentum equation is then solved for the tidal mean velocity profile in such a way that it is equated to the sum of the contributions of tidal straining resulting from the temporal correlation between eddy viscosity and vertical shear gravitational circulation resulting from the depth varying forcing by a constant horizontal buoyancy gradient wind straining and depth mean residual flow resulting from net freshwater runoff this definitio

near bottom turbulence measurements in a partially mixed estuary turbulent energy balance velocity structure and along channel momentum balance abstract a set of moored bottom mounted and shipboard measurements obtained in a straight section of the lower hudson estuary during late summer and early fall of 1995 determine velocity density and along channel pressure gradient throughout the 15 m water column as well as providing direct eddy correlation estimates of reynolds stress and indirect inertial range estimates of dissipation within 3 m of the bottom the analysis focuses on testing 1 a simplified turbulent kinetic energy equation in which production balances dissipation 2 the prandtl karman law of the wall which is a relationship between bottom stress and near bottom velocity gradient and 3 a simplified depth integrated along channel momentum balance involving local acceleration pressure gradient and bottom stress estimates of production and dissipation agree well throughout the entire record the relationship between bottom stress and velocity gradient is consistent with the law of the wall within approximately 1 m of the sea

the impact of climate change tectonism and hydrology on the formation of carboniferous tropical intermontane mires the springhill coalfield cumberland basin nova scotia abstract both climate and tectonism are influential in determining basin and mire hydrology in the rapidly subsiding intermontane basins of euramerica which formed in response to the variscan hercynian alleghenian orogeny however the record of climate change has been muted and may therefore go unrecognized the complex interplay of climate and tectonism in a tropical continental setting is recorded in the 4 km thick westphalian a b fill of the cumberland basin thick peat accumulation was favoured at the southern basin margin where rheotrophic forested mires 4 9 km wide flourished between basin axis rivers and coalesced alluvial fans derived from the cobequid highlands as a result of their geomorphic setting the thicker coals 4 3 m exhibit distinct areal zones piedmont inner mire and riverine evidence that the forest swamps were nourished both by rainfall and by groundwater discharge from alluvial fans includes the stratigraphic affinity of thick coals and basin margin conglomerates interfingering of distal fan sheetflood and mire deposits petrographic evidence of elevated ph partial gelification of tissues and predominance of the arboreous lycopsids lepidodendron and paralycopodites whereas such groundwater supply is crucial to maintenance of modern wetlands in drier periods a subhumid climate is implied coals at joggins further removed from groundwater discharge at the basin margin are less well developed a 600 m thick coal window within the fining and reddening upward basin fill sequence at springhill is inferred to represent a coincidence of optimal groundwater supply and net subsidence the ultimate decline of peat accumulation in the basin may reflect decrease in catchment area and fan size and loss of rainshadow as the cobequid massif was denuded and the basin filled the coal window ca 6 9 10 5 yr is punctuated by non marine cyclothems of coal grey sideritic mudrock and multistorey sandstone that share similar time frames with astronomic cycles of axial precession ca 1 4 10 4 yr the stress of related climate change is inferred to have caused peat accumulation to fall into disequilibrium with sediment flux and basin subsidence the late quaternary history of certain african mires illustrates the dramatic impact of climate change especially temperature and seasonality and orographic effects on tropical continental peat accumulation aspects of the groundwater recharge model may be applicable to the westphalian stephanian intermontane mires of spain and mesozoic coal basins of northern china

architecture of coastal and alluvial deposits in an extensional basin the carboniferous joggins formation of eastern canada abstract the joggins formation was deposited in the cumberland basin which experienced rapid mid carboniferous subsidence on bounding faults a 600 m measured section of coastal and alluvial plain strata comprises cycles tens to hundreds of metres thick the cycles commence with coal and fossiliferous limestone siltstone intervals interpreted as widespread flooding events these intervals are overlain by coarsening upward successions capped by planar based sandstone mounds up to 100 m in width that represent the progradation of small river generated delta lobes into a standing body of open water developed during transgression the overlying strata contain sand rich heterolithic packages 1 8 m thick that are associated with channel bodies 2 3 m thick and 10 50 m wide drifted plant debris calamites groves and erect lycopsid trees are preserved within these predominantly green grey heterolithic sediments which were deposited on a coastal wetland or deltaic plain traversed by channel systems the cycles conclude with red siltstones containing calcareous nodules that are interbedded with thin sandstones and associated with both single storey channel bodies 1 1 5 m thick and 2 3 m wide and larger multistorey channels 3 6 m thick with incised margins numerous channel bodies at the same level suggest that multiple channel anastomosed river systems were developed on a well drained floodplain many minor flooding surfaces divide the strata into parasequences with dominantly progradational and aggradational stacking patterns multistorey channel bodies are relatively thin fine grained and modestly incised and palaeosols are immature and cumulative the abundance and prominence of flooding surfaces suggests that base level rise was enhanced whereas the lack of evidence for abrupt basinward stepping of facies belts coupled with the absence of strong fluvial incision and mature palaeosols suggests that base level fall was suppressed these architectural features are considered to reflect a tectonic architectural signature in accordance with the high subsidence basinal setting evidence for restricted marine influence and variation in floral assemblages suggests modulation by eustatic and climatic effects although their relative importance is uncertain

calcium isotopic ratios and rare earth element abundances in refractory inclusions from the allende cv3 chondrite abstract refractory inclusions in primitive meteorites are the oldest objects formed in the solar system they exhibit large mass dependent isotopic effects in many elements including si mg and ca indicative of their complex origin we report data for both mass dependent and mass independent e ca isotopic effects and rare earth element ree abundances in six refractory inclusions from the allende cv3 meteorite our data reveal large mass dependent ca isotopic effects in these refractory inclusions with 44 40 ca ranging from 5 60 to 0 35 relative to nist srm 915a which are significantly lower than that of the bulk silicate earth 44 40 ca 1 05 0 04 importantly 44 40 ca is correlated with ree patterns refractory inclusions with group ii ree patterns have lighter ca isotope compositions compared to those with group i ree patterns specifically the studied refractory inclusions form negative 44 ca 40 ca tm er and 44 ca 40 ca nd er trends implying segregation of up to 3 of an ultrarefractory evaporation residue from a chondritic reservoir prior to the formation of refractory inclusions this residue would have to be characterized by high 44 ca 40 ca and low tm er and nd er at 2 levels of 0 5 and 1 5 for e 40 44 ca and e 43 44 ca respectively the six refractory inclusions studied show no detectable 40 ca or 43 ca anomalies relative to the terrestrial standards however five out of the six refractory inclusions do show a 48 ca excess of several e units clearly resolvable from the terrestrial standards

on balanced and unbalanced accommodation peat accumulation ratios in the cretaceous coals from gates formation western canada and their sequence stratigraphic significance coal composition was investigated by means of photometric and maceral analyses on closely spaced lithotype based strip samples over the full thickness of several paralic coal seams from the cretaceous gates formation of the western canadian sedimentary basin the aim of this investigation was to test various methods of identifying accommodation trends in coal and use them to refine sequence stratigraphic interpretation of continental sediments conventional sequence stratigraphy derives its subdivisions and significant surfaces from the records left by relative sea level oscillations these records either do not project into the continental realm or are difficult to recognise in clastic non marine sediments paralic coal seams have been selected to study this problem because they are not entirely removed from marine influence and compared with most inorganic deposits coal has stored a greater wealth of information that can be analysed at a higher level of resolution the study has led to the identification of five new surfaces with chronostratigraphic potential in the sequence stratigraphic analysis of non marine sediments two of these surfaces called paludification surface pas and terrestrialisation surface tes occur at the bases of the investigated coal seams while two other surfaces referred to as non marine flooding surface nfs and give up transgressive surface guts form the tops of the coal the fifth and probably most important new surface called the accommodation reversal surface ars is independent of any particular facies and may either coincide with some of the other surfaces or occur separately the proportion of detrital minerals has been used as the chief discriminator between different mire types and accommodation trends other useful indicators of mire type and peat dispersal have been the proportions of sporinite and inertodetrinite as well as some derived maceral and or mineral ratios e g the groundwater influence index and the tissue preservation index isometamorphic variations of telovitrinite reflectance and fluorescence as well as their coefficients of variation were also found to contribute to the identification of cyclic shifts between balanced and unbalanced accommodation peat accumulation ratios some of these cycles which are backed up by clastic stratigraphy appear to correspond to the development of shallowing upward and deepening upward parasequences superimposed high frequency low amplitude perturbations in the coal cycles relate to smaller scale accommodation cycles of sub parasequence level not always recognised in non marine strata these sub parasequence coal cycles do not always continue the shallowing upward trend typical of conventional parasequences several coals were found to contain stacks of small scale cycles with upward increasing accommodation signatures either in their lower or upper halves or over the whole seam section

structural and sedimentary history of the quaco head area southern new brunswick remapping of the quaco head area of southern new brunswick has revealed a more complex structure than had been previously documented the structure is dominated by two major thrust faults that dip to the south and southeast at between 35 and 45 the lower younger thrust emplaces precambrian basalts and tuffaceous siltstones coldbrook group over alluvial sediments of the boss point and tynemouth creek formations westphalian a b resting unconformably on the upper surface of the basalt is a thin layer 10 m of marine basal windsor group limestone disconformably overlain by alluvial conglomerates of inferred hopewell group age this sequence is truncated by an older southeast dipping thrust fault to the southeast of which lie hopewell conglomerates overturned towards the west and northwest the latter sequence probably forms the lower limb of a large recumbent fold folding and thrusting in the quaco head area may have begun during westphalian b times although major movement was probably post westphalian c and occurred contemporaneously with dextral strike slip movement on the minas geofracture following this alleghenian variscan deformation the area underwent deep erosion prior to the deposition of a thick sequence of triassic alluvial sediments the more southerly reverse fault was reactivated as a normal fault during a phase of late triassic or jurassic faulting along the bay of fundy that was probably related to early atlantic rifting

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

convergent morphology in small spiral worm tubes spirorbis and its palaeoenvironmental implications calcareous tube worms generally identified as spirorbis range from ordovician to recent often profusely encrusting shells and other substrates whereas recent spirorbis is a polychaete annelid details of tube structure in pre cretaceous spirorbis suggest affinities with the microconchida an extinct order of possible lophophorates although characteristically palaeozoic microconchid tube worms survived the permian mass extinction before being replaced in late mesozoic ecosystems by true spirorbis recent spirorbis is stenohaline but spirorbiform microconchids also colonized freshwater brackish and hypersaline environments during the devonian triassic anomalies in the palaeoenvironmental distributions of fossil spirorbis are explained with the recognition of this striking convergence between microconchids and true spirorbis

temperature micro mapping in oscillatory zoned chlorite application to study of a green schist facies fault zone in the pyrenean axial zone spain oscillatory compositional zoning in minerals has been observed in hydrothermal magmatic and metamorphic environments and is commonly attributed to chemical or physical cyclical changes during crystal growth chemical zoning is a common feature of solid solutions which has been rarely reported in phyllosilicates in this study oscillatory zoning in chlorite is described in samples from the pic de port vieux thrust a minor thrust fault associated to the major gavarnie thrust fault zone central pyrenees spain the pic de port vieux thrust sheet comprises a 1 20 m thick layer of triassic red pelite and sandstone thrust over mylonitized cretaceous dolomitic limestone the thrust fault zone deformation comprises secondary faults and cleavage affecting the triassic pelite and sandstone an important feature responsible to this deformation is a set of veins filled by quartz and chlorite chlorite is present in crack seal extension veins and in shear veins both structures opened under the same stress conditions in some shear veins chlorite occurs as pseudo uniaxial plates arranged in rosette shaped aggregates these aggregates appear to have developed as a result of radial growth of the chlorite platelets oscillatory zoning has been imaged by backscattered scanning electron microscopy and by x ray quantitative micro mapping these oscillations correspond to chemical zoning with alternating iron rich and magnesium rich bands the chlorite composition ranges from a fe rich pole to a mg rich pole fe 3 fe values were measured in chlorite using xanes spot analyses and vary from 0 23 to 0 44 the highest values are in the fe rich area temperature maps built from standardized microprobe x ray images and redox state using the program xmaptools indicate oscillatory variations from about 310 to 400 50 c during chlorite crystallization these temperature variations are correlated with a fe 3 fe variation by al 3 fe 3 1 and di trioctahedral substitutions highlighted by mg and fe tot contents fe mg zoning chemical variations could be then explained by alternation of cooling times and cyclical pulses of a fluid hotter than the host rock it is however not excluded that kinetic effects influence the incorporation of mg or fe during chlorite crystallization

sediment dynamics in the lower mekong river transition from tidal river to estuary a better understanding of flow and sediment dynamics in the lowermost portions of large tropical rivers is essential to constraining estimates of worldwide sediment delivery to the ocean flow velocity salinity and suspended sediment concentration were measured for 25 h at three cross sections in the tidal song hau distributary of the mekong river vietnam two campaigns took place during comparatively high seasonal and low seasonal discharge and estuarine conditions varied dramatically between them the system transitioned from a tidal river with ephemeral presence of a salt wedge during high flow to a partially mixed estuary during low flow the changing freshwater input sediment sources and estuarine characteristics resulted in seaward sediment export during high flow and landward import during low flow the dinh an channel of the song hau distributary exported sediment to the coast at a rate of about 1 t s 1 during high flow and imported sediment in a spatially varying manner at approximately 0 3 t s 1 during low flow scaling these values results in a yearly mekong sediment discharge estimate about 65 smaller than a generally accepted estimate of 110 mt yr 1 although the limited temporal and spatial nature of this study implies a relatively high degree of uncertainty for the new estimate fluvial advection of sediment was primarily responsible for the high flow sediment export exchange flow and tidal processes including local resuspension were principally responsible for the low flow import the resulting bed sediment grain size was coarser and more variable during high flow and finer during low and the residual flow patterns support the maintenance of mid channel islands

deciphering high pressure metamorphism in collisional context using microprobe mapping methods application to the stak eclogitic massif northwest himalaya the stak massif northern pakistan is a newly recognized occurrence of eclogite formed by the subduction of the northern margin of the indian continent in the northwest himalaya although this unit was extensively retrogressed during the himalayan collision records of the high pressure hp event as well as a continuous pressure temperature p t path were assessed from a single thin section using a new multiequilibrium method this method uses microprobe x ray compositional maps of garnet and omphacitic pyroxene followed by calculations of 200 000 p t estimates using appropriate thermobarometers the stak eclogite underwent prograde metamorphism increasing from 650 c and 2 4 gpa to the peak conditions of 750 c and 2 5 gpa then retrogressed to 700 650 c and 1 6 0 9 gpa under amphibolite facies conditions the estimated peak metamorphic conditions and p t path are similar to those of the kaghan and tso morari high to ultrahigh pressure hp uhp massifs we propose that these three massifs define a large hp to uhp province in the northwest himalaya comparable to the dabie sulu province in china and the western gneiss region in norway

observations and numerical modeling of the pearl river plume in summer season a cruise survey of the pearl river plume during southeasterly and southwesterly winds two typical wind patterns in summer in guangdong coastal waters is reported and the cruise data are analyzed to unveil the plume dynamics the kelvin number is derived from the in situ data revealing that the pearl river plume exhibits two different scales in response to the two kinds of the wind forcing numerical model simulations based on the regional oceanic modeling system roms with nesting domains are implemented to explore details of the plume dynamics validated by cruise observations and tidal gauge sea level data modeling results suggest that there is a subtidal anticyclonic recirculation bulge on the west side out of the estuary mouth under southeasterly winds showing a recirculating plume in the near field when the wind changes to the southwesterly however the recirculating plume vanishes the distinct supercritical tidal plume front occurs with southeasterly winds prevailing in spring tide due to the strong advection in the tidal plume the tidal salt deficit flux can reach as high as 12 5 of the mean current flux and illustrates the combined forcing of tide and wind key points the paper clarifies the pearl river plume anatomy under two typical winds spring tide facilitates the supercritical pearl river tidal plume front tide determines tidal salt deficit flux strength wind determines the direction

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

chondritic lu hf in the early crust mantle system as recorded by zircon populations from the oldest eoarchean rocks of yilgarn craton west australia and enderby land antarctica abstract a persistent question in early earth investigations is the depletion history of the mantle as recorded in the isotopic compositions of the oldest rocks and minerals here we present new in situ sensitive high resolution ion microprobe shrimp u th pb geochronology and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icpms lu hf tracing data for individual zircons extracted from the oldest rocks of the antarctic and australian continents these are 3 88 and 3 85 ga orthogneisses from the gage ridge and mt sones in enderby land and a 3 73 ga meeberrie gneiss from the yilgarn craton the zircons from each sample show complex u th pb systematics due to the mobile behaviour of pb resulting in several age populations with discordant to reversely discordant arrays on concordia plots in contrast measured 176hf 177hf compositions from the same analysis sites show narrowly defined compositional ranges with 3 or fewer groups for each sample reflecting the resistance of 176hf 177hf in zircons to disturbance even under high temperature granulite conditions the initial 176hf 177hf calculated for the most primitive hf population for each sample using the best age estimate yields near chondritic weighted mean compositions of 1 6 0 5 1 6 0 4 and 0 6 0 7 epsilon units deviations in parts per 10 000 from a chondritic uniform reservoir chur reference at 3877 62 3850 50 and 3731 4 ma respectively these results provide no evidence for significant lu hf fractionation on the early earth expected to result from processes including accretion intra mantle differentiation or massive hadean crustal growth

siliciclastic sequence stratigraphic patterns in foreland ramp type basins stratal patterns within shelf depositional sequences are dependent on tectonically controlled subsidence rates and their regional patterns in active tectonic basin settings regional subsidence patterns can be very different from passive continental margin settings resulting in substantial modifications of the basic sequence stratigraphic model in ramp type foreland basins on the tectonically active side subsidence rates decrease seaward in contrast with passive continental margins where the opposite subsidence pattern exists analysis of the interplay between eustasy and subsidence suggests the existence of two tectono stratigraphic zones occurring proximally and distally with respect to the basin margin zone a is defined as the region within which the rate of subsidence always exceeds the rate of eustatic fall consequently relative sea level rises continuously during a eustatic cycle albeit at varying rates zone b is defined as the region within which the rate of eustatic fall periodically exceeds the rate of subsidence resulting in an interval of relative sea level fall during a eustatic cycle on the tectonically active sides of foreland basins zone a lies on the landward side of the basin margin proximal to the orogenic belt and zone b lies seaward off zone a away from the orogenic belt where subsidence rates are lower on passive continental margins because of the opposite subsidence patterns zone a lies seaward of zone b where subsidence rates are greater the location of the shoreline relative to these zones determines the stacking patterns and stratal discontinuities within a depositional sequence if the shoreline remains in zone a then only type 2 sequence boundaries will occur if sufficient sediment flux is available allowing the shoreline to prograde into zone b then type 1 sequence boundaries can occur in foreland basins these type 1 sequence boundaries would become type 2 sequence boundaries updip in zone a the pattern of seaward decreasing subsidence on the tectonically active sides of foreland basins results in characteristic longitudinal facies and stratal patterns when the two zones occur the updip region of the basin proximal to the orogenic belt is characterized by nearly continuous nonmarine deposition albeit at varying rates the downdip region is characterized by forced regressions and deposition primarily of lowstand and transgressive systems tracts a transitional region containing deposits of all three systems tracts commonly occurs between the updip and downdip areas

metalliferous coals of the westphalian a joggins formation cumberland basin nova scotia canada petrology geochemistry and palynology abstract five coals of westphalian a early middle pennsylvanian age were sampled from the joggins formation section exposed along chignecto bay at joggins nova scotia coal beds along the bay were mined beginning in the early 17th century yet there have been few detailed published investigation of the coal beds of this classic section the lowermost coal the upper coal 28 upper fundy is a high vitrinite coal with a spore assemblage dominated by arboreous lycopsid spores with tree ferns subdominant the upper portions of the coal bed have the highest ratio of well preserved to poorly preserved telinite of any of the coals investigated coal 19 clam coal has 88 total vitrinite but unlike the fundy coal bed the telinite has a poor preservation ratio and half the total vitrinite population comprises gelocollinite and vitrodetrinite the latter coal bed is directly overlain by a basin wide limestone bed the lower kimberly coal shows good preservation of vitrinite with relatively abundant telinite among the total vitrinite the middle kimberly coal which underlies the tetrapod bearing lycopsid trees found by lyell and dawson in 1852 exhibits an upward decrease in arboreous lycopod spores and an upward increase in the tree fern spore punctatisporites minutus telinite preservation increases upwards in the middle kimberly but overall is well below the preservation ratio of the upper fundy coal bed the coals all have high sulfur contents yielding up to 13 7 total sulfur for the lower lithotype of the upper fundy coal bed the kimberly coals are not only high in total and pyritic sulfur but also have high concentrations of chalcophile elements zinc ranging up to 15 000 ppm ash basis is present as sphalerite in fusain lumens arsenic and lead each exceed 6000 ppm ash basis in separate lithotypes of the kimberly coals together these data are consistent with elevated ph in planar mires the source of the elemental enrichment in this presumed continental section is enigmatic

observations of turbulence in a partially stratified estuary the authors present a field study of estuarine turbulence in which profiles of reynolds stresses were directly measured using an adcp throughout a 25 h tidal day the dataset that is discussed quantifies turbulent mixing for a water column in northern san francisco bay that experiences a sequence of states that includes a weak ebb and flood that are stratified followed by a strong and eventually unstratified ebb and flood these measurements show that energetic turbulence is confined to a bottom mixed layer by the overlying stratification examination of individual reynolds stress profiles along with profiles of richardson number and turbulent froude number shows that the water column can be divided into regions based on the relative importance of buoyancy effects using the measured turbulence production rate p the dissipation rate e is estimated the observed turbulence had values of e nn 2 20 all of the time and e nn 2 200 most of the time suggesting that the observed motions were buoyancy affected turbulence rather than internal waves however at times turbulent froude numbers in much of the upper water column were less than one indicating important stratification effects taken as a whole the data show that stratification affects the turbulent velocity variance q2 most severely that is observed reductions in u9w9 are largely associated with small values of q2 rather than with a dramatic reduction in the efficiency with which turbulent motions produce momentum fluxes finally the dataset is compared to predictions made using the popular mellor yamada level 2 5 closure these comparisons show that the model tends to underestimate the turbulent kinetic energy in regions of strong stratification where the turbulence is strongly inhomogeneous and to overestimate the turbulent kinetic energy in weakly stratified regions the length scale does not appear to compensate for these errors and as a result similar errors are seen in the eddy viscosity predictions it is hypothesized that the underestimation of q2 is due to an inaccurate parameterization of turbulence self transport from the near bed region to the overlying stratification

turbulent mixing in a strongly forced salt wedge estuary up to about 400 m 3 s 1 above which a majority of the mixing occurs offshore observed buoyancy fluxes were more consistent with the k turbulence closure than the mellor yamada closure and more total mixing occurred in the estuary with k calculated buoyancy fluxes were sensitive to horizontal grid resolution as a lower resolution grid yielded less integrated buoyancy flux in the estuary and exported lower salinity water but likely had greater numerical mixing

upland ecology of some late carboniferous cordaitalean trees from nova scotia and england abstract permineralised logs and charcoal fragments composed of dadoxylon type wood and derived from cordaitalean trees are described from the upper carboniferous westphalian of nova scotia and england they exclusively occur in sandstone bodies interpreted as the deposits of braided meandering and anastomosing river channels the architecture and ecology of this type of cordaitalean has not yet been satisfactorily described estimates of tree height using an allometric approach suggest that the largest trees attained an approximate height of ca 45 m the absence of true growth rings in the logs indicate that they grew under non seasonal humid tropical conditions however the presence of charred wood fragments implies that droughts of sufficient intensity to permit wildfire did occasionally occur the charcoal fragments are usually associated with incised poorly sorted chaotically bedded channel facies interpreted as flood deposits dramatic increases in runoff and sediment discharge are known to follow the destruction of vegetation in modern wildfire events and the high energy charcoal bearing channel facies described may represent a similar geomorphic response to cordaitalean vegetation fires geomorphic sensitivity to fire is greatest for steeply sloping terrains and it is therefore probable that the cordaitaleans described in this paper occupied upland settings this palaeoecological interpretation is supported by occurrence of the cordaitalean remains in river channel deposits immediately downstream of regions of palaeo upland and by the palynological record the presence of upland forests in late carboniferous times has important implications for numerical modelling of global geochemical cycles

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

microconchid tubeworms class tentaculita from the joggins formation pennsylvanian nova scotia canada microconchids have been described from the classic pennsylvanian locality at joggins nova scotia these encrusting tentaculitoid tubeworms have previously been mentioned and described from joggins

tide induced variation of the dynamics of a salt wedge estuary abstract the time variations of the salt wedge intrusion in the fraser estuary british columbia were monitored during a variety of tidal and run off conditions using instruments and sampling methods that provided high resolution of the velocity and water properties in space and time the salt wedge was found to vary considerably in position and vertical structure through the tidal cycle due to the interaction of the tidal flow with the density driven motion of the salt wedge during the flood the salt wedge progressed up the estuary as a gravity current while during the ebb the salinity structure was eroded by shear instability the difference in character of the flow between flood and ebb is attributed to the transition between a subcritical and supercritical internal froude number during flood tide the internal state is subcritical and the estuarine shear flow is maintained with a small amount of vertical mixing while in the supercritical ebb flow vertical shears become so large that the pycnoc

lu hf and sm nd isotopic systematics in chondrites and their constraints on the lu hf properties of the earth sm nd and lu hf isotopic data are presented for 19 chondritic meteorites six carbonaceous chondrites five l chondrites seven h chondrites and a single enstatite chondrite the primary goal of the study is to better define the bulk silicate earth bse reference values for hf isotopes except for one sample with lower sm nd the sm nd data define a cluster around the accepted reference values for chondrites and terrestrial planets giving a mean 147sm 144nd of 0 1960 0 0005 and a mean 143nd 144nd of 0 512631 0 000010 uncertainties are two standard errors it seems appropriate to retain the presently accepted sm nd reference parameters 147sm 144nd 0 1966 and 143nd 144nd 0 512638 when fractionation corrected to 146nd 144nd 0 7219 lu hf isotopic data are not clustered but spread along an approximate 4 5 ga isochron trend with a range of 176lu 177hf from 0 0301 to 0 0354 the data are similar to many of the samples of chondrites presented by bizzarro et al nature 421 2003 931 but lack the range to lower lu hf shown by those authors our chondrite data define a regression line of 4 44 0 34 ga when 1 867 10 11 year 1 is used for the decay constant of 176lu science 293 2001 683 earth planet sci lett 219 2004 311 324 combining our data with the main population of analyses from bizzarro et al nature 421 2003 931 yields 4 51 0 24 ga unless samples of eucrite meteorites and deviating replicates of chondrites with 176lu 177hf less than 0 030 are employed no combination of the main population of chondrite lu hf data yields a regression with sufficiently low error to constrain the decay constant of 176lu sample heterogeneity seems to hinder the acquisition of reproducible lu hf analyses from small manually ground pieces of chondrites and we suggest that analysis of powders prepared from large volumes of meteorite will be needed to adequately characterize the lu hf isotope systematics of chondritic reservoirs and of bse our results for carbonaceous chondrites show higher average 176lu 177hf and 176hf 177hf than ordinary chondrites and the mean of carbonaceous chondrites also coincides with replicate analyses of a powder representing a large volume of meteorite the allende powder from the smithsonian institution use of the carbonaceous chondrite mean for bse lu hf characteristics results in a bse hf nd point that lies well within the array of terrestrial compositions and leads to plausible initial ehf values for precambrian rocks an improved objective resolution of meteorite data and of meteoritic models for the earth needs to occur before bse can be established for lu hf

salt intrusion in the tweed estuary abstract results are presented from a 2 week field programme in the tweed estuary u k maximum values of the empirically based estuarine richardson number rie occurred during neap tides and minimum values occurred during spring tides estimated values of rievaried between 0 3 and 2 3 suggesting the occurrence of partially mixed to stratified conditions depending on tidal state and freshwater inflow these relatively large values of riewere consistent with both observed strong salinity stratification and large salt fluxes due to vertical shear transport low values 0 5 values in the halocline a velocity maximum occurred within the halocline during the early flood wave like spatial oscillations of the halocline occurred on the ebb the oscillation troughs were situated above deep holes located just down estuary of the rail and old road bridges there was an indication that the constricted flow between the bridges arches resulted in enhanced mixing of near surface waters and a thickening of the halocline it is also possible that these wave like structures were stationary near critical internal lee waves triggered by the deep holes trapping of high salinity waters occurred on the ebb saline pools were isolated within a deep hole or deeper section of bed by the falling halocline when the salt wedge moved further down estuary the trapped waters were subjected to strongly ebbing overlying freshwater and were subsequently entrained and flushed the salinity intrusion was a strong function of spring neap tidal state and a weaker function of freshwater inflow the estimated salinity intrusion varied from about 4 7 to 7 6 km during the fieldwork period the strong dependence on tidal range followed from the comparable lengths of the tidal excursion and salinity intrusion long excursion lengths were also partly responsible for the short residence or flushing times and their strong dependence on spring neap tidal state for typical summer freshwater inflows of 40 m3s 1 the estimated residence times varied from one tide at large spring tides removal on one ebb to two tides removal over two ebbs at neap tides computed residence times were shorter for typical winter inflows

fvcom validation experiments comparisons with roms for three idealized barotropic test problems 1 the unstructured grid finite volume coastal ocean model fvcom is evaluated using three idealized benchmark test problems the rossby equatorial soliton the hydraulic jump and the three dimensional barotropic wind driven basin these test cases examine the properties of numerical dispersion and damping the performance of the nonlinear advection scheme for supercritical flow conditions and the accuracy of the implicit vertical viscosity scheme in barotropic settings respectively it is demonstrated that fvcom provides overall a second order spatial accuracy for the vertically averaged equations i e external mode and with increasing grid resolution the model computed solutions show a fast convergence toward the analytic solutions regardless of the particular triangulation method examples are provided to illustrate the ability of fvcom to facilitate local grid refinement and speed up computation comparisons are also made between fvcom and the structured grid regional ocean modeling system roms for these test cases for the linear problem in a simple rectangular domain i e the winddriven basin case the performance of the two models is quite similar for the nonlinear case such as the rossby equatorial soliton the second order advection scheme used in fvcom is almost as accurate as the fourth order advection scheme implemented in roms if the horizontal resolution is relatively high fvcom has taken advantage of the new development in computational fluid dynamics in resolving flow problems containing discontinuities one salient feature illustrated by the three dimensional barotropic winddriven basin case is that fvcom and roms simulations show different responses to the refinement of grid size in the horizontal and in the vertical

ree bearing sulfide in bishunpur ll3 1 a highly unequilibrated ordinary chondrite abstract this is a report of the first unambiguous discovery of rare earth elements ree in iron sulfide fes in an ordinary chondrite the content and the pattern of ree as well as the reduced state of the chondrules with the ree containing sulfide suggest that the sulfide inside the bishunpur ll3 1 chondrules is of igneous origin formed during crystallization of the chondrule melts the similarities in the content and the pattern of ree between chondrule sulfide and matrix sulfide in bishunpur indicate a genetic relationship the presence of igneous sulfide inside chondrules provides constraints on the ambient nebular temperature and the duration of chondrule formation the results of this study allow on the basis of ree content and pattern discrimination of igneous sulfide from condensate and secondary sulfide in chondrites and other interplanetary materials

ree and hf distribution among mineral phases in the cv ck clan a way to explain present day hf isotopic variations in chondrites chondrites are among the most primitive objects in the solar system and constitute the main building blocks of telluric planets among the radiochronometers currently used for dating geological events sm nd and lu hf are both composed of refractory lithophile element they are thought to behave similarly as the parent elements sm and lu are generally less incompatible than the daughter elements nd and hf during geological processes as such their respective average isotopic compositions for the solar system should be well defined by the average of chondrites called chondritic uniform reservoir chur however while the sm nd isotopic system shows an actual spread of less than 4 in the average chondritic record the lu hf system shows a larger variation range of 28 bouvier a vervoort j d and patchett p j 2008 the lu hf and sm nd isotopic composition of chur constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets earth planet sci lett 273 48 57 to better understand the contrast between sm nd and lu hf systems the ree and hf distribution among mineral phases during metamorphism of karoonda ck and vigarano type cv carbonaceous chondrites has been examined mineral modes were determined from elemental mapping on a set of five ck chondrites from types 3 6 and one cv3 chondrite trace element patterns are obtained for the first time in all the chondrite forming minerals of a given class ck chondrites as well as one cv3 sample this study reveals that ree are distributed among both phosphates and silicates only 30 50 of sm and nd are stored in phosphates at least in chondrites types 3 5 as such they are not mobilized during early stages of metamorphism the remaining fraction of sm and nd is distributed among the same mineral phases these elements are therefore not decoupled during metamorphism of the whole rock total of lu the fraction held in phosphate decreases significantly as the degree of metamorphism increases 30 for types 3 and 4 less than 5 in type 6 in contrast to lu hf is mainly hosted by silicates with little contribution from phosphates throughout the ck metamorphic sequence a significant part of sm and nd are stored in phosphates in types 3 5 and these elements behave similarly during ck chondrite metamorphism that explains the robustness of the sm nd ratios in chondrites through metamorphism and the slight discrepancies observed in the present day isotopic nd values in chondrites on the contrary lu and hf are borne by several different minerals and consequently they are redistributed during metamorphism induced recrystallization the lu hf ratios are therefore significantly disturbed during chondrites metamorphism leading to the high discrepancies observed in present day hf isotopic values in chondrites

internal hydraulics and mixing in a highly stratified estuary shipboard acoustic doppler current profiler and conductivity temperature depth data obtained during highly stratified conditions in the hudson river estuary along a section of variable width and breadth are presented the observations emphasize tidal period asymmetries in the vertical structure of current and salinity however these asymmetries exhibit significant along channel structure which is determined by channel morphology during the ebb the flow is linearly sheared and steep halocline slopes in the vicinity of channel contractions are maintained by momentum advection a minimum in vertical shear across the pycnocline occurs in channel contractions during food the pycnocline sharpens and flattens with a middepth velocity maximum embedded in the pycnocline which separates a stratified surface layer from a bottom mixed layer the along channel structure in vertical shear is consistent with a lateral vorticity equation estimates of richardson numbers suggest that vertical mixing across the pycnocline is enhanced downstream of channel contractions

broadly distributed and locally enhanced turbulent mixing in a tidal estuary abstract spatial variations of vertical turbulent mixing along a stretch of the hudson river estuary are examined with focus on the vicinity of a hydraulic control point at the george washington bridge at which the cross section narrows and the thalweg takes a bend richardson numbers are lowered and mixing is enhanced downstream of this modest morphological feature qualitatively following predictions based on hydraulic theory by chant and wilson the enhancement in the viscous dissipation rate e is only a modest factor of 2 3 however extending over 2 km along the river upon averaging over tidal and fortnightly cycles and multiple cruises streamwise variations of e along the probed 15 km stretch of the estuary are surprisingly small given that individual depth averages of e across the halocline vary by over three orders of magnitude the principal result is that the observed part of the hudson river showed strong broadly distributed mixing everywhere with little local concentration

sm nd systematics of chondrites we have studied the 147sm 143nd and 146sm 142nd isotopic systems in phosphate fractions and chondrules from six ordinary chondrites and one carbonaceous chondrite previously dated with pb pb method 147sm 144nd ratios vary between 0 182 and 0 191 in phosphates and between 0 179 and 0 243 in chondrules the 147sm 143nd isochron regression through all 34 phosphate and chondrule analyses yields a date of 4588 100 ma and is in good agreement with more precise pb pb dates of the same chondrites the initial 143nd 144nd is 0 50665 0 00014 the same analyses define a 146sm 142nd isochron with a slope corresponding to 146sm 144sm 0 0075 0 0027 initial 142nd 144nd 1 14160 0 00011 corresponds to e142nd 2 62 0 93 compilation of the published chondritic whole rock sm nd analyses yields the median 147sm 144nd 0 1964 0 0003 0 0007 which is our preferred chondritic uniform reservoir chur value using this value and its error limits we find the present day chur 143nd 144nd 0 512637 0 000009 0 000021 from the chondritic sm nd isochron that includes all available data for whole rocks chondrules and phosphates this value is identical within error with the currently accepted number an estimate of the bulk earth 147sm 144nd 0 1941 0 0059 is obtained from intercept of chondritic 146sm 142nd isochron with the terrestrial value of 142nd 144nd this estimate is independent of measured sm nd ratios in chondrites the same approach was applied to published 146sm 142nd internal isochrons for differentiated meteorites and yielded similar although less precise values our data are completely consistent with the currently accepted chur parameters and substantiate their use as terrestrial reference values

ree and actinide microdistribution in sahara 97072 and alha77295 eh3 chondrites a combined cosmochemical and petrologic investigation abstract we report the results of rare earth elements rees and u th inventory of individual minerals oldhamite enstatite and niningerite in two of the most unequilibrated and primitive eh3 known so far alha77295 and sahara 97072 under the highly reducing condition that prevailed during the formation of enstatite chondrites rees are mainly chalcophile and concentrated in oldhamite the study is guided by detailed petrographic investigations of the individual minerals in chondrules complex sulfide metal clasts and enstatite dominated matrices we developed two textural parameters in order to resolve the evolution of oldhamite condensates and their residence in the solar gas prior to their accretion in the individual objects or in matrices and relate these textural features to the measured ree patterns of the individual oldhamite crystals these textural parameters are the crystal habit of oldhamite grains idiomorphic or anhedral and their host assemblages ree concentrations were measured by sims and la icpms oldhamite grains display ree enrichments 10 100 ci four types of ree patterns are encountered in oldhamite in alha77295 in general the ree distributions cannot be assigned to a specific oldhamite bearing assemblage the most represented ree pattern is characterized by both slight to large positive eu and yb anomalies and is enriched in light rees relative to heavy rees this pattern is present in 97 of oldhamite in sahara 97072 suggesting a different source region in the reduced part of the nebula or different parental eh asteroids for the two eh3 chondrites different parental asteroids are also supported by mgs fes zoning profiles in niningerite grains adjacent to troilite revealing both normal and reverse zoning trends and different mns contents the observed homogeneity of ree distribution in oldhamite grains in sahara 97072 is not related to the mild metamorphic event identified in this meteorite that caused breakdown of the major k and rb bearing sulfide djerfisherite ree concentrations in enstatite range between 0 2 and 8 ci hence enstatite is an important ree host next to oldhamite most patterns are characterized by negative eu and yb anomalies niningerites are negligible contributors to bulk eh3 ree inventory average positive eu and yb anomalies observed in most oldhamite are complimentary to the negative ones in enstatite thus explaining the flat patterns of the bulk meteorites the condensation calculations based on cosmic abundances predict that the first oldhamite condensates should have flat ree patterns with eu and yb depletions since eu and yb condense at lower temperature than other ree however this pattern is seen in enstatite our findings are at odds with the predicted negative eu and yb anomalies in oldhamite earliest condensates from a closed system in a reduced solar source our petrographic mineral chemistry and ree abundances of oldhamite enstatite and niningerite discards an origin of oldhamite by impact melting rubin et al 2009 our results do not support in first order the scenario of the incorporation of ree in the earth s core to explain 142nd excess in terrestrial samples relative to chondrites because oldhamite is the major ree carrier phase and has super chondritic sm nd ratios

the neodymium stable isotope composition of the silicate earth and chondrites abstract the non chondritic neodymium nd 142nd 144nd ratio of the silicate earth potentially provides a key constraint on the accretion and early evolution of the earth yet it is debated whether this offset is due to the earth being formed from material enriched in s process nd isotopes or results from an early differentiation process such as the segregation of a late sulfide matte during core formation collisional erosion or a some combination of these processes neodymium stable isotopes are potentially sensitive to early sulfide segregation into earth s core a process that cannot be resolved using their radiogenic counterparts this study presents the first comprehensive nd stable isotope data for chondritic meteorites and terrestrial rocks stable nd measurements were made using a double spike technique coupled with thermal ionisation mass spectrometry all three of the major classes of chondritic meteorites carbonaceous enstatite and ordinary chondrites have broadly similar isotopic compositions allowing calculation of a chondritic mean of 146 144nd 0 025 0 025 2 s d n 39 enstatite chondrites yield the most uniform stable isotope composition 146 144nd 26 ppm with considerably more variability observed within ordinary 146 144nd 72 ppm and carbonaceous meteorites 146 144nd 143 ppm terrestrial weathering nucleosynthetic variations and parent body thermal metamorphism appear to have little measurable effect on 146 144nd in chondrites the small variations observed between ordinary chondrite groups most likely reflect inherited compositional differences between parent bodies with the larger variations observed in carbonaceous chondrites being linked to varying modal proportions of calcium aluminium rich inclusions the terrestrial samples analysed here include rocks ranging from basaltic to rhyolitic in composition morb glasses and residual mantle lithologies all of these terrestrial rocks possess a broadly similar nd isotope composition giving an average composition for the bulk silicate earth of 146 144nd 0 022 0 034 n 30 in the samples here magmatic differentiation appears to only have an effect on stable nd in highly evolved magmas with heavier 146 144nd values observed in samples with 70 wt sio2 the average stable nd isotope composition of chondrites and the bulk silicate earth are indistinguishable at the 95 confidence level however mantle samples do possess variable stable nd isotope compositions 146 144nd 75 ppm with an average 146 144 nd value of 0 008 if these heavier values represent the true composition of pristine mantle then it is not possible to completely rule out some role for core formation in accounting for some of the offset between the mantle and chondrites overall these results indicate that the mismatch of 142nd between the earth and chondrites is best explained by a higher proportion of s process nd in the earth rather than partitioning into sulfide or s rich metal in the core

tectonic event stratigraphy in a fluvio lacustrine strike slip setting the boss point formation westphalian a cumberland basin maritime canada abstract the boss point formation westphalian a was deposited in a rapidly subsiding strike slip basin the formation about 800 m thick comprises alternate braidplain and lacustrine facies associations sixteen megacycles defined by sharp but nonerosive lacustrine flooding surfaces each comprise a lower lacustrine and an upper braidplain package braidplain deposits invariably scour deeply into lacustrine strata the lacustrine facies association consists of very fine sandstone mudstone claystone coal and limestone deposited in shallow hydrologically open freshwater lakes lakes were filled by small elongate river dominated deltas and by suspended and biogenic sediment sand rich deltaic facies represent mouth bar subaqueous levee crevasse channel and splay and straight and sinuous distributary channel subenvironments evidence of wave reworking is very scarce interdeltaic areas accumulated platy gray mudstone as interdistributary bays aggraded to water level they were subject to oxidation and pedogenic modification forming bright colors prismatic desiccation fabrics pseudo anticlines and calcretes thin but laterally extensive possibly up to 40 km abandonment facies comprising black organic rich mudstones coals and ostracod limestones suggest periods of clastic starvation dunes current ripples and rarely adhesion ripples are common on the top surfaces of braidplain sandstone packages preserved beneath a blanket of lacustrine mudstone rare oscillation ripples attest to localized reworking of the fluvial sand during or soon after flooding flooding surfaces can be traced for 12 km and possibly up to 40 km and are attributed to instantaneous subsidence along the northwest margin of the basin during major earthquakes one locality preserves evidence of abrupt 180 paleoflow reversals above and below a lacustrine unit this is interpreted to record abrupt basin tilting first to the northwest forming a lake that filled from the southeast followed by tilting to the southeast we interpret boss point megacycles to reflect the interaction of episo ic tectonic subsidence with longer term changes in sediment supply controlled by cyclical climatic variation in the milankovitch band during periods of pronounced wet dry seasonality when clastic supply was high sandy and gravelly braidplain deposits prevailed and any lakes that formed by earthquake related subsidence were rapidly filled during more humid periods higher vegetative cover greatly reduced clastic supply and lakes persisted for many thousands of years hydrologic changes accompanying the transition from relatively humid to strongly seasonal wet dry periods might have resulted in the deep fluvial erosion observed at the base of each braidplain package

the pennsylvanian tropical biome reconstructed from the joggins formation of nova scotia canada the pennsylvanian langsettian joggins formation contains a diverse fossil assemblage first made famous by lyell and dawson in the mid 19th century collector curves based on c 150 years of observation suggest that the joggins fossil record is relatively complete a key feature of the site is that fossils occur in par autochthonous assemblages within a narrow time interval

magnetic polarity stratigraphy and carboniferous paleopole positions from the joggins section cumberland structural basin nova scotia one hundred seventy seven samples were taken in stratigraphic sequence in redbeds from approximately 2100 m of namurian westphalian strata from the shepody enrage boss point and lower joggins formations between minudie and joggins nova scotia for the purpose of constructing a magnetic polarity stratigraphy in addition five samples from each of four sites were taken from north dipping strata of the cumberland group for the purpose of conducting a fold test for the joggins formation this yields a total coverage of 412 samples from approximately 2400 m of south dipping strata in the composite section when combined with previous results from the maringouin peninsula divenere and opdyke 1990 and 88 samples from north dipping strata collected for the purpose of conducting fold tests two components of magnetization are identified in these sediments a prefolding component termed c and a synfolding component termed b the present results extend the mid carboniferous magnetic polarity stratigraphy to include eight normal and eight reversed magnetozones in the namurian a through early westphalian a interval the results are dominantly to completely reversed in samples from the remainder of the westphalian a and the westphalian b but because of the complication of varying degrees of remagnetization and an 800 m sampling gap it is not possible to verify the base of the permo carboniferous reversed superchron in this time period northward plate motion is inferred from an observed shallowing of inclinations upsection a 5 7 cm yr average poleward drift rate is calculated for this time period from these results yielding a low latitude southern hemisphere paleogeographic position