observations and geologic significance of marine snow in a shallow water partially enclosed marine embayment because of their fragile nature marine snow sized aggregates aggregates 0 5 mm in longest dimension have been generally overlooked in shallow water environments we report in situ observations and measurements in cape lookout bight north carolina that indicate that marine snow is probably always present and usually abundant underwater photographs show that over a period of hours marine snow varies in size from 8 to 71 10 5 ml and in abundance from 291 to 489 l 1 but that such variations in size and abundance are not obviously related to tide total suspended sediment concentration or current speeds in the 10 to 20 cm s 1 range photographs and concurrent transmissometer records suggest that variations in size shape and abundance of marine snow may be sufficiently great that particulates do not remain optically constant and thus affect beam transmission irrespective of total suspended sediment concentration levels marine snow is significant geologically in that it has high settling rates 50 to 200 m per day and may be the package in which much of the vertical mass flux occurs if so it offers an explanation for the high accumulation rates observed in coastal and estuarine fluid mud deposits

abrupt mousterian aurignacian boundary at c 40 ka bp accelerator 14c dates from l arbreda cave catalunya spain abstract the cultural transition from mousterian to aurignacian is abrupt at l arbreda cave and occurs within a homogeneous sedimentary unit with no visible lithologic changes fragments of milligram size charcoal were collected immediately above and below the cultural boundary for radiocarbon dating by accelerator four charcoal fragments from the lowest basal aurignacian level yielded dates of 37 7 1 0 37 7 1 0 39 9 1 2 and 38 7 1 2 ka bp average 38 5 1 0 ka bp these ages are similar to three dates from the same cultural horizon at el castillo cave in cantabria and both sets of dates are significantly older than the earliest reported for the aurignacian in the aquitaine and in other parts of central and western europe the dates are in accord with similarly early dates for aurignacian in bulgaria and suggest that appearance of aurignacian peoples is synchronous across europe three fragments from the uppermost mousterian level yielded dates of 39 4 1 4 34 1 0 75 and 41 4 1 6 ka bp discounting the spurious 34 1 ka bp result these dates are slightly older average 40 4 1 4 ka bp but overlap with counting error the basal aurignacian dates the data show that the transition from mousterian to aurignacian was chronologically abrupt at this location these results strongly support the replacement hypothesis

the source of alluvium in large rivers of the lower coastal plain of north carolina summary despite high erosion rates in the north carolina piedmont and extensive sediment delivery to coastal plain reaches of piedmont draining streams sediment budget studies and estuarine sedimentology suggest that relatively little piedmont derived sediment reaches the lower coastal plain dominant sources of alluvium in the lower coastal plain reaches of piedmont draining rivers were inferred from alluvial floodplain soils piedmont derived alluvial soils are characterized by mixed mineralogy and presence of mica flakes alluvial soils derived from erosion of coastal plain uplands are characterized by siliceous mineralogy and an absence of mica flakes the coastal alluvial soils which occur in fluvial estuarine transition zones being drowned by rising sea level are organic or buried organic soils the distribution of these soils along the tar and neuse rivers in the lower coastal plain shows almost complete domination of fluvial estuarine transition zones by soils of the coastal group and by soils of the coastal plain and coastal groups for 40 km or more inland of the upper estuaries no soils of the piedmont group were found in fluvial estuarine transition zones or lowermost fluvial reaches this suggests that the piedmont is a relatively insignificant source of alluvium in the lower reaches of the rivers the absence of piedmont sediment in the lower coastal plain is attributed to extensive sediment storage upstream dilution by coastal plain sediments and coastal plain erosion rates which may be higher than was previously believed

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

calibration of an empirical thermometer and oxybarometer based on the partitioning of sc y and v between olivine and silicate melt the evolution of basaltic magmas depends on their redox state hence oxygen fugacity but there is increasing evidence that this intensive thermodynamic variable may be less well understood in basalts than commonly supposed the redox state of terrestrial basalts has to a large extent been inferred from the fe3 fe2 ratios of their quenched glasses however this quantity appears to be significantly affected during late and post eruptive processes in magmatic systems e g by degassing charge transfer reactions of redox variable species and alteration so that the degree to which the fe3 fe2 ratios preserved in basaltic glasses reflect the oxidation state of the magma at high temperature is unclear because olivine is the first silicate mineral to crystallize from primitive basaltic liquids on cooling following decompression the equilibrium partitioning relations preserved in olivine phenocrysts in basalts are in principle less disturbed by these late and post eruptive processes and therefore may better reflect the high temperature pre eruptive conditions of the magma here we calibrate an oxybarometer based on the strong sensitivity of the partitioning of vanadium between olivine and silicate melt to oxygen fugacity our empirical parameterization calibrated over a range of redox conditions between four log10 units above and below the quartz fayalite magnetite qfm oxygen buffer takes into account the effects of temperature olivine composition i e mg fe ratios and melt composition namely the activities of cao sio2 alo1 5 nao0 5 and ko0 5 and allows oxygen fugacity determinations to within 0 25 log10 units we also explore the sensitivity of the exchange partitioning of sc and y between olivine and melt to temperature as a geothermometer our calibration indicates that this geothermometer allows temperature to be estimated to within 158c but precision is strongly dependent on the sc and ymeasurements in olivine and melt

the geochemical evolution of clinopyroxene in the roman province a window on decarbonation from wall rocks to magma abstract we present results from magma carbonate interaction experiments designed to shed light on the geochemical evolution of clinopyroxene in the roman province central italy atmospheric pressure experiments were performed at 1140 1160 and 1180 c under nno mh and air oxygen buffering conditions the starting materials were a shoshonite and a phonotephrite doped with different amounts of cao and cao mgo whose stoichiometric proportions reproduced the assimilation by magmas of calcite and dolomite respectively the results show that clinopyroxenes spinels and residual glasses are ubiquitous phases in all run products calcite doped runs crystallize more clinopyroxene than dolomite doped runs at the same conditions this leads to the formation of strong desilicated cao rich melts showing compositions comparable to those of magmatic skarns during magma carbonate interaction the content of fe3 in clinopyroxene increases with increasing fo2 promoting the substitution of al for si in tetrahedral site local charge imbalances are also compensated by the incorporation of highly charged cations such as ti into the crystal lattice according to this cation substitution al ca fe3 ti rich clinopyroxenes of the skarn environment testify to continuous co2 fluxes produced by the thermal decomposition of carbonate wall rocks nevertheless the oxidative capacity of co2 progressively decreases from the skarn shells towards the interior of the magma chamber driving the crystallization of si fe2 mg rich clinopyroxenes

primary magmatic calcite reveals origin from crustal carbonate abstract we have investigated lava flows representative of the whole eruptive history of the colli albani ultrapotassic volcanic district central italy one of the most intriguing features concerning some of these lava flows is the occurrence of primary magmatic calcite in the groundmass the primary magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i interstitially associated with clinopyroxene nepheline and phlogopite ii in spherical ocelli associated with nepheline fluorite and tangentially arranged clinopyroxene and iii in corona like reaction zones around k feldspar xenocrysts these microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass implying that the temperature of the system was above the solidus of the hosted lava flow 850 c geochemical features of calcite crystals i e stable isotope values and trace element patterns corroborate their primary nature and give insights into the origin of the parental carbonate melt the trace element patterns testify to a high temperature crystallization process not hydrothermal involving a carbonate melt coexisting with a silicate melt the high 18o around 27 smow and wide 13c 18 to 5 pdb values measured in the calcites preclude a mantle origin but are consistent with an origin in the crust in this framework the crystallization of calcite can be linked to the interaction between magmas and carbonate bearing wall rocks and in particular to the entrapment of solid and or molten carbonate in the silicate magma the stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn eruptive time scales

petrological statistical approach to interpret recent and subrecent lagoon subfacies idku nile delta of egypt abstract an approach combining petrology and statistics cluster analysis is developed to better distinguish a series of subfacies in surficial and short core samples from idku lagoon in the northwestern nile delta egypt the method integrates lithology physical and biogenic structures grain size and composition of the sand size fraction seven lithofacies eight grain size types and six clusters reveal comparable geographic distributions that are a direct response to geomorphic setting and depositional processes both of which have been modified by man although positioned in an arid setting and affected by anthropogenic factors land reclamation pollutants regional subfacies distribution patterns in idku lagoon are largely a function of the spatial configuration of freshwater dominated to brackish to higher salinity dominated near inlet zones typical of lagoons receiving significant freshwater input within idku a northern depositional province near the inlet and along the coastal sand barrier is defined by associations of terrigenous and coarse grained sediment types a southern province bounded by lagoon margins and marshes is characterized by finer grained sediment types with a high biogenic content recording lower energy levels the petrological statistical approach is used to identify and interpret lagoon subfacies in older to 6000 years b p core sections in idku region and in former abu qir lagoon additionally cluster analysis serves to determine specific lagoon subfacies from hand samples alone whether from surface grabs or cores this is based on a comparison of lithofacies and clusters determined for surficial and short core samples in the idku region to test the method a separate cluster analysis also using surficial and short core samples was used to define manzala lagoon subfacies in the northeastern nile delta results are generally comparable to those obtained in the idku study and show a close relation among manzala lagoon subfacies geomorphic configuration and depositional processes the petrological statistical method could be applied to other regions and also to the geological record

formation and preservation of pedogenic carbonates in south india links with paleo monsoon and pedological conditions clues from sr isotopes u th series and rees the influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the western ghats karnataka plateau south west india has been studied along the climosequence the current mean annual rainfall mar varies within a 80 km transect from 6000 mm at the edge of the plateau to 500 mm inland pedogenic carbonates occur in the mar range of 500 1200 mm in the semi arid zone mar 500 900 mm carbonates occur i as rhick hardpan calcretes on pediment slopes and ii as nodular horizons in polygenic black soils i e vertisols in the sub humid zone mar 900 1500 mm pedogenic carbonates are disseminated in the black soil matrices either as loose irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size they also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate cemented lumps of centimetric to decimetric size chemical and isotopic sr 87 sr 86 compositions of the carbonate fraction were determined after leaching with 0 25 n hcl the corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed the trend defined by the sr 87 sr 86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition considering the residual fraction of each sample as the most likely lithogenic source of ca in carbonates it is estimated that from 24 to 82 55 on average of ca is derived from local bedrock weathering leading to a consumption of an equivalent proportion of atmospheric co2 these values indicate that climatic conditions were humid enough to allow silicate weathering mar at the time of carbonate formation likely ranged from 400 to 700 mm which is 2 to 3 fold less than the current mar at these locations the sr u and mg contents and the u 234 u 238 activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation the relatively high concentrations of sr u and mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite possibly due to a better confinement of the pore waters which is supported by their high u 234 u 238 signatures and or to higher content of dissolved carbonates in the pore waters the occurrence of ce mn and fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation the carbonate ages determined by the u th method range from 1 33 0 84 kyr to 7 5 2 7 kyr and to a cluster of five ages around 20 kyr i e the last glacial maximum period the young occurrences are only located in the black soils which therefore constitute sensitive environments for trapping and retaining atmospheric co2 even on short time scales the maximum age of carbonates depends on their location in the climatic gradient from about 20 kyr for centimetric nodules at mule hole mar 1100 mm yr to 200 kyr for the calcrete at gundlupet mar 700 mm yr durand et al 2007 the intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils c 2010 elsevier ltd all rights reserved

two high levels of continental waters in the southern tunisian chotts at about 90 and 150 ka uranium and thorium content and activity ratios were measured on 20 samples 19 molluscs and 1 calcareous concretion from the great chotts in southern tunisia results were studied by the isochron method and by age frequency histograms they suggest that two major flood episodes took place about 150 and 90 ka uranium activity ratios indicate a ground water supply of continental origin in agreement with biological indicators which show large variations in salinity from fresh to marine like conditions the existence of a lacustrine phase radiocarbon dated to 17 40 ka as previously suggested for the northern sahara is highly questionable

new 230th u and 14c ages from lake lahontan carbonates nevada usa and a discussion of the origin of initial thorium five sets of coeval lacustrine carbonate samples from pleistocene lake lahontan in western nevada were dated by both the ams 14c and 230th u isochron methods all five groups of samples were analyzed for u th isotopes by alpha spectrometry and one of the groups was additionally measured by thermal and secondary ionization mass spectrometry tims and sims for comparison the 14c ages were corrected to calendar years using the calibration curve recommended by bard et al 1992 without local reservoir correction on the 14c ages mean 230th u isochron ages of some sets are apparently older than their calendar corrected 14c ages by up to 2300 years modern carbon contamination of these carbonate samples through recrystallization or deposition of secondary calcite is likely to be responsible for part of the age discrepancies we explored additional biases associated with the isochron ages maybe produced by the presence of initial th coprecipitated from the lake water it can be shown that if dissolved hydrogenous th is directly incorporated into the pure carbonates then the three component mixing among 1 detrital th 2 hydrogenous th adsorbed on detritus and 3 hydrogenous th incorporated by the carbonate can introduce a positive age bias we have developed an approach to estimate the magnitude of this bias of the lake lahontan carbonates the preliminary estimates suggest a positive age bias of 1000 to 2000 years for two sets of the samples

element partitioning between minerals and melt melt composition and melt structure abstract mineral melt trace element partition coefficients d i mineral melt concentration ratio mineral melt can vary by up to two orders of magnitude in the melt composition range of natural magmatic liquids as most geochemically interesting minor and trace elements are network modifiers in silicate melts one would expect as observed positive correlation between mineral melt partition coefficients d i mineral melt and the degree of polymerization of the silicate melt nbo t linear relationships between d i mineral melt and nbo t sometimes exist over restricted nbo t ranges where the type of q n species in the melt does not change and their abundance does not vary greatly other experimental d i mineral melt vs nbo t data suggest log linear or log log relations in some cases whereas in other studies there are no simple relationships between d i mineral melt and nbo t of the melt when relating mineral melt partition coefficients to degree of melt polymerization nbo t it is assumed that a principal melt structural control on d i mineral melt is the activity of nonbridging oxygen in the melt a nbo the a nbo is related to nbo t the nbo t is not however a quantitative measure of a nbo because the nonbridging oxygens in coexisting q n species in melts are energetically non equivalent this is evident in relationships between activity coefficient ratios of melt network modifying cations i j where the ionization potentials of i and j differ and nbo t of the melt such relationships are parabolic with minima or maxima at nbo t near 1 and resemble the relations of abundance ratio x q3 x q2 vs nbo t of the melt interestingly this nbo t value is near that of natural basalt melt these observations suggest that i nbo q 3 and j nbo q 2 bond characteristics differ from one another govern trace element solution behavior in silicate melts and therefore control the effect of melt composition on mineral melt partitioning in silicate systems

sedimentation in the albemarle pamlico lagoonal system synthesis and hypotheses abstract relative to its size and in terms of its sedimentary processes the albemarle pamlico lagoonal system is one of the least studied coastal lagoons in the united states a synthesis of the current knowledge about sedimentation in the albemarle pamlico system is presented based on archived data published over the last 30 years and new unpublished data collected over the past two years the literature reflects considerable past research effort on sediment grain size and mineralogy but very little on sediment dynamics or flux of suspended particulate material the physiographic complexity of the system which includes barrier islands a deep central basin four river systems and extensive fringing embayments does not appear to be reflected in the form of sedimentologic complexity in general the surficial cover of sediments ranges from medium sands in the inlets and on the shoals of the outer banks to fine silts and organic rich clays in the central basin and embayed river mouths and channels the transition zones from sands to muds are typically sharp and are usually related to bathymetry it is concluded that 1 parts of the albemarle pamlico lagoonal system may have high sedimentation rates relative to rates of sediment input and that rapid vertical flux by large aggregates offers an explanation for the fluid mud deposits that would otherwise be absent 2 fine grained sediments that escape the estuarine sediment trap are confined to pamlico sound by the outer banks barrier islands and are simply recycled until finally coming to rest in the deep basin 3 short term advective processes are secondary to longer term processes such as sea level rise and barrier island migration in the net advection of albemarle pamlico sediments and 4 at the present rate of terrigenous sediment input and relative sea level rise the albemarle pamlico lagoonal system will never reach a sediment filled state

hydrous basalt limestone interaction at crustal conditions implications for generation of ultracalcic melts and outflux of co 2 at volcanic arcs abstract high degassing rates for some volcanoes typically in continental arcs e g colli albani volcanic district etna vesuvius italy merapi indonesia popocatepetl mexico are thought to be influenced by magma carbonate interaction in the crust in order to constrain the nature of reaction and extent of carbonate breakdown we simulated basalt limestone wall rock interactions at 0 5 1 0 gpa 1100 1200 c using a piston cylinder and equal mass fractions of calcite caco3 and a hydrous 4 wt h2o basalt in a layered geometry contained in aupd capsules all experiments produce melt fluid calcite clinopyroxene plagioclase calcic scapolite spinel with increasing t plagioclase is progressively replaced by scapolite clinopyroxene becomes cats rich and fluid proportion as inferred from vesicle population increases at 1 0 gpa 1200 c our hydrous basalt is superliquidus whereas in the presence of calcite the experiment produces calcite clinopyroxene scapolite melt with the consumption of calcite with increasing t and decreasing p melt on a volatile free basis becomes silica poor 58 1 wt at 1 0 gpa 1100 c to 34 9 wt at 0 5 gpa 1200 c and cao rich 6 7 wt at 1 0 gpa 1100 c to 43 7 wt at 0 5 gpa 1200 c whereas al2o3 drops e g 19 7 at 1100 c to 12 8 wt at 1200 c at 1 0 gpa as clinopyroxene becomes more cats rich high t or low p melt compositions are ultracalcic potentially presenting a new hypothesis for the origin of ultracalcic melt inclusions in arc lava olivines wall rock calcite consumption is observed to increase with increasing t and decreasing p at 0 5 gpa our experiments yield carbonate assimilation from 21 6 to 47 6 between 1100 and 1200 c using measured co2 outflux rates for mts vesuvius merapi etna and popocatepetl over a t variation of 1100 to 1200 c at 0 5 gpa we calculate 6 92 of magmatic input estimates undergo this extent of assimilation suggesting that up to 3 of the current global arc co2 flux may be crustally derived application of the assimilation extent bracketed in this study to the estimated elevated number of carbonate assimilating arc magmatic systems active during the late cretaceous to early paleogene suggests that magma induced upper plate decarbonation alone had the potential to contribute up to 2 7 10 14 5 6 10 15 g y co2 assuming no dilution and complete gaseous release of all assimilated carbon using an estimated assimilation extent averaged from current systems gives a slightly lower though still significant value of 5 5 10 14 g y of excess co2 being released into the atmosphere

simulating the evolution of coastal morphology and stratigraphy with a new morphological behaviour model geombest abstract a new morphological behaviour model is used to simulate evolution of coastal morphology associated with cross shore translations of the shoreface barrier and estuary the model encapsulates qualitative principles drawn from established geological concepts that are parameterized to provide quantitative predictions of morphological change on geological time scales order 10 3 years as well as shorter time scales applicable for long term coastal management order 10 1 to 10 2 years changes in sea level and sediment volume within the shoreface barrier and estuary drive the model behaviour further parameters defining substrate erodibility sediment composition and time dependent shoreface response constrain the evolution of the shoreface towards an equilibrium profile results from numerical experiments are presented for the low gradient autochthonous setting of north carolina and the steep allochthonous setting of the washington shelf simulations in the currituck region of north carolina examined the influence of sediment supply substrate composition and substrate erodibility on barrier transgression results demonstrate that the presence of a lithified substrate reduces the rate of barrier transgression compared to scenarios where an erodible sand rich substrate exists simulations of the washington coast 20 km north of the columbia river confirmed that the model can reproduce complex stratigraphy involving regressive and transgressive phases of coastal evolution results suggest that the first major addition of sediment to the shelf occurred around 12 900 years ago and resulted from the rapid addition of sediment volume from the columbia river attributed to the missoula floods this was followed by a period where little or no sediment was added 12 400 9100 bp and a third period when most sediment was added to the shelf 9100 bp to present from the columbia river comparing results from each setting demonstrates an indirect control that substrate slope has on shoreface transgression rates shoreface transgression is shown to be sensitive to the rate of estuarine sedimentation with the sensitivity increasing as substrate slope decreases

oxygen isotope geochemistry of pyroclastic clinopyroxene monitors carbonate contributions to roman type ultrapotassic magmas the oxygen isotope geochemistry and chemical composition of clinopyroxene crystals from alban hills pyroclastic deposits constrain the petrological evolution of ultrapotassic roman type rocks volcanic eruptions in the 560 35 ka time interval produced thick pyroclastic deposits bearing clinopyroxene phenocrysts with recurrent chemical characteristics clinopyroxenes vary from si mg rich to al fe rich with no compositional break indicating that they were derived from a continuous process of crystal fractionation based on the 18o and trace element data no primitive samples were recovered monomineralic clinopyroxene cumulates set the oxygen isotope composition of primary magmas in the range of uncontaminated mantle rocks 5 5 but their ree composition resulted from extensive crystal fractionation departing from these mantle like 18ocpx values the effects of crustal contamination of clinopyroxene o isotope composition were identified and used to monitor chemical variations in the parental magma 18o values in si mg rich clinopyroxene are slightly higher than typical mantle values 5 9 6 2 and the low ree contents are representative of early stages of magmatic differentiation 18o values as high as 8 2 are associated with al fe3 rich clinopyroxene showing high ree contents these 18o values are characteristic of crystals formed during the late magmatic stages of each main eruptive phase geochemical modelling of 18o values vs trace element contents indicates that these ultrapotassic magmas were derived from fractional crystallization plus assimilation of limited amounts of carbonate wall rocks starting from a primary melt and from interaction with co2 derived from country rocks during crystal fractionation

distribution of modern salt marsh foraminifera in the albemarle pamlico estuarine system of north carolina usa implications for sea level research abstract we described the distributions of foraminifera from ten physiographically distinct salt marshes in the albemarle pamlico estuarine system north carolina using 193 surface samples we defined elevation dependent ecological zones at individual sites using cluster analysis and detrended correspondence analysis additionally seven principal biozones of salt marsh foraminifera were identified that have distinctive spatial distributions reflecting a pattern of salinity regimes caused by the current configuration of barrier island inlets high salinity sites along the southern outer banks are associated with sub tidal calcareous assemblages low marshes dominated by miliammina fusca and high marsh environments defined by haplophragmoides wilberti trochammina inflata and arenoparrella mexicana in contrast lower salinity marshes have ammobaculites spp in sub tidal settings miliammina fusca dominated low marshes and high marsh settings characterized by jadammina macrescens spatial variation of foraminiferal populations and the potential for biozones to migrate in response to changing inlet configuration and salinity suggests that datasets of modern salt marsh foraminifera from multiple environments would be appropriate for reconstructing holocene relative sea level in north carolina

u series isochron dating a generalized method employing total sample dissolution the age of a sedimentary deposit can be determined by measuring 238u 234u 232th and 230th in two or more samples of the deposit with the requirement that these samples have different u th ratios but an identical 230th232th ratio when deposited this paper presents the theoretical and experimental aspects of the dating method the latter involves techniques for securing samples of varied u th ratios from the same deposit plotting isochrons of the radiochemical data obtained on totally dissolved samples for age analysis and estimating the errors involved although applications to impure carbonates and lacustrine evaporite sediments are given as examples in this paper the method potentially can be generalized for dating a variety of authigenic deposits such as rock varnish peat opal sulfate minerals and marine phosphorites

uranium series dated authigenic carbonates and acheulian sites in southern egypt field investigations in southern egypt have yielded acheulian artifacts in situ in authigenic carbonate deposits caco 3 cemented alluvium along the edges of nowaggraded paleovalleys wadi arid and wadi safsaf uranium series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45 141 and 212 ka thousand years ago most of the carbonate appears to have been precipitated from groundwater which suggests that these three episodes of deposition may be related to late pleistocene humid climates that facilitated human settlement in this now hyperarid region carbonate cements from sediments containing acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys

an experimental study of the influence of oxygen fugacity on fe ti oxide stability phase relations and mineral melt equilibria in ferro basaltic systems

the univariant curve liquid forsterite anorthite diopside in the system cmas at 1 bar solid solutions and melt structure one atmosphere liquid present experiments were carried out in the cmas system using an ordinary quench furnace apparatus the runs including reversal and duplicate experiments describe the univariant curve l fo an di between the invariant points q l fo an di sp and f l fo an di oen located respectively at 1245 1 c and 1244 1 c the thermal divide on this curve m3 l fo an di is located at 1275 1 c and plots well within the silica saturated field in agreement with longhi s 1987 experiments along the univariant curve l fo an di liquid composition evolves away from the thermal divide either toward invariant points q or f and pierces the silica saturation plane i e the join di an en in the silica saturated field in this compositional range the al solubility in clinopyroxene changes drastically from one side of the thermal divide to the other with great increase of al solubility in the silica undersaturated field four endmembers must be used to describe the complex solid solution of anorthite caal2si2o8 camgsi3o8 mgal2si2o8 and si4o8 the last two of these are present only within the silica saturated field unlike clinopyroxene the mg content of anorthite is insensitive to the thermal barrier but is only sensitive to silica saturation plane olivine composition can be described by a binary solid solution of forsterite and monticellite with no ca in the m2 site as with anorthite olivine compositions exhibit a marked change with crossing of the silica saturation plane the above features imply that the solubility of minor elements in crystalline phases al in clinopyroxene ca in olivine and mg in anorthite selectively respond to only one or another of these particular plane results have many important consequences one is the likelihood of changes in melt speciation depending on position with respect to the thermal divide and the silica saturation plane

cova del rinoceront castelldefels barcelona a terrestrial record for the last interglacial period mis 5 in the mediterranean coast of the iberian peninsula abstract the cova del rinoceront a site in ne iberia contains a thick sedimentary fill preserving a faunal archive from the penultimate glacial and the the last interglacial periods layers i to iii have been dated to between 74 and 147 ka coinciding with mis 5a to 5e a period poorly represented in the mediterranean terrestrial record the results from cova del rinoceront are of broader interest for the reconstruction of ecological dynamics during warm stages and the understanding of the evolution and geographical variation of several taxa the palaeoecological evidence suggests a landscape dominated by mixed wooded vegetation with mild climatic conditions slightly more humid than today several vertebrate taxa including haploidoceros mediterraneus stephanorhinus hundsheimensis and glis glis are documented for the first time in the early upper pleistocene of europe showing that these species persisted across the region for longer than previously thought in addition the recovery of a small lithic assemblage indicates human presence in the surroundings of the site the 11 m thick stratigraphic section also provides an ideal setting in which to compare several geochronological methods u th dating of the flowstones that cap the deposit of speleothems formed along the cave walls and of speleothems buried by the deposit at different elevations provides minimum and maximum ages of 74 and 175 ka respectively for the accumulation the ages obtained by luminescence electron spin resonance esr amino acid racemisation aar palaeomagnetism and u series dating of bone are in good agreement with each other and are stratigraphically consistent this well dated faunal succession presents a unique opportunity to assess changes in the pleistocene fauna of the mediterranean coast over an interval of more than 100 ka

fluvial sediment delivery to a coastal plain estuary in the atlantic drainage of the united states abstract drastic changes in sediment production in drainage basins can have significant impacts on sediment yield to estuaries however significant but less spectacular changes in fluvial sediment regimes have not greatly influenced sediment output of some rivers in the united states atlantic drainage the limited influence of moderate or incremental changes in fluvial sediment systems on estuarine sediment delivery may be attributable to the large proportion of eroded sediment which is stored within the basins and the transport limited nature of long term sediment yields a sediment budget for the pee dee river basin and waccamaw river winyah bay estuary of the carolinas shows that only a small proportion of gross eroded sediment within the basin about 4 reaches the estuary on an average annual basis because the system appears to be transport limited it is estimated that an 88 reduction in the quantity of eroded sediment reaching streams would be necessary to produce significant change in sediment yield to the estuary any increase in sediment production would not be reflected at all in the estuary unless it was accompanied by a corresponding increase in fluvial sediment conveyance capacity estuarine sedimentary records thus may not reflect some significant changes in fluvial sediment systems

the effects of feo on the system cmas at low pressure and implications for basalt crystallization processes the common occurrence of olivine clinopyroxene and plagioclase in natural basalts may suggest that crystallization of these phases exerts important controls on the evolution of natural basalts at low pressure in order to understand the effects of such an assemblage on the evolution of basalt an experimental study of the divariant assemblage 1 an cpx ol in the system cmas feo was undertaken at 1 bar and under very reducing conditions experiments have been performed along three isothernal sections detailed electron microprobe data have been collected on all the coexisting phases combining these data with available data in the system cmas the compositions of all the coexisting phases have been described as functions of temperature and cao content in the melt by applying a multiple linear regression method this allows a quantitative characterization of the divariant assemblage 1 an epx ol in the system cmas feo from 1275 c to 1160 c with liquid compositions ranging from mg 1 to mg 0 28 knowing the composition temperature relationships the basic t x configuration of the assemblage 1 an cpx ol has been analysed and mass balance calculations have been performed to examine the feo effect on different crystallization processes addition of feo to the system cmas transforms the thermal divide in the assemblage 1 an cpx ol to a thermal ridge and shifts the spine of the thermal ridge towards sio2 poor compositions with decreasing temperature this indicates that tholeiitic basalts can be relatively silica poor and evolve towards slightly more silica poor compositions with increasing feo content pigeonite replaces ortheonstatite as a crystallizing phase along the silica rich boundary of the assemblage 1 an cpx ol in some iron and silica rich composition olivine possibly terminates its crystallization or even starts resorption prior to pigeonite precipitation this suppresses silica enrichment in the melt crystallization paths of the assemblage 1 an cpx ol are determined by the detailed t x relations of the thermal ridge with the melt evolving away from the spine the liquid evolution trend depends strongly on the initial compositions a tholeiitic liquid can follow a moderate silica enrichment path at the same very reducing condition of there is a high modal proportion of olivine a fenner mechanism therefore is at work at the same place as a bowen mechanism

magma chambers emplaced in carbonate substrate petrogenesis of skarn and cumulate rocks and implications for co2 degassing in volcanic areas crystal rich lithic clasts occurring in volcanic deposits are key tools to understand processes of storage cooling and fractionation of magmas in pre eruptive volcanic systems these clasts represent snapshots of the magma chamber host rock interface before eruption and provide information on crystallization differentiation and degrees of interaction between magma and wall rock in this study we have focused on the petrology of clasts of cumulate and skarn rocks from the colli albani volcanic district with the aim of shedding light on magma carbonate interaction and co2 emission in volcanic areas by means of phase relations bulk rock chemistry mineral compositions and isotope data we have identified different types of cumulates and skarns cumulates containing either clinopyrox

the late pleistocene laurentide glacier thu dating of its major fluctuations and δ18o range of the ice abstract direct information on the isotopic composition and timing of the now vanished laurentide glacier can be found in subglacial calcite or in early diagenetic concretions from glaciolacustrine deposits th u isotopic measurements on early diagenetic concretions frome lake deschaillons varves st lawrence lowland quebec date the early wisconsinan major ice advance at ca 80 000 yr isotopic stage 5a 4 transition significant retreat occurred at ca 46 000 yr isotopic stage 3 as indicated by th u isochrones on early diagenetic concretions from lake gayhurst varves in the appalachian foothills of quebec during the maximum extension of the ice which is dated at ca 22 000 yr by th u measurements on subglacial calcite at cantley northern margin of the st lawrence lowland 18o values vs pdb ranging from 16 19 surficial ice to ca 30 basal ice are inferred for the laurentide ice isotopic composition superimposition of two phases of carbonate precipitation does not prevent the establishment of their respective age and isotopic composition through correlation of independent parameters and calculation of mixing lines

the 1994 sefidabeh eastern iran earthquakes revisited new evidence from satellite radar interferometry and carbonate dating about the growth of an active fold above a blind thrust fault in 1994 three shallow earthquakes of mw 6 occurred close together on blind thrusts near sefidabeh in eastern iran in an earlier study of the teleseismic waveforms the geomorphology and the faulting in the epicentral region it was suggested that these earthquakes were associated with the growth of a ridge above a blind thrust fault system whose activity could be detected by its effect on the surface drainage in this study we present a sar interferogram that precisely determines the location and amount of coseismic surface displacements showing that the earthquakes in the sefidabeh sequence probably occurred on en echelon fault segments associated with three stepping ridges we also present u th dates of 100 ka for lake deposits uplifted by the growing ridge from the cumulative dated uplift and knowledge of the surface displacements due to an earthquake sequence we estimate that 120 such events have occurred in the past 100 ka with an average recurrence interval of 830 yr and an average convergence rate of 1 5 mm yr 1 on the sefidabeh thrust each estimate has an uncertainty of a factor of two either way we argue that the sefidabeh fault originally formed by coalescence of many small fault segments and has grown in length at about 2 cm yr 1 in the past 100 ka though the coseismic surface deformation observed in the sar interferogram closely resembles folding the overall topography does not because of inherited topography associated with earlier geological deformation in spite of this the activity of the buried thrust fault can easily be detected by its effect on the surface drainage a significant lesson when interpreting landscapes that are not entirely due to the present day deformation

on the principles of the u trend method for dating quaternary sediments i model experimental procedures and data abstract the u trend method for dating a wide range of quaternary sediments was first presented by john rosholt in a series of u s geological survey open file reports the thinking was that upon fluviation uranium filtering down through the unit left behind a trail of daughter products in a systematic fashion a trend the exponential decrease of this u flux was defined by a flux factor the significance of which was not known exactly equivalently the flux of u could be characterized by a half period which appeared to act analogously to a radioactive decay half life by using leaching techniques the loosely bound isotopes would define a trend when plotted on a u trend isochron diagram this trend was characterized in the plot by a gradient and intercept which could be referred to calibration diagrams in order to recover the half period and the age of the unit such age estimates have now appeared in the more fully refereed literature though without the fuller descriptions found in the usgs publications the assumptions of the method are examined here together with the details of the method from the earlier publications various problems with the method stand out among which are i it is not clear how recoil effects are included in the empirical equations ii the use of independently dated sediments as calibration units has not been fully justified iii the leaching techniques appear to be too strong to select only the loosely bound isotopes and no others and iv several of the key data sets do not show a sufficiently strong variation of isotope ratios with depth to warrant being described as a trend despite these and other difficulties and because of its potential importance to quaternary chronology it is felt that the continuing study of u trend type methods is worth the effort

u series dating of impure carbonates an isochron technique using total sample dissolution abstract u series dating is a well established technique for age determination of late quaternary carbonates materials of sufficient purity for nominal dating however are not as common as materials with mechanically inseparable aluminosilicate detritus detritus contaminates the sample with extraneous th we propose that correction for contamination is best accomplished with the isochron technique using total sample dissolution tsd experiments were conducted on artificial mixtures of natural detritus and carbonate and on an impure carbonate of known age results show that significant and unpredictable transfer of radionuclides occur from the detritus to the leachate in commonly used selective leaching procedures the effects of correcting via leachate residue pairs and isochron plots were assessed isochrons using tsd gave best results followed by isochron plots of leachates only

downstream trends in discharge slope and stream power in a lower coastal plain river conceptual models of river estuary interaction are typically based on a notion of systematic downstream change in the intensity of fluvial processes low slopes backwater effects and effects of antecedent topography and landforms may complicate downstream tends in water and sediment flux in coastal plain rivers an analysis of the lower trinity river texas shows no consistent downstream pattern of increases or decreases in the discharge stream power or water surface slope flows may decrease downstream due to coastal backwater effects in the lowermost reaches and due to diversion of flow into valley bottom depressions during high flows in both the fluvial and fluvial estuarine transition reaches in general however stream power and slope decrease in the lower reaches consistent with earlier findings of limited fluvial sediment delivery to the coastal zone some tributaries may become distributaries at high but sub bankfull flows as backwater effects reverse flows into depressions associated with paleomeanders the paleomeanders and possibly the locations of these reversible channels are related to antecedent topography associated with aggradation degradation cycles over the past 100 ka low gradient coastal plain rivers may not function as simple conduits from land to sea further the transition from fluvial to coastal dominance may be variable along the river with the variability controlled not just by the relative magnitude of river and tidal or backwater forcing but also by valley topography controlled in part by antecedent landforms

modeling hydrodynamics of large lagoons insights from the albemarle pamlico estuarine system abstract large estuaries are influenced by winds over adjacent coastal ocean and land areas causing significant spatial variations in water levels currents and surface waves in this study we apply a numerical model to simulate hydrodynamics and waves in the albemarle pamlico estuarine system a large and shallow back barrier basin in eastern north carolina over a one month study period september 2008 with observations from several storm wind events of differing time scales and directions model performance is evaluated for a spatially varying wind field from the north american regional reanalysis narr dataset in comparison to spatially uniform forcing from wind observations at offshore coastal and land based sites across the region a spatially uniform wind field from offshore winds observations results in statistically better hydrodynamic simulations of water levels r 0 88 in the estuaries than narr r 0 48 after comparison with measurements and indicates the importance of strong marine winds over most of the estuary surface area the influence of a prominent bathymetric feature on hydrodynamics in pamlico sound is also investigated by numerically removing a 30 km long and 2 3 m deep shoal from the model grid and replacing it with an idealized depth of 6 m the removal of the shoal increases water level setup by 14 at the estuarine shoreline decreases current magnitudes by up to 40 in the shoal region and increases significant wave heights locally by up to 25 in the sound indicating the importance of this relict geomorphic feature as a major control on the hydrodynamic response of the system during wind events the results suggest that increasing the water depth over the shoal can lead to higher storm surges and wave heights with the possibility of increased inundation and erosion of the back barrier and mainland coastal regions the complex bathymetry and marine wind influence are critical input conditions for modeling large and shallow lagoonal estuaries like the albemarle pamlico estuarine system

complexities in barrier island response to sea level rise insights from numerical model experiments north carolina outer banks using a morphological behavior model to conduct sensitivity experiments weinvestigate the sea level rise response of a complex coastal environment to changes ina variety of factors experiments reveal that substrate composition followed in rankorder by substrate slope sea level rise rate and sediment supply rate are the mostimportant factors in determining barrier island response to sea level rise we find thatgeomorphic threshold crossing defined as a change in state e g from landward migratingto drowning that is irreversible over decadal to millennial time scales is most likely tooccur in muddy coastal systems where the combination of substrate composition depth dependent limitations on shoreface response rates and substrate erodibility mayprevent sand from being liberated rapidly enough or in sufficient quantity to maintain asubaerial barrier analyses indicate that factors affecting sediment availability such aslow substrate sand proportions and high sediment loss rates cause a barrier to migratelandward along a trajectory having a lower slope than average barrier island slope therebydefining an effective barrier island slope other factors being equal such barrierswill tend to be smaller and associated with a more deeply incised shoreface therebyrequiring less migration per sea level rise increment to liberate sufficient sand to maintainsubaerial exposure than larger less incised barriers as a result the evolution of larger lessincised barriers is more likely to be limited by shoreface erosion rates or substrateerodibility making them more prone to disintegration related to increasing sea level riserates than smaller more incised barriers thus the small deeply incised north carolinabarriers are likely to persist in the near term although their long term fate is less certainbecause of the low substrate slopes that will soon be encountered in aggregate results point to the importance of system history e g previous slopes sediment budgets etc in determining migration trajectories and therefore how a barrier island will respondto sea level rise although simple analytical calculations may predict barrier responsein simplified coastal environments e g constant slope constant sea level rise rate etc our model experiments demonstrate that morphological behavior modeling is necessary toprovide critical insights regarding changes that may occur in environments havingcomplex geometries especially when multiple parameters change simultaneously

natural and anthropogenic induced changes in a tidal inlet morphological evolution of oregon inlet abstract natural processes driving the dynamics of tidal inlets have been studied in length however as human influence in the coastal environment persists there is a need to comprehend how both natural and human induced processes drive different aspects of tidal inlet morphological evolution an effort to understand the combined effects of natural and anthropogenic induced processes in a tidal inlet is pursued by studying oregon inlet considered one of the most dynamic inlets in the outer banks of north carolina usa the temporal and spatial scales of the anthropogenic processes driving the morphological evolution of this tidal inlet are studied by means of remotely sensed data and in situ observations gathered from 2005 until 2015 effects of natural process that cannot be gathered from observations are studied via a morphological model based on delft3d evolutional trends include the cyclical response of the main channel of the inlet to dredging a 13 northward rotation of the main channel and frequent sediment transport reversal in the southern shoulder simulations indicate a net sediment transport rate into the inlet of 205 000 m3 yr tidal currents are responsible for 55 of such transport while waves account for the remaining 45 after a 2 year non dredging modeling scenario sediments from the subaqueous spit form a detached shoal in the north side of the flood delta and the main channel remains open branching into two dominant channels observations and model results indicate that oregon inlet has been in a state of stable equilibrium in the past decade natural and human induced processes contribute to such equilibrium this study exemplifies the decadal behavior of a tidal inlet influenced by natural processes infrastructure and dredging

experimentally determined mineral melt partition coefficients for sc y and ree for olivine orthopyroxene pigeonite magnetite and ilmenite our current lack of understanding of the partitioning behavior of sc y and the ree rare earth elements can be attributed directly to the lack of a sufficiently large or chemically diverse experimental data set to address this problem we conducted a series of experiments using several different natural composition lavas doped with the elements of interest as starting compositions microprobe analyses of orthopyroxene pigeonite olivine magnetite ilmenite and co existing glasses in the experimental charges were used to calculate expressions that describe ree partitioning as a function of a variety of system parameters using expressions that represent mineral melt reactions versus element ratio distribution coefficients it is possible to calculate terms that express low ca pyroxene melt partitioning behavior and are independent of both pyroxene and melt composition compositional variations suggest that sc substitution in olivine involves either a paired substitution with al or more commonly with vacancies the partitioning of sc is dependent both on melt composition and temperature our experimentally determined olivine melt ree ds partition coefficients are similar to but slightly higher than those reported by mckay 1986 and support their conclusions that olivines are strongly lree depleted y and ree mineral melt partition coefficients for magnetite range from 0 003 for la to 0 02 for lu ilmenite partition coefficients range from 0 007 for la to 0 029 for lu these experimental values are two orders of magnitude lower than many of the published values determined by phenocryst matrix separation techniques

a test of uranium series dating of fossil tooth enamel results from tournal cave france abstract a series of well preserved mammal bones and horse teeth was analyzed from archaeological levels of tournal cave magdalenian aurignacian and mousterain to test the hypothesis that well crystallized enamel behaves more as a closed system than does whole bone the isotopic composition of bones and tooth enamels from this deposit meet criteria for confidence and gave no reasons to suspect contamination or open system behavior two samples for which231pa could be analyzed showed internal concordance with the respective230th ages in spite of the favourable isotopic criteria however comparison of the u series ages of the bones and the tooth enamel with stratigraphic position and14c control indicated the dates were not meaningful in general both bones and tooth enamels gave ages too young although some were clearly too old neither group showed any systematic increase of age with stratigraphic depth tooth enamel therefore shows no advantage over bone for u series dating for this site in tournal cave both bones and enamel are apparently open to u which is probably cycling as a consequences of post depositional groundwater movement

shoreline erosion and decadal sediment accumulation in the tar pamlico estuary north carolina usa a source to sink analysis abstract estuaries contain vital habitats and it is important to understand how these areas respond to human activities and natural processes such as sea level rise and wave attack as estuarine shorelines erode or become modified with hard structures there is potential for significantly altering the availability of sediment and the filling of coastal systems this study used a source to sink approach and quantified rates of shoreline erosion in the tar pamlico sub estuary a tributary of the larger albemarle pamlico estuarine system apes the average shoreline change rate scr determined using an end point method was 0 5 0 9 m yr 1 for the tar pamlico incorporating bulk density estimates this contributes 0 6 105 tons of fine sediment to the system annually or after accounting for fluvial input about 40 of the total sediment supply to the sub estuary the role of the tar pamlico as a sink for these sediments was addressed using the radionuclide tracers 210pb and 137cs radionuclide activities and sediment accumulation rates identified several depositional regions in particular in the middle of the estuary linear sediment accumulation rates ranged from 0 10 0 02 to 0 38 0 02 g cm 2 yr 1 and total storage of fine sediment in the system was 1 6 105 t yr 1 it was not possible to confidently discern a change in the rate of shoreline erosion or seabed accumulation a preliminary budget for fine sediments grain size

thorium uranium disequilibrium dating of late quaternary ferruginous concretions and rinds radioactive ferruginous nodules from the alligator rivers uranium province northern territory australia were systematically examined by optical microscopy xrd alpha and fission track autoradiography and analysed for u th ra and major stable elements correlation of autoradiographs with microscopic structure and analyses of selective extractions confirmed that u and th were strongly associated with fe oxides fission track autoradiography showed no concentration gradient evidence for postdepositional leaching of uranium strong acid leaching studies showed that irreversibly adsorbed u and authigenic 234u and 230th but not 226ra are quantitatively retained by accumulated oxide oxyhydroxide correlation of the groundwater activity ratio with oxidic 234u 238u activity ratios indicated the latter was radiogenically consistent with oxidic 230th 234u activity ratios 1 dense accumulated fe mn oxide matrices are apparently capable of forming radiogenic closed systems in respect of the 230u 234u 230th decay set 234u 238u and 230th 234u activity ratios were used to derive similar mean ages of rinds for four nodules in the same horizon th u ages were also determined using a th index detrital correction method previously used for impure carbonates of pedogenic fe mn accumulations having background concentrations of u and th from other locations in australia these ages were compared with tl and 14c ages of the host sediments the comparisions suggest that th u dating could be used to age indurated layers of fe mn oxides in soil horizons 350 ka old

middle palaeolithic refugium or archaeological misconception a new u series and radiocarbon chronology of abric agut capellades spain new u series and c14 ams dates are provided for the abric agut capellades barcelona spain this site was previously considered to be of middle palaeolithic age according to the characteristics of the lithic assemblage in addition human teeth were uncovered and attributed to neandertals however radiometric dating clearly indicates a late pleistocene early holocene age

use of uranium thorium dating to determine past 14c reservoir effects in lakes examples from antarctica the chronologies of many lacustrine records suffer from radiocarbon reservoir effects due to the presence of dissolved dead carbon or to slow air water exchange here we use the tims uranium thorium disequilibrium method in conjunction with ams radiocarbon dating to determine the age of lacustrine carbonates and to quantify the past radiocarbon reservoir effect in two antarctic lakes with differing characteristics by correcting a single sample u th age for detrital contamination a 14 c offset of v18 000 yr was obtained for carbonates from the former grounding line of the ross sea ice sheet in glacial lake trowbridge this large reservoir effect is believed to result from the direct input of old co2 from glacial meltwater in the second example an isochron approach on coeval samples formed at the bottom of lake vida now exposed due to lower lake level yielded an age of 9550 340 yr b p and a radiocarbon reservoir age of 3600 yr this offset was probably the result of lack of aeration due to perennial ice cover and or strong density stratification this evidence for long term isolation of the lake bottom indicates another level of hardship for life in the dry valley lacustrine environment an environment studied as an analogue for extreme periods of earth history as well as for exobiological implications the success of the u th technique on these two examples indicates that tims u th dating will be of widespread use in dating the important climate information recorded in the dry valleys both within and beyond the 14 c age range fl 2001 elsevier science b v all rights reserved

uranium series age estimates and paleoclimatic significance of pleistocene tufas from the lahontan basin california and nevada abstract an extended chronology of lahontan basin lake levels based on uranium series age estimates correlates with the global ice volume record lake highstands occur at or shortly after times of maximum ice sheet size moderate size lakes occur when the global ice volume is about 80 of its maximum the data indicate that lake levels rise and fall relative to the proximity of the mean position of the jetstream when the continental ice sheet is above some threshold size or shape it appears that the large scale circulation and climatic conditions are right for producing lakes of moderate to large size within the lahontan basin

controls on the stratigraphic framework and paleoenvironmental change within a holocene estuarine system pamlico sound north carolina usa abstract this study examines the holocene stratigraphic record and paleoenvironmental evolution of a large estuarine system at high temporal and spatial resolution in the context of changing climate sea level and hydrodynamics new data are used to examine two time periods of increased marine influence within pamlico sound in northeastern north carolina interpreted to be the result of extensive barrier island segmentation synchronous with periods of rapid climate change during the late holocene the study reveals the controls on the stratigraphic development and the highly dynamic character of the coastal system in response to climate and sea level change as it interacts with paleotopography these findings can be used to inform projections of future environmental changes estuarine waters occupied paleovalleys in the pamlico sound region as early as ca 7500 cal bp and pleistocene interfluves separated the paleovalleys from the atlantic ocean until ca 5500 cal bp when they were flooded by rising sealevel forming the broad shallow pamlico sound initial barrier islands and shoals likely formed sometime between 5500 and 5000 cal bp providing the geomorphic setting for continued estuarine conditions behind the barriers at ca 4000 cal bp an increase in marine influence and sand content is detected in multiple cores and is correlated to seismic data within the pamlico sound basin this change is interpreted to be the result of increased segmentation of barrier islands thus a greater number of inlets or wider inlets which is consistent with a rapid transgression seen in other areas of the u s east coast the segmentation may have been partially facilitated by a rapid increase in lagoonal area and tidal prism by overtopping of interfluves greater barrier island continuity is evident from 3500 to 1200 cal bp as indicated by muddy deposits with low brackish estuarine foraminiferal assemblages at ca 1200 cal bp seismic sedimentological and micropaleontological data suggest an increase in wave and current energy and marine influence throughout southeastern pamlico sound these changes are interpreted to represent extensive segmentation of the barrier islands during the medieval climate anomaly mca since ca 500 cal bp the pamlico sound system has returned to a more restricted state as inlets have closed currently only three major inlets segment the outer banks the barrier island system fronting pamlico sound but warming climate and increasing rates of sea level rise suggest that another episode of barrier island segmentation began about a half century ago and appears that it may extend into the near future

controls on late quaternary incised valley dimension along passive margins evaluated using empirical data incised valleys are canyon like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium gradient profiles in response to sea level fall most of these valleys flood during sea level rise to form estuaries incised valley morphology strongly controls the rate of creation of sediment accommodation valley fill facies architecture and the preservation potential of coastal lithosomes on continental shelves and affects coastal physical processes nonetheless little is known about what dictates incised valley size and shape and whether these metrics can be used to explain principal formation processes the main control on alluvial channel morphology over human time scales is discharge this is based on numerous empirical studies and is well constrained because all variables are easily measured at this short time scale knowledge of long term river evolution over a complete glacio eustatic cycle on the contrary remains largely conceptual experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified in spite of this difficulty existing models of incised valley formation at the coast suggest that valley evolution is driven largely by downstream forcing mechanisms highlighting sea level and shelf gradient morphology as the dominant controls on valley incision although valleys are cut by rivers whose channels are a direct reflection of discharge little empirical data exist in coastal areas to address the degree to which valley evolution is governed by upstream controls the late quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables including sea level tectonics substrate lithology and drainage network characteristics are accurately constrained here 38 late quaternary valleys along the coast of two different passive continental margins are compared which suggests that valley shape and size are governed primarily by upstream intrinsic controls such as discharge valley width depth and cross sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea level

low pressure phase relationships in the system na2o cao feo mgo al2o3 sio2 at 1100 c with implications for the differentiation of basaltic magmas

terrestrial environments during mis 11 evidence from the palaeolithic site at west stow suffolk uk abstract multidisciplinary investigations of the sequence at beeches pit west stow suffolk uk have a direct bearing the age of the hoxnian interglacial and its correlation with the continental holsteinian and with the global marine record at this site glacial deposits till and outwash gravels referable to the anglian lowestoft formation fill a subglacial channel cut in chalk bedrock above these glacial deposits a series of interglacial sediments occurs consisting of limnic tufaceous and colluvial silts lacking pollen but rich in shells ostracods and vertebrates lower palaeolithic flint artefacts of acheulian character have also been recovered including refitting examples charred material is abundant at certain horizons and many of the bones have been burned several discrete areas of burnt sediment are interpreted as hearths the molluscan fauna comprises some 78 taxa and includes species of considerable zoogeographical and biostratigraphical importance the land snail assemblage from the tufa consists of woodland taxa with no modern analogue including species that are either extinct e g zonitoides sepultus or which no longer live in britain e g platyla polita p similis neniatlanta pauli this is also the type locality of retinella lyrodiscus skertchlyi which belongs to a subgenus of zonitid land snail now living only on the canary islands there are indications from this fauna the lyrodiscus biome that the climate was wetter and perhaps warmer than the present day the vertebrate fauna is also noteworthy with species of open habitats such as rabbit oryctolagus cf cuniculus and of closed forest such as squirrel sciurus sp and garden dormouse eliomys quercinus present at different times the occurrence of southern thermophiles such as aesculapian snake zamenis longissimus indicates temperatures warmer than those of eastern england today the upper levels include much material reworked from the interglacial sediments although there is clear faunal evidence for climatic deterioration both the molluscan and vertebrate faunas suggest correlation of the interglacial sediments with the hoxnian uranium series dates from the tufa 455 ka bp tl dates from burnt flints 414 30 ka bp and a range of amino acid racemization data all support correlation of this interglacial with mis 11 however four osl dates from sand beneath the interglacial sequence yield a mean age of 261 31 ka bp far younger than all other age determinations and far younger than implied by the biostratigraphy archaeologically the site is unusual in showing prolonged human occupation within closed deciduous forest and evidence for controlled use of fire in a lower palaeolithic context biostratigraphical correlations with other lower palaeolithic sites support the suggestion that acheulian and clactonian industries both occurred in southern britain during the same substage of the hoxnian although not necessarily at precisely the same time the characteristics of the mis 11 interglacial in britain are discussed in the light of evidence from beeches pit and elsewhere

delivery of upper basin sediment to the lower neuse river north carolina u s a extensive storage of upper basin piedmont sediment and apparent low sediment supply to streams in lower basin coastal plain areas generates questions as to the source of alluvium in lower reaches of rivers of the u s atlantic drainage this was investigated on the neuse river north carolina using a mineralogical indicator of sediment source areas the utility of mica flakes for discriminating between piedmont and non piedmont sources of sediment in the lower coastal plain reaches of the neuse was established on the basis of an examination of the u s national soils database and of 26 soil surveys of the north carolina coastal plain from the neuse river estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments mica flakes become more common upstream this suggests that a very small proportion of the sediment eroded in the piedmont portion of the watershed is delivered to the river mouth the small amounts which presumably do reach the lower coastal plain are so diluted by coastal plain derived alluvium that no piedmont origin can be discerned this demonstrates a dominantly coastal plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems more importantly results suggest that upper and lower basin sediment dynamics are not only non linearly related but may be virtually decoupled

the effect of cao on the partitioning behavior of ree y and sc between olivine and melt implications for basalt carbonate interaction processes abstract the partitioning of ree y and sc r3 between olivine and melt has been investigated experimentally during basalt carbonate interaction three synthetic basalts meltmg 72 meltmg 75 and meltmg 78 were doped with 0 10 and 20 wt caco3 and then equilibrated for 72 h at 1 atm 1 150 1 200 and 1 250 c and the qfm oxygen buffer the thermal decomposition of caco3 produced cao contents in the melt up to 22 wt regular relationships are found between the ionic radius and the partition coefficient dr3 showing typical near parabolic patterns dr3 is weakly dependent on temperature but decreases with increasing caco3 in the starting material e g dsc decreases from 0 20 to 0 13 from the point of view of the lattice strain theory dr3 is described in terms of the radius of the crystal site r0 the young modulus e due to the elastic response of that site to lattice strain caused by cation insertion and the strain free partition coefficient d 0 3 the value of r0 decreases as ca cations are accommodated into the more distorted m2 site of olivine via progressive ca fe substitutions this mechanism is accompanied by a higher proportion of mg cations entering into the smaller m1 site making the optimum ionic radius smaller and favoring the crystallization of more forsteritic olivines from decarbonated melts the enrichment of ca in the crystal lattice is also proportional to the number of si and ca cations available in the melt this causes e to be anticorrelated either with ca in olivine or the activity of cao in the melt r3 cations behave as network modifiers and during basalt carbonate interaction the increasing abundance of non bridging oxygens enhances the solubility of ree y and sc in the melt as a consequence d 0 3 is negatively correlated with the degree of melt depolymerization additionally the strain of the crystal lattice dominates the dr3 parabolic patterns and d 0 3 is strongly controlled by forsterite and aluminium concentrations in olivine the accommodation of ree y and sc in the crystal lattice requires maintenance of local charge balance by the generation of vacancies in accord with a paired substitution of r3 and a vacancy for mg in octahedral sites

uranium series isochron dating at el castillo cave cantabria spain the acheulean mousterian question abstract a massive flowstone layer level 23 near the base of the stratigraphic sequence in el castillo cave cantabria spain is dated by the uranium series isochron method to 89 11 10 ka bp the flowstone separates cultural layers traditionally labelled mousterian above and acheulean below the date reported here in association with other recent age determinations for mousterian and acheulean artifact assemblages in western europe calls into question the temporal significance of these archaeological designations in addition it further underlies the importance of the castillo cultural sequence and allows tentative discussion of changing rates of sedimentation in the vestibule of the cave where some 18 m of cultural and geological deposits were laid down during the course of the upper pleistocene

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

quaternary hinterland evolution of the active banda arc surface uplift and neotectonic deformation recorded by coral terraces at kisar indonesia abstract coral terrace surveys and u series ages of coral yield a surface uplift rate of 0 5 m ka for kisar island which is an emergent island in the hinterland of the active banda arc continent collision based on this rate kisar first emerged from the ocean as recently as 450 ka these uplifted terraces are gently warped in a pattern of east west striking folds these folds are strike parallel to more developed thrust related folds of similar wavelength imaged by a seismic reflection profile just offshore this deformation shows that the emergence of kisar is influenced by forearc closure along the south dipping kisar thrust however the pinnacle shape of kisar and the protrusion of its metamorphic rocks through the forearc basin sediments also suggest a component of extrusion along shear zones or active doming coral encrusts the island coast in many locations over 100 m above sea level terrace morphology and coral ages are best explained by recognizing major surfaces as mostly growth terraces and minor terraces as mostly erosional into older terraces all reliable and referable coral u series ages determined by mc icp ms correlate with marine isotope stage mis 5e 118 128 ka the only unaltered coral samples are found below 6 m elevation however an unaltered tridacna giant clam shell in growth position at 95 m elevation yields a u series age of 195 31 ka which corresponds to mis 7 this age agrees with the best fit uplift model for the island loose deposits of unaltered coral fragments found at elevations between 8 and 20 m yield u series ages of

element partitioning between transition zone minerals and ultramafic melt under hydrous conditions 1 element partitioning between wadsleyite garnet and hydrous ultramafic melt has been determined at 16 gpa and 1600 c using a kawai type multi anvil high pressure apparatus element partitioning between olivine and hydrous ultramafic melt was also studied at 5 gpa and 1500 c in order to compare element partitioning behavior between wadsleyite and olivine major and trace elements analyses of the quenched melt and coexisting wadsleyite garnet and olivine were made with an epma and la icp ms respectively the experimental results demonstrate that lil rb sr ba and hfs ti zr nb hf ta th u elements are preferably incorporated into wadsleyite relative to olivine suggesting that the concentration of these elements in the hydrous transition zone could be greater than that in upper mantle our results contribute to understand magmatism and chemical differentiation in the earth s interior

facies analysis of a 1 9 ga continental margin back arc felsic caldera province with diverse zn pb ag cu au sulfide and fe oxide deposits bergslagen region sweden the bergslagen mining district in south central sweden has been a major metal producer for more than 1 000 years in geologic terms bergslagen is the intensely mineralized part of a large early proterozoic mainly 1 90 1 87 ga felsic magmatic region of mainly medium to high metamorphic grade in the baltic shield the district contains a diverse range of ore deposit types including banded iron formation magnetitecalc silicate skarn manganiferous skarn and carbonate hosted iron ore apatite bearing iron ore stratiform and strata bound zn pb ag cu au sulfide ores and w skarn most ore deposits occur in hydrothermally altered metavolcanic rocks and associated metalimestones and skarns this study is a field oriented regional facies analysis based on recognition of primary volcanic and sedimentary features through the strong overprints of hydrothermal alteration deformation and metamorphism the region is interpreted as an extensional probably back arc active continental margin magmatic region it evolved through stages of intense magmatism thermal doming and crustal extension followed by waning extension waning volcanism thermal subsidence reversal from extension to compressional deformation regional metamorphism and structural inversion the volcanic successions comprise interfingering proximal near vent medial volcano flanks and distal volcano margin facies associations of rhyolitic pyroclastic caldera volcanoes and subordinate dacite rhyolite complexes nonwelded to poorly welded pyroclastic flow and fallout units and their rapidly resedimented subaerial and subaqueous equivalents are the most abundant volcanic facies subvolcanic porphyritic intrusions and cryptodomes are also abundant the pyroclastic debris was shed from mainly shallow water and subaerial proximal areas to shallow and moderately deep water above and below storm wave base distal areas most ore deposits formed during the regional waning volcanic stage and occur in medial to distal facies associations that comprise rhyolitic ash siltstone limestone and vitric crystal sandstone and breccia these mineralized facies associations were deposited in subaqueous environments mainly below the fair weather wave base but locally above the storm wave base water depths are interpreted to have been mainly 10 to 500 m with local deeper areas although the ore deposits occur in medial to distal facies associations many occur above or laterally adjacent to subsided volcanic vent complexes this suggests a spatial temporal and possible genetic relationship between several ore deposit types and the late magmatic stage of these volcanic centers except for the apatite bearing iron deposits it is uncertain if the ores are genetically related to specific magmatic hydrothermal events from specific volcanoes this is possible especially for the base metal sulfide deposits which have intense localized footwall alteration in felsic volcanic rocks however an important role of the volcanic centers may have been to provide strong positive pertubations or magmatic hydrothermal input to the regional convective geothermal system the main zn pb ag cu au ore deposits span a range between two end member types stratiform ash siltstone hosted sea floor deposits that have similarities to some stratiform sediment hosted zn pb ag deposits especially the broken hill type deposits and strata bound volcanic associated limestone skarn subsea floor replacement deposits that more closely resemble felsic volcanic associated massive sulfide deposits facies models are presented for both the banded iron formations are interpreted as chemical suspension deposits rhythmically interbedded with rhyolitic ash siltstone the skarn iron ores are strata bound in limestones and include metamorphosed sedimentary ores and metasomatic replacements apatite bearing iron ores differ in setting from the other ores in being formed within a dacitic intrusive complex that may be the root zone of a dacite rhyolite volcanic center

human responses to younger dryas in the ebro valley and mediterranean watershed eastern spain the archaeological and chronological records of the ebro river valley and the mediterranean watershed eastern spain are examined to evaluate the effects of the younger dryas greenland stadial 1 on the foragers of an area between 36