organic geochemical characteristics and generating potential of source rocks from the lower middle jurassic coal bearing strata in the east junggar basin nw china abstract the junggar basin located in nw china is a large intracontinental superimposed basin samples were collected from the lower middle jurassic coal bearing strata of the eastern junggar basin and include mudstones carbargilites and coal the origin of organic matter thermal maturity paleoenvironment of sediment deposition and hydrocarbon potential of drill core samples was investigated organic geochemical analysis performed on 65 source rock samples indicates a wide range of toc values from 0 81 wt to 81 06 wt this study combined sedimentology biomarker organic petrography and stable carbon isotopic composition of kerogen and extracts analysis demonstrating the organic matter of the source rocks is derived from terrestrial higher plants with a minor contribution of aquatic algae and microbes rock eval data elemental composition of kerogen and odd over even normal alkane distribution reveal immaturity to low maturity with a humic type organic matter the source rocks were deposited in a freshwater oxic to sub oxic environment indicated by high pr ph ratios a predominance of c29 steranes low tricyclic terpanes and a low gammacerane index high dia regular c29 sterane ratios and moderate to high c29 c30 hopane ratios found in most samples are related to the presence of clay minerals based on the following parameters h c vs o c toc s1 s2 hydrogen index saturated hydrocarbons aromatic hydrocarbons and chloroform a we concluded that the samples collected from organic rich coal bearing strata may yield not only gas but also have the capability to generate and release liquid hydrocarbons

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

origin of calcium in pedogenic carbonate nodules from silicate watersheds in the far north region of cameroon respective contribution of in situ weathering source and dust input significant amounts of pedogenic ca carbonate nodules have been observed in the far north region of cameroon in the carbonate free watershed of the mayo tsanaga thus a priori not favourable for carbonate nodules accumulations these nodules are associated with a clay rich parent material crpm covering either a granitic upstream or a greenstone bedrock downstream in this peculiar context the amount of pedogenic carbonate nodules represents large quantities of ca and c therefore determining the ca sources for pedogenic carbonate nodules is a key point regarding the mechanisms leading to carbonate nodule precipitation and their role in the biogeochemical cycle of ca three sites two on granite and one on greenstone were studied by combining sr et nd isotope systematics in order to assess the ca sources of carbonate nodules and the origin of the crpm associated with nodules carbonate nodules have a distinct sr isotopic composition in each profile pointing to the contribution of a local source for ca sr isotopic compositions of plagioclases and carbonate nodules display a concomitant variation in each profile indicating that plagioclases acted as a sr and thus ca source for the carbonate nodules nevertheless carbonate nodules have a higher sr isotopic signature than plagioclases implying the contribution of another more radiogenic sr source sr and nd isotope data from the crpm show that it is a mixture of weathered bedrock compounds and saharan dust this result highlights two other potential sr and ca sources biotite and saharan dust calculations of their respective contributions demonstrate that in situ weathering significantly adds to the ca source of nodules this result contrasts with many other studies from similar settings that highlight the importance of allochthonous marine aeolian inputs this conclusion points out that a substantial part of ca is transferred from the local bedrock to the carbonate nodules this mechanism seems to have been possible as peculiar edaphic conditions preserved the primary ca sources making in situ weathering a significant process for providing ca

a flexible approach to assessing synchroneity of past events using bayesian reconstructions of sedimentation history the dating of depths in two or more cores is frequently followed by a study of the synchroneity or otherwise of events reflected in the cores the difficulties most frequently encountered are a determining precisely the depths associated with the events and b determining the ages associated with the depths there has been much progress in recent years in developing tools for the study of uncertainties in establishing chronologies this has not yet been matched by similar progress in modelling event depth relationships this paper proposes a simple and flexible approach showing how uncertain events can be married to uncertain chronologies difficulties in studying event depth age relationships typically involve a confounding of two different problems first what exactly do we mean by an event a point in history a single depth in the core corresponding to a single time or a depth time range sometimes event is in fact a shorthand for a space time process do the data reflect more than one type of event process this can reflect vagueness in definition second what are the sources and implications of the uncertainties here we illustrate the issues involved by examination of several features seen in north european holocene pollen records the alnus rise is regarded as a diachronous early holocene event in contrast the ulmus decline is widely seen as a near synchronous event in the mid holocene the third feature we examine is the interval between the ulmus decline and the first occurrence of cerealia type pollen the evidence for these events lies in cores of lake sediment from which are determined a the proportions of pollen at many depths and b radiocarbon age estimates from usually fewer depths for this illustration we focus on six sites we draw attention to a new and flexible method implemented in the free r software package bchron haslett j parnell a 2008 a simple monotone process with application to radiocarbon dated depth chronologies journal of the royal statistical society series c 57 4 399 418 for the establishment of the uncertainties surrounding the dating of samples in such cores we illustrate its flexibility by assessing the synchroneity of past events

generation of gas and oil from coal and other terrestrial organic matter abstract late carboniferous permian sedimentary rocks contain the world s largest coal reserves which have generated and released gas but little if any oil in comparison organic matter deposited in lacustrine fluvial deltaic or brackish water sediments has sourced large quantities of waxy oils in countries such as china australia the u s a argentina venezuela and indonesia plus gas and condensate in deltas worldwide why is more oil coming from land derived organic matter disseminated in sediments than from the carboniferous permian coal beds which also are land deposits the answer appears to be in the hydrogen content and the ease of migration when organic matter and coals have high hydrogen contents relative to carbon they can form oil when the hydrogen is low mainly gas is formed most of the world s coal is low in hydrogen whereas much of the terrestrial organic matter disseminated in sediments is higher in hydrogen so it forms more oil also both gas and oil are adsorbed on coal more strongly than on the disseminated kerogen of sedimentary rocks this makes migration of oil out of the coal more difficult compared to migration from conventional shale source rocks

geochemistry of aliphatic rich coals in the cooper basin australia and taranaki basin new zealand implications for the occurrence of potentially oil generative coals

wave current interaction in willapa bay 1 this paper describes the importance of wave current interaction in an inlet estuary system the three dimensional fully coupled coupled ocean atmosphere wave sediment transport coawst modeling system was applied in willapa bay washington state from 22 to 29 october 1998 that included a large storm event to represent the interaction between waves and currents the vortex force method was used model results were compared with water elevations currents and wave measurements obtained by the u s army corp of engineers in general a good agreement between field data and computed results was achieved although some discrepancies were also observed in regard to wave peak directions in the most upstream station several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind tide and wave current interaction process comparison of the horizontal momentum balances results identified that wave breaking induced acceleration is one of the leading terms in the inlet area the enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress the pressure gradient showed significant changes with respect to the pure tidal case during storm conditions the momentum balance in the inlet shares the characteristics of tidal dominated and wave dominated surf zone environments the changes in the momentum balance caused by waves were manifested both in water level and current variations the most relevant effect on hydrodynamics was a wave induced setup in the inner part of the estuary

pedo sedimentary constituents as paleoenvironmental proxies in the sudano sahelian belt during the late quaternary southwestern chad basin abstract climate and environmental changes since the last glacial maximum in the tropical zone of west africa are usually inferred from marine and continental records in this study the potential of carbonate pedo sedimentary geosystems i e vertisol relics to record paleoenvironmental changes in the southwestern part of chad basin are investigated a multi dating approach was applied on different pedogenic organo mineral constituents optically stimulated luminescence osl dating was performed on the soil k rich feldspars and was combined with radiocarbon dating on both the inorganic 14cinorg and organic carbon 14corg soil fractions three main pedo sedimentary processes were assessed over the last 20 ka bp 1 the soil parent material deposition from 18 ka to 12 ka bp osl 2 the soil organic matter integration from 11 cal ka to 8 cal ka bp 14corg and 3 the pedogenic carbonate nodule precipitation from 7 cal ka to 5 cal ka bp 14cinorg these processes correlate well with the chad basin stratigraphy and west african records and are shown to be related to significant changes in the soil water balance responding to the evolution of continental hydrology during the late quaternary the last phase affecting the vertisol relics is the increase of erosion which is hypothesized to be due to a decrease of the vegetation cover triggered by i the onset of drier conditions possibly strengthened by ii anthropogenic pressure archaeological data from far north cameroon and northern nigeria as well as sedimentation times in lake tilla northeastern nigeria were used to test these relationships the increase of erosion is suggested to possibly occur between c 3 cal ka and 1 cal ka bp finally satellite images revealed similar geosystems all along the sudano sahelian belt and initial 14cinorg ages of the samples collected in four sites gave similar ages to those reported in this study consequently the carbonate pedo sedimentary geosystems are valuable continental paleoenvironmental archives and soil water balance proxies of the semiarid tropics of west africa

late quaternary climate and vegetation of the sudanian zone of northeast nigeria the lake tilla crater lake in northeastern nigeria 10 23 n 12 08 e provides a ca 17 000 14c yr multiproxy record of the environmental history of a sudanian savanna in west africa evaluation of pollen diatoms and sedimentary geochemistry from cores suggests that dry climatic conditions prevailed throughout the late pleistocene before the onset of the holocene the slow rise in lake levels was interrupted by a distinct dry event between ca 10 900 and 10 500 14c yr b p which may coincide with the younger dryas episode the onset of the holocene is marked by an abrupt increase in lake levels and a subsequent spread of guinean and sudanian tree taxa into the open grass savanna that predominated throughout the late pleistocene the dominance of the mountain olive olea hochstetteri suggests cool climatic conditions prior to ca 8600 14c yr b p the early to mid holocene humid period culminated between ca 8500 and 7000 14c yr b p with the establishment of a dense guinean savanna during high lake levels frequent fires were important in promoting the open character of the vegetation the palynological and palaeolimnological data demonstrate that the humid period terminated after ca 7000 14c yr b p in a gradual decline of the precipitation evaporation ratio and was not interrupted by abrupt climatic events the aridification trend intensified after ca 3800 14c yr b p and continued until the present

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

a revised picture of the structure of the monsoon and land itcz over west africa this article presents an overview of the land itcz intertropical convergence zone over west africa based on analysis of ncar ncep reanalysis data the picture that emerges is much different than the classic one the most important feature is that the itcz is effectively independent of the system that produces most of the rainfall rainfall linked directly to this zone of surface convergence generally affects only the southern sahara and the northern most sahel and only in abnormally wet years in the region a second feature is that the rainbelt normally assumed to represent the itcz is instead produced by a large core of ascent lying between the african easterly jet and the tropical easterly jet this region corresponds to the southern track of african easterly waves which distribute the rainfall this finding underscores the need to distinguish between the itcz and the feature better termed the tropical rainbelt the latter is conventionally but improperly used in remote sensing studies to denote the surface itcz over west africa the new picture also suggests that the moisture available for convection is strongly coupled to the strength of the uplift which in turn is controlled by the characteristics of the african easterly jet and tropical easterly jet rather than by moisture convergence this new picture also includes a circulation feature not generally considered in most analyses of the region this feature a low level westerly jet termed the african westerly jet plays a significant role in interannual and multidecadal variability in the sahel region of west africa included are discussions of the how this new view relates to other aspects of west africa meteorology such as moisture sources rainfall production and forecasting desertification climate monitoring hurricanes and interannual variability the west african monsoon is also related to a new paradigm for examining the interannual variability of rainfall over west africa one that relates changes in annual rainfall to changes in either the intensity of the rainbelt or north south displacements of this feature the new view presented here is consistent with a plethora of research on the synoptic and dynamic aspects of the african easterly waves the disturbances that are linked to rainfall over west africa and spawn hurricanes over the atlantic and with our knowledge of the prevailing synoptic and dynamic features this article demonstrate a new aspect of the west africa monsoon a bimodal state with one mode linked to dry conditions in the sahel and the other linked to wet conditions the switch between modes appears to be linked to an inertial instability mechanism with the cross equatorial pressure gradient being a critical factor the biomodal state has been shown for the month of august only but this month contributes most of the interannual variability this new picture of the monsoon and interannual variability shown here appears to be relevant not only to interannual variability but also to the multidecadal variability evidenced in the region between the 1950s and 1980s

spectral modeling of wave dissipation on negative current gradients abstract hindcast studies for the dutch wadden sea using the spectral wind wave model swan have shown the significant influence of currents on wave predictions in the tidal inlets in a number of cases with strong gradients in opposing partially blocking current wave heights are significantly overestimated ris and holthuijsen 1996 propose that such overestimations are due to insufficient steepness dissipation of waves on an opposing current gradient the present paper presents a new formulation for the enhanced breaking dissipation of waves on negative current gradients accelerating opposing current decelerating following current nonlinear effects are not included in detail for these partial blocking conditions but handled parametrically unlike the expression by ris and holthuijsen 1996 the proposed expression isolates the steepening effect of the current gradient on the waves so that inherently steep young wind sea is not overly dissipated this expression contains one additional unknown parameter which was calibrated using laboratory observations validation of this enhanced dissipation term for field cases of the amelander zeegat tidal inlet dutch wadden sea shows an improvement in the tidal channel for both opposing and following current situations with negative gradients in particular the results for the young wind sea on the tidal flats are not significantly affected as desired unlike with the expression of ris and holthuijsen 1996 however since the remaining dissipation terms in swan have been calibrated without this enhanced dissipation term the addition of the proposed formulation results in some deterioration of the overall statistics

centennial scale climate instabilities in a wet early holocene west african monsoon a holocene gulf of guinea record of riverine runoff based on ba ca in tests of a shallow dwelling planktic foraminifer and sea surface temperature sst based on mg ca reveals centennial scale instabilities in west african monsoon wam precipitation and eastern equatorial atlantic eea thermal conditions the long term holocene climate trend is characterized by a warm and wet early mid holocene and gradual drying and cooling during the late holocene superimposed on this trend are numerous centennial scale drops in precipitation during the early mid holocene the greatest declines in early holocene monsoon precipitation were accompanied by significant sst cooling in the eea and correlate with drops in air temperature over greenland and fresh water outbursts into the north atlantic na this observation suggests that early holocene climate instabilities in the na were closely linked to changes in the wam the strong imprint of na events in summer monsoon precipitation suggests that these events were not confined to winter time the late holocene does not show large amplitude changes in riverine runoff at the centennial level the relatively stable late holocene conditions likely reflect a weakening and stabilization of the monsoon system probably due to diminished influence of the na region due to a reduction in ice sheet

the southern oscillation index wave climate and beach rotation short embayed beaches bounded by headlands are a common feature along the southern and central coastline of new south wales australia many of these embayed beaches have experienced severe erosion at their southern end over the last decade previous studies have suggested that this erosion may be the result of an oscillatory medium term phenomenon known as beach rotation the present study was undertaken with the objectives of 1 establishing definitive links between the southern oscillation index soi wave climate and beach rotation and 2 determining the physical processes governing beach rotation data from two similar new south wales beaches were analysed using time series analysis techniques and image processing techniques using argus video images in this study the results indicate that the northern end of this type of beach accretes during el nino phases while the southern end erodes resulting in a net clockwise rotation of the beach the opposite occurs during la nina phases resulting in a net anti clockwise rotation of the beach the beach response at the northern and southern ends lags soi trend shifts by 3 and 17 months respectively waves are predominantly incident from the southeast during both el nino and la nina phases offshore wave height is positively correlated with the soi while offshore wave direction is negatively correlated with the soi on average the number of storms per year doubles from el nino to la nina based on these links between beach width fluctuations soi and incident wave conditions a conceptual model of beach rotation is presented the model describes the combinations of cross shore and longshore sediment transport and hydrodynamic processes that are expected to result in the observed clockwise and anti clockwise beach rotation during el nino and la nina phases respectively

tidal inlet sediment bypassing at mixed energy barrier islands abstract the large scale littoral sediment drift along barrier island coasts involves alongshore sand transport at the islands surf zone and across tidal inlets mechanisms of sediment bypassing at non migrating mixed energy tidal inlets are discussed based on process based numerical modeling of sediment dynamics at an exemplary barrier island system in the southern north sea residual transport pathways of distinct sediment grain size fractions and morphological changes reveal the complexity of processes at tidal inlets driven by the non linear interaction of competing tidal and wave forces sediment bypassing from the updrift to the downdrift shoreline of a tidal inlet is evaluated and the ratio of bypassed to recirculated sand volumes is estimated common inlet bypassing schemes are discussed and verified it is shown that the different bypassing mechanisms can happen simultaneously and are related to the transport behavior of particular sediment grain size fractions very fine to fine sand bypasses the inlet along the entire ebb tidal delta periphery by wave induced transport processes fine to medium sand is transported by the ebb directed tidal currents in the inlet throat to the ebb tidal delta where wave driven transport processes and bar welding bypasses the sediments to the downdrift shore for fine to medium and medium sands a sediment recirculation cell at the downdrift ebb tidal delta and reversal to the main inlet throat is identified

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

coal as a source rock for oil a review the geological debate about whether and to what extent humic coals have sourced oil is likely to continue for some time despite some important advances in our knowledge of the processes involved it is clear that not only liptinites but also perhydrous vitrinites have the potential to generate hydrocarbon liquids in the course of natural coalification some liptinites especially alginite cutinite and suberinite contain a higher proportion of aliphatic moieties in their structure than other liptinites such as sporinite and resinite and are therefore more oil prone it is of potential value to be able to predict the several environments of deposition in which coals with high liptinite contents or containing perhydrous vitrinites may have been formed review of the distribution of oil prone coals in time and space reveals that most are jurassic tertiary with key examples from australia new zealand and indonesia methods based both on experimental simulations and the examination of naturally matured samples have been used to determine the order of generation of hydrocarbons from different macerals results are not entirely consistent among the different approaches and there is much overlap in the ranges of degradation but it seems probable that in the natural environment vitrinites begin to generate early followed by labile liptinites such as suberinite then cutinite sporinite and finally alginite petroleum potential may be determined by experimental simulation of natural coalification or inferred through various micro techniques especially fluorescence and infrared ir spectroscopy or bulk techniques such as elemental analysis and 13c nmr spectroscopy the latter three techniques enable a measure of the polymethylene component of the coal which now appears to be one of the best available approaches for determining petroleum potential no method of experimental simulation of petroleum generation from coals is without criticism and comparative results are highly variable however hydrous pyrolysis confined pyrolysis and forms of open system hydrous pyrolysis approach acceptable simulations whether and to what degree generated liquid hydrocarbons are expelled has long been the central problem in oil from coal studies the structure of vitrinite was believed until recently to contain an interconnected microporous network in which generated oil would be contained until an expulsion threshold was attained recent studies show the pores are not interconnected combined with a dynamic model of pore generation it now seems that expulsion of hydrocarbons is best explained by activated diffusion of molecules to maceral boundaries and ultimately by cleats and fractures to coal seam boundaries the main reason for poor expulsion is the adsorption of oil on the organic macromolecule which may be overcome 1 if coals are thin and interbedded with clastic sediments or 2 if the coals are very hydrogen rich and generate large quantities of oil the existence of oil in vitrinite is attested to by solvent extractions fluorescence properties and by microscopic observations of oil and bitumen experimental simulation of expulsion of oil from coals has only recently been attempted the relative timing of release of generated co2 and ch4 could have considerable importance in promoting the expulsion of liquid hydrocarbons but the mechanism is unclear as it is universally agreed that dispersed organic matter dom in some shales readily generates and expels petroleum it is curious that few consistent geochemical differences have been found between coal macerals and dom in interbedded shales unambiguous evidence of expulsion from coals is limited and in particular only a few commercial oil discoveries can be confidently correlated to coals these include upper cretaceous fruitland formation coals in the usa from which oil is produced new zealand tertiary coals and middle jurassic coals from the danish north sea it is likely that coals have at least contributed to significant oil discoveries in the gippsland basin australia in the turpan basin china and in the kutei and ardjuna basins in indonesia but this remains unproven early reports that early jurassic coals in mid norway were a major source of the reservoired oils have been shown to be inaccurate none of the proposed rules of thumb for generation or expulsion of petroleum from coals seem particularly robust decisions on whether a particular coal is likely to have been an active source for oil should consider all available geological and geochemical information the assumptions made in computational models should be well understood as it is likely with new understandings of processes involved that some of these assumptions will be difficult to sustain

relevance of infragravity waves in a wave dominated inlet this study investigates the relevance of infragravity ig waves at albufeira lagoon inlet a shallow wave dominated inlet located on the western coast of portugal a field experiment carried out in september 2010 revealed the occurrence of low frequency oscillations i e 25 300 s in water levels and current velocities while these fluctuations were present over the ebb tidal delta along the whole tidal cycle they only appeared between the beginning of the flood and up to 2 h after high tide inside the lagoon the xbeach modeling system was applied to albufeira lagoon inlet and reproduced the generation and propagation of ig waves and their blocking during the ebb this behavior was explained by blocking due to opposing tidal currents reaching 2 5 m s 1 in shallow water depths numerical results suggest that the breakpoint mechanism and the long bound wave shoaling mechanisms contributed significantly to the generation of ig waves in the inlet ig waves induced fluctuations in flood currents inside the lagoon reaching temporarily 100 of their magnitude the fact that these fluctuations occur mostly at flood and not at ebb could promote flood dominance in the lagoon this hypothesis will have to be verified namely under storm wave conditions

observed and modeled drifters at a tidal inlet material transport and dispersion near the mouth of a tidal inlet new river inlet nc are investigated using gps tracked drifters and numerical models for ebb tide releases velocities are largest 1 m s 1 in two approximately 30 m wide channels that bisect the 1 3 m deep ebb shoal in the channels drifter and subsurface current meter velocities are similar consistent with strong vertical mixing and 2 d hydrodynamics drifters were preferentially entrained in the channelized jets where drifter cluster lateral spreading rates in were small in 0 5 m2 s 1 at the seaward edge of the ebb shoal jet velocities decrease linearly with distance to 0 2 m s 1 about 1 km from shore and cluster spreading rates are larger with out 3 m2 s 1 although the models coawst and nearcom generally reproduce the observed trajectory directions certain observed drifter properties are poorly modeled for example modeled mean drifter velocities are smaller than observed and upon exiting the inlet observed drifters turn north more than modeled drifters the model simulations do reproduce qualitatively the spreading rates observed in the inner inlet the flow deceleration and the increase in out observed in the outer inlet however model spreading rates increase only to out 1 m2 s 1 smaller modeled than observed out may result from using unstratified models noncoincident in space observations show evidence of a buoyant plume 1 kg m 3 in the outer inlet likely affecting drifter lateral spreading generally drifter based model performance is good within the inlet channels where tidal currents are strongest whereas model data differences are significant farther offshore

high resolution pollen record from core kw31 gulf of guinea documents the history of the lowland forests of west equatorial africa since 40 000 yr ago abstract pollen data from core kw31 recovered off the mouth of the niger river 3 31 1n 05 34 1e 1181 m water depth provide an exceptional record of vegetation changes in the west african lowlands between 40 000 and 3500 cal yr b p the highly diverse microflora testify for the permanency of rain and secondary forests in the niger river catchment at least as gallery formations along rivers during the last glacial period when dry conditions occurred in relation to enhanced trade wind circulation the direct consequence of the post glacial warming and the correlative increase in monsoon fluxes over west africa was the increase in forest diversity and the expansion of rain and secondary forests on the nearby continent comparison between kw31 pollen record and continental pollen data from 5 s to 25 n allows the evaluation of migration rates of tropical forest populations throughout north west africa at the beginning of the holocene and the vegetation response to the shift toward aridity recorded widely at the end of the african humid period around 4000 cal yr b p

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

petroleum geochemistry of middle magdalena valley colombia abstract twenty five crude oil samples from tertiary reservoirs in the middle magdalena valley colombia were studied by geochemical methods in order to understand their genetic relationships the oils were probably derived from both calcareous and siliciclastic facies of the upper cretaceous la luna formation some oils in the eastern margin contain relatively higher concentrations of land plant derived biomarkers than the remaining oil samples the molecular compositions of the oils observed in this study appear to be consistent with the inferred depositional sequence of anoxic marine pelagic carbonate facies in the north and western sectors of the middle magdalena valley while the eastern sector received a higher proportion of clastic input biomarker maturity parameters indicate that most of the oils were generated from the early phase of the oil window except for the colorado 38 oil that was generated during the peak of the oil window geochemical data support local generation and migration of the middle magdalena oils as opposed to longer distance migration from the region of the eastern cordillera the range of oil gravities measured in the middle magdalena valley is attributed to organic facies variations different levels of biodegradation and late charge of condensate rather than to thermal maturity and migration related effects

source rock facies distribution predicted from oil geochemistry in the central sumatra basin indonesia the molecular and compound specific isotopic composition of the n alkanes in 30 oil samples from the central sumatra basin were analyzed with the purpose of determining facies variations of the source rock in this basin the oil samples were generated by the eocene oligocene lacustrine brown shale formation biomarkers in the oil samples indicate varying contributions from algal and terrigenous organic matter primarily under oxic or suboxic depositional conditions five source rock facies were identified based on the relative concentrations of n alkanes isoprenoids tricyclic terpanes and steranes the individual facies were also distinguished by the compound specific isotopic composition of the n alkanes source rock depositional environments vary from deep lacustrine shallow lacustrine and lacustrine saline to coal and mixed coal and lacustrine shale deep lacustrine facies predominate in the aman and bengkalis troughs whereas saline and shallow lacustrine facies predominate in the south aman and kiri troughs respectively oils derived from coal and mixed coal and lacustrine shale facies predominate in the northern part of the central sumatra basin in the tanjung medan and north of the balam grabens

shore and bar cross shore migration rotation and breathing processes at an embayed beach a principal component analysis pca is used to decompose data on the coupled morphodynamics of the shoreline and nearshore sandbar of a typical single barred embayed beach tairua beach new zealand dynamic patterns are classified into simultaneous modes where the bar and shoreline move at the same time and non simultaneous modes where the shore moves independently from the bar and vice versa two simultaneous modes accounting for 65 of the variance of the shoreline and barline dominate the system one mode describes inverse shoreline and sandbar cross shore migrations alongshore averaged occurring with simultaneous rotations in the same direction the other mode accounts for migration in the same direction accompanied by variations of the barline curvature similar to breathing modes previously described in embayed beach shoreline modelling studies two non simultaneous modes of lesser importance account separately for independent shoreline and barline rotations 10 to 15 of the variance explained a pca applied to the shore and sandbar behaviours modelled by four standard equilibrium models simulating shore and sandbar cross shore migrations and rotations show that these are interrelated because of a correlation between wave energy and direction shore and bar rotations are coupled partially because the shape of the bay induces a correlation of their respective drivers the wave angle of incidence and the alongshore gradient of wave energy however this correlation depends on the wave energy this in combination with different shore and sandbar response times quantified using the models also explains the independent rotations reflected by the non simultaneous modes

radiocarbon chronology of the mammoth site at niederweningen switzerland results from dating bones teeth wood and peat abstract the peat section at niederweningen is a site of spectacular excavations of numerous bones of mammoth and other animals that was first recognized in the late 19th century in 1987 1990 new excavations provided more peat material which was radiocarbon dated to 33 000 14 c years bp and 42 000 14 c years bp the first ams radiocarbon ages of mammoth bones from 1890 1891 excavations placed the age between 33 000 14 c years bp and 35 000 14 c years bp in this study new results were obtained on bones teeth wood and peat from the layer that buried the mammoths the ages confirm that the mammoths as well as the peat section in which they were found are older than 40 000 14 c years bp in order to explain the discrepancy between the previous chronology and the new results two preparation techniques were applied for the dating of bones an organic fraction called collagen used to obtain the first radiocarbon ages was dated as well as gelatine prepared using the modified longin method the differences of up to 7000 years between ages obtained on collagen and gelatine fractions show contamination of the collagen fraction with modern carbon the oldest age of 45 870 1080 14 c years bp was obtained on base cleaned gelatine from mammoth bone this age is close to an age of 45 430 1020 14 c years bp obtained for the peat layer that buried the mammoths

analysis of the effects of different storm events on shoreline dynamics of an artificially embayed beach a five year dataset of argus derived mean intertidal positions has been analysed to characterize the shoreface variability in a beach protected by a system of groynes and a parallel low crested structure lido di dante ravenna italy for the period 2004 2009 84 intertidal beach bathymetries and shorelines at the zero sea level were used as indicators to assess beach changes in between a number of selected surveys and to determine characteristic patterns of the beach response to storm events from different directions variations in the shoreline at the zero sea levels have been quantified and analysed in conjunction with nearshore wave conditions and provenance linked to storm events these fall into two categories 1 storm events occurring during bora north eastern wind conditions and 2 storm events occurring during scirocco south eastern wind conditions the results show that apart from main beach advances of the whole protected beach due to nourishments periodically carried out a marked variability is observed among the four sub cells into which the shoreface behaviour has been separately analysed in particular a dependence of beach rotation in the artificially embayed area on the substantially bi directional wave climate has been shown bora and scirocco storm events produce shoreline rotation in counterclockwise and clockwise directions respectively due to the occurrence of longshore currents in the opposite direction in the nearshore an attempt was made to correlate the shoreface dynamics for the main rotation events 14 selected ones to the wave attack intensity as the total energy flux due to storm events a relationship seems to occur for each storm category between the shoreline displacements estimated for each sub cell and the total energy flux computed for inter survey periods supporting the occurrence of a link between the observed morphological changes and the hydrodynamic forcing associated with storm events in the five year monitoring period copyright 2011 john wiley sons ltd

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition abstract the deposition of aeolian or windblown dust is widely recognized as an important physical and chemical flux to ecosystems dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients there have been many studies that characterize the physical and chemical composition of dust however few studies have synthesized these observations in order to examine patterns geochemical fluxes we have compiled observations of dust deposition rates particle size distributions psd mineralogy and bulk elemental and organic chemistry the rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m 2 yr 1 sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions when compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales the distance from the source region that dust is deposited also influences the particle size distributions mineralogy and chemical composition of dust however more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns on average the concentrations of most major elements si al fe mg ca k in aeolian dust tend to be similar 20 to the composition of the upper continental crust ucc but there is substantial variability from sample to sample in contrast some elements tend to be depleted na or enriched ti in dust likely as a result of soil weathering processes prior to dust emissions trace elements especially heavy metals are consistently enriched in dust relative to the ucc ecologically important nutrients such as n and p are also present in dust deposition the geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions we calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition these estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models

mixed oils derived from multiple source rocks in the cainan oilfield junggar basin northwest china part i genetic potential of source rocks features of biomarkers and oil sources of typical crude oils abstract there are four generative hydrocarbon source rocks of carboniferous permian triassic and jurassic age in the east of the junggar basin geochemical study of these has shown that permian source rocks which contain high abundances of organic matter with good genetic potential are the best hydrocarbon source rocks in this area triassic source rocks are shown to be next best in these aspects the abundance of mainly type iii organic matter in jurassic and carboniferous source rocks varies greatly and the genetic potential of these rocks is lower than that of permian and triassic rocks these four source rock units in the fukang sag all reach a mature to highly mature stage of thermal generation and have generated large amounts of oil permian extracts are isotopically light with 13 c ratios generally less than 29 they have low pr ph ratios are rich in carotane tricyclic terpanes gammacerane and c 28 and c 29 steranes contain almost no diasteranes and have a low content of c 27 steranes the carbon isotopic composition of the triassic extracts is similar to that of the permian but they are characteristically rich in ts c 29 ts and diahopanes and have low gammacerane contents the carbon isotopic composition of jurassic extracts is noticeably heavier than that of permian and triassic extracts with 13 c being generally greater than 28 jurassic source rocks have pr ph ratios generally 3 0 and are rich in pentacyclic hopanes and c 29 steranes but poor in tricyclic terpanes gammacerane and c 27 and c 28 steranes using carbon isotopic and biomarker data the crude oils in this area can be divided into five groups the first group of crude oils a is derived from the permian the second group b from the triassic and the third group c from the jurassic source rocks the geochemical properties of the fourth group d of oils are intermediate between the properties of typical permian triassic and jurassic oils and they are interpreted as mixed oils derived from multiple source rocks including the permian triassic and jurassic the fifth group of crude oils e is particularly isotopically heavy and originates from carboniferous source rocks

mesoscale evolution of a headland bay beach rotation processes abstract the morphology change of a headland bay beach tenby west wales gr 212200 198599 has been analysed over a mesoscale timeframe 1830 2009 gis cross shore profiles off shore wave climate have been utilised to assess the role of atmospheric variability on long term shoreline change previous studies have suggested that plan form change seen in recent times has been caused by closure of ritec valley estuary circa 1855 and whilst admittedly closure did have an initial effect with northerly dune field migration and reductions in inter tidal and nearshore estuary flushing this study suggests that climatic variations also contribute to evolution of this bay mesoscale analysis qualitatively highlights two distinct time periods of plan form evolution characterised by total reversals in trend that take place around 1919 more recent bay rotation about a stable central sector is shown quantitatively the southern sector shows progressive retreat r2 0 93 whilst the northern sector is shown to advance r2 0 56 points of rotation show steady migration northwards as retreat is encountered within the south sector r2 0 79 which confirms that the bay is still evolving on a decadal level correlation can be found between positive nao index values and beach level and volume reductions based on a visually active beach profile r2 0 44 and 0 53 respectively whilst normalised wave height variability is also closely linked with index change t 0 952 df 82 p 0 05 over a similar timeframe positive index values result in stormier south westerly winds 180 270 where it is found that 54 of high winds emanate from this quadrant further correlation is found between these winds and nao index r2 0 47 winds from this direction produce waves that diffract and refract around giltar headland and off shore caldey island that induce a south to north movement of sediment increasing southerly shoreline retreat and conversely northerly advance qualitative observations of hind casts produced using decadal analysis regression equations and mesoscale nao data suggest that the atmospheric variation is a contributory factor in bay evolution similar scenarios are likely to exist at other locations therefore assessments should be repeated more widely to develop appropriate management strategies

a natural pyrolysis experiment hopanes from hopanoic acids abstract the formation or generation of hopanes are important processes during both the natural heating of organic rich sediments and laboratory pyrolysis experiments molecular maturity parameters as well as the amounts ng g rock of the c31 hopanes and c30 c32 hopanoic acids were quantified in a jurassic silty shale horizon isle of skye scotland as a function of distance from an igneous intrusion the maturity profiles of the homohopanes and the hopanoic acids are comparable there is also a correlation between the decreasing amounts of c30 c32 hopanoic acids and concomitant increases in c29 c31 hopanes suggesting that free hopanoic acids could be one potential source of hopanes in this particular horizon other possible sources could include hopanoic acids that are bound into the macromolecular fraction

climate induced fluvial dynamics in tropical africa around the last glacial maximum abstract the alluvia of the ntem nyong and sanaga fluvial systems in southern cameroon recorded repeated fluvial activity fluctuations during the late pleistocene including the last glacial maximum lgm the beginning of the african humid period and the northern hemispheric bolling allerod we applied a multi proxy approach on alluvial stratigraphies dated between 22 4 and 13 0 cal ka bp including remote sensing sedimentological and morphogenetic methods phytoliths sponge spicules 14c and 13c data a distinct ne sw gradient of landscape and fluvial dynamics around the lgm can be drawn with evidence for the persistence of extended fluvial rainforest refuges only in the ntem catchment the sanaga and nyong catchment areas were characterized by frequent channel migrations floodplain reorganization and unstable vegetation subject to fire including grasslands woodlands and gallery forests with bamboo thickets in spite of increasing rainfall after 16 4 cal ka bp persisting landscape instability played the major role for fluvial system dynamics floodplain transformations and vegetation development until 13 0 cal ka bp before a general landscape stabilization and rainforest expansion set in at the beginning of the holocene

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

processes controlling morphodynamics of artificially breached barriers abstract naturally and artificially breached tidal inlets can promote fast morphological changes along the adjacent detrital barriers as they evolve in response to the contemporaneous wave regime inlet migration results in downdrift barrier erosion while updrift sand accumulation and concomitant barrier extension are commonly observed this study addresses the performance of placement of a sandfill designed to create an artificial dune along the updrift tip of a sand barrier aiming to constrain inlet migration stabilize its location and reduce sand transfers from the ocean into the lagoon induced by storm overtopping of the barrier herein we investigate the patterns of inlet drifting and processes regulating the progressive loss of efficiency of this soft engineering solution we show that besides updrift inlet migration which occurs with temporary reversal of the prevailing direction of drift currents meandering of the ebb channels that envelop the flood delta is quite effective in triggering or enhancing erosion of the updrift barrier tip in periods when the inlet main channel is migrating in the opposite direction this additional erosional process which acts along the back barrier facade is responsible for the increase of the erosion rate of the artificial dune and regardless of the direction of wave induced drift direction of the inlet this finding discloses the relevance of taking into account not only the oceanic processes waves but also processes operating on the lagoonal side of the barriers in future engineering operations designed for tidal inlet management

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

hydropedology of a mildly arid loess covered area southern israel extensive loess covered areas characterize the mildly arid areas of western israel where average annual rainfall is 280 mm hydrological data point to a peculiar hydrological behavior of the ephemeral streams the frequency of sporadic flash floods is very high however even in extreme rain events peak discharges are extremely low hydrographs are usually characterized by very steep rising and falling limbs representative of saturated areas extending over a limited part of the watershed following this observation we advanced the hypothesis that storm channel runoff originated in the channel itself with negligible contribution from the adjoining hillslopes the study was based on two complementary approaches the hydrological approach was based on the detailed analysis of rainfall runoff relationships in a small watershed 11 km2 and on the analysis of the hydrological characteristics of the drainage network the second approach was based on the toposequence concept several boreholes were dug along a hillslope 400 m long chemical data obtained show no significant difference in the downslope direction similar results were also obtained for the particle size distribution and soil moisture content data obtained perfectly fit the concept of partial area contribution as it presents an extreme case of hydrological discontinuity at the hillslope channel interface the lack of pedological trends in the downslope direction is an additional indication of the limited connectivity between the hillslopes and the adjoining channel the limited connectivity is attributed to the prevalence of low rain intensities in the study area the present study is also relevant to our understanding of pedological processes in dry land areas the high frequency of intermittent low intensity rainstorms limits runoff generation and flow distances and casts doubt on the general application of the toposequence approach this article is protected by copyright all rights reserved

dating constituent formation in soils to determine rates of soil processes a review abstract rates of soil processes are poorly known one approach to determine them could be through the radiogenic isotopic dating of soil constituents such methods have been recently used to date minerals in soils and weathering profiles thanks to the development of high resolution techniques such as 40ar 39ar u series of micro drilled samples u series by laser ablation and u th he and to the development of suitable methodology expanding application of the techniques to a variety of supergene minerals e g fe and mn oxihydroxides carbonates etc in this paper we identify i the main soil constituents that can be dated through these isotopic methods that are mainly fe oxides mn oxides pedogenic carbonates and organic matter ii the main pedogenic processes that leads to their formation in soils and iii the different soil settings that allow transforming soil constituent ages into rates of soil processes namely growth bands transformation fronts and chronosequences

hydrological processes in a small arid catchment scale effects of rainfall and slope length many studies have been concerned with the scale issue in geomorphology and hydrology most studies focus on the possibility of data transfer from small to large watersheds less attention has been given to the scale problem within very small watersheds where differences in slope length may seriously affect the spatial distribution and extent of runoff contributing areas to the channel it is usually assumed that runoff and erosion increase as slope length and angle increase however field observations in the negev highlands show positive relationships between slope length and deposition rates regardless of slope angles short hillslopes are devoid of colluvial mantle while thick colluvial deposits with well developed soil profiles indicative of long term stability are found at the base of long hillslopes the hypothesis advanced is that temporal variations in effective rainfall control the spatial structures of surface properties that further enhance the effects of temporal variations in rainfall long term monitoring of rainfall and runoff 1982 1998 conducted at spatial scales varying from few hundreds of m2 up to 0 3 km2 show a decrease in runoff at the hillslope scale the low efficiency of runoff and erosion processes on long hillslopes is because the concentration time required for continuous flow along such slopes is longer than the duration of most effective rain showers prevailing in the area field data lead to the notion that runoff and erosion models in which a positive relationship between slope length and angle and runoff and erosion rates is assumed should not be applied to arid and semiarid areas more attention should be given in latter areas to the complex hydrological relationships between rainfall scales and spatial scales the implications of data obtained regarding the spatial distribution of areas contributing to channel flow at a geological time scale and under changing climatic conditions are discussed

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

evolution of tricyclic alkanes in the espirito santo basin brazil abstract the distributions of tricyclic isoprenoid alkanes were characterized in the neocomian sequence from the espirito santo basin brazil by high resolution gas chromatography mass spectrometry and co injection with synthetic standards where available a suite of homologous components ranging from c 20 to c 28 were present throughout the sequence as a mixture of stereoisomers whose relative abundance changed with depth the epimerization rates were similar for the various tricyclic compounds irrespective of side chain length achieving equilibrium ratios before the main stage of oil generation this new maturity parameter should be useful as a supplement to sterane hopane measurements

coastal monitoring solutions of the geomorphological response of beach dune systems using multi temporal lidar datasets vendee coast france abstract three beach and dune systems located in the northeastern part of the bay of biscay in france were monitored over 5 years with a time series of three airborne lidar datasets the three study sites illustrate a variety of morphological beach types found in this region reproducible monitoring solutions adapted to basic and complex beach and dune morphologies using lidar time series were investigated over two periods bounded by the three surveys the first period between may 2008 and august 2010 is characterized by a higher prevalence of storm events and thus has a greater potential for eroding the coast than the second period between august 2010 and september 2013 during the first period the central and northeastern part of the bay of biscay was notably impacted by storm xynthia with water levels and wave heights exceeding the 10 year return period and 1 year return period respectively despite differences in dune morphology between the sites the dune crest dhigh and the dune base dlow are efficiently extracted from each dem based on the extracted dune base an original shoreline mobility indicator is built displaying a combination of the horizontal and vertical migrations of this geomorphic indicator between two lidar datasets a geomorphic change detection is also completed by computing dems of difference dod resulting in segregated maps of erosion and deposition and sediment budgets accounting for the accuracy of lidar datasets a probabilistic approach at a 95 confidence interval is used as a threshold for the geomorphic change detection showing more reliable results however caution should be taken when interpreting thresholded maps of changes and sediment budgets because some beach processes may be masked especially on wide tidal beaches by only keeping the most significant changes the results of the shoreline mobility and geomorphic change detection show a high variability in the beach responses between and within the three study sites explained mainly by beach orientation and local factors despite variable site specific mechanisms the recovery processes redistribute the available sand more on the upper parts of the beach producing significant deposition generally in the form of embryo dunes the monitoring of the beach and dune systems with airborne lidar datasets reveals that the three study sites show diverse behaviours during the first period likely associated with storms while the analysis show more homogenous beach responses during the second period likely associated with a recovery phase

single grain optical dating of grave infill associated with human burials at lake mungo australia abstract recent age constraints on australia s oldest human remains mungo i and iii found at lake mungo in western new south wales relied on optical dating of sands from the same stratigraphic units as those into which the remains had been inserted 42 3 ka and those that overlay the graves 38 2 ka giving a burial age of 40 2 ka this indirect means of dating the burials was necessary because the original site from which the remains had been excavated had been completely eroded away at the time of the original excavation of the mungo iii grave blocks of sediment from the grave infill were collected for sediment fabric analysis these sediment blocks were impregnated with polyester resin sectioned for analysis and the remaining resin impregnated sediment blocks were then stored in a cupboard where they have lain for the last 30 years here we report on optical dating of single grains of quartz extracted from one of these sediment blocks grains extracted from the centre of the block show a wide distribution of equivalent doses 0 0 0 3 to 43 7 8 3 gy indicating that not all of the grains have remained hidden from light light safe following excavation we show that the population of grains with the maximum equivalent dose produces an age consistent with that of the previous study indicating that some of the grains have remained light safe we also use linearly modulated optically stimulated luminescence to identify light safe grains these yield an age of 41 4 ka which represents a direct optical age for the grave infill and which is consistent with the age obtained in the previous study for sands from the same stratigraphic unit as that containing the burial the results reported here demonstrate the potential of applying optical dating to archived sediment samples that have not been stored in a light safe environment

hydrocarbon genesis of jurassic coal measures in the turpan basin china abstract a typical case of coal derived oils in china i e the crude oils from the middle lower jurassic coal measure strata in the turpan basin is presented by means of oil source correlation it is confirmed that low maturity crude oil in the shengjinkou oil field is derived from the coal bearing qiketai formation of middle jurassic age a brackish lacustrine sediment mature crude oils in the qiketai oil field and in well taican 1 are sourced from the badaowan formation of lower jurassic age which contains coal seams as thick as 100 m results show that commercial accumulations of liquid crude oils can be generated from coals and coal measure strata containing high volatile coal of bituminous rank despite unfavourable types of source material the total hydrocarbon generating potential can be great due to the unusual abundance of organic matter

alongshore sediment bypassing as a control on river mouth morphodynamics river mouths shoreline locations where fluvial and coastal sediments are partitioned via erosion trapping and redistribution are responsible for the ultimate sedimentary architecture of deltas and because of their dynamic nature also pose great management and engineering challenges to investigate the interaction between fluvial and littoral processes at wave dominated river mouths we modeled their morphologic evolution using the coupled hydrodynamic and morphodynamic model delft3d swan model experiments replicate alongshore migration of river mouths river mouth spit development and eventual spit breaching suggesting that these are emergent phenomena that can develop even under constant fluvial and wave conditions furthermore we find that sediment bypassing of a river mouth develops though feedbacks between waves and river mouth morphology resulting in either continuous bypassing pathways or episodic bar bypassing pathways model results demonstrate that waves refracting into the river mouth bar create a zone of low alongshore sediment transport updrift of the river mouth which reduces sediment bypassing sediment bypassing in turn controls the river mouth migration rate and the size of the river mouth spit as a result an intermediate amount of river discharge maximizes river mouth migration the fraction of alongshore sediment bypassing can be predicted from the balance between the jet and the wave momentum flux quantitative comparisons show a match between our modeled predictions of river mouth bypassing and migration rates observed in natural settings

can mima like mounds be vertisol relics far north region of cameroon chad basin abstract non anthropogenic earth mounds defined as mima like mounds in this study have recently been observed in non carbonate watersheds along the sudano sahelian belt in the chad basin in the diamare piedmont northern cameroon they are particularly well developed within stream networks in less eroded areas they occur as whaleback flattened morphologies or even as buried features all these shapes are composed of clay rich sediment associated with high proportions of secondary carbonate nodules and fe mn micro nodules their soil structure is prismatic to massive and vertical cracks are observed locally grain size distributions emphasize the clay rich nature of the sediment with average clay contents of 32 12 8 n 186 which is significantly higher than the clay content in the adjacent sediments in the landscape mean 10 4 n 21 moreover high proportions of smectite characterize the soil with average contents of 34 7 n 25 at the micro scale the groundmass has a cross striated b fabric with embedded smooth subangular quartz and feldspar grains of the silt size fraction all the characteristics point to altered vertic properties in the clay rich sediment composing the mima like mounds mima like mounds are thus interpreted as degraded vertisols compared to present day vertisols occurring in the piedmont mima like mounds are located upstream it is thus proposed that the vertisol areas were more extensive during a former and wetter period than the present day subsequent changing climatic conditions increased erosion revealing the gilgai micro relief by preferential erosion in micro lows rather than in micro highs mima like mounds of the chad basin might thus result from pedogenesis combined with later erosion these local processes can be inherited from regional climatic variations during the late pleistocene holocene and likely be related to the african humid period

examining the spatial consistency of palaeosol proxies implications for palaeoclimatic and palaeoenvironmental reconstructions in terrestrial sedimentary basins terrestrial sediments are a significant archive of past conditions and the critical zone in particular is important for understanding past and ongoing interactions between the atmosphere biosphere and lithosphere understanding the details of a palaeolandscape or palaeocatena record can greatly improve palaeoenvironmental descriptions and palaeoclimate reconstructions during crucial time periods in the past this article presents multi proxy data including palaeosol descriptions major element geochemistry magnetic composition and stable isotope geochemistry from an early eocene palaeosol transect which show distinct trends in palaeosol features and geochemistry across the landscape particularly in terms of the differences between a horizon and b horizon samples a horizon geochemical and physical features are highly variable and reflect other not strictly pedogenic controls whereas b horizon composition is extremely consistent given that most palaeoclimatic or palaeoenvironmental proxies based on palaeosols use b horizon features these results highlight the robustness of those proxies at the same time the difference between a horizons and b horizons and the variability within a horizons of the same palaeosol in different geomorphic settings underscores the importance of palaeosol description detailed sampling and a multi proxy approach to produce both precise and accurate reconstructions of past environments and climates using terrestrial sedimentary records

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

control of hydrocarbon seepage intensity on level of biodegradation in sea bottom sediments offshore surface geochemical surveys which target the surface expression of potential migration pathways for sampling such as fault scarps or diapiric features have become a commonly applied approach in the petroleum industry results of such surveys help to reduce risk on key exploration play elements and are used to evaluate prospects and to predict hydrocarbon phase and expected properties based on geochemical surveys conducted by exxonmobil in many basins worldwide there is an interrelation of the seep intensity concentration and level of biodegradation results from offshore west africa where many active macroseeps show moderate to severe biodegradation and a frontier basin offshore united kingdom rockall trough where active microseeps show no evidence of biodegradation are compared the specific biochemical controls on the difference in biodegradation proneness are not known although it appears that a certain threshold of oil concentration is needed to sustain an active bacterial community or to exceed clay adsorption capacities that may protect microseeps from biodegradation it is notable that the 25 norhopane series often considered an indication of severe biodegradation in reservoir oils has not been recognized in even ultra severely biodegraded seeps this suggests that different biodegradation pathways may be followed in marine surface seeps versus those in subsurface hydrocarbon accumulations a likely scenario in light of the fact that physiologically diverse bacterial communities are prevalent under different physiochemical conditions

a reevaluation of coastal embayment rotation the dominance of cross shore versus alongshore sediment transport processes collaroy narrabeen beach southeast australia 1 over 30 years of wave and beach survey data at collaroy narrabeen beach in southeast australia are analyzed to investigate the extent to which shoreline variability within this coastal embayment is dominated by shoreline oscillations due to cross shore sediment exchange or shoreline rotations due to alongshore exchange between the beach s extremities offshore wave data are derived from both buoy measurements and era 40 reanalysis data eof analysis of the monthly shoreline data suggests that the dominant mode of shoreline variability 60 of variability is an onshore offshore sediment exchange that is greater at the more exposed northern end of the beach than at the predominantly sheltered southern end this mode is primarily associated with variability in wave energy storms which by the nature of the wave climate of this region chiefly occurs from the south southeast the secondary mode of shoreline variability 26 of variability is a rotational signal between either end of the beach which coincides with 24 of the offshore wave climate shifting between the south southeast and east as well as changes in the wave period and wave energy storms a distinct annual cycle is identified in this rotation signal it is concluded that alongshore sediment transport processes associated with embayment rotation is more subtle than previously thought and a refined conceptual model of coastal embayment variability in this region is presented highlighting the dominance of cross shore sediment exchange processes

long term morphological modeling of a tidal inlet the arcachon basin france abstract the arcachon lagoon on the french atlantic coast is a triangular shaped lagoon of 20 km on a side connected to the ocean by a 3 km wide inlet between the mainland and an elongated sand spit this tidal inlet exhibits a particularly active morphology due to locally strong tidal currents and rough wave conditions during the past 300 years minimum and maximum spatial extents of the cap ferret sand spit have varied by 8 km while one or two channels have alternately allowed circulation between the lagoon and the ocean these impressive morphological changes have never prevented regular flushing of the lagoon eventhough the spit came as close as 300 m from the coast during the 18th century according to bruun s concept of tidal inlet stability theory and engineering 1978 510 pp the balance between longshore littoral transport and the tidal prism ensures the perpetuity of the inlet process modeling was believed to give better insight into the respective roles of tides and waves in driving the long term morphological changes of the inlet a two dimensional horizontal morphodynamic model was therefore developed combining modules for hydrodynamics waves sediment transport and bathymetry updates the use of process models at a scale of decades requires a schematization of the input conditions we defined representative mean annual wave and tide conditions with respect to sediment transport i e conditions that induce the same annual transport as measured in the field driven by these representative conditions simulations run from the 1993 bathymetry show that the tide is responsible for the opening of a new channel at the extremity of the sand spit where tidal currents are the strongest while waves induce a littoral transport responsible for the longshore drift of sand bodies across the inlet one particular simulation consisted in running the model from a hypothetical initial topography where the channels are filled with sand and the entire inlet is set to a constant depth 3 m the results show the reproduction of a channel and bar system comparable to historical observations which supports the idea that the lagoon is unlikely to be disconnected from the ocean provided tide and wave conditions remain fairly constant in the following decades

surface wave breaking over sheared currents observations from the mouth of the columbia river measurements of waves and currents from freely drifting buoys are used to evaluate wave breaking parameterizations at the mouth of the columbia river where breaking occurs in intermediate depths and in the presence of vertically sheared currents breaking waves are identified using images collected with cameras onboard the buoys and the breaking activity is well correlated with wave steepness vertical shear in the currents produces a frequency dependent effective current that modifies the linear dispersion relation accounting for these sheared currents in the wavenumber spectrum is essential in calculating the correct wave steepness without this wave steepness can be over under estimated on opposing following currents by up to 20 the observed bulk steepness values suggest a limiting value of 0 4 the observed fraction of breaking waves is in good agreement with several existing models each based on wave steepness further a semi spectral model designed for all depth regimes also compares favorably with measured breaking fractions in this model the majority of wave breaking is predicted to occur in the higher frequency bands i e short waves there is a residual dependance on directional spreading in which wave breaking decreases with increasing directional spread this article is protected by copyright all rights reserved

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

on the dynamics of the mouth of the columbia river results from a three dimensional fully coupled wave current interaction model numerical simulations were performed using a 3d ocean circulation model roms two way coupled to a phase averaged wave propagation model swan in order to expand our understanding of the dynamics of wave current interactions at the mouth of the columbia river mcr first model results are compared with water elevations currents temperature salinity and wave measurements obtained by the u s army corp of engineers during the mega transect experiment in 2005 we then discuss the effects of the currents on the waves and vice versa results show that wave heights are intensified notably at the entrance of the mouth in the presence of the tidal currents especially in ebb flows we also find non local modifications to the wave field because of wave focusing processes that re direct wave energy towards the inlet mouth from adjacent areas resulting in the presence of a tidal signatures in areas where local currents are weak the model also suggests significant wave amplification at the edge of the expanding plume in the later stages of ebb some tens of kilometers offshore of the inlet mouth with potential implications for navigation safety the effect of waves on the location of the plume is also analyzed and results suggest that the plume is shifted in the down wave direction when wave effects are considered and that this shift is more pronounced for larger waves and consistent with the presence of alongshore advection terms in the salt advection equation which are related to the stokes velocities associated with waves

evaluating the use of dune sediments as a proxy for palaeo aridity a southern african case study abstract the dominance of dryland environments in the southern hemisphere makes the study of these regions of critical importance for the development of regional hemispheric and global models of environmental change unfortunately the wetting and drying cycles associated with semi hyperarid climates are not conducive to the preservation of traditional organic proxy data sources the last decade however has seen the development of a number of alternative archives including the application of luminescence dating techniques to dunes and other aeolian deposits in continental situations the existence of relict dune fields has long been thought to be evidence of drier conditions during the pleistocene and direct ages from these features have been interpreted almost exclusively as indicating phases of aridity however an increasing number of ages from a broader range of environments are calling into question the assumption that aeolian activity can be simply equated with aridity presented here is a comparison of dune ages that have been obtained from across southern africa with a range of proxies from both terrestrial and marine records taken as a whole three primary phases of activity can be identified at 60 40 35 20 and 17 4 ka the frequent discordance with other terrestrial records indicating coeval increases in humidity and the close correlation of these phases with wind strength proxies suggest that aridity is unlikely to be the sole or even primary forcing mechanism for aeolian activity in the region and the palaeoclimatic significance of these sedimentary archives needs to be reassessed

some observations of wave current interaction abstract using data collected during the scawvex project the effect of depth and current changes particularly tidal on waves and the effect of waves on tidal currents were examined the possible interaction mechanisms between waves tides and surges are reviewed these include the effective surface wind stress bottom friction depth and current refraction and modulation of the absolute and relative wave period the usefulness of tidal periodicity in identifying both interactions in wave parameters and the effects of the waves on the tide is noted for correct analysis to obtain wave free tidal conditions or tidally averaged wave statistics it is particularly important to understand the interaction mechanisms for example the amplitude of the tidal current was found to be reduced in periods of high waves ideally waves and currents should always be measured simultaneously since the correct determination of either in shallow water requires knowledge of the other various remote sensing systems which can potentially do this are discussed since the algorithms are quite complex and may depend on a good first guess the future probably lies in combining remote sensing plus modelling together with ground truth in situ data

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

coastal flooding from wave overtopping and sea level rise adaptation in the northeastern usa abstract in the northeastern united states flooding arising from wave overtopping poses a constant threat to coastal communities during storm events the purpose of this study is to construct a novel integrated atmosphere ocean coast and overtopping drainage modeling framework based on the coupled tide surge and wave model swan adcirc to assess risk and facilitate coastal adaptation and resilience to flooding in a changing climate in this region the integrated modeling system was validated against the field observations of water level wave height and period during the january 2015 north american blizzard the water level collected by a sensor in the avenues basin behind the seawall in scituate massachusetts were combined with the basin relationship between basin area and water level given by the usgs lidar data to obtain the field measurements of wave overtopping water volume in order to verify the model predictions at the storm peak the significant wave height was increased by 0 7 m at the coast by tide and surge the wave setup along the coast varied from 0 1 m to 0 25 m depending on the coastline geometry the interaction between tide surge and waves increased the wave overtopping rate by five folds mainly due to the increased wave height at the toe of the seawall the wave overtopping discharge would approximately double in an intermediate sea level rise scenario of 0 36 m by 2050 for a storm like the january 2015 north american blizzard the wave overtopping discharge would increase by 1 5 times if the seawall crest elevation was raised by the same amount as sea level rise as an adaptation strategy an increase of 0 9 m in the seawall crest elevation instead of 0 6 m currently planned by the town is required to bring the wave overtopping discharge to the current level under a 0 36 m sea level rise scenario this result is primarily due to larger waves arriving at the seawall without breaking in the presence of larger water depth

wave current interactions in a wave dominated tidal inlet 1 wave current interactions play a major role in the dynamics of shallow tidal inlets this study investigates these interactions at a natural inlet with a strong focus on current induced changes on wave propagation the analysis of hydrodynamic data collected at the albufeira lagoon portugal revealed spatiotemporal variations of water levels and wave heights along the inlet attributed to wave current interaction processes we compared the simulations of a coupled wave circulation modeling system computed with and without waves and propagated with and without current feedback the wave induced setup inside the lagoon represented 7 15 of the offshore significant wave height the accuracy of the wave s predictions improved when current feedback was included during ebb the currents increased the wave height at the mouth of the inlet up to 20 and decreased the wave height in the inlet up to 40 due to current induced refraction steepness dissipation and partial blocking during flood the currents decreased the wave height in the inlet up to 10 and increased the wave height at the exterior parts of the ebb shoal up to 10 due to current induced refraction these effects significantly attenuate seaward sediment fluxes during ebb and contribute to the sediment accretion in the inlet

the mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern negev israel

the nature and origin of the aeolian mantles of central northern nigeria abstract evidence is presented here to show that the upland soils of central northern nigeria are formed in aeolian mantles deposited by two aeolian processes aeolian suspension or dust deposition and aeolian saltation or dune sand deposition the soils to the south and west of kano are largely the product of harmattan dust deposition whereas the northern soils appear to originate from dune sand migration from the quaternary dune fields to the east of the study area the spatial pattern of particle size populations or quanta and quartz grain roundness characteristics within the mantles and dune sands indicates that considerable mixing of dune sands and dust has occurred in the formation of these mantles

late pleistocene holocene vegetation and climate change in the middle kalahari lake ngami botswana abstract pollen spores and microscopic charcoal from a sediment core from lake ngami in the middle kalahari reflect paleovegetation and paleoclimatic conditions over the last 16 600 cal years bp the location of lake ngami allows for the receipt of moisture sourced from the indian and or atlantic oceans which may have influenced local rainfall or long distance water transport via the okavango system we interpret results of statistical analyses of the pollen data as showing a complex dynamic system wherein variability in tropical convective systems and local forcing mechanisms influence hydrological changes our reconstructions show three primary phases in the regional precipitation regime 1 an early period of high but fluctuating summer rainfall under relatively cool conditions from 16 600 12 500 cal bp with reduced tree to herb and shrub ratio 2 an episode of significantly reduced rainfall centered around c 11 400 cal bp characterized by an increase in xeric asteraceae pollen but persistent aquatic elements suggesting less rainfall but cool conditions and lower evaporation that maintained water in the basin and 3 a longer phase of high but fluctuating rainfall from 9000 cal bp to present with more woody savanna vegetation vachellia acacia and combretaceae we propose a model to relate these changes to increased indian ocean sourced moisture in the late pleistocene due to a southerly position of the african rain belt a northerly contraction of tropical systems that immediately followed the younger dryas and a subsequent dominance of local insolation forcing modulated by changes in the se atlantic basin

sedimentology organic geochemistry and petroleum potential of jurassic coal measures tarim junggar and turpan basins northwest china lower and middle jurassic coal bearing strata occur widely throughout central asia and are well developed in northwestern china where their thicknesses in the southern junggar northern tarim and turpan basins exceed 2500 2300 and 1500 m respectively examination of these strata along 13 transects across basin margin outcrop belts indicates that they are entirely nonmarine meandering fluvial deposits with local development of braided fluvial and lacustrine deltaic facies chinese subsurface data suggest that regional jurassic lacustrine facies are present down depositional dip consistent with predictions from global circulation modeling of early and middle jurassic monsoonal precipitation laboratory analyses of coals and organic rich shales show a dominance of terrestrial higher plant components visual kerogen analysis indicates that vitrinite inertinite and exinite are the dominant macerals and elemental analysis characterizes most kerogens as type iii rock eval analyses yield moderate hydrogen index values 50 300 and very low oxygen index values 20 jurassic source rock extracts are characterized by odd over even normal alkane distributions high pristane phytane and high hopane sterane ratios dominance of c29 sterane homologs local abundance of diterpenoid compounds and low abundance of tricyclic terpanes geochemical correlation with four petroleums from the junggar tarim and turpan basins strongly suggests that the jurassic coaly deposits and their lacustrine equivalents downdip are petroleum source rocks sterane and hopane distributions of petroleums and extracts of their putative jurassic source rock are similar and can be easily distinguished from published distributions of these compounds in other source rock layers additional correlation parameters include high pristane phytane low abundance or lack of tricyclic terpanes but similar distributions where present and lack of gammacerane with one exception and carotanes compounds that characterize permian and ordovician source rocks and their respective petroleums pyrolysis gas chromatography of selected jurassic samples s ggests that they possess potential for liquid hydrocarbon generation expulsion of c15 hydrocarbons from jurassic source rocks appears likely despite the traditional view that bituminous coals are incapable of expelling long chain hydrocarbons end page 929

implementation and comparison of the recent three dimensional radiation stress theory and vortex force formalism in an unstructured grid coastal circulation model abstract given the importance of wave current interaction in estuarine and coastal dynamics it is crucial to revisit impacts of surface gravity waves on three dimensional 3d nearshore circulation this work investigates wave induced circulation in three typical coastal systems including an idealized inlet and planar and natural barred beaches by implementing the recent 3d radiation stress rs theory and vortex force vf formalism to an unstructured grid finite volume community ocean model fvcom in the idealized inlet case 3d rs generated appreciable currents near barriers and lateral boundaries while vf forced strong flows via breaking and roller induced accelerations in front of the inlet both simulations indicate vertically varying wave induced circulation that decreases markedly in the planar beach with obliquely incident waves both methods successfully produced surface onshore and bottom undertow as well as the wave breaking and roller induced longshore currents nevertheless 3d rs generated unrealistic offshore currents close to the shoreline the coupled models were validated against observations in the natural barred beach and results indicate that the 3d rs model agrees slightly better with the observed longshore currents while 3d vf captures the vertical shear of the onshore offshore flows reasonably further investigations suggest that both methods produce the wave breaking induced surface onshore and bottom undertow successfully yet they are located further offshore resulting from the 3d rs induced unrealistic offshore currents successful implementations of the paired wave current theories to the unstructured model would be fundamental and beneficial to the coastal ocean modeling community

paleosols as indicators of paleoenvironment and paleoclimate paleosols are ancient soils that have been incorporated into the geological record soils form in response to interactions among the lithosphere hydrosphere biosphere and atmosphere so paleosols potentially record physical biological and chemical information about past conditions near earth s surface as a result paleosols are an important resource for terrestrial environmental and climatic reconstructions long standing paleosol research topics include morphology classification and clay mineralogy all of which provide information about pedogenic processes and local paleoenvironments paleosols are also used to infer processes involved in the development of stratigraphic architecture and basin evolution recent paleosol research has introduced semiquantitative and quantitative measures for environmental and chronometric reconstructions that provide insight into major regional to global changes in temperature precipitation and atmospheric pco2 these new proxies focus on morphological and chemi

dune ages in the sand deserts of the southern sahara and sahel in this paper we aim to document the history of aeolian processes within the southern sahara as part of the inqua dune atlas we review available luminescence ages for sand dunes across the southern sahara to develop an improved understanding of the dune chronology on a regional basis and attempt to correlate periods of sand accumulation this was achieved by analysing dune age by country as well as by latitude and longitude the results show a very patchy spatial distribution of dune ages with large gaps that encompass some of the largest sand seas despite these gaps some related patterns in dune morphology and stratigraphy appear to be consistent between northern nigeria and southern mali where older linear dunes are distinct from younger late holocene transverse and barchanoid dunes elsewhere in mauretania linear dunes with different orientations appear to have accumulated at different times most likely in response to changes in atmospheric circulation regional climatic changes are identified where dunes are transgressed by lake deposits within endorehic basins we identify four locations where dune accumulation is terminated by lacustrine transgressions two of which in lake chad and the bodele depression occur shortly after the last glacial maximum lgm the third example at gobiero in niger occurred later in the early holocene around 8 4 ka and a fourth marks a later transgression of palaeolake megachad after 4 7 ka larger scale latitudinal and longitudinal distributions in dune ages across the southern sahara do not show any consistent patterns though this may be due to the small sample size relative to the study area in addition local variations in external controls such as wind regime rainfall vegetation and sand supply need to be considered sometimes on a site by site basis limiting the analysis to dune ages determined using the single aliquot regenerative dose sar protocol indicates a lack of dune preservation during the lgm and the younger dryas times associated with increased dust input to the oceans which is assumed to indicate increased aeolian activity the sar dune dates suggest that preservation of dunes at the onset of succeeding humid intervals is an important component of the dune record the most striking examples of this phenomenon occur where dunes are preserved within endorehic basins by lacustrine transgressions

momentum balance across a barrier reef this paper reports on a combined experimental and numerical study dedicated to barrier reefs hydrodynamics a network of pressure sensors and velocity profilers has been deployed for more than 2 months over the ouano reef barrier new caledonia the primary aim of the study is to assess the relevance of the classical depth averaged momentum balance in such a complex and poorly documented environment the combined analysis of experimental and numerical measurements reveals a specific hydrodynamic behavior contrasting with sandy beaches and fringing reefs the cross reef current induced by wave breaking over the barrier reef plays an important role in the momentum budget in particular through friction processes the hydrodynamic behavior over the barrier reef is thus characterized by the progressive transition from a nearly classical beach type behavior on the forereef where the gradient of radiation stress is balanced by a barotropic pressure gradient associated to the wave setup to an open channel type regime dominated by frictional head loss the reef top wave setup shows a clear depth dependency mainly attributed to the forereef curvature during extreme wave events the measurements tend to indicate a transition toward a critical hydraulic regime above the reef top the numerical simulations involving a non hydrostatic wave resolving model coupled to a urn x wiley jgrc media jgrc23848 jgrc23848 math 0001 turbulence model highlight the vertical structure of the flow over the reef flat a classical log layer profile is observed in agreement with measurements while above the forereef an anticlockwise circulation develops under the breaking zone

organic geochemical evaluation of cretaceous shale samples from the orange basin south africa abstract organic geochemical evaluation of thirty two aptian to campanian shale samples from seven wells drilled on the shelf of the orange basin southwestern atlantic margin was carried out in order to determine their origin depositional environment thermal maturity and hydrocarbon potential the shale samples selected to represent highstand lowstand and transgressive systems tracts were analysed by rock eval pyrolysis for total organic c characteristics and by gas chromatography gc and gas chromatography mass spectrometry gc ms for n alkanes aliphatic isoprenoid hydrocarbons and biomarkers steranes hopanes and tricylic terpanes for most of the shale samples rock eval data hydrogen hi and oxygen index oi point to mainly type iii terrigenous organic matter only a few samples of turonian age reveal a higher proportion of marine organic matter being classified as type ii iii or type ii biomarker parameters suggest that the samples are deposited under suboxic to oxic environmental conditions rock eval data and biomarker maturity parameters assign for most of the samples a maturity level at the beginning of the oil window with some more mature samples of aptian albian and cenomanian age the hydrocarbon generation potential is low for most of the shelf shales as indicated by the s2 s3 ratio and hi values exceptions are some samples of turonian and aptian age

characterization of organic matter and depositional environment of tertiary mudstones from the sylhet basin bangladesh abstract the sylhet basin of bangladesh is a sub basin of the bengal basin it contains a very thick up to 22 km tertiary stratigraphic succession consisting mainly of sandstones and mudstones the sylhet succession is divided into the jaintia paleocene late eocene barail late eocene early miocene surma middle late miocene tipam late miocene pliocene and dupitila groups pliocene pleistocene in ascending order the origin of the organic matter om and paleoenvironment of deposition have been evaluated on the basis of c n s elemental analysis rock eval pyrolysis and gas chromatography mass spectrometry gc ms analysis of 60 mudstone samples collected from drill core and surface outcrops total organic carbon toc content ranges from 0 11 to 1 56 sulfur content is low in most samples toc content in the sylhet succession varies systematically with sedimentation rate with low toc caused by clastic dilution produced by high sedimentation rates arising from rapid uplift and erosion of the himalaya the om in the succession is characterized by systematic variations in pristane phytane pr ph oleanane c30 hopane n c29 n c19 alkane tm ts 17 h 22 29 30 trisnorhopane 18 h 22 29 30 trisnorhopane and sterane c29 c27 c28 c29 ratios during the middle eocene to pleistocene based on biomarker proxies the depositional environment of the sylhet succession can be divided into three phases in the first middle eocene to early miocene deposition occurred completely in seawater dominated oxic conditions with abundant input of terrestrial higher plants including angiosperms the second phase middle to late miocene consisted of mainly freshwater anoxic conditions along with a small seawater influence according to eustasic sea level change with diluted om derived from phytoplankton and a lesser influence from terrestrial higher plants oxygen poor freshwater conditions prevailed in the third phase post late miocene planktonic om was relatively abundant in this stage while a high angiosperm influx prevailed at times tmax values of ca 450 c vitrinite reflectance ro of ca 0 66 and methylphenanthrene index mpi 3 of ca 1 indicate the om to be mature the lower part middle eocene to early miocene of the succession with moderate toc content and predominantly terrestrial om could have generated some condensates and oils in and around the study area

the influence of tidal jet current ocean wave interaction on the embayed beach processes abstract many embayed beaches are formed by barriers that block embayments to create barrier enclosed estuaries these embayed beaches are characterized by strong tidal jets that drain the estuaries through a tidal inlet often debouching at one end a field study was conducted on buffalo beach in mercury bay waikato new zealand to study wave energy changes caused by the ebb tidal jet acoustic doppler current meter observations showed that during peak ebb jet flow a decrease in wave height occurred along the beach sites that were in close proximity to the ebb jet a delft3d hydrodynamic and wave model was used to further show that wave height variance was due to the jet current causing shoaling and refraction between the central beach and inlet adjacent southern beach the resulting wave energy focused along the southern beach diverged along the central beach and increased the alongshore radiation stress gradient under modeled storm conditions within the bay when wave heights exceed 1 5 m the jet was found to increase spreading and overall jet width the jet orientation was also deflected shoreward towards the inlet adjacent headland the radiation stresses driving alongshore transport became increasingly dominant with increased wave height suggesting that alongshore sediment mobility increases substantially during a storm event due to the presence of the jet implications are that jet strength and orientation play a role in embayed beach rotation

tidally discontinuous ocean forcing in bar built estuaries the interaction of tides infragravity motions and frictional control shallow bar built estuaries on wave dominated coasts in mediterranean climates experience an intermittent connection to the ocean in the presence of low streamflow their inlets may completely close as a result of nearshore sand transport but even in the open condition these inlets remain constricted extensive field measurements in the highly salt stratified pescadero estuary in northern california show that the shallow mouth causes these estuaries to experience discontinuous tidal forcing while the ocean and estuary are fully connected with near equal water levels tidal velocities are slow but infragravity motions in the nearshore induce large velocity oscillations within the estuary as the ocean tide falls infragravity forcing is cut off because the estuarine mouth is perched above the low tide ocean water level and ebbing velocities are set by bed friction observations reveal this oscillation between ocean forced and frictionally controlled conditions characterizes and sets estuarine hydrodynamics additional wave setup of the lagoon emphasizes the dependence of these estuaries on nearshore ocean conditions but the diurnal or semidiurnal retreat of the ocean below the mouth cuts off this nearshore influence so it too is tidally varying here we present detailed observations and a framework for understanding hydrodynamics in small shallow bar built estuaries

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

sahara and sahel vulnerability to climate changes lessons from holocene hydrological data abstract the examination of more than 1500 paleohydrological dated records collected between 10 and 28 n during the last 50 years have been used to improve our knowledge and understanding of the sahara and sahel vulnerability to the atlantic monsoon changes in the long term we have analyzed the distribution of water bodies mainly lakes and wetlands over time and space the central saharan massifs played a major role in favoring water supply to the lowlands throughout the whole african humid period in addition distinct east west dynamics is recorded with humidity starting and stopping several millennia earlier to the east than to the west of the sahara a series of time lags are discussed 1 between the maximum of deep fresh water lake formation during the early holocene and the maximum of water body extensions during the mid holocene which highlight the primary role of aquifer water level in lake response to climate change 2 between the hydrological history of the sahara and the sahel and the forcings mainly insolation changes during the early and mid holocene which involves complex interactions between remnant ice sheet in the northern hemisphere open water bodies in the sahara and sahel and the atlantic monsoon system

organic geochemical characteristics of crude oils from the masila basin eastern yemen the masila basin is an important hydrocarbon province in yemen but the origin of hydrocarbons and their generation history are not fully understood in this regard 10 crude oils from different petroleum reservoir sections in the masila basin were characterized by a variety of biomarker and non biomarker parameters using gc gc ms and stable carbon isotope techniques oils from the masila basin display pristane phytane pr ph ratios ranging from 1 7 to 2 0 low sulfur content high c35 homohopane index relatively high c27 sterane concentrations and relatively high tricyclic terpanes suggesting a marine clay source rock that was deposited in mildly anoxic to suboxic conditions with dominantly algal organic matter c29 20s 20s 20r steranes and bb bb aa sterane ratios indicate that the masila oils have reached peak oil window maturity another related feature of these oils is the absence of 18a h oleanane which suggests a source age older than cretaceous the carbon isotope compositions are similar to those of the potential source rocks which range from 25 4 to 28 3 indicating a marine environment the new data presented in this paper suggest that the masila oils constitute one oil family and that the oil originated from the upper jurassic madbi source rock in the basin