modeling equilibrium dynamics of the benguela current system the regional ocean modeling system roms is used to systematically investigate equilibrium conditions and seasonal variations of the benguela system at a resolution of 9 km including both the large scale offshore flow regime and the economically and ecologically important coastal upwelling regime a shelf edge poleward flow exists in the northern benguela region i e north of 28 s and is driven primarily by the wind stress curl via the sverdrup relation as such it is strongly seasonal and is most intense during spring and summer when the wind stress curl is most negative the poleward flow deepens as it moves southward between 25 and 27 s much of it veers offshore because of the nature of the wind stress curl and its interaction with the northwestward path of the benguela current which is influenced by alongshore topographical variations the benguela current is driven by nonlinear interactions of passing agulhas rings and eddies and does not have a striking seasonal signal in the mean state it is characterized by two streams the more inshore stream is topographically controlled and follows the run of the shelf edge the meandering nature of the offshore stream is a result of the preferential path of agulhas rings the model simulates all seven of the major upwelling cells within its domain the three southernmost cells have the strongest seasonal signal and experience their greatest upwelling during spring and summer months whereas the two northernmost cells have less seasonal variability but nevertheless have increased upwelling from autumn to spring and least upwelling in summer and the central benguela upwelling cells experience year round upwelling the effect of topography on coastal upwelling was investigated by smoothing alongshore coastline and topography variations which showed that in all of the seven major upwelling cells upwelling is enhanced on the downstream side of capes

facies and facies architecture of paleogene floodplain deposits willwood formation bighorn basin wyoming usa abstract paleogene deposits of the willwood formation were analyzed in two areas of the bighorn basin to provide a better understanding of the facies and facies arrangement of floodplain deposits and the various processes that influence floodplain construction and facies variability despite similar facies and facies organization floodplain deposits in the two areas differ in grain size hydromorphy and maturity of the paleosols and scale and organization of ribbon sandstones in the avulsion deposits these differences appear to be controlled by basin position of the study areas and differences in avulsion between the areas two kinds of cumulative floodplain paleosols red and purple paleosols formed on overbank deposits the red paleosols were better drained and formed on less clay rich parent material intense mottling and iron oxide nodules indicate that the purple paleosols which formed on more clay rich parent material were poorly drained the grain size differences reflect basin position in particular distance from a local sediment source avulsion deposits are volumetrically important comprising about half of the floodplain deposits in both areas the avulsion deposits resemble the stage iii splays described by smith et al 1989 smith n d cross ia dufficy j p clough s r 1989 anatomy of an avulsion sedimentology 36 1 24 in terms of characteristics of their ribbon sandstones and the presence of thin sheet sandstones or siltstones paleosols that formed on the fine grained facies show morphologic differences interpreted as developmental differences and attributed to differing rates of avulsion in the two study areas this study shows that avulsion belt paleosols provide a key to understanding avulsion rate in the stratigraphic record other differences between the willwood avulsion deposits in the two areas and between these ancient deposits and the modern avulsion deposits described by smith et al may reflect 1 problems in clearly recognizing ancient avulsion deposits in the field and 2 sampling bias resulting from the areally restricted view provided by the stratigraphic record of an areally extensive modern depositional feature at the same time because exposures are three dimensional the willwood strata reveal aspects of the facies and facies arrangement of avulsion belts not readily observed in the modern ones

ephemeral fluvial deposits integrated outcrop and simulation studies reveal complexity ephemeral fluvial sandstones form the main reservoirs in many oil and gas fields production histories and development difficulties suggest these deposits are more complex than is commonly supposed in the petroleum industry there is inadequate published information to account for this observation relevant sedimentological literature on such deposits is qualitative and unsuitable for detailed reservoir characterization studies therefore integrated sedimentological petrophysical and fluid flow simulation studies have been conducted on outcrop analogs in the southwestern united states our key objectives were to define flow units and to find areas of sensitivity inherent both in the sediments and in the analytical and statistical procedures used to describe and model s ch systems we report results of integrated studies on the lower jurassic kayenta formation in southeastern utah the kayenta formation is a relatively proximal sand rich succession dominated by channel fill sandstones sedimentological analysis identified eight main genetic units in contrast reservoir simulations based on probe permeameter data collected at outcrop show that six of the main genetic units have uniform flow behavior intraformational mudclast conglomerates are the dominant permeability barriers both because of the clasts themselves and because they act as sites of preferential cementation stochastic permeability models conditioned to the outcrop data produce results little different from models based on averaged values for each facies the most sensitive feature of the mode s concerns the assumptions made about the mudclast conglomerates the model results show that only by integrating analytical approaches can we understand the full character of an outcrop analog in such a way that we can use it predictively

respective roles of the guinea current and local winds on the coastal upwelling in the northern gulf of guinea abstractthe northern gulf of guinea is a part of the eastern tropical atlantic where oceanic conditions due to the presence of coastal upwelling may influence the regional climate and fisheries the dynamics of this coastal upwelling is still poorly understood a sensitivity experiment based on the regional oceanic modeling system roms is carried out to assess the role of the detachment of the guinea current as a potential mechanism for coastal upwelling this idealized experiment is performed by canceling the inertia terms responsible for the advection of momentum in the equations and comparing with a realistic experiment the results exhibit two major differences first the guinea current is found to be highly sensitive to inertia as it is no longer detached from the coast in the idealized experiment the guinea current adjusts on an inertial boundary layer the inertial terms defining its lateral extension second the upwelling east of cape palmas disappears in absence of the guinea current detach

provenance of lower paleogene strata in the huerfano basin implications for uplift of the wet mountains colorado u s a abstract sedimentary basins throughout the western interior of north america preserve a record of late cretaceous through latest eocene sedimentation derived from flanking laramide uplifts and sevier hinterland in northern and western basins the strata contain a well documented record of laramide style exhumation however the tectonic histories of more southerly basins such as the huerfano basin studied herein are comparatively poorly known despite being key for understanding the spatiotemporal evolution of laramide tectonism in this study we address this issue with a comprehensive analysis of provenance for the poison canyon cuchara and huerfano formations in the huerfano basin south central colorado u s a as part of our provenance analysis we characterized gravel clast composition petrographic compositions of sandstone bodies n 31 thin sections and u pb detrital zircon age spectra n 848 age determinations from fluvial sandstone units in each of the three formations the results are used to construct a new unroofing and source history for the sediments in the basin that contradicts previous hypotheses diagnostic zircon peaks at 516 517 ma 1423 1430 ma and 1678 1687 ma show that sediment delivered to the huerfano basin did not originate in the san luis highlands or the incipient sangre de cristo mountains but from the precambrian crystalline core and associated cambrian plutons of the wet mountains which were exposed by the time laramide deposition began in the basin there are no detected provenance shifts upsection indicating a largely stable or lithologically uniform sediment source from the paleocene through at least 51 ma this suggests that the major changes recorded in the rock record were more likely related to variations in tectonic and climatic conditions rather than changes in lithology of the rocks being eroded

solutions in chronostratigraphy the paleocene eocene boundary debate and aubry vs hedberg on chronostratigraphic principles abstract in several recent papers m p aubry et al have argued that hedbergian principles of chronostratigraphy are being violated by the international commission on stratigraphy ics when selecting global stratotype sections and points gssps for the formal divisions of the geological time scale the current debate over the definition of the paleocene eocene p e boundary has been a major focus of their arguments unfortunately aubry et al have obscured matters by misusing the term unit stratotype and by equivocally using the term stage for the very different concepts of synthem and global chronostratigraphic stage the p e boundary option most repugnant to aubry et al carbon isotope excursion cie p e thanetian ypresian boundary is perfectly compatible with h d hedberg s views in contrast another option preferred by aubry et al recognition of new 1 m y duration age stage between thanetian and ypresian is inconsistent with hedberg s views additional problems with the p e boundary arguments of aubry et al include the fact that a ypresian unit stratotype does not exist the fact that the base of the ypresian synthem is not immutable and the fact that the nannofossil tribrachiatus digitalis is of dubious relevance to the boundary debate as for chronostratigraphy in general aubry et al have misrepresented hedberg s views by 1 falsely claiming that the content of a stage is what determines its boundaries 2 misunderstanding the general concept of the boundary stratotype 3 distorting the base defines boundary principle 4 falsely claiming that traditional pre gssp chronostratigraphic boundaries cannot be changed 5 falsely implying that traditional stage unit stratotype boundaries can be adjusted by no more than 300 000 years when defining formal age stage boundaries with gssps 6 falsely claiming that the definition of a geochronologic chronostratigraphic boundary should precede its correlation 7 claiming that traditional unconformable stage boundaries may be suitable horizons for gssps 8 distorting the meaning of arbitrariness in regard to the definition of geochronologic chronostratigraphic boundaries and 9 claiming that gssps are inherently unstable in that they are subject to redefinition whenever a more powerful element of correlation is discovered if taken seriously the unit stratotype sanctifying chronostratigraphic philosophy of aubry et al would require the creation of perhaps dozens of new phanerozoic ages stages of relatively very short duration wherever there was a significant gap between two successive historical stage unit stratotypes for all of these reasons the arguments of aubry et al have no merit

complex trace fossils from the terminal proterozoic of namibia we document for the first time the occurrence of the complex trace fossil treptichnus from the terminal proterozoic nama group namibia these traces differ in detail from the cambrian index fossil treptichnus pedum but document precursors with the same basic behavior the producer of the trace is not known in its complexity however this trace fossil provides strong evidence for advanced latest proterozoic bilaterians

trace fossils and biofabrics at the precambrian cambrian boundary interval in western mongolia a small suite of trace fossils from the zavkhan basin govi altay includes many of the ichnotaxa typical of the nemakit daldynian tommotian and younger cambrian stages and other indeterminate forms the traces are almost entirely from the sandstone intervals of the large scale alternations of carbonate and siliciclastic sediments thus emphasizing the facies and taphonomic controls on trace fossil distribution and hence the inherent difficulties in using trace fossils in detailed global correlation especially in using first appearances the assemblage of traces and biofabrics is seen as resulting from the partly non uniformitarian non actualistic sedimentary environments that pertained over the boundary interval rather than as evolutionary failures and subsequently vacated environments

geologically constrained electrofacies classification of fluvial deposits an example from the cretaceous mesaverde group uinta and piceance basins statistical classification methods consisting of the k nearest neighbor algorithm k nn a probabilistic clustering procedure pcp and a novel method which incorporates outcrop based thickness criteria through the use of well log indicator flags are evaluated for their ability to distinguish fluvial architectural elements of the upper mesaverde group of the piceance and uinta basins as distinct electrofacies classes data utilized in training and testing of the classification methods come from paired cores and well logs consisting of 1626 wireline log curve samples each associated with a known architectural element classification as determined from detailed sedimentologic analysis of cores n 9 thickness criteria are derived from outcrop based architectural element measurements of the upper mesaverde group through an approach which integrates select classifier results with thickness criteria an overall accuracy number of correctly predicted samples total testing samples of 83 6 was achieved for a four class fluvial architectural element realization architectural elements were predicted with user s accuracies accuracy of an individual class of 0 891 0 376 0 735 and 0 985 for the floodplain crevasse splay single story channel body and multi story channel body classes respectively without the additional refinement by incorporation of thickness criteria the k nn and pcp classifiers produced similar results in both the k nn and pcp techniques the combination of gamma ray and bulk density wire line log curves proved to be the most useful assemblage tested

mesoscale and submesoscale processes in the southeast atlantic and their impact on the regional thermohaline structure the turbulent processes in the cape basin the southeasternmost gate of the atlantic ocean play a key role in the transport and mixing of upper to intermediate water masses entering the area from the indian ocean making them especially relevant for the indo atlantic transfer of heat and salt in this paper two numerical simulations at different horizontal resolutions are used to study meso and submesoscale dynamics their phenomenology their evolution and their impact on the local water masses submesoscale processes seasonally affect both the upper and intermediate layers but there are clear dynamical differences between the two layers several types of instabilities underline this spatial and temporal variability near the surface mixed layer instabilities occur during winter while mesoscale driven instabilities as the symmetric type prevail in summer the connection between these two seasonal regimes is ensured in anticyclonic eddies and within the mixed layers by charney baroclinic instabilities involved in the local formation and subduction of mode water that we have dubbed as agulhas rings mode water intermediate depths are instead characterized by mesoscale mechanisms of density compensation and lateral stirring of the tracer variance triggering a significant filamentogenesis whose vertical scales are comparable to those mentioned in previous studies this leads to a particularly efficient mixing of antarctic intermediate waters of indian and atlantic origins lagrangian estimates highlight the new and significant role of fine scale structures in setting the water masses properties of upper and lower thermocline waters materializing the indo atlantic exchange and therefore potentially affecting the global ocean circulation

calcic paleosols of the plio pleistocene camp rice and palomas formations southern rio grande rift usa abstract seventy four separate paleosols are recognized in the plio pleistocene camp rice and palomas formations of the southern rio grande rift seven types of profiles are present a bw bk c a bt bk c bw bk c bt bk c bt k c bk c and ak calcic and petrocalcic horizons bk and k commonly overlain by argillic horizons bt dominate most paleosol profiles greater pore size and enhanced permeability typical of sandy and silty parent material favored the development of argillic horizons however micrite is the dominant form of calcium carbonate in bk and k horizons regardless of parent material grain size non calcified a horizons are typically lighter in color than adjacent subsurface pedogenic intervals due to their oxidized nature or lower clay content they are only rarely preserved probably due to erosion prior to final burial calcified root mats ak are not directly associated with other pedogenic horizons abundant horizontal roots suggest root mats formed under high water table conditions restriction of ak horizons to the distal piedmont lithofacies supports their development as spring or pond deposits near the toes of alluvial fans individual pedogenic horizons can often be traced hundreds of meters to kilometers normal and parallel to a basin s axis paleosol maturity and preservation potential are greatest for symmetrical basins especially where pedogenesis was far removed from active channels within the axial fluvial system or within distal piedmont settings of asymmetrical basins

respective roles of remote and local wind stress forcings in the development of warm sst errors in the south eastern tropical atlantic in a coupled high resolution model processes involved in the development of the warm sea surface temperature sst bias in the tropical south eastern atlantic seta in a high resolution hr version of the cnrm cm model are evaluated based on full field initialized seasonal hindcasts starting at 1 february of each year for 2000 2009 whereas the initial sst growth is likely associated with local atmospheric forcing its further development is due to remote oceanic processes a mixed layer heat budget analysis in seta indicates a spurious warm horizontal advection observed as far as south of 25 s that appears at the beginning of march it is associated with an erroneous oceanic mean state at the equator resulting from the mean equatorial westerly wind bias a sensitivity experiment with corrected wind stress over the equatorial region suggests that the remote forcing explains about 57 of the seta sst bias in march may comparison with a lower resolution lr version of the model reveals that in general similar processes are responsible for the sst bias in both models a strong reduction of the bias in the hr model is observed only over the near coastal southern benguela region due to a better representation of atmospheric and oceanic processes controlling the coastal upwelling overall the results of the inter comparison of the seta sst bias evolution in different sensitivity experiments performed in this study can be interpreted in terms of the relative contributions of erroneous warm horizontal advection associated with equatorial forcing and cold horizontal advection associated with local offshore ekman transport

a quantitative approach to soil occurrence in alluvial deposits and its application to the old red sandstone of britain palaeosols fossil soils are a major component of alluvial deposits in the geological record not only do these typically show considerable variations in their degrees of development within single formations but they also exhibit highly complex stratigraphic relationships with one another a simple quantitative approach to these variations is presented which provides a graphical means of assessing differences in soil palaeosol development within a sequence with calcic or petrocalcic horizons to illustrate the approach a range of palaeosols from the siluro devonian old red sandstone of britain are characterized in terms of the likely frequency and magnitude of depositional events which occurred during their formation in particular two alluvial suites from the manorbier area of south wales are analysed using this approach the technique should be widely applicable to other alluvial successions and provides a means of graphicallv presenting relationships between multiple palaeosols although the wide range of rates of formation of calcic and petrocalcic horizons precludes their use to provide narrow estimates of deposition rates

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

quantification of a distributive fluvial system the salt wash dfs of the morrison formation sw u s a abstract recent analysis of modern aggradational continental sedimentary basins reveals that sedimentation patterns are dominated by distributive fluvial systems dfss the salt wash member of the late jurassic morrison formation has previously been described as a fan shaped fluvial system this study characterizes facies variations across the salt wash dfs to quantitatively test predicted trends in conceptual dfs models notable proximal to distal trends include a change in total thickness of the fluvial succession from 174 m to 40 m and an average grain size from coarse sand to silt while the percentage of sand decreased from 70 in the proximal region to 8 in the distal region the proportion of amalgamated channel belt deposits decreased from 67 to 0 while floodplain facies and lacustrine deposits increase 38 to 94 and 0 1 to 7 respectively a downstream decrease in average channel belt thickness 15 m to 3 8 m from thickest to thinnest and average story thickness 7 7 m to 2 3 m from thickest to thinnest is also recorded significant downstream changes in deposit architecture were also noted with proximal regions dominated by stacked channel belt deposits with a high degree of amalgamation distal deposits are dominated by floodplain muds and sheet sandstones and sparse ribbon channels with little to no amalgamation of channel deposits this study provides quantified information for an ancient dfss with the aim of providing a dataset that can be used for objective comparison between different dfss as well as providing numerical data to aid resource exploration and modelling efforts

origins and variability of the benguela current a subset of the benguela sources and transports best 1992 1993 data is analyzed to study the magnitude and variability of the large scale transports in the area the data consist of inverted echo sounder series and conductivity temperature depth stations the mean 16 month transport values for the upper 1000 m indicate that of the 13 sv northward transport within the benguela current 50 is derived from the central atlantic which from geometry may be chiefly south atlantic water 25 comes from the indian ocean which may be chiefly agulhas water and the remaining 25 may be a blend of agulhas and tropical atlantic water a simple schematic of the transport pattern with a somewhat restricted corridor for agulhas eddies translation is envisioned to the west of the eddy corridor flows the south atlantic source for the benguela current to the east is the agulhas indian ocean source the corridor is breached by south atlantic and indian water as the transient eddy field stirs these water masses

oxygen cycling in the northern benguela upwelling system modelling oxygen sources and sinks abstract this paper elucidates the oxygen dynamics in the northern benguela upwelling system by means of process oriented numerical modelling owing to the complex physical biological interaction in this system a coupled hydrodynamic biogeochemical model is required to grasp the various aspects of the oxygen dynamics we used high resolution atmospheric fields derived from observations to force our model available since 1999 the model results represent a 15 years consistent data set of realistic hydrographic and ecosystem variables including oxygen distribution patterns after a concise description of the main aspects of the model we use the model data to analyse the components contributing to the oxygen dynamics namely the ocean circulation the exchange between ocean and atmosphere as well as the local biogeochemical oxygen cycling in the system we thoroughly validate the model with available field observations and remote sensing data the strengths of coastal upwelling which controls the nutrient supply to the euphotic zone as well as the poleward undercurrent that carries oxygen and nutrients to the shelf in the northern benguela upwelling system are well reproduced in the model among the biological oxygen sinks mineralisation in the sediment respiration of zooplankton and nitrification in the water column are important we also found that vertical migration of zooplankton in response to the oxygen conditions provides a regulating feedback which may prevent a complete deoxygenation of suboxic waters as long as oxygen or nitrate are available in the bottom waters the activities of chemolithoautotrophic sulphur bacteria on the sediment surface keep the redoxcline within the sediment and prevent the release of hydrogen sulphide into the water column by horizontal integration of the simulated ocean atmosphere oxygen flux it can be shown that the kunene upwelling cell between 16 s and 18 s is a boundary between the equatorial ocean characterise by weak oxygen release to the atmosphere and the subtropical benguela upwelling system governed by an enhanced and seasonal varying flux furthermore a comparison of oxygen fluxes controlled by physical transport versus biogeochemical processes shows that the physical processes dominate in the northern benguela upwelling system

braided river deposits in a muddy depositional setting the molina member of the wasatch formation paleogene west central colorado u s a the molina member is a paleogene sand rich interval up to 125 meters thick found within the otherwise mud dominated nonmarine wasatch formation of west central colorado sandstone beds of the molina member form sheet like units interbedded with subordinate volumes of mudstone the sandstones contain a low diversity assemblage of sedimentary structures that is commonly dominated by horizontal planar laminae and bedding is locally contorted by large scale soft sediment deformation a braided fluvial model best explains the characteristics of these strata yet the existing braided river models do not fully account for the assemblage of sedimentary structures or the relatively high volumes up to half of the section of interbedded mudstones two modern braided rivers medano creek colorado and the prairie dog town fork of the red river texas have rapid shallow flows that form horizontal planar bedding in both systems the presence of large volumes of easily mobilized sandy sediment a flashy discharge regime and a lack of reworking between flood stages lead to the development of high energy shallow water bedforms and the preservation of the resulting high energy sedimentary structures similar conditions and processes are suggested to have controlled deposition of the sand dominated molina member which is a depositional anomaly within the otherwise muddy wasatch formation short term availability of readily eroded second cycle sandstones from a newly elevated source area to the southeast is the most likely reason for the abrupt change from a mud dominated fluvial system to the sandy molina system

sandy high energy flood sedimentation some criteria for recognition with an example from the devonian of s w england abstract many modern sand deposits resulting from episodic floods in semi arid zones are dominated by parallel laminations but parallel laminated sands are not a major feature in perennial streams single flood events may deposit over 1 5 m of parallel laminated sand hence ancient parallel laminated sand dominated alluvial deposits may be the product of ephemeral flows the trentishoe formation hangman sandstone group middle devonian of north devon consists in part of laterally extensive beds of parallel laminated fine grained red sandstones that build multistorey sand bodies individual beds are little more than 1 m thick but may extend laterally for hundreds of metres a vertical sequence of erosion surface sparse silt clasts parallel laminations silt drape is often found suggesting high flow stage deposition of plane bedded sand followed by a very rapid waning of flow with silt fallout in the final stages of the flood this sequence bears marked similarity to certain modern ephemeral flow sands

sedimentology and stratigraphic architecture of the late permian betts creek beds queensland australia abstract the late permian betts creek beds form a succession of coal bearing alluvial coastal plain sediments in a basin marginal setting within the northeastern galilee basin queensland australia the unit is 50 60 m in thickness at porcupine creek national park where outcrop is laterally continuous for several kilometers eight facies have been identified within the formation and can be grouped into 2 facies associations a channel deposits and b floodbasin deposits the channel association consists of conglomerate a1 and trough cross bedded multistorey sandstone facies a2 both interpreted as deposits of low sinuosity river systems tidally influenced fluvial channels a3 interbedded sandstone and siltstone a4 interpreted as the abandonment fill of the alluvial systems and diamictite a5 interpreted as debris flows the floodbasin facies association is composed of sandy siltstone b1 proximal distal floodbasin carbonaceous siltstone b2 mire and bioturbated siltstone b3 estuarine facies the overall sediment body architecture can be resolved into 6 unconformity bounded cycles interpreted as sequences in the genetic sense which are sheet like in geometry and in general consist of amalgamated multistorey multilateral braided fluvial deposits at the base overlain by extensive sheet like overbank mudstones carbonaceous shales and coals sea level change is interpreted as the primary control on the sequence architecture of the formation while the internal stratigraphic architecture however varies between sequences and is a function of a combination of sea level tectonic and autogenic controls

tectonic control on facies distribution of the camp rice and palomas formations pliocene pleistocene in the southern rio grande rift the pliocene pleistocene camp rice and palomas formations in the rio grande rift of southern new mexico provide an excellent test of the role of basin symmetry in the distribution of piedmont and axial fluvial facies in the asymmetrical palomas and northern mesilla basins the axial fluvial facies is characterized by multistory channel sands and sandstones and is concentrated near the locus of maximum subsidence within a few kilometers of the footwall scarp fanglomerate derived from the footwall uplift extends only a few kilometers or less from the footwall scarp whereas alluvial fan and alluvial flat conglomerate sand and mudstone deposited on the hanging wall dip slope occupy a much wider outcrop belt in the symmetrical hatch rincon basin the axial fluvial facies extends to within a few kilometers of both the northern and southern basin margins and has a much higher percentage of fine grained overbank deposits some of which contain calcareous paleosols in all three basins a tongue of fanglomerate as much as 30 m thick prograded over the axial fluvial facies near the end of camp rice and palomas deposition the distribution of facies of the camp rice and palomas formations supports previously published models that predict a two stage history of asymmetrically subsiding basins during tectonically active periods axial river channels preferentially avulse into the topographically lowest area of the alluvial plain which is directly above the axis of maximum subsidence during the postorogenic stage when erosion rate exceeds subsidence rate coarse transverse dispersed sediment progrades toward the center of the basin

new carbon isotope stratigraphy of the ediacaran cambrian boundary interval from sw china implications for global correlation the yangtze platform preserves relatively thick carbonate successions and excellent fossil records across the ediacaran cambrian boundary interval the intensely studied meishucun section in east yunnan was one of the global stratotype section candidates for the precambrian cambrian boundary however depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified the laolin section located in ne yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the precambrian cambrian boundary however the stratigraphic framework and correlations were controversial we studied and systematically sampled the laolin section and present here new carbon isotope data for this section the laolin section consists of in ascending order the baiyanshao dolostone of the dengying formation the daibu siliceous dolostone zhongyicun dolomitic phosphorite lower dahai dolostone and upper dahai limestone of the zhujiaqing formation and the black siltstone of the shiyantou formation our data reveal a large negative 13 c excursion 7 2 l1 in the daibu member which matches the previously published data for the laolin section and a large positive excursion 3 5 l4 in the dahai member which was not shown in the published data the excursion l1 correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in siberia and mongolia similar magnitude excursions are also known from morocco and oman for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 ma thus confirming a global biogeochemical event near the ediacaran cambrian boundary our data also indicate that deposition was more continuous at the laolin section compared with the meishucun section where there are no records of a comparable negative excursion near the ediacaran cambrian boundary nor any comparable positive excursion in the dahai member therefore the laolin section has proven potential to be a supplementary global stratotype section for the ediacaran cambrian boundary on the yangtze platform

precambrian cambrian boundary global stratotype ratified and a new perspective of cambrian time the precambrian cambrian boundary global stratotype is the base of the phycodes pedum zone at fortune head southeastern newfoundland the initial two stage radiation of the phanerozoic fauna the appearance of phanerozoic aspect trace producers and subsequent origin of diverse skeletalized metazoans was earliest cambrian fossil assemblages with deep complex burrows or originally mineralized skeletal fossils with exception of cloudina are early cambrian or younger correlation into avalon indicates that strata once referred to the proterozoic e g manykaian or nemakit daldynian and rovno stages are lowest cambrian and that the siberian tommotian stage is middle lower cambrian the thick sequence and complex epeirogenic history of the placentian series as compared with the trilobite bearing branchian series suggest that most early cambrian time is represented by the subtrilobitic lower cambrian

paleoclimatic controls on stable oxygen and carbon isotopes in caliche of the abo formation permian south central new mexico u s a abstract the stable oxygen and carbon isotopic composition of caliche in fluvial and supratidal rocks of the abo formation permian south central new mexico is controlled by paleoclimate and depositional environment fluvial caliche consists of low mg calcite nodules and vertically oriented tubules that display stage ii texture micrite matrix support brecciation ooids pisoliths aveolar septal texture and peloids are common in the fluvial caliche and along with red color and slickensides in the host shale indicate pedogenesis in a well oxidized vadose zone in contrast periodic waterlogging of the supratidal paleosols probably due to high water table is indicated by drab colors carbonaceous flecks horizontal rhizoliths and the paucity of vadose textures in the stage ii caliche n dules stable oxygen isotopes are similar in the fluvial and supratidal caliches and range from 21 6 to 30 5 smow the data exhibit a crude bimodality and 18o enrichment with a decrease in age higher in the section consideration of these data in the context or temperature relations suggests that 1 surface waters responsible for caliche formation increased in 18o from roughly 8 to 1 over the 18 m y time interval that separated the lowest stratigraphic nodule horizon from the highest 2 the inc easing 18o values also reflect a warming trend approximately 15 to nearly 3 c in the mean monthly temperature over this same time period with perhaps an associated increase in permian ocean temperatures and 3 the significant variation in 18o from oldest to youngest caliche was probably enhanced by the amount effect such that as the temperature increased the amount of precipitation decreased resulting in high 18o values caliches in the abo are enriched in heavy carbon 7 2 to 1 5 pdb compared to that of soil carbonate derived exclusively from c plants 12 pdb and the supratidal caliches contain somewhat heavier carbon compared to the fluvial caliche the 13c values for both environments increase with a decrease in caliche age these results indicate that as the temperature increased and rainfall decreased with time the level of c3 plant productivity apparently declined allowing a greater influx of atmospheric co2 into the soil this can only occur when soil respiration rates are quite low or at very sha low depths less than 10 cm or both atmospheric co2 seems to have invaded the supratidal soils to a somewhat greater extent than the fluvial soils

when did the anthropocene begin a mid twentieth century boundary level is stratigraphically optimal abstract we evaluate the boundary of the anthropocene geological time interval as an epoch since it is useful to have a consistent temporal definition for this increasingly used unit whether the presently informal term is eventually formalized or not of the three main levels suggested an early anthropocene level some thousands of years ago the beginning of the industrial revolution at 1800 ce common era and the great acceleration of the mid twentieth century current evidence suggests that the last of these has the most pronounced and globally synchronous signal a boundary at this time need not have a global boundary stratotype section and point gssp or golden spike but can be defined by a global standard stratigraphic age gssa i e a point in time of the human calendar we propose an appropriate boundary level here to be the time of the world s first nuclear bomb explosion on july 16th 1945 at alamogordo new mexico additional bombs were detonated at the average rate of one every 9 6 days until 1988 with attendant worldwide fallout easily identifiable in the chemostratigraphic record hence anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal while also being recognized using a wide range of other stratigraphic criteria this suggestion for the holocene anthropocene boundary may ultimately be superseded as the anthropocene is only in its early phases but it should remain practical and effective for use by at least the current generation of scientists

coastally trapped eddies in the north of the gulf of guinea cyclonic eddies generated downstream of cape palmas and cape three points have been suggested to contribute to the coastal upwelling along the northern coast of the gulf of guinea a numerical analysis using a high resolution model is used to investigate the mesoscale activity and the coastal upwelling generation processes an eddy detection and tracking tool is applied to altimeter and model data showing good agreement between these data sets about two cyclonic eddies per year with an average radius of 60 km were identified downstream of both capes these cyclonic eddies have an average lifetime of about 60 days during the major coastal upwelling period boreal summer and an eastward propagation these cyclonic eddies are shallow energetic their relative vorticity can reach 3 times the earth s rotation and dimensionless parameters show that they are in an eddy shedding regime mean flow interactions and barotropic instabilities associated with capes are their main generation processes an idealized experiment is conducted in order to analyze the effect of capes on eddy generation and on coastal upwelling it reveals that these cyclonic eddies generated downstream of capes are not the process responsible for this coastal upwelling this experiment also suggests that the cyclonic eddies are the cause of the westward and coastal guinea counter current that is associated with a transfer of energy from eddy kinetic to the mean flow

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

bed form dependent pulsating flow in medano creek southern colorado some sand bed streams exhibit unsteady supercritical flow in the form of periodic bores that propagate downstream the bores are formed by unstable antidunes which store water while growing in amplitude and then release the stored water when the antidunes wash out to form a plane bed a cyclic process of antidune growth oversteepening antidune breaking then bed form washout produced bores on regular periodic intervals of roughly 15 s in medano creek great sand dunes national monument colorado this periodic bore generating pulsating flow is bed form dependent and it requires sufficiently high flow velocities and sediment transport rates to form unstable breaking antidunes the froude number maximum is 1 8 below that required for slug flow pulsating flow has been observed in flumes arroyos and rivers and it may be more common than initially anticipated its high erosive capacity can influence both channel morphology and the character of associated sedimentary deposits

reconstructing the ancestral plio pleistocene rio grande in its active tectonic setting southern rio grande rift new mexico usa deposits of the ancestral rio grande arg belonging to the camp rice formation are preserved and exposed in the uplifted southern portion of the robledo mountains horst of the southern rio grande rift the sediments are dated palaeomagnetically to the gauss chron upper pliocene the lower part of the succession lies in a newly discovered palaeocanyon cut into underlying eocene rocks whose margins are progressively onlapped by the upper part detailed sedimentological studies reveal the presence of numerous river channel and floodplain lithofacies indicative of varied deposition in channel bar complexes of low sinuosity pebbly sandbed channels that traversed generally dryland floodplains and shifted in and out of the study area five times over the 1 myr or so recorded by the succession notable discoveries in the deposits are 1 complexes of initial avulsion breakout channels at the base of major sandstone storeys 2 common low angle bedsets ascribed to deposition over low angle dunes in active channels 3 palaeocanyon floodplain environments with evidence of fluctuating near surface water tables sandbody architecture is generally multistorey with palaeocurrents indicative of funnelling of initial avulsive and main fluvial discharge from the neighbouring mesilla basin through a narrow topographic gap into the palaeocanyon and out over the study area an avulsion node was evidently located at the stationary southern tip to the east robledo fault during gauss times with arg channels to the north flowing close to the fault and preventing fan progradation subsequent matuyama growth of the fault caused 1 deposition to cease as the whole succession was uplifted in its footwall 2 development of a thick petrocalcic horizon and 3 fan progradation into the mesilla basin parameters for the whole arg fluvial system are estimated as active single channels 2 m deep and 25 m wide valley slope 0 24 0 065 maximum mean aggradation rate 0 05 mm year 1 major channel belt avulsion interval 200 ky individual channel recurrence interval 100 ky minimum bankfull mean flow velocity 1 54 m s 1 minimum single channel discharge 77 m3 s 1 bed shear stress 22 3 n m 2 and stream power 34 3 w m 2

the benguela upwelling system quantifying the sensitivity to resolution and coastal wind representation in a global climate model abstractof all the major coastal upwelling systems in the world s oceans the benguela located off southwest africa is the one that climate models find hardest to simulate well this paper investigates the sensitivity of upwelling processes and of sea surface temperature sst in this region to resolution of the climate model and to the offshore wind structure the community climate system model version 4 is used here together with the regional ocean modeling system the main result is that a realistic wind stress curl at the eastern boundary and a high resolution ocean model are required to well simulate the benguela upwelling system when the wind stress curl is too broad as with a 1 atmosphere model or coarser a sverdrup balance prevails at the eastern boundary implying southward ocean transport extending as far as 30 s and warm advection higher atmosphere resolution up to 0 5 does bring the atmospheric jet closer to the coast but there can be too strong a wind stress curl the most

new uppermost cambrian u pb date from avalonian wales and age of the cambrian ordovician boundary a crystal rich volcaniclastic sandstone in the lower peltura scarabaeoideszone at ogof ddu near criccieth north wales yields a u pb zircon age of 491 1 ma this late late cambrian date indicates a remarkably young age for the cambrian ordovician boundary whose age must be less than 491 ma hence the revised duration of the post placentian trilobite bearing cambrian indicates that local trilobite zonations allow a biostratigraphic resolution comparable to that provided by ordovician graptolites and mesozoic ammonites

seasonal variability of alongshore winds and sea surface temperature fronts in eastern boundary current systems seven years of satellite observations 2003 2009 are used to describe variability in sea surface temperature sst fronts and in the alongshore component of ocean winds and to investigate their relations in four eastern boundary current systems ebcs the general patterns of sst frontal activity are remarkably similar in all ebcs with high frontal probabilities along the coast decreasing with distance from the coastline results from empirical orthogonal function decompositions reveal that the seasonal evolution of sst fronts and wind stress are significantly correlated with intensified upwelling favorable winds associated with an increase in frontal probabilities an offshore migration of the region of high frontal activity is observed during the period of upwelling favorable alongshore wind stress in ebcs in all regions the seasonal variability of frontal activity and wind stress is stronger at mid than at low latitudes the width of the region of high frontal activity is relatively broader in the california and benguela current systems and narrower in the canary and humboldt current systems the width of the band of high frontal activity may be influenced by multiple factors including wind forcing flow topography interactions and mesoscale dynamics while seasonal variability in frontal activity in the california current system acts to reinforce or weaken the average pattern they are substantially different in the canary current system where there is little overlap in the areas characterized by persistent and seasonally varying front activity

hydrographic variability in the st helena bay region of the southern benguela ecosystem cross shelf distributions of temperature salinity water masses and dissolved oxygen in st helena bay revealed substantial vertical and seasonal variations in the surface layers nearshore and offshore temperature and salinity patterns differed with bay scale variability linked to upwelling dynamics and coastal processes while the offshore region was influenced by solar insolation spectral analysis revealed that an annual signal prevailed at most stations and corroborated contrasting patterns between the offshore and nearshore regions with phase differences suggesting shoreward propagation of the offshore temperature signal the shelf was dominated by modified upwelled water muw and subantarctic mode water samw which comprised the primary source of upwelled water clear zonation of muw was evident across the shelf resulting from seasonal variations in locations of the oceanic and bifurcated shelf break fronts dynamics within st helena bay consistently differed from those further offshore due to the influences of the shelf break front cape columbine upwelling plume and cyclonic recirculation which appeared to be associated with an intraannual signal with a periodicity of 3 4 months persistent hypoxia in the bottom waters suggested the occurrence of a permanent reservoir of low oxygen water low seasonal shoreward and offshore expansion of low occurred throughout the upwelling season with maximum extent reached during summer and autumn due to the coupled effects of advection and local phytoplankton decay while wind mixing ventilated the water column at nearshore stations in winter and the onset of upwelling during spring introduced oxygen richer water from further offshore hypoxia persisted in the center of the bay

medano creek colorado a model for upper flow regime fluvial deposition abstract medano creek in colorado provides a unique opportunity to study upper flow regime deposition it is a steep aggrading fluvial system in which antidunes are the dominant bedform medano creek is a straight single channel stream where flow is largely confined to a sequence of upstream migrating topographic steps pools and riffles a stable channel geometry antidunes and upperflow regime plane beds are arranged in an organized pattern on the surface of pool and riffle sequences as a response to spatially varied flow conditions in the creek antidunes form sedimentary structures consisting of low angle backset and foreset beds and subhorizontal laminae grouped into lenses laminae in a lens are often subparallel to the lens bounding surfaces on the downcurrent end and are truncated y the upper bounding surface on the upcurrent end upper flow regime plane bed and rhomboid ripples produce planar laminae through lateral shifting of the active channel and upstream migration of pools and riffles medano creek produces a facies sequence consisting of alternating 10 40 cm thick layers of planar laminae and low angle cross stratified lenticular bedding

a deep root for the cambrian explosion implications of new bio and chemostratigraphy from the siberian platform much uncertainty remains as to the temporal relationship between the ediacaran and cambrian biotas yet this is critical to our understanding of the rise of metazoans here we present new high resolution carbon isotope chemostratigraphy and biostratigraphy for a terminal ediacaran to cambrian succession on the eastern siberian platform russia which shows the presence of a succession of diverse fossil assemblages before the start of the basal cambrian negative carbon isotope excursion bace soft bodied ediacaran biota beltanelliformis occur before the start of the late ediacaran positive carbon isotope plateau epip a mixed ediacaran and cambrian skeletal biota cloudina anabarites cambrotubulus appears within the epip and diverse cambrian type small shelly fossils including protohertzina and other protocondonts halkieriids chancelloriids hyoliths hyolithelminthes and the burrowing trace fossil diplocraterion appear at the beginning of the bace these integrated data show that taxa attributed to so called ediacaran and earliest cambrian skeletal biotas in fact overlap without notable biotic turnover and thus refute the presence of a large isotope excursion coincident with mass extinction of all ediacaran biota we propose a new biozone the cloudina namacalathus sinotubulites assemblage zone to precede the known small shelly fossil ssf zones these observations raise doubts as to whether there is any true separation between the ediacaran and cambrian skeletal biotas and suggest that there is a deep root for the cambrian explosion of metazoans

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents

geochemical changes across the proterozoic cambrian transition in the durmala phosphorite mine section mussoorie hills garhwal himalaya india abstract the transition from the neoproterozoic nemakit daldynian 1 krol e dolomite to the tommotian lower tal phosphorite chert black shale sequence denotes a period of drastic change in the depositional environment and the chemical milieu of the sedimentation basin these changes are reflected by a marked negative excursion of carbon isotopes phosphorus enrichment trace metal content high organic carbon burial and notably the first appearance of prolific small shelly fauna and burrowing organisms recent studies have documented these changes along several stratigraphic profiles in the mussoorie hills of the garhwal himalaya for which a single profile from the durmala phosphorite mine provides a key section discussed here

the benguela a laboratory for comparative modeling studies abstract equilibrium dynamics of the benguela system is investigated using the holistic nature of the spatially and temporally cohesive output of a numerical model the regional ocean modeling system roms is used to simulate the benguela system in its entirety it successfully simulates the cool coastal upwelling regime and its division into seven distinctly separate cells as well as the large scale offshore regime and the respective seasonal fluctuations it does however present a cool bias at the coast due to an underestimation of the coastal wind drop off as well as a warm bias offshore in the southern benguela due to the overestimation of agulhas current input the benguela can be divided into northern and southern regimes based on dynamic as well as topographic differences topographically the division between the northern and southern regimes coincides with an abrupt narrowing of the continental shelf toward the north at 28 s the large scale depth integrated flow to the north of this feature is weak but distinctly poleward while to the south the flow regime is governed by the meandering nature of the equatorward benguela current and is the pathway for eddies that originate at the agulhas retroflection the poleward flowing regime of the northern benguela is tied to the sverdrup relation which links meridional transport with wind stress curl the luderitz upwelling cell at 27 s experiences the most vigorous upwelling throughout the year and as a result offshore volume fluxes in this region are extremely large this upwelling cell divides the northern and southern benguela coastal upwelling systems into separate regimes based on the fact that their seasonal signals are out of phase the offshore gradient of eddy kinetic energy eke is generally strong in the benguela system and exceptionally so in the southern benguela due to vigorous mesoscale activity offshore of the shelf edge originating from the agulhas retroflection area the juxtaposition between the steep offshore eke gradients in the south and much weaker offshore gradients of eke in the northern benguela has different implications for cross shore exchanges