onset of scour below pipelines and self burial abstract this paper summarizes the results of an experimental study on the onset of scour below and self burial of pipelines in currents waves pressure was measured on the surface of a slightly buried pipe at two points one at the upstream side and the other at the downstream side of the pipe both in the sand bed the latter enabled the pressure gradient which drives a seepage flow underneath the pipe to be calculated the results indicated that the excessive seepage flow and the resulting piping are the major factor to cause the onset of scour below the pipeline the onset of scour occurred always locally but not along the length of the pipeline as a two dimensional process the critical condition corresponding to the onset of scour was determined both in the case of currents and in the case of waves once the scour breaks out it will propagate along the length of the pipeline scour holes being interrupted with stretches of soil span shoulders supporting the pipeline as the span shoulder gets shorter and shorter more and more weight of the pipeline is exerted on the soil in this process a critical point is reached where the bearing capacity of the soil is exceeded general shear failure at this point the pipe begins to sink at the span shoulder self burial it was found that the self burial depth is governed mainly by the keulegan carpenter number the time scale of the self burial process on the other hand is governed by the keulegan carpenter number and the shields parameter diagrams are given for the self burial depth and the time scale of the self burial process

terrigenous sediment supply in the scotia sea southern ocean response to late quaternary ice dynamics in patagonia and on the antarctic peninsula geochemical and mineralogical compositions of modern and late quaternary marine sediments from the scotia sea trace sources and transport paths of terrigenous sediment we discuss downcore variations of compositional data of two sediment cores from the northern and southern scotia sea that correlate with fluctuations in magnetic susceptibility sediments were derived from very different sources at both localities as revealed by contrasting clay mineral assemblages however a common feature is the input of more basic and undifferentiated crustal material with the potential of high magnetic susceptibility during glacial periods indicated by variable quartz feldspar ratios and major trace and rare earth elements terrigenous sediments mainly originate from nearby terrestrial sources or are introduced through interbasinal sediment transfer from adjacent seas the observed temporal compositional variations have to be attributed to changes in the relative detrital contributions from the diverse source areas ice mass extensions in southern patagonia on the antarctic peninsula and adjacent islands likely control the supply of glaciogenic detritus to the open ocean during times of glacial expansion diluting the sediment input of interbasinal origin current transport is mainly responsible for sediment dispersal to the pelagic scotia sea and may amplify the glaciological source signals during glacial climate periods because of a stronger wind forcing of the antarctic circumpolar current

a numerical model for onset of scour below offshore pipelines abstract a numerical model is developed to predict the onset of local scour below offshore pipelines in steady currents and waves the scour is assumed to start when the pressure gradient underneath the pipeline exceeds the floatation gradient of the sediments in this model the water flow field above the bed is determined by solving the two dimensional 2 d reynolds averaged navier stokes equations with a k turbulence closure the seepage flow below the seabed is calculated by solving the darcy s law laplace s equation with known pressure distribution along the common boundaries of the flow domains seabed the numerical method used for both the turbulent flow around the pipeline and darcy s flow in the seabed is a fractional finite element method the average pressure gradient along the buried pipe surface is employed in the evaluation of onset condition with a calibration coefficient the numerical model is validated against experimental data available in literature a unified onset condition for steady currents and waves is proposed influences of flow parameters including water depth embedment depth boundary layer thickness reynolds number re and keuleagan carpenter kc number on the pressure drop coefficient over the pipeline are studied systematically

late pleistocene holocene eolian deposits of the southern buenos aires province argentina a preliminary model abstract the aim is to reconstruct the sedimentological history of the late pleistocene holocene eolian deposits of southern buenos aires province hence a preliminary model is proposed in order to analyze the different stages of the sedimentological cycle the deposits include sandy loess fine sand sheets and dunefields the southern buenos aires province represents the depositional area whereas the source and transport environments are located in the northern patagonian andes and northern extra andean patagonia according to the mineralogical characteristics of the material explosive volcanism is considered the predominant process of particle formation particularly as generator of pyroclastic deposits which were reworked by different erosive processes glacial fluvial eolian during the late glacial maximum and the holocene alluvial deposits which were mainly generated by fluvial erosion of volcaniclastic sedimentary units were deposited along the floodplains of the colorado and negro rivers including those distal segments located in the emerged offshore platform the fluvial regime depended upon the regime of the glaciers hence it reflected the major glacial fluctuations which took place in the andes floodplains were deflated by southwest winds transporting the material towards the southern buenos aires province sandy loess and loessial sands and to la pampa province dunefields

quaternary glaciations in the southern hemisphere an overview abstract large glacier systems in antarctica have existed at least since the early miocene glaciers in the patagonian andes advanced in the late miocene and fluctuated several times during the pliocene as did ice masses elsewhere in the southern hemisphere sedimentological evidence of glaciation during the early and middle quarternary is best preserved in volcanic regions patagonia new guinea africa but is poorly constrained by dating there is evidence of glaciation during oxygen isotope stages 10 8 and 6 in several parts of the southern hemisphere but the only well dated advance of the middle quarternary is that of stage 6 in the transantarctic mountains during the last glaciation montane glaciers in parts of the southern hemisphere were as large during isotope stage 4 as during isotope stage 2 the last glaciation maximum stage 2 is well dated in tasmania new zealand and patagonia culminating as 21 18 ka bp following slight recession from the lgm limits late glacial advances peaked at 15 14 ka bp and at 12 10 ka bp major holocene advances occurred on at least three occasions during the last 5 ka in areas presently glacier covered

clear water scour below underwater pipelines under steady flow experiments on clear water scour below underwater pipelines initially laid on the sediment bed in uniform and nonuniform sediments under steady flow were conducted equilibrium scour profiles were modeled by a cubic polynomial the experimental results are examined to describe the influence of various parameters on equilibrium scour depth the equilibrium scour depth ds increases with increase in approach flow depth h for shallow flow depths becoming independent of higher flow depths when h b 5 where b pipe diameter however the curves of scour depth versus sediment size d and froude number fb have a maximum value of ds b 1 65 at b d 27 and fb 0 6 the influence of sediment gradation on scour depth is prominent for nonuniform sediments which reduce scour depth to a large extent due to the formation of armor layer within the scour hole the influence of different shaped cross sections of pipes on the scour depth was investigated where the shape factors for circular 45 diagonal facing and 90

pedosedimentary and palaeoenvironmental significance of a holocene alluvial sequence in the southern pampas argentina a representative section of the holocene alluvial record of the southern pampas argentina com prises a sequence of clastic sediments a diatomite and two palaeosols detailed macro and micromorphological descriptions provide the basis for the reconstruction of its pedosedimentary history combining the pedosedi mentary reconstruction with palaeoecological data allows a detailed overview of alluvial landscape development and associated palaeoenvironmental change in the region during the holocene the early holocene shift from a subhumid dry to humid climate was marked initially by a diminution in clastic sedimentation the development of the puesto callejon viejo soil and then re establishment of fluvial aggradation with a dominance of bioclastic sedimentation loess inputs increased during the mid holocene as the climate reverted to subhumid dry and temporary subaerial exposure of the sediments led to the formation of the puesto berrondo soil more variable environmental conditions followed with natur

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

climatic interpretation of a 1 9 ma environmental magnetic record of loess deposition and soil formation in the central eastern pampas of buenos aires argentina abstract much of what we know about quaternary climate has been learned from sedimentary records from the world s oceans with the exception of the extensive studies of the chinese loess paleosol sequence and more recent studies of long lake records there are few long terrestrial climate records particularly from the southern hemisphere the loess record of argentina provides an important opportunity to further our understanding of climate change from a terrestrial environment but its complexity and discontinuity have led to difficulty in formulating a climatological model of depositional and pedogenic processes in this study we present one of the longest and most continuous loess loessoid records from the central eastern pampas of argentina our age model is based on optically stimulated luminescent dates and a paleomagnetic reversal stratigraphy and indicates a basal age around 1 9 ma within the age model uncertainties we characterize the environmental magnetic properties associated with loess deposition and soil formation with respect to wind patterns moisture availability and temperature major changes in magnetic grain size are linked to a differential northward shift of the subtropical high pressure cell during glacial periods we suggest that coarser finer magnetic grains correspond to weaker stronger glacial periods when the high pressure cell is located in a more southerly northerly position and the source region is more proximal distal to our study area an abrupt increase in the ultrafine grained magnetic material around 0 9 ma is related to an increase in moisture transport from the south atlantic driven by an increase in summer sea surface temperatures at the mid pleistocene transition 1 ma in addition to these grain size variations there is a relative decrease in the amount of goethite compared to hematite beginning around 0 5 ma which has been related to the temperature increase observed after the mid brunhes event 450 ka in the epica ice core temperature record a more detailed comparison to insolation indicates that for portions of the record ferrimagnetic minerals are depleted during periods of low insolation this result suggests that argentine loess deposition and soil formation follows a model more similar to the alaskan loess sequences than the chinese loess sequences although further work is needed to validate the models and mechanisms proposed in this study our record indicates that the mineral magnetic properties of the loess and paleosol deposits record major changes in deposition and soil formation and provide insight into possible mechanisms relating to global and or hemispheric climate change

magnetic fingerprint of the late holocene inception of the rio de la plata plume onto the southeast brazilian shelf abstract measurement of changes in the assembly of magnetic particles in sediment records is useful both for paleoclimatic and paleoceanographic reconstructions and for assessing provenance and pathways of sediment transport in this study we provide detailed rock magnetic analysis along with scanning electron microscopy sem ti ca ratio and particle size distribution of the decarbonated fraction of sediments to trace terrigenous source changes during the last 6 cal kyr bp in core 7610 collected on the se brazilian continental shelf magnetic mineralogy data indicate a gradual shift between two distinct sources of sediments 1 dust from southern south america patagonia central western argentina and puna altiplano plateau and 2 sediments eroded from the weathered volcanics of parana basin these materials reached the continental margin off argentina and uruguay by different pathways and were transported northward by the brazilian coastal current bcc the chronology of events related to the environmental record of core 7610 indicates that between 6 and 4 7 cal kyr bp dry conditions over continental south america resulted in enhanced eastward eolian transport of the argentinean loess and a limited discharge of the rdlp river load into the atlantic ocean at this time the sedimentary magnetic fraction that reached the se brazilian shelf reflect predominantly loessic sources transported from the pampean terraces to the argentinean and uruguay shelves and then distributed northward by the shelf current system from 4 7 to 2 cal kyr bp the climate became gradually wetter over the continent and the contribution of oxidized phases from the weathered parana basin mainly from the basaltic and acidic volcanics started to become important this change in climate overlaps in time a with the late holocene sea level fall recorded along the se south american coast later from 2 up to 0 9 cal kyr bp even wetter conditions were prevalent in s and se south america and the rdlp sedimentary load became the main source of sediments transported to the se brazilian shelf by the bcc the magnetic record of core 7610 reported here together with other paleoenvironmental tracers palynology geochemistry and stable isotopes thus indicates that the inception of the rdlp plume onto the se brazilian shelf started as early as 4 7 cal kyr bp and has been strengthened since then mostly due to changes in precipitation over south america and to a smaller extent by sea level changes

effects of biodegradation on australian permian coals abstract permian coals from blackwater poitrel and moura bowen basin queensland have been extracted and characterised by detailed organic geochemical techniques a variety of source related aliphatic and aromatic biomarker parameters indicate that these coals from three different locations are similar in terms of organic matter type and palaeoenvironment of deposition the hydrocarbons extracted from these coals appear to have been generated from predominantly plant derived organic matter deposited in a fluvio deltaic environment moderately high pr ph ratios the high proportion of c 29 steranes and very low sterane to hopane ratios are indicative of their largely terrestrial source molecular maturity parameters derived from aliphatic and aromatic biomarkers corroborate a measured maturity of 1 0 1 1 r o for these medium volatile bituminous coals the aliphatic and aromatic hydrocarbon distributions in these coals also allow their differentiation into two groups biodegraded moura coals and non degraded blackwater and poitrel coals comparison of various compound ratios from the degraded and non degraded coals indicate the dependence of susceptibility to biodegradation on precise molecular structures major aromatic compound classes in coals generally regarded as being more resistant may be microbially altered before branched cyclic alkanes are affected and even before the n alkanes are completely removed as reported in crude oils susceptibility to biodegradation of aromatic hydrocarbons decreases with increasing number of aromatic rings and with increasing number of alkyl substituents furthermore alkylnaphthalenes with 1 6 dimethyl substitution patterns are more susceptible to degradation than other alkylnaphthalene isomers this study reveals that biodegradation may alter the hydrocarbon composition of coals in a similar way to that observed in crude oils or oil spills except that aromatic hydrocarbons are altered relatively earlier than aliphatic hydrocarbons in coals compared to oils

depositional provinces dispersal and origin of terrigenous sediments along the se south american continental margin abstract continental margin sediments of se south america originate from various terrestrial sources each conveying specific magnetic and element signatures here we aim to identify the sources and transport characteristics of shelf and slope sediments deposited between east brazil and patagonia 20 48 s using enviromagnetic major element and grain size data a set of five source indicative parameters i e fd arm irm s0 3t sirm fe and fe k of 25 surface samples 16 1805 m water depth was analyzed by fuzzy c means clustering and non linear mapping to depict and unmix sediment province characteristics this multivariate approach yields three regionally coherent sediment provinces with petrologically and climatically distinct source regions the southernmost province is entirely restricted to the slope off the argentinean pampas and has been identified as relict andean sourced sands with coarse unaltered magnetite the direct transport to the slope was enabled by rio colorado and rio negro meltwaters during glacial and deglacial phases of low sea level the adjacent shelf province consists of coastal loessoidal sands highest hematite and goethite proportions delivered from the argentinean pampas by wave erosion and westerly winds the northernmost province includes the plata mudbelt and rio grande cone it contains tropically weathered clayey silts from the la plata drainage basin with pronounced proportions of fine magnetite which were distributed up to 24 s by the brazilian coastal current and admixed to coarser relict sediments of pampean loessoidal origin grain size analyses of all samples showed that sediment fractionation during transport and deposition had little impact on magnetic and element source characteristics this study corroborates the high potential of the chosen approach to access sediment origin in regions with contrasting sediment sources complex transport dynamics and large grain size variability

parabolic megadunes in a subtropical quaternary inland dune field southwestern pampas argentina abstract the utracan paleo dune field la pampa province argentina southern south america was examined by remote sensing morphometric analyses and field surveys as a case study of complex megadunes of inland deserts the paleo dune field is within the utracan argentino valley one of the transverse valleys of la pampa province excavated into a regional structural plain similar paleo dune fields occur within these valleys utracan dunes are mostly stabilized by grasses deeply disturbed by cattle grazing and agriculture the paleo dune field is formed by complex parabolic megadunes with superimposed dunes parabolic megadunes present lengths of trailing arms of 3 3 12 9 km widths between them of 2 2 9 km and heights of 7 38 m the position of the dune noses at the northeastern tip of the bedform and measured sw ne orientation of arms indicate a mean transport direction to azimuth 68 2 above the parabolic arms and isolated in the paleo dune field there are compound blowout dunes clusters of several blowouts forming a larger bedform they show the depositional lobes to the ne with a measured mean transport direction to azimuth 58 1 the sw ne longitudinal length varies between 324 and 1302 m and the nw se transverse length between 114 and 622 m other parabolic arms show low

data analysis of bed concentration of suspended sediment an empirical relation for the bed concentration of suspended sediment cb defined at a few grain diameters above the bed is developed its derivation is based on the experimental data sets of guy et al in 1966 the values of the near bed concentration were obtained by first isolating the suspended load transport from the observed rates of total load transport by use of a bed load formula the suspended load was then equated to einstein s formulation which allowed the determination of cb the influence of large concentrations of suspended sediment and of the reference level for cb on the calculated values of bed concentration has been analyzed the proposed relation compares satisfactorily to values of near bed concentration obtained from independent data sets the procedure used to derive cb provides a simple method for the calculation of the total transport rate of noncohesive sediment

making the material the formation of silt sized primary mineral particles for loess deposits abstract in 1911 e e free wrote it may be well to point out that there are really two problems of the loess a problem of the origin of material and a problem of deposition the problem of the origin of material has been relatively neglected in comparison to problems of deposition of the formation of deposits and latterly in comparison to studies of loess stratigraphy if we are to understand the true nature of loess this fascinating material we need to be aware of all the significant events in the processing of the particles which form a deposit a large amount of silt sized primary mineral material has to be produced to make a loess deposit loess is a quaternary phenomenon and we see the entire process being completed in quaternary times some powerful quaternary forces are able to produce very large amounts of granular material glacial grinding vigorously supported by smalley 1966a provides an obvious source for some loess material but the vast deposits of north china and central asia have no obvious glacial connection however they are adjacent to high asia a region of vast tectonic activity and an enormous release of terrestrial energy in the last several million years high asia is a large producer of loess silt much of which finds its way south to make the ganges delta but large amounts are moved north and east to make huge loess deposits africa presents a problem recent work e g coude gaussen 1987 suggests that there is a region of peri saharan loess but earlier observations e g penck indicate quite clearly that the sahara region is free of loess rathjens 1928 in his study of tripolitania indicated the presence of loess like deposits and described their nature but he did point out that 90 of the granular material was greater than 100 pm in diameter which would remove it from a strict loess definition on the soil taxonomy map of africa there is a belt of soil d3 which could include considerable loess deposits it stretches from the matmata loess in tunisia across northern libya to the western part of the egyptian coastal region if d3 contains loess this points to a genuine desert loess particle producing mechanism operating in the sahara

geomorphology and chronology of late quaternary dune fields of western argentina abstract stabilized dune fields are common in western argentina and potentially reflect drought variability in the late quaternary this study focussed on deciphering geomorphic and stratigraphic record of three vegetated dune fields from east to west san luis medanos negros and medanos grandes with a mean annual precipitation from 700 to 91 mm optically stimulated luminescence single aliquot regeneration protocols yield ages on eolian quartz grains constraining depositional events the san luis dune field the wettest area exhibits evidence for repeated activation during the last glaciation ca 33 20 ka generally coincident with regional loess deposition these dunes were locally reformed in the past 100 years which is apparently coincident with intensified agrarian use and drying in the late 19th and early 20th century the two driest and western most dune fields medanos negros and medanos grandes show reactivation at ca 2 5 ka 0 9 and 0 5 ka and ca 4 3 4 2 1 and 0 6 0 4 ka respectively eolian depositional events at ca 2 5 2 1 ka and 0 6 0 4 ka may be coeval for medanos grandes and negros dune fields sustained drought conditions conducive for eolian activity is associated with warmer sea surface temperatures in the south atlantic a weakened south american convergent zone and a dispersed and southeasterly flow of tropical moisture from the low level chaco jet this nascent analysis indicates drought variability beyond historic observations with potentially at least four dune reactivation events in the past ca 4 5 ka

high frequency controls on alluvial successions an integrated sedimentological and palaeopedological approach to the plio pleistocene of argentina abstract plio pleistocene palaeosol bearing alluvial strata are continuously exposed along the marine cliffs of southeastern buenos aires province argentina the study interval was deposited by a mixed predominantly suspended load fluvial system outcrops are dominated by floodplain siltstones and mudstones that exhibit a cyclic alternation between calcic and vertic palaeosols this cyclicity is represented by meter scale alluvial cycles that show as a general trend a gradual increase in the proportion of channel fill deposits up section cyclic variations in palaeosols facies and architectural elements can be related to allogenic drivers such as climate and eustasy for the lower punta san andres alloformation the stratigraphic arrangement of the recognised palaeosols and the clay mineral distribution indicate that the palaeoclimate was subhumid average mean annual precipitation map 840 mm seasonal and temperate average mean annual temperature mat 7 85 c for at least 1 ma from ca 2 9 ma to ca 1 8 ma late pliocene early pleistocene with several intervals in which conditions became drier and probably colder even though climate was a major control on palaeosol development it is suggested here that it was not the main control on high frequency cycles variations in the orbital parameters more specifically in insolation were interpreted as having controlled the sedimentation and architectural evolution of the lower punta san andres alloformation depositional systems

quaternary mammalian faunas of the pampean region abstract knowledge of the fossil mammals from the pampean region of argentina has greatly increased in recent years to analyze the patterns of change in regional climates and environments through the quaternary the fossil record of land mammals was used two principal factors affected mammalian diversity in the pampean region during the pleistocene glaciations and the climatic environmental and sea level changes associated with them and the large numbers of north american taxa that immigrated to south america from the pliocene the regional climatic conditions changed from being warm and wet to being colder drier and more seasonal during the pleistocene as a consequence of glacial cycles cold and dry conditions were interrupted by relatively short warmer and wetter periods several pulses of expansion and contraction of steppes and subtropical forests are recorded this change in habitat produced the provincialism that has characterized the mammal faunas from the pampean region finally the most notable characteristic of the quaternary mammal fauna of south america is the almost complete extinction of large mammals during the latest pleistocene earliest holocene the evidence presented here is most consistent with a model that explains megafaunal extinction through climatic fluctuations as it appears that only a few species of large mammals survived until the holocene nevertheless a human presence could have accelerated the process of extinction

allochthonous versus autochthonous organic matter in cenozoic sediments of the norwegian sea evidence for the onset of glaciations in the northern hemisphere the cenozoic sediments sampled in odp leg 104 on the voring plateau show a distinct variability of the total organic carbon content toc and the accumulation rates of toc based on the geochemical and organic petrographic characterization of the sedimentary organic matter om the allochthonous and autochthonous proportion of the om could be quantified the results clearly demonstrate that high toc percentages and toc accumulation rates in cenozoic sediment sections display a generally high input of allochthonous organic matter oxidized and partly well rounded organic particles built up the main portion of om within the miocene toc rich sediments the most probable source of this oxidized om are reworked sediments from the scandinavian shelf changes in the input of these organic particles are to some degree correlative with sea level changes the cenozoic accumulation of autochthonous om is low and does not reveal a clear variation during the miocene and early pliocene in spite of a high accumulation rate of biogenic opal during the early miocene the accumulation rate of autochthonous toc is low the autochthonous particle assemblage is dominated by relatively inert om like dinoflagellate cysts this points to an intensive biological and or early diagenetic degradation of the marine om under well oxidized bottom water conditions during the last 23 myr nevertheless a continuation of marine om degradation during later stages of diagenesis cannot be excluded a prominent dominance of allochthonous om over autochthonous is documented with the beginning of the pliocene at 2 45 ma the episodic occurrence of ice rafted thermally mature om reflects the onset of the glacial erosion of mesozoic coal and black shale bearing sediments on the scandinavian and barents sea shelves the first occurrence of these in view of the actual burial depth thermally overmature om particles is therefore a marker for the beginning of the strong scandinavian glaciation and the advance of the glacial front toward the shelves

quaternary glaciations of the southern andes abstract the southern andes comprise the southernmost portion of the andean cordillera beginning at the edge of the puna altiplano lat 27 s and ending at isla de los estados lat 55 s the late cainozoic glacial record of these mountains spans the interval from the late miocene to the present and is one of the most complete to be found anywhere in the world this has arisen for several reasons i the conterminous mountain ice cap extended to the piedmont zone on both flanks of the range where the sedimentary and morphological record has been well preserved ii periodic volcanism mainly from monogenetic fissure eruptions of basalt east of the range and from central tephra producing cones along the mountain crest has provided opportunity for the preservation and radiometric dating of interbedded glacial deposits iii a tectonically induced interval of stream incision in the mid pleistocene and simultaneous uplift has preserved glacial sediments on interfluves iv in the chilean lakes region west of the mountains late quaternary glaciers terminated in a well vegetated landscape thus creating scope for radiocarbon dating of interbedded and incorporated organic materials consequently the last glaciation in the llanquihue area of chile is one of the best dated sequences in south america thus the llanquihue glaciation is proposed as the south american equivalent of the wisconsin and weichsel glaciations of north america and north west europe respectively

predicting the rate of scour beneath subsea pipelines in marine sediments under steady flow conditions abstract model scale experiments of scour beneath a submarine pipeline coupled with erosion testing have been undertaken using two marine sediments and five artificial sediments having a wide range of grain size the experiments reveal that for both the marine and artificial sediments the time scale of scour beneath the pipeline depends on the erosion properties of the sediment for coarser sediments mobilised mainly in transport along the bed the rate of scour is found to agree well with the existing empirical formula of fredsoe et al 1992 in contrast for finer sediments that are mobilised mainly through entrainment into suspension and can have relatively high erosion resistance the rate of scour is different to that predicted using the same empirical formula to explain this result theoretical arguments are used to relate the rate of scour beneath a pipeline to the fundamental erosion properties of the sediment namely the transport rate along the bed and the true erosion rate of the sediment these arguments lead to two new empirical formulas that may be used to predict the time scale of the scour process beneath subsea pipelines the first formula is appropriate when the sediment scours predominantly via transport of sediment along the bed and is consistent with the empirical formula due to fredsoe et al 1992 the second formula is appropriate when sediment erodes mainly via entrainment into suspension as is often the case for fine or cohesive sediments collectively the two formulas may be used in practice to make predictions of the rate of scour for pipelines in marine sediments and artificial sediments provided erosion testing results are available

numerical model for local scour under offshore pipelines a numerical model based on potential flow theory is proposed for simulating the equilibrium scour hole formed by unidirectional flow underneath offshore pipelines the model employs a finite difference method to solve the laplace equation in terms of velocity potential in a curvilinear coordinate system a boundary adjustment technique based on the newton raphson method is used to calculate the free boundary formed by the eroded seabed by means of the equilibrium of all forces acting on a sediment particle on a sloping bed because the solution of flow field and adjustment of the seabed topography are carried out in an iterative manner the model takes into account the interactions between the flow pipe and the seabed the comparison of the present model with empirical formulas on the prediction of the maximum scour depth indicates that the present model is useful for approximate estimation of scour depth at a pipeline on the seabed for the case of clear water scour

impact melts and glasses on mars 1 dark mobile materials on mars are widely considered to be volcanically derived windblown particulates such a conclusion is consistent with the large volcanic edifices on mars and the assumption that a volatile rich crust would not favor significant impact melt generation several post viking discoveries however provide new perspectives for reconsidering alternative origins not only for some of the mobile dark veneers but also certain materials at the pathfinder and viking landing sites first certain dark materials on mars do not exhibit the expected mafic absorption features in their reflectance spectra second the pathfinder mission revealed unexpected feldspathic compositions of vesicular blocks that lead to a preliminary conclusion that they represent andesites or basaltic andesites rather than basalts third recent discoveries of holocene to miocene impacts in argentine loessoid deposits provide new insights for the nature of melts generated from eolian sediments fourth global dispersal of impact melt products are now recognized in the terrestrial record throughout the cenozoic consequently the generation and preservation of impact glass on mars should be reconsidered possible occurrences include possible tektite like strewnfields downrange from recent oblique impacts dark avalanches emerging from backwasting cliffs of easily eroded unconformable deposits global dispersal of glassy ejecta from hesperian and amazonian craters of chicxulub scale and dark mobile veneers emerging from noachian craters we propose that the mobile dark materials comprising many of the named features of mars as well as some blocks at the pathfinder viking landing sites may represent impact melt products

a quantitative model of magnetic enhancement in loessic soils we present a quantitative model for the climatic dependence of magnetic enhancement in loessic soils the model is based on the widely accepted hypothesis that ultrafine magnetite precipitates during alternating wetting and drying cycles in the soil micropores the rate at which this occurs depends on the frequency of drying wetting cycles and on the average moisture of the soil both parameters are estimated using a statistical model for the soil water balance that depends on frequency and intensity of rainfall events and on water loss by evapotranspiration monthly climatic tables are used to calculate the average soil moisture and the rate of pedogenic magnetite production which is proportional to a new parameter called magnetite enhancement proxy mep our model is tested by comparing mep calculated for known present day climates with the magnetic enhancement of modern soils the magnetic enhancement factor defined as the ratio between a given magnetic enhancement parameter and mep is expected to be a site independent constant we show that magnetic enhancement differences between soils from the chinese loess plateau and from midwestern u s are explained by our model which yields similar magnetic enhancement factors for the two regions our model is also successful in predicting the mean annual rainfall threshold above which magnetic enhancement declines in a given type of climate

variable infiltration and river flooding resulting in changing groundwater quality a case study from central europe summary the changes in groundwater quality occurring in a buried valley aquifer following a reduction in groundwater exploitation and enhanced infiltration due to extensive flooding of the odra river in 1997 were investigated long time series data for the chemical composition of groundwater in a large well field for drinking water supply indicated the deterioration of groundwater quality in the wells capturing water from the flooded area which had been intensively cultivated since the 1960s infiltration of flooded river water into the aquifer is suggested by an elevated chloride concentration although salt flushing from the rewatered unsaturated zone due to the enhanced recharge event is much more feasible concomitantly with chloride increases in the concentrations of sulphate ferrous iron manganese and nickel imply the oxidation of pyrite fes 2 which is abundant in the aquifer the proton production resulting from pyrite oxidation is buffered by the dissolution of calcite while the ca so 4 stoichiometry of the groundwater indicates that pyrite oxidation coupled with nitrate reduction is the dominant process occurring in the aquifer the pyritic origin of so 4 2 is confirmed by the sulphur isotopic composition the resultant fe 2 increase induces mn oxide dissolution and the mobilisation of ni 2 previously adsorbed to mn oxide surfaces the study has a major implication for groundwater quality prediction studies where there are considerable variations in water level associated with groundwater management and climate change issues

the organic geochemistry of coal from plant materials to coal coalification is a process that transforms plant remains under the influence of time temperature and possibly pressure to a black generally lustrous solid organic fossil fuel having a very complex chemistry although much has been learned in the past two centuries on coal chemistry we still have little knowledge of the way plant materials undergo these transformations the problem has been the existence of adequate characterization tools the advent of some new tools for structural elucidation of macromolecules has led to some revised thinking on coalification originally thought to be a process involving the full degradation of plant remains and subsequent reconstitution of these remains the general consensus today is that the process involves a selective preservation of certain resistant plant components followed by some minor reorganization of the biopolymers that survive the major components of plants do degrade and the resistant ones often constitute only a small fraction of the original mass of the plant materials this paper examines the most recent literature concerning coalification and focuses on the chemistry associated with coalification of certain recognizable plant remains that have been at the center of research activity for the past two decades thus we examine the recent knowledge of the chemistry of resistant biopolymers in extant and fossil wood cuticles resins spores and algae knowledge that has been assembled to establish the reaction pathways towards coal macromolecules

numerical investigation of local scour beneath a sagging subsea pipeline in steady currents abstract two dimensional 2 d numerical simulations are conducted to predict scour below the midsection of the suspended span of a pipeline that sags naturally into a scour pit the deflection of the pipeline is calculated based on the suspension length or span length of the pipeline which is predicted by an empirical formula for the length of the scour pit the general properties of the scour process are investigated for various pipeline properties pipeline embedment depths and shields parameters the effect of each of these parameters on pipeline sagging are combined into one non dimensional sagging parameter a touchdown time is defined as the time when the pipeline touches the bottom of the sand pit empirical formulae are proposed for predicting the final scour depth at touchdown and the time scale required for touchdown it is found that the final sagging depth is a function of the sagging parameter and the shields parameter whilst the touchdown time is only a function of the sagging parameter a formula is also developed for predicting the time history of scour depth prior to touchdown collectively the empirical formulae and numerical simulations are found to be in reasonable agreement with an existing theoretical model available in the literature

local scour around two pipelines in tandem in steady current abstract in this study local scour around two identical pipelines in a tandem arrangement are investigated numerically the two dimensional reynolds averaged navier stokes rans equations together with the conservation equation of the sediment mass are solved to simulate the flow around two pipelines and the evolution of the local scour profile below the pipelines the gap ratios between the two pipelines g d range from 0 5 to 5 with an interval of 0 5 where g is the gap between the two pipelines and d is the diameter of the pipelines the focus of the study is to investigate the effects of the gap ratio on the scour depth and scour time scale it is found that the scour depth below the downstream pipeline is greater than that below the upstream pipeline under both clear water and live bed conditions because of the effect of the vortex shedding from the upstream pipeline the maximum scour depth below the downstream pipeline occurs at g d 2 5 under both clear water and live bed conditions which is about the critical gap ratio beyond which vortex shedding from the upstream pipeline occurs as the gap ratio exceeds 2 5 the scour depth below the downstream pipeline decreases with increasing gap ratio due to the weakening effect of the vortex shedding from the upstream pipeline on the scour the scour under the clear water condition is simulated at a velocity 25 lower than the critical velocity for live bed scour the variations of the scour depths below the two pipelines in the clear water and live bed conditions are found to be similar to each other strong positive mean lift coefficient on the downstream pipeline was observed during the scour process which is believed to have a negative effect on the stability of downstream pipeline the rms lift coefficient on the downstream pipeline increases significantly when the vortex shedding from the upstream pipeline occurs

environmental changes in the pampean area of argentina at the matuyama brunhes c1r c1n chrons boundary abstract the so called pampean sediments are the uppermost sedimentary levels of the chacopampean basin they record the sequence of geologic changes that occurred during the late cenozoic in the pampean area the most important environmental and faunistic changes occurred close to the end of the matuyama chron and beginning of the brunhes chron the relatively wet climate recorded in the region at the end of matuyama chron turned to drier and colder conditions during the beginning of the brunhes chron which also seems to be characterized by an important volcanic activity in the cordillera de los andes an important faunistic turnover between tolypeutes pampaeus and megatherium americanum biozones coincides with lithostratigraphic changes between the ensenada and buenos aires formations the change of polarity matuyama brunhes is observed below this boundary

origin and paleoclimatic significance of late quaternary loess in nebraska evidence from stratigraphy chronology sedimentology and geochemistry muhs d r bettis iii e a aleinikoff j n mcgeehin j p beann j skipp g marshall b d roberts h m johnson w c benton r 2008 origin and paleoclimatic significance of late quaternary loess in nebraska evidence from stratigraphy chronology sedimentology and geochemistry gsa bulletin 120 11 12 1378 1407

magnesium isotopic variations in loess origins and implications abstract loess deposits serve as important continental archives for studying quaternary climatic variations and for estimating the average chemical composition of the upper continental crust here we report high precision mg isotopic data for 19 loess samples from china argentina and europe which were previously used to estimate the composition of the upper continental crust the results show that global loess samples have heterogeneous mg isotopic compositions with 26mg per mil deviation of the 26mg 24mg ratio from the dsm3 standard values ranging from 1 64 to 0 25 and a weighted average of 0 89 which is lighter than both crust and mantle silicates mgo content and 26mg of loess positively correlate with cao al2o3 ratio suggesting a two component mixing between carbonates and secondary silicate minerals the large variation in mg isotopic composition of loess results from a combination of factors including source heterogeneity eolian sorting during transport of the loess and chemical weathering during formation of the loess deposit our results suggest that mg isotopic composition of loess has potential to be a proxy indicator to characterize the paleoclimatic change but may not represent the average mg isotopic composition of the upper continental crust due to mixing sorting of isotopically distinct components and isotope fractionation during loess deposit formation

composition and provenance of late pleistocene holocene alluvial sediments of the eastern andean piedmont between 33 and 34 s mendoza province argentina abstract the andean cordillera and its piedmont in the central western argentina has been long considered as one of the main source areas of detritus for the chaco pampean plain sand dune fields and loess loess like deposits of central argentina the main goal of this study is to evaluate the composition of the late pleistocene holocene alluvial deposits of the andes cordillera piedmont from 33 to 34 s the results are interpreted in the context of the regional geology tectonic setting of the study area and its implications in the continent wide perspective of modern alluvial sands proposed by potter 1994 sampling was conducted at the alluvial stratigraphic sequences of four study sites along three andean piedmont arroyos modal mineralogy in the very fine sand fraction 3 phi to 4 phi was determined using standard petrographic microscope methods q f lf average compositions indicate that the late pleistocene holocene very fine grained alluvial sands of the cordillera frontal piedmont reflects the modern lithic arenites of the argentine association reported by potter 1994 the results show two geologically distinct sources in the catchment areas volcaniclastic and metamorphic rocks high concentrations of mica and volcanic glass are likely related to particle morphologies and to the deposition sedimentary environment recorded in the alluvial sequences floodplains the overabundance of micas over the volcanic glass in the mid late holocene alluvial sequence indicates the drainage of a metamorphic area at the expense of other lithological sources source areas are located mainly in the frontal cordillera and to a lesser extent in the piedmont tertiary deposits another likely source for the analyzed quaternary alluvial sediments the mineralogical signature of the late pleistocene and holocene alluvial sequences is in agreement with the composition of the southern pampean sand mantles loess and loess like deposits mainly formed by a volcanic mineral assemblage with source areas placed at the headwaters of the main andean rivers

sedimentological study of aeolian soil parent materials in the rio sauce grande basin buenos aires province argentina abstract sedimentological characteristics of aeolian soil parent materials in the rio sauce grande basin southern buenos aires province were analysed using grain size distributions transport mechanisms dynamics of the sedimentary process and the nature of calcareous layers samples were collected from c horizon of 13 profiles distributed over all the piedmont areas and plains calcium carbonate in these materials is either inherited from the parent material or was redistributed by pedogenic processes their amounts in ck horizons increase from the upper to the lower basin and are inversely related to the thickness of soil parent material to mean annual rainfall and to the calcrete depth the cumulative grain size plots show that the sediments were transported by both aeolian saltation and aeolian suspension most of them have coarser and more heterogeneous grain size distributions than typical loess of the northern hemisphere indicating a larger and more fluctuating wind energy than is required for the formation of typical loess deposits in the upper and middle basins were deposited in two main aeolian episodes which can be related to the dry periods of the late pleistocene and the late holocene recorded in southern buenos aires province in some thin profiles of the middle and lower basins the large clay content of the calcic c horizon was probably inherited from one or more previous pedogenic events there is a systematic increase of particle size towards the lower basin which may be related to an increase of energy towards the lower basin or to the influence of littoral dune fields along much of the atlantic coastal zone

dust deposits on la graciosa island canary islands spain texture mineralogy and a case study of recent dust plume transport abstract la graciosa volcanic island evolved in the late pleistocene holocene it is situated along the northeast of the canarian archipelago with a subaerial surface of 27 km2 this island is located close to the western sahara being 80 km from the north western african continental shelf and 145 km from the coast the island supports a very small permanent population the climate is coastal arid 116 mm precipitation per annum regular occurrences of saharan dust plumes about 30 of the year with a dust accumulation rate of 20 g 2 year 1 produce sedimentation of dust on the island of ca 540 t year 1 wind blown sediments cover a large area more than 52 of the otherwise volcanic island forming sandy beaches sand sheets nebkhas and other aeolian deposits re distributed dust deposits often occur on the leeward sides of inter volcano areas inter dune areas and in endorheic sediment traps many of these deposits are edaphized and carbonatized textural analysis of the dust deposit samples shows a variable proportion of silt 80 20 clay 19 9 and fine to very fine sand 71 4 the general mineralogical composition of these sediments as measured by xrd and sem eds is calcite 26 illite 26 quartz 11 augite 10 aragonite 6 anorthite 8 kaolinite 5 and montmorillonite 3 the mineralogy in different size fractions is very consistent for example quartz content decreases from 15 in the coarse silt fraction to 5 in the fine sand a mineral and grain size comparison with airborne dust collected on gran canaria island was undertaken close similarities were found in the two sample sets such closely matched characteristics point to a similar origin for both airborne dust and dust deposits in line with the saharan plume dust that regularly traverses this archipelago it is unusual to find so much quartz in the fine sand fraction of these aeolian dust deposits individual quartz grains with an intermediate axial length of 160 m were identified by sem eds previous investigators have found similar giant particles in long range transported aeolian dust middleton et al 2001 in contrast to the classic model for gravity settling of airborne dust particles the debate on this subject remains open for discussion we present evidence of long range wind transported large mineral particles and a 2004 case study of uplift wind velocity vs plume dust generation as well as a transport efficiency model that can explain the existence of fine sand in the dust deposits on la graciosa island and in the airborne samplers on gran canaria island recent saharan dust shows that about 10 of similar coarse grained particulate matter is also present

3d scour below pipelines under waves and combined waves and currents this paper presents the results of an experimental investigation on three dimensional local scour below a rigid pipeline subjected to wave only and combined wave and current conditions the tests were conducted in a conventional wave flume the major emphasis of the investigation was on the scour propagation speed free span expansion rate along the pipeline after local scour was initiated at a controlled location the effects of flow ratio steady current velocity vs combined waves current velocity flow incidence angle and pipeline initial embedment depth on free span expansion rate were investigated it was observed that the scour along the pipeline propagated at a constant rate under wave only conditions the scour propagation rate decreased with increasing embedment depth however increased with the increasing keuglegan carpenter kc number under combined wave and current conditions the effect of velocity ratio on scour propagation velocity along the pipeline was quantified empirical relationships between the scour propagation rate vh and key parameters such as the kc number and embedment depth e d were established based on the testing results

rock magnetism in two loess paleosol sequences in cordoba argentina this work presents new rock magnetic results along two loess paleosol profiles in nearby locations in argentina the main objective of this study is to compare the magnetic signals and mineral content of two profiles and determine if the climate during marine isotope stage 5 mis 5 and mis 3 were similar to the present one the two profiles are located in two different geomorphological settings with effects on the water saturation characteristics and seasonality selected samples taken at these profiles were analyzed using laboratory procedures and environmental magnetism parameters to determine the climatic influence during the late pleistocene despite their proximity there are several differences between both profiles such as their depth and geomorphological positions among others the results of these analyses led to the following conclusions climate conditions during mis 5 were very similar to those of the present conditions the hypothesis for this area suggests a slight increase in the magnetic signal associated with the generation of small amounts of magnetite and preservation of detrital magnetite and titano magnetite the results in this paper show a slight gain in the buried soils of cordoba that would confirm the hypothesis

using remote sensing to quantify aeolian transport and estimate the age of the terminal dune field dunas pampa blanca in southern peru abstract aeolian dunes are widely used to reconstruct paleoenvironmental conditions however terminal dune fields ergs in the coastal desert of southern peru where information regarding quaternary paleoenvironmental conditions is very limited have until now not been used for paleoenvironmental reconstructions and the time depth of their accumulation is unknown here different estimates are derived to constrain the time depth recorded in the dunas pampa blanca a terminal dune field in coastal southern peru dune field age is calculated using the volume of the dunas pampa blanca and i recent aeolian transport rate in migrating transverse dunes feeding the dunas pampa blanca derived from digital processing of sequential landsat and quickbird images and ii limitations posed by recent fluvial sediment supply to the source of aeolian transport the resulting maximum age estimate of 70 8 ka from aeolian transport compares with a minimum age estimate of 4 75 ka from sediment supply however a minimum age estimate of 110 450 ka is deduced from the tectonic and topographic evolution of the region this discrepancy contradicts the hypothesis of late quaternary stability in the peruvian coastal desert and indicates that recent conditions of aeolian sediment supply and transport are not representative for the late quaternary

isotopic constraints on the source of argentinian loess with implications for atmospheric circulation and the provenance of antarctic dust during recent glacial maxima we present rare earth element ree and sr nd isotopic data for argentinian loess 28 38 s with two aims 1 to examine the source regions of argentinian loess and the constraints that these put on palaeo wind directions 2 to further investigate the source of antarctic ice core dust and to test the hypothesis that some of it could be derived from a region to the north of patagonia into which the dry dusty westerly dominated patagonian climate expanded during quaternary glacial maxima sr nd isotopic data for argentinian loess from north of 37 s are distinct from patagonian loess compositions in that they have more radiogenic sr 87sr 86sr 0 7059 0 7123 and less radiogenic nd nd 0 8 to 6 4 ree patterns and sr nd isotopic values are relatively homogeneous for multiple samples taken from single loess sections but show significant differences between sections in general there is a northward change from patagonia like ree patterns and isotopic values away from volcanogenic signatures and towards those that are more like the continental crust the latitudinal nd isotopic pattern is remarkably similar to that for andean volcanic rocks and suggests derivation of loess from the andes by more or less direct westerly transport for loess sections in the north the data imply a contribution from palaeozoic gneisses to the northwest in the chilean altiplano sr nd data for extra patagonian argentinian loess north of 37 s do not support a significant role for this source region in supplying dust to antarctica at the last glacial maximum this conclusion contrasts with previous studies that suggest a significant northward shift in the climatic belts and in particular the westerlies and the antarctic polar front during quaternary glacial maxima very systematic relations between the sr nd isotopic composition of loess and their andean source highlights shifts in the sr isotopic composition of loess to more radiogenic values and strongly suggests that the slight offset between patagonian loess and ice core dust identified by previous workers is due to grain size differentiation effects

cation exchange capacity and mineralogy of loess soils with different amounts of volcanic ashes the cation exchange capacity of soils cec is largely affected by the mineralogy of their parent material soils of the argentinean pampas develop on illitic loess mixed in variable proportions with volcanic ashes it is whether a question of how pedogenesis can modify this mineralogy affecting cec differentially in order to answer this question we analyzed four soils two of them placed in semiarid conditions and developing on parent materials with high volcanic ash contents and two placed in the humid pampas developing on ash free parent materials results indicated that pedogenesis transformed coarse lithogenic illites into smaller illites in ash free soils accumulating them not only in clays but also in silts in ash enriched soils illites were not altered by pedogenesis but they were the volcanic glasses which were transformed into less crystallized smectites these smectites accumulated mainly not only in clays but also in fine silts the mineral fraction of ash free soils had higher cec 15 07 cmolc kg 1 than ash enriched soils 9 50 cmolc kg 1 being the contribution of the 50 m sized fractions to the total cec similar in all the studied soils on average 54 as a consequence of this clays and silts of ash free soils made a relatively low contribution to the total cec while poorly crystallized smectites of ash enriched soils made a relatively high contribution this was explained on the basis of the kind of minerals present smectitic minerals with high cec rather than on the proportion of the mineral fraction itself in ash enriched soils and on the relatively high content of the mineral fractions rather than on their mineralogy illites with low cec in ash free soils the contribution of silts to cec was similar and relatively high in all the studied soils 17 5 of the total cec and 32 of the mineral fraction cec these results confirm that the electrochemical properties of the studied soils are defined not only by clays but also by silts mainly those with sizes between 2 and 20 m

stable isotope analyses on the last 30 ka molluscan fauna from pampa grassland bonaerense region argentina abstract fossil and living shells of terrestrial and freshwater molluscs collected from various sites in the bonaerense and patagonia regions of argentina were analysed for their stable isotope content as a possible tool for palaeoclimatic and palaeoenvironmental reconstruction the oxygen isotope composition of calcareous shell from freshwater samples was interpreted in terms of a change in moisture condition and the related evaporative effect on surficial bodies of water linked to a climatic shift the carbon isotope composition mainly records changes in biological productivity interpretation of the isotopic composition of the land snail carbonate is more complex and worldwide data from living shells have been used to decipher to some extent the palaeoenvironmental record contained in their isotopic composition overall the interpretations deduced from isotopic data of land snails as well as from nearby freshwater molluscs are quite comparable the isotopic data suggest that arid conditions occurred between 35 and 15 ka b p and warmer conditions around 35 25 ka b p a shift toward a new phase comparable with the present meteorological and climatic situation probably began around 9 ka b p and it was linked to some short but severe climatic fluctuations thus suggesting that high climatic stress characterised this period moreover a trend toward slightly arid conditions is suggested by isotopic data possibly sometimes after 5 ka the differences arising from the geographical location and the short duration of each single series studied still hamper an extensive interpretation of the isotopic data

on the formation of desert loess sequences of quartz rich coarse 20 63 m silt occur in many low and midlatitude unglaciated arid and semiarid areas and have been termed desert loess the processes by which these deposits are generated have been debated for decades all hypotheses to explain their origin seek to provide mechanisms for the generation of silt sized material without glacial grinding which is the main process involved in the production of coarse silt at high latitudes possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones mechanical weathering of silicate rocks and abrasion of sand grains in active dune environments during intense transport events examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt improvements in the characterization of desert loess particle size mineralogy and geochemistry are needed however to identify sources and sinks of coarse silt especially when combined with climatic back trajectory analysis properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations

the nature distribution and formation of pans in arid zones abstract pans closed depressions are a widespread feature of many of the world s drylands by using literature survey air photographs topographic maps orbital photographs and imagery combined with field work it is possible to describe the major areas where these features occur their distribution is controlled to a great extent by the availability of susceptible surfaces they also develop in certain particular environmental settings palaeolacustrine basins palaeodrainages interdunes and on coastal plains many of the pans have a distinctive morphology while on their lee sides they may have lunette dunes many processes combine to create and maintain pans and these can be considered in a general model which has certain key elements the first of these is that the area should not be one where fluvial processes are fully integrated it should also not be one where aeolian accumulation is such as to infill any irregularities in the land s surface if these two predisposing conditions are fulfilled then under dryland conditions if susceptible surfaces are present there are various circumstances that may lead to hollow development and enlargement although in some cases such processes as solution suffosion and animal activities may play a role we believe that the predominant reason why pans have the characteristics that they do including their shapes lunettes alignments etc is that they result from the operation of the twin processes of salt weathering and aeolian deflation

a stable carbon isotope and biological marker study of polish bituminous coals and carbonaceous shales abstract biological marker and carbon isotopic compositions of coals and carbonaceous shales from the upper carboniferous strata of the upper silesian uscb lower silesian lscb and lublin lcb coal basins were determined to assess depositional conditions and sources of the organic matter n alkane sterane and isoprenoid distribution and carbon isotope ratios are consistent with an origin from higher plants in some cases pristane phytane pr ph ratios of carbonaceous shales roof and floor shales are 29 stereoisomers typical but not conclusive of higher plant origin carbonaceous shales exhibit a wider range of sterane composition suggesting local significant input of algal organic matter significant amounts of benzohopanes and gammacerane are present in some coals although benzohopanes are present at least in small amounts in samples from many different environments they have been reported to occur most commonly in marine environments the present study seems to provide the first example where benzohopanes have been reported in significant amounts in terrestrial organic matter gammacerane is abundant in rocks or sediments deposited in carbonate or highly saline marine environments the finding of high gammacerane concentrations in the coals expands the depositional settings in which it has been observed and questions its utility as an independent indicator of hypersaline carbonate environments stable carbon isotope composition of coals and type iii kerogen in carbonaceous shales as well as correlation of stable carbon isotope composition of saturated and aromatic hydrocarbons in carbonaceous shales from both the uscb and the lscb indicate terrigenous origin bitumens are always co genetic with associated coals and kerogens isotopic data reveal that sofer s genetic classification of oils is not applicable to organic matter in coals

three dimensional scour below offshore pipelines in steady currents this paper presents the results of an experimental investigation on three dimensional scour below offshore pipelines subject to steady currents the major emphasis of the investigation is on the scour propagation velocity along the pipeline after the scour initiation physical experiments were conducted to quantify the effects of various parameters on scour propagation velocity along the pipeline in a water flume of 4 m wide 2 5 m deep and 50 m long local scour depths directly below the model pipeline were measured using specifically developed conductivity scour probes effects of various parameters such as pipeline embedment depth incoming flow shields parameter and flow incident angle relative to the pipeline on scour propagation velocity along the pipeline were investigated it was found that scour propagation velocity generally increases with the increase of shields parameter but decreases with the increase of the pipeline embedment depth a general predictive formula for scour propagation velocity is proposed and validated against the experimental results

experimental and numerical investigation of local scour around a submerged vertical circular cylinder in steady currents abstract local scour around a submerged vertical circular cylinder in steady currents was studied both experimentally and numerically the physical experiments were conducted for two different cylinder diameters with a range of cylinder height to diameter ratios transient scour depth at the stagnation point upstream edge of the cylinder was measured using the so called conductivity scour probes three dimensional 3d seabed topography around each model cylinder was measured using a laser profiler the effect of the height to diameter ratio on the scour depth was investigated the experimental results show that the scour depth at the stagnation point is independent on cylinder height to diameter ratio when the later is smaller than 2 the increase rate of equilibrium scour depth with cylinder height increases with an increase in shields parameter a three dimensional finite element numerical model is developed for simulating local scour around submerged vertical cylinders steady flow around the cylinder is simulated by solving the reynolds averaged navier stokes rans equations with a k turbulence closure both suspended load and bed load sediment transport rates were included in the model efforts are made to reduce the computational time associated with three dimensional morphological modelling including the use of wall function to avoid resolving the near wall boundary layers large morphological time step and parallel computing techniques scour around a submerged vertical circular cylinder founded on the seabed is simulated and the numerical results are validated against the test data the scour mechanisms around the submerged cylinder are investigated using the numerical model

numerical modeling of flow and scour below a pipeline in currents part ii scour simulation abstract a vertical two dimensional 2d numerical model for time dependent local scour below offshore pipelines subject to unidirectional steady flow is developed the governing equations for the flow and sediment transport are solved by using finite difference method in a general curvilinear coordinate system the performance of two turbulence models the standard k model and smagorinsky subgrid scale sgs model on modeling time dependent scour processes is examined both suspended load and bed load are considered in the scour model the suspended load model is verified against two channel sediment transport cases the change of bed level is calculated from the continuity equation of total sediment transport a new time marching scheme and a sand slide scheme are proposed for the scour calculation it is found that the proposed time marching scheme and sand slide model work well for both clear water and live bed scour situations and the standard k turbulence closure is more preferable than the sgs model in the 2d scour model developed in this study

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

first data on volume and type of deflated sediment from southern puna plateau and its role as source of the chaco pampean loess abstract this paper presents the first attempt at qualitatively and quantitatively evaluating the sedimentary contribution of the puna plateau to the loess and soils of the argentinean pampas the origin of the pampean sediment has been traditionally ascribed to northern patagonia but new evidence supports a dual supply western central andes north patagonia and puna altiplano plateau three different lines of evidence show here that puna dust supply is active and produces significant sedimentary deposition up to places like buenos aires city the first evidence is meteorological and we show here one event related to an abnormal rainfall that deposited large quantities of a reddish brownish silt eroded out from the puna calling the attention of the environmental agency of buenos aires city the second evidence is the sampling of active wind transport collecting extremely coarse material carried out in the saltation layer suggesting the fine grained material escapes the area as fugitive dust this also demonstrates that observed gravel bearing bedforms of the puna are active and that the transport system seems to be activated by polar fronts only results show that the saltation curtain is abnormally thick and coarse suggesting that the kinetic energy peaks ca 7 10 times higher than for normal saltation while the transported grain size coincides with the lagged sediment in this basin composing different bedforms varying between sandy gravel and gravelly sand the third evidence is the quantification of the exported material by defining a reference surface as the initial time of evolution and the present day surface the initial surface is an alluvial surface of an estimated age of 11 12 ka bp volume balance was achieved by a detailed topographic stratigraphic and geophysical survey reconstructing old alluvial and present surfaces two gridding methods were used and more conservative results of the volume balance indicate a total erosion of ca 3 386 hm 3 of sediment in 72 ha spliced in 0 963 hm 3 of sediment that was left within the place forming gravel dunes while the remaining volume of ca 2 423 hm 3 is sediment truly exported from the surveyed area results imply a continuous blanket of ca 4 m thick of sediment exported out of this basin in the holocene these findings prove that the puna contribution to the chaco pampean plain is significant although not unique thus true proportions of sediment contribution to soils and loess from these multiple sources should be better evaluated in future studies

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

toarcian climate and carbon cycle perturbations its impact on sea level changes enhanced mobilization and oxidation of fossil organic matter abstract organic geochemistry and palynology reveal major organofacies changes in the marginal marine polish basin during the early toarcian linked to changes in environmental conditions increasing water salinity and enhanced biomass contributions from phytoplankton adopted to brackish conditions attest to periodic marine ingressions into the paralic hyposaline polish basin marine ingressions occurred upon reoccurring sea level rises concomitant with i the pliensbachian toarcian boundary carbon isotope excursion pl toa cie and ii the stepped toarcian carbon isotope excursion toa cie the latter marking the toarcian oceanic anoxic event toa oae strata with marine influences indicate an intermittent connection of the polish basin with the tethys and attest to a close correlation between regional shoreline progradation and evolution of global climate and sea level organic geochemistry indicated the link between sea level fluctuations and the toa cies although in some areas of the polish basin the sea level rise was balanced by massively increased sediment delivery caused by enhanced hydrological cycling that lead to intensified weathering and erosion in the hinterland enhanced hydrological cycling further led to the remobilization of organic matter of pre toarcian age this points to erosion of older organic rich rocks containing significant abundances of marine and terrestrial organic matter that was partly oxidized and re deposited along with autochthonous toarcian organic matter provenance areas identified point to two main sources most likely carboniferous terrestrial paralic and ordovician silurian marine sediments fossil organic matter should be considered as additional source in toarcian carbon cycling particularly in times of enhanced hydrological cycling erosion and weathering remobilization of sedimentary fossil carbon has not been hitherto considered as a carbon source during the toa oae

late quaternary vegetational and climatic changes in the pampa grassland of argentina abstract the vegetation and climate of the pampa grassland argentina during the late quaternary are reconstructed from pollen recovered from dated stratigraphic sections from arroyo walls and from archaelogical excavations prior to 10 500 yr b p herbaceous psammophytic steppe existed in the central part of the pampa grassland while xerophytic woodland associated with psammophytic and halophytic steppe occurred in the southwestern part of the pampa these types of vegetation and the continental conditions that prevailed in the area of the present day coast 38 s indicate subhumid dry climate and annual precipitation 100 mm lower than present a subsequent change toward a vegetation characteristic of ponds swamps and foodplains or toward environments with locally more effective moisture occurred ca 10 500 yr b p suggesting annual precipitation close to modern levels or a higher availability of water in the central part of the pampa grassland this type of vegetation existed until 8000 yr b p when it was replaced by grassland communities that lasted until 7000 yr b p in the southwestern part of the pampa grassland this vegetation developed before 7000 yr b p and persisted until ca 5000 yr b p sea level higher than the present ca 6200 yr b p is consistent with sharp modification of the vegetation and development of local halophytic communities dominant at 38 s a return to subhumid dry conditions occurred after 5000 yr b p the late holocene vegetation is characterized by pollen assemblages similar to the psammophytic and halophytic communities of the southern pampa grassland associated with communities with more edaphic conditions at the same time at 38 s a sea level regression is suggested by the dominance of fresh water pollen assemblages and micropaleontological remains the trend toward humid temperate conditions ca 1000 yr b p suggested by vertebrate remains characteristic of temperate and humid conditions as well as a very short but dry episode during the 18th century suggested by the geology are not clearly evidenced in the pollen sequences vegetational and climatic changes are explained by the latitudinal shifts and changes in intensity of the southern atmospheric circulation and changes in sea level

terrigenous flux in the rio grande rise area during the past 1500 ka evidence of deepwater advection or rapid response to continental rainfall patterns surface sediment samples and three gravity cores from the eastern terrace of the vema channel the western flank of the rio grande rise and the brazilian continental slope were investigated for physical properties grain size and clay mineral composition discharge of the rio doce is responsible for kaolinite enrichments on the slope south of 20 and at intermediate depths of the rio grande rise the long distance advection of kaolinite with north atlantic deep water from lower latitudes is of minor importance as evidenced by low kaolinite chlorite ratios on the mid atlantic ridge cyclic variations of kaolinite chlorite ratios in all our cores with maxima in interglacials are attributed to low and high latitude forcing of paleoclimate on the brazilian mainland and the related discharge of the rio doce a long term trend toward more arid and glacial conditions from 1500 ka to present is superimposed on the glacial interglacial cyclicity

reactivity of organic matter in aquifer sediments geological and geochemical controls reduction rates in aquifers are commonly carbon limited but little is known about the molecular composition and degradability of sedimentary organic matter som in aquifer sediments the composition source and degradation status of som in aquifer sediments of fluvio glacial pleistocene and shallow marine pliocene origin were determined using flash pyrolysis gas chromatography mass spectrometry incubation experiments 106 d were used to assess the reactivity of som towards molecular oxygen a dominance of lignin derived components and long chain odd over even predominant alkanes indicate that terrestrial higher land plants were the main source of som even in the shallow marine sediments while bacterial lipid derived hopanoids and iso and anteiso c15 and c17 fatty acids indicate a minor contribution of microbial biomass no compositional difference was observed between som present in the fine 63 m and coarse fraction 63 2000 m a significant part of som was not present as low molecular weight compounds but was macromolecularly bound for the fluvio glacial sediments a relatively higher abundance of resistant macro molecular compounds was in agreement with stronger signs of aerobic lignin alkane and hopanoid oxidation the more degraded status of som in the fluvio glacial sediments was consistent with their significantly lower som mineralization 2 6 during incubation as compared with the shallow marine sediments 9 14 the reactivity towards oxygen of som was controlled by the extent of past aerobic oxidation not the age of som but the extent of oxygen exposure during syn and postdepositional conditions seems most important in affecting the degradation status of som in aquifer sediments and thus their ability to reduce oxidants copyright 2004 elsevier ltd

numerical investigation of local scour below a vibrating pipeline under steady currents local scour below a vibrating pipeline under steady current is investigated by a finite element numerical model the flow sediment transport and pipeline response are coupled in the numerical model the numerical results of scour depths and pipeline vibration amplitudes are compared with measured data available in literature good agreement is obtained it is found that pipeline vibrations cause increases of scour depth below the pipeline the scour pit underneath a two degree of freedom vibrating pipeline is deeper than that under a pipeline vibrating only in the transverse flow direction the effects of water depth are also investigated the present numerical result shows that water depth has weak effect on the scour depth however it does affect the time scale of the scour the shallower the water depth is the less time it requires to reaches the equilibrium state of scour it is found that the vibration forces vortices to be shed from the bottom side of the pipeline then vortex shedding around a vibrating pipeline is closer to the seabed than vortex shedding around a fixed pipeline this contributes to the increase of the scour depth

lifelong embedment and spanning of a pipeline on a mobile seabed abstract seven years of field survey measurements of a subsea pipeline obtained using sonar profilers and underwater video indicate significant lowering of the pipeline into the seabed due to sediment mobility and scour the majority of the lowering occurs within 2 years of pipeline laying and appears to result from sustained ambient tidal and soliton currents as opposed to large storms the lowering results in an increase in pipeline embedment relative to the far field seabed of up to 0 8 times the pipe diameter referenced at a distance 8 d from the pipeline at most locations along the pipeline this increase in far field embedment is uniform and occurs after the formation of many closely spaced scour holes this suggests that the pipeline lowered mainly through sinking into the seabed at span shoulders rather than sagging into widely spaced scour holes for much of the pipeline length a beam bending analysis confirmed the dominance of sinking but did show some evidence of pipeline sagging calculating deflections of up to 0 3 pipeline diameters at the time of surveying in contrast to the traditional conception of span growth and self burial which conceives of complete pipeline burial as an endpoint this pipeline primarily appears to exhibit self lowering towards a mature state that consists of a pseudo static profile of alternating spanning and embedded sections that are distributed at regular intervals the observed changes appear to be predictable given sufficient pipeline setting data which suggests that they can be quantified in the stability design of new pipelines this opens up the possibility of more efficient on bottom stability design as the beneficial shielding and support provided by the self lowering process is not usually accounted for

late quaternary aeolian and fluvial aeolian deposits from southwestern pampas of argentina southern south america abstract the central region of argentina southern south america is characterized by an extensive quaternary aeolian record in this context three locations from the southwestern pampas an andean foreland region bearing a rich fossil mammal record that contributed to the south america biostratigraphic scheme were selected to carry out a comprehensive sedimentological analysis of the late quaternary deposits the case studies are located at the transverse valleys of la pampa province chapalco quehue and utracan argentino valleys and exhibit a high resolution of the late quaternary in comparison with others areas of the southwestern pampas the toay locality 36 41 s 64 24 w records aeolian dominant activity since the end of the late pleistocene 30 ka onwards soil formation at some point during the holocene and early mid 20th century reactivation of aeolian process the arroyo quehue locality 37 04 s 64 42 w presents a late pleistocene holocene succession mostly related to an ephemeral endorheic fluvial system with an interval of relative surface stabilization and aeolian aggradation during the late holocene the utracan locality 37 17 s 64 35 w exhibits a prevailing aeolian and fluvial aeolian interaction succession developed in the mid to late holocene in a sand mud flat environment of a shallow saline lake the three studied cases are representative of aeolian aggradation in association with ephemeral fluvial shallow lake and pedogenic processes in a currently subhumid dry region numerical ages indicate sedimentation during the last 30 kyr they allow constraining and evaluating the paleoenvironmental conditions in this inland region of southern south america and provide age constraints for the regional databases of paleoclimatic proxies the results are in agreement with other late quaternary paleoclimatic paleoenvironmental archives of central argentina and show a fragile aeolian landscape that is susceptible to deterioration under extreme conditions including both aeolian reactivation during dry phases and erosion of sandy silty sediments during wet phases

paleoenvironments in the paso otero locality during late pleistocene holocene pampean region argentina an interdisciplinary approach the recently excavated paso otero 4 site is located within the paso otero archaeological locality necochea district pampean region the site is characterized by the presence of a great variety of archaeological materials and a rich and complex stratigraphic record which allows use of an interdisciplinary approach the objective of this paper is to present the results of the geoarchaeological palynological phytolith and diatom analyses in order to reconstruct the paleoenvironmental conditions for the final late pleistocene through holocene these lines of research allow inference of paleoenvironmental and palaeoclimatic conditions on both local and regional scales at the site the rio salado member unit 2 where the archaeological deposit is buried underwent sudden and fluctuating changes in water availability conditions although the setting was basically characterized by calm depositional processes within and along the margins of interconnected lagoons paleoclimatic reconstructions indicate the existence of abrupt climatic changes throughout the sequence early holocene human occupations took place under regionally temperate warm climates while the end of the middle holocene witnessed cold and arid or cold temperate climates in general terms paleoenvironmental conditions inferred for paso otero 4 are in accordance with regional reconstructions proposed for the pampas

a biomarker approach to the organic matter deposited in the north atlantic during the last climatic cycle abstract the study of the composition of total organic carbon toc c37 alkenones and c23 c33 n alkanes in the north atlantic ocean cores su90 08 and su90 39 has allowed the development of a model for the differentiation of marine and terrigenous toc this model gives rise to results in good agreement with inorganic markers such as magnetic susceptibility ms and non carbonate content according to this model the terrigenous toc accounts for most of the organic matter in the glacial sediments thus the higher toc of the glacial periods 0 1 0 45 vs 0 05 0 15 in the interglacials is due to the increase in terrigenous toc the changes in marine toc those associated to sea surface productivity are independent of the glacial interglacial evolution the terrigenous toc is more important at higher latitudes probably due to higher terrigenous detrital inputs associated with iceberg transport in this respect the correlation between n alkanes and ms strongly suggests that the main source of these hydrocarbons are ice rafted materials and that aeolian inputs only represent minor contributions the four peaks of reworked n alkanes in the su90 08 core that are coincident with the heinrich layers h1 h2 h4 and 115 are in agreement with this hypothesis on the other hand the abrupt marine toc peaks of su90 08 show a 23 ka periodicity indicating that the marine productivity at 43 n in the north atlantic ocean was precessionally driven the productivity maxima in this core correlate with low latitude oceanographic processes such as periods of enhanced trade wind intensity and equatorial upwelling which are also tuned to precession and independent of the global glacial interglacial evolution

pedostratigraphy and pedological and geochemical characterization of las carreras loess paleosol sequence valle de tafi nw argentina abstract the las carreras loess paleosol sequence is considered the most complete quaternary pedostratigraphic record in south america it consists of 32 paleosols formed during the past 1 15 ma chronological control is provided by magnetostratigraphy sediment and paleosol characterization is based on a variety of methods including soil chemistry geochemistry and micromorphology the main pedogenic processes identified are carbonate leaching and reprecipitation ped formation and translocation of clay and organic matter in many cases the boundaries between individual paleosols are not clearly defined due to indistinct transitional zones based on both pedological and sedimentological characteristics the sequence was subdivided into three units with paleosols in units i and iii designated as luvisols and paleosols in unit ii tentatively classified as luvic kastanozems this subdivision reflects environmental changes associated with the mid pleistocene transition overall geochemical variability is low and largely related to pedogenesis the homogeneity suggests a rather constant provenance that seems to be linked to the central andes pursuant to the chaco model of iriondo 1997 models of deposition of loess and loessoids in the upper quaternary of south america journal of south american earth sciences 10 71 79 and includes direct volcanic ash falls and local sources in a subordinate manner in a paleoclimatic context loess paleosol alternation is interpreted to reflect climatic cycles that were primarily caused by the variability of the south american monsoon system

new insights on sources contributing dust to the loess record of the western edge of the pampean plain during the transition from the late mis 2 to the early holocene high resolution studies of palaeorecords located closer to the dust source areas of south america are relevant for increasing the knowledge on past climatic conditions in the southern hemisphere i

raman spectroscopy and biomarker analysis reveal multiple carbon inputs to a precambrian glacial sediment extractable biomarkers can help elucidate the environment and biota of ancient glaciations although the method must be applied with care as glacial sediments have a potential for incorporation of older detrital carbon in phanerozoic glacial sediments the distinct elemental molecular and isotopic compositions of the terrestrial and marine biomass allow discrimination between primary marine and redeposited terrestrial organic matter however as the proterozoic biosphere was largely microbial and marine biomarker and isotopic analyses are insufficient for distinguishing primary organic matter from secondary reworked organic matter here we report the combined application of raman spectroscopy and biomarker analysis to precambrian glacial sediments which together allows discrimination between mixed pools of organic carbon and provides a promising new approach for rapidly screening precambrian sediments for immature organic matter amenable to biomarker analysis

geochemical features of re deposited organic matter occurring in fluvioglacial sediments in the raciborz region poland a case study abstract the erosion of rocks rich in organic matter typically leads to the complete mineralization of the organic material however in some cases it is re deposited to become a part of sediments once more this process should be considered to be a part of global carbon cycle possibly much more significant than assumed to date the research presented here aims to characterize re worked organic matter occurring in post glacial sediments of southern part of poland in the oder river valley the raciborz town region miocene pleistocene and holocene age organic substances extracted from the sediments originated from organic matter that had resided in rocks eroded by glaciers sediments were sampled in two boreholes which sediments were correlated sediments were extracted and extracts analyzed with gas chromatography mass spectrometry gc ms to assess distributions of biomarker groups organic matter of selected samples was pre concentrated and analyzed with py gc ms in the extracts several biomarker parameters of source environment and thermal maturity were calculated organic substances in the investigated sediments come from variable re deposited organic matter occurring in rocks eroded by glaciers three main parent types of re deposited organic material are identified showing variable geochemical features 1 organic matter of recent or almost recent age being the source of polar labile compounds probably formed in situ 2 re deposited organic matter of the middle diagenesis showing features similar to lignites huminite reflectance rf 0 25 0 35 deriving from angiosperm remains mainly monocotyledons and to the lower extend also deciduous trees 3 re deposited organic matter at the middle catagenesis rf 0 65 0 75 being the source of most of aromatic hydrocarbons and biomarkers such as steranes hopanes of the more thermally advanced distribution type its geochemical properties and assumed directions of sediment transport indicate bituminous coals of upper silesian coal basin together with coaly shales as a possible source of this organic matter such mixed origin of organic matter caused large discrepancies in values of thermal maturity parameters depending on input from the particular sources and occurrence both geochemical biomarkers and their biochemical precursors in the same samples

geochemical differentiation of quaternary sediments from the pampean region based on soil phosphorus contents as detected in the early 20th century abstract data obtained in the early 20th century on the total phosphorus tp content in soil materials from the pampean region have been processed and plotted on maps of the region approximately 1200 subsoil data and 1400 surface horizon data obtained using the same analytical method have been processed according to differences in phosphorus content several areas have been demarcated limits and characteristics of these areas have been correlated with data from the more recent literature regarding the p distribution and with both mineralogical and sedimentological information on surface materials results suggest that a confluence of sediments from different provenances i e the andean range the pampean hills and the brazilian shield is found in the argentine pampean region

implications for paleomobility studies of the effects of quaternary volcanism on bioavailable strontium a test case in north patagonia argentina abstract strontium isotopes 87sr 86sr are used as geochemical tracers for paleomobility studies because they display predictable and stable patterns in ecosystems primarily controlled by the underlying geological regimes while bedrock geology is stable over thousands of years geomorphological processes can influence the 87sr 86sr in ecosystems over archeologically relevant timescales among these geomorphological processes the deposition and reworking of volcanic sediments over quaternary timescales are little studied but could be an important control of 87sr 86sr variations in many archeological regions north patagonia is a key archeological region to address animal and human movements and an ideal location to test the influence of quaternary volcanism on 87sr 86sr variation as it is located downwind of major volcanic centers in this study we aim to assess the main environmental and geological controls of bioavailable 87sr 86sr and to build a high resolution isoscape using a machine learning regression framework for forthcoming paleomobility studies we sampled several locations and analyzed different types of samples n 94 the ratios show a limited range of variation which is not related to the bedrock geology rather bioavailable 87sr 86sr variations display a progressive increase going eastward away from the andes following dust aerosol deposition and elevation variations r2 0 71 rmse 0 00041 we argue that this trend relates to the deposition and reworking of unradiogenic volcanic sediments by aeolian fluvial and glacial erosion during the quaternary as most of this sediment reworking occurred during glacial periods the current bioavailable 87sr 86sr variations across the study area likely represent a long term average that varied little during the holocene consequently our isoscape provides a solid base for holocene paleomobility studies in north patagonia and underlines the importance of quaternary volcanism processes for interpreting 87sr 86sr data in paleomobility studies in volcanic regions

genesis and distribution of the late pleistocene and holocene loess of argentina a regional approximation abstract an overview of the current state of knowledge of the loess of argentina is presented the spatial distribution of the loess typical or reworked is described and in particular reference is made to the relationship between landforms and superficial materials in the sub tropical loess region the description of extrinsic and intrinsic characteristics demonstrates the influences of regional factors in loess distribution and the existence of a sw ne loess transport path throughout argentine territory the available dating confirms the age of the superficial loess as pleistocene and holocene it is pointed out that the temporal interval of deposition of the late pleistocene loess coincides with the highest dust concentrations as shown in the ice core records at both poles the prominent influence of volcanic materials affecting not only the mineral composition of the loess but also the genesis and evolution of the loess palaeosol sequences is emphasised finally the importance of the palaeosols as indicators of palaeoenvironmental conditions is clearly demonstrated by the descriptions of outcrops in the pre andean valleys of north western argentina

interaction of the south american monsoon system and the southern westerly wind belt during the last 14 kyr abstract surface currents and sediment distribution of the se south american upper continental margin are under the influence of the south american monsoon system sams and the southern westerly wind belt swwb both climatic systems determine the meridional position of the subtropical shelf front stsf and probably also of the brazil malvinas confluence bmc we reconstruct the changing impact of the sams and the swwb on sediment composition at the upper rio grande cone off southern brazil during the last 14 cal kyr bp combining sedimentological geochemical micropaleontological and rock magnetic proxies of marine sediment core geob 6211 2 sharp reciprocal changes in ferri and paramagnetic mineral content and prominent grain size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments our interpretations support the assumption that the sams over se south america was weaker than today during most of the late glacial and entire early holocene while the swwb was contracted to more southern latitudes resembling modern austral summer like conditions in consequence the stsf and the bmc were driven to more southern positions than today s favoring the deposition of fe rich but weakly magnetic la plata river silts at the rio grande cone during the mid holocene the northern boundary of the swwb migrated northward while the stsf reached its northernmost position of the last 14 cal kyr bp and the bmc most likely arrived at its modern position this shift enabled the transport of antarctic diatoms and more strongly magnetic argentinean shelf sands to the rio grande cone while sediment contributions from the la plata river became less important during the late holocene the modern el nino southern oscillation set in and the sams and the austral tradewinds intensified causing a southward shift of the stsf to its modern position this reinforced a significant deposition of la plata river silts at the rio grande cone these higher magnetic silts with intermediate fe contents mirror the modern more humid terrestrial climatic conditions over se south america

the argentine neotropical loess an overview abstract the neotropical loess primary and reworked covers a large part of argentina north of 30 s it is different in some ways from the loess of the pampa which is generally considered the typical argentine loess the mineralogical chemical and physical composition of the neotropical loess has been analyzed and is here compared with both pampean and northern hemisphere european and north american loess the distribution of neotropical loess is established following the former teruggi scheme and the bio stratigraphical data indicating a late pleistocene age is described the great climatic variability of this period is documented through description of a loess paleosol sequence that mantles the pre andean valleys the influence of loess influx upon the genesis of the paleosols and the stadial interstadial environmental changes are considered in relation to the generalized truncation of paleoedaphic sequences the migration of the polar front and the weakness of the pacific high pressure system are also analyzed in relation to south american environmental evolution during the upper quaternary in that sense the genesis of pre andean fluvial valleys and mega fans extending outward into the andean piedmont plains having sources on the eastern dry side of the andes would have been influenced by such a paleoclimatic situation

bone diagenesis and taphonomic history of the paso otero 1 bone bed pampas of argentina samples of guanaco bone from an archaeological site in the pampas of argentina have been analysed to understand the diagenetic profile of the bone assemblages that characterized the taphonomic history of the site two archaeological occupations of paso otero 1 were investigated encompassing similar landscape settings climates and depositional environments the time span is a c 2000 year period from c 4800 to 2800 years bp a total of 30 bone samples taken from both occupations were used to provide a preliminary characterization of the diagenetic pathways at the site the parameters investigated provide a comprehensive account of how both mineral hydroxyapatite and bone protein collagen have been altered in order to compare the two bone assemblages in terms of their diagenetic parameters multivariate analyses were conducted results indicate two different diagenetic profiles in the site n being one of the variables that accounts for most of the variation in paso otero 1 the diagenetic analyses indicate that protein is less preserved in the bone assemblage from the middle stable landscape alternative interpretations of the diagenetic profiles are discussed in light of the taphonomic history of the site and palaeoenvironmental information of the region one hypothesis stresses the importance of the role of climate in defining the different diagenetic pathways and the other the continued action of the combined diagenetic factors along time as the main explanation for the variability in the state of preservation of the bones in paso otero 1

quaternary evolution of the cordillera frontal piedmont between c 33 and 34 s mendoza argentina fil zarate marcelo aristides consejo nacional de investigaciones cientificas y tecnicas instituto de ciencias de la tierra y ambientales de la pampa universidad nacional de la pampa facultad de ciencias exactas y naturales instituto de ciencias de la tierra y ambientales de la pampa argentina

numerical modeling of flow and scour at pipelines a numerical model for the description of fluid flow and suspended and bed load sediment transport is presented density effects are included in the momentum reynolds equations and in the turbulence kappa and epsilon equations changes in bed levels are calculated from sediment continuity and the finite element grid is adapted to the geometry the reynolds equations and the transport equation for suspended sediment are solved numerically using a taylor galerkin finite element method the flow at a surface mounted cylinder in a steady flow is predicted in good agreement with experiments periodic vortex shedding from a cylinder placed above a rigid bed is predicted in good agreement with laboratory experiments provided that sufficiently detailed grids approximately 5 000 nodes are used scour calculations are performed for a cylinder in a steady flow with its underside placed at the level of the original flat bed predicted scour at a pipeline in steady flow is in good agreement with laboratory measurements reported in the literature