channel arrangements and depositional styles in the sao lourenco fluvial megafan brazilian pantanal wetland abstract the brazilian pantanal is an extensive lowland tropical basin characterized by the presence of fluvial megafans and seasonally inundated savanna floodplain wetlands with an area of about 16 000 km 2 the sao lourenco is the second largest megafan in the pantanal three distinct fluvial channel styles that formed at different times during the late quaternary are found here a geomorphological and sedimentary assessment of these depositional patterns provides valuable insight on the environmental context of their evolution new optically stimulated luminescence data indicate that the upper five meters of sediment in the sao lourenco megafan has been accumulating since the late pleistocene ancient fan lobes located in upper and intermediate fan settings consist of medium and coarse grained fluvial sands and exhibit well preserved distributary braided paleochannels on their surfaces as the megafan evolved through time pleistocene lobes were incised by a prominent valley filled with holocene aged meander belt deposits which consist of silts interbedded with very fine sands and clays currently the incised valley is a zone of sediment bypass modern deposition occurs along the distal toe of the megafan system where lobes characterized by distributary channel levee ridges are widespread these features formed by progradation of avulsion belts into a broad swampy floodbasin which caused the lower portion of the meander belt to be abandoned the significant differences observed in intra fan morphology appear to be linked to the variability in effective precipitation fan lobes deposited with braided distributary channels occurred under relatively dry conditions in the late pleistocene by contrast aggradational meander belt deposits and lobes with distributary channel levee ridges formed during fluctuating precipitation conditions of the holocene when the pantanal emerged from deglacial aridity modern lobes form under heavy seasonal flooding and deposition occurs in response to very rapid and common avulsion events these results have implications for interpreting the complexity of megafan facies in similar continental basins

sedimentological characteristics of small rivers with loessic headwaters in the chaco south america some sedimentological characteristics of uvial environments located in the northeastern region of the chaco pampa plain were analysed in order to determine the possible in uence of the loessic headwaters of local basins concentrations of suspended sediments as well as grain size of the river beds were compared unexpectedly it was found that the suspended load has an inverse relationship with the hydrometric levels with the exception of highly saline streams conductivity values between 4300 and 11 000 l sc m 1 the mean concentration of suspended sediments was 63 1 and 206 3 mg l 1 in ood and low water periods respectively the grain size of bed sediments was relatively homogeneous along the whole hydrological cycle sandy silty bottoms predominate in channels followed by silty sandy and clayey silty bottom types sediment transport mainly occurs in accelerating ow suspension overcoming the critical erosion velocity during ood periods some parameters exceeded by 70 the values recorded during the low water phase 2000 elsevier science ltd and inqua all rights reserved

a new method for the estimation of cooling and denudation rates using paramagnetic centers in quartz a case study on the eldzhurtinskiy granite caucasus we present a new method for the assessment of the most recent cooling and denudation rates using paramagnetic centers in quartz measured by electron spin resonance esr spectroscopy these centers have a relatively low thermal stability for cooling rates of 40 o and 1000oc myr effective closure temperatures vary between 55 o and 82oc ti center and 49 o and 64 oc a1 center respectively samples were collected from two cores that were drilled into the eldzhurtinskiy granite which has an emplacement age of 2 ma as measured by u pb analyses of zircons one 1500 rn core was taken from a drill hole into the dome of the granite a second core of 4000 rn from a drill hole at the base of the baksan valley our results yield cooling rates of between 160 and 250oc myr for the upper core and between 570 o and 600oc myr for the lower core the corresponding denudation rates are 2 5 upper core and 5 5mm a lower core the shape of the temperature profile of the lower core indicates recent erosion when fitting the temperature data with a two dimensional heat transfer model we obtain a net denudation rate of 10 mm a and cooling rates in the range of 500oc myr thus confirming the cooling rates estimated by esr however the esr denudation rates underestimate the erosion rate of the baksan valley because the geothermal gradient is not equilibrated between the surface and the depth of the annihilation temperatures 950 and 1800 rn for the a1 and ti centers respectively we conclude that esr measurements of paramagnetic centers in quartz will allow the recon struction of landscape dynamics for the past 10 1000 kyr and that in conjunction with u pb fission track and ar ar analyses it will be possible to develop dynamic models for quaternary tectonic movements

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

vegetation and climate change since 14 810 14c yr b p in southeastern uruguay and implications for the rise of early formative societies abstract this article presents a combined pollen and phytolith record of a 1 70 m sediment core from the wetlands of india muerta 33 42 s 53 57 w in the lowland pampa grasslands of southeastern uruguay six 14c dates and the pollen and phytolith content of the samples permitted the recognition of four distinct climatic periods between 14 850 14c yr b p and the present the late pleistocene period between ca 14 810 and ca 10 000 14c yr b p was characterized by drier and cooler conditions indicated by the presence of a c3 dominated grassland these conditions prevailed until the onset of the warmer and more humid climate of the holocene around 9450 14c yr b p the early holocene between around 10 000 and 6620 14c yr b p was characterized by the establishment of wetlands in the region as evidenced by the formation of black peat the increase in wetland taxa and the replacement of c3 pooideae by c4 panicoideae grasses during the mid holocene around 6620 14c yr b p began a period of environmental change characterized by drier climatic conditions which resulted in the expansion of halophytic communities in the flat low lying areas of the wetlands of india muerta about 4020 14c yr b p a massive spike of amaranthaceae chenopodiaceae coupled with a radical drop in wetland species indicates another major and more severe period of dryness after ca 4000 14c yr b p a decrease of halophytic species indicates the onset of more humid and stable climatic conditions which characterized the late holocene the findings reported in this article substantially improve our knowledge of the late glacial and holocene climate and vegetation in the region the data provide a detailed record of the timing and severity of mid holocene environmental changes in southeastern south america significantly the mid holocene drying trend coincided with major organizational changes in settlement subsistence and technology of the pre hispanic populations in the region which gave rise to early formative societies this study also represents the first combined pollen and phytolith record for southeastern south america reinforcing the utility of phytoliths as significant indicators of long term grassland dynamics

late quaternary paleosols and their paleoenvironmental significance along the andean piedmont eastern bolivia the andean piedmont of eastern bolivia is situated at the southern margin of amazonia characterized by an overall humid climate regime with a marked contrast between the rainy and dry seasons the nearby subandean foothills deliver abundant sandy sediments to the piedmont leading to a complex array of sediments and paleosol horizons within this setting the presented study analyzes four profiles of paleosol sediment sequences along incised ephemeral streams near santa cruz de la sierra with a focus on past pedogenic variability in the context of the regional late quaternary geomorphic and environmental evolution based on field observations micromorphological analysis geochemical and clay mineralogical data five classes of paleosol horizons could be distinguished the individual paleosol horizons as well as the sediments in which they developed were interpreted regarding their paleoenvironmental significance taking into consideration the various controls on soil formation with particular focus on changes of local environmental conditions through time thus three different pathways of soil formation were established on the late quaternary timescale the results suggest a strong relation between paleoenvironmental conditions climate vegetation etc soil environment soil water flow micro environment and the type of paleosol horizons developed in the study area the formation of red beds bw horizons implies very dry soil environments under dominantly dry conditions which seem to have prevailed in the study area some time before 18 cal ka bp moderately dry but markedly seasonal environmental conditions with a long dry season and strong seasonal contrasts in soil water flow could explain the formation of moderately developed bwt horizons around 18 cal ka bp and much of the mid holocene the formation of bt horizons and or clay lamellae in relation to intense neoformation of clay and dominant clay illuviation by soil water points to wet conditions similar to today which have probably prevailed in the study area before 8 cal ka bp and since 5 cal ka bp

geochemical characterization correlation and optical dating of tephra in alluvial sequences of central western argentina the synthesis of paleoclimatic archives provided by loess and alluvial sequences of central argentina has been hindered by the lack of a cohesive lithostratigraphic framework extending across the chaco pampean plains and catchments of the rios desaguadero colorado and negro this condition originates in part from the dearth of absolute chronological controls the occurrence of discrete tephra layers across this region may provide an opportunity to address this deficiency if a tephrochronological framework can be established the potential of such a project is assessed within the context of a pilot study constrained within alluvial sequences of central western argentina proximal to potential source vents in the southern volcanic zone the intersite discrimination and correlation of tephra layers on a geochemical basis is examined with indirect chronological control for the eruption of each generated by optical dating alluvial sediments on either side of each of five tephra units at a type site were dated using the optically stimulated luminescence of fine silt sized quartz thus providing an age control on each tephra ca 24 000 30 000 32 000 39 000 and 48 000 yr the geochemical composition of each tephra was derived using these data tephra layers at other sites in the study area were geochemically analyzed and in instances of statistical concordance in major oxide structure correlated to the type site and therefore ascribed ages this methodology identified a further sixth volcanic event between ca 24 000 and 30 000 yr not registered by type site tephras the extension of this initial tephrochronological framework beyond the alluvial sequences of central western argentina is encouraged by the occurrence of geochemically distinct tephra verified and dated in this study

concentration of oxygen vacancies in quartz from sedimentspotential for geochronometry abstract the concentration of oxygen vacancies in 13 quartz samples from lower tertiary sandstones 24 42 ma of the liaohe basin were measured by esr it was found that the concentration of oxygen vacancies in quartz is correlated to the total absorbed dose this implies that these centres may be used as a new tool for dating sediments on a million years time scale

single quartz grain electron spin resonance esr dating of a contemporary desert surface deposit eastern desert egypt abstract signal resetting by sunlight prior to burial is a crucial assumption in electron spin resonance esr dating of sediments this resetting process is expected to be completed to a greater extent in arid than in fluvial environments the present paper investigates the natural and artificially irradiated signal intensity of ti related centres in single quartz grains collected from the desert surface eastern desert egypt in order to test this hypothesis the results suggest that in most grains both the ti li and ti h signal are completely reset to zero additive dose curves based on the sum of both ti centres show an anomaly in the low dose region possible causes for this behaviour are briefly discussed three fitting procedures are conducted and each of them shows a different palaeodose distribution with a rather large spread in d e values it is concluded that similar fossil deposits would be datable by single grain esr using q band measurements of the ti li or ti h signals in quartz

modern sands of south america composition provenance and global significance standard petrographic methods were used to study 604 modern sands from south america of which 351 came from rivers and 253 from beaches in spite of the wide geomorphic contrasts these sands belong to only three great families 1 an immature andean family of lithic arenites rich in volcanic and metamorphic grains that covers about 30 of south america 2 a cratonic association rich in quartz that covers about 62 of the continent and 3 a transitional molasse association which occurs between these two and covers only about 8 of the continent the grand arithmetic average q f rf ratio for the entire continent is 60 11 29 and the area weighted carbonate free average qa fa rfa is 68 10 22 a superior continental estimate and the first ever for an entire continent

clay mineral assemblages from late quaternary deposits on vancouver island southwestern british columbia canada resume dans le secteur de l ile de vancouver les formations de dashwood drift cowichan head quadra sand et vashon drift se sont deposees au cours des periodes glaciaires et non glaciaires du pleistocene terminal elles presentent des variations importantes du cortege argileux dont certaines sont relatives aux fluctuations climatiques les periodes glaciaires sont caracterisees par des chlorites riches en fer des illites toutes deux bien cristallisees et des smectites avec une morphologie rappelant celle de smectites developpees a partir de roches volcaniques la mineralogie des argiles des depots non glaciaires est plus complexe elle est marquee en outre par la presence de vermiculite kaolinite halloysite et de mineraux interstratifies irreguliers ces assemblages sont mediocrement preserves et montrent une degre d alteration pedologique plus eleve par rapport aux assemblages glaciaires les variations importantes enregistrees dans les depots nonglaciaires sont egalement dues a des facteurs secondaires tels la sedimentation differentielle les sources sedimentaires variantes et des possibles modification diagenetiques toutefois ces facteurs ne semblent pas obliterer de maniere significative les empreintes climatiques des mineraux argileux cette etude permet egalement de differencier des sediments remanies sous regime glaciaire de determiner les relations entre les unites lithologiques d une meme coupe et d etablir l origine des mineraux argileux rencontres

holocene landscape evolution along the andean piedmont bolivian chaco abstract as part of the gran chaco the andean piedmont in eastern bolivia is characterized by a highly seasonal climate and large rainfall variability it receives sediments from small drainage basins in the subandean ranges therefore it should constitute a suitable sedimentary and geomorphic archive for the detection of past environmental changes this study reconstructs holocene landscape evolution along the andean piedmont in the bolivian chaco by combining large scale geomorphological analysis and the investigation of sedimentary sequences fluvial aggradation and channel avulsions are the dominant processes of piedmont construction and were particularly pronounced during the mid holocene this is interpreted to reflect a generally active landscape characterized by reduced forest cover as result of increased aridity widespread soil formation and landscape stability in all investigated catchments start after 4 cal ka bp indicating the onset of wetter conditions and successively denser forest cover in the bolivian chaco renewed sedimentation during the last millennium could imply a shift to more arid environmental conditions probably in relation to larger scale climatic phenomena such as the little ice age lia particularly during the last centuries the fluvial system of the study area has undergone the most profound changes of the entire holocene with sedimentation of very coarse sediments and subsequent incision this reflects important changes both in discharge and sediment supply and might be the result of either shorter term climate changes or increasing human impact

esr studies for absolute dating of fault movements the principle of absolute dating of fault movements is based on the initialization or resetting of some clock system by faulting in the case of esr dating heating is more effective in resetting esr signals than fracturing according to a computer simulation of resetting by shear heating during faulting the esr signals can never be completely reset at depths of less than 100 200 m below the surface of the earth therefore esr samples must be collected from depth by coring or tunnelling or from outcrop with consideration of the rate of exhumation of the fault outcrop in general unpaired electrons trapped at lattice defects in crystals can diffuse much more easily than atoms hence samples for other dating methods which are based on the diffusion of atoms should be collected at even greater depth on the other hand if no esr signal is observed from unfractured quartz in the wall rocks one may directly determine the age of the fault movement using esr signals in the fractured quartz whose precursors were formed by faulting the age obtained t should then satisfy the following relationship t b t t e where t b and t e are the ages of the beginning and end of the fault movements and it may show the time of a fault movement

chute channel dynamics in large sand bed meandering rivers meander bends of many large sand bed meandering rivers are partitioned by chute channels that convey permanent flow and co exist with the mainstem for decades as a first step toward understanding the dynamics and morphodynamic implications of these bifurcate meander bends this study applied binary logistic regression analysis to determine whether it is possible to predict chute initiation based on attributes of meander bend character and dynamics regression models developed for the strickland river papua new guinea the lower paraguay river paraguay argentina and the beni river bolivia revealed that the probability of chute initiation at a meander bend is a function of the bend extension rate the rate at which a bend elongates in a direction perpendicular to the valley axis trend image analyses of all rivers and field observations from the strickland suggest that the majority of chute channels form during scroll slough development rapid extension is shown to favour chute initiation by breaking the continuity of point bar deposition and vegetation encroachment at the inner bank resulting in widely spaced scrolls with intervening sloughs that are positively aligned with primary over bar flow the rivers plot in order of increasing chute activity on an empirical meandering braided pattern continuum defined by potential specific stream power pv and bedload calibre d50 increasing stream power is considered to result in higher bend extension rates with implications for chute initiation in addition chute stability is shown to depend on river sediment load relative to flow discharge qs q such that while the beni may plot in the region of highly braided rivers by virtue of a high potential specific stream power the formation of stable chute channels is suppressed by the high sediment load this tendency is consistent with previous experimental studies and results in a planform that is transitional between single thread meandering and braided copyright 2011 john wiley sons ltd

large wetlands of south america a model for quaternary humid environments abstract large wetlands are important landscapes in south america where today they cover one million square kilometers such environments probably were as important in the quaternary of other continents tensional tectonic processes in the andean foreland and other lowlands result in the sinking of blocks several thousand square kilometers in surface under humid climates such depressions become occupied by shallow waters and a dense paludal vegetation these features are a special case of wetlands which owing to their areal extension complexity internal fluxes of sediments and salts must be considered as macrosystems neiff et al large tropical south american wetlands a review unesco ecotones workshop seattle unesco paris 1994 15pp and are a major depositional environment in south america such areas are plains characterized by more or less periodic flooding and complex ecosystems adapted to large water fluctuations such water bodies have frequent anaerobic conditions and accumulate organic matter in various degrees of decomposition south america contains 14 wetlands with areas larger than 10000 km 2 other somewhat smaller wetlands appear in abandoned fluvial belts inside megafans examples of this type can be found in the pilcomayo river system in argentina where an old belt is at present a swamp 250 km long and 7 12 km wide large inland wetlands in south america can be grouped in two types pantanales or sandy swamps and mud wetlands both are clearly different in geomorphology sediments types of salts and ecology from the point of view of quaternary science the degree of knowledge of the large wetlands is really poor in general it is restricted to the survey of the present conditions which is itself important because similar environments have generally been reclaimed for agriculture since hundreds of years in other continents an example of a large wetland of late pleistocene age the tapebicua fm argentina is presented in this article it is also clear that tropical swamps did exist throughout the quaternary and they very probably were hot spots for evolution of plants and animals and refuges for particular ecosystems

a gis based method for evaluating sediment storage and transport in large mining affected river systems currently the evaluation of sediment storage and transport for large river systems with variable flow has proven to be a challenge that often requires complex numerical models to be applied and sometimes costly direct data acquisition to be made the present study proposes a low cost widely available gis based method through which an initial assessment can be made on areas of sediment storage transport and deposition as well as possible environmental risks that the accumulation of contaminated material may pose to riverine communities along the rivers channel the method mainly relies on satellite imagery and elevation data to devise a quick model of the channel the model has been successfully applied to study the bolivian sector of the well known mining contaminated rio pilcomayo the analysis shows that the portion of the channel from villamontes to d orbigny accounts for more than half of the total c 314 km2 sedimentation area of the pilcomayo in bolivia and that the most environmentally problematic area is centreed around puente sucre where agriculture is practiced on the contaminated floodplain combined with supplementary bathymetric data on the depth of the river in various points around the channel the method could offer further insight into the sediment fluxes and transport capacity of the pilcomayo in various sectors and could thus be successfully used to assess other large mining contaminated river channels around the world

quaternary fluvial systems of tropics major issues and status of research abstract fluvial systems in tropical regions are not only the lifeline for modern civilizations there but also form an important continental archive for reconstructing quaternary palaeoclimates and palaeoenvironments tropical rivers drain through a variety of geological and geomorphological settings across the world and have been studied for their hydrology sediment transport characteristics facies models stratigraphic development and flood hazards this paper presents an overview of the research on tropical rivers globally and identifies major gaps and unanswered research questions as a part of the igcp 582 on tropical rivers the participants of this project are continuing to tackle many of these issues the collection of papers in this special issue is an outcome of this activity and presents new data on processes and alluvial stratigraphy of the tropical rivers from china india south america and northern australia

investigation of the potential use of esr signals in quartz for palaeothermometry abstract in order to investigate the possible use of esr signals for palaeothermometry samples from three petroleum exploration drill holes in eastern china were studied we found that the ratio of the intensities of the natural e signal 1 over the signal after heating at 250 c for 60 min i 2 is higher for the deeper samples generally exposed to higher temperatures than those of the shallower samples this behaviour can be used for establishing the contemporary storage temperatures at least up to 100 c

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

a review of late quaternary inland dune systems of south america east of the andes abstract inland dune systems of south america occur in a variety of environmental settings under different climatic conditions from humid subhumid to semiarid arid this contribution provides the state of the art on dune research of inland systems east of the andes tropical northern 10 n 10 s including the dune fields of llanos del orinoco and the amazonian basin are mainly formed from parabolic blowout or deflation basins and linear dunes developed on river floodplains aeolian activity was reported to occur near the late pleistocene holocene boundary in llanos del orinoco over the last 17 ka in the branco river basin and 32 6 ka in the negro river basin both in the amazonian region in general the attributed aeolian origin is controversial the morphology difficult to determine and the chronology still extremely limited and rather debatable in some cases the southern tropical region 10 s 22 s includes aeolian systems situated across the extensive lowlands of the gran chaco and those located in fluvial basins related to the cratonic brazilian shield sao francisco river pantanal and mato grosso the oldest barchanoid barchan ridges at the gran chaco were dated 36 33 ka and subsequent aeolian sand accumulation occurred at 18 ka 14 12 ka 10 9 ka and mid to late holocene times parabolic dunes at the sao francisco river floodplain show an oldest episode generated between 28 and 11 ka followed by eolian activity during the early to mid holocene no chronological data is available for the linear and lunette dunes described at the pantanal linear ridges were distinguished in the upper parana river mato grosso with associated sand accumulation at different intervals of the holocene the last reviewed region is the andean piedmont and western pampas at subtropical eastern south america comprising a large variety of dune morphologies barchan barchanoid linear parabolic transverse and lunette dunes deflation basins and sand sheets luminescence ages suggest the occurrence of aeolian activity intervals during late glacial times and the holocene the general understanding on the dynamic of south american dune systems is hampered by the paucity of chronological information and the representativeness of some dune records whether they reflect local or regional environmental conditions is still a matter of discussion in several areas that need further studies

thermoluminescence of feldspar as a multi thermochronometer to constrain the temporal variation of rock exhumation in the recent past abstract natural thermoluminescence tl in rocks reflects a dynamic equilibrium between radiation induced tl growth and decay via thermal and athermal pathways when rocks exhume through earth s crust and cool from high to low temperature this equilibrium level increases as the temperature dependent thermal decay decreases this phenomenon can be exploited to extract thermal histories of rocks the main advantage of tl is that a single tl glow curve has a wide range of thermal stabilities lifetime 100 c ma whereas deeper traps i e with higher activation energies provide constraints on thermal histories for higher cooling rates 300 c ma finally we show how the path of rock exhumation i e depth vs time can be constrained using an inverse approach the newly developed methodology is applied to rapidly cooled samples from the namche barwa massif eastern himalaya to suggest a trend in exhumation rate with time that follows an inverse correlation with global temperature and glaciers equilibrium altitude line ela

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

the enigma of fine grained alluvial basin fills the permo triassic cumbrian coastal and sherwood sandstone groups of the solway basin nw england and sw scotland the late permian to triassic sediments of the solway basin consist of a layer cake succession of mature predominantly fine grained red clastics laid down in semi arid alluvial plain to arid sabkha and saline marginal marine or lacustrine environments the cumbrian coastal group consists of basal clastics and eden shales the basal clastics are thin regolith deposits resting unconformably on all underlying units and are composed of mixtures of angular local gravel and far transported fine to very fine grained sands deposited as basal lag the eden shales are predominantly gypsiferous red silty mudstones with thin very fine grained sandstone beds and with thick marine gypsum beds at the base deposited at a saline lake margin the overlying triassic sherwood sandstone group consists of the annan and kirklinton sandstones the annan sandstones are predominantly thick bedded multi storied fine grained mature red quartz sandstones in which coarse sand is practically absent despite channels with clay pebbles up to 30 cm in diameter the overlying predominantly aeolian kirklinton sandstones consist of festoon cross bedded and parallel laminated fine grained sandstones almost identical to the annan sandstones except that mica and clay are absent the stanwix shales located above consist of interbedded red blue and green mudstones siltstones and thin very fine grained sandstones with gypsum layers although the entire succession can plausibly be interpreted as deposited in a large desert basin opening into a hypersaline marine or lacustrine embayment to the southwest the uniformly fine grained nature of the succession is unusual as is the absence of paleosols and body and trace fossils there is almost no coarse sand even in the river channel units and it seems likely that the basin was not only extremely arid but supplied predominantly by wind rather than water

esr dating of xenolithic quartz in volcanic rocks abstract selected quaternary volcanoes of the eifel volcanic field germany and of the eger rift west bohemia were dated using esr on quartz xenoliths in basanites typical sizes of the quarzites and sandstones were a few cm with the exception of one large xenolith with dimensions of 22 and 46 cm investigations on the optical and thermal properties of the al center in our samples show that these properties are determined by one or several unknown electron traps esr ages using the al center show good agreement with independent ages up to 500 ka but also show that the thermal stability can vary significantly from sample to sample age overestimation due to incomplete resetting of the esr signals at the time of eruption is found for two samples and weak or non existent e and ohc signals are discussed as possible indicators of complete zeroing

collapse of the pilcomayo river the pilcomayo river flows south eastwards from the bolivian andes across the chaco plains setting the border between argentina and paraguay it flows down along 1000km in principle to finally join the paraguay river it spills over the plains during the rainy season from january to march the sediment load of the pilcomayo is one of the largest in the world 140milliontons per year which is mostly wash load from the upland andes the mean concentration of suspended sediment is 15g l the maximum recorded concentration is as high as 60g l the river has built a large fan covering a surface of 210 000km2 with many abandoned channels today it is a river prone to avulsion raising border disputes between the two lowland countries argentina and paraguay moreover the very special feature of pilcomayo river is that it does not actually flow into the paraguay river very far upstream of the mouth in the paraguay the channel blocks itself with sediment and wood debris forcing water and sediment to spread across the plains moreover the point of blockage has moved hundreds of kilometers upstream throughout the 20th century many environmental issues arise because of this collapse channel discontinuity not the least of them is the migration of fish the future of the river concerns bolivia and the two lowland countries 2012 elsevier b v

trapped charge thermochronometry and thermometry a status review abstract trapped charge dating methods including luminescence and electron spin resonance dating have high potential as low temperature 200 c ma 1 or elevated temperature underground settings 30 c despite this limitation trapped charge thermochronometry comprises a diverse suite of versatile methods and we explore potential future applications and research directions

a climatic model for southwestern amazonia in last glacial times abstract multidisciplinary data indicate that southwestern amazonia was a savanna environment during last glacial times interpretation of biogeographical and geological records as compared with the present climatic conditions permit us to postulate a dry season more pronounced and prolonged than the present one dry northerly winds vinculated with southern bemisphere trade winds dominated during the dry season and the southerly cold air masses locally termed friagem or surazo would have been more frequent and intensive than today

quaternary of the pantanal west central brazil abstract the pantanal is a tectonic depression located at the left margin of the upper paraguay river the paraguay is the trunk river of an alluvial depositional tract composed by several large marginal alluvial fans the taquari fan being the largest one the present landscape is a complex tropical wetland characterized by month long floods every year with geomorphic features derived from the present conditions and others inherited from successive pleistocene and holocene climates some areas containing ponds are landscape relicts generated by eolian deflation during the last glacial maximum many ponds closed depressions isolated from the superficial waters by vegetated crescent ridges of fine sands were interpreted as salt pans bordered by lunette sand dunes initiation of the modern wetland has occurred during the pleistocene holocene transition with the change to a more humid climate and the individualization of lacustrine systems active tectonics has been playing an important role in the development of the pantanal landscape nowadays the paraguay river meanders in a large flood plain with extensive swamp surfaces being structurally constrained by faults in the west border of the basin sedimentation within the pantanal wetland is also affected by tectonic activity especially along faults associated with the transbrasiliano lineament

detrital clay grain coats in estuarine clastic deposits origin and spatial distribution within a modern sedimentary system the gironde estuary south west france

late quaternary cuiaba megafan brazilian pantanal channel patterns and paleoenvironmental changes the brazilian pantanal wetlands comprise some of the largest quaternary megafans in south america the origin of these megafans has been linked to climate changes during the late quaternary this study focuses on the cuiaba megafan the second largest megafan of the pantanal which has not been studied from the perspective of its basic geomorphology river channel patterns and sediment deposition ages analysis of the channel and floodplain morphology as well as optically stimulated luminescence dating enable us to establish the succession of events that built up the cuiaba megafan since the last glacial period abandoned lobes indicate that a phase of fan aggradation occurred between 48 and 19 ka with a network of distributary paleochannels suggesting that there was relatively low precipitation and reduced vegetation cover subsequently abrupt changes in discharge and sediment supply triggered the channel incision of the upper fan valley indicating a degradational phase after the last glacial maximum 19 ka a new phase of fan aggradation began at the early holocene when meandering and anabranching channels were constrained into the incised valley on the upper fan in the distal part of the fan the development of modern depositional lobes has been driven by numerous single sinuous channels that shift laterally due to successive avulsions regional tectonic features suggest that modern cuiaba lobes are in a subsiding area that provides accommodation space for sediment accumulation and prolonged flooding events changes in the channel patterns observed in the cuiaba megafan are related to changes in the south american monsoon strength which driven precipitation variation during the late quaternary periods of monsoon intensification and relatively high precipitation lead to channel incision while periods of fan aggradation correlate to times of fewer oscillations our findings highlighted the diversity of fluvial styles in the pantanal and its importance as a climate changes archives in the south american lowlands

quaternary lakes of argentina abstract the quaternary lakes of argentina are grouped into eight main environments swamps and playas of the hernandaries formation middle quaternary of northeastern argentina pampean swamps chaco swamps swamps and shallow lakes of the parana system salt lakes of the puna northwestern salt lakes and playas glacial lakes of the southern cordillera and patagonian closed depressions

facies associations detrital clay grain coats and mineralogical characterization of the gironde estuary tidal bars a modern analogue for deeply buried estuarine sandstone reservoirs abstract estuarine tidal bar sandstones are complex reservoir geobodies commonly exploited by the oil and gas industry in order to better predict the reservoir potential of these geobodies this study provides a modern day reservoir analogue describing tidal bars in the inner and outer gironde estuary from the microscopic to the macroscopic scale the originality of this work lies in the multi scale study of modern estuarine tidal bars based on numerous piston cores extracted in a high energy environment this work demonstrates that these tidal bars are composite sedimentary bodies made up of individual reservoir sand units separated by thick muddy layers their vertical facies associations and internal architectures are controlled by local hydrodynamic variations and seasonal river influxes detrital clay grain coats are notably characterized using a portable and handheld mineral spectrometer from the base to the top of the tidal bars x ray diffraction and electron microscopes reveal that these coats are mainly composed of di octahedral smectite illite chlorite and kaolinite associated with other components such as diatoms or pyrite the best reservoir geobodies are those with the minimum clay permeability barriers at the macro and mesoscale an optimum coated grain content and clay fraction volume is also needed for generating authigenic clay coatings and inhibiting quartz overgrowth these conditions are met within the tidal sand bars of the outer estuary funnel that are expected to be the best reservoir geobodies in deeply buried sandstones

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

diet and habitat of toxodont megaherbivores mammalia notoungulata from the late quaternary of south and central america abstract the toxodont megaherbivores toxodon and mixotoxodon were endemic to south and central america during the late quaternary isotopic signatures of 47 toxodont teeth were analyzed to reconstruct diet and ancient habitat tooth enamel carbon isotope data from six regions of south and central america indicate significant differences in toxodont diet and local vegetation during the late quaternary toxodonts ranged ecologically from c3 forest browsers in the amazon mean 13c 13 4 to mixed c3 grazers and or browsers living either in c3 grasslands or mixed c3 forested and grassland habitats in honduras mean 13c 9 3 buenos aires province argentina 13c 8 7 and bahia brazil mean 13c 8 6 to predominantly c4 grazers in northern argentina 13c 4 4 to specialized c4 grazers in the chaco of bolivia 13c 0 1 although these toxodonts had very high crowned teeth classically interpreted for grazing the isotopic data indicate that these megaherbivores had the evolutionary capacity to feed on a variety of dominant local vegetation in the ancient amazon region carbon isotope data for the toxodonts indicate a c3 based tropical rainforest habitat with no evidence for grasslands as would be predicted from the neotropical forest refugia hypothesis

predominance of arid climates indicated by mammals in the pampas of argentina during the late pleistocene and holocene abstract south american climates during the pleistocene and holocene are poorly known especially in the lowlands east of the andean ranges however there is relatively good biostratigraphic and climatic information for the late lujanian and platan local ages latest pleistocene to holocene of the pampas region most of the climatic data from the pampean area are based on land mammal assemblages pollen records and geology contrasting with north american faunal associations there are many non analogue assemblages in the holocene of the pampean area the climate was arid and relatively cold during most of the early lujanian however several relatively wet and warm events are suggested by the presence of subtropical mammals and evidence of tchernozoid paleosoils the late lujanian is well represented by the fossiliferous sediments of the la chumbiada and guerrero members of the lujan formation ca 30 000 and 21 000 13 000 yr b p respectively cropping out in stream valleys in the buenos aires province mammal assemblages suggest a change from a temperate to a cool climate from the la chumbiada member to the guerrero member the latter representing the last glacial maximum the lower portion of the eolian la postrera formation has been dated at 11 000 8000 yr b p this section was deposited on basin divides under dry and cool conditions the mammal association was similar to that of the gueffero member and includes the last megaherbivore mammals in south america e g megatherium americanum mammals occurring in platan beds usually indicate dry but not cool conditions warm and probably wetter conditions were detected in continental beds deposited synchronously with a mid holocene marginal marine ingression ca 7000 6000 yr b p a holocene non analogue assemblage of subtropical mammals and dry cold indicators occurred at latitude 38 30 s at ca 2000 yr b p subtropical mammals that require wetter conditions have been migrating southwards in the pampean region since 1500 1000 yr b p eolian sediments in the la postrera formation dated ca 440 yr b p yielded an arid to semiarid mammal assemblage which could relate to the little ice age period remarkably most of the present day manual biocenoses and climatic conditions in the pampas seem to have been recently established paleogeographic maps for the last glacial maximum and the mid holocene are also provided

the raft of the saint jean river gaspe quebec canada a dynamic feature trapping most of the wood transported from the catchment abstract the rivers of the gaspe peninsula quebec canada a coastal drainage system of the st lawrence river receive and transport vast quantities of large wood the rapid rate of channel shifting caused by high energy flows and noncohesive banks allows wood recruitment that in turn greatly influences river dynamics the delta of the saint jean river has accumulated wood since 1960 leading to frequent avulsions over that time period the wood raft there is now more than 3 km in length which is unusual but natural this jam configuration allows a unique opportunity to estimate a wood budget at the scale of a long river corridor and to better understand the dynamics of large wood lw in rivers a wood budget includes the evaluation of wood volumes i produced by bank erosion input ii still in transit in the river corridor deposited on sand bars or channel edges and iii accumulated in the delta output the budget is based on an analysis of aerial photos dating back to 1963 as well as surveys carried out in 2010 all of which were used to locate and describe large wood accumulations along a 60 km river section the main results of this paper show that the raft formation in the delta is dynamic and can be massive but it is a natural process considering the estimated wood volume trapped in the delta from 1963 to 2013 25 000 m3 two important points are revealed by the quantification of the wood recruitment volume from 1963 to 2004 27 000 m3 400 m3 and of the wood volume stored on the bars in 2010 5950 m3 first the recruitment of large wood from lateral migration for the 40 year period can account for the volume of large wood in the delta and in transit second the excess wood volume produced by lateral migration and avulsion represents a minimum estimation of the large wood trapped on the floodplain owing to wood volume that has decomposed and large wood that exited the river system rafts are major trapping structures that provide good potential sites to monitor wood delivery from the catchment through time and allow estimations of lw residence time while in transit these results contribute to understanding the interannual large wood dynamics in the saint jean river and can assist river managers in determining sustainable solutions for coping with the issue of wood rafts in rivers

effective closure temperature in leaky and or saturating thermochronometers abstract the classical equation of closure temperature t c in thermochronometry dodson 1973 assumed i no storage limitation for the accumulating radiogenic product ii a negligible product concentration at the initial temperature of cooling t 0 and iii a negligible product loss at the final present day temperature t p a subsequent extension ganguly and tirone 1999 provided a simple correction for systems cooling from an arbitrary t 0 at which presence of an initial concentration profile may affect final concentrations here we use a combination of analytical and numerical solutions to derive a general expression for the effective closure temperature in i systems which cool between arbitrary initial and final temperatures potentially still suffering from thermal product loss at t p termed leaky and ii systems which may contain a physical limit on the maximum amount of product that can be stored termed saturating while all conservative results can be easily reproduced an extended use of our formulation provides meaningful effective closure temperatures even when the standard calculation schemes fail for a first order loss radiometric system governed by k t s exp e r t where e j mol 1 and s s 1 are the arrhenius parameters and r is the gas constant we find that the effective closure temperature t c t 0 t p is given by t c t 0 t p 1 t p r e k p ln 1 k p k p e k p k p k 0 1 where k 0 and k p s 1 are shorthand for k t 0 and k t p respectively s 1 the production rate s a time constant and a z the upper incomplete gamma function under conventional conditions our solution reduces to dodson s formula although the solution strictly applies only to systems where 1 t increases linearly with time it is nevertheless a useful approximation for a broad range of cooling functions in systems where closure occurs close to the system s initial final thermal boundary conditions we clarify the use and the meaning of t c t 0 t p by drawing a comparison between i a hypothetical application of apatite u pb dating t c 450 c on venus mean surface temperature of 450 c leaky behaviour and ii the recently introduced thermochronometric application of optically stimulated luminescence osl dating on earth both leaky and saturating behaviour

accumulation of fine grained material in a danish tidal area abstract the exchange of fine grained material m between the north sea and the tidal area of gradyb in the danish wadden sea has been determined by means of the 210 pb dating method the amount of fine grained material accumulating in the area 169 km 2 has been calculated to be 142 10 3 t yr 1 of this approximately 85 is derived from the north sea 5 6 from rivers 4 from internal coastal erosion and another 5 6 from the combined effect of waste atmospheric deposition and net primary production these results have been verified through a budget for excess 210 pb it is demonstrated that fine sediments from the north sea are sorted before accumulating in the wadden sea with the result that the deposited material contains more coarse silt and less clay than is found in the source material from the north sea the relation between accumulated fine grained material and the volume of exchanged water is found to be in the same order of magnitude in gradyb as in jadebusen and dollard this relation is suggested to be a characterising parameter of the sedimentation in tidal areas

clay mineral and heavy metal distributions in the northeastern north sea abstract clay mineralogy and heavy metal distribution of surface sediments of the northeastern north sea have been analysed in order to show the origin and transport pathways of fine grained sediments the distribution patterns of clay minerals largely reflect regional current patterns fine material enriched in smectite derived mostly from the german bight sector in the south is transported by the jutland current parallel to the west coast of denmark into the skagerrak where a decreasing proportion of smectite indicates the increasing influence of the central and northern north sea currents illite and chlorite have identical distribution patterns in the northeastern north sea which suggests a common origin for both clay minerals this origin is located in pleistocene relict sediments of the northern north sea rather than in a contribution from the north atlantic zinc cadmium copper and lead in surface sediments of the north sea when compared to background values are significantly enriched sediments of the inner german bight are in comparison with other north sea sediments highly polluted a zone of high heavy metal contents zn cd and cu is found along the german and danish coasts comparable to the smectite distribution indicating the transport of fine grained polluted sediments to the north further to the north these sediments are diluted by less polluted sediments finally in the skagerrak and the norwegian trench a relatively low stage of pollution is reached

paleoenvironmental reconstruction of the semi arid chaco region of argentina based on multiproxy lake records over the last six hundred years abstract in this paper we analyze the paleoclimatic and paleoenvironmental evolution of laguna yema in semi arid chaco region of argentina over the past six hundred years high resolution multiproxy studies of lake sediments utilize analyses of lithology mineralogy geochemistry palynology and are constrained by radiocarbon and gamma spectrometry dating laguna yema sediments were mainly composed of well stratified fine sediments silts and clays with variable proportions of quartz clays illite and feldspar microcline and albite twelve light and heavy geochemical elements were registered most elements al si k ti fe rb ba and br are associated with illite and albite different material transport processes related to the changes in aridity and humidity of the basin were identified using the main mineralogical origins of geochemical elements palynological records indicate cycles of contraction and expansion of the lake with an increase in concentration of alternanthera aquatica during wet periods expansion of lake and an increase in ambrosia poaceae and fern spores during dry periods contraction of lake these changes are linked to fluctuations in moisture conditions in the subandean mountains and semi arid chaco regions in response to interactions between the south american monsoon system sams and the south american low level jet sallj which send warm and humid air to northern argentina in a regional context the laguna yema records are in accordance with the analyses of the temporal and spatial pattern of moisture distribution for the last six centuries

increase of radiation sensitivity of esr centres by faulting and criteria of fault dates abstract the esr spectra and ages of the fractured rocks along the itoigawa shizuoka tectonic line a major fault in japan were measured the esr signal intensities tend to become larger with decreasing distance from the fault boundary because the radiation sensitivities of the esr centres have increased by faulting according to fracturing and heating experiments when the radiation sensitivities of esr centres have visibly increased the signals may have been almost completely reset by faulting as a result of the increase of radiation sensitivity the error range of the td values for incompletely reset esr signals is comparatively large whereas it is smaller in the case of completely reset signals therefore by assessing the error range of td values we can determine whether esr signals were completely reset at the time of faulting

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

the cooling history of the late pliocene eldzhurtinskiy granite caucasus russia and the thermochronological potential of grain size age relationships abstract isotopic age investigations have been carried out on samples from the late pliocene eldzhurtinskiy granite great caucasus russia in order to elucidate the cooling history of this kilometere sized plutonic body the samples were taken from a horizontal profile from the edge to the centre of the granite and from a vertical profile from the top to a depth of 4570 m the 40ar 39ar results on biotites ranging from 2 5 to 1 2 ma indicate a vertical age zoning of the granite caused by regional uplift an uplift rate of 4 mm a is calculated from the age differences together with the results of fission track dating on apatite and zircon and the present day rock temperatures the biotite ages can be used to evaluate cooling rates below 400 c the cooling rates of about 180 c ma are relatively high and spatially and temporarily fairly uniform throughout the granite a geothermal gradient of 45 c km is derived from uplift and cooling rates this is identical to the present day borehole gradient the 40ar 39ar ages of distinct biotite grain fractions from one and the same sample specimen are discordant generally they show clear age grain size correlation as expected from ar diffusion theory for cooling systems thus the biotite results support the additional detailed thermochronological information the cooling rates in the temperature range of biotite closure based on the grain size age correlations of the biotites are close to 180 c ma they provide evidence that within a certain temperature interval the time temperature path of a rock may be determined exclusively by isotopic dating of different grain size fractions of only one type of mineral

modeling heterogeneity in a low permeability gas reservoir using geostatistical techniques hyde field southern north sea hyde field is a small 133 gcf footnote reserves gas field in the united kingdom southern north sea the reservoir the permian rotliegende group contains eolian fluvial and sabkha facies the eolian facies constitute the dominant flow units illite cementation results in low reservoir quality in the eolian facies permeability averages 2 5 md and rarely exceeds 10 md to maximize recovery from this field with its thin gas column and low reservoir quality hyde has been developed with three long reach horizontal wells a reservoir model that could accurately predict future production had to include a full range of heterogeneities from the effects of thin muddy laminations at the core plug scale to the spatial distribution of eolian fluvial and sabkha facies over the entire field at the largest scale by carefully defining the model s layering scheme we incorporated strongly deterministic elements where facies trends were influenced by laterally extensive stratigraphic surfaces the distribution of facies within stratigraphic units was modeled using geostatistical techniques average permeability values were assigned to the poorest quality fluvial and muddy sabkha facies permeability values for the eolian and sandy sabkha facies were determined by upscaling models of their internal permeability structure the resulting distribution of permeabilities across the field present in a 2 2 million cell model was upscaled into a coarser grid suitable for simulating the full field this new model produced a significantly better match to dynamic data than did an earlier simple layer model that was used to take the field to sanction the results of our work suggest that stochastic modeling allowed us to represent a level of heterogeneity that was not captured by the earlier simple layer model by capturing this level of heterogeneity we were able to achieve a significantly better match of model predictions to production data

stratigraphic relationships in the upper rotliegend interpretations from horizontal and vertical well borehole images core and logs in the lancelot area southern north sea uk

inside auk the anatomy of an eolian oil reservoir auk field is located in the central north sea uk sector and produces from permian zechstein carbonates and the underlying rotliegend sandstones thirty wells have been drilled at spacings between 70 m and 3 6 km the rotliegend is about 300 m thick and can be divided into five possibly distinct phases of desert sedimentation the upper three of these are oil bearing with eolian slipface sands forming the main productive horizons 1 the earliest deposits are localized fluviatile conglomerates which infill topography on the unconformity with the devonian 2 the overlying highly porous sands form a large wedge shaped body onlapping the devonian they comprise predominantly eolian slipface sands with slipfaces oriented toward the southeast 3 this interval represents a change in eolian deposition with a marked increase of tighter wind ripple laminated sandsheet dry interdune and dune apron sands this unit fluctuates in thickness by about one third over the field area stacked dune slipface sands are oriented toward the east and cannot be correlated over a few hundreds of meters across wind 4 an even greater proportion of wind ripple laminated deposits are contained in this interval its geometry is that of a depositional mound 100 m thick and 7 km across more wind dune and possibly dry slipface sands oriented east occur where it is thickest fine grained eolian sands are banked up on its northern flank 5 finally waterlain mass flow sands partially infill depositional lows and appear to represent rainfall reworking of a largely abandoned erg the marine zechstein transgressed and draped remaining topography less

integration of horizontal well geological data into reservoir descriptions rotliegende sandstone lancelot area southern north sea lancelot guinevere and excalibur are rotliegende group gas fields that were developed mainly by horizontal drilling horizontal well geological data from these fields are interpreted and integrated with vertical well data to evaluate the target zone and enhance the reservoir description lateral variations in reservoir quality and eolian facies are interpreted in a horizontal core borehole images and conventional electric logs are used to identify facies record the lateral extent and orientation of eolian dune cross bed sets characterize diagenetic trends and locate fractures through the uncored horizontal well sections the cored interval consists of gently dipping medium grained dune base strata separated by a set boundary from moderately steeply dipping fine grained dune top sediments permeability varies with grain size and is therefore greater in the dune base than the dune top in this cored section the main facies in the horizontal wells as a whole are of eolian dune interdune and fluvial to marine reworked eolian origin comparison of facies in horizontal and vertical wells defines reservoir units in the upper part of the formation that show large scale mound and intermound infilling geometries reflecting relic dune field geomorphology comparison of the lateral extents and heights of eolian cross bed sets and patterns of foreset bed dip vector swing suggest that the sets are strongly trough shaped in copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received may 25 1995 revised manuscript received march 6 1996 final acceptance august 14 1996 2robertson research international limited llandudno north wales ll30 1sa united kingdom current address robertson blackwatch ltd netherton business centre fetternear kemnay inverurie aberdeenshire ab1 5lx united kingdom 3mobil north sea limited 3 6 clements inn london wc2a 2eb united kingdom we thank mobil north sea ltd brabant oilex ltd and robertson research international ltd for permission to publish this paper we thank the following people for their helpful discussions peter corbett richard wood john ebbern peter lucas rob crossley and carl watkins and aapg referees peter hutchinson neil hurley and roy nurmi whose critical reviews helped improve the organization of the paper the opinions expressed and any misconceptions however are entirely ours

slope of alluvial fans in humid regions of japan taiwan and the philippines abstract this study constructed a database for 690 alluvial fans in humid regions of japan taiwan and the philippines and analyzed their slopes and other morphometric parameters such as the area and relief ratio of the source area this type of comprehensive geomorphological research on alluvial fans in humid regions has been limited although numerous studies have dealt with fans in arid and semi arid regions semi conical depositional landforms larger than 2 km2 and steeper than 0 11 0 002 m m were selected as alluvial fans about 60 of the fans formed during the holocene and the rest 40 formed during the pleistocene mean fan slopes for both all the quaternary fans and holocene fans follow a lognormal frequency distribution the distribution also fits slopes of fans belonging to a certain areal range the area and relief ratio of the source area which correlate well with the fan slope also follow a lognormal distribution indicating the dimensions of fan basin systems vary gradually rather than abruptly these findings contrast with a previous notion that depositional landforms rarely have slopes of 0 5 0 009 to 1 5 0 026 and hence only semi conical landforms steeper than 1 5 should be called alluvial fans

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

late quaternary paleosol sediment sequences and landscape evolution along the andean piedmont bolivian chaco abstract as part of the bolivian chaco the andean piedmont is situated in the transitional zone between the tropical humid climate regime to the north amazonia and the subtropical semiarid regime to the south gran chaco in this zone which is sensitive to climatic changes late quaternary landscape and climate history was reconstructed based on detailed sedimentological pedological and geochemical analyses of paleosol sediment sequences along the andean piedmont the determination of characteristic lithofacies allowed correlation between the investigated profiles and their interpretation in terms of paleoenvironmental conditions i e geomorphic stability soil formation or geomorphic activity fluvial or fluvio aeolian sedimentation erosion etc coarse fluvial deposits gravels sands form the base of the investigated profiles and have likely been deposited in a braided river environment with low vegetation cover and intensive discharge events before and during the last glacial maximum well developed paleosols formed in the upper part of these sediments during the lateglacial documenting geomorphic stability high vegetation cover and wet conditions overlying palustrine sediments dated to the early holocene indicate a dramatic change in seasonality i e increased winter precipitation and decreased summer precipitation subsequent erosion followed by accumulation of fluvial and fluvio aeolian sands points to much drier conditions during the mid holocene since 2 9 cal ka bp soil formation indicates a return to geomorphic stability and wetter conditions characteristic of the present day climate interrupted by short arid intervals

osl thermochronometry of feldspar from the ktb borehole germany the reconstruction of thermal histories of rocks thermochronometry is a fundamental tool both in earth science and in geological exploration however few methods are currently capable of resolving the low temperature thermal evolution of the upper 2 km of the earth s crust here we introduce a new thermochronometer based on the infrared stimulated luminescence irsl from feldspar and validate the extrapolation of its response to artificial radiation and heat in the laboratory to natural environmental conditions specifically we present a new detailed na feldspar irsl thermochronology from a well documented thermally stable crustal environment at the german continental deep drilling program ktb there the natural luminescence of na feldspar extracted from twelve borehole samples 0 1 2 3 km depth corresponding to 10 70 c can be either i predicted within uncertainties from the current geothermal gradient or ii inverted into a geothermal palaeogradient of 29 2 c km 1 integrating natural thermal conditions over the last 65 ka the demonstrated ability to invert a depth luminescence dataset into a meaningful geothermal palaeogradient opens new venues for reconstructing recent ambient temperatures of the shallow crust 200 c ma 1 range although na feldspar irsl is prone to field saturation in colder or slower environments the method s primary relevance appears to be for borehole and tunnel studies where it may offer remarkably recent 0 3 ma information on the thermal structure and history of hydrothermal fields nuclear waste repositories and hydrocarbon reservoirs

late quaternary climate history of the bolivian altiplano abstract sediment cores and outcrops from the bolivian altiplano are used to interpret late pleistocene holocene paleoclimates and lake evolution based on a multi proxy approach ostracod content palynology sedimentology and radiocarbon dating despite the different sensitivity of the lacustrine basins to environmental changes interpreting the records in terms of paleohydrology climate and more especially timing of events is difficult notwithstanding these problems lake titicaca in the north and lake pocoyu lake poopo salars of coipasa and uyuni in the south reveal a similar evolution in general trends through the course of time during the minchin phase until 30 26 kyr bp the altiplano was wetter than present the last glacial maximum ca 26 14 kyr bp marked by cooler drier conditions was followed by a return to a wetter climate interrupted by short arid events between ca 14 and 10 5 kyr bp another cycle of aridity between 10 5 and 8 kyr bp took place abruptly just after the humid tauca phase the mid holocene is interpreted as climatically unstable with an alternation of humid and dry episodes since 3 9 kyr bp wetter conditions have persisted and intensified to the present the data are interpreted in terms of changes in inter tropical convergence zone extension summer precipitation and in polar air mass intensity winter precipitation

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor

settling speeds of floes in fresh water and seawater the settling speeds of floes of fine grained natural sediments approximately 10 200 m in diameter have been measured in both fresh water and seawater these floes were formed at fluid shears of 100 200 and 400 s 1 and at sediment concentrations of 10 100 and 400 mg l values typical of conditions in the near shore areas of lakes and oceans especially during storm conditions it is demonstrated that the settling speed of a floe is a strong function of fluid shear and sediment concentration as well as of the diameter of the floe but it is a weak function of salinity for the same diameter and salinity floes produced at the lower fluid shears and sediment concentrations have lower settling speeds than do floes produced at higher fluid shears and sediment concentrations if the conditions of fluid shear and sediment concentration under which the floes were produced are unknown or ignored it is shown that the settling speed of a floe is a weak function of diameter and salinity

coagulation rates of clay minerals and natural sediments abstract coagulation experiments conducted using illite kaolinite montmorillonite and four natural sediment samples in blade and couette reactors with solutions of various salinities yielded collision efficiency factors significantly higher than those in the previous literature indicating that coagulation begins at lower salinities 1 2 1 the natural sediments do not generally behave as might be predicted for a mixture of the standards of the minerals of which the natural sediment samples were comprised the half times for coagulation of the particles indicate that in nature the coagulation process would probably be completed in the first few parts per thousand salinity

towards single grain esr dating of sedimentary quartz first results abstract in optically stimulated luminescence dating apparent ages of individual grains are thought to reflect a wide distribution of initial bleaching levels in hard to bleach sediments although having a larger age range up to 1 ma and beyond this approach has not been used yet in electron spin resonance esr dating here we report on the first results of esr measurements on single sedimentary quartz grains initial bleaching levels are evaluated for two different river meuse deposits in limburg ne belgium measurements were done with a q band esr spectrometer on transparent quartz grains of sufficiently large diameter 0 5 0 7 mm single crystal esr properties were used to identify different esr active centres in about 50 of the selected grains an al and or ti li signal was detected and the latter has been selected for further measurements artificial bleaching experiments show a strong signal decrease with uv light exposure after gamma ray irradiation a number of different signal intensity vs artificial dose curves could be observed exponential growth exponential saturation linear with inflexion points and unclear ones many grains show increasing esr signals with doses up to 1000 gy suggesting that the age range could be extended over 1 ma covering the middle pleistocene and part of the early pleistocene accumulated doses of individual grains were calculated using the additive dose method the results show a large dose distribution of individual grains for both deposits it is concluded that insufficiently bleached grains can be detected using single grain esr measurements of sedimentary quartz in a fluvial environment

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

natural accumulation of schottky frenkel defects implications for a quartz geochronometer electron spin resonance esr analyses have been made of natural quartz samples ranging in age from 100 ka to 1 4 ga signal intensities of two esr centers that can be associated with schottky frenkel sf defects are significantly correlated with age these defects are thought to accumulate naturally as a result of elastic collisions in the quartz lattice initiated by the recoil of alpha emitting nuclides present as impurities preliminary indications are that recoil induced sf defects can be significantly more abundant than original sf defects in samples older than several million years these considerations provide the theoretical basis for a long ranging quartz geochronometer

alluvial fans and fluvial fans at the margins of continental sedimentary basins geomorphic and sedimentological distinction for geo energy exploration and development alluvial fans and fluvial fans are the most common depositional landforms along the margins of continental sedimentary basins their occurrence is determined by the area relief and hydrology of the catchment which ultimately control the relative ratios of sediment v flow discharge and runoff regimes fundamental morphological and process distinctions exist between these two kinds of deposystem which are seen as essentially different facies associations and internal architectures for the corresponding deposits alluvial fans commonly develop over short radial distances hundreds of metres to a few kilometres and are constructed by ephemeral flash flow events that lead to poor organization of the sedimentary facies and overall architecture of the corresponding deposits by contrast fluvial mega fans are fed by proper river systems which aggrade much larger volumes of clastic sediment over distances of up to a few hundred kilometres distinct channel belt and overbank domains are developed with a marked heterogeneity in the distribution of sedimentary facies represented by hierarchically well organized fluvial deposits the general properties of alluvial and fluvial fans reflect the different potentials for the corresponding successions to host economically attractive oil and gas resources and the different approaches required in exploration and prediction

an integrated sedimentary systems analysis of the rio bermejo argentina megafan character in the overfilled southern chaco foreland basin abstract the chaco foreland is well known for its spectacular fluvial megafans and this basin frequently serves as a modern analog for studies that use the geological record to investigate tectonic processes in convergent orogenic systems yet little sedimentary data has been recovered from the southern chaco particularly at the latitude of northern argentina which limits both its utility as an analog and our understanding of andean megafan development in the subtropics the southern chaco is particularly amenable for a modern time slice sedimentary systems analysis as environmental gradients controlled by tectonics and climate are relatively well documented deposition in the southern chaco foreland is dominated by the rio bermejo which was studied by integrating geomorphological observations made using geographic information systems with analyses of composition texture and u pb ages of modern detrital sediments remote sensing data reveal changes in rio bermejo channel width sinuosity and bifurcation from west to east across the foreland which are compatible with aspects of geomorphic models for distributive fluvial systems the rio bermejo fully spans the foreland and connects with the south flowing rio paraguay fluvial sediments and reworked loess bury and obscure any surficial expression of a flexural forebulge therefore the rio bermejo megafan rbm stands as an important example of a megafan in an overfilled foreland basin variability in rbm morphology and landforms appears to have only subtle linkages to flexural partitioning of the chaco which is likely a consequence of sediment supply overwhelming available accommodation trend surface analysis highlighted topographic contrasts in rbm architectural elements and indicates the presence of distributary channels with variable surficial expression shallow accommodation marked by ponds is most pervasively developed at the eastern end of the rbm this pattern is consistent with model predicted locations of a back bulge depozone although three environmentally distinct hinterland areas contribute sediment to the rbm sands from the foreland cannot distinguish these zones rather provenance is controlled chiefly by parent lithologies and transport distance sands in the rbm plot within the recycled orogen provenance field mean qtfl 77 6 17 and compositional maturity increases with distance from the thrust front such that quartzose sublitharenites dominate in the distal back bulge distinct intra foreland gradients are captured in sand texture and clay mineral abundances rio bermejo sand sizes become progressively finer towards the forebulge and back bulge mean 98 m whereas mean particle sizes in the wedgetop and foredeep are 280 and 195 m respectively detrital clays suspended in the rio bermejo consist of illite smectite chlorite and kaolinite in rank order of abundance with smectite concentrated in the foredeep due to reworking of the semiarid floodplain by water and wind the results of this study provide novel sedimentary ground truth for distributive fluvial systems in overfilled retroarc forelands that can be used to improve facies models and interpretations of the geological record

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

the exhumation of the western greater caucasus a thermochronometric study this study provides 39 new thermochronometric analyses from the western part of the greater caucasus a region in which existing data are extremely limited and of questionable quality the new results are consistent with field studies that identify triassic to middle jurassic cimmerian and oligo miocene alpine orogenic erosional events an inverse relationship between the fission track and depositional ages of oligo miocene sedimentary samples also implies some degree of eocene erosion of the greater caucasus and intermediate sediment storage cooling ages and field relationships within the core of the range west of mt elbrus require 5 km of permo triassic exhumation and restrict the overall amount of cenozoic exhumation to 2 5 km current exhumation rates are typically low and do not support a plio pleistocene increase in climate driven denudation high 1 km ma 1 rates of exhumation are restricted to the southern flank of the range in northwest georgia despite a general lack of significant seismicity within the study region this exhumation peak is close to the largest instrumentally recorded earthquake in the caucasus ms 7 0 this may suggest that exhumation is associated with the decoupling of the sedimentary succession from its crystalline basement in the southern part of the range and the inversion of the largely jurassic fill of the greater caucasus basin rates of exhumation are compatible with this being driven by active shortening further sampling and analysis are required to provide a higher resolution low temperature thermochronology of alpine exhumation to isolate the drivers for palaeogene dziruli massif cooling and uplift and to constrain better the extent of the current localized phase of rapid exhumation

effect of flow depth ions and salinity on suspended sediment concentration abstracteffects of flow depth ions and salinity on the evolution of suspended sediment concentration ssc are presented experiments are conducted in an annular flume using three different sediments rhine mud alumina and silica in ionic and saline water observations show that at a constant bed shear stress in ionic water the ssc of all sediments decreases because of an increase in the flow depth h at a constant h the ssc increased with an increase in when h and remained constant alumina and silica particles quickly flocculated and attained a lower equilibrium concentration ceq in ionic water than in saline water similarly the flocculation process of rhine mud is faster in ionic water but the ceq in ionic water is higher than that of saline water for all the sediments tested the time to reach ceq is greater in saline water than in ionic water in saline water the evolution of ssc of rhine mud is in between that of alumina and silica

electron spin resonance esr dating of pre quaternary faults in the sichuan basin sw china abstract the electron spin resonance esr dating method is thought to be limited to the quaternary period in this study we attempt to expand the esr dating range to the pre quaternary using three fault zone samples collected from faults in the sichuan basin and its surroundings we adopt a ray radiation dose of up to 2 104 gy which is much greater than that typically employed and find that the esr intensity of the e1 center a type of signal for esr dating in quartz continuously increases with the ray dose and is slightly influenced by the radiation dose rate this indicates the potential of esr to date pre quaternary faults by simulating environmental radiation under geological burial conditions we use esr to date the latest extension event in the western hubei and hunan thrust belt to 9 17 0 76 ma and the thrusting of the longmenshan fault zone toward the sichuan basin to approximately 6 14 0 73 ma conversely the saturated esr intensity of fault zone samples from the daba fault zone suggests a lack of strong tectonic activity in the southern daba fault zone in the last 10 ma our results are consistent with fission track ages and the regional tectonic evolution history therefore esr is a practical method for dating pre quaternary faults in structural and petroleum geology applications

geomorphology and late quaternary of the chaco south america the chaco is a large tropical plain located in the interior of south america consisting of parts of argentina paraguay and bolivia it is 840 000 km2 in area and is characterized by forests savannas and extensive swamps which give it a marked climatic and biogeographic identity it encompasses five huge alluvial fans built by the major rivers which cross the region salado bermejo pilcomayo parapeti and grande the fans are composed of several sedimentary units deposited during different times of the late quaternary under diverse climates two fluvial terraces appear at the apex of each fan the older one is probably late pleistocene in age the second was formed in postglacial times humid climates such as the present one favoured the generation of soils and stable fluvial belts drier climates led to widespread sedimentation along small ephemeral channels and large spill outs during two intervals on in the late quaternary glacial maximum and the late holocene dry climates occurred in the region leading to the formation of dune fields and loess mantles

40ar 39ar and 18o 16o studies of the chegem ash flow caldera and the eldjurta granite cooling of two late pliocene igneous bodies in the greater caucasus mountains russia volcanic and intrusive rocks of the chegem caldera and the nearby eldjurta eldzhurtinskiy granite record a late pliocene episode of silicic magmatism in the north central caucasus mountains surface exposures created by the recent rapid uplift and erosion of the caucasus mountains span a 2 km vertical section of chegem caldera fill and 1150 m of the eldjurta granite cored mineral exploration drillholes in the eldjurta granite extend the sampling to a depth of 4 km the unique sampling range available in these two young igneous bodies affords an excellent opportunity to study their denudation and cooling histories which we examine by means of 40 ar 39 ar and 18 o 16 o measurements on an extensive sample suite total fusion biotite and sanidine ages from eight chegem tuff samples both intracaldera and outflow are analytically indistinguishable with a weighted mean of 2 82 0 02 ma a cross cutting granodiorite porphyry intrusion has a sanidine total fusion age of 2 84 0 03 ma and whole rock incremental heating of a post caldera andesite flow which caps the caldera fill yields an age of 2 82 0 02 ma thus caldera formation and post caldera resurgence and volcanism all occurred within a very short time 50 000 yr biotite total fusion ages of ten eldjurta granite samples including seven from 500 m intervals in the 4 km deep drillhole show a systematic linear decrease in age with depth from 1 90 ma near the roof contact of the granite to 1 56 ma at a depth of 3700 m assuming these ages were set at the same temperature this age depth gradient implies an isotherm migration rate of 13 mm yr between 1 90 and 1 56 ma this migration rate is due to a combination of rapid denudation and downward relaxation of isotherms with cooling rates between 200 and 500 c ma during this period oxygen isotopic compositions of quartz k feldspar plagioclase and biotite from the drillhole samples below the 800 m depth are fairly uniform and record primary igneous 18 o values with little evidence for subsolidus hydrothermal activity however in surface outcrop samples and in the shallowest drillhole sample mineral 18 o values have been lowered by up to 3 by interaction with an external meteoric hydrothermal fluid the primary mineral 18 o values of the eldjurta granite are distinctly higher than the corresponding phenocryst 18 o values in the chegem volcanic rocks indicating that the two bodies evolved as separxate magma batches

palaeoenvironments and palaeotectonics of the arid to hyperarid intracontinental latest permian late triassic solway basin u k abstract the late permian to late triassic sediments of the solway basin consist of an originally flat lying laterally persistent and consistent succession of mature dominantly fine grained red clastics laid down in part of a very large intracontinental basin the complete absence of body or trace fossils or palaeosols indicates a very arid hyperarid depositional environment for most of the sediments at the base of the succession thin regolith breccias and sandstones rest unconformably on basement and early permian rift clastics overlying gypsiferous red silty mudstones very fine sandstones and thick gypsum were deposited in either a playa lake or in a hypersaline estuary and their margins these pass upwards into thick bedded multi storied fine to very fine grained red quartzo felspathic and sublithic arenites in which even medium sand is rare despite channels with clay pebbles up to 30 cm in diameter above thick trough cross bedded and parallel laminated fine grained aeolian sandstones deposited in extensive barchanoid dune complexes pass up into very thick multicoloured mudstones and gypsum deposited in marginal marine or lacustrine sabkha environments the latter pass up into marine lower jurassic shales and limestones thirteen non marine clastic lithofacies are arranged into five main lithofacies associations whose facies architecture is reconstructed where possible by analysis of large exposures the five associations can be compared with the desert pavement arid ephemeral stream sabkha saline lake and aeolian sand dune environments of the arid to hyperarid areas of existing intracontinental basins such as lake eyre and lake chad the accommodation space in such basins is controlled by gradual tectonic subsidence moderated by large fluctuations in shallow lake extent caused by climatic change and local variation and this promotes a large scale layer cake stratigraphy as exemplified in the solway basin here the dominant fine grained mature sandstones above the local basal reg breccias suggest water reworking of wind transported sediment as in the northern part of the lake chad basin growth faulting occurs in places in the solway basin caused by underlying evaporite movement but these faults did not significantly affect pre late triassic sedimentation and did not expose pre permian units above the basal breccias there is no evidence of post early permian rifting anywhere during deposition of the late permian to middle triassic british succession although the succession is often interpreted with a rift basin model the arid to hyperarid palaeoclimate changed little during deposition of the solway basin succession in contrast to lakes eyre and chad and this is attributed to tectonic and palaeolatitude stability unlike the later mesozoic cenozoic only limited plate movements took place during the triassic in western europe palaeolatitude changed little and the solway basin remained in the northern latitudinal desert belt from early to mid triassic times however the influence of the early triassic impoverished biota on environmental interpretations needs further study

a laboratory examination of floc characteristics with regard to turbulent shearing abstract turbulent shear generated within the water column is recognised as having a controlling influence over both the flocculation of fine grained cohesive sediments within estuarine waters and their respective aggregate break up this study examines the inter relationships between floc characteristics over increasing turbidity 80 200 mg l 1 and turbulent shear 0 0 6 n m 2 environments by the use of a laboratory flume within which a suspension can be sheared at a controlled rate and with an unintrusive macro lens miniature video camera mounted in a viewing port on the flume channel wall the camera enables the direct simultaneous measurement of both floc size and settling velocity from which accurate estimates of floc effective density and porosity can be made measurements were made 120 s after the induced turbulence has ceased the instrument has an upper viewing turbidity limit of 210 mg l 1 and a lower resolution of 20 m the sediment was collected from the inter tidal mudflats at weir quay on the tamar estuary in devon southwest england the results indicated that increasing turbidity at low shear levels encouraged floc growth but the effect of the increasing turbulent shear 0 35 n m 2 together with increasing concentration in suspension causes disruption rather than enhancing the flocculation process at shears up to 0 35 n m 2 the largest size and settling velocity flocs were produced at high concentrations whereas above 0 35 n m 2 disruption caused smaller flocs at higher concentrations the use of algorithms which were based either on a single floc characteristic i e size or settling velocity or a mean fractal dimension were seen not to accurately approximate the experimental data a multiple regression analysis of the experimental data produced the following formula based on mean values of the 20 largest flocs sampled under each of the imposed environmental conditions referred to as max20size mean values settling velocity 0 301 0 00337 rms of the gradient in turbulent velocity fluctuations 0 000606 spm 0 00335 floc size which proved to be the most accurate representation with an r 2 value of 0 95 a similar formula was determined for the average value of the four fastest settling flocs within each sample group max4w s this highlights the importance of modelling algorithms that are developed from data that take into account effective density variations i e simultaneous size and settling velocity measurement