stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

rapid deposition of sand and gravel mixtures downstream of a negative step the role of matrix infilling and particle overpassing in the process of bar front accretion an experimental flow channel was used to investigate the rapid deposition of sand and gravel mixtures downstream of a negative step hydraulic processes give rise to the quasi simultaneous accumulation of openwork gravels matrix filled contact framework and dilated framework gravels the resultant structure is analogous to a bar front in gravel bed streams flow conditions were non uniform but steady in time whereas open and closed gravel fabrics are usually interpreted as representing deposition from unsteady flows for example a varying discharge regime consideration of the percentage of sand in the deposits indicated that in terms of packing the sediments may be considered as a simple binary mixture with partial framework dilation occurring with sand percentages in excess of c 32 despite dilation for sand percentages less than 50 structural stability of the foreset gravels was maintained so that the bar front exhibited a distinct brinkpoint and a planar slip face at the angle of initial yield which made an angular contact with the base of the flume for sand percentages in excess of 80 individual gravel clasts were completely supported by sand the original structural stability was lost so that the bar front eroded by reverse currents assumed a tangential contact with the flume base below the angle of initial yield the brinkpoint was rounded and indistinct in addition to altering the bar front slope increasing the quantity of sand in the bed sediments had a major influence on the dip of gravel particles on the foresets in all experimental runs a surface sand seal with openwork gravels beneath developed upstream of the brinkpoint the mechanics of sand seal formation require further investigation however an overpassing mechanism was noted to be very important in sorting gravel particles rolling over the brinkpoint a published mathematical model describing the overpassing mechanism was found to be appropriate to the present experimental observations

towards realistic aquifer models three dimensional georadar surveys of quaternary gravel deltas singen basin sw germany abstract understanding sedimentary heterogeneities has nowadays become crucial for sophisticated aquifer management the methods used so far for aquifer characterization e g pump test coring analysis cannot provide the needed resolution for a sufficient prediction of the subsurface properties e g sudicky 1986 this calls for the application of the outcrop analogue approach to aquifers e g macfarlan et al 1994 aigner 1995 in this project we used georadar ground penetrating radar or gpr to acquire the subsurface information for high resolution three dimensional images and radar facies mapping of glaciolacustrine delta sediments in the singen basin sw germany a three dimensional reconstruction of sedimentary heterogeneities for a detailed aquifer characterisation becomes possible by combining gpr profiling and outcrop information a case study is presented showing a complex three dimensional architecture of a quaternary gravel body consisting of the following three types of architectural elements 1 glaciolacustrine delta foresets 2 erosional surfaces with scour pool fills and 3 horizontal glaciofluvial gravel sheets although this seems a relatively simple architectural inventory the three dimensional georadar profiling shows considerable internal heterogeneities the radar data are interpreted following the seismic stratigraphic approach i e the delineation of radar facies types and of radar sequences the three dimensional heterogeneities are visualized by means of time slices 3 d block or chair diagrams or series of radar facies maps

hydrogeologic facies models to delineate large scale spatial trends in glacial and glaciofluvial sediments recent interest in contaminant transport in ground water has led hydrogeologists to the conclusion that predicting the movement of solutes requires information on the distribution of spatial trends and heterogeneities in porous media description of spatial trends has long been of interest to sedimentologists who have produced a large body of geologic information on the subject in this paper facies models are used to construct conceptual models of hydrogeologic facies for glacialmeltwater stream sediment and till these hydrogeologic facies models which delineate large scale trends in heterogeneity are appropriate for use in designing hydrogeologic field tests and for estimating input to regional ground water flow and transport models this paper treats each facies as a homogeneous anisotropic hydrogeologic unit the models presented herein conceptualize the hydrogeologic relationships among facies and illustrate one method of converting the apparent chaos in nature into an orderly system that can be tested scientifically and modeled mathematically the principles used to create conceptual models of hydrogeologic facies for the types of sediment considered in this paper can be extended to other sedimentary environments it should be recognized however that such models do not address the small scale heterogeneity present within individual facies additional basic research is required to measure hydraulic conductivity variation within representative hydrogeologic facies and to develop statistical descriptions to represent the variations such detailed descriptions of hydraulic conductivity may be necessary to describe ground water flow at a local scale for analysis of contaminant transport

the grain fluid interaction as a self stabilizing mechanism in fluvial bed load transport a grain scale model of fluvial bed load transport is described with particular emphasis on the equilibrium between the saltating grains and the near bed flow and its role in determining transport rate the model calculates explicitly the modification of the velocity profile by the moving grains together with the consequential reduction in surface fluid shear stress as the surface fluid shear stress is reduced by the moving grains so the entrainment rate decreases and the model reaches a steady state the results provide insight into two important questions at a macroscopic level first they show that in the absence of large static roughness the dynamic roughness caused by the moving grains may be a significant contributor to flow resistance secondly the model indicates the manner in which transport may be limited by a combination of the transport capacity of the flow and the availability of sediment for entrainment only in the case of high sediment availability does the fluid shear stress acting at the surface approach the critical entrainment value reproducing the behaviour suggested by bagnold 1956 and owen 1964 this suggests that prediction formulae based on this assumption only describe the bed load transport system under particular conditions

separating multidomain and single domain like remanences in pseudo single domain magnetites 215 540 nm by low temperature demagnetization it has long been hypothesized that the pseudo single domain properties of submicron magnetites are a result of coexisting multidomain and single domain like remanences we have separated these two types of remanence by low temperature demagnetization ltd in which samples are cooled through the low temperature magnetite isotropic point and rewarmed to room temperature all in zero field at the isotropic point the first crystalline anisotropy constant vanishes and multidomain remanence due to displaced domain walls will be unpinned we measured stepwise alternating field af and thermal demagnetization curves of weak field thermoremanent magnetization trm and anhysteretic remanent magnetization and of saturation isothermal remanent magnetization irms both with and without prior ltd for magnetites with mean particle sizes of 215 390 and 540 nm the memory fraction of remanence recovered after ltd which represents the single domain like component decreased from 44 for 215 nm grains to 23 for 540 nm grains in the case of irms memory of trm was approximately twice as large af decay curves were soft and multidomain like before ltd but became harder and single domain like in shape after ltd ltd removed most low unblocking temperature trm and irms distributed low unblocking temperatures are therefore a multidomain phenomenon probably resulting from successive adjustments of domain walls to changing internal fields and pinning strengths during heating

using two and three dimensional georadar methods to characterize glaciofluvial architecture abstract the threat of pollution in the shallow subsurface has led to an increasing need to understand how complex heterogeneities in gravel aquifers influence groundwater transport to characterize these heterogeneities we have conducted extensive two dimensional 2 d and three dimensional 3 d ground penetrating radar gpr or georadar surveys in two quarries within the rhine valley of northeastern switzerland the quarries comprised gravel and sand deposited in a proglacial braided river system that followed the maximum wurm stage glaciation after the surveys the terrace walls beneath the two study sites were photographed as they were being excavated by combining information extracted from the 2 and 3 d georadar images with the outcrop photographs it was possible to correlate georadar facies with the various glaciofluvial architectural elements the dominant elements were scour pools formed at or near the confluences of two stream channels and horizontally bedded and massive gravel sheets deposited during moderate to high water flow conditions and exposed during low flow conditions architectural elements were generally elongated parallel to the mean flow directions of the ancient river system variations in the strike of their long axes reflected lateral and vertical changes in the local flow direction time slices showed structural trends not evident on 2 d georadar images and photographs data interpretation was quicker more complete and less ambiguous when georadar facies analyses were based on a combination of georadar vertical profiles and time slices than when based on georadar vertical profiles alone

heterogeneity patterns of quaternary glaciofluvial gravel bodies sw germany application to hydrogeology abstract the architecture of sedimentary bodies determines the heterogeneity of many aquifers thus for environmental risk assessment and quantification of clean up efficiencies determination of the spatial distribution of hydraulic properties is required in this study outcrop analogues of glaciofluvial gravel bed deposits are used for a process based analysis of sedimentary heterogeneities which in turn are transformed into hydraulic parameters three scales of heterogeneities are distinguished a the lithofacies scale is formed by unique transport and depositional processes that form the fundamental building blocks hydrofacies types b the depositional element scale shows distinct geometrical characteristics internal structure and bounding surfaces and determines the local distribution of lithofacies and hence the correlation structure of permeabilities c the architectural scale of gravel bodies is formed by the stacking of depositional elements which is controlled by the dynamics of aggrading paleofluvial systems comparison of numerous gravel pits in sw germany revealed three major architectural patterns of glaciofluvial gravel bodies that can be distinguished statistically by the preservation of depositional elements as well as the frequency of lithofacies types the facies analysis results in three conceptual facies models of proglacial river systems which are regionally classified as main intermediate and minor discharge types based on calculated and laboratory measured hydraulic properties of the various lithofacies types detailed outcrop wall maps were digitized into polygons of defined hydrofacies types by using the gis system arc info the two dimensional fields of hydraulic properties were then transferred into a numerical model of groundwater flow modeling results clearly illustrate that the three heterogeneity patterns of gravel bodies also have distinguishable hydraulic response characteristics

sedimentology and hydrogeology of two braided stream deposits abstract two approaches were used to quantify the spatial distribution of hydrofacies in braided stream deposits one approach involved mapping a 50 by 60 by 3 3 m section of a proximal braided stream deposit in a second study we generated a 400 by 400 by 2 6 m section of a medial braided stream deposit using a computer model in both cases we produced three dimensional images showing connected hydrofacies with high permeabilities that form preferential flow paths this information was input to a groundwater flow model and flow paths were analyzed by following the transport of imaginary particles in both systems particles that were uniformly distributed at the up gradient end of the model clustered along preferential flow paths during transport showing that connection among high permeability facies is a critical factor in hydrogeological investigations involving assessment of contaminant movement and remediation

mechanisms of anabranch avulsion within gravel bed braided rivers observations from a scaled physical model the physical modelling of gravel bed braided rivers using a 1 20 froude scale model permits analysis of the types and relative occurrence of different avulsion mechanisms anabranch avulsion within braided rivers involves three main mechanisms choking avulsion caused by blockage of one channel by a sediment lobe constriction avulsion produced by deflection confinement and subsequent diversion of the flow by a barform and apex avulsion following erosion at the outside of sinuous thalwegs and confined meander bends each avulsion mechanism is described and analysis of the abundance of each type illustrates choking avulsion to be predominant without braided rivers three factors are found to control anabranch avulsions namely flow discharge sediment flux and floodplain topography these are briefly discussed together with the implications of avulsion type for the alluvial architecture of gravelly braided alluvium

partial anhysteretic remanent magnetization in magnetite 2 reciprocity 1 one necessary condition for successful determination of relative paleomagnetic field intensity using anhysteretic remanent magnetization arm methods is reciprocity a partial arm produced by a steady field h applied over a narrow interval 2 1 of alternating field af must demagnetize over the same interval 2 1 experimentally we find that partial arms of single domain sd and pseudosingle domain psd grains demagnetize mainly between 2 and 1 whereas 50 of partial arms of large psd and multidomain md grains are erased below 1 giving a low field tail in the coercivity distribution natural pumices granites and oceanic basalts violated reciprocity but lake sediments gabbros andesite and red scoria had relatively small low coercivity tails and are better candidates for paleointensity work using total arm to simulate natural remanence we carried out pseudo thellier paleointensity determinations for coarse psd and md grains arm demagnetization outweighed partial arm acquisition at the same af step resulting in convex down curves of arm remaining versus partial arm gained pseudo arai plot pseudo arai plots predicted from experimentally determined distributions of blocking and unblocking fields agreed well with measured pseudo thellier results in particular explaining convex down md curves

high resolution observations of the small scale flow pattern associated with a poleward moving auroral form in the cusp 1 in this paper we present high resolution observations by the eiscat svalbard radar of the localized ionospheric flow response due to one single flux transfer event and the relative location of a poleward moving auroral form in a fast scan mode the radar was tracking a 50 60 km wide channel of westward flow in the cusp region this flow channel was surrounded by flow running in the opposite direction at the poleward edge of the narrow flow channel a poleward moving auroral form was situated consistent with the auroral form being the signature of an upward birkeland current filament our observations can be interpreted in terms of the southwood 1985 1987 flux transfer model and the fte twin cell flow pattern appears to be a ripple onto the larger scale background convection

braided stream aggradation on an alluvial fan margin emerald lake fan british columbia evolving bar and channel patterns were observed at the distal margin of an active alluvial fan at emerald lake british columbia during peak midsummer flows at the fan margin bed slope is 0 024 sediment is predominantly coarse gravel flow is shallow and fluctuating and sediment transport and deposition are dominated by chutes and lobes flow unconfinement at the exit of rapidly formed shallow scour channels typically results in deposition of sediment lobes 0 2 m thick and 10 250 m2 in area closely spaced deposition of a number of these sediment lobes results in aggradation of composite sediment sheets one such sheet monitored daily over a 15 day period deposited 129 m3 of gravel over 710 m2 of adjacent marsh sediment locally extending the distal fan margin by 39 m thickness of the aggraded bed varied up to 0 37 m depending on surface topography during active deposition individual lobe deposits formed simple unit bars that partly projected above the water surface these bars caused local flo

observing thermomagnetic stability of nonideal magnetite particles good paleomagnetic recorders the thermomagnetic behavior of remanence induced magnetite fe3o4 particles in the pseudo single domain psd size range 0 1 10 m which dominate the magnetic signature of many rock lithologies is investigated using off axis electron holography construction of magnetic induction maps allowed for the visualization of the vortex domain state in an individual fe3o4 grain 200 nm in diameter as a function of temperature acquisition of a series of electron holograms at 100 c intervals during in situ heating up to 700 c demonstrates the vortex state of the fe3o4 grain in this instance remains thermally stable close to its unblocking temperature and exhibits a similar in plane remanent state upon cooling i e the particle is effectively behaving like a uniaxial single domain particle to temperatures near tc such particles are thought to be robust magnetic recorders it is suggested that evidence for psd behavior should therefore not preclude paleomagnetic investigation

introduction to the special issue on aquifer sedimentology problems perspectives and modern approaches abstract progress towards a better understanding of groundwater circulation and transport processes in aquifers demands a multidisciplinary approach to a host of unresolved problems although much progress has been made within recent years in interpreting the dynamic character of groundwater systems many key issues remain to be addressed in particular several areas demand attention the role of sedimentological information heterogeneity in groundwater and transport models the scaling up of observations from outcrop scale to larger scales and the integration of geological and geophysical information of different quality into the description of an aquifer structure still nowadays many of the heterogeneities cannot be recognized directly because of the limitation of measurement techniques this is probably one of the reasons for the limited application of aquifer sedimentology and geophysics in practical cases in order to consolidate expand and make a larger number of people aware of the contribution of modern aquifer sedimentology including modelling and ultra high resolution geophysical methods several lines of intervention were identified 1 a better collaboration of the different disciplines on site specific applied problems 2 development of new modelling techniques combining data of different quality 3 development of optimizing tools position and number of wells additional geophysical methods baysian techniques 4 development of a common language among sedimentologists and hydrogeologists to overcome communication problems

structures and textures in triassic braided stream conglomerates bunter pebble beds in the sherwood sandstone group north staffordshire england in the northern parts of the needwood and stafford eccleshall basins england the pebble beds of the sherwood sandstone group contain thick successions of texturally mature fluvial pebble cobble conglomerates which are organized into either horizontal or cross stratified sets the horizontally lying sets generally coarser grained and more poorly sorted than the cross bedded sets are usually disorganized and either matrix or clast supported although thin lenses of well sorted occasionally openwork units interpreted as falling stage phenomena are often present the cross stratified conglomerates have foresets exhibiting remarkable textural organization with a coarse bimodal sometimes matrix supported part grading upwards or being abruptly overlain by a finer well sorted occasionally openwork part and finally capped by sandstone these rhythmic textural changes are attributed partly to an avalanche process at high stage and partly to falling stage conditions the most common types of vertical association are thick successions of horizontally bedded conglomerates up to 20 m and sequences of an upwards coarsening nature 2 12 m in which cross stratified sets are overlain by flat lying sets the environment of deposition of the gravels is interpreted as one in which water depths at high stage were greater than depths in most modern braided stream plains proglacial or alluvial fan but shallower than depths associated with the pleistocene catastrophic floods from which texturally mature giant gravel bars have been recorded recent braided streams with relatively confined channels and considerable bar channel relief are better analogues in particular medial or mid channel bars with a two tier structure subaqueous and partly emergent portions may explain the upward coarsening sequences in which horizontally lying conglomerates overlie cross stratified conglomerates the thicker sequences of horizontally stratified conglomerates represent proximal longitudinal bar deposits sheets of pebbly sandstone and argillaceous sandstone lying between the conglomerates and commonly occurring towards the top of the succession largely represent deposition from sandwaves and dunes finer interbedded argillaceous sandstones siltstones and mudstones are interpreted as overbank and waning flood deposits basin forming tectonism of increasing intensity probably caused the initial coarsening upwards of the lower part of the succession whilst more stable tectonic conditions and decreasing relief on the margins of the basins and in the areas of provenance in the midlands and the hercynides account for the upwards fining of the upper part of the succession

trough cross bedded conglomerate facies abstract gravel bed river deposits contain a range of facies that includes planar cross bedded gravel gp massive gravel gm and trough cross bedded gravel gt of these the gt facies is commonly interpreted to represent deposits of channel fills and or three dimensional 3d gravel dunes and or scours or pools in this study a calcrete conglomerate sheet built up of gt facies is found to consist of trough cross beds of 3d dune origin gtd and of bedload sheet origin gtb whereas gtd occurs as sets gtb is found to occur as isolated large troughs the gtd facies is characterised by high dips low width height ratios and foreset bed thickness of about 100 140 mm in contrast the gtb facies has low dips high width height ratios and foreset bed thickness usually less than 50 mm the bivariate plot of width height of troughs vs maximum dip effectively discriminates between these varieties of troughs a third variety of gt may be recognised by the presence of a scoop or spoon shaped lower bounding surface as seen in the depositional dip direction this facies has been demonstrated in other works to represent filling of scours or pools on the streambed and is designated as gtc for the preservation of 3d gravel dunes in the stratigraphic record special flow conditions are necessitated of prime importance is the rapid recession of flow subsequent to a short duration of peak discharge such discharge patterns are critical to the preservation of gravel dunes in the stratigraphic record and appear to have been met with in the case of glacial outburst floods or floods in the seasonal tropics

nrm irm s demagnetization plots an aid to the interpretation of natural remanent magnetization af demagnetization of thermoremanent magnetization trm and saturation isothermal remanent magnetization irm s are used to establish diagnostic criteria for primary trm and for secondary magnetization in igneous rocks in applying the approach to the interpretation of natural remanent magnetization nrm the demagnetization of irm s documents the nature of the magnetic phases in the rock while the demagnetization of the nrm gives information about the process of magnetization the ratio of nrm irm s measures the efficiency of the magnetization process

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

sediment transport and bed morphology at river channel confluences river channel confluences form important morphological elements of every river system being points at which rapid changes in flow sediment discharge and hydraulic geometry must be accommodated this article presents results of a quantitative investigation of sediment transport at channel confluences accomplished through both scaled laboratory flume simulation and complementary monitoring of a natural channel confluence bed morphology at channel confluences is characterized by three distinct elements avalanche faces at the mouth of each confluent channel a deep central scour and a bar within the separation zone formed at the downstream junction corner these elements are controlled predominantly by the confluence angle and the ratio of discharges between the tributary and mainstream channels as confluence angle and discharge ratio increase the sediment contributions from the confluent channels are progressively segregated in their paths through the junction with sediment being transported around rather than through the centre of the confluence this segregation of sediment loads is accompanied by the retreat of the main channel avalanche face from the confluence an increase in the scour depth a change in the orientation of the scour and an increase in the size of the separation zone bar field measurements closely replicate the flume simulation a model of sediment transport and bed morphology links these features to the fluid dynamics of these sites an understanding of confluence dynamics is important not only in considerations of channel morphology and design criteria but must form the basis for the interpretation of confluence sediments in the ancient record

morphology sedimentology and palaeohydraulic significance of large gravel dunes altai mountains siberia coarse gravel bedforms which resulted from pleistocene glacial outburst floods are identified as subaqueous dunes comparison of the morphology of these fossil structures with modern dunes shows that the form of two dimensional 2 d transverse dunes and 3 d cuspate and lunate dunes developed in coarse gravels is comparable with sand dune morphology within lesser scale geophysical flows the similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform internal structure indicates that flow over 2 d dunes was relatively uniform but over 3 d bedforms flow was locally variable flow separation and complex streaming of flow occurred over the steepest 3 d dunes cross beds are thin and few approach the angle of repose consequently most dunes did not migrate primarily by avalanching but by stoss entrained gravel transported over the crests rolling down and depositing on the lee slopes the lee formed when flood power was waning some dunes were siightly planed down during falling stage because lee side cross beds tend to be steeper than the angle of the preserved lee slope however silt rich caps indicate that any height reduction was contemporary with the final deposition of foresets post flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs lee side sediments are often finer than the stoss slope sediments which indicates

a synthetic trm induction curve for fine particles generated from domain observations a synthetic thermoremanent magnetization trm induction curve is produced from domain observations of an ensemble of pseudosingle domain psd titanomagnetite particles in oceanic basalts the observations were made after the samples were given a trm in fields of 0 1 2 4 6 and 8mt an observation was also made of the domain state for saturation isothermal remanent magnetization irms the number and maximum size of grains which remain in a metastable single domain sd state increases with increasing field this in turn gives rise to a field dependence of the total moment carried by such particles in the ensemble by observing the number of metastable sd grains and estimating their volume one can construct a trm induction curve this curve approximates the known trm induction curve for fine particles demonstrating that the magnitude of trm in fine particles of titanomagnetites is controlled by nucleation this nucleation model also explains why weak field trm is more stable against alternating field af demagnetization than irms

thermoremanent magnetization of nonuniformly magnetized grains a simple and elegant interpretation of thermoremanent magnetization trm in uniformly magnetized single domain sd grains was given by neel 50 years ago but the trm acquisition processes in larger nonuniformly magnetized grains are more varied and difficult to describe theoretically sd trm is a frozen high temperature partition between two microstates spins parallel or antiparallel to an applied magnetic field nonuniformly magnetized grains have a much greater choice of microstates local energy minimum or lem states and partitioning among various lem states continues to change during cooling these changes may involve barkhausen jumps of domain walls between positions of minimum local energy or nucleation of new domains and walls because of the lower remanence capacity of nonuniform microstates compared to the uniform sd state trm intensity decreases as grain size increases although certain microstates e g single vortex states seem to contribute little to trm thermal demagnetization of trm begins just above room temperature and continues to the curie point quite unlike the sharp unblocking of sd trm this continuous demagnetization resulting from changes in microstates driven by the changing internal demagnetizing field during heating profoundly affects the separation of different components of natural remanent magnetization and the determination of paleomagnetic field intensity

relating lithofacies to hydrofacies outcrop based hydrogeological characterisation of quaternary gravel deposits abstract a considerable part of today s drinking water supplies in europe and north america rely on clean groundwater from gravelly valley aquifers of quaternary age the sedimentary architecture the distribution of lithofacies and of architectural elements in such heterogeneous deposits are of fundamental importance for the analysis of groundwater flow and contaminant transport as the aquifers are not directly accessible for observation representative outcrop analogues were used to study the sedimentology on a local scale conventional sedimentological classification schemes were adapted for the purpose of hydrogeological evaluations measurements of hydraulic properties were then used to define a set of 5 hydrofacies from 23 possible sediment lithofacies a digital photographic mapping procedure was developed to allow fast data acquisition in the field the sedimentologically interpreted outcrops were stored in a gis style database and thus allow the output for further sedimentological or hydrogeological analysis