theoretical models of magnetic anisotropy to strain relationship revisited abstract mathematical modelling of the relationships between the low field magnetic anisotropy and strain are redeveloped and the calculated data are compared with the degree of anisotropy for various rock types it is found that the degree of anisotropy for realistic strain magnitudes is unrealistically high in the passive model the ductile model for which the degree of anisotropy depends on the magnetic grain the matrix viscosity ratio becomes realistic at high viscosity contrasts in the line plane model the theoretical degree of anisotropy corresponds well to the natural degree of anisotropy for rocks in which the carrier of magnetic anisotropy is either magnetite or phyllosilicate minerals by contrast in the case of haematite and pyrrhotite the modelled degree of anisotropy is much higher than the natural values in the viscous model the calculated degree of anisotropy corresponds well to that measured in sedimentary and volcanic rocks in the models imposing pure shear strain the natural logarithm of the degree of anisotropy to natural strain relationship can be approximately represented by a straight line at least for low to intermediate strains the proportionality constant varies according to the specific model and the specific carrier of the anisotropy of magnetic susceptibility

flow directions in dikes from anisotropy of magnetic susceptibility data the bootstrap way one of the first applications of anisotropy of magnetic susceptibility ams was an attempt to determine flow directions from mafic dikes khan 1962 since the seminal work of knight and walker 1988 defining the expected behavior of ams in response to magma flow there has been increasing interest in using ams for this purpose here we present a quantitative method for interpretation of ams data from dikes using a parametric bootstrap first dikes must be sampled with at least five and preferrably more samples from within 10 cm of the dike margin the distributions of the eigenvalues and eigenvectors of the ams tensor are delineated by calculating eigenparameters of many bootstrapped paradata sets we generate paradata sets by first selecting a sample at random then calculating a replacement set of data by drawing tensor elements from normal distributions with the mean and standard deviation of the entire site the bounds containing 95 of the eigenparameters of the bootstrapped data serve as confidence limits for the parameter of interest classification of dikes proceeds as follows sites whose maximum and intermediate eigenvalues could not be distinguished are deemed uninterpretable in addition sites with principal eigenvectors with angles 45 away from the dike margin inverse or with markedly different directions on either side of the dike scissored are excluded the remaining dikes are classified as having unique flow direction information if the principal eigenvectors from at least one side are distinct from the dike plane based on the distribution of the bootstrapped principal eigenvectors if neither side has principal eigenvectors distinct from the dike plane the dikes are classified as having lineation information only a study comprising 251 dikes from the troodos ophiolite has 151 sites with directional data 38 sites with lineations only 7 inverse sites 5 scissored sites and 55 sites not fitting into any other category the flow directions interpreted from the data were generally southerly toward a fossil transform zone

conceptual models of the evolution of transgressive dune field systems abstract this paper examines the evolutionary paths of some transgressive dune fields that have formed on different coasts of the world and presents some initial conceptual models of system dynamics for transgressive dune sheets and dune fields various evolutionary pathways are conceptualized based on a visual examination of dune fields from around the world on coasts with high sediment supply dune sheets and dune fields tend to accumulate as large scale barrier systems with little colonization of vegetation in arid hyper to arid climate regimes and as multiple active discrete phases of dune field and deflation plain couplets in temperate to tropical environments active dune fields tend to be singular entities on coasts with low to moderate sediment supply landscape complexity and vegetation richness and diversity increases as dune fields evolve from simple active sheets and dunes to single and multiple deflation plains and basins precipitation ridges nebkha fields and a host of other dune types associated with vegetation e g trailing ridges slacks remnant knobs gegenwalle ridges and dune track ridges tree islands and bush pockets three principal scenarios of transgressive dune sheet and dune field development are discussed including dune sheets or dune fields evolving directly from the backshore development following foredune and or dune field erosion and development from the breakdown or merging of parabolic dunes various stages of evolution are outlined for each scenario knowledge of evolutionary patterns and stages in coastal dune fields is very limited and caution is urged in attempts to reverse change and or modify dune fields to restore some perceived loss of ecosystem or dune functioning

magnetic susceptibility anisotropy strain and progressive deformation in permian sediments from the maritime alps france abstract the relationships among magnetic susceptibility anisotropy finite strain and progressive deformation have been studied in permian red shales and slates of the maritime alps southeastern france these rocks contain deformed reduction spots which serve as finite strain indicators the magnetic fabric of undeformed regions is modified during deformation to yield characteristic magnetic susceptibility anisotropy patterns and a magnetic equivalent of the deformation path derived from strain measurements the magnetic fabric changes progressively from oblate to prolate and back to oblate as deformation increases the quantitative relationships between natural strain and magnetic anisotropy in these rocks have been determined they differ between the less and more deformed areas perhaps due to a change in deformation mechanism accompanying an increase in metamorphism the relationships provide a rapid means of strain determination using magnetic measurements but their variation emphasizes the need for local structural control

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

recent stabilization of active sand dunes on the canadian prairies and relation to recent climate variations the historical activity of sand dunes on the southern canadian prairies was investigated in order to determine the relation with recent climate variations changes in dune activity were determined from historical aerial photographs at seven sites with active parabolic dunes in saskatchewan and manitoba the methodology developed combines digital image processing and geographical information system gis analysis to measure changes in dune activity from the aerial photographs as well as correlation analysis to determine the relation between dune activity and climate variations overall dune activity has been decreasing since the early to mid 1900s as evidenced by greater vegetation colonization than sand dune migration or reactivation the decrease in dune activity is significantly correlated with decadal scale variations in aridity and is coincident with a decrease in annual wind speed evidence suggests that this response is superimposed on a longer trend towards stabilization possibly in place since the late 1700s taken together the effect of this complex response is that dune recovery on the southern canadian prairies is prolonged well after an initial disturbance and therefore gives the impression of anomalous levels of activity for extended periods thereafter for this reason dune mobility indices predicated on short term climate variations years to decades do not fully describe the present level of dune activity on the southern canadian prairies

biogeomorphic model of dunefield activation and stabilization on the northern great plains abstract a conceptual model is proposed for the activity of sand dune systems on the northern great plains that incorporates vegetation growth theory and geomorphic system theory dunefield activity is modeled as a cyclic phenomenon alternating between active and stable states with the latter as the system state attractor the model is divided into two constituent parts an activation model and a stabilization model the activation model is qualitative and describes the transition from stable to active dunes as the result of a climatic perturbation such as drought that decreases vegetation cover the intensity and duration of the climatic perturbation determines the rate of decline of vegetation cover the stabilization model is quantitative and describes the transition from active to stable dunes using a logistic model of vegetation growth small perturbations during stabilization can prolong the duration of recovery enabling dunes to remain active well after the initial perturbation despite the geographic focus of this study the model appears applicable to a variety of environments where dune activity is limited in part by vegetation cover

modelling vegetated dune landscapes this letter presents a self organising cellular automaton model capable of simulating the evolution of vegetated dunes with multiple types of plant response in the environment it can successfully replicate hairpin or long walled parabolic dunes with trailing ridges as well as nebkha dunes with distinctive deposition tails quantification of simulated landscapes with eco geomorphic state variables and subsequent cluster analysis and pca yields a phase diagram of different types of coastal dunes developing from blow outs as a function of vegetation vitality this diagram indicates the potential sensitivity of dormant dune fields to reactivation under declining vegetation vitality e g due to climatic changes nebkha simulations with different grid resolutions demonstrate that the interaction between the abiotic geomorphic processes and the biological vegetation component life introduces a characteristic length scale on the resultant landforms that breaks the typical self similar scaling of un vegetated bare sand dunes

using morphospaces to understand tafoni development tafoni research has tended to focus on issues around definition and differences rather than trying to develop general concepts for understanding the nature of tafoni this paper uses the concepts of fitness landscapes and morphospaces to develop a standardized and dimensionless phase space within which to represent visualize and analyse a dataset of 800 tafoni collected from antarctica within this phase space it is possible to identify clustering of tafoni forms and to illustrate how tafoni development is constrained by a relational hierarchy of rock structure processes and geometry or form

a process based hypothesis for the barchan parabolic transformation and implications for dune activity modelling the introduction of vegetation to bare barchan dunes can result in a morphological transformation to vegetated parabolic dunes models can mimic this planform inversion but little is known about the specific processes and mechanisms responsible here we outline a minimalist quantitative and process based hypothesis to explain the barchan parabolic transformation the process is described in terms of variations in the stabilization of wind parallel cross sectional dune slices we hypothesize that stabilization of individual dune slices is the predictable result of feedbacks initiated from colonization of vegetation on the slipface which can only occur when slipface deposition rates are less than the deposition tolerance of vegetation under a constant vegetation growth regime the transformation of a barchan dune into a parabolic dune is a geometric response to spanwise gradients in deposition rates initial vegetation colonization of barchan horns causes shear between the anchored sides and the advancing centre of the dune which rotates the planform brinkline angle from concave to convex downwind this reduces slipface deposition rate and allows vegetation to expand inward from the arms to the dune centre the planform inversion of bare barchans dunes into vegetated parabolic dunes ultimately leads to complete stabilization our hypothesis raises several important questions for future study i are parabolic dunes transitional landforms between active and vegetation stabilized dune states ii should stabilization modelling of parabolic dune fields be treated differently than linear dunes and iii are stabilized parabolic dune fields armoured against re activation copyright 2012 john wiley sons ltd

regional kinematics inferred from magnetic subfabrics in archean rocks of northern ontario canada strain analysis observations of l s fabrics and studies of the anisotropy of magnetic susceptibility ams and of anisotropy of isothermal remanence airm reveal a sequence of progressive fabric development during regional deformation l s fabrics of quartz and feldspar grains are most transposed in regional transpression whereas the ams subfabrics controlled by the properties of late metamorphic silicates record a later orientation of the ambient stress field anisotropy of magnetic remanence is caused by the still younger minerals magnetite and pyrrhotite its anisotropy is less transposed than the ams subfabric consequently the relative orientations of the three types of fabric yield a kinematic sequence of subfabrics developed during transpression the l s fabrics are most transposed the ams less transposed and the airm fabrics least transposed toward the plane of regional flattening the results indicate that the deformation recorded by the three subfabrics was non coaxial in the most general sense with all three principal directions spinning with respect to the rocks during progressive straining

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

deconstructing a polygenetic landscape using lidar and multi resolution analysis abstract it is difficult to deconstruct a complex polygenetic landscape into distinct process form regimes using digital elevation models dems and fundamental land surface parameters this study describes a multi resolution analysis approach for extracting geomorphological information from a lidar derived dem over a stabilized aeolian landscape in south texas that exhibits distinct process form regimes associated with different stages in landscape evolution multi resolution analysis was used to generate average altitudes using a gaussian filter with a maximum radius of 1 km at 20 m intervals resulting in 50 generated dems this multi resolution dataset was analyzed using principal components analysis pca to identify the dominant variance structure in the dataset the first 4 principal components pc account for 99 9 of the variation and classification of the variance structure reveals distinct multi scale topographic variation associated with different process form regimes and evolutionary stages our results suggest that this approach can be used to generate quantitatively rigorous morphometric maps to guide field based sedimentological and geophysical investigations which tend to use purposive sampling techniques resulting in bias and error

predictability of dune activity in real dune fields under unidirectional wind regimes we present an analysis of 10 dune fields to test a model derived hypothesis of dune field activity the hypothesis suggests that a quantifiable threshold exists for stabilization in unidirectional wind regimes active dunes have slipface deposition rates that exceed the vegetation deposition tolerance and stabilizing dunes have the opposite we quantified aeolian sand flux slipface geometry and vegetation deposition tolerance to directly test the hypothesis at four dune fields bigstick white sands stable white sands active and cape cod we indirectly tested the hypothesis at six additional dune fields with limited vegetation data hanford ano nuevo skagen odde salton sea oceano stable and oceano active inverse calculation sites we used digital topographic data and estimates of aeolian sand flux to approximate the slipface deposition rates prior to stabilization results revealed a distinct quantifiable and consistent pattern despite diverse environmental conditions the modal peak of prestabilization slipface deposition rates was 80 of the vegetation deposition tolerance at stabilized or stabilizing dune fields results from inverse calculation sites indicate deposition rates at stabilized sites were near a hypothesized maximum vegetation deposition tolerance 1 m a 1 and active sites had slipface deposition rates much higher overall these results confirm the hypothesis and provide evidence of a globally applicable simple and previously unidentified predictor for the dynamics of vegetation cover in dune fields under unidirectional wind regimes

environmental controls morphodynamic processes and ecogeomorphic interactions of barchan to parabolic dune transformations the transformation of barchans into parabolic dunes has been observed in various dune systems around the world precise details of how environmental controls influence the dune transformation and stabilisation mechanism however remain poorly understood a horns anchoring mechanism and a nebkhas initiation mechanism have previously been proposed and selected environmental controls on the transformation have been explored by some modelling efforts but the morphodynamic processes and eco geomorphic interactions involved are unclear and comparison between different dune systems is challenging this study extends a cellular automaton model informed by empirical data from fieldwork and remote sensing to fully explore how vegetation characteristics boundary conditions and wind regime influence the transformation process and the resulting dune morphologies a dynamic growth function is introduced for clump like perennials to differentiate between growing and non growing seasons and to simulate the development of young plants into mature plants over multiple years modelling results show that environmental parameters interact with each other in a complex manner to impact the transformation process the study finds a fundamental power law relation between a non dimensional parameter group so called the dune stabilising index s and the normalised migration distance of the transforming dune which can be used to reconstruct paleo environmental conditions and monitor the impacts of changes in climate or land use on a dune system four basic eco geomorphic interaction zones are identified which bear different functionality in the barchan to parabolic dune transformation the roles of different environmental controls in changing the eco geomorphic interaction zones transforming processes and resulting dune morphologies are also clarified

formation of parabolic dunes from barchan and transverse dunes along israel s mediterranean coast the mediterranean coastal dunes of israel underwent a land use change during the second half of the 20th century due to intense agricultural and pastoral activity the coastal dunes were stripped of natural vegetation until the end of the first half of the 20th century the barchan and transverse dunes were shaped by strong southwesterly winter winds a decrease in human activity during the second half of the 20th century brought about a renewal of natural vegetation on the dune crest the only area with neither erosion nor deposition the establishment of vegetation on the crest changes the dynamics of these barchan and transverse dunes so that not all of the sand eroded from the windward side is carried to the lee slip face some is trapped by plants consequently there is a change in the shape of the windward slope from convex to concave and the dune gradually becomes parabolic in this study we trace the morphodynamics of the dunes by analysing 12 sets of aerial photographs which were taken from 1944 to 1995 the average rate of advance of 15 dunes has decreased from 3 4 m a 1 to 1 9 m a 1 while the vegetation cover has increased from 4 3 to 17 per cent during this period copyright 2002 john wiley sons ltd

parabolic dune development modes according to shape at the southern fringes of the hobq desert inner mongolia china since the 1970s parabolic dunes at the southern fringe of the hobq desert inner mongolia china have exhibited many different shapes v shaped u shaped and palmate each with a unique mode of development in the study area parabolic dunes are mainly distributed in regions a b and c with an intermittent river running from the south to the north we used high resolution remote sensing images from 1970 to 2014 and rtk gps measurements to study the development modes of different dune shapes the modes are characterized by the relationship between the intermittent river and dunes formation of the incipient dune patterns the predominant source supply of dunes and the primary formation of different shapes v shaped u shaped and palmate most parabolic dunes in region a are v shaped and closer to the bank of the river the original barchans in this region exhibit disconnected arms behavior with the sand blown out of the riverbed through gullies the nebkhas on the disconnected arms acquire the external sand source through the fertile island effect thereby developing into triangular sand patches and further developing into v shaped parabolic dunes most parabolic dunes in regions b and c are palmate the residual dunes cut by the re channelization of river from transverse dune fields on the west bank are the main sand source of region b the parabolic dunes in region c are the original barchans having then been transformed the stoss slopes of v shaped parabolic dunes along the riverbank are gradual and the dunes are flat in shape the dune crest of v shaped parabolic dune is the deposition area which forms the arc shaped sand ridge their two arms are non parallel the lateral airflow of the arms jointly transport sand to the middle part of dunes resulting in a narrower triangle that gradually becomes v shaped palmate parabolic dunes have a steeper stoss slope and height the dune crest of the palmate parabolic dune is the erosion area which forms a long and narrow trough between nebkhas by the funnelling effect this process forces sand towards lee slopes which transform from concave original barchans into convex ultimately resulting in the formation of palmate parabolic dunes

grain size characteristics of surface sediments of nebkhas at the southern margin of the mu us dune field china abstract the grain size characteristics of nebkhas are considered to differ from those of mobile dunes in relation to differences in vegetation influences however minimal research has been conducted in this respect therefore this study investigates the grain size characteristics of surface sediments of a nebkha field with 50 80 vegetation cover at the southern margin of the mu us dune field the grain size composition and parameters were determined at different positions on nebkhas and in interdune areas the results indicate that the nebkha sediments were significantly finer than those of mobile dunes had weaker sorting and were more positively skewed and more leptokurtic in relation to the interception of fine particles by vegetation associated prevention of movement and pedogenesis we infer that the influence of pedogenesis resulted in minimal differences between grain size compositions and parameters in samples obtained from different positions on nebkhas between nebkhas and in interdune areas the creep populations of interdune sediments can be transported to the windward toe but further transportation along the windward slope of a nebkha to the crest or leeward slope is limited because of vegetation interception

late quaternary glaciation in the tropics future research directions abstract glacier snowline depressions in the tropics of 800 1000 m indicate an atmospheric cooling of 5 7 c during the late pleistocene such a temperature depression and the presence of large glaciers in the tropics in the past suggests that on glacial interglacial time scales the tropics have undergone substantial climatic and hydrologic change however uncertainties in the chronology of glaciation the response of glacial mass balance in the tropics to a variety of climate forcings and the relation of proxy records in alpine regions to synoptic tropical paleoclimate limit the full utility of the snowline proxy future research in these three areas will provide information on the phasing of climate change in the tropics in comparison to higher latitude regions and the correspondence of tropical glaciation to large scale changes in precipitation temperature and solar radiation

aeolian dune field geomorphology modulates the stabilization rate imposed by climate 1 the activity of inland aeolian dune fields is typically related to the external forcing imposed by climate active bare dunes are associated with windy and or arid settings and inactive vegetated dunes are associated with humid and or calm environments when a climate shifts the dune field reacts however the behavior rate and potential impact of diverse dune geomorphologies on these transitions are poorly understood here we use a numerical model to systematically investigate the influence of dune field geomorphology dune height organization and collisions on the time a dune field takes to stabilize to generate diverse initial un vegetated dune field geomorphologies under unidirectional winds we varied pre stabilization growth time and initial sediment thickness termed equivalent sediment thickness est following dune field development from a flat bed we introduced vegetation simulating a climate shift and transport vegetation feedbacks slowly stabilized the dune fields qualitatively very young and immature dune fields stabilized quickly whereas older dune fields took longer dune fields with greater est stabilized quicker than those with less est larger dunes stabilized quicker because of low celerity which facilitated higher vegetation growth rates extended stabilization times were associated with the extension of parabolic dunes dune dune collisions resulted in premature stabilization the frequency of collisions was related to dune spacing quantitatively comparing the distribution of deposition rates in a dune field to the deposition tolerance of vegetation provides a promising predictor of relative stabilization time dune fields with deposition rates dominantly above the deposition tolerance of vegetation advanced unimpeded and prolonged stabilization as parabolic dunes paleoenvironmental reconstructions or predictions of dune field activity should not assume that dune activity directly translates to climate considerable lags to stabilizing climate shifts may exist in unidirectional dune forms

correlation of strain and the anisotropy of magnetic susceptibility in the onaping formation evidence for a near circular origin of the sudbury basin abstract measurements of finite strain the anisotropy of magnetic susceptibility the magnetic carrier of the susceptibility and fieldwork have been carried out in the onaping formation of the sudbury basin ontario the magnetic fabric indicates that changes in the magnitude and type of magnetic susceptibility ellipsoids closely mirror the changing pattern of deformation from northwest to southeast across the onaping formation outcrops a quantitative correlation has been established between finite strain measurements and the magnetic susceptibility results and this allows the number of available strain measurements to be extended by more than 500 samples the finite strain results suggest a deformation path in which the onaping formation was first affected by nw se directed horizontal layer parallel shortening which produced an upright tectonic cleavage subsequently components of overthrust nw directed simple shear were superimposed upon the already deformed rocks of the onaping formation the result of removing the strain according to the sequence of superimposed deformations revealed by the deformation path suggests that the sudbury basin was nearly circular in shape prior to its deformation consequently a major objection to the meteorite impact theory for origin of the sudbury structure is eliminated

foredunes and blowouts initiation geomorphology and dynamics this paper reviews the initiation dynamics geomorphology and evolution of incipient foredunes established foredunes and blowouts incipient foredunes may be initiated in a variety of ways leading to the formation of ramps terraces or ridges depending on progradation rates vegetation type and cover sediment transport rates and scale of erosional processes vegetation cover morphology growth rates and types combine with aerodynamic processes to determine dune and swale morphology established foredunes are classified into five morpho ecological types and the flow behaviour over two types is detailed a new model of foredune evolutionary paths at various possible time scales is presented blowout initiation dynamics and sediment transport and evolution is examined throughout the review the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided

evolution of a dune from crescentic to parabolic form in response to short term climatic changes rabjerg mile skagen odde denmark abstract rabjerg mile a complex parabolic dune reaches a height of 20 m above the deflation plain the width of the dune is 900 m and the length of the whole dune is 1500 m the dune is covered by 0 5 1 5 m high transverse dune ridges the dune has migrated approximately 1 km since 1887 a d accompanied by a change in the migration direction from ese 100 to ene 68 the morphology of rabjerg mile through the last 100 years is illustrated by a geographical information system arc info applied to a series of high quality topographical maps based on the digitized contour lines the evolution of rabjerg mile can be followed from an initial crescentic form in 1887 a d to a complex parabolic dune in this century dune dynamics and sites of erosion and deposition are evaluated from the digital terrain models changes in vegetation cover documented from the maps and air photos indicate that vegetation in the study area steadily increased with time calculations of resultant drift directions and gross bedform normal transport are based on climatic data from the skagen changed from an almost perfect transverse bedform 1887 1924 to an oblique imperfectly transverse bedform 1966 to present the bedform alignment followed the gross bedform normal transport rule in most years the evolution of a parabolic dune after 1924 is related to a period of reduced wind energy and increased vegetation cover this parabolic dune was maintained after 1960 when wind energy increased and the wind regime was more complex at the same time the dune became markedly asymmetric because of the frequent occurrence of strong southerly and easterly winds

anisotropy of magnetic remanence a brief review of mineralogical sources physical origins and geological applications and comparison with susceptibility anisotropy the magnetic fabric of rocks and sediments is most commonly characterized in terms of the anisotropy of low field magnetic susceptibility ams however alternative methods based on remanent magnetization measured in the absence of a magnetic field rather than induced magnetization measured in the applied field have distinct advantages for certain geological applications this is particularly true for 1 adjunct studies in paleomagnetism in order to assess the fidelity with which a natural remanence records the paleofield orientation 2 studies of weakly magnetic or weakly deformed rocks for which susceptibility anisotropy is very difficult to measure precisely and 3 quantitative applications such as strain estimation the fundamental differences between susceptibility and remanence and their respective anisotropies are due to several factors 1 susceptibility arises from all of the minerals present in a sample whereas remanence is carried exclusively by a relatively small number of ferromagnetic minerals 2 ferromagnetic minerals are generally more anisotropic than para and diamagnetic minerals 3 for ferromagnetic minerals remanence is inevitably more anisotropic than susceptibility and 4 a number of common minerals including single domain magnetites possess an inverse anisotropy of susceptibility i e they tend to have minimum susceptibility parallel to the long axis of an individual particle remanence is immune to this phenomenon as a consequence of all these factors remanence anisotropy may generally provide a better quantitative estimate of the actual distribution of particle orientations in a rock sample

remote sensing and spatial analysis of aeolian sand dunes a review and outlook abstract for more than four decades remote sensing images have been used to document and understand the evolution of aeolian sand dunes early studies focused on mapping and classifying dunes recent advances in sensor technology and software have allowed investigators to move towards quantitative investigation of dune form evolution and pattern development these advances have taken place alongside progress in numerical models which are capable of simulating the multitude of dune patterns observed in nature the potential to integrate remote sensing rs spatial analysis sa and modeling to predict the future changes of real world dune systems is steadily becoming a reality here we present a comprehensive review of significant recent advances involving rs and sa our objective is to demonstrate the capacity of these technologies to provide new insight on three important research domains 1 dune activity 2 dune patterns and hierarchies and 3 extra terrestrial dunes we outline how several recent advances have capitalized on the improved spatial and spectral resolution of rs data the availability of topographic data and new sa methods and software we also discuss some of the key research challenges and opportunities in the application of rs and sa dune field including the integration of rs data with field based measurements of vegetation cover structure and aeolian transport rate in order to develop predictive models of dune field activity expanding the observational evidence of dune form evolution at temporal and spatial scales that can be used to validate and refine simulation models the development and application of objective and reproducible sa methods for characterizing dune field pattern and expanding efforts to quantify three dimensional topographic changes of dune fields in order to develop improved understanding of spatio temporal patterns of erosion and deposition overall our review indicates a progressive evolution in the way sand dunes are studied whereas traditional field studies of airflow and sand transport can clarify event based process form interactions investigators are realizing a synoptic perspective is required to address the response of dune systems to major forcings the integration and evolution of the technologies discussed in this review are likely to form a foundation for future advances in aeolian study

11 11 dune morphology and dynamics this chapter discusses the key types of sand dunes and how they can be classified and assesses the major controls on their development the processes of dune dynamics are reviewed leading to a discussion of the concept of equilibrium in solitary dune form recent advances in modeling are reviewed that show how interactions between dunes may result in equilibrium at the dune field scale rather than at the single dune scale

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

chaos fractals and self organization in coastal geomorphology simulating dune landscapes in vegetated environments complex nonlinear dynamic systems are ubiquitous in the landscapes and phenomena studied by earth sciences in general and by geomorphology in particular concepts of chaos fractals and self organization originating from research in nonlinear dynamics have proven to be powerful approaches to understanding and modeling the evolution and characteristics of a wide variety of landscapes and bedforms this paper presents a brief survey of the fundamental ideas and terminology underlying these types of investigations covering such concepts as strange attractors fractal dimensions and self organized criticality their application in many areas of geomorphological research is subsequently reviewed in river network modeling and in surface analysis amongst others followed by more detailed descriptions of the use of chaos theory fractals and self organization in coastal geomorphology in particular these include self organized behavior of beach morphology the fractal nature of ocean surface gravity waves the self organization of beach cusps and simulation models of ripples and dune patterns this paper further presents a substantial extension of existing dune landscape simulation models by incorporating vegetation in the algorithm enabling more realistic investigations into the self organization of coastal dune systems interactions between vegetation and the sand transport process in the model such as the modification of erosion and deposition rules and the growth response of vegetation to burial and erosion introduce additional nonlinear feedback mechanisms that affect the course of selforganization of the simulated landscape exploratory modeling efforts show tantalizing results of how vegetation dynamics have a decisive impact on the emerging morphology and conversely how the developing landscape affects vegetation patterns extended interpretation of the modeling results in terms of attractors is hampered however by want of suitable state variables for characterizing vegetated landscapes with respect to both morphology and vegetation patterns d 2002 elsevier science b v all rights reserved

ecogeomorphic state variables and phase space construction for quantifying the evolution of vegetated aeolian landscapes cellular automaton modelling for the simulation of dune field formation and evolution has developed progressively in aeolian geomorphology in the last decade or so a model that incorporates the effects of vegetation and its interactions with geomorphic landscape development the discrete ecogeomorphic aeolian landscapes decal model can replicate a number of important visual and qualitative aspects of the complex evolution of aeolian dune landscapes under the influence of vegetation dynamics in coastal environments a key challenge in this research area is the analysis and comparison of both simulated and real world vegetated dune landscapes using objective and quantifiable principles this study presents a methodological framework or protocol for numerically quantifying various ecogeomorphic attributes using a suite of mathematically defined landscape metrics to provide a rigorous and statistical evaluation of vegetated dune field evolution within this framework the model parameter space can be systematically explored and simulation outcomes can be methodically compared against real world landscapes based on a simplified scenario of parabolic dunes developing out of blow outs the resulting dune field realizations are investigated as a function of variable growth vigour of two simulated vegetation types pioneer grass and successional woody shrub by establishing a typological phase diagram of different landscape classes the set of simulation outcomes furthermore defines a higher dimensional phase space whose axes or dimensions can be interpreted by analysing how individual ecogeomorphic landscape metrics or state variables contribute to the data distribution principal component analysis can reduce this to a visual three dimensional 3d phase space where landscape evolution can be plotted as time trajectories and where we can investigate the effects of changing environmental conditions partway through a simulation scenario the use of landscape state variables and the construction of a 3d phase space presented here may provide a general template for quantifying many other eco geomorphic systems on the earth s surface

complex systems in aeolian geomorphology aeolian geomorphology provides a rich ground for investigating earth surface processes and landforms as complex systems sand transport by wind is a classic dissipative process withnon linear dynamics while dunefield evolution is a prototypical self organisation phenomenon bothofthesebroadareasofaeoliangeomorphologyarediscussedandanalysedinthecontextofcomplexityandasystems approach afeedbackloopanalysisoftheaeolianboundary layer flow sediment transport bedforminteractions basedoncontemporary physicalmodels revealsthatthesystemisfundamentallyunstable oratmostmeta stable andlikelytoexhibitchaoticbehaviour recent field experimental research on aeolian streamers and spatio temporal transport patterns however indicates that sand transport by wind may be wholly controlled by a self similar turbulence cascade in the boundary layer flow and that key aspects of transport event timeseriescanbefullyreproducedfromacombinationof self organised 1 fforcing motionthreshold andsaltationinertia theevolutionof various types of bare sand dunes and dune field patterns have been simulated successfully with self organising cellular automata that incorporateonlysimplifiedphysically basedinteractions rules becauseoftheirundefinedphysicalscale however itnotclearwhether they in fact simulate ripples bedforms or dunes landforms raising fundamental cross cutting questions regarding the difference between aeolian dunes impact ripples and subaqueous current ripples and dunes an extended cellular automaton ca model currently under development incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas blow outs and parabolic coastal dunes preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes progress is limited however by a serious lack of appropriate concepts for quantifying meaningful state variables at the landscape scale state variables currently used in the bare sand models are far from capturing the rich 3d topography and patterns and are not sufficiently discriminative to distinguish different attractors the vegetationcomponentintheextendedmodel andindeedecogeomorphicsystemsingeneral poseevengraverchallengestoestablishing

deconstructing aeolian landscapes abstract semi stabilized dune systems are important indicators of quaternary drought variability across central north america the south texas sand sheet stss is the southernmost relict dune system on the great plains and is exposed to higher evapotranspiration and moisture variability than similar landscapes farther north in this study a combination of surface and sub surface remote sensing is used to analyze the semi stabilized dune landscapes of the stss in order to delineate distinct aeolian sediments that can represent generations of sedimentation or particular climate conditions the combination of multi resolution analysis of a lidar dataset electromagnetic conductivity surveys and xrf scans of soil cores are shown to be useful tools for deconstructing and modeling the environmental history of the stss optically stimulated luminescence osl dating of identified surfaces suggests that the stss is older than previously thought since dune systems are excellent repositories of climate and biophysical data for a landscape and are also sensitive to changes in climate and ecology the methodology employed in this study can be used to characterize the vulnerability of other similar environments to climate change through the holocene and over the next century

the relationship of strain and preferred orientation of phyllosilicate grains in rocks a review abstract the calculation of strain from the preferred orientation of platy phyllosilicate grains taking strain to be homogeneous is surprisingly often successful from a pragmatic point of view although numerous theoretical objections to this procedure can be and have been raised for the calculation to succeed the original distribution of mica or clay mineral grains must be known or assumed the usual assumption that the starting distribution was random and therefore nearly uniform implies that the strain history of pelitic sediments is taken to start when the watery sediment was last stirred by waves or bioturbation or if it was laid down in still anoxic waters from the moment of first deposition it therefore includes compaction as part of the strain history which is usually neglected by structural geologists originally random distribution of clay flake orientations has been observed in recently deposited sediments in many instances and has been theoretically explained in various ways exceptions probably exist but their frequency has not been estimated biologically disturbed sediments may be brought nearer to a state of random orientation of clay flakes than they were at deposition with the exception of whole beds or concretions in which pores are early filled with cement mudrocks are almost always compacted by the weight of later deposits the strain so induced is axially symmetric about the vertical and thus about the pole of the bedding planes compaction acts on soft unconsolidated rocks but may continue with increasing overburden on rocks strengthened by cementation and by increasing interlocking of grains tectonic deformation may start early before the rock is fully compacted or it may begin only much later and the mechanisms of deformation increase in complexity with the increasing temperature and hydrostatic stress of deeper burial up to a certain level of mild metamorphism however phyllosilicate grains seem to be rather permanent if not as mineral species then at least by preservation of their constituent sheets of silica tetrahedra given this permanence the mechanisms of rock deformation whether intergranular slip cataclasis or dissolution and reprecipitation and various intragranular processes in the non phyllosilicate matrix hardly matter as far as the recording of strain is concerned even a certain amount of stress solution at especially heavily loaded points of the phyllosilicate grains themselves does not destroy their value as strain markers as long as the dissolved material is disposed of mainly by crystallographically continuous overgrowth on existing grains the same holds for local dissolution of phyllosilicates in portions of old grains that have become thermodynamically unstable by bending widespread irregular or random nucleation and growth of newly nucleated phyllosilicate grains at intermediate or high grades of metamorphism can reduce the reliability of the strain record and so can domainal structure of the deformed rock if both the volume fraction of phyllosilicate grains and the intensity of total strain differ sharply from one domain to another if distinct domains are not equant and have themselves a strong preferred orientation of shape nevertheless rocks containing an anastomosing network of zones rich in phyllosilicate grains as slates and other deformed mudrocks commonly do have in many cases been found to have average preferred orientations of mica or chlorite which if used to estimate the strain give results similar to those obtained from independent strain markers in the same rocks thus the most significant verification of the usefulness of strain estimates by measurement of preferred orientation is the mutual confirmation with independently determined strain the limit to such verification is the rarity of strain markers so that the coexistence of two independent ones is exceptionally rare for this reason however it is important to make full use of the orientation of phyllosilicate grains where they are available the alternative to have no strain measurements at all causes structural geologists to miss potential information

investigating parabolic and nebkha dune formation using a cellular automaton modelling approach vegetation plays an important role in shaping the morphology of aeolian dune landscapes in coastal and semi arid environments where ecogeomorphic interactions are complex and not well quantified we present a discrete ecogeomorphic aeolian landscape model decal capable of simulating realistic looking vegetated dune forms permitting exploration of relationships between ecological and morphological processes at different temporal and spatial scales the cellular automaton algorithm applies three simple rules that lead to self organization of complex dune environments including nebkhas with distinctive deposition tails that form in association with mesquite type shrubs and hairpin long walled parabolic dunes with trailing ridges that evolve from blowouts in association with vegetation succession changing the conditions of simulations produces differing landscapes that conform qualitatively to observations of real world dunes the model mimics the response of the morphology to changes in sediment supply vegetation distribution density and growth characteristics as well as initial disturbances the introduction of vegetation into the model links spatial and temporal scales previously dimensionless in bare sand cellular automata grid resolutions coarser than the representative size of the modelled vegetation elements yield similar morphologies but when cell size is reduced to much smaller dimensions the resultant landscape evolution is dramatically different the model furthermore demonstrates that the relative response characteristics of the multiple vegetation types and their mutual feedback with geomorphological processes impart a significant influence on landscape equilibria suggesting that vegetation induces a characteristic length scale in aeolian environments this simple vegetated dune model illustrates the power and versatility of a cellular automaton approach for exploring the effects of interactions between ecology and geomorphology in complex earth surface systems

anisotropy of diamagnetic susceptibility in thassos marble a comparison between measured and modeled data abstract a study of shear zones within the calcite marble complex of the island of thassos greece shows that the low field anisotropy of magnetic susceptibility ams technique can be successfully applied to diamagnetic rocks for characterizing rock fabrics the strain path involves both an early pure shear stage and a simple shear overprint that is documented by a transition from triaxial neutral to uniaxial prolate shapes of ams ellipsoids the maximum susceptibility is oriented perpendicular to the rock foliation reflecting the preferred orientation of calcite c axes in the protolith as well as in the mylonites for three samples that represent different types of calcite fabrics the ams was recalculated from neutron and electron backscatter diffraction textural data a comparison of the measured and modeled data shows a good coincidence for the orientation of the principal ams axes and for the recalculated anisotropy data both measured and modeled data sets reflect the change from neutral to distinct prolate ellipsoids during progressive deformation

finite strain patterns and their significance in permian rocks of the alpes maritimes france abstract more finite strain data has been obtained from autochthonous permian mudstones of the alpes maritimes s e france these new data were computed from field measurements of green spots on all available sections deformed mudcracks and from the quantitative correlation between magnetic susceptibility anisotropy and finite strain in these rocks previously published finite strain data and the new results are presented on a series of structural maps and cross sections for the dome de barrot the tinee and vionene region and the roya region as in previous studies difficulties arise in explaining the apparently variable extension parallel with the 100 subhorizontal bedding cleavage intersection either this is real or there were large volume changes during the tectonic deformation study of quartz fibres developed in deformed mudcracks in the tinee valley suggest that early in the tectonic history incremental stretching directions were parallel with the bedding cleavage intersection while later they were down dip in the 100 trending cleavage since these permian rocks have remained stuck to the argentera basement they also record displacements and deformations in the basement the early 100 subhorizontal stretching is consistent with nw se dextral strike slip basement faulting while later down dip stretching in the cleavage is consistent with contraction faults in the basement this information and new palaeomagnetic data on the same samples are combined with recent geophysical evidence and regional tectonic studies to provide a new precision to the tectonic history of this part of the western alpine external zone

late quaternary aeolian dunes on the presently humid blue mountains eastern australia abstract sand dunes on the newnes plateau 1000 m a s l west of sydney were active during the last glacial maximum the scattered sand dunes are forested under the modern humid temperate climate regime dune types range from parabolic to transverse lee dunes and sand sheets or patches all point to the presence of conditions marginal for aeolian activity made possible through wind acceleration on windward slopes ready sand supply from the weathered sandstone of the plateau and sparse vegetation cover modern climate envelopes of sand dune activity in australia predict that unrealistically drier conditions are necessary to allow wind transport at this site only additional impediments to plant growth such as lower temperature and lower atmospheric carbon dioxide concentrations appear to allow the necessary conditions for dune formation these observations and conclusions extend our understanding of the extremes of the lgm climate in humid eastern australia confirming that the widespread treeless vegetation was also sparse even in areas that today have annual rainfall above 1000 mm

interdependence of geomorphic and ecologic resilience properties in a geographic context abstract ecology and geomorphology recognize the dynamic aspects of resistance and resilience however formal resilience theory in ecology has tended to deemphasize the geomorphic habitat template conversely landscape sensitivity and state and transition models in geomorphology downweight mechanisms of biotic adaptation operative in fluctuating spatially explicit environments adding to the interdisciplinary challenge of understanding complex biogeomorphic systems is that environmental heterogeneity and overlapping gradients of disturbance complicate inference of the geographic patterns of resistance and resilience we develop a conceptual model for comparing the resilience properties among barrier dunes the model illustrates how adaptive cycles and panarchies the formal building blocks of resilience recognized in ecology can be expressed as a set of hierarchically nested geomorphic and ecological metrics the variance structure of these data is proposed as a means to delineate different kinds and levels of resilience specifically it is the dimensionality of these data and how geomorphic and ecological variables load on the first and succeeding axes that facilitates the delineation of resistance and resilience the construction of dune topographic state space from observations among different barrier islands is proposed as a way to measure the interdependence of geomorphic and ecological resilience properties

emplacement of the ardara pluton ireland new constraints from magnetic fabrics rock fabrics and age dating the ardara pluton as part of the donegal batholith was intruded into neoproterozoic metasediments and metadolerites at mid crustal levels the emplacement mechanism of the ardara granite is very controversial and mechanisms ranging from diapirism ballooning and stoping followed by nested diapirism have been proposed magnetic fabrics rock fabrics and k ar dating of micas are used here to constrain the emplacement history the compositional zoning of the ardara pluton is clearly reflected in the different bulk magnetic susceptibilities between the outer quartz monzodiorite and the central granodiorite whereas the intervening tonalite is of intermediate nature the magnetic carriers are characterized by the anisotropy of the magnetic susceptibility ams thermomagnetic measurements and through high field analyses hfa the separation of the ferrimagnetic and paramagnetic contributions revealed that biotite and magnetite control the ams in the quartz monzodiorite both minerals are oriented in such a way that their summed contribution is constructive and originates from the shape fabric of magnetite and the texture of biotite biotite is responsible mainly for the ams in the tonalite and granodiorite the magnetic foliation can be directly related to the macroscopic foliation and also to the d4 structures in the country rocks the foliation is consistent with the geometry of the roughly circular shape and has a mostly steep to vertical dip towards the central granodiorite the magnetic foliation dies out although plagioclase texture measurements indicate a weak magmatic shape fabric with the exception of the tail the kmax axes magnetic lineation vary from steeply to gently plunging the so called lineation factor is approximately 1 01 and therefore points to a less significant axial symmetry these observations coincide with strain estimates on mafic enclaves that show a very consistent pattern of k 0 flattening strain texture analyses of biotite and quartz additionally support the observations made by the strain analyses and the magnetic fabric data microstructural investigations give evidence that the fabrics are associated with the emplacement over a range of temperatures from truly magmatic to high temperature solid state conditions the age of the intrusion is still under discussion but a new cooling age was determined by k ar dating of biotite at 403 7 8 ma corresponding to a temperature range between 450 and 300 c for a mylonite along the southern contact between the ardara pluton and the country rock a k ar muscovite age of 378 8 7 ma indicates a minimum age for the shear zone when the ardara pluton must have already been cooled down below 350 50 c

magnetic anisotropy rock fabrics and finite strain in deformed sediments of sw sardinia italy abstract although some empirical relationships have been established between the anisotropy of magnetic susceptibility ams and the state of finite strain in studies from specific geologic areas the mechanisms governing correlations are not well understood a comparative study has been made in order to elucidate the ams strain relationship by investigating mineral preferred orientations and the responsible microstructural deformation processes detailed analyses are presented from low grade metamorphic slates of a palaeozoic sequence exposed in the variscan of sw sardinia rock magnetic experiments suggest that paramagnetic minerals dominate the ams in these rocks excellent agreement was found between magnetic fabrics and lattice preferred orientations 001 of mica and chlorite determined from x ray texture goniometry measurements depending on the oblate or prolate ellipsoidal shape of anisotropy the minimum principal axes of ams and x ray textures can coincide with the poles to slaty cleavage or the maximum principal axes can coincide with the bedding cleavage intersection respectively the measured ams and x ray textures only partially reflect the finite strain determined from deformed micro pebbles and reduction spots axial orientations of magnetic fabrics mica and chlorite preferred orientations and finite strain ellipsoids are generally in good agreement depending on development of oblate or prolate fabric ellipsoidal shapes linear correlations can be established for magnitudes of minimum and intermediate axes of the ams and finite strain ellipsoids but shape comparisons are complex microstructural studies by scanning electron microscopy sem indicate that the preferred orientation of the phyllosilicates is caused by different grain scale deformation mechanisms such as kinking micro folding and preferential growth thus magnetic fabrics and mineral preferred orientations evidently result from different deformation mechanisms than the finite strain they reflect the heterogeneous deformation due to micro mechanical reorientation processes of mineral grains while finite strain reflects the homogeneous deformation accommodated cumulatively by the strain markers

the correlation of magnetic anisotropy with strain in the chelmsford formation of the sudbury basin ontario abstract a quantitative correlation has been established between finite strain and the anisotropy of magnetic susceptibility ams in sandstones of the precambrian chelmsford formation of the sudbury basin ontario investigations of the progressive acquisition of isothermal remanent magnetization and its destruction with reverse field and thermal demagnetization as well as microscopic examination of polished thin sections show that both pyrrhotite and magnetite are present in the sandstone measurements of the ams have been carried out at 16 sites distributed throughout the chelmsford formation outcrop considerable variation in the shapes of the magnetic susceptibility ellipsoids axes k max k int k min exists within each site with the k max and k int axes contained in the cleavage planes where developed the magnitudes of the magnetic susceptibility axes have been quantitatively correlated with strain measurements carried out by clendenen et al this issue two different strain to magnetics correlations have been carried out between the site mean strain determined using deformed concretions and the mean values of the ams at each site and between individual specimen strain values determined at the microscopic scale and the individual specimen ams in both cases separate correlations were made between strain long intermediate and short axes and their corresponding magnetic k max k int and k min axes at 10 sites the site mean strain values were derived from strain analysis of the concretions and at an additional 6 sites the site mean strain values were derived from the ams to strain correlation 527 individual cores were converted to equivalent strain values using the ams structural correlation of individual specimens this study extends the use of ams methods to include strain determination in sandstones and provides an order of magnitude increase in the available number of such data for further structural analysis

automated classification of landform elements using object based image analysis this paper presents an automated classification system of landform elements based on object oriented image analysis first several data layers are produced from digital terrain models dtm elevation profile curvature plan curvature and slope gradient second relatively homogenous objects are delineated at several levels through image segmentation these object primatives are classified as landform elements using a relative classification model built both on the surface shape and on the altitudinal position of objects so far slope aspect was not used in classification the classification has nine classes peaks and toe slopes defined by the altitudinal position or the degree of dominance steep slopes and flat gentle slopes defined by slope gradients shoulders and negative contacts defined by profile curvatures head slopes side slopes and nose slopes defined by plan curvatures classes are defined using flexible fuzzy membership functions results are visually analyzed by draping them over dtms specific fuzzy classification options were used to obtain an assessment of output accuracy two implementations of the methodology are compared using 1 romanian datasets and 2 berchtesgaden national park germany the methodology has proven to be reproducible readily adaptable for diverse landscapes and datasets and useful in respect to providing additional information for geomorphological and landscape studies a major advantage of this new methodology is its transferability given that it uses only relative values and relative positions to neighboring objects the methodology introduced in this paper can be used for almost any application where relationships between topographic features and other components of landscapes are to be assessed

inverse magnetic fabric in deformed limestones of the morcles nappe switzerland anisotropy of magnetic susceptibility ams was measured at 15 sites in deformed helvetic limestones of the morcles nappe in western switzerland inverse magnetic fabrics characterized by axes of maximum susceptibility subperpendicular to bedding or cleavage were observed at four sites in the root zone of the nappe acquisition and thermal demagnetization of isothermal remanent magnetization show that the ferromagnetic mineralogy is dominated by pyrrhotite with various proportions of magnetite hematite and goethite the matrix minerals were studied in thin section with a staining technique to distinguish different carbonates by x ray texture goniometry and by microprobe analysis observations of ams at room and liquid nitrogen temperatures and of the temperature dependence of bulk susceptibility lead to the conclusion that the inverse fabrics result from a paramagnetic component due to fe2 ions in the calcite matrix

the origin of tectonic fabrics in undeformed clays the early stages of deformation in extensional sedimentary basins 1 an integrated approach was used to detect tectonic effects in apparently undeformed fine grained clay sediments filling extensional basins in southern italy results from low and high field anisotropy of magnetic susceptibility and mineral fabric deduced by neutron texture analysis show penetrative deformation on a grain scale the well defined tectonic magnetic lineation is parallel to the stretching direction and located at the intersection of the basal planes of phyllosilicates forming grain scale folds and crenulations this spatial configuration reflects basin scale deformation processes and suggests the existence of a nearly uniaxial stress field during the incipient extensional phases the integrated approach of magnetic and mineral fabric investigations is a valid tool to detect grain scale and regional deformation pattern in weakly deformed extensional basins where macroscopic evidence of deformation is not visible

mathematical simulations of anisotropy of magnetic susceptibility on composite fabrics 1 the anisotropy of magnetic susceptibility ams is an integral measure of the preferred orientation of all minerals present in a rock when the ams is carried by paramagnetic minerals alone the principal directions of the susceptibility ellipsoid should reflect the crystallographic orientation of the minerals the relationship between the ams and deformation depends on several factors which control the development of lattice preferred orientation lpo in a rock a mathematical model is presented that simulates the magnetic susceptibility ellipsoid for samples composed of more than one mineral phase measurements of the ams are compared with fabric based anisotropy models for black slates from the navia alto sil slate belt in northern spain the ams is carried by paramagnetic minerals as has been confirmed by high field torque magnetometry low temperature ams and magnetization curves the lpo of mica and chlorite has been determined by x ray texture goniometry pole figures and orientation ellipsoids show the changes in the degree of alignment of the phyllosilicates the models have been tested in samples displaying three types of pole figures a high intensity point maximum a medium intensity elliptical maximum and a girdle shaped distribution at one site displaying kink bands the lpo shows variations between these types at the outcrop scale the case studies illustrate the success in modeling different lpo types

conversion of the magnetic susceptibility tensor into the orientation tensor in some rocks abstract the preferred orientation of minerals in a rock with a structural or sedimentary fabric can be referred to by the orientation tensor this paper describes the determination of the orientation tensor of the crystallographic c axes from the rock magnetic anisotropy and the mineral anisotropy degree in rocks in which the magnetic anisotropy is dominantly carried by one mineral with uniaxial magnetic anisotropy e g phyllosilicates pyrrhotite hematite the orientation tensor of biotite c axes in four samples of the bites orthogneiss determined in this way is similar to that determined independently through the universal stage measurement of biotite leaves in thin sections and is obtained much more rapidly by the magnetic method

formation of linear and parabolic dunes on the eastern snake river plain idaho in the nineteenth century abstract geomorphic and stratigraphic evidence show periods of distinct hydrologic excess and deficit sometime in the past 500 years on the eastern snake river plain natural exposures at the current shore of mud lake contain a lacustrine silty sand beneath eolian sands the latter deposit is expressed at the surface as hairpin parabolic and linear dunes these dunes can be traced into and across lakes a clear sign of recent aridity two shallow water gastropods and two wood fragments from the lacustrine silty sand yield the respective ams 14 c ages of ca 705 and 988 year bp and 195 and 305 year bp the offset in ages indicates a lake hard water effect of aquatic gastropods with the wood ages providing the closest age constraint optically stimulated luminescence single aliquot regeneration ages of 150 30 and 120 20 year bp on quartz grains from the overlying eolian sands further constrains a drop in lake level and subsequent aridity to the 19th century this lacustrine dune sequence is probably the geomorphic expression of a distinct wet period followed by a severe drought between ad 1845 and 1856 which has been documented in the dendroclimatic records for the rocky mountains and the western great plains lake fluctuations and dune formation is associated with greater subdecadal variability in spring precipitation than recorded in the past 100 years

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

event scale dynamics of a parabolic dune and its relevance for mesoscale evolution parabolic dunes are widespread aeolian landforms found in a variety of environments despite modeling advances and good understanding of how they evolve there is limited empirical data on their dynamics at short time scales of hours and on how these dynamics relate to their medium term evolution this study presents the most comprehensive data set to date on aeolian processes airflow and sediment transport inside a parabolic dune at an event scale this is coupled with information on elevation changes inside the landform to understand its morphological response to a single wind event results are contextualized against the medium term years allowing us to investigate one of the most persistent conundrums in geomorphology that of the significance of short term findings for landform evolution our field data suggested three key findings 1 sediment transport rates inside parabolic dunes correlate well with wind speeds rather than turbulence 2 up to several tonnes of sand can move through these landforms in a few hours and 3 short term elevation changes inside parabolic dunes can be complex and different from long term net spatial patterns including simultaneous erosion and accumulation along the same wall modeled airflow patterns along the basin were similar to those measured in situ for a range of common wind directions demonstrating the potential for strong transport during multiple events mesoscale analyses suggested that the measured event was representative of the type of events potentially driving significant geomorphic changes over years with supply limiting conditions playing an important role in resultant flux amounts

thermal alteration of the magnetic mineralogy in ferruginous rocks the northampton ironstone contains the paramagnetic minerals siderite and berthierine and a trace of the ferrimagnetic mineral magnetite the magnetic fabric of this sedimentary rock as defined by the anisotropy of magnetic susceptibility is controlled by bedding compaction but is inverse i e the maximum susceptibility axes are normal to the bedding plane this inverse fabric is attributed to the dominating presence of siderite the rocks were incrementally heated to 600 c and the magnetic fabric was measured at room temperature and at near liquid nitrogen temperature after each heating step cooling the samples in liquid nitrogen enhances the paramagnetic contribution to the magnetic fabric after heating the samples above 250 c the room temperature magnetic fabric became normal with the minimum susceptibility axes perpendicular to the bedding plane the low temperature magnetic fabric remains inverse until the samples are heated to about 500 c after heating to higher temperatures a normal fabric was observed at both room temperature and low temperature rock magnetic evidence shows that magnetite is created during the heating the start of mineralogical changes in the rock was detected by electron spin resonance spectroscopy powder x ray diffraction and acquisition of isothermal remanence berthierine starts to break down at approximately 250 c and is totally oxidized by 500 c the creation of magnetite in the heating experiments corresponds with this mineralogical change the change in the room temperature magnetic fabric is associated with the decomposition of berthierine part of which alters to magnetite the new magnetite phase has a normal magnetic fabric which overprints the inverse magnetic fabric of siderite

linking environmental regimes space and time interpretations of structural and functional connectivity connectivity as a concept has been increasingly part of discussions or explanations in hydrology geomorphology and ecology we address recent critiques of this approach by demonstrating how a refinement which distinguishes structural connectivity from functional connectivity can be used to explain patterns observed in very different environmental systems these systems are found in linkages between surface and subsurface flowpaths and the hyporheos in the river don a temperate river channel in yorkshire uk in surface and subsurface fluxes in agricultural land in the uk and in vegetation and surface conditions in a degrading environment at the sevilleta lter site in the semi arid southwest usa first we demonstrate long term geological and structural controls mediated by in channel processes second human organization of landscape elements is a significant control on runoff and erosion so that similar events can produce very different responses and vice versa third linkages between the removal of grass vegetation and runoff and erosion produce non linear and path dependent feedbacks which control the subsequent degradation of the landscape making the process difficult to reverse as a result of these studies we argue that even in cases where connectivity cannot be directly quantified at least at present this limitation does not prevent the concept from being a useful heuristic device for exploring responses of complex systems furthermore this result implies that an increasing need exists for disciplinary connectivity to investigate such systems

twentieth century dune migration at the great sand dunes national park and preserve colorado relation to drought variability abstract the great sand dunes national park and preserve in southern colorado contains a large dune mass banked against the sangre de cristo mountains the dune mass is bounded for hundreds of kilometers by a vegetated low relief sand sheet with abundant active parabolic and barchanoid dunes the clear morphology of these dunes formed by winds mostly from the southwest and the unambiguous identification of these forms in remotely sensed images provide straightforward targets to assess temporal changes in dune position a digital database of georeferenced remote sensing images from 1936 to 1999 is used to quantify parabolic and barchan dune migration rates and surface reflectance an indicator of vegetation cover with evolving drought conditions in the twentieth century the total net migration of 13 parabolic dunes in 63 years is 0 31 to 0 66 km whereas 11 barchan dunes moved an average of 0 12 to 0 47 km compared to intervening wet year there is at least a three fold increase in average parabolic dune migration during well documented droughts in the 1930s 1950s and 1990s with a concomitant reduction in vegetation cover and surface water resources the landscape response to the most recent drought in the late twentieth century is documented by an average parabolic dune migration rate of 30 m year which is a six fold acceleration over prior wet years and similar to dune response during the 1930s a nonlinear threshold for parabolic dune migration is indicated with lower quartile palmer drought severity index values of

mobility of a remobilised parabolic dune in kennemerland the netherlands abstract a parabolic dune in the netherlands was remobilised in december 1998 by removing vegetation and soil the main aim of the experiment was ecological to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes if processes can be reactivated at coarse scale periodic rejuvenation of the landscape over the long term is possible without the need for managers to interfere further the experiment provides the opportunity to address another important question can large parabolic dunes in the netherlands be mobile in the present climate mobility of the dune is investigated by means of erosion pins aerial photography and measurement of cross sections activity indices are derived from erosion pin recordings and correlated to weather conditions from 1999 to 2001 displacement of the dune ranged from 0 to 12 m in east northeasterly direction activity of the dune is related to wind conditions but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods periods with extreme wind speeds resulted in much less geomorphic change than expected

measurements and numerical simulations of the degree of activity and vegetation cover on parabolic dunes in north eastern brazil in this work we present measurements of vegetation cover over parabolic dunes with different degrees of activation along the north eastern brazilian coast we extend the local values of the vegetation cover density to the whole dune by correlating measurements with the relative brightness index c of high resolution quickbird panchromatic satellite images of the dune field we then introduce the vegetation data into a continuous model for vegetated dunes coupling sand erosion and vegetation growth and perform simulations of the evolution of the morphology and vegetation cover of parabolic dunes finally from the comparison of both the measurements and the simulation results we show that the model is able to predict the dune shape and the vegetation distribution of real parabolic dunes as result of the evolution of a blow out