tectonic control on 10 be derived erosion rates in the garhwal himalaya india erosion in the himalaya is responsible for one of the greatest mass redistributions on earth and has fueled models of feedback loops between climate and tectonics although the general trends of erosion across the himalaya are reasonably well known the relative importance of factors controlling erosion is less well constrained here we present 25 10 be derived catchment averaged erosion rates from the yamuna catchment in the garhwal himalaya northern india tributary erosion rates range between 0 1 and 0 5 mm yr 1 in the lesser himalaya and 1 and 2 mm yr 1 in the high himalaya despite uniform hillslope angles the erosion rate data correlate with catchment averaged values of 5 km radius relief channel steepness indices and specific stream power but to varying degrees of nonlinearity similar nonlinear relationships and coefficients of determination suggest that topographic steepness is the major control on the spatial variability of erosion and that twofold to threefold differences in annual runoff are of minor importance in this area instead the spatial distribution of erosion in the study area is consistent with a tectonic model in which the rock uplift pattern is largely controlled by the shortening rate and the geometry of the main himalayan thrust fault mht our data support a shallow dip of the mht underneath the lesser himalaya followed by a midcrustal ramp underneath the high himalaya as indicated by geophysical data finally analysis of sample results from larger main stem rivers indicates significant variability of 10 be derived erosion rates possibly related to nonproportional sediment supply from different tributaries and incomplete mixing in main stem channels

prediction of alluvial channel pattern of perennial rivers abstract purely braided meandering and straight channels can be considered as end members of a continuum of alluvial channel patterns several researchers have succeeded in separating channel patterns in fields defined by flow related parameters however the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry in this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains the method is based on two almost channel pattern independent boundary conditions median grain size of the river bed material and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient this can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition p 1 based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with p 1 5 the function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation with a bankfull or mean annual flood discharge above 10 m3 s and a median bed material grain size between 0 1 and 100 mm

emplacement and deformation of granites during transpression magnetic fabrics of the archean sparrow pluton slave province canada abstract the sparrow pluton is part of the prosperous suite of two mica granites that crop out within amphibolite grade meta greywackes of the southern yellowknife domain in the slave province of the canadian shield the magnetic susceptibility k and the anisotropy of magnetic susceptibility ams were used to systematically map the structural patterns in the pluton and to establish the relationship between plutonism and late archean tectonics in the region paramagnetic fe phyllosilicates biotite chlorite and very fine grained magnetite contribute to k and to the ams the magnetic foliation and the magnetic lineation are predominantly controlled by the biotite fabrics and their orientations are consistent with the regional d 2 strain field the horizontal magnetic lineations in the sparrow pluton suggest a horizontal stretching component associated with the regional d 2 event the zonation defined by k values is compatible with a fold pattern trending parallel to the regional f 2 folds and s 2 foliation and to the magnetic fabric trends in the pluton the intensities and symmetries of the ams also define map patterns that are consistent with d 2 deformation microstructural study indicates the pluton recorded d 2 strain as it crystallized and cooled from the solidus demonstrating syn d 2 emplacement the results indicate the pervasive structural patterns in the sparrow pluton are an integral part of the regional strain field and that they are kinematically consistent with a transpressive d 2 strain regime mapping the fabric patterns within syntectonic plutons provides a useful approach to the kinematic analysis of synemplacement deformation events in multiply deformed metamorphic terranes

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

models of magnetic anisotropy variations in sedimentary thrust sheets abstract magnetic anisotropy variation in sedimentary thrust sheets was modelled through the extension of strain models in thrust sheets coward and kim 1981 sanderson 1982 using the empirical relationship between the magnetic anisotropy and strain and respecting the pre deformational anisotropy of sedimentary rocks in thrust sheets deformed by simple shear and lateral lengthening the magnetic foliations remain near the bedding while in thrust sheets deformed by simple shear and lateral shortening the magnetic foliation may deviate strongly from the bedding even creating a girdle pattern in its poles

spatial variation in the power of mountain streams in the sangre de cristo mountains new mexico the principle indicator of river energy expenditure stream power has a significant influence on many forms and process attributes of the fluvial system yet few basin wide analyses of stream power variations have ever been conducted recent studies hypothesize a peak in the mean stream power distribution in small 10 km2 to intermediate 100 km2 sized basins to test hypothetical stream power profiles in a high mountain setting 129 cross sections of stream networks within the costilla basin of northern new mexico and southern colorado were measured for channel form local sediment conditions and basin characteristics geomorphic and hydrologic analysis of these river sites throughout the costilla basin yielded evidence of abundant local control over fluvial processes and forms within the basin the spatial deviations of stream power from the hypothetical patterns derived from hydraulic geometry in some cases 200 deviation match areas of specific geologic and hydrogeologic control as an alternative to traditional hydraulic descriptions of downstream channel form a probabilistic process response model can incorporate local and basin scale variables and allow more realistic feedback mechanisms than in traditional regime theory the probabilistic nature of this type of model also allows prediction of multiple modes of channel adjustment an ever present challenge to extremal and physically based simulations

microstructure and magnetic susceptibility applied to emplacement kinematics of granites the example of the foix pluton french pyrenees abstract the variscan foix granite 40 km 2 central pyrenees was subjected to detailed microstructural magnetic susceptibility and anisotropy studies magnetic susceptibility is shown to be of dominant paramagnetic origin its magnitudes clearly define a zoning which compares with the petrographic zoning and reveals that the pluton is the southern remnant of a normally zoned pluton truncated during alpine tectonics magnetic susceptibility anisotropy characterizes the planar and linear preferred orientations of the main iron bearing silicates namely biotite and accessory amphibole it is argued that these fabrics also reflect the flow pattern of the granite microstructural observations aid in distinguishing the magmatic and late magmatic fabric signatures main body from the post magmatic solid state signature leucogranite in order to account for the consistently subhorizontal and ne sw directed magmatic lineations in the northern sector of the foix granite an oblique intrusion is proposed it may be coeval with the early variscan regional sw trending shearing event steepening of the structures in at least part of the southern sector may be coeval with the late development of upright folds and vertical cleavage in the country rocks the utility of combined microstructural and magnetic susceptibility studies is demonstrated as an aid in the structural interpretation of granite intrusions which act as kinematic markers of their host terranes

lichenometric application to historical and subrecent dynamics and sediment transport of a corsican stream figarella river france abstract lichenometry has been applied to blocks canyon walls and terrace deposits a growth curve specific to corsica was made based on information obtained from tombstones old monuments from the genoese occupation of corsica and roman megaliths this allowed us to create a curve going as far back as 2000 years the curve is similar to those developed in mediterranean environments cevennes and eastern pyrenees but is very different from those developed in alpine and arctic regions lichens present on boulders of the bedload allow the time at which the boulders were laid down to be determined the lichenometric study of the figarella shows firstly that there is high stream competence blocks approximately 100 cm wide are moved during the 5 year flood recent important flood events were identified in 1973 and 1869 these correspond well with historical sources other older and much more important floods were also identified this analysis has allowed us to extend the specific streampower curves proposed by costa geol soc am bull 94 1983 986 and williams geogr ann 65a 1983 227 to blocks of more than 2 m wide lichens present on the canyon walls and on terrace sides in the plain allowed the last main incision phase to be dated to the little ice age aerial photograph analysis has shown that the present braided system in the lower course of the river is no longer active

modeling large scale fluvial erosion in geographic information systems variants of the stream power model have become standard for large scale erosion modeling in geographic information systems gis because they can be applied over broad areas without the need for detailed knowledge of stream characteristics gis based implementations of the shear stress stream power per unit length and stream power per unit area models are closely related to one another and related also to empirical sediment yield models derived from continental scale factor analyses based on a detailed examination of the implementation of stream power analyses at the scale of continental mountain ranges we demonstrate that 1 the careful selection of a digital elevation model dem projection can minimize length and area distortion when analyzing large portions of the earth such as the himalaya or andes in the two dimensional plane of a dem 2 the area discharge proxy frequently employed in gis based stream power studies may not be appropriate for rivers that flow through significant rain shadows or climatic zones 3 decreasing the resolution of a dem from 30 to the 900 m typical for studies of large extent decreased the mean slopes of 15 rivers in the olympic mountains by 65 increased the mean drainage basin size by 14 and caused a 17 reduction in median main stem channel length 4 the coefficients k m and n common to different versions of the stream power law are themselves sensitive to grid resolution when determined from an analysis of area slope plots 5 stream power per unit area decreased in the olympics mountains as grid resolution decreased d 2002 elsevier science b v all rights reserved

controls on morphological variability and role of stream power distribution pattern yamuna river western india abstract understanding the controls on the morphological variability of river systems constitutes one of the fundamental questions in geomorphic investigation channel morphology is an important indicator of river processes and is of significance for mapping the hydrology ecologic connectivity in a river system and for predicting the future trajectory of river health in response to external forcings this paper documents the spatial morphological variability and its natural and anthropogenic controls for the yamuna river a major tributary of the ganga river india the yamuna river runs through a major urban centre i e delhi national capital region the yamuna river was divided into eight geomorphically distinct reaches on the basis of the assemblages of geomorphic units and the association of landscape valley and floodplain settings the morphological variability was analysed through stream power distribution and sediment load data at various stations stream power distribution of the yamuna river basin is characterised by a non linear pattern that was used to distinguish a high energy natural upstream reaches b anthropogenically altered low energy middle stream reaches and c rejuvenated downstream reaches again with higher stream power the relationship between stream power and channel morphology in these reaches was integrated with sediment load data to define the maximum flow efficiency mfe as the threshold for geomorphic transition this analysis supports the continuity of river processes and the significance of a holistic basin scale approach rather than isolated local scale analysis in river studies

magnetic fabric and structural setting of plio pleistocene clayey units in an extensional regime the tyrrhenian margin of central italy abstract results are presented of structural analysis and anisotropy of magnetic susceptibility ams analysis of plio pleistocene clayey units from the extensional tyrrhenian margin of central italy data have been collected in different tectonic settings mainly strike slip and transverse extensional structures at the sites with major evidence of plio pleistocene tectonics there appears a close relationship between magnetic lineations and stretching directions stretching processes that were able to modify the original magnetic fabric pre dated significant normal fault related tilting and therefore were active at the very first stage of extensional deformation the relationships between ams and structural trends in an extensional regime seem distinctively different from those reported in compressional regimes this kind of analysis may be useful in the geodynamic interpretation of ambiguous structures

dynamics of bedload transport in turkey brook a coarse grained alluvial channel automatic and continuously recording samplers are deployed in a hertfordshire gravel bed stream to show that bedload transport is related to stream power the pattern is similar to that already established for north american channels but because the record is so detailed it is possible to identify the cause of the considerable scatter that is normal in such relationships a major factor is the occurrence of rhythmic pulses in bedload discharge that are not matched by similar fluctuations in hydraulic variables it is suggested that these pulses reflect downstream differences in the concentration of mobile particles in a slow moving traction carpet and that they may be likened to kinematic waves the record also reveals that the threshold of sediment transport always presumed hithero to be associated with incipient motion is related to the cessation of bedload transport in a river flood indeed the mean value of stream power at the finish of bedload transport is only 20 percent of that prevailing at the moment of incipient sediment motion because of this there is an inevitably poor correlation between actual bedload transport rates and those predicted by bedload equations which rely upon a single traction threshold these new data show that the general inverse relationship between bedload discharge and water depth grain size ratio proposed by bagnold 1977 1980 is not universal transport efficiency for this gravel bed stream is typically 0 05 per cent of available stream power which compares with 1 6 per cent for a river moving both gravel and sand and 5 per cent for another channel where bedload is composed predominantly of sand sized particles it is argued that coarse and fine grained alluvial channels may need to be considered separately by allowing for differences in traction threshold at the beginning and end of bedload events and by averaging bedload discharge flood by flood in order to smooth out the effect of pulses it is possible to achieve a reasonably good prediction of average bedload transport rate in terms of stream power

sr and nd isotopes in river sediments from the ganga basin sediment provenance and spatial variability in physical erosion 1 sr and nd concentrations and isotope compositions in sediment of the ganga river from gangotri to rajmahal and its tributaries have been measured to determine provenance and the spatial variability in physical erosion among the ganga subbasins sr and nd in silicates range from 37 to 138 and from 10 to 36 g g with 87sr 86sr and nd of 0 7474 0 8428 and 25 5 to 15 5 respectively the results suggest that 65 of ganga mainstream sediments are derived from the higher himalayan crystallines highlighting intense physical erosion in this region the 87sr 86sr values of sediments in the gangetic plain show nearly identical trends during two seasons with a sharp and significant decrease at barauni downstream of gandak confluence this brings out the major impact of the sediment contribution from the gandak to the ganga mainstream model calculation suggests that about half of the ganga sediment at rajmahal is sourced from the gandak the erosion rates in the himalayan subbasins of the ganga range between 0 5 and 6 mm a where a is years with the gandak having the highest erosion rate high relief and intense precipitation over the headwater basins of the gandak appear to drive the rapid and focused erosion of this basin the results of this study and those in literature suggest that the eastern syntaxis brahmaputra the western syntaxis indus and the gandak have much higher physical erosion rates than the other himalayan basins focused erosion in the hot spots of these river basins contributes significantly to the global riverine sediment budget and influence regional tectonics

magnetic fabrics and strain in pencil structures of the knobs formation valley and ridge province us appalachians pencil structures which are found in weakly deformed mudrocks reflect the bedding cleavage intersection in weak to moderatelycleaved rocks their presence indicates conditions where bedding and cleavage fabrics are approximately equal in intensity we have determined the anisotropy of magnetic susceptibility ams in pencil structures from a sequence of mudstones of the ordovician knobs formation in the valley and ridge province of the us appalachians magnetic mineralogy was determined by x ray analysis and lowtemperature susceptibility measurements distribution of the magnetic ellipsoid axes is consistent with the incipient tectonic fabric of the pencil mudstones the maximum susceptibility axes parallel the pencils long axes while the minimum axes of susceptibility are normal to the primary sedimentary fabric independent strain quantification permits a correlation between magnetic fabric and tectonic strain an exponential relationship between the ams shape parameter t and tectonic shortening has been found for the interval of 10 25 shortening shortening 17 p exp t this relationship appears to be supported by tectonic strains up to 40 the t parameter t lnf 2 lnl lnl lnf where l lineation is kmax kint and f foliation is kint kmin describes the shape of the magnetic susceptibility ellipsoid which appears more sensitive to strain than past correlation attempts with the magnetic intensity parameter p or p 0 whereas this correlation between strain and ams is only valid within a restricted window of strain 10 40 shortening it establishes the magnitude and directions of tectonic strain in weakly deformed clay rich rocks where strain indicators are otherwise lacking or are poorly developed q 2003 published by elsevier science ltd

distance of movement of coarse particles in gravel bed streams distributions of distance of bedload particle movement were examined in two gravel bed streams using several hundred magnetically tagged cobbles and pebbles the compound poisson model of einstein hubbell sayre and a simple gamma function model were compared with observed distributions of moved particles and of all particles both models fit the data reasonably well for small mean displacements but notable misfits occurred in an event with large mean displacement when mean particle travel distance approaches the scale of bar spacing trapping in the bars interrupts particle progress and the dispersion process the data remain very noisy so definitive discrimination of suitable models will require trials with more than 103 particles

evaluation of a regional strain gradient in mylonitic quartzites from the footwall of the main central thrust zone garhwal himalaya india inferences from finite strain and ams analyses abstract the footwall of the main central thrust mct zone along the bhagirathi valley comprises a wide zone of mylonitic quartzite and deep level tectonites the systematic variation of finite strain parameters es k and v in the mylonites indicates heterogeneous deformation which is determined to vary between simple shear and non coaxial flattening type in such a strain regime the outer boundary of the quartz clasts are no longer preserved thus leading to an error in finite strain measurement in order to supplement the finite strain studies anisotropy of magnetic susceptibility ams analyses were carried out on the mylonitic quartzites a systematic variation in degree of anisotropy p with distance from the mct is documented and is interpreted to be tectonic in origin based on these results it is concluded that p can be used as a strain intensity gauge at least on an outcrop scale where a systematic variation in p values from one part of the outcrop to the other can be established however the quantitative relation between principal axes of finite strain ellipsoid and ams axes magnitude of principal susceptibility difference k1 and k3 and finite strain magnitude e1 ln 1 e1 and e3 ln 1 e3 were related by a logarithmic relationship with a correlation coefficient of 0 844

ice sheet erosion patterns in valley systems in northern sweden investigated using cosmogenic nuclides erosion patterns associated with glaciation of trunk and hanging valley systems in northern sweden were investigated using cosmogenic nuclide 10be apparent exposure ages and inferred nuclide inheritance sequences of samples taken across valleys known to have been covered repeatedly by the fennoscandian ice sheet revealed two primary patterns of erosion in vavlavagge the exposure age pattern is consistent with 2 m of glacial erosion during the last glacial cycle along the entire profile at ravtasvaggi dievssavaggi and alisvaggi exposure ages in the valley bottom contrast with apparent exposure ages two to four times older on the valley sides the older ages on the valley sides reflect cosmogenic nuclide inheritance due to limited 2 m bedrock erosion of the valley sides during the last glacial cycle the pattern and scale of erosion in these valleys indicates that glacial valley formation is a result of multiple glacial cycles rather than the result of topographic modification during a single glacial cycle initial data comparing hanging valley and trunk valley sites do not show distinct differences in apparent exposure ages slightly older ages for samples from hanging valley bottoms may suggest nuclide inheritance indicating lower erosion than in trunk valley bottoms as would be expected given the marked topographic step between hanging and trunk valleys although quantifying the amount of erosion depends on the assumed cosmogenic nuclide inheritance prior to the onset of erosion the pattern of erosion is independent of this hence the observed pattern of cosmogenic nuclide concentrations provides constraints on spatial patterns of erosion and helps to refine understanding of the timing and extent of landform modification by glaciation copyright 2005 john wiley sons ltd

phyllosilicate fabric characterization by low temperature anisotropy of magnetic susceptibility lt ams 1 this paper examines the use and applicability of anisotropy of magnetic susceptibility at low temperature 77 k called lt ams paramagnetic susceptibility increases significantly with low temperature which permits high precision determination of the anisotropy of paramagnetic susceptibility of a rock from measurements at liquid nitrogen temperature we describe a new procedure that measures directional susceptibility in an oriented rock specimen while immersed in liquid nitrogen our procedure overcomes the problem of temperature heterogeneity within a rock sample while its susceptibility is being measured offering the opportunity to measure low temperature susceptibility in multiple orientations this non destructive method provides a way of characterizing the principal paramagnetic minerals present in a rock based on temperature induced changes of the anisotropy degree moreover the method offers a better resolved relationship between anisotropy degree and grain alignment which is used to quantify rock fabrics

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

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

subtle stretching lineation revealed by magnetic fabric of callovian oxfordian black shales french alps abstract the anisotropy of magnetic susceptibility ams of callovian oxfordian black shales from the subalpine massifs of the french alps has been measured the magnetic susceptibility of these formations originates from ferromagnetic titanomagnetite and paramagnetic phyllosilicates illite and chlorite although the magnetic fabric is complicated by the interaction of planar and linear structural elements and the presence of variable amounts of minerals two types of lineation are preserved a stretching lineation which exhibits counterclockwise rotation as a result of deformation from south to north and an intersection lineation parallel to the fold axis this set of new structural data together with semiquantitative analysis of ams is in agreement with the geodynamic evolution of the western alps

study of ductile shear zones galicia spain using texture goniometry and magnetic fabric methods abstract a joint magnetic and mica fabric study has been carried out on rocks from recognised shear zones in galicia spain the two main aims of the study are to determine strain gradients in a foliated material without any significant strain markers and to obtain a quantitative relationship between the magnetic susceptibility anisotropy ellipsoid and the mica fabric axes the intensity parameters of the fabric on profiles intersecting the studied areas indicate the dominant influence of two major shear zones on the fabric development the regional fabric shows less significant variations across minor less developed shear zones the empirical relationship between magnetic fabric and strain reported by rathore 1979 1980 and rathore and henry 1982 is found to hold in the magnetic and mica fabrics comparison the relationship found in this study is i j l i l j 0 240

where do floodplains begin the role of total stream power and longitudinal profile form on floodplain initiation processes understanding downstream transitions in river character and behavior is a basic concept in fluvial geomorphology downstream patterns of depositional processes can be differentiated between channel and floodplain components in this study a generic set of methods is used to analyze floodplain initiation and continuity in relation to downstream changes in total stream power slope and discharge and longitudinal profile form for river courses in the upper hunter catchment australia absolute values of these controlling factors are shown to be poor indicators of threshold conditions at which floodplains begin to form along river courses catchment scale patterns of stream power and the form of longitudinal profiles provide better predictors of this transitional zone the total stream power plot derived along longitudinal profiles represented by a second order exponential curve has a bimodal pattern in most cases floodplains begin to form in a transition zone characterized by a trough area within the bimodal stream power distribution this bimodal stream power pattern provides a better means to identify this transition in depositional processes along longitudinal profiles than more conventional single peak stream power analyses based on first order exponential longitudinal profiles indirect controls such as basin geology and accommodation space also influence the initiation and pattern of floodplains

a comparison of srtm and high resolution digital elevation models and their use in catchment geomorphology and hydrology australian examples the recently released shuttle radar topography mission srtm 3 arc second digital elevation data set provides a complete global coverage of the earth s land surface in this paper we examine the srtm data for three catchments in australia over a range of climates geology and resultant geomorphology to test this new data set the srtm data are compared with high resolution digital elevation models we use basic hydrological and geomorphological statistics and descriptors such as the area slope relationship cumulative area distribution and hypsometric curve along with strahler and networking statistics the above measures describe the surface morphology of a catchment therefore integrating catchment geology climate and vegetation the srtm data were also assessed as input into the siberia landscape evolution and soil erosion model as were runoff properties using a wetness index the results demonstrate that the 90 m srtm data provide a poor catchment representation hillslopes appear as a linked set of facets and display little of the complex curvature that is observed in high resolution data while catchment area slope and area elevation hypsometry properties are largely correct catchment area relief and shape as measured by the width function are poorly captured by the srtm data also results in working statistics are also variable the large grid size of the srtm data also results in incorrect drainage network patterns and different runoff properties consequently care must be used for quantitative assessment of catchment hydrology and geomorphology as in all cases srtm derived catchment area is incorrect and smaller digital elevation grid sizes are required for accurate catchment wide assessment while only a limited number of catchments have been examined we believe our findings are applicable to other areas

the influence of deformation mechanisms on magnetic fabrics in weakly deformed rocks abstract magnetic fabrics of weakly deformed rocks are not simply correlated with the principal finite strain directions depositional magnetic fabrics persist at 30 shortening where the rocks are deformed by particulate flow grain boundary sliding rocks with a spaced stylolitic cleavage believed to be formed by pressure solution and shortened by 20 50 have maximum susceptibility parallel to the intersection of cleavage and bedding this type of magnetic fabric is attributed to the interference of a depositional magnetic fabric between cleavage surfaces with a tectonic magnetic fabric in the cleavage surfaces

a transtensional basin model for the organya basin central southern pyrenees based on magnetic fabric and brittle structures summary the purpose of this paper is to explain the kinematics of the inverted extensional organy basin centralsouthernpyrenees duringitsextensionalevolution thestudyoftheanisotropy of magnetic susceptibility ams and the study of brittle mesostructures are the instruments used to decipher the extensional kinematics separation of magnetic subfabrics analyses of ams at low temperature and anisotropy of the anhysteretic remanence aarm has been also done to properly interpret the obtained magnetic fabric data the combination of all magnetic fabric and brittle mesostructures analyses has provided new information to clarify thestructuralevolutionofthebasin whichsupportanewtectonicmodelfortheaptian albian basinal stage 20 sites for the magnetic fabric analysis were sampled in aptian lower albian marls the ams ellipsoids obtained at room temperature show their kmin axes perpendicular to bedding and kmax axes oriented nw se in 70 per cent of the samples n s in 15 per cent and ne sw in 15 per cent analyses of ams at low temperature show a better clustering of the axes of the magnetic ellipsoid pointing out that phyllosilicates constitute the carriers of the ams whereas the analyses of the aarm confirm the scattering of the ferromagnetic grains these results suggest that the obtained ams in the organy a basin was acquired during or shortly after deposition of the aptian lower albian marls without any subsequent overprint the direction of the magnetic lineation obtained from the ams at room and low temperatures agrees with the orientation of the stress axes obtained from the analysis of brittle mesostructures mainly faults and calcite filled tension gashes indicating its tectonic origin we interpret the orientation of the magnetic ellipsoids related to the transtensional movements linked to the formation of the organy a basin during the aptian albian interval which are consistent with the eastward displacement and rotation of iberia with respect to europe analysis oftensiongashesalsoindicatesamainnw seextensiondirection whereaspalaeostressanalysis of striated faults shows a more n s trending 3 the transtensional model proposed from magnetic fabric and brittle mesostructures for the organy a basin during the aptian albian is consistent with the creation of a strongly subsiding area south of the axial zone during the cretaceous and implies that rotation and separation of iberia respect to europe took place simultaneously

magnetic fabric and deformation in the navia alto sil slate belt northwestern spain abstract ries and schackleton ries a c schackleton r m 1976 patterns of strain variation in arcuate fold belts philos trans r soc london a 283 281 288 discussed the distribution of finite strain in the ibero armorican arc and suggested that the arc was produced by tectonic bending of a straight or gently curved fold belt later investigations by others revealed different strain patterns in the fold thrust belt and so its evolution continues to be controversial this study focuses on the strain pattern in the navia alto sil slate belt the low field anisotropy of magnetic susceptibility ams was measured in ordovician black slates and cambrian to lower ordovician quartzites sampled around the arcuate belt the magnetic fabric is controlled primarily by the slaty cleavage in both lithologies the ams was also measured with a high field torsion magnetometer and the results indicate that paramagnetic minerals are responsible for the magnetic fabric in the slates and diamagnetic and paramagnetic minerals in the quartzites strain markers i e pressure shadows around pyrite grains and rutile distribution are found in the slates and the orientation of the principal axes of strain ellipsoids agrees with those of the ams ellipsoid a systematic variation in the orientation of the strain ellipsoid and anisotropy ellipsoid suggests that there is strain heterogeneity along the slate belt and that the arc did not form by tectonic bending

slaty cleavage development and magnetic anisotropy fabrics the shale to slate transition preserved in the ordovician martinsburg formation at the lehigh water gap pennsylvania provides an opportunity to study the relationship between magnetic anisotropy fabrics and the development of slaty cleavage our previous work has indicated that anisotropy of magnetic susceptibility ams does not record changes in finite strain associated with cleavage development in these rocks but instead measures the degree of dissolution and new growth of ehlorite additional ams data presented in this paper lend further support to this conclusion conversely anhysteretie remanent magnetization anisotropy arma which is not affected by paramagnetie ehlorite accurately reflects the strain induced rock fabrics associated with cleavage formation arma results show that magnetite dimensional orientations vary from bedding parallel in shale samples to cleavage parallel in samples with well developed slaty cleavage samples with weak and pencil cleavage display scattered arma orientations which lie in between bedding and cleavage these intermediate orientations may be due to either passive rotation of magnetite from bedding parallel to cleavage parallel or re crystallization of magnetite if rotation occurred grain rotation was highly heterogeneous in the samples with incipient cleavage the intermediate arma orientations may also reflect the varying contribution of two magnetite preferred orientations a depositional orientation parallel to bedding and a new growth orientation parallel to cleavage

geomorphic effectiveness of a long profile shape and the role of inherent geological controls in the himalayan hinterland area of the ganga river basin india abstract long profiles of rivers provide a platform to analyse interaction between geological and geomorphic processes operating at different time scales identification of an appropriate model for river long profile becomes important in order to establish a quantitative relationship between the profile shape its geomorphic effectiveness and inherent geological characteristics this work highlights the variability in the long profile shape of the ganga river and its major tributaries its impact on stream power distribution pattern and role of the geological controls on it long profile shapes are represented by the sum of two exponential functions through the curve fitting method we have shown that coefficients of river long profile equations are governed by the geological characteristics of subbasins these equations further define the spatial distribution pattern of stream power and help to understand stream power variability in different geological terrains spatial distribution of stream power in different geological terrains successfully explains spatial variability in geomorphic processes within the himalayan hinterland area in general the stream power peaks of larger rivers lie in the higher himalaya and rivers in the eastern hinterland area are characterised by the highest magnitude of stream power

assessment of downstream trends in channel gradient total and specific stream power a gis approach geographic information systems gis analyses of digital elevation models dems coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient total stream power and in riverscapes conducive to regime analysis also specific stream power for a small high relief coastal catchment in se australia good agreement was obtained between channel gradients derived from a 25 m cell size dem and field survey equivalents over distances of several kilometres indicating that channel gradients derived from dems can have a reasonable degree of absolute as well as relative accuracy over multi kilometre reach scales assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream modelling of downstream trends in channel gradient total and specific stream power from catchment wide dems has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient stream power and the form and dynamics of river systems

understanding erosion rates in the himalayan orogen a case study from the arun valley understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution denudation rates derived from terrestrial cosmogenic nuclides tcns are commonly used to quantify erosion and bridge tectonic myr and climatic up to several kiloyears time scales however how the processes of erosion in active orogens are ultimately reflected in 10be tcn samples remains a topic of discussion we investigate this problem in the arun valley of eastern nepal with 34 new 10be derived catchment mean denudation rates the arun valley is characterized by steep north south gradients in topography and climate locally denudation rates increase northward from 0 2 mm yr 1 to 1 5 mm yr 1 in tributary samples while main stem samples appear to increase downstream from 0 2 mm yr 1 at the border with tibet to 0 91 mm yr 1 in the foreland denudation rates most strongly correlate with normalized channel steepness r2 0 67 which has been commonly interpreted to indicate tectonic activity significant downstream decrease of 10be concentration in the main stem arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample this results in 10be concentrations and denudation rates that do not uniformly represent the upstream catchment area we observe strong impacts on 10be concentrations from local nonfluvial geomorphic processes such as glaciation and landsliding coinciding with areas of peak rainfall rates pointing toward climatic modulation of predominantly tectonically driven denudation rates

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

basin scale hydrology and sediment dynamics of the kosi river in the himalayan foreland abstract hydrological and sediment transport characteristics for the kosi basin which covers parts of nepal and india were analysed to understand the spatiotemporal variability of the hydrology and sediment dynamics of the kosi basin and its implications for flood hazard and sediment dynamics the study revealed that 56 of the discharge at chatara where all major tributaries of the kosi meet is contributed from the western part of the basin even though this constitutes only 34 of the total basin area in contrast the central and eastern parts of the basin constitute 57 and 8 of the basin area but contribute 38 and 16 of the discharge at chatara respectively the contribution of sediment load at chatara from the different tributaries of the kosi river also shows a similar pattern of a total of 100 million tonnes of the annual sediment load at chatara 56 is transported from four tributaries the indrawati bhote kosi tama kosi all draining from the west and tamor the remaining 44 is transported by other tributaries upstream of chatara the most important being the arun dudh kosi and sun kosi sediment budgeting in this study based on annual sediment load data suggested that 20 million tonnes of sediments are deposited between chatara and birpur annually this study also found that 53 million tonnes of sediments are being accommodated between birpur and baltara annually sediment dynamics in the kosi basin emerges as the most important river management issue and this is closely linked to channel instability and frequent flooding in the alluvial plains

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

critical specific stream power in gravel bed rivers experiments with marked pebbles were carried out on different sized rivers of the belgian ardenne catchment areas varying from less than 1 km2 to 2700 km2 specific stream power required to cause bedload movement was evaluated and critical values were obtained three types of relationship between critical specific stream power 0 and grain size d were established the values for 0 in the largest river the ourthe were the lowest and were close to the values obtained for mountainous rivers carrying large boulders in medium sized rivers catchment area between 40 and 500 km2 the critical unit stream power was higher it is likely that it is due to the bedform s greater resistance this resistance would use up some of the energy that can cause movement and transport of bedload the amount of resistance of the bedform can be expressed as bedform shear stress determined by the relationship between grain shear stress that determines movement and transport of the bedload and the total shear stress this ratio varies between 0 4 and 0 5 in the medium sized rivers compared to 0 7 in the ourthe in headwater streams less than 20 km2 there is greater loss of energy due to bedform resistance 0 3 critical specific stream power is higher in this third type of river than in the other two

river systems and their sediment flux indo gangetic plains northern bihar india river systems of part of the himalayan foreland northern bihar plains india are described in terms of their channel morphology hydrology and suspended sediment characteristics a simple classification of the river systems based mainly on the source area characteristics is proposed i mountain fed ii foothills fed iii plains fed and iv mixed fed rivers distinct differences are noted between these classes of river systems most rivers show evidence of channel movement mainly by avulsion but cut offs also occur locally the mountain fed rivers are characterized by very high discharge and low suspended sediment concentration and the plains fed rivers have relatively low discharge and high suspended sediment concentration the foothill fed rivers have moderate values of discharge and suspended sediment concentration the mountain fed rivers have built megafans of large extent whereas the foothills fed and plains fed rivers have formed muddy interfan areas semi quantitative estimates of water and sediment flux suggest that about 99 9 of the mass transfer into the plains is water with the remaining 0 1 being sediment and that 10 s of the latter 0 01 of the total is retained in the basin the remainder being transferred to the bengal fan

virtual rate and mean distance of travel of individual clasts in gravel bed channels travel distances in gravel bed rivers of tagged particles of various sizes are related to excess stream power estimated for peak discharge mean distance of movement irrespective of grain size is weakly correlated with stream power especially near the threshold of movement there may be several reasons for the weak correlation including variable effects of bed structure varying magnitudes of sediment mobilizing events and sampling problems grain size itself is of marginal significance the virtual rate of travel calculated using total time for which the flow is larger than that needed to initiate clast movement also bears a weak relation to the excess stream power over the period better results are obtained by relating the virtual rate of travel to the first peak of the flow event only this implies that the initial seeding of the tagged particles dominates the observations nonetheless an underlying general relation is indicated by the data which are derived from a wide range of flow regime types

downstream trends in discharge slope and stream power in a lower coastal plain river conceptual models of river estuary interaction are typically based on a notion of systematic downstream change in the intensity of fluvial processes low slopes backwater effects and effects of antecedent topography and landforms may complicate downstream tends in water and sediment flux in coastal plain rivers an analysis of the lower trinity river texas shows no consistent downstream pattern of increases or decreases in the discharge stream power or water surface slope flows may decrease downstream due to coastal backwater effects in the lowermost reaches and due to diversion of flow into valley bottom depressions during high flows in both the fluvial and fluvial estuarine transition reaches in general however stream power and slope decrease in the lower reaches consistent with earlier findings of limited fluvial sediment delivery to the coastal zone some tributaries may become distributaries at high but sub bankfull flows as backwater effects reverse flows into depressions associated with paleomeanders the paleomeanders and possibly the locations of these reversible channels are related to antecedent topography associated with aggradation degradation cycles over the past 100 ka low gradient coastal plain rivers may not function as simple conduits from land to sea further the transition from fluvial to coastal dominance may be variable along the river with the variability controlled not just by the relative magnitude of river and tidal or backwater forcing but also by valley topography controlled in part by antecedent landforms

cleavage duplexes in the marcellus shale of the appalachian foreland abstract cleavage duplexes are zones of platy spaced cleavage that either parallel bedding or ramp through shale sections examples are 2 60 m thick the cleavage within the zones is generally subperpendicular to the zone boundaries but sigmoidally dragged against floor roof and internal thrusts between the well developed floor thrust and the more obscure roof thrusts of the duplexes the shale has been shortened 30 perpendicular to cleavage the thrusts are sharp strain discontinuities because both overlying and underlying shale is uncleaved and less deformed

structure and tectonics of central and southern appalachian valley and ridge and plateau provinces west virginian and virginia the valley and ridge and eastern allegheny plateau from pennsylvania into tennessee is subdivided into distinct allochthonous sheets emplaced over an essentially featureless precambrian basement surface sheet development is related to variations in stratigraphic thickness and lithology as well as regional basement configuration three sheets control central appalachian structural style the massanutten blue ridge sheet is easternmost and is bounded on the west by the little north mountain pulaski fault system continuing westward into the plateau the martinsburg sheet contains anticlinoria and synclinoria uncut by major thrust faults both massanutten blue ridge and martinsburg sheets are seated in upper ordovician martinsburg reedsville shales the underlying waynesboro sheet is rooted in lower cambrian waynesboro rome shales and its imbrication has controlled the locations of major anticlinoria and synclinoria in the upper sheet within the southern appalachians greater imbrication of the lower sheet and increased thrust fault displacement at longitudinal ramps have destroyed the lateral continuity along strike of the central appalachian waynesboro and overlying martinsburg sheets there imbrication to the surface has formed the saltville sheet continuous into alabama as well as the st clair narrows copper creek cove mountain and st paul honaker sheets southwest of the trend change the holston stone mountain sheet adjacent to the blue ridge is rooted primarily in lower and middle cambrian strata and is underlain by the pulaski sheet in the westernmost sector of this region the pine mountain and richlands sheets are seated in devonian shales the pulaski and massanutten blue ridge sheets rooted primarily in upper ordovician shales form a continuous structural unit and include blue ridge and piedmont rocks

overprinting of magnetic fabrics in granites by small strains numerical modelling abstract the anisotropy of magnetic susceptibility ams is used to determine weakly defined mineral preferred orientation fabrics in granites however the effects of small strains superimposed on the low intensity ams fabrics typical of these rocks is not well understood numerical simulations are presented which investigate the effects of small superimposed strains on the shapes magnitudes and orientations of pre existing ams fabrics which are similar to those reported in the literature for undeformed granites a computer generated biotite petrofabric is subjected to progressive strain using march s strain response model for pure shear plane strain axially symmetric shortening and simple shear regimes results indicate that a pre existing ams fabric might be significantly modified or overprinted by small strains 10 15 strain in the pure shear and axially symmetric shortening regimes 0 5 1 0 for simple shear a new ams fabric may develop with an orientation similar to that expected for shearing of an initially isotropic petrofabric at low strains the evolution of the shape of the ams ellipsoid depends strongly on the orientation of the initial petrofabric with respect to the strain framework the ams ellipsoid may evolve towards either oblate or prolate shapes and the evolution in the ellipsoid shape may be reversed during progressive strain this modelling suggests that small strains affecting a pluton following its emplacement could mask ams fabrics developed earlier the results also suggest that in simple shear the orientation of the ams ellipsoid may serve as a shear sense indicator for small strains even if the earlier fabric is not isotropic

chlorite control of correlations between strain and anisotropy of magnetic susceptibility abstract anisotropy of magnetic susceptibility ams has in the past been used as an indicator of finite strain mathematical relationships between the measured ams ellipsoid and the finite strain ellipsoid in slates are numerous the ordovician martinsburg formation at lehigh gap pennsylvania provides a unique opportunity to test this correlation as a complete shale to slate transition is preserved magnitudes of the principal susceptibility axes appear to reflect a strain gradient at this location apparent strain values derived from ams using equations from rathore and hrouda have x y z ratios from 2 79 1 87 0 19 shale to 2 92 0 82 0 42 slate the orientations of the susceptibility axes characterize two fabrics i k int k max planes at 20 to bedding and ii k int k max planes parallel to cleavage anisotropy of magnetic susceptibility fails to show any intermediate orientations of the principal susceptibility axes in the zone in which cleavage is developed comparison with phyllosilicate crystallographic orientations indicates that the ams intermediate and maximum susceptibility axes are parallel to chlorite basal planes because chlorite reoriented via dissolution and new growth as cleavage developed in this location and because models correlating ams and strain instead assume that strain is reflected by the rotation of the magnetic susceptibility carriers the apparent strain values calculated from ams reflect only the degree of dissolution and neocrystallization in these rocks and not the finite strain

thresholds and the spatial variability of flood power during extreme floods abstract analysis of the effects of extreme events on overall landscape form has shifted geomorphic attention away from a focus on the magnitude and frequency relationship of discharge to a focus on flood power this paper analyzes the variation in flood power both at a station and downstream in a basin of differing lithologies and discusses the geologic and geomorphic controls on flood power design floods ranging from the 2 year discharge tothe 500 year discharge are routed trough a drainage basin and channel boundary shear stress and unit stream power are calculated using hec 2 along 21 cross valley transects because of the strong lithologic control on valley width and channel slope an irregular downstream pattern of flood power emerges which reflects primarily the pattern in valley width narrow valleys correspond to a greater percent of channel conveyance during large magnitude floods and increasing rates of depth increases thus maximizing flood power in these zones the opposite occurs in anomalously wide valleys where flood power is minimized a downstream spatial pattern emerges reflecting both local and general controls for a given probability event flood power varies at least threefold within the basin with a maximum occuring in a specific downstream section holding flood power constant produces an extremely wide range in flow probabilities in order to establish a link between critical flood power magnitude and flow frequency minimum flood powers are developed from an analysis of previous work on catastrophic flooding for humid alluvial channels these minimum thresholds tentatively correspond to 100 n m2 or 300 w m2 for shear stress and unit stream power respectively discharges required to attain these critical flood powers vary from events roughly twice the 100 year flood to a maximum of roughly 18 times the discharge of the 100 year flood

exploring the limits of identifying sub pixel thermal features using aster tir data abstract understanding the characteristics of volcanic thermal emissions and how they change with time is important for forecasting and monitoring volcanic activity and potential hazards satellite instruments view volcanic thermal features across the globe at various temporal and spatial resolutions thermal features that may be a precursor to a major eruption or indicative of important changes in an on going eruption can be subtle making them challenging to reliably identify with satellite instruments the goal of this study was to explore the limits of the types and magnitudes of thermal anomalies that could be detected using satellite thermal infrared tir data specifically the characterization of sub pixel thermal features with a wide range of temperatures is considered using aster multispectral tir data first theoretical calculations were made to define a thermal mixing detection threshold for aster which quantifies the limits of aster s ability to resolve sub pixel thermal mixing over a range of hot target temperatures and pixel areas then aster tir data were used to model sub pixel thermal features at the yellowstone national park geothermal area hot spring pools with temperatures from 40 to 90 c and at mount erebus volcano antarctica an active lava lake with temperatures from 200 to 800 c finally various sources of uncertainty in sub pixel thermal calculations were quantified for these empirical measurements including pixel resampling atmospheric correction and background temperature and emissivity assumptions

magnetic fabrics rock magnetism cathodoluminescence and petrography of apparently undeformed bambui carbonates from sao francisco basin minas gerais state se brazil an integrated study abstract magnetic measurements were performed on apparently undeformed limestones and carbonate shales from 44 sites in nearly horizontal stratigraphic layers mainly from the basal units of the neoproterozoic bambui group in the southern part of the sao francisco basin rock magnetism cathodoluminescence transmitted and reflected light microscopy analyses reveal that there is a mix of ferromagnetic minerals mainly magnetite and pyrrhotite in most sites in some sites however the ferromagnetic minerals are magnetite and hematite fine grained pyrrhotite and pyrite accompany rare fine grained graphite and probably amorphous carbon in some of stylolites while pyrrhotite is also present as larger interstitial masses in coarse grained domains outside but close to the stylolites magnetic fabrics were determined applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence magnetization aar the aar tensor was less well defined than the ams fabric due to the low ferromagnetic mineral content the analysis at the individual site scale defines three ams fabric types the first type two sites shows k min perpendicular to the bedding plane while k max and k int are scattered within bedding plane itself this fabric is usually interpreted as primary sedimentary compactional typical of totally undeformed sediments the second type shows the three well clustered ams axes with k min still perpendicular to the bedding plane this fabric is the most important since it was found in the majority of the sites the third type two sites is characterized by well clustered k max in the bedding plane while k min and k int are distributed along a girdle the second and third fabric types are interpreted as combinations of sedimentary compactional and tectonic contributions at the earliest and at a slightly later stage of deformation respectively ams represents the contribution of all the rock forming minerals while aar isolates the contribution of remanence bearing minerals from the matrix minerals however rock magnetism shown that anhysteretic remanence only reaches grains with coercivity k max and a max respectively in general k max is well developed and follows the trend of the main regional thrusts fold axes and faults generated in the first deformational phase while a max follows both this trend and that of structural lineaments formed during the second deformational phase these deformation phases arose from the compression which occurred during the evolution of the brasilia fold belt during the last stages of the brasiliano event the magnetic fabrics of the apparently undeformed bambui limestones are typical of very weakly deformed sediments in which the depositional compaction fabric has been partly overprinted by a tectonic one with minimum susceptibility direction remaining perpendicular to bedding this result is in agreement with the textures given by the petrographic observations

comparative assessment of three approaches for deriving stream power plots along long profiles in the upper hunter river catchment new south wales australia abstract the downstream distribution of stream power is derived and analysed for 11 different streams in the upper hunter river catchment australia stream long profiles were produced in a gis environment using dem data and catchment area discharge analysis these profiles were analysed using three approaches namely long profile smoothing curve fitting and a theoretical model the methodology for deriving stream power profiles using these three approaches is discussed the long profile smoothing method provides a good approximation of the subcatchment variability in stream power trends the curve fitting method shows that higher order exponential curves provide a better fit for long profile data for the streams of the upper hunter river catchment second order exponential curves fit well with significantly less error the curve fitting method predicts a bimodal upstream and midstream distribution of stream power which is a deviation from our earlier understanding of a single midstream peak the theoretical approach provides a mathematical expression of the observed bimodal stream power distribution the bimodal distribution emphasises the erosion potential of headwater reaches the resultant stream power distribution provides a catchment scale characterisation of the distribution of available energy in any given system using these approaches the variability of stream power in headwater reaches is explained by discharge variability while variability in midstream and downstream reaches is related to high variability in channel gradient

an approach for measuring confinement and assessing the influence of valley setting on river forms and processes valley setting and confinement or lack thereof are primary controls on river character and behaviour although there are various proxies for valley confinement direct measures that quantify the nature and extent of confinement are generally lacking and or inconsistently described as such they do not lend themselves to consistent analysis over large spatial scales here we clearly define forms of confinement to aid in quantification of degrees of confinement types of margin that can induce confinement are differentiated as a valley margin valley bottom margin and or anthropogenic margin such margins sometimes overlap and share the same location and in other situations are separated giving immediate clues as to the valley setting we apply this framework to examples from australia united states and new zealand showing how this framework can be applied across the spectrum of river diversity this method can help to inform interpretations of reach scale river behaviour highlighting the role of antecedent controls on contemporary forms and processes clear definitions of confinement are shown to support catchment scale analysis of river patterns along longitudinal profiles and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments e g process zone distribution lateral sediment inputs and dis connectivity copyright 2015 john wiley sons ltd

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

downstream variation in stream power abstract stream power has a significant influence on many form and process attributes of the fluvial system using a similar approach to that suggested by d m lawler in 1992 and 1995 a model is developed to explore how stream power might vary in the downstream direction based on the assumption that the longitudinal profile of the river has an exponential form no particular discharge is necessarily specified but near bankfull flows are regarded as significant morphologically and one such discharge is the focus here total stream power per unit channel length qs is predicted to peak at an intermediate location the position of which depends on the ratio b where b and are the downstream rates of change of discharge and slope respectively if b is a relatively conservative quantity then the form of the longitudinal profile and in particular its degree of concavity will have the major influence on the position of maximum stream power specific stream power w is even more sensitive to and is expected to peak closer to the headwaters about half way between source and the location of the stream power maximum although this will depend on how channel width w varies with distance from source the model is tested along three connected streams of different size in the catchment of the river trent taking advantage of a relationship between mean annual flood and link magnitude which enables this near bankfull discharge to be estimated at any point within the network the model is verified in so far as stream power does attain a mid basin maximum but the observed and predicted locations of the maxima do not always correspond largely because of the distinctive variation in discharge and especially slope along individual pathways for example maximum power lies far downstream along the trent because of the large increase in mid basin discharge associated with a series of large closely spaced tributaries the importance of slope is borne out by the near headwater locations for specific power maxima which tend to be further upstream than predicted along all three rivers as a result of the steepness of upper reaches the variety of geomorphic settings produces deviations from expectation which has implications for the movement and storage of material in the fluvial system

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

composite magnetic fabrics from s c mylonites magnetic anisotropy data are presented for samples of s c mylonites from a shear zone developed in the veiga granodiorite a late kinematic pluton located in the northern part of the iberian variscan belt spain the magnetic susceptibility is geometrically represented by an ellipsoid whose principal axes k 2 kint 1 kmi often show a one to one correlation with the principal directions x y and 2 f finite strain we report an exception to this rule since our results reflect composite magnetic fabrics arising from the contribution of both the c and s structures the magnetic foliation defined as the plane normal to k i shows an intermediate orientation between the c and s planes and rotates towards the orientation of the c planes as finite strain increases the magnetic lineation parallel to k and the stretching lineation present a similar trend but different values of plunge copyright 0 1996 elsevier science ltd

water slope and discharge in the amazon river estimated using the shuttle radar topography mission digital elevation model 1 we find that the standard deviation hence error of the water surface elevation data from the shuttle radar topography mission srtm is 5 51 m for basin wide regional and local amazon mainstem reaches this error implies a minimum reach length of 733km in order to calculate a reliable water surface slope resulting slopes are 1 92 0 19 cm km for manacapuru 2 86 0 24 cm km for itapeua and 3 20 0 34 cm km for tupe manning s equation is applied with these slopes and with channel width measurements from the global rain forest mapping project synthetic aperture radar mosaics grfm sar channel depths averaged from nautical charts and reasonable estimates of manning s n resulting discharge values are 84 800 m3 s at manacapuru 79 800 m3 s at itapeua and 62 900 m3 s at tupe averaged over the srtm mission period these values are within 6 2 at manacapuru 7 6 at itapeua and 0 3 at tupe of the in situ gage based estimates for the same or similar time period

spatiotemporal trends in erosion rates across a pronounced rainfall gradient examples from the southern central andes abstract the tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern central andes of northwestern argentina cause strong contrasts in elevation rainfall and surface process regimes the climatic gradient in this region ranges from the wet windward eastern flanks 2 m yr rainfall to progressively drier western basins and ranges 0 1 m yr bordering the arid altiplano puna plateau in this study we analyze the impact of spatiotemporal climatic gradients on surface erosion first we present 41 new catchment mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns second we re evaluate paleoclimatic records from the calchaquies basin 66 w 26 s a large intermontane basin bordered by high 4 5 km mountain ranges to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late pleistocene and holocene three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time 1 first order spatial patterns of erosion rates can be explained by a simple specific stream power ssp approach we explicitly account for discharge by routing high resolution satellite derived rainfall this is important as the steep climatic gradient results in a highly nonlinear relation between drainage area and discharge this relation indicates that erosion rates er scale with er ssp1 4 on cosmogenic nuclide time scales 2 we identify an intrinsic channel slope behavior in different climatic compartments channel slopes in dry areas 0 75 m yr with equal drainage areas thus compensating lower amounts of discharge with steeper slopes 3 erosion rates can vary by an order of magnitude between presently dry 0 05 mm yr and well defined late pleistocene humid 0 5 mm yr conditions within an intermontane basin overall we document a strong climatic impact on erosion rates and channel slopes we suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport which is primarily responsible for maintaining the balance between surface uplift erosion sediment routing and transient storage in the orogen

magnetic anisotropy in the trenton limestone results of a new technique anisotropy of anhysteretic susceptibility a new method for determining magnetic anisotropy using anhysteric remanence susceptibility is described the magnetic fabric of a collection of trenton limestone specimens has been determined using this method as well as by conventional anisotropy of magnetic susceptibility the results demonstrate the usefulness of the new method for finding the magnetic fabric of rock units such as the trenton in which the bulk magnetic susceptibilities are low a model is proposed to explain the observed foliated and lineated fabric as a consequence of overburden compaction and regional horizontal stresses the original fabric is inferred to have been isotropic the anisotropy resides in secondary magnetite of late paleozoic age it is argued that the observed magnetic fabric must therefore be alleghenian or younger in age our method has the potential to determine paleostress directions in carbonates elsewhere provided our assumptions are correct

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

spatial coincidence of rapid inferred erosion with young metamorphic massifs in the himalayas a spatially distributed rate of erosion index ei based on models of bedrock river incision documents a strong spatial correspondence between areas of high erosion potential and young metamorphic massifs as well as structural highs throughout the himalayas the ei is derived from slopes and drainage areas calculated from a hydrologically cor rected digital elevation model gtopo30 combined with precipitation data iiasa to generate synthetic annual stream discharges these variables drive three generalized pro cess models to produce ei maps that while differing in detail provide an internally con sistent spatially continuous index of large scale erosion rates the large spatial variation in potential erosion rates in the himalayas suggested by the ei patterns contrasts with the uniform convergence of the indian subcontinent if these ei gradients persist through time they support the emerging view of a positive feedback between localized rapid ero sion and upward advection of lower crust

spatio temporal variability in stream power distribution in the upper kosi river basin central himalaya controls and geomorphic implications abstract river processes in a drainage basin are strongly governed by the spatio temporal variability in stream power recently various approaches have been developed to derive the spatial variability of stream power in a river basin however the temporal variability in stream power due to hydrological changes remains poorly understood an assessment of the temporal variability of stream power is critical for river studies in monsoonal regimes because significant geomorphic work is performed during this period particularly in the himalayan rivers this paper presents a novel methodology to derive the stream power distribution at a basin scale using a physically based hydrological model the soil and water assessment tool swat hydrological changes in the upper kosi also called koshi basin in the central himalaya were analysed and integrated with slope variability and channel width to obtain the basin scale distribution of total stream power and specific stream power most of the tributaries of the kosi river are characterized by a multi peak distribution of stream power stream power distribution in the basin shows no systematic downstream increase or decrease of either total stream power or specific stream power total and specific stream power peaks during the monsoon period are 100 1500 times higher compared to the non monsoon period and exceed the threshold for erosion and sediment transport processes the swat model also helped to assess controls on the stream power distribution in the basin the downstream distribution of stream power between confluence points is influenced by slope variability while major increases at confluence points are due to discharge variability geological characteristics control the spatial distribution of stream power while the annual rainfall distribution influences the seasonal variability of stream power

composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics housen b a richter c and van der pluijm b a 1993 composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics tectonophysics 220 1 12 magnetic fabrics from rocks with multiple mineral preferred orientations may have anisotropy ellipsoids whose shape and orientation arise from the addition of two or more component fabrics our numerical models and experiments demonstrate that such composite magnetic fabrics do not directly reflect the shapes and or orientations of the individual mineral fabrics and we provide criteria for the recognition and interpretation of composite fabrics in natural rocks these criteria include 1 the orientation of the maximum susceptibility axis is located at the intersection of two planar fabrics and 2 the shape of the susceptibility ellipsoid changes from oblate to prolate and the degree of anisotropy decreases as the relative intensity of two planar component fabrics becomes equal and as the angle between the planar fabrics increases composite magnetic fabrics are observed in the shales and slates of the martinsburg formation lehigh gap pennsylvania modeling of the ams anisotropy of magnetic susceptibility and arma anhysteretic remanent magnetization anisotropy behavior constrains the relative degree of anisotropy of the bedding parallel and cleavage parallel fabrics in particular arma model results allow a good estimate of magnetite fabric strength we conclude that in the presence of composite magnetic fabrics quantitative measures of finite strain in deformed rocks are limited by the ability to accurately determine the degree of anisotropy and relative susceptibility of each component fabric such determinations require knowledge of the mineral s that are responsible for the measured magnetic fabric and their behavior during deformation

anisotropy of magnetic susceptibility as a strain gauge in the flamanville granite nw france the relationship between strain and anisotropy of magnetic susceptibility ams has been investigated in the carboniferous flamanville granite in the armorican massif nw france we measured the axial ratios of elliptical inclusions and the orientation of cleavage planes at eight sites around the granite margin measurements of ams were made on 73 specimens using a schonstedt spinner magnetometer ams measurements are shown to provide accurate predictions of cleavage and lineation direction even where these structures are difficult to measure in the field the strain and ams ellipsoids show similar regional variations in shape and intensity and a good correlation between the lengths of the principal axes finally our data are consistent with the hypothesis that the flamanville granite was syntectonically emplaced during the late stages of the hercynian orogeny

evaluating magnetic lineations ams in deformed rocks magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility kmax of the anisotropy of magnetic susceptibility ams tensor in deformed rocks magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones our ams determinations based on a variety of samples that were taken from mudstones slates and schists from the pyrenees and appalachians show that strain is not the only factor controlling the development of magnetic lineation we find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original ams tensor which in turn depends on the lithology and the deformation intensity rocks having a weak pre deformational fabric will develop magnetic lineations that more readily will track the tectonic extension

magnetic fabrics of diamagnetic rocks and the strain field associated with the dead sea fault northern israel in order to exploit the potential of ams axes k1 k2 k3 and magnitudes as a tool to estimate the strain field around major faults the ams of calcite bearing diamagnetic rocks that crop out next to the dead sea fault transform dsf were measured the calcite bearing bar kokhba limestone contains magnetic fabrics due mainly to the diamagnetic phase as indicated by the low iron content 130 ppm and strong negative susceptibilities of all the ams principal axes the magnetic fabrics are solely controlled by the alignment of c axes of almost pure calcite crystals and help to assess the strain fields prevailing post deposition and during the tectonic evolution of the dsf based on the ams measurements of 146 diamagnetic samples as well as 65 paramagnetic samples three groups of minimum k3 ams axes are defined 1 wnne plunging axis 2 wnwese axis and 3 weew axis the latter two groups of k3 axes are aligned sub parallel to neogene to pleistocene finite strain axes inferred from meso scale structures i e folds faults and veins next to the dsf this indicates that k3 axes of diamagnetic rocks can be excellent proxies for strain field directions around major faults differences in the degree of anisotropy p 0 up to w2 and in susceptibility difference dk up to w0 2 of the diamagnetic rocks are related to differences in strain magnitudes based on the proximity of the studied outcrops to the fault traces the values of these variables reflect the stored inelastic strain within the calcite matrix due to repeated faulting activity

channel planform geometry and slopes from freely available high spatial resolution imagery and dem fusion implications for channel width scalings erosion proxies and fluvial signatures in tectonically active landscapes article i nfo the rapid expansion of high spatial resolution optical sensors and imagery over the last decade presents ex ceptional opportunities for quantifying visible attributes of geomorphic systems in this study we detail a simple robust methodology changeom to extract continuous channel width and centerline datasets for single thread channels using freely available high spatial resolution imagery currently available in google earth and bing maps comparisons with a global dataset of field and lidar derived channel widths indicate minimal errors associated with the imagery and changeom methodology b1 overall while examples from the goriganga river indian himalaya and the yakima river wa usa emphasize the benefit of em pirical width values over established channel width scalings in deciphering fluvial responses to complex landscape forcings in tectonically active regions additionally accurate centerline delineation from the changeom methodology provides improved sinuosity measurements and when fused with coarse resolution digital elevation models dems removes along profile shortening and coincident increases in reach scale channel slope lastly comparisons of aster gdem v2 srtm v4 1 and lidar channel profiles extracted in moderate to high relief regions demonstrate the inferiority of the aster gdem for channel slope calcula tions despite the apparent spatial resolution advantages 9 the methodology presented here will facili tate new discoveries in the fluvial environment that have historically been difficult due to access and imagery resolution issues and provide greater perspective on channel signatures and responses to a host of landscape forcings especially in tectonically active bedrock and lower order drainage systems

pencil structure and strain in weakly deformed mudstone and siltstone abstract weakly deformed mudstone and siltstone middle ordovician knobs formation of the appalachian valley and ridge province south western virginia u s a show strain dependent transitions between bedding fissility pencil structure and cleavage pencil structures are associated with a bulk inhomogeneous shortening deformation where minimum principal strain z ranges between 9 and 26 shortening assuming a plane strain and constant volume where strains are less bedding fissility dominates pencil fragments are defined by intersecting fracture sets subparallel to the pre existing bedding fissility and cleavage their long axes are both parallel to the bedding cleavage intersection and to the inferred y axis of the tectonic strain ellipsoid pencil development is considered to result from fracturing along both fabric anisotropies during weathering and post tectonic stress relaxation pencils show variations in size and shape depending on lithology grain size and composition degree of initial clay preferred orientation degree of cleavage development type of cleavage total bulk strain and degree of strain homogeneity their shape l w however is a direct measure of total y z strain since strain determinations from chlorite pressure fringes on framboidal pyrite within the pencil fragments give y z 0 913 0 019 l w pencil structure is therefore a potential strain marker in weakly deformed rocks

plastic behavior of magnetite and high strains obtained from magnetic fabrics in the parry sound shear zone ontario grenville province abstract magnetic anisotropy and quantitative petrology of a transition from relatively undeformed metaanorthosite protolith to highly deformed ultramylonite in the parry sound shear zone provide information on magnetite as a kinematic indicator rock magnetic experiments show that anisotropy of magnetic susceptibility ams is controlled by magnetite in the mylonites and ultramylonites and by paramagnetic minerals hornblende biotite ilmenite in the protolith geothermometry in the ultramylonite indicates a temperature of 630 50 c during deformation a deformation mechanism map calculated from published experimental work for 630 c indicates that magnetite in the parry sound shear zone deformed plastically rather than via rigid body rotation the ams orientations accurately track a foliation trajectory in a portion of the shear zone which allows the utilization of orientation based strain models to determine shear strains shear strains of 1 9 were obtained and an empirical correlation of strain with the ellipsoid shape resulted in the logarithmic relationships mmax 0 15 ln x and mmin 0 13 ln z where mi ki kmean describes the principal ams axes or k max k min x z 0 14 these ams strain correlations were subsequently applied to mylonites and ultramylonites elsewhere in the shear zone predicting shear strains as high as 13 these observations also reveal that ams fabrics do not saturate at high strains as would be expected for rigid body rotation due to the plastic behavior of magnetite during deformation

differences between magnetic and mineral fabrics in low grade cleaved siliciclastic pelites a case study from the anglo brabant deformation belt belgium abstract theoretically within a given pelitic rock in which the main paramagnetic carriers are white mica and chlorite and in which judging from the ams parameters ams is controlled by the paramagnetic carriers the results of x ray pole figure goniometry should show a qualitative relationship with ams this idea is tested on single phase deformed low grade pelites of the lower palaeozoic brabant massif belgium representing the southeastern part of the anglo brabant deformation belt for the vast majority of the samples investigated the different lf ams parameters suggest a paramagnetic control on lf ams different parameters of lf ams measured at 77 k low t lf ams and a comparison of these with the lf ams parameters indicate that lf ams is controlled virtually entirely by paramagnetic carriers high field torque magnetometry hf ams indicates further that ams is controlled entirely by paramagnetic carriers for the vast majority of the samples two apparent discrepancies are observed however these are 1 a frequent mismatch between the lf ams fabric on the one hand and the paramagnetic fabric indicated by low t lf ams and hf ams on the other hand and 2 a rather common mismatch between the preferred orientation of chlorite and white mica suggested by x ray pole figure goniometry on the one hand and the lf ams fabric low t lf ams fabric and hf ams paramagnetic fabric on the other hand these apparent discrepancies may partly be attributed to the composite nature of both the lf ams fabric and the paramagnetic susceptibility fabric the presence of different populations of paramagnetic carriers possibly in combination with minor traces of ferromagnetic s l carriers which are not picked up by the methods applied may explain some of the mismatches observed and are compatible with the basin evolution history of the brabant massif in addition it is possible that the low temperatures low t lf ams and high fields hf ams are capable of enhancing one of the paramagnetic phases thus leading to discrepancies between methods that define the mineral and the magnetic fabrics the results of this study show that even when the lf ams data suggest that the lf ams of a given pelitic rock in which phyllosilicates form the main paramagnetic carriers is controlled entirely by paramagnetic carriers alternative methods such as phyllosilicate x ray pole figure goniometry will not necessarily reflect the paramagnetic carrier orientation although a number of cases have successfully correlated lf ams with mineral fabric and occasionally even strain this study serves as an example for how methods to define mineral and magnetic fabrics can be sensitive in detecting different paramagnetic phases

estimating critical stream power for bedload transport calculations in gravel bed rivers the physical basis of bagnold s equation for critical stream power is examined although the general approach is well founded the original equation can be criticised for 1 failing to distinguish between the grain size in transport and the grain size that represents bed roughness 2 requiring a knowledge of critical flow depth in addition to gross channel properties 3 failing to allow for hiding and protrusion effects on the mobility of mixed size stream beds more general equations are presented which overcome these limitations they require a knowledge of channel slope but not depth the analysis suggests that the presence of form resistance in addition to grain roughness does not affect the calculation of critical power critical power is expected to depend more sensitively on grain size between reaches than within reaches

magnetic fabrics and petrofabrics their orientation distributions and anisotropies abstract magnetic fabric and other petrofabric anisotropies may be described by second rank tensors represented by ellipsoids for a homogeneous petrofabric that is adequately sampled a stereoplot of the orientation distribution of the tensors principal axes maximum intermediate and minimum should show three orthogonal concentrations the concentrations form some combination of shapes from circular clusters through partial girdles to full girdles the concentrations elliptical eccentricities are constrained by the symmetry of the sample orientation distribution i e l l s l s etc as well as the individual sample anisotropies the mean orientations of principal axes must be orthogonal just as with individual sample tensors this requires tensor statistics for their calculation jelinek 1978 furthermore elliptical confidence cones for the means should parallel principal planes preserving overall orthorhombic symmetry however in practice sub orthorhombic symmetry may arise from unrepresentative sampling but it may also be a useful indicator of multiple or heterogeneous petrofabrics in the case of magnetic fabrics the wide range in average susceptibility values and variation in magnetic mineralogy permit small numbers of high susceptibility samples to deflect the orientation of the tensor mean away from the majority of samples normalizing the samples by their bulk susceptibility overcomes this but the orientation of high susceptibility outliers may signify an event or subfabric of importance that we should not discard therefore stereoplots of both normalized and non normalized orientation distributions should be compared preferably also identifying the outliers it is important to distinguish the shape of the orientation distribution ellipsoid from the shape of the individual magnetic fabric ellipsoids the qualitative l s nomenclature is best replaced by tj where tj 1 oblate tj 1 prolate jelinek 1981 invariably the orientation distribution is described by an ellipsoid whose shape is more spherical than that of the individual sample anisotropy ellipsoids because the latter have scattered orientations furthermore the shape of the orientation distribution ellipsoid need bear no relation to the shape of individual sample ellipsoid anisotropies the concepts are illustrated with 1119 measurements of anisotropy of magnetic susceptibility ams from seven areas and with 188 measurements of anisotropy of anhysteretic remanence aarm from two areas