magnetic susceptibility as a high resolution correlation tool and as a climatic proxy in paleozoic rocks merits and pitfalls examples from the devonian in belgium low field magnetic susceptibility in measurements are quick and sensitive enabling the creation of high resolution records making in an attractive correlation tool and a proxy for paleoclimate and paleoenvironments in geologically young material foremost in cenozoic sediments in belongs to the geoscientist s toolkit however in is a convolved signal and may reflect other processes than the often implicitly inferred depositional conditions diagenesis remagnetization and low grade metamorphism can potentially obscure the original depositional in signal this aspect is particularly important when interpreting in records from paleozoic rocks here we review data obtained from a large sample collection of middle to upper devonian sections in belgium comparison of in trends with paleoenvironmental indicators facies and with detrital input proxies zr th ti al allowed to assess the persistence of depositional trends furthermore the in signal was deconvolved into its dominant mineralogical contributions with the help of magnetic property analysis the main results are pointing to a magnetic signal dominated by fine grained magnetite of which paleomagnetic analysis indicated a formation during carboniferous remagnetization this prompts a potentially strong influence of post depositional processes and it complicates the interpretation of in records in terms of depositional environments however in most of the sections there is a relatively good relationship between in trends and facies evolution and between in and geochemical proxies for detrital inputs this indicates that the newly formed magnetite grains would at least partly remain where they are formed and this allows a relative preservation of the original signal despite the strong influence of diagenesis two sections show a stronger impact of diagenesis where for about half of these sections the primary depositional information is lost the eifelian givetian monts de baileux section was selected for time series analysis of the in series the average spectral misfit asm method is applied to explicitly evaluate the null hypothesis of no orbital signal and in this section there is 99 05 chance that the ms signal is reflecting an orbital imprint

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

magnetostratigraphy susceptibility of the přidolian lochkovian silurian devonian gssp klonk czech republic and a coeval sequence in anti atlas morocco abstract the magnetosusceptibility event and cyclostratigraphy msec record for the p idolian lochkovian silurian devonian global boundary stratotype section and point gssp klonk prague basin czech republic is described and used to establish a magnetostratigraphy susceptibility profile for the gssp gssp msec data are summarized into three magnetozones msz the tma msz late p idolian with 13 msszs mssz the klonk msz latest p idolian and earliest lochkovian with 17 msszs and the voskop msz early lochkovian with 7 msszs the base of klonk mssz 2 is coincident with the base of lochkovian and the devonian the proposed magnetostratotype for the p idolian lochkovian boundary is supported by ms data from a nearby core through the gssp sequence and into the upper ludlow three additional mszs are recognized for the portion of the core sequence older than the gssp boundary sequence the extension of the mszs and msszs away from the proposed magnetostratotype is tested by comparison with a lochkovian sequence in the western sahara of southeastern morocco mszs are the result of global sea level fluctuations that alter base level and the pattern of erosion and influx of detrital paramagnetic mineral components into the marine environment large scale transgressive and regressive patterns interpreted from the msec data establish that the silurian devonian boundary in the barrandian region falls between a short lived transgressive pulse in the latest p idolian and an equally short lived regressive pulse in the earliest lochkovian msszs identified in the gssp and core sequences are the result of variation in climate cycles and the resulting periodicity can explained by either the 38 9 ka silurian and devonian equivalent of the modern 54 ka obliquity cycle or the eccentricity cycle of 106 ka periodicity use of the obliquity periodicity gives a duration for the barrandian lochkovian of 4 46 ma which agrees with the most recent geochronometric estimate of 4 5 ma for the lochkovian use of the eccentricity periodicity gives a duration for the barrandian lochkovian of 12 16 ma which agrees with the previous geochronometric estimates of 12 2 and 12 5 ma for the lochkovian in any case the cyclic nature of the msec data established by the msszs can be explained by variations in the rate of supply of weathered terrigenous paramagnetic grains to the marine system these variations in supply occurred due to climate changes resulting from the either the obliquity or eccentricity of the earth s orbit knowledge of the periodicity of lochkovian cycles in the barrandian area allows estimation of the rates of sediment accumulation the duration of fossil ranges and the rates of evolution depending on the choice of obliquity or eccentricity to explain the cyclicity in the barrandian lochkovian the estimated rate of sediment accumulation in the gssp outcrop averaged either 51 or 140 ka m the range of the graptoloid monograptus uniformis angustidens wholly contained within the lochkovian sequence at the gssp is also estimated at either 51 or 140 ka

widespread chemical remagnetization orogenic fluids or burial diagenesis of clays paleomagnetic rock magnetic and geochemical results from mesozoic carbonates in the vocontian trough in southeast france support a hypothesized acquisition of a chemical remanent magnetization crm during burial diagenesis of smectite and are inconsistent with an orogenic fluid remagnetization mechanism the geographic and vertical distribution of a widespread crm which resides in magnetite is parallel to the degree of burial diagenesis of clays the crm is absent only where there is no evidence for clay diagenesis the crm is poorly developed where significant smectite is still present and is well developed with higher natural and anhysteretic remanent intensities where smectite has completely altered to illite strontium isotope results do not support alteration by orogenic type fluids a commonly invoked mechanism for similar crms the results suggest that the burial diagenesis of clays is a viable remagnetization mechanism for limestones in the vocontian trough

removal of artifact depressions from digital elevation models towards a minimum impact approach artifact depressions in digital elevation models dems interrupt flow paths and alter drainage directions techniques for removing depressions should enforce continuous flow paths in a way that requires the least modification of the dem impacts on the spatial and statistical distributions of elevation and its derivatives were assessed for four methods of removing depressions 1 filling 2 breaching 3 a combination of filling and breaching with breaching constrained to a maximum of two grid cells 4 a combination of filling and breaching based on an impact reduction approach ira the ira removes each depression using either filling or breaching depending on which method has the least impact in terms of the number of modified cells and the mean absolute difference in the dem analysis of a lidar dem of a landscape on the canadian shield showed significant differences in the impacts among the four depression removal methods depression filling a removal method that is widely implemented in geographical information system software was found to impact terrain attributes most severely constrained breaching which relies heavily on filling for larger depressions also performed poorly both depression breaching and the ira impacted spatial and statistical distributions of terrain attributes less than depression filling and constrained breaching the most sensitive landscapes to depression removal were those that contained large i e 10 flat areas because of the occurrence of relatively large depressions in these areas copyright 2005 john wiley sons ltd

kaolinite and dickite formation during shale diagenesis isotopic data abstract x ray diffraction scanning electron microscopy and o isotope geochemistry have been used to investigate the origin and possible controls on polymorphic transformation of kaolin minerals filling veins in cretaceous shales from the gibraltar strait area southern spain the mineralogy of the enclosing shales indicates that kaolin minerals formed from smectite dissolution a process that silmultaneously originated i s mixed layers and quartz kaolinite and dickite 18o values suggest that an increase in the water isotopic composition from cretaceous sea water values 1 to values of about 3 occurred parallel to smectite dissolution the intensity of this process being the main factor controlling the isotopic composition of kaolin minerals the minimum formation temperature ranges from 62 c for kaolinite to 86 96 c for dickite indicating that the depth of burial was the main control on polymorph formation this temperature range agrees with that deduced for illite smectite ordering the passage from kaolinite to dickite rich veins was accompanied as deduced from sem examination by a morphologic evolution characterized by the division of large vermiculae dominant in kaolinite samples and the formation of short stacks and platy crystals which are predominant in dickite the mechanism of dickite formation however remains uncertain

stress and flow beneath island arcs summary the flow pattern stress distribution topography and gravity anomalies were computed from numerical models having density and viscosity distributions resemblant to the aleutian arc the results were compatible with the hypothesis that the excess density of the slab drives its descent and that hydrodynamic forces are responsible for topographic and gravity highs over the outer rise seaward of the trench and the frontal arc and lows over the trench in models with simple distributions of rheological parameters the force from the slab was transmitted directly upward producing a negative gravity anomaly over the arc material with low resistance to flow was needed along the fault plane above the slab or within the crust of the frontal arc and within the wedge of asthenosphere above the slab to reduce that force and to allow the horizontal lithosphere to move with the slab models with the resistance to flow thus reduced had outer rises deep trenches horizontal tension seaward of the trench horizontal compression under the trench and downdip tension in the slab free air gravity anomalies which are the sum of between deflections of the free surface due to hydrodynamic forces and direct attractions from the masses driving the flow were not fit excellently by any of the models in part because the coarse grid used precluded accurate representation of the fault zone above the slab and the frontal arc an alternate to the hypothesis that about 5 kb of stress on the fault plane is needed to produce an outer rise is offered by these models shear stress between the slab and the island arc was always below 700 bars in the more successful models if the density distribution was scaled to match the topography of the trench this is much less than the 2000 bars stresses needed if frictional heating causes island arc volcanism

mineralogic and climatic interpretations of the luochuan loess section china based on diffuse reflectance spectrophotometry we examined the top 135 m that is the entire pleistocene of the classic luochuan section on the chinese loess plateau with a diffuse reflectance spectrophotometer from the near ultraviolet through the visible and into the near infrared from the reflectance data we calculated sample brightness which with some caveats is a reasonable proxy for magnetic susceptibility mineralogic changes were identified by factor analyzing the first derivative of the percent reflectance data and examining samples with high factor scores two factors which explain about 96 of the cumulative variance are distinguished by the relative proportion of hematite and goethite the minerals that are responsible for the color changes in the loess sequence both hematite and goethite are present in both loess and paleosol but goethite dominates in loess whereas hematite dominates in paleosol the goethite factor exhibits an inverse correlation with magnetic susceptibility the hematite factor exhibits a weak positive correlation with susceptibility paleoclimatic interpretations are drawn from comparison of susceptibility to the concentration of spectrally identified hematite based on this comparison paleosols in the early pleistocene wucheng formation are characterized by conditions that are drier than today a dry summer monsoon whereas later pleistocene paleosols are characterized by a wet summer monsoon

cross basin variations in magnetic susceptibility influenced by changing sea level paleogeography and paleoclimate upper devonian western canada sedimentary basin abstract upper devonian rocks in western canada were deposited as carbonate platform and surrounding slope and basinal rocks during a second order sea level cycle characterized by long term climatic warming that ended with cooling associated with the frasnian famennian mass extinction event in this contribution we assess the hypothesis that high resolution magnetic susceptibility ms data records cross basin variations that are intimately tied to sea level and associated climatic change the depositional environment and the paleogeographic location of siliciclastic sediment sources four main trends are apparent in the ms data 1 the magnitude of the ms signature increases from west to east across western canada 2 platform facies generally have low ms signatures compared with off platform facies 3 the overall ms signature increases and then decreases throughout the stratigraphic profile largely in response to changes in depositional setting i e item 2 4 ms is generally high during third and fourth order sea level lowstand and early transgression and lower during late transgression and highstand during the late middle givetian to early late frasnian devonian siliciclastic sediments silt and fine sand size sourced from the west alberta arch and peace river arch contributed to relatively high ms signatures in facies deposited proximal to these source areas other important detrital sediment sources were the ellesmerian orogenic belt in northern canada and the laurussian continental landmass to the east these latter sources supplied fine grained sediments that were dispersed basinwide and resulted in a nearly order of magnitude increase in ms values to the east this trend and fine grain size implies that some detrital sediment was delivered from the east as eolian dust from the old red continent by the early frasnian the west alberta arch was submerged and by middle to late frasnian time the peace river arch was largely covered during the late middle frasnian a pronounced rise in ms signatures can be tied directly to deposition of the clay and locally silt rich mount hawk formation during the late middle to late frasnian carbonate ramp facies prograded from east to west resulting in seaward migration of the shoreline and increased siliciclastic input to the ramp slope that influenced the pronounced increase in ms signatures to the east by the late frasnian cross basin ms profiles record uniformly low susceptibilities indicating that high ms siliciclastic detritus was either bypassed seaward was swamped by carbonate input or was dominated by diamagnetic quartz individual ms events can be accurately correlated across much of the basin at a resolution that is higher than single conodont zones despite the local influences on variability of the signature variations in the ms signature can thus be explained partly by depositional environment platforms with low ms basins with higher ms and partly by third and fourth order sea level and associated climatic changes fourth order changes in sea level are routinely interpreted to result from variations in paleoclimate in the milankovitch band and recent work indicates that third order sea level changes may be linked to longer term modulation of milankovitch band orbital variations the increase in ms during prolonged frasnian warming thus appears to be directly linked to paleoclimatic change and comparison of the ms signature with more direct measures like oxygen isotopes would serve as a test of its utility as a paleoclimate proxy

bacterial mediation red matrices diagenesis devonian montagne noire southern france abstract two devonian red carbonate rock sections are studied in the montagne noire at coumiac frasnian famennian and at the pic de vissou eifelian givetian the sediments are grey red mudstones and wackestones rich in pelagic fossils they are characteristic of an outer ramp the coumiac sequence is condensed with numerous hardgrounds and hiatuses the pic de vissou succession is more complete and of shallower origin in both cases the origin of the red coloration of the micritic matrix is probably linked to bacterial activity which produced submicronic hematite both iron and manganese concentrations are low average 0 2 bacteria form ferruginous microstromatolites blisters microtufts hedgehogs filling sponge perforations and thin continuous mineralized films probably biofilms hardgrounds are underlined by ferruginous microstromatolites the origin of the matrix color is probably related to the destruction of these bacterial constructions the submicronic hematite ultimately coating the crystal faces of the calcite mosaic during early lithification microfissures appeared and were invaded by microbial colonies scanning electron microscopy sem shows that these colonies are composed of spheroidal beads this suggests continuity of the bacterial activity during early diagenesis later on these early fissures were cut by burrows subsequently a secondary fissure network transected all the previously mentioned sedimentary structures this late fissure network is characterized by diagenetically remobilized hematite and or calcite the latest alterations are stylolites and ultimate tectonic fractures

height above the nearest drainage a hydrologically relevant new terrain model summary this paper introduces a new terrain model named hand and reports on the calibration and validation of landscape classes representing soil environments in amazonia which were derived using it the hand model normalizes topography according to the local relative heights found along the drainage network and in this way presents the topology of the relative soil gravitational potentials or local draining potentials the hand model has been demonstrated to show a high correlation with the depth of the water table providing an accurate spatial representation of soil water environments normalized draining potentials can be classified according to the relative vertical flowpath distances to the nearest drainages defining classes of soil water environments these classes have been shown to be comparable and have verifiable and reproducible hydrological significance across the studied catchment and for surrounding ungauged catchments the robust validation of this model over an area of 18 000 km2 in the lower rio negro catchment has demonstrated its capacity to map expansive environments using only remotely acquired topography data as inputs the classified hand model has also preliminarily demonstrated robustness when applied to ungauged catchments elsewhere with contrasting geologies geomorphologies and soil types the hand model and the derived soil water maps can help to advance physically based hydrological models and be applied to a host of disciplines that focus on soil moisture and ground water dynamics as an original assessment of soil water in the landscape the hand model explores the synergy between digital topography data and terrain modeling presenting an opportunity for solving many difficult problems in hydrology

diagenetic versus detrital origin of the magnetic susceptibility variations in some carbonate frasnian famennian boundary sections from northern africa and western europe implications for paleoenvironmental reconstructions to provide a new insight into the diagenetic versus detrital origin of the magnetic susceptibility variations in ancient carbonate sequences a study was conducted within four frasnian famennian platform carbonate sections from germany france and morocco the study includes along section magnetic susceptibility and carbonate content measurements complemented by analyses of magnetic hysteresis parameters inorganic geochemistry and clay mineralogy our results show that the magnetic susceptibility evolution is dominantly controlled by the variations in the concentration of low coercivity ferromagnetic magnetite grains and to a lesser extent of paramagnetic clays in more detail hysteresis ratios suggest the coexistence of two magnetite populations with significantly different grain size 1 a dominantly coarse grained detrital fraction including a mixture of multi domain and single domain particles 2 an authigenic fine grained fraction composed of a mixture of single domain and superparamagnetic particles despite a diagenetic imprint on the clay assemblages no relationship is established between magnetic susceptibility and illite crystallinity therefore discarding a noticeable distortion of primary within section magnetic susceptibility evolution the overall inherited character of the magnetic susceptibility fluctuations is corroborated by a significant correlation of magnetic susceptibility with terrigenous proxies zr th the poorer correlation of magnetic susceptibility with the fe content is consistent with the existence of a very fine grained authigenic magnetite component that possibly induces a global magnetic susceptibility increase at the section scale but no distortion of the within section evolution the magnetic susceptibility curves presented here provide a general record of climate driven detrital influx and carbonate productivity through frasnian lower famennian times

a new triangular multiple flow direction algorithm for computing upslope areas from gridded digital elevation models 1 gridded digital elevation data often referred to as dems are one of the most widely available forms of environmental data topographic analysis of dems can take many forms but in hydrologic and geomorphologic applications it is typically used as a surrogate for the spatial variation of hydrological conditions topographic indices and flow routing here we report on a new flow routing algorithm and compare it to three common classes of algorithms currently in widespread use the advantage of the new algorithm is that unrealistic dispersion on planar or concave hillslopes is avoided whereas multiple flow directions are allowed on convex hillslopes we suggest that this new triangular multiple flow direction algorithm md1 is more appropriate for a range of flow routing and topographic index applications

magnetization carriers of grey to red deep water limestones in the gssp of the givetian frasnian boundary puech de la suque france signals influenced by moderate diagenetic overprinting limestones at the puech de la suque global boundary stratotype section and point gssp of the givetian frasnian boundary show a drastic change towards much higher magnetic susceptibility values in the givetian rocks different rock magnetic parameters indicate that ferromagnetic minerals are the main controlling factor the ferromagnetic fraction is composed of low magnetite type and high coercivity hematite and goethite phases confirmed by the spectral reflectance high coercivity minerals are fluctuating along the section with a higher abundance in the basal frasnian these phases may be of secondary origin and produced during burial stage the magnetite type phase contains two different grain size populations the identified that stable single domain superparamagnetic ssd sp particles are of diagenetic origin and their amount decreases slightly upwards a second group of magnetite grains correspond to coarse grained particles identified using the squareness v coercive force plot it is tentatively suggested here that these particles present throughout the section are of primary origin on the contrary the paramagnetic minerals underwent a clear diagenetic overprinting and may represent secondary minerals the presence of a primary ferromagnetic carrier allowed the use of spectral analyses leading to the detection of spectral peaks at 1 25 and 4 cycles m which can be interpreted as the result of 405 kyr and 100 kyr eccentricity forcing respectively

carving and adaptive drainage enforcement of grid digital elevation models 1 an effective and widely used method for removing spurious pits in digital elevation models consists of filling them until they overflow however this method sometimes creates large flat regions which in turn pose a problem for the determination of accurate flow directions in this study we propose to suppress each pit by creating a descending path from it to the nearest point having a lower elevation value this is achieved by carving i e lowering the terrain elevations along the detected path carving paths are identified through a flooding simulation starting from the river outlets the proposed approach allows for adaptive drainage enforcement whereby river networks coming from other data sources are imposed to the digital elevation model only in places where the automatic river network extraction deviates substantially from the known networks an improvement to methods for routing flow over flat regions is also introduced detailed results are presented over test areas of the danube basin

a climate driven model and development of a floating point time scale for the entire middle devonian givetian stage a test using magnetostratigraphy susceptibility as a climate proxy abstract here we propose an approach to establish a preliminary age chronology for complete stages within the phanerozoic by applying cyclostratigraphic methods that employ high resolution data sets this requires use of geochemical or geophysical data known to serve as a cyclic climate proxy to demonstrate the method we use the magnetostratigraphic susceptibility technique as the basis for fitting a climate model to the givetian stage of the middle devonian system we show a milankovitch eccentricity climate zonation for the givetian that is pinned to time series analyses from outcrop samples from its upper givetian frasnian france and lower eifelian givetian morocco stage boundaries using these data sets we construct a uniform cyclicity model designed to conform to a 405 kyr cyclicity with a duration corresponding to the published duration for the givetian of 4 4 myr kaufmann 2006 to this model we fit two well established conodont zonation schemes thus allowing time estimates for conodont ranges for the givetian indicating a range from 1 8 myr to 100 kyr before extinction of an individual conodont species we then test and adjust the model using independent data sets from the eastern united states adjustments to the initial model yield a duration of 28 climate half cycles zones for the givetian stage and an increased age to 5 6 myr these zones allow high correlation among sections to better resolve timing of major bio events and provide a floating point time scale to which absolute ages can be applied

quantitative reassessment of brick red lutites evidence from reflectance spectrophotometry abstract brick red lutites are distinctive bright red sediments deposited in the western north atlantic these unique sediments were derived from permo carboniferous outcrops in the canadian maritime provinces transported out the gulf of st lawrence through the cabot straits and redistributed by the western boundary undercurrent along the north american continental margin in this study we used fourteen cores taken off eastern north america to more precisely examine the input and depositional history of brick red lutites our study differs from previous studies in the manner in which the red sediment was identified unlike previous studies which used color charts to assess the presence of brick red lutites we used visible light reflectance spectrophotometry the primary mineral imparting a red color to brick red lutites is hematite experiments with known quantities of hematite in a matrix mineralogically similar to western north atlantic sediment indicate that the presence of hematite can be detected at weight percentages of less than 0 1 using spectral reflectance data we characterized the distribution of brick red lutites for two broadly defined time levels latest glacial and early holocene as expected the maximum input of brick red lutite was during late glacial time and input decreased reaching a minimum during the early holocene since the early holocene there has been little change in the distribution of this unique red sediment on the north american margin however our reflectance spectra indicate renewed accumulation of hematite rich sediment at the present time in the cabot straits

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

drainage networks from grid digital elevation models current algorithms that deduce the drainage network from a digital elevation model dem represented by a regular array of surface elevations share a fault unless the terrain is rugged the derived water channels tend to flow in parallel lines along preferred directions engendered by the sampling grid orientation we present a simple solution to the problem a second difficulty is the presence of noise that creates artificial pits we briefly describe a method which deals with pits in what we believe to be a more efficient manner for virtual memory environments than previous efforts our system has treated dems of nearly 9 000 000 pixels we show how depth first search of the resulting drainage network permits segmentation of the dem into basins by various criteria analysis of stream sediment anomaly dilution profiles improved hydrological models and other applications

stratigraphy of the middle devonian boundary formal definition of the susceptibility magnetostratotype in germany with comparisons to sections in the czech republic morocco and spain abstract one major difficulty in geology is high resolution correlation among widely separated sections especially in the paleozoic where magnetostratigraphy polarity is not well established because rocks are often remagnetized where critical biostratigraphic zonation may be poor or lacking or where structural complexities make correlations very difficult to address this problem we have been using magnetostratigraphy susceptibility measurements here we report our work from the middle devonian in europe and north africa the middle devonian emsian eifelian global boundary stratotype section and point gssp located in the eifel hills western germany was ratified by the international subcommission on stratigraphy in 1985 after careful evaluation of the biostratigraphy for this and many other sections the boundary interval has been characterized using biostratigraphy and the beginning of the eifelian stage has been specifically defined by the first occurrence of the conodont polygnathus costatus partitus we have collected the eifel hills section for magnetic susceptibility ms measurement and here we establish it as the magnetostratotype for the emsian eifelian stage boundary by formally defining the magnetostratigraphy susceptibility for the section we then collected measured and compared the magnetostratotype to four other sections for which conodont biostratigraphy has been studied and where p costatus partitus is present two emsian eifelian sections in morocco and two sections in the czech republic including the emsian eifelian parastratotype finally we have measured the ms for the el puerto creek section in the cantabrian mountains of spain and identified the location of the emsian eifelian boundary within the section based on ms comparison to the gssp in conjunction with excellent biostratigraphic indicators primarily brachiopods while the conodont zonation in the el puerto creek section is poorly defined we believe that the correspondence between the ms and biostratigraphy in the section allows the identification of the emsian eifelian boundary these results indicate that this method can be successfully applied to marine sequences where ambiguities in correlation exist

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

paleosecular variation of brunhes age lava flows from british columbia canada 1 brunhes age lava flows have been sampled for paleosecular variation studies from several volcanic fields of southern british columbia silverthrone garibaldi lake mt meager clearwater wells gray park and kelowna area a total of 52 lava flows were sampled and 7 to 10 samples were drilled at each site previous radiometric studies indicate that the ages of these lava flows range from 2 3 to 760 ka stepwise thermal demagnetization 14 to 21 steps was carried out for all the samples in each site and af demagnetization was performed on one sample per site forty five sites were selected based on rigorous criteria 95 5 to calculate a mean direction d 356 9 i 70 2 95 2 8 that is statistically indistinguishable from the direction of the dipole field at the area i 68 3 virtual geomagnetic poles vgps do not show the far sided effect and the angular standard deviation is 17 5 a value in agreement with the paleomagnetic field dispersion for that latitude these high quality results are expected to improve the time averaged field taf and secular variation models

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

hand a new terrain descriptor using srtm dem mapping terra firme rainforest environments in amazonia optical imagery can reveal spectral properties of forest canopy which rarely allows for finding accurate correspondence of canopy features with soils and hydrology in amazonia non floodable swampy forests can not be easily distinguished from non floodable terra firme forests using just bidimensional spectral data accurate topographic data are required for the understanding of land surface processes at finer scales topographic detail has now become available with the shuttle radar topographic mission srtm data this new digital elevation model dem shows the feature rich relief of lowland rain forests adding to the ability to map rain forest environments through many quantitative terrain descriptors in this paper we report on the development of a new quantitative topographic algorithm called hand height above the nearest drainage based on srtm dem data we tested the hand descriptor for a groundwater topographic and vegetation dataset from central amazonia the application of the hand descriptor in terrain classification revealed strong correlation between soil water conditions like classes of water table depth and topography this correlation obeys the physical principle of soil draining potential or relative vertical distance to drainage which can be detected remotely through the topography of the vegetation canopy found in the srtm dem data

path based methods for the determination of nondispersive drainage directions in grid based digital elevation models 1 path based methods for the determination of nondispersive drainage directions in grid based digital elevation models are presented these methods extend the descriptive capabilities of the classical d8 method by cumulating the deviations between selected and theoretical drainage directions along the drainage paths it is shown that either angular or transversal deviations can be employed accordingly two classes of methods designated d8 lad eight drainage directions least angular deviation and d8 ltd eight drainage directions least transversal deviation are developed detailed tests on four synthetic drainage systems of known geometry and on the liro catchment central italian alps indicate that the proposed methods provide significant improvement over the d8 method for the determination of drainage directions and drainage areas