soil development of three chernozem like profiles from north bulgaria revealed by magnetic studies abstract a detailed magnetic study of three soil profiles of calcic chernozem luvic phaeozem and orthic luvisol described in the soil atlas of bulgaria was carried out in order to reveal the potential of magnetic methods for characterization of soil forming processes and properties of pedogenic iron oxides thermomagnetic analysis of susceptibility and sem edx observations revealed that the main pedogenic mineral in all three soils is fine grained superparamagnetic to single domain maghemite thermal stability of this pedogenic phase up to temperatures of 500 c is revealed by the partial thermomagnetic analyses of susceptibility depth variations of magnetic parameters and ratios point to the presence of stable single domain to pseudo single domain grains in humic horizons the quantity of which decreases sharply towards lower soil horizons these magnetic grain size changes are best expressed in orthic luvisol and reflect intensified processes of translocation of substances downward

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

the impact of redox conditions on the rare earth element signature of redoximorphic features in a soil sequence developed from limestone abstract redox processes which are widespread in soils need to be quantified for an improved comprehension of the dynamics of fe and mn oxides and their associated trace elements the classical methodology used to study these redox processes generally relies on the quantification of all mineral species in the various pedological features that can be related to different redox stages however this approach usually encounters the difficulty of precisely quantifying the different forms of poorly crystallised fe and mn oxides in this study we use the signature of rare earth elements rees to visualise and eventually quantify the importance of redox processes in soils our approach relies on that developed by laveuf et al 2008 and the idea that the relative contribution to the mobilisation of rees that is made by the primary minerals reactive to redox conditions depends on the following factors i their initial proportion in the different pedological features that can be related to various redox processes ii their relative mobilisation during the redox process in question and iii their initial ree signatures the catena studied is characterised by two stages of redox conditions the first is related to the formation and subsequent dissolution of fe mn concretions and the second is related to the bleaching of the soil matrix due to morphological degradation in this soil the main minerals reactive to redox conditions are mn oxides ferrihydrite goethite and fluor apatite the results indicate that the primary redox conditions can be characterised by a positive ce anomaly on the ree pattern which has been attributed to a preferential immobilisation of this element due to its association with mn oxides the results also indicate that the secondary redox conditions can be characterised by depletion in medium rees mrees in the ree pattern which has been attributed to a preferential release of these elements during the dissolution of fluor apatite and to a lesser extent of ferrihydrite these results emphasise the potential of ree signatures of the visualisation of the various redox processes that have been active in a soil additionally ree signatures are a proxy of the frequency and intensity of the redox conditions

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

magnetite weathering in a vertisol with seasonal redox dynamics abstract we investigated soil samples from a vertisol in a flat lying flood plain in the savannah woodland of southern mali which is characterized by a water regime governed by regularly occurring wet and dry seasons the soil was subdivided into four horizons which differed in the content and speciation of the redox sensitive elements and in the length of waterlogging magnetically the profile could be subdivided into two parts the magnetic susceptibility the hysteresis parameters m r m s and b c as well as the coercivity of remanence b cr indicate that the upper two horizons differed from the lower two horizons by a higher content of magnetite and a larger contribution of multi domain size magnetite grains as compared to single domain size grains a comparison of the chemical and magnetic data suggests that dissolution of magnetite in our soil is driven by a seasonal change between anoxic and oxic conditions

environmental magnetic study of a xeralf chronosequence in northwestern spain indications for pedogenesis article i nfo magnetic enhancement of a and b horizons during soil development is a common phenomenon to better understand the exact mechanism for the magnetic enhancement especially the mineral transformation pathways systematic rock magnetic studies were conducted on a xeralf chronosequence in northwestern spain a positive correlation was found between the average grain size and the concentration of pedogenic maghemite particles with the exception of some a horizons in which multiple factors seem to influence the nature and concentration of neoformed ferrimagnets it is argued that the interaction between the positively charged iron oxides and the anionic ligands present in the solution of these acidic soils plays an important role in this respect the time trends of the average grain size of pedogenic ferrimagnets and the strong correlation between the concentrations of hematite and maghemite in the magnetically enhanced horizons a and b are consistent with the hypothesis of a gradual formation of maghemite later converted into hematite via a precursor most likely ferrihydrite therefore this study provides strong evidence for the dynamic evolution of magnetic minerals upon pedogenesis

late miocene to early pliocene vegetation of southern europe 7 4ma as reflected in the megafossil plant record abstract assemblages of plant megafossils from the late miocene to early pliocene sites in southern europe have been re evaluated in order to get data for reconstructing the development of vegetation and climate during this time interval 7 4 ma main areas of the survey are centred in greece and adjacent countries italy southern france and spain as a product of this study maps of the studied area for the late miocene have been produced showing main physiognomic features of the forests expressed in the proportions of broad leaved deciduous broad leaved evergreen legume type and sclerophyllous components respectively

evolution of the lower gangetic plain landforms and soils in west bengal india abstract three major landforms uplands old fluvial deltaic plains and young fluvial plains are identified from the lower gangetic plains of west bengal india on the basis of remote sensing and field studies morphologic quantitative and thermoluminescence studies of soils of the study area have been conducted two types of uplands are recognised upland in the west overlain by red soils autochthonous and allochthonous types and upland in the north barind tract characterised by three topographic levels aspects of the autochthonous upland red soils lower to middle pleistocene age show the ferrugination ferrisol phase of development soils of the old fluvial deltaic plains 6 3 ka and lower level of the barind tract have argillic horizons and exhibit the fersiallitisation phase of development development of ferrugination and fersiallitisation phases was favored due to the pre weathered nature of the parent material soils of the old fluvial deltaic plains barind tract lower level and young fluvial plains show effects of hydromorphism due to waterlogging in the form of segregations of fe mn oxides gleying and chloritisation probably due to ferrolysis in the upper horizons of some of these soils neotectonics seems to have affected development of landforms and soils significantly due to reactivation of some basement faults in the western region some tectonic blocks subsided causing transgression during the early pleistocene and at ca 7 ka subsequent uplift of these blocks caused regressions and development of soils on the exposed landscapes episodic uplift of the barind tract in the northern region may have given rise to three topographic levels some faults confine the courses of the damodar ganga and bhagirathi rivers

magnetic minerals in calcic luvisols chromic developed in a warm mediterranean region of spain origin and paleoenvironmental significance abstract soil formation under aerobic conditions usually enhances magnetic signals mainly through neoformation of sub micron magnetite and or maghemite in order to better understand the nature and magnitude of the enhancement in this work we characterized the iron fe oxides and magnetic properties of two calcic luvisols chromic developed on calcareous orthoquartzites in a spanish region with a warm mediterranean climate weathering of the fe bearing minerals in the parent material mostly fe rich smectite had resulted in the neoformation of hematite and maghemite rather than goethite thus causing a substantial increase in magnetic susceptibility saturation magnetization m s and other magnetic signals the absolute frequency dependent magnetic susceptibility fd which is a typical proxy for the concentration of sub micron superparamagnetic pedogenic maghemite was strongly correlated with the concentration of hematite hm the estimated percent frequency dependent magnetic susceptibility fd was 15 7 this and various other magnetic indicators indicate that the grain size distribution gsd of the pedogenic maghemite is narrower around the superparamagnetic single domain threshold than is that of maghemite in soils and paleosols developed under other temperate climates e g the chinese loesss plateau where fd fd ratio fd the hematite goethite ratio and several indicators of the degree of weathering provides a better tool for paleoclimatic reconstructions than does the current use of alone

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

magnetic mineralogy of soils across the russian steppe climatic dependence of pedogenic magnetite formation formation of ferrimagnets in well drained buffered unpolluted soils appears to be related to climate and especially rainfall if robust this magnetism rainfall couple can be used to estimate past rainfall from buried soils particularly the multiple soils of the quaternary loess soil sequences of central asia however dispute exists regarding the role of climate vs dust flux for the magnetic properties of modern loessic soils here we examine the mineralogical basis of the magnetism rainfall link for a climate transect across the loess mantled russian steppe where critically dust accumulation is minimal at the present day magnetic and independent mineralogical analyses identify in situ formation of ferrimagnets in these grassland soils increased ferrimagnetic concentrations are associated with higher annual rainfall xrd and electron microscopy show the soil formed ferrimagnets are ultrafine grained 50 nm and pure ferrimagnetic contributions to ma ssbauer spectra range from 17 in the parent loess to 42 for a subsoil sample from the highest rainfall area total iron content varies little but the systematic magnetic increases are accompanied by decreased fe2 content reflecting increased silicate weathering for this region parent materials are loessial deposits topography is rolling to flat and duration of soil formation effectively constant the variations in soil magnetic properties thus predominantly reflect climate and its co variant organic activity statistical analysis identifies strongest relationships between rainfall and magnetic susceptibility and anhysteretic remanence this magnetic response correlates with that of the modern soils across the chinese loess plateau such correlation suggests that the rainfall component of the climate system not dust flux is a key influence on soil magnetic properties in both these regions

a study of vertisol genesis in north eastern greece abstract four pedons from the alluvial plain of drama ne greece were investigated in order to provide detailed information on their morphology chemical physical and mineralogical properties classification and genesis the clay content of all the samples is relatively high 35 soil reaction with hcl ranges from slightly alkaline 7 2 to alkaline ph 8 3 the organic matter content ranges from 0 53 to 1 03 in the surface horizons while the other horizons contain considerably less the caco 3 equivalent content ranges between 0 1 and 18 1 due to ploughing gilgai microrelief is absent but slickenside was apparent in all of the soils studied smectite montmorillonite is the dominant clay mineral and was mainly inherited from the parent sediments and by neoformation high smectite content in combination with alternating wet dry periods xeric soil moisture regime results in the formation of the morphological characteristics that are typical for vertisols the pedons located in the highest points of the alluvial plain were classified as chromic haploxererts and those in the lowest landscape were classified as typic haploxererts free iron oxides range between 1 3 and 1 9 for the chromic haploxererts to only 0 4 0 9 for the typic haploxererts the properties of these vertisols reflect the impact of climate alternating wet dry periods landscape position alluvial plain seasonally water saturated and parent material clayey smectite dominated fluvio lacustrine highly calcareous sediments

sp grain production during thermal demagnetization of some chinese loess palaeosol summary progressive thermal demagnetization of natural samples to above 300 c may cause significant alterations of magnetic mineral phases such changes are commonly monitored by magnetic susceptibility ms determinations at every demagnetization step in an attempt to characterize in more detail alteration products created during thermal demagnetization of some chinese loess palaeosols l1 s1 ms was measured at both room temperature ms293k and at liquid nitrogen temperature ms77k between each demagnetization step we have used the difference between ms77k and ms293k temperature dependent susceptibility ktd ms293k ms77k to monitor production of superparamagnetic sp magnetic grains ktd is a function of 1 paramagnetic susceptibility according to the curie law k 1 t that predicts a theoretical 3 83 times increase in ms at 77k 2 sp grains at 293 k that passes into the single domain sd state on cooling to 77 k causing a dramatic reduction in ms77k 3 magnetite grains exhibiting magnetic changes when passing through the verwey transition at 120 k will also reduce ms77k we observe a linear relationship between frequency dependent ms kfd and temperature dependent susceptibility ktd indicating that sp sd blocking of magnetite may be the dominant factor of ms change during cooling high values of ktd indicates high sp concentrations and an increase of ktd with increasing demagnetization temperature is mainly attributed to the production of sp grains since the amount of magnetite exhibiting changes in ms at the verwey transition is unlikely to increase during heating of loess palaeosol to 600 c in air this interpretation is also based on results from zero field heating irm77k 1t zero field cooling of irm77k 1t and short time 100 s viscous decay of irm500mt our findings suggest that sp grains are produced continuously in both loess and palaeosol with thermal treatment and that sp production in palaeosol apparently commence at the surprisingly low temperature of around 200 c

mineral magnetic properties of chinese paddy soils and its pedogenic implications abstract magnetic susceptibility ms of paddy soils hydragric anthrosols and their corresponding dryland soils formed on the same parent materials in zhejiang province of eastern china were measured in order to understand better magnetic profile discrimination and pedogenic magnetic minerals in paddy soils magnetic measurements showed that the ms values of paddy soils were much lower than those of dryland soils formed on the same parent materials the higher the ms value of the original dryland soil is the more remarkable the decrease in the ms value is when the soil is put under rice cultivation gleyed paddy soils exhibited very low ms value

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

pedogenic processes and domain boundaries in a vertisol climosequence evidence from titanium and zirconium distribution and morphology abstract the occurrences of titanium ti and zirconium zr within eight vertisols formed in a climosequence on the upper beaumont formation of the texas gulf coastal plain were investigated in order to determine processes responsible for ti and zr redistribution during pedogenesis discontinuities defined by significant shifts in particle size distribution and the content in volume percent of zr are present at 160 to 260 cm depth in each pedon the discontinuities are interpreted to be functional boundaries i e physico chemical expressions of pedogenic domains between an upper soil domain dominated by open system pedogenesis and a lower more closed system domain dominated by chemical weathering the depth at which the functional boundary occurs is dependent on physical and hydrogeochemical influences which are largely a function of available water soil materials above the discontinuities are slightly coarser textured and enriched in zr whereas below the sediments are finer textured and have lower and more constant zr contents the zr is associated almost exclusively with zircon and zr contents correlate positively to the weight percent sand coarse silt with negligible zr present in the profile volume loss gain i e soil strain e a mass balance calculation that assumes zr or ti immobility during pedogenesis indicate ezr values nearly four times greater than eti large values of ezr within the upper soil domains are due primarily to sand and coarse silt additions to the vertisols and preclude use of zr as a basis of mass balance calculations in these soils despite its relative chemical stability by comparison ti is generally conserved within the clay rich soil profiles and is therefore better suited for mass balance calculations of volume change and mobile element translocation during pedogenesis

characterizing and quantifying iron oxides in chinese loess paleosols implications for pedogenesis to accurately decode the paleoclimatic and paleoenvironmental significance of magnetic properties in chinese loess paleosols neoformation of magnetic iron oxides via pedogenesis as well as the relationship between ferrimagnetic maghemite and magnetite and antiferromagnetic minerals hematite and goethite of both detrital and pedogenic origins should be well determined to resolve this problem magnetic iron oxides from a contiguous loess paleosol sequence lower part of the loess unit l1 paleosol unit s1 and the upper part of l2 at luochuan center of the chinese loess plateau were well characterized and quantified by using an integrated approach including chemical dissolution diffuse reflectance spectroscopy and rock magnetism methods results showed that these magnetic minerals have distinct coercivity and dissolution behavior which is highly grain size dependent more specifically the paleosol is enriched with nano sized pedogenic hematites with a medium coercivity of 130 mt which are also preferentially dissolved in a weak reductive environment in contrast the coarse grained micro sized detrital hematites with a medium coercivity of 1 t are dominant in loess in addition these coarse grained detrital hematites are more stoichiometric than their pedogenic counterparts as evidenced by the higher band position on the diffuse reflectance spectrum goethite can be well distinguished from hematite by its higher coercivity 4 7 t at low temperature 10 k the consistent dissolution behavior of goethite for both loess and paleosol samples in citrate bicarbonate dithionite solution indicates that goethite could be less relevant to the pedogenic processes the reductive dissolution of pedogenic maghemite lags the dissolution of pedogenic hematite and fine grained goethite which suggests that average grain size of pedogenic maghemite is relatively larger than those of pedogenic hematite and fine grained goethite detrital magnetite is hard to dissolve and 50 of its initial remanence survived after dissolution on the basis of these contrasting behaviors pedogenic hematite fine grained goethite and maghemite content was further quantified our results suggest that single domain pedogenic hematite was produced after initial formation of pedogenic maghemite this provides direct evidence for the recently proposed pathway in which ferrihydrite is transformed into a transient maghemite like phase before its final transformation into hematite

stable isotope compositions of pedogenic carbonates and soil organic matter in a temperate climate vertisol with gilgai southern russia abstract a vertisol gilgai complex from the north caucasus russia was studied to evaluate the climatic and environmental conditions governing pedogenesis the stable isotope compositions of soil organic matter som and carbonate pedofeatures in the vertisol record a complex but interpretable pedogenic history variability in the isotopic composition of pedogenic carbonate as a function of morphology position in gilgai microrelief and soil depth emphasizes the importance of these parameters to interpreting pedogenic conditions the isotopic compositions and age of som record evidence of pedogenesis in an earlier 5000 yr bp environment that was warmer and drier than modern conditions with a significant component of c4 flora up to 30 this portion of the soil history is preserved only in the deepest portions of the microlow 140 cm or in the central portion of the microhigh chimney a change to cooler and wetter conditions was accompanied by a shift to an ecosystem dominated by c3 vegetation 95 and resulted in a wetter soil environment particularly in gilgai microlow positions most pedogenic carbonate preserves isotopic compositions reflecting only the more recent climate history the wetter environment contributed to recrystallization of pedogenic carbonate nodules and formation of soft carbonate masses there are systematic differences in the isotopic composition of hard nodules and soft masses that indicate the influence of greater soil water evaporation a greater proportion of xerophytic plants and or lower rates of soil respiration in the gilgai microhighs self consistent interpretation of the pedogenic and paleoclimate history of these vertisols requires consideration of a full suite of information including carbonate pedofeature micromorphology the stable isotope composition and age absolute and relative of these features and other soil characteristics

rock magnetic properties of a soil developed on an alluvial deposit at buttermilk creek texas usa 1 the evolution of magnetization within a floodplain soil begins with initial deposition of magnetic particles during sedimentation and continues via subsequent alteration and growth of iron bearing compounds by pedogenic and biologic processes measurements of soil magnetic properties capture information about the developmental history of the soil and are a convenient method by which to investigate environmental change and pedogenesis using a range of magnetic measurements a comprehensive scenario for soil development was constructed for floodplain sediments at the debra l friedkin site an important archeological site near buttermilk creek texas floodplain deposits have traditionally been avoided for soil magnetism studies because it is thought that the episodic input of sediment would form soils characterized by discrete sedimentary units rather than a continuous record of pedogenesis we demonstrate that alluvial deposits can sometimes carry a straightforwardly interpretable magnetic signal similar to those typically seen in loess deposits smooth variation of rock magnetic parameters as a function of depth also leads us to conclude that the soil at this site is largely undisturbed and that the age of lithic artifacts found within the soil may be interpreted within stratigraphic context

microearthquakes at yucca mountain nevada abstract we operated a microearthquake array in the neighborhood of the proposed high level nuclear waste repository at yucca mountain nevada the array consists of four high gain up to 34 million narrow band 25 hz telemetered stations based on approximate magnitude calibration of the array we expect during quiet periods for distances less than 15 km complete recording of events at yucca mt for m 1 we have operated the four stations for 12 hour periods overnight between august and october 1990 and intermittently afterward until april 1991 when we began more or less continuous operation the pattern of microearthquake activity confirms the existence of a zone of seismic quiescence in the vicinity of proposed repository we recorded only about 10 events with s p times of less than 3 sec d s p times between 3 and 6 5 sec consistent with the higher seismic activity at distances between 24 and 52 km observed by rogers et al 1987 and gomberg 1991 oliver et al 1966 found contrary to what has been observed by us for yucca mountain that in seismically active areas most of the events had s p times of less than 3 sec we confirmed this expectation for four microearthquake stations near mammoth lakes where we observed microearthquake rates of over 100 per day most with s p times of less than 3 sec extrapolation of seismicity data from the southern great basin seismic network confirms the low microearthquake activity in the immediate vicinity of yucca mountain

late oligocene and miocene climate and vegetation in the eastern paratethys area northeast bulgaria based on pollen data abstract the results of palynological studies of the oligo miocene in the western part of the euxinian basin eastern paratethys are based on the analysis of 57 samples from core c 136a drilled near the town of balchik varna district some samples were barren or contained very little pollen and were not included in the analysis quantitative data are thus confined to 26 polleniferous samples we present results for the upper oligocene as well as the tarkhanian karaganian bessarabian and chersonian stages of the middle to upper miocene mixed deciduous forests were widespread during the time period studied swamp forests are also recorded with distribution maxima observed in the oligocene and in the bessarabian the widest extent of herbaceous vegetation is recorded in the late bessarabian and chersonian when it occupied open landscapes after a marine regressional phase the climatic data reconstructed by the coexistence approach indicate mean annual temperatures mats of ca 15 17 c and mean annual precipitation maps of 800 1300 mm for the upper oligocene the narrowest coexistence intervals of the tarkhanian and karaganian display mats of 14 17 c and maps of 800 1300 mm the most substantial data are for the bessarabian in which the lower part is characterized by mats of 15 6 16 6 c and maps from 800 1200 1300 mm the results for the upper part of the bessarabian are more variable especially with respect to precipitation that is generally lower 700 800 mm the same is true for the chersonian where besides lower precipitation lower annual temperature and temperature of coldest month are observed these results correlate with previous vegetation and palaeoclimate data from the forecarpathian basin nw bulgaria

magnetic discrimination between al substituted hematites synthesized by hydrothermal and thermal dehydration methods and its geological significance received 22 june 2011 revised 20 december 2011 accepted 24 december 2011 published 23 february 2012 1 hematite a ubiquitous mineral in aerobic sediments and soils of temperate and warm areas is weakly magnetic however it carries a stable natural remanent magnetization and thus can reflect paleoenvironment changes to quantify the influence of al content in hematite on its magnetic properties two series of hematite particles were prepared by hydrothermal transformation of ferrihydrite in aqueous suspension hfh series and by thermal dehydration of goethite hg series crystal morphological and mineral magnetic properties of these two types of hematites differ distinctively more specifically the hfh series samples display oblate plate like morphologies while the hg series samples are prolate highly acicular hfh series samples display higher saturation magnetization but lower magnetic coercivity than that of the hg series it is tenable that a better lattice ordering of al substitution occurs during the process of dehydration of goethite than after transformation from ferrihydrite resulting in weaker saturation magnetization for hg series samples the origin of single domain sd hematite in nature can be diagnosed by the correlation of unblocking temperature and magnetic coercivity a positive correlation indicates the presence of pure al free sd hematite while a negative correlation indicates a chemical origin of sd al substituted hematite these results bear new information on decoding the complex magnetic properties of sd al hematite in nature environments and thus deepen our understanding of the mechanism of variations in both paleomagnetic and paleoenvironmental signals carried by al hematite

significance of soil modifiers ca zeolites and gypsum in naturally degraded vertisols of the peninsular india in redefining the sodic soils abstract earlier hypothesis on the factors and processes of natural degradation in vertisols and also their evaluation for crops on the basis of only hydraulic properties was developed on limited soils by the division of soil resource studies dsrs of the national bureau of soil survey and land use planning nbss lup nagpur india in order to validate the above similar soils occurring in major states of the peninsular india and also to document the extent of modification by gypsum and ca zeolites therein the present study on twenty six benchmark vertisols representing a climosequence from sub humid moist to arid dry climate was undertaken the results of the present study validates the hypothesis that formation of pedogenic calcium carbonate pc at the expense of non pedogenic calcium carbonate npc is the prime chemical reaction for the natural chemical degradation realized in terms of impairment of hydraulic properties of soils mediated through the development of subsoil sodicity presence of gypsum and ca zeolites on the other hand prevented the rise of ph decrease in ca mg ratio of exchange sites and improved the hydraulic properties amidst an exchangeable sodium percentage esp 15 the improvement in saturated hydraulic conductivity shc 10 mm h 1 of zeolitic sodic soils does commensurate fairly well with the performance of rainy season crops thus characterization of sodic soils in terms of shc 1 weighted mean in 0 100 cm depth of soil instead of any esp or sodium adsorption ratio sar emerges as a robust criterion that stands for a universal acceptance for the better use and management of such naturally degraded soils not only in the indian semi arid tropics but also in similar climatic and geologic areas elsewhere

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

evaluating the use of weathering indices for determining mean annual precipitation in the ancient stratigraphic record abstract different quantitative methods have been developed to determine paleo rainfall using paleosols of particular interest are methods that use bulk geochemistry to calculate a weathering index and from that mean annual precipitation twenty three paleosols that formed during a time of significant climate change the paleocene eocene thermal maximum petm were analyzed to evaluate the relative merits of two geochemical proxies that have been developed for estimating paleoprecipitation one depends on the chemical index of alteration without potash cia k and the other uses the calmag weathering index which depends on cao and mgo the paleosols are located in the paleogene fort union and willwood formations in the bighorn basin wy morphologic differences among the paleosols indicate that they formed under varied soil moisture conditions a morphology index was developed from pedogenic features that are sensitive to soil drainage and thus to rainfall to assess that variability quantitative mean annual precipitation map values were calculated for each paleosol using the cia k index and the calmag index which was developed specifically for vertisols those results were compared to the morphology index for 23 paleosols the results indicate that increases and decreases in map calculated from both methods correlate relatively well to changes in the soil morphology index however the results from the calmag weathering index show a stronger correlation the results suggest that the calmag proxy provides a more robust map estimate for vertisols in addition to comparing map estimates to the soil morphology index we compared the map values to paleorainfall estimates determined from paleofloras at the same stratigraphic levels as three of the paleosols that comparison confirms that the calmag method is reliable for reconstructing map from ancient vertisols the results also show that in the bighorn basin vertisols with a b horizon

miocene vegetation and climate dynamics in eastern and central paratethys southeastern europe abstract from the cretaceous to modern time the earth s climate system has changed repeatedly from a greenhouse to an icehouse the miocene appeared as the last warm episode in earth history prior to the establishment of large northern hemisphere ice sheets furthermore the miocene was characterized by both large scale marine transgressions and pronounced episodes of regressions e g opening and closure of marine corridors as well as appearance and disappearance of lakes and swamps the sea level changes and instability of the climate system strongly influenced not only marine ecosystems but also the terrestrial biota to throw new light on the miocene evolution of european ecosystems and climate dynamics we compared plant assemblages from southeastern europe palaeogeographically this area is a transitional belt between tethyan and paratethyan realms and it thus constitutes a crucial geographical position when one tries to comprehend the exchange pathways of various floristic elements appearance and evolution of steppe vegetation interaction between forest and steppe vegetation and of course the corresponding climates influencing the vegetation dynamics both macro and microfloristic plant associations were considered in our analysis large palaeofloristic and palaeocoenotic transformations occurred during the miocene the early to middle miocene flora is rich and diverse in thermophilous elements which formed polydominant mesophytic to hygromesophytic forests early miocene climate was warm and humid with mean annual temperatures mainly above 16 c and annual rainfalls over 1000 mm the middle miocene was the warmest period of the whole miocene with annual temperatures ranging from 17 c to 19 c and winter temperatures from 7 c to 12 5 c climatic changes after the miocene climatic optimum caused changes in floristic composition and vegetation structure the vegetation shows a decreasing trend in abundance of palaeotropic and thermophilous elements reduction of macrothermic elements and disappearance of evergreen laurel forests together with these changes is a corresponding increase in the role of arctotertiary species in plant communities and they became dominants in mesophytic forests the available data indicate that major vegetation changes occur in the late miocene this period is characterized by more diverse climatic conditions which were directed by global climatic changes and probably complicated by regional palaeogeographic reorganizations and tectonic processes slight cooling and some drying is recorded for the beginning of the late miocene followed by fluctuations of palaeoclimate parameters observed which display cycling change of humid dryer and warmer cooler conditions our study provides a new insights on the miocene vegetation and climate dynamics and evolution in southeastern europe

attenuation of high frequency shear waves in the crust measurements from new york state south africa and southern california we compare the attenuation of high frequency 3 30 hz shear waves for crustal paths in new york state south africa and southern california over source receiver distances of about 10 400 km the data consist of digital recordings of s waves 5 100 km and lg waves 100 400 km produced by earthquakes we use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the s and lg waves over the entire distance range studied 10 400 km the amplitude decay of 3 hz shear wave energy is considerably less for the tectonicaily stable areas of new york and south africa than for the tectonicaily active region of southern california high frequency 30 hz s wave attenuation is significantly less for new york and south africa than for southern california for distances between 15 and 90 km we parameterize the decay with distance r of coda normalized shear wave amplitudes with a frequency independent q and geometrical spreading exponent where geometrical spreading is proportional to r for new york state the s wave amplitude decay 3 30 hz is well described by a frequency independent q of 2100 330 490 and of 1 3 0 1 the decay of lg wave amplitudes from 3 to 15 hz in the new york state region is fit with a frequency independent q of 1600 280 330 of 0 70 0 2 the s wave amplitudes 3 30hz in south africa yield a q of 1500 190 380 and of 1 3 0 1 fixing the geometrical spreading at r 0 5 produces an lg wave q estimate at 3 hz in south africa of 360 50 80 this lg wave q is low considering that south africa is a cratonic tectonicaily stable area the s wave amplitudes from southern california are described with a frequency independent q of 800 150 240 and a large geometrical spreading exponent of of 1 9 0 2 we find an lg wave q at 3 hz of 260 30 for southern california after constraining the geometrical spreading at r 0 5

new weathering index improves paleorainfall estimates from vertisols vertisols are clayey shrink swell soils that are widely recognized in the rock record thus generating the need to better understand the dynamics of elemental concentrations on the development of weathering indexes for climate interpretations we assessed the weathering performance of the four major base forming oxides cao mgo na 2 o k 2 o along a modern vertisol climosequence spanning a strong precipitation gradient and discovered that the concentration of bulk soil cao and mgo yields the strongest correlation to mean annual precipitation map based on this fi nding we introduce the calmag weathering index defi ned as al 2 o 3 al 2 o 3 cao mgo 100 which improves rainfall estimates for vertisols relative to the wellestablished cia k chemical index of alteration minus potassium weathering index rather than documenting the hydrolysis of weatherable minerals common in many other soil orders in vertisols calmag principally tracks the fl ux of calcium and magnesium sourced from calcium carbonate detrital clay and exchangeable ca 2 and mg 2 application to two mesozoic paleosols reveals that in drier climates cia k yields higher map estimates than calmag but that the reverse is true in wetter climates this work improves paleorainfall estimates from vertisols and suggests that a family of weathering indexes is needed for different paleosol types

temperature dependence of magnetic susceptibility in an argon environment implications for pedogenesis of chinese loess palaeosols summary temperature dependence of magnetic susceptibility t has been widely used to determine changes in mineralogy of natural samples during heat treatment we carried out integrated rock magnetic experiments to interpret the t curves of the chinese loess palaeosols in argon we used both raw materials and heated samples in addition we also investigated the magnetic properties of magnetic extracts and residues to quantify contributions from each fraction to the bulk magnetic properties for the heating curves the susceptibility loss 30 per cent between 300 400 c is caused by the inversion from pedogenic fine grained maghemite to haematite suggesting that the susceptibility loss can be used as a new concentration index of the pedogenic fine grained superparamagnetic sp particles in the chinese loess palaeosols unlike the warming curves the cooling curves are dominated by newly formed fine grained magnetites with a dominant size of 35 nm the onset for the new production of these fine grained magnetic particles occurs at 400 c it is interesting that the room temperature magnetic susceptibility ph of the samples heated after a 700 c run is independent of the degree of pedogenesis and saturates at approximately 33 35 10 7 m3 kg 1 indicating that the susceptibility enhancement is controlled only by the reduction of fe bearing aeolian minerals during heating it appears that the 700 c thermal treatment in argon could be in some sense an analogue to the pedogenic processes thus we predict that 33 35 10 7 m3 kg 1 is the maximum susceptibility that pedogenesis can generate for the last interglacial palaeosol unit s1 in practice ph would be useful to quantify the aeolian inputs to the chinese loess plateau

pedogenic iron manganese nodules in vertisols a new proxy for paleoprecipitation the total fe content of pedogenic iron manganese fe mn nodules taken from a vertisol climosequence on the texas gulf coastal plain correlates with mean annual precipitation map r 2 0 92 no significant trend of total fe fetot with depth was noted in profiles using the regression developed from modern vertisol data fetot contents of paleozoic paleo vertisol fe mn nodules yielded map regimes comparable to previously inferred paleoenvironmental interpretations paleoprecipitation estimates derived from fe mn nodules for an uneroded late mississippian paleo vertisol are very close to estimates determined from a depth to pedogenic carbonate horizon dch proxy determined from the modern vertisol climosequence the lack of soil depth dependence of the fe mn nodule proxy provides a consistent paleoprecipitation estimate even in eroded paleo vertisols and in combination with the dch may be useful in determining original paleosol thickness

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

hydraulic fracturing stress measurements at yucca mountain nevada and relationship to the regional stress field hydraulic fracturing stress measurements and acoustic borehole televiewer logs were run in holes usw g 1 and usw g 2 at yucca mountain as part of the nevada nuclear waste storage investigations for the u s department of energy eight tests in the saturated zone at depths from 646 to 1288 m yielded values of the least horizontal stress s h that are considerably lower than the vertical principal stress s v in tests for which the greatest horizontal principal stress s h could be determined it was found to be less than s v indicating a normal faulting stress regime the borehole televiewer logs showed the presence of long in excess of 10 m vertical drilling induced fractures in the first 300 m below the water table these are believed to form by the propagation of small preexisting cracks under the excess downhole fluid pressures up to 5 2 mpa applied during drilling the presence of these drilling induced hydrofractures provides further confirmation of the low value of the least horizontal stresses a least horizontal principal stress direction of n60 w n65 w is indicated by the orientation of the drilling induced hydrofractures n25 e n30 e and the orientation of stress induced well bore breakouts in the lower part of usw g 2 n65 w this direction is in good agreement with indicators of stress direction from elsewhere at the nevada test site the observed stress magnitudes and directions were examined for the possibility of slip on preexisting faults using these data the coulomb criterion for frictional sliding suggests that for coefficients of friction close to 0 6 movement on favorably oriented faults could be expected for coefficients of friction of 1 0 preexisting faults of all orientations should be stable laboratory studies on the yucca mountain tuffs reported elsewhere yield coefficients of friction ranging from 0 6 to 0 9

meteorological overview of the arctic boundary layer expedition able 3a flight series a meteorological overview of the arctic boundary layer expedition able 3a flight series is presented synoptic analyses of mid tropospheric circulation patterns are combined with isentropic back trajectory calculations to describe the long range 400 3000 km atmospheric transport mechanisms and pathways of air masses to the arctic and sub arctic regions of north america during july and august 1988 siberia and the northern pacific ocean were found to be the two most likely source areas for 3 day transport to the study areas in alaska transport to the barrow region was frequently influenced by polar vortices and associated short wave troughs over the arctic ocean while the bethel area was most often affected by lows migrating across the bering sea and the gulf of alaska as well as ridges of high pressure which built into interior alaska july 1988 was warmer and dryer than normal over much of alaska as a result the 1988 alaska fire season was one of the most active of the past decade airborne lidar measurements verified the presence of biomass burning plumes on many flights often trapped in thin subsidence layer temperature inversions several cases of stratosphere troposphere exchange were noted based upon potential vorticity analyses and aircraft lidar data especially in the barrow region and during transit flights to and from alaska

rock magnetic properties of recent soils from northeastern bulgaria summary in this paper basic rock magnetic studies of holocene loess soil samples from northeastern bulgaria are reported the sites are related to the danube river and located at different distances southwards thus representing various pedogenic conditions the study is primarily aimed at determining the main magnetic carrier and their physical characteristics grain size distribution magnetic enhancement etc oxyhydroxides maghemite and titanomagnetites of various oxidation degrees are assumed to be the main ferromagnetic minerals present our results suggest that the uppermost part of recent soil profiles is rich in stable near single domain sd particles while the illuvial horizons are characterized by a gradual decrease in grain sizes from highly viscous to a true superparamagnetic sp domain state the properties of samples from carbonate rich horizons of recent soils are basically controlled by detrital minerals while those from sites with more intensive pedogenesis and especially grey forest soils are influenced by strongly magnetic minerals formed in situ

the role of magma overpressure in suppressing earthquakes and topography worldwide examples in an extending terrane basaltic magma supplied at a pressure greater than the least principal stress overpressure may be capable of suppressing normal faulting and the earthquakes and topographic relief that commonly accompany normal faulting as vertical dikes intrude they press against their walls in the direction opposite the least principal stress and increase its magnitude the emplacement of tabular intrusions causes the internal magma pressure to act selectively in opposition to tectonic stresses this process tends to equalize the stresses and thus diminishes the deviatoric stress difference between maximum and minimum stresses that creates faults and causes earthquakes observations of the pattern of seismicity and magmatism worldwide indicate that magmatism commonly supplants large earthquakes as the primary mechanism for accommodating tectonic extension recognizing the extent of magmatic stress accommodation is important in assessing seismic and volcanic risks

vertisol genesis in a humid climate of the coastal plain of texas u s a numerous genetic studies of vertisols have been conducted using qualitative and semi quantitative methods across a broad range of climates however no detailed investigations exist on vertisols formed in humid climates using multiple pedogenic techniques on both a microlow ml and microhigh mh hence we sampled and characterized a ml and mh from a lake charles pedon mean annual rainfall 1090 mm mean annual temperature 20 c in the late pleistocene coastal plain beaumont formation of east texas according to the official series description the lake charles classifies as a fine smectitic hyperthermic typic hapludert with mollic and calcic diagnostic horizons coupled with field morphology and characterization data micromorphology and constituent mass balance interpretations were used to reconstruct the major pathway of pedogenesis in response to greater water recharge the ml contains darker colors more organic carbon greater depth of carbonate leaching and lower ph the proportion of oxalate extractable iron increases toward the surface and is in greater abundance in the ml than mh in contrast dithionite extractable iron increases with depth and has similar quantities in both the ml and mh the parent material and lower profiles contain asepic microfabric dominated by micaceous rich coarse clay and silt the asepic zone deep contains an abundance of soft carbonate masses and iron manganese segregations that appear to be forming contemporaneously with the presence of argillans substantiating clay translocation during the early history of soil formation sepic microfabric dominates the upper profiles of both the ml and mh in part from the transformation of biotite to smectite which is more pronounced in the microlow because of more intense weathering hard carbonate nodules and iron manganese concretions are abundant in the upper sepic zone and contain skelsepic microfabric suggesting that they are no longer growing dilation was the dominant strain force during pedogenesis from volume expansion in response to crack infills and shrink swell processes mass flux calculations indicate that total clay gains occurred in both the ml and mh during pedogenesis late pleistocene vertisols appear to approach steady state when forming in humid climates the soil mechanics model best explains the observed depth distribution of properties including slickensides with pedoturbation playing a secondary role in the genesis of these humid climate vertisols