magnetotelluric analysis using mohr circles the mohr circle most commonly met in the analysis of mechanical stress is used to depict magnetotelluric impedance information taking the real and quadrature parts of magnetotelluric tensors separately the magnetotelluric concepts of two dimensionality three dimensionality skew and anisotropy are then all given quantitative expression on a diagram as are various magnetotelluric invariants in particular a new invariant the central impedance becomes evident in a discussion of effective impedances some insight is gained into impedance rotations and an anisotropy angle is defined analogous to skew angle mohr circles are also tested to depict the effects of the shear and twist operations on a regionally two dimensional structure generally the application of shear or twist results in an impedance tensor with a mohr circle of typical three dimensional form

flow and electrical anisotropy in the upper mantle finite element models constraints on the effects of olivine crystal preferred orientation and microstructure long period magnetotelluric mt data shows that electrical conductivity in the upper mantle is highly anisotropic agreement between high electrical conductivity directions and seismic anisotropy fast directions suggests that anisotropic diffusion of hydrogen along oriented olivine crystals controls the anisotropy of electrical conductivity in the upper mantle since both seismic waves and hydrogen diffusion are faster along the 1 0 0 axis of olivine thus mt electrical anisotropy data like seismic anisotropy may be used to map flow patterns in the upper mantle however observed electrical anisotropies are significantly higher than seismic ones to quantify the influence of strain induced crystal preferred orientations of olivine on upper mantle bulk electrical conductivities we calculate the macroscopic electrical conductivity anisotropy of a series of naturally and experimentally deformed peridotites using an anisotropic finite element model these models which fully take into account the microstructure crystal and shape preferred orientations based on orientation maps obtained by indexation of electron back scattered diffraction ebsd patterns show macroscopic electrical anisotropy factors ranging from 3 to 16 the intensity of electrical anisotropy depends to first order on the intensity of the olivine crystal preferred orientations but the relation saturates for strong crystal preferred orientations in addition the spatial distribution of the various crystal orientations may significantly enhance influence the anisotropy in strongly textured mantle rocks the strongest anisotropy factors 10 occur in mantle rocks in which deformation by dislocation creep has produced not only crystal but also strong shape preferred orientations even if the latter is masked by recrystallization higher anisotropy factors 100 observed in a few mt experiments imply however an additional as yet unknown mechanism controlling electrical conduction at asthenospheric depths in these regions

quaternary mammals and the end villafranchian dispersal event a turning point in the history of eurasia the history of land mammals is characterized by dispersal events i e short periods of rapid intercontinental migrations and faunal replacements one of these the elephant equus event of lindsay et al may be dated somewhere between 3 and 2 5 ma a second event the wolf event may fall near 1 7 ma the end villafranchian event is discussed in detail it may be dated between 1 0 and 0 9 ma and is marked by a practically total rejuvenation of the fauna with the appearance of new types of adaptation unknown in the villafranchian this faunal revolution is easily recognized all over eurasia and is accompanied by wide ranging changes in climate and vegetation this whole sequence of phenomena may have been triggered by extensive tectonic movements in the mountain belts of central and southern asia

lands and endemic mammals in the late miocene of italy constrains for paleogeographic outlines of tyrrhenian area the pre messinian land mammal localities of italy contribute substantial information for reconstructing the complex history of the land masses of the central mediterranean at the present state of knowledge the available paleogeographic maps do not have the adequate time resolution for providing an effective picture of the evolution of the physiographic and of the oceanographic characteristics of the area this can only be accomplished through detailed comparative analyses of the geology and of the land and marine faunas in the course of the miocene the pre messinian late miocene land mammals localities of italy document the existence of three distinct bioprovinces two of the latter are characterised by faunas with manifestly endemic features thus attesting to the occurrence of isolated emerged areas one of these areas is called the abruzzi apulia paleobioprovince it was located on the adriatic side of apennines the other one is the so called tusco sardinian paleobioprovince and was located in the peri tyrrhenian side of italy a third bioprovince testified by sites in calabria and sicily is characterised by non endemized mammals counterparts of which were identified in north africa and europe this area was therefore at least in part a northern extension of the late miocene mediterranean border of the african plate these three areas belong to completely different tectonic domains and kept separated for a considerable time span and each one has a peculiar biogeographic and tectonic history

magnetotelluric tensor decomposition part ii examples of a basic procedure the decomposition procedure suggested for magnetotelluric mt data in a companion paper is illustrated by examples adjacent pairs of stations are examined to test for common features in their mt response the method analyzes the real and quadrature parts of an impedance tensor separately and the results for the real and quadrature parts are compared and in some cases combined at the end values are obtained which are interpreted directly in terms of nearest 2 d principal impedances local geologic strike and regional geologic strike the requirement for valid data derived in the companion paper that zxyrzyxr zxxrzyyr together with zxyqzyxq zxxqzyyq is shown to be a useful criterion in the winnowing of erroneous data the examples presented typically show the direction interpreted as local geologic strike to be well determined period independent and consistent between real and quadrature mt matrices in these examples however the direction interpreted as regional geologic strike is period depen

anisotropy and phase splits in magnetotellurics abstract several recent papers suggesting that the electrical conductivity of the lower crust and upper mantle are anisotropic have been based upon magnetotelluric mt observations of phase splits the mt analogue of shear wave splitting the emphasis on the phase rather than the amplitude response results from the distorting effect of conductivity variations in the overlying crust these variations distort the amplitude response from deeper levels and make inferences based on the amplitude difficult at the long periods needed to probe the conductivity at upper mantle depths the mt phase response a tensor is negligibly affected by small scale conductivity variations in the overlying crust however the mt phase response of a half space with a uniform but anisotropic conductivity is independent of polarization direction and no phase split occurs using simple anisotropic layered models we demonstrate that a phase split is produced by the conductivity change at the interface between the isotropic and anisotropic layers the maximum phase difference reflecting the conductivity contrast gradient between the principal conductivities of the anisotropic layer and the isotropic layer s conductivity in the general case where none of the principal axes of the anisotropic conductivity layer lie in the plane of the surface the orientation at which the maximum phase difference occurs i e the principal axis of the phase tensor is determined by the horizontal projection of conductivity tensor s ellipsoid in such cases the orientation of the maximum phase split will not be aligned parallel to any of the conductivity tensor s principal axes mt phase splits are a consequence of spatial differences or gradients in conductivity not the intrinsic bulk properties of the conductivity tensor itself and in this respect are fundamentally different from shear wave splitting

dispersal of the canini mammalia canidae caninae across eurasia during the late miocene to early pleistocene abstract an analysis of the taxonomy and distribution of the mio pliocene and pleistocene eucyon like and canis like canids of the tribe canini of eurasia was performed with a description of several fossils from the late miocene and early pliocene of asia the changes in the assemblages of the canini generally coincided with the most significant eurasian faunal turnovers but the european and asian diversities of the canini peaked asynchronously in the late miocene a wide expansion of the genus eucyon to the old world took place being designated here as the eucyon event the diversity of eucyon like canini peaked at the beginning of the early pliocene in asia and at the end of the early pliocene in europe the wolf sized species of the canis group made their first appearance in eurasia in the middle pliocene the canis event the peak of their diversity occurred in the late pliocene in asia and at the beginning of the early pleistocene in europe at the end of the pliocene eucyon and eucyon like canids completely went extinct in eurasia the diversity of the canis group appreciably decreased by the end of the early to middle pleistocene being limited by the occurrence of small wolves of the canis mosbachensis canis variabilis group and large hypercarnivorous canis xenocyon lycaonoides in eurasia the true gray wolves made their appearance at the end of the middle pleistocene at about 0 5 0 3 ma

earliest record of sinicuon in zanda basin southern tibet and implications for hypercarnivores in cold environments abstract the out of tibet hypothesis envisions late cenozoic tibetan mammals acquiring adaptations to cold environments and being ancestral to several eurasian megafaunal species in the pleistocene here we report an early record of a hypercarnivorous canid sinicuon cf sinicuon dubius from zanda basin in the himalaya range although the new record is recovered from reworked sediments in a pleistocene alluvium we can constrain the fossil to within a narrow age range of 3 8 3 4 ma in the middle pliocene presence of this hypercarnivorous canid in the pliocene of tibet along with the recently described pantherine cat and arctic fox suggests a predator guild with predominately carnivorous diet characteristic of modern arctic carnivorans such as the arctic fox and polar bear wintering in extremely cold climates may have been the cause of such adaptations sinicuon shows transitional morphology to modern hypercarnivorous hunting dogs in southern asia cuon suggesting linkage of the high tibetan plateau to the southern continents

anomalous phases exceeding 90 in magnetotellurics anisotropic model studies and a field example summary a study of synthetic anisotropic models that explain phases exceeding 90 in magnetotellurics is presented the basic model comprises an anisotropic layer overlain by a shallow local anisotropic block with both structures inserted in a 2 d model the 2 d strike and the anisotropy strikes layer and block differ the influence of the following parameters was analysed anisotropy strike geometry of the block and the layer and anisotropy ratios of the block and the layer we show that according to this model the anomalous phase effect is limited to those sites above the shallow block and does not influence the regional structure which can therefore be recovered these results were applied to field data from a magnetotelluric profile in sw iberia where phases greater than 90 occurred in an area in which alternating bands of schist and graphite rich blackschists crop out giving rise to strong macroanisotropy

the north american central plains conductivity anomaly and its correlation with gravity magnetic seismic and heat flow data in saskatchewan canada abstract the north american central plains conductivity anomaly nacp lies virtually in its entirety within the trans hudson orogen accordingly should these two features prove to be contemporaneous then the geometrical relationship between these two is of foremost importance to any evolutionary tectonic model proposed to explain the collision of the superior and churchill provinces in the hudsonian and a model that does not include a mechanism for the generation of this anomaly is obviously untenable in order to map better the trend of the nacp in the province of saskatchewan canada two magnetotelluric mt profiles were conducted over the nacp previously defined by magnetometer arrays and profiles data from these two profiles along with an earlier mt profile just north of the u s canadian border suggest that the nacp is not a continuous feature but rather that it exhibits a definite break at latitude 51 n other geophysical evidence examined herein is concordant with this characteristic if a second mt anomaly mapped to the northwest of this break is in fact a manifestation of the same geological structure then one possible interpretation is of a major nw se trending sinistral fault in the deep crust previously undetected with a movement of some 100 150 km along strike the mt data from the southernmost profile after correction for static shift are modelled in a 2d manner and it is shown that the nacp is consistent with an arcuate structure in vertical section of high conductivity 2 s m 1 beginning at a depth of 10 km centred on 103 w dipping down to the west reaching possibly the base of the crust it is also shown that such an arcuate shape in section can explain an observed gravity high of 40 mgal such high conductivities cannot be explained in terms of connected fluids as it would require implausibly high porosities 12 20 a comprehensive interpretation of all the geophysical data would have to account for the observed characteristics of the anomalous region which are high electrical conductivity positive density contrast no magnetization and high heat flow in the basement in terms of a single causative body one possible explanation is presented in terms of a zone of lithospheric weakness along which was emplaced low density differentia from a mantle derived body an alternative explanation could be the phase transformation of obducted material into eclogite or serpentinite however difficulties exist with both of these explanations and further data are required

magnetotelluric response of a laterally inhomogeneous anisotropic inclusion abstract the field of h polarisation is studied for an anisotropic two dimensional conducting inclusion embedded in a less conducting isotropic surrounding using a finite difference approximation technique contour lines for the re h x have been plotted laterally across the inclusion it is shown that 1 for larger anisotropic factors in the inclusion the contour lines converge in the embedded inclusion and 2 the effects of changing lateral conductivity variations are reflected significantly in the apparent resistivity versus lateral distance variation patterns our results may provide an insight into the interpretation of magnetotelluric investigations over anisotropic inhomogeneities frequently encountered in mapping natural resources in sedimentary and fissured zones in geothermal fields

plio pleistocene fossil record of large predators in iberia diversity home range and climatic change abstract we investigated the patterns of change in diversity and home range size structure of the latest miocene pleistocene iberian carnivores to recognize the tempo and mode of the major shifts and place them in the context of late cenozoic climatic changes the database consists of 36 selected and taxonomically revised faunal lists a general pattern of carnivore diversity from iberia shows three maxima in diversity that can be correlated with major global changes the first coincides with the glacial trend during pliocene starting at 2 7 2 6 ma with the onset of glacial cycles of 41 ka second maximum happened at the beginning of the middle pleistocene and can be correlated with the switch at 1 ma third maximum in diversity occurs at the end of middle pleistocene when the amplitude of interglacials shifted from cooler to warmer interglacials the most significant shifts in carnivora diversity and home range size patterns were linked to dispersal phases that were tracked by a renovation of the carnivore guild from the patterns in home range size structure it seems that some multifaceted and not always straight interactions exist between ecological and climatic change and shifts in home range size the onset of the holocene home range size structure in iberian carnivores traces back to a high diversity pulse at the end of the middle pleistocene

upper cenozoic bio magnetic stratigraphy of central asian mammalian localities abstract this research is focused on biostratigraphic and palaeomagnetic correlations of upper cenozoic mammalian localities of central asia in the territory of tadjikistan uzbekistan kyrgyzstan and southern kazakhstan the absence of the lithological markers and absolute dates emphasizes the true importance of using bio magnetic evidence for stratigraphy of terrestrial molasse late turolian villafranchian and middle pleistocene faunal assemblages are recorded in central asian localities providing a good basis for a broad interregional stratigraphic correlation

tectonic fabric of the subcontinental lithosphere evidence from seismic magnetotelluric and mechanical anisotropy abstract knowledge of anisotropy is key to our understanding of tectonic fabrics in the lithosphere and sublithospheric mantle anisotropy provides a unique constraint on the character of past and present deformation and thus is critical to our understanding of dynamics of the plate tectonic system in particular how continents with their thick lithospheric mantle roots form stabilize and interact with underlying mantle regions improved observational methods and rapid developments of geophysical inversion techniques are contributing to more realistic earth models that include various types of anisotropy and heterogeneity a more robust characterization of anisotropic parameters can be achieved by integrating complementary datasets incorporating constraints from seismology magnetotellurics geodynamics and mineral physics valid comparisons between different measures of anisotropy however require a solid understanding of the principles and limitations of the various techniques to this end we briefly summarize a new compilation of original articles with a common focus on anisotropy of continental lithosphere including theory laboratory experiments and observations that span a range of different geophysical techniques

the site of coste san giacomo early pleistocene central italy palaeoenvironmental analysis and biochronological overview abstract facies and ostracod analyses have been performed on a continental core drilled at coste san giacomo anagni central italy where a middle villafranchian faunal assemblage was first discovered in 1978 the core intercepted the palaeontological level and penetrated the underlying sedimentary succession previously largely unknown for a total sediment recovery of 40 m in addition new field surveys led to the discovery of hippopotamus sp remains at the faunal site thus pre dating the dispersal of this large ungulate into europe to the middle villafranchian the new sedimentological and palaeoecological data allowed to define a palaeoenvironment mainly ascribable to an alluvial plain characterized by a marsh evolving into a floodplain with overbank deposits and a sand bed fluvial channel this scenario is supported by the reassessed coste san giacomo faunal assemblage consistent with running and or clear waters as well as prairies and grasslands under mild climatic conditions

the pliocene pleistocene succession of kvabebi georgia and the background to the early human occupation of southern caucasus abstract this article analyzes and discusses the chronological and zoogeographic context of the pliocene site of kvabebi in order to shed light into the background of the early human occupation of eurasia as evidenced by the early pleistocene site of dmanisi new paleontological and paleomagnetic research has allowed this site to be placed in a reverse interval which can be identified as chron 2an 1r the age of this site is therefore close to 3 07 ma coeval to the hadar beds of the afar depression and slightly older than the last hipparionine faunas in europe such as villarroya in spain the fauna of kvabebi is composed of a number of species common to europe and asia but also includes others with african affinities such as kvabebihyrax kachethicus protoryx heinrichi parastrepsiceros sokolovi and gazella postmitilinii however the presence these species cannot be explained as the result of a pliocene dispersal from africa but rather as the last remnants of the so called greek iranian province

magnetotelluric inversion for anisotropic conductivities in layered media abstract electrical anisotropy in the earth s crust and upper mantle has recently gained attention as a significant linking factor between electrical models and underlying structural and tectonic patterns this interest has also motivated new methodological studies into the modelling and inversion for electrically anisotropic structures we present an algorithm for the inversion of magnetotelluric data over layered anisotropic conductors which is a straightforward extension of the standard occam 1 d inversion to anisotropic models owing to the essential limitation of magnetotellurics to resolve the complete conductivity tensor we formulate the inversion for azimuthal anisotropy only we treat the non linear inverse problem as a multi criterion minimization of the structure complexity data misfit and anisotropy to constrain the structure complexity we employ the standard roughness penalty as well as non quadratic penalties of the total variation and gradient support type that produce more focused model sections and thus conform better to the idea about sharp non diffuse boundaries of anisotropic structures in the earth application of the anisotropy penalty is crucial for suppressing spurious anisotropy in the inverse models we use a 2 d extension of the heuristic l curve method to estimate the quasi optimal penalty weights with two non linear iteration solvers specifically the reweighted conjugate gradient method and the lagged diffusivity iteration we can arrive at the minimum of the target functional for one selected pair of regularization weights typically after a few tens of iteration steps to demonstrate the inverse solution we present two simple yet not completely trivial synthetic examples the first one based on data generated by a model with two anisotropic layers with discordant strikes and the other showing possible misinterpretations in case a 1 d inversion with anisotropy is formally applied to data produced by simple 2 d block structures field data from the variscan structures in southern portugal bear indications both geological and geophysical on possible crustal anisotropy due to shearing and graphitization we present results of a 1 d anisotropic imaging and a preliminary 2 d modelling for a short section of five sites over an old suture between the south portuguese zone and ossa morena zone aimed at explaining some essentially non 2 d effects in the data as e g systematic frequency variations of the regional strike or phases rolling out of their natural quadrants

new data on the early villafranchian fauna from vialette haute loire france based on the collection of the crozatier museum le puy en velay haute loire france abstract vialette 3 14 ma like seneze chilhac sainzelles ceyssaguet or soleilhac is one of the historical sites located in haute loire france the lacustrine sediments of vialette are the result of a dammed lake formed by a basalt flow above oligocene layers and show a geological setting typical for this area where many localities are connected with maar structures that have allowed intra crateric lacustrine deposits to accumulate based on previous studies and this work a faunal list of 17 species of large mammals has been established eight species typical of this time period and well known occur in the collection of the crozatier museum of le puy en velay pliocrocuta perrieri lynx issiodorensis mammut borsoni anancus arvernensis stephanorhinus jeanvireti tapirus arvernensis cervus pardinensis and croizetoceros ramosus the presence of gazella cf g borbonica is newly established in addition to which the oldest known occurrences of canis sp cf eucladoceros sp and of the genus equus in western europe are also described these are the new data which pushed back the age of the arrival of the genus equus cf eucladoceros and canis in western europe five taxa are not found in the crozatier collection primates indet agriotherium sp ursus gr minimus thibetanus bovidae middle sized pliotragus ardei or gallogoral meneghinii procapreolus cf cusanus

late pliocene to early mid pleistocene mammals in eurasia faunal succession and dispersal events abstract four major dispersal events mark european villafranchian and galerian faunas about 3 2 0 4 ma the beginning of the villafranchian is evidenced by the arrival of leptobos and of large cervids and felids the fauna still retains typical forest elements mammut tapirus etc the elephant equus event about 2 5 2 6 ma brought in grassland elements elephant horse while several forest dwellers disappeared the massive arrival of a primitive wolf a large hyaena and leptobos etruscus approximately marks the plio pleistocene boundary wolf event about 1 7 ma this was followed by a new wave of prairie fauna praeovibos leptobos vallisarni allophaiomys canis arnensis a coyote canis falconeri possibly a lycaonid cervalces and hippopotamus also arrived at this time the villafranchian galerian transition saw a total faunal turnover with massive extinctions and new previously unknown adaptations end villafranchian event 1 0 0 9 ma the late pleistocene and living fauna of eurasia took its origin at this time mammalian stratigraphy of asia is more poorly known but faunas are easily correlated with european ones and the end villafranchian event is clearly recognised faunal events are correlated with climatic and physiographic changes late himalayan orogeny

dimensionality imprint of electrical anisotropy in magnetotelluric responses abstract dimensionality analysis of magnetotelluric data is a common procedure for inferring the main properties of the geoelectric structures of the subsurface such as the strike direction or the presence of superficial distorting bodies and enables the most appropriate modeling approach 1d 2d or 3d to be determined most of the methods currently used assume that the electrical conductivity of individual parts of a structure is isotropic although some traces of anisotropy in data responses can be recognized in this paper we investigate the imprints of anisotropic media responses in dimensionality analysis using rotational invariants of the magnetotelluric tensor we show results for responses generated from 2d synthetic anisotropic models and for field data that have been interpreted as showing the effects of electrical anisotropy in parts of the subsurface structure as a result of this study we extend the wal dimensionality criteria to include extra conditions that allow anisotropic media to be distinguished from 2d isotropic ones the new conditions require the analysis of the strike directions obtained and take into account the overall behavior of different sites in a survey