large striated burrows from fluvial deposits of the neogene vinchina formation la rioja argentina a crab origin suggested by neoichnology and sedimentology abstract this study includes three aspects 1 the ichnotaxonomic treatment of large and dominantly vertical burrows ornamented with sharp bioglyphs from the fluvial neogene vinchina and toro negro formations northwest argentina 2 the description and interpretation of the sedimentary facies where these burrows occur and 3 neoichnologic observations on large ornamented burrows from seasonal wetlands of the rio pilcomayo national park argentina as possible modern analogues of the trace fossils and the sedimentary environment a new ichnogenus and ichnospecies capayanichnus vinchinensis is proposed to include the large striated burrows the new ichnotaxon is distinguished by a combination of a predominantly vertical orientation overall l shape when fully developed absence of lining and burrow bifurcation a distinct surface texture and lack of burrow enlargements the hosting sedimentary facies of the vinchina formation can be grouped into fluvial channel and splay floodplain facies associations the rivers of that unit were of two main types single channel rivers with frequent channel avulsion and overbank flow and multichannelised rivers with poorly defined margins at least some of these rivers were ephemeral or with intermittent discharge the climate was probably seasonal and semiarid as suggested by sedimentologic evidence c vinchinensis was dominantly recorded from the top of fluvial channels interpreted as abandoned channels and proximal intermediate and distal splay facies the large ornamented burrows found in an extant comparable example were constructed by freshwater crabs these burrows can be distinguished by the overall architecture the taxonomy and sex of its occupants and the environmental setting where they were found the neoichnologic signatures used in the interpretation of the fossil example include the common oval burrow cross section and the surface texture in particular the surface texture in the modern crab burrows includes abundant comma shaped marks sets of grooves oblique to burrow axis and long segmented grooves the predominantly oval cross section absence of lining and the strongly ornamented burrow surface suggest that c vinchinensis was produced by freshwater crabs the key features of the surface ornament are long sets of three four ridges whose width is in average one third of the burrow major axis other features that also point to a crab origin are a massive filling common burrow ends in a casing mudstone chevron pattern in sets of surface ridges and possible cheliped marks the new ichnotaxon is restricted in the vinchina and toro negro formations to fluvial facies and is absent in shallow lacustrine facies

sources of magnetic susceptibility in a slate abstract magnetic susceptibility and its anisotropy in the borrowdale volcanic slates at kentmere in the english lake district are attributed largely to preferred orientation of a paramagnetic chlorite of diabantite ripidolite composition in units of 10 6 cgs g the principal susceptibilities for the slates are 9 61 9 42 8 69 and for the chlorite grains the minimum anisotropy is represented by principal susceptibilities of 11 57 11 22 and 9 15 because the magnetic susceptibility is carried by a tightly packed matrix forming mineral that has recrystallised during the deformation it is not possible to imagine simple grain rotation as being responsible for the anisotropy of susceptibility

correlation between magnetic fabrics strain and biotite microstructure with increasing mylonitisation in the pretectonic wyangala granite australia abstract the wyangala granite is a foliated porphyritic silurian granite from the palaeozoic circum pacific type eastern lachlan orogen elo of australia it is a paramagnetic ilmenite bearing s marginal i type two mica to mainly biotite granite with different biotite contents and local chlorite alteration very highly strained quartz epidote bands are present in this contribution anisotropy of magnetic susceptibility ams is compared with independently measured intensity and 3d style of strain biotite microstructure and degree of mylonitisation for low strain granites with weak s foliations through medium strain protomylonitic granites with moderate s and c foliations to a high strain altered granite with a strong single foliation the samples are further analysed for possible contributions from sample heterogeneity magmatic flow and sub magmatic deformation a good correlation p ams 1 02 0 04 ln p e qtz is obtained between site average degree of ams p ams in the granite and degree of finite strain anisotropy p e qtz from aspect ratios of quartz aggregates in s foliations in hand specimen and outcrop p ams 1 03 1 14 p e qtz 1 4 19 the magnetic fabric ellipsoids agree with a kinematic regime between neutral and pure oblate predicted by the march model the observed quartz strains however exceed the ams march strains and are near neutral plano linear character the geological factors that may have contributed to these differences include intra and inter crystalline deformation of biotite and bimodality in s and c magmatic fabric is not clearly evident in either the ams or the biotite data new data for synkinematic oligoclase low titanium biotite and low sodium k feldspar show that conditions during deformation were approximately transitional greenschist amphibolite facies i e well below solidus this agrees with published age data that put the granite emplacement in an extensional back arc setting in already deformed country rocks and before later convergent regional deformation in middle devonian tabberabberan event to early carboniferous kanimblan event time

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

the anisotropy of magnetic susceptibility in biotite muscovite and chlorite single crystals the anisotropy of magnetic susceptibility ams of single crystals of biotite muscovite and chlorite has been measured in order to provide accurate values of the magnetic anisotropy properties for these common rock forming minerals the low field ams and the high field paramagnetic susceptibility are defined for the high field values it is necessary to combine the paramagnetic deviatoric tensor obtained from the high field torque magnetometer with the paramagnetic bulk susceptibility measured from magnetization curves of the crystals this leads to the full paramagnetic susceptibility ellipsoid due to the anisotropic distribution of iron cations in the silicate lattice the ellipsoid of paramagnetic susceptibility which was obtained for the three phyllosilicates is highly oblate in shape and the minimum susceptibility direction is subparallel to the crystallographic c axes the anisotropy of the susceptibility within the basal plane of the biotite has been evaluated and found to be isotropic within the accuracy of the instrumental measurements the degree of anisotropy of biotite and chlorite is compatible with previously reported values while for muscovite is smaller than previously published values the shape of the chlorite ams ellipsoid for all the samples is near perfect oblate in contrast with a wide distribution of oblate and prolate values reported in earlier studies reliable values are important for deriving models of the magnetic anisotropy where it reflects mineral fabrics and deformation of rocks d 2003 elsevier science b v all rights reserved

well preserved late precambrian paleosols from northwest scotland abstract two paleosol profiles were developed side by side on gneiss sheigra clay paleosol and amphibolite staca clay paleosol along the same unconformable contact of lewisian metamorphic rocks 2 7 1 7 ga overlain by torridonian sandstones 0 8 ga in northwestern scotland although altered during burial by compaction and illitization these profiles are well preserved compared with most other precambrian paleosols that are metamorphosed to at least greenschist facies in addition deformation of pegmatite veins in a manner similar to soil creep can be taken as an indication that upper horizons of these paleosols have been preserved soil development in both profiles was characterized by the oxidation of iron in biotite and magnetite and by hydrolysis of plagioclase orthoclase and hornblende clay skins soil like microfabrics and pedogenic smectite have been preserved in the profiles alteration of silicate grains other than quartz microcline and biotite has been intense but chemical analyses failed to show dramatic removal of alkalis and alkaline earths from the profiles microscopic concretions similar to pedogenic carbonate were found in subsurface horizons of the staca clay rare earth elements are more abundant within the paleosols than in their parent materials these paleosols developed on a well drained landscape that was buried by torridonian alluvial fans atmospheric oxidation was greater than revealed by studies of archean paleosols but probably still short of modern levels paleoclimate was subhumid and probably seasonal organic carbon and its light isotopic composition in the paleosol is evidence for photosynthetic microbial crusts paleosols of such great antiquity do not fit comfortably within modern soil taxonomies and are for the moment assigned to the informal category of green clays

quantitative correlation of texture and magnetic anisotropy of compacted calcite muscovite aggregates abstract deformation of carbonate rocks leads to crystallographic preferred orientations cpos of calcite which in turn generates an anisotropy of magnetic susceptibility ams the use of the diamagnetic anisotropy which arises from the preferential orientation of calcite for texture characterization is usually hindered by 1 the weakness of the anisotropy and 2 overlapping contributions from paramagnetic and ferromagnetic minerals to the ams in this study the diamagnetic paramagnetic and ferromagnetic sub fabrics of synthetic calcite muscovite samples have been separated using high field torque measurements the cpo of calcite and muscovite has been determined by neutron diffraction and the magnetic sub fabrics are compared to the ams that was re calculated from the cpo the isolated diamagnetic sub fabric shows a good correlation with the calcite texture for calcite concentrations above 70 the paramagnetic sub fabric is shown to be a reliable texture parameter for muscovite even at a concentration of 5 the results demonstrate the capability of the ams method as a texture parameter in impure carbonate rocks

sediment provenance and dispersal in a deep marine foreland basin the lower carboniferous culm basin czech republic the lower carboniferous culm basin of the czech republic represents the most easterly and southerly part of the european variscan foreland basin system the nne ssw trending basin is exposed along the eastern flank of the bohemian massif it contains up to 7 5 km of deep marine sediment deposited as an axial turbidite system sourced from south southwest of the basin heavy mineral data and clast types indicate that for much of the visean sediment was sourced from a predominantly low grade metamorphic terrane and visean limestones in the latest visean a progressive change in source material is recorded by an increase in high grade metamorphic detritus studies of variscan nappe pile emplacement along the eastern flank of the bohemian massif allow an assessment of the relationship between basin development and nappe emplacement basin initiation coincided with underthrusting of high grade metamorphic moldanubian nappes at 340 ma sedimentation was synchronous with nappe emplacement throughout the visean which resulted in uplift and erosion of a low grade metamorphic terrane moldanubian nappes were exhumed at approximately 330 ma when high grade metamorphic detritus entered the basin two phases of northward directed sediment progradation are recognized sediment progradation is considered to be related to changes in drainage basin size and or climatic fluctuations within the variscan orogen since sediment is inferred to have been supplied to the basin axially rather than laterally and subsidence curves show no significant change in subsidence rates in contrast to many models of foreland basin sediment distribution filling of the culm basin was largely independent of tectonic activity adjacent to the basin margin and or of subsidence rate changes sedimentation in the culm basin commenced 10 15 ma earlier than the rest of the variscan foreland and records the first impact of the northwardly propagating variscan orogen in northern europe

high level surfaces plateau uplift and foreland development bolivian central andes newly dated tertiary strata in the bolivian central andean plateau and synthesis of the tertiary record in the adjacent subandean fold thrust belt constrain the age of deformation in both regions age of deformation within the plateau is determined by dated crosscutting relations associated with a regionally extensive high level surface known as the san juan del oro surface new 40 ar 39 ar dates on undeformed strata above the high level surface preclude significant upper crustal shortening within the eastern cordillera after 10 ma tertiary strata within the adjacent subandean region demonstrate that formation of the fold thrust belt occurred after 10 ma on the basis of these data we propose a two stage model of late cenozoic andean growth that links plateau uplift to the development of the fold thrust belt in the first stage early plateau uplift occurred in response to widespread compressional deformation of the plateau eastern cordillera and altiplano during the second stage beginning after 10 ma upper crustal deformation within the plateau terminated and the subandean fold thrust belt developed crustal scale eastward thrusting along the eastern margin of the eastern cordillera drove subandean folding and thrusting the eastern cordillera served as the bulldozer for the deforming subandean wedge

early to middle tertiary foreland basin development and the history of andean crustal shortening in bolivia a 2 5 km thick succession of tertiary strata in the eastern cordillera of southern central bolivia consists of predominantly fluvial and lacustrine deposits the age of the base of the succession is middle paleocene and its upper part which is erosionally truncated is probably late oligocene early miocene the lower 50 130 m of the succession consists of interbedded fluvial sandstone and mudstone including minor paleosols of the santa lucia formation these strata are overlain by up to 50 m of pervasively pedogenically altered mudstone and sandstone in the upper part of the santa lucia formation and lower part of the impora formation that may represent much of late paleocene eocene time above the paleosol zone is a thin zone 10 m of lacustrine carbonate and clastic rocks in the uppermost impora formation and this in turn is overlain by a 2000 m thick upward coarsening succession of clastic fluvial deposits in the cayara camargo and suticollo formations paleocurrent data indicate that fluvial channels that deposited the santa lucia impora and cayara formations flowed mainly westward whereas channels responsible for the camargo and suticollo formations flowed generally eastward modal sandstone petrographic data show a long term evolution from subarkosic during santa lucia deposition to quartz arenitic during impora and cayara deposition to sublitharenitic during camargo and suticollo deposition compositions we argue that the lithofacies and sediment accumulation history of this succession are most consistent with deposition in an eastward migrating foreland basin system e mail decelles geo arizona edu critical to this interpretation is the zone of extreme stratigraphic condensation in the lower impora formation the inferred upper paleocene eocene part of the succession the abrupt decrease in sediment accumulation represented by this zone is difficult to reconcile with the leading alternative model in which continuous postrift thermal subsidence resulted in a gradual continuous decay of early tertiary sediment accumulation rates stratigraphic condensation is however consistent with passage of the forebulge through the region an interpretation that also can be reconciled with the record of foreland basin development in the altiplano to the west and gross sediment accumulation patterns in the subandean zone and modern foreland basin to the east simple flexural modeling and palinspastic reconstruction of the complete cenozoic migration history of the foreland basin system suggest that 1000 km of foreland lithosphere has been underthrust westward beneath the andean orogenic belt at the latitude of southern bolivia the amount of middle and lower crust that would have been added to the andean infrastructure is sufficient to explain the present crustal thicknesses in bolivia

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

crystallographic preferred orientation magnetic and seismic anisotropy in rocks from the finero peridotite ivrea verbano zone northern italy interplay of anisotropy contributions from different minerals abstract mineral alignment can provide valuable information on a rock s geological history many structural tectonic or geodynamic studies rely on determining the preferred orientation of rock forming minerals either by direct texture determination or using anisotropy measurements as proxies robust interpretations of anisotropy require detailed understanding of its relationship with texture this study investigates the texture magnetic and seismic anisotropies of ultramafic rocks from the ivrea verbano zone ivz northern italy with a special focus on the interplay between anisotropy contributions carried by different minerals texture was obtained from electron backscatter diffraction magnetic anisotropy from low and high field anisotropy of susceptibility measurements and seismic anisotropy from p and s wave velocities along the three principal directions of the macroscopic fabric using 22 mm diameter cores texture based models of magnetic anisotropy agree well with corresponding measurements larger variability is observed for seismic anisotropy possible explanations are 1 velocities were measured in three directions insufficient to determine the full elasticity tensor and 2 seismic anisotropy depends on grain boundaries pores and cracks in addition to crystallographic preferred orientation the contributions to magnetic and seismic anisotropy of each constituent mineral can interfere positively leading to a larger overall anisotropy or negatively resulting in a weaker anisotropy seismic anisotropy is mostly controlled by olivine whereas magnetic anisotropy can be dominated by olivine pyroxene or hornblende this study illustrates that although the relationship between texture and anisotropy can be complex it is possible to quantitatively predict magnetic and to a lesser degree seismic anisotropy from texture data even though both magnetic and seismic anisotropies are common proxies for texture they are not coaxial and no simple relationship between the degree of magnetic and seismic anisotropy was found these results underline the importance of understanding different minerals contributions to anisotropy in upper mantle rocks

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

magnetic polarity stratigraphy of inchasi a pliocene mammal bearing locality from the bolivian andes deposited just before the great american interchange abstract the newly discovered section at inchasi located about 50 km southeast of potosi bolivia in the eastern cordillera consists of about 120 m of undeformed terrestrial sediments containing fossil mammals paleomagnetic analysis of 54 sites indicates a polarity pattern with an estimated duration of about 0 64 ma the rich inchasi local fauna indicates a montehermosan and or chapadmalalan land mammal age pliocene given these constraints inchasi correlates from the interval between the late gilbert within the cochiti subchron to the early gauss within the mammoth subchron chrons that is between about 4 0 and 3 3 ma the distinct lack of north american mammals in the inchasi local fauna provides some of the first well calibrated evidence that the great american interchange occurred after about 3 0 ma as has been previously stated based on other calibrations of the earliest immigrant uquian faunas

stable isotope evidence for multiple pulses of rapid surface uplift in the central andes bolivia paleoelevation histories from mountain belts like the central andes of bolivia provide important constraints on the timing and geodynamic mechanisms associated with surface uplift we present new oxygen and carbon isotope data 18 o 13 c and 47 from oligocene miocene strata exposed in the eastern cordillera of the bolivian central andes in order to reconstruct both the deformation and paleoelevation history of the region prior to late miocene time paleosol carbonate in strata 24 ma have 18 o c values between 5 7 and 9 7 and 47 values indicating paleotemperatures of 32 42 c paleosol carbonate in strata ca 17 ma have 18 o c values between 11 6 and 13 8 and 47 values indicating paleotemperatures of 15 23 c these data interpreted within the context of recent paleoclimate topography models suggest oligocene early miocene 29 24 ma paleoelevations were between 0 and 1 5 km a s l while middle miocene ca 20 15 ma paleoelevations were 2 5 km a s l oligocene and miocene strata are relatively undeformed and overlap folded and faulted paleozoic rocks in this portion of the bolivian eastern cordillera indicating much of the change in elevation occurred after upper crustal deformation collectively data from the area record an initial period of upper crustal deformation and exhumation a subsequent period of sediment deposition and overlap and then an episode of surface uplift accompanied by negligible upper crustal deformation the disconnect between the timing of upper crustal deformation and the timing of surface uplift requires geodynamic processes other than upper crustal thickening to explain the oligocene miocene basin and elevation history in the eastern cordillera we propose accommodation for oligocene miocene strata was created in response to the formation and removal of negatively buoyant material in the lowermost crust and mantle lithosphere and the subsequent increase in surface elevation between ca 24 and 15 ma resulted from its removal other locations in the central andes record similar geological histories over different time periods suggesting spatial and temporal variation in the removal of lithospheric mantle documenting basin extent age and elevation history provides important constraints on the size and timescale of the geodynamic processes that control surface uplift

ichnotaxonomy and ichnostratigraphy of chambered trace fossils in palaeosols attributed to coleopterans ants and termites

paleosurfaces paleoelevation and the mechanisms for the late miocene topographic development of the altiplano plateau abstract we construct a topographic datum across the central andes between 18 s and 22 s using extensive well preserved paleosurfaces that span the entire range this datum combined with estimates of topographic change from paleoaltimetry in the altiplano and geomorphic relief generation estimates from the plateau flanks allow us to reconstruct the paleo topography of the range at 10 ma using the 10 ma topography we explore which geophysical processes can create the observed topographic change over the

late cenozoic paleomagnetism and chronology of andean basins of bolivia evidence for possible oroclinal bending new paleomagnetic and radioisotopic data are reported from two late tertiary high elevation non marine basins in the eastern cordillera of bolivia 1 quebrada honda located at 22 s lat consists of a 300 m thick section containing abundant santacrucian or friasian middle miocene fossil mammals this locality is constrained by mean 40 k 40 ar ages of 12 83 0 11 ma and 11 96 0 11 ma and the local magnetostratigraphy is correlated to chrons c5aa through c5a on the magnetic polarity time scale mpts the fossil mammals from quebrada honda have an extrapolated age of about 13 0 to 12 7 ma 2 micana located at 17 s lat consists of a 205 m thick section containing late miocene fossil mammals including a megatheriid sloth and the tiny mesothere microtypotherium cf m choquecotense this locality is constrained by a fission track age determination of 6 9 1 1 ma and the local magnetostratigraphy is correlated to chron 7 on the mpts the fossil mammals from this section have an extrapo

anisotropy of magnetic susceptibility in diamagnetic limestones reveals deflection of the strain field near the dead sea fault northern israel abstract to exploit the potential of anisotropy of magnetic susceptibility ams as a tool to estimate the strain field around major faults we measured the ams of calcite bearing diamagnetic rocks that crop out next to the dead sea fault dsf in northern israel through integrated magnetic and geochemical methods we found that the rocks are almost pure calcite rocks and therefore the magnetic fabric is primarily controlled by preferred crystallographic orientation pco with the minimum principal ams axes k 3 parallel to calcite c axes we applied a separation procedure in several samples with high fe content in order to calculate the ams anisotropy parameters and compare them to pure diamagnetic rocks aarm thermo susceptibility curves and irm were used to characterize the magnetic phases we found that for fe content below 500 ppm the ams is mostly controlled by the diamagnetic phase and showed that differences in the degree of anisotropy p up to 3 p 1 005 to 1 023 and in anisotropy difference k up to 0 25 10 6 si in diamagnetic rocks are related to differences of strain magnitudes the spatial distribution of the magnetic fabrics indicates n s maximum shortening parallel to the strike of the hula western border fault hwbf one of the main strands of the dsf in northern israel the anisotropy parameters suggest that the strain magnitudes increase eastward with the proximity to the hwbf these results suggest that the strain field near the hwbf is locally deflected as a consequence of the dsf activity in light of the fault weakness model and geological setting of the study area we suggest that the area accommodates dominant transtension during the pleistocene the present study demonstrates the useful application of ams measurements in iron free limestones as recorders of the strain field near plate boundaries

control of magnetic rock fabrics by mica preferred orientation a quantitative approach magnetic anisotropy analysis represents a well established and frequently used method in structural geology several attempts were made to relate the anisotropy of magnetic susceptibility ams to rock fabrics and to discover the sources of the ams in gneissic rocks paramagnetic phyllosilicates with lattice dependent magnetic properties are assumed to control the whole rock ams i e it is dominated by mica lattice preferred orientation texture in this study ams was modelled on the basis of the mica texture the rock composition and compared to the experimentally determined ams the orientations of the modelled and experimental tensors agree quite well whereas all the other characteristic parameters shape anisotropy mean susceptibility display large differences it has been concluded that accessory high susceptible phases as well as the diamagnetic rock constituents may have significant influence on ams consequently mica pole figure measurements cannot be replaced by ams measurements without control of the sources of ams it was also concluded that the march model to evaluate strain from mica preferred orientations is not valid for highly strained rocks beside the fact that the obtained strains are too low the deformation is generally inhomogeneous which leads to an overprint of the mica texture since the microstructural fabric elements which originate in different strain regimes prolate or oblate may create similar modifications of the mica orientation patterns it is obvious that the relationship between ams and deformation is rather complex

magnetic fabric study of the se rhenohercynian zone bohemian massif implications for dynamics of the paleozoic accretionary wedge the progressive deformation recorded in the magnetic fabric of sedimentary rocks was studied in the se rhenohercynian zone rhz eastern margin of the bohemian massif czech republic almost 800 oriented samples of the lower carboniferous mudstones and graywackes were collected from the sse part of the czech rhz so called the drahany upland the anisotropy of magnetic susceptibility ams is predominantly controlled by the preferred orientation of paramagnetic phyllosilicates mainly iron bearing chlorites a regional distribution of the magnetic fabric within the drahany upland revealed an increasing deformation from the sse to the nnw in the se the magnetic fabric is bedding parallel with magnetic lineation scattered in the bedding plane or trending n s to nne ssw further to the nw the magnetic foliation rotates from the bedding parallel orientation to the orientation parallel to the evolving cleavage

lower eocene alluvial paleosols pedogenic development stratigraphic relationships and paleosol landscape associations abstract two kinds of cumulative floodplain paleosols red and grey paleosols formed on overbank deposits of the willwood formation in the sand coulee area of the bighorn basin wyoming although both kinds experienced down profile iron movement due to seasonal saturation of a clay rich a horizon the red paleosols were better drained and their b horizons were rubified various redoximorphic features indicate that the grey paleosols were poorly drained the red paleosols show progressive increases in the degree of profile development away from an associated channel sandstone a paleosol landscape relationship termed pedofacies by bown and kraus 1987 although the grey paleosols show relatively systematic changes in hydromorphy consistent pedofacies changes were not recognized furthermore no lateral relationship between the red and grey paleosols was observed these features suggest that because of the retarding effects of poor drainage on soil weathering poorly drained soils are not amenable to pedofacies modelling and that the landscape associations of well drained and poorly drained soils may be difficult to document without unusually extensive exposures results of this study also show that the pedofacies model is limited by sediment accumulation rates and the kind of fine grained facies on which paleosols developed although readily observable in sand coulee pedofacies are difficult to recognize in the elk creek area where accumulation rates were approximately half as rapid as in sand coulee the attainment of steady state conditions is believed to have obscured pedofacies in the elk creek area finally pedofacies are only developed on true overbank deposits which in the willwood formation and probably many other ancient alluvial sequences make up only a fraction of the fine grained deposits only immature soils formed on the remainder of the fine grained facies because they were deposited very rapidly as a result of channel avulsion

numerical analysis of x ray texture data an implementation in fortran allowing triclinic or axial specimen symmetry and most crystal symmetries abstract the use of complete descriptions of preferred orientation for studies of experimentally and naturally deformed rocks is discussed diagrammatic representations of preferred orientations are defined and conventions for coordinate systems are given methods of extracting information from the orientation distribution function are described a system of fortran programs which enables the orientation distribution function to be calculated for most suitable minerals is described

middle pleistocene age of the fossiliferous sedimentary sequence from tarija bolivia abstract the highly fossiliferous sediments of the tolomosa formation from tarija southern bolivia represent one of the most important localities in south america that documents the great american biotic interchange over the past several decades chronostratigraphic studies have indicated a middle pleistocene age for the tolomosa formation from 1 1 to 0 7 ma this interval correlates to the ensenadan south american land mammal age as it is characterized from classic localities in argentina recently however a new interpretation based on ams 14c ages indicates that the fossiliferous sediments from tarija are latest pleistocene i e

the origin of tectonic lineation in extensional basins combined neutron texture and magnetic analyses on undeformed clays abstract in extensional sedimentary basins fine grained sediments that appear undeformed at the outcrop scale can carry a magnetic fabric consistent with the regional deformation pattern the origin of the magnetic lineation which is often found in extensional basins is not yet well understood in clays from extensional basins in southern italy the magnetic lineation is tectonically controlled and oriented perpendicular to the main normal faults a combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a lineation in extensional settings low field high field and low temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy the magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes results demonstrate that the orientation of the magnetic lineation is related to the spatial distribution of chlorite lying parallel to the common axis of differently oriented basal planes a quantitative correlation between the magnetic and rock fabric was made comparing the low and high field magnetic anisotropy ams hfa to the theoretical anisotropy calculated from the chlorite preferred orientation a good linear correlation is found between the degree of theoretical anisotropy and the ams and hfa results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins where macroscopic evidence of deformation is often not visible

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

phyllosilicate preferred orientation as a control of magnetic fabric evidence from neutron texture goniometry and low and high field magnetic anisotropy se rhenohercynian zone of bohemian massif

magnetic fabrics in the bjerkreim sokndal layered intrusion rogaland southern norway mineral sources and geological significance abstract magnetic anisotropy can provide important information about mineral fabrics and thus magmatic processes particularly when it is known how multiple mineral species contribute to the anisotropy it may also affect the direction of induced or remanent magnetization with important consequences for paleomagnetic studies or the interpretation of magnetic anomalies here we aim at describing the magnetic fabrics in the bjerkreim sokndal layered intrusion and identifying their carriers anisotropies of magnetic susceptibility and remanence were measured on samples covering different geographic locations and stratigraphic units within the bjerkreim sokndal layered intrusion the intrusion is characterized by magmatic layering and has a synform structure with strong foliation on the limbs detailed comparison between magnetic and mineral fabric shows that they are not necessarily coaxial but the minimum susceptibility and minimum anhysteretic remanence are generally normal to the foliation or the magmatic layering the minimum susceptibility and anhysteretic remanence are associated with pyroxene 100 axes and the maximum susceptibility and anhysteretic remanence are sub parallel to the pyroxene 001 axes in layers mcu ivc and mcu ive for which electron backscatter data are available however the paramagnetic anisotropy of pyroxene is too weak to explain the observed anisotropy we propose that the magnetic anisotropy of magnetite free specimens is carried by hemo ilmenite exsolutions within pyroxene in addition to pyroxene itself when present multi domain magnetite dominates both the anisotropy of magnetic susceptibility and anhysteretic remanence due to shape preferred orientation and distribution anisotropy the orientation of the magnetic fabric appears independent of carrier due to their common deformation history but the degree of anisotropy is stronger for magnetite bearing specimens the results of this study will facilitate future structural interpretations and may be used to correct for magnetization deflection

influence of static alternating field demagnetization on anisotropy of magnetic susceptibility experiments and implications anisotropy of magnetic susceptibility ams indicates the preferred orientation of a rock s constituent minerals however other factors can influence the ams e g domain wall pinning or domain alignment in ferromagnetic minerals therefore it is controversial whether samples should be alternating field af demagnetized prior to ams characterization this may remove the influence of natural remanent magnetization nrm or domain wall pinning on ams however it may also result in field induced anisotropy this study investigates the influence of stepwise af and low temperature demagnetization on mean susceptibility principal susceptibility directions ams degree and shape for sedimentary metamorphic and igneous rocks alternating fields up to 200 mt were applied along the sample x y and z axes rotating the order for each step to characterize the relationship between ams principal directions and the last af orientation the changes in anisotropy defined by the mean deviatoric susceptibility of the difference tensors are between 2 and 270 of the ams in nrm state variations in ams parameters range from small changes in shape to complete reorientation of principal susceptibility axes with the maximum susceptibility becoming parallel to the last af direction this is most prevalent in samples with low degrees of anisotropy in the nrm state no clear correlations were found between field induced anisotropy and hysteresis properties therefore we propose that future studies check any samples whose ams is carried by ferromagnetic minerals and low anisotropy degrees for af induced artifacts these results highlight the need for understanding the ams sources and carriers prior to any structural interpretation

crystallographic and magnetic preferred orientation of hematite in banded iron ores abstract the crystallographic preferred orientation of hematite in banded iron ores and the orientation of both the measured and the calculated principal susceptibility axes are strongly related the maximum susceptibility is aligned with the lineation and the pole of the foliation coincides with the minimum susceptibility although there are often distinct differences between the measured and calculated values of the susceptibilities a wide variety of configurations of c axis pole figures modeled by varying the parameters of the bingham distribution and bingham mardia distribution reveal that quite different c axis patterns of hematite ores may have the same anisotropy of the magnetic susceptibility ams parameters large deviations between calculated and experimental ams data should initiate further investigations to resolve a probably unnoticed heterogeneity of the fabric the present investigations show that the structural analysis of the preferred orientation of hematite ores by means of the rather inexpensive and fast magnetic method must be accompanied by the more expensive but unambiguous determination of preferred orientation by x ray and neutron diffraction experiments in order to accomplish a complete and sound interpretation

magnetic polarity stratigraphy and mammalian fauna of the deseadan late oligocene early miocene salla beds of northern bolivia the salla beds contain a rich assemblage of deseadan mammals that traditionally has been considered of early oligocene age these deposits located 90 100 km se of la paz bolivia consist of more than 540 m of principally fluviatile clays and silts with numerous interbedded tuffs paieomagnetic samples were collected from 104 sites spaced at stratigraphic intervals of about 6 m as a result of thermal demagnetization at 400 c or greater unambiguous polarities were determined for 76 of the 104 originally sampled sites the pattern of reversals stage of evolution of the fossils and preliminary isotopic dates including a k ar age of 26 4 pm 1 0 ma and zircon fission track ages of ca 22 ma from interbedded tuffs suggest that the salla beds correlate to chrons c10 through c6 of the magnetic polarity time scale or an absolute time interval from about 28 5 to 24 ma pyrotherium and caviomorph rodents occur throughout the section the primate branisella is known to occur at about 27 ma the salla f

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

rapid late miocene rise of the bolivian altiplano evidence for removal of mantle lithosphere abstract the oxygen isotopic compositions of carbonates deposited in the northern altiplano demonstrate a rapid change in late miocene time which we attribute to an increase in elevation rainfall samples over an elevation transect adjacent to the altiplano of northern bolivia display a systematic decrease in mean annual 18 o values and define a local 18 o vs altitude gradient r gonfiantini m a roche j c olivry j c fontes g m zuppi the altitude effect on the isotopic composition of tropical rains chem geol 181 2001 147 167 which we apply to paleo meteoric water values determined from carbonates age constraints from magnetostragraphy and paleoelevation estimates suggest surface uplift of 2 5 to 3 5 km occurred between 10 3 ma and 6 8 0 4 ma when the altiplano rose to its current elevation only the removal of dense eclogitic lower crust and mantle lithosphere can generate a change of this magnitude and rapidity this change coincides with an 30 decrease in the rate of convergence between the south america and nazca plates and the propagation of deformation into the eastern subandean zone which we infer to have resulted from the increase in the force per unit length applied by the elevated andean plateau to the surrounding lowlands

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

interpretation quantitative de l anisotropie de susceptibilite magnetique abstract we propose a model in which the magnetic susceptibility anisotropy is considered as resulting from the distinct properties of two rock components this model suggests that differences in the susceptibility ellipsoid can be principally related to mineralogical variations thus some difficulties in the quantitative interpretation of anisotropy data may be explained this model is consistent with a detailed analysis carried on dalradian rocks from scotland a new methodology of anisotropy analysis is derived it is based on the fact that in specimens from a same sample the susceptibility ellipsoid often varies but relations nevertheless exist between values of the principal and mean susceptibilities for each sample measurements are made on 6 12 specimens the study of the relations between principal and mean susceptibilities permits separation of the anisotropies of the rock components the anisotropy determination appearing the best for the high susceptibility component

paleomagnetic study of neoarchean paleoproterozoic dykes in the kaapvaal craton 431 oriented samples were collected from 27 dolerite dykes at 17 sites belonging to 2 95 2 65 and 1 90 ga swarms that trend se e and ne respectively from the bushveld igneous complex into the eastern kaapvaal craton ages determined by olsson et al 2010 olsson in soderlund et al this volume samples were analyzed for paleomagnetism and also anisotropy of magnetic susceptibility ams for the 2 95 ga se trending dykes high temperature coercivity p component has unblocking temperatures up to 590 degrees c and coercivity 40 90 mt and demonstrate ssw declination and intermediate positive inclination based on positive contact and conglomerate tests we argue for a primary origin of this component the paleopole bad calculated from component does not correspond to any of the previously obtained archean paleoproterozoic paleopoles for the kaapvaal craton and represents a new key pole for 2 95 ga the high coercivity h component for the 2 65 ga old e trending dykes has a ssw declination and steep positive inclination paleomagnetic pole ryk recalculated from this component is close to the paleopoles obtained by wingate 1998 and strik et al 2007 for 2 78 ga ventersdorp volcanics the third group ne trending dykes of the 1 90 ga black hill swarm demonstrate an m component with dual polarity high coercivity component with sse declination and negative intermediate inclination the paleopole bhd calculated from this component is close to the 1 87 ga pole of the kaapvaal craton obtained by hanson et al 2004 overprint directions include a very well developed thermo chemical overprint dec 329 degrees inc 36 degrees which is believed to be associated with a similar to 0 18 ga regional karoo thermal event c 2010 elsevier b v all rights reserved less

paleoelevation reconstruction using pedogenic carbonates paleoelevation reconstruction using stable isotopes although a relatively new science is making a significant contribution to our understanding of the recent growth of the world s major orogens in this review we examine the use of both light stable isotopes of oxygen and the new clumped isotope 47 carbonate thermometer in carbonates from soils globally the oxygen isotopic composition 18 o of rainfall decreases on average by about 2 8 km of elevation gain this effect of elevation will in turn be archived in the 18 o value of soil carbonates and paleoelevation can be reconstructed provided 1 temperature of formation can be estimated 2 the effects of evaporation are small 3 the effects of climate change can be accounted for and 4 the isotopic composition of the carbonate is not diagenetically altered we review data from modern soils to evaluate some of these issues and find that evaporation commonly elevates 18 o values of carbonates in deserts an effect that would lead to underestimates of paleoelevation some assessment of paleoaridity using qualitative indicators or carbon isotopes from soil carbonate is therefore useful in evaluating the oxygen isotope based estimates of paleoelevation sampling from deep 50 cm in paleosols helps reduce the uncertainties arising from seasonal temperature fluctuations and from evaporation the new clumped isotope 47 carbonate thermometer expressed as 47 offers an independent and potentially very powerful approach to paleoelevation reconstruction in contrast to the use of 18 o values nothing need be known about the isotopic composition of water from which carbonate grew in order to estimate of temperature of carbonate formation from 47 values using assumed temperature lapse rates with elevation paleoelevations can thereby be reconstructed case studies from the andes and tibet show how these methods can be used alone or in combination to estimate paleoelevation in both cases the potential for diagenetic alteration of primary carbonate values first has to be assessed clear examples of both preservation and alteration of primary isotopic values are available from deposits of varying ages and burial histories 47 values constitute a relatively straightforward test since any temperature in excess of reasonable surface temperatures points to diagenetic alteration for 18 o values preservation of isotopic heterogeneity between different carbonate phases offers a check on diagenesis results of these case studies show that one area of south central tibet attained elevations comparable to today by the late oligocene whereas 2 7 0 4 km of uplift occurred in the bolivian altiplano during the late miocene

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

paramagnetic metamorphic mineral assemblages controlling ams in low grade deformed metasediments and the implications with respect to the use of ams as a strain marker a regional analysis of the anisotropy of magnetic susceptibility ams has been performed on low grade metamorphic deformed homogeneous siltstone beds hsbs of the plougastel formation in the central armorican domain together with exhaustive compositional analyses of the studied specimens despite sampling a single horizon different paramagnetic minerals are controlling the ams in the crozon peninsula sites white mica and chlorite and in the inland sites of the central armorican domain white mica chloritoid and some chlorite both the crozon peninsula and inland datasets show a hockey stick shaped pattern on a plot of the shape parameter t versus the corrected degree of anisotropy p j although the whole pattern is shifted to higher p j values for the inland dataset high field ams indicates that the low field p j and t values from two inland sites are slightly enhanced by a small ferromagnetic sensu lato contribution furthermore variation in p j and t values within single sites can be attributed to an effect of the observed quartz white mica ratio as quartz grains disrupt the petrofabric intensity our findings clearly demonstrate that the ams of the hsbs in the central armorican domain is strongly influenced by compositional variations and does not merely indicate tectonic strain even in very similar tectonostratigraphic settings supplementary material outcrop coordinates with information on the hsbs and samples and the summarized low field room temperature ams data are available at www geolsoc org uk sup18578

paleosol and ichnofossil evidence for significant neotropical habitat variation during the late middle miocene serravallian we use paleopedology and ichnology to elucidate the habitat of the late middle miocene fossil site of quebrada honda southern bolivia the paleosols represent three pedotypes type 1 and type 2 paleosols are interpreted as inceptisols eutrudepts and entisols udifluvents respectively which formed on proximal and distal floodplains in a seasonal sub humid to humid wooded grassland like vegetative community type 3 paleosols are interpreted as inceptisols calciustepts that formed in more densely vegetated wooded grassland like vegetative communities on distal floodplains in a strongly seasonal sub humid to semi arid environment the ichnofossil assemblage of quebrada honda includes celliforma coprinisphaera taenidium fictovichnus planolites skolithos katarrhedrites and root traces and represents heterogeneous communities dominated by soil arthropods and plants the physical and geochemical properties of the paleosols including low maturity poor development of horizons and the overall moderate estimates of mean annual precipitation indicate changes in soil moisture due to seasonal precipitation and flooding and low but varying degrees of temporal stability the diverse ichnofossil assemblage of quebrada honda reflects environments with greater primary productivity and temporal stability than those of nearby cerdas bolivia which are several million years older quebrada honda s inferred paleoenvironments differ markedly from those of la venta colombia indicating that dissimilar habitats may partly or principally account for the vastly different faunas of these two well sampled and contemporaneous fossil localities

significance of different modes of rhizolith preservation to interpreting paleoenvironmental and paleohydrologic settings examples from paleogene paleosols bighorn basin wyoming u s a abstract different modes of preservation of root traces rhizoliths provide information on soil moisture regimes in alluvial paleosols in the paleogene fort union and willwood formations of the bighorn basin wyoming u s a this paper links different styles of rhizolith preservation to paleosols whose other pedogenic attributes provide information on ancient soil drainage consequently the paleodrainage significance of different rhizolith preservation patterns is established more confidently rhizoliths consisting of elongate gray mottles rhizohaloes with red rims are common in relatively well drained red paleosols the gray zones are depleted of iron fe whereas the color of the rims indicates hematite accumulation these features are typical of surface water gley processes that caused fe and manganese mn to move from the root channel outward to the soil matrix calcareous rhizocretions either calcareous tubular concretions or micro accumulations of carbonate within gray rhizotubules are also common in moderately well drained red paleosols more poorly drained purple paleosols also have rhizoliths consisting of fe depletion zones however the rhizohaloes are surrounded by yellow brown goethite rims rather than red hematitic rims in many paleosols the red and yellow brown accumulation rims were partly removed by continued depletion producing abundant irregular shaped mottles the nature of the rhizohalo and the color of the fe oxide rim provide information about the intensity of gleying that a paleosol underwent the poorly drained paleosols also show rhizoliths preserved as goethite accumulations contained within gray depletion zones indicating movement of reduced fe from the matrix towards the root channel probably as a result of groundwater gley processes the goethite accumulations are intermingled locally with lignite representing preservation of the root organic material some rhizoliths are preserved as tube shaped concentrations of small 0 1 0 2 mm diameter black spheres whose color indicates a mix of mn and fe oxides these are most common in paleosols with low chroma gray matrix colors indicating very poor drainage the very poorly drained paleosols also show rhizoliths preserved in jarosite which is an oxidation product of pyrite careful observational and geochemical analysis of rhizoliths which are common in continental deposits can help produce a clearer and more thorough interpretation of ancient drainage conditions information about degree of ancient soil wetness or moisture is important for understanding past climatic conditions and for reconstructing terrestrial paleolandscapes

tectonic evolution of pliocene pleistocene wedge top basins of the southern apennines new constraints from magnetic fabric analysis in the last decades multidiscipline investigation of the apennine mountain belt of peninsular italy has provided fundamental insights into the genesis and evolution of wedge top basins in this study we focus on shallow water to conti nental pliocene quaternary basins that formed on top of the southern apennine allochthonous wedge after its emplacement onto a large foreland carbonate platform domain apulian platform the wedge top basins analyzed in this study are mostly asymmetric being bounded to the north by a normal fault showing evidence of synsedimentary activity the basin succes sions are generally deformed by open folds and reverse faults resulting from shortening coeval with the sedimentation of the lower pliocene to lower middle pleistocene upper part of the basin fill anisotropy of magnetic susceptibility data from the basin successions are consistent with a basin evolution characterized by an initial stage of tectonic subsidence controlled by roughly north northwest south southeast oriented extension followed by southwest northeast shortening active during subse quent basin filling the latter shortening is marked by a dominant northwest southeast mean trend of the magnetic lineation obtained from most sites in the study area and is interpreted as a result of upward propagation of deep seated deformation tectonic inversion taking place within the buried apulian platform sitting in the footwall to the allochthonous wedge there fore our results emphasize a complex interplay of different tectonic processes controlling wedge top basin development resume au cours des dernieres decennies une etude multidisciplinaire de la chaine de montagnes des apennins dans la peninsule italienne a donne des apercus de la genese et de l evolution des bassins sur le prisme d accretion wedge top ba sins dans cette etude nous ciblons les bassins d eau peu profonde a continentaux datant du pliocene quaternaire qui se sont formes sur le dessus du prisme allochtone du sud des apennins apres sa mise en place sur un vaste domaine de plate forme de carbonate d avant pays la plate forme apulienne les bassins sur le prisme d accretion analyses dans la presente etude sont surtout asymetriques puisqu ils sont delimites au nord par une faille normale montrant des evidences d activite syn sedimentaire les successions de bassins sont generalement deformees par des plis ouverts et des failles inverses prove nant d un retrecissement contemporain de la sedimentation du pliocene inferieur au pleistocene inferieur moyen dans la par tie superieure du remplissage du bassin l anisotropie des donnees de susceptibilite magnetique provenant des successions de bassin concorde avec une evolution du bassin caracterisee par un stade initial de subsidence tectonique controlee par une extension a orientation generale nord nord ouest sud sud est suivie d un retrecissement sud ouest nord est actif durant le remplissage subsequent du bassin ce dernier retrecissement montre une tendance moyenne dominante nord ouest sud est de la lineation magnetique obtenue de la plupart des sites dans le secteur a l etude et il est interprete comme le resultat d une propagation vers le haut d une deformation situee en profondeur inversion tectonique qui s est produit dans la plate forme apulienne enfouie se trouvant dans l eponte inferieure du prisme allochtone nos resultats soulignent donc une interaction complexe entre les differents processus tectoniques qui controlent le developpement des bassins sur les prismes d accretion traduit par la redaction

resolution of ferrimagnetic and paramagnetic anisotropies in rocks using combined low field and high field measurements summary a method of separation of ferrimagnetic and paramagnetic components of magnetic anisotropy from the total anisotropy is developed from the anisotropy measurement of a specimen in a low field susceptibility anisotropy and from measurement in two high fields stronger than the saturation field of the ferrimagnetic fraction present the following anisotropy components can be calculated susceptibility anisotropy field independent of the paramagnetic fraction low field susceptibility anisotropy of the ferrimagnetic fraction and high field anisotropy of the ferrimagnetic fraction errors possibly arising from imperfect saturation of the ferrimagnetic fraction in the field practically available are analysed

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

preferred mineral orientation of a chloritoid bearing slate in relation to its magnetic fabric 2014 elsevier ltd a regional analysis of the anisotropy of the magnetic susceptibility on low grade metamorphic chloritoid bearing slates of the paleozoic in central armorica brittany france revealed very high values for the degree of anisotropy up to 1 43 nonetheless high field torque magnetometry indicates that the magnetic fabric is dominantly paramagnetic chloritoid s intrinsic degree of anisotropy of 1 47 0 06 suggests that chloritoid bearing slates can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic s l minerals to validate this assumption we performed a texture analysis on a representative sample of the chloritoid bearing slates using hard x ray synchrotron diffraction the preferred orientation patterns of both muscovite and chloritoid are extremely strong 38 6m r d for muscovite 20 9m r d for chloritoid and display roughly axial symmetry about the minimum magnetic susceptibility axis indeed suggesting that chloritoid may have a profound impact on the magnetic fabric of chloritoid bearing rocks however modeling the anisotropy of magnetic susceptibility by averaging single crystal properties indicates that the cpo of chloritoid only partially explains the slate s anisotropy

magnetic anisotropy of chloritoid 1 the magnetocrystalline anisotropy of monoclinic chloritoid a relatively common mineral in aluminum rich metapelitic rocks has been determined for the first time by measuring the high field anisotropy of magnetic susceptibility hf ams using two independent approaches i e a directional magnetic hysteresis measurements and b torque magnetometry on a collection of single crystals collected from different tectonometamorphic settings worldwide magnetic remanence experiments show that all specimens contain ferromagnetic s l impurities being mainly magnetite the determined hf ams ellipsoids have a highly oblate shape with the minimum susceptibility direction subparallel to the crystallographic c axis of chloritoid in the basal plane of chloritoid though the hf ams can be considered isotropic the degree of anisotropy is found to be 1 47 which is significantly higher than the anisotropy of most paramagnetic silicates and even well above the frequently used upper limit i e 1 35 for the paramagnetic contribution to the ams of siliciclastic rocks the obtained values for the paramagnetic curie temperature parallel and perpendicular to the basal plane indicate that this pronounced magnetocrystalline anisotropy is related to strong antiferromagnetic exchange interactions in the direction of the crystallographic c axis 0 as a consequence chloritoid bearing metapelites with a pronounced mineral alignment can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic s l minerals the newly discovered magnetocrystalline anisotropy of chloritoid thus calls for a revised approach of magnetic fabric interpretations in chloritoid bearing rocks

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

late oligocene bunch grassland and early miocene sod grassland paleosols from central oregon usa abstract fossil soils burrows and mammals of the upper john day formation in central oregon are evidence of bunch grasses and open semiarid vegetation as old as late oligocene earliest arikareean 30 ma root traces in these paleosols include both stout tapering tubes like roots of trees as well as sinuous filamentous tubes similar to roots of grasses paleosol structure is fine subangular blocky with patchy distribution of grass like roots as in wooded grassland and sagebrush steppe with bunch grasses cursoriality in horses mesohippus miohippus and hypsodonty in rhinos diceratherium is also evidence for open grassy vegetation trace fossils of pallichnus dung beetle boli and edaphichnium earthworm chimneys are characteristic of wooded grassland paleosols whereas taenidium cicada burrows dominates desert shrubland paleosols as has also been found in quaternary paleosols and soils of eastern washington in both oligocene and quaternary paleosol sequences arid shrubland and semiarid grassland paleosols alternate on milankovitch frequencies 23 41 100 ka the oldest known paleosols in oregon with crumb structure and abundant fine fossil root traces characteristic of sod grasslands are dated by mammalian biostratigraphy as hemingfordian early miocene ca 19 ma wooded grassland habitats are indicated by scattered chalcedony calcite rhizoconcretions from large woody plants and by fossil chalicotheres moropus camels gentilicamelus paratylopus and horses parahippus silty texture and silcrete horizons are evidence of semiarid to arid paleoclimate and are in striking contrast to highly calcareous and clayey underlying paleosols of the john day formation these silcrete paleosols may represent the miocene onset of summer dry mediterranean seasonality as opposed to a summer wet monsoonal pattern of seasonality found in this region during the oligocene oregon s early rangelands can be compared with those in the north american great plains granular structured calcareous paleosols of the brule formation of south dakota are evidence of dry bunch grasslands as old as 33 ma early orellan early oligocene and crumb structured paleosols of the anderson ranch formation of nebraska are evidence of sod grasslands as old as 19 ma late arikareean early miocene although grasses were a conspicuous part of dry rangelands well back into the oligocene early and middle miocene sod grasslands in north america were restricted to regions estimated to have had less than 400 mm mean annual precipitation

the origin and sedimentary diagenetic and metamorphic evolution of chlorite mica stacks in llandovery sediments of central wales u k chlorite mica stacks in the llandovery sedimentary rocks of central wales have been studied both within cleaved turbidite mudrocks and within early diagenetic apatite carbonate and monazite concretions stacks show a graded distribution within turbidite units indicating an origin as detrital particles concretions provided an arrested diagenetic environment which restricted subsequent deformation and so revealed the nature of the stack precursor minerals these included detrital mica and also probable pyroxenes amphiboles and volcanic rock particles relic textures of which can be seen preserved within the concretions diagenetic alteration to chlorite probably with some white mica intergrowth occurred most probably via smectite and then mixed layer or swelling chlorite intermediates subsequent modification during the caledonian cleavage forming episode determined the present shape and mineralogy of the stacks outside concretions chlorite pseudomorphs were rotated by tectonic compression crushed at their margins and pulled apart along 001 cleavage and slip planes growth of at least two generations of secondary mica infillings has been recognized and this was probably accompanied by the growth of secondary chlorite this resulted in barrel shaped stacks elongated parallel with cleavage and with the 001 plane rotated from the bedding towards the perpendicular to the cleavage within early diagenetic concretions it is evident that some stacks had formed prior to lithification however these have a relatively simple morphology and the original bedding parallel grain shapes are largely preserved

clumped isotope evidence for diachronous surface cooling of the altiplano and pulsed surface uplift of the central andes spatially extensive paleoelevation records of the altiplano plateau are critical to determining the geodynamic mechanisms that formed and support high elevations over a broad area prior stable isotope data reveal a climate history for the northern bolivian altiplano that has been interpreted to show rapid surface uplift of 2 5 1 0 km between 10 and 6 ma this study applies clumped isotope paleothermometry to paleosol carbonates formed at both a low elevation site and temporally overlapping high elevation sites in the southern altiplano eastern cordillera during the middle to late miocene surface paleotemperature decreased by 14 c in the southern altiplano eastern cordillera relative to stable low elevation paleotemperatures implying surface elevation increase of 1 9 0 7 km between 16 and 13 ma and an additional 0 7 0 6 km between 13 and 9 ma both the large magnitude of surface temperature decrease and earlier onset 7 4 myr in the south as compared to the north suggest rapid elevation increase by piecemeal removal of lower lithosphere beneath the plateau and possible northward lower crustal flow

current challenges and future developments in magnetic fabric research abstract magnetic fabrics are used extensively as proxies for mineral fabrics and to correct paleomagnetic data and have been proposed to quantify pore fabrics today s understanding and interpretation of magnetic anisotropy benefits from decades of carefully observing anisotropic mineral and rock properties establishing and testing empirical relationships between magnetic and mineral fabrics and developing models to quantify aspects of anisotropy each advance was preceded by some puzzling observations i e data that could not be explained based on the models available at the time e g oblique or inverse fabrics or lithology dependent anisotropy strain relationships these observations led to numerous experimental and numerical techniques designed to characterize magnetic fabrics and determine their origin despite the successful application of magnetic fabrics in many structural and tectonic problems there are still phenomena and measurements that cannot be explained based on today s magnetic fabric theory with the purpose of fostering future development i will touch on three main areas where i see challenges in magnetic fabric research 1 experimental characterization of magnetic anisotropy including the non uniqueness of reported tensors and non linearity 2 anisotropy modelling and defining the carrier minerals and origin of the magnetic fabric 3 selection of adequate sets of anisotropy tensors to correct paleomagnetic data the description of the challenges presented here will hopefully help define directions for future research inform those that are new to anisotropy and advance our field

trace fossils and rhizoliths as a tool for sedimentological and palaeoenvironmental analysis of ancient continental evaporite successions abstract recognition of evaporite formations from continental tertiary basins of spain provides evidence that trace fossils including rhizoliths can be abundant in some saline lake systems and their study helps in palaeoenvironmental interpretation of ancient continental evaporite sequences six main types of trace fossils have been distinguished and include 1 networks of small rhizoliths 2 large rhizoliths 3 tangle patterned small burrows 4 isolated large burrows 5 l shaped traces and 6 vertebrate tracks rhizoliths were related to both marginal areas of hypersaline lakes and lakes of moderately high saline waters in these settings pedoturbation resulted from colonization by grasses and bushes of distinct lake subenvironments the activity of burrowing invertebrate faunas was especially intense in lakes of moderately concentrated brines from which gypsum was the main evaporite mineral deposited a specific gypsum lithofacies bioturbated gypsum deposits forming thick massive beds has a widespread occurrence in many of the basins tangle patterned small burrows and minor isolated large burrows constitute the typical trace fossil types within the gypsum the traces are interpreted as having been caused by burrowing insect larvae probably chironomids coleopterans and annelids the behaviour of these organisms in recent lake environments yields information about the salinity range of lake waters from which gypsum precipitated concentration values averaging 100 150 g l may be thus deduced though some organisms involved in the formation of the traces can tolerate higher salinities the combined analysis of lithofacies and trace fossils from the lacustrine evaporite sequences contributes to the study of distinct saline lake subenvironments as well as changes in the sedimentary evolution of the lake systems consequently trace fossils can provide valuable insight for palaeoenvironmental analysis of at least some evaporite formations that accumulated in continental settings

neogene paleomagnetism and oroclinal bending of the central andes of bolivia geophysical and tectonic evidence suggests that the principal vertical axis bending of the bolivian orocline is a late cenozoic event related to subduction and andean uplift to further test this hypothesis paleomagnetic data are presented from miocene basins within the altiplano and cordillera oriental of bolivia located in the presumed southern limb of the orocline to factor out potential vgp data samples were collected from sedimentary sections spanning at least 0 5 m y new paleomagnetic data are presented for two sites i e gerdas 21 s latitude 16 15 ma and quehua 20 s latitude 13 7 ma in conjunction with previously published paleomagnetic results from middle to late tertiary rocks from bolivia and peru spanning some 16 of latitude 6 22 s a consistent pattern of oroclinal development is as follows significant counterclockwise rotation about 15 20 in the northern limb negligible rotation in the axis at the latitude of the arica deflection and significant clockwise rotation about 15 20 in the southern limb although these paleomagnetic data could represent independent mesoscale 102 to 104 km2 block rotations the preferred interpretation is that they confirm the hypothesis that a significant portion about 30 40 of the oroclinal bending occurred during the late cenozoic using the unit mean paleomagnetic declinations in the well dated sections minimum rates of oroclinal bending during the late cenozoic are calculated to range from 0 6 m y to 1 7 m y the remaining 15 20 of observed curvature of the orocline probably resulted from an earlier phase of andean deformation or may represent the shape of the ancestral andes

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

a paleopedologic and ichnologic perspective of the terrestrial pennsylvanian landscape in the distal appalachian basin u s a abstract the conemaugh group of southeastern ohio contains numerous ichnofossil bearing paleosols in both the lower glenshaw and upper casselman formations which were deposited during the kasimovian and gzhelian 305 301 ma along the distal edge of the appalachian basin this study examined the small scale twenty four stratigraphic sections were measured from ten sites in athens county ohio from which thirty paleosols were identified and described detailed field descriptions allowed differentiation of four distinct pedotypes one in the glenshaw formation and three in the casselman formation the glenshaw pedotype gpt is a vertisol that formed on a proximal to distal floodplain the three casselman pedotypes represent entisols inceptisols cpti alfisols cptii and vertisols cptiii all four types contain evidence of alteration by post pedogenic processes such as drowning by migrating river channels or rising sea level or a gradual transition from one alluvial subenvironment to another as a result of channel migration eight morphologically distinct ichnofossils were observed in the conemaugh group paleosols including three types of rhizoliths lined and unlined vertical to subhorizontal shafts chambers sinuous burrows with and without bioglyphs and general burrow mottling these ichnofossils occur in distinct assemblages that form unique ichnocoenoses within each of the four pedotypes they were produced by various plants arthropod detritivores carnivores and herbivores as well as amphibians and early reptiles as temporary to permanent members of complex soil ecosystems pedogenic properties combined with ichnofossil diversity abundance and distribution increase the understanding of the complexity of late pennsylvanian soil ecosystems and provide details on the small scale variations in paleosols due to short term autogenic changes in alluvial environments although broad regional studies across 10 2 10 3 of kilometers are important small scale variations over less than 1 km are needed to understand the effects of localized changes in hydrology topography organisms and sedimentary processes on soil formation and soil biodiversity consideration of these types of localized studies is also vital when attempting to interpret regional to global scale aspects of environment such as climate from paleosols

from qualitative to quantitative magnetic anisotropy analysis the prospect of finite strain calibration abstract a method of separating low field susceptibility anisotropies due to ferrimagnetics and the matrix proposed hitherto in cases where the principal axis of these two components are merged is generalized in cases where the axes are distinct the method consists of analysing in specimens close in the same sample anisotropies the differences of which are due to the variation of respective percentages of the two components although the strain rate remains constant one thus uses the cause which itself renders global anisotropy unusable a first application is presented where a control using the anisotropy of isothermal remanent magnetization allows the validity of the method to be tested a discussion of the choice of the best ellipsoid relative either to the matrix or to the ferrimagnetics to give the best indication of relative finite strain rate is opened

paleoenvironmental analysis of the neotropical fossil mammal site of cerdas bolivia middle miocene based on ichnofossils and paleopedology abstract the early middle miocene langhian age site of cerdas in the southern bolivian altiplano has produced a diverse fauna of extinct mammals 15 species in seven orders and 11 families in this study we use paleosols and ichnofossils to reconstruct its paleoenvironment and the conditions in which its fossils were preserved the described paleosols represent three pedotypes and three distinct landscape surfaces in an alluvial system type 1 paleosols are interpreted as haplusteps inceptisols that formed on a proximal floodplain in a subhumid to humid patchy shrubland with seasonal variation in precipitation and associated changes in soil moisture conditions landscape 1 type 2 paleosols are interpreted as dystrudepts that formed on a well vegetated distal floodplain in a seasonal humid climate with ground covering shrubland vegetation landscape 2 type 3 paleosols are interpreted as calciustolls mollisols that formed in a shifting alluvial environment in a seasonal sub humid to semi arid open environment landscape 3 ichnofossil assemblages of cerdas include skolithos planolites macanopsis parowanichnus rhizohaloes and rhizotubules these were produced by detritivorous herbivorous and faunivorous soil arthropods as well as plant roots and represent soil communities not normally preserved as body fossils that were living within a heterogeneous alluvial environment the physical and geochemical properties of the paleosols and associated ichnofossil assemblages indicate that the paleolandscapes were composed of shrublands and open environments that experienced changes in moisture regimes due to seasonal precipitation and flooding events and had varying degrees of temporal stability our analysis is the first detailed study of pre pleistocene cenozoic paleosols and trace fossils from the southern tropics mid latitudes of south america and one of the few focused on important fossil mammal bearing sediments

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

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

tem and aem constraints on the origin and significance of chlorite mica stacks in slates an example from central wales u k chlorite mica stacks grains of intergrown chlorite and white mica in a matrix of fine grained white mica and chlorite have been studied using xrd sem empa tem and aem methods the stacks occur in a weakly cleaved llandoverian mudstone central wales which has a white mica illite crystallinity index of 0 35 a20 corresponding to the lower anchizone white mica occurs as packets 100 to 8 m thick interleaved with dominant chlorite packets in stacks with both apparent coherent interfaces or cross cutting small angle boundaries with chlorite layers it is well crystallized 2m polytype with phengitic composition and low paragonite component na na k 0 0 07 chlorite in stacks is fe rich and relatively homogeneous tio2 crystals surround stacks and occur within chlorite and white mica is ti rich compared to matrix white mica fine grained white mica and chlorite in the matrix have two different orientations one parallel to bedding and one parallel to cleavage which is approximately 30 50 to bedding matrix white mica is predominantly a 2m1 polytype but some cleavage parallel white mica is 3 t and some bedding parallel white mica is 1md it is na rich na na k 0 14 0 42 and relatively heterogeneous some discrete paragonite and phengitic muscovite are observed to coexist in the cleavage orientation matrix white mica and chlorite each contain less fe than corresponding white mica and chlorite in stacks both matrix and stack chlorite are one layer polytypes the data imply that chlorite in the stacks is largely derived from the replacement of volcanogenic biotite and other ferromagnesian minerals probably via intermediate expandable trioctahedral phyllosilicates most intergrowths of chlorite and mica in stacks formed by mica replacement of chlorite and altered biotite along cleavage fissures subsequent deformation caused further modification of pre existing chlorite mica stacks whereas partial dissolution of stacks and bedding parallel matrix phyllosilicates resulted in the formation of cleavage parallel phyllosilicates

miocene vertebrate and invertebrate burrows defining compound paleosols in the pawnee creek formation colorado u s a abstract ichnofossils from two compound paleosols in the middle miocene pawnee creek formation pcf of northeastern colorado u s a indicate a diverse soil ecosystem that included plants invertebrates and vertebrates the 2 4 m thick paleosols are characterized by blocky textures shallow depth calcareous horizons overlying silty bioturbated horizons calcareous nodules dense mats of fine ichnofossils attributed to ground beetles ants reptiles and mammals represent a complex variety of behaviors including temporary to permanent dwelling nesting and food storing rhizoliths and burrows used to interpret media consistency organic content soil moisture and water table level are tiered from shallow intermediate to deep levels within paleosols with respect to physical and biological factors separate bioturbated intervals permits the recognition of two different paleosols that otherwise might not have been recognized such well developed paleosols with high densities of terrestrial burrows have substantial sequence stratigraphic significance since they define surfaces of low sedimentation base level and accommodation the pcf ichnofossil assemblages represent at least three distinct ichnocoenoses the kladosystemites ichnocoenosis with kladosystemites polychoredrites parowanichnus and 1 10 mm diameter rhizoliths is present in the upper profile of well drained consolidated and nutrient rich paleosols with dense concentrations of small to large plants at the surface the beaconites ichnocoenosis with beaconites katarrhedrites and 5 10 mm rhizoliths is present in the lower profile of moderately organic paleosols above the influence of the water table but subject to seasonally variable saturated and unsaturated conditions due to precipitation the daimonelix ichnocoenosis with daimonelix beaconites small to large katarrhedrites and 5 10 mm diameter rhizoliths is present in the lower profile of very organic rich paleosols generally above the influence of the water table but subject to seasonally variable saturated and unsaturated conditions integration of data from body fossils ichnofossils paleosols and sedimentary environments provides new insight into neogene ecosystems paleosol properties combined with the ichnofossil distribution abundance and diversity indicates that miocene pcf paleosols formed under a seasonal climate subject to wide variation in temperature and precipitation the diverse assemblage of burrow morphologies records adaptation of the local fauna to these environmental conditions the response of soil ecosystems to short and long term changes in climate is therefore vital to any study of the effects of climate change in the geologic record

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

spatial temporal changes in andean plateau climate and elevation from stable isotopes of mammal teeth abstract paleoelevation constraints from fossil leaf physiognomy and stable isotopes of sedimentary carbonate suggest that significant surface uplift of the northern andean plateau on the order of 2 5 1 km occurred between 10 3 and 6 4 ma independent spatial and temporal constraints on paleoelevation and paleoclimate of both the northern and southern plateau are important for understanding the distribution of rapid surface uplift and its relation to climate evolution across the plateau this study focuses on teeth from modern and extinct mammal taxa including notoungulates pyrotheres and litopterns spanning 29 ma to present collected from the altiplano and eastern cordillera of bolivia 16 2 s to 21 4 s and lowland brazil tooth enamel of large water dependent mammals preserves a record of surface water isotopes and the type of plants that animals ingested while their teeth were mineralizing previous studies have shown that the 18o of modern precipitation and surface waters decrease systematically with increasing elevations across the central andes our results from high elevation sites between 3600 and 4100 m show substantially more positive 18o values for late oligocene tooth samples compared to