rb sr systematics of permian volcanites in the schwarzwald sw germany from the quartz porphyry occurrences of haigerach and geisberg central schwarzwald which were dated by minerals and whole rock samples the whole rock samples generally yielded lower ages than the minerals this result agrees with other studies on apparently rejuvinated whole rock ages of acid volcanic rocks compare mckerrow et al 1980 petrographic and geochemical observations show that two processes disturbed the rb sr relations 1 fast alterations immediately after extrusion such as sericitization during autohydrothermal bleaching in the pipe area of the volcanoes gain of rb addition of common sr 2 loss of radiogenic 87sr due to long lasting exchange processes with groundwaters

floodplain aggradation and pedogenesis in a semiarid environment alluvial valley fills in the upper republican river basin southwestern nebraska provide evidence for processes of aggradation and pedogenesis on semiarid cut and fill floodplains sheetflow deposition on unchanneled valley floors represents an important mechanism of valley aggradation sheetflow deposits contain parallel to sub parallel laminae and discontinuous lobate sedimentary structures rates of sediment deposition on cut and fill floodplains strongly determine the degree to which pedogenic features develop within aggrading alluvium three pedofacies common to semiarid alluvial deposits correspond with increasing aggradation rates 1 cumulic soils 2 multiple buried soils and 3 no pedogenic features radiocarbon age determinations from alluvial fills indicate that floodplain aggradation greater than approximately 0 5 cm year 1 limits soil formation this represents a threshold rate of pedogenic assimilation floodplain soils formed under aggradation rates lower than this exhibit a strong positive relationship between aggradation rate and total caco3 percent and a negative relationship between aggradation rate and organic carbon percent recognizing the associations between pedogenic sedimentologic features and floodplain aggradation rates can help interpret past rates of sediment transport storage and deposition

topographic inversion and changes in the sediment routing systems in the variscan orogenic belt as revealed by detrital zircon and monazite upb geochronology in post collisional continental basins abstract the basal alluvial and fluvial siliciclastic successions within the late carboniferous intracontinental basins of the west central bohemian massif provide an intriguing sedimentary record of changes in paleotopography and paleodrainage systems during and after orogenic collapse we analyze this record using the u pb laser ablation icp ms detrital zircon and monazite geochronology five distinct age groups have been identified across the examined stratigraphic succession i archean paleoproterozoic ii late neoproterozoic iii cambro ordovician iv late devonian and v mid to late carboniferous these age groups indicate mixing of both local and distal extra basinal sources and also point to a two stage post convergent geodynamic evolution of the variscan belt the first stage followed collapse of the central bohemian orogenic plateau at around 346 337 ma and involved rapid cooling at ca 340 320 ma and removal of ca 2 3 km of sedimentary overburden from the top of the plateau no sedimentary record of this erosional event suggests that the river systems transported detritus radially outwards from the inner part of the orogen to its forelands a paleorelief inversion and thus major reorganization of the sediment routing systems were then associated with uplift in the southerly and southwesterly peripheral domains of the orogen at ca 330 310 ma in turn these uplifted domains occupied by rapidly unroofed voluminous granite plutons shed detritus into the bohemian sink this was represented by the former plateau collapsed to relatively low elevations but still with significant internal paleorelief dominated by a system of tens of kilometers long nne ssw trending paleovalleys some of the material was further transported in extensive river systems crossing the former plateau to the northerly variscan foreland basin thus the radial sediment routing system changed into axial unidirectional finally we suggest that these major inversions of paleorelief and changes in the surface processes and paleodrainage systems may have been linked to distinct late orogenic lithospheric mantle delamination events first stage delamination occurred beneath the center of the bohemian massif to cause the plateau collapse denudation and radial sediment transport whereas the second stage delamination occurred along its periphery to cause uplift sourcing the intracontinental basins and unidirectional sediment transport end of deposition and magmatic shutdown at around 305 ma may then define the very cessation of late orogenic vertical movements and the transition to a post orogenic intra plate setting

late carboniferous late permian paleomagnetic overprinting of carboniferous granitoids in southern bohemian massif austria paleomagnetic investigations on early middle carboniferous granitoids of the austrian part of the south bohemian pluton 48 5 n 14 2 e yielded two groups of characteristic remanent magnetization chrm directions one being characterized by ssw declinations and positive inclinations and labelled a1 d 200 i 14 k 67 n 9 virtual geomagnetic pole vgp 31 n 170 e the other group having the same declinations but with negative inclinations d 201 i 21 k 88 n 18 vgp 48 n 162 e both magnetizations are considered as magnetic overprints owing to distinct recrystallization processes that occurred in different hydrothermal and tectonic conditions in late carboniferous and late permian times in some cases the original magnetizations may remain after the remagnetization processes but as a whole this study confirms that the paleomagnetic history of a magmatic crystalline basement in this case of late carboniferous to late permian age maybe differ significantly from its intrusion history in this case early to middle or late carboniferous

structure and emplacement of a rhyolitic obsidian flow little glass mountain medicine lake highland northern california many rhyolitic obsidian flows show consistent stratigraphic relations among textural units exposed in the flow fronts of undissected flows and in cross sections of older flows the stratigraphy of the holocene little glass mountain rhyolitic obsidian flow consists of from bottom to top air fall tephra deposits basal breccia coarsely vesicular pumice obsidian finely vesicular pumice and surface breccia slightly crystalline rhyolite occurs near the vent areas a model of obsidian flow emplacement based on these textural relations is presented this stratigraphy may reflect the distribution of volatiles within the magma source region with the interlayered contact between coarsely vesicular pumice and overlying obsidian indicating stratification of volatiles in the magma body the distribution of pumiceous and glassy zones along with the orientations of flow banding can be used to map the surface structure of rhyolitic obsidian flows this complex structure as mapped on the little glass mountain flow reflects both the initial flow stratigraphy and subsequent deformational processes during emplacement of the lava three processes disrupt the initial flow configuration the rise of coarse pumice diapirs from the base of the flow the inward propagation of fractures in areas of extension and surface folding in sites of flow parallel compression subvertical flow banding in vent areas indicates that fracturing accompanies the emergence of lava most of the observed upper surface of a dome originates as a fracture plane the structure of domes that form over vent areas may reflect the orientation of dike like conduits as well as the local state of stress during extrusion

a full glacial biota from southeastern iowa usa wisconsinan full glacial silts filling a swale exposed in conklin quarry johnson co iowa contain a large and diverse biota that includes pollen bryophytes vascular plant macrofossils small mammals molluscs and insects radiocarbon dates on wood from the top middle and bottom of the swale fill respectively were 16710 270 17 170 205 and 18090 190 yr bp the pollen diagram is dominated by picea spruce pinus pine and cyperaceae sedge and it records low pollen accumulation rates plant macrofossils include a number of tundra species along with picea and larix larch needles and small pieces of wood the insect fauna contains many species now confined to the forest tundra transition zone of northwestern yukon and alaska small mammals include the tundra indicators dicrostonyx collared lemming and probably microtus miurus singing vole together with boreal forest taxa the molluscs include extinct and relict species and show the widest range in present geographic distribution but rocky mountain and especially northern elements predominate in the swale fill all these lines of evidence lead to consistent palaeoclimato logical interpretation and palaeoecological reconstruction the dominant habitats represented by the biota and sedimentary environment collectively included open calcareous silty to sandy or gravelly upland sites minerotrophic fens wetlands pond or stream side clayey to sandy shores and shallow possibly ephemeral cold clear water ponds mean july temperatures were probably 11 to 13 c cooler than at present the biota indicates that a picea larix krummholz with extensive tundra openings was present in southeastern iowa between 18090 and 16710 yr bp

evidence of cyclic dust deposition in the us great plains during the last deglaciation from the high resolution analysis of the peoria loess in the eustis sequence nebraska usa the peoria loess unit is a well defined stratigraphical unit in the upper pleistocene of the north american quaternary deposited between 30 25 ka and about 12 ka ago it has been indicated that this unit shows the highest known worldwide depositional rate for eolian deposits as its thickness varies near the source area between 19 m and 46 m extreme values that are not even recorded in the chinese sequences the results of our present investigation indicate that this particular unit is not homogenous its shows different subunits where lithological variation can be observed through the occurrence of embryonic gley horizons alternating with laminated loess furthermore the grain size analysis shows cycles corresponding to variations in the eolian dynamics responsible for dust transportation and deposition a grain size index interpreted as characterizing the eolian dynamics higher values corresponding to stronger wind conditions shows higher values than those observed in europe a comparison of this index is proposed with the greenland dust and 18 o records it shows that the main climatic history as corresponding to events occurring mainly in north atlantic domain is recorded in the peoria loess deposits however the variation in the magnitude of the eolian events indicates differences from the european loess sequences the strong north atlantic coolings expressed by heinrich events as recorded in europe by coarser deposits are not differentiated in the studied sequence hence they follow more closely observations obtained off california for the north east pacific domain 2007 elsevier b v all rights reserved

what was the paleogene latitude of the lhasa terrane a reassessment of the geochronology and paleomagnetism of linzizong volcanic rocks linzhou basin tibet the paleogene latitude of the lhasa terrane southern tibet can constrain the age of the onset of the india asia collision estimates for this latitude however vary from 5 n to 30 n and thus here we reassess the geochronology and paleomagnetism of paleogene volcanic rocks from the linzizong group in the linzhou basin the lower and upper parts of the section previously yielded particularly conflicting ages and paleolatitudes we report consistent 40ar 39ar and u pb zircon dates of 52 ma for the upper linzizong and 40ar 39ar dates 51 ma from the lower linzizong are significantly younger than u pb zircon dates 64 63 ma suggesting that the lower linzizong was thermally and or chemically reset paleomagnetic results from 24 sites in lower linzizong confirm a low apparent paleolatitude of 5 n compared to the upper part 20 n and to underlying cretaceous strata 20 n detailed rock magnetic analyses end member modeling of magnetic components and petrography from the lower and upper linzizong indicate widespread secondary hematite in the lower linzizong whereas hematite is rare in upper linzizong volcanic rocks of the lower linzizong have been hydrothermally chemically remagnetized whereas the upper linzizong retains a primary remanence we suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower linzizong we estimate that the paleogene latitude of lhasa terrane was 20 4 n consistent with previous results suggesting that india asia collision likely took place by 52 ma at 20 n

the rotations of the variscides during the carboniferous collision paleomagnetic constraints from the vosges and the massif central france abstract this study aims at completing and refining results from previous paleomagnetic investigations carried out in various outcrops of the european variscan belt sampling was performed in visean effusive and intrusive rocks of the southern vosges basin and the northern massif central all emplaced in the time range 345 340 ma stepwise thermal demagnetization of 254 specimens from 13 sites of the doller valley and nine sites of the massif central has yielded a very similar paleomagnetic record for both areas with the exception of post carboniferous overprints isolated in the southern vosges two groups of directions with both normal and reversed polarity have been evidenced the first group of directions labelled c occurs in both areas and is characterized by scarce pre tectonic magnetizations two sites and by syn tectonic overprints five sites acquired during the late visean convergence i e in the time range 340 328 ma the mean pole co is 28 s 45 e k 139 95 5 the main group labelled b shows a negative fold test and a positive reversal test indicating that the magnetizations are post tectonic overprints acquired after the main tightening phase i e after 328 ma at a few sites in both areas were evidenced syn tectonic b magnetizations that are in favour of an overprinting in the context of post visean extension tectonics the mean post tectonic b direction of the doller valley southern vosges 62 25 k 52 95 6 n 11 vgp 8 n 127 e is consistent with the mean post tectonic b direction 72 23 k 126 95 5 n 6 vgp 3 n 114 e obtained from the tuffs the grey microgranite and the dyke intrusive into the microgranite of the massif central the occurrence of similar paleomagnetic records in the eastern and central variscides implies that from the massif central to the sudetes the belt has probably moved as one block since early carboniferous the change in inclination of the c components suggests a southward drift of the moldanubian and saxothuringien variscides in the late visean 340 328 ma according to geological features in the same time the rhenohercynian crust was underplating the saxothuringian arc and fore arc zone subsequent to 328 ma the drift turned into a rapid clockwise rotation by about 70 around a pole located on southeastern corner of baltica leading to the closure of the rhenohercynian oceanic basin in the namurian large scale overprinting b components likely related to post rotation extension affected the internal belt the convergence continuing the variscides underwent a second clockwise rotation by about 45 in the late namurian westphalian 320 305 ma stacking of the rhenohercynian sedimentary cover and thrusting over the london brabant basement may be related with this motion

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

flux of ice rafted detritus from sea ice in the fram strait abstract a three year particle flux record from the eastern fram strait between greenland and svalbard revealed a rather untypical seasonal flux pattern compared to other particle flux studies from the nordic seas in the eastern fram strait this pattern is characterised by a sudden four to six fold increase of the particle flux in january when no daylight is available to support any biological productivity comparison with sea ice distribution maps led to the conclusion that the sudden increase in the flux is due to ice rafted detritus released from sea ice which originated from the svalbard archipelago and from the northern barents sea detailed grain size analyses of the silt fraction indicated the 10 m fraction of the lithogenic matter to be clearly enriched due to ird input even more important is the observation that lithogenic material 40 m occurs exclusively during the ice rafting event and therefore appears to be a suitable indicator for ird transported on sea ice thus in addition to coarse ird e g 500 m which is mainly derived from icebergs the analysis of fine ird 40 m in deep sea sediments can be used to reconstruct paleo sea ice extensions

plate and intraplate processes of hercynian europe during the late paleozoic abstract it is speculated that until late carboniferous time the region of hercynian europe was occupied by an elongated island arc system underlain by a segment of continental crust in the upper carboniferous two subduction zones are assumed to have extended from the north and south beneath hercynian europe an extensive zone of hot partially molten upper mantle lay above and between these and diapiric uprise of portions of this material led to separation of mafic magmas widespread partial melting in the lower and middle crust high temperature low pressure metamorphism in crustal rocks and regional uplift and extension of the crust as indicated by intermontane troughs and their associated volcanic rocks in visean to westphalian time hercynian europe collided with both the large neighbouring plates north america europe and africa during these diachronous collisions and owing to reduced rigidity of the relatively hot island arc crust the irregular continental margins of the larger and thicker continental plates induced oroclinal bending of hercynian europe after the collision processes had been terminated processes of upper mantle activity continued causing further crustal uplift and even enhanced crustal extension for several tens of million years into the lower permian decline of the upper mantle activity beneath hercynian europe is indicated by crustal subsidence and formation of a peneplain in permian time followed by the upper permian transgression of both the zechstein sea and the tethys sea which mark the end of the hercynian geodynamic cycle

ams radiocarbon age of the upper mississippi valley roxana silt abstract accelerator mass spectrometer radiocarbon ages of the roxana silt loess along the upper mississippi valley of wisconsin and minnesota indicate that loess sedimentation of the roxana silt occurred between about 55 000 and 27 000 14 c yr b p however due to local environmental controls the basal age at any given site may range from 55 000 to 35 000 14c yr b p the radiocarbon ages presented here are in agreement with previous radiocarbon ages for the roxana silt in its type area of west central illinois but indicate that long term sedimentation rates along the bluffline of the upper mississippi valley were very slow 4 8 cm 1000 yr compared to long term sedimentation rates along the bluffline of the type area 40 70 cm 1000 yr comparison of radiocarbon ages for midcontinent middle wisconsinan loess deposits indicates that sedimentation along the mississippi river valley may have preceded loess sedimentation along the missouri river valley by as much as 20 000 yr or that basal ages for middle wisconsinan loess along the missouri valley are erroneously young the bracketing ages for the upper mississippi valley roxana silt indicate that the mississippi river valley was receiving outwash sedimentation between 55 000 and 27 000 14c yr b p

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

a palaeomagnetic investigation of a permian redbed sequence from a mining drill core summary samples spanning 66 m of permian redbeds were collected from a vertical but azimuthally unoriented drill core obtained during a uranium exploration programme in the lodeve basin of southern france inclinations are well grouped 6 5 k 121 5 and consistent with the known permian palaeolatitude of europe declinations have been estimated by using a sedimentological model involving tectonically rotated cross bed laminations the results are very encouraging and suggest a pole at 151 e 53 n p 1 m 2 n 43 which agrees well with the eurasian apparent polar wander curve the small polar discrepancy could well be due to secular variation which is consistent with the small variance and presumed short time spanned by the sequence fully oriented surface samples confirm these findings and support the validity of the orientation model temporal variations revealed by the stratigraphic ordering can be interpreted as slow dipole wobble on a time scale of 105 yr or more on which is superimposed a more rapid nondipole secular variation it appears that the core stores of the world could become at least under favourable circumstances an important source of palaeomagnetic information

role of increased marine silica input on paleo pco2 levels changing the supply of silica to the ocean may alter pco2 levels the increase in dust delivered to the ocean during glacial times increased the availability of silica for biological uptake the increased silica levels shifted species composition diatom populations increased and coccolith populations decreased decreasing the population of coccoliths decreased the flux of calcite to the sediments which in turn lowered pco2 levels enough to explain the glacial interglacial pco2 transition furthermore the contemporary increase in dust delivered to the ocean s mixed layer may be removing significant amounts of carbon dioxide from the atmosphere at present to set the stage this silica hypothesis is compared with the iron fertilization and nitrogen fixation hypotheses

guadalupian middle permian paleobiogeography of the neotethys ocean abstract a matrix of presence absence data of guadalupian middle permian brachiopod genera from sicily tunisia oman turkey north iran central afghanistan karakoram salt range and south thailand has been analyzed by multivariate methods cluster analysis principal coordinate analysis minimum spanning trees and parsimony analysis of endemicity the application of these different and independent paleobiogeographical methods has led to the individuation of three bioprovinces the cathaysian sicily and tunisia cimmerian oman turkey north iran salt range south thailand and transhimalayan karakoram and central afghanistan provinces these provinces have been placed on a paleogeographical reconstruction based on paleomagnetic data which we used to decipher the principal factors that governed brachiopod distribution in the neotethys ocean during the guadalupian as a conclusion the pattern of biotic provinces at this time resulted from the complex interplay between latitudinal thermal gradient oceanic paleocurrents and the continental drift of the cimmerian terranes across zonal climate belts

relative rates of peoria loess accumulation and pedogenic processes implications for paleoclimatic inference abstract where it is thick enough to extend below the surface soil profile the late wisconsinan peoria loess in the midcontinent of north america has characteristics suggesting relatively little syndepositional pedogenesis in these thicker sections the peoria loess below the surface soil profile commonly displays massive macroscopic structure low organic carbon content and retention of detrital carbonate grains late wisconsinan climatic conditions provide one potential explanation for these observations this paper considers two other non climatic explanations 1 loess accumulation was more rapid than carbonate dissolution or oc accumulation and 2 post depositional diagenesis has removed evidence of syndepositional pedogenesis the approach used is comparison of potential rates for pedogenic processes and loess accumulation even when wide ranges of controlling factors precipitation evapotranspiration and soil carbon dioxide levels are considered loess accumulation was probably too rapid at many sites for carbonate mineral dissolution to keep pace on the other hand data from modern tundra and boreal forest environments suggest that soil oc accumulation could have kept pace with loess deposition in many cases low oc contents observed in the loess today probably reflect post depositional oxidation climatic factors may provide partial or local explanations for the apparent minor extent of syndepositional pedogenesis but loess accumulation rates and diagenesis are key factors as well

loess depositional dynamics and paleoclimatic changes in the yili basin central asia over the past 250 ka abstract widely distributed loess deposits within the tianshan mountains are important archives for studying late quaternary climate in this central asian region however insufficient age control for these regional loess records especially over glacial interglacial cycles severely limits our understanding of loess depositional dynamics and accurate interpretation of paleoclimate conditions across central asia in this study we applied k feldspar optical dating and magnetic susceptibility grain size distribution caco3 and color to loess paleosol sections in the yili basin of the tianshan mountains to constrain loess depositional dynamics identify timing of loess paleosol formation and clarify the role of paleoclimate influence in this region since the late middle pleistocene our results demonstrate that loess deposition started as early as 350 ka in the yili basin following river down cutting associated with glacial interglacial transitions and exposure of riverbed sediments enhanced dust emission from flood plains played an important role in loess deposition very rapid loess deposition as high as 60 120 g cm 2 ka 1 on river terraces occurred during the last interglacial when loess accumulation at different locations of the site had remarkably different rates ranging from 10 to 100 g cm 2 ka 1 this heterogeneous behavior indicates that not only climatic changes influenced yili basin loess deposition and preservation but by complex interaction of local geomorphology wind velocity and changes of materials in dust origins depositional hiatuses frequently occurred during the past 250 ka likely induced by strong erosion resulting from increased wind strength and dry cold climate with poor vegetation cover in the region magnetic susceptibility grain size distribution caco3 and color analyses of the loess paleosol sequences showed that paleosols formed around 288 ka 230 191 ka 120 106 ka 92 89 ka and 84 71 ka hence a generally moist climate characterized the yili basin before marine isotope stages mis 9 mis 7 mis 5d mis 5b and the mis 5 mis 4 transition respectively this study suggests a climate pattern of moist interglacial and dry glacial periods in the tianshan mountains whereas substages of interglacials had cold moist and warm dry climate characteristics

triassic magnetic overprints related to albitization in granites from the morvan massif france the morvan massif located in the northern part of the french massif central shows widespread unusual deep alteration profiles in the palaeozoic basement rocks gneisses granites and rhyolites they are characterised by overall albitization chloritisation and haematisation albite and chlorite constitute their characteristic mineral paragenesis haematite pigmentation comes with this paragenesis and gives an overall pink coloration to the weathered rocks a paleomagnetic analysis was conducted after detailed petrographical and mineralogical studies of the alteration that lead to the albitized profiles special attention was devoted to the occurrence of haematite the main paleomagnetism carrier with the though to date this palaeoweathering event petrographical checking after heating treatments showed that deshydroxylation of chlorite also led to the formation of secondary haematite this haematite formed by recrystallization acquired remanence properties and thus superimposed and hided the original magnetic signal this problem has prevented the extraction of the original magnetic signal especially in the sections made up of rhyolites virtual geomagnetic poles vgps obtained from the characteristic directions carried by haematite have been compared to the european apparent polar wander path apwp an early triassic magnetic overprint has been recorded in the albitized basement rocks of the morvan massif the age obtained for this albitization phenomena strengthens the hypothesis that albitization developed in relation with palaeoweathering processes linked with the triassic palaeosurface therefore large scale continental weathering could be the main mechanism for late permian early triassic remagnetizations which are widespread throughout the palaeozoic formations of western europe as far as we know this is the first time that deep palaeoweathering phenomena affecting hard and non disaggregated weathered rocks of the basement have been directly dated palaeomagnetism appears as a precious tool to date alteration events developed in widely and long lasting emerged areas of the basement

isotopic and rock magnetic expression of environmental change at the pleistocene holocene transition in the central great plains abstract in a region too dry for the effective use of the traditional palynological approach loess deposits of the central great plains offer a source of proxy information for the reconstruction of past climates the brady soil a ubiquitous feature developed within the uppermost late pleistocene peoria loess recorded the character of vegetation change associated with climate shifts during the pleistocene holocene transition stable carbon isotope ratio analysis and two room temperature magnetic parameters were used to examine the nature of the change during this period 13 c values derived from soil organic matter indicate that in the late pleistocene minor populations of drought tolerant c4 plants were interspersed among the dominant cool season grasses c3 in the west while c3 grasses were accompanied by trees in the east by the early holocene c4 grasses were the dominant vegetation in the west and contributed substantially to the 13 c signal in the east magnitude of the 13 c shift suggests an increase in july mean daily temperature of 8 10 c according to existing models magnetic susceptibility and frequency dependence signal the cessation of loess deposition and development of the brady soil and indicate a spatial pattern in the intensity of weathering across the region

loess record of dry climate and aeolian activity in the early to mid holocene central great plains north america thick holocene bignell loess sections provide new evidence for the timing of early to middle holocene aridity in the central great plains the immediate source of loess in these sections was dune fields just upwind based on thickness trends and grain size data thus periods of rapid loess accumulation indicate episodes of extensive dune activity under drier than present climate in typical bignell loess sections a thick zone of coarse textured loess with minimal pedogenic alteration is interpreted as a record of the most rapid sustained holocene loess accumulation optical ages indicate that loess in this zone was deposited beginning about 9000 10000 years ago at five study sites accumulation ended shortly after 6500 years ago at three sites but possibly earlier at the other two in two well dated sections the average rate of loess accumulation between 9000 10000 and 6500 years ago was about 1 6 3 5 times greater than in the late holocene thus we infer that the most extensive sustained holocene

paleomagnetic investigations in the thuringer forest g d r abstract in the thuringer forest the whole rotliegende is well exposed and was chosen as beginning of a permian traverse via czechoslovakia austria into italy rockmagnetic experiments established haematite as main carrier of the nrm except a few localities where magnetite was found to be present sediments and volcanites show consistent chrm directions the comparison with krs s 1978 compilation proves a good permian pole position

pseudogleyed loess derivates the most common soil parent materials in the pannonian region of croatia abstract loess derived sediments represent the most widespread soil parent materials in the pannonian region of croatia pseudogley as the most common soil type in this region developed mainly on such parent materials pseudogleys largely correlate with the wrb reference soil group of stagnosols on the general soil map of croatia at scale 1 50 000 gsm of croatia the distinction is made between pleistocene loams pl and loess as pseudogley parent materials the initial purpose of this research was to investigate if the criteria for this distinction were clear and consistent and if the terms used for labeling these parent materials were adequate hence we investigated parent materials of 18 pseudogleys across 6 different locations three on loess and three on pl in the pannonian region of croatia we analyzed their morphology including micromorphology of three representative parent materials particle size distribution total porosity ph and mineral assemblages by modal analysis of three representative parent materials following these analyses no systematic differences between the loess parent materials and the pl parent materials were found additionally it was concluded that due to significant geogenetic and or pedogenetic alterations of all studied parent materials none of them should be labeled simply as loess hence parent material at one location was labeled as leached loess derivate and parent materials at all other locations were labeled as pseudogleyed loess derivates both types of parent materials were described in detail and defined in addition the terminology and the classification of loess derived parent materials in general was proposed the analyzed pseudogleyed loess derivates were not completely uniform across the investigated locations primarily this was due to the polygenesis of loess reflected by differences in particle size distributions and compositions of light and heavy mineral fractions secondarily it was due to the 600 1100 mm map gradient along the study region reflected by differences in ph values and properties of redoximorphic features although pedogenesis of the investigated parent materials might have started already during the late glacial and have continued throughout the holocene at varying and overall decreasing rates their morphology indicates that pseudogleization and lessivage are still active processes which occur simultaneously in the analyzed parent materials and agree with the present climate

the apparent polar wander path of the european plate in upper triassic lower jurassic times and the liassic intraplate fracturing of pangaea new palaeomagnetic constraints from nw france and sw germany summary in order to constrain the european plate motions during triassic lower jurassic times new palaeomagnetic data were acquired from various triassic liassic sediments of northeastern france and southwestern germany a carnian palaeopole 49 n 131 e k 193 a95 7 n 4 was obtained for keuper marls with consistent directions of normal and reversed polarities rhaetian sandstones also with both polarities and carnian dolomites with a magnetization of probable secondary origin provide a mean pole 51 n 112 e k 109 a95 6 n 6 more westerly than that given above the lower hettangian sampled in limestones of the xeuilley quarry near nancy shows a n r n polarity sequence with well defined anti parallel directions the mean hettangian pole is 55 n 100 e k 123 a95 11 n 3 induan sandstones from the northern vosges show two distinct overprints one consistent with the ladinian carnian magnetizations already observed in the same region the second consistent with the recalculated mean lower jurassic pole of europe five other sites with different rock types also exhibit late overprints with lower jurassic directions the mean pole calculated from these overprints is 74 n 124 e k 125 a95 6 n 6 the revised apparent polar wander path apwp presented here shows that for the mid permian to the earliest jurassic the palaeopoles of europe stayed around 50 latitude while the longitudes drifted from 185 e to 100 e the previously established upper triassic lower jurassic loop of the apwp is shifted westwards by about 25 the revised apwp involves the following plate motions after the late alleghanian tectonic phase which marked the end of the variscan orogeny central western europe rotated counterclockwise during about 70 myr up to the earliest jurassic the south north drift in latitude by 35 nearly 4000 km remained regular from 320 to 205 ma with a constant rate of 3 4cm yr 1 around 205 ma this motion ceased probably because of a collision somewhere in the north of eurasia then in the lower liassic the plate underwent a rapid counterclockwise rotation with a eulerian pole located in northeastern asia synchronous with fracturing in the atlantic and the neotethys areas it is proposed that the intraplate fracturing of pangaea was initiated by the rapid change of the megacontinent motion at the end of the trias

lacustrine sedimentation in a permian intermontane basin the ville graben vosges france abstract the permian ville graben located on a major fault of the vosges basement has several stages of fluvial fill interrupted by a period of lacustrine sedimentation the lacustrine deposits of the autunian 2 series include various facies marginal and fan delta clastics and permanent lacustrine carbonate facies evolving into evaporitic playa facies differential subsidence of tectonic blocks controlled the facies patterns from the margin to the centre of the basin the sedimentation is determined by three components terrigenous volcanosedimentary and carbonate fan delta progradation with resedimentation processes provided the clastic material in the upper part of the lacustrine formation volcanosedimentary material was deposited primary ash fall sedimentation was followed by sub aqueous erosion and redeposition towards the edge of the basin the lacustrine facies is thin and was subject to frequent emergence sediments were occasionally oxidized and iron was redistributed to give mottled horizons cabonate crusts were precipitated and some silicification took place in the centre of the basin sapropelic carbonate sedimentation develops into a eutrophic lake with anoxic bottom waters the sapropels are massive to finely laminated they include monospecific ostracod faunas type ii to type iii kerogens and a total organic carbon content reaching 2 7 cyanobacterial and microbial activity in these organic rich sediments produced early diagenetic carbonate phosphate and sulfide phases at the top of the formation important sedimentological changes follow a lacustrine regression a restricted and evaporative environment leads to the development of an evaporitic playa lake with stromatolites

palaeomagnetism of the permian volcanic rocks of moissey french jura implications for the palaeofield and tectonic evolution rocks from the massif de la serre in the french jura latitude 47 3 n longitude 5 6 e belonging to an ignimbritic assemblage dominated by vitrophyric rhyolites and whose age of formation is probably permian autunian to saxonian have been studied by applying thermal and alternating field demagnetization the characteristic magnetization has a mean direction derived from 89 samples of d 170 i 16 k 26 2 95 3 and a corresponding north palaeopole at 41 n 172 e a95 5 the pole which is very close to the permian european poles can thus be considered as a new contribution some samples are found to carry a unique normal polarity magnetization others carry both normal and reverse polarities it therefore seems that similar to permian series in the ussr these west european rocks have registered a normal event in the kiaman interval from a structural point of view we may conclude that during the alpine tectonic phases the massif de la serre has not been subjected to substantial rotation

paleoposition of the northern margin of armorica in late devonian times paleomagnetic and rock magnetic results from the frankenstein intrusive complex mid german crystalline rise a detailed rockmagnetic and paleomagnetic study of the frankenstein intrusive complex fic 363 7 ma in age southwestern germany has been carried out in order to test whether the paleomagnetic declinations within the internal parts of the european variscides follow a common trend controlled by the structural grain of the orogen or whether the distribution of declinations follows a random pattern in addition new paleomagnetic data will contribute to further refine the drift history of the armorican terrane assemblage during late paleozoic times the unmetamorphosed frankenstein igneous complex forms part of the mid german crystalline rise within the armorican terrane assemblage amalgamated to avalonia and baltica during the variscan orogeny stepwise thermal and alternating field af demagnetization experiments identify four components a b c n and c r of magnetization component a is a recent viscous overprint that parallels the present day geomagnetic field the high unblocking temperatures of a in some samples can be explained by the presence of multidomain magnetite component b is carried by hematite and is considered to be a late carboniferous remagnetization components c r and c n found in 110 samples from 20 sites are antiparallel and pass a class c reversal test their primary origin is further supported by a contact test c r and c n have maximum unblocking temperatures of up to 580 c and occasionally above over 600 c indicating magnetite and hematite to carry the characteristic remanent magnetization ore microscopy revealed that primary hematite lamellae in ilmenite carry c r and c n and that a secondary generation of hematite is the carrier of b the overall site mean direction of c r and c n 20 sites based on endpoints and remagnetization circle analysis of 198 40 declination inclination with a 95 confidence limit 95 of 4 9 and a precision parameter k of 45 0 defines a paleopole at 15 s 9 w when comparing to the apparent polar wander path for stable europe this result indicates up to 27 counterclockwise rotation of the fic region this is significantly less than reported previously for the odenwald spessart black forest and the vosges massifs of the central european variscides furthermore the resulting paleolatitude indicates significant separation between baltica and this sector of the armorican terrane assemblage in the latest devonian

the late carboniferous to early triassic geodynamic evolution of variscan europe in the light of magnetic overprints in early permian rhyolites from the northern vosges france and central black forest germany summary this paper demonstrates how magnetic overprints of a geological series can provide information over a long time period which can be interpreted in terms of geotectonic evolution according to these new results the late carboniferousearly permian rhyolites from the northern vosges have recorded the magnetic field over a major part of the permian recent radiometric dating assigns a late carboniferous early permian age 298 ma to the previously middle permian rhyolitic volcanism of the northern vosges a palaeomagnetic study was undertaken on rhyolites of the nideck donon massif and on neighbouring permian basins villc saint die in order to obtain a new pole for the early permian and to detect overprints standard palaeomagnetic and rock magnetic experiments demonstrate that over 90 per cent of the characteristic directions of magnetizations are of secondary origin the high temperature magnetizations carried by secondary haematite and haematized titano magnetite fail the fold test and display directions consistent with the saxonian thuringian directions from variscan europe nideckdonon 186 17 k 167 for 26 sites vgp 50 n 178 e saint dic basin 184 20 5 for two sites vgp 53 n 180 e villc basin 191 5 25 for two sites vgp 53 n 168 e vosges dikes 197 5 26 5 for two sites vgp 53 n 158 e part of the magnetizations with intermediate unblocking temperatures of magnetite consists also of post tectonic overprints two consistent mean directions with lower inclinations obtained in the nideck donon rhyolites 182 7 k 459 for 13 sites vgp 45 n 1840 e and pyroclastic deposits from the villc basin 178 9 k 519 for three sites vgp 46 n 190 e were probably acquired during late autunianearly saxonian times in rhyolites the pre and post tectonic characteristic mag netizations are carried by magnetite while in the ash fall deposits the carrier is allogenic haematite a few older magnetizations 191 3 two sites vgp 42 n 173 e consistent with magnetizations carried by magnetite from rhyolites of the central black forest and results from coeval volcanics as well as from autunian sediments have been observed in tuffs from the villi basin 188 1 5 two sites vgp 40 n 177 e the oldest magnetizations 207 10 k 329 vgp 32 n 155 e presumably of stephanian age were identified in two rhyolitic stocks within the granitic basement from the central vosges and central black forest the distribution of the palaeomagnetic directions suggests that from the late autunian to the late thuringian overprinting due to low temperature alteration of titano magnetite and crystallization of secondary haematite was more or less continuous the apparent polar wander path apwp computed with the new results and the published poles shows a hairpin which implies a drastic change of the european plate motion during the permian the clockwise rotation of europe initiated in the late visean namurian stopped in the late autunian early saxonian this event corresponds to the end of the variscan convergence and of the appalachian

character of the alleghanian orogeny in the southern appalachians part iii regional tectonic relations geological and geochronological studies in the eastern piedmont of the southern appalachians have documented a polyphase late paleozoic deformational chronology d 2 d 4 that is contemporaneous with the alleghanian orogeny recorded in the western appalachian foreland the scale and vergence of d 3 anticlinoria in the eastern piedmont are similar to those of anticlinoria in the western appalachians which are related to ramping of underlying thrust surfaces we suggest that the appalachian decollement extends southeastward beneath the entire piedmont province and that all of the piedmont rocks were displaced at least 175 km northwestward relative to north america during the alleghanian orogeny late paleozoic deformational effects in the eastern piedmont thus are considered cogenetic with alleghanian foreland deformation we interpret the alleghanian orogeny to be the result of oblique dextral convergence and collision of gondwana and laurentia

vegetation dynamics during the pleistocene holocene transition in the central great plains usa the holocene pleistocene transition in the upland loess mantled regions of the central great plains is punctuated by the brady soil which separates the late pleistocene peoria loess and the holocene bignell loess previous research on the brady soil at the old wauneta roadcut site in southwestern nebraska has produced paleoenvironmental information based on well constrained luminescence and radiocarbon ages stable carbon isotope data and chemical and physical data while the research indicated high effective moisture during formation of the brady soil and a shift to warm season c4 vegetation from the cool season c3 dominated vegetation of the peoria loess those data do not provide any detail as to plant community composition and significant underlying climatic inferences assemblages of phytoliths and other biosilicates extracted from the brady soil provide specific information on vegetation communities and indicate shifts of plant taxa comprising these assemblages short cell phytolith count data rev

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

a data driven model of the global calcite lysocline gridded maps of sediment calcium carbonate calcite concentration and overlying water saturation state archer 1996 are combined with maps of benthic oxygen fluxes and sediment accumulation rates from jahnke 1996 and cweink 1986 to drive a diagenetic model of calcium carbonate preservation in deep sea sediments the only model input for which we cannot draw a detailed map is the rain rate of calcite to the seafloor so i use the model to calculate the calcite rain rate required to simulate the observed distribution of calcite concentration on the seafloor the predictive power of the model can be checked by searching for input parameters to which the model is sensitive and comparing the model requirements with independent data the model is sensitive to the ratio of organic carbon to calcite rain rates the rain ratio and within the constraint of pelagic sediment trap rain ratio data is unable to reproduce the calcite field without respiratory dissolution the promotion of calcium carbonate dissolution by the oxic degradation of organic carbon however relative to variability in sediment trap data the required model rain ratio is insensitive to the extent of anoxic respiration the stoichiometric ratio of o c during respiration the bioturbation rate the dissolution rate constant the effect of borate chemistry and small offsets in the saturation state for caco3 the model is sensitive to the accumulation rate of non caco3 material and predicts an atlantic pacific difference in non caco3 rain rate which is consistent with observations the model predicts that the dissolution flux of caco3 from sediments is 25 40 1012 mol yr 1 roughly half of the total deep sea caco3 dissolution rate estimated from the water column alkalinity distribution broecker and peng 1987 archer and maier reimer 1994 wollast 1994 the model also predicts that only 20 30 of the flux of caco3 to the seafloor globally escapes dissolution

plant and insect remains from the wisconsinan interstadial stadial transition at wedron north central illinois abstract organic material exposed within a small swale fill in pit 6 of the wedron silica sand co near wedron in lasalle county illinois includes well preserved pollen plant macrofossils and insect remains this material occurs in slackwater sediment in the lower part of the peddicord formation which was deposited as existing valleys were dammed by fluvial aggradation during the initial late wisconsinan advance of laurentide ice into the wedron area wood from the organic horizon has a radiocarbon age of 21 460 470 yr b p isgs 1486 the pollen spectrum is dominated by picea pinus and cyperaceae plant macrofossils comprise a mix of boreal forest taxa including picea larix laricina and the moss campylium stellatum subarctic species including betula glandulosa empetrum nigrum and selaginella selaginoides along with the predominantly arctic vaccinium uliginosum var alpinum dryas integrifolia and rhododendron lapponicum the insect fauna contains the western montane ground beetle opisthius richardsoni several arctic subarctic ground beetles including diacheila polita helophorus sibiricus and pterostichus cryobius caribou and a diverse assemblage of insects that today inhabit the boreal forest we interpret the biotic record to record a phase in the transition from closed boreal forest to open tundra as climatic conditions deteriorated in advance of continental glaciation

a middle triassic paleomagnetic pole for the eurasian plate from heming france the paleomagnetic study of middle triassic limestones 91 cores 160 samples from a 40 m thick section in heming france yields a paleomagnetic pole for stable europe at lat 53 5 n lon 140 8 e dp 2 3 dm 3 9 this pole fills an important gap of the apparent polar wander path apwp of the eurasian plate the comparison of this pole with available data shows a standstill of the eurasian plate from the late paleozoic to the middle triassic followed by a rapid drift until the lower jurassic the beginning of the rapid drift is contemporaneous with the initiation of main rifting processes in the tethyan oceans

remagnetization and chemical alteration of sedimentary rocks remagnetization is a common phenomenon in rocks and developing a greater understanding of its mechanisms has several benefits acquisition of a secondary magnetization is usually tangible evidence of a diagenetic or thermal event which can be dated using palaeomagnetic techniques this is important because the timing of diagenetic and thermal events is commonly difficult to determine remagnetization can also obscure primary magnetizations and a better understanding of remagnetization could improve our ability to uncover primary magnetizations many chemical remagnetization mechanisms have been proposed including those associated with chemical alteration by a number of different fluids e g orogenic weathering mineralizing hydrocarbons and burial diagenetic processes e g clay diagenesis maturation of organic matter this book contains case studies and review articles that focus on remagnetization chemical remagnetization mechanisms and magnetic changes associated with chemical alteration by hydrocarbons

can a primary remanence be retrieved from partially remagnetized eocence volcanic rocks in the nanmulin basin southern tibet to date the india asia collision paleomagnetic dating of the india asia collision hinges on determining the paleogene latitude of the lhasa terrane southern tibet reported latitudes range from 5 n to 30 n however leading to contrasting paleogeographic interpretations here we report new data from the eocene linzizong volcanic rocks in the nanmulin basin which previously yielded data suggesting a low paleolatitude 10 n new zircon u pb dates indicate an age of 52 ma negative fold tests however demonstrate that the isolated characteristic remanent magnetizations with notably varying inclinations are not primary rock magnetic analyses end member modeling of isothermal remanent magnetization acquisition curves and petrographic observations are consistent with variable degrees of posttilting remagnetization due to low temperature alteration of primary magmatic titanomagnetite and the formation of secondary pigmentary hematite that unblock simultaneously previously reported paleomagnetic data from the nanmulin basin implying low paleolatitude should thus not be used to estimate the time and latitude of the india asia collision we show that the paleomagnetic inclinations vary linearly with the contribution of secondary hematite to saturation isothermal remanent magnetization we tentatively propose a new method to recover a primary remanence with inclination of 38 1 35 7 40 5 95 significance and a secondary remanence with inclination of 42 9 41 5 44 4 95 significance the paleolatitude defined by the modeled primary remanence 21 n 19 8 n 23 1 n is consistent with the regional compilation of published results from pristine volcanic rocks and sedimentary rocks of the upper linzizong group corrected for inclination shallowing the start of the tibetan himalaya asia collision was situated at 20 n and took place by 50 ma

paleomagnetic evolution of the armorican massif in late paleozoic times in the light of overprints recorded in cadomian and paleozoic units abstract previous investigations have shown that in paleozoic outcrops of the variscides the major part of the paleomagnetic record consists of overprints after identification and dating of these overprints the magnetic record can be used to constrain the geotectonic evolution of the investigated area after the major tectonic event in order to test this hypothesis a paleomagnetic investigation was carried out on various volcanic and plutonic units from northern brittany 48 5 n 3 w emplaced and metamorphosed in the late proterozoic during the cadomian orogeny to calibrate the overprints in terms of their ages doleritic dykes intruded into the cadomian basement in the early paleozoic as well as early carboniferous intrusive and extrusive rocks were also sampled thermal demagnetization often shows multivectorial behaviour of most nrms and indicates a wide range of magnetic components characterized by various unblocking temperatures a large majority of the components isolated in cadomian units display directions that are consistent whith the results from the younger paleozoic units with exception of the d components mean vgp 7 s 152 e which are interpreted as being ordovician in age all other mean directions poles agree with results obtained from visean volcanic plutonic and metamorphic rocks of the central part of the variscan belt this means that no cadomian magnetization has survived the tectonic magmatic and metamorphic phases that have affected the cadomian basement during the paleozoic the major part of the magnetic overprints were acquired during the variscan orogeny particularly in relation to visean and westphalian magmatism the early carboniferous 340 328 ma cn 7 s 53 e co 29 s 60 e and cp 51 s 62 e components the middle carboniferous 328 310 ma b components 11 n 124 e the late carboniferous 310 300 ma a1 30 n 151 e the late permian a 51 n 154 e and the jurassic j1 overprints 72 n 107 e delineate an apparent polar wander path that can be interpreted in terms of geotectonic evolution since the late visean this evolution was the same as for the massif central the vosges the black forest and the odenwald spessart the variable inclinations of the c components suggest a northwestward tilting of the area north of saint brieuc and a possible latitudinal drift of the whole massif in late visean times the c b and b a1 segments of the apwp reveal two successive clockwise rotations by 70 80 in the latest visean and by 30 in the late namurian early westphalian the first rotation closed the rhenohercynian basin during the last rotation the variscan belt was tied to northern europe the a and j1 overprints give evidence of hydrothermal activity in northern brittany in the late permian and the early jurassic

diversity and peculiarities of soil formation in eolian landscapes insights from the mineral magnetic records abstract magnetic properties of loess paleosol sequences are widely utilized as sensitive easily obtained and reliable proxy archives of past climate change in continental settings however soil formation in aeolian landscapes may occur under different and changing conditions of dust sedimentation which will affect the growth and development of the pedogenic magnetic component this phenomenon is explored in our study by analyzing depth variations of the following magnetic characteristics frequency dependent magnetic susceptibility anhysteretic magnetic susceptibility and the ratio between anhysteretic susceptibility and isothermal remanent magnetization acquired in a 100 mt back field arm irm 100 mt along three loess paleosol profiles from ne bulgaria a conceptual model for the time evolution of the grain size of the pedogenic magnetic fraction with soil depth is proposed which is build upon the mechanism of soil formation accretional or in stable land surfaces or a combination of the two another magnetic ratio isothermal remanence acquired in a 300 mt back field divided by low field magnetic susceptibility irm 300 mt is utilized as a proxy for the changes in the ratio of silt to clay fractions indicative of changes in dust sedimentation regimes during glacial interglacial transitions according to the proposed conceptual model verified by the magnetic signature of three holocene soils from ne bulgaria discrimination between accretional soils and soils developed without dust additions during soil forming period can be done accretional soils are characterized by parallel changes in grain size sensitive magnetic proxies soils developed at stable landscape conditions show gradation of the depths at which maximum enhancement of various proxies occurs with deepest occurrence of the maximum in fd followed by depth of maximum arm and arm irm 100 mt another implication of the new conceptual model is that the mean coercivity of the pedogenic component of accretional soils will be higher than that of soils developed without eolian input at equal temperature conditions because of the soils thermal gradient and different depths at which pedogenic minerals form in the two settings the results revealed that the holocene soils so has developed under different soil forming conditions than paleosols from the same sites

an upper carboniferous lower permian 280 ma palaeomagnetic pole from the western margin of the bohemian massif summary in the area of the drill site of the german continental deep drilling project ktj3 on the western margin of the bohemian massif 15 sites of uppermost carboniferous to lowermost permian rocks quartz porphyries granites and a siltstone geographic mean coordinates 12 e 49 8 n have been studied in order to obtain a reliable pole position for this time interval the investigated rocks are syngenetic or only slightly younger than the youngest granites of the fichtelgebirge for which a k ar and rb sr age of 280 ma has been determined by besang ef al 1976 while four sites quartz porphyries showed too weak intensities of the natural remanent magnetization nrm the results of two sites with otherwise good rock magnetic properties had to be discarded because of uncertain tectonic position in a shear zone the remaining nine sites have all reversed polarity as expected for a remanence age within the reversed kiaman interval and a mean pole position at 165 9 e 42 3 n with n 9 r 8 8776 a 6 4 this is in good agreement with the mean upper carboniferous lower permian european pole position of stable europe according to irving irving 1982 and of the bohemian massif krs 1968 rock magnetic investigations revealed that the chrm of the siltstone is due to primary magnetite while the mostly single component characteristic remanent magnetization chrm of the magmatic rocks is carried by primary magnetite and by primary haematite produced by syngenetic high temperature oxidation of primary magnetite

magnetoclimatology teleconnection between the siberian loess record and north atlantic heinrich events new environmental magnetic data from loess and paleosol successions in outcrops in the upper reaches of the ob river drainage southern siberia track the major climatic variations over the last glacial interglacial cycle profiles of magnetic susceptibility and alternating deposition of loess and soil formation events correspond to oxygen isotope stages 1 5 the magnetic susceptibility data in association with the stratigraphic succession confirm that the wind vigor magnetoclimatological model is a viable alternative to the classic pedogenic model interpretation of magnetic susceptibility data from loess paleosol successions must therefore consider eolian dynamics available source materials and transport directions in addition to pedogenic processes rapid magnetic fluctuations are also observed these are identified for the first time in siberian records as the signature of the abrupt cold pulses responsible for the heinrich layers in north atlantic marine sediments the data thus form a component of climatic teleconnections across the northern hemisphere allowing correlations to be made among 1 siberian magnetic susceptibility stratigraphy 2 data recorded from other loess paleosol successions in china european russia europe and north america 3 north atlantic ice rafted detritus and 4 sea surface temperatures derived from molecular stratigraphy of marine sediments off the northwest coast of africa

paleomagnetic evidence for rotation during stephano permian extension in southern massif central france we present results of a preliminary paleomagnetic study devised as a test of a tectonic model proposed by van den driessche and brun 1 to interpret the main structural features of the montagne noire south massif central france this model suggests that crustal extension during stephanian to permian times is responsible for a major fiat lying detachment the inferred geometrical relationships between fault azimuth and extension direction is befieved to induce a counter clockwise rotation of the paleozoic cover during its northward motion in order to test this model we have sampled autunian lower permian grey and red sandstone beds within two basins opened during the extension the lod ve and the st affrique basins the paleomagnetic study of six sites three in each basin using thermal demagnetization procedures reveals the presence of 3 magnetization components a first one a which is unblocked below 400 o c is interpreted as a recent overprint due to weathering of the sandstones the b component is unblocked between 400 o and 575 o c this b component is assumed to be primary although the gentle dip of the beds does not allow a fold test it fits the lower permian field direction in the lod ve basin in situ d m 194 i m 6 o k 50 tilt corrected d m 194 i m 10 o k 53 in contrast it shows a systematic difference in declination in the st affrique basin in situ d m 173 i m 2 5 o k 101 tilt corrected d m 172 lm 6 o k 37 this is interpreted as a post autunian counter clockwise rotation of at least 20 o of the st affrique basin thus supporting one of the main implications of the tectonic model finally red sediments from two sites of the lod ve basin yield a third component c with unblocking temperatures up to 670 c and carried by hematite its direction is also consistent with the permian field direction showing that hematite crystallisation occurred early in the diagenesis history of the sediments

evidence for mid permian compressive tectonics in western europe supported by a comparison with the alleghanian geodynamic evolution abstract the final continental collision of gondwana with the appalachian variscan fold belt during mid permian times is evident from 1 the simultaneous deformation of the entire fold belt marked by a thin skin structural style in the appalachians and in parts of the variscan front midi fault 2 the disruption of the hercynian zones in western europe and 3 left lateral transcurrent displacement visible in features such as the leucogranite belt in france and associated with thrusting of the ales saint etienne and saar lorraine basins the line along which the main transcurrent movement occurs stretches through western europe from ales to ireland and it nearly coincides with the paris basin magnetic anomaly it is consistent with the movement along the biscay fault and with the existence of stable areas iberia aquitaine and armorica where local extension occurred there are symmetrical movements and deformations on both the american and european sides the alleghanian orogeny is interpreted as being the result of oblique dextral convergence and collision of gondwana with laurasia on the european side this collision resulted in sinistral displacement laterally associated with thrusting such a geometrical pattern can be achieved through a frontal intracontinental compression

magnetic overprints in granitoids and metamorphic rocks from limousin france evidence for late variscan rotations crustal folding and tilting abstract generally the lack of bedding criteria in basement units hampers the interpretation of paleomagnetic results in terms of geotectonics nevertheless this work demonstrates that successive remagnetizations recorded in early carboniferous metamorphic and plutonic units without clear bedding criteria can be used to constrain a polyphased tectonic evolution consisting of a regional clockwise rotation followed by a folding phase a tilting phase and a second regional clockwise rotation metamorphic ultrabasic tonalitic and granitic rocks from different parts of limousin western french massif central 45 5 n 1 25 e which underwent metamorphism during devonian early carboniferous or were intruded in the early middle carboniferous were sampled in order a to identify the magnetic overprinting phases and the related tectono magmatic events and b to constrain the regional and plate tectonic evolution of limousin paleomagnetic results from 32 new and 26 sites investigated previously show that at least 90 of the magnetization isolated in rocks older than 330 ma are overprints in agreement with results from adjacent areas of the variscan belt the major overprinting phases occurred a in the last stages of the major exhumation phase 332 328 ma mean virtual geomagnetic pole vgp cp 37 n 70 5 e b during the post collisional syn orogenic extension 325 315 ma vgp b 11 n 114 e c in the latest carboniferous and early permian vgp a1 27 n 149 e and d in the late permian vgp a 48 n 146 e the middle late carboniferous overprints cp and b are contemporaneous with emplacement of leucogranitic crustal derived plutons and probably result from the hydro thermal activity related to the magmatism the drift from cp directions to b directions implies that after 330 ma limousin underwent a clockwise rotation by 65 together with the central europe variscides the bt components the vgps of which deviate from the mean apparent polar wander path apwp of the belt are interpreted as b overprints tilted during late variscan tectonics that is in the time range 325 315 ma the first and most important generation of bt overprints was tilted during nw se folding associated with ne sw shortening updoming and emplacement of leucogranitic plutons the second generation reveals southeastward tilting due to ne striking normal faulting the drift from b to a1 directions implies that limousin has participated to the second clockwise rotation by 40 of the whole belt in westphalian times

late paleozoic orogenies in western africa and eastern north america the diachronous closure of theic ocean the carboniferous evolution in western morocco southeastern canada and new england was dominated by intracontinental processes the subsidence of pull apart sedimentary basins and their subsequent deformation during middle carboniferous to early permian times with the development of autochthonous structures and mainly low to medium grade metamorphism on the other hand the structural style of the late carboniferous deformation in the southern appalachians and to a substantial degree also in new england that is related to a continental collision is characterized by deep seated northwest vergent thrusts and medium to high grade metamorphism the mauritanides structures are symmetrically east vergent thrusts this pattern is explained by the diachronous closure of the theic ocean that separated the avalon and carolina microcontinental blocks from paleo gondwana the closure of the theic ocean occurred during devonian times between the northern appalachians and the northwestern edge of paleo gondwana morocco whereas it was achieved only at the end of carboniferous times between the southern appalachians and western africa mauritania senegal the late devonian to early carboniferous counterclockwise rotation of gondwana induced the opening of the pull apart basins of canada new england and morocco as well as later the oblique collision in the southern appalachians and the generalized late paleozoic dextral transcurrent faulting along the northern edge of paleo gondwana

factors controlling the flux of organic carbon to the bathypelagic zone of the ocean 1 particle fluxes measured with time series sediment traps deployed below 2000 m at 68 sites in the world ocean are combined with satellite derived estimates of export production from the overlying water to assess the factors affecting the transfer of particulate organic matter from surface to deep water multiple linear regression is used to derive an algorithm suggesting that the transfer efficiency of organic carbon defined as the settling flux of organic carbon normalized to export production increases with the flux of carbonate and decreases with water depth and seasonality the algorithm predicts 80 of the organic carbon transfer efficiency variability in diverse oceanic regions the influence of the carbonate flux suggests that the ballasting effect of this biogenic mineral may be an important factor promoting export of organic carbon to the deep sea by increasing the density of settling particles however the lack of a similar effect for biogenic opal suggests that factors other than particle density also play a role the adverse effect of increasing seasonality on the transfer efficiency of carbon to the deep sea is tentatively attributed to greater biodegradability of organic matter exported during bloom events in high latitude opal dominated regions with high f ratios and seasonality while a higher fraction of net production is exported a higher fraction of the exported organic matter is remineralized before reaching bathypelagic depths on the other hand in warm low latitude carbonate dominated regions with low f ratios and seasonality a higher fraction of the exported organic matter sinks to the deep sea

a magnetotectonic study of the hercynian montagne noire france a paleomagnetic study of eleven sites of devonian limestones sampled along the flanks and hinge of a polyphase hercynian recumbent fold in the montagne noire reveals well defined directions of characteristic remanent magnetization chrm the directions have good within site precision but a large between site scatter which fails to be reduced by a classical tilt correction this is readily understood if widespread remagnetization occurred between the two major hercynian phases of folding a and b which are known to have shaped the montagne noire this remagnetization appears to be an instance of a continent wide chemical event that wiped out much of the magnetic memory of devonian and lower carboniferous rocks in laurasia baltica and northern gondwana possibly due to groundwater circulation following the major hercynian tectonic phases comparison of observed and predicted hercynian magnetic directions allows one to determine through a fairly simple geometric construction the tectonic elements of the later phase b it is found that different rotations affected the flanks and hinge zone of the folds generated by phase a thus demonstrating how a pre existing structure can control the development of deformation in a later tectonic phase the effects of the non cylindrical phase b can next be removed to reveal the broad tectonic features of phase a deformations the reversed kiaman polarity of the chrm allows a determination of the age of phase b which is found to be about 300 310 ma and of the age of the remagnetization itself at about 310 320 ma the search for the age of remagnetization included paleomagnetic measurements at two lower permian sites from the nearby lodeve basin these provide new data for the permian pole of europe and point out the limitations of some earlier studies due to insufficient magnetic cleaning finally the principal shortening directions of the two phases can be determined from the magnetic data and are found to have rotated counterclockwise by 30 between phase a and phase b this feature already observed in the collision of india against eurasia may be related to the progressive suturing of former subduction zones during the hercynian collision of gondwana against laurasia this study demonstrates the potential of remagnetizations for the solution of rather complex tectonic problems we propose the term magnetotectonics for this rapidly expanding field of studies in which the methods of paleomagnetism and structural analysis are closely associated

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

ice wedge casts and relict patterned ground in central illinois and their environmental significance abstract sediment features and soil patterns indicate that permafrost developed beyond the late wisconsinan woodfordian ice margin in illinois vertical wedge shaped bodies in woodfordian glacigenic deposits and buried by woodfordian loess are interpreted to be ice wedge casts large scale patterned ground common on the late wisconsinan drift plain and on the illinoian drift plain to the south and west also is interpreted to be the result of ice wedge formation permafrost extended to about 38 30 n latitude and formed during the interval from about 21 000 to 16 000 yr b p formation and degradation of permafrost was time transgressive directly related to the ice marginal climate and probably restricted temporally to less than 1000 years at a site the following environmental conditions are suggested near the ice margin mean annual ground temperature 3 c mean annual air temperature 6 2 c less precipitation than modern particularly in winter strong and likely dry wind systems and relatively open vegetation with few woody plants

paleopositions of the western europe hercynides during the late carboniferous deduced from paleomagnetic data consequences for stable europe abstract paleomagnetic investigations have been carried out in different areas of the variscan belt armorican massif central massif ardenne vosges and the black forest in order to unravel the paleogeographic evolution of the hercynides during the carboniferous subsequent to important southerly or northerly drifts the central massif and vosges underwent a large rotation of a still undetermined direction in latest visean namurian times during the namurian westphalian the whole belt was oriented n s all investigated areas yield wsw ene directions for that period these directions question the validity of carboniferous mean poles available for stable europe a european plate rotated counterclockwise by about 40 relative to its permian position would be more consistent with these results during the latest westphalian stephanian period i e within the 310 290 ma timespan the western europe hercynides rotated clockwise by 40 50 perhaps together with the whole of europe late variscan strike slip faulting and overthrusting probably result from that rotation

a geomagnetic polarity timescale for the carboniferous the geomagnetic polarity pattern for the carboniferous is incompletely known but with the best resolved parts in the serpukhovian and bashkirian hence data from both igneous and sedimentary units are also used in an additional polarity bias evaluation in the tournaisian to mid visean interval polarity is mainly derived from palaeopole type palaeomagnetic studies allowing identification of polarity bias chrons seven polarity bias chrons exist in the mississippian mi1nb to mi4nb with an additional 33 conventional magnetochrons and submagnetochrons mi4r to mi9r the moscovian and gzhelian polarity is best resolved in magnetostratigraphic studies from the donets basin and the southern urals dispute about the reliability of these data is ill founded since an assessment of supporting data from palaeopole type studies suggests that these datasets currently provide the best magnetic polarity data through the pennsylvanian polarity bias assessment indicates a normal polarity bias zone in the kasimovian in the pennsylvanian there are 27 conventional magnetochrons and submagnetochrons pe1n to ci1r and one normal polarity bias chron pe8nb the kiaman superchron begins in the mid bashkirian with clear data indicating brief normal polarity submagnetochrons within the superchron the magnetochron timescale is calibrated using 31 u pb zircon dates and a quantitative bayesian based age scaling procedure

episodic holocene loess deposition in central nebraska abstract the mirdan canal section in central nebraska usa provides evidence for multiple episodes of holocene loess deposition in the central great plains this irrigation canal cut exposes more than 4 m of holocene sediment that overlies the late wisconsinan peoria loess the oldest holocene sediment is local slopewash that fills gullies but overlying beds are interpreted as holocene loess bignell loess three buried soil profiles occur within the holocene sediment and have yielded uncalibrated 14 c ages of 3010 yr bp uppermost buried soil and 8790 yr bp third buried soil from top a fourth buried soil yielded an age of 9330 yr bp and is correlated with the brady soil the bignell loess has a darker color slightly more organic matter more clay more coarse silt and sand less smectite and less volcanic glass than the underlying peoria loess the bignell loess is most plausibly interpreted as dust from local flood plains containing a mixture of reworked peoria loess and older silts with contrasting mineralogy episodes of loess deposition occurred in the early middle and late holocene probably during periods of dry climate but possibly also as a consequence of large erosive floods that made wind erodible sediment available on nearby flood plains

stratigraphy geochemistry and thermoluminescence ages of lower mississippi valley loess four periods of loess deposition in the lower mississippi valley can be identified on the basis of geochemical and mineralogical criteria radiocarbon dating and thermoluminescence dating these are designated loess units 1 2 3 and 4 in order of increasing age carbonate rich unit 1 loess comprises more than 70 per cent of the thickness of the loess profiles 14c and tl dates indicate this loess was deposited between 9 000 and 20 000 years ago a maximum sedimentation rate of 2 17 mm yr 1 has been recorded near vicksburg just after the last laurentide glacial maximum between 17 190 and 15 580 years ago the unit 2 loess which is thin and partly decalcified was deposited slowly between about 25 000 and 20 000 years ago the unit 3 and unit 4 loess formations which are both highly weathered have yielded tl ages of 76 000 85 000 years and 119 000 132 000 years suggesting they were deposited during the altonian substage of the early wisconsinan and the illinoian glacial stage respectively the four loess units are stratigraphically equivalent to the peoria farmdale roxana and loveland loess formations previously recognized in illinois the source of dust in both areas was glacial outwash in the mississippi valley during interglacials and interstadials when the supply of glacial debris was reduced and the mississippi river changed from a braided to a meandering regime dust sedimentation in southern mississippi virtually ceased allowing weathering and pedogenesis to proceed

the importance of both geological and pedological processes in control of grain size and sedimentation rates in peoria loess abstract the loess paleosol succession in the peoria loess in southern illinois is characterized as alternating loess layers and weathering bands known as paleosol a horizons the fast loess accumulation during the late wisconsin glaciation interacted with the incipient pedogenesis and caused unclear boundaries of loess paleosol alternations in soil horizonation and mineralogy parameters of grain size distribution sedimentation rate matrix carbonate content and diffuse reflectance i e soil colors and iron oxides are used in this paper to discuss the geological and pedological influences for the peoria loess in keller farm section in southern illinois the multi proxy analysis revealed that many paleosol a horizons defined by the diffuse reflectance variability contain finer grained materials with a relatively higher sedimentation rate it suggests that glaciofluvial sediments were available in the source areas for uploading eolian dust during the temporary ice sheet retreats the denser vegetation and wetter surface soils on the loess deposit area could increase the dust trapping efficiency and caused a greater accumulation rate of loess deposits the coarser grained materials and slower sedimentation rate are often found in loess layers it suggests that strong surface winds transported the coarser grained materials from local dust sources and sparse vegetation and dry surface soils reduced the dust trapping efficiency during the ice sheet readvance the strong interactions between the geological and pedological processes played an important role on the loess paleosol alternations in southern illinois during the late wisconsin glaciation

particle settling rates increase with depth in the ocean abstract time and depth scales of particulate organic carbon degradation and caco3 and biogenic opal dissolution are critical to understanding the depth distribution of co2 and dissolved nutrients in the ocean the speed at which particles sink and the factors that control sinking speed are of primary importance to the distribution of oceanic nutrient concentrations and to the preservation of biogenic material in the sediment record sequencing sediment trap collectors deployed at us jgofs sites in the equatorial pacific and arabian sea provided a time series of particle fluxes from which particle settling rates were estimated a comparison of settling velocities obtained from 100 500 m pilskaln et al deep sea research 45 1998 1803 to settling velocities obtained for depths between 1000 and 3500 m indicate an increase of a factor of 2 10 between 100 and 2000 m and an increase of 15 60 between 2000 and 3500 m the increase in settling velocity in the deep ocean is generally correlated with the loss of corg with depth lithogenic content does not appear to impact particle settling rate variability in particle settling rate is systematically related to physical forcing of the surface ocean in the equatorial pacific but not in the arabian sea the increase in particle settling rate with depth likely influences the delivery of caco3 to the sea floor

seasonal variations of the particle flux in the peru chile current at 30 s under normal and el nino conditions abstract time series sediment traps were deployed 180 km off the chilean coast at 30 s in the peru chile current during the el nino period 1991 1992 6 months and during the normal period 1993 1994 12 months under normal conditions in 1993 1994 the particle fluxes display a pronounced seasonal cycle marked by a settling phytoplankton bloom in september intermediate fluxes until january and low fluxes between january and july this seasonal pattern is also reflected in stable isotope data measured on the planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides which indicate persistent upwelling conditions between august and february followed by a stratified water column between march and july the total flux under normal conditions amounts to 65 1 g m 2 a 1 with the main flux constituents contributing 47 6 carbonate 26 4 lithogenic matter 17 4 biogenic opal and 8 6 organic matter respectively based on these particle flux data the export production has been estimated to be 42 gc m 2 a 1 although the main flux event in september was not sampled in the el nino period 1991 1992 the available record from november 1991 to april 1992 allows an interesting comparison with the fluxes of the normal year the total amount of fluxes and the timing of minor flux events are very similar under normal and under el nino conditions however increased proportions of organic carbon and lithogenic matter under el nino conditions are interpreted to reflect faster sedimentation and preferred scavenging of organic matter by elevated lithogenic fluxes rather than increased productivity the higher lithogenic fluxes under el nino conditions are probably due to increased precipitation and terrestial runoff in the arid to semiarid northern part of chile

roxana silt of the upper mississippi valley lithology source and paleoenvironment significant lithological differences exist between the middle wisconsinan roxana silt loess of the upper mississippi valley the valley north of 41 5 and that of the type area near st louis missouri primary differences are that the upper mississippi valley roxana silt is much thinner finer textured and more weathered than that of the type area extrapolation of radiocarbon dates brackets sedimentation of upper mississippi valley roxana silt between 55 and 27 ka which is in close agreement with dates from the type area radiocarbon dates and paleobotanical data indicate that the upper mississippi valley roxana silt accumulated at a maximum long term average sedimentation rate of about 7 cm 1 000 yr within a boreal forest environment whereas the type area roxana silt accumulated at a maximum long term average sedimentation rate of about 60 cm 1 000 yr within a prairie like environment multiple regression analysis shows that more than 75 of the variance in thickness and texture between the upper mississippi valley roxana silt and that of the type area is explained by parameters of source valley width source valley azimuth and distance of the depositional site from the source valley this indicates that although the lithologic characteristics and sedimentation rates between the two regions are quite different they are consistent with a unified loess sedimentation sys tem linked to the ancient mississippi river valley a proglacial source for the roxana silt and a middle wisconsinan advance of the lauren tide ice sheet is a topic of scientific debate because recent findings show a lack of roxana correlative till deposits in the midwest alternative hypotheses include a glaciolacustrine source a regional slope erosion source and a cold climate desert dust source tests of these hypotheses support a proglacial origin for the roxana silt multiple regression analysis of loess thickness and texture along with paleobotanical evidence indicates that the roxana silt was blown from the ancient mississippi valley rather than from a cold climate desert source or from flood plains linked to a glaciolacustrine source geochemical and mineralogical composition of the upper mississippi valley roxana silt compared to out wash derived peoria loess indicates that detritus from regional hillslope erosion is not a unique component of the roxana silt combined data indicate that the midcontinental roxana silt was derived as loess blown from flood plains of middle wisconsinan proglacial rivers between 55 and 27 ka

paleomagnetic investigations and k ar dating on the variscan plutonic massif of the champ du feu and its volcanic sedimentary environment northern vosges france abstract paleomagnetic investigations have been carried out on samples from the plutonic series of the champ du feu massif and the devonian ordovician host rocks in order to date the different phases of magnetization a series of samples has been selected for k ar analysis on micas amphiboles and feldspars the diorites granodiorites diabases and hornfelses are characterized by high susceptibilities of up to 10 1 si thermal demagnetization reveals several groups of directions of characteristic magnetization the a direction d 202 i 23 49 n 153 e is consistent with the permian virtual geomagnetic pole for europe the b 1 direction d 59 i 22 11 n 128 5 e was obtained from the effusive parts of the kagenfels granite dated at 284 ma diorites microdiorites and volcanics emplaced a short time after the intrusion of the natzwiller granite dated at 344 and 351 ma display three groups of directions the c 1 direction d 328 i 15 27 n 223 5 e the c 2 d 323 i 38 13 s 222 e and the c 3 d 272 i 41 16 s 260 e the c 1 and c 2 directions agree well with those obtained previously for visean volcanics from the southern vosges in the host rocks we have identified b and c overprintings despite the lack of tectonic control the paleomagnetic data demonstrate at least two important motions of the vosges first a rotation of undetermined direction relative to stable europe which affected the variscan belt between the late visean and 320 ma and second a clockwise rotation which occurred during the stephanian autunian in late variscan time

paleopositions of the saxothuringian northern vosges pfalz odenwald spessart in variscan times paleomagnetic investigation abstract in the saxothuringian zone thermal demagnetization of 581 specimens of late devonian early carboniferous gabbros diorites granodiorites gneisses and schists yields different time dependent paleomagnetic directions the oldest c n directions vgp northern vosges 19 n 222 e spessart 27 5 n 227 e were emplaced during crystallization of the visean plutonics in the time range 340 330 ma c p directions n v 47 n 241 e mostly characterized by low unblocking temperatures are interpreted as slightly younger overprints or as resultant vectors of c n and present day directions the b directions northern vosges 14 n 132 e odenwald 6 n 128 e exist as primary magnetizations in middle late carboniferous rhyolites and as overprint in the late devonian early carboniferous plutonics the a directions sp 28 n 175 e od 26 n 168 e correspond to overprints emplaced later in the late carboniferous the a directions northern vosges 49 n 155 e pfalz 45 n 154 e odenwald 48 n 151 e spessart 47 n 165 e are consistent with the permian early triassic european directions and are present as primary directions in permian volcanics the late carboniferous permo triassic overprints are mainly characterized by high unblocking temperatures due to the presence of secondary hematite the deviations from c to b and from b to a are interpreted as due to two successive block rotations the first 90 clockwise or counterclockwise the second 40 clockwise and the deviation from a to a to a 2500 km northward drift of the saxothuringian