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

riverine evidence for a fractionated reservoir of ca and mg on the continents implications for the oceanic ca cycle analysis of river water rock travertine and soil from the high altitude negligible vegetation setting of the southern tibetan plateau demonstrates that ca and mg isotope ratios are fractionated during weathering dissolved ca in the two rivers studied is derived primarily by limestone dissolution 44 42ca in the rivers averages 0 43 and is statistically distinct from limestone at 0 31 the range in 44 42ca in these small rivers is 0 43 equivalent to the entire range in 44 42ca recorded in marine carbonate over the last 80 ma precipitation of isotopically light travertine with a 44 42ca of 0 21 enriches solute ca in heavy isotopes the mg isotope composition of the rivers is intermediate between limestone and silicate rock averaging 1 5 silicate soil has a 26mg of 0 03 heavier than silicate rock by 0 5 these fractionations in the soil create a companion groundwater reservoir of heavy ca and light mg seasonal variations in ca and mg isotope ratios in the dissolved load are small but define an array which can be modelled as a mixture between a fractionated groundwater reservoir and surface runoff reflecting the isotopic composition of the lithology fractionation of ca during the weathering of the continents is of importance to the global cycle of ca the riverine input of ca to the oceans dominated by carbonate weathering is controlled not only by the composition of the primary continental crust but also by the size and composition of a fractionated reservoir on the continents the impact on the oceanic cycle of ca depends on the relative residence times of dissolved ca in the ocean and the storage time of fractionated ca

tectonic implications of paleomagnetic data from sills and dykes in the sverdrup basin canadian arctic mesozoic intrusives 71 sills and 12 dykes from different structures in the folded eastern sverdrup basin contain stable well grouped paleomagnetic directions of both normal and reverse polarity the mean direction is 274 79 k 173 95 3 7 with a corresponding pole position at 157 67 n k 61 a95 6 6 the paleomagnetic fold test shows that the major deformation involving tilting of strata around strike postdated the emplacement of sills and dykes minor preintrusion deformation may also have occurred but more importantly an offset of the paleopole from the cretaceous section of the polar wander path permits a postintrusion anticlockwise rotation of eastern sverdrup basin of about 15 20 with respect to stable north america if the intrusives are cretaceous the degree of rotation is close to that 11 estimated for greenland during the opening of the labrador sea no positive evidence has been found to support models of distributed shear with block rotations to accommodate the contentious northeast translation of greenland along the nares strait

the palaeozoic variscan oceans revisited abstract geological evidence supported by biogeographical data and in accord with palaeomagnetic constraints indicates that one ocean models for the variscides should be discarded and confirms instead the existence of three gondwana derived microcontinents which were involved in the variscan collision avalonia north armorica franconia and thuringia subdivided by a failed vesser rift and south armorica central iberia armorica bohemia all divided by small oceans in addition parts of south eastern europe including adria and apulia are combined here under the new name of palaeo adria which was also peri gondwanan in the early palaeozoic oceanic separations were formed by the break up of the northern gondwana margin from the late cambrian onwards most of the oceans or seaways remained narrow but much like the alpine cenozoic oceans gave birth to orogenic belts with hp uhp metamorphism and extensive allochthons the saxo thuringian ocean between north and south armorica and the galicia moldanubian ocean between south armorica and palaeo adria only the rheic ocean between avalonia and peri gondwana was wide enough to be unambiguously recorded by biogeography and palaeomagnetism and its north western arm closed before or during the emsian in europe ridge subduction under the northernmost part of armorica in the emsian created the narrow and short lived rheno hercynian ocean it is that ocean and not the rheic whose opening and closure controlled the evolution of the rheno hercynian foldbelt in south west iberia south west england germany and moravia czech republic devonian magmatism and sedimentation set within belts of early variscan deformation and metamorphism are probably strike slip related the first arrival of flysch on the forelands and or the age of deformation of foreland sequences constrains the sequential closure of the variscan seaways galicia moldanubian in the givetian saxo thuringian in the early famennian rheno hercynian in the tournaisian additional mid to late devonian and partly early carboniferous magmatism and extension in the rheno hercynian saxo thuringian and galicia moldanubian basins overlapped with variscan geodynamics as strictly defined the early carboniferous episode was the start of episodic anorogenic heating which lasted until the permian and probably relates to tethys rifting

structural evolution of intermediate crustal rocks in a strike slip and extensional setting variscan odenwald sw germany differential upward transport of metamorphic complexes and changing deformation mechanisms abstract the variscan basement exposed in the odenwald mountains southwest germany is composed of several allochthonous metamorphic complexes showing low pressure metamorphism with varying pt conditions and of syntectonic plutons i and s type during the late devonian early carboniferous times rapid uplift of these rocks caused rapid cooling before and during the thermal peak of metamorphism the metamorphic rocks experienced penetrative strain d 1 d 2 which was probably generated by crustal shortening and stacking the resulting micro structures infer distributed strain activation of c slip in quartz and postkinematic annealing during and after the thermal peak of metamorphism ne sw trending zones of normal oblique sinistral strike shearing d 3 and nne ssw trending zones of normal shearing d 4 developed these episodes of deformation are characterized by strong localization of strain strain softening was caused by reorientation of the lattice of quartz toward an orientation more favorable for easy glide along a and by a change in deformation mechanisms of feldspar from dislocation creep to grain size sensitive creep normal oblique strike shearing and normal shearing caused juxtaposition of mid crustal slivers of dissimilar pt and structural histories and provided mechanisms for their denudation detachment of rocks occurred along domains in which strain softening was operative further transtension and extension facilitated uplift and emplacement of syntectonic plutons which experienced also d 3 and d 4 strain in the plutonic rocks strain was broadly distributed in the initial hot stages and became increasingly localized as the deformation continued through cooling

calcium and magnesium isotope systematics in rivers draining the himalaya tibetan plateau region lithological or fractionation control abstract in rivers draining the himalaya tibetan plateau region the 26mg 24mg ratio has a range of 2 and the 44ca 42ca ratio has a range of 0 6 the average 26 mg values of tributaries from each of the main lithotectonic units tethyan sedimentary series tss high himalayan crystalline series hhcs and lesser himalayan series lhs are within 2 standard deviation analytical uncertainty 0 14 the consistency of average riverine 26 mg values is in contrast to the main rock types limestone dolostone and silicate which range in their average 26 mg values by more than 2 tributaries draining the dolostones of the lhs differ in their 44 42 ca values compared to tributaries from the tss and hhcs the chemistry of these river waters is strongly influenced by dolostone solute mg ca close to unity and both 26 mg 1 31 and 44 42 ca 0 64 values are within analytical uncertainty of the lhs dolostone these are the most elevated 44 42 ca values in rivers and rock reported so far demonstrating that both riverine and bedrock 44 42 ca values may show greater variability than previously thought although rivers draining tss limestone have the lowest 26 mg and 44 42 ca values at 1 41 and 0 42 respectively both are offset to higher values compared to bedrock tss limestone the average 26 mg value of rivers draining mainly silicate rock of the hhcs is 1 25 lower by 0 63 than the average silicate rock these differences are consistent with a fractionation of 26 mg values during silicate weathering given that the proportion of mg exported from the himalaya as solute mg is small the difference in 26mg 24mg ratios between silicate rock and solute mg reflects the 26mg 24mg isotopic fractionation factor silicate dissolved mg between silicate and dissolved mg during incongruent silicate weathering the value of silicate dissolved mg of 0 99937 implies that in the tss solute mg is primarily derived from silicate weathering whereas the source of ca is overwhelmingly derived from carbonate weathering the average 44 42 ca value in hhcs rivers is within uncertainty of silicate rock at 0 39 the widespread hot springs of the high himalaya have an average 26 mg value of 0 46 and an average 44 42 ca value of 0 5 distinct from riverine values for 26 mg but similar to riverine 44 42 ca values although rivers draining each major rock type have 44 42 ca and 26 mg values in part inherited from bedrock there is no correlation with proxies for carbonate or silicate lithology such as na ca ratios suggesting that ca and mg are in part recycled however in spite of the vast contrast in vegetation density between the arid tibetan plateau and the tropical lesser himalaya the isotopic fractionation factor for ca and mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of ca and mg in these catchments the discrepancy between solute and solid ca and mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of ca and mg bound as minerals in rock and released as cations in rivers the fractionation of ca and mg isotope ratios may prove useful for tracing mechanisms of chemical alteration ca isotope ratios of solute riverine ca show a greater variability than previously acknowledged the variability of ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global ca cycling if past variations in oceanic ca isotope ratios are to be of use in constraining the past carbon cycle

elucidating modern geochemical cycles at local regional and global scales using calcium isotopes abstract in earth s surface environment calcium ca is an important mobile metal that is actively and passively transported in solution and within organic and mineral phases being cycled and recycled during various biogeochemical processes with the development of modern mass spectrometric techniques small variations in the stable and radiogenic isotopic compositions of ca can be measured revealing insight in these complex biogeochemical cycles and tracing and quantifying components across a range of spatial and temporal scales similar to other more routine isotope systems more than three decades of work reveal systematic variations in the partitioning of ca isotopes due to both abiotic and biological processes an overview of processes that fractionate ca isotopes at local regional and global scales is outlined here we present detailed examples of instances in which ca isotopes have provided unique insight into the functioning of earth surface processes and the cycling of ca at multiple scales future studies should target questions for which ca isotopic analysis provide unique insight and when combined with other isotope and trace element multi proxy studies better constrain the system of interest at the same time we challenge the scientific community to explore new frontiers including polar regions and other extreme environments

paleomagnetism of permian through early triassic sequences in central spitsbergen implications for paleogeography upper carboniferous through lower triassic sediments from spitsbergen have yielded paleomagnetic results with those for the late gzhelian early permian being the more reliable the corresponding pole 38 n 171 e is fully concordant with the early permian segment of the apparent polar wander path for baltica it does not support hypotheses about post carboniferous mobilism of spitsbergen with respect to stable europe neither mesozoic nor later rifting processes changed the position of spitsbergen considerably in relation to the stable europe

effect of heat treatment on siliceous rocks used in prehistoric lithic technology stone tool manufacture by many prehistoric and recent societies was characterized by deliberate heating of fine grained siliceous rocks to improve their flaking properties extensive mechanical testing of heated and unheated cryptocrystalline and macrocrystalline quartz lithologies has shown that thermal treatment causes a consistent marked reduction in fracture toughness this mechanical property can be used as an objective measurement of the flaking qualities of stone materials and a reliable criterion for the recognition of intentionally heated artefacts in the archaeological record x ray diffraction studies and scanning electron microscopy have demonstrated that the change in fracture toughness with heating is the result of recrystallization the poorly ordered strongly interlocking cryptocrystalline fabric of the unheated samples becomes more equigranular and better crystallized with thermal treatment as a consequence fractures propagate more readily in heated samples accounting for their better flaking properties

late paleozoic rotations of corsica and sardinia new evidence from paleomagnetic and k ar studies abstract a detailed paleomagnetic investigation of so called permian volcanics was undertaken in southeastern and northwestern sardinia k ar dating on separate minerals representing 30 sites on corsica and sardinia showed that the first calc alkaline cycle had taken place in westphalo stephanian times and the second alkaline one at the end of the stephanian 246 paleomagnetic specimens from 28 sites of southeastern sardinia and 2 sites from the northwest were demagnetized by alternating field and thermal processes the directions of characteristic magnetizations are d 85 i 6 95 5 for the volcanics of southeastern sardinia and d 126 i 1 for the nurra samples these mean directions differ from those of northwestern corsica and northern sardinia gallura the paleomagnetic results display good grouping for each volcanic complex but exhibit a geographical dispersion of the mean directions this scattering suggests significant motions in late hercynian times

chemical and isotopic signature of old groundwater and magmatic solutes in a costa rican rain forest evidence from carbon helium and chlorine 1 c he and cl concentrations and isotopes in groundwater and surface water in a lowland costa rican rain forest are consistent with the mixing of two distinct groundwaters 1 high solute bedrock groundwater representing interbasin groundwater flow igf into the rain forest and 2 low solute local groundwater recharged in the lowlands in bedrock groundwater high 13c 4 89 low 14c 7 98 pm high r ra for he 6 88 and low 36cl cl 17 10 15 suggest that elevated tracer concentrations are derived from magmatic outgassing and or weathering of volcanic rock beneath nearby volcan barva in local groundwater the magmatic signature is absent and data suggest atmospheric sources for he and cl and a biogenic soil gas co2 source for dissolved inorganic carbon dating of 14c suggests that the age of bedrock groundwater is 2400 4000 years most likely at the lower end of the range local groundwater has 14c 100 pm indicating the presence of bomb carbon and thus ages less than 55 years overall data are consistent with a conceptual hydrologic model originally proposed on the basis of water budget and major ion data 1 large variation in solute concentrations can be explained by mixing of the two distinct groundwaters 2 bedrock groundwater is much older than local groundwater 3 elevated solute concentrations in bedrock groundwater are derived from volcanic fluids and or rock and 4 local groundwater has not interacted with volcanic rock tracers with different capabilities converge on the same hydrologic interpretation also transport of magmatic co2 into the lowland rain forest via igf seems to be significant relative to other large ecosystem level carbon fluxes

ca isotope constraints on chemical weathering processes evidence from headwater in the changjiang river china abstract this study aims to clarify the relationship between chemical weathering of rocks and the carbon budget of rivers and better understand the weathering mechanisms of plateau watersheds we chose to study the jinsha river which originates from the tibetan plateau and also is in the upper reaches of the changjiang river analysis of hydrochemistry radiogenic strontium isotope and stable calcium isotopes were conducted of the jinsha river water samples which were collected along its mainstream and main tributaries in the summer the results show that the water chemistry of the mainstream waters is dominated by evaporite weathering which have low 87sr 86sr values 0 7098 0 7108 and wide range of sr contents 2 70 9 35 mol l in contrast tributaries of the jinsha river have higher 87sr 86sr 0 7090 0 7157 and lower sr contents 1 mol l moreover the ca isotopic compositions in the mainstream 0 87 1 11 are heavier than the tributaries 0 68 0 88 and could not be fully explained by the conventional mixing of different sources we suggest that secondary carbonate precipitation fractionates ca isotopes in the jinsha river and fractionation factors are between 0 99935 and 0 99963 at least 66 of ca was removed in the mainstream of the jinsha river through secondary mineral precipitation and the average value is 35 in the tributaries the results highlight that evaporite weathering results in more carbonate precipitation influencing ca transportation and cycling in the riverine system constrained by stable ca isotopic compositions and water chemistry

the calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance calcium isotope ratios relative to seawater were studied in natural waters in order to constrain the ca isotopic flux to the oceans and to discuss the oceanic ca budget this study includes the analysis of 1 ca isotopes in continental waters at the regional scale of the upper rhine valley and 2 the determination of the 44ca values of some major rivers and hydrothermal vents the data indicate that the global 44ca variability of the studied waters with a maximal range of 1 is limited and must be linked to mass fractionation processes at the scale of a small watershed aubure vosges france the 44ca river flux changes due to the variation of the proportion of waters resulting from chemical alteration of rocks and biologically fractionated soil solutions ca isotopes could therefore be an important tool to quantify the impact of the plants and the biosphere on the river water chemistry at the regional scale of the rhine valley as well as at the global scale of world rivers the 44ca variability of river samples ranges from 0 5 to 1 without any relationship with the lithology of the watershed or the climate similarly the 44ca value of hydrothermal vents is also uniform and close to the mean value of river waters consequently the 44ca flux to the ocean should remain rather constant through time with a mean of 1 1 0 2 this value confirms that the ca budget of the present day seawater is in steady state this was not necessarily the case in the past non steady state periods should have been due to intensity variations of incoming and outcoming ca fluxes rather than to the variations in their isotopic signatures

a review of paleomagnetic results from the carboniferous of north america the concept of carboniferous geomagnetic field horizon markers results from the east coast carboniferous basin contain an important time stratigraphic horizon of possible global significance late carboniferous units are found to have mostly reversed magnetizations while older carboniferous units may have normal reverse or most frequently dual polarity magnetizations this feature records the change in geomagnetic field from a period of common polarity changes to a period of mainly reversed polarity the kiaman magnetic interval recognition of the stratigraphic position of this polarity feature provides a time line for correlation of units within and among carboniferous basins in the east coast carboniferous basin of atlantic canada this horizon has now been located at the riversdale group level early pennsylvanian namurian westphalian boundary since remanence acquisition of red sediments is often a lengthy process possibly spanning field reversal time scales red bed units pre dating and post dating this time line can in most instances be readily distinguished the former generally recording both polarities and the latter just one reverse polarity a polar displacement of at least 16 is recorded in the results from the east coast carboniferous basin paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8 during the pennsylvanian it cannot be ascertained if those observations are representative of the whole of north america or merely the atlantic seaboard poles derived from other areas of north america do not all fit the regular pattern observed on the atlantic coast using the horizon marker as a tool it is suggested that those poles are post time line in age so that none of them is representative of the position of north america prior to the time line

palaeomagnetism of palaeozoic ultrabasic rocks from the sudetes mts sw poland tectonic implications summary a complex palaeomagnetic rock magnetic and mineralogical study of ultrabasic rocks from the sowie gory block gsb and jordanow gogolow serpentinite massif jgsm revealed the presence of several components of natural remanent magnetization nrm the authors found three groups of palaeozoic as well as triassic and recent components of the geomagnetic field the palaeozoic components of nrm are carried mainly by magnetite of several generations formed during several serpentinization episodes permo carboniferous component a1 present overall the sudetes was isolated in one jgsm and two gsb exposures whereas the late devonian early carboniferous component a2 was found in two exposures from the gsb the corresponding remanent components were already revealed in palaeontologically dated sediments from other west sudetic units in the gsb it was probably acquired during its unroofing dated isotopically for ca 370 360 ma the newly determined group of palaeozoic directions a3 was found in three localities from jgsm and in two from gsb is interpreted as the oldest overprint in jgsm it was acquired probably shortly after the first oceanic serpentinization phase dated isotopically for ca 400 ma its acquisition in gsb corresponds to the time of emplacement of ultrabasic xenoliths dated isotopically at ca 390 ma so we suppose that the mean a3 calculated for five exposures corresponds to the 380 400 ma time span and that at that period both massifs formed one microplate mean inclination of a3 places this microplate at 380 400 ma at the palaeolatitude of 23 s whereas the west sudetes were situated during the early devonian at 16 s we suggest that during the early devonian the microplate comprising gsb and jgsm massifs was situated to the south from the west sudetes and accreted them during middle late devonian

detecting heat treatment on silcrete experiments with methods abstract we describe experiments aimed at detecting heat treatment of silcrete a siliceous rock of inhomogeneous lithology widely used in prehistoric australia our samples n 66 come from eastern new south wales two methods widely used on other materials are found to be inadequate scanning electron microscope sem analyses allow conflicting interpretations of the same piece of material while colour changes are too variable to be a reliable indicator two other methods are more reliable increase in lustre is rare but clearly indicates heat treatment when its thermal origin is certain palaeomagnetism assessments of modern n 18 and archaeological n 23 samples show that while the method does not give false positives it indicates heating and not necessarily heat treatment a combination of palaeomagnetism and lustre assessments is recommended

paleomagnetic constraints on the assembly of the old red continent abstract a model is proposed on the basis of paleomagnetic and geological arguments for the assembly of the old red continent which in the devonian comprised north america the baltic shield and russian platform as well as a third element called armorica the latter is thought to have included most of hercynian europe and southern england and wales as well as possibly the avalonian terranes of northeastern north america and perhaps some parts of the atlas ranges and moroccan meseta the model envisions a late ordovician taconic collision of north america and armorica which are joined in the late silurian by the baltic shield and russian platform not until the late early carboniferous did gondwana join the old red continent in a collision responsible for a large internal megashear parallel to the caledonian orogenic belt as well as the hercynian alleghenian orogeny subduction of the large siluro devonian ocean between gondwana and the old red continent is held responsible for the mid devonian acadian orogeny

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

determination of sr and ca sources in small tropical catchments la selva costa rica a comparison of sr and ca isotopes summary a comparative study of sr and ca isotopes was conducted to assess solute sources and effects of biogeochemical processes on surface water and groundwater in four small tropical catchments located at la selva biological station costa rica variable concentrations of dissolved sr 2 and ca 2 in the catchments are related to mixing of waters from different origin three catchments are influenced by high solute bedrock groundwater while another catchment is primarily supplied by local recharge 87 sr 86 sr ratios were employed to discriminate contributions from mineral weathering and atmospheric sources solutes in bedrock groundwater have a predominant geogenic origin whereas local recharge is characterized by low solute inputs from rainwater and minor in situ weathering releases from nutrient depleted soils bedrock groundwater contributes more than 60 of dissolved sr 2 to surface discharge in the salto saltito and arboleda catchments whereas the taconazo catchment receives more than 95 of dissolved sr 2 from rainwater 44 40 ca values of dissolved ca 2 vary greatly in the catchments mainly as a result of heterogeneous ca isotope compositions of the contributing sources based on differences in 44 40 ca values two distinct bedrock groundwaters discharging at the salto and the arboleda catchments are suggested effects of biological processes in the plant soil system on solute generation in the catchments are indicated by variable ca sr ratios however these effects cannot clearly be assessed by ca isotopes due to the strong heterogeneity of 44 40 ca values of ca 2 sources and high ca 2 concentrations in bedrock groundwater

late hercynian remagnetization of tournaisian series from the laval syncline armorican massif france abstract paleomagnetic investigations have been conducted on tournaisian volcanics and sediments from the laval syncline in order to evaluate the consequences of the late variscan tectonic and thermic phases on the southern flank of the syncline anisotropy measurements have yielded maximum susceptibility in the schistosity planes thermal demagnetization exhibits only remagnetizations characterized by a large range of blocking temperatures from 350 to 670 c two phases of remagnetization seem to follow each other the first may have occurred during the tournaisian major orogenic phase the second has taken place during the latest stephanian earliest permian in relation with the latest variscan thermal event all results are in favour of a clockwise rotation by 15 40 of the laval syncline after the latest overprints according to results from other regions of brittany this clockwise rotation involved the whole armorican massif this motion may be related to the latest compression phase which has tightened the ibero armorican arc well before the permo triassic opening of the bay of biscay

halloysite versus gibbsite silicon cycling as a pedogenetic process in two lowland neotropical rain forest soils of la selva costa rica abstract halloysite and gibbsite although known to require quite different conditions for their formation commonly occur together in the same horizon in oxisols derived from andesitic parent materials in tropical costa rica we selected two soils of similar parent material but of different ages and soil moisture regimes to identify possible clues to the coexistence of these two minerals we employed selective dissolution procedures x ray fluorescence analysis and x ray diffraction on field moist and air dry bulk soil samples to investigate how mineralogy changes with depth we further separated the size fraction we found both soils to be depleted of primary minerals and pedogenesis to have progressed to advanced weathering stages particularly in the subsoils gibbsite xrd signal intensities were linearly and significantly related to weathering indices corroborating the residual nature of gibbsite as an endproduct of weathering processes the si bearing quartz and kaolinite group minerals were enriched in the topsoils indicating i their independence from a primary mineral si source and ii the existence of a mechanism capable of protecting them against the continuous tropical weathering pressure as we found no indications for retrospective additions of soil material through mass movement or aeolian additions we believe a vegetation dependent biological pumping mechanism to be the most plausible explanation for the presence of silica bearing minerals in the la selva topsoils the vertical distribution of 1 0 nm halloysite and its accumulation in the lower reaches of the wetter alluvial soil suggest that this metastable mineral forms as a result of si enrichment where the residence time of the pore water is long enough to allow for si concentrations to exceed the halloysite precipitation threshold taken together our evidence indicates gibbsite in the la selva soils to be the endproduct of intense tropical weathering while the presence of hydrated halloysite seems to have mainly kinetic reasons and is most probably coupled to the contemporary soil moisture regime

chemical mixing model of streamflow generation at la selva biological station costa rica abstract la selva biological station occupies an area of lowland tropical rainforest in central costa rica sodium and chloride data were used to quantify the mixing proportions of local runoff and geothermal groundwater at several sites throughout the stream channel system in late april at the end of the dry season the fraction of streamflow accounted for by geothermal groundwater varied spatially between 0 and 0 85 indicating a significant contribution to streamflow and to stream solute loads from geothermal groundwater at some sites in general higher inputs of geothermal groundwater were found at lower elevations over half the flow from one basin the salto was due to geothermal groundwater suggesting a minimum annual runoff of about 0 7 m of geothermal groundwater from this basin a plot of na cl vs fraction of geothermal groundwater revealed watershed scale chemical differences between the two major drainage systems the sura and the salto differences that were not apparent from a traditional two solute plot of cl vs na concentration a small 21 mm storm produced relatively little change in mixing proportions as most throughfall was apparently retained in the relatively dry soils

baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications torsvlk t h smethurst m a van der voo r trench a abrahamsen n and halvorsen e 1992 baltlca a synopsis of vendlan permmn palaeomagnetic data and their palaeotectonlc implications earth sci rev 33 133 152 in light of recent additions to the palaeozoic palaeo magnetlc data base particularly for the ordovlclan era a revised apparent polar wander apw path for baltica has been constructed following a rigorous synthesis of all late precambrlan perm lan data the apw path is characterized by two prominent loops firstly a late precambrlan camb rlan loop probably relating to a rifting event and secondly a younger loop relating to a mid silurian scandlan colhsion event these features imply major change in plate tectonic reconfiguratlon baltlca probably represented an individual continental unit m early palaeozoic times and was positioned m high southerly latitudes in an inverted geographic orientation in such a reconstruction baltlca was separated from the northern margin of gondwana by the tornqulst sea and from laurentla by the iapetus ocean the tornqulst zone is thus interpreted as a passive or dextral transform margin during the early palaeozoic while undergoing counter clockwise rotations up to 1 6 ma baltica drifted northward through most ol the palaeozoic except for a short period of southerly movement in late silurian early devonian times after colhslon with laurentla rapid movements in latitude up to 9 cm yr are noted m late precambrlan earl y palaeozoic times and slgmficant decrease in velocities throughout palaeozoic time probably reflect the progressive amalgamation of a larger continent by early devonian euramerlca and permian pangea times the tornqulst sea had a principal component of palaeo east west orientation hence it is difficult to be precise in the timing of when micro continents such as eastern avalonla and the european masslfs ultimately collided along the southwestern margin of baltica these micro continents are considered to have been peripheral to gondwana m high southerly latitudes during the early ordovlclan eastern avalonla clearly had rifted off gondwana by llanvlrn llanded o times and may have collided with baltlca during late ordovlclan times although the present available sdunan palaeomagnetlc data from eastern avalonia may suggest colhslon in late silurian times across the lapetus facing margin of baltica laurentla was s tuated in equatorml to southerly latitudes during most of the lower palaeozoic these continents collided in mid silurian times l e a first collision between southwestern norway and greenland scotla nd which gave rise to the early scandlan orogeny 425 ma in southwestern norway possible followed by a later but less dramatic scandlan event in northern norway at around 410 ma since baltlca was geographically reverted m early palaeozoic times the colhsional margin could not have been a margin that once rifted off laurentm as assumed in a number of plate tectonic models

paleomagnetic evidence for crustal and thin skinned rotations in the european hercynides devonian and carboniferous paleomagnetic data from the european hercynides show a coherent pattern in inclination but significant dispersion in declination the declination anomalies with respect to expected declinations for stable europe indicate a strong correlation with the regional changes in the structural trend of the mountain belt detailed analysis of the paleomagnetic and structural data revealed the highest degree of correlation between changes in strike and declination anomalies for external parts of the orogen where thin skinned nappe emplacement has been most prevalent the correlation between changes in strike and declination anomalies from interior parts of the hercynides is less well defined and displays a greater degree of scatter nevertheless the partly secondary character of the arcuate shape can be demonstrated thus the internal hercynides are at least in part a true orocline with secondary bending in the sense of s w carey we infer that the bending of the european hercynides resulted from the combination of multiple deep reaching deformations of the european lithosphere as well as the effects of thin skinned rotations the decreasing degree of rotations toward the crystalline interior of the belt appears to favor a geodynamic model involving indentations and or buttressing effects the indentation of hercynian europe by a microplate or an african promontory during the hercynian orogeny might be one of the principal causes for the secondary bending and the associated nappe rotations

testing for the presence of thermal pretreatment of flint in the mesolithic and neolithic of sweden abstract through ethnographic accounts the method of heat treatment of silica materials to improve the flaking qualities is shown to have been known almost worldwide some mesolithic and neolithic flint artifacts from southern sweden were examined in order to determine if they too were heat treated from several methods proving or indicating thermal alteration of flint analysis using scanning electron microscopy was chosen two samples were taken from each artifact one being examined unaltered the other being heat treated no two samples from the same artifact had the same kind of surface appearance thus these analyses prove that the artifacts examined had not been heat treated

ca cycling and isotopic fluxes in forested ecosystems in hawaii 1 biogeochemical processes fractionate ca isotopes in plants and soils along a 4 million year developmental sequence in the hawaiian islands we observed that plants preferentially take up 40ca relative to 44ca and that biological fractionation and changes in the relative contributions from volcanic and marine sources produce a significant increase in 44ca in soil exchangeable pools our results imply moderate fluxes enriched in 44ca from strongly nutrient depleted old soils in contrast with high 40ca fluxes in young and little weathered environments in addition biological fractionation controls divergent geochemical pathways of ca and sr in the plant soil system while ca depletes progressively with increasing soil age sr ca ratios increase systematically sr isotope ratios provide a valuable tracer for provenance studies of alkaline earth elements in forested ecosystems but its usefulness is limited when deciphering biogeochemical processes involved in the terrestrial ca cycle ca isotopes in combination with sr ca ratios reveal more complex processes involved in the biogeochemistry of ca and sr

δ44ca evolution in a carbonate aquifer and its bearing on the equilibrium isotope fractionation factor for calcite abstract to improve understanding of ca isotope transport during water rock interaction on the continents we measured dissolved 44 ca values along a 236 km flow path in the madison aquifer south dakota where fluids have chemically evolved according to dolomite and anhydrite dissolution calcite precipitation and ca for na ion exchange over a timescale spanning 15 kyr we used a reactive transport model employing rate data constrained from major ion mass balances to evaluate the extent to which calcite precipitation and ion exchange fractionate ca isotopes elevated 44 ca values during the initial and final stages of water transport possibly result from calcite precipitation under supersaturated conditions and ca for na ion exchange respectively however for the bulk of the flow path 44 ca values evolve by mixing between anhydrite and dolomite dissolution with no fractionation during calcite precipitation under saturated conditions we attribute the absence of ca isotope fractionation to the long timescale of water rock interaction and slow rate of calcite precipitation which have enabled fluids to chemically and isotopically equilibrate with calcite we therefore conclude that the equilibrium ca isotope fractionation factor between calcite and water cal w is very close to zero to the extent that the madison aquifer typifies other groundwater systems where calcite slowly precipitates from solutions at or near chemical equilibrium this study suggests that groundwater contributions to 44 ca variability on the continents can be modeled according to simple mixing theory without invoking isotope discrimination

transformation of a magmatic arc and an orogenic root during oblique collision and it s consequences for the evolution of the european variscides mid german crystalline rise the architecture of the european variscides has been subdivided by kossmat 1927 into paleogeographically coherent units which are presently interpreted as former plate fragments the mid german crystalline rise mgcr separates two fragments rhenohercynian and saxothuringian belts at the site of an inferred plate boundary and reequilibrated orogenic root the commonly favoured model interprets the mgcr as the magmatic arc on saxothuringian crust above a south dipping subduction zone in upper devonian and carboniferous times data from the mgcr the kinematic evolution of the mid european variscides and first order volume balancing suggest a reinterpretation of this unit which challenges classical views on the mgcr as well as on the subdivision of variscan architecture the mgcr is composed of two rock groups with different tectonic identity a lower carboniferous low pressure high temperature magmatic arc association on lower paleozoic basement rests tectonically on a stack of medium pressuremedium temperature rocks of inferred rhenohercynian origin the latter were tectonically accreted to the base of the overriding plate by tectonic underplating the entire process was controlled by oblique convergence this led to regional partitioning of the plate kinematic vector into contractional domains lower rhenohercynian plate and back arc area of the upper saxothuringian plate bulk heterogeneous plate margin parallel extensional domains mgcr and plate margin parallel wrench domains mgcr boundaries during this process material was continually transferred from the lower plate to the upper plate uplifted and exhumed by net crustal extension the concomitant removal of parts of the former arc and the entire orogenic root necessitates a reappraisal of variscan architecture and evolution

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

geodynamic evolution of the european variscan fold belt palaeomagnetic and geological constraints the variscan fold belt of europe resulted from the collision of africa baltica laurentia and the intervening microplates in early paleozoic times over the past few years many geological palaeobiogeographic and palaeomagnetic studies have led to significant improvements in our understanding of this orogenic belt whereas it is now fairly well established that avalonia drifted from the northern margin of gondwana in early ordovician times and collided with baltica in the late ordovician early silurian the nature of the gondwana derived armorican microplate is more enigmatic geological and new palaeomagnetic data suggest armorica comprises an assemblage of terranes or microblocks palaeobiogeographic data indicate that these terranes had similar drift histories and the rheic ocean separating avalonia from the armorican terrane assemblage closed in late silurian early devonian times an early to mid devonian phase of extensional tectonics along this suture zone resulted in formation of the relatively narrow rhenohercynian basin which closed progressively between the late devonian and early carboniferous in this contribution we review the constraints provided by palaeomagnetic data compare these with geological and palaeobiogeographic evidence and present a sequence of palaeogeographic reconstructions for these circum atlantic plates and microplates from ordovician through to devonian times

tectono thermal evolution of a part of a variscan magmatic arc the odenwald in the mid german crystalline rise geothermobarometric studies of plutonic and medium to high grade metamorphic rocks of the odenwald sw germany provide data for the construction of pt paths of four different crustal sections within a part of a magmatic arc of the mid european hercynian orogen

ca sr and 87sr 86sr ratios as tracers of ca and sr cycling in the rio icacos watershed luquillo mountains puerto rico abstract we investigated ca and sr cycling in a humid tropical forest by analyzing ca sr ratios and 87sr 86sr ratios in soil minerals soil exchangeable cations soil porewater and plant roots wood and leaves and calculating the relative contributions of sr from atmospheric inputs and weathering of local bedrock an unexpectedly large contribution of bedrock derived sr and presumably ca is cycled through the vegetation reflecting the important role of geological processes in controlling the cycling of base cation nutrients even in a system with intensely weathered soil this is surprising because over 99 of the ca and sr that was originally in the bedrock is leached out of the soil and saprolite during early stages of weathering at this site and because there are large atmospheric inputs to the site of both sea salt and saharan dust substantial differences in ca and sr cycling are seen on small spatial scales between a ridgetop and an adjacent steep hillslope site measured ca sr ratios reflect fractionation between these elements during biogeochemical cycling fractionation was particularly evident between wood and foliar tissue but fractionation during soil exchange processes is also likely in comparing the ca sr ratios of plants exchangeable cations and bulk soils we found that foliar ca sr ratios were greater than exchangeable cation ca sr ratios which in turn were greater than soil ca sr ratios similar to patterns observed at other highly weathered tropical sites

thermal curved fragments a method for identifying anthropogenic fire in the archaeological record abstract the archaeology of fire is a developing field one challenge centers on equifinality distinguishing the affects of wildfire versus anthropogenic fire especially where evidence for control of fire by humans in the early pleistocene remains debated there is little consensus regarding what constitutes clear evidence of human control another concern is preservation bias which reduces clearly identifiable archaeological signatures of fire in this paper we argue that a peculiar lithic angular fragment termed thermal curved fragment tcf exhibits statistically distinct quantitative evidence of the confluence of human knapped stone tools and exposure to a high energy long duration ground level fire i e campfires experimental tcfs are described and compared to unfired knapping debitage natural exfoliations and suspected archaeological tcfs the provenance of these archaeological specimens has previously been argued to infer hominin controlled fire at 1 5 1 6 ma at the koobi fora formation we also present data from experiments exposing stone flakes arranged as scatters of similar raw materials to those found in the koobi fora formation to usda prescribed burns in a variety of conditions approximating landscape fires results indicate that tcfs are formed specifically where previously knapped stone is exposed to high energy ground level fires similar to those seen in ethnographic campfires our analysis indicates that tcfs can be used in conjunction with other lines of evidence indicating the presence of anthropogenic fire in the archaeological record

palaeomagnetism of the lower ordovician orthoceras limestone st petersburg and a revised drift history for baltica in the early palaeozoic summary palaeomagnetic investigation of lower ordovician limestone in the vicinity of st petersburg yields a pole position at latitude 34 7 n longitude 59 1 e dp dm 5 7 6 4 a probable primary remanence origin is supported by the presence of a field reversal the limestone carries one other remanent magnetization component associated with a mesozoic remagnetization event an apparent polar wander path is compiled for baltica including the new result ranging in age from vendian to cretaceous ages of the published lower to midpalaeozoic palaeomagnetic pole positions are adjusted in accordance with the timescale of tucker mckerrow 1995 the new arenig result is the oldest of a series of ordovician and silurian palaeomagnetic pole positions from limestones in the baltic region there are no data to constrain apparent polar wander for the tremadoc cambrian and latest vendian if the fen complex results previously taken to be vendian in age c 565 ma are reinterpreted as permian remagnetizations an early ordovician cambrian vendian cusp in the polar wander path for baltica is eliminated the apparent polar wander curve might then traverse directly from poles for vendian dykes on the kola peninsula c 580 ma towards our new arenig pole c 480 ma the consequence of this change in terms of the motion of baltica in cambrian times is to reduce significantly a rotational component of movement the new arenig pole extends knowledge of ordovician apparent polar wander an increment back in time and confirms the palaeolatitude and orientation of baltica in some published palaeogeographies exclusion of the fen complex result places baltica in mid to high southerly latitudes at the dawn of the palaeozoic consistent with faunal and sedimentological evidence but at variance with some earlier palaeomagnetic reconstructions

the source of calcium in wet atmospheric deposits ca sr isotope evidence tracing the origin of calcium in wet atmospheric deposits is important for environmental studies since it is a dominant acid neutralising cation and an essential nutrient here we present the first calcium isotope ratio measurements for rain and snow samples from northeastern and southern locations france switzerland luxembourg california and japan suggest a carbonate origin only at a local scale in a forested watershed vosges mountains france the ca isotopic compositions of rainwater indicate that the rainwater becomes admixed with throughfall solution which is a mixing product of ca from dissolved atmospheric dust particles and leave excretions if this proves to be widely true the contribution of ca from the canopy could be very important for the neutralisation of acid rain and of the corresponding soil system in forested watersheds in such cases ca and sr cycles are decoupled in the lower atmosphere in contrast to sr isotopes ca isotopes can be applied to tracing processes occurring in the biosphere

reconstructions of the continents around the north atlantic at about the 60th parallel abstract late carboniferous early tertiary apparent polar wander apw paths 300 40 ma for north america and europe have been tested in various reconstructions these paths demonstrate that the 500 fathom bullard et al fit is excellent from late carboniferous to late triassic times but the continental configuration in northern pangea changed systematically between the late triassic ca 214 ma and the mid jurassic ca 170 ma due to pre drift extension best fit north atlantic reconstructions minimize differences in the late carboniferous early jurassic and late cretaceous tertiary segments of the apw paths but an enigmatic difference exists in the paths for most of the jurassic whereas for the early cretaceous the data from europe are nearly non existent greenland s position is problematic in a bullard et al fit because of a late triassic early jurassic regime of compression 300 km that would be inherently required for the norwegian shelf and the barents sea but which is geologically not defensible we suggest a radically new fit for greenland in between europe and north america in the early mesozoic this fit keeps greenland locked to europe for the late paleozoic early mesozoic and maintains a reconstruction that better complies with the offshore geological history of the norwegian shelf and the barents sea pre drift a24 extension amounted to approximately 450 km on the mid norwegian shelf but with peak extension in the late cretaceous

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

palaeomagnetic investigations in the hercynian mountain belt of central europe abstract the palaeomagnetism of sediments and volcanics of middle devonian to early carboniferous age has been studied in the hercynian realm of the vosges harz and franconian forest france and germany after appropriate cleaning characteristic directions of natural remanent magnetization nrm have been determined which are considered to be of pretectonic origin according to rock magnetic and structural geological evidence a mean palaeopole for the devonian rocks in the areas investigated was determined at 29 7 n and 9 0 e the site latitude derived from the devonian rocks agrees very well with that observed in great britain and britanny the significant difference in longitude between our devonian poles and the other european data may be due to an anticlockwise rotation of central europe with respect to the northern hercynian foreland the carboniferous rocks yield a mean palaeopole at 41 7 n and 340 4 e matching the carboniferous part of the european polar wander path a fold test within carboniferous greywackes from the harz mountains proves a pre folding origin of the nrm of these rocks however this stable magnetization direction indicates local or regional tectonic displacement our results do not support any major latitudinal motions of continental segments in central europe during the hercynian orogeny the palaeozoic palaeomagnetic data from the vosges franconian forest harz britanny and central massif can be used to interpret the hercynides in terms of a large scale shear belt

age of intrusion and rapid cooling of the frankenstein gabbro odenwald sw germany evidenced by40ar 39ar and single zircon207pb 206pb measurements the frankenstein gabbro complex in the northern odenwald fr germany is one of the hercynian plutonic bodies of the saxothuringian zone in the variscan belt 87sr 86sr isotopic investigations on pyroxene 40ar 39ar age determinations on hornblendes plagioclases biotites and pyroxenes and207pb 206pb dating on single zircon crystals have been carried out

the tectonic implications of solundian upper devonian magnetization of the devonian rocks of kvamshesten western norway the allochthonous old red sandstone of kvamshesten western norway records polyphase orogenic deformation and palaeomagnetic results from both the devonian sediments and mylonites associated with the basal thrust define a syn to post tectonic magnetization withd 218 i 3 and 95 9 7 the corresponding pole position lat 21 s long 324 e suggests a late devonian early carboniferous magnetization age solundian and probably dates the time of thrust movements

eastern variscan fold belt paleomagnetic evidence for oroclinal bending the rhenohercynian zone of variscan europe trends from southern portugal around the ibero armorican arc into southern britain belgium northern germany and the moravo silesian zone of the east czech republic although the geodynamic evolution of the central and western segments of this arcuate belt is now fairly well understood the scenario for the more easterly parts remains enigmatic a paleomagnetic study of upper devonian rocks from the moravo silesian zone has been undertaken two ancient directions of magnetization have been identified the first the a magnetization is secondary in origin and relates to a remagnetization of permian carboniferous age the b magnetization passes the fold test is considered late devonian in age and agrees in terms of inclination to previously published paleomagnetic results from coeval rocks of the harz mountains and franconian forest central europe the declination however differs by about 90 restoring the moravo silesian zone to its original devonian orientation as defined by the new paleomagnetic data brings the structural trends of central and eastern europe into agreement because they were previously part of the same tectonostratigraphic unit as suggested by the stratigraphic record this implies that rotational oroclinal bending around the northern and eastern flanks of the bohemian massif occurred sometime between the late devonian and late carboniferous

unexpected calcium sources in deep soil layers in low fertility forest soils identified by strontium isotopes lorraine plateau eastern france forest ecosystems are often found on acid soils where calcium availability depends on two main inputs atmospheric deposition and the weathering of soil minerals and on the biological cycling of nutrients in the context of global change decreasing atmospheric inputs increasing biomass exportation climate change it is important to determine calcium sources to the ecosystem and tree nutrition to better understand how forest ecosystems will respond to these changes over time the aim of this study was to study and compare ca pools and cycling in two mature forest ecosystems clermont en argonne and azerailles developed on two contrasting polycyclic soils lorraine plateau eastern france and identify the ca sources contributing to ecosystem functioning at both sites soil ca pools were measured atmospheric deposition of ca was monitored from bulk precipitation and throughfall chemistry ca biological cycling was assessed by measuring litterfall and by a litter decomposition experiment strontium 87sr 86sr isotope data in the soil profile fine roots exchangeable pool bulk soil was used to estimate the distribution of sr and ca uptake in the soil profile and the relative contribution of mineral weathering in the soil layers to total ecosystems inputs despite important differences in ca availability in the topsoil between both sites tree growth and nutrition indicators showed no significant difference this discrepancy is not explained by the biological cycling of ca but may be partly explained by higher ca deposition at the ca poorer site strontium isotope data enabled to show important differences of ca sources for tree uptake at the ca poorer site deep soil layers 105 cm potentially represent from 32 to 100 of total sr uptake at the ca richer site results suggest that uptake is more evenly distributed in the soil profile sr isotope data coupled with a modeling approach suggest that two different mineral sources exist in the soil profile a radiogenic sr source in the topsoil 87sr 86sr 0 717 and a less radiogenic source in depth 87sr 86sr 0 717 the deep mineral source may represent from 40 to 86 of total sr inputs at the poorer site and from 25 to 86 at the richer site the origin of this deep strontium source is unclear but soil mineralogy suggests an allochthonous origin we hypothesize that this deep source originates from capillary rise of the groundwater aquifer this nutrient input to forest ecosystems is not commonly taken into account but may strongly participate in maintaining the chemical fertility of soils over time

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

a new devonian palaeomagnetic pole for the russian platform and baltica and related apparent polar wander summary of published palaeomagnetic data from the russian platform and britain for mid palaeozoic times places an ocean between the two of the order of 2000 km latitudinal width this contradicts geological evidence which favours contiguity between the two continental units by devonian times we propose that this discrepancy can be attributed to the incorrect dating of palaeomagnetic remanence we strove to remedy this situation by conducting a new palaeomagnetic investigation of silurian and devonian sediments in west ukraine ussr latitude 48 7 n longitude 26 e that investigation uncovered a pervasive upper palaeozoic remagnetization corresponding to a palaeomagnetic pole at lat 45 8 s long 348 2 e dpldm 1 6 3 1 n 25 sites reversed polarity a second primary or near primary devonian remanence was identified with pole at lat 3 7 n long 325 5 e dpldm 5 2 8 7 n 25 samples mixed polarity the age determination for this devonian result is based on its dual polarity evidence for a detrital remanent mode and early host mineral phase haematite the new devonian result for the russian platform is conformable with the devonian parts of the british apparent polar wander paths and therefore eliminates the aforementioned discrepancy between palaeomagnetic and geological evidence for the timing of assembly of the old red continent

changing sources of base cations during ecosystem development hawaiian islands 87 sr 86 sr evidence from a soil chronosequence in the hawaiian islands demonstrates that the atmosphere supplies 85 of putatively rock derived sr in older sites initially bedrock is the dominant source for sr and other lithophile elements such as ca but high rates of weathering and leaching of the substrate by 20 ka lead to a shift to atmospheric sources the loss of weathering inputs coincides with other physio chemical changes in the soil and results in a steep decline of base cations in the soil pool while these patterns imply the potential for limitation of biological productivity by low base cation supply the atmosphere provides a supply of base cations in excess of nutritional needs even after nearly all rock derived base cations have been leached from the soil this raises the possibility that p limitation in terrestrial ecosystems may develop at least as much because of low rates of atmospheric deposition of p relative to ca k and other rock derived elements as because of its chemical interaction in soil

biological control of calcium isotopic abundances in the global calcium cycle measurements of 44ca 40ca expressed as 44ca were made on igneous rocks and on shell and bone material from modern organisms to investigate the magnitude and origins of calcium isotopic fractionation in nature the results document a span of 4 in 44ca measured with the double spike technique to a precision of 0 15 volcanic rocks including basalt and rhyolite show little variability and cluster near 44ca 0 0 2 systematic analysis of biological samples indicates that biological processing of calcium discriminates against heavy isotopes and that biological fractionation is the primary generator of calcium isotopic fractionation in nature preliminary data suggest that calcium becomes isotopically lighter as it moves through food chains calcium carbonate shells of marine microorganisms and deep sea carbonate ooze have 44ca about 1 0 lower than seawater this fractionation causes seawater to be enriched in heavy calcium 44ca 0 9 relative to igneous rocks marine organisms consequently are isotopically heavier than their terrestrial counterparts at similar trophic level the calcium isotopic composition of living and fossil organisms may record information on diet and environment

paleomagnetism and paleothermometry of the sydney basin 2 origin of anomalously high unblocking temperatures the milton monzonite of southeastern australia was thermoviscously remagnetized as a result of cretaceous burial and uplift thermal demagnetization separates the low unblocking temperature lt overprint from the high unblocking temperature ht primary remanence with a relatively sharp junction between lt and ht components in vector projections for single domain grains the junction temperature tl between two such vectors corresponds to the maximum blocking temperature tr reactivated in nature apart from a correction for the difference between natural and laboratory timescales however measured tl values are distributed over an implausibly wide range 250 c for burial remagnetization of an untilted intrusion like the milton monzonite furthermore many tl values are anomalously high compared to the predictions of single domain theory multidomain grains are the cause of these anomalies samples pretreated before thermal demagnetization by zero field cycling to liquid nitrogen temperature so as to erase multidomain remanence and isolate single domain remanence do have the theoretically expected tl values in these samples realistic remagnetization time and temperature tr tr conditions in nature are predicted using the t t contours of pullaiah et al 1975 the anomalously high tl values before low temperature treatment are due to multidomain grains which carry 50 of the lt overprint the lt thermal demagnetization curve in samples dominated by multidomain grains is quasi exponential in shape with a high temperature tail extending almost to the curie point as predicted by multidomain theory these high lt unblocking temperatures which are much greater than plausible remagnetization temperatures reached in nature overlap and mask the lower part of the ht unblocking temperature spectrum driving up tl values and leading to inflated estimates of tr although multidomain remanence is a sufficient explanation of anomalously high unblocking temperatures of thermoviscous overprints in the milton monzonite chemical overprinting may be a factor in other lithologies and tectonic settings

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

the impact of water rock interaction and vegetation on calcium isotope fractionation in soil and stream waters of a small forested catchment the strengbach case this study aims to constrain the factors controlling the calcium isotopic compositions in surface waters especially the respective role of vegetation and water rock interactions on ca isotope fractionation in a continental forested ecosystem the approach is to follow changes in space and time of the isotopic composition and concentration of ca along its pathway through the hydro geochemical reservoirs from atmospheric deposits to the outlet of the watershed via throughfalls percolating soil solutions and springs the study is focused on the strengbach catchment a small forested watershed located in the northeast of france in the vosges mountains the 44 40ca values of springs brooks and stream waters from the catchment are comparable to those of continental rivers and fluctuate between 0 17 and 0 87 soil solutions however are significantly depleted in lighter isotopes 44 40ca 1 00 1 47 whereas vegetation is strongly enriched 44 40ca 0 48 to 0 19 these results highlight that vegetation is a major factor controlling the calcium isotopic composition of soil solutions with depletion in light calcium in the soil solutions from deeper parts of the soil compartments due to preferential 40ca uptake by the plants rootsystem however mass balance calculations require the contribution of an additional ca flux into the soil solutions most probably associated with water rock interactions the stream waters are marked by a seasonal variation of their 44 40ca with low 44 40ca in winter and high 44 40ca in spring summer and autumn for some springs nourishing the streamlet a decrease of the 44 40ca value is observed when the discharge of the spring increases with in addition a clear covariation between the 44 40ca and corresponding h4sio4 concentrations high 44 40ca values and low h4sio4 concentrations at high discharge low 44 40ca values and high h4sio4 concentrations at low discharge these data imply that during dry periods and low water flow rate the source waters carry a ca isotopic signature from alteration of soil minerals whereas during wet periods and high flow rates admixture of significant quantities of 40ca depleted waters vegetation induced signal from uppermost soil horizons controls the isotopic composition of the source waters this study clearly emphasizes the potential of ca isotopes as tracers of biogeochemical processes at the water rock vegetation interface in a small forested catchment