isotropy or weak vertical transverse isotropy in d beneath the atlantic ocean 1 shear velocity properties of d beneath the central atlantic ocean are explored using predominantly european seismic recordings of intermediate and deep focus 100 km south american earthquakes broadband data are analyzed and when possible corrected for upper mantle models of receiver side anisotropic structure regional shear velocity heterogeneity in d is mapped by analysis of 306 s sks differential times that have been corrected for three dimensional seismic velocity structure above d using a whole mantle tomographic model this correction yields modest less than 2 estimates of seismic velocity heterogeneity in d with a transition from high to low seismic velocities traversing from west to east beneath the central atlantic in agreement with global tomographic models additionally shear wave splitting of s and sdiff for the same recordings was analyzed to assess seismic anisotropy in d the highest quality data provide 105 splitting times between sh and sv onsets that are mostly within the 1 s uncertainty level the few larger values generally exhibit sv delayed relative to sh assuming an anisotropy geometry involving vertical transverse isotropy vti as preferred in most regions of d that have been studied to date 0 5 anisotropy strength within a 100 km thick layer or 0 25 anisotropy within a 300 km thick layer are compatible with the data these values are low in comparison to those found in high velocity regions beneath the circum pacific ocean or in the low velocity region beneath the central pacific and many observations are in fact consistent with isotropic structure the lack of strong vti relative to other regions may be due to 1 the absence of stress from overlying midmantle downwelling 2 relatively weaker shear flow in the d boundary layer and or 3 lack of chemical heterogeneity that could develop either lattice preferred orientation or shape preferred orientation the azimuthal sampling of this region of d is quite limited thus the precise geometry and mechanism of any anisotropy are difficult to constrain it remains possible that this region may contain subtle azimuthal anisotropy that could couple the sv and sh signals however amplitude observations suggest that any such coupling is minor

magnetic mineralogy of pelagic limestones summary due to their extremely small size and low concentration the carriers of magnetization in limestones are usually identified through indirect rock magnetic methods this paper describes a method for extracting tiny ferromagnetic grains from consolidated calcareous rocks and summarizes a scanning electron microscope sem investigation of magnetic phases from several palaeomagnetically important pelagic limestones details of surface characteristics and elemental composition are readily accessible with the sem and complement normal rock magnetic experiments in giving a more complete assessment of the major ferromagnetic phases their origin and the timing and acquisition of magnetization the results confirm many indications of the indirect methods and introduce several important new features in addition to detrital titanomagnetite diagenetic titanohaematite and iron sulphides there is a significant contribution by authigenic microcrystalline haematite detrital cosmic spherules chromian spinels and skeletal titanomaghaemite

palaeomagnetism of devonian ring complexes from the bayuda desert sudan new constraints on the apparent polar wander path for gondwanaland summary the approach of gondwana and or microplates derived from its northern margins towards laurentia and the closure of the intervening palaeo tethys is a controlling factor in the geodynamic evolution of the atlantic bordering continents during the early and mid palaeozoic however the currently available palaeomagnetic data for gondwana especially for the geodynamically critical silurian to devonian interval are still rather sparse and are compatible with a number of palaeogeographic scenarios in order to address this issue 114 samples 18 sites have been collected from a series of high level acidic intrusive rocks rhyolitic lavas and tuffs of mid devonian age 377 5 ma rb sr along the southern escarpment of the gilif hills sudan 17 83 n 32 67 e detailed demagnetization experiments revealed the presence of three directionally distinct components of magnetization labelled a b and c the overall mean direction of component a dec 0 9 inc 29 8 95 4 6 k 91 1 n 12 sites is indistinguishable from either the direction of the present field or the geocentric axial dipole field in northern sudan mixed polarities suggest a recent or pleistocene age of this component component b also displays mixed polarities the site mean directions for this component average to 6 5 declination 40 2 inclination with 95 7 0 and k 48 1 based on 10 sites and yield a palaeomagnetic pole at 48 8 s 23 5 e dp 5 1 1 dm 8 4 maghaemite and haematite have been identified to be the predominant magnetic phases in samples which carry component a and or b both a and b are the probable results of low temperature oxidation of magnetite although the age of component b can not be directly determined it is inferred by correlation with published data to reflect a late carboniferous overprint component c identified in 11 sites 39 samples is characterized by a very steep downward magnetization dec 296 2 inc 79 3 95 10 8 k 18 7 n 11 sites which corresponds to a palaeomagnetic pole position in the southwestern corner of libya 25 9 n 11 6 e dp 19 6 dm 20 6 maximum blocking temperatures of component c generally below 580 c are indicative of magnetite as carrier of this remanence the results of thermal remanent magnetization experiments demonstrate that component c is a thermo remanent magnetization probably primary and suggest this component to be representative for the direction of the earth s magnetic field during emplacement of the gilif hills volcanic rocks in mid devonian times the position of the resulting palaeomagnetic pole lends new support to geodynamic scenarios advocating the existence of a wide approx 5000 km pre hercynian ocean during devonian times the simplest reconciliation of component b with the reference apparent polar wander path is achieved by assuming it to be of carboniferous age and by invoking a westward cusp in the carboniferous part of the apparent polar wander path taken at face value the age of this cusp coincides with large scale post orogenic right lateral strike slip movements in hercynian europe and north africa this interpretation does not require the apparent polar wander apw loop and very high rates of plate motion implied by some alternative models however if it is valid it will require reinterpretation of the remanence age of one west african intrusive suite and of some eastern australian palaeozoic rocks

the fold test in palaeomagnetism summary the fold test suggested by mcelhinny is shown to be inappropriate more correctly one should determine whether the mean direction of a group of sites from one limb of a fold may be distinguished statistically from the mean direction of a group of sites from another limb details of the application of this test are given with examples it is shown that the test indicates significance under far less severe folding than does the test suggested by mcelhinny

uncertainties about the proterozoic and paleozoic polar wander path of the west african craton and gondwana evidence for successive remagnetization events abstract the importance of remagnetization phenomena in rocks which is without doubt the main cause of uncertainties in paleomagnetic interpretations is illustrated by the study of proterozoic and early paleozoic redbeds from mauritania cratonic west africa except for one formation these units carry multicomponent or secondary magnetizations up to three components are found in a single unit in the absence of geochronological arguments dating of these components relies only on comparisons with previous paleomagnetic data here we critically review the paleomagnetic data set available for the paleozoic of gondwana and the proterozoic of the west african craton using geologic as well as magnetic criteria for the selection of reliable data the selected paleopoles are not regularly arranged in space and time but tend to fall into groups which we interpret as remagnetization periods our interpretation recognizes three or four remagnetization events from middle proterozoic to late paleozoic in addition to the well established late paleozoic overprint paleomagnetic data suggest the existence of a middle paleozoic silurian an early paleozoic late cambrian and maybe a late middle proterozoic remagnetization event these overprints may correspond to generalized geological or climatic events or alternatively be simply related to intervals with low rate of geomagnetic reversals

chemical remagnetizations in the illizi basin saharan craton algeria and their acquisition process summary during remagnetization chemical changes limited to moderate grain growth from pre existing single domain sd grains do not modify the palaeomagnetic direction carried by these grains palaeomagnetic direction from new sd grains on the contrary is that of the magnetic field during remagnetization the resulting direction becomes intermediate between the directions carried by previous and new sd grains as it appears often in case of a partial magnetic overprint if the growth of pre existing grains is more important these grains become large multidomain md and loose the primary magnetization stable magnetization is then only related to the new sd grains which carry the total remagnetization in the illizi basin saharan platform these different cases of partial or total magnetic overprint have been observed resulting from palaeomagnetic studies of different palaeozoic and mesozoic formations

rock magnetic study on the yetti eglab intrusions sahara contribution to the west african craton geology new palaeopoles have been calculated for the west african craton wac using palaeomagneticdata obtained on 178 cores of the yetti eglab intrusions and stromatolite bearing formation one two orthree components of magnetization on 172 14 sites and 37 6 sites oriented specimens or cores were isolatedmainly on doleritic dykes high and low unblocking temperature components were evidenced in the dykes butalso at four sites of the well dated hank stromatolite bearing formation 875 890 ma rock magnetic analysesshow stable remanent magnetizations mainly carried by magnetite or titanomagnetite but may also reveal thepresence of hematite pyrrhotite and goethite regarding the recently constructed apparent polar wander path ofthe wac until 500 ma these newly computed remanent components seem to be mainly older some of whichcould be remagnetizations at different periods however according to geological dating and literature the yettiand eglab terranes belonging to thewacwere amalgamated around 1 9 ga and involved in the formation of thecolumbia supercontinent the palaeopole computed for the stromatolite bearing formation corresponds with thelocation of rodinia supercontinent at its early stages of amalgamation the geodynamic evolution of the wacwith respect to both supercontinents suggests that the eglab and yetti could be separated by oceanic crust before1 9 ga a volcanic arc developed during the subduction of this ocean followed by crustal thickening that generatedan intrusive suite aftout granites when it was at low northern latitudes baltica and rio de la plata cratonswere close to the wac after 1 7 ga following a nearly similar path between 1 7 and 0 9 ga in africa the collapseof the birimian orogen was probably contemporaneous with the fragmentation of columbia at 0 9 ga baltica was probably not attached to the wac since the latter was not affected by the later grenvillian orogen

deformation in the lowermost mantle from polycrystal plasticity to seismic anisotropy in the deep earth deformation occurs at many scales large scale convection produces subduction of slabs and upwelling of plumes in the mantle at the high temperature high pressure conditions strain is accommodated through crystal plasticity either by diffusion or the movement of dislocations slip causes crystal rotations and thus produces a characteristic pattern of crystal preferred orientation and corresponding anisotropy of physical properties at the macroscopic scale in this study we use polycrystal plasticity with experimentally derived deformation mechanisms for perovskite post perovskite and magnesiowuestite to predict texture development along streamlines in a 2d geodynamic convection model of the lowermost mantle strong preferred orientation develops during subduction and upwelling while during spreading along the core mantle boundary the orientation pattern is relatively stable from preferred crystal orientation and single crystal elastic properties bulk elastic properties can be calculated and compared with seismic observations post perovskite with predominant 001 slip and magnesiowuestite with 110 and 111 slip produce anisotropy patterns which are consistent with observed anisotropy i e fast s waves polarized parallel to the core mantle boundary and anti correlation between p and s wave anisotropies in contrast perovskite with dominant 001 slip and two post perovskite models with dominant slip on 010 and 100 produce anisotropy patterns which are inconsistent with seismic observations

multimodal investigation of thermally induced changes in magnetic fabric and magnetic mineralogy summary low field magnetic susceptibility and its anisotropy ams were measured for a suite of sandstone and siltstone samples ams orientations measured on two systems bartington and digico divered before thermal treatment of the samples but became the same after thermal demagnetization in air to 600 c six position measurement schemes for the bartington system do not eliminate the evects of specimen inhomogeneity and other errors whereas 12 and 24 position measurements give good agreement with the digico anisotropy meter and with the observed petrofabric thermal demagnetization from temperatures between 400 and 650 c had the evect of enhancing both the magnetic susceptibility and ams although the most profound mineralogical change due to heating was the conversion of kaolinite into metakaolin irm xrd

north atlantic influences on climate conditions in east central europe in the late holocene reflected by flowstone compositions abstract a stalagmitic flowstone deposit from the beke cave called nagy tufa deposit east central europe is characterized by complex climate related textural and geochemical records as documented from a drill core bnt 2 core covering the period of 4 to 1 ka cal bp the core location was monitored in an earlier study based on monitoring textural and chemical relationships it has been hypothesized that the stable carbon isotope signal of the flowstone deposit is a regional humidity record indicating wet periods 3 8 to 3 4 3 0 to 2 8 and 2 0 to 1 6 ka cal bp and a prominent dry period between 2 1 and 2 7 ka cal bp furthermore stable h isotope data of inclusion hosted water were used to reconstruct the atmospheric temperatures that fit independent regional paleotemperature records indicating warm conditions around 2 7 ka bp and a relatively cold period between 2 5 and 1 5 ka bp comparisons with regional speleothem records and reconstructed north atlantic oscillation data indicate that the late holocene paleohumidity changes recorded by the bnt 2 stable carbon isotope record can be detected in the entire western central european region with further links to the north atlantic realm

guano derived δ 13 c based paleo hydroclimate record from gaura cu musca cave sw romania the 13c values of 23 unevenly spaced guano samples from a 17 cm long clay sediment profile in gaura cu musc cave gm in sw romania made it possible to preliminarily characterize the medieval warm period summer hydroclimate regime the beginning of the sequence ad 990 was rather wet for more than a century before becoming progressively drier after a brief yet distinct wet period around ad 1170 drier conditions with a possible shift from c3 to a mixed c3 dominated c4 type vegetation 2 lower 13c values prevailed for almost half a century before the climate became colder and wetter at the onset of the little ice age when bats left the cave the guano inferred wet and dry intervals from the gm cave are mirrored by changes in the color and amount of clay accumulated in the cave they also agree well with reconstructions based on pollen and charcoal from peat bogs and 13c and 18o on speleothems from other romanian sites overall these results indicate that the 13c of bat guano can provide a sensitive record of the short term coupling between local regional climate and the plant insect bat guano system

different styles of remagnetization in devonian sediments from the north western sahara algeria summary sediments of devonian age located in three areas of north africa have been affected to different degrees by the hercynian orogeny they show various remagnetizations of carboniferous permian and pleistocene age in the ben zireg anticline near the variscan front in algeria the main phase of magnetic overprinting occurs during the tournaisian it is superimposed on a famennian primary direction carried by magnetite in the beni abbes area to the south of the variscan belt griotte limestones of famennian age show a strong recent remagnetization with few residual permian directions this overprinting shows a shallower inclination than the present day field with a small westward declination remagnetization is associated to magnetic transformation of sulphides the transition of sulphides into magnetite type minerals as revealed in the thermomagnetic curves from rocks of the variscan belt preserved the carrier against future magnetic overprinting compared to partially remagnetized rocks this mechanism is referable to recrystallization during deformation

reconstruction of late holocene autumn winter precipitation variability in sw romania from a high resolution speleothem trace element record abstract we present the first high resolution trace element mg ca sr ca ba ca record from a stalagmite in southwestern romania covering the last 3 6 ka which provides the potential for quantitative climate reconstruction precise age control is based on three independent dating methods in particular for the last 250 yr where chemical lamina counting is combined with the identification of the 20th century radiocarbon bomb peak and 230th u dating long term cave monitoring and model simulations of drip water and speleothem elemental variability indicate that precipitation related processes are the main drivers of speleothem mg ca ratios calibration against instrumental climate data shows a significant anti correlation of speleothem mg ca ratios with autumn winter october to march precipitation r 0 61 p during the late holocene our data suggest a heterogeneous pattern of past regional winter hydroclimate in the carpathian balkan realm along with intermittent weakening of the dominant influence of north atlantic forcing in agreement with other regional paleo hydrological reconstructions the observed variability reveals periodically occurring strong nw se hydro climate gradients we hypothesize that this pattern is caused by shifts of the eastern edge of the area of influence of the nao across central eastern europe due to the confluence of north atlantic forcing and other climatic features such as the east atlantic western russia eawr pattern

paleomagnetic and ams evidence for a variscan ductile clockwise rotation of the ile de groix blueschists south brittany france consequence on the late hercynian structural pattern of westernmost europe abstract the terrigenous sedimentary rocks and blueschists of the ile de groix france and surrounding sea floor display a complex metamorphic history comprising three major episodes of deformation that took place between 420 and 294 ma paleomagnetic measurements show that three components of magnetization can be isolated the low unblocking temperature component isolated below 300 c is close to the present magnetic dipole field the high component which reaches 580 c and even 680 c in some places corresponds to pre variscan magnetic directions already obtained for armorica since the groix island has always been part of the armorican microplate the corresponding magnetic inclinations can be used for dating tectonic events by comparing with the armorican apparent polar wander path apwp l1 lineations associated with sheath folds are contemporaneous with remagnetization that took place between 336 and 359 ma this is in good agreement with published radiogenic data the anisotropy of the magnetic susceptibility study shows that l1 lineations are the magnetic markers of tectonic rotation part of the dextral d2 ductile rotation of l1 around a vertical axis occurred around 310 ma paleomagnetic data also suggest that the clockwise rotation started earlier near the close of blueschist metamorphic event the clockwise rotation increases towards the southern end of groix where it trends 80 an early magnetization at 420 ma is regarded as the age of the initial emplacement of the klippe of groix restoration of the initial shape of groix island shows that the l1 fabric was broadly east west oriented before its impingement by an unevenness of the south armorican suture zone

trace elements in speleothems as recorders of environmental change speleothems are now established as important palaeoenvironmental archives and contain a number of suitable proxies although trace elements have been much less widely used than oxygen and carbon isotopes the complexity of the cave environment helps to explain this since the fluids from which speleothems form vary greatly in composition in space even within a cave chamber seasonally and over longer periods understanding the forcing factors for this variability is the key to decoding the significance of the trace element records a variety of techniques are available for trace element work and it is important to understand the strengths and limitations of each and also to seek an understanding e g by micro imaging techniques of whether the elements are associated with inclusions in the caco3 or are isolated within the crystal lattice for some elements there is a more or less predictable relationship between element ratios to ca in the water and in the calcite individual trace elements may be derived from atmospheric deposition superficial deposits or bedrock and can be recycled in soil processes before being transferred to the cave some components show an instantaneous response to water infiltration whereas others are only leached by slow flowing seepage waters changing in the proportion of water from fracture fed and seepage flow aquifer compartments is an important factor in influencing trace element supply high flows lead to higher fluxes of soil derived colloidally transported elements conversely under relatively dry conditions degassing of co2 results in prior calcite precipitation upflow of the site of speleothem deposition and leads to higher ratios of sr ca and mg ca some trace element variations in speleothems over time are induced during crystal growth whereby faster growth leads to a greater departure from equilibrium element partitioning despite the demonstrated temperature dependence of mg partitioning into calcite attempts at deriving palaeotemperature records from speleothems have been so far confounded by variations in solution mg ca and or crystallographic effects a number of case studies have effectively used trace elements such as speleothem mg as records of palaeo aridity using supporting arguments from modern monitoring or covariations with other parameters such as stable isotopes sr and u isotopes can also be indicators of palaeohydrology although sr isotope variations can also reflect varying aeolian input considerable progress has been made in decoding the meaning of annual trace element variations using criteria for understanding dripwater hydrology and ph this should lead in the future to more specific interpretations of how seasonality evolves through time

fabric transitions in quartz via viscoplastic self consistent modeling part i axial compression and simple shear under constant strain quartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures leading to the development of different types of crystallographic preferred orientation cpo patterns in this contribution we present the results of an extensive modeling of quartz fabric transitions via a viscoplastic self consistent vpsc approach for that we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems we have performed these simulations in axial compression and simple shear regimes under constant von mises equivalent strain of 100 1 73 assuming that the aggregates deformed exclusively by dislocation glide some of the predicted cpos patterns are similar to those observed in naturally and experimentally deformed quartz nevertheless some classical cpo patterns usually interpreted as result from dislocation glide e g y maxima due to prism slip are clearly not developed in the simulated conditions in addition we reported new potential preferred orientation patterns that might happen in high temperature conditions both in axial compression and simple shear we have demonstrated that cpos generated under axial compression are usually stronger that those predicted under simple shear due to the continuous rotation observed in the later simulations the fabric strength depends essentially on the dominant active slip system and normally the stronger cpos result from dominant basal slip in followed by rhomb and prism c slip whereas prism slip does not produce strong fabrics the opening angle of quartz 0001 fabric used as a proxy of temperature seems to be reliable for deformation temperatures of 400 c when the main slip systems have similar behaviors

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

origin of the magnetization of permo carboniferous sediments of spitsbergen svalbard archipelago rock magnetic investigations of permo carboniferous carbonate sediments from two areas on spitsbergen are described conducted to identify the carriers of the nrm in these rocks since microscopic and magnetic separation techniques could not profitably be applied the nature of magnetic minerals was investigated by thermal demagnetization of the nrm and decay of saturation isothermal remanence irs during heating to 600 c as well as by the distribution of the median destructive fields of the nrm and observation of magnetic susceptibility after subsequent heatings the results show that the nrm of these limestones resides mainly in magnetite but creation of magnetic pyrrhotite and of fresh magnetite is observed during heating to 600 c presence of sulphides indicates that magnetite is an oxidation product of pyrite or of non magnetic pyrrhotite examination of rock magnetic properties of limestones leads to the conclusion that most of the magnetite in the rocks of the bellsund area is of detrital origin whereas the rocks at festningen contain magnetite derived from pyrite probably during an early stage of the diagenetic process

atmospheric circulation and the differentiation of precipitation sources during the holocene inferred from five stalagmite records from demanova cave system central europe five stalagmites from the demanova cave system dcs western carpathians slovakia spanning the period from 13 000 to 500 a bp were analyzed for their oxygen and carbon stable isotopic compositi

evidence for a ubiquitous seismic discontinuity at the base of the mantle a sharp discontinuity at the base of earth s mantle has been suggested from seismic waveform studies the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first order discontinuity superimposed on global seismic velocity structure derived from tomography the observations can be modeled by a solid solid phase transition that has a 200 kilometer elevation above the core mantle boundary under adiabatic temperatures and a clapeyron slope of about 6 megapascal per kelvin

holocene and late pleistocene climate in the sub mediterranean continental environment a speleothem record from poleva cave southern carpathians romania the pp10 stalagmite from poleva cave provides a late pleistocene and holocene isotopic record characteristic for the sw of romania a sub mediterranean climatic region the speleothem was dated by eight tims and one alpha u series dates which showed that it was precipitated between 75 ka and 2 ka with at least two hiatuses the basal sector of the stalagmite showed a slow growing regime of 0 26 cm ka while the upper one grew relatively fast with about 5 cm ka the temporal resolution for the isotopic sampling is thus 2 ka sample for the lower sector and 150 years sample for the upper one the relationship between 18 o and temperature was found positive the isotopic record of the lower sector shows two marked cold intervals during 67 and 58 ka and 40 35 ka respectively which correlate well with the villars and soreq records the upper sector record is so far the most detailed holocene isotopic record in romania and the only one available for the regions located at the exterior of the carpathians range the signal shows a gradual warming after the gs1 event punctuated by several cold events at 8 7 2 and 4 2 ka and also by warm oscillations centered at about 5 2 and 3 3 ka the results seem to indicate that if the north atlantic firstorder signals may extend well to the south eastern europe their amplitude and general trend may be diminished by the interferences with the mediterranean circulation

detrital events and hydroclimate variability in the romanian carpathians during the mid to late holocene the romanian carpathians are located at the confluence of three major atmospheric pressure fields the north atlantic the mediterranean and the siberian despite its importance for understanding past human impact and climate change high resolution palaeoenvironmental reconstructions of holocene hydroclimate variability and in particular records of extreme precipitation events in the area are rare here we present a 7500 year long high resolution record of past climatic change and human impact recorded in a peatbog from the southern carpathians integrating palynological geochemical and sedimentological proxies natural climate fluctuations appear to be dominant until 4500 years before present yr bp followed by increasing importance of human impact sedimentological and geochemical analyses document regular minerogenic deposition within the bog linked to periods of high precipitation such minerogenic depositional events began 4000 yr bp with increased depositional rates during the medieval warm period mwp the little ice age lia and during periods of societal upheaval e g the roman conquest of dacia the timing of minerogenic events appears to indicate a teleconnection between major shifts in north atlantic oscillation nao and hydroclimate variability in southeastern europe with increased minerogenic deposition correlating to low nao index values by linking the minerogenic deposition to precipitation variability we state that this link persists throughout the mid to late holocene

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

fabric development in mg fe o during large strain shear deformation implications for seismic anisotropy in earth s lower mantle abstract large strain shear deformation experiments were performed on mg 1 x fe x o x 0 25 1 0 one of the important minerals in earth s lower mantle deformation experiments were made on coarse grained 15 20 m grain size hot pressed aggregates at conditions of t t m 0 46 0 65 t temperature t m melting temperature and 0 4 10 3 to 0 9 10 3 differential stress shear modulus up to the shear strain of 7 8 under these conditions deformation occurs by dislocation creep the microstructural development in mg fe o is found to be sluggish and the complete dynamic recrystallization and nearly steady state fabric lattice preferred orientation are achieved only after shear strains of 4 at nearly steady state mg fe o shows strong fabrics characterized by the 1 1 0 axes being parallel to the shear direction and the poles of the 1 0 0 planes and to a lesser extent the poles of the 1 1 1 planes normal to the shear plane the seismic anisotropy corresponding to the deformation fabrics in mg fe o was calculated the nature of anisotropy corresponding to a given flow geometry changes significantly with strain as a result of fabric evolution anisotropy changes also with depth pressure due to the large variation of elastic anisotropy of mg fe o with depth seismic anisotropy caused by the deformation fabric of mg fe o is very weak in the shallow lower mantle v sh v sv anisotropy assuming that mg fe o occupies 20 volume fraction of the lower mantle and little shear wave splitting of vertically travelling waves a result that is consistent with the seismological observations in the d layer of the circum pacific regions thus the deformation fabric of mg fe o is a vital candidate of the cause of seismic anisotropy in these regions anisotropy caused by the lattice preferred orientation of mg fe o has a distinct azimuthal anisotropy with a strong 4 term azimuth the direction of propagation of the fastest slowest sh or p wave is parallel perpendicular to the flow direction and the slowest fastest sh or p wave is at 45 from these two directions

anisotropy in the deep earth abstract seismic anisotropy has been found in many regions of the earth s interior its presence in the earth s crust has been known since the 19th century and is due in part to the alignment of anisotropic crystals in rocks and in part to patterns in the distribution of fractures and pores in the upper mantle seismic anisotropy was discovered 50 years ago and can be attributed for the most part to the alignment of intrinsically anisotropic olivine crystals during large scale deformation associated with convection there is some indication for anisotropy in the transition zone particularly in the vicinity of subducted slabs here we focus on the deep earth the lower mantle and core where anisotropy is not yet mapped in detail nor is there consensus on its origin most of the lower mantle appears largely isotropic except in the last 200 300 km in the d region where evidence for seismic anisotropy has been accumulating since the late 1980s mostly from shear wave splitting measurements recently a picture has been emerging where strong anisotropy is associated with high shear velocities at the edges of the large low shear velocity provinces llsvps in the central pacific and under africa these observations are consistent with being due to the presence of highly anisotropic mgsio 3 post perovskite crystals aligned during the deformation of slabs impinging on the core mantle boundary and upwelling flow within the llsvps we also discuss mineral physics aspects such as ultrahigh pressure deformation experiments first principles calculations to obtain information about elastic properties and derivation of dislocation activity based on bonding characteristics polycrystal plasticity simulations can predict anisotropy but models are still highly idealized and neglect the complex microstructure of polyphase aggregates with strong and weak components a promising direction for future progress in understanding the origin of seismic anisotropy in the deep mantle and its relation to global mantle circulation is to link macroscopic information from seismology and microscopic information mineral physics through geodynamics modeling anisotropy in the inner core was proposed 30 years ago to explain faster p wave propagation along the direction of the earth s axis of rotation as well as anomalous splitting of core sensitive free oscillations there is still uncertainty about the origin of this anisotropy in particular it is difficult to explain its strength based on known elastic properties of iron as it would require almost perfect alignment of iron crystals indeed the strongly anomalous p travel times observed on paths from the south sandwich islands to alaska may or may not be due to inner core anisotropy and will need to be explained before consensus can be reached on the strength of anisotropy in the inner core and its origin

fabric development in experimentally sheared quartzites abstract a fine grained quartzite was deformed under a combination of simple shear and axial compression to varying amounts of shear strain 1 3 to 2 9 the experiments were conducted at 800 c 1500 mpa and an axial strain rate of 10 6 s in the dislocation creep regime shear zone boundaries were oriented at 45 or 30 to the compressior axis the progressive development of deformation microstructures including planar fabrics and c axis preferred orientations was studied as a function of increasing shear strain elongate original grains define a foliation s which rotates from 45 to 0 to the shear zone boundary with increasing strain producing a sigmoidal foliation in a single shear zone a second foliation invariant in orientation is defined by elongate recrystallized grains which lie at about 30 40 to the shear zone boundaries no c surfaces parallel to the shear zone boundaries were observed however extensional crenulation cleavages c defined by parallel zones of recrystallized grains as well as impurity and melt segregations were observed even at low strain lying at approximately 30 to the shear zone boundaries and these could easily be mistaken for c surfaces c axis preferred orientations of original grains define symmetric type i crossed circle girdles at low strain 2 with the greater concentration of c axes in the direction of shear these features are very similar to those observed in natural ductile shear zones

plastic anisotropy and slip systems in ringwoodite deformed to high shear strain in the rotational drickamer apparatus abstract high shear strain deformation experiments up to equivalent strains of 180 were performed on ringwoodite at conditions of 23 gpa and 1800 k at very large shear strains deviation in the strengths of the 3 1 1 and 4 0 0 lattice planes is observed indicating plastic anisotropy lattice strain theory was applied to calculate effective viscosities of the available slip systems from the observed plastic anisotropy we find that the effective viscosities unitless are proportional to 0 43 0 46 and 1 54 for the 1 1 1 1 1 0 1 1 0 1 1 0 and 0 0 1 1 1 0 slip systems respectively this indicates that 1 1 1 1 1 0 slip is slightly softer than 1 1 0 1 1 0 at these conditions additionally the 1 1 1 1 1 0 slip system has significantly more symmetric variants than the slip systems involving other lattice planes thus it is expected to dominate deformation this is confirmed by polycrystal plasticity modeling using the viscoplastic self consistent code vpsc which indicates that simulations with dominant 1 1 1 1 1 0 slip provide the best match to experimental textures

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

temperature driven seasonal calcite growth and drip water trace element variations in a well ventilated texas cave implications for speleothem paleoclimate studies abstract a two year cave monitoring study at westcave preserve in central texas provides insight into the controls on the rate of calcite growth and drip water mg ca sr ca and ba ca variations the cave is shallow and has a large ratio of its opening area to its volume which results in year round ventilation of the cave unlike larger and deeper caves in the region that ventilate seasonally cave air temperature and co2 concentrations at westcave are near atmospheric throughout the year and calcite growth is continuous changes in the rate of calcite growth positively correlate with seasonal temperature variations at all six drip sites studied r2 0 12 0 76 mean r2 0 47 average monthly surface air temperature is positively correlated with drip water sr ca at five of six drip sites studied r2 0 21 0 80 mean r2 0 44 and ba ca at all six sites r2 0 41 0 85 mean r2 0 57 whereas this correspondence is only seen in one of six drip sites for mg ca applying geochemical modeling of mineral solution reactions to the sr ca and ba ca time series at westcave indicates that the evolution of drip water sr ca and ba ca can be accounted for by two mechanisms 1 prior calcite precipitation and or incongruent calcite dissolution pcp icd which dominate drip water evolution at one site and 2 a combination of pcp icd and water rock interaction wri at the other five drip sites the results suggest a possible seasonality in the operation of the mechanisms of drip water evolution whereby pcp icd plays a larger role than wri during the warmer months of the year understanding drip water seasonal sr ca and ba ca variations has implications for paleoclimate studies using speleothems it is important to first determine if seasonal geochemical variations in drip waters can be identified one can then determine if these variations are preserved as geochemical laminae in speleothems which may then provide seasonal temperature variations and thus seasonal age constraints for speleothems determining the proportional contributions of the mineral solution reactions that drive drip water trace element variations for different drip sites as well as the extent to which trace element concentrations vary seasonally will help inform speleothem sample selection and interpretation of geochemical data for paleoclimate study our results indicate that speleothems near the well ventilated entrances of many larger and deeper caves may warrant further consideration for paleoclimate studies

heterogeneous deformation and texture development in halite polycrystals comparison of different modeling approaches and experimental data modeling the plastic deformation and texture evolution in halite is challenging due to its high plastic anisotropy at the single crystal level and to the influence this exerts on the heterogeneity of deformation over halite polycrystals three different assumptions for averaging the single crystal responses over the polycrystal were used a taylor hypothesis a self consistent viscoplastic model and a finite element methodology the three modeling approaches employ the same single crystal relations but construct the polycrystal response differently the results are compared with experimental data for extension at two temperatures 20 and 100 degreesc these comparisons provide new insights of how the interplay of compatibility and local equilibrium affects the overall plastic behavior and the texture development in highly anisotropic polycrystalline materials neither formulation is able to completely simulate the texture development of halite polycrystals while at the same time giving sound predictions of microstructural evolution results obtained using the finite element methodology are promising although they point to the need for greater resolution of the individual crystals to capture the full impact of deformation heterogeneities c 2003 elsevier b v all rights reserved

comparison of high resolution sub annual records of trace elements in a modern 1911 1992 speleothem with instrumental climate data from southwest australia high spatial resolution measurements of mg p u sr ba and na using 193 nm excimer laser ablation inductively coupled plasma mass spectrometry has revealed clearly resolvable annual cycles in a modern speleothem from southwestern australia the age of this stalagmite is established by the dates of emplacement and removal of the boardwalk where it grew 1911 1992 this chronological constraint allows for the first confident comparison between the instrumental climate record and speleothem trace element content eleven laser ablation transects across a 0 5 mm wide section of the speleothem growth axis were measured cycles that could be matched between adjacent transects were stacked into a master record to minimise variability between tracks and permit greater confidence in comparing the trace elements to the instrumental climate record p and u positively and mg inversely mimic the sudden 20 decrease in annual rainfall experienced by this region since 1965 we argue that p from seasonal vegetation decay is transported to the speleothem before it is mineralised in the soil owing to the low p retention capacity of southwest australian soils both vegetation activity and the transport of vegetation derived hpo42 are sensitive to rainfall groundwater p concentration may also influence the transport of u through the strong affinity between phosphate and uranyl ions mg appears to be sensitive to groundwater residence time as this affects drip water mg ca composition by preferential loss of ca during drier episodes when calcite precipitates before reaching the stalagmite the effects of groundwater residence time may also be important for sr on inter annual scales however the behaviour of sr on the annual cycle is opposite to mg but compatible with ba and na which are shown to depend on speleothem growth rate

seasonal trace element and stable isotope variations in a chinese speleothem the potential for high resolution paleomonsoon reconstruction abstract we report the presence of clear annual cycles in trace element mg ca sr ca ba ca and u ca and stable isotope 18o and 13c composition in an annually banded stalagmite from heshang cave hubei province china 30 44 n 110 42 e through a combination of micromilling and in situ analysis la mc icpms we measured geochemical variations across 16 annual growth bands to assess their potential as seasonal resolution paleomonsoon proxies to facilitate comparison with modern climatic and environmental data we created composite annual cycles for each proxy by stacking 6 well defined years speleothem 18o variations 10 8 to 8 5 are controlled by seasonal variations in temperature and drip water 18o which lead to maximum values during may around the time of summer monsoon onset this provides a chronological marker which can be used to constrain the timing of the other geochemical cycles the composite cycles reveal a strong positive correlation between mg ca sr ca ba ca and 13c values in the micromilled section r2 0 65 0 98 with minimum values occurring around may maximum u ca values occur at the same time we present simple models which show that these correlations as well as the observed ranges of mg ca 14 1 to 22 4 mmol mol sr ca 0 2 to 0 4 mmol mol and 13c 12 5 to 10 7 may be fully explained by progressive co2 degassing and calcite precipitation from an initially saturated solution using realistic initial conditions for heshang cave t 18 c mg casolution 0 84 mol mol sr casolution 0 69 mmol mol 13ctdic 16 75 we find that the observed relationships can be produced by using dmg 0 016 and dsr 0 30 within the range of expected values the model suggests that the fraction of ca removed from the solution ranges from 0 to 30 to produce the observed seasonal cycles this variation may be due to two related processes which occur during drier periods 1 increased prior precipitation of calcite in the epikarst or on the cave ceiling and or 2 a greater degree of co2 degassing and calcite precipitation on stalagmite surfaces when drip rates are lower both mechanisms would have the effect of enriching speleothem mg ca sr ca ba ca and 13c values during drier periods past variations in heshang carbonate chemistry may therefore be useful as seasonal resolution proxies for past rainfall

microstructure and mechanical properties of halite coarse muscovite synthetic aggregates deformed in torsion abstract we investigated the behavior of a synthetic two phase aggregate composed of 80 halite 20 coarse muscovite under torsion deformation at 100 200 and 300 c a confining pressure of 250 mpa and a constant strain rate of 3e 4 s 1 at all temperatures the two phase aggregate deformed homogeneously at the sample scale the strength of the aggregate and muscovite deformation depended on temperature strain rate and initial orientation of muscovite greatest dimension relative to the shear plane with muscovite initially parallel to the shear plane halite flowed plastically and long muscovite grains were not strong enough to behave as a rigid inclusion rotating in a ductile matrix instead high aspect ratio grains deformed by folding which was visibly accomplished by slip along mica 001 cleavage and by great flattening of halite in the core of the folds when initially normal to the shear plane high aspect ratio muscovite grains passively rotated towards the shear plane in both cases small and low aspect ratio muscovite grains behaved mostly as mica fish with mica grains tilted opposite to shear sense similarly to natural mylonites porphyroclast systems and rolling structures were also common in the microstructure a strong foliation made of halite ribbons and aligned muscovite flakes rapidly developed but did not make the composite aggregate weaker when compared with single phase halite comparison with synthetic aggregates of single phase halite shows that the two phase aggregate was much stronger than single phase halite in all cases comparison with a synthetic aggregate with calcite porphyroclasts shows that the strength of the aggregate with muscovite at 100 c was lower below a strain of ca 2 6 and higher beyond this value and that the aggregate with calcite was stronger at 200 c strain rate stepping tests 1e 5 s 1 2e 3 s 1 indicate that the two phase aggregate behaved as power law viscous with stress exponents of ca 12 and 10 at 100 and 200 c respectively the mechanical data obtained in this study represent the actual rheological behavior of the aggregates because we used soft polymer jackets

characterization by scanning precession electron diffraction of an aggregate of bridgmanite and ferropericlase deformed at hp ht scanning precession electron diffraction is an emerging promising technique for mapping phases and crystal orientations with short acquisition times 10 20 ms pixel in a transmission electron microscope similarly to the electron backscattered diffraction ebsd or transmission kikuchi diffraction tkd techniques in a scanning electron microscope in this study we apply this technique to the characterization of deformation microstructures in an aggregate of bridgmanite and ferropericlase deformed at 27 gpa and 2 130 k such a sample is challenging for microstructural characterization for two reasons i the bridgmanite is very unstable under electron irradiation ii under high stress conditions the dislocation density is so large that standard characterization by diffraction contrast are limited or impossible here we show that detailed analysis of intracrystalline misorientations sheds some light on the deformation mechanisms of both phases in bridgmanite deformation is accommodated by localized amorphous shear deformation lamellae whereas ferropericlase undergoes large strains leading to grain elongation in response to intense dislocation activity with no evidence for recrystallization plastic strain in ferropericlase can be semiquantitatively assessed by following kernel average misorientation distributions

new african lower carboniferous paleomagnetic pole from intrusive rocks of the tin serririne basin southern border of the hoggar algeria a paleomagnetic study has been conducted on intrusive doleritic rocks cropping out within devonian horizontal tabular formations of the saharan craton tin serririne basin south of hoggar shield the 40k 40ar dating of the dolerites gave an age of 347 6 8 1 ma i e tournaisian the paleomagnetic data present three different directions the first has a paleomagnetic pole close to the previous african poles of permian age this direction is therefore interpreted as a permian remagnetization the second direction which is defined by both linear regression and remagnetization circles analysis is considered as the primary magnetization it yields a new african tournaisian paleomagnetic pole 18 8 s phi 31 2 e k 29 a95 7 5 very close to the ben zireg tounaisian pole aifa t feinberg h pozzi j p 1990 devonian carboniferous paleopoles for africa consequences for hercynian geodynamics tectonophysics 179 288 304 the third direction has intermediate orientation between those of the first or second directions and that of the upper cenozoic field it is interpreted as related to a composite magnetization this new tin serririne pole improves the apwp of gondwana for this key period of the evolution of the pangea this apwp confirms the previous paleogeographic reconstruction which shows that the pre hercynian ocean between gondwana and laurussia is still not close during the beginning of the carboniferous

large strain shearing of halite experimental and theoretical evidence for dynamic texture changes abstract we report results from torsion experiments on polycrystalline halite nacl to shear strains 8 and observe a very complex texture evolution the same behavior was reproduced with polycrystal plasticity simulations suggesting that we capture the underlying mechanisms while crystal shapes gradually rotate into the shear plane crystal orientations change continuously and dynamic texture patterns evolve with increasing shear this is highly significant for ultra large deformation as for example implied from geodynamic modeling for the deep earth where seismic anisotropy patterns may develop and locally disappear again as material is deformed during convection the study also suggests that caution is required when interpreting deformation mechanisms from simple shear preferred orientation patterns

paleomagnetism of the western cape fold belt south africa and its bearing on the paleozoic apparent polar wander path for gondwana in order to test two different proposals for the poorly defined african paleozoic apparent polar wander path apwp a paleomagnetic study was carried out on ordovician through carboniferous clastic sediments from the cape fold belt west of the 22nd meridian one proposal involves a relatively simple apwp connecting the ordovician gondwana poles in north africa with the late paleozoic poles to the east of south africa in a more or less straight line crossing the present equator in the devonian the other proposal adds a loop to this path connecting ordovician poles in north africa with poles to the southwest of south africa and then returning to central africa this loop would occur mainly in silurian time new results reported herein yield paleopoles in northern and central africa for ordovician to lowermost silurian and lower to middle devonian formations the best determined paleopole of our study is for the early ordovician graafwater formation and falls at 28 n 14 e k 25 0t95 8 8 n 28 samples the other paleopoles are not based on sufficient numbers of samples but can help to constrain the apparent polar wander path for gondwana our results give 0nly paleopoles well to the north of south africa and we observe no directions within the proposed loop hence if the loop is real it must have been of relatively short duration 60 70 ma and be essentially of silurian early devonian age implying very high drift velocities for gondwana with respect to the pole during that interval

an illustration of the advantages of a complete texture analysis described by the orientation distribution function odf using quartz pole figure data abstract the preferred orientation of eight crystal directions of quartz was measured with an x ray texture goniometer for selected quartz bearing tectonites with a clear pattern of c axis preferred orientation the advantages of data analysis by means of calculations of the orientation distribution function and other forms of data presentation derived from the odf are demonstrated

i stal a model for interpretation of mg ca sr ca and ba ca variations in speleothems and its forward and inverse application on seasonal to millennial scales 1 trace element ratios mg ca sr ca and ba ca are readily measured in speleothems and may be closely related to hydrological balance enhancing paleoclimate information inferred from stable isotope measurements we develop a model which simulates the variation in dripwater chemistry resulting from variable degree of water rock interaction and prior calcite precipitation pcp with the latter process depending both on drip interval and drip oversaturation with respect to caco3 partition coefficients between speleothem and dripwater are dependent on temperature for mg and on speleothem growth rate for sr and ba as observed in laboratory experiments the drip oversaturation state regulated both by cave pco2 and the dilution and soil karst dissolution processes strongly affects stalagmite trace element concentrations by modulating the extent of pcp and speleothem growth rates application of an inverse model confirms that seasonal co2 cycles can explain the uncorrelated seasonal cycles in mg ca and sr ca observed in our speleothem records from nw spain for which high co2 coincides with dry season in absence of seasonal variations in drip interval cycles in cave pco2 can produce seasonal covariation in sr ca mg ca and ba ca in long time series 104 yr where seasonal sampling resolution is not obtained in stalagmites a change from dominance of summer to winter rainfall can shift the season of strongest stalagmite deposition to one of lower mean co2 and hence greater pcp and higher mg ca sr ca and ba ca ratios caves best suited to record a dominantly water balance signal such as mean drip intervals are those with minimal seasonal variation in cave pco2

the influence of water on deformation microstructures and textures in synthetic nacl measured using ebsd abstract wet nacl with 10 15 ppm water shows weakening behaviour compared with dry nacl containing

modeling lower mantle anisotropy development in a subducting slab a model is presented that simulates anisotropy development in a subducting slab from the upper lower mantle boundary 661 km to the core mantle boundary 2891 km two phases are considered orthorhombic mgsio3 perovskite and cubic magnesiowuestite mg fe o single crystal elastic properties at mantle conditions are obtained from existing density functional theory calculations and quasiharmonic approximation it is assumed that deformation is accommodated by slip a polycrystal plasticity model predicts strong texture development for perovskite and weaker texture for magnesiowuestite when averaging single crystal elastic properties with the orientation distribution this results for both phases in weak p wave anisotropy and shear wave splitting in the upper part of the lower mantle but pronounced anisotropy near the core mantle boundary up to 4 for vp and 7 for vs the anisotropy pattern is complex and asymmetric and local heterogeneity is expected these predictions are consistent with seismic observations

stalagmite growth and palaeo climate an inverse approach abstract the growth of stalagmites is controlled by climatic conditions such as temperature soil activity and precipitation hence a stalagmite stratigraphy reflects fluctuations of palaeo climate conditions on various time scales from annual variations to ice age cycles however no attempt has been made to infer palaeo climate fluctuations from the stratigraphy itself we describe the complicated growth of a stalagmite with a simple mathematical model in which both the growth rate and the equilibrium diameter of stalagmites are functions of palaeo climate variables hence inverting a given stalagmite stratigraphy in terms of growth rate and equilibrium diameter can in principle recover the palaeo climate signal the strongly nonlinear dependence of these two geometrical parameters however limits the success of a formal inversion of stratigraphical data in this paper we explore the resolving power of both growth rate and equilibrium diameter data for the palaeo climate signals temperature carbon dioxide concentration and precipitation we use numerically generated stalagmite stratigraphies as observational data thus we know beforehand the palaeo climate signal contained in the stratigraphic record our results indicate that both variations in carbon dioxide concentrations as a proxy of soil cover and drip interval as a proxy of precipitation can be recovered from the stratigraphy however temperature variations are poorly resolved

rheological behaviour of synthetic rocksalt the interplay between water dynamic recrystallization and deformation mechanisms abstract the ductile deformation of rocks in nature can be greatly enhanced by the presence of water part of the water induced weakening of rocks at depth may come from fluid assisted deformation or recrystallization mechanisms that are absent in dry rocks in this study we investigate the effect of water on the rheological behaviour of rocksalt we focus on quantification of the contribution of individual deformation and recrystallization mechanisms to deformation we also aim to calibrate a flow law that incorporates the effect of all the relevant microphysical processes and hence more accurately describes the flow of rocksalt in nature for this purpose the mechanical behaviour and microstructural evolution of synthetic rocksalt samples that are similar except for differences in water content determined using ftir analysis are investigated the samples are deformed to natural strains of 0 07 0 46 at 50 mpa confining pressure strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c resulting in flow stresses of 7 22 mpa the flow stress of samples with a water content below 5 ppm dry is higher than that of samples with a water content of 9 46 ppm wet at all strains under the investigated conditions the difference in flow stress can be explained as due to the operation of only work hardening dislocation creep without dynamic recrystallization in the dry material versus combined dislocation and solution precipitation creep plus fluid assisted grain boundary migration in the wet material the results allow us to calibrate a flow law for wet rocksalt that incorporates the effects of solution precipitation creep and fluid assisted grain boundary migration the results also suggest that strain localization in natural rocksalt is more likely to be localized due to fluid infiltration and associated rheological weakening than due to progressive removal of strain hardening substructure by grain boundary migration

isotopic climate record in a holocene stalagmite from ursilor cave romania the pu 2 stalagmite from ursilor cave provides the first dated romanian isotope record for the holocene the overall growth rate of the speleothem was 3 5 cm kyr 1 corresponding to a temporal resolution of 142 y between each isotope analysis the hendy tests indicate that isotopic equilibrium conditions occurred during the formation of pu 2 and hence that it is suitable for palaeoclimatic studies the relationship between 18 o and temperature was found to be positive this can be interpreted either as rain out with distance from the west northwest ocean source of evaporation or shifts in air mass source with changing north atlantic oscillation indices applying five u th thermal ionisation mass spectrometric tims dates to a 17 5 cm isotope profile 18 o

structural geology meets micromechanics a self consistent model for the multiscale deformation and fabric development in earth s ductile lithosphere abstract earth s lithosphere is made of rheologically heterogeneous elements of a wide range of characteristic lengths a micromechanics based self consistent multiorder power law approach is presented to account for lithospheric deformations and the accompanying multiscale fabric development the approach is principally based on the extended eshelby theory for the motion of a power law viscous ellipsoid in a power law viscous matrix and the idea of embedding inhomogeneities within inhomogeneities the extended theory provides a general means for investigating deformation partitioning in heterogeneous rocks the inhomogeneities within inhomogeneities method allows multi hierarchical levels of flow field partitioning and hence multiscale deformations to be investigated partitioned flow fields are used to investigate fabric development being based fully on micromechanics the approach generates model predictions of both kinematic quantities strain strain rates and vorticity and stress histories the former can be directly compared with field and laboratory structural observations while the latter can help to understand the physics of natural deformations the self consistent and multiscale approach is applied to a natural example of the cascade lake shear zone in the east sierra nevada of california the modeling shows that the fabrics are most consistent with a steeply dipping transpression zone with a convergence angle of 20 and a strike slip displacement about 26 km further the strength evolution of the model zone confirms that a transpression zone is a weakening system with respect to the simple shearing component and a hardening one for the pure shearing component this is consistent with slip partitioning in obliquely convergent plate boundaries boundary normal convergence tends to spread over a broad area whereas boundary parallel shear tends to localize in major strike slip zones

evidence of rainfall variations in southern brazil from trace element ratios mg ca and sr ca in a late pleistocene stalagmite trace element ratios in the bt2 stalagmite from botuveracave southern brazil are explored as a proxy for changes in the local rainfall recharge during the last 116 ky bp mg ca and sr ca ratios measured with an electron microprobe are signif icantly positively correlated with one another throughout the entire record and vary in a way that is very consistent with variations of d 18 o in the same speleothem during the last glacial period we suggest that prior calcite precipitation in the vadose zone of the cave system is the main factor affecting the incorporation of mg and sr into calcite of the stalagmite this interpretation is supported by trace element correlation patterns and by results from a hydrochemistry study performed in a cave located in the same region and in a similar environmental setting therefore we conclude that higher lower mg ca and sr ca values are associated with lower higher levels of recharge into the karstic aquifer as such conditions lead to an increase decrease in the volume of calcite precipitated in the unsaturated zone above the cave during dry wet climate periods trace element variations point to generally dryer wetter conditions during lower high phases of summer insolation in the southern hemisphere these periods coincide with decreased increased activity of the south american summer monsoon as revealed by d 18 o stalagmite records in addition trace element variations show that rather wet conditions persisted through out most of the last glacial period from approximately 70 to 17 ky bp we suggest that during this period the glacial boundary conditions especially ice volume buildup in the northern hemisphere played an important role for monsoon rainfall inten sification in the region 2007 elsevier ltd all rights reserved

rheology and microstructure of synthetic halite calcite porphyritic aggregates in torsion abstract polymer jacketed porphyritic samples of 70 halite 30 coarse calcite were subjected to torsion deformation to investigate the effects of a mixture of coarse calcite on the microstructure and mechanical properties of a two phase aggregate the experiments were run at 100 and 200 c a confining pressure of 250 mpa and a constant shear strain rate of 3e 4 s 1 ultimate strengths of single phase halite synthetic aggregates at 100 and 200 c were ca 32 and 8 nm respectively and of the two phase aggregate 39 and 18 nm respectively this shows that the two phase aggregate was much stronger especially at 200 c stepping strain rate tests show that the two phase aggregate behaved as power law viscous with stress exponents of ca 19 and 13 at 100 c at 200 c respectively from these high exponents we infer that the active deformation mechanisms were not efficient enough to rapidly relax the applied stress halite stress exponents at 100 and 200 c are typically much lower in the order of 4 6 which means that the calcite porphyroclasts were obstacles to halite plastic flow and hampered stress relaxation the drop of the stress exponent with temperature indicates that the main deformation mechanism s was temperature sensitive matrix halite deformed plastically while calcite rotated rigidly or deformed in a brittle fashion with grain size reduction by fracturing e g bookshelf and boudinage we conclude that halite was softer than calcite in the investigated temperature range strain was homogeneous at the sample scale but not at the grain scale where the foliation delineated by plastically flattened halite contoured the rigid calcite clasts the microstructures experimentally produced at 100 and 200 c are very similar and find their counterparts in natural mylonites rolling structures and porphyroclast systems bookshelf and boudinage in brittle calcite porphyroclasts and ductile y and c micro shear bands in the halite matrix

long term summer temperature reconstruction inferred from tree ring records from the eastern carpathians the first 1 000 year long carpathian tree ring width chronology was established based on living and subfossil stone pine pinus cembra l samples from an upper timberline forest located in calimani mts romania tree ring data were standardized using the regional curve standardization method in order to preserve the low and medium frequency climate signals the de trended index strongly correlates with summer mean temperature both at annual and decadal scales the calimani summer mean temperature anomalies were reconstructed for the period ad 1163 2005 applying the rescaling method this new climate proxy from the carpathians shows similar fluctuations to other north hemispheric temperature reconstructions but with periods of distinct differences the fingerprint of little ice age in the calimani area is visible between ad 1370 and 1630 followed by lagged cold decades in ad 1820 and 1840 the recent warming is evident only after the 1980s in our reconstruction

palaeomagnetism of the early to mid ordovician salala igneous ring complex red sea hills sudan summary palaeomagnetic samples were collected from the early to mid ordovician igneous ring complex at salala northern red sea hills sudan detailed demagnetization experiments on 114 samples from 17 sites yield two distinct groups of characteristic directions of the natural remanent magnetization component a predominant in samples from the quartz syenitic central part and minor ring dyke of the complex displays rather high blocking temperatures well above 600 c and is presumably carried by haematite the direction of this component dec inc 1 37 is virtually identical with the direction of the present day earth s magnetic field at the sampling locality dec inc 0 37 mixed polarities of a magnetization strongly suggest a recent pre brunhes age of this component and the effects of long term weathering and low temperature oxidation component b pointing to the southeast and upward has been identified in seven sites from the major ring dyke composed of aegirine syenite maximum blocking temperatures of this component do not exceed 580 c and together with the results of rock magnetic and optical examinations are indicative of primary magnetite as the carrier of the characteristic magnetization the mean direction dec inc 124 50 95 9 2 k 44 1 differs significantly from component a and is thought to be primary and representative for the direction of the earth s magnetic field during emplacement and cooling of the ring complex in mid ordovician times the resulting palaeomagnetic pole 40 n 30 w dp 8 dm 12 situated off the coast of west africa plots very close to a cluster of ordovician palaeomagnetic poles from africa these poles have not been integrated into the majority of the various apparent polar wander paths for gondwana but this new result re enforces their correctness the application of recently revised rotation parameters for eastern gondwana significantly reduces the longitudinal gap between the african data and that from eastern gondwana particularly australia for the ordovician

devonian carboniferous paleopoles for africa consequences for hercynian geodynamics abstract paleomagnetic analysis of marine formations in the northwestern sahara algeria yields the following results three sites in the lower devonian orthoceras bearing limestones of beni abbes 29 67 n 2 15 w indicate a mean direction of remanence dm 149 6 im 1 6 95 6 8 this typical permian direction implies a complete remagnetization of the sites the famennian griotte limestones of the ben zireg anticline 31 92 n 1 82 w show high remanent magnetization intensities in this structure which has undergone polyphase tectonism multicomponent analysis evidences a high unblocking temperature htb component carried by haematite leading to a positive fold test after partial unfolding at the 95 confidence level with a mean direction d 156 4 i 47 6 95 0 9 and attributed to the early carboniferous 355 ma with a paleopole at 25 3 s 21 1 e dp 0 8 dm 1 2 an intermediate unblocking temperature itb component of magnetization carried probably by magnetite also present satisfies a positive fold test after tilt correction with a mean direction d 154 9 i 54 3 95 3 7 this pre folding direction of magnetization is attributed to the famennian it gives a paleopole at 19 2 s 19 8 e dp 3 7 dm 5 3 comparison with previous results shows a significant s n crustal shortening of about 2500 km during carboniferous times accompanied by a clockwise rotation of the saharan region of about 25 these new results give information about the tectonic phenomena involved in the collision between gondwanaland and laurasia they argue for a pangea a2 dominating model and define mean values for shortening rate and plate velocity comparable to the present ones 3 cm yr

inferences on flow at the base of earth s mantle based on seismic anisotropy we applied global waveform tomography to model radial anisotropy in the whole mantle we found that in the last few hundred kilometers near the core mantle boundary horizontally polarized s wave velocities vsh are on average faster by 1 than vertically polarized s wave velocities vsv suggesting a large scale predominance of horizontal shear this confirms that the d region at the base of the mantle is also a mechanical boundary layer for mantle convection a notable exception to this average signature can be found at the base of the two broad low velocity regions under the pacific ocean and under africa often referred to as superplumes where the anisotropic pattern indicates the onset of vertical flow

carboniferous palaeomagnetic investigations in morocco permian remagnetizations and possible large carboniferous rotations occurring in mesetian sedimentary and jebilets intrusive rocks summary carboniferous limestone and sandstone formations from the moroccan meseta and visean gabbros from the jebilets massif have been investigated palaeomagnetic results reveal the occurrence of different magnetic components these are i a permian component dm 141 5 zm 1 7 n 4 virtual geomagnetic pole vgp 33 s 43 9 e similar to that found in the anti atlas and in other parts of the hercynian chain ii a carboniferous component dm 116 6 zm 25 lo n 9 vgp 7 4 s 54 5 e consistent with other carboniferous data from central sahara and morocco and iii a component not previously described from africa and still undated with a direction dm 77 4 im 1 5 this direction and it s opposite polarity counterpart were found only at one site 21 specimens in the jebilets and at two sites 20 specimens in the meseta opposite polarity it may represent an older magnetization possibly of lower carboniferous age which would imply important rotations of africa during this period

geodynamical implications of a moscovian palaeomagnetic pole from the stable saharan craton illizi basin algeria abstract four different characteristic remanent magnetization chrm orientations have been isolated in the el adeb larache formation of the algerian sahara 27 45 n 8 9 e two of them are interpreted as overprints developed respectively during recent and permian times the two others give new moscovian 28 7 s 55 8 e and probably stephano autunian 38 5 s 57 5 e palaeopoles in good agreement with those previously obtained from the sahara but significantly different from the dwyka varves pole mcelhinny and opdyke 1968 comparison with lower carboniferous results shows that the latitudinal displacement of africa during the carboniferous is mainly related to a clockwise rotation about 25 around an axis close to the northeastern border of africa such a motion of africa agrees well with geological observations and with the pangea a2 hypothesis

quantitative temperature reconstruction based on growth rate of annually layered stalagmite a case study from central china we used the annual growth rate of a stalagmite xl21 collected from xianglong cave central china to quantitatively reconstruct regional terrestrial temperature changes over the last 95 years 1912 2006 ad based on a significant positive correlation between the growth rate and the observed temperature a transfer function was designed and the temperature from the previous september to may p9 5 was reconstructed with an explained variance of 43 5 our results show an increasing trend in temperature during the last century and especially over the last 30 years the temperature variability from central china recorded here bears a striking similarity to that in the northern hemisphere and also to global trends however the cooling between the 1980s and the early 1990s seen in the stalagmite record which interrupted the warming trend that began in the 1960s is not observed in the mean conditions found in china the northern hemisphere neither globally this methodology for reconstructing historical temperature from stalagmite growth rates overcomes the limitation of the short meteorological observation period and supports the potential of stalagmite lamina climatology

magnesium and strontium systematics in tropical speleothems from the western pacific abstract we present bulk average sr and mg data for 13 speleothems from different locations in the western equatorial pacific guam solomon islands and vanuatu these data plot on a single straight line in a graph of ln sr ca vs ln mg ca with a slope of 0 9 a 22 000 year record of sr and mg in one of these samples from guam also plots with the same slope suggesting that the process partitioning mg and sr within the guam speleothem is the same as the one that partitions mg and sr between the different pacific speleothems we rule out temperature growth rate detrital phases and sea spray as likely mechanisms for this correlation we construct mathematical models of limestone diagenesis and show that this cannot explain the slope of the correlation our favoured explanation for the correlation is calcite water interaction in the form of prior calcite precipitation pcp and or incongruent calcite dissolution icd we present a formal mathematical model of pcp and prove that the slope of a graph of ln sr ca and ln mg ca is given by kd sr 1 kd mg 1 a similar equation is derived for icd in a companion paper sinclair 2011 using published values for kdsr and kdmg this slope is calculated to be 0 88 in excellent agreement with our observations because the slope is independent of solution and host limestone composition it can be used to diagnose calcite water interaction in individual cave water studies where host rock composition is unknown or in speleothems for which no field drip water data or host rock geochemistry exists approximately half of published drip and speleothem mg sr studies plot within error of this slope we hypothesize that the overall trend in our pacific speleothem data results from the individual dripwater systems evolving from a roughly similar initial rock composition set by late quaternary reef limestone in the guam speleothem the broad peak in mg and sr centred on the early mid holocene reflects a change in hydrology rainfall with the most likely scenario being that dry conditions prevailed on guam at this time

effect of scaling and regression on reconstructed temperature amplitude for the past millennium 1 examination of large scale millennial long temperature reconstructions reveals a wide range of datasets and methods used for calibration proxy time series are commonly calibrated against overlapping instrumental records representing different seasons northern hemisphere latitudinal bands and including or excluding sea surface temperature data methodological differences include using scaling or regression the calibration time period and smoothing data before calibration we find that these various approaches alone can result in differences in the reconstructed temperature amplitude of about 0 5 c this magnitude is equivalent to the mean annual temperature change for the northern hemisphere reported in the last ipcc report for the 1000 1998 period a more precise assessment of absolute reconstructed temperature amplitudes is necessary to help quantify the relative influences of forcing mechanisms in climate models

microstructural and mechanical effects of strong fine grained muscovite in soft halite matrix shear strain localization in torsion 1 torsion experiments were performed on polymer jacketed samples of 80 halite 20 fine mica at 373 473 and 573 k a confining pressure of 250 mpa and a shear strain rate of 3 10 4 s 1 the strength of the aggregate depended on temperature strain rate mica distribution produced by cold pressing and mica orientation emerging during experiments comparison with synthetic aggregates of pure halite shows that halite mica mixtures were stronger in all cases from strain rate stepping tests we deduced stress exponents of 12 and 10 at 373 and 473 k respectively in contrast to values of approximately 4 and 3 for halite at the same temperatures strain localized only at 573 k except for one run at 373 k and high strain shear bands formed parallel to the applied shear plane at 573 k we infer that the strength contrast between halite and mica increased with temperature and promoted strain localization which occurred where the local mica content was low while unstrained domains persisted where the locally high mica content formed a strong framework mica reorientation and strain softening at 573 k increased with strain from which we deduce that mica alignment promoted softening we conclude that small amounts of a strong mineral phase can significantly increase the strength and stress dependence of a rock and that the heterogeneous connectivity between strong grains can trigger shear strain localization

lattice preferred orientation in deformed polycrystalline mg fe o and implications for seismic anisotropy in d abstract magnesiowustite mg fe o is an important constituent of the lower mantle probably occupying about 20 25 of its volume laboratory and theoretical studies have shown this mineral to be highly elastically anisotropic at lower mantle pressures and temperatures thus strain induced formation of lattice preferred orientation lpo in magnesiowustite is a candidate mechanism for the origin of anisotropic structure in d although observations of seismic anisotropy within d are robust both the occurrence and the style of that anisotropy are spatially variable two hypotheses have been offered to explain the observations of d anisotropy lpo of intrinsically anisotropic minerals or shape preferred orientation spo perhaps in the form of horizontal layering or oriented inclusions to investigate the first hypothesis we performed confined simple shear deformation experiments in the dislocation creep regime using a gas medium deformation apparatus over a range of compositions the mgo and feo endmembers and three intermediate compositions samples were deformed at 1273 1473 k at a confining pressure of 300 mpa to large shear strains 3 5 4 5 using deformation pistons cut at 45 after deformation the lpo was measured by electron backscatter diffraction ebsd the lpo produced varied for differing compositions indicating the activity on individual slip systems and or the nature of grain boundary migration in mg fe o are affected by composition and or homologous temperature we predicted seismic anisotropy from the measured lpos and theoretically determined single crystal elastic constants anisotropic behavior predicted from lpo agrees well with observations of d anisotropy so the lpo hypothesis appears to satisfy the seismological constraints our calculated anisotropy patterns suggest that if d anisotropy is due to lpo of mg fe o then azimuthal variations in anisotropy in the horizontal plane should be present such azimuthal variations are not generally predicted for spo type hypotheses and this may provide a means for distinguishing the cause of d anisotropy

the 2002 2003 el nino recorded in australian cave drip waters implications for reconstructing rainfall histories using stalagmites 1 a 30 month study of drip hydrochemistry from kooringa cave eastern australia revealed a clear geochemical response to the 2002 2003 el nino through the drought drip discharge fell to base flow drip ca2 concentrations fell by half and drip mg ca and sr ca increased in a co varying pattern calcite mg ca and sr ca predicted from drip waters displayed a marked increase through and just beyond the period of greatest moisture deficit the results suggest that stalagmites from shallow caves in drought sensitive eastern australia potentially preserve a valuable record of el nino la nina history

paleomagnetism of proterozoic and cambrian strata adrar de mauritanie cratonic west africa four paleomagnetic poles are reported from red beds of the adrar de mauritanie cratonic west africa thirteen localities were occupied and 224 samples were collected in seven units from a middle proterozoic to early paleozoic sedimentary section two poles are reported from middle and late proterozoic strata a third pole is reported from cambrian strata the magnetizations for these reside in stable high temperature components revealed by progressive thermal demagnetization analysis to 675 c the fourth pole is interpreted to reflect a permian overprinting in the cambrian strata two cambrian ordovician units sampled contained directions too scattered to allow the calculation of any pole the pole from middle proterozoic strata 998 32 ma rb sr date on argillite derived from four localities 52 samples single polarity plots at 48 7 n 206 9 e dp 1 1 dm 2 9 the pole from late proterozoic strata 775 52 ma rb sr date derived from two localities 15 samples mixed polarity plots at 34 0 n 246 9 e dp 4 6 dm 8 6 neither has correlatives in age in the paleomagnetic data set for cratonic west africa nor are there obvious correlatives with the paleomagnetic data set from the remainder of africa the pole that we consider to reflect a cambrian direction comes from three localities 23 samples mixed polarity plotting at 0 3 s 249 3 e dp 5 7 dm 11 5 its antiparallel pole corresponds with one group of cambrian poles reported from africa but differs markedly from another group of cambrian poles the late paleozoic overprint direction obtained from three units 50 samples from four localities single polarity provides a reversed polarity pole that plots at 47 2 s 42 6 e dp 1 5 dm 3 0 which is in good agreement with permian poles reported from elsewhere in africa in spite of the large number of poles already reported from africa additional data are needed before a reliable apparent polar wandering path can be constructed for the paleozoic and proterozoic of africa

a 500 yr speleothem derived reconstruction of late autumn winter precipitation northeast turkey a verified instrumental calibration of annually resolved 18o for a stalagmite from gumushane in northeast turkey is presented and cross validated using a leave one out technique the amount of late autumn to winter precipitation is negatively correlated with stalagmite 18o between ad 1938 and 2004 the observed relationship is extrapolated back to ad 1500 leading to the first long winter precipitation reconstruction for this region modern day october to january precipitation is linked to pressure fields in western russia anomalously lower reconstructed rainfall is recorded in ad 1540 1560 at which time higher pressure over the caspian sea region is inferred