electron spin resonance esr techniques applied to mollusc shells from south america chile argentina and implications for palaeo sea level curve esr dating of marine mollusc shells gives no evidence for a so called mid wisconsin sea level high stand in argentina and chile the idea of this high stand around 30 000 40 000 bp is still alive especially in argentina but the evidence for it is in our opinion and that of others solely based on the misinterpretation of 14c dates all esr ages from southern south america belong either to the holocene or the last interglacial or older interglacial periods apart from the regional aspect this paper deals with some methodological problems in esr dating estimates have been improved by using only mollusc shells that are still closed and in living position and by introducing a plateau screening test for the determination of the accumulated dose ad the estimate of the environmental dose has been refined by analysing the infill sediments in the shells for their u th and k contents separately from the embedding matrix special interest has been paid to the debated problem of early or continuous u uptake the u contents of recent holocene molluscs support the early uptake model a probable solution to the problem of age overestimation of holocene shells is also presented present day shells are shown to possess frequently a fully developed signal and to give ad of 2 4 in one case up to 9 gy if the holocene ad values of 14c dated shells are corrected by subtracting these recent and spurious values the resulting age estimates are more consistent with radiocarbon ages

a comparison of archaeointensity results from chinese ceramics using thellier s and shaw s palaeointensity methods summary a collection of chinese ceramics covering the time period 2700 7500 bp has been investigated using adaptations of both the thellier thellier 1959 and shaw 1974 palaoeintensity techniques several rock magnetic techniques were used to investigate the magnetic properties of the samples and on the basis of these measurements some samples were rejected because of their poor magnetic behaviour anisotropy of magnetic susceptibility ams thermo remanent magnetization trm and anhysteretic remanent magnetization arm were investigated based on the relationship between arm and trm anisotropy modified arms were used for anisotropy correction twenty samples were studied using the shaw method and 34 were studied using the thellier method an acceptable agreement between the results from the two methods was found general features of the secular variation of geomagnetic intensity determined from the present study are consistent with those of the global model of mcelhinny senanayake 1982

the properties and geological environments of helicoids axially symmetric surfaces in torsional and non torsional deformations abstract a helicoid is a non developable surface swept out by a line the generator which rotates with constant sense about another non parallel line the heliaxis whilst moving parallel to that line in a constant direction torsion may produce helicoids though this is not a necessity previous references to helicoids and helices in structural geology are reviewed and the basic properties of helicoids are compared with those of cylindrical and conical surfaces a map and stereogram technique is developed for the recognition of nested initially parallel equally rotated coaxial macroscopic helicoids the typically sigmoidal outcropping traces of nested helicoids show dip direction reversals along trend on stereograms linear loci each representing the poles from a single helicoid trace diverge from a common pole a nested set of macroscopic helocoidal cleavage surfaces from the hill end trough southeastern australia are modelled and interpreted to have formed in two stages of torsion associated with accommodation of an adjacent granitoid intrusion the volume affected by torsion is bound by curviplanar scissor faults helicoids may be found associated with rotational porphyroblasts deformed cylindrical bodies or strip like surfaces e g intrafolial fold axial planes cylindrical diapirs with helical flow patterns cylindrical scissor faults ductile shear zones zones of constrictional strain and en echelon segmented dykes and fracture planes

microstructure and magnetic susceptibility applied to emplacement kinematics of granites the example of the foix pluton french pyrenees abstract the variscan foix granite 40 km 2 central pyrenees was subjected to detailed microstructural magnetic susceptibility and anisotropy studies magnetic susceptibility is shown to be of dominant paramagnetic origin its magnitudes clearly define a zoning which compares with the petrographic zoning and reveals that the pluton is the southern remnant of a normally zoned pluton truncated during alpine tectonics magnetic susceptibility anisotropy characterizes the planar and linear preferred orientations of the main iron bearing silicates namely biotite and accessory amphibole it is argued that these fabrics also reflect the flow pattern of the granite microstructural observations aid in distinguishing the magmatic and late magmatic fabric signatures main body from the post magmatic solid state signature leucogranite in order to account for the consistently subhorizontal and ne sw directed magmatic lineations in the northern sector of the foix granite an oblique intrusion is proposed it may be coeval with the early variscan regional sw trending shearing event steepening of the structures in at least part of the southern sector may be coeval with the late development of upright folds and vertical cleavage in the country rocks the utility of combined microstructural and magnetic susceptibility studies is demonstrated as an aid in the structural interpretation of granite intrusions which act as kinematic markers of their host terranes

high fidelity archeointensity results for the late neolithic period from central china author s cai s tauxe l wang w deng c pan y yang l qin h abstract 2020 american geophysical union all rights reserved archeomagnetism focuses on exploring high resolution variations of the geomagnetic field over hundreds to thousands of years in this study we carried out a comprehensive study of chronology absolute and relative paleointensity on a late neolithic site in central china ages of the samples are constrained to be 3 500 3 000 bce a period when available paleointensity data are sparse we present a total of 64 high fidelity absolute paleointensities demonstrating the field varied quickly from 55 to 90 zam2 between 3 500 3 000 bce our results record a new archeomagnetic jerk around 3 300 bce which is probably non dipolar origin the new results provide robust constraints on global geomagnetic models we calculated a revised chinese archeointensity reference curve for future application the variations of absolute and relative paleointensity versus depth show good consistency reinforcing the reliability of our results this new attempt of combining absolute and relative paleointenstiy provides a useful tool for future archeomagnetic research

intensity of the geomagnetic field near loyang china between 500 bc and ad 1900 there are remarkably few data on the intensity of the geomagnetic field in early china new results reported here indicate that the total intensity of the magnetic field of the earth in the region near loyang lat 34 42 n long 112 40 e has changed considerably during the past 2 400 yr 500 bc ad 1900 the maximum value reached about 1 700 yr ago is as much as 54 higher than the present one

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

patterns of folding and strain influenced by linearly anisotropic bands are there characteristic patterns of deformation in rocks dominated by linear fabrics detailed examination of deformed calcite fibres shows strain partitioning into shortening normal to the fibres achieved by pressure solution by buckling of inclusion bands within the fibres and shear parallel to the fibre long axes folding of rocks with opposed directions of anisotropy may lead to discontinuities due to the incompatibility of the folding directions

high fidelity paleointensity determination from historic volcanoes in japan 1 providing high fidelity paleointensity estimates is pivotal to identify temporal fluctuation of ancient geomagnetic field despite abundance of available paleointensity data in japan only dozen of them satisfy modern standards with systematic alteration checks high fidelity paleointensity estimates were obtained from historic andesitic lavas collected from mt aso ojodake 700 bc mt kirishima iwoyama ad 1768 ohachi ad 1235 and mt sakurajima an ei ad 1779 nabeyama ad 764 766 variation of geomagnetic field intensity is distinctively different from the prediction of global models arch3k 1 cals3k 3 cals3k 4 cals7k 2 and cals10k 1b for the past 4000 years in japan the compilation of high fidelity thellier data set in japan showed two obvious high intensities at ad 590 765 and ad 1330 1435 and one low intensity at 700 bc these time intervals with anomalous high low intensities are nearly identical to three of the four potential archeomagnetic jerks recognized from the european archeomagnetic data implying that the archeomagnetic jerks were global or at least northern hemispheric features to improve the poor representation of regional geomagnetic field variation with respect to the global model prediction more high fidelity paleointensity determinations are required in east asia

procedures used for luminescence dating of sediments abstract an account of the procedures for thermoluminescence tl and optically stimulated luminescence osl dating of sediments used at the nordic laboratory for luminescence dating is given the topics discussed include sampling sample preparation separation of quartz and feldspars using heavy liquids dose rate estimation and methods for estimating the equivalent dose special attention is paid to the partial bleach tl technique of mejdahl 1988 which appears to give reliable results for partially bleached sediments optically stimulated luminescence dating using stimulation by infra red ir and green light has been taken up and especially added dose methods using stimulation by ir or green light have been tried with some success some sources of error are discussed including the adverse effect of shallow traps

emplacement history of pasupugallu gabbro pluton eastern ghats belt india a structural study structural mapping of the pasupugallu pluton an elliptical intrusive gabbro anorthosite body emplaced into the western contact zone between the eastern ghats mobile belt and the archaean east dharwar craton along the east coast of india reveals concentric helicoidal and inward dipping magmatic and or tectonic foliations we identify a 1 km wide structural aureole characterized by pronounced deflection of regional structures into margin parallel direction mylonitic foliations with s c fabrics sigmoidal clasts moderately plunging stretching lineations non cylindrical intrafolial folds and stretched elliptical mafic enclaves in the aureole rocks our results suggest that the pluton emplacement is syn tectonic with respect to the regional ductile deformation associated with the terrane boundary shear zone at the western margin of the eastern ghats we present a tectonic model for the emplacement of the pluton invoking shear related ductile deformation rotation and a minor component of lateral expansion of magma the intrusive activity 1450 800 ma along the western margin of the eastern ghats can be correlated with the significant event of recurring mafic alkaline and granitic magmatism throughout the global grenvillian orogens associated with the continent continent collision tectonics possibly related to the amalgamation and the breakup of the supercontinent rodinia

till fabric associated with deformable beds this paper investigates the development of till fabric associated with glaciers overlying deformable beds first the till fabrics from both modern and ancient soft bed and hard bed subglacial environments are investigated and then soft bedded sites with specific strain histories are examined the results indicate that lodgement tills had a strong fabric whilst there is a wide range of much weaker fabric strengths associated with soft bed tills it is suggested from a theoretical study of soft bed till deposition that longitudinal and vertical processes in the subglacial deforming layer are important in fabric development field sites were chosen to isolate these two factors and fabrics investigated in areas of known relative shear strain and known relative thickness of the deforming layer the results indicate that 1 for a fixed deforming layer fabric strength does increase with increasing deformation except at very high strains where the development of a transverse fabric can lead to a reduction in the overall fabric strain and 2 lodgement tills and soft bed tills associated with a thin deforming layer have a high fabric strength whilst soft bed tills associated with a thick deforming layer have a low fabric strength where the deforming layer is thin clasts are oriented parallel with the glacier direction either by lodging against a hard bed or ploughing against a soft bed however where the deforming layer is thicker and shear strains are high melt out processes encourage a parallel fabric but the increased shear strain and changes in the deforming layer thickness cause the clasts to develop both a parallel and transverse fabric these processes combine to reduce the overall fabric strength till fabric studies are a further sedimentological technique to separate the depositional processes associated with a homogeneous till

patterns of fold interference influence of early fold shapes abstract model experiments were specifically designed to test the effect of different profile shapes of early folds on refolding patterns comparison of natural examples with experimental results and analogy with engineering information on buckling of fold shapes suggest that when layers are mechanically active during refolding the profile shape of the early folds markedly affects the patterns of fold interference open rounded folds tend to refold to form dome and basin patterns of interference whereas isoclinal folds tend to refold by folding their axial plane forming type 2 patterns of interference hence the dimensions and shape of the profile of the early folds control the preferred buckling mode during refolding

sheeted and bulbous pluton intrusion mechanisms of a small granitoid from southeastern australia implications for dyke to pluton transformation during emplacement abstract the small late syn tectonic carboniferous davys creek granite dcg of southeastern australia consists of microgranitic intrusive bodies of diverse geometry and structure these bodies include 1 subvertical concordant sheets 2 bulbous peneconcordant plutons with apophyses and discordant lobes and 3 subvertical dykes and stocks the sequence of changing intrusive style is broadly 1 2 3 transition from 1 to 2 was probably a response to rising magma pressures or declining tectonic stresses the parameter of emerman and marrett 1990 which discriminates between stable sheet like and potential stock pluton batholith emplacement modes adequately predicts the transitions between sheet and pluton emplacements for the dcg ductile dyking along actively forming foliations appears to have been an important early intrusive mechanism a transition from sheet to bulbous pluton intrusion style is suggested to have been in response to magma pressure increases

esr dating of quaternary shells recent advances abstract this paper deals with the key problems of the esr dating of subfossil mollusc shells the estimation of the stored palaeodose of natural radiation it is shown that the use of the analytical line or peak in the integrated spectrum at g 2 0012 0 0001 with the half width 0 6 mt seems most advisable for the estimation of the relative concentration of radiation defects equivalent to the stored palaeodose in the calcareous shell skeleton optimal esr spectrometer settings have been determined results of esr dating of subfossil mollusc shells from eemian deposits of boreal transgression are discussed

s1 cleavage fans in the moselmulde of the rheinische schiefergebirge federal republic of germany may be due to a d3 tectonic event open folding and reverse faulting a major problem in the moselmulde is to explain the change in orientation of both s1 and s2 cleavages in distinct regional zones existing models used to explain this are not consistent with established field data penetrative s1 fabrics gradually change attitude in sections perpendicular to their regional sw ne strike involute constructions on s1 reveal an open fold structure that could explain the gradually changing attitude misfits in the fold profile coincide with sites where narrow s1 cleavage fans have been traces for over 50 km along strike in the field s3 fabrics discovered at two sites along one of the three regional s1 cleavage fans suggest that the fans are partly due to penetrative microfolding microshearing and pressure solution it is suggested here that the large scale structure of the moselmulde is essentially due to a deformational event d3 which caused apparent narrow cleavage fans along moderately nw dipping reverse faults the gradual change in attitude of the bedding s1 and s2 cleavage in the zones separated by the regional fans is due to open folding associated with the reverse fault motion the faults may be generated from a sole thrust which is reconstructed in my profiles at 10 to 15 km depth

tracking a non dipole geomagnetic anomaly using new archaeointensity results from north east china summary a collection of ceramics and samples collected from north east china with ages ranging from 1000 to 7000 years have been investigated using a modified version of the shaw palaeointensity techniques shaw 1974 rolph shaw 1985 in which only partial nrms and trms pnrms and ptrms with blocking temperatures t above 300 c are used after pre selection of samples by mineral magnetic analysis a secular variation curve obtained from this study is quite consistent with previous results from other areas of china wei et af 1987 tang et af 1991 as well as with the global model of mcelhinny senanayake 1982 comparison of the chinese results with contemporaneous results from greece aitken el af 1989 has allowed us to track the movement of a large non dipole anomaly as it drifts westwards

the interpretation and classification of subglacially deformed materials abstract a general classification of subglacially deformed materials is proposed based on sediment properties and their relationship to styles of subglacial strain deformation till is defined as homogenized usually diamictic material formed by glacially induced shear of subsole materials three types are recognized type a formed by pervasive ductile deformation type b formed by brittle shear and comminution till produced by the reduction of void space by in situ crushing and abrasion the term glacitectonite is adopted for materials that have undergone subglacial shear but retain some of the structural characteristics of the parent material original structures may be truncated by glacitectonic fabric elements type a or distorted but not truncated type b the principles of strain and material response particle orientation mechanisms fabric development and drainage conditions are reviewed examples of deformation tills and glacitectonites from breidamerkurjokull iceland slettmarkbreen norway loch lomond scotland and east yorkshire england are used to illustrate the nature of subglacially deformed materials and their relationship to former subglacial strain and drainage conditions the geologic evidence suggests a continuum of bed strengths can be recognized in deforming substrata ranging from high strength low strain type b deformation till and comminution till to low strength high strain type a deformation till

study of secular variation 2000 bc 1900 ad based on comparison of contemporaneous records in marine sediments and baked clays abstract paleomagnetic records derived from a marine sediment core for the region of the mouth of the yellow river are presented and compared with relevant archaeomagnetic results some characteristics of the secular variation of declination for the east asia region during the last 4500 yr are discussed

variations in the geomagnetic dipole moment over the last 12 000 years summary an analysis has been made of archaeointensity data for the past 12 000 years there are 3243 results from diverent areas of the world covering the past 12 000 years of these 2203 are from the european region and 1040 are from the rest of the world the archaeointensity data set analysed in the present study is almost three times larger than that used by mcelhinny senanayake 1982 although there is no major diverence between our global data and the earlier data the data for the non european region have been improved and we now have a data set for asia

vertical axis rotation associated with folding and thrusting an example from the eastern subbetic zone of southern spain the differential rotation about a vertical axis across a southeast vergent recumbent fold and thrust fault within a single nappe from the eastern subbetic zone of southern spain has been determined using paleomagnetism the upper limb has rotated clockwise by 68 22 relative to the lower limb mapping of the structure indicates that the syncline is an isoclinal fold in the northeast and an open fold in the southwest the differential vertical axis rotation across this structure appears to have been accommodated by a pro gressive increase in along strike horizontal shortening reaching 8 5 km at 3 7 km from the pivot point this differential shortening and the rotation are probably the result of increased drag on the underlying thrust close to the pivot point compared to the farthest extent of the structure the lateral boundary of the rotating sheet is a sinistral strike slip fault which is consistent with the rotational geometry pinning is probably enhanced by lateral heterogeneities within the stratigraphy this result ties rotational deformation to early middle miocene folding and thrusting rather than to late miocene holocene strike slip deformation rotation by pinning of thrust sheets may prove to be an important aspect of deformation in many fold and thrust belts

non glacial paleoenvironments and the extent of weichselian ice sheets on severnaya zemlya russian high arctic abstract the extent of the barents kara sea ice sheet northern europe and russia during the last glacial maximum lgm in marine isotope stage mis 2 is controversial especially along the southern and northeastern russian high arctic margins we conducted a multi disciplinary study of various organic and mineral fractions obtaining chronologies with 14 c and luminescence dating methods on a 10 5 m long core from changeable lake 4 km from the vavilov ice cap on severnaya zemlya the numeric ages indicate that the last glaciation at this site occurred during or prior to mis 5d 4 early middle weichselian deglaciation was followed by a marine transgression which affected the changeable lake basin after the regression the basin dried up in late middle weichselian time ca 25 40 ka reworked marine sediments were deposited in a saline water body during the late weichselian mis 2 the basin was not affected by glaciation and lacustrine sediments were formed which reflect cold and arid climate conditions during the termination of the pleistocene and into the holocene warmer and wetter climate conditions than before led to a higher sediment input thus our chronology demonstrates that the northeastern margin of the lgm barents kara sea ice sheet did not reach the changeable lake basin this result supports a modest model of the lgm ice sheet in northern europe determined from numeric ice sheet modelling and geological investigations

unravelling the spirals a serial thin section study and three dimensional computer aided reconstruction of spiral shaped inclusion trails in garnet porphyroblasts seventy seven spatially orientated serial thin sections cut from a single rock reveal changes in the geometry of spiral shaped inclusion trails sslts in garnet porphyroblasts the observed sits are doubly curved non cylindrical surfaces with total inclusion trail curvature decreasing systematically from the cores to the rims of porphyroblasts the three dimensional geometry of the ssits reconstructed with the aid of computer graphics shows that the orientations of spiral axes defined by the ssits are not related in any expected nor predictable way to the main foliation in the matrix this suggests continued deformation after or during the latest stages of porphyroblast growth which has important implications for the use of ssits as shear sense indicators whether the formation of ssits involves significant porphyroblast rotation with respect to a geographically fixed reference frame cannot be determined from the available data key wocds computer graphics garnet porphyroblasts serial thin sections spiral shaped inclusion trails three dimensional reconstruction

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

geomagnetic intensity variations for the past 8 kyr new archaeointensity results from eastern china abstract in this study we have carried out paleointensity experiments on 918 specimens spanning the last 7 kyr including pottery fragments baked clay and slag collected from shandong liaoning zhejiang and hebei provinces in china approximately half of the specimens yielded results that passed strict data selection criteria and give high fidelity paleointensities the virtual axial dipole moments vadms of our sites range from 2 10 22 to 13 10 22 am 2 at 2250 bce our results suggest a paleointensity low of 2 10 22 am 2 which increases to a high of 13 10 22 am 2 by 1300 bce this rapid less than 1000 yrs six fold change in the paleointensity may have important implications for the dynamics of core flow at this time our data from the last 3 kyr are generally in good agreement with the arch3k 1 model but deviate significantly at certain time periods from the cals3k 4 and cals10k 1b model which is likely due to differences in the data used to constrain these models at ages older than 3 ka where only the cals10k 1b model is available for comparison our data deviate significantly from the model combining our new results with the published data from china and japan we provide greatly improved constraints for the regional model of eastern asia when comparing the variations of geomagnetic field in three global representative areas of eastern asia the middle east and southern europe a common general trend of sinusoidal variations since 8 ka is shown likely dominated by the dipole component however significant disparities are revealed as well which we attribute to non dipolar components caused by movement of magnetic flux patches at the core mantle boundary

do principal surfaces of stress and strain always exist variations of stress and strain are commonly expressed by patterns of stress or strain trajectories three mutually orthogonal families of continuous lines parallel to maximum intermediate and minimum stress or strain axes it might be assumed that there are equivalent continuous principal surfaces of stress or strain for any state of continuously varying stress or strain we demonstrate that this will not generally be the case for three dimensionally varying states of stress or strain whether or not principal surfaces of stress or strain exist is governed by the abnormality of the vector field of principal trajectories we consider the z vector fields for examples of many types of three dimensional heterogeneous deformation and show that most of these do not lead to definable principal xy strain surfaces an alternative geometric test is presented termed the continuity loop for simply demonstrating the existence or not of principal surfaces using geometrical and orientational information it is important to the understanding of geological structures to know which kinds of heterogeneous deformation give rise to principal surfaces of stress or strain we conclude with examples of structures which might be indicative of the absence of continuous principal surfaces of stress segmented faults echelon veins and dykes a discussion of the implication for strain fabrics and foliations and a warning that foliation trace trajectories on maps or sections may not necessarily indicate the existence of real foliation surfaces in three dimensions

paleosecular variations refining the chronology of the sediments from the pearl river delta southern china a high resolution paleosecular variations record since 6 kyr including direction and relative intensity was derived from the pearl river delta prd sediments in southern china constrained by the radiocarbon ages in this paper the comparison of both direction and relative intensity with other adjacent records confirmed that the non dipole field has common fluctuations in the centennial to millennial timescales this pattern provides some profound tied points to correlate the sediment sequence in the different deposition environments the significant age offsets of the similar secular variation features between the different records corroborate the radiocarbon errors in dating the sediments this work further showed that the geomagnetic secular variations can serve as an effective tool to determine the sediments age and correlate the stratigraphy for the different deposition environments in a wide region

late quaternary stratigraphy of western yamal peninsula russia new constraints on the configuration of the eurasian ice sheet ice sheet reconstructions for the last glacial maximum in northern eurasia range from nearly complete coverage by a contiguous marine based ice sheet to large unglaciated areas stratigraphic records from yamal peninsula russia provide new insight on the eastern limit of the eurasian ice sheet in the kara sea radiocarbon and infrared stimulated luminescence ages from coastal cliff sections date the emplacement of the kara diamicton as older than ca 40 ka reflecting regional glaciation ice wedge growth peat accumulation and eolian and fluvial deposition characterized the past 40 k y and do not support coverage of yamal peninsula by an ice sheet or proximity to a glacier margin thus the late weichselian eurasian ice sheet was largely confined to barents sea and its global sea level contribution is reduced to 7 m of sea level equivalent

archaeomagnetic determination of the ancient intensity of the geomagnetic field in tamilnadu india abstract a detailed study of the ancient intensity of the earth s magnetic field in tamilnadu india is presented using pottery bricks tiles etc obtained from the excavations that have been carried out at some of the important places of historical and archaeological interest an attempt is made to reconstruct the secular variation of the geomagnetic field intensity the results reported here reveal considerable changes in the earth s magnetic field in this region during the past 2400 y it is observed that the intensity of the geomagnetic field has been previously 57 greater than at present

numerical reconstructions of the eurasian ice sheet and climate during the late weichselian abstract geological investigations undertaken through the quaternary environments of the eurasian north programme established ice sheet limits for the eurasian arctic at the last glacial maximum lgm sedimentary records of palaeo ice streams and uplift information relating to ice sheet configuration and the pattern of deglaciation ice sheet numerical modelling was used to reconstruct a history of the eurasian ice sheet compatible with these geological datasets the result was a quantitative assessment of the time dependent behaviour of the ice sheet its mass balance and climate and predictions of glaciological products including sediments icebergs and meltwater at the lgm ice cover was continuous from scandinavia to the arctic ocean margin of the barents sea to the north and the kara sea to the east in the west along the continental margin between the norwegian channel and svalbard the ice sheet was characterised by fast flowing ice streams occupying bathymetric troughs which fed large volumes of sediment to the continental margin that were deposited as a series of trough mouth fans ice streams may also have been present in bathymetric troughs to the north between svalbard and franz josef land further east however the ice sheet was thinner across the kara sea the ice thickness was predicted to be less than 300 m while on severnaya zemlya the ice cover may have been thinner at the lgm than at present it is likely that the taymyr peninsula was mainly free of ice at the lgm in the south the ice margin was located close to the shoreline of the russian mainland the climate associated with this ice sheet is maritime to the west and in stark contrast desert like in the east atmospheric general circulation modelling has revealed that such a contrast is possible under relatively warm north atlantic conditions because a circulation system develops across the kara sea isolating it from the moisture laden westerlies which are diverted to the south ice sheet decay began through enhanced iceberg calving in the deepest regions of the barents sea which caused a significant ice embayment within the bear island trough by about 12 000 years ago further iceberg calving reduced ice extent to the northern archipelagos and their surrounding shallow seas ice decay was complete by about 10 000 years ago

hydrography and mollusc faunas of the baltic and the white sea north sea seaway in the eemian abstract palynologically dated mollusc and cirriped faunas from a region extending from the north sea through the baltic and karelia to the arkhangelsk region show that the hydrography of the baltic was very different from the holocene for 2 2 5 ka in the early eemian a seaway existed from the barents to the north sea through karelia until it was severed at the present continental watershed to the north of lake onega after this the ladoga onega trough remained an arm of the baltic for several millennia the benthic faunas are comparable to the holocene but their boundaries were displaced much further into the baltic notable differences from the holocene are the absence or rarity of the macoma balthica biocoenosis and the presence of cold portlandia dominated biocoenoses in karelia in the belt sea and western baltic winter sea surface temperatures and salinity were higher than now by ca 6 c and 15 and the distinctly brackish top layer was missing at the same time cold bottom water 2 5 c with a tendency to anoxia characterised the karelian arm of the baltic water exchange through this area was inhibited by the constriction to the north of lake onega and the basin and threshold bathymetry water transport through the white sea baltic seaway was too sparse to play an active role in the north atlantic surface circulation or climatic change in the region the high salinity and temperature in the belt sea and western baltic persisted throughout the eemian and are explained by wider and deeper passage from the north sea to kattegat wider straits through denmark higher salinity in the north sea higher evaporation as well as more dispersed fresh water supply the advection of oceanic water into the baltic culminated in the early eemian before the carpinus zone and probably resulted in an oceanic climate in the baltic region while at the same time cold winters produced cold bottom water in the karelian arm

depositional history of the north taymyr ice marginal zone siberia a landsystem approach the sediment landform associations of the northern taymyr peninsula in arctic siberia tell a tale of ice sheets advancing from the kara sea shelf and inundating the peninsula probably three times during the weichselian in each case the ice sheet had a margin frozen to its bed and an interior moving over a deforming bed the north taymyr ice marginal zone ntz comprises ice marginal and supraglacial landsystems dominated by thrust block moraines 2 3 km wide and large scale deformation of sediments and ice large areas are still underlain by remnant glacier ice and a supraglacial landscape with numerous ice walled lakes and kames is forming even today the proglacial landsystem is characterised by subaqueous e g deltas or terrestrial e g sandar environments depending on location altitude and time of formation dating results osl c 14 indicate that the ntz was initiated ca 80 kyr bp during the retreat of the early weichselian ice sheet and that it records the maximum limit of a middle weichselian glaciation ca 65 kyr bp during both these events proglacial lakes were dammed by the ice sheets part of the ntz was occupied by a thin late weichselian ice sheet 20 12 kyr bp resulting in subaerial proglacial drainage copyright c 2002 john wiley sons ltd

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

magnetic fabric of the řicany granite bohemian massif a record of helical magma flow abstract a highly unusual fabric pattern and inferred flow mechanism was discovered in the shallow level icany granite pluton bohemian massif using an integrated structural and anisotropy of magnetic susceptibility ams study the pluton consists of an outer strongly porphyritic and an inner weakly porphyritic biotite granite separated by a wide gradational contact both varieties share a steep margin parallel magmatic foliation defined by k feldspar phenocrysts and biotite and magnetic ams foliation carried by biotite the steep foliation bears a shallowly plunging magnetic lineation arranged parallel to the circumference of the pluton margin and a steep magnetic lineation in the weakly porphyritic pluton center we propose a new mechanism of magma flow in which the bulk ascent along a steep sided cylindrical conduit was partitioned into a high viscosity phenocryst rich outer margin flowing helically and a low viscosity phenocryst poor center flowing vertically this interpretation is supported quantitatively by a simple model of magma flow within a cylindrical pipe in which the linear decrease in phenocryst content from the pluton margin inwards causes a power law decrease in the effective viscosity of the magma according to the poiseuille equation such a power law viscosity distribution across the conduit produces a central zone of high magma ascent velocity the magnetic ams fabric pattern in the icany pluton may thus preserve a record of helical magma ascent driven by viscosity partitioning in a steep sided conduit which presumably linked an underlying magma chamber with a volcanic feeder at the surface except for one deep seated granite migmatite complex no such helical fabric pattern has been documented in a granite pluton as of yet we propose that the viscosity partitioned helical flow may be a more common magma ascent mechanism in shallow level volcano plutonic systems than previously envisaged

deep drilling of glaciers in eurasian arctic as a source of paleoclimatic records abstract results of the deep drilling 80 100 m of eurasian arctic glaciers svalbard severnaya zemlya and franz josef land from the middle of the 1970s to the end of the 1990s have been discussed all spectra of the techniques used for ice core and borehole studies results of ice core dating and major paleoclimatic conclusions have been analyzed particular emphasis has been placed on the problem of accuracy and comparison of dates suggested by different authors new integrated time scale for eurasian arctic glaciers based on the ice core dating of vetreniy ice cap graham bell island and franz josef land which covers the last 700 800 years has been developed methods and results of the new paleo temperature reconstructions have been analyzed

structures indicative of helicoidal flow in a migmatitic diapir bacao complex southeastern brazil abstract the migmatitic bacao complex southeastern brazil shows foliation and lineation patterns that depict an internal flow structure with helicoidal geometry microstructures show that a rheological transition exists from a predominantly magmatic flow represented by isotropic undeformed granitic textures to solid state flow mylonites towards the diapir margins nebulites and contorted migmatites occur in the diapir core whereas the peripheral domains show different kinds of banded migmatites gneisses and high temperature mylonites along the margins low temperature mica rich mylonites and phyllonites occur two major flow domains were recognized the central cell and the peripheral cell each cell is characterized by one or more systems of concentric foliations subcells the mineral lineation produced by the morphological alignment of biotite flakes on the foliation planes defines helicoidal geometries in all subcells this lineation was interpreted as being parallel to the local flow vector the foliation and lineation patterns suggest that the principal ascent trunk occurred along a medium plunge spiral in the central cell a dip flow regime the constant injection of molten material in the central cell pushed the material previously emplaced into the peripheral cell where flow upwards continued through a shallower plunge spiral a strike flow regime

secular variation of the direction of the ancient geomagnetic field for loyang region china abstract curves of the variation of the inclination and declination of the geomagnetic field for the loyang region during the last 2400 years are presented an i d diagram of secular variation like that for london has been drawn for loyang

globally strong geomagnetic field intensity circa 3000 years ago abstract high fidelity geomagnetic field intensity determination was carried out using 191 baked fragments collected from 20 kilns or hearths with ages ranging between 1200 bc and ad 1725 in south korea geomagnetic field intensity variation displayed three narrow minima at 800 700 bc ad 700 and ad 1600 and two maxima at 1200 1100 bc and ad 1000 1100 in most time intervals virtual axial dipole moment vadm variation is confined within 20 of the present vadm however geomagnetic field intensity circa 3000 yr ago is nearly 40 larger than the present value such high vadms circa 3000 yr ago are in phase with those in other longitudinal bands in northern hemisphere centered at 5e france 30e the middle east and 200e hawaii although strong geomagnetic field intensity circa 3000 yr ago is globally synchronous the highest vadm occurs at slightly different time intervals in different locations hence it is possible that the globally strong geomagnetic field intensity circa 3000 yr ago reflects the migration of persistent hemispheric flux in northern hemisphere or an episode of geomagnetic field hemispheric asymmetry

discontinuous fault zones abstract many tectonic faults and tension fractures are at least initially composed of separate segments this note deals with a little explored reason for this phenomenon which in faulting has obvious implications both for the migration of hydrocarbons and for the sealing capacity of faults theoretical arguments based on coulombmohr s theory of shear failure and on a theorem for the integrability of vector fields lead to the expectation that in general non uniform and truly three dimensional stress fields will impede the formation of smooth coherent fault surfaces this is in contrast to the stress fields that are associated with plane deformation examples are given and special attention is drawn to the role of tectonic stress fields with horizontal principal stresses that change with depth in magnitude and direction

late weichselian ice sheets in arctic and pacific siberia abstract interpretation of space images coupled with field data on glacial geomorphology and glacial geology of northern eurasia have provided compelling evidence for a continuous late weichselian ice sheet covering the entire arctic margin of the continent in addition to the scandinavian ice sheet three ice sheets of the same order the karan east siberian and beringian are identified within the major eurasian ice sheet also there is evidence and other considerations suggesting a former ice sheet in the sea of okhotsk ice spreading centers of the ice sheets were situated on the continental shelves off the siberian coasts thus we can term the ice sheets siberian so far the conventional stratigraphic approach to the problem of siberian glaciation has proven fruitless and yielded nothing but uncertainty while geomorphological studies have discovered a wealth of glacial landforms in arctic siberia it was these landforms and their spacing that made the existence of former siberian ice sheets evident the east siberian ice sheet rested on the shelves of the eastern laptev and east siberian seas and its flow was directed radially including up the yana and indigirka rivers the beringian ice sheet was grounded on the chukchi bering and beaufort sea shelves overriding the chukchi and seward peninsulas from the north and flowing through the bering strait it was continued by a thick floating ice shelf buttressed by the submarine aleutian commander ridge the okhotsk ice sheet was grounded on the okhotsk shelf specific gemorphic signatures of marine ice sheets the glacially cut corners have been identified on all promontories jutting out into the bering and okhotsk seas the beringian and okhotsk ice sheets are consistent with the results of deep sea drilling in the adjacent north pacific during leg 145 of d v joides resolution

severnaya zemlya arctic russia a nucleation area for kara sea ice sheets during the middle to late quaternary quaternary glacial stratigraphy and relative sea level changes reveal at least four expansions of the kara sea ice sheet over the severnaya zemlya archipelago at 79 degrees n in the russian arctic as indicated from tills interbedded with marine sediments exposed in stratigraphic superposition and from raised beach sequences that occur at altitudes up to 140 m a s l chronologic control is provided by ams c 14 electron spin resonance green stimulated luminescence and aspartic acid geochronology major glaciations followed by deglaciation and marine inundation occurred during mis 10 9 mis 8 7 mis 6 5e and mis 5d 3 the mis 6 5e event associated with the high marine limit implies ice sheet thickness of 2000m only 200km from the deep arctic ocean consistent with published evidence of ice grounding at similar to 1000m water depth in the central arctic ocean till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively suggesting wet based ice cap advance followed by cold based regional ice sheet expansion local ice caps over highland sites along the perimeter of the shallow kara sea including the byrranga mountains appear to have repeatedly fostered initiation of a large kara sea ice sheet with exception of the last glacial maximum mis 2 when kara sea ice did not impact severnaya zemlya and barely graced northernmost taymyr peninsula

the last ice sheet of the kara sea terrestrial constraints on its age abstract the ice dispersal features on the siberian mainland unanimously indicate that the last ice domes were positioned on the kara sea shelf and adjacent coastal plains the age of the last glacial maximum evokes much controversy the problem may be solved by sorting out the available radiocarbon dates both statistically and using geological common sense over 200 finite radiocarbon dates have been analysed 77 of the entire population represent sediments overlying the topmost till including dating the most reliable organics such as mammoth remains the rest of the dates 23 have been obtained from the underlying sediments mostly on materials readily prone to redeposition and contamination such as driftwood and shells the last culmination of the shelf ice sheet must have occurred beyond the range of the conventional radiocarbon method and after the last warm water sea transgression correlative to the eemian the early weichselian age for the last kara sea ice sheet is also supported by the lack of proglacial lacustrine sediments with finite radiocarbon dates in periglacial west siberia