late quaternary geomagnetic secular variation from historical and 14c dated lava flows on hawaii a paleomagnetic record of geomagnetic paleosecular variation psv is constructed for the last 4400 years based on 191 sites in historical and 14c dated lava flows from mauna loa kilauea and hualalai volcanoes on the island of hawaii the features of this new record are similar to those recorded by sediments from lake waiau near the summit of mauna kea volcano but overall mean inclinations for the lava flows 31 to 33 depending on window size are nearer the expected dipole field value 35 than is that for the sediments 27 divergence of the inclination records with increasing age suggests that the lake waiau values at depths below 2 m have been affected by compaction related inclination shallowing although magnetic terrain effects cannot be ruled out the rate of psv indicated by the record presented here is highly variable 20 century and a pronounced shift in inclination from 25 to 40 occurred between 1030 and 975 years b p paleomagnetic directions from undated materials can be correlated with our calibrated curve but the resolution is largely dependent on the psv rate and data densities for both the reference and unknown directions the upper part of the puna basalt 18 lava flows previously sampled for paleomagnetism along the northern wall of kilauea s caldera uwekahuna bluff was likely deposited sometime between 1030 and 750 years b p but the lowest two flows beneath the uwekahuna ash 2100 years b p are correlated with an age of 3034 years b p paleomagnetic data for 54 lava flows of the ka u basalt exposed in the northwest wall of mauna loa s summit caldera mokuaweoweo indicate that they probably accumulated over a relatively short time interval 200 years and are assigned to a 1000 to 1199 year b p time window the mean of ages within this window is 1030 years b p but mapping and other 14c dates indicate that these summit overflows are probably closer to 1200 years b p in age

latest pleistocene and holocene geomagnetic paleointensity on hawaii geomagnetic paleointensity determinations from radiocarbon dated lava flows on the island of hawaii provide an estimate of broad trends in paleointensity for holocene time and offer a glimpse of intensity variations near the end of the last glacial period when the data from hawaii are compared with others worldwide the intensity of the geomagnetic field seems to have been reduced from the holocene average by about 35 percent between 45 000 and 10 000 years ago a long term reduction of this magnitude is compatible with reported increases in the production rate of cosmogenic nuclides during the same interval

along strike variation in the stratigraphical and structural profile of the southern uplands central belt in galloway and down the modern interpretation of the southern uplands depends on the recognition of laterally extensive linear fault bounded tracts of northward younging lower palaeozoic sediments with rare volcanics the tracts become progressively younger southwards and are thought to have been sequentially accreted by northward underthrusting above a subduction zone detailed mapping and tentative correlation of three well exposed coastal profiles through the central belt in sw scotland and ne ireland offers a new test of the southern uplands model comparison of the northern parts of each section indicates the presence of strike parallel tracts with model structure moffat shale outcrops associated with the tract defining faults demonstrate a diachronous incremental southerly decrease in the age of the base of the overlying turbidites essentially as in the northern belt southward this becomes markedly less pronounced particularly in down where the central belt is much wider than in galloway distinctive hawick group lithologies permit the correlation of the southern parts of the sections large areas of predominantly southward younging occur in each section especially in galloway where the southward younging area is 12 km across here northerly verging d 1 fold pairs are consistent with observed fault movement opposite in sense to the northerly underthrusting of the model back thrusting in the style of the pleistocene cascadia basin is invoked to account for the landward verging structure of these areas and to explain the narrowing of the central belt in galloway the structure of the central belt thus differs significantly from that of the northern belt and the accretionary prism model

geomagnetic intensity spike recorded in high resolution slag deposit in southern jordan article i nfo in paleomagnetism periods of high field intensity have been largely ignored in favor of the more spectacular directional changes associated with low field intensity periods of excursions and reversals hence questions such as how strong the field can get and how fast changes occur are still open in this paper we report on data obtained from an archaeometallurgical excavation in the middle east designed specifically for archaeomagnetic sampling we measured 342 specimens from 72 samples collected from a 6 1 m mound of well stratified copper production debris at the early iron age 12th 9th centuries bce site of khirbat en nahas in southern jordan seventeen samples spanning 200 yr yielded excellent archaeointensity results that demonstrate rapid changes in field intensity in a period of overall high field values the results display a remarkable spike in field strength with sample mean values of over 120 t compared to the current field strength of 44 t a suite of 13 radiocarbon dates intimately associated with our samples tight control of sample location and relative stratigraphy provide tight constraints on the rate and magnitude of changes in archaeomagnetic field intensities

broad trends in geomagnetic paleointensity on hawaii during holocene time paleointensity determinations have been obtained from 22 basaltic lava flows on the island of hawaii using the thelliers method radiocarbon dating indicates that these flows erupted at intervals ranging from about 200 to 1000 years and results of the experiments provide an estimate of broad trends in geomagnetic paleointensity during holocene time in the vicinity of hawaii most of the samples were obtained from quickly cooled flow margins and as a consequence typically contain two titanomagnetite populations only two of the 79 samples analyzed failed to yield an estimate of the paleofield demonstrating that paleointensities can be obtained from such samples if carefully selected virtual dipole moments calculated for the flows are compared with a published curve of dipole field intensity that was constructed using worldwide archeomagnetic data the large nondipole fields that were previously postulated for the vicinity of hawaii are confirmed and the present data indicate that they were present from about 5000 years b p to perhaps as recently as the past 200 years the data indicate however that these nondipole sources must have been virtually absent between about 12 000 and 5000 years b p as they are at the present time

paleomagnetic correlation of late quaternary lava flows in the lower east rift zone of kilauea volcano hawaii paleomagnetic data reflecting paleosecular variation psv of the geomagnetic field are used to correlate individual lava flows in the lower east rift zone of kilauea volcano this area has been recently mapped based on petrography stratigraphy soil development and degree of weathering of the flows eight 14c dates also provide a framework for the relative age assignments site mean directions of remanent magnetization for historic flows in this region indicate that local magnetic anomalies do not mask the psv signal that within flow angular differences are generally 5 and that temporal resolution of the paleomagnetic directions is of the order of 100 years the paleomagnetic correlations do not conflict with the observed stratigraphic relationships and psv reference curves from dated lava flows and lake sediments have also been used to help determine the sequence of directional groups paleomagnetic grouping of flows into eruptive events indicates a different and perhaps more refined eruptive history for the lower east rift zone than implied by the geologic mapping alone the number of individual flows based on petrographic distinctions is likely the same but the frequency of events including petrographically distinct flows is apparently lower than previously thought flows from ridge crest vents bifurcated by the rift indicate formation of the central graben in this region after 300 years ago possibly related to the 1790 eruptions along dual fractures

palaeointensity study of the hawaiian 1960 lava implications for possible causes of erroneously high intensities summary it is known that the hawaiian 1960 lava sometimes yields higher palaeointensities than the igrf 36 2 t in order to clarify the causes we have performed a comprehensive investigation of palaeointensity measurements on 19 cores from the lava according to various rock magnetic analyses they are classified into three groups with degrees of the deuteric oxidation in coe s version of the thellier method a significantly larger mean palaeointensity of 49 0 9 6 t n 17 was observed similar to previous studies these palaeointensities showed a dependence on the oxidation indices which can be explained by thermochemical remanent magnetization tcrm acquisition during the natural cooling stage of the lava although it is generally difficult to distinguish the tcrm from thermoremanent magnetization trm a lowtemperature demagnetization ltd treatment on nrm and trm in the thellier experiment seems to allow us to detect the influence of the tcrm on nrm another possible tool for tcrm detection is the double heating technique dht of the shaw method combined with ltd ltd dht shaw method it gave a better average of 39 4 7 9 t n 9 though the success rate was much lower most of the inappropriate results were screened by a combination of the double heating test the arm correction and the ltd treatment if two outliers are further excluded the average is improved to be 35 7 3 3 t n 7 which agrees well with the expected intensity the results of both methods emphasize the importance of taking and measuring samples from the parts of various oxidation degrees in a lava flow

how fast does rock varnish grow rates of rock varnish accumulation have never been systematically documented owing to the difficulty in accurately determining both varnish thickness and age in this study we quantitatively assess varnish accumulation rates through thin sectioning and microscopic examination of rock varnish from radiometrically dated geomorphic features of late quaternary age in the western united states drylands our data indicate that rock varnish grows at rates ranging from 1 to 40 m k y on subaerially exposed rock surfaces and rarely reaches a thickness exceeding 200 m regardless of age our data also indicate that varnish accumulation rates vary greatly from sample to sample at a given site suggesting that varnish thickness does not correlate with the age of the associated geomorphic feature invalidating the potential use of varnish thickness as a relative age indicator in geomorphology and archaeology nevertheless being the slowest known accumulating terrestrial sedimentary deposit rock varnish constitutes a unique long term microscale sedimentary archive of past environmental changes in deserts

improvements in procedure and paleointensity selection criteria picrit 03 for thellier and thellier determinations application to hawaiian basaltic long cores abstract in this paper we first describe the paleointensity furnaces and the procedures specifically designed to minimize oxidation of the samples during thellier and thellier paleointensity experiments routinely used at gif we also propose some improvements to the set of criteria commonly used to select the results of the thellier experiments in order to further increase the reliability of paleointensity determination finally to be included in databases the new set of paleointensity criteria picrit 03 paleointensity criteria in 2003 is discussed and the results obtained from two long hawaiian basaltic cores the scientific observation hole 4 soh 4 and the hawaiian scientific drilling project 1 hsdp1 are used to illustrate its effectiveness some of the results are re evaluated and a new composite record of absolute paleointensity and inclination spanning 420 kyr is presented the inclination values obtained from the two cores combined support the hypothesis of persistent shallow inclinations at hawaii in intensity the upper 100 kyr are covered by the data from soh 4 with 309 reliable determinations out of 766 examined obtained from 143 units which belong to the kilauea volcano at the top of this core the 341 reliable data covering the 100 420 kyr interval are from 149 units of core hsdp1 belonging to the mauna kea volcano the interval 320 to 420 kyr is particularly detailed because of high extrusion rate of the volcano the use of more stringent criteria decreases the number of determinations considered as reliable in previous publications but it improves their accuracy and robustness

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

interaction between faulting and sedimentation during dinantian extension of the solway basin sw scotland the ene wsw trending north solway fault acted as a northern marginal fault to the solway basin during dinantian sedimentation structural sedimentological and diagenetic relationships suggest syn sedimentary dinantian movement was dip slip and normal a later carboniferous phase of dextral transtension is also indicated allokinetic deformation features increase in abundance and intensity towards the north solway fault their presence and nature being strongly facies dependent syn sedimentary fault deformation of the hanging wall sediments also increases towards this fault both distributed and localized shearing characterizes these early faults and is thought to be related to the water content of beds at the time of deformation local minor thrusting and reverse fault movement also occurred within the sediments during basin extension due to dextral transtensional movement on the north solway fault n s and nw se trending faults appear to show no evidence for syn sedimentary dinantian movement and are interpreted as the products of 9hercynian9 basin shortening and mesozoic basin formation

factors controlling tungsten concentrations in ground water carson desert nevada an investigation of a childhood leukemia cluster by us centers for disease control and prevention revealed that residents of the carson desert nevada are exposed to high levels of w and this prompted an investigation of w in aquifers used as drinking water sources tungsten concentrations in 100 ground water samples from all aquifers used as drinking water sources in the area ranged from 0 27 to 742 g l ground water in which w concentrations exceed 50 g l principally occurs se of fallon in a geothermal area the principal sources of w in ground water are natural and include erosion of w bearing mineral deposits in the carson river watershed upstream of fallon and possibly upwelling geothermal waters ground water in the fallon area is strongly reducing and reductive dissolution of fe and mn oxyhydroxides may be releasing w however direct evidence that the metal oxides contain w is not available although w and cl concentrations in the carson river a lake and water from many wells appear to be controlled by evaporative concentration evaporation alone cannot explain the elevated w concentrations found in water from some of the wells concentrations of w exceeding 50 g l are exclusively associated with na hco3na hco3 and na cl water types and ph 8 0 in these waters geochemical modeling indicates that w exhibits 10 adsorption tungsten concentrations are strongly and positively correlated with as b f and p indicating either common sources or common processes controlling their concentrations geochemical modeling indicates w concentrations are consistent with ph controlled adsorption of w the geochemical model phreeqc was used to calculate iap values which were compared with published ksp values for primary w minerals fewo4 mnwo4 na2wo4 and mgwo4 were undersaturated and cawo4 and srwo4 were approaching saturation these conclusions are tentative because of uncertainty in the thermodynamic data the similar behavior of as and w observed in this study suggests ground water in areas where elevated as concentrations are present also may contain elevated w concentrations particularly if there is a mineral or geothermal source of w and reducing conditions develop in the aquifer

new and revised 14c dates for hawaiian surface lava flows paleomagnetic and geomagnetic implications radiocarbon dates have been obtained for 30 charcoal samples corresponding to 27 surface lava flows from the mauna loa and kilauea volcanoes on the island of hawaii the submitted charcoal was a mixture of fresh and archived material preparation and analysis was undertaken at the nerc radiocarbon laboratory in glasgow scotland and the associated suerc accelerator mass spectrometry facility the resulting dates range from 390 years b p to 12 910 years b p with corresponding error bars an order of magnitude smaller than previously obtained using the gas counting method the new and revised 14c data set can aid hazard and risk assessment on the island the data presented here also have implications for geomagnetic modelling which at present is limited by large dating errors

tectono magmatic controls of post subduction gold mineralisation during late caledonian soft continental collision in the southern uplands down longford terrane britain and ireland a review abstract the southern uplands down longford terrane sudlt within the british caledonides hosts several economically significant gold occurrences including a 45 km long gold trend in central ireland that includes the proven deposit at clontibret however the region is relatively underexplored for gold and the well constrained geology and tectonic history of the terrane provide a firm geological framework for investigating the roles of tectonic magmatic and metamorphic processes in gold mineralisation during the transition from subduction of oceanic lithosphere to soft thin skinned continental collision the sudlt is an ordovician silurian fore arc accretionary complex that evolved into a foreland basin fold and thrust belt during continental collision in earliest devonian times comparable terranes in phanerozoic orogenic belts globally host significant orogenic gold deposits however the sudlt exhibits a very low metamorphic grade and mineralisation exhibits similarities with orogenic intrusion related and post subduction porphyry gold systems gold in the sudlt predominantly occurs as a lattice constituent of arsenopyrite and pyrite within quartz carbonate veins and disseminated within phyllic and propylitic potassic alteration haloes around quartz carbonate veins and some minor intrusions fluid inclusion data indicate that the gold was deposited from a low salinity mesothermal 330 c carbonic fluid of mixed magmatic metamorphic origin consistent with caledonian orogenic conditions gold mineralisation occurred at shallow crustal depths of less than 10 km and exhibits a broad spatial association with major ne sw trending caledonoid shear zones d1 economically significant gold mineralisation in the sudlt is most commonly hosted by transverse nw se and n s trending fractures d3 constrained to between 418 and 410 ma that cut anchizone epizone facies volcaniclastic turbiditic metasedimentary host rocks the mineralised d3 structures cut and are cut by broadly coeval polyphase diorite and granodiorite intrusions gold mineralisation is associated with the early dioritic i type metaluminous oxidised phase of trans suture suite magmatism that straddles the iapetus suture but predates the later emplacement of s type granitic magma the host structures were subsequently reactivated during late palaeozoic mesozoic and cenozoic times and host younger base metal deposits pb zn cu sn sb mineralisation occurred in early devonian times 418 and 410 ma following arrival of the avalonian continental margin at the subduction trench at 420 ma coeval with the onset of regional transtension post subduction lithospheric mantle delamination and k lamprophyric and mafic to intermediate calc alkaline magmatism gold in the sudlt therefore provides a case study for relationships between post subduction porphyry and orogenic gold mineralisation in soft continental collision zones the transient geodynamic setting between subduction and transtension common during soft continental collision provided the critical elements of the mineralising system a metasomatically fertilised mantle source transient geodynamics favourable lithospheric architecture for the rapid transfer of mass and energy from subcrustal to upper crustal levels thin skinned deformation and relatively low exhumation favours the preservation of mineral deposits in the upper crust

the structure and evolution of the northumberland trough from new seismic reflection data and its bearing on modes of continental extension an 18 km long n s seismic reflection profile has been acquired across the faulted boundary between the alston block and the northumberland trough a nw se geological cross section has been constructed across the trough by integrating this line with other data and a tricentrol seismic profile confirms the suitability of this model the trough has a markedly asymmetric form with a thickness of more than 4 2 km of dinantian strata adjacent to its faulted southern margin the present day surface faults stublick ninety fathom are related to variscan and later inversion and transpression and do not everywhere correspond precisely to the earlier syn depositional normal faults the basin is believed to have formed in response to reactivation of the iapetus suture in a dominantly n s extensional stress field basin evolution has been analysed by fault restorations and subsidence modelling the fault restorations indicate an upper crustal extension factor of 1 15 to 1 19 subsidence modelling indicates a whole crustal extension factor of 1 30 with similar sub crustal lithospheric extension it is possible that the difference between the inferred extension factors is due to non uniform increasing downwards lithospheric extension but the uncertainties inherent in both methods are such that this cannot yet be confirmed

paleointensity determination from sao miguel azores archipelago over the last 3 ka elsevier editorial system tm for physics of the earth and planetary interiors manuscript draft manuscript number pepi d 14 00015 title paleointensity determination from sao miguel azores archipelago over the last 3 ka article type research paper keywords paleomagnetism paleointensity azores atlantic ocean global spike corresponding author dr anita di chiara corresponding author s institution usp first author anita di chiara order of authors anita di chiara lisa tauxe prof fabio speranza dr abstract paleointensity data from the atlantic ocean are rare we present new paleointensity data from sao miguel azores islands portugal based on 20 paleomagnetic sites from 13 lava flows emplaced over the last 3 000 years ten lava flows are radiocarbon dated moore 1990 1991 moore and rubin 1991 whereas three flows were archeomagnetically dated by di chiara et al 2012 and one site was dated using stratigraphic relations all the samples previously investigated to recover paleodirections di chiara et al 2012 were subjected to izzi experiments importantly the new data are internally consistent agree with moroccan and european datasets and offer new constraints for cals style models e g korte and constable 2011 the inferred virtual axial dipole moments vadms range from 68 2 zam2 and 163 5 zam2 a peak in field strength with an estimated age of around 600 bce is well supported by two sites from the same flow furna and is comparable to the spike of intensity found in portugal of the same age nachasova et al 2009 and at about 1000 bce in the levant ben yosef et al 2009 shaar et al 2011 a gradient in vadm values with latitude observed by mitra et al 2013 between 100 to 1000 ad is confirmed as well as its absence from between 0 to 100 ad

holocene paleointensity of the island of hawai i from glassy volcanics this study presents new high quality paleointensity records and 14c radiocarbon age determinations from the island of hawai i during the holocene previous studies on hawai i use experimental methods and statistical selection criteria that may produce inaccurate geomagnetic field strength estimates additional high quality paleointensity results can be used to evaluate the existing hawaiian dataset and investigate holocene geomagnetic field behavior new paleointensity sites from 22 lava flows were calculated using the izzi thellier laboratory technique and a strict set of selection criteria rapidly cooled glassy volcanic material was collected for all sites isotopic age determinations range from 270 10 000 years before present nine new 14c ages are also presented as part of this study the median intensity for the 22 flows is 47 5 t with a median absolute deviation uncertainty of 5 6 t substantially greater than the present day field strength at hawai i 36 t these new results are comparable to previously published data from this location and are consistent with global paleointensity models there is no evidence of an intensity spike at 3 000 years before present as seen in the levant and elsewhere previously published data vary in intensity by experimental technique relative to data using glassy material and strict selection criteria non thellier type data are biased low a result of these techniques estimating intensity from possibly non single domain magnetic carriers thellier thellier data are biased high the reasons for which remain unclear as no cooling rate effect was demonstrated and we were unable to reproduce the high bias with different selection criteria

geochronology of carboniferous permian magmatism in the midland valley of scotland implications for regional tectonomagmatic evolution and the numerical time scale four new u pb isotope dilution thermal ionization mass spectrometry dates from carboniferous igneous rocks of the midland valley of scotland are integrated with 16 recently published 40ar 39ar dates the numerical and stratigraphical ages of the dated samples are compatible to stage level allowing improved intrabasinal and regional correlations early carboniferous extension related volcanism in the midland valley was pulsed with a date of 343 4 1 0 ma from the garleton hills volcanic formation and dates of 334 7 1 7 and 335 2 0 8 ma from the clyde plateau volcanic formation the magmatic pulses are synchronous with synrift phases in the northumberland solway basin volcanism continued in mid to late carboniferous time contemporaneous with dextral strike slip tectonics in contrast to a post rift tectonic setting in northern england after late carboniferous basin inversion tholeiitic magmatism dated at 307 6 4 8 ma provides a maximum westphalian d age for post variscan magmatism and extension dextral transtension across scotland and northern england in the early permian as rift systems developed across nw europe alkaline extension related magmatism resumed in the midland valley from c 298 to 292 ma the improved geochronology provides important data for poorly constrained parts of the numerical carboniferous time scale such as stages within the visean and provides a well controlled tie point that supports a tournaisian visean boundary age of c 345 4 ma

absolute paleointensity from hawaiian lavas younger than 35 ka abstract paleointensity studies have been conducted in air and in argon atmosphere on nine lava flows with radiocarbon ages distributed between 3 3 and 28 2 ka from the mauna loa volcano in the big island of hawaii determinations of paleointensity obtained at eight sites depict the same overall pattern as the previous results for the same period in hawaii although the overall average field intensity appears to be lower since the present results were determined at higher temperatures than in the previous studies this discrepancy raises questions regarding the selection of low versus high temperature segments that are usually made for absolute paleointensity the virtual dipole moments are similar to those displayed by the worldwide data set obtained from dated lava flows when averaged within finite time intervals the worldwide values match nicely the variations of the sint 200 synthetic record of relative paleointensity and confirm the overall decrease of the dipole field intensity during most of this period the convergence between the existing records at hawaii and the rest of the world does not favour the presence of persistent strong non dipole components beneath hawaii for this period

a 20 15 ka high resolution paleomagnetic secular variation record from black sea sediments no evidence for the hilina pali excursion abstract a comprehensive magnetostratigraphic investigation on sixteen sediment cores from the southeastern black sea yielded a very detailed high quality paleosecular variation psv record spanning from 20 to 15 ka the age models are based on radiocarbon dating stratigraphic correlation and tephrochronology further age constraints were obtained by correlating four meltwater events described from the western black sea ranging in age from about 17 to 15 ka with maxima in k ti ratios obtained from x ray fluorescence xrf scanning and minima in s ratios reflecting increased hematite content in the studied cores since the sedimentation rates in the investigated time window are up to 50 cm ka 1 the obtained psvs records enabled a stacking using 50 yr bins a directional anomaly at 18 5 ka associated with pronounced swings in inclination and declination as well as a low in relative paleointensity rpi is probably contemporaneous with the hilina pali excursion originally reported from hawaiian lava flows however virtual geomagnetic poles vgps calculated from black sea sediments are not located at latitudes lower than 60 n which denotes normal though pronounced secular variations during the postulated hilina pali excursion the vgps calculated from black sea data migrated clockwise only along the coasts of the arctic ocean from ne canada 20 0 ka via alaska 18 6 ka and ne siberia 18 0 ka to svalbard 17 0 ka then looping clockwise through the eastern arctic ocean

the effects of secondary mineral formation on coe type paleointensity determinations theory and simulation thellier type experiments are the most widely applied approaches for determining the absolute paleointensities of earth s magnetic field one major problem however is that specimens are prone to thermal alteration due to the intensive thermal treatment during experiments linear arai plots with acceptable partial thermal remanent magnetization ptrm checks have been considered as evidence for the absence of or negligible effects of thermal alteration and as reliable indicators of high quality paleointensity estimates however by simulating the coe variant of the thellier method on assemblages of single domain sd magnetite particles it is demonstrated that new magnetic minerals which form during thermal treatments can result in linear concave up or concave down arai plots depending on the magnetic properties of both the primary and secondary magnetic phases among this range of behavior pseudoideal arai plots which are linear with acceptable ptrm check statistics would lead to paleointensity underestimates it is further demonstrated that ptrm checks are proportional to the degree of underestimate with a magnetic granulometry dependency for sd particles due to the complexity of this dependency ptrm check statistics are only comparable when specimens have similar magnetic properties this suggests that a universal threshold for ptrm check statistics is not likely to be effective since the criteria of linearity and low ptrm check statistics are insufficient to guarantee the fidelity of the estimates auxiliary rock magnetic methods such as temperature dependent hysteresis parameters and anhysteretic remanent magnetization are highly recommended to identify the presence of alteration

high intensity geomagnetic field spike observed at ca 3000 cal bp in texas usa abstract by observing the fluctuations in direction and intensity of the earth s magnetic field through time we increase our understanding of the fluid motions of the earth s outer core that sustain the geomagnetic field the geodynamo recent archaeomagnetic studies in the near east have found extremely rapid increases spikes in geomagnetic field intensity at ca 3000 yr cal bp these observations have proved problematic for our current understanding of core flow however until now these geomagnetic spikes had not been observed outside of the near east where they have been preserved in metallurgical slag and fired mud brick walls we present a new fully oriented geomagnetic secular variation and relative palaeointensity rpi record for the last 17 000 yr from hall s cave texas whose complete 3 8 m thick sedimentary sequence spans from the present to 16 850 110 rc yr bp modern to 20 600 cal bp within the stable cool climate of the cave pedogenic and bioturbation processes are negligible to non existent thereby limiting post depositional physical and geochemical alteration of the magnetic record the sub aerial and subterranean setting of the sedimentary sequence in hall s cave enabled us to collect oriented palaeomagnetic cubes from a previously excavated stratigraphic section the palaeomagnetic samples yielded high quality vectors an age model for the sequence determined using 15 ams 14c dates on individual bones from microvertebrates was combined with the palaeomagnetic data to construct a secular variation record the record is in broad agreement with predictions by holocene field models for the site s location however starting ca 3000 yr ago the rpi data indicate an almost four fold increase in geomagnetic field intensity lasting several hundred years this record presents well dated evidence obtained using conventional techniques for the existence of a geomagnetic intensity spike in north america that is contemporaneous with the shorter duration decadal scale spikes reported from the near east

paleosecular variation during sequential geomagnetic reversals from hawaii abstract paleomagnetic directions measured from 175 flows in four volcanic sequences on the island of o ahu hawaii cover about 0 3 m y of geomagnetic field changes and include detailed records of the successive gilbert gauss 3 57 ma and lower mammoth reversals 3 33 ma the dominant pattern of the directional changes is the presence of large inclination variations with increasing amplitude and steep values during the transitional periods the morphology of these recurring features during different transitions is reminiscent of the characteristics of the non dipole field inferred from studies of paleosecular variation in the pacific these observations are consistent with transitional mechanisms yielding the emergence of non dipole components with characteristics similar to those during periods of stable polarity the three different records of the lower mammoth reversal show that clusters of transitional pole positions are not reproducible between parallel sections and are thus linked to local eruptions and not to long lived states of the transitional field

the development of a regional scale intraplate strike slip fault system alpine deformation in the north of ireland abstract a paucity of displacement markers can make constraining the kinematics and interaction of regional scale strike slip faults difficult in this study a high resolution aeromagnetic survey allows quantitative analysis of kilometre scale paleogene faulting in the north of ireland mapping offset dykes and igneous centres reveals the presence of two orientations of cenozoic strike slip faults attributed to broadly n s alpine shortening arising from the convergence of africa and europe reactivated ne sw striking faults accommodated up to 2 3 km of sinistral displacement mainly during the paleocene following tectonic quiescence up to 2 5 km of oligocene aged dextral movement was accommodated on newly formed nnw sse striking faults displacement analysis suggests that the faults were kinematically linked and experienced a switch in polarity of the predominantly active fault orientation during the paleogene forming an apparent conjugate system with asymmetric displacement distributions the switch in fault polarity is attributed to a rotation in the regional maximum horizontal stress orientation and the locus of deformation moving from pre existing reactivated structures to newly formed faults the analysis also illustrates that despite low strain rates the interaction of the principal components of the fault system controlled the formation of sedimentary basins and defined the present day geography of the region far from an active plate boundary

secular variation of the intensity of the geomagnetic field in mexico during the first millennium bce in western eurasia the first millennium bce is characterized by the fastest secular variation of the earth magnetic field observed over the last millennia and by a geomagnetic anomaly centered on the middle east on the global scale the variation of the dipolar field during this period remains poorly constrained because of the lack of data in other geographical areas here we presented 23 new mean archaeointensity data on ceramic sherds dated between 1500 bce and 200 ce from chalcatzingo archaeological site in central mexico archaeointensities were determined using the classical thellier thellier protocol with corrections for trm anisotropy and cooling rate effects our work doubles the number of high quality archaeointensity data in mexico during the considered period using a bayesian approach a new secular variation curve was calculated at mexico city between 1500 bce and 200 ce after selection of mexican archaeointensity data after a period of oscillations of the intensity between 20 and 40 t from 1500 to 300 bce the curve shows a large maximum 65 t in the second century bce the corresponding vadm varied between 4 0 and 11 0 1022 am2 which highlights further that the intensity of the geomagnetic field could vary at regional scale over a larger range as previously thought however this amplitude variation may be overestimated as it does not take into account the fast directional variation observed at this time

geomagnetic intensity and inclination variations at hawaii for the past 98 kyr from core soh 4 big island a new study and a comparison with existing contemporary data abstract reliable thellier thellier paleointensity determinations were obtained from 321 out of 766 examined samples from the upper 200 units 675 m of core soh 4 drilled in the kilauea volcano the main trend of the soh 4 record is a marked decrease from values higher than present in the last 4 kyr to values about 40 smaller from about 20 kyr to the bottom of the sampled interval three main lows coinciding with shallow or negative inclinations observed in the record were identified with an excursion previously documented in hawaii and the mono lake and laschamps events for the last 15 kyr the soh 4 intensities are largely in agreement with the worldwide distribution of volcanic data in the 15 75 kyr interval the general lack of volcanic data makes comparison with the soh 4 data difficult the soh 4 record is similar to a composite record of paleointensity largely based on a recent north atlantic sedimentary paleointensity stack napis 75 the soh 4 record is also generally consistent with a record of geomagnetic field intensity obtained from a study of 36 cl in the grip ice core calculated with the assumption that the production rate of 36 cl is controlled only by the geomagnetic field one pronounced discrepancy between the different records is observed around 50 kyr bp when the sedimentary and cosmogenic based records document high intensities which are not observed in soh 4 these high intensities are also absent in a recent record based on the analyses of sea floor magnetic anomalies the histogram of vadms obtained from soh 4 is different from that obtained from the sedimentary or 36 cl based records and is more skewed than the distribution given by kono and tanaka for the last 2 5 million years

a detailed palaeointensity and inclination record from drill core soh1 on hawaii abstract a new record of absolute palaeointensity was obtained from drill core scientific observation hole 1 soh1 on kilauea volcano hawaii kilauea s high eruption rate resulted in a relatively continuous record and stratigraphic constraints preserved the chronological order three hundred and sixty samples were studied with the thellier thellier technique which gave 195 successful palaeointensity and 271 successful inclination determinations three geomagnetic excursions were observed which exhibited intensity reductions of about 50 initial age control from k ar and ar ar dating only constrained the total age between 20 and 120 ka the final age model was obtained by stretching the soh1 record relative to other hawaiian palaeomagnetic data this gave an age range of 0 45 ka for the flows and identified the excursions as the hilina pali mono lake and laschamp events the soh1 record of the hilina pali event is the most detailed ever incorporating data from around 40 flows this age model suggests that kilauea had a burst of activity at the soh1 site around 20 ka all available data was combined to form a composite record of palaeointensity and inclination on hawaii for 0 45 ka

the onset and timing of caledonian sinistral shear in county down in the south westerly irish continuation of the southern uplands ample evidence of sinistral transpression includes a the clockwise transection of f 1 folds by s 1 cleavage combined with sub horizontal extension in the cleavage plane b local development of vein arrays deformed by sinistral simple shear and c an abundance of sinistral wrench faults the sinistral movements are dated relative to the local history of caledonian deformation and the intrusion of two suites of caledonian lamprophyre dykes clockwise transection of folds by cleavage is not a feature of the northern belt or of the northern tracts of the central belt in county down its geographic distribution suggests that sinistral transpression was first effective during the accretion of llandovery age tracts mid way south in the central belt sinistral movements continued episodically during the deformation of early pre and post s 1 vein sets and was finally expressed in widespread wrench faulting which continued beyond the date of intrusion of the younger dykes at about 400 ma

geomagnetic field intensity at hawaii for the last 420 kyr from the hawaii scientific drilling project core big island hawaii four hundred twenty five new paleointensity thellier thellier determinations out of 545 analyzed samples have been obtained from core hsdp which penetrates about 1000 meters 208 flows of the mauna loa and mauna kea volcanic series encompassing the last 420 kyr rock magnetic investigations identify pseudo single domain magnetite as the main magnetic mineral inclinations are shallower than expected from a geocentric dipole field but are consistent with data from other geographical regions at the same latitude the inclination record reveals three episodes of negative inclination whose interpolated age correlates well with that of known geomagnetic events the paleointensity record from the mauna loa sequence is not very detailed and does not allow precise comparison with other data in the 0 50 kyr interval the record from the mauna kea sequence on the contrary is very detailed and documents relatively short lived episodes of low and high field strength from 15 to 60 t the average virtual dipole moment 8 7 3 0 10 22 a m 2 is not significantly different from the value reported by kono and tanaka 1995 for the last 2 5 myr a comparison with other data from hawaii and other geographical regions is described in detail there are no drastic changes in paleointensity with the inclination anomaly in agreement with previous results from hawaii but in contrast with most published results which however consider data from polarity transition spectral analysis of a particularly detailed portion of the record between 420 and 326 kyr documents significant periodicities at 36 8 5 and 4 ka in the inclination record but not in the intensity record suggesting that changes in time of the inclination are to a certain extent independent from those of the intensity

geomagnetic field secular variation in pacific ocean a bayesian reference curve based on holocene hawaiian lava flows abstract hawaii is an ideal place for reconstructing the past variations of the earth s magnetic field in the pacific ocean thanks to the almost continuous volcanic activity during the last 10 000 yrs we present here an updated compilation of palaeomagnetic data from historic and radiocarbon dated hawaiian lava flows available for the last ten millennia a total of 278 directional and 66 intensity reference data have been used for the calculation of the first full geomagnetic field reference secular variation sv curves for central pacific covering the last ten millennia the obtained sv curves are calculated following recent advances on curve building based on the bayesian statistics and are well constrained for the last five millennia while for older periods their error envelopes are wide due to the scarce number of reference data the new bayesian sv curves show three clear intensity maxima during the last 3000 yrs that are accompanied by sharp directional changes such short term variations of the geomagnetic field could be interpreted as archaeomagnetic jerks and could be an interesting feature of the geomagnetic field variation in the pacific ocean that should be further explored by new data

palaeomagnetic intensities from 14 c dated lava flows on the big island hawaii 0 21 kyr thellier thellier experiments were carried out on 216 lava samples collected by the usgs on the big island 35 individual flows from the kilauea mauna loa and hualalai volcanoes are represented and independent radiocarbon dating of the flows yields absolute ages ranging from 290 to 20 240 yrs old the palaeomagnetic analysis was carried out at the laboratoire des sciences du climat et de l environnement in gif sur yvette france in two custom built large capacity furnaces that have been specifically designed to minimise oxidation the temperature steps were adapted to accommodate the characteristic loss of magnetisation at low temperatures seen in the curie balance results and the use of half size samples allowed secondary experiments to be carried out where necessary the strict picrit 03 selection criteria were rigorously applied to the data and a high success rate of 53 has been achieved on a sample level the flow averaged results almost double the existing 14c dated palaeointensity dataset for this time window and confirm a period of high intensity over the past 4 kyr preceded by a period in which the dipole moment was weaker however the values attained in this study are on average higher than previously published data reliability of these values is discussed

rock varnish in the sonoran desert microbiologically mediated accumulation of manganiferous sediments rock varnish occurs in virtually all environments most commonly in arid and semi arid climates including antarctica rock varnish consists of thin layers of intimately mixed aeolian and chemical sediments often showing botryoidal and more rarely stromatolite like morphologies typical rock varnish samples collected at twin peak mountain park near phoenix arizona consist of abundant quartz with plagioclase illite and a mixed layer fe clay mineral probably corrensite eds sem bse and tem analyses revealed that the typical mn fe minerals occur as minute particles some of these particles and other mineral grains are attached to filaments xrd and electron diffraction showed that the mn fe bearing particles are poorly crystalline the filaments based on morphological criteria are virtually indistinguishable from fungal filaments most filaments are fragments probably broken by scraping during sample collection coccoid and rod shaped forms resembling cyanobacteria and other bacteria respectively are also present unlike definitive minerals these filaments disintegrated in the concentrated energy of the sem electron beam at the instrumental and experimental conditions used in addition no filamentous rod shaped or coccoid forms were observed in samples hydrolysed with 6 n hcl for 24 h at 100 c bacteria and fungi in powdered rock varnish were cultured on four media incubated aerobically in the dark at 25 c the culture media yielded dense growths of spore forming bacteria and filamentous fungi one fungus and two bacillus isolates oxidized and concentrated manganese control experiments revealed that fungi and bacteria are present on and below the surfaces of rock varnish free and hydrolysed peptide protein bound amino acids were identified in the rock varnish amino acids showed virtually no racemization with the exception of d l asp 0 1 relatively high molecular weight humic matter was also separated from the rock varnish high resolution mass spectrometry revealed non hydrocarbon moieties similar to a suwannee river fl humic acid standard micro organisms and their original biochemical compounds do not seem to be preserved for long in the accreting varnish layer the studies showed that the filaments helped to trap mineral particles of rock varnish and that bacteria and fungi abetted mn concentration some structures in the layers of rock varnish resemble stromatolites and present definitions would allow them to be termed as such

40ar 39ar geochronology of carboniferous permian volcanism in the midland valley scotland twenty one new 40 ar 39 ar step heating experiments on mineral separates from intrusive and extrusive carboniferous and permian igneous rocks in the midland valley of scotland yielded 17 concordant experiments with a relative age precision better than 1 2 these ages resolve inconsistencies between existing k ar dates on the same samples and their stratigraphical constraints correlated to recently published timescales the precise 40 ar 39 ar dates are stratigraphically constrained to stage level and can contribute to carboniferous timescale tie points at the tournaisian visean boundary within the visean and at the carboniferous permian boundary situated in the extending variscan foreland two distinct phases of extension related transitional alkaline volcanism have been resolved in the dinantian the garleton hills volcanic formation in the eastern midland valley near the tournaisian visean boundary 342 1 1 3 and 342 4 1 1 ma and the clyde plateau volcanic formation in the western midland valley during the mid visean 335 2 329 2 1 4 ma alkaline basic sills near edinburgh previously thought to be namurian appear to be coeval with the clyde plateau volcanic formation at 331 8 1 3 329 3 1 5 ma the new ages allow correlation between these short lived dinantian magmatic pulses and extensional and magmatic phases in the northumberland solway and tweed basins to the south after late westphalian end variscan compression and a regionally important tholeiitic intrusive phase at c 301 295 ma alkaline magmatism related to post variscan extension occurred in the central and western midland valley during the latest carboniferous or permian from 298 3 1 3 to 292 1 1 1 ma this correlates well with post varsican extension and magmatism observed across the nw european foreland from 300 to 280 ma

microwave palaeointensities from holocene age hawaiian lavas investigation of magnetic properties and comparison with thermal palaeointensities abstract sixteen c 14 dated hawaiian surface lava flows spanning 0 4 5 ka have been investigated using the microwave perpendicular applied field palaeointensity technique and classical thermal thellier thellier palaeointensity technique in parallel the overall microwave experimental success rate is 63 compared to 59 in the thermal experiments nineteen percent of the microwave results are deemed to be first class compared to 52 of the thermal results high palaeointensities and a large amount of within flow variation are seen in the microwave results with reliable palaeointensity estimates ranging from 25 10 to 82 94 t these variations do not appear to be systematically related to variations in rock magnetic properties such as mineralogy grain size texture or oxidation state the flow means from the microwave and thermal studies agree for 9 of the 13 flows that can be directly compared and the average difference between the two techniques is not significantly different from zero neither experimental technique produces mean palaeointensities systematically lower or more precise than the other suggesting that the differences seen are a reflection of natural within flow variation rather than experimental technique

paleomagnetic secular variation and relative paleointensity during the holocene in south china huguangyan maar lake revisited the scarcity of reliable paleomagnetic secular variation psv records from east asia especially from low latitude regions impedes better understanding of global psv mechanisms here we report on a radiocarbon dated holocene psv record from a composite 6 7 m long core collected from the high sedimentation rate huguangyan maar lake hml in subtropical tropical south china rock magnetic results demonstrate that the natural remanent magnetization resides in single domain magnetite alternating field demagnetization experiments at 1 cm spacing on u channel samples reveal six distinct inclination highs at 7 500 bce 5 100 bce 4 600 bce 3 600 3 400 bce 1 600 1 200 bce and 600 800 ce three inclination lows at 4 800 bce 600 300 bce and 1 000 1 300 ce and three eastward declination trends at 3 600 3 200 bce 2 600 2 400 bce and 400 bce to 200 ce the similarity between the hml psv record and other independently dated records from east asia and geomagnetic field models corroborates the robustness of our age model and holocene psv record strikingly centennial to millennial scale psv features of the hml are comparable within age uncertainties with other holocene records from europe north america and canada suggesting that such directional patterns are likely to be hemispheric in scale although relative paleointensity data of hml are affected by environmental factors e g organic matter diagenesis the record still provides a regionally important new psv reference curve whose conspicuous features may serve as stratigraphic markers for east asian paleorecords

caledonian extension in the north irish dalradian implications for the timing and activation of gravity collapse following caledonian crustal thickening and prograde metamorphism of the dalradian rocks on the se laurentian margin in mid ulster down dip gravity controlled extension due to orogenic collapse was concentrated in the inverted limbs of the major ese facing fold nappes structural and metamorphic studies show that this extensional collapse which can be correlated along strike for at least 100 km occurred immediately after the crustal thickening episode such a relationship is compatible with dynamic wedge models for orogenic belts our data also imply that a collapse was triggered by the release of fluids during the prograde metamorphism and b late stage mobilization of the extensional zone created the gold mineralization in the sperrin mountains

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

variations in the geomagnetic dipole moment during the holocene and the past 50 kyr all absolute paleointensity data published in peer reviewed journals were recently compiled in the geomacia50 database based on the information in geomagia50 we reconstruct variations in the geomagnetic dipole moment over the past 50 kyr with a focus on the holocene period a running window approach is used to determine the axial dipole moment that provides the optimal least squares fit to the paleointensity data whereas associated error estimates are constrained using a bootstrap procedure we subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment including those based on cosmogenic radionuclides be 10 and c 14 this comparison generally lends support to the axial dipole moments obtained in this study our reconstruction shows that the evolution of the dipole moment was highly dynamic and the recently observed rates of change 5 per century do not appear unique we observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non dipole field this study also shows that the holocene geomagnetic dipole moment was high compared to that of the preceding similar to 40 kyr and that similar to 4 10 22 am 2 appears to represent a critical threshold below which geomagnetic excursions and reversals occur c 2008 elsevier b v all rights reserved less

strike slip terranes and a model for the evolution of the british and irish caledonides evidence is presented that many of the major strike faults in the british and irish caledonides were active as sinistral strike slip zones in the end silurian to pre mid devonian period some such as the highland boundary fault moved in this way at an earlier stage in the ordovician these data allow the caledonian rocks lying between the laurentian miogeocline whose basement is represented by the lewisian moine and possibly the dalradian and the gondwanaland miogeocline midland platform and welsh basin to be re analysed as a group of disorganized terranes which originated to the southwest in north america and southwest europe africa prior to the silurian the highland border terrane and northern belt terrane are interpreted as duplicated pieces of a mid ordovician sequence which was a back are to northwest subduction the midland valley terrane is interpreted as a slice of laurentian foreland onto which ophiolites were obducted in the lower ordovician but which became the basement of a continental margin arc to northwest subduction in the mid ordovician the cockburnland terrane is inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip the connemara terrane is regarded as an allochthonous piece of the dalradian miogeocline and the south mayo terrane as a remnant of an early ordovician arc and fore arc which in mid ordovician times became a back arc marginal basin to northwest subduction the lake district wexford terrane is part of an arc to southeast subduction under gondwanaland whose activity climaxed in the mid ordovician the central terrane is interpreted as a silurian overstep assemblage which blankets the junction between laurentian and gondwanaland derived oceanic terranes and therefore iapetus is regarded as an ordovician ocean which closed prior to the silurian the model suggests that at the end of the silurian a clockwise rotating gondwanaland having carried laurentia into collision with baltica broke free and created a major sinistral strike slip zone which disrupted the ordovician palaeogeography in the british isles north american sector of iapetus

evolution of the nw margin of the north permian basin uk north sea mapping of depositional zones within the zechstein supergroup using semi regional 2d and 3dseismic data constrains the geological evolution of the northwestern margin of the north permian basinin uk offshore quadrants 14 15 19 20 and 21 four depositional zones are identified on the basis of mappable seismic facies which are assumed to vary with halite content well control characterizes the most reflective seismic facies as an interbedded carbonate and anhydrite shelf succession which grades laterally through clastic rich sequences to the least reflective a thick halite basinal equivalent the trendsof the depositional zones illustrate the geometry of the north permian basin and may have been locally controlled by basement lineaments within the north permian basin a n s trending axis devil s hole high characterized by thick reflective facies separates the central north sea from the forth approaches basin basement fault blocks control facies type and thickness along the northwest margin of the north permian basin in the moray firth area permian tilt of the zechstein shelf related to regional flexure played a role in precipitating gravity driven tectonics within the seismically reflective facies on the east flank of the devil s hole high this permian phase of salt tectonics resulted in numerous intra zechstein structures which can be interpreted as rafted and folded zones of interbedded halite carbonate sulphate and clastics the rafts initially slid downdip towards the main halite basin then their evolution became dominated by differential subsidence of the interbeds which forced salt layers into adjacent passive diapirs this episode predates deposition of the triassic smith bank shales which rest upon the zechstein with local angular unconformity the spatial distribution of zechstein facies influenced the tectonostratigraphy of the triassic jurassic and cretaceous systems boundaries between zechstein facies correspond to the limit of triassic halokinesis on the west central shelf and the limit of detachment of jurassic and lower cretaceous thin skinned tectonics in moray firth half graben

direct major and trace element analyses of rock varnish by high resolution laser ablation inductively coupled plasma mass spectrometry la icpms laser ablation inductively coupled plasma mass spectrometry la icpms was used to determine major and trace element concentrations in rock varnish samples from the lahontan range near fallon nv and from a remote wilderness area near the san juan river in southeastern utah the data indicate that rapid la icpms analyses provide ample analytical resolution for semi quantitative compositional determinations of both trace and major elements in the varnish despite the presence of a rock substrate component in most analyses the overall major element contents of rock varnish from the two localities are grossly similar to rock varnish from other locations analyzed by solution icpms electron microprobe and energy dispersive scanning electron microscopy sem differences between microprobe and la icpms analyses may stem from different sampling scales and different degrees of substrate involvement it was possible to detect significant variations in trace element contents in the rock varnish samples the lahontan range is situated within a belt of w mineralization and varnish from that locality contained significantly higher w and mo contents than varnish from localities outside the w belt lead tl bi cd and as contents of varnish coated pebbles from near the san juan river in southeastern utah varied by an order of magnitude as a function of the position of the sampling site on the pebble elevated heavy element contents on the skyward facing varnish surfaces indicate that heavy elements may be preferentially scavenged at the locations most likely to receive direct inputs of atmospherically deposited airborne particulates the source of metal rich airborne particulates in this case is probably any one of several large coal fired power plants in the four corners region proximal to the san juan study area these patterns indicate that rock varnish chemistry is influenced by atmospherically derived fluxes of both dissolved and particulate constituents and that rock varnish can be used as a passive environmental indicator for a wide variety of elements in much the same manner as moss and lichens

relative paleointensity rpi in the latest pleistocene 10 45 ka and implications for deglacial atmospheric radiocarbon abstract we report magnetic properties and relative paleointensity rpi proxies from a suite of 10 conventional piston cores and kasten cores from the sw iberian margin collected during cruise jc089 of the rss james cook in august 2013 mean sedimentation rates are in the 10 20 cm kyr range age models were acquired by correlation of ca ti and zr sr xrf core scanning data to l reflectance from the cariaco basin that is in turn tied to the greenland ice core chronology the natural remanent magnetization nrm is represented by a single magnetization component carried by a low coercivity mineral magnetite although reflectance and bulk magnetic properties indicate the presence of a high coercivity hematitic magnetic phase possibly from eolian dust the presence of fine grained hematite means that the sediments are not ideal for rpi studies however the detrital hematite does not appear to contribute to the nrm or anhysteretic remanent magnetization arm in order to test the usefulness of the rpi data we construct a stack of 12 rpi records from the sw iberian margin for the 0 45 ka interval and compare it with a stack of 12 globally distributed marine and lake records chosen on the basis of mean sedimentation rates 15 cm kyr and superior age models the two stacks are similar but different from published rpi stacks particularly for the 10 30 ka interval and imply a virtual axial dipole moment vadm high at 15 18 ka followed by a drop in field strength from 15 to 13 ka a revised vadm estimate calculated from greenland 10be ice core flux using a contemporary age model is remarkably consistent with the new overall rpi stack based on iberian margin and global rpi records the elevated atmospheric 14c levels of the last ice age cannot however be fully explained by this rpi stack although relative changes such as the long term drop in atmospheric 14c from 30 to 15 ka are reproduced supporting the hypothesis of a combined influence of production rate and ocean ventilation on 14c during the last ice age

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

the east irish sea and adjacent basins new faults or old the east irish basin is characterized by three sets of faults striking n s ne sw and e w the menai strait fault system bounds the basin to the south and shows pre caledonian to cenozoic movement this span of activity contrasts with similarly oriented faults to the north of the basin which did not exist before the early carboniferous n s faults have a similarly diverse history some may have influenced silurian sedimentation and controlled the disposition of ordovician volcanic centres in snowdonia a contrast with n s striking faults in the north of the area which originated as steep strike slip faults during the late silurian e w faults control dinantian and permo triassic thickness variations although unlike the other fault trends pre carboniferous precursors are not apparent some of the basin bounding faults developed as wholly new faults during permo triassic extension

are systematic differences between thermal and microwave thellier type palaeointensity estimates a consequence of multidomain bias in the thermal results a meta analysis which directly compares 13 datasets of microwave and thermal thellier palaeointensity measurements obtained from igneous rocks is reported the results clearly indicate systematic differences in the measurements made using the two approaches the thermal results tend to be higher often by several tens of percent and associated with slightly noisier arai plots additionally in nearly half of the cases considered higher thermal palaeointensity estimates were reported to be calculated from the lowtemperature portions of concave up arai plots while microwave measurements made on specimens from the same core sample or rock unit were derived from more linear arai plots the most plausible explanation for the bulk of these differences appears to be that non ideal behaviour caused by multidomain vortex state and or interacting ferrimagnetic grains is exaggerated in the results of the thermal experiments over their microwave counterparts a detailed investigation of the individual studies concludes that such effects may be adversely affecting some of the measurements thermal and or microwave in 10 of the 13 datasets considered it is probable that these non ideal effects are enhanced in the thermal results over their microwave counterparts at least in part because of the different thellier type protocols that are used in the two types of study the findings of this study suggest that biasing of absolute palaeointensity estimates by multidomain effects may be much more prevalent than previously thought and that this effect might be responsible for certain discrepancies that have been observed in the geomagia50 database they also clearly indicate that in addition to taking the steps they already do to avoid biasing from secondary overprints and thermally induced alteration future absolute palaeointensity studies of

diachronous variscan late orogenic collapse as a response to multiple detachments a view from the internides in france to the foreland in the irish sea