thermomagnetic characteristics in late orogenic granites and gneisses of the southern appalachian piedmont abstract thermomagnetic curves have been obtained for samples from 25 granites and gneisses in georgia south carolina and north carolina this data set can be divided into two distinct curve types type i includes rocks which exhibit no distinct curie points and a linear decrease in magnetization with increasing temperature type ii curves exhibit a distinct curie point over a range of temperatures expected for magnetite 500 580 c synthetic samples constructed from magnetite and hematite powder exhibit type i behavior when the hematite to magnetite ratio is high e g 15 1 examination of polished sections shows relatively coarse grained magnetite only in type ii rocks we interpret our data to indicate that type i thermomagnetic curves are dominated by relatively large hematite magnetite ratios while type ii granites are characterized by relatively coarse grained magnetite type i granite samples have low magnetic susceptibility values less than 4 10 4 cgs while most type ii granite samples have higher values the type i granites are invariably18o enriched whereas type ii granites typically exhibit low18o 16o ratios these relationships are consistent with previously reported correlations of susceptibility generally indicative of magnetite content and oxygen isotopic trends in the southern appalachian piedmont

paleomagnetic study of cambrian potsdam group sandstones st lawrence lowlands quebec abstract we report paleomagnetic results from oriented drill core samples collected at 10 sites 80 samples from the covey hill and 19 sites 96 samples from the overlying fossiliferous cha teauguay formations of the gently dipping late cambrian potsdam group sandstones exposed in the st lawrence lowlands of quebec stepwise thermal demagnetization analyses ave revealed the presence of two predominant groups of coherent magnetizations c 1 and c 2 after simple correction for bedding tilt the c 1 group magnetization is a stable direction d 332 i 18 with unblocking temperatures t ub between 550 and 650 c present in the older covey hill formation this direction is probably a chemical remanence acquired during the covey hill diagenesis and carried predominantly by hematite the c 2 group magnetization d 322 i 9 is present at 13 sites of the younger cha teauguay formation this is probably carried by magnetite and represents a penecontemporaneous depositional drm characterized by t ub spectra 400 550 c we believe that c 2 is relatively younger than c 1 based on a combination of arguments such as the presence of opposite polarities internal consistency similarity and common occurrence of c 1 and c 2 respectively in the covey hill and cha teauguay members the corresponding paleomagnetic poles c 1 46 n 149 e dp dm 3 5 and c 2 37 n 156 e dp dm 2 5 are not significantly different from most of the other late cambrian dresbachian franconian poles derived from sediments exposed in the southern region texas of the north american craton which are also believed to have been deposited during croixian sauk sea transgression similar to the potsdam sandstones although adequate faunal control is lacking in particular for the covey hill formation this comparison with the cratonic poles suggests a late cambrian age to the potsdam poles the agreement between the results also gives the evidence for internal consistency of cratonic poles at least for late cambrian the incoherent c 3 group remanence d 250 i 15 is commonly present at 7 sites in both the formations this may not correspond to a reliable paleomagnetic signal the other remanence c 4 d 180 i 10 is found only at 3 sites located in the uppermost stratigraphic levels of the cha teauguay formation the corresponding paleomagnetic pole 40 n 107 e does not differ significantly from the ordovician and some late cambrian poles the present data are insufficient to resolve a problem in apparent polar wander for middle and late cambrian time posed by the existence of high latitude poles for some strata of middle cambrian age and low latitude poles for some strata of late cambrian age

secondary palaeoremanence of tethyan sediments from the zanskar range nw himalaya summary palaeomagnetic investigations have been carried out on tethyan sediments from the nw zanskar range 33 9 n 76 5 e a total of 455 oriented samples from 41 sites were drilled from four stratigraphic units of middle cretaceous to early eocene age shillakong formation marpo limestone spanboth formation stumpata quartzarenite spanboth formation kong formation a characteristic remanence chrm could be isolated for 27 sites 254 specimens through detailed thermal and alternating field demagnetization and multicomponent analysis all the chrm directions identified are similar irrespective of geological age they fail the fold test and yield an overall in situ mean direction of d 336 6 i 39 6 with 95 5 9 and k 22 9 this corresponds to a palaeopole position at 66 5 n 323 5 e n pole isothermal remanence irm acquisition and thermal demagnetization of a saturation irm identify pyrrhotite as the dominant ferrimagnetic mineral and carrier of the chrm the pyrrhotite remanence is probably a thermoremanent magnetization acquired when the temperature of low grade metamorphism decreased below about 300 c the chrm directions are thus clearly secondary in origin and a negative conglomerate test carried out on the kong formation demonstrates that remanence acquisition post dates the early eocene the mean chrm inclination suggests that the remanence was acquired at about 20 n cooling events in the higher himalayan crystallines indicate an oligocene age for this remanence acquisition the mean chrm declination shows a counterclockwise rotation of 23 4 since remanence acquisition assuming remanence acquisition at about 30 myr ago a slight counterclockwise rotation of about 10 relative to the stable indian plate can be concluded this does not fit with the general pattern of palaeomagnetic results from neighbouring areas within the western syntaxis of the himalaya from which a clockwise rotation relative to the stable indian plate is expected for the zanskar range

arctic ocean circulation patterns revealed by grace abstractmeasurements of ocean bottom pressure obp anomalies from the satellite mission gravity recovery and climate experiment grace complemented by information from two ocean models are used to investigate the variations and distribution of the arctic ocean mass from 2002 through 2011 the forcing and dynamics associated with the observed obp changes are explored major findings are the identification of three primary temporal spatial modes of obp variability at monthly to interannual time scales with the following characteristics mode 1 50 of the variance is a wintertime basin coherent arctic mass change forced by southerly winds through fram strait and to a lesser extent through bering strait these winds generate northward geostrophic current anomalies that increase the mass in the arctic ocean mode 2 20 reveals a mass change along the siberian shelves driven by surface ekman transport and associated with the arctic oscillation mode 3 10 reveals a mass dipole with mass decreasing

the palaeolatitude controversy in the silurian of newfoundland resolved new palaeomagnetic results from the central mobile belt abstract a detailed palaeomagnetic investigation of early silurian volcanics of the lawrenceton formation in the central mobile belt cmb of newfoundland reveals primary remanence that places the sampled part of the cmb on the margin of laurentia in low southerly latitudes in the early silurian the palaeomagnetic data indicate large vertical axis net clockwise rotations within the cmb and between the cmb and cratonic laurentia the volcanics were folded faulted and in places cleaved in silurian to early devonian times anisotropy of magnetic susceptibility measurements on lava flow samples verify field observations of a primary flow parallel foliation and confirm field measurements of the palaeo horizontal a well developed tectonic fabric was detected at one sampling site near the reach fault silurian redbeds of the big indian pond formation were also sampled for palaeomagnetic study the sediments are folded faulted and cleaved a statistically sound syn folding remanence was identified which in a tectonically corrected state is consistent in direction with the remanence in the silurian volcanics the sampled sediments are more intensely deformed than the volcanics and magnetic anisotropy measurements indicate both primary layering and secondary cleavage related fabrics in varying degrees from site to site it is possible that cleavage development resulted in remanence reorientation leading to the illusion of syn folding remanence when in fact the remanence was acquired prior to folding previously published palaeomagnetic investigations of silurian rocks in the cmb revealed a discrepancy in palaeofield inclination between volcanic and sedimentary rock types the sedimentary rocks yielded shallow inclinations and the volcanics intermediate inclinations inclination shallowing in the sediments was put forward as an explanation as well as contamination of the sedimentary results with a shallow overprint others argued that the results from the volcanics were in error the present investigation demonstrates that key volcanics carry a shallower remanence than previously thought bringing them into approximate agreement with the majority of the results from sediments steep results from the springdale volcanics and very shallow results from the king george iv lake sediments are at variance with the rest of the data the springdale result has large error limits that overlap with the other data the anomalous king george iv result remains an outlier

multicomponent magnetizations from the mississippian mauch chunk formation of the central appalachians and their tectonic implications previous paleomagnetic study of mississippian red beds of the mauch chunk formation from the central appalachians reported shallow inclination directions a positive fold test was obtained after thermal demagnetization typically to only 550 c the near equatorial position for north america indicated by these results has been used to support the idea of a circa 15 latitudinal tectonic offset of the acadia displaced terrain in the northern appalachians the present study of 153 samples from 29 sites occupied in the mauch chunk formation of eastern and southern pennsylvania reveals multicomponent magnetizations a characteristic component declination d 161 0 inclination i 27 8 alpha95 a95 7 9 with unblocking temperatures usually concentrated above 650 c and with dual polarity 10 sites normal 13 sites reversed is isolated in 23 sites and passes a fold test at the 99 confidence level it is interpreted as an early acquired hematitic detrital or chemical magnetization of pre alleghanian orogeny and pre kiaman reverse polarity interval age a southern hemisphere paleolatitude of 15 for the sampling area is indicated another component has generally lower unblocking temperatures which however can extend up to 650 c or more and therefore is also likely to be carried by hematite this secondary magnetization d 170 6 i 5 3 a95 5 0 isolated in 25 sites is of uniform reverse polarity and application of fold tests suggests that it is of synfolding origin a near equatorial paleolatitude 3 n at the time of acquisition is obtained consistent with permo carboniferous kiaman directions from north america incomplete removal of the secondary component can explain the previous results from the mauch chunk comparison of the present paleomagnetic results with those from similar age rocks in the canadian maritimes does not support a latitudinal offset of acadia with respect to interior north america in the early carboniferous in fact according to these and other paleomagnetic data thought to be representative of this age the atlantic bordering continents already were near to a pangea configuration the alleghanian and particularly the hercynian orogenies therefore may not be associated with the closure of a large latitudinal ocean later in the carboniferous and permian alleghanian deformation however may have resulted in the partial bending of the pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

coupling of late orogenic tectonics and secondary pyrrhotite remanences towards a separation of different rotation processes and quantification of rotational underthrusting in the western himalaya northern india abstract the total amount of crustal shortening within the indian plate includes straight forward and rotational shortening the complex tectonic history of the western himalaya impedes a direct observation of rotational shortening between india and its northern margin a combination of palaeomagnetic results and tectonic structures along a 300 km nw se section from nw zanskar 33 9 n 76 5 e to malari 30 0 n 79 6 e in northern india enable a separation of rotations on different scales correction of the observed rotations and quantification of uniform rotational shortening new palaeomagnetic results from metacarbonates of the tethyan himalaya in sarchu losar and spiti and earlier studies from nw zanskar and malari reveal a characteristic remanent magnetisation carried by pyrrhotite unblocking spectrum 250 330 c negative fold tests 99 level indicated remanence acquisition after the main folding of the himalaya the formation of pyrrhotite during thermal events t 200 c suggests a remanence acquisition related to exhumation and cooling temperatures of about 200 300 c indicate a thermochemical remanence acquisition with an eohimalayan age dated in two areas by 40k 39ar techniques on illites the resulting rotation angles in respect to stable india show an anomalous counterclockwise rotation in nw zanskar and a trend of decreasing clockwise rotations to the se these variations may be attributed to meso scale 100 km tectonic features and oroclinal bending for the first time block rotations with respect to stable india are separated into local meso scale and regional significant ones after elimination of local and meso scale effects using structural analysis of late orogenic features modelled rotations due to oroclinal bending were subtracted regionally significant rotations of 0 20 clockwise are interpreted to be caused only by uniform rotational underthrusting

local diagnostics to estimate density induced sea level variations over topography and along coastlines 1 in the open ocean sea level variability is primarily steric in origin steric sea level is given by the depth integral of the density field raising the question of how tide gauges which are situated in very shallow water feel deep ocean variability here this question is examined in a high resolution global ocean model by considering a series of assumptions we show that if we wish to reconstruct coastal sea level using only local density information then the best assumption we can make is one of no horizontal pressure gradient and therefore no geostrophic flow at the seafloor coastal sea level can then be determined using density at the ocean s floor when attempting to discriminate between mass and volume components of sea level measured by tide gauges the conventional approach is to take steric height at deep ocean sites close to the tide gauges as an estimate of the steric component we find that with steric height computed at 3000 m this approach only works well in the equatorial band of the atlantic and pacific eastern boundaries in most cases the steric correction can be improved by calculating steric height closer to shore with the best results obtained in the depth range 500 1000 m yet for western boundaries large discrepancies remain our results therefore suggest that on time scales up to about 5 years and perhaps longer the presence of boundary currents means that the conventional steric correction to tide gauges may not be valid in many places

paleomagnetism of the cambrian moore hollow group texas evidence for a primary magnetization carried by detrital magnetite petrographic and paleomagnetic studies of the cambrian moore hollow group texas establish the presence of three magnetic minerals and several components of magnetization hematite is the dominant carrier of the magnetic remanence in most samples and is primarily a diagenetic replacement of preexisting fe bearing phases hematite dominant samples have characteristic directions which range from shallow easterly to shallow southerly this distribution suggests multiple components of magnetization acquired at various times in the paleozoic the paleopole obtained for an unmineralized breccia 135 7 e 15 4 n represents either a chemical remanent magnetization of middle ordovician to early silurian age or a vector addition of two or more cambrian through silurian components mineralized breccias at the silver creek mississippi valley type deposit yield a permian direction 117 0 e 51 6 n because hematite in this deposit predates mineralization the permian age represents a maximum age for the mineralization at silver creek many samples contain goethite as a replacement of fe dolomite glauconite and pyrite the direction of magnetization carried by goethite is near the present geomagnetic field or in a minority of samples antipodal to it rounded ti magnetite was identified by sem in magnetic extracts from siliciclastic poor facies irm acquisition and thermal demagnetization confirms the presence of magnetite in these samples some samples contain an apparent modern viscous remanent magnetization the dominant component 72 samples 10 sites has a site mean declination of 93 8 and inclination of 14 5 with an 95 8 5 corresponding to a pole position at 163 0 e 0 6 s the presence of detrital magnetite polarity changes lack of evidence for prolonged burial and the proximity of this pole position to other late precambrian cambrian poles suggest that this component of magnetization indeed reflects the late cambrian paleopole for cratonic north america

widespread late mesozoic to recent remagnetization of paleozoic and lower triassic sedimentary rocks from south china kent d v zeng x zhang w y and opdyke n d 1987 widespread late mesozoic to recent remagnetization of paleozoic and lower triassic sedimentary rocks from south china in d v kent and m krs editors laurasian paleomagnetism and tectonics tectonophysics 139 133 143 paleomagnetic results are described from eighteen formations sampled in the nanjing jiangsu province and yichang hubei province areas of south china the marine platform carbonates and elastics range in age from early cambrian to early triassic progressive alternating field and or thermal demagnetization analyses reveal predominantly single component magnetizations sometimes of both normal and reverse polarity these magnetizations isolated in 457 of the 549 samples studied typically have directions in geographic coordinates coincident with late mesozoic to recent fields a secondary origin for the magnetizations is supported by negative fold tests in several units a lower carboniferous and possibly a lower triassic limestone may have escaped the pervasive remagnetization if the remanences isolated are indeed prefolding a large counterclockwise tectonic rotation of the nanjing area is implied by comparison with available carboniferous and triassic paleopoles reported from elsewhere in south china this rotation may have been associated with mesozoic left lateral motion on the tancheng lujiang fault zone

sea surface height and dynamic topography of the ice covered oceans from cryosat 2 2011 2014 we examine 4 years 2011 2014 of sea surface heights ssh from cryosat 2 cs 2 over the ice covered arctic and southern oceans results are from a procedure that identifies and determines the heights of sea surface returns along 25 km segments of satellite ground tracks variability in the retrieved sshs is between 2 and 3 cm standard deviation in the arctic and is slightly higher 3 cm in the summer and the southern ocean average sea surface tilts along these 25 km segments are 0 01 3 8 cm 10 km in the arctic and slightly lower 0 01 2 0 cm 10 km in the southern ocean intra seasonal variability of cs 2 dynamic ocean topography dot in the ice covered arctic is nearly twice as high as that of the southern ocean in the arctic we find a correlation of 0 92 between 3 years of dot and dynamic heights dh from hydrographic stations further correlation of 4 years of area averaged cs 2 dot near the north pole with time variable ocean bottom pressure from a pressure gauge and from grace yields coefficients of 0 83 and 0 77 with corresponding differences of 3 cm rms these comparisons contrast the length scale of baroclinic and barotropic features and reveal the smaller amplitude barotropic signals in the arctic ocean broadly the mean dot from cs 2 for both poles compares well with those from the icesat campaigns and the dot2008a and dtu13mdt fields short length scale topographic variations due to oceanographic signals and geoid residuals are especially prominent in the arctic basin but less so in the southern ocean

using palaeomagnetism to determine late mesoproterozoic palaeogeographic history and tectonic relations of the sinclair terrane namaqua orogen namibia

patterns of erosion sedimentation heavy mineral concentration and grain size to interpret boundaries of littoral sub cells of the nile delta egypt abstract analyses have been undertaken of 68 beach nearshore profiles spanning the years 1971 1995 to interpret sub littoral cells of the nile delta that developed during cross shore and alongshore sediment transport bottom sediments of these profiles taken along the 240 km length of the delta coastline have been analyzed to determine seabed level changes textural and heavy mineral concentration distributions the spatial distribution of seabed depth changes linked with the heavy mineral concentration allows identification of three zones of erosion source areas associated with accretion sink areas erosion zones occur off the nile promontories at rosetta 20 to 50 cm yr burullus and damietta 0 to 20 cm yr accretion ranging from 0 to 40 cm yr occurs between erosion zones at abu quir bay the rosetta saddle gamasa embayments and along the western side of the jetty at the suez canal entrance port said this pattern was generally induced from the temporal variability in the direction and intensity of the incoming waves currents orientation of coastline seafloor morphology and local protective structures the correspondence among patterns of seabed depth change heavy mineral concentration and to some extent the texture of seabed sediments refine boundaries of littoral sub cells of the nile including sediment paths sources sinks nodal points and zones of sediment transport convergence and divergence this correspondence is not strongly correlated as might be expected in this deltaic system where sediment has been recycled between recent and relict seabed settings moving in the alongshore and cross shore directions nevertheless the present investigation shows that the relationship between seabed level changes heavy mineral concentration and to some extent mean grain size of the littoral zone can be practically applied in other deltaic settings to interpret sediment transport pathways particularly where there are less relict sediments

correlation of eocene oligocene marine and continental records orbital cyclicity magnetostratigraphy and sequence stratigraphy of the solent group isle of wight uk the magnetostratigraphy clay mineralogy cyclostratigraphy and sequence stratigraphy of the estuarine and continental solent group isle of wight hampshire basin uk which is of late eocene early oligocene age were investigated a new magnetostratigraphy for the solent group is correlated to the chronostratigraphic standard using limited biostratigraphical data and it is concluded that the base of the oligocene falls close to the base of the bembridge limestone formation a long time series of clay mineral xrd data was generated which shows striking variation in illitic clay abundance illite is interpreted to have formed in gley palaeosols through repeated wetting and drying in response to high seasonality high illitic clay values are tuned to c 400 ka eccentricity maxima to develop an age model in addition to a very strong c 400 ka signal in the data spectral analysis of the clay data also confirms the influence of short eccentricity c 100 ka and obliquity c 40 ka cycles the succession displays seven conspicuous 10 20 m thick sequences which represent transitions from transgressive estuarine environments through highstand floodplains to freshwater lakes the sequences correspond exactly to the long eccentricity c 400 ka cycles a sea level curve is derived using the amount of incision as a minimum measure of eustatic fall but there is no evidence of a major eustatic drop of 30 90 m corresponding to the early oligocene glaciation of antarctica it is likely that incision was suppressed by rapid rates of subsidence

cambro ordovician paleogeography of the southeastern new england avalon zone implications for gondwana breakup paleomagnetic measurements and u pb geochronology of alkalic igneous rocks intruding the ediacaran cambridge argillite and the lower cambrian weymouth formation north of boston at nahant massachusetts yield a well constrained paleopole the oldest intrusive phases are a syenodiorite sill and a granite dike with 206 pb 238 u crystallization ages of 490 19 0 90 ma and 489 03 0 82 ma respectively this sequence along with undated mafic sills penetrating both the argillite and weymouth strata are cut by 488 53 0 81 ma gabbro locally associated with 488 48 0 79 ma syenite forming a steep sided intrusive plug ten paleomagnetic sampling sites within the mafic sills and the gabbro contain a stable a magnetic component with a mean direction of d 278 5 i 76 7 a 95 3 9 n 10 this is considered to be the primary magnetization direction because it passes both fold and reversals tests the corresponding paleopole at 320le 34 n a 95 7 2 n 10 places the southeastern new england avalon zone at a southerly paleolatitude of 65 slightly removed from the african margin of gondwana and suggests that bimodal nahant magmatism is linked with latest cambrian early ordovician rifting of west avalonia to form the rheic ocean stable b and c magnetic components in nahant syenodiorite and syenite give rise to virtual geomagnetic poles that track late silurian through carboniferous segments of the north american apparent polar wander path indicating docking of west avalonia by mid paleozoic time

thermohaline circulation at three key sections in the north atlantic over 1985 2002 efforts are presently underway to monitor the thermohaline circulation thc in the north atlantic a measuring strategy has been designed to monitor both the meridional overturning circulation moc in the subtropics and dense outflows at higher latitudes to provide a historical context for these new observations we diagnose an eddy permitting ocean model simulation of the period 1985 2002 we present time series of the thc moc and heat transport at key hydrographic sections in the subtropics the northeast atlantic and the labrador sea the simulated thc compares well with observations we find considerable variability in the thc on each section most strikingly in the labrador sea during the early 1990 s consistent with observed changes overturning in the northeast atlantic declines by 20 over the 1990 s coincident with an increase in the subtropics we speculate that moc weakening may soon be detected in the subtropics if the decline continues in mid latitudes

high frequency barotropic ocean variability observed by grace and satellite altimetry 1 previous theoretical and model based studies of the relationship between ocean bottom pressure pb and sea level suggest primarily barotropic variability at mid to high latitudes for scales greater than a few hundred kilometers and periods less than a few months we use 7 day grace solutions and equivalent satellite altimetry maps spatially smoothed over 750 km to investigate the relation between pb and the observed fields are significantly coherent at high latitudes for periods of 14 180 days and mid latitudes for periods of 30 100 days the admittance amplitude between observed pb and is close to 1 for higher frequencies and drops off for lower frequencies the results provide for the first time global observational evidence for the barotropic nature of large scale ocean variability at mid and high latitudes we also demonstrate that grace data contain significant information over the oceans at periods 60 days i e shorter than the nominal monthly time resolution

relation between sea level and bottom pressure and the vertical dependence of oceanic variability 1 the relation between large scale sea level and bottom pressure variability is studied using long 50 yr simulations of a general circulation model under realistic forcing admittance and coherence analyses are used to characterize the bottom pressure and sea level relationship as a function of period horizontal spatial scale and location at the model grid scale 1 bottom pressure is found to be essentially equivalent to sea level at periods 60 and in shallow depths 200 m elsewhere bottom pressure and sea level fields can differ significantly results indicate an increase of the importance of baroclinic signals with decreasing latitude and spatial scale with significant baroclinic signals at intra seasonal and longer periods present in many subtropical and mid latitude regions variability is clearly baroclinic at inter annual periods regardless of location and spatial scale results have broad implications for the interpretation and processing of both satellite altimetry and gravity data and for their assimilation into numerical models

determining north atlantic meridional transport variability from pressure on the western boundary a model investigation 1 in this paper we investigate the possibility of determining north atlantic meridional transport variability using pressure on the western boundary focusing on the 42 n latitude of the halifax wave array we start by reviewing the theoretical foundations of this approach next we present results from a model analysis both statistical and dynamic that demonstrate the feasibility of the approach we consider how well we can quantify the meridional transport variability at 42 n given complete knowledge of bottom pressure across the basin and to what degree this quantification is degraded by first ignoring the effect of intervening topography and then by using only bottom pressure on the western boundary we find that for periods of greater than 1 year we can recover more than 90 of the variability of the main overturning cell at 42 n using only the western boundary pressure provided that we remove the depth averaged boundary pressure signal this signal arises from a basin mode of bottom pressure variability which has power at all time scales but that does not in truth have a meridional transport signal associated with it and from the geostrophic depth independent compensation of the ekman transport an additional benefit of the removal of the depth averaged pressure is that this high frequency ekman signal which is essentially noise as far as monitoring the meridional overturning circulation for climatically important changes is concerned is clearly separated from other modes

effect of anisotropy on the paleomagnetic contact test for a grenville dike we report a detailed paleomagnetic contact test for a mafic dike and its tonalitic gneiss host rock in the precambrian grenville province of canada directions of natural remanent magnetization nrm in the country rock were corrected for assumed deflection by the strong magnetic anisotropy due to the rock fabric using the measured anisotropy of laboratory induced thermoremanent magnetization trm the trm ellipsoids have the same principal axes as the anisotropy of magnetic susceptibility ams ellipsoids but the anisotropy of remanence is more pronounced than the ams anisotropy correction moves nrm directions in the unbaked zone almost 20 bringing them close to typical grenvillian paleofield directions the anisotropy seems to be controlled by multidomain rather than single domain magnetic minerals nrm directions from the baked gneiss near the dike contact after anisotropy correction agree well with the nrm directions from the chilled margin of the early cambrian 570 3 ma dike this positive baked contact test is augmented by the presence of a hybrid zone in which country rock nrms are increasingly overprinted by the dike nrm as one moves from the unbaked toward the baked zone the dike nrm is therefore primary however the virtual geomagnetic pole vgp for the dike nrm 51 n 131 w dp 10 dm 12 n 24 samples or 41 n 153 w dp 13 dm 18 n 4 chilled margin samples does not fall near most established cambrian paleopoles post emplacement tectonic movement of the dike is unlikely it may be that the dike cooled and acquired trm during a geomagnetic field excursion because of its geologically short cooling blocking period of a few tens of years

a window on the deep ocean the special value of ocean bottom pressure for monitoring the large scale deep ocean circulation we show how by focusing on bottom pressure measurements particularly on the global continental slope it is possible to avoid the fog of mesoscale variability which dominates most observables in the deep ocean this makes it possible to monitor those aspects of the ocean circulation which are most important for global scale ocean variability and climate we therefore argue that such measurements should be considered an important future component of the global ocean observing system to complement the present open ocean and coastal elements our conclusions are founded on both theoretical arguments and diagnostics from a fine resolution ocean model that has realistic amplitudes and spectra of mesoscale variability these show that boundary pressure variations are coherent over along slope distances of tens of thousands of kilometres for several vertical modes we illustrate the value of this in the model atlantic by determining the time for boundary and equatorial waves to complete a circuit of the northern basin 115 and 205 days for the first and second vertical modes showing how the boundary features compare with basin scale theoretical models and demonstrating the ability to monitor the meridional overturning circulation using these boundary measurements finally we discuss applicability to the real ocean and make recommendations on how to make such measurements without contamination from instrumental drift

evolution of beach dune fields systems following the construction of jetties in estuarine mouths cantabrian coast nw spain the morphology of many spanish estuarine mouths has been modified over recent decades to improve access to the harbours located inside the normal practice has been the construction of jetties along one or both sides of the mouth to improve the flow though the main estuarine channel and thereby prevent the formation of bars in the main channel bed and ebb tidal delta lobes or mouth bars in the mouths the new wave refraction diffraction dynamics created by these structures induces a strong modification of the beach dune systems in the zones adjacent to the jetties a rapid migration occurs until the beach profile and the associated dune field stabilise which occurs when the confined space is unable to retain more sediment this process may include the reworking of outer sandy bottoms and the generation of new stabilised bars a portion of the sand used by waves to form this accretion is supplied by erosive processes occurring during the same period on the beaches and dune fronts located in areas further away from the jetties which in many cases are heavily used the aim of this paper was to analyse the accretion geometries and rates of beach dune systems in several estuaries that drain into the cantabrian coast and the subsequent erosion in the outer dune belt testing a conceptual model formulated to explain the factors that determine the beach dune response to human actions the methodology applied can be exportable to other regions to facilitate the prediction of anthropic effects from harbour development and coastal management policies and the subsequent conservation of these environments

an ocean resonance in the southeast pacific 1 satellite altimeter observations of sea surface height show an extensive region of high variability in the southeastern pacific which previous studies have suggested is a rossby wave trapped by topography here we investigate the feature using results from a high resolution global ocean model we calculate the empirical orthogonal modes and find that 29 of the ssh variability is due to a single mode we correlate the time series of the mode with the local ekman pumping and find that the correlation is largest when the wind curl is averaged over a region roughly the size of the mode we calculate the response function relating the two time series and find that it is dominated by a resonance at zero frequency with a decay time of about two days we conclude that the feature is a highly damped geostrophic mode of the ocean

origin of the magnetization of the wichita mountains granites oklahoma summary the magnetization of the cambrian wichita mountains basement complex consists of several components two of which are shown to be significant the residual primary remanence is associated with the original titanomagnetite and the dominant secondary component is carried by minerals of the ilmenite haematite series the latter has been acquired at temperatures up to 300 c as a result of the regional hydrothermal alteration during late palaeozoic the secondary remanence is of thermochemical origin and carries a memory of a variable ambient field direction which may be modelled as a resultant of the geomagnetic field direction contemporaneous with the hydrothermal process and of the direction of the magneto static field of the primary titanomagnetite although the destruction of the original presumably cambrian remanence has been extreme in a few cases its direction appears to have been recovered the results are complicated by the possibility of a self reversal of secondary remanence as well as geomagnetic field reversal an issue unresolved by the investigation relates to the possibility of generation of magnetite by heat treatment of rock material in the laboratory it is generally concluded that it is difficult to recover the original cooling thermoremanence direction in an igneous intrusion which has been subjected later in its life to extreme conditions of hydrothermal alteration

beach and nearshore morphodynamic changes of the tabarka coast northwest of tunisia aerial photographs taken in the 1963 and 2001 and bathymetric charts in conjunction with coastal processes are analyzed to assess changes in rate of shoreline position seabed level and seabed grain sizes along the tabarka berkoukech beach at the north western tunisian coastline the littoral cell of this beach 12 km long is bounded by pronounced embayments and rocky headlands separated by sandy stretches although not yet very much undeveloped this littoral is still experienced degradation and modification especially along its shoreline with significant coastal erosion at some places results obtained from analysis of shoreline position indicate that el morjene beach is experienced a landward retreat of more than 62 m at a maximum rate of 1 64 m year whereas the el corniche beach is advanced about 16 144 m at an average rate of 0 42 m 3 78 m year this beach accretion has been formed on the updrift side of the tabarka port constructed between 1966 and 1970 comparison of bottom contours deduced from bathymetric charts surveyed in 1881 and 1996 off the coastline between tabarka port and el morjene beach identifies erosional areas sediment source and accretionary zones sediment sink erosion 0 87 4 35 cm year occurs between el kebir river mouth and el morjene beach whereas accretion exists in the zone down wind of the port ranges between 0 87 and 5 21 cm year morphological analyses of the shoreline and the seabed of the study nearshore area indicate that shoreline retreat corresponds to areas of seabed scour sediment source while shoreline accretion is associated with areas of seabed deposition sediment sink furthermore simulation of wave propagation using stwave model combined with grain size distributions of the seabed shows that fine sands are much dominated in depositional areas with low wave energy whereas coarser sands in erosive zones with high wave energy the results obtained suggest that the change of seabed morphology wave height pattern and grain size sediment have a great influence on the modification of shoreline morphology and dynamics

a basin coherent mode of sub monthly variability in arctic ocean bottom pressure 1 a sub monthly mode of non tidal variability of ocean bottom pressure obp is observed in a 5 year record of deep sea bottom pressure at the north pole obp records from other regions in the arctic show that the north pole non tidal mass fluctuation is part of a non propagating basin coherent variation that is well represented by the ice ocean model piomas with a basin averaged winter only rms of 3 3 cm wavelet analysis of the modeled obp shows that the basin averaged mass variations are non stationary and only significant during the winter the basin averaged obp is strongly related to the meridional wind component over the nordic seas the ocean response is consistent with episodic wind forcing driving a northward geostrophic slope current the mass transport anomaly associated with the mode is significant relative to the annual net mean flow

interpretation of moment measures derived from water lain sediments although mean size provides a useful value for characterizing sediments it is an inadequate expression of the interaction between sediments and hydraulic regimes and many authors have explored the significance of other statistical moment measures in different parts of the particle size spectrum few publications however have described such relationships over a very wide range of particle sizes using a combined data base of marine and lacustrine sediments we have been able to demonstrate the following the distributions of standard deviation and entropy values are repeated in similar form on either side of the sand size class describing mixtures between sands and gravel and sands and clay skewness is modified by the hydraulic response of the sediment and a skewness divide is present at about 2 7 where it coincides with the minimum shear velocity required to initiate particle motion this divide may be used to distinguish between high and low energy regimes kurtosis like standard deviation is a measure of the mixing of end member populations but it is more sensitive to changes in the tails of distribution curves the maximum positive peak of kurtosis at about 2 5 lies close to the skewness divide in our data by using skewness kurtosis plots it is possible to define separate field distribution for sediments which to a greater or lesser degree appear to conform to hydraulic equilibrium by using sediments which are close to equilibrium and lie at or close to our skewness kurtosis boundary curves it should be possible to define hydraulic shear velocities at the time of formation values may be established by empirical relationships or by defining the break point traction and intermittent suspension between linear components of individual sample size probability distribution plots such relationships should be enhanced by using hydraulic equivalent diameters instead of sieve diameters in fine sediments the use of fractional silt clay ratios offers sensitivity at a level comparable to that of skewness kurtosis plots and may be more easily computed

a quasi linear structure of the southern margin of eurasia prior to the india asia collision first paleomagnetic constraints from upper cretaceous volcanic rocks near the western syntaxis of tibet we report the first combined geochronologic and paleomagnetic study of volcanic rocks from the shiquanhe and yare basins at the westernmost lhasa terrane which aims to provide an accurate constraint on the shape and paleoposition of the southern margin of asia prior to the india asia collision three new 40ar 39ar ages of 92 5 2 9 ma 92 4 0 9 ma and 79 6 0 7 ma determined by fresh matrix or feldspar from lava flows suggest a late cretaceous age for the investigated units characteristic remanent magnetizations have been successfully isolated from 38 sites which pass positive fold and or reversal conglomerate tests and are hence interpreted as primary in origin the two paleopoles obtained from yare and shiquanhe yield consistent paleolatitudes of 13 6 n 9 6 n and 14 2 n 2 7 n respectively for a reference site of 31 5 n 80 e indicating that the southern margin of asia near the western syntaxis was located far south during the late cretaceous time a reconstruction of the lhasa terrane in the frame of eurasia with paleomagnetic data obtained from its western and eastern parts indicates that the southern margin of eurasia probably had a quasi linear orientation prior to the collision formerly trending approximately 315 e this is compatible with the shape of the neo tethys slab observed from seismic tomographic studies our findings provide a solid basis for evaluating cenozoic crustal shortening in the asian interior and the size of greater india near the western syntaxis

new and revisited paleomagnetic data from permian triassic red beds two kinematic domains in the west central pyrenees abstract new paleomagnetic results of permian triassic red beds from bielsa aure and somport anayet sectors in the pyrenean axial zone are presented and combined with revisited and reviewed paleomagnetic data from the west central pyrenees the paleomagnetic data from the red beds vary between different sectors that share similar structural position i e whilst all sectors share the existence of a characteristic prefolding component a cenozoic postfolding component is found only in one area but not in other areas with similar structural position and kinematics previous paleomagnetic data to the west of the studied zone reveal a pre turonian remagnetization component but this secondary component is not found in an area that shares a similar structural position aure this variability suggests that the paleomagnetic behavior is the result of a series of factors related to the particular tectonic history of the region sedimentation burial and deformation during basin inversion and therefore paleomagnetic data demands careful assessment in order to unravel the kinematics of areas with equivalent structural positions in orogens however important kinematic implications that hold in the pyrenees can be inferred from the restoration of the permian triassic characteristic magnetizations to positions previous to the paleomagnetic rotations recorded by cretaceous or cenozoic paleomagnetic data the restoration reveals on one hand the lack of large rotations in the south pyrenenan zone except in the nogueras area according to bates 1989 and on the other hand the contrasting rotations recorded to the west of the studied zone in the paleozoic basque massifs pbm and the south pyrenean zone indicating the existence of two different tectonic domains in the west central sector of the pyrenees the strong clockwise rotations postdating the early cretaceous remagnetization that are recorded in the pbm and in the north pyreneean zone suggest a late dextral shear deformation affecting areas near the north pyrenean fault zone

ocean bottom pressure variability can it be reliably modeled ocean bottom pressure obp variability serves as a proxy of ocean mass variability the knowledge of which is needed in geophysical applications the question of how well it can be modeled by the present general ocean circulation models on time scales in excess of one day is addressed here by comparing the simulated obp variability with the observed one to this end a new multi year data set is used obtained with an array of bottom pressure gauges deployed deeply along a transect across the southern ocean we present a brief description of obp data and show large scale correlations over several thousand kilometres at all time scales red using daily and monthly averaged data annual and semi annual cycles are weak close to the agulhas retroflection signals of up to 30 cm equivalent water height ewh are detected further south signals are mostly intermittent and noisy it is shown that the models simulate consistent patterns of bottom pressure variability on monthly and longer scales except for areas with high mesoscale eddy activity where high resolution is needed to capture the variability due to eddies furthermore despite good agreement in the amplitude of variability the in situ and simulated obp show almost no correlation

paleomagnetism and age of mafic plutons wichita mountains oklahoma a paleomagnetic reconnaissance 43 samples of the raggedy mountain gabbro group which is comprised of a layered complex of anorthosites anorthositic gabbros and massive gabbro shows 1 stable remanent magnetization and 2 consistent directions which differ significantly from those of the nearby cambrian wichita granite group with exception of one site near the granite contact these results suggest a precambiran age for the gabbro group the difference in pole positions between the granitic and mafic groups demonstrates that the plutonic episodes responsible for the mafic and granitic magmas are significantly separated in time models of formation of the wichita aulacogen should be altered to account for the difference in time between the mafic and silicic plutonism

paleomagnetic and petrologic study of the age origin and significance of early and late paleozoic events in the long mountain granite wichita mountains oklahoma the cambrian long mountain granite exposed in the western wichita mountains oklahoma is red granophyric alkali feldspar granite the red granite abruptly transitions into a green granite in the subsurface both red and green granites have similar geochemical signatures anisotropy of magnetic susceptibility analysis shows that the green granite retains a primary magnetic fabric that is consistent with the sill like emplacement of the wichita granite group demagnetization of green granite specimens yields a characteristic remanent magnetization chrm residing in magnetite with east declinations and moderate down inclinations the paleopole 9 0 n 314 6 e is interpreted as a primary cambrian thermal remanent magnetization or an early magnetization related to deuteric hydrothermal alteration the paleopole position is consistent with some other poles for cambrian igneous rocks in southern oklahoma but is to the southwest of the cambrian part of the apparent polar wander path the red granite contains abundant secondary hematite that occurs in fractures as grain boundary coatings and along cleavage and exsolution planes in alkali feldspars the iron in the hematite appears to be sourced from the oxidation of primary magnetite and ilmenite and the breakdown of silicate ferromagnesian minerals the red granite has about two orders of magnitude lower magnetic susceptibility and natural remanent intensity than the green granite the magnetic fabric is interpreted as an alteration fabric the chrm of red granite has southeast declinations and shallow inclinations and is interpreted as a chemical remanent magnetization crm residing in hematite the paleopole 44 9 s 304 9 e falls near the 290 300 ma segment of the north american apparent polar wander path which is consistent with inferred timing of exposure of the long mountain granite the crm is interpreted to have been acquired during alteration by low temperature weathering fluids near the surface during the late paleozoic the results from the red granite are not consistent with alteration caused by widespread paleoclimatic conditions in the late permian and they are interpreted as related to local tectonic and or weathering events

lithostratigraphic and allostratigraphic framework of the cambrian ordovician potsdam group and correlations across early paleozoic southern laurentia the potsdam group is a cambrian to lower ordovician siliciclastic unit that crops out along the southeastern margins of the ottawa graben from its base upward the potsdam consists of the ausable hannawa falls and keeseville formations in addition the potsdam is subdivided into three allounits allounit 1 comprises the ausable and hannawa falls and allounits 2 and 3 respectively the lower and upper parts of the keeseville allounit 1 records early to middle cambrian syn rift arkosic fluvial sedimentation ausable formation with interfingering mudstone arkose and dolostone of the marine altona member recording transgression of the easternmost part of the ottawa graben rift sedimentation was followed by a middle cambrian climate change resulting in local quartzose aeolian sedimentation hannawa falls formation allounit 1 sedimentation termination coincided with latest middle cambrian tectonic reactivation of parts of the ottawa graben allounit 2 lower keeseville records mainly upper cambrian quartzose fluvial sedimentation with transgression of the northern ottawa graben resulting in deposition of mixed carbonate siliciclastic strata of the marine riviere aux outardes member sedimentation was then terminated by an earliest ordovician regression and unconformity development allounit 3 upper keeseville records diachronous transgression across the ottawa graben that by the arenigian culminated in mixed carbonate siliciclastic shallow marine sedimentation theresa formation the contact separating the potsdam group and theresa formation is conformable except locally in parts of the northern ottawa graben where the presence of localized islands and or coastal salients resulted in subaerial exposure and erosion of the uppermost potsdam strata and accordingly unconformity development

discrepancies between experimental observations in natural and synthetic samples abstract the evidence is reviewed by comparing the data obtained from synthetic samples with those derived from natural samples of magnetic minerals present in rocks it is shown that there are many issues which are still unresolved some suggestions are made concerning the future direction of rock magnetic research such as the need for intensified studies of natural samples the aim of this note is not to disclose anything new but rather to open up some lines of thought and draw attention to questions and ideas that may have been lurking in our minds from the very beginnings of paleomagnetism

impact of assimilating bottom pressure anomalies from grace on ocean circulation estimates 1 the impact of assimilating global ocean bottom pressure obp information from the gravity recovery and climate experiment grace gravity anomalies on the circulation estimate was investigated for this an estimate of the ocean circulation is being inferred by extending the 50 year long german part of the estimating the circulation and climate of the ocean gecco ocean synthesis into recent years the assimilation system is an improved version of the previous gecco optimization which now includes a sea ice model has enhanced resolution on a truly global domain including the arctic ocean by analyzing differences to a synthesis that additionally assimilated obp the grace data was found to provide complementary information to standard ocean data sets including satellite altimetry when assimilated although in principle standard ocean data sets include the obp information the reason why this cannot be extracted is the much larger prior errors for hydrographic and altimeter data in comparison to obp data owing to the fact that only the former two need to include the unresolved eddy signal the largest impact of gravity data is found to be on the barotropic circulation particularly in the subtropical gyres and the polar latitudes remaining differences between the simulated and observed obp information are associated with meridional stripes in the grace gravity maps and with the leakage of terrestrial hydrological information into the ocean additional differences close to the continental boundaries are related to the self attraction and loading processes that are not included in the models

satellite derived interannual ocean bottom pressure variability and its relation to sea level 1 knowledge of the relationship between bottom pressure pb and sea level is important for understanding ocean circulation and climate we use recent gravity recovery and climate experiment grace release 05 data along with altimetry to investigate the relationship between and pb over long periods 1 year and large scales 750 km elevated pb signals are observed over deep extratropical regions e g southern ocean basins and shallow or semi enclosed areas e g indonesian and nordic seas in these places considerable variance is explained by pb variance correlation between and pb is significant in many regions including instances of significant negative correlation suggestive of active baroclinic processes results exemplify the good quality of grace release 05 data and demonstrate that contemporary regional variability cannot always be interpreted in terms of steric changes alone

ocean dynamics associated with rapid j2 fluctuations importance of circumpolar modes and identification of a coherent arctic mode 1 fluctuations of the earth s dynamic oblateness j2 are a measure of global redistributions of mass between equatorial and polar regions sensitive to the component which is symmetric about the equator cox and chao recently published a time series of monthly values of j2 based on satellite orbit determination which showed rapid fluctuations from month to month as well as a large change in j2 in 1997 1998 we here investigate the ocean dynamics associated with these rapid fluctuations using a barotropic ocean model forced by atmospheric wind stress and pressure we find that the model has significant skill in reproducing the observations though not the change in 1997 1998 much of the model variability is related to coherent circumpolar fluctuations in arctic and antarctic bottom pressure which despite their apparent symmetry are forced by quite different mechanisms the antarctic mode is forced by circumpolar winds whereas the arctic mode is forced by northward winds over the entrances to the polar sea comparison with in situ observations shows that the model has skill in reproducing the polar modes arctic tide gauge records confirm the presence of a coherent mode at short periods and at long periods over at least the eurasian arctic shelf if barotropic and representative of the whole arctic this would be large enough to make a major contribution to measured j2 fluctuations but does not account for the 1997 1998 event

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

paleomagnetism of the upper devonian catskill formation from the southern limb of the pennsylvania salient possible evidence of oroclinal rotation multiple components of magnetization were isolated in the natural remanent magnetiza tion of samples of the upper devonian catskill formation red beds taken from the southern limb of the pennsylvania salient the dominant ther mally distributed component sf previously thought to predate folding is demonstrably syn folding in origins the mean direction for sf based on data from the current study and a pre vious study is declination inclination 161 6o 7 9 o a95 3 9 o pole position 127 3oe 43 1on a95 3 1 o n 14 sites although the remagnetization is clearly synfolding in most areas the relative ages of folding and remagne tization vary locally a subordinate high unblocking temperature component ht has a mean tilt corrected direction of 160o 36 o a95 16 o pole position 123 5oe 26 ion a95 15 4 o s n m 7 samples comparison of ht with the prefolding magnetization isolated in the northern limb of the salient suggests that the paleolatitude of this part of north america was about 16os and that part of the curvature of the salient was acquired during orogenesis

diagenetic apatite character and in situ ion microprobe u pb age keeseville formation potsdam group new york state an occurrence of diagenetic fluorapatite cement is documented within the cambro ordovician keeseville formation potsdam group near chateaugay in new york state the fluorapatite cement occurs as stratiform layers within ephemeral fluvial quartz arenites which have been reworked by aeolian processes prior to burial the paragenetic sequence includes the following compaction of dust rimmed grains quartz cementation minor kaolinite fluorapatite cementation followed by secondary dissolution porosity and telogenetic hematite cementation mesogenetic illitization of kaolinite may have taken place prior to or following fluorapatite cementation the fluorapatite occurs as elongated bladed crystals that characteristically contain ladder like inclusion rich cores running parallel to crystal length surrounded by clearer rims and larger blocky crystals towards the middle of interstices in situ shrimp analyses of blocky fluorapatite crystals yield a u pb age of 486 29 ma indicating that the cement for

a palaeomagnetic study of the builth wells llandrindod wells ordovician inlier wales palaeogeographic and structural implications summary discrepancies exist in the southern british ordovician palaeomagnetic data set with individual studies indicating either high southerly or temperate southerly palaeolatitudes although previous palaeomagnetic investigations from the builth inlier have delineated a three component remanence structure doubts have been raised concerning i the magnetization age of the supposed primary component p ii the structural setting of the sampling area llanelwedd quarry within a zone of strike slip deformation and iii whether detailed step wise demagnetization has fully separated the various magnetization components in addressing these problems we present new palaeomagnetic results as follows i a positive palaeomagnetic conglomerate test establishing a pre late llanvirn age for component p ii an enlarged geographic sampling embracing several tectonic domains indicating that relative rotations linked to strike slip tectonism are minor within the builth sampling area and iii evidence that component p is uncontaminated by overprints at some sites suggesting the resulting palaeolatitude of 35 s to be representative for the builth inlier we also present evidence for local syn volcanic deformation within llanvirn volcanics and for intrusion related deformation of llanvirn shales when the revised llanvirn pole from the inlier 3 s 4 e is combined with other data from southern britain in a statistical spline analysis a mean palaeolatitude of 44 5 s is calculated for builth in llanvirn times a palaeoreconstruction for 468 474 ma c mid llanvirn is presented utilizing this analysis

the relationship between sea level and bottom pressure variability in an eddy permitting ocean model we investigate the relationship between sea level after application of an inverse barometer correction and ocean bottom pressure in an eddy permitting ocean model we find the presence of eddies can disrupt this relationship even on timescales as short as 10 20 days but only in the regions of most energetic eddy variability away from eddies the relationship is similar to that seen in a coarserresolution model with a tight relationship between sea level and bottom pressure at high frequencies but with significant correlations between sea level and bottom pressure at interannual timescales seen only in shelf sea regions in the deep ocean regions where sea level and bottom pressure remain related out to the longest timescales are in the arctic ocean and regions of the southern ocean where particularly large amplitude barotropic fluctuations are found but where the mesoscale signal is weak

extreme tectonic rotations within an eastern mediterranean ophiolite baer bassit syria palaeomagnetic results from 27 sites at five localities within the dismembered bae r bassit ophiolite of northern syria are presented the ophiolite forms part of a series of thrust sheets emplaced over mesozoic carbonates of the arabian platform in the middle maastrichtian a positive inclination only area wide tilt test applied to four locality mean remanences and positive fold and reversal tests from palaeohorizontal units pillow lavas lava flows within one of these localities indicate that the ophiolite preserves pre deformation magnetisations variable directions of remanence between localities demonstrate that the ophiolite has experienced extreme relative anticlockwise rotations on a kilometric scale within the most extensively sampled ophiolite massif bassit sheet there is a progressive increase in rotation from north to south the southernmost units at the lowest structural level in the imbricate thrust stack record the highest rotation exceeding 200 although tectonic rotation during imbricate thrusting has been reported in a number of orogenic belts the pattern of rotations in the bassit sheet is difficult to explain by differential thrust sheet rotation instead regional comparisons with the hatay ophiolite of southern turkey and the troodos ophiolite of cyprus suggest that a significant component of rotation may be ascribed to intraoceanic deformation of a coherent region of oceanic crust within the southern neotethyan basin prior to ophiolite emplacement the partially rotated bae r bassit ophiolite was then emplaced and structurally dismembered by thrust faulting during the late tertiary the ophiolitic units were further rotated during the initiation and development of a major sinistral strike slip fault zone linking the cyprus subduction zone to the dead sea transform system the extreme rotations observed in the study are therefore of composite origin and reflect the complex development of structural fabrics within the ophiolite 2002 elsevier science b v all rights reserved

annual sea level changes on the north american northeast coast influence of local winds and barotropic motions abstractunderstanding the relationship between coastal sea level and the variable ocean circulation is crucial for interpreting tide gauge records and projecting sea level rise in this study annual sea level records adjusted for the inverted barometer effect from tide gauges along the north american northeast coast over 1980 2010 are compared to a set of data assimilating ocean reanalysis products as well as a global barotropic model solution forced with wind stress and barometric pressure correspondence between models and data depends strongly on model and location at sites north of cape hatteras the barotropic model shows as much if not more skill than ocean reanalyses explaining about 50 of the variance in the adjusted annual tide gauge sea level records additional numerical experiments show that annual sea level changes along this coast from the barotropic model are driven by local wind stress over the continental shelf and slope this result is interpreted in the light of a simple dynamic

palaeomagnetism of early cambrian brigus red shale eastern newfoundland abstract studies of the early cambrian brigus br red shale exposed in conception bay yielded a single stable mean remanence direction of d 265 i 58 reverse polarity before tilt correction and d 279 i 48 k 47 95 6 9 forn 7 sites 25 samples after correction for gentle tilt the corresponding north pole palaeopole position is 27 s 51 e dp dm 6 9 this magnetization is characterized by a linear vector trajectory at higher unblocking temperature t ub spectra 400 680 c the magnetization directions at the low t ub range 400 c are more variable from sample to sample although they typically have steep downward inclinations with no evidence of kiaman overprinting marginal but not statistically significant improvement k 44 77 in the grouping of site means after tilt correction suggests that the predominant univectorial westerly remanance was probably acquired after deposition based on both geological and magnetic evidence the brigus shale formation appears to be remagnetized during siluro devonian times the position of the far sided antipole br 27 n 129 w located in the vicinity of the pole for the cambrian morrison river formation mr at 20 n 146 w which is discordant from the younger palaeozoic late ordovician carboniferous poles reported for the avalon zone is fortuitous since the magnetization of br is most likely secondary the magnetization is younger than the iapetus closure date determined geologically late ordovician consequently the displacement of the avalon zone with respect to the north american craton cannot be estimated the width of the proto atlantic ocean cannot be calculated

time variations in ocean bottom pressure from a few hours to many years in situ data numerical models and grace satellite gravimetry in situ ocean bottom pressure obp obtained from 154 different locations irregularly scattered over the globe is carefully processed to isolate signals related to the ocean general circulation and large scale sea level changes comparison against a global numerical ocean model experiment indicates poor correspondence for periods below 24 hr possibly related to residual tidal signals and small timing errors in the atmospheric forcing applied to the ocean model correspondence increases rapidly for periods between 3 and 10 days where wind driven dynamics are already well understood and consequently well implemented into numerical models coherence decreases again for periods around 30 days and longer where processes not implemented into ocean general circulation models as barystatic sea level changes become more important correspondence between in situ data and satellite based obp as obtained from the gravity recovery and climate experiment grace german research centre for geosciences rl05a gravity fields critically depends on the postprocessing of level 2 stokes coefficients that also includes the selection of appropriate averaging regions for the grace based mass anomalies the assessment of other available grace level 2 products indicates even better fit of more recent solutions as itsg grace2016 and the center for space research and jet propulsion laboratory rl05 mascons in view of the strong high frequency component of obp however a higher temporal resolution of the oceanic grace products would be rather advantageous

middle eocene paleomagnetic data from the eastern sakarya zone and the central pontides implications for the tectonic evolution of north central anatolia 1 a paleomagnetic investigation has been carried out on middle eocene volcanic rocks at 23 sites in the eastern sakarya zone and the central pontides of north central anatolia in order to better understand the regional tectonic evolution of the main zones of northeastern anatolia in the middle eocene the results constrain the tectonic evolution of the area when evaluated in conjunction with earlier published paleomagnetic directions from 92 localities small counterclockwise rotations in the range of r r 1 3 1 4 to r r 17 2 16 8 with respect to eurasia are observed in the central pontides on the northern side of the north anatolian fault naf clockwise rotations ranging between r r 8 5 15 1 and r r 29 7 12 0 are observed between the naf and the sungurlu fault sf in the eastern sakarya zone counterclockwise rotations of r r 18 9 12 4 to r r 42 2 6 9 are observed to the south of the sf our findings combined with previous data support the indentation model of kaymakci et al 2000 2003a 2003b which postulates the collision and northeast directed indentation of the kirsehir block into the sakarya zone this model which was developed to explain the evolution of the cankiri basin can also explain the variable magnitudes of paleomagnetically determined rotations thrust directions and the curvature of the north anatolian ophiolite belt

observing ocean heat content using satellite gravity and altimetry 1 a method for combining satellite altimetry observations with satellite measurements of the earth s time varying gravity to give improved estimates of the ocean s heat storage is presented over the ocean the time variable component of the geoid can be related to the time varying bottom pressure the methodology of estimating the ocean s time varying heat storage using altimetric observations alone is modified to include observations of bottom pressure a detailed error analysis of the methodology is undertaken it is found that the inclusion of bottom pressure improves the ocean heat storage estimates the improvement comes from a better estimation of the steric sea surface height by the inclusion of bottom pressure in the calculation over using the altimeter observed sea surface height alone on timescales of the annual cycle and shorter the method works particularly well however long timescale changes in the heat storage are poorly reproduced because of deficiencies in the methodology and the presence of contaminating signals in the bottom pressure observations index terms 4556 oceanography physical sea level variations 1223 geodesy and gravity ocean earth atmosphere interactions 3339 1227 geodesy and gravity planetary geodesy and gravity 5420 5714 6019 1243 geodesy and gravity space geodetic surveys 4275 oceanography general remote sensing and electromagnetic processes 0689 keywords ocean heat content altimetry satellite gravity steric height remote sensing

on the use of satellite altimetry to detect ocean circulation s magnetic signals oceanic magnetic signals are sensitive to ocean velocity salinity and heat content the detection of respective signals with global satellite magnetometers would pose a very valuable source of information while tidal magnetic fields are already detected electromagnetic signals of the ocean circulation still remain unobserved from space we propose to use satellite altimetry to construct proxy magnetic signals of the ocean circulation these proxy time series could subsequently be fitted to satellite magnetometer data the fitted data could be removed from the observations or the fitting constants could be analyzed for physical properties of the ocean e g the heat budget to test and evaluate this approach synthetic true and proxy magnetic signals are derived from a global circulation model of the ocean both data sets are compared in dependence of location and time scale we study and report when and where the proxy data describe the true signal sufficiently well correlations above 0 6 and explained variances of above 80 can be reported for large parts of the antarctic ocean thus explaining the major part of the global sub seasonal magnetic signal

internal crustal deformation in the northern part of shan thai block new evidence from paleomagnetic results of cretaceous and paleogene redbeds in order to describe the internal deformation of the northeast part of the shan thai block resulting from the penetration of the indian plate into asia a paleomagnetic study was carried out on the cretaceous and paleogene strata in the southern part of the simao terrane high temperature magnetic components with unblocking temperatures around 680 degrees c were isolated and positive fold test shows its primary nature of magnetization the tilt corrected site mean directions of the lower cretaceous and upper cretaceous from the menglun area are d s 46 2 degrees i s 45 9 degrees k 11 0 alpha 95 10 6 degrees and d s 33 2 degrees i s 30 9 degrees k 68 4 alpha 95 8 2 degrees respectively the site mean directions of the upper cretaceous and lower paleogene for the mengban area are d s 50 5 degrees i s 31 0 degrees k 207 6 alpha 95 6 4 degrees and d s 43 5 degrees i s 23 0 degrees k 26 1 alpha 95 13 4 degrees respectively the results of the lower cretaceous and upper paleogene from the mengla area are d s 46 9 degrees i s 42 2 degrees k 27 3 alpha 95 7 7 degrees and d s 41 8 degrees i s 23 8 degrees k 38 9 degrees alpha 95 5 8 degrees respectively in comparison with previous paleomagnetic data of the simao terrane the rotational deformation can be divided into four stages the cretaceous and paleocene sediments of the simao terrane experienced intensive folding before the early oligocene during the early oligocene to early miocene the shan thai and indochina blocks experienced southeastward extrusion with similar to 20 degrees clockwise rotation relative to the south china block during the middle to late miocene the shan thai blocks experienced more 15 degrees clockwise rotation since the late miocene the activity of strike slip faults surrounding the simao terrane enhanced the internal differential rotations of the terrane these deformation processes finally resulted in a complex internal deformation of the simao terrane c 2013 elsevier b v all rights reserved

a palaeomagnetic study of recumbently folded and thermally metamorphosed torridon group sediments eishort anticline skye scotland two geologically significant palaeomagnetic components have been isolated in samples of torridon group sandstones from the kishorn nappe of nw scotland the samples were collected from the eishort anticline a large recumbent fold of caledonian age the softer component which is demagnetized by low temperatures and weak magnetic fields when in situ displays a steep upward direction typical of reversed tertiary magnetizations both polarities of the harder component which is demagnetized by high temperatures only are present and when dip corrected display either northwesterly upward or southeasterly downward directions characteristic of torridonian remanences it is suggested that the tertiary component is of chemical origin and the result of alteration of magnetite titanomagnetite grains the geographical distribution of these grains is irregular and as a result the distribution of the tertiary overprint is irregular the torridonian palaeomagnetic components from both limbs of the fold can be restored by rotation about the fold axis to internally consistent directions which lie close to previously published data from the caledonian foreland no correction is necessary for finite strain which suggests that the eishort anticline formed by a flexural slip mechanism however an anticlockwise rotation of 26 is required to reconcile the torridonian directions from the kishorn nappe with those of the caledonian foreland which suggests that during emplacement the thrust sheet rotated on the underlying fault surface

new paleomagnetic results from cretaceous sediments near lisboa portugal and implications for the rotation of iberia abstract paleomagnetic study of outer platform sediments of late jurassic early cretaceous age from portugal lisboa area leads to characteristic remanent magnetization directions for the hauterivian barremian d 317 i 58 and the aptian d 344 i 47 the absolute rotation of iberia between 125 and 110 ma is consequently of about 27 in an anticlockwise sense a later rotation of about 14 follows the first one in the same sense from 110 ma the total absolute rotation of iberia from the hauterivian age determined by paleomagnetism is thus about 41 the comparison of declinations measured with paleodeclinations calculated in lisboa from the eurasian and african poles of similar age indicates that the main phase of relative rotation of iberia with respect to eurasia occurs during the first stage of relative motion i e hauterivian to aptian the tectonic history of the bay of biscay is in good agreement with these two stages of rotation the total relative rotation with respect to europe is 34 this value is consistent with results previously established by van der voo 2 3 25 but we have established that the main phase of rotation 30 occurs in the hauterivian aptian interval the movement of iberia is clearly linked to the movement of africa in direction and age but the amount of rotation of iberia during the early cretaceous is much larger and implies that iberia was not a real part of the african plate

paleomagnetism and rock magnetism of early silurian dunn point volcanics avalon zone nova scotia abstract paleomagnetic results have been obtained from the subaerial volcanics andesites rhyolites ignimbrites from the dunn point formation exposed in the antigonish highlands of the avalon zone nova scotia an early silurian age of 430 15 ma is assigned to these volcanic rocks the age is in agreement with the fossil evidence from conformably overlying sedimentary rocks the volcanic units were tightly folded and metamorphosed to sub greenschist facies during one major and one secondary phase of deformation probably associated with the mid late devonian acadian orogeny this paleomagnetic study is based on 45 samples collected from nine sites the site mean directions of the natural remanent magnetization nrm make a large deviation from the present earth s field with nrm intensities ranging from 10 2 to 10 am 1 the most commonly observed remanence direction a d 153 i 28 obtained from both alternating fields 30 75 mt and thermal 500 560 c treatments yields a corresponding direction a d 0 i 63 after correction for geological tilt a large scatter in direction up to 60 is observed in a and the fold test is not significantly positive a second and less common remanence component b d 146 i 54 which presumably postdates folding is also observed this component is mainly isolated by thermal treatment in the 540 630 c range room temperature isothermal experiments and optical examination of polished sections indicate the presence of magnetite and hematite as the carriers of both a and b directions the corresponding reversed paleomagnetic poles fall at a 163 e 52 n and b 146 e 4 n in close agreement with cratonic north american upper jurassic and late devonian poles respectively in the mid late devonian time interval the avalon zone was situated slightly to the south but close to the north american eastern margin

weighing the ocean using a single mooring to measure changes in the mass of the ocean 1 combining ocean and earth models we show that there is a region in the central pacific ocean where ocean bottom pressure is a direct measure of interannual changes in ocean mass with a noise level for annual means below 3 mm water equivalent and a trend error below 1 mm yr we demonstrate this concept using existing ocean bottom pressure measurements from the region from which we extract the annual cycle of ocean mass amplitude 8 5 mm peaking in late september which is in agreement with previous determinations based on complex combinations of global data sets this method sidesteps a number of limitations in satellite gravity based calculations but its direct implementation is currently limited by the precision of pressure sensors which suffer from significant drift development of a low drift method to measure ocean bottom pressure at a few sites could provide an important geodetic constraint on the earth system citation hughes c w m e tamisiea r j bingham and j williams 2012 weighing the ocean using a single mooring to measure changes in themass ofthe ocean geophys res lett 39 l17602 doi 10 1029 2012gl052935

an ocean resonance in the indian sector of the southern ocean 1 satellite altimeter observations of sea surface height show an extensive region of long wavelength fluctuations in the indian sector of the southern ocean a previous study showed that a similar feature found in the south pacific is due to a trapped geostrophic mode of the ocean here we investigate the feature in the indian sector and find that it is due to a similar mode with a decay time of approximately 3 5 days these previously unsuspected large scale modes of the ocean will have a significant effect locally on the satellite based gravity measurements currently underway

fragmentation of asia in the permian asia is a composite continent formed by the accretion of crustal blocks1 3 a likely sequence of events is that siberia collided with a kazakhstan block which together then collided with europe along the urals in permo triassic times2 this was followed by the sucessive accretion of various blocks of south and east asia to siberia culminating in the collision of india with asia during the cenozoic palaeomagnetic data have already demonstrated that the kolyma and sikhote alin blocks of eastern asia collided with the main continent along the late mesozoic fold belts of verkhoyansk and sikhote alin4 furthermore results from the malay peninsula5 and japan6 suggest that south east asia and japan were situated near the equator in permian times and were therefore separated from the asian continent we report here some palaeomagnetic results from the permian of the sino korean and yangtze blocks of china that show they were also situated near the equator were not in their present relationship to one another and were widely separated from siberia

circum iapetus paleogeography of the precambrian cambrian transition with a new paleomagnetic constraint from laurentia abstract the paleogeography of the precambrian cambrian transition is still poorly known but is fundamental for understanding late neoproterozoic climate extremes and the spatial associations of the rapidly evolving ediacaran and cambrian fauna this period has also been proposed to host unusual geodynamic events such as rapid plate motions and or the bulk tumbling of the earth with respect to its spin axis called true polar wander tpw new paleomagnetic and 40ar 39ar geochronologic results have been obtained from a pair of shallowly emplaced syenitic intrusions in western quebec the mont rigaud and the chatham grenville stocks are related to a failed rift arm of the iapetus ocean both intrusions bear hornblendes which provide overlapping 40ar 39ar plateau ages of 533 2 1 1 ma mont rigaud and 531 4 3 4 ma chatham grenville corresponding to early cambrian nemakit daldynian time characteristic paleomagnetic reversed directions from both intrusions are easterly and shallow d 89 3 i 30 1 95 6 2 k 38 8 n 15 sites and the mont rigaud intrusion also carries antipodal normal polarity directions the combined result yields a north paleopole at location 11 9 s 184 6 e dp 3 8 dm 6 9 placing the montreal region at 16 4 s paleolatitude in the early cambrian in good agreement with late ediacaran and middle to late cambrian paleomagnetic results from laurentia laurentia likely resided at low southerly paleolatitudes throughout the cambrian ruling out a major inertial interchange tpw event for early to middle cambrian time a comparison of late ediacaran to middle cambrian paleomagnetic results from laurentia baltica siberia and elements of west gondwana implies that by early cambrian time a large paleolatitudinal gap existed between laurentia and its presumed conjugate rift margins thus placing a wide iapetus ocean between them the position of baltica within the circum iapetus paleogeography is contentious due to differing interpretations of the few paleomagnetic results during ediacaran time laurentia underwent large apparent polar wander that is manifested as motion from low latitude at 615 ma to the south polar region at 590 575 ma and then rapidly back to low latitude by 565 550 ma the large and perhaps rapid apparent polar wander of laurentia and other continents in the ediacaran remains enigmatic and controversial

first report of coupled early permian paleomagnetic and geochronologic data from the dunhuang block nw china and implications for the tectonic evolution of the paleo asian ocean abstract in order to better understand the tectonic relationship between the dunhuang block dhb and its adjacent blocks and to constrain the timing of the closure of the paleo asian ocean a combined geochronologic and paleomagnetic investigation has been undertaken on early permian tuff basalt flows and sandstones from the shuangbaotang formation in the northwestern part of the dhb u pb zircon dating indicates that the age of the strata is between 280 6 2 9 ma and 291 4 2 6 ma thermal demagnetization of a three component isothermal remanent magnetization irm and curie point experiment suggest that magnetite dominates in the rock samples analyzed in addition there is a minor amount of hematite in some sandstones stepwise thermal demagnetization successfully isolated stable characteristic remanent magnetization chrm from 11 tuff layers two lava flows and nine sandstone beds two components were isolated from all samples a lower temperature component ltc and a higher temperature component htc the ltc is near the direction of the present day geomagnetic field and produced a negative fold test indicating it is a viscous remanent magnetization in the present day geomagnetic field most of the htc are reverse polarity normal 4 reverse 158 which is in accordance with the kiaman reversed superchron that spans the late carboniferous permian interval in addition the htc of all studied sites passed the fold and reverse tests suggesting that they likely represent primary remanent magnetization the tilt corrected mean direction from all sites tuff basalts and sandstones is ds 1 7 is 43 1 ks 403 95 1 5 n 22 the mean paleopole of the site mean direction corresponded vgps lies at 74 5 n 268 5 e with a95 1 6 considering the consistent inclination values recorded among the studied tuff basalts and sandstones and the low degrees of anisotropy within all samples we suggest that there is no significant inclination shallowing caused by depositional compaction in the sedimentary layers of the studied section taking into account the results from this study as well as previous late paleozoic paleomagentic studies from adjacent tectonic blocks we conclude that the dhb formed part of the amalgamated dunhuang north china alxa qaidam mega block during the early permian but was separated from the tarim block by a small ocean here named the qiemo xingxingxia paleo ocean at this time a comparison of the early permian paleolatitudes of these and other adjacent blocks suggest that the paleo asian ocean sensu lato was still open at this time combined with other geological evidence a paleogeographic reconstruction of the paleo asian ocean has been reconstructed for the early permian

a new paleogeographic configuration of the eurasian landmass resolves a paleomagnetic paradox of the tarim basin china 1 new paleomagnetic data from permian red beds and middle jurassic limestones from the tarim basin pose a paradox their declinations are similar to upper carboniferous to neogene rocks collected from the same sections and their inclinations parallel present values when assuming that lower than expected inclinations in continental sedimentary rocks arise from inclination shallowing effects then the paleolatitudes of all upper carboniferous to present rocks from tarim are indistinguishable local vertical axis block rotations occurring in the last 20 million years explain why declinations vary at different localities in the basin our middle jurassic data positions tarim 23 6 8 4 farther south than that predicted from the coeval reference pole for eurasia however no geologic argument exists to support the closure of a large ocean basin between tarim and siberia since the middle jurassic thus the paradox are the rocks from tarim totally overprinted or is the middle mesozoic part of the reference eurasian apparent polar wander path erroneous several lines of evidence suggest the tarim rocks are not remagnetized we conclude that tarim has experienced little or no apparent polar wander since the carboniferous moreover our middle mesozoic reconstruction of eurasia using the new middle jurassic pole from tarim results in a more geologically compatible solution for the eastern asian blocks over previous reconstructions

palaeomagnetic study of the late precambrian west greenland kimberlite lamprophyre suite definition of the hadrynian track abstract kimberlite and potassic lamprophyre dykes were intensively intruded into the early proterozoic nagssugtoqidian mobile belt of west greenland during an important phase of brittle reactivation in late precambrian early cambrian times ca 580 570 ma and during at least one other minor phase thermal and alternating field demagnetisation studies of 52 of these dykes identify primary components residing in the critical blocking temperature range distributed between shallow westerly and steep positive directions near the axis of the proterozoic shear belt the dykes predominantly lamprophyres have closely grouped shallow directions with a reversal near the margins of the shear belt dykes predominantly kimberlites have steeper and distributed directions the cleaned components of magnetisation appear to be single and the distribution of directions is interpreted to record a migration of the palaeofield axis which intersecting relationships show to have been from shallow to steep the dyke directions are grouped to define representative mean palaeopoles of 215 e 3 n lk1 a 95 3 9 213 e 18 n lk2 a 95 6 1 203 e 46 n lk3 a 95 10 4 and 259 e 54 n lk4 a 95 11 0 a subsidiary direction recorded in five dykes near the southern margin of the shear belt lk5 palaeopole at 297 e 16 s a 95 12 5 is derived entirely from lamprophyres and is possibly silurian in age an rb sr isochron on three lamprophyres of 1227 ma and agreement of the remanence direction with ca 1220 ma rocks from elsewhere in greenland suggests that the lk1 component is wholly or partly of that age the remaining sequence of palaeopoles falls along the hadrynian polar track and the age data relating to this track are re evaluated evidence for a pre 800 ma age is no longer valid and the new data from west greenland confirm that the track is latest precambrian to early cambrian in age it is shown to connect poles of late precambrian and lower cambrian age and to embrace other data from the laurentian shield the rapid passage of the shield across the south pole is consistent with the sedimentation sequences and suggests a high latitude origin for the tillite horizon of this age the hadrynian track is also compared with the contemporaneous record from gondwanaland and it is shown that the two shields were in juxtaposition in the identical reconstruction to the proterozoic supercontinent until earliest cambrian times this discovery links the lower cambrian marine transgression and the widespread ca 580 560 ma alkaline province in the gondwanaland laurentian and fennoscandian shields to major continental break up and it conforms with evidence that the iapetus ocean did not open until cambrian times