the magnetostratigraphy of leg 73 sediments abstract the main objectiveof dsdp leg 73 was to obtain high quality records of major paleooceanographic events in the south atlantic this was achieved by coringsix sites on the african plate the sediments thus recovered span the cenozoic and five of the six sites proved ideally suited for magnetostratigraphic analysis the results presented in this paper and elsewhere in this volume constitute the first opportunity to extend the direct correlation of the magnetostratigraphic and biostratigraphic time scales into the paleogene in deep sea cores the magnetostratigraphic analyses from dsdp leg 73 sediments are presented in this paper the correlation of the magnetostratigraphy to the magnetic polarity time scale provides tight age depth control for the five sites analyzed allowing the accurate calculation of sediment accumulation rates the data presented here represent a remarkable record of the fine scale polarity history of the earth s magnetic field these data place constraints on the interpretation of small scale marine magnetic anomalies which are modelled equally effectively by field intensity fluctuations as polarity reversals at least some of the tiny wiggles correspond to very short polarity units in the magnetostratigraphic record by assuming an axial geocentric dipole the inclination of the time averaged magnetic field recorded in the sediments can be used to calculate the paleolatitude at which the sediments were deposited combining the age and average inclination information available from the magnetostratigraphy we present paleolatitudes versus time for the leg 73 drill sites

paleomagnetic evidence for neogene rotational deformations in the aegean domain new paleomagnetic data are reported from the islands of skyros and lesbos in central aegea and the izmir foca region in western anatolia together with previous results obtained in northwestern greece and with results from northern aegea reported by others authors these data suggest that the lower miocene arc was almost rectilinear trending e w and that the curvature was acquired by opposed rotational deformations at each termination moreover the observed inclinations which are shallower than those expected on the basis of a geocentered dipole field suggest a large northward drift since middle miocene

the drift history of adria and africa from 280 ma to present jurassic true polar wander and zonal climate control on tethyan sedimentary facies article i nfo the orogenic belts surrounding the undeformed adriatic sea represent the margins of an area known as adria the african promontory we have undertaken a critical appraisal of paleomagnetic data from regions of adria considered parautochthonous relative to africa obtained either from biostratigraphically dated sed imentary rocks corrected for inclination shallowing or from igneous rocks that are regarded as free from any inclination shallowing bias paleomagnetic directions were used to calculate paleomagnetic poles for compar ison with coeval and inclination flattening free paleomagnetic poles from stable africa visual coherence of paleopoles for several time slices from the early permian to the eocene supports the construction of a com posite apparent polar wander path apwp valid for parautochthonous adria and stable africa this compos ite apwp is compared to previous apwps finding good agreement with the global apwp of kent and irving 2010 both apwps show a remarkable and rapid polar shift of 40 in the jurassic that other apwps tend to underestimate we interpret this shift to represent a major episode of true polar wander tpw from 183 ma in the early jurassic to 151 ma in the late jurassic using a simple zonal climate model the drift motion of adria attached to africa appears to be consistent with the distribution of permian cretaceous sed imentary facies on adria

new paleomagnetic data from oligocene formations of northern aegea new paleomagnetic data obtained from volcanic and plutonic formations in thrace northern aegea show that this region has not undergone any significant rotation since the lower oligocene the mean value of the inclination is shallower than expected on the basis of a geocentered dipole field implying a large northward drift of about 1000 km although a comparison with published data from bulgaria leads to a puzzling large shortening between these two regions the measured shallow inclinations are coherent with most of other paleomagnetic studies from oligocene formations throughout the entire mediterranean area together with published results from chalkidiki peninsula our data suggest that the circum rhodopean belt was almost rectilinear and trending e w in lower oligocene time

earliest oligocene increase in south atlantic productivity as interpreted from rock magnetics at deep sea drilling project site 522 the magnetic properties of the sediments rock magnetics at dsdp site 522 in the south atlantic exhibit clear differences between the latest eocene and earliest oligocene based on low temperature behavior of saturation remanence and hysteresis loops we attribute the difference to a slightly greater proportion of the finest grained so called superparamagnetic magnetite in the eocene sediments we believe that the lower proportion of very fine grained magnetite in the oligocene sediments is a result of incipient reduction diagenesis caused by increased productivity and hence increased labile organic carbon transport to the sediments due to an early oligocene increase in thermohaline circulation the eocene to oligocene transition at site 522 is also expressed by changes in microfossil assemblages increased carbonate content decreased insoluble residue and decreased foraminiferal shell fragmentation the increase in carbonate is synchronous with and parallels a change in the ratio of two of the rock magnetic parameters a ratio that tracks the decrease in the very fine grained magnetite component also parallel to these is a trend toward heavier 13c values in foraminiferal tests the increase in organic carbon transport to the sediments led to chemical dissolution of the finest grain size fraction of magnetite in the oligocene sediments hence a reduction in the superparamagnetic component and the change in the rock magnetic ratio in this way rock magnetics can be sensitive indicators of environmental changes such as fluctuations in organic carbon transport which may leave little other trace in the sedimentary record

the tertiary geodynamical evolution of the aegean arc a paleomagnetic reconstruction abstract the paleomagnetic results obtained in the last 5 6 years from tertiary formations in the aegean domain indicate that the lower miocene arc was almost rectilinear with an e w trend and that its curvature has been acquired tectonically in two major phases during the middle miocene a first phase of deformation is characterized by rotations occurring at the two terminations of the arc clockwise in the west epirus anticlockwise in the east southeastern anatolia a second phase of rotation occurring in the last 5 ma about a pole situated in the southern adriatic sea has affected only the northwestern part the data also indicate that the antalya basin has not been involved in the geodynamical evolution of the arc so that the bey daglari represent its easternmost unit a more complex rotational pattern is observed in the internal zones the large rotations measured in evia 48 and skyros 26 probably occurred in the last 5 ma and result from rotation of fault bounded blocks in a shear zone connecting the north aegean trough to the external arc in the izmir region in the karaburun peninsula of western anatolia and in the island of lesbos significant counterclockwise clockwise or null rotations of coherent blocks have taken place during the neotectonic extensional regime furthermore the values of the inclination obtained from both sedimentary and volcanic oligo miocene formations are systematically shallower than expected on the basis of a geocentered dipole field this suggests that the entire studied area has undergone a northward drift of over 1000 km since the middle miocene

magnetostratigraphic biostratigraphic and stable isotope stratigraphy of an upper miocene drill core from the sale briqueterie northwestern morocco a high resolution chronology for the messinian stage we report a high resolution stable isotope carbonate magnetostratigraphic and biostratigraphic record from a 175 m drill core from the sale briqueterie which is part of the bou regreg section in northwestern morocco the sale drill core spans the interval from paleomagnetic chron c4n partim to c3r earliest gilbert which represents the time leading up to and including the isolation and desiccation of the mediterranean i e the messinian salinity crisis during chrons c3an and c3ar 6 935 to 5 894 ma the isotope and carbonate signals display quasi periodic variations with estimated periods of 40 and 100 kyr respectively we interpret the 40 kyr 18o variations as reflecting changes in global ice volume caused by obliquity induced changes 41 kyr in solar insolation in polar regions the 100 kyr carbonate variations probably represent long term modulation of the amplitude of the precessional cycle 21 kyr which is not resolved by our sampling frequency the cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of shackleton et al 1994a from stage tg24 in chron c3r earliest gilbert to stage c3ar 18o 18 at the base of chron c3ar 6 935 ma a major change in paleoceanographic conditions is recorded across the tortonian messinian boundary which we correlate to chron c3bn at 7 04 ma benthic foraminiferal 18o values increased by an average of 0 4 in two steps at 7 17 ma and 6 8 ma and 13c values decreased by 0 7 0 8 between 7 1 and 6 8 ma representing the late miocene carbon shift the first step in 18o values coincides with an inferred reversal in deep water circulation through the rifian corridor and the second correlates with the base of the tripoli formation and onset of crisis conditions in the mediterranean we suggest that the increase in 18o values represents at least in part an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the mediterranean average 18o values remained high throughout most of chrons c3ar and c3an reaching maximum 18o values during isotope stages tg20 and 22 in chron c3r earliest gilbert the glacio eustatic falls associated with these events may have resulted in the complete isolation of the mediterranean from the world ocean shackleton et al 1994a following stage tg12 in the sale record there exists a trend toward progressively lower 18o values that may represent a series of marine transgressions that eventually reflooded the mediterranean and ended the salinity crisis

oligocene paleoceanography of the south atlantic paleoclimatic implications of sediment accumulation rates and magnetic susceptibility measurements paleoceanographic changes during the oligocene in the south atlantic have been examined using paleomagnetic rock magnetic carbonate content and sediment accumulation rate sar data we show that magnetic susceptibility ms is largely controlled by carbonate content at deep sea drilling project site 522 which in turn is the primary control on sar at the site over 5000 ms measurements were averaged over magnetostratigraphic polarity intervals for use as indicators of carbonate content and sar proxies the study produced three primary results 1 a spectral analysis of the ms data from one upper oligocene core reveals two dominant periodicities 44 7 10 4 kyr and 26 4 3 6 kyr which approximate milankovitch obliquity 41 kyr and precession 23 kyr periods 2 four pulses of increased sar lasting 1 to 2 m y punctuate the section implying longer term climatic changes these events are also seen in the contessa quarry section of the italian tethyan oligocene and 3 two of the sar maxima correspond to times of global cooling and possible ice volume increases at 31 and 36 ma

testing models of the tertiary paleomagnetic field we examine selected paleomagnetic data of tertiary age in order to assess previously suggested models of the non dipole portion of the paleomagnetic field data from three localities on the african plate from dsdp leg 73 odp leg 115 and from gubbio indicate that the axial octupole contribution was near zero in the paleocene and was likely no greater than 5 6 of the axial dipole in the oligocene additional data from north america which can be linked to africa using well known relative plate motion parameters suggest that a positive axial quadrupole field has been present throughout the tertiary to investigate some of the practical consequences of these estimates we apply a non dipole field model 3 to 4 go go 0 g g l to paleomagnetic data from two odp sites on the african plate sites 710 711 and from the deccan traps we show that paleomagnetic directions from these deep sea sediments and from this flood basalt province appear consistent with a fixed hotspot model suggesting in particular that there has been little or no cenozoic drift of the rrunion hotspot 1 the paleomagnetic field configuration the application of paleomagnetic measurements to tectonic studies requires that the paleomagnetic reference field be accurately known usual practice in most tectonic studies invokes the dipole hypothesis to determine paleolatitude from the observed paleomagnetic directions observations from rocks that are only a few million years old generally support the dipole hypothesis the time averaged field configuration largely matches the field of a geocentric axial dipole gad however non dipole components can also be detected in the time averaged field 1 2 3 4 this long term non dipole field amounts to a few percent of the geocentric axial dipole and suggests that in detailed tectonic studies non dipole field effects cannot be neglected without consequence although these non dipole components of the mean field have been relatively small during the past few million years less than 5 of the gad larger non dipole fields may have existed during other intervals in earth history indeed two spherical harmonic studies of the time averaged field available for pre pliocene times 2 5 indicate significantly larger non dipole fields during parts of the tertiary and mesozoic amounting at times 0012 821x 90 03 50 1990 elsevier science publishers b v to 10 15 or more of the gad non dipole components of such magnitudes would lead to substantial systematic errors in paleomagnetic pole positions and thus could complicate tectonic interpretations and reconstructions considerably in this paper we attempt to test the reality of these prior indications of large non dipole contributions

palaeolatitudes from dsdp leg 73 sediment cores implications for the apparent polar wander path for africa during the late mesozoic and cenozoic summary palaeolatitudes estimated from dsdp sediments provide important constraints on the apparent polar wander path apwp of africa during the cenozoic a revised apwp is suggested based on new information about palaeomagnetic poles from the african continent and predicted palaeolatitudes are compared with those determined from leg 73 sediments other published paths are discussed

a major late tortonian rotation phase in the crotone basin using ams as tectonic tilt correction and timing of the opening of the tyrrhenian basin abstract paleomagnetic studies of sediments from the calabro peloritan block in southern italy consequently imply a 15 clockwise rotation for the late tortonian to middle pleistocene sedimentary cover but the results of older sediments are generally less consistent earlier paleomagnetic results of tortonian sites from the basilicoi section crotone basin northern calabria suggested a major counterclockwise rotation of 97 scheepers 1994 here we studied the basilicoi section in detail and we used anisotropy of the magnetic susceptibility ams to reconstruct the bedding plane needed for tilt correction this reduced the 97 counterclockwise rotation to a 25 counterclockwise rotation the lese section also in northern calabria shows the same counterclockwise rotation in sediments with an age between 10 4 and 8 6 ma thus confirming the results from the corrected basilicoi section a comparison of the magnetostratigraphy and planktonic foraminiferal biostratigraphy with the magneto biostratigraphic framework of the mediterranean late miocene allows a correlation of the basilicoi and lese sections to the gpts and a timeframe for the rotation it is concluded that the 25 counterclockwise rotation phase took place between 7 6 0 1 and 8 6 ma we speculate that the timing of this tectonic phase is related to the opening of the tyrrhenian sea and the separation of calabria from sardinia we compare our results with those of odp leg 107 and we suggest an age between 8 6 and 7 8 ma for the timing of the opening of the tyrrhenian sea

paleomagnetic study of sicily consequences for the deformation of italian and african margins over the last 100 million years abstract paleomagnetic analysis of cenozoic sediments from the iblean platform 12 sites 100 samples has provided four new poles these data are combined with those available from volcanic series to yield a new apparent polar wander path for stable sicily since the upper cretaceous this curve when compared to a revised curve for africa using a selection of available data points demonstrates a 15 rotation of sicily with respect to africa during the plio pleistocene this rotation accounts for the extensional tectonic regime that prevails in the pelagian sea and which is evidenced by en relais rifts malta pantelleria linosa associated with alkaline volcanism of pliocene and quaternary age paleomagnetic directions from various areas of the italian peninsula also indicate anticlockwise rotations with diverse amplitudes the chronology of these rotations is consistent with a deformation of the western italian margin during progressive suturation from north to south of the corsican sardinian block since the end of the oligocene

a clockwise rotation of southern apulia new paleomagnetic results from 13 sites sampled in eo oligocene autochthonous formations in the extreme south of the apulian platform in southeastern italy are presented they suggest that this region has undergone a clockwise rotation of about 25 since the eo oligocene this rotation is opposite in sense to that obtained from the cretaceous formations in the gargano which has generally been assumed to affect the entire foreland these new data suggest that the tertiary structural evolution of this region may be distinct from that of central peninsular italy and related to that of northwestern greece on the other side of the southern adriatic sea

magnetostratigraphy in pursuit of missing links since the last quadrennial report magneto stratigraphy has continued to flourish the primary issues have been 1 refinements to the geomagnetic reversal time scale grts including recalibrations correlation of biostratigraphic data to the crts and revision of the terminology 2 use of magnetostratigraphic data for estimating rates of such processes as sediment accumulation evolution and faunal migration and 3 magnetic mineralogy and the origin of remanence for convenience we have divided the publications into studies of continental and marine sediments and highlight the most exciting issues within each of these sub headings in the first section of this review we will concentrate on the development of the geomagnetic reversal time scale grts with particular emphasis on refinements from the last few years we then turn our attention to applications of magnetostratigraphy in marine and continental sequences

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

palaeomagnetism of some cenozoic sediments cairo fayum area egypt abstract the palaeomagnetic and rock magnetic characteristics of some cenozoic rocks from the cairo fayum area have been investigated a total number of 259 oriented core samples were collected at 32 sites located in rocks of eocene 13 sites oligocene 11 sites and pliocene 9 sites ages most of these rocks carry a weak but stable remanent magnetisation that is principally carried by hematite goethite and magnetite are also found in some samples as subordinate constituents careful thermal demagnetisation successfully enabled the isolation of the characteristic remanent magnetisation normal and reversed polarities that passed a reversal test have been recorded in the three age groups this magnetisation is probably of primary origin and reflects the ages of the rocks the resultant palaeomagnetic poles are considered reliable and represent a good contribution to the african palaeomagnetic database and should help in further refining of the cenozoic apwp for africa

early oligocene geomagnetic field behavior from deep sea drilling project site 522 hydraulic piston coring operations at deep sea drilling project site 522 in the south atlantic retrieved an unusually continuous section of late eocene to late oligocene pelagic sediments which we sampled at 3 4 cm intervals 3 5 kyr natural remanent magnetization demagnetization studies indicate a well behaved remanence various rock magnetic procedures strongly suggest the magnetic carrier is dominated by pseudo single domain magnetite appropriate for recording relative intensity variations of the paleomagnetic field nine zones of unusually low relative paleointensity were identified within the 2 my chron c12r interval seven can be typified by a 20 40 kyr interval of low field intensity accompanied by apparently random low amplitude short duration directional fluctuations the other two are of approximately equal duration and intensity but exhibit an orderly progression of directional changes that result in well defined virtual geomagnetic pole vgp paths confined along a preferred meridian of 70 90 w longitude we propose that both styles occur when the main dipole term diminishes significantly but that the former result when undiminished normal secular variation is continuous during the period of low axial dipole moment we propose that the other two lows in relative paleointensity along with one reversal record reflect a field structure of low axial dipole moment dominated by a low degree nonzonal spherical harmonic term alternatively the confined vgp paths could be an artifact of heavy remanence smoothing between nonantipodal semistable transitional geomagnetic pole positions geographical control of vgp paths particularly along 70 90 w longitude has recently been noted for much younger reversals the site 522 record may indicate that the underlying cause of this phenomenon was present at 32 ma we compare our c12r record of paleointensity lows with c12r marine magnetic anomaly tiny wiggles these data appear to indicate that c12r tiny wiggles resulted from periods of low geomagnetic field intensity that were sometimes accompanied by directional excursions

paleomagnetic reconstruction of the cenozoic evolution of the eastern mediterranean abstract a total of 113 paleomagnetic sites were sampled along an anatolian s n transect from the arabian platform the hatay region the eastern taurides the kirsehir block the sivas basin and the eastern pontides reliable characteristic remanent paleomagnetic directions were retrieved from 37 of these sites spanning in time from paleocene to miocene in a general way declinations are westerly deviated and inclinations are shallower than the geocentered dipole value at the present latitudes when combined with previously published results these data indicate that a large scale counterclockwise rotation of anatolia of some 25 has occurred since the miocene assuming that the pole of rotation of anatolia with respect to europe has remained constant in time at the location given by macclusky et al j geophys res 105 2000 5695 on the basis of the geodetic data this rotation implies that a large westward displacement 500 km at the average latitude of 40 has taken place assuming that the rotation was initiated by the arabia europe collision about 12 ma ago this corresponds to an average displacement of about 40 mm year together with previous results from the western part of the aegean arc these results indicate that the main trends of the cenozoic evolution of the eastern mediterranean appear to consist of two post early miocene rotations of opposite senses a clockwise rotation of the western part of the aegean tectonophysics 146 1988 183 around a pole situated in northern albania and a counterclockwise rotation around the pole given by mcclusky et al j geophys res 105 2000 5695 comparison with gps data suggest that both rotations are still active today

paleomagnetism and the adriatic promontory a reappraisal the geodynamic evolution of the western mediterranean area was influenced strongly by the adriatic promontory of the african plate which can be outlined at present by current seismicity and by facies and ophiolite distributions paleomagnetic results from different parts of the promontory contribute useful information about its past history the evaluation of these data is made difficult by the lack of a well defined apparent polar wander path for africa this has resulted in occasional overinterpretation of some paleomagnetic studies results from umbria and the southern alps cover a long enough period of time to define part of an apw path and support the idea that the promontory moved as an adjunct to the african plate during the late mesozoic and early cenozoic a conservative evaluation of cretaceous paleomagnetic data the most abundant for the promontory as a whole shows no strong evidence for previously proposed counterclockwise rotations of sicily or the southern alps relative to the african plate paleomagnetic data however suggest about 17 degrees counterclockwise rotation of autochthonous gargano and istria and about 25 degrees counterclockwise rotation of allochthonous umbria tectonic rotation of the middle part of the promontory appears to have occurred without significant rotation of its northern and southern extremities

magnetization of the pacific ocean lithosphere deduced from magsat data magsat anomalies over the pacific ocean are related to volcanic plateaus and the edge effect of the pacific cretaceous quiet zone pcqz four prominent plateaus shatsky rise the mid pacific mountains hess rise and manihiki plateau are considered in this study the major lateral magnetization contrasts associated with these plateaus are considered to arise from the topographic swells and the crustal roots with root thicknesses estimated from topography using an airy isostatic model shatsky rise and the mid pacific mountains are older than the cretaceous quiet period and their natural remanent magnetization nrm is not a significant component of the magnetization contrasts that cause the magsat anomalies associated with these plateaus their magnetic properties are characterized by effective magnetic susceptibility contrasts of 0 07 0 01 s i per unit volume averaged over their topographic swells and crustal roots equivalent to 0 04 if averaged over the entire crustal thicknesses swell plus root plus intervening layer this value agrees well with the estimates of previous investigators for these plateaus and for similar plateaus in other oceans two plateaus of cretaceous quiet period age within the pcqz hess rise and manihiki plateau have origins similar to those of shatsky rise and the mid pacific mountains and they probably have similar effective susceptibility contrasts but they may also carry cretaceous quiet period nrm magnetic anomalies due to hess rise and manihiki plateau calculated from the effective susceptibility contrast deduced for shatsky rise and the mid pacific mountains are substantially larger than the observed magsat anomalies of these plateaus there are also magsat anomalies over parts of the pacific where no plateaus exist some of these anomalies are demonstrated as probably due to a contrast in nrm between the pcqz and its surroundings the total remanent magnetization contrast magnetization contrast in amperes per meter times thickness in meters equivalent to the dipole moment per unit area of the pcqz is 14 000 20 000 amperes 30 which cannot be simply explained by the absolute values of remanent magnetization predicted by conventional models of oceanic crustal magnetic properties modelling of the cretaceous quiet zones in the northern atlantic indicates a similar total remanent magnetization contrast these results may be explained by including uppermost mantle remanent magnetization with an intensity of about 1 2 a m 1 if magnetization persists to a depth of 7 below the seismic moho i e down to the depth of the crustal roots of the plateaus including nrm in the uppermost mantle of the pcqz also serves to reduce the calculated amplitude of the hess rise and manihiki plateau magsat anomalies if the nrm of the crustal roots is less than the nrm of the surrounding uppermost mantle on this basis the estimated intensity of nrm in the uppermost 7 km of the pcqz mantle is 1 3 a m 1 in very good agreement with the intensity estimated from the pcqz edge effect anomalies these estimates of uppermost mantle nrm are probably a maximum limit recognizing that other sources may also contribute to the total remanent magnetization contrasts of the cretaceous quiet zones

on the possibility of a widespread remagnetization of pre oligocene rocks from northeast japan and the miocene rotational opening of the japan sea abstract we present new paleomagnetic results from the well dated miyako cretaceous sediments 100 110 ma from northeast japan these results combined with those of tosha 1 yield an in situ characteristic directiond 321 i 54 5 95 4 5 n 14 sites reduced to a reference point at 40 n 142 e this direction is found to coincide with that of most older plutonic and sedimentary rocks of devonian to lower cretaceous age it is also identical with the westerly pre folding direction which is preserved in many oligocene 20 40 ma formations from northeast japan 1 2 in contrast all recent formations 0 17 ma have been magnetized in the direction of the present axial dipole field only the oligocene and miocene results appear to be primary or at least pre folding the miyako sulfide bearing sediments and lower cretaceous 110 125 ma magnetite bearing granites could either still bear a primary magnetization or be completely remagnetized by a low temperature chemical event evidence for such events is now found in many places and as close as south korea available data constrain the oligo miocene history of northeast japan and indicate at least20 30 counterclockwise rotation with respect to mainland asia during the opening of the sea of japan on the other hand the pre 40 ma history of northeast japan is not well constrained and three models are proposed which are compatible with various interpretations of the data none of them can presently document pro oligocene motion of northeast japan with respect to asia the most economical model implies widespread remagnetization we conclude that because of the scarcity of well tested primary magnetization directions the classical bending of the japanese islands rests on weaker grounds than generally realized and that no pre 40 ma apparent polar wander path of the japanese islands can safely be proposed

aegean paleomagnetic inclination anomalies is there a tectonic explanation abstract more than a decade of paleomagnetic research in the aegean area mainly by french investigators c laj c kissel and their colleagues has provided a valuable data base for the evaluation of cenozoic aegean tectonics systematic rotations are documented and have been interpreted by the original investigators in the light of the evolution of the hellenic arc however less attention has been paid to the significance of the paleomagnetic inclinations which also are anomalous twenty one out of 22 paleomagnetic studies performed to date within the general aegean region have yielded paleolatitudes that are too shallow when compared with reference curves for either africa or eurasia suggesting northward relative transport with respect to both continents sedimentary volcanic and plutonic units are involved ages range from oligocene to pliocene some of these apparent paleolatitude anomalies may merely be the result of inclination flattening in certain kinds of clastic sedimentary rocks however shallow inclinations in igneous rocks cannot be so easily dismissed the explanation for these anomalously shallow inclinations does not appear to lie with the reference curves because several other reference curves calculated in several different ways yield essentially the same result we suggest that the paleomagnetic pattern may reflect real northward displacement of crustal blocks within the aegean region measured with respect to both europe and africa the amount of displacement appears to increase systematically to the west the pattern of local block rotations noticed by earlier investigators argues that the displacement did not involve a single coherent aegean block but rather a collection of smaller blocks moving quasi independently geological consequences of northward relative displacement of the aegean block ought to include mid tertiary and or later compressional structures in the north e g rhodope and extensional structures in the leading edge of the african plate

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

late mesozoic and cenozoic palaeomagnetism of australia iii bias corrected pole paths for australia antarctica and india summary palaeomagnetic results from part i of this study and their analysis in part ii are combined to eliminate bias from the cenozoic apparent polar wander path for australia a bias due to non dipole components in past geomagnetic fields or for poles calculated from hot spot data due to the motion of hot spots relative to the earth s rotational axis this path is extended in approximately bias free form to the late mesozoic and indicates a significant change in the drift direction of the continent between 26 and about 60 ma the bias corrected australian path is used first with seafloor spreading data for the southern ocean to derive a corresponding late mesozoic cenozoic pole path for antarctica the latter shows that the antarctic drift direction reversed in the early tertiary it is suggested that the early tertiary directional changes of both australia and antarctica are part of a global reorganization of plates during the eocene postulated by rona richardson cande mutter and patriat achache next the australian path is compared with hot spot data from the african and australian plates indicating a movement of the hot spots relative the earth s rotational axis during the cenozoic the direction of this movement is found to be consistent with previous results from other parts of the world finally the australian path is used together with non dipole components in the geomagnetic field to explain a prominent westward displacement of the mid and late cenozoic poles of india relative to those of australia because of uncertainties in the original poles and in the analysis the present results are likely to contain appreciable errors nevertheless their consistency with independent findings supports the dipole quadrupole model of part ii for mid and late cenozoic geomagnetic fields

eocene biostratigraphy and magnetic stratigraphy from possagno italy the calcareous nannofossil response to climate variability a study of quantitative calcareous nannofossil biostratigraphy and magnetostratigraphy of a 68 m thick marine limestone section of late paleocene middle eocene age outcropping at possagno in northern italy shows that the section encompasses nannofossil zones np9 np15 equivalent to cp8 cp13b and chrons c24r c21n the paleocene eocene boundary was placed at the base a of d 13 c negative excursion from the literature that was found virtually coincident with the base of zone np9b the base of the middle eocene lutetian was placed at the base of chron c21r biostratigraphic events were generally found to be consistent with parallel events in recent time scales several potentially useful new events are also described in particular we detected the earliest specimens of dictyococcites at the base of chron c22r np12 np13 zonal transition which is several million years older than previous estimates correlation of possagno data to the oxygen isotope record from the literature allowed us to describe the temporal relationships between climate variability and calcareous nannofossil assemblages modifications in the nannofossil assemblage coeval to both the paleocene eocene thermal maximum petm and the early middle eocene long term climatic trend are recognized the short lived petm was coeval to provisional adaptations malformations and or ecophenotypes in the coccolithophores communities that were reabsorbed upon return to long term varying climatic conditions the early middle eocene long term climatic trend was instead coeval to true evolutionary trends with the appearance of the very successful noelaerhabdaceae clade whose offsprings include the most important bloom forming coccolithophorids in the modern ocean the early middle eocene can thus be considered the time in which nannoplankton communities set course toward modern structure triggering a reconfiguration of the global ocean life chain d 2005 elsevier b v all rights reserved

new paleocene eocene paleomagnetic results from the foreland of the southern alps confirm decoupling of stable adria from the african plate abstract from the undeformed foreland of the southern alps paleocene through early miocene rocks mostly biostratigraphically well dated sediments with sub horizontal bed attitude were collected for a paleomagnetic study from 23 geographically distributed localities the samples were subjected to standard paleomagnetic measurements and evaluation while the miocene samples are unstable most of the older localities yielded statistically well defined paleomagnetic directions these are interpreted as primary for the compact marls supported by positive between locality tilt and reversal tests this large group of localities is characterized by ccw rotated declinations with respect to the present north combined with paleomagnetic directions of corresponding age from stable istria these allow definition of the apw for stable adria for the 61 6 33 9 ma interval which is significantly displaced from the coeval segment of the african apw due to the decoupling of the former to the latter by a moderate ccw rotation this post eocene final separation exact age is not constrained directly but estimated as end of miocene was preceded by a small cw rotation of adria with respect to africa suggested by unchanged orientation of the former across the cretaceous paleocene boundary while the latter continued its ccw rotation

paleomagnetism of the patagonian plateau basalts southern chile and argentina a total of 505 paleomagnetic samples were collected from 65 sites volcanic flows of the patagonian plateau basalts at four locations in southern chile and argentina k ar analyses indicate that 38 flows from two locations form a late cretaceous group 64 79 ma while the remaining 27 flows are eocene in age 42 56 ma progressive demagnetization indicates that a characteristic remanent magnetization chrm has been successfully isolated from 59 flows rock magnetic properties and analysis of chrm directions within and between sites allow the secure inference that the chrm is a thermoremanent magnetization acquired during original cooling the eocene flows yield 15 independent samplings of the paleomagnetic field however these data fail the reversals test and probably do not adequately average geomagnetic secular variation the late cretaceous flows yield 18 independent samplings of the paleomagnetic field six of normal polarity and 12 of reversed polarity these data pass the reversals test and have angular dispersion of virtual geomagnetic poles vgps consistent with adequate sampling of geomagnetic secular variation the mean of these 18 vgps yields a late cretaceous paleomagnetic pole for south america latitude 78 7 s longitude 358 4 e a95 6 3 k 31 6 s 14 5 this pole is consistent with similar age poles from north america and africa when the atlantic is reconstructed to 70 ma contrary to previous indications the south american apparent polar wander path does not reach the present rotation axis until after late cretaceous time

paleomagnetism of mesozoic kimberlites in southern africa and the cretaceous apparent polar wander curve for africa including those previously published good paleomagnetic data have been obtained from 48 of 51 sites in 28 separate kimberlites radiometric dates by one or more methods are available for 17 of these bodies and range from 81 to 145 ma with maxima around 90 and 120 ma these ages correlate with geochemical contrasts distinguishing what have been designated group i younger and ii older kimberlites smith et al 1985b stable magnetization appears to be associated with magnetite developed deuterically after emplacement but in most bodies secular variation has not been completely averaged in the remanence acquired the distribution of vgps calculated is distinctly but not sequentially streaked yet correlates broadly with the older and younger petrochemical types mean north poles calculated on this basis yield kp1 n 14 81 100 ma 64 1 n 226 1 e a95 5 2 and kp2 n 10 113 145 ma 47 6 n 269 9 e a95 9 7 with the exception of one undated pipe meltonwold which was not included in the averages and the melilititic male fissure at swartruggens in group ii average all the kimberlites sampled are normally magnetized including these new data 10 of 17 published african cretaceous poles meet acceptability criteria specified and define an apparent polar wander apw curve from 130 to 75 ma the curve appears to consist of two segments trending latitudinally before 100 ma and meridionally thereafter the latter trend is evident even in the distribution of the individual kp1 poles and may be related to the true polar wander speculated by gordon and livermore 1987 to have occurred in that interval

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

paleomagnetic constraints on the tectonic evolution of the sakarya continent northwestern anatolia comment abstract thirteen sites were sampled in northwestern anatolia in order to gather paleomagnetic information concerning the tectonic evolution of this region through jurassic to early tertiary time an interval encompassing much of the history of the neo tethys in this area specifically information concerning the history and behaviour of a crustal block the sakarya continent was sought in order to place some constraints on geologic models that have been proposed for the region four jurassic sites are believed to exhibit early magnetization signatures that yield similar paleolatitudes for all sites these results when compared with paleolatitude information for eurasia suggest that sakarya lay in close proximity to the southern eurasian margin at least during the jurassic part of its history significantly different declinations from the same four sites are interpreted to reflect the deformation of sakarya when it docked with eurasia during the early tertiary these rotations are not attributed to motions of the north anatolian fault since results from three paleocene sites in the same area show no evidence of significant rotation with respect to eurasia

tertiary geodynamical evolution of northwestern greece paleomagnetic results abstract paleomagnetic results have been obtained from 29 sites sampled in lower to upper oligocene flysch sections of the ionian zone in northwestern greece they indicate a clockwise rotation of about 45 of the entire region a comparison with previously published results relative to both younger and older formations shows that this rotation has occurred in two phases of comparable amplitude one during middle miocene and the other during pliocene and quaternary separated by a period of at least 7 ma during which no significant rotation has occurred no major rotation has occurred during the entire paleocene and eocene stages this large measured rotation implies a horizontal displacement of at least 100 km in epirus possible mechanisms involving a rotation of the nappe sheets rotation of the basement or a combination of the two are discussed the two phases of paleomagnetic rotation can be correlated with the tertiary and quaternary calc alkaline volcanic activity in the aegean sea a palinspastic reconstruction shows that the orientation of the major structures now striking n155 was almost east west in the middle miocene at the epoch of their formation

plate motions and the geomagnetic field ii jurassic to tertiary summary the analysis of the time averaged geomagnetic field is extended back to 200ma palaeomagnetic poles from the major plates have been carefully selected from recent compilations of reliable results for each region these were returned with their corresponding sampling sites to their locations at the estimated dates of magnetization in a fixed hotspots framework the corrected results were then grouped into 20ma windows at intervals of 10ma representing the past 100ma and 40ma windows at 30ma intervals for the more sparse 100 200ma data global means and fisher statistics were calculated for each window having included the axial quadrupole in the calculation the value of this coefficient which gave the maximum value for the fisher precision parameter tightest grouping of poles was taken as representative of each interval the results indicate that a small axial quadrupole of the same sign as the axial dipole may have persisted throughout the cenozoic this is equivalent to a northward offset axial dipole field far sided effect during the late cretaceous this component appears to have changed sign with respect to the dipole negative values seem to have obtained throughout the cretaceous long normal polarity interval corresponding to a southward offset dipole near sided effect the data distribution is inadequate for the resolution of the quadrupole at earlier times and zero values cannot be discounted little relative motion is implied between the hotspots and the geomagnetic axis for the past 90 ma the global mean polar path curving around the predicted fixed hotspots pole at a distance of typically 5 latitude with little sign of rapid tertiary polar wander as implied by studies of pacific data alone between 100 and 200 ma however there is a clear difference between the two reference frames amounting to 17 19 in the jurassic this may reflect motion of the mantle relative to the geomagnetic axis but may also include errors due to inaccurate determination of hotspot tracks and inter hotspot motion

paleomagnetically determined rotations in the western sicilian fold and thrust belt new paleomagnetic data from the west sicilian fold and thrust belt indicate large scale clockwise rotations during tectonic transport for the platform and seamount paleogeographic units of the fold and thrust belt panormide and trapanese units there is a general consistency in the magnitude of rotation along strike suggesting the existence of large coherent structural units for the panormide platform clockwise rotations in the range of 90 to 140 relative to the underlying iblean parautochthon are recorded along 125 km of outcrop strike in the case of the trapanese unit clockwise rotations in the range of 47 to 70 relative to iblei are recorded along about 90 km of outcrop strike intervening basinal paleogeographic units imerese and sicanian units show clockwise rotations of similar magnitude although few reliable data are available from these units palinspastic reconstruction of the thrust belt incorporating the rotations and arguments for the present orientation of the margins of the paleogeographic units implies that the panormide platform and trapanese seamounts were originally elongated more or less north south relative to the present orientation of iblei the two units apparently coalesced to the south and were discontinuous to the north they and their intervening basins were part of a passive continental margin which occupied a large part of the area that was subsequently rifted to form the tyrrhenian sea

experimental reproduction of tectonic deformation lamellae in quartz and comparison to shock induced planar deformation features planar features can develop in quartz during comparatively slow tectonic deformation and during very fast dynamic shock metamorphism despite their very different structural nature tectonically induced deformation lamellae have sometimes been mistaken as shock induced planar deformation features pdfs to understand the formation of deformation lamellae and to address the substantial differences between them and pdfs we have conducted deformation experiments on single crystals of quartz in a griggs type apparatus at a temperature of 800 c a confining pressure of 12 kbar and a strain rate of 0 7 1 1 x 10 6 the deformed samples were analyzed with transmission electron microscopy tem and compared to natural pdfs from the ries crater germany tem revealed that tectonic deformation lamellae are associated with numerous sub parallel curved subgrain walls across which the orientation of the crystal changes slightly the formation of deformation lamellae is due to glide and climb controlled deformation in the exponential creep regime in contrast the pdfs in shocked quartz from the ries are perfectly planar crystallographically controlled features that originally represented amorphous lamellae due to postshock annealing and hydrothermal activity they are recrystallized and decorated with fluid inclusions

11 million years of oligocene geomagnetic field behaviour summary an 11 million year long record of the oligocene geomagnetic field has been obtained from pelagic sediments of dsdp hole 522 an average sample spacing of 4 cm yielded approximately one specimen per 4 to 8 kyr the rock magnetics are remarkably consistent across the entire interval previous work demonstrated a magnetic mineralogy dominated by magnetically stable magnetite the natural remanent magnetism nrm carries an oligocene polarity timescale that is in excellent agreement with the oligocene reversal record as determined from marine magnetic anomalies mmas including many of the so called crypto chrons normalized nrm intensities from the undisturbed portions of the record yield a time series of variations with features consistent with a number of other palaeointensity time series derived from both sedimentary and lava sequences these features include consistent major decreases in palaeointensity dips at reversal boundaries and occasional dips between reversal boundaries that could correspond to lineated tiny wiggles in the mma records the data set suggests that the overall field strength was 40 per cent higher in the first half of the oligocene when the average reversal frequency was 1 6 myr l than in the second half when the reversal frequency was 4myr there is also a weak dependence of average field strength on length of polarity interval finally in the three cores suited to spectral analysis of coherent polarity and relative intensity independent of lithological contamination there is a persistent ca 30 50 ka periodicity in the variations of the relative intensity suggesting that the geomagnetic field pulses at about this frequency not only during the brunhes as demonstrated by tauxe shackleton 1994 but in the oligocene as well