The Experts below are selected from a list of 1833 Experts worldwide ranked by ideXlab platform
Gordon Osinski - One of the best experts on this subject based on the ideXlab platform.
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A Paleozoic age for the Tunnunik impact structure
Meteoritics and Planetary Science, 2019Co-Authors: Camille Lepaulard, Jerome Gattacceca, Nicholas Swanson-hysell, Yoann Quesnel, François Demory, Gordon OsinskiAbstract:We report paleomagnetic directions from the target rocks of the Tunnunik impact structure, as well as from lithic impact breccia dikes that formed during the impact event. The target sedimentary rocks have been remagnetized after impact-related tilting during a reverse polarity interval. Their magnetization is unblocked up to 350 degrees C. The diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 degrees C. The impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks. The comparison of the resulting Virtual Geomagnetic Pole for the Tunnunik impact structure with the apparent polar wander path for Laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an impact age in the Late Ordovician or Silurian, around 430-450 Ma, soon after the deposition of the youngest impacted sedimentary rocks. Our results from the overprinted sedimentary rocks and diabase dikes imply that the postimpact temperature of the studied rocks was about 350 degrees C.
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A Paleozoic age for the Tunnunik impact structure
eScholarship University of California, 2019Co-Authors: Lepaulard C, Gattacceca J, Swanson-hysell N, Quesnel Y, Demory F, Gordon OsinskiAbstract:© The Meteoritical Society, 2019. We report paleomagnetic directions from the target rocks of the Tunnunik impact structure, as well as from lithic impact breccia dikes that formed during the impact event. The target sedimentary rocks have been remagnetized after impact-related tilting during a reverse polarity interval. Their magnetization is unblocked up to 350 °C. The diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 °C. The impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks. The comparison of the resulting Virtual Geomagnetic Pole for the Tunnunik impact structure with the apparent polar wander path for Laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an impact age in the Late Ordovician or Silurian, around 430–450 Ma, soon after the deposition of the youngest impacted sedimentary rocks. Our results from the overprinted sedimentary rocks and diabase dikes imply that the postimpact temperature of the studied rocks was about 350 °C
Ulrich R. Christensen - One of the best experts on this subject based on the ideXlab platform.
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Simulated Geomagnetic reversals and preferred Virtual Geomagnetic Pole paths
Geophysical Journal International, 2004Co-Authors: Carsten Kutzner, Ulrich R. ChristensenAbstract:SUMMARY The question of whether Virtual Geomagnetic Poles (VGPs) recorded during reversals and excursions show a longitudinal preference is a controversial one amongst palaeomagnetists. One possible mechanism for such VGP clustering is the heterogeneity of heat flux at the core–mantle boundary (CMB). We use 3-D convection-driven numerical dynamo models with imposed non-uniform CMB heat flow that show stochastic reversals of the diPole field. We calculate transitional VGPs for a large number of token sites at the Earth's surface. In a model with a simple heat flux variation given by a Y22 harmonic, the VGP density maps for individual reversals differ substantially from each other, but the VGPs have a tendency to fall around a longitude of high heat flow. The mean VGP density for many reversals and excursions shows a statistically significant correlation with the heat flow. In a model with an imposed heat flux pattern derived from seismic tomography we find maxima of the mean VGP density at American and East Asian longitudes, roughly consistent with the VGP paths seen in several palaeomagnetic studies. We find that low-latitude regions of high heat flow are centres of magnetic activity where intense magnetic flux bundles are generated. They contribute to the equatorial diPole component and bias its orientation in longitude. During reversals the equatorial diPole part is not necessarily dominant at the Earth's surface, but is strong enough to explain the longitudinal preference of VGPs as seen from different sites.
Brett F Denny - One of the best experts on this subject based on the ideXlab platform.
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widespread inclination shallowing in permian and triassic paleomagnetic data from laurentia support from new paleomagnetic data from middle permian shallow intrusions in southern illinois usa and Virtual Geomagnetic Pole distributions
Tectonophysics, 2011Co-Authors: Mathew Domeier, Brett F DennyAbstract:Abstract Recent paleomagnetic work has highlighted a common and shallow inclination bias in continental redbeds. The Permian and Triassic paleomagnetic records from Laurentia are almost entirely derived from such sedimentary rocks, so a pervasive inclination error will expectedly bias the apparent polar wander path of Laurentia in a significant way. The long-standing discrepancy between the apparent polar wander paths of Laurentia and Gondwana in Permian and Triassic time may be a consequence of such a widespread data-pathology. Here we present new Middle Permian paleomagnetic data from igneous rocks and a contact metamorphosed limestone from cratonic Laurentia. The exclusively reversed Middle Permian magnetization is hosted by low-Ti titanomagnetite and pyrrhotite and yields a paleomagnetic Pole at 56.3°S, 302.9°E (A95 = 3.8, N = 6). This Pole, which is unaffected by inclination shallowing, suggests that a shallow inclination bias may indeed be present in the Laurentian records. To further consider this hypothesis, we conduct a Virtual Geomagnetic Pole distribution analysis, comparing theoretical expectations of a statistical field model (TK03.GAD) against published data-sets. This exercise provides independent evidence that the Laurentian paleomagnetic data is widely biased, likely because of sedimentary inclination shallowing. We estimate the magnitude of this error from our model results and present and discuss several alternative corrections.
Jeffrey L. Eighmy - One of the best experts on this subject based on the ideXlab platform.
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A Revision to the U.S. Southwest Archaeomagnetic Master Curve
Journal of Archaeological Science, 2002Co-Authors: Stacey N. Lengyel, Jeffrey L. EighmyAbstract:Abstract Recently, two problems have been recognized with the United States Southwest archaeomagnetic master curve (Eighmy, 1991; LaBelle & Eighmy, 1997; Sternberg, 1989). One of these problems, the damping problem, is inherent to the moving window method of curve construction proposed by Sternberg (1989). The other is due to the fact that the small number of independently dated Virtual Geomagnetic Pole determinations available for the period between ad 900–1100 are not representative of secular variation during this period. The analyses presented here confirm the existence of these two problems and suggest that they distort the curve by less than 1·0° and between 1·0° and 2·0° respectively. Based on these findings, a new curve is proposed for the U.S. Southwest.
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ADDITIONAL ARCHAEOMAGNETIC DATA ON THE SOUTH-WEST USA MASTER Geomagnetic Pole CURVE*
Archaeometry, 1997Co-Authors: Jason M. Labelle, Jeffrey L. EighmyAbstract:Archaeomagnetic dating in the American south-west is progressing rapidly in terms of both method and application. Of particular importance has been the creation of a master curve of Geomagnetic direction change for the region. However, confirmation, extension and refinement of this curve are always welcome contributions to the technique. So, efforts are under way to accumulate a large body of well-dated Virtual Geomagnetic Pole positions and document these through publication so that the basis for dating samples of unknown age can be evaluated. This article adds 23 new dated Pole positions to the list discussed in Eighmy (1991) and reports the results of our experiments with refining the south-west USA master curve, especially the creation of a new south-west master curve, SWCV595.
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Archaeomagnetic dating and the Bonito phase chronology
Journal of Archaeological Science, 1994Co-Authors: David E. Doyel, Jeffrey L. EighmyAbstract:Abstract A method is presented for the reanalysis of a large archaeomagnetic data set from the Chaco Canyon region in northwest New Mexico, U.S.A., for which Virtual Geomagnetic Pole (VGP) position data have not been reported. Reanalysis based upon the archaeomagnetic curve model SWCV590-CSU resulted in large age ranges. The level of precision reported in the past was not reproducible given available data. The consistent lateness of archaeomagnetic dates reported by Robert DuBois is accounted for by recent research that has altered segments of the archaeomagnetic curve. Archaeomagnetic and tree-ring data from the Late Bonito phase Chacoan community of Bis sa'ani are used to contrast the results of two different methods of interpretation. Factors that have influenced the composition of the archaeomagnetic data base are identified. Recommendations are made for reporting archaeomagnetic dates.
Carsten Kutzner - One of the best experts on this subject based on the ideXlab platform.
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Simulated Geomagnetic reversals and preferred Virtual Geomagnetic Pole paths
Geophysical Journal International, 2004Co-Authors: Carsten Kutzner, Ulrich R. ChristensenAbstract:SUMMARY The question of whether Virtual Geomagnetic Poles (VGPs) recorded during reversals and excursions show a longitudinal preference is a controversial one amongst palaeomagnetists. One possible mechanism for such VGP clustering is the heterogeneity of heat flux at the core–mantle boundary (CMB). We use 3-D convection-driven numerical dynamo models with imposed non-uniform CMB heat flow that show stochastic reversals of the diPole field. We calculate transitional VGPs for a large number of token sites at the Earth's surface. In a model with a simple heat flux variation given by a Y22 harmonic, the VGP density maps for individual reversals differ substantially from each other, but the VGPs have a tendency to fall around a longitude of high heat flow. The mean VGP density for many reversals and excursions shows a statistically significant correlation with the heat flow. In a model with an imposed heat flux pattern derived from seismic tomography we find maxima of the mean VGP density at American and East Asian longitudes, roughly consistent with the VGP paths seen in several palaeomagnetic studies. We find that low-latitude regions of high heat flow are centres of magnetic activity where intense magnetic flux bundles are generated. They contribute to the equatorial diPole component and bias its orientation in longitude. During reversals the equatorial diPole part is not necessarily dominant at the Earth's surface, but is strong enough to explain the longitudinal preference of VGPs as seen from different sites.
