Late Permian palaeomagnetic data east and west of the Urals

We studied Upper Permian redbeds from two areas, one between the Urals and the Volga River in the southeastern part of Baltica and the other in north Kazakhstan within the Ural-Mongol belt, which are about 900 km apart; a limited collection of Lower-Middle Triassic volcanics from north Kazakhstan was also studied. A high-temperature component that shows rectilinear decay to the origin was isolated from most samples of all three collections. For the Late Permian of north Kazakhstan, the area-mean direction of this component is D = 224.3°, I =−56.8°, k = 161, Α 95 = 2.7°, N = 18 sites, palaeopole at 53.4°N, 161.3°E; the fold test is positive. The Triassic result ( D = 55.9°, I =+69.1°, k = 208, Α 95 = 4.2°, N = 7 sites, pole at 57.0°N, 134.1°E) is confirmed by a positive reversal test. The corresponding palaeomagnetic poles from north Kazakhstan show good agreement with the APWP for Baltica, thus indicating no substantial motion between the two areas that are separated by the Urals. Our new mean Late Permian direction for SE Baltica ( D = 42.2°, I = 39.2°, k = 94, Α 95 = 3.5°, N = 17 sites; palaeopole at 45.6°N, 170.2°E) is confirmed as near-primary by a positive tilt test and the presence of dual-polarity directions. The corresponding pole also falls on the APWP of Baltica, but is far-sided with respect to the coeval reference poles, as the observed mean inclination is shallower than expected by 13°± 4°. In principle, lower-than-expected inclinations may be attributed to one or more of the following causes: relative tectonic displacements, quadrupole and octupole terms in the geomagnetic field, higher-order harmonics (incl. secular variation) of the same field, random scatter, non-removed overprints, or inclination error during remanence acquisition and/or diagenetic compaction. Our analysis shows that most mechanisms from the above list cannot explain the observed pattern, leaving as the most likely option that it must be accounted for by inclination shallowing. Comparison with selected coeval results from eastern Baltica (all within Russia) shows that all of them are biased in the same way. This implies that they cannot be used for analysis of geomagnetic field characteristics, such as non-dipole contributions, without a more adequate knowledge of the required correction for inclination shallowing.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71899/1/j.1365-246X.2008.03727.x.pd

The first results of mass U-Pb isotope dating (LA-ICP-MS) for detrital zircons from the Asha Group, South Urals: Paleogeography and paleotectonics

[No abstract available

The first results of mass U-Pb isotope dating (LA-ICP-MS) for detrital zircons from the Asha Group, South Urals: Paleogeography and paleotectonics

[No abstract available

Magnetic field hyperactivity during the early Neoproterozoic: A paleomagnetic and cyclostratigraphic study of the Katav Formation, southern Urals, Russia

We present a detailed magnetostratigraphic and cyclostratigraphic profile through the Riphean (Tonian) Katav Formation in the southern Urals. The study confirms the primary nature of the magnetization in these rocks. The cyclostratigraphic study identified several orbital periods including the 405 ka long eccentricity. This allows us to quantify the reversal frequency in the Katav and our estimates range of 7–12 reversals per million years. Based on our study, we identify an interval of magnetic field reversal hyperactivity in the Neoproterozoic interval. Age estimates for the Katav are contentious and range somewhere between 800 Ma and 900 Ma based on carbonate Pb-Pb ages and stable isotope correlations. The paleomagnetic poles obtained in this study of the Katav (and overlying Inzer) Formation do not fit anywhere on the Baltica apparent polar wander path between 1100 Ma and 900 Ma. Furthermore, they lie 90° away from the 900 Ma segment of the path. We tentatively estimate their age to be closer to 800 Ma and perhaps confirm a previously hypothesized pulse of rapid true polar wander between 825 Ma and 790 Ma