Paleogeography of Baltica in the Ediacaran: Paleomagnetic and geochronological data from the clastic Zigan Formation, South Urals

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• 作者：Natalia M. Levashova ; Mikhail L. Bazhenov ; Joseph G. Meert ; Nikolay B. Kuznetsov ; Inessa V. Golovanova ; Konstantin N. Danukalov ; Natalia M. Fedorova
• 关键词：Ediacaran ; Paleogeography ; Paleomagnetism ; Geochronology ; Baltica ; South Urals
• 刊名：Precambrian Research
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：236
• 期：Complete
• 页码：16-30
• 全文大小：3322 K

文摘

The paleoposition of Baltica at the end of Neoproterozoic is of utmost importance for global paleogeography, but paleomagnetic data of Ediacaran age are very controversial. Neoproterozoic and Ediacaran clastic rocks are wide spread along the deformed eastern margin of Baltica. Paleomagnetic and geochronological studies were carried out at the several sections of the uppermost Zigan Formation of the Ediacaran Asha Series along with Paleozoic rocks from the same region. An ash bed interlayered in the upper part of the Asha series yields a zircon deposition age of 547.6 ¡À 3.8 Ma. With the aid of stepwise thermal demagnetization, a dual polarity high-temperature remanence was successfully isolated from red beds of the Zigan Fm, and its primary origin is indicated by the positive reversal test and regional consistency test. The overall mean direction of this remanence (declination D¡ã = 107.7 (287.7), inclination I¡ã = ?15.4 (15.4), radius of confidence circle ¦Á₉₅¡ã = 4.8, N = 36 sites) corresponds to a paleolatitude of 7.8¡ã ¡À 2.5¡ã, N or S. Geological data indicate that the study area was a part of the Baltic craton at least since the early Neoproterozoic, while paleomagnetic results on Paleozoic rocks from the westernmost zones of the Ural fold belt reveal not local and regional rotation with respect to Baltica. Also, several lines of evidence imply that the inclination shallowing in these rocks either absent altogether, or at worst less than 10¡ã; hence the position of Baltica can be reliably reconstructed for time about 550 Ma. The analysis of the existing paleomagnetic and geological data place Baltica to the east of Laurentia in tropical southern latitudes with the Uralian margin facing north in Late Ediacaran time.