Complex tunnel systems of early Fortunian macroscopic endobenthos in the Ediacaran-Cambrian transitional strata of the Olenek Uplift (NE Siberian Platform)

In spite of the fact, that during the last two decades some number of new paleomagnetic poles, more or less meeting the modern standards of quality [Van der Voo, 1993], have been obtained for Mesoproterozoic of Siberia [Evans et al., 2016]. The problem of the Precambrian segment of the apparent polar wander path (APWP) for Siberia, rests still to be far from its solution.The latter, obviously, hampers the elaboration of Precambrian paleogeographic reconstructions, solution of numerous other important tasks of the Earth Sciences.The Late Precambrian key section of the Udzha Uplift seemed to be one of the most promising object to elaborate the Mesoproterozoic segment of APWP of the Siberian platform. Until recently, the rocks composing this section have been considered to be of the Mesoproterozoic and Vendian age.As a result of isotope studies in recent years, the age of formations of the Udzha Uplift has been significantly increased (1386&#177;30 Ma, apatite, U-Pb, [Malyshev et al., 2018]). In particular, age of the Udzha Fm, which forms the uppermost part of the Udzha riphean sequence is considered currently to be Mesoproterosoic. On the base of our new paleomagnetic data this formation has been formed about the same time as the Khaypakh Fm from the Olenek Uplift (NE Siberia), whose Mesoproterozoic age has been established earlier from independent isotopic data [Zaitseva et al., 2017].During last several years we have carried out the paleomagnetic studies of Late Precambrian rocks of the Udzha Uplift including the Mesoproterozoic Udzha and Unguokhtakh formations as well as intrusions representing two Mesoproterozoic magmatic events.In this abstract we present new paleomagnetic poles for the Mesoproterosoic rocks (1500 Ma, ca.1400 Ma, 1385 Ma) of the Siberian platform.These paleomagnetic poles significantly complement the Mesoproterozoic segment of APWP of the Siberian Platform.The studies were supported by the Russian Science Foundation project &#8470; 19-77-10048.

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Quo vadis, Tommotian?

Geological Magazine ◽

10.1017/s0016756819001286 ◽

2019 ◽

Vol 157 (1) ◽

pp. 22-34 ◽

Cited By ~ 3

Author(s):

Dmitriy V. Grazhdankin ◽

Vasiliy V. Marusin ◽

Olga P. Izokh ◽

Galina A. Karlova ◽

Boris B. Kochnev ◽

...

Keyword(s):

Siberian Platform ◽

Cambrian Explosion ◽

Sudden Increase ◽

Earth System ◽

Multidisciplinary Study ◽

Stratotype Section ◽

Quo Vadis ◽

Depositional Setting ◽

Olenek Uplift ◽

Open Shelf

AbstractThe concept of the Tommotian Regional Stage of the Siberian Platform has been closely linked to the idea of the ‘Cambrian Explosion’ of animals and protists when the entire Earth system shifted rapidly into Phanerozoic mode. We conducted a multidisciplinary study of an informal ‘synstratotype’ of the lower Tommotian boundary in the upper Mattaia Formation, Kessyusa Group in the Olenek Uplift, NE of the Siberian Platform. The Mattaia Formation characterizes an upper shoreface to inner-shelf depositional setting and provides important faunal ties and correlation with carbonate-dominated and aliminosiliciclastic open-shelf areas. A section of the upper Mattaia Formation at Boroulakh, Olenek River is suggested here as a model for the Global Boundary Stratotype Section and Point for the base of the Cambrian Stage 2. This level contains the lowermost occurrence of the cosmopolitan fossil helcionelloid mollusc Aldanella attleborensis. Section global markers near the base of the stage include a positive excursion of δ13C values reaching +5.4‰, a U–Pb zircon date of 529.7 ± 0.3 Ma, massive appearance of diverse small skeletal fossils (including Watsonella crosbyi), a sudden increase in diversity and abundance of trace fossils, as well as a conspicuous increase in depth and intensity of bioturbation. Coincidently, it is this level that has always been regarded as the lower Tommotian boundary on the Olenek Uplift.

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