Palаeomagnetism of the Vendian traps of Volyn, southwestern margin of the East European platform. P. 1: palаeomagnetic directions and poles

Abstract

In Earth’s geological evolution the Vendian is significant because: 1) it preceded the «Cambrian Evolutionary explosion» when the multicellular organisms became suddenly much more diverse; 2) it is associated with the global tectonic and palaeogeographic restructuring of supercontinents, a change in geomagnetic field generation and other global processes affecting different layers of the Earth. At the same time, recent publications indicate an extremely irregular behavior of the geomagnetic field in the Vendian, which significantly differs from the recent regime of the geomagnetic field generation. New information on the configuration and magnitude of the geomagnetic field is crucial for understanding the reasons that can cause different modes of geodynamo. The article describes the new results of palaeomagnetic studies of the Volyn traps — basalts and tuffs of the Volyn series with ages about 560—580 My. The determined palaeodirections and palaeopoles are in good agreement with the previously published data of other authors and substantially complement them. The ChRM-component of «low-titanium» basalts was isolated in high-temperature (>500 °C) and characterized as primary. The same samples were used for palaeointensity determinations which showed the extremely low values of the geomagnetic field — an order of magnitude lower than the present one. The ChRM-component of «high-titanium» basalts was yielded in the temperature range of 200—400 °C. No results were obtained from palaeointensity experiments, and the complex nature of remanent magnetization remains unclear. The new data are compared with the palaeo-magnetic data of the Vendian—Early Cambrian poles of the East European Platform determined by other authors. To test the hypothesis of an anomalous Ediacaran magnetic field characterized by a low dipole moment and a high inversion frequency, more data are necessary. These data can be obtained from the studies of a stratigraphically more complete section of the Volyn traps opened by boreholes. These results will be presented in the next part of the article.

Palaeomagnetism of the Vendian traps of Volyn, southwestern margin of the East European Platform, P. 2: magnetostratigraphy

“…We present new results of palaeomagnetic studies of the Vendian (Ediacaran) rocks of the Volyn Basalt Province revealed by six boreholes on the NW Ukraine. This is a continuation of previous studies of upper part of the Volyn series described by Bakhmutov et al [2021]. In the recent works [Shcherbakova et al, 2020;Thallner et al, 2022], the results of palaeointensity determinations of the Volyn series basalts showed the ultra-low dipole moment of Earth's magnetic field which coincident with other palaeomagnetic data for Ediacaran indicating an extremely weak geomagnetic field.…”

“…order of magnitude weaker than the presentday field (see references in [Shcherbakova et al, 2020;Bakhmutov et al, 2021]).…”

“…44,2022 rocks are most complete in the territory of Ukraine in Volyn and Rivne regions where they protrude onto the pre-Cretaceous surface and are exposed in the quarries northern of Rivne city. Palaeomagnetic studies of Volyn traps were carried out by different research groups [Glevasskaya et al, 2000;Iosifidi et al, 2000;Nawrocki et al, 2004;Elming et al, 2007;Shcherbakova et al, 2020;Bakhmutov et al, 2021]. But only the upper part of the trap formation is outcropped by quarries.…”

“…New palaeomagnetic data on extremely low values of palaeointensity by Volyn basalts [Shcherbakova et al, 2020] and their palaeomagnetic directions [Bakhmutov et al, 2021] led us to further studies of the Volyn series traps with the aim to get more information about Ediacaran geomagnetic field. We continued these studies for the boreholes cores.…”

“…In this paper, we are presented detailed information about palaeomagnetic study and magnetostratigraphy of the sequence in addition to palaeointensity determination presented in [Thallner et al, 2022]. This sequence stratigraphycally lies below the sections described in [Bakhmutov et al, 2021].…”