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On the correlation possibilities in the Berriasian – Hauterivian interval of the Boreal / Tethysian successions
Evgenij Baraboshkin

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-05 05:20 PM – 05:40 PM
Last modified: 2018-11-23

Abstract


The problem of correlation of Tethysian and Boreal biostratigraphic scales is one of the most difficult for the early Cretaceous, especially in the Jurassic – Cretaceous boundary interval. It is still unsolved because of the absence or poor marine connections between Peri-Tethysian and high-Boreal basins. By the term “high-Boreal” I mean Arctic regions of Russia, Canada, Greenland, and some other countries. It generally coincides with the “Arctic Realm/Subrealm” of Saks et al. (1964) adopted by Westermann (2000) to paleogeographic terminology.

One of the most important seaways connected Peri-Tethys and high-Boreal basins was the Russian Platform sea, which provided Tethysian-Boreal marine fauna migrations, including ammonites and belemnites (Baraboshkin et al., 2007). Meridional fauna distribution and adaptation to changing conditions took some hundred thousand years even in case of rapidly evolved ammonites (Guzhikov & Baraboshkin, 2006). The diachronism of the fauna makes any inter-Realm biostratigraphic correlation also diachronous, even tin the case of existence of migration path. Using of integrated biostratigraphic, paleomagnetic and stable-isotope correlation helps to make isochronous inter-Realm correlation. This way we significantly precise Tethysian / Boreal correlation in the Berriasian – Hauterivian interval on the base of integrated study of reference sections in the Boreal Realm (Baraboshkin & Guzhikov, 2018). A number of best-traceble levels were recognised:

  • Base of M18r Chrone corresponds to the ± base P. grandis Zone (Tethysian, T) and ± Ch. chetae Zone (Boreal, B) and to δ13C excursion (Dzyuba, Izokh, Shurygin, 2013). It is near the base of recently used Jurassic / Cretaceous (Volgian / Ryazanian) boundary.
  • Base of M11r Chrone corresponds to the ± base S. verrucosum T-Zone, and the base of ± P. polyptychus B-Zone and to δ13C excursion (“Weissert event”). It is near the base of the Lower / Upper Valanginian boundary.
  • “Faraoni event” above the base of M5n Chrone is in the mid-P. ohmi T-Zone, and the base of ± C. discofalcatus B-Zone.
  • Base of M3r Chrone is in the mid-T. hughi T-Zone, corresponds to the ± base C. discofalcatus B-Zone. It is near the base of the Hauterivian / Barremian boundary.

Other levels which could be potentially well-traceble, are the base / top of the largest magnetic Chrones in this interval – M19n, M17r and M16n.

We believe that the best boundary between Stages and especially between Systems is well-correlatable isochronous level based on non-paleontological method (paleomagnetic and / or stable isotope). It is facies- and latitude-independent and has therefore the highest potential for the correlation all over the World.

To follow this idea, one should recognize such non-paleontological markers first, and then look at the supporting paleontological markers.