|mhorn||Дата: Wednesday, 26.11.2014, 22:36 | Сообщение # 1|
|Rogov M.A., Poulton T.P. (2015) Aulacostephanid ammonites from the Kimmeridgian (Upper Jurassic) of British Columbia (western Canada) and their significance for correlation and palaeobiogeography // Bulletin of Geosciences. Vol.90. no.1. P.7–20. |
We present the first description of aulacostephanid (Perisphinctoidea) ammonites from the Kimmeridgian of Canada, and the first illustration of these ammonites in the Americas. These ammonites include Rasenia ex gr. cymodoce, Zenostephanus (Xenostephanoides) thurrelli, and Zonovia sp. A from British Columbia (western Canada). They belong to genera that are widely distributed in the subboreal Eurasian Arctic and Northwest Europe, and they also occur even in those Boreal regions dominated by cardioceratids. They are important markers for a narrow stratigraphic interval in the Cymodoce Zone (top of Lower Kimmeridgian) and the lower part of the Mutabilis Zone (base of Upper Kimmeridgian) of the Northwest European standard succession. In Spitsbergen and Franz Josef Land, the only Upper Kimmeridgian aulacostephanid-bearing level is the Zenostephanus (Zenostephanus) sachsi biohorizon, which very likely belongs to the Mutabilis Zone. Expansion of Zenostephanus from Eurasia, where it is present over a large area, into British Columbia, is approximately correlative with a transgressive event that also led to expansion of the Submediterranean ammonite genus Crussoliceras through the Submediterranean and Subboreal areas slightly before Zenostephanus.
Middle Jurassic - Lower Cretaceous ammonites & aptychi