Abstract
The latest Ordovician is marked by a severe climate change, the Hirnantian glaciation. This climatic event affected many marine taxa including ostracods. Rich and abundant ostracod assemblages of the Baltic Palaeobasin were severly impoverished. Many of the typical pre-Hirnatian warm-water ostracod species died out, but also some distinct, cold-water species appeared. Two very different but likely coeval latest Ordovician ostracod assemblages are recorded in the Baltic countries and north-eastern Poland. The latest Ordovician Estonian Shelf (inner ramp) is characterized by the Medianella aequa association whilst sections in the Livonian Basin (middle to outer ramp) reveal the Harpabollia harparum association that is thought to represent a cold-water assemblage belonging to the Dalmanitina-Hirnantia Fauna sensu lato . A transitional assemblage composed of a “species mixture” of typical Hirnantian cold-water and some pre-Hirnantian warm-water ostracod species is described for the first time from the Ketrzyn IG1 borehole, north-eastern Poland. The assemblage is dominated by Cryptophyllus pius sp. n. The genus Cryptophyllus is rare in the two other well-known assemblages. The discovery suggests that marginal parts of the Baltic Palaeobasin could serve as a kind of refuge for the last representatives of the ostracod faunas of the inner shelf of Baltic Palaeobasin. The Hirnantian assemblage is replaced by the low-diversity recovery assemblage that is dated as late Hirnantian-Silurian in Estonia and other areas. This suggests that the position of the systemic boundary in the Ketrzyn borehole and elsewhere in north-eastern Poland should be re-evaluated.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.