New biostratigraphically important chitinozoans from the Kukruse Regional Stage, Upper Ordovician of Baltoscandia

Three new chitinozoan species, Conochitina savalaensis, Conochitina viruana and Belonechitina intonsa, are described. All these species are stratigraphically restricted to the Kukruse age (lowermost Sandbian, Laufeldochitina stentor chitinozoan Zone) and have been recorded in numerous East Baltic sections as well as from NE Poland and NW Ukraine and Sweden. Their short temporal range and relative abundance point to a great biostratigraphical value for regional correlations near the base of the Upper Ordovician

Darriwilian (Middle Ordovician) conodont biostratigraphy in NW Estonia

Darriwilian conodonts have been studied in numerous sections of Baltoscandia, but few data are available from the classical outcrop area in northern Estonia. In this paper we report the succession of Darriwilian conodonts and chitinozoans from the bed-by-bed sampled Uuga and Osmussaar cliffs, NW Estonia. Standard Baltoscandian conodont and chitinozoan zones and subzones were identified from the topmost Volkhov to Uhaku regional stages. The global Dapingian–Darriwilian boundary coincides with the Volkhov–Kunda boundary in NW Estonia. The Kunda Stage is represented by its middle or upper part only, and the Aseri Stage is probably missing in both sections studied. The lowermost part of the Lasnamägi Stage with the conodont Yangtzeplacognathus foliaceus is also very condensed. The rest of the Lasnamägi and Uhaku stages, corresponding to the main part of the Pygodus serra conodont Zone, is well represented and can be correlated across Estonia and Sweden. Subtle regional variations in this interval indicate very uniform depositional conditions over wide areas of the Baltoscandian palaeobasin. Our results suggest that the Y. foliaceus Subzone in Estonia needs further assessment. Stratigraphically well-constrained Y. protoramosus appears to be more common than previously thought, and is thus a valuable regional subzonal index. The integrated conodont and chitinozoan scale provides more than 20 biostratigraphically important levels for local and regional correlations, probably approaching temporal resolution in the order of 0.1 Ma for the late Darriwilian

Microfossils in the Ordovician erratic boulders from Southwestern Finland

Chitinozoans, ostracods and acritarchs found in four glacially transported limestone boulders from the south-western coast of Finland have been studied in order to test the usefulness of these microfossil groups in age determinations. Also rare specimens of conodonts, inarticulated brachiopods and foraminifers were found. Baltic limestone (or Östersjö limestone) was the most problematic, because only fossils with calcitic or phosphatic shells are preserved. It is concluded that the boulders identified correlate with the Uhaku and Rakvere stages of the Middle Ordovician

Polar front shift and atmospheric CO₂ during the glacial maximum of the Early Paleozoic Icehouse

Our new data address the paradox of Late Ordovician glaciation under supposedly high pCO2 (8 to 22× PAL: preindustrial atmospheric level). The paleobiogeographical distribution of chitinozoan (“mixed layer”) marine zooplankton biotopes for the Hirnantian glacial maximum (440 Ma) are reconstructed and compared to those from the Sandbian (460 Ma): They demonstrate a steeper latitudinal temperature gradient and an equatorwards shift of the Polar Front through time from 55°–70° S to ~40° S. These changes are comparable to those during Pleistocene interglacial-glacial cycles. In comparison with the Pleistocene, we hypothesize a significant decline in mean global temperature from the Sandbian to Hirnantian, proportional with a fall in pCO2 from a modeled Sandbian level of ~8× PAL to ~5× PAL during the Hirnantian. Our data suggest that a compression of midlatitudinal biotopes and ecospace in response to the developing glaciation was a likely cause of the end-Ordovician mass extinction