Leho Ainsaar

... The bed-by-bed ostracode record is in accordance with the bed nomenclature in the Paite section (Fig. ... VSEGEI, St. Petersburg (in Russian). Jaanusson, V. 1973. Aspects of carbonate sedimentation in the Ordovician of Baltoscandia. Lethaia, 6, 11-34. Jaanusson. ...

The Upper Ordovician (uppermost Caradoc-Ashgill) section of western Estonia consists of a series of seven open-shelf carbonate sequences. Depositional facies grade laterally through a series of shelf-to-basin facies belts: grain-supported facies (shallow shelf), mixed facies (middle shelf), mud-supported facies (deep shelf and slope) and black shale facies (basin). Locally, a stromatactis mud mound occurs in a middle-to-deep shelf position. Shallow-to-deep

ABSTRACT Comparison of the Hirnantian and Rhuddanian δ13C curves of the new core sections from the Pandivere area, central Estonia, suggests some changes in the traditional stratigraphic correlation scheme of Estonia. The Ärina Formation, Porkuni Regional Stage, has previously been considered as the early Hirnantian while the upper Hirnantian was supposed to be missing in the area and the Varbola Formation was dated as the early Llandovery. The sandy unfossiliferous Kamariku Member in the uppermost part of the Ärina Formation is located on the falling limb of the HICE and may thus be of late Hirnantian age. It is possible, that the Kamariku Member belongs to the interval between the widespread Hirnantian unconformities HA and HB, like the Saldus Formation in Latvia and southern Estonia. The basal part of the Varbola Formation, the Koigi Member, falls into the interval of upward declining δ13C values in the sections of the Pandivere area and obviously represents the latest part of the HICE. This suggests the age of the Koigi Member to be late Hirnantian and places the Ordovician/Silurian boundary into the lower part of the Varbola Formation.The second phase of the Hirnantian extinction related to the unconformity HB was followed by a slow faunal recovery. This recovery is characterized by the slow appearance of postextinction biota that obviously included some “Silurian-type” shelly fossil groups that were used in traditional correlation schemes of non-graptolitiferous Ordovician/Silurian boundary successions for positioning the system boundary. The detailed chemostratigraphic comparison of these sections with graptolitiferous successions allowed testing and correcting the position of the Ordovician/Silurian boundary, which is likely be positioned higher in the succession than the traditional placement.

ABSTRACT The role of carbon dioxide in regulating climate during the early Paleozoic, when severe glaciations occurred during a putative greenhouse world, remains unclear. Here, we present the first molecular carbon isotope proxy-based estimates for Late Ordovician (early Katian) pCO2 levels, and explore the limitations of applying this approach to the reconstruction of Paleozoic pCO2. Carbon isotope profiles from three sites in Laurentia (Iowa, Ontario and Pennsylvania) and one site in Baltica (Estonia) exhibit overall low isotope fractionation between organic and inorganic carbon during photosynthesis (εp) and these values declined during the early Katian carbonate carbon isotope excursion (or Guttenberg Carbon Isotope Excursion, GICE). Algal εp values are sensitive to changes in CO2 concentrations, algae cell morphologies, and cell growth rates. To constrain these factors, we present molecular evidence that a decrease in the relative abundance of cyanobacteria and a change in the eukaryotic algae community co-occurred with the GICE. Regardless of local biotic or oceanographic influences, a decline in εp values indicates photosynthesis was sensitive to carbon concentrations, and via analogy with modern taxa, constrains pCO2 to below ∼8× pre-industrial levels (PIL), or about half of previous estimates. In addition, the global, positive carbon isotope excursions expressed in a wide variety of sedimentary materials (carbonate, bulk organic matter, n-alkanes, acyclic and cyclic isoprenoid hydrocarbons), provide compelling evidence for perturbation of the global carbon cycle, and this was likely associated with a decrease in pCO2 approximately 10 million years prior to the Hirnantian glaciations. Isotopic records from deeper water settings suggest a complex interplay of carbon sources and sinks, with pCO2 increasing prior to and during the early stages of the GICE and then decreasing when organic carbon burial outpaced increased volcanic inputs.

... Haq, BU and Schutter, SR, 2008. A Chronology of Paleozoic Sea-Level Changes. Science, 322, 64-68. Harris, M. T, Sheehan, PM, Ainsaar, L., Hints, L., Mannik, P., Nolvak, J. and Rubel, M., 2004. Upper Ordovician sequences of western Estonia. ...

... University of Wales Press, Cardiff, p. 301-326. Jacobson, SR, Finney, SC, Hatch, JR and Ludvigson, GA, 1995. ... The Pacific Section Society for Sedimentary Geology, Fullerton, p. 305-308. Kaljo, D. and Nestor, H.(eds), 1990. Field Meeting, Estonia 1990. ...