The Llandovery–Wenlock boundary interval in west-central continental Estonia: an example from the Suigu (S-3) core section

Abstract

A gap corresponding to several conodont and chitinozoan zones occurs in the Llandovery-Wenlock boundary interval in some sections in the western coastal region of Estonia and on islands in the Muhu Strait. New data from the Suigu (S-3) core section demonstrate that the gap has geographically wider distribution in western continental Estonia. Detailed study of faunas from that section revealed that here the gap corresponds to at least four conodont zones (from below): the Lower and Upper Pseudooneotodus bicornis and Lower and Upper Pterospathodus pennatus procerus zones, but probably also the upper(most) Upper Pt. amorphognathoides amorphognathoides Subzone and the Lower Kockelella ranuliformis Zone (or part of it) are missing. In sense of chitinozoan biostratigraphy, the gap correlates with most of the Margachitina margaritana Zone. Only the uppermost part of this zone is represented in the section. However, although the gap in the Suigu (S-3) core section is distinct and well dated biostratigraphically, the δ 13 C curve demonstrates no evidence of it. Causes of this controversy are still waiting to be revealed.Our data indicate that changes in sedimentation in the Llandovery-Wenlock boundary interval occurred earlier in the distal graptolite-bearing and later in the proximal environments. Most probably, sedimentation in the Baltic Palaeobasin in the late Telychian and early Sheinwoodian was strongly affected by tectonic evolution of the Baltoscandian foreland basin.

Emended Sandbian (Ordovician) conodont biostratigraphy in Baltoscandia and a new species ofAmorphognathus

“…From comparison of the first Amorphognathus elements in the Mehikoorma, Ruhnu (Männik, 2003) and Velise (Paiste et al 2022) drill cores of Estonia, and in the Fjäcka main section and in the Smedsby Gård drillcore in Sweden, along with a personal communication (S. M. Bergström, 2022), it is evident that there is currently no evidence that A. inaequalis could be present in Estonian or Swedish sections. It is therefore likely that A. inaequalis was not present on the Baltica Palaeocontinent during early Sandbian time.…”

Effects of early marine diagenesis and site-specific depositional controls on carbonate-associated sulfate: Insights from paired S and O isotopic analyses

“…The Nurmekund formation represents the upper part of the "Early-Middle Llandovery macrocycle" (Nestor & Einasto, 1997); it is followed by a regional hiatus and denudation during the late Aeronian. The "Late Llandovery -Middle Wenlock macrocycle" is represented by a full transgressive-regressive cycle in the Paatsalu core: a gradual deepening to inner-mid shelf settings (Rumba Formation) and even deeper mid-outer shelf facies (Velise Formation) during the Telychian; then a sequence boundary that coincides with a gap (Männik et al, 2014) and marks a return to inner-mid shelf settings (oolite at the base of the Jaani Formation) with a subsequent flooding surface to outer-shelf facies (Jaani Formation) and then shallowing into peritidal environments (Muhu Formation). As a result of the early-mid Wenlock regression the basin transformed into a more restricted gulf-like pericratonic sea (Nestor & Einasto, 1997).…”

Chrono-, litho- and conodont bio-stratigraphy of the Rauchkofel Boden Section (Upper Ordovician – Lower Devonian), Carnic Alps, Austria

“…s. rhenana Walliser . Jeppsson (1997) subdivided this interval into two biozones at Gotland, and this scheme is accepted in various papers in Baltica and Laurentia (i. e., Cramer et al 2010, Männik et al 2014, but this subdivision is not applicable in the condensed sequence of the Carnic Alps. The named Zone is discriminated at the Rauchkofel Boden Section in the lower part of the Kok Fm.…”