Conodont biozonation in the upper Arenig of Sweden

Abstract

Conodont faunas from the Arenigian Lanna/Volkhov Stage in Baltoscandia have been the subject of intensive study, particularly during the last decade, and different biozonations based on them have been proposed. The application of some of these zones is discussed here. The present investigation is mainly based on 64 samples from ten sections in Sweden, but conodont collections from Bornholm (Denmark) and Tamsalu (Estonia) have also been studied. Lindström's (1971) concept of the upper Arenigian Microzarkodina parva Zone is essentially replaced by a revised Baltoniodus norrlandicus Zone. The zone corresponds closely to Bagnoli & Stouge's (1997) recently distinguished B. norrlandicus and Lenodus antivariabilis zones, which can be recognized in sections where a more detailed subdivision and correlation is possible under the names of the T. quadrangulum Subzone and the L. antivariabilis Subzone, respectively. *

An Early to Middle Ordovician succession of conodont faunas at Mäekalda, northern Estonia

“…Bagnoli & Stouge (1997) subdivided the overlying interval into a lower B. norrlandicus Zone and an upper Lenodus antivariabilis Zone. Trapezognathus quadrangulum, which has its last occurrence in their lower zone, is present in all three samples representing the B. norrlandicus Zone at Mäekalda (Mä95-30, -31 and -38), the entire thickness of which is less than 0.3 m. It can thus be concluded that the uppermost Volkhov-lowermost Kundan L. antivariabilis Zone of Bagnoli & Stouge (1997), or the L. antivariabilis Subzone sensu Löfgren (2000a), is lacking in the section. Between samples Mä95-38 and Mä95-37, at the boundary between the Lahepere Member of the Toila Formation and the Kallaste Member of the Pakri Formation, there is thus a considerable stratigraphic gap in the succession, since the basal Pakri includes at most 0.1 m of the combined upper Volkhov-lower Kunda up to the base of the Eoplacognathus pseudoplanus Zone represented by sample Mä95-35.…”

“…This is indicative of the base of the B. norrlandicus Zone sensu Bagnoli & Stouge (1997) and Löfgren (2000a), which is thus situated in the middle part of the Lahepere Member. Bagnoli & Stouge (1997) subdivided the overlying interval into a lower B. norrlandicus Zone and an upper Lenodus antivariabilis Zone.…”

“…For instance, T. brevibasis is generally more abundant and P. originalis much less common than in the Swedish samples. At Mäekalda the P. originalis Zone is c. 3 m thick, whereas in the Gillberga section on Öland this interval is only slightly more than 1 m thick (Löfgren, 2000a). In most sections on the Swedish mainland the P. originalis Zone, however, is thicker, for instance 4.6 m at Lanna, Närke (Löfgren, 1995), and between 8 and 9 m at Kalkberget, Jämtland (Löfgren, 1978).…”

“…The Baltoniodus norrlandicus Zone at Mäekalda is equivalent to the lower part of the same zone at the Horns Udde quarry section, the section north of Horns Udde (Bagnoli & Stouge, 1997) and the Gillberga quarry (Löfgren, 2000a) on Öland, for instance. Species that have been found in this interval in one or more of the Öland sections but not at Mäekalda are Scolopodus rex, Parapaltodus sp., Microzarkodina flabellum (in sections investigated by Bagnoli & Stouge, 1997) and Decoriconus mercurius Löfgren (in the Gillberga quarry, cf.…”

Intraspecific variation and polymorphism in the ostracode Conchoprimitian socialis (Brøgger, 1882) from the early Middle Ordovician Baltoscandian Palaeobasin

“…The stratigraphic distribution of Conchoprimitia species from the Floian to lower Darriwilian (Billingen, Volkhov and Kunda regional stages) of Baltoscandia is presented in Table 1. Conchoprimitia is (Löfgren 1995(Löfgren , 2000Nõlvak et al 2006). Data for Västergötland from Jaanusson (1982) and Dronov et al (2001); Oslo region from Owen et al (1990).…”