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Untangling a Darriwilian (Middle Ordovician) palaeoecological event in Baltoscandia: conodont faunal changes across the ‘Täljsten’ interval

Published online by Cambridge University Press:  01 December 2009

Johanna I. S. Mellgren
Affiliation:
Department of Earth and Ecosystem Sciences, Division of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden Email: Johanna.Mellgren@geol.lu.se; Mats.Eriksson@geol.lu.se
Mats E. Eriksson
Affiliation:
Department of Earth and Ecosystem Sciences, Division of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden Email: Johanna.Mellgren@geol.lu.se; Mats.Eriksson@geol.lu.se

Abstract

Conodont faunal dynamics and high-resolution biostratigraphy in the lithologically and faunally anomalous ‘Täljsten’ succession, which spans the Darriwilian Lenodus variabilisYangtzeplacognathus crassus Zone boundary, were investigated in a 2·5 m-thick section on Mt Kinnekulle that includes an interval yielding fossil meteorites and extraterrestrial chromite. The previous interpretation that this interval reflects a regression is consistent with the occurrence and abundance patterns of some conodont taxa. The disappearance of e.g., Periodon, suggests that the regression began prior to the deposition of the grey ‘Täljsten’. The transition from red to grey limestone coincides with a conspicuous faunal re-arrangement. The lower half of the ‘Täljsten’ reflects a gradual shallowing favourable for some taxa, such as Lenodus, and the immigration of Microzarkodina cf. ozarkodella and Histiodella holodentata. In the middle of the ‘Täljsten’ interval, coinciding with the appearance of abundant cystoids, conditions became less hospitable for conodonts, resulting in a low diversity and low abundance fauna, which occurs to the top of the interval. The overlying red limestone, apparently deposited during a deepening event, marks a return to pre-‘Täljsten’ conditions with a re-organised fauna. The close correlation between the lithologic shifts and conodont faunal changes demonstrates the usefulness of conodonts as environmental indicators.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 2010

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