The lower Silurian (Llandovery) Osmundsberg K-bentonite in Baltoscandia and the British Isles: Chemical fingerprinting and regional correlation

Abstract

The lower Silurian Osmundsberg K-bentonite is a widespread altered volcanic ash bed that occurs throughout Baltoscandia and other parts of northern Europe. K-bentonite samples from sections containing the Osmundsberg K-bentonite bed were investigated to determine whether the chemical composition of this bed is sufficiently unique and diagnostic that it can serve as a basis for high-resolution chemostratigraphic correlation on a regional scale. Eleven known and five suspected Osmundsberg K-bentonite samples along with 26 samples of accompanying ash beds from 13 different localities were analyzed for major and trace elements. The data were statistically treated using discriminant function analysis to determine if the trace element data provide a unique chemical fingerprint for the Osmundsberg K-bentonite bed. Comparison with the correlation model of Bergström et al. [Bergström, S.M., Huff, W.D. & Kolata, D.R., 1998b: The lower Silurian Osmundsberg K-bentonite. Part I: Stratigraphic position, distribution, and palaeogeographic significance. Geological Magazine 135, 1–13.] based on biostratigraphic evidence shows that results from two independent techniques are in general agreement with the exception of five samples whose presumed Osmundsberg affinity is rejected. The results demonstrate that the unique and identifiable chemical fingerprint of the Osmundsberg K-bentonite bed can provide an additional stratigraphic tool for local and regional correlation of these K-bentonites.

Keywords:

• Silurian
• K-bentonite
• Baltoscandia
• discriminant analysis
• Osmundsberg

Acknowledgements

We are indebted to H. Bauert, D. Kaljo and L. Ainsaar for much appreciated assistance during this project, and to R. Batchelor and T. Kiipli for providing very constructive and helpful reviews. Financial support was provided by NSF grants EAR-9004559 and EAR-9005333.