What is it about?
Altered volcanic ash interbeds (bentonites) in upper Katian of Baltoscandia indicate significant volcanic activity in neighbouring tectonically active areas. Studied volcanic ash beds occur in Tanuchitina bergstroemi and Conochitina rugata chitinozoan zones. Katian bentonites in the East Baltic can be reliably correlated using sanidine phenocryst composition. Ratios of immobile trace elements TiO2, Nb, Zr and Th with Al2O3 enable to extend the correlations to Scandinavia. At least seven volcanic eruptions were recognized in Baltoscandian sections. Several bentonites found in deep sea sediments are absent in shallow sea sediments, indicating extensive breaks in sedimentation and erosion during late Katian and Hirnantian times. The areal distribution pattern of Katian bentonites in Baltoscandia indicates a volcanic source from North or North-West (present day orientation) from the margins of the Iapetus Palaeo-Ocean. Geochemical similarities between Baltoscandian and Dob`s Linn bentonites from southern Scotland suggest a common volcanic source in Katian times.
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Why is it important?
Integrated bio- and volcanic stratigraphy
Perspectives
Further study of Katian volcanism will give better insight to the development of the ancient Iapetus palaeo-ocean between Baltica and North America.
Dr Tarmo Kiipli
Tallinna Tehnikaulikool
Read the Original
This page is a summary of: Upper Katian (Ordovician) bentonites in the East Baltic, Scandinavia and Scotland: geochemical correlation and volcanic source interpretation, Geological Magazine, October 2014, Cambridge University Press,
DOI: 10.1017/s001675681400051x.
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