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Atypical diagenetic effects on strontium-isotope composition of Early Jurassic belemnites, Queen Charlotte Islands, British Columbia, Canada

Gröcke, D.R.; Hesselbo, S.P.; Findlay, D.J.

Authors

S.P. Hesselbo

D.J. Findlay



Abstract

In this study, strontium-, carbon- and oxygen-isotope data are reported from Early Jurassic belemnites from Yakoun River, Queen Charlotte Islands (QCI), British Columbia. Assuming that the established ammonite correlations between Canada and Europe are accurate, the seawater 87Sr/86Sr curve between Europe and QCI should be similar. However, the Rarenodia planulata and Phymatoceras crassicosta ammonite biozones from Yakoun River record 87Sr/86Sr values that are lower than expected. This shift is interpreted to be a result of diagenetic alteration by later hydrothermal fluid (87Sr-depleted). In general, the diagenetic samples have more negative δ13Cbel and δ18Obel values, and higher Mn concentrations, but show no difference in Fe concentration. A δ13Cbel curve from diagenetically screened samples exhibits only slightly depleted values with respect to a similar curve generated from Europe. A similar curve for δ18Obel shows a striking similarity with that generated from Europe. This study illustrates that diagenetic effects on Sr-isotope composition can lower values from the expected seawater 87Sr/86Sr curve, thus potentially producing erroneous correlations between ammonite biostratigraphic schemes. Traditional screening methods for diagenesis, such as cathodoluminescence and trace-element abundances, were inadequate for evaluating diagenesis in the Yakoun River sections. Other such studies must also consider alternative and (or) a combination of methods in evaluating geochemical data from belemnites.

Citation

Gröcke, D., Hesselbo, S., & Findlay, D. (2007). Atypical diagenetic effects on strontium-isotope composition of Early Jurassic belemnites, Queen Charlotte Islands, British Columbia, Canada. Canadian Journal of Earth Sciences, 44(2), 181-197. https://doi.org/10.1139/e06-087

Journal Article Type Article
Publication Date Feb 1, 2007
Deposit Date Jun 4, 2010
Journal Canadian Journal of Earth Sciences
Print ISSN 0008-4077
Electronic ISSN 1480-3313
Publisher Canadian Science Publishing
Peer Reviewed Peer Reviewed
Volume 44
Issue 2
Pages 181-197
DOI https://doi.org/10.1139/e06-087