A positive trend in seawater ⁸⁷Sr/⁸⁶Sr values over the Early–Middle Frasnian boundary (Late Devonian) recorded in well-preserved conodont elements from the Holy Cross Moun

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• 作者：Eleanor H. John ; Robert Cliff ; Paul B. Wignall
• 关键词：Devonian ; Early&#x2013 ; Middle Frasnian boundary ; Strontium isotopes ; Geochemistry ; Conodonts ; Holy Cross Mountains ; Poland
• 刊名：Palaeogeography, Palaeoclimatology, Palaeoecology
• 出版年：2008
• 出版时间：15 November 2008
• 年：2008
• 卷：269
• 期：3-4
• 页码：166-175
• 全文大小：1496 K

文摘

Over the Early–Middle Frasnian boundary interval (Late Devonian), the oceans experienced major changes in global carbon cycling and nutrient dynamics with a prominent positive carbon isotope shift at the base of the Palmatolepis punctata Zone (Middle Frasnian). The aim of this study was to construct seawater ⁸⁷Sr/⁸⁶Sr ratio curves for the Pa. transitans–Pa. hassi zonal interval using well-preserved conodont apatite from two sections in the Holy Cross Mountains, south-central Poland. The final curves suggest that seawater ⁸⁷Sr/⁸⁶Sr values were steady at ~ 0.70794–0.70799 during the transitans Zone but began to rise in the early punctata Zone towards a value of ~ 0.70814 in the late punctata Zone (an increase of ~ 0.0002). The increase in seawater ⁸⁷Sr/⁸⁶Sr values over the Early–Middle Frasnian boundary appears to be the second of two prominent short-term rises in ⁸⁷Sr/⁸⁶Sr values, which led to an overall shift in values from a Givetian plateau of between ~ 0.70780 and 0.70785 to a Late Frasnian plateau of between 0.7080 and 0.7082. Correlation with a regional positive δ¹³C anomaly and evidence for eutrophication in the marine environment suggests that the causes of these phenomena may be linked and that the positive ⁸⁷Sr/⁸⁶Sr shift was caused by an increase in the continental flux of Sr to the oceans, i.e., the weathering flux. A possible explanation for an increase in the weathering flux is the denudation of a new Acadian–Eovariscan orogen, which would have been mostly weathered in the humid, warm tropical/equatorial region.