The Late Wenlock Mulde positive carbon isotope (δ¹³C_carb) excursion in North America

Abstract

Marine carbonates from two well-studied areas of the Silurian of North America were analyzed for stable carbon isotope (δ¹³C_carb) stratigraphy. A graptolite-bearing sequence from the eastern margin of the Panthallasic Ocean (Nevada) and a conodont-bearing sequence from the mid-continent epeiric seaway (Tennessee) were sampled for δ¹³C_carb stratigraphy in order to improve the correlation between these areas and the Swedish island of Gotland, which has become the global standard for Wenlock conodont and carbon isotope stratigraphy. The Homerian (Late Wenlock) Mulde positive carbon isotope excursion serves as a useful chronostratigraphic marker for Homerian sequences, especially in regions such as the two included in this investigation, where zonal fossils are absent or poorly represented. In Nevada, using presently available biostratigraphic data, a detailed modern graptolite zonation cannot be applied due to a lack of several key species. Likewise, the zonally important conodont species are poorly represented in Tennessee. Our recognition of the dual-peaked Mulde δ¹³C_carb excursion in North America allows improved correlation between these sequences and any other locality where the Mulde Excursion has been recorded in sufficient detail.

Keywords:

• Wenlock
• Ludlow
• Silurian
• carbon isotope
• stratigraphic correlation
• conodont
• graptolite
• extinction