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Geological Magazine; September 2006; v. 143; no. 5; p. 657-678; DOI: 10.1017/S0016756806002469
© 2006 Cambridge University Press (CUP)
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First record of the Hirnantian (Upper Ordovician) {delta}13C excursion in the North American Midcontinent and its regional implications

STIG M. BERGSTRÖM*,{ddagger}, MATTHEW M. SALTZMAN* and BIRGER SCHMITZ{dagger}

* Department of Geological Sciences, The Ohio State University, Columbus, Ohio 43210, USA
{dagger} Department of Geology, GeoBiosphere Science Center, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden

{ddagger} Author for correspondence: stig{at}geology.ohio-state.edu

The most prominent of the two major global {delta}13C excursions in the Ordovician, the Hirnantian {delta}13C excursion (HICE), which is previously recorded from the uppermost Ordovician in a few sections in Nevada, Quebec, Arctic Canada, Baltoscandia, Scotland and China, is documented for the first time from the North American Midcontinent. Samples through the Girardeau Limestone and Leemon Formation in Missouri and Illinois show elevated {delta}13C values of + 4 {per thousand}to + 5 {per thousand}. Although not determined precisely, the beginning of the HICE is likely to be in the upper part of the Orchard Creek Shale, and it ends in the upper Leemon Formation. Being extraordinarily useful chronostratigraphically, the presence of the HICE makes it possible to provide a firm dating of the study interval, whose age has long been controversial. Comparison between the study sections and coeval HICE sequences in North America and Europe show striking similarities, especially in sea-level history, indicating that major local lowstands reflect eustatic sea-level changes. A comparison with Hirnantian diamictite successions in North and South Africa and Argentina suggests that these lowstands correspond to two major Gondwanan glacial episodes.

Key Words: carbon isotope excursion • Hirnantian • Upper Ordovician • Missouri–Illinois • Gondwana glaciation • sea-level changes




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S. M. BERGSTROM, C. XU, B. SCHMITZ, S. YOUNG, R. JIA-YU, and M. R. SALTZMAN
First documentation of the Ordovician Guttenberg {delta}13C excursion (GICE) in Asia: chemostratigraphy of the Pagoda and Yanwashan formations in southeastern China
Geological Magazine, January 1, 2009; 146(1): 1 - 11.
[Abstract] [Full Text] [PDF]


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