Graptoloid graptolites, conodonts and chitinozoans from the lower part of the Racine Dolomite Formation at the Material Services Corporation quarry at Thornton indicate that the Fossil Konservat-Lagersta??tte here is of late Sheinwoodian (early Wenlock) age. It is thus of an age approximately midway between those of the other Midwest Lagersta??tten: within the Brandon Bridge Formation at Waukesha (Telychian), and the Mississinewa Shale (Gorstian) and Lecthaylus Shale (Gorstian). Conodonts indicate that the Fossil Konservat-Lagersta??tte at Thornton corresponds to the 'post Kockelella walliseri interregnum' sensu Jeppsson (1997, Transactions of the Royal Society of Edinburgh: Earth Sciences 88: 91-114). Copyright ?? 2002 John Wiley and Sons, Ltd.
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Biostratigraphical dating of the Thornton Fossil Konservat-Lagersta??tte, Silurian, Illinois, USA