Biostratigraphical dating of the Thornton Fossil Konservat-Lagerstätte, Silurian, Illinois, USA

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-Lagerstätte here is of late Sheinwoodian (early Wenlock) age. It is thus of an age approximately midway between those of the other Midwest Lagerstätten: within the Brandon Bridge Formation at Waukesha (Telychian), and the Mississinewa Shale (Gorstian) and Lecthaylus Shale (Gorstian). Conodonts indicate that the Fossil Konservat-Lagerstätte at Thornton corresponds to the ‘post Kockelella walliseri interregnum’ sensu Jeppsson (1997, Transactions of the Royal Society of Edinburgh: Earth Sciences88: 91–114)