LATEST EIFELIAN-EARLY GIVETIAN (MIDDLE DEVONIAN) SUCCESSION IN THE SUBSURFACE OF SOUTHERN ONTARIO: CORRELATION OF SEQUENCES/BIOEVENTS BETWEEN THE APPALACHIAN AND MICHIGAN BASINS

Correlation of late Eifelian –early Givetian (Middle Devonian) strata in the Lake Erie region is of key importance in establishing detailed temporal relationships between the Hamilton Group in the Appalachian foreland and the Traverse Group of the Michigan Basin. Based on gamma logs, Rickard (1985) correlated the Bell Shale and the overlying Rockport Quarry Ls. of the Ontario subsurface with the upper Eifelian Union Springs black shale and Cherry Valley Ls., respectively, in NY. These correlations align dissimilar faunas in the two basins and suggest marked diachroneity of faunal turnover. However, Uyeno (in Sparling, 1988) identified early Givetian (u. ensensis Z.) conodonts in the Rockport Quarry Limestone in Ontario, raising doubts about earlier correlations.

Detailed examination of drill cores from southern Ontario (Port Stanley, Sarnia) indicates that upper Eifelian-lower Givetian Appalachian Basin sequences can be traced through the Ontario subsurface to the margin of the Michigan Basin. A thin shaly limestone succession, lying between buff, dolomitic Dundee carbonates and typical Bell Shale, can be directly related to the upper Eifelian stratigraphic succession of the Appalachian basin. The Dundee grades upward into 2 m of sparsely fossiliferous, dark shales/shaly limestones comparable to the NY Union Springs Shale. These are overlain by ~1 m of dark, auloporid-rich micritic limestone, reminiscent of the Cherry Valley Mbr. The overlying Bell Shale is divisible into three units: a) ~2 m of dark gray shales containing rare leiorhynchid brachiopods, b) ~1 m of very fossiliferous, medium grey shale with abundant brachiopods including Ambocoelia, ?Mediospirifer, Longispina and Hallinetes cf. lineatus, and, c) ~12 m of dark gray to black, sparsely fossiliferous shales, again with rare leiorhynchids. Each of these units has a counterpart in both the Appalachian and Michigan basins, establishing detailed correlations between the Bell (MI) and Oatka Creek (NY) formations. Rockport Quarry beds would correlate with the Stafford Ls. of NY, as suggested by Uyeno. The fauna and position of unit b link it to both the Halihan Hill bed (Oatka Creek Shale) in NY and an unnamed fossil bed in the lower Bell Shale of MI. This bed lies near the Eifelian-Givetian boundary and yields the lowest Hamilton-like faunas in both basins.