REVISED CONODONT BIOSTRATIGRAPHY OF LOWER SILURIAN STRATA OF SOUTHEASTERN WISCONSIN

Lower Silurian strata exposed in quarries in southeastern Wisconsin in the Waukesha area include, in stratigraphical order from lowest to highest unit: Mayville Dolomite, Burnt Bluff Group, Manistique Group (?), Brandon Bridge Formation, and Waukesha Dolomite. The Mayville Dolomite is likely within the Distomodus kentuckyensis Zone, based on a few broken conodont elements likely referable to the nominative species. The Burnt Bluff Group is likely within the Pseudolonchodina fluegeli Zone because it yielded elements of the nominative species, but no elements of the zonal indices for either the older Ps. expansa Zone or younger D. staurognathoides Zone. The unit tentatively recognized as Manistique Group strata yielded elements of Pseudooneotodus tricornis and of a Distomodus species, but no elements of any other species known from the Pterospathodus eopennatus Zone, indicating that it is likely within the D. staurognathoides Zone, the oldest zone from which elements of P. tricornis have been reported. The lower part of the Brandon Bridge Formation is within the Pt. eopennatus Superzone, as it yielded elements of the nominative species and of additional conodont species typical of that zone. The top of the lower part of the Brandon Bridge is the highest portion of the formation within the Pt. eopennatus Superzone, and is the level of the formation from which the Waukesha biota (Konservat Lagerstätte) was recovered. A thin interval in the middle of the Brandon Bridge is possible to assign to the Pt. celloni Superzone, based on the occurrence of elements of Pt. amorphognathoides subspecies that are not elements of Pt. am. amorphognathoides. The upper part of the Brandon Bridge is within the Pt. am. amorphognathoides Zone, based on occurrence of elements of the nominative subspecies in samples from its base and top and the last occurrence of elements of Nudibelodina sensitiva in the basal portion of the overlying Waukesha. The Waukesha Dolomite is within the Pt. am. amorphognathoides Zone to Upper Kockelella ranuliformis Zone, based on the occurrence of elements of N. sensitiva, Ozarkodina polinclinata, Pt. am. amorphognathoides, D. staurognathoides, K. ranuliformis, and K. walliseri.