THE LATE SILURIAN WAUBAKEE FORMATION OF MILWAUKEE AND OZAUKEE COUNTIES, WISCONSIN

The Waubakee Formation, the youngest Silurian unit in Wisconsin, ranges from 20 to 30 m thick and consists of dolomite of intertidal to supratidal origin. In the Milwaukee subsurface, the Waubakee conformably overlies the Wenlockian Racine Formation across a 50 cm stratigraphic interval in which bioturbation declines and fossils dissappear; it is probably Late Wenlockian to Ludlovian age. The top of the Waubakee contains up to 50% sulfides and interconnecting fractures to 20 cm deep that are filled with clay-rich carbonate and angular dolostone clasts; this surface is disconformably overlain by the Givetian Thiensville Formation. Lithologies in the Waubakee include fenestral crytptalgal-laminated mudstone, fenestral parallel-laminated mudstone, bioturbated mudstone, ripple-laminated mudstone, and rare ooid-intraclast packstone. Mudcracks and auto-brecciated horizons are common, and decimeter- to meter-thick shallowing-upwards sequences from bioturbated to laminated mudstone are present throughout the formation. Musem collections from the Waubakee include brachiopods, bivalves, cephalopods, leperditiid ostracods, and phyllocarids. Core and outcrop examined by us have yielded only rare ostracods.