Description: Solid hydrocarbons, generally unanalyzed in detail, are found at a number of localities within the Paleozoic rocks around the state. They may be alternately described as "bitumen" or "asphaltum". These usually occur as black tarry substances within vugs in limestones or as finally divided kerogen in local outcrops of oil shale. In addition, the Nonesuch formation and its equivalents, which contain liquid hydrocarbons, is present at the surface and in subsurface into northwestern Wisconsin. This formation has been the subject of occasional petroleum exploration. Despite this, there are no known economically viable hydrocarbon deposits in Wisconsin.
CLARK COUNTY: Lustrous black particles of hydrocarbon occur in the matrix of the Mayville iron ore (Hawley and Beavan, 1934).
DOOR COUNTY: Solid "bitumen" occurs in limestone of the Milwaukee Formation exposed at low water stands of Lake Michigan 2 miles north of Whitefish Bay (Nelson and Roberts, 1963).
FOND DU LAC COUNTY: Solid hydrocarbon occurs in the Niagara formation east of Fond Du Lac (Irving, 1883).
GRANT COUNTY: Oil shale occurs as beds within the Platteville formation throughout the county. At the Empire-Enterprise mine near Platteville, it ranged from 1 to 8 feet thick (Wheeler, 1908).
LAFAYETTE COUNTY: Oil shale occurs as beds within the Platteville Formation throughout the county. It was widely exposed at some of the mines in the Upper Mississippi Valley zinc-lead district, including the so-called "Gasoline Mine" in T.1N R.1E near Benton (Wheeler, 1908).
MILWAUKEE COUNTY: Irving (1883) describes solid hydrocarbon as often found in the Hamilton Limestone in or near Milwaukee. Bagrowski (1940) describes bitumen as in vugs with millerite, pyrite and other minerals in the Milwaukee Formation along the Milwaukee Formation at Estabrook Park (Sec. 5 T.7N R.22E).
OZAUKEE COUNTY: Irving (1883) reports solid hydrocarbons in the "lower Helderburg" limestone exposed near Freedonia.
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