Lithostratigraphy: Ottawa Limestone Megagroup >>Platteville Group >>Plattin Subgroup >>Mifflin Formation >>Hazelwood Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Blackriveran Stage
Allostratigraphy: Tippecanoe Sequence
H. B. Willman and T. C. Buschbach
The Hazelwood Member of the Mifflin Formation (Templeton and Willman, 1963, p. 82) is named for Hazelwood School, Lee County, 2 miles west of the type section.
The type section of the Hazelwood Member is located in a quarry on the east side of the Rock River Valley 3.5 miles north of Dixon (SW SW NW 22, 22N-9E), where it is 5.7 feet thick.
Extent and Thickness
The Hazelwood Member is widespread, but it is missing in Calhoun County. It is commonly 4-6 feet thick in the northern outcrop area, but it thickens southward and, judging from exposures near Cape Girardeau, Missouri, is probably as much as 50 feet thick in subsurface in southern Illinois.
In the northern outcrop area, the Hazelwood is relatively pure, gray, thick-bedded to massive, lithographic limestone generally dolomite mottled, fucoidal, and with few fossils. A ferruginous corrosion surface occurs on the top. In the southern area, the Hazelwood is relatively pure, brown, fucoidal, fine-grained limestone, thicker bedded than the members above and below.
TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.
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