Historical:Hadley Gravel Member
Lithostratigraphy: Embayment Megagroup >>Baylis Formation >>Hadley Gravel Member
Chronostratigraphy: Mesozoic Erathem >>Cretaceous System >>Gulfian Series
Authors
H. B. Willman and John C. Frye
Name Origin
The Hadley Gravel Member of the Baylis Formation (Frye et al., 1964, p. 4, 8), the basal member, is named for Hadley, Pike County, 4 miles northwest of the type section.
Type Section
The type section for the Hadley Gravel Member is the same as that for the Baylis Formation, an exposure and small pit along a branch of Kiser Creek (NW SW SE 31, 4S-4W).
Extent and Thickness
The member is generally present in the outcrop area of the formation. It is as much as 15 feet thick but is generally less than 10 feet and in places is only a layer of pebbles.
Description
The Hadley Gravel Member is predominantly pebbles and small cobbles of brown, dark gray, and red chert, but 20-30 percent of the pebbles are quartz, and 1-2 percent are quartzite. It differs only slightly from the Grover Gravel of the Tertiary System, which probably was largely reworked from the Cretaceous gravels, but in the Grover Gravel the brown chert pebbles are more abundant, rounder, and more highly polished. Some of the isolated patches of chert gravels long assigned to the Tertiary may be remnants of the Hadley Gravel Member, which originally may have had wide distribution in western and northern Illinois.
References
FRYE, J. C., H. B. WILLMAN, and H. D. GLASS, 1964, Cretaceous deposits and the Illinoian glacial boundary in western Illinois: Illinois State Geological Survey Circular 364, 28 p.
ISGS Codes
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