Historical:Starved Rock Sandstone Member
H. B. Willman and T. C. Buschbach
The Starved Rock Sandstone Member of the St. Peter Sandstone (Templeton and Willman, 1963, p. 46), the uppermost member, is named for Starved Rock in Starved Rock State Park, La Salle County.
The type section of the Starved Rock Sandstone Member is in Starved Rock and French Canyon (W1/2 NW 22, 33N-2E), where the member is 90 feet thick. All except the upper few feet of the member is exposed in Starved Rock.
Extent and Thickness
The Starved Rock Member of the St. Peter Sandstone is commonly 60-100 feet thick and occurs in a broad band, extending southwestward from the Chicago area to the Mississippi River in the Quincy area (fig. O-18). It is locally present in extreme southern Illinois.
The Starved Rock Sandstone differs from the Tonti Member in being largely medium grained rather than fine grained and somewhat more cross bedded. It has a sharp contact with the Tonti Sandstone in most exposures (Willman and Payne, 1942). At Starved Rock the lower part of the member contains thin beds with the poor sorting characteristic of the sandstones in the Glenwood Formation.
The Starved Rock Member is believed to represent an offshore bar that separated Glenwood sedimentation on the north from Joachim sedimentation on the south, and it has a facies relation to both.
TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.
WILLMAN, H. B., and J. N. PAYNE, 1942, Geology and mineral resources of the Marseilles, Ottawa, and Streator Quadrangles: Illinois State Geological Survey Bulletin 66, 388 p.
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