H. B. Willman and John C. Frye
The Grover Gravel (Rubey, 1952) is named for Grover, Missouri. The name "Grover" was applied by Rubey (1952) to the brown chert gravel and associated red sand that occur on upland surfaces in the type area and in Calhoun County, Illinois. In that region the gravel truncates Pennsylvanian and older bedrock formations and was deeply weathered and eroded before deposition of the Loveland Silt of Illinoian age.
The Grover Gravel is well exposed in the overburden of clay pits south of U. S. Highway 50, 2 miles west of Grover, SE NW SW Sec. 3, T. 44 N., R. 3 E., St. Louis County, Missouri (Willman and Frye, 1958). The type section exposes 1 to 3 feet of loess overlying 40 feet of the Grover Gravel and 20 feet of Pennsylvanian shale. In the type section the Grover Gravel consists of four units (from the base):
(1) 20 feet of sand and gravel, well bedded, red and clayey at the top, tan brown, less clayey and loose in the lower part (samples P-3081, bottom; 3082, top).
(2) 9 inches of sand, silt and clay, gray to pink-tan (samples P-3083 to 3086).
(3) 15 feet of sand and gravel with a matrix of red clay and sand; contains cobbles and boulders to 1 foot in diameter; clay streaks in middle (samples P-3087 to 3089).
(4) 4 feet of sand and gravel, gray, cobbly; contains a few boulders; sharp contact at base (sample P-3090).
Extent and thickness
The gravel is as much as 40 feet thick in the type locality, but it is generally less than 10 feet thick, and in many areas it is represented only by a thin line of pebbles between the loess and the bedrock.
The Grover Gravel consists of noncalcareous, dominantly subangular light brown chert pebbles with abundant small, well rounded quartz pebbles, a few purple quartzite pebbles, and a very few pebbles of coarsely micaceous clay that appear to be weathered igneous rocks. The matrix is tan to red quartz sand with a small percentage of feldspar. The heavy minerals of the sand are dominantly zircon and tourmaline; the minerals typical of glacial sands -- hornblende, garnet, and epidote -- are scarce to absent (table 4).
Age and correlation
In this report the Grover Gravel is extended to include many isolated deposits of similar composition and stratigraphic position that occur north of the Shawnee Hills of southern Illinois. In the glaciated area the deposits are overlain and partially truncated by Kansan and younger drifts. They have been called Lafayette, Lafayette-type, or Tertiary gravel. The brown chert gravel in extreme southern Illinois that also has been called Lafayette Gravel differs in the character, color, type, and shape of chert pebbles, and it has a contrasting heavy mineral suite. It is assigned to a new formation, the Mounds Gravel. North of Illinois similar gravel is generally called Windrow Gravel (Thwaites and Twenhofel, 1920; Andrews, 1958). The Grover Gravel is classified as a formation.
The gravel at Grover, Missouri, and north of Golden Eagle, Calhoun County, Illinois, contains boulders of purple quartzite that are almost certainly derived from the Precambrian Baraboo Quartzite of Wisconsin; some are 2 feet in diameter, which seems to require glacial transportation. The local presence of a few weathered igneous pebbles of northern derivation also favors glacial origin. The position of the gravel on the highest upland surfaces, which were deeply dissected before Kansan glaciation, restricts the deposits, if Pleistocene, to a very early glacial age. As previously noted, the gravel conceivably can be the product of a glaciation earlier than the type Nebraskan. Therefore, we at present assign the Grover to a Pliocene-Pleistocene age.
The gravel is similar in appearance and composition to the Hadley Gravel Member of the Baylis Formation of Cretaceous age in Adams and Pike Counties (Frye, Willman, and Glass, 1964). Some deposits that have been assigned to the Grover Gravel may, in fact, be the Hadley Gravel; others may be Tertiary in age and result from the reworking of the Hadley Gravel; and still others may be the product of reworking during Pleistocene time.
Chert gravel deposits that are now included in the Grover Gravel have been described in several reports (Fenneman, 1910; Horberg, 1946b, 1950b, 1956; Lamar and Reynolds, 1951; Leighton and Willman, 1949; Rubey, 1952; Salisbury, 1892; Wanless, 1957; Willman and Payne, 1942).
ANDREWS, G. W., 1958, Windrow Formation of the upper Mississippi Valley region — A sedimentary and stratigraphic study: Journal of Geology, v. 66, p. 597-624.
FENNEMAN, N. M., 1910, Physiography of the St. Louis area: Illinois State Geological Survey Bulletin 12, 83 p.
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, p. 28.
HORBERG, C. L., 1946b, Preglacial erosion surfaces in Illinois: Journal of Geology, v. 54, no. 3, p. 179-192.
HORBERG, C. L., 1950b, Preglacial gravels in Henry County, Illinois: Illinois Academy of Science Transactions, v. 43, p. 171-175.
HORBERG, C. L., 1956, Pleistocene deposits along the Mississippi Valley in central western Illinois: Illinois State Geological Survey Report of Investigations 192, 39 p.
LAMAR, J. E., and R. R. REYNOLDS, 1951, Notes on the Illinois "Lafayette" Gravel: Illinois Academy of Science Transactions, v. 44, p. 95-108.
LEIGHTON, M. M., and H. B. WILLMAN, 1949, Late Cenozoic geology of Mississippi Valley: Itinerary 2nd Biennial State Geologists Field Conference, Illinois State Geological Survey, 86 p.
RUBEY, W. W., 1952, Geology and Mineral Resources of the Hardin and Brussels Quadrangles: United States Geological Survey Professional Paper 218, 179 p.
SALISBURY, R. D., 1892, On the northward and eastward extension of the pre-Pleistocene gravels of the Mississippi Basin: Geological Society of America Bulletin, v. 3, p. 183-186.
THWAITES, F. T., and W. H. TWENHOFEL, 1920, Windrow formation; an upland gravel formation of the driftless and adjacent areas of the Upper Mississippi Valley [abs.]: Geological Society of America Bulletin, v. 31, p. 133.
WANLESS, H. R., 1957, Geology and mineral resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey Bulletin 82, 233p.
WILLMAN, H. B., and J. C. FRYE, 1958, Problems of Pleistocene geology in the greater St. Louis area: Geological Society of America Guidebook, St. Louis Meeting, 2nd Field Trip, p. 9-19.
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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