Harold Bowen Willman

Note 27--Morphostratigraphic Units in Pleistocene Stratigraphy: STRATIGRAPHIC COMMISSION

A morphostratigraphic unit is a body of rock that is identified primarily from the surface form it displays; it may or may not be distinctive lithologically from contiguous units; and it may or may not transgress time throughout its extent. It may or may not represent a climatic episode that can be traced widely, as for a geologic-climate unit. Morphostratigraphic units in glaciated areas are moraines, outwash aprons, and associated forms, whereas the term also can be applied to alluvial terrace deposits, alluvial fans, lake plains, beach ridges, pediment veneers, and other such deposits. These units serve a need long apparent to those working in the bordering fields of geomorphology and stratigraphy, and furnish a formal category that permits many surficial deposits to be treated as legitimate stratigraphic entities while allowing the full use of geomorphic criteria.

CONTINENTAL GLACIATION IN RELATION TO McFARLAN'S SEA-LEVEL CURVES FOR LOUISIANA

McFarlan9s sea-level curve for Louisiana is compared with an interpretative glacial-advance curve for the Wisconsinan of the Lake Michigan glacial lobe. A significant ice withdrawal during Farmdalian time is not recorded in the sea-level curve. World-wide glacial fluctuations should be reflected in sea-level variations when sufficient data become available from both environments.

DEVELOPMENT OF WISCONSINAN CLASSIFICATION IN ILLINOIS RELATED TO RADIOCARBON CHRONOLOGY

The evolution of the classification of the Wisconsinan Stage in Illinois is shown in graphic form. More than 75 radiocarbon dates from the Midwest region are used to place the various named units in a uniform chronology. The historical analysis emphasizes the need for multiple classification in the Pleistocene and the extended time span of the Wisconsinan in the type region.

Early Ordovician Strata along Fox River in Northern Illinois

A nearly complete sequence of Ordovician strata along Fox River, southwest of Aurora, indicates the presence of the Kankakee arch-a major structure trending northwest-southeast across northeastern Illinois -and the probable location of the Sandwich fault, which parallels the arch for many miles and had been found previously by studies of well records. Outcrops of sandstone and dolomite which have long been correlated with the St. Peter and Galena-Platteville formations have been found to belong to the New Richmond sandstone and the Shakopee dolomite. Study of the outcrops and well records shows that the anticlinal structure underwent major movements both before and after deposition of the St. Peter sandstone.