ILLINOIAN AND PRE-ILLINOIAN STRATIGRAPHY OF SOUTHEAST IOWA AND ADJACENT ILLINOIS
G.R. Hallberg (Editor)
Iowa Department of Natural Resources, Geological Survey Bureau,
Technical Information Series 11, 1980, 206 p.
The Pleistocene stratigraphy of southeast Iowa was investigated as a part of ongoing stratigraphic and engineering-geologic investigations. The stratigraphy and materials were analyzed in exposures and drill-cores which penetrated the entire Pleistocene sequence.
The deposits in the area below the Wisconsinan loess are formally subdivided into three formations: the Alburnett and Wolf Creek Formations of Pre-Illinoian age, and the Glasford Formation of Illinoian age. The formations are composed principally of till and some inter-till stratified sediments. The Pre-Illinoian tills were deposited by glaciers which moved through Iowa, whereas the Illinoian age till was deposited by Lake Michigan lobe ice which moved through Illinois into Iowa. The differences in provenance of the tills produced differences in physical and mineralogic properties which allow differentiation of the deposits. The till deposits in the formations are recognized and correlated by their physical stratigraphy, pebble lithologies, and by the quantitative characterization of their clay mineralogy, particle-size distribution, matrix carbonates, and sand-fraction lithologies.
The Alburnett and Wolf Creek Formations are composed of uniform, dense, overconsolidated, basal tills. The Alburnett and Wolf Creek Formations are separated by their distinct differences in clay mineralogy.
Only one till of the Alburnett Formation was recognized at any locality in southeast Iowa. The Wolf Creek Formation is subdivided into the Winthrop, Aurora, and Hickory Hills Till Member. The stratigraphic relations and the physical and mineralogical properties of the till members are essentially identical to their properties in their type areas.
Soil-stratigraphic units are also associated with the Wolf Creek Formation. The Franklin Paleosol occurs below the Aurora Till Member, and in the study area is developed in unnamed sediments and the Winthrop Till. The Yarmouth Paleosol occurs below the base of the Illinoian age deposits of the Glasford Formation. In its type area, and throughout the study area, the Yarmouth Paleosol is developed in unnamed fine-textured sediments and the underlying Hickory Hills Till Member. Beyond the depositional limits of the Glasford Formation the Yarmouth and Sangamon Paleosols and surfaces merge. In this area the Yarmouth-Sangamon and Late-Sangamon Paleosols are developed in undifferentiated sediments and in the underlying Wolf Creek Formation deposits (principally the Hickory Hills Till Member in the study area).
The Glasford Formation is represented in southeast Iowa by the Kellerville Till Member and some related sediments. The Kellerville is the oldest till of Illinoian age and overlies the Yarmouth Paleosol. The Kellerville Till Member is readily separated from the Pre-Illinoian tills by its relatively high illite content, high dolomite content, and the abundance of Pennsylvanian lithologies in the very coarse sand through cobble sizes. The Kellerville Till Member is separated into a subglacial or basal till and a superglacial facies based on stratigraphic relations, sedimentological properties, and the consistency-density-consolidation properties of the deposits. The basal till facies is comprised of firm, dense, overconsolidated till of rather uniform texture. The superglacial facies is composed of a wide variety of sediments and is highly variable in texture and density. The sediments in the superglacial facies include: till, diamictons, or reworked till such as superglacial debris flows, sorted fluvial and lacustrine sediments, and peat beds. In some sections these deposits are clearly interbedded, but in others they occur as a contorted melange.
The Sangamon and Late-Sangamon Paleosols are developed in the top of the Kellerville Till Member, and/or sediments which overlie the Kellerville in a variety of settings from modified remnants of the Kellerville depositional surface to erosion surface positions.
The broad tabular divides in southern Iowa exist because they are bedrock-defended. Other landscape differences in the region may be related to the nature of the superglacial facies of the Kellerville Till Member.
The classic type location for the Yarmouthian Stage and Yarmouth soil was designated by Leverett in 1898 from his interpretation of the sediments in two dug wells, near Yarmouth, Des Moines County, Iowa. For this study, cores from the type location were obtained and analyzed. Leverett's "interglacial" deposits are composed of interbedded tills, diamictons, peats and bedded sands and silts, that are part of the superglacial facies of the Kellerville Till Member, Glasford Formation. These strata are interpreted as pro-glacial sediment flows, fluvial, and paludal sediments deposited along the early-Illinoian ice margin. Pollen samples and wood from these pre-Illinoian deposits indicate that the vegetation coeval with the sediments was a Picea-Larix forest, and that climate was full-glacial rather than interglacial. This type-section for the Yarmouth is redefined as the well-developed paleosol underlying these Illinoian pro-glacial sediments ;in the cores at Yarmouth. A stream cut near Mediapolis that exposes a Yarmouth Paleosol between the Illinoian and Pre-Illinoian tills is designated a principal reference section.
The Kellerville Till Member of the Glasford Formation is the westernmost Illinoian till unit in western Illinois and extends into southeast Iowa. The till was deposited by the lake Michigan Lobe which advanced across western Illinois from the northeast. The composition of the Kellerville Till is similar to other lake Michigan Lobe tills and reflects incorporation of Paleozoic bedrock in the Lake Michigan Basin and adjacent areas. In vertical profiles, the till sometimes varies in texture and mineralogy because of sedimentologic breaks and/or weathering effects. in its lateral extent, the Kellerville Till has regional variations in composition. However, the regional variations do not fit a simple trend and localized changes are also evident. Based on available data in the study area, the Kellerville Till member is a single stratigraphic unit and should not be subdivided as previously proposed.
No abstract available for this section.
The percentage calcite, dolomite and total carbonate in the <2 mm size matrix of Illinoian and Pre-Illinoian tills in SE Iowa were measured using a Chittick apparatus. The matrix carbonate data were found to be useful for characterizing and differentiating the till units. Using C/D (calcite/dolomite) ratios the eastern-derived, Illinoian Kellerville Till Member of the Glasford Formation can be differentiated from the western-derived Pre-Illinoian tills. The Kellerville Till Member exhibits C/D ratios less than 0.40, whereas 95% of the Pre-Illinois till samples have C/D ratios greater than 0.40.
All of the tills studied exhibit a very well-defined linear, inverse relationship between the percentage of total matrix carbonate and the percentage of clay (or conversely, a direct relationship with percentage sand plus silt). Analysis of this relationship aids in understanding and evaluating the wide range in total carbonate values from individual samples or locations. Using the linear relationships between the total matrix carbonate and clay content, the till members of the Pre-Illinoian Wolf Creek Formation may generally be discriminated.
As in previous studies which used different particle size fractions, the eastern-derived Kellerville Till Member has higher dolomite (or dolostone) contents than the western-derived Pre-Illinoian tills. However, unlike in these previous studies, the western-derived tills generally exhibit more dolomite than calcite.
Matrix calcite and dolomite are analyzed by the Iowa State University Soils Lab on the <2 mm size fraction of pedologic and geologic soil samples. The analysis uses the Chittick apparatus, with slight modifications of the procedure by Dreimanis (1962). The percentage of calcite and dolomite are calculated from empirical graphs relating the volumes of carbon dioxide that are evolved from known amounts of calcite and dolomite. The procedure is outlined and discussed. Caution must be used in comparing matrix carbonate data between labs because of differences in sample preparation or calculation method.
Dreimanis, A., 1962, Quantitative gasometric determination of calcite and dolomite by using Chittick apparatus: Journal of Sedimentary Petrology, v. 32, p. 520-529.