APPLICATION OF PORTABLE XRF TO STRATIGRAPHIC STUDIES AND EVENT TIMING IN IOWA GLACIAL DEPOSITS

Iowa has one of the most complete Quaternary stratigraphic sequences in the midcontinent. However, differentiation of till sheets, particularly in the field, can be challenging if not impossible. Portable X-ray fluorescence (pXRF) analyses are being investigated as a cost-effective and relatively rapid method for till stratigraphy. The Iowa Geological Survey (IGS) has compared the elemental concentrations of various till sheets and loess deposits in Iowa to assess their utility in determining source area and correlating units. Constraining the distribution and timing of Quaternary deposits helps to inform climate models and better understand the regional environment throughout Quaternary history.

Portions of Iowa were glaciated during the Pre-Illinoian, Illinoian, and Wisconsin episodes. Each of these intervals of glaciation has a different primary source area. Therefore, the elemental composition of the till units, both the matrix and coarse-grained lithology, represents these differences. Previous studies have differentiated till units in Iowa on the basis of clay mineralogy, grain-size, carbonate content (calcite to dolomite ratios) and pebble lithology. Not all methods were used in the same region or on deposits of the same age, making correlations problematic. The IGS has archived samples of all units and has completed pXRF analyses on each to establish a methodology that has potential for differentiating glacial deposits in the field or without rigorous laboratory work. This is especially useful in settings where only one till unit is exposed. The ability to correlate units across Iowa, and regionally, has extreme value in establishing a more robust event chronology throughout the Quaternary record.