WEATHERING PROFILES OF QUATERNARY SEDIMENTARY MATERIALS OF EAST-CENTRAL IOWA

Physical and chemical transformations produced as microbes mediate the interaction of meteoric water with earth materials form weathering profiles in all surficial materials. Weathering profiles extend into deposits along fractures that facilitate the vertical and lateral movement of meteoric water, oxygen, colloids and solutes. The physical and geochemical properties of weathering profiles exert strong influences on water and solute movement through the vadose zone and can provide information on long-term evolution of the landscape. We are investigating two eastern Iowa weathering profiles; one formed during the Holocene in moderately thick Peoria Loess and another formed over at least two glacial/interglacial cycles in glacial till now buried by moderately thick loess. Our initial study is focusing on bulk geochemistry and weathering indices determined using portable X-ray fluorescence (pXRF). Preliminary results reveal a less weathered zone in the lower Peoria Loess that likely corresponds with the period of rapid loess accumulation during the full glacial period and a greater degree of weathering in the Sangamon Geosol relative to that of the modern soil. Weathering is intermediate between these two end members in the Farmdale Geosol formed in Pisgah Formation loess. Implications of this study may be used to determine the rate of weathering and the effects that this may have for the given landscape.