GRAIN-SIZE, MINERALOGICAL, AND GEOCHEMICAL CHARACTERIZATIONS OF LOESS DEPOSITS IN NORTHWESTERN MISSOURI, USA

Loess is the most prominent and widespread surficial deposit forming the landscape of northern Missouri. These glacial deposits decrease in thickness with distance from their source. The sediment sources for these aeolian features are proglacial deposits associated with the advance and retreat of the Laurentide Ice Sheet. Sediment samples were collected in 10 cm intervals from a seven-meter section of loess exposed north of Kansas City along Highway 210 within the Missouri River valley. Grain size patterns, clay through medium silt, mirror each other with three strong peaks in the first meter and one in the second meter. Coarse silt and very fine sand are inverse to the finer sediments. The largest grain size, fine sand, has very little presence in the lower sediments, but increases in amount with strong fluctuations in the upper sediments. Inductively coupled plasma mass spectrometry (ICP-MS) and X-ray powder diffraction (XRD) results confirm the dominance of quartz, feldspar, gypsum, and zircon with elevated readings of silica, aluminum, iron and magnesium. The Chemical Index of Alteration (CIA) of loess deposits has an average of 68.96, indicating medium to high weathering intensity. The CIA varies throughout the section with values increasing from bottom to the top of the section. The variations of the CIA values may indicate the weathering throughout the last ice age, or fluctuations in climate conditions during deposition. Between 3.50 and 3.60 meters there is an orders of magnitude spike in the heavy metals copper, lead and zinc. This high concentrations of heavy metals could potentially impact local groundwater.