Genesis of clayey sediments and associated upland soils near the Upper Iowa River, Northeast Iowa
Loess-derived soils along the upland divides in northeastern Allamakee County, Iowa occur with polygenetic soils formed where landscape dissection by fluvial erosion has exposed red (2.5YR hue) and brown (7.5YR, 10YR hues), clayey paleo-argillic horizons along hillslope shoulder and backslope components. This research describes the morphology, composition and soil-stratigraphic relationships of the loess-derived and paleosolic soils along a hillslope traverse near the Irish Hollow Creek. Ten cores (3-10 m depth) and for soil pedons were examined for morphological, chemical and mineralogical characteristics. A gray (10YR 6/1), sandy Sangamon paleosol was merged with the basal loess paleosol. The upper paleosolum was polygenetically welded to a subjacent, red (2.5YR 4/8), clayey paleosol formed in erosional sediments. The red paleosol's lower portion was formed in residuum from interbedded sandstone-shale-dolomitic limestone. Total elemental, and CBD- and oxalate-extractable Si, Al, Fe, and Mn, documented weathering trends. Elemental depth distributions for ground soils and paleosols were related to weathering processes with paleosols displaying more pronounced changes from lithogenic and pedogenic factors;Early Wisconsinan sediments displayed evidence of "mixing" by either cryo-bioturbation or erosion. A periglacial environment may have induced the formation of an involute-injective disturbance. Identification of glacial till or till-derived erosional sediments supports the hypothesis of Pre-Illinoian glaciation. Paleo-surface depressions of karstic collapse features may have preserved the glacial sediments in the erosionally-modified landscape;Soil-stratigraphic units were the informally-named basal loess paleosol (BLP) and isolated remnants of the Sangamon Soil with well-developed polygenetic paleosols, and Late Sangamon paleosols. Iowan erosion surface complexes occur where loessial soils, with no intervening paleosols, formed above pediments and bedrock surfaces.