GEOLOGY, HYDROGEOLOGY AND LANDUSE OF SNY MAGILL AND BLOODY RUN WATERSHEDS
E.A. Bettis III(1), L.S. Seigley(1), G.R. Hallberg(2), and J.D. Giglierano(1)
(1) Iowa Department of Natural Resources,
Geological Survey Bureau
109 Trowbridge Hall
Iowa City, IA 52242-1319
(2) University of Iowa Hygienic Laboratory
University of Iowa; Oakdale Campus
Iowa City, IA 52242
The Sny Magill and Bloody Run watersheds are located in the Paleozoic Plateau landform region in northeast Iowa. The area is dominated by Paleozoic age bedrock, including the sandstones and sandy dolostones of the Upper Cambrian-age Jordan Sandstone Formation, the oldest bedrock in the area, through the Upper Ordovician-age Maquoketa Formation. The sequence of bedrock exposed in these two watersheds includes sandstones, sandy dolostones, dolostones, shales, shaly carbonates, and limestones. The sandstones and limestones form important aquifers in the area, including the Galena aquifer and St. Peter aquifer. Water movement through the carbonate bedrock units is influenced by bedding planes and vertical fractures. Dissolution along bedding planes and fractures has caused some local karst development. Sinkholes occur in both watersheds. Most sinkholes occur near the top of the Galena carbonates, often at the contact between the Galena and the shaly carbonates of the overlying Elgin Member of the Maquoketa Formation.
The surficial deposits in the watersheds owe their origin to the direct or indirect effects of glacial advances. Upland deposits include loam-textured pre-Illinoian glacial till, Sangamon and Farmdale paleosols, and Peoria Loess. Wedges of colluvium are present along most steeply sloping valley walls. Valley fills include slack water deposits associated with the melting of glaciers during the late-Wisconsinan, and loamy, sandy and silty late-Wisconsin and Holocene alluvial deposits of the DeForest Formation.
Landuse for both watersheds was compiled for 1991. Five landuse classes were delineated from color infrared aerial photographs; those classes include row crop, cover crop/pasture, forest/forested pasture, farmstead/urban, and other. Most of Sny Magill Watershed is forest/forested pasture (49%), row crop (26%), and cover crop/pasture (24%). Bloody Run Watershed is dominated by row crop (39%), followed by forest/forested pasture (30%), and cover crop/pasture (29%).