Five rock bodies and four major erosional surfaces are recognized in the subsurface; these are a lower till Kansan(?), a middle till Tazewell(?), a middle silt, an upper till (Cary), and a complexly interconnecting sand and gravel body. Erosion surfaces occur at the top of each rock body. The lower till is confined to the Squaw Buried Valley where it reaches a maximum thickness of 100 feet. The middle till averages 40 feet in thickness but ranges from 100 feet in buried valleys to absent over bedrock topographic highs. The middle silt is largely confined to the Squaw Buried Valley where it reaches thicknesses of 60 feet. The Cary till mantles the area, reaching thicknesses of over 100 feet in bedrock valleys and thinning to less than 25 feet over bedrock uplands. The distribution of the rock bodies suggests that the Squaw Buried Valley ceased to be the major drainage after Kansan (?) deposition and that the amount of pre-Tazewell (?) erosion was sufficient to remove all Kansan (?) drift from the uplands. The discontinuous distribution of the middle silt and Tazewell (?) till on the bedrock uplands indicates that erosion by the Cary glacier removed much of these rock bodies. The shape of the modern landscape mimics the shape of the buried bedrock valleys, though the relief in the area decreased from over 100 feet in pre-Kansan times to around 50 feet in pre-Cary times. The comparison of depositional landforms on the Cary surface to the till thicknesses suggests that washboard moraines. transverse features and circular features become dominant with progressively greater till thicknesses.
Proceedings of the Iowa Academy of Science
© Copyright 1974 by the Iowa Academy of Science, Inc.
Palmquist, Robert C.; Bible, Gary; and Sendlein, L. V. A.
"Geometry of the Pleistocene Rock Bodies and Erosional Surfaces Around Ames, Iowa,"
Proceedings of the Iowa Academy of Science: Vol. 81:
, Article 8.
Available at: http://scholarworks.uni.edu/pias/vol81/iss4/8