Paper No. 20-3
Presentation Time: 1:30 PM-5:30 PM
SURFICIAL GEOLOGIC MAP OF THE BLOOMINGTON-EAST 7.5 MINUTE QUADRANGLE, MCLEAN COUNTY, ILLINOIS
The state of Illinois lacks crucial surficial geology maps that are used by geologists and scientists alike to assess local environments. This project contributes a 7.5 minute Quadrangle map, scaled at 1:24,000 of the Bloomington-East Quadrangle, located at 40⁰20’30” to 40⁰30’ north latitude and 89⁰00’ to 88⁰52’30” east longitude, to fill a necessary gap in this field. Developing cities such as Bloomington-Normal can utilize quadrangle maps to determine where next to expand and the evolving of new and existing resources. For example, the Bloomington-East Quadrangle has both urban and agricultural land uses that are important for scientists and developers but as of yet, no 7.5 minute Quadrangle map has been published. This new surficial geology map of the Bloomington-East Quadrangle was constructed using the McLean County Soil Survey data and Illinois State Geologic Survey well log data. Soils data provided information on the parent material of the soil, the different soils where then grouped based on the material. Well logs indicated how thick certain lithologies were; to be considered mappable units had to be at least 5 feet thick. The interpretations of this map are consistent to the entirety of McLean County in which the deposits are glacially borne. The completed map reveals that the surficial geology is influenced by the Wisconsin glacial episode wherein two moraines and an outwash plain are present. The two moraines are the Normal Moraine in the north and the Bloomington Moraine in the south. Each moraine is comprised of Wedron Group tills; with the Normal Moraine being of the Lemont Formation and the Bloomington Moraine consisting of the Tiskilwa Formation. Both tills can be described as red to grayish-blue diamict clays and gravel, with a thickness of 70 meters. South of the Bloomington Moraine is an outwash plain of the Mason Group Henry Formation which is a sand and gravel mix with a thickness of 8 to 10 meters.