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North-Central Section - 49th Annual Meeting (19-20 May 2015)

Paper No. 6
Presentation Time: 8:00 AM-12:00 PM

UNDER THE SCOPE:  INVESTIGATING THE IDLEWILD MEMBER OF THE LITHOGRAPH CITY FORMATION, DEVONIAN (FRASNIAN), IOWA BASIN


HARVEY-COSTELLO, Nydra, Geology-Geography, Eastern Illinois University, 600 Lincoln Ave., Charleston, IL 61920, LEWANDOWSKI, Katherine J., Department of Geology-Geography, Eastern Illinois University, 600 Lincoln Ave, Charleston, IL 61920, DAY, James E., Geography& Geology, Illinois State University, Campus Box 4400, Normal, IL 61790-4400 and CHESNER, Craig A., Geology/Geography, Eastern Illinois University, 600 Lincoln Avenue, Charleston, IL 61920, nlhaveycostel@eiu.edu

Field work conducted in the fall of 2013 at Johlas Quarry in Floyd County, Iowa led to the collection of rocks to make thin sections. These rocks (carbonates) are Upper Devonian (Early Frasnian) in age from the Idlewild Member of the Lithograph City Formation of the Iowa Basin. Samples were collected from fossiliferous beds with abundant stromatoporoids. Petrographic thin sections were made in order to study the microfacies of these rocks.

Within the Devonian sea that existed in the Iowa Basin during this time, stromatoporoids, ostracodes, brachiopods, corals, and bryozoans, mollusks, and conodonts proliferated. Sea level continued rising during this part of the Devonian (Frasnian). The fossils found in the Idlewild Member of the Lithograph City Formation represent a vibrant and diverse seafloor community. A paleoecological reconstruction including a tiering scheme has been undertaken to describe the seafloor community present at the time.

As part of this investigation, allochems have been identified in order to classify the type of carbonate according to Folk (1959). These carbonate classifications are compared to those made solely from field investigations at this site, as well as, petrographic investigations of the unit in other locations (Day, Witzke, and Lundy, 2013; Groves, Walters, and Day, 2008).

Session No. 32--Booth# 30

Sedimentology & Stratigraphy (Posters)
Wednesday, 20 May 2015: 8:00 AM-12:00 PM
Grand Terrace (Monona Terrace Convention Center)
Geological Society of America Abstracts with Programs. Vol. 47, No. 5, p.82
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