Geology & Geography Faculty Work


The Stratigraphy of the East Liberty Quarry (Logan County, Ohio) in the Bellefontaine Outlier

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Geological Society of America Abstracts with Programs

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The stratigraphic relationships of the units underlying the Ohio Shale in the Bellefontaine Outlier to the strata beneath the Ohio Shale in central Ohio, 46 km east, have remained problematic since the initial report on the geology of Logan County in 1878. Recent publications by the Ohio Geological Survey convey the general working view that many geologists have used for the outlier; the carbonates (primarily dolostones) beneath the Ohio Shale are considered to be Lucas Columbus undifferentiated with the Delaware Limestone situated directly above the Columbus Limestone and the overlying Olentangy Shale, both present in central Ohio, being absent. Recently, a 16 cm thick by 7 m long lens, consisting of interbedded brownish black shales and green-gray shales, resting within a slight swale upon the top of the dolostone (the East Liberty Bone Bed of the Columbus-Lucas undifferentiated unit) and beneath the Ohio Shale, was discovered in the East Liberty quarry, Logan County, Ohio. In the middle of this exposure the lens contains, in ascending order, a 5 cm brownish-black (5YR 2/1) shale, a 4 cm medium greenish-gray (5GY 5/1) clay shale, a 4 cm brownish-black (5YR 2/1) shale, and a 3 cm medium olive-gray (5Y 5/1) clay shale. The color and alternation of these thin shales is very similar to that found within the Upper Olentangy Shale in central Ohio. The conodont fauna (including Palmatolepis triangularis and P. subperlobata) of these pyritic shale layers conservatively constrains this new interval to within the triangularis Zone. Both the lithology and conodont fauna of these beds make correlation with the uppermost beds of the Upper Olentangy Shale in central Ohio tenable. The conodont fauna of the underlying, approximately 45 cm thick, dolomitic East Liberty Bone Bed contains a broad mixture of conodonts, including a number of late Frasnian species (Ancyrodella buckeyensis, A. curvata, and Ancyrognathus asymmetricus); thus, placing the Frasnian-Famennian boundary at the contact of the East Liberty Bone Bed with the overlying newly-discovered lens or, where it is absent, with the overlying Ohio Shale. The 19 meters of dolostone that underlie the East Liberty Bone Bed in the East Liberty quarry contain a sequence of Eifelian conodonts similar to that recorded in the Columbus and Delaware limestones of central and north-central Ohio.


Presented at the Geological Society of America Annual Meeting, Denver, CO

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