A proposed stratigraphic package for filling a mid-Proterozoic rift basin under the Bellefontaine Outlier area, Ohio, and the consequences of the rift on the formation of the Outlier
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Date
2005-06
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Publisher
The Ohio State University
Abstract
The discovery of a mid-Proterozoic rift basin in the crystalline basement rocks
under the Bellefontaine Outlier area, Ohio has had a number of consequences on our
understanding of Precambrian tectonics and stratigraphy of western Ohio and the northcentral
North American midcontinent. In this study, a new stratigraphic package has
been proposed to fill the ancient rift basin and a geolbgical history of the area from the
mid-Proterozoic to the Devonian, has been synthesized to study the consequences of this
deep basement feature through time.
Three new proposed rift basin-filling volcanic and sedimentary units encode the
development, maturation, and termination of the rift. A fourth proposed sedimentary
unit, lying above the basin-filling sequence, documents the initial changes of the region
to a massive foreland basin in front of newly developed Grenvillian thrust sheets during
the late-Proterozoic. The lower contact of the Middle Run Formation has also been
extended to a much greater depth overlying the fourth proposed unit and represents welldeveloped
foreland basin sediments.
Another goal of this study considers tectonic events from the mid-Proterozoic
initiation of rifting through the Devonian Acadian Orogeny, to explain the development
and incomplete Paleozoic stratigraphy of the Bellefontaine Outlier. Compressive forces
associated with the Grenville Orogeny may have propagated the rift-defining fault
complexes up through the overlying late-Proterozoic strata and imposed significant
structural weaknesses that could be exploited by the compressive forces of the Devonian
Acadian Orogeny. During the Acadian, the Outlier block may have been exhumed by the
reactivated faults and the Devonian Delaware Limestone and Olentangy Shale units, not
present within the Outlier block, may have been syntectonically deposited in flanking
basins during the exhumation.
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Keywords
Bellefontaine Outlier, Ohio, Precambrian tectonics, stratigraphy