The Cincinnati Arch: a stationary peripheral bulge during the Late Ordovician - Perspectives in Carbonate Geology - page 250

The Cincinnati Arch: a stationary peripheral bulge during the Late
Ordovician

MICHAEL C. POPE * , STEVEN M. HOLLAND † and MARK E. PATZKOWSKY ‡
* School of Earth and Environmental Sciences, Washington State University, Pullman, WA 99164-2812, USA
(E-mail: [e-mail])
† Department of Geology, University of Georgia, Athens, GA 30602-2501, USA
‡ Department of Geosciences, Pennsylvania State University, University Park, PA 16802-2714, USA

ABSTRACT

Shallow-water features, including peritidal carbonate complexes, tidally infl uenced
shoal-water facies, biostromes, and coincident subaerial unconformities on the
peritidal complexes were restricted to the Cincinnati Arch during the Late Ordovician
Taconic Orogeny. Persistence of these features along the Cincinnati Arch indicate that
this area experienced decreased subsidence relative to surrounding areas, forming the
peripheral bulge within the Taconic foreland basin. These shallow-water features
are surrounded on all sides by deeper water, shallow subtidal to deep subtidal facies.
The Jessamine and Nashville Domes were prominent topographic highs on the arch
and were the locus of shallow-water deposition and subaerial erosion, but many of
these shallow-water features also occur in the subsurface between the two domes.
The shallow-water features and unconformities on the Cincinnati Arch occur in a
narrow band repeatedly throughout the Late Ordovician. The width of these features
is much too narrow to have formed solely by fl exure of the lithosphere and their
persistent formation in the same location indicates they did not form as a viscoelastic
response to orogenesis. Rather the boundary between the Grenville Front and the
Eastern Granite-Rhyolite Province acted as a focusing mechanism for the orogenic
load stresses to the east, producing a relatively stationary peripheral bulge. A temporal
and spatial change in the stratigraphy and subsidence on the Nashville and Jessamine
Domes during the Edenian probably records a northward shift of loading, possibly
sedimentary loading, during the Taconic Orogeny.

Keywords Peripheral bulge, foreland basin, Taconic Orogeny, fl exure, stratigraphy.

INTRODUCTION (or forebulge) over time, in particular, whether

it is a static or mobile feature, and what such
behaviour implies about the rheology of the
lithosphere and the movement of the loads that
generate the foreland basin (Sinclair et al ., 1991;
Sinclair & Allen, 1992).
As such, the peripheral bulge and its sedimen-
tary record may provide insights into large-scale
tectonism. For instance, the backstepping of
carbonate reefs may record advancement of a
thrust load where there is little record of this
loading recorded in the basin itself (Dorobek,
1995; Galewsky et al ., 1996; Galewsky, 1998).
Additionally, the geographical position of the
peripheral bulge with respect to the orogenic belt
can be calculated if the peripheral bulge is mod-
elled as being solely generated by fl exure; com-
monly its position is dependent on the age of the
continental crust being deformed (Crampton &

Stratigraphic modelling of foreland basins
demonstrates that the regional stratigraphy in
these basins refl ects the interplay of sediment
supply, eustasy, fl exural loading from thrust
sheet emplacement and possibly long-wavelength
dynamic loading (Mitrovica et al ., 1989; Gurnis,
1992a,b). The stratigraphic models are useful
both in the forward mode, for understanding the
principles underlying the stratigraphic architec-
ture of foreland basins in general (Flemings &
Jordan, 1989, 1990), and in the inverse mode, for
reconstructing the shifting geographical location
of thrust loads and changing eustatic sea level
during the history of particular foreland basins
(Quinlan & Beaumont, 1984; Beaumont et al .,
1988). Studies of foreland basins have frequently
emphasized the behaviour of the peripheral bulge