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that evolved separately, rarely forming extensive
regional units (Pratt & James, 1986).
After the M4 sequence, the ramp was more
clearly differentiated, with grainstone shoals,
peritidal facies and skeletal buildups arrayed
as linear features along the Cincinnati Arch
(Mackey, 1972; Holland & Patzkowsky, 1996,
1997; Pope & Read, 1997a; Ettensohn
et al
., 2002,
2004). Beginning with the C1 sequence, there was
a signifi cant change in sedimentation and strati-
graphy from the Nashville and Jessamine Domes.
The Jessamine Dome continued to be the locus
of peritidal and shoal-water facies whereas the
Nashville Dome has a dearth of these facies. There
also is a change in the orientation of shoals from
persistent north-south orientations to subtle
east-west orientations. This C1 (Edenian) change
in sedimentation and stratigraphy coincides
with a structural reorganization on the Nashville
Dome as evidenced by abrupt change in subsid-
ence rates, followed by the erosional bevelling
of the C2-C4 sequences on the southern portion
of the Nashville Dome. The abrupt change in sub-
sidence rates on the Nashville Dome, but not on
the Jessamine Dome, is most likely a refl ection of
the coeval northward migration of the orogenic
load (i.e. Rodgers, 1971; Read, 1989). However, it
is quite possible that the differential subsidence
along this arch also may refl ect sedimentary load-
ing onto the continent from erosion of the coeval
orogenic highland, which is more pronounced to
the north, or the reactivation of basement faults
transverse to the arch controlling lateral subsid-
ence patterns (Burgess & Gayer, 2000).
relative to the width of the coeval foreland
basin are best explained by a lithospheric slab
that contains lateral heterogeneities. The crustal
boundary between the Grenville front and con-
tinental crust (EGRP) weakened by a subsequent
rift event (ECRB) probably controls the fl exural
rigidity of the lithosphere in this area, serv-
ing as the locus of basement fault reactivation,
syndepositional seismites and control of facies
patterns along the Cincinnati Arch during the
Taconic Orogeny.
Large-scale lateral variations in the facies
3
along the Cincinnati Arch were probably
caused by regional variations in subsidence
produced by shifting centres of orogenic
loading and syndepositional reactivation of
basement faults.
ACKNOWLEDGEMENTS
Funding for Mike Pope's portion of this research
was provided by NSF EAR-9316057 (P.I. Fred
Read). Acknowledgment is made to the Donors
of the Petroleum Research Fund, administered
by the American Chemical Society, for support of
this research to Steven Holland. Mike Pope thanks
Fred Read, Aus Al-Tawil, Taury Smith and Anna
Balog for instructive discussions in forming many
of the ideas put forth in this paper. Insightful
reviews by Frank Ettensohn and Maya Elrick on
an earlier version of this manuscript are greatly
appreciated.
REFERENCES
CONCLUSIONS
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1
The Cincinnati Arch was the peripheral
bulge to the Blountian and Taconic phases of the
Taconic Orogeny. The Cincinnati Arch, with the
Nashville and Jessamine Domes in particular,
were the consistent locus of peritidal, shoal and
build-up facies, as well as third-order uncon-
formities throughout the Late Ordovician, and
collectively indicate that this peripheral bulge
was a stationary feature for 10-12 Myr during
this period. Subsidence analyses suggest that
the Cincinnati Arch was either a slowly sub-
siding feature or that it was a slowly uplifting
feature during a period of even greater net
eustatic rise.
The static position of the Cincinnati Arch and
2
Sebree Trough, as well as their narrow widths
