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laminated dolostone with abundant desiccation
cracks and sparse, short vertical burrows. These
peritidal facies consistently pass northwards into
coeval shallow subtidal facies (Weir
et al
., 1984;
Holland, 1993; Pope & Read, 1997b). Localization
of these peritidal facies demonstrates that the
Jessamine Dome in central Kentucky was a per-
sistent shallow area throughout the Cincinnatian
Series. Only in the upper Cincinnatian (C5-C6)
do these peritidal facies expand northward and
down-ramp on the Cincinnati Arch into Ohio and
Indiana (Hatfi eld, 1968).
are rich in phosphate, and indicate that strong
waves and tidal currents commonly affected the
Jessamine Dome during this transgression.
Tidally infl uenced skeletal grainstone facies of
the Lexington Limestone (Fig. 6) are best devel-
oped along the axis of the Cincinnati Arch and
over the Jessamine Dome (Hrabar
et al
., 1971;
Cressman, 1973; Borella & Osborne, 1978; Pope &
Read, 1997, 1998). These shoal-water facies are
rich in phosphate, comprised predominantly of
brachiopods, bryozoans and crinoids and com-
monly have herringbone cross bedding oriented to
NW-SE (Hrabar
et al
., 1971; Pope & Read, 1997a).
These grainstone shoals developed on local topo-
graphic highs over the Jessamine Dome (Hrabar
et al
., 1971; Cressman, 1973; Ettensohn, 1992).
The Garrard Siltstone, the coarsest siliciclastic
unit along the Cincinnati Arch in the Upper
Ordovician, was deposited in shallow to deep
waters (Ettensohn
et al
., 1986a; Jacobs, 1986)
and is laterally equivalent to high-energy skeletal
grainstones in the subsurface to the south (Pope &
Read, 1997b). Bimodal palaeocurrent measure-
ments in the Garrard Siltstone suggest at least
part of the Garrard Siltstone was deposited in a
tidal setting. Outcrops of the Garrard Siltstone are
restricted to a linear trend along the southeastern
side of the Cincinnati Arch, suggesting its distri-
bution was structurally controlled (Weir
et al
.,
1984; Ettensohn, 1986a; Jacobs, 1986).
A belt of grainstone shoals is sporadically
present during the C3 to C5 sequences on the
northern fl ank of the Jessamine Dome, but is ori-
ented east-west (Weir
et al
., 1984; Holland, 1993).
These grainstones are restricted to the trans-
gressive systems tracts of these sequences and
separate restricted lagoonal mudstones and
wackestones to the south (e.g. Gilbert, Sunset
Members) from open-marine shallow subtidal
packstones and fossiliferous mudstones to the
north (e.g. Mount Auburn, Oregonia formations).
These grainstone shoals are typically approxi-
mately 1 m thick and display large-scale trough
cross-bedding. They are composed primarily of
crinoid ossicles and highly abraded skeletal mater-
ial, but are also rich in phosphate and are locally
enriched in thick ramose, frondose and massive
bryozoans, all highly abraded and bored.
On the Nashville Dome, transgressive grain-
stones of the Curdsville Member lying above the
M4-M5 unconformity are restricted to the fl anks
of the Nashville Dome and correlate to a well-
developed hardground/unconformity developed
on the Stones River Group (i.e. Curdsville Island of
Shoal-water facies
Peloidal-skeletal grainstone shoals were com-
monly affected by tidal currents along the
Cincinnati Arch during the Late Ordovician.
These shoals separated open-marine facies from
more restricted facies deposited in semi-restricted
lagoons, subtidal pools or tidal fl ats. The facies
behind the grainstone shoals are mud-rich wacke-
stone/packstone containing abundant stromato-
poroids, molluscs, ostracods and rare corals
(Wilson, 1949; Walker & Laporte, 1970; Mackey,
1972; Cressman, 1973; Holland, 1993). Shoal
facies consistently developed in relatively fi xed
positions on the Jessamine and Nashville Domes
in the Late Ordovician.
Blountian phase
On the Jessamine Dome, cross-bedded peloidal
packstone/grainstone is rare, and only locally
developed in the High Bridge Group. Cross-
bedded carbonate sand-shoal facies developed
sporadically in the Pierce, Ridley, Lebanon
and Carters limestones of the Nashville Dome,
and they are nearly always local in their occur-
rence, suggesting the presence of isolated, ephem-
eral skeletal to peloidal sand shoals (Holland &
Patzkowsky, 1998). One exception to this pattern
is the massive member of the Lebanon Limestone,
which is a widespread ooid-skeletal cross-bedded
grainstone, that occurs over the entire Nashville
Dome without systematic variations in thickness
(Wilson, 1949).
Taconic phase
On the Jessamine Dome, skeletal packstone and
grainstone of the transgressive Curdsville Member
of the Lexington Limestone are widespread and
form a series of hardground-bounded parase-
quences (Pope & Read, 1997a). These grainstones
