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In-Depth Information
pattern of truncation, with at least 7 m more strata
eroded at this sequence boundary in the west
than the east (Holland & Patzkowsky, 1998, their
Fig. 9). A major truncation surface is also pres-
ent at the C5 sequence boundary, which displays
the progressive loss of the underlying C4, C3 and
partially the C2 sequences from north to south
(Holland & Patzkowsky, 1998, their Fig. 11). This
pattern, strikingly different from that seen in the
M5 through C4, suggests a tectonic reconfi guration
on the Nashville Dome prior to deposition of C5.
Pope & Read, 1995, 1997a). The Kentucky River
Fault system and other unnamed faults that
delineate this structure are basement features that
were probably reactivated by Taconic orogenesis
(Ettensohn, 1992; Ettensohn
et al
., 2002, and ref-
erences therein). Synsedimentary growth faults
are documented from the Lexington Limestone
in Kentucky (Black & Haney, 1975; Pope
et al
.,
1997). It is not known whether fault structures are
responsible for the persistent position of shoals
and tidal fl ats on the Nashville Dome, but such
consistency in their occurrence hints at the role of
prior structures.
Peritidal facies of the Perryville Member of
the Lexington Limestone commonly are laterally
equivalent to deeper water shale that occurs in
east-west trending zones, which may refl ect dif-
ferential subsidence perpendicular to the regional
trend of the Cincinnati Arch (Mackey, 1972; Kulp,
1995; Kulp & Ettensohn, 1995; Ettensohn
et al
.,
2002). Structurally controlled east-west trending
troughs produce alternating topographic highs and
lows along the arch with tidal fl ats restricted to
highs and slightly deeper water channels (Mackey,
1972) occupying lows. The close association
of these channels with exposed fault segments
suggests that these were produced by reactiva-
tion of Precambrian or earlier Palaeozoic faults
(Cressman, 1973; Black, 1986; Kulp, 1995; Kulp &
Ettensohn, 1995; Rast & Goodman, 1995; Pope &
Read, 1997a; Ettensohn
et al
., 2002, 2004).
The Sebree Trough is an enigmatic narrow
(25-150 km wide) and elongate (600 km long)
deep-water basin that formed west of the
Cincinnati Arch and fi lled with black shale dur-
ing the Chatfi eldian-Richmondian (Kolata
et al
.,
2001). The Sebree Trough is interpreted to have
formed over the Precambrian-Cambrian Reelfoot
rift (Kolata
et al
., 2001) or through the reactivation
of basement structures by far-fi eld stresses from
foreland basin loading (Ettensohn
et al
., 2002).
EVIDENCE OF TECTONIC ACTIVITY
Several lines of evidence, including seismites,
syntectonic faulting and differential subsidence,
all suggest that the Cincinnati Arch was subjected
to seismic activity during the Late Ordovician.
Seismites
Several horizons of seismically induced, synsedi-
mentary ball-and-pillow beds (seismites) occur
within Upper Ordovician strata of the Jessamine
Dome (Pope
et al
., 1997; Ettensohn
et al
., 2002;
Jewell & Ettensohn, 2004; MacLaughlin & Brett,
2004). These seismites indicate that occasional large
earthquakes (Moment Magnitude 5-8) occurred
in this region of the Cincinnati Arch during the
Late Ordovician (Pope
et al
., 1997). However,
whether these faults formed as a response to local
stress or by stresses generated much farther afi eld
in the foreland basin (Jewell & Ettensohn, 2004;
McLauglin & Brett, 2004) is unclear.
Similar seismite beds occur in M5-C5 strata
on the Nashville Dome (Holland & Patzkowsky,
1997). Most of these are visible in the southern
half of the Nashville Dome, where individual
horizons can be correlated for tens of miles from
east to west. Some of these seismites are closely
associated with sequence boundaries, such as at
the C5 sequence boundary and at the Ordovician-
Silurian unconformity; it is unclear if this associa-
tion refl ects enhanced preservation or increased
seismicity (cf. McLaughlin & Brett, 2004).
Subsidence history
Backstripping was used to reconstruct the accom-
modation history of the Jessamine and Nashville
Domes (Fig. 8; see Holland & Patzkowsky (1998)
for details on methods). Although the eustatic and
tectonically driven subsidence components cannot
be separated from these limited data, it is assumed
that the longer-term features of this accommo-
dation history refl ect tectonic subsidence, whereas
the short-term features (<1-3 Myr) are thought to
refl ect eustasy (Holland & Patzkowsky, 1998).
Faults and structural features
The Jessamine Dome is a fault-bounded structure
that localized the development of tidally infl u-
enced skeletal grainstones and stromatoporoid
buildups in the Lexington Limestone (Hrabar
et al
., 1971; Cressman, 1973; Ettensohn, 1992;
