MRCSP Phase I Geologic Characterization Report - Midwest ...

62 CHARACTERIZATION OF GEOLOGIC SEQUESTRATION OPPORTUNITIES IN THE MRCSP REGION
grained sandstone, dolomitic sandstone, and dolostone (Becker and
others, 1978). Where both sandstones occur, they cannot easily be
distinguished from one another (Becker and others, 1978; Shaver
and others, 1986). Both sandstones become increasingly dolomitic
and thin to the south and east (Becker and others, 1978). The Franconia
consists of glauconitic, pink to gray, fine- to medium-grained
dolomitic sandstone, quartz arenites, dolostone, shaly dolostone,
dolomitic siltstone, and interbedded shales (Milstein, 1983; Shaver
and others, 1986). Like the Eau Claire, the Franconia is feldspathic
(Galarowicz, 1997). The Franconia has a similar thickness distribution
to the underlying Galesville and Ironton Sandstones. Also, like
those units, it becomes more dolomitic and thinner eastward and
southward, where it grades into the upper part of the Davis Formation,
or into the lower part of the Potosi Dolomite (Becker and others,
1978; Shaver and others, 1986). The Davis Formation is composed
of siltstone, shale, limestone, and dolostone that conformably
overlie the Eau Claire Formation in eastern and southern Indiana
(Becker and others, 1978; Shaver and others, 1986). The Upper
Munising/Davis units are overlain by the Trempealeau Formation
and the laterally equivalent Potosi Dolomite in the western MRCSP
study area. In Michigan, the Trempealeau is a buff to light brown
dolostone, locally sandy and containing chert, with minor amounts
of dolomitic shale and shaly dolostone. The Trempealeau contains
a large amount of glauconite and minor amounts of anhydrite
(Lilienthal, 1978; Milstein, 1983). Similarly, the equivalent Potosi
Dolomite in Indiana is a pale gray to tan, dense, micritic to mediumgrained
dolostone with interbeds of shale and siltstone. The lower
and upper parts of the Potosi may be glauconitic (Shaver and others,
1986). Eastward, the Potosi/Trempealeau interval is equivalent to
the Copper Ridge Dolomite (Knox Group). The Copper Ridge is a
thick interval of sandy dolostone with interbeds of sandstone and
dark gray, argillaceous limestone in the eastern part of the MRCSP
study area (Ryder and others, 1996, 1997). Dolostones of the Copper
Ridge in parts of northern Kentucky, eastern Indiana, and Ohio
range from dense to vuggy. Vuggy dolostones may occur throughout
an interval of at least 400 feet in this area (Shrake and others,
1990). Farther eastward, in eastern West Virginia, Pennsylvania, and
Maryland, the upper carbonate interval is equivalent to the Conococheague
Group/Limestone and part of the Gatesburg Formation.
The Conococheague is a thick carbonate-dominated sequence that is
divided into several formations in Pennsylvania (Kauffman, 1999).
The Conococheague contains sandy dolostone, which may be argillaceous
and contain local layers of dolomitic, quartzose sandstones
near the base of the unit; limestones with chert; and thin interbeds
of limestone and dolostone (Kauffman, 1999). Cycles of intra-formational
conglomerates, cross bedded grainstones, alternating thinbedded
limestone and dolostone (called “ribbon rock”), and planar
laminated to mud-cracked dolostone are documented in Virginia,
where this unit is exposed (Demicco, 1983, 1985). The part of the
Gatesburg Formation beneath the Rose Run-equivalent in Pennsylvania
is a dolostone similar to the Copper Ridge, which tends to be
sandy toward the base (Ryder, 1991, 1992b)
DISCUSSION OF DEPTH AND THICKNESS RANGES
The Basal Sandstone to top of Copper Ridge Interval ranges in
thickness from slightly more than 1,100 feet in the western portion
of the MRCSP study area to more than 9,000 feet in the Rome
trough in West Virginia (Figure A3-1). Isopachs are not projected
beyond the trough into southern West Virginia because there are
no wells deep enough in this area to penetrate the interval. However,
those wells in southeastern Kentucky, southwest Virginia (just
outside of the MRCSP study area), and northern West Virginia that
reach basement indicate that there is substantial thinning of the interval
south and east of the trough-bounding faults so that thinning
is expected in southern West Virginia. Most of the thickness variation
within the trough occurs within the Rome Formation and lower
part of the Conasauga Group (Ryder and others, 1996, 1997; Harris
and others, 2004).
The Basal Sandstone to top of Copper Ridge Interval also thickens
into the Michigan basin (Figure A3-1). Thickening of the Franconia
and Trempealeau formations into central Michigan indicates that the
proto-Michigan basin continued to develop at this time (Catacosinos
and Daniels, 1991). Subsidence occurred at a much slower rate than
during the deposition of the basal sandstone. The proto-Appalachian
basin also developed during this time, as indicated by southeastward
thickening of units east of the Rome trough.
The shallowest depth at which the top of the Basal Sandstone to
top of Copper Ridge Interval occurs is across the Cincinnati arch
(in some cases less than 500 feet) (Figure A3-2). In the center of the
Michigan basin, the top of this interval may be deeper than 10,000
feet, and in the Appalachian basin, the depth exceeds 20,000 feet.
DEPOSITIONAL ENVIRONMENTS/
PALEOGEOGRAPHY/TECTONISM
During deposition of the Basal Sandstone to top of Copper Ridge
Interval, a shallow epicontinental sea covered the MRCSP study
area. Subsidence above the Rome trough and lesser subsidence in
the proto-Michigan and Appalachian basins influenced depositional
facies, as did sea-level fluctuations. The pervasive dolomitization
of the upper part of this interval (Copper Ridge equivalents)
throughout the North American continent continues to be enigmatic,
although it may be related to the expulsion and migration of fluids
from the Ordovician Sevier or late Paleozoic Alleghanian orogenies
(Glumac and Walker, 2002; Montanez, 1994).
Tomstown/Rome/Waynesboro/lower Conasauga Formations—The
Shady-Tomstown Dolomite was deposited as a carbonate ramp
along the Cambro-Ordovician passive margin of the craton (Read,
1989a, 1989b). Because the thickness of the dolostone does not
change substantially across the southern bounding faults of the
Rome trough, it is presumed to represent pre-rift deposition (Harris
and others, 2004). The great thickness of the Rome Formation
within the trough document growth during rifting (Harris and
others, 2004). Evidence suggests that sediments were transported
into the trough from the north. The deeper parts of the trough were
occupied by a distal clastic shelf or ramp. Along the northwest
margin of the trough, delta front and shallow marine shelf deposits
dominated a shallower structural platform , with sand supplied by
fluvial systems to the north. Presumably, the areas north and west
of the trough at this time were dominated by nondeposition or erosion
on the Precambrian surface. Age correlations for this interval
are hampered by a lack of cores with usable biostratigraphic data.
During the time of deposition of the upper Rome Formation, the
deeper Rome trough was occupied by a carbonate ramp. A deeper
water, intra-shelf basin is interpreted in south-central Kentucky,
based on the few wells drilled there (Harris and others, 2004).
Lateral facies of the lower Conasauga Formation may represent
downslope facies equivalents of Rome clastic wedges building off
the northern trough margin into deeper water (Ryder, 1992b; Ryder
and others, 1996, 1997). Thickening of these units into the trough
indicates continued (but lessened) growth faulting. Outside of the
Rome trough, in southern West Virginia, anhydrites and redbeds
in the Rome and Waynesboro Formations may indicate upper tidal