MRCSP Phase I Geologic Characterization Report - Midwest ...

APPENDIX A: LOWER DEVONIAN SYLVANIA SANDSTONE
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any other formations within the northern Appalachian basin (AGA,
2001). At least 32 gas storage fields are found within the Oriskany,
with a combined storage capacity of nearly 1 TCF, and located in
pinchout, stratigraphic, and structural traps (Table A11-1). Many of
these storage fields have been in operation since the 1950s, attesting
to the integrity of the fields and seals.
In all likelihood the Oriskany Sandstone would make a suitable
target for storage of CO 2-miscible fluids, but only after thorough
evaluation of the formation at potential target sites. Such target sites
include: 1) zones of high porosity and high permeability associated
with updip sandstone pinchout, typical of eastern Ohio, and along
the southern and eastern boundaries of the “Oriskany no-sand area”
in northwestern Pennsylvania; 2) areas of highly fractured Oriskany
Sandstone associated with salt solution and migration within
the central depositional area of western Pennsylvania and central
West Virginia; and 3) areas of intensely faulted and multi-tiered
(duplexed) Oriskany Sandstone in the Valley and Ridge of central
Pennsylvania, western Maryland, and eastern West Virginia.
12. LOWER DEVONIAN SYLVANIA SANDSTONE
The Sylvania Sandstone, late Early Devonian in age, is a
quartzose sandstone that grades laterally into sandy limestone
and dolostone in parts of the Michigan basin. The Sylvania is the
basal formation of the Detroit River Group and, along with the
Bois Blanc and Garden Island Formations, overlie the Kaskaskia
unconformity (Figure 5). Gardner (1974) suggests the lower part of
the Sylvania may be in facies relationship with the underlying Bois
Blanc, especially in northern and western regions of the Michigan
basin. However, the relationship of this lower contact is poorly
documented, and the recent revision of the Michigan stratigraphic
column by the Michigan Geological Survey shows an unconformity
between the Sylvania and Bois Blanc Formations. The upper
part of the Sylvania intertongues with carbonates of the overlying
Amherstburg Formation, another unit in the Detroit River Group.
Although arenaceous units are present at various stratigraphic
positions above the Kaskaskia unconformity in Michigan, as well
as in the Appalachian basin portion of the MRCSP study area—for
example the Oriskany Sandstone in Ohio, Pennsylvania, and West
Virginia—use of the name Sylvania Sandstone should be restricted
to the sandstone that occurs at the base of the Detroit River Group in
the Michigan basin (Fisher and others, 1988). In general, details on
the vertical and lateral stratigraphic relationships of the Sylvania, its
internal lithologic variations, and those attributes making it suitable
as a geologic reservoir for CO 2 sequestration, are uncertain for most
of the Michigan basin.
ORIGIN OF NAMES, TYPE SECTION,
SIGNIFICANT EARLIER STUDIES
Orton (1888) applied the name Sylvania Sandstone to exposures,
incorrectly identified as Oriskany by Newberry (1871),
in Sylvania Township, Lucas County, Ohio. Other significant
investigations on the Sylvania include Grabau and Sherzer (1910),
Alty (1933), Carman (1936), and Hatfield and others (1968). Also,
Gardner (1974), as part of a detailed subsurface study, presented
regional isopach and lithofacies maps of the Sylvania Sandstone
in Michigan.
NATURE OF LOWER AND UPPER CONTACTS
The Sylvania Sandstone overlies the Kaskaskia unconformity
in southeastern Michigan above the truncated Silurian-age Bass
Islands Group. The Sylvania is thin, discontinuous, or completely
absent in some areas, especially on the southern and western margins
of the Michigan basin. Typically the Bois Blanc underlies
the Sylvania although the exact stratigraphic relationship between
these two units is unclear. The lateral extent and isopach pattern of
the Sylvania Sandstone (Figure A12-1) and Bois Blanc Formation
suggests a northwest- to southeast-trending shallow marine basin
existed in the area at the time of deposition of the Sylvania (Gardner,
1974). This basin may be related to the trend of the Mid-Michigan
rift (Figure 6). The Sylvania Sandstone is the basal unit of the Detroit
River Group; its upper contact with the overlying Amherstburg
Formation is gradational and intertonguing.
LITHOLOGY
Regional lithologic variations within the Sylvania Sandstone
are known mainly from the analysis of geophysical logs (Gardner,
1974). These analyses suggest the Sylvania Sandstone typically
consists of dolomitic to cherty, fine- to medium-grained, well-sorted
and rounded, quartzose sandstone in central and southeastern lower
Michigan but grades into cherty, sandy carbonate in other regions
of the Michigan basin. Carbonate interbeds, sometimes containing
chert, are common throughout the unit. The Sylvania, in general, is
very porous in outcrops and in materials recovered from shallow
subsurface cores and exploratory drill holes, particularly in southeastern
lower Michigan. Locally, quartz overgrowths and carbonate
cement are present in the unit. Most quartz sand grains of the Sylvania
are frosted and pitted. Marine fossils, mainly brachiopods, are
common in many of the calcareous interbeds. Cross beds and other
current-induced sedimentary structures are common in outcrops but
rarely observed in cores.
DISCUSSION OF DEPTH AND THICKNESS RANGES
The Sylvania Sandstone ranges from just a few feet thick in
northeastern and southwestern areas of the Michigan basin to a maximum
thickness of about 350 feet; the area of maximum thickness
occurs mostly along a northwest- to southeast-trending belt across
the central portion of the basin (Figure A12-1). These thickness
estimates are based on geophysical log picks but are problematic
due to the complex lithologic variations above, below, and within
the geologic interval containing the Sylvania. As previously noted,
the northwest- to southeast-oriented isopach pattern is similar to the
underlying Bois Blanc Formation, suggesting a similar depositional
and structural setting for both units. Moreover, the area of maximum
thickness of the Sylvania closely mimics the eastern margin of the
Mid-Michigan rift, a feature interpreted as a pre-Paleozoic age failed
continental rift. Structural movement resulting from reactivation of
parts of the rift may have influenced depositional trends within the
Sylvania. These structures may have created basin topography/bathymetry
that existed during the transgressive phase of Lower and
Middle Devonian sediments that were deposited on top of the Kaskaskia
unconformity. The Sylvania Sandstone ranges in depth from
in excess of 400 feet above sea level in the southeastern corner of
the state to over 4,400 feet below sea level in the central portion of
the basin (Figure A12-2).