Geologic units in Adams county, Ohio

Estill Shale (Silurian) at surface, covers 22 % of this area

Shale and minor dolomite interbedded, reddish to greenish gray, weathers light gray, planar to irregular bedding, thin to thick bedded, 30 to 180 feet thick. Diagnostic features include dominance of shale and the units susceptibility to be unstable on slopes and cause landslides.

Preacherville Member of the Drakes Formation, Waynesville and Arnheim Formation, Undivided (Ordovician) at surface, covers 19 % of this area

Shale, limestone, and dolomite, interbedded; gray to maroon in upper part, weathers yellowish-gray to light-gray; planar to irregular to wavy to nodular, thin to thick bedded; shale increases upward.

Ohio Shale (Devonian) at surface, covers 17 % of this area

Shale; brownish black to greenish gray, weathers brown; carbonaceous to clayey, laminated to thin bedded, fissile parting; carbonate and/or siderite concretions in lowermost 50 feet; petroliferous odor; 250 to 500+ feet thick. Includes Olentangy Shale south of central Delaware Co.

Peebles Dolomite, Lilley and Bisher Formations, Undivided (Silurian) at surface, covers 16 % of this area

Peebles Dolomite, bluish gray weathers light gray; planar to irregular, thick to massive bedded; 0 to 120 feet thick; vuggy to cavernous porosity; cliffs former. Lilley Formation, dolomite with minor limestone, chert, and shale; bluish gray to gray weathers reddish gray to gray; planar to irregular, thin to thick bedded; 20 to 80 feet thick; fossiliferous. Bisher Formation, dolomite with minor shale; bluish gray to gray weathers yellowish-orange; argillaceous and silty in part; planar to lenticular, thin to thick bedded; 20 to 90 feet thick; Interval ranges from 80 to 160 feet in thickness. Peebles Dolomite overlies Lilley Formation and underlies Greenfield Dolomite, Hillsboro Sandstone, or Ohio Shale in southern OH. Age is Silurian (Wenlockian and Ludlovian) (Rexroad and Kleffner, 1984). Wenlockian age of the Lilley Formation is based on 10 species of conodont fauna. The Lilley Formation, Lilley-Peebles transition unit, and the Peebles Dolomite compose the upper Niagaran sequence along the east flank of the Cincinnati arch in southern OH. The Lilley consists of two main lithologies: 1) gray to blue gray, fine-grained argillaceous, variably fossiliferous uneven- to thin-bedded dolomite with dolomitic shale partings and 2) light-gray, medium to coarse-grained fossiliferous dolomite. Thickness averages 15 m in Adams and southeastern Highland Cos. and thickens to 24 m in western and northwestern Highland Co. Eustatic sea-level fall in early to middle Wenlockian is proposed as the cause for shoaling during deposition. Underlies Peebles Dolomite and overlies Bisher Formation (Kleffner, M.A., 1990).

Maxville Limestone; Rushville, Logan, and Cuyhoga Formations, Undivided (Mississippian) at surface, covers 10 % of this area

Shale, siltstone, and sandstone, interbedded; various shades of gray, yellow to brown weather similar color; sandstone, silty to granular, local stringers of quartz pebbles. Shale, clayey to silty, locally fossiliferous. Medium to dark gray, thin to thick bedded limestone locally preserved at top of interval where unit crops out in southern half of state. Lithologies percentages vary in different areas where unit crops out; laterial and vertical gradation common at regional scale.

Drowning Creek Formation (Silurian) at surface, covers 10 % of this area

Limestone, and shale, interbedded; limestone, shades bluish, greenish, and yellowish gray to grayish-pink weathers light gray to shades of red; planar to irregular to nodular, thin to thick bedded; fine to very coarse grained; locally silty, dolomitic, cherty, glaconitic; moderate to abundant fossils. Shale, greenish-gray to bluish-gray weathers light gray, thin bedded; silty.

Sunbury Shale, Berea Sandstone, and Bedford Shale, Undivided (Devonian and/or Mississippian) at surface, covers 3 % of this area

Shale and sandstone; upper 10 to 50 feet shale; black to brown, weathers light brown; carbonaceous; thin, planar bedding. Underlain by 10 to 50 feet sandstone; brown, weathers light brown to reddish brown; thin to thick bedded, planar to lenticular bedding; minor shale interbeds. Basal 80 to 100 feet shale and interbedded sandstone; gray to brown, weathers light gray to light brown; thin to medium bedded, planar to lenticular bedding; thick. Interval thickness ranges from 100 to 200 feet.

Grant Lake Limestone and Fairview Formation, Undivided (Ordovician) at surface, covers 1 % of this area

Limestone and shale, interbedded; gray to bluish-gray weathers light gray to yellowish-gray; planar to lenticular, thin to medium bedded in lower half; wavy to irregular to nodular, thin to thick bedded in upper half; fossiliferous.

Kope Formation (Ordovician) at surface, covers 0.7 % of this area

Shale (75%) and limestone (25%) interbedded; gray to bluish gray weathers light gray to yellowish gray; planar, thin to thick bedded; 200 to 260 feet thick.

Mississippian and Devonian Undifferentiated (Devonian and/or Mississippian) at surface, covers 0.4 % of this area

Sandstone and shale, interbedded. Occurs only in Serpent Mound Impact Structure.

Estill Shale and Drowning Creek Formation, Undivided (Silurian) at surface, covers 0.2 % of this area

Estill Shale, reddish to greenish gray, weathers light gray, minor interbedded dolomite, planar to irregular bedding, thin to thick bedded, 30 to 180 feet thick. Forms unstable slopes susceptible to landslides. Drowning Creek Formation; dolomite with minor shale; bluish gray to gray weathers yellowish orange; argillaceous and silty in part; planar to lenticular, thin to thick bedded; 20 to 90 feet thick.

Ordovician Undifferentiated (Ordovician) at surface, covers < 0.1 % of this area

Shale, dolomite, and limestone, interbedded; various shades of gray; thin to medium bedding, structurally disturbed. Occurs only in Serpent Mound Impact Structure.

Alluvium (Pleistocene to Holocene) at surface, covers < 0.1 % of this area

Alluvium; includes glacial deposits along the Ohio River and its tributaries west of Cannelton locks

Waynesville and Arnheim Formations, Undivided (Ordovician) at surface, covers < 0.1 % of this area

Waynesville Formation, shale (70%) and limestone (30%) interbedded; gray to bluish gray weathers light gray; planar to irregular, thin to thick bedded; 90 to 120 feet thick. Arnheim formation, shale (60%) and limestone (40%) interbedded; gray to bluish gray weathers light gray; planar, wavy, irregular, to nodular (in upper portion), thin to thick bedded; 50 to 100 feet thick. Contains multiple sedimentary cycles consisting of the alternation of shale and limestone displaying planar to irregular bedding with limestone and shale exhibiting wavy to nodular bedding. Ranges from 140 to 220 feet. The Geological Survey of Ohio recognizes the Cincinnati Group proposed by Meek and Worthen (1865), but at this time retains it as an informal term. The unit will be formally reinstated as a lithostratigraphic term after revision of its lower boundary and minor lithologic redescription of its units are completed. The ten formations included in the group are the (ascending) Clays Ferry Formation, the Kope Formation, the Fairview Formation, the Miamitown Shale, the Grant Lake Limestone, the Arnheim Formation, the Waynesville Formation, the Liberty Formation, the Whitewater Formation, and the Drakes Formation. Six members have been identified in the course of field mapping: the Point Pleasant Tongue of the Clays Ferry, the informal Bellevue, Corryville, Mount Auburn, and Straight Creek members of the Grant Lake Limestone, and the Preachersville Member of the Drakes Formation. The Backbone Creek and Elk Creek beds are recognized as excellent stratigraphic marker beds (Shrake and others, 1988).

Ashlock Formation, Grant Lake and Calloway Creek Limestones, and Fairview Formation, undivided (Ordovician) at surface, covers < 0.1 % of this area

Ashlock Formation, Grant Lake and Calloway Creek Limestones, and Fairview Formation, undivided

Dayton and Brassfield Limestones (Silurian) at surface, covers < 0.1 % of this area

Dayton Limestone; gray to bluish-gray weathers grayish-white; medium to thick bedded; fine grained; dolomitic; 5 to 15 feet thick. Brassfield Limestone; white to pink, locally gray to reddish brown; irregular, thin to medium bedded; coarsely crystalline; abundant pelmatozoan fossils; grayish-green glauconitic partings; cliff forming; 20 to 50 feet thick. Interval ranges from 32 to 100 feet in thickness.