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Hamilton Group or
Millboro Shale
Hamilton Group or; Millboro Shale
Stratigraphic range: Eifelian - Famennian
Type	Group
Sub-units	Mahantango Formation; Clearville Siltstone Frame Shale Donation Siltstone Crooked Creek Shale Backbone Ridge Siltstone Chaneysville Siltstone Gander Run Shale Moscow Formation; North Evans limestone Windom Shale Kashong Shale Tichenor Limestone Ludlowville Formation; Jaycox Shale Owasco Shale Spafford Shale Wanakah Shale, Ivy Point Shale Ledyard Shale, Otisco Shale Centerfield Limestone Skaneatales Formation; Levanna Member Stafford Limestone Marcellus Formation; Otaka Creek Member Cherry Valley Member Union Spring Member Tioga Bentonites
Underlies	Tully Limestone and Harrell Shale
Overlies	Onondaga Limestone
Thickness	up to 2,500 feet (800 m)
Lithology
Primary	Shale
Other	Limestone, Siltstone, Claystone
Location
Region	Appalachian Basin of; eastern North America
Extent	Maryland, New York, Pennsylvania, Virginia, West Virginia and Ontario, Canada
Type section
Named for	Hamilton, New York
Named by	James Hall

The Hamilton Group is a Devonian-age geological group which is located in the Appalachian region of the United States. It is present in New York, Pennsylvania, Maryland, Ohio, West Virginia, northwestern Virginia and Ontario, Canada,^[1]^[2] and is mainly composed of marine shale with some sandstone.

There are two main formations encompassed by the group: the Mahantango Formation and the Marcellus Shale. In southwestern Virginia, where the two sub-units are not easily distinguishable, the Hamilton Group is broadly equivalent to the Millboro Shale or Millboro Formation.^[3]

The group is named for the village of Hamilton, New York.^[4]^[5] These rocks are the oldest strata of the Devonian gas shale sequence.^[6]

Stratigraphic Setting

In western Pennsylvania, Ohio and West Virginia the Hamilton Group consists of the Mahantango Formation, a gray, dark gray, brown, and olive laminated shale; siltstone; and very fine-grained sandstone or claystone containing marine fossils. The uppermost clay layers of the Mahantango Formation are particularly rich in fossils.^[8] In New York, central and eastern Pennsylvania the upper sections contain several thick grey shale formations, occasionally marked with limestone stringer. It overlies the Marcellus Shale, a fissile gray-black to black, thinly laminated, pyritic, carbonaceous thin shale with sparse marine fauna and siderite concretions. The total thickness of the Hamilton Group in Pennsylvania runs about 970 feet. In New York State, it thickens from 250 feet near Lake Erie to over 2,500 feet in Ulster and Greene counties. Depths ranging from outcrops to 8,000 feet below the surface of Sullivan County, in the southeastern part of New York state.^[6]

In the interior lowlands of New York and north eastern and north central Pennsylvania, the Hamilton Group contains the Marcellus, Skaneateles, Ludlowville, and Moscow Formations, in ascending order, with the Tully Limestone above.^[9]

These units are divided by the Stafford, Centerfield, and Tichenor limestones.^[10]

In Ontario, Canada, the Hamilton Group formations are, in ascending order, Bell, Rockport Quarry, Arkona, Hungry Hollow, Widder, and Ipperwash; the Kettle Point Formation of the late Devonian lies unconformably above.^[11]

The Mahantango Formation includes these members in descending order: Sherman Ridge, Montebello sandstone, Fisher Ridge, Dalmatia, and Turkey Ridge. In south-central Pennsylvania, it includes Clearville, Frame, Chaneysville, and Gander Run Members. Its thickness in Maryland ranges from 600 feet in the west, increasing to 1,200 feet in the east,^[12] and approximately 1000 feet thick in central Pennsylvania.^[8]

The Marcellus Formation contains a local limestones Purcell Member and Cherry Valley as well as Tioga Bentonites at the base in central and eastern Pennsylvania. Its thickness in Maryland ranges from 250 feet in east, increasing to 500 feet in the west.^[12]

The Hamilton Group, Tioga Bentonites, and Needmore Shale were formerly called the Romney Formation.^[12]

The Geneseo Shale is a dark grey to black shale that overlies the Tully Limestone; it includes the Filmore beds.^[13]
The Tully Limestone is a shallow-water carbonaceous unit.
The Moscow Formation (Middle Devonian / Givetian) comprises grey to black shales interbedded with limestones and calcareous mudstones and usually bioturbated.^[14]

Age

Relative age dating of the Hamilton places it in the middle and lower Devonian period. In Maryland, it rests conformably atop the Tioga Metabentonite, a thin layer of laminated shale lying over the Needmore Shale. In other regions, the Needmore Shale is replaced by laterally equivalent units such as limestone and shale of the Onondaga Formation, or chert of the Huntersville Chert.^[15]

The Hamilton Group lies conformably below the Brallier Formation (formerly Woodmont Shale, dark laminated shale) at its southern extent. Further north, it is overlain by the Tully Limestone, though some consider the Tully Limestone a subunit of the Mahantango Formation. The Tully Limestone is succeeded by the dark laminated Harrell Shale.^[16] In 2012, Read and Erikson reported the group as dating from the Eifelian to Famennian in Virginia.^[15]^[12]

Fossils

Source:^[17]

Brachiopoda

Tropidoleptus carinatus

Nucfeospira concinna

Mucrospirifer

Athyris

Coral

Pleurodictyum americanum

Mollusca

Bivalvia

Orthonota undulate

Trilobita

Dipleura

Economic Resources

The Hamilton is a good source of road material, riprap and building stone,^[18] that is used locally for shale aggregate and common fill.^[8]

References

^ Ryder, R.T., Swezey, C.S., Crangle, R.D., Jr., and Trippi, M.T., 2008, Geologic cross section E-E’ through the central Appalachian Basin from the Findlay Arch, Wood County, Ohio, to the Valley and Ridge Province, Pendleton County, West Virginia: U.S. Geological Survey Scientific Investigations Map SIM-2985, 2 sheets with 48-page pamphlet. https://pubs.er.usgs.gov/publication/sim2985
^ Ryder, R.T., Trippi, M.H., Swezey, C.S., Crangle, R.D., Jr., Hope, R.S., Rowan, E.L., and Lentz, E.E., 2012, Geologic cross section C-C’ through the central Appalachian basin from near the Findlay Arch, north-central Ohio, to the Valley and Ridge Province, Bedford County, south-central Pennsylvania: U.S. Geological Survey Scientific Investigations Map SIM-3172, 2 sheets with 70-page pamphlet. https://pubs.er.usgs.gov/publication/sim3172
^ "Map Unit Descriptions" (PDF). Virginia Department of Mines, Minerals and Energy. 2007-09-28. Archived from the original (PDF) on 2008-02-11. Retrieved 2008-05-03.
^ Wood, G.H., Trexler, J.P., Kehn, T.M., (1964). Geology of the West-Central Part of the Southern Anthracite Field and Adjoining Areas, Pennsylvania. United States Geological Survey, C-46.
^ "Geolex — Hamilton".
^ ^a ^b Martin, John P. "The Middle Devonian Hamilton Group Shales in the Northern Appalachian Basin: Production and Potential". New York State Energy Research and Development Authority. Archived from the original on 2006-10-11. Retrieved 2008-04-02.
^ Milici, Robert C.; Swezey, Christopher S. (2006). "Assessment of Appalachian Basin Oil and Gas Resources: Devonian Shale–Middle and Upper Paleozoic Total Petroleum System" (PDF). Open-File Report Series 2006-1237. United States Geological Survey. Retrieved 2008-04-05.
^ ^a ^b ^c McElroy, Thomas A.; Hoskins, Donald M. (2007). "Bedrock Geology of the Allensville Quadrangle, Huntingdon and Mifflin Counties, Pennsylvania" (PDF). Pennsylvania Geological Survey. Archived from the original (PDF) on June 9, 2011. {{cite journal}}: Cite journal requires |journal= (help)
^ Sinclair, James P. (1993). Final Generic Environmental Impact Statement for Promulgation of 6 NYCRR Part 382: Regulations for Low-Level Radioactive Waste Disposal Facilities. DIANE Publishing. ISBN 1-56806-746-1.
^ Goldman, D.; Mitchell, C.E. (1990). "Morphology, systematics, and evolution of Middle Devonian Ambocoeliidae (Brachiopoda), western New York". Journal of Paleontology. 64 (1): 79–99. Bibcode:1990JPal...64...79G. doi:10.1017/S0022336000042256. ISSN 0022-3360. JSTOR 1305546. S2CID 133456873.
^ "Geology of the Southwestern District". Resident Geologist Program - Southern Ontario. Ontario Ministry of Northern Development and Mines. Archived from the original on 2007-09-22.
^ ^a ^b ^c ^d "Geologic Maps of Maryland". Retrieved 2008-01-26.
^ Baird, Gordon C. (March 2001). Eustatic and Flexural events recorded in the Late Middle Devonian Tully Formation, New York State and Pennsylvania. Retrieved 2013-12-08.
^ "Moscow Formation". United States Geological Survey. Retrieved 2011-08-30.
^ ^a ^b Read, J. Fred; Eriksson, Kenneth A. (2012). "Paleozoic Sedimentary Successions of the Virginia Valley & Ridge and Plateau" (PDF). Virginia Tech Scholarly Works, Department of Geosciences.
^ Jackson, Margaret S.; Hanley, Peter M.; Sak, Peter B. (2007). "Preliminary Bedrock Geologic Map of the Middle Portion of the Susquehanna River Valley, Cumberland, Dauphin, And Perry Counties, Pennsylvania" (PDF). Open File Report OFBM-07-05.0. Pennsylvania Geological Survey. Archived from the original (PDF) on June 9, 2011. Retrieved 2008-01-26.
^ STOKES, PHILIP J.; ZAMBITO, IV, JAMES J. "USING MARINE FOSSILS TO UNLOCK THE MIDDLE DEVONIAN PALEOENVIRONMENTS OF WESTERN NEW YORK" (PDF). /ottohmuller.com.
^ McElroy, Thomas A.; Hoskins, Donald M. (2007). "Preliminary Bedrock Geologic Map of the Middle Portion of the Susquehanna River Valley, Cumberland, Dauphin, and Perry Counties, Pennsylvania" (PDF). Pennsylvania Geological Survey. Archived from the original (PDF) on June 9, 2011. {{cite journal}}: Cite journal requires |journal= (help)