The

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

Old Port Formation is a mapped bedrock unit in

Pennsylvania Pennsylvania (; (Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Ma ...

, USA. Details of the type section and of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line at the National Geologic Map Database. Current nomenclature usage by U.S. Geological Survey restricts the name Old Port Formation to Pennsylvania, but correlative units are present in adjacent states.

Description

The Old Port Formation consists of limestone, sandstone, shale, and chert.

Stratigraphic Setting

The Old Port Formation is divided into several members with varying

lithologies The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lith ...

, which are (in ascending

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers ( strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostr ...

order): New Creek Member (limestone), Corriganville Member (limestone), Mandata Member (shale), Shriver Member (cherty limestone), and Ridgeley Member (sandstone). Where the Shriver Chert does not occur it may be replaced by the Licking Creek Limestone. It was originally combined from the Helderberg Group and Oriskany Group by Conlin and Hoskins in 1962 to form a single Formation with the above members.

Ridgeley Member

The Ridgeley Member was first described as a member of the Oriskany Formation by Swartz and others (1913), as a calcareous sandstone which passes into an arenaceous limestone.Swartz, C.K., Rowe, R.B., Schuchert, Charles, and Maynard, T.P., 1913, Lower Devonian in Maryland; Local sections of the Lower Devonian f Maryland Correlation of the Lower Devonian, IN Swartz, C.K., and others, Lower Devonian, text: Maryland Geological Survey Systematic Report, p. 23-66, 96-190. It is still mapped as part of the Oriskany Group in New Jersey.Monteverde, D.H., 1992, Bedrock geologic map of the Sussex County, New Jersey, portions of the Culvers Gap and Lake Maskenozha quadrangles: New Jersey Geological Survey Geologic Map, 92-1, 1 sheet, scale 1:24,000 The type locality is at the town of Ridgeley, Mineral County, West Virginia. The sandstone of the Ridgeley Member has been extensively mined due to its very pure

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

suitable for

glass Glass is a non-Crystallinity, crystalline, often transparency and translucency, transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most ...

. The glass derived from the sandstone was used for lenses on the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most ver ...

. A separate formation, the Oriskany Sandstone, is a lateral equivalent of the Ridgeley Member, but bounded above and below by unconformities.

Shriver Member

The Shriver Member, or Shriver Chert, was first described as a member of the Oriskany Formation by Swartz and others (1913), as dark siliceous shale with much black impure chert in nodules or layers of nodules. It is named after Shriver Ridge (the type locality), Allegany County, Maryland, and was originally mapped as the basal unit of the Oriskany Formation. In Maryland and West Virginia, the Shriver is mapped as part of the Helderberg Group. In central Pennsylvania it is mapped as part of the Old Port Formation. In New Jersey it is mapped as the middle unit of the Oriskany Group.

Mandata Member

The Mandata Shale of the Helderberg Group was first introduced by F. M. Swartz in 1938,Swartz, F.M., 1938, (Abstract) GSA Bulletin, v. 49, no. 12, pt. 2, p. 1923 mainly with reference to the overlying Licking Creek Limestone. The type locality is about 0.25 miles south of Mandata, Pennsylvania, on Route 225.

Corriganville Member

The Corriganville Limestone was first described by J. W. Head in 1972 as part of the Helderberg Group in Allegany County, Maryland, as a gray limestone with chert.Head, J.W., III, 1972, Upper Silurian-Lower Devonian stratigraphy and nomenclature in the central Appalachians, IN Guidebook for the 37th annual field conference of Pennsylvania geologists
Field Conference of Pennsylvania Geologists
no. 37, p. 96-103. C. R. Wood first mapped it as part of the Old Port Formation in Pennsylvania. The type locality is a railroad cut 0.3 mi southeast of Corriganville, Alleghany County, Maryland.

New Creek Member

The New Creek Member was first described by Bowen only as a limestone that is replaced by the Elbow Ridge Sandstone near Hancock, Maryland. Bowen later described it as a massive limestone overlying the Keyser Formation. C. R. Wood first mapped it as part of the Old Port Formation in Pennsylvania.Wood, C.R., 1980, Summary groundwater resources of Centre County, Pennsylvania: Pennsylvania Geological Survey Water Resource Report, 4th series, no. 48, 60 p.

Licking Creek Member

The Licking Creek Limestone of the Helderberg Group was first introduced by F. M. Swartz in 1938, and was described more fully in 1939. The unit consists of layers and nodules of black chert interbedded with light-gray crystalline limestone. The type locality is a bluff on the south side of Licking Creek, about one mile east of Warren Point, Franklin County, Pennsylvania.

Notable Exposures

* Old quarry in Tyrone, Pennsylvania, west of Sink Run and along U.S. Route 22 * Two exposures in Everett, Pennsylvania: ** U.S. Route 30 (Everett Bypass) roadcut through Warrior Ridge north of Everett **Another exposure along business Route 30 on the west side of Everett (pictured above) * The Sinnett-Thorn Mountain Cave System is developed in the Keyser Formation and overlying New Creek and Corriganville Limestone Members ''See also type localities listed in subsections above.''

Fossils

Brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, ...

s are occasionally abundant (as casts) in the Ridgeley Member. The brachiopods ''Costispirifer arenosus'', ''Beachia immatura'', ''Leptocoelia flabellites'', ''Metaplasia paucicostata'', ''Plicoplasia tribuarius'', and '' Chonetes hudsonicus'' are present in the Shriver Member around the type locality of Shriver Ridge.

Ostracods Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typi ...

are also present in the Shriver Member.Swartz, F. M., 1932, Revision of the Ostracode Family ''Thlipsuridae'', with Descriptions of New Species from the Lower Devonian of Pennsylvania.

Journal of Paleontology The ''Journal of Paleontology'' is a peer-reviewed scientific journal covering the field of paleontology. It is published by the Paleontological Society. Indexing The ''Journal of Paleontology'' is indexed in: *BIOSIS Previews *Science Citatio ...

, Vol. 6, No. 1, Mar. 1932, pp. 36-5

/ref>Swartz, F. M., 1936, Revision of the ''Primitiidae'' and ''Beyrichiidae'', with New Ostracoda from the Lower Devonian of Pennsylvania.

, Vol. 10, No. 7, Oct. 1936, pp. 541-58

/ref> The Old Port Formation contains

conodont Conodonts ( Greek ''kōnos'', " cone", + ''odont'', " tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, w ...

Age

Relative age dating of the Old Port places it in the Lower

period. It rests conformably atop the Keyser Formation and usually unconformably below the Needmore Formation''Stratigraphic correlation chart of Pennsylvania'', T. M. Berg, M. K. McInerney, J. H. Way, and D. B. MacLachlan. 1983; 3rd printing, revised, 1993. 1 sheet, 42" x 58", plus 2 p. addendum. or below the

Onondaga Formation The Onondaga Limestone is a group of hard limestones and dolomites of Devonian age that form an important geographic feature in some areas in which it outcrops; in others, especially its Southern Ontario portion, the formation can be less promin ...