|Geologic age||Middle Devonian|
|Comments||part of Onondaga Limestone and Oriskany Sandstone 75-150 ft. (23-45 m) Secondary unit descriptions from USGS Lexicon website (ref. NY046) and reference NY017: Middle Devonian Onondaga of NY represents broad, carbonate platform facies deposited during early to middle Eifelian time. Carbonates are characterized by calcarenitic to cherty to argillaceous limestones and minor shales deposited in a shallow epicontinental sea. The Selinsgrove Limestone Member of the Needmore Formation of central PA is the direct equivalent of the Onondaga Limestone in NY. The Onondaga is generally subdivided into four members across NY: Edgecliff, Nedrow, Moorehouse, and Seneca. These four members are directly equivalent to those of the Buttermilk Falls Limestone of eastern PA. The Clarence Member has been recognized only in western NY and is here designated a local informal facies of the Edgecliff. The informal Jamesville Quarry facies of the Edgecliff is also named in this report for the chert-poor, crinoidal pack- and grainstone that occurs at the Edgecliff type locality. Several marker beds within the Nedrow Member are recognized and the upper boundary with the Moorehouse Member is redefined. The Moorehouse contains several fossil horizons and the Seneca contains several bentonite beds, including the Tioga B or Onondaga Indian Nation Bentonite, which defines its base. The Lower-Middle Devonian (Emsian-Eifelian) boundary, long placed at the base of the Onondaga in NY, could lie as high as the base of the Nedrow Member according to Kirchgasser and Oliver (1993), as there are no age diagnostic fossils in the Edgecliff (Brett and Ver Straeten, 1994). The Seneca Member of the Onondaga Formation as now defined is part of a general fining-upward trend that extends from the underlying upper part of the Moorehouse Member into the overlying Marcellus Formation at its type section. Deposition of member is more complex than previously thought as details reveal that it contains two cycles rather than one, indicating two deepening intervals. The upper contact of the Seneca as defined in this report is marked by a thin, apparently widespread lag bed with fish bone material. Member is thickest in the central Finger Lakes area. Thins eastward and is eventually cutout near Albany. Contains a relatively low diversity fauna. Chonetid and atrypid brachiopods are abundant and LEPTAENA, common; rugose corals are uncommon. Fine to medium-grained wacke- to packstones dominate the unit. In outcrop appears as thick-bedded to massive limestones separated by thin shaly to bentonitic partings. Light-weathering chert is present mainly in the western region. Thin dark shales increase in number toward the top. Base is marked by the Onondaga Indian Nation Ash (Tioga B of PA), which differs from boundary as defined by Conkin, who placed the base of the Seneca 0.47 to 1.25 m above the base of the bentonite. As many as eight Tioga Ash Beds may occur in the Seneca Member, including the Tioga B. At the Seneca Stone quarry, 8.5 km northwest of the type section, the member is 7.1 to 8.4 m thick, depending upon placement of the upper contact, and underlies the Bakoven Member of the Union Springs Shale [shown in chart as assigned to Marcellus subgroup]. Zone L, as the transitional 1.3-m-interval was labeled by Oliver (1954) was assigned by him to the Seneca. However, authors follow Conkin and Conkin (1979) in assigning interval to the overlying Union Springs. Age of the Seneca is Middle Devonian (Eifelian) (Brett and Ver Straeten, 1994). The Nedrow Member overlies the Edgecliff Member, which in this report has been subdivided into a Clarence facies (previously Clarence Member of western NY) and a Jamesville Quarry facies. The Nedrow does not pass laterally into cherty limestone (Clarence facies) as originally thought, but overlies it. Authors have recognized several marker beds within the Nedrow that aid in correlating the western NY sections. The contact between the Nedrow and the overlying Moorehouse Member was originally placed within an interval of interbedded shales and limestones. Authors have found that this interval cannot be traced any great distance. They have recently recognized a pair of black to dark gray shale-dominated beds within the upper Nedrow and use them "functionally" as the upper boundary. At Seneca Stone quarry, the Nedrow is approximately 4.2 m thick. The basal shales are typically medium dark gray, but contain scattered brachiopods and rugose corals. The lower 3 m consists of alternations of medium gray, sparsely fossiliferous, calcareous shales, and gray, somewhat nodular, highly argillaceous and noncherty limestones. Above this interval are several prominent marker beds, including the shaly SCHIZOPHORIA bed at the top of the Nedrow that can be traced from the Syracuse region to central PA in the middle portion of the Selinsgrove Limestone, and to the mid-Hudson Valley area in the Onondaga. Age is Middle Devonian (Eifelian) (Brett and Ver Straeten, 1994). Authors informally propose two dominant, widespread facies of the Edgecliff Member of the Onondaga Limestone: the cherty, micritic Clarence facies, formerly known as the Clarence Member of western NY, and a coarse crinoidal, non- to sparsely cherty Jamesville Quarry facies. The Jamesville Quarry is present at the Edgecliff type locality near Syracuse, where it reaches a thickness of about 5.7 m. To the west the Edgecliff thins to a minimum of 2.5 m at Seneca Stone quarry. The only trace of Clarence-like lithology at this location is a distinctive 0.5 m-thick band of cherty calcisiltite 1.8 m above the base of the Edgecliff. Between Seneca Stone quarry and Phelps the Edgecliff thickens and is composed primarily of sparsely fossiliferous calcisiltites with abundant bands of dark gray to black chert, closely resembling the typical western NY Clarence facies. Total thickness of the Edgecliff reaches a maximum of 14 m. Unit underlies calcareous shale-dominated strata and laterally equivalent argillaceous limestones of the Nedrow Member. The Foxtown Member of the Buttermilk Falls Limestone of eastern PA is directly equivalent to the Edgecliff. The basal contact is conformable in parts of eastern NY, but westward becomes unconformable and overlies increasingly older Devonian to Silurian strata. In some parts of west-central to western NY, overlies upper Lower Devonian Tristates Group and elsewhere the Middle Devonian Hamilton Group. This basal unconformity is known as the Wallbridge Unconformity. The Lower-Middle Devonian (Emsian-Eifelian) boundary, long placed at the base of the Onondaga in NY, could lie as high as the base of the Nedrow Member according to Kirchgasser and Oliver (1993), as there are no age diagnostic fossils in the Edgecliff (Brett and Ver Straeten, 1994).|
|Primary rock type||limestone|
|Secondary rock type||chert|
|Other rock types|
Sedimentary > Carbonate > Limestone
Sedimentary > Chemical > Chert
NYS Museum, NYS Geological Survey, NYS Museum Technology Center, 1999, 1:250,000 Bedrock geology of NYS, data is distributed in ARC/INFOr EXPORT format (with ".e00" extension) in 5 seperate files based on printed map sheets, http://www.nysm.nysed.gov/gis.html.
D. W. Fisher; Y. W. Isachsen, L. V. Rickard, 1970, Geologic Map of New York State, consisting of 5 sheets: Niagara, Finger Lakes, Hudson-Mohawk, Adirondack, and Lower Hudson, New York State Museum and Science Service, Map and Chart Series No. 15, scale 1:250000.