|Name||Irondequoit Limestone thru Kodak Sandstone|
|Geologic age||Lower Silurian|
Sedimentary > Clastic > Mudstone > Shale
Sedimentary > Carbonate > Limestone
Sedimentary > Clastic > Sandstone
Sedimentary > Carbonate > Dolostone
Sedimentary > ChemicalWolcott Furnace Hematite, Furnaceville Hematite
Sedimentary > Chemical > Phosphoritepart of Williamson Shale
|Comments||part of the Clinton Group 150-325 ft. (40-100 m). Descriptions from USGS Lexicon website (ref. NY046) and references NY018 and NY032: Revised the Irondequoit Limestone of the Clinton Group by removing the Rockway Dolomite Member (herein raised to formation rank) and its Salmon Creek Phosphate Bed. The Irondequoit consists of thick-bedded to massive, medium greenish-gray to pinkish-gray, buff-weathering, dolomitic, crinoidal- and brachiopod-rich packstone to grainstone. The lower 1 to 2 ft are typically altered to aphanitic dolomite. Upper beds consist of medium-bedded to massive crinoidal limestone. Thin tongues of green shale with small micritic intraclasts are common. Upper beds include small bioherms that are sparsely fossiliferous, pale greenish-gray, non-bedded micrite masses. Brachiopods and rugose corals are common. Thickness is 11.5 to 22.4 feet. Well exposed on Irondequoit Creek in Webster, NY, and in the Genesee River Gorge in Rochester, NY. Unconformably overlies the Rockway Dolomite and conformably underlies the Rochester Shale in western NY, but unconformably underlies the Rochester in Ontario, CAN. Unit extends eastward from Rochester, NY, to the Clinton type area where it laterally grades into the Kirkland Limestone. Extends westward to the Bruce Peninsula region of CAN and grades into the lower part of the Colpoy Bay Member of the Amabel Formation. The Irondequoit is of Early Silurian (earliest Wenlockian) age based on conodonts and ostracodes. [Report uses Early and Late Silurian time scale of Harland and others (1982).] (Brett and others, 1995). The Williamson Shale of the Clinton Group in western NY consists of greenish-gray to black, fissile to platy, graptolite-bearing shale with a thin quartz and phosphate pebble bed at its base (the Second Creek Phosphate Bed). Thickness ranges from a featheredge in Niagara Co. to 78.5 ft at Lakeport, Oneida Co. Unit is well exposed in Browncroft Creek and at the Genesee River Gorge in east Rochester, NY. Unconformably overlies the Merritton Limestone, Reynales Limestone, or Neahga Shale, and unconformably underlies the Rockway Dolomite. Eastward, the Williamson thickens and grades laterally into the Willowvale Shale near Utica, NY; westward, unit thins and pinches out between Lockport and the Niagara River Gorge. The Williamson is of Early Silurian (latest Llandoverian) age. [Report uses Early and Late Silurian time scale of Harland and others (1982).] (Brett and others, 1995). Bear Creek - Greenish gray shales of the Wallington Member of the Reynales Limestone thicken westward, until at Bear Creek, in eastern Wayne Co., the unit has become more than half shale and is referred to as the Bear Creek Shale. The Reynales and Bear Creek are capped by the Sterling Station Bed, a thin oolitic hematite. Overlies the Furnaceville Member of the Reynales and underlies the Sodus Shale (LoDuca and Brett, 1994). Wallington Member of Reynales Limestone consists of about 4.0 to 6.0 m of dolostone, commonly cherty brachiopod/crinoid pack- and grainstone, pelletal grainstone, and greenish gray shale. Base of the Wallington is defined at the base of a phosphate granule-bearing thin grainstone bed that overlies the Seneca Park Bed (new) of the Brewer Dock Member. Similar in lithology to the underlying Brewer Dock Member and can be divided into about six carbonate-to-shale cycles. Uppermost cycle thins eastward and merges into the Sterling Station Hematite of Gillette (1947) that marks the top of the Reynales and equivalent Bear Creek Shale in Wayne and Oswego Cos. Westward from Genesee Gorge, outcrops become infrequent. At Lockport the entire Reynales is assigned to the Hickory Corners Member, though the strata there are equivalent to the Brewer Dock Member and the lower 120 cm of the Wallington. Unconformably(?) underlies the Sodus Shale (LoDuca and Brett, 1994). Furnaceville Member of the Reynales Formation in Wayne Co. can be correlated nearly bed for bed with the Brewer Dock Member of the Reynales to the west. Basal beds correlate with the Budd Road Bed (new) of the Brewer Dock and uppermost beds with the Seneca Park Bed (new) of the Brewer Dock. Unconformably underlies the Bear Creek Shale facies (a correlative of the Wallington Member) and unconformably overlies the Webster Bed (new) (a correlative of the Maplewood and Neahga Shales) (LoDuca and Brett, 1994). Maplewood - As currently defined, the basal formation of the Clinton Group in Monroe Co., NY, is the Maplewood Shale, and in western NY and adjacent Ontario, the Neahga Shale. The base of both formations is marked by the distinctive phosphatic Densmore Creek Bed (new). The Maplewood varies in thickness thinning both east and west of the type section. Formation is absent at Webster, 10 km northeast of Glen Edith where it is 5.0 m thick. The Maplewood underlies the Reynales Limestone, the base of which is marked by the Budd Road Bed, and overlies the Kodak Sandstone or Cambria Shale of the Medina Group. The Maplewood has a sparser fossil assemblage than the correlative Neahga Shale to the west and its Llandoverian B-2 to C-1 age assignment is based for the most part on its physical continuity with the Neahga (LoDuca and Brett, 1994). The Kodak Sandstone of the Medina Group in western NY consists of medium-gray to white, argillaceous, quartzose sandstone. Thickness is 5 to 11 ft. Unit is uppermost formation of Medina Group. Overlies the Cambria Shale of the Medina Group and unconformably underlies the Neahga Shale of the Clinton Group. The Kodak is of Early Silurian (early Llandoverian) age based on ostracodes (Brett and others, 1995).|
Fisher, D.W., Isachsen, Y.W., and Rickard, L.V., 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 1:250,000.
Brett, C.E., Tepper, D.H., Goodman, W.M., LoDuca, S.T. and Eckert, Bea-Yeh, 1995, Revised stratigraphy and correlations of the Niagaran Provincial Series (Medina, Clinton, and Lockport Groups) in the type area of western New York: U.S. Geological Survey Bulletin, 2086, 66 p., Prepared in cooperation with the U.S. Environmental Protection Agency and the University of Rochester, Department of Earth and Environmental Sciences.
LoDuca, S.T. and Brett, C.E., 1994, Revised stratigraphic facies relationships of the lower part of the Clinton Group (middle Llandoverian) of western New York State, IN Landing, Ed, ed., Studies in stratigraphy and paleontology in honor of Donald W. Fisher: New York State Museum Bulletin, no. 481, p.161-182.
USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/
|Counties||Monroe - Wayne|