Irondequoit Limestone thru Kodak Sandstone (NYSik;4)

State	New York
Name	Irondequoit Limestone thru Kodak Sandstone
Geologic age	Lower Silurian
Original map label	Sik
Comments	part of the Clinton Group 100-150 ft. (34-45 m). Descriptions from USGS Lexicon website (ref. NY046) and reference NY018: 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 Rockway is raised in rank to the Rockway Dolomite of the Clinton Group in western NY because it can be separated from the Irondequoit Limestone by an unconformity. Consists of medium-gray, pale buff-weathering, thin- to medium-bedded, dolomitic wackestone separated by medium-gray, very thin dolomitic shales. The dolomitic shale interbeds thicken eastward from Niagara Co. In the Niagara region, the Rockway contains a distinctive succession of beds that includes a lower shale-rich zone that grades upward into medium-bedded dolomite, followed by a thick, blocky bed of dolomitic wackestone, overlain by thin to medium beds and a shaly zone, followed by an uppermost dolomicrite bed. Thickness is 12 feet at its type locality and is 6.6 to 9.2 feet in the subsurface of western NY. Well exposed in the Genesee River Gorge in Rochester, NY and in the Niagara River Gorge. Unconformably overlies the Williamson Shale or the Merritton Limestone, both of the Clinton Group, and underlies the Irondequoit Limestone of the Clinton Group by a minor unconformity. Eastward, the Rockway can be traced into the Dawes Formation in Madison Co., NY, and northwestward, it appears to grade laterally into the Lions Head Member of the Amabel Formation near Orangeville, Ont, CAN. The Rockway is of Early Silurian (latest Llandoverian and earliest Wenlockian) age based on conodont fauna (Brett and others, 1995). The Hickory Corners Member of the Reynales Limestone in western NY consists of thin- to medium-bedded, gray to pink, nodular, locally fossiliferous, dolomitic limestone with thin shale partings; chert is common near top. A phosphate horizon, the Budd Road Phosphate Bed, forms the base of the member. Characteristic fossils include brachiopods, crinoid columnals, and bryozoa. The Hickory Corners is the only part of the Reynales Limestone occurring in the Niagara region of NY. Thickness is 0 to 12 ft. Well exposed along railroad tracks south of intersection with Niagara Road immediately west of Lockport, NY, and in Niagara River Gorge south of Artpark, Lewiston, NY. Unconformably overlies the Neahga Shale and unconformably underlies the Merritton Limestone, or where the Merritton is absent, the Second Creek Phosphate Bed of the Williamson Shale. The Hickory Corners is of Early Silurian (Llandoverian) age (Brett and others, 1995). The Neahga Shale of the Clinton Group consists of green to gray, slightly silty, slightly calcareous, soft, and highly fissile shale. Fossils are scarce and consists mainly of linguloid brachiopods. Unit is lowest formation in Clinton Group. The basal bed of the Neahga is the Densmore Creek Phosphate Bed. The Neahga is 2 to 6 ft thick. Unit is well exposed along railroad track north of junction with Niagara Road immediately west of Lockport, NY; roadcut along Budd Road 1.3 mi west of Hickory Corners, NY; and in cliff in east wall of Niagara River gorge about 0.3 miles north of Robert Moses powerplant and 1.4 mi south of Artpark, in Lewiston, NY. Unconformably overlies the various units of the Medina Group (Kodak Sandstone, highest formation) and unconformably underlies the Reynales Limestone. The Neahga is of Early Silurian (Llandoverian) age (Brett and others, 1995). 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).
Primary rock type	sandstone
Secondary rock type	shale
Other rock types	limestone; dolostone (dolomite); chert; phosphate
Lithologic constituents	Major Sedimentary > Clastic > Sandstone Minor Sedimentary > Clastic > Mudstone > Shale Sedimentary > Carbonate > Dolostone Sedimentary > Carbonate > Limestone Incidental Sedimentary > Chemical > Chert Sedimentary > Chemical > Phosphorite
Map references	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. [http://www.nysm.nysed.gov/gis.html.]
Unit references	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. 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. [http://pubs.er.usgs.gov/publication/b2086] USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Monroe - Niagara - Orleans - Wayne