Mineral Resources On-Line Spatial Data
Mineral Resources > Online Spatial Data > Geology > by state > New York
|Geologic age||Lower Silurian|
|Original map label||Scl|
|Comments||part of the Clinton Group 100-150 ft. (34-45 m). Descriptions from USGS Lexicon website (ref. NY046) and reference NY018: The DeCew Dolomite, the uppermost formation of the Clinton Group, in western NY consists of variably bedded, dark-gray to olive-gray, argillaceous to sandy, fine-grained dolomite that locally contains shaly partings and interbeds. A middle bed of up to 3 ft thick is present in the southern Niagara River Gorge. Unit weathers to a distinctive light olive gray. Its most distinctive feature is soft-sediment deformation features that include flame structures and overturned and isoclinal folds. Thickness is 8 to 12 ft. Well exposed at Lockport Junction Road (Rte 429) west of Lockport, NY. Conformably overlies the Rochester Shale in most areas, but is unconformable at the southern end of the Niagara River Gorge; unconformably underlies the Gasport Dolomite. The DeCew is of Early Silurian (middle Wenlockian) age based on conodonts. [Report uses Early-Late Silurian boundary of Harland and others (1982) between the Wenlockian and the Ludlovian.] (Brett and others, 1995). The Rochester Shale of the Clinton Group in western NY consists of medium-dark gray to black calcareous mudstone with thin interbeds of calcareous to dolomitic calcisiltite (pelletal grainstone) and calcarenite (fossil packstone and grainstone). Unit has been divided into (ascending) the Lewiston and Burleigh Hill Members with the division occurring at the top of a series of skeletal packstones to grainstones that are typically rich in bryozoans and brachiopod shell fragments. Thickness in western NY is 58 to 65 feet. Well exposed in cliffs of Niagara River Gorge near Lewiston, NY. Conformably overlies the Irondequoit Limestone and underlies the DeCew Dolomite. The Rochester is of Early Silurian (early and middle Wenlockian) age. [Report follows Early and Late Silurian time scale of Harland and others (1982). Division between Early and Late falls at the Wenlockian-Ludlovian boundary.] (Brett and others, 1995). 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 (Brett and others, 1995).|
|Primary rock type||black shale|
|Secondary rock type||limestone|
|Other rock types||dolostone (dolomite); shale|
Sedimentary > Clastic > Mudstone > Shale > Black-shaleRochester Shale
Sedimentary > Clastic > Mudstone > Shale
Sedimentary > Carbonate > Limestone
Sedimentary > Carbonate > Dolostone
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.
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