Decew Dolostone and Rochester Shale

Decew Dolostone and Rochester Shale
State New York
Name Decew Dolostone and Rochester Shale
Geologic age Lower Silurian
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Shale
Minor
Sedimentary > Carbonate > Dolostone
Sedimentary > Clastic > Mudstone > Shale > Black-shaleRochester Shale
Incidental
Sedimentary > Clastic > Sandstone > Arenite > CalcareniteRochester Shale
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).
References
NGMDB product
Counties Monroe - Niagara - Orleans