Lockport Group

Lockport Group
Stratigraphic range: Sheinwoodian-Homerian ~
Type	Group
Unit of	Cayugan Series
Sub-units	Guelph Formation Eramosa Formation Goat Island Formation Gasport Formation
Underlies	Vernon Formation
Overlies	Clinton Group
Lithology
Primary	Dolomite
Other	Limestone, Chert
Location
Region	New York, Ohio, Pennsylvania, West Virginia, Ontario
Country	United States, Canada
Extent	Appalachian Basin, Michigan Basin

The Lockport Group is a geologic group in the Appalachian Basin and Michigan Basin in the northeastern United States and Canada. This unit makes up the Niagara Escarpment. Its most famous feature is Niagara Falls. The unit outcrops in New York, Ontario, Michigan, Wisconsin, and Illinois.

Description

The Lockport Group is made up of four formations. From base to top: Gasport Formation, Goat Island Formation, Eramosa Formation and Guelph Formation. The entire unit is composed of dolomite, with the exception of the Gasport which can be limestone, as well as occasional chert nodules.

Stratigraphy

The Guelph Formation is at the top of the Lockport Group. It has been called the "Vernon Transition Zone" due to thin beds and laminations between carbonates, claystones and evaporates. Its base is delimited by a stromatolite bed.

Below the Guelph is the Eramosa Formation. This formation is typically a thinly laminated packstone and grainstone. There are stromatolite beds as well as corals preserved in this formation. Near the base the unit becomes vuggy. Again the top of this formation is marked by a sharp change between grainstone and a stromatolite bed.