Genesee Formation

The Genesee Formation (Group) is a geologic formation in New York. It is equivalent the Harrell Shale in Pennsylvania. It dates back to the Upper Devonian period. It is the basal unit of the Frasnian and Upper Devonian period. The Genesee Formation was defined by de Witt and Colton, 1959 as all strata between the Middlesex Unit of the Sonyea Group and the Tully Formation, where present or the Moscow Formation where the Tully is not present.

The Genesee includes several members. Moving westward towards the Findley and Cincinnati Archs the formation thins to less than 9 feet. To the east it feathers in with coarser grained formations.

The Genesee has several members. With coarser clastic material coming mostly from the east there are several members that are feathered to the West River and Penn Yann on the eastern flanks.

Below are listed the units found within the Genesee.

Clarke and Luther (1904, p. 28) coined the name for the West River. Later, de Witt and Colton, 1959, assigned it to the Genesee formation. The West River is one of the most expansive members of the Genesee making it as far south as West Virginia.

The West River is composed chiefly of shale and mudrocks. The color is usually medium to dark gray. As with most members the grain size increases moving eastward, making the formation silty in the east. Thin beds may be grey black and contain some iron staining.

The Genundewa is a 12' - 15' limestone bed found at the base of the West River Shale. Originally defined by Clarke (1903), this unit was reevaluated by de Witt and Colton, 1959 and defined at just the singular bed. Other limestone noted previously was found to be micro-concretions with in the Penn Yan.

The Genundewa's lithology is made up of calcareous shale and mud supported limestones. Some beds are made up of a large number up to 70% shells from Styliolina fissurella. The color tends to be darker, grey black to brownish black.