South Wales Formation (Pepper and deWitt, 1951):

Type Locality: Cazenovia Creek, 3 mi. south of South Wales, NY

Equivalent Names: none

Thickness: 16.4 m (~53.8 ft)

Lithology: The South Wales Formation is characterized by interbedded gray shales, siltstones and thin sandstones with uncommon thin, black shales and siltstones; calcareous concretions occur sporadically.  The lower contact with the Dunkirk Formation is gradational.  The working definition of the contact to the west was the base of the lowest thick sandstone (Jacobi et al., 1994) In the present study area major element geochemistry (Bechtel et al., 1996) shows a break at the lowest, thick (60+ cm), fine-grained sandstone with load casts.  The upper contact with the Mills-Mills Formation is sharp, with thick cross-bedded sandstones of the Mills-Mills Formation overlying very thin, planar bedded silty-shales and thin sandstones of the South Wales Formation.  The South Wales Formation sandstones are micaeous and become slightly calcareous toward the top of the section.  The sandstones are typically rippled with 3-D linguoid ripples and HCS common.  The South Wales Formation becomes sandier towards the top, although the thickest sandstone bed is the basal contact sandstone.

Ichnology: The basal sandstone of the South Wales Formation contains vertical burrows that we interpret to be escape-structures due to the isolated occurrence of the vertical burrows in this single sandstone bed.  The trace fossil assemblage for the rest of the formation is typical Cruziana ichnofacies.

Depositional Environment: The interbedded gray shales and thin sandstones are interpreted to represent deposits in the lower to upper offshore environment.  The South Wales Formation represents a shallowing from the Dunkirk Formation as evidenced by the abundance of HCS, and the change in lithology from black shales to gray shales.  The South Wales Formation contains few fossils or trace fossils; however, the contact between the Dunkirk Formation and the South Wales Formation is marked by a thick (approximately 60 centimeters), fine-grained sandstone that has load casts and vertical worm burrows.  These vertical worm burrows are likely to represent escape burrows of fauna carried in the turbidity flow.  Studies of the South Wales Formation northwest of Allegany County (Gutmann and Jacobi, 1988; Jacobi et al., 1994) have suggested that the siltstones were turbidite lobe-fringe sand deposits.

South Wales Formation

Close up of the South Wales Fm. basal sandstone at a small tributary along the east side of the Genesee River.

Climbing ripples are exhibited at this location. Ruler is 60cm.

South Wales Fm.-Mills-Mills Fm. contact at Wiscoy Creek at Mills-Mills Falls.

The contact is the base of the caprock at the top of the falls.