Tully Formation

The Tully Formation is a geologic unit in the Appalachian Basin. The Tully was deposited as a carbonate rich mud, in a shallow sea at the end of the Middle Devonian.^[1] Outcrops for the Tully are found in New York State and Pennsylvania.^[2] It is also found subsurface in western Maryland and northern West Virginia. A number of fossil remains from marine organisms may be found in Tully outcrops.

Tully Formation
Stratigraphic range: Devonian
Tully Formation at Taughannock Falls State Park
Type	Formation
Sub-units	New York New Lisbon Member Laurens Member West Brook Member Pennsylvania Weissport Member Brodhead Creek Member Lehighton Member
Underlies	Harrell Shale/Genesee Group
Overlies	Hamilton Group
Lithology
Primary	Limestone
Other	Shale, Siltstone, and Sandstone
Location
Region	Maryland  New York  Pennsylvania  West Virginia
Country	United States Canada
Type section
Named for	Tully, NY
Named by	Vanuxem (1839)

Description

The Tully is primary made up of limestone. There there are also layers with much higher clay contend resulting in a calcareous shale. To the east the Tully becomes siliciclastic. This is due to sediments being washed in from the Acadian Mountains to the east. By the time the Tully was being deposited the Appalachian Basin had been nearly filled in that the Tully was deposited on a broad planform of rock.^[3] The Tully ranges in thickness to less than 1' in western New York to 70'+ thick in central Pennsylvania and 90'+ thick in southwestern Pennsylvania and northern West Virginia.

Fossils

Brachiopods

Tullypothyridina, Camarotoechia Mesocostale, Rhyssochonetes, Emanuella, Pseudoatrypa, Spinatrypa, Tylothyris, Mucrospirifer tulliensis, Cyrtina, Tullypothyridina, Echinocoelia, Strophodonta