Tomstown Dolomite

Tomstown Dolomite
Stratigraphic range: Cambrian
USGS photo 1 mile east of Bakerton, West Virginia
TypeSedimentary
UnderliesRome Group and Waynesboro Formation
OverliesAntietam Formation and Chilhowee Group
Thickness200 - 1000 feet
Lithology
Primarydolomite
OtherChert, limestone, shale
Location
RegionAppalachia, Mid-Atlantic United States, and Southeastern United States
CountryUnited States
ExtentMaryland, Pennsylvania, Virginia,[1] West Virginia

The Tomstown Dolomite or Tomstown Formation is a geologic formation in Maryland, Pennsylvania, Virginia and West Virginia.[2][3][4] It preserves fossils dating to the Cambrian Period.

In Maryland it is described as "Interbedded light gray to yellowish-gray, thin- to thick-bedded dolomite and limestone; some shale layers; gradational contact with Antietam; thickness 200 to 1,000 feet."[2]

In southern Maryland it is divided into four members:[5]

Dargan Member Interbedded and cyclical dolomite and limestone.
Benevola Member Light gray to white, massive to poorly bedded, highly fractured sugary dolomite.
Fort Duncan Member Medium- to dark-gray, thick bedded, mottled dolomite with white, void-filling sparry dolomite.
Bolivar Heights Member Three lithologies from the basal layer of a tan, vuggy dolomite, to a light gray dolomitic marble called the Keedysville bed, to thin- to medium bedded layers of lime mudstone containing burrows.