| Tomstown Dolomite | |
| Type: | Sedimentary |
| Age: | Cambrian |
| Period: | Cambrian |
| Prilithology: | dolomite |
| Otherlithology: | Chert, limestone, shale |
| Region: | Appalachia, Mid-Atlantic United States, and Southeastern United States |
| Country: | United States |
| Underlies: | Rome Group and Waynesboro Formation |
| Overlies: | Antietam Formation and Chilhowee Group |
| Thickness: | 200 - 1000 feet |
| Extent: | Maryland, 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.