The Beaverdam Formation is an upper Pliocene geologic formation on the Delmarva Peninsula in southern Delaware and eastern Maryland.[2][3] It is the largest major surficial layer on the Delmarva Peninsula and has a lower stream-deposited unit and an upper estuarine unit. These units may represent a cycle of regression and transgression.[4] The Beaverdam Formation is heterogeneous and ranges from very coarse sand with pebbles to silty clay.[2] It unconformably overlies the Manokin or St. Mary's formations and it is up to 75-100 feet thick.[5]
| Beaverdam Formation | |
|---|---|
| Stratigraphic range: late Pliocene, ~ | |
| Type | Formation |
| Unit of | Columbia Group |
| Underlies | Walston silt (unconformably), Omar Formation (unconformably) |
| Overlies | Bethany Formation (possibly unconformably), Manokin Formation (unconformably), St. Mary's Formation (unconformably) |
| Thickness | 75-100 feet |
| Location | |
| Region | Delmarva Peninsula |
| Country | United States |
| Type section | |
| Named for | Beaverdam Creek |
| Named by | W.C. Rasmussen and T.H. Slaughter[1] |
| Year defined | 1955 |
| Country | United States |
The extent of the Beaverdam Formation is recognized from Delmar to the west and to Milford and Georgetown to the northeast.[3]
History
editThe Beaverdam Formation was originally named the Beaverdam Sand when it was recognized in Wicomico County, Maryland in 1955 by William C. Rasmussen and Turbit H. Slaughter.[1][6] The name comes from Beaverdam Creek, the east branch of the Wicomico River.[1] The Beaverdam Sand was renamed the Beaverdam Formation and given an expanded lithologic definition by Kelvin W. Ramsey and William S. Schenck in 1990.[7][6]
Microflora
editThe lower Beaverdam Formation is characterized by a Quercus-Carya pollen assemblage, very few non-arboreal pollen, and the exotic constituents Pterocarya and Sciadopitys. The upper Beaverdam has a very high non-arboreal pollen concentration, and the sole exotic constituent is Pterocarya. Other significant taxa include Cupuliferoidaepollenites fallax, Tricolporopollenites edmundii, and Tsuga diversifolia-type. The pollen assemblage of the lower Beaverdam is similar to that of the Bethany Formation in Delaware, the Brandywine Formation in Maryland, and the Eastover Formation in Virginia; and the pollen assemblage of the upper Beaverdam is similar to that of the Bacons Castle Formation in Virginia.[3]
| Group | Formation |
|---|---|
| Columbia Group | Omar Formation |
| Beaverdam Formation | |
| Chesapeake Group | Bethany Formation |
| Manokin Formation | |
| St. Mary's Formation | |
| Choptank Formation | |
| Calvert Formation | |
| Lithostratigraphic units of the Chesapeake and Columbia groups in southeastern Sussex County, Delaware.[3] | |
See also
editReferences
edit- ^ a b c Rasmussen, William C.; Slaughter, Turbit H. (1955). "The Ground-Water Resources". The water resources of Somerset, Wicomico, and Worcester Counties (PDF) (Report). Bulletin 16. Maryland Geological Survey. Retrieved 7 June 2018.
- ^ a b Ramsey, Kelvin W. (May 2010). Baxter, Stefanie J. (ed.). GM15 Geologic Map of the Georgetown Quadrangle, Delaware (Map). 1:24,000. Geologic Map Series No. 15. Cartography by Wang, Lillian T. Delaware Geological Survey. § Beaverdam Formation. Retrieved 7 June 2018.
- ^ a b c d Groot, Johan J.; Ramsey, Kelvin W.; Wehmiller, John F. (Feb 1990). RI47 Ages of the Bethany, Beaverdam, and Omar Formations of Southern Delaware (PDF) (Report). Report of Investigations No. 47. Delaware Geological Survey. Retrieved 9 June 2018.
- ^ Means, John (2010). Roadside Geology of Maryland, Delaware, and Washington. Illustrated by Moran, Matthew; Moran, Suzannah. Missoula, MT: Mountain Press Publications. pp. 230–231. ISBN 9780878425709.
- ^ Ramsey, Kelvin W. (Jan 2001). GM11 Geology of the Ellendale and Milton Quadrangles, Delaware (Map). 1:24,000. Geologic Map Series No. 11. Delaware Geological Survey. Retrieved 7 June 2018.
- ^ a b Andres, A. Scott; Ramsey, Kelvin W. (Sep 1996). "Beaverdam Formation". RI53 Geology of the Seaford Area, Delaware (PDF) (Report). Delaware Geological Survey. Retrieved 7 June 2018.
- ^ Ramsey, Kelvin W.; Schenck, William S. (June 1990). Geologic Map of Southern Delaware (Map). 1:100,000. Open File Report No. 32. Delaware Geologic Survey. Retrieved 7 June 2018.