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Beaverdam Formation (Delmarva)

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Beaverdam Formation
Stratigraphic range: late Pliocene, ~3.6–2.58 Ma
TypeFormation
Unit ofColumbia Group
UnderliesWalston silt (unconformably), Omar Formation (unconformably)
OverliesBethany Formation (possibly unconformably), Manokin Formation (unconformably), St. Mary's Formation (unconformably)
Thickness75-100 feet
Location
RegionDelmarva Peninsula
CountryUnited States
Type section
Named forBeaverdam Creek
Named byW.C. Rasmussen and T.H. Slaughter[1]
Year defined1955
CountryUnited States

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]

The extent of the Beaverdam Formation is recognized from Delmar to the west and to Milford and Georgetown to the northeast.[3]

History

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The 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

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The 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

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References

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  1. ^ 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.
  2. ^ 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.
  3. ^ 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.
  4. ^ 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.
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