Beaverdam Formation | |
---|---|
Stratigraphic range: late Pliocene, ~3.6–2.58 Ma | |
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 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]
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]
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 |
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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] |