Geologic units in Virginia Beach City, Virginia

Tabb Formation; Lynnhaven Member (Quaternary) at surface, covers 46 % of this area

Lynnhaven Member (Johnson, 1976). Pebbly and cobbly, fine to coarse gray sand grades upward into clayey and silty fine sand and sandy silt; locally, at base of unit, medium to coarse cross-bedded sand and clayey silt containing abundant plant material fill channels cut into underlying stratigraphic units. Unit is surficial deposit of broad swale that is traceable southward from Norfolk; extensive low lands bounded on landward side by river-, bay-, and ocean-facing scarps having toe altitudes of 15 to 18 feet. Thickness is 0 to 20 feet.

Marsh and Intertidal Mud Deposits (Quaternary) at surface, covers 20 % of this area

Medium to dark-gray soft mud, and grayish-brown peat, comprising sediment of marshes in coastal areas and Chesapeake Bay; thickness is 0 to 10 feet. Also, sandy mud and muddy fine sand, light- to dark-gray. Locally, contains abundant shell material characterized by Crassostrea virginica and Mercenaria mercenaria. Comprises sediments of shallow bays and flats in area of Atlantic coastal lagoons of the Eastern Shore.

Tabb Formation; Poquoson Member (Quaternary) at surface, covers 16 % of this area

Poquoson Member (Johnson, 1976). Medium to coarse, pebbly sand grades upward into clayey fine sand and silt, light- to medium-gray; underlies ridge and swale topography (altitude ranges from sea level to 11 feet) along the margin of Chesapeake Bay and in the lower and middle parts of Coastal Plain rivers. Thickness is 0 to 15 feet.

Tabb Formation; Sedgefield Member (Quaternary) at surface, covers 11 % of this area

Sedgefield Member (Johnson, 1976). Pebbly to bouldery, clayey sand and fine to medium, shelly sand that grades upward into sandy and clayey silt; locally channel fill at base of unit includes as much as 50 feet of fine to coarse, cross-bedded sand and clayey silt and peat containing in-situ tree stumps. Sandy bay facies commonly contains Crassostrea biostromes, Mercenaria, Anadara, Polynices, Ensis, and other mollusks. Specimens of the coral Astrangia have yielded estimated uranium-series ages averaging 71,000 ± 7,000 yrs B.P. (Mixon and others, 1982). Unit constitutes surficial deposit to river and coast-parallel plains (altitude 20-30 feet) bounded on landward side by Suffolk and Harpersville scarps. Thickness is 0 to 50 feet.

Beach Sand and Dune Sand Deposits (Quaternary) at surface, covers 7 % of this area

Pale-gray to light-yellowish gray, fine to coarse, poorly sorted to well-sorted, shelly in part; contains angular to rounded fragments and whole valves of mollusks. Comprises deposits of coastal barrier islands and narrow beach dune ridges bordering brackish-water marshes of Chesapeake Bay. Thickness is as much as 40 feet.

Swamp Deposits (Quaternary) at surface, covers 0.9 % of this area

Peat, mud, and sand.

Surficial Deposits, Undivided (Quaternary) at surface, covers < 0.1 % of this area

Sand, clay, gravel, and peat deposited in marine, fluvial, eolian, and lacustrine environments. Quaternary deposits not shown at altitudes greater than approx. 205 feet above mean sea level (Suffolk Scarp, in part).