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Lower Tertiary Deposits (VATl;0)

Geologic Formation in VA, MD

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Lithology

Limestone

Sand

Silt

Geologic Age

Tertiary (66 Ma – 2.58 Ma ago)

Geologic Unit Label

May include the following formation - Brightseat, Aquia, Marlboro, Nanjemoy, and Piney Point (Pamunkey Group), and Old Church. Lower Tertiary deposits (Oligocene, Eocene, and Paleocene). Mostly fine- to coarse-grained glauconitic quartz sand and clay-silt, shelly in part; includes lesser amounts of sandy limestone and limey sand. In outcrop, unit comprises the Pamunkey Group (Brightseat, Aquia, Marlboro, Nanjemoy, and Piney Point Formations) and the Old Church Formation. In subsurface, unit includes Eocene and Oligocene strata not included in the Pamunkey and Old Church. Ages of formational units based on foraminiferal, nannofossil, dinocyst, pollen, and molluscan studies (Frederiksen, 1979; Gibson and others, 1980; Gibson and Bybell, 1984; Edwards, 1984, 1989; Edwards and others, 1984; Poag, 1989; Ward, 1985; Ward and Krafft, 1984). Stratigraphic sections vary widely, comprising one or more of the following formations: Old Church Formation (Ward, 1985) and unnamed glauconitic sands (upper Oligocene). In inner and middle Coastal Plain, unit is 0 to 5 feet of olive-gray, fine- to coarse-grained, shelly, very sparsely glauconitic quartz sand of the Old Church Formation; typical fossils include Anomia ruffini, Lucina sp., and Mercenaria capax. In subsurface of outer Coastal Plain, unit includes about 45 feet of dark-olive-gray to greenish black glauconite sand with lesser amounts of quartz; sand has olive-brown clay-silt matrix. Lower Oligocene beds. Olive-gray to grayish-olive sand, very-fine-grained, clayey and silty, micaceous, glauconitic; coarsens upward to a very-fine- to fine-grained sand. Unit is 0 to 50 feet thick; identified only in subsurface of Eastern Shore area (Exmore, core hole, R. B. Mixon and D. S. Powars, personal communication). Chickahominy Formation (upper Eocene, Cushman and Cederstrom, 1945). Predominantly olive-gray clayey silt and silty clay, very compact, glauconitic, micaceous, contains abundant finely crystalline iron sulfide. Coarsens downward to a very-fine- to fine-grained sand, pebbles at base. Rare fragmental shell, microfossils very abundant. Thickness is 0 to 100 feet; present in subsurface of southeastern Virginia. Piney Point Formation (middle Eocene, Otton, 1955). Olive-gray and grayish-olive-green, glauconitic quartz sand, medium-to coarse-grained, poorly sorted, contains scattered quartz pebbles, interbedded with carbonate-cemented sand and moldic limestone. Unit is characterized by large, calcitic shells of the oyster Cubitostrea sellaeformis, a middle Eocene marker. Aragonitic mollusks are generally leached, leaving only molds and casts. Thickness is 0 to 60 feet. Nanjemoy Formation (lower Eocene, Clark and Martin,1901). Dark-olive-gray, greenish-gray, and olive-black glauconitic quartz sand, fine- to coarse-grained, very clayey and silty, intensely burrowed, sparsely to abundantly shelly, interbedded with sandy clay-silt. Sand in upper part of unit is less clayey, very micaceous, and contains scattered quartz pebbles. Typical mollusks include Venericardia potapacoensis, Venericardia ascia, and Macrocallista subimpressa. Unit is 0 to 140 feet thick. Marlboro Clay (lower Eocene (?) and upper Paleocene, Clark and Martin, 1901). Light-gray, pinkish-gray, and reddish- brown kaolinitic clay, massively bedded to laminated, interbedded with lesser amounts of laminated and ripple cross-laminated silt and very-fine-grained sand. Contains rare molds of small mollusks and arenaceous foraminifera. Thickness is 0 to 30 feet. Aquia Formation (upper Paleocene, Clark and Martin, 1901). Light- to dark-olive gray, glauconitic quartz sand, fine- to coarse-grained, clayey and silty, thick- to massively bedded, sparsely to abundantly shelly. Lower part of unit is more poorly sorted and more calcarious than upper part and contains a few thin to medium beds of olive-gray, white, and pale greenish-yellow limestone. Upper part of unit is moderately well sorted and characterized by thin beds of the large, high-spired gastropod Turritella mortoni. Other common mollusks in clude Cucullaea gigantea, Ostrea sinuosa, and Crassatellites alaeformis. Thickness is 0 to 130 feet. Brightseat Formation (lower Paleocene, Bennett and Collins, 1952). Olive-gray to olive-black, micaceous quartz sand, fine- to very fine-grained, clayey and silty, variably glauconitic. Thickness is 0 to 20 feet.

— USGS