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Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation (MDKp;5)

Geologic Formation in MD, DE

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Lithology

Sand

Silt

Clay

Geologic Age

Cretaceous (145 Ma – 66 Ma ago)

Geologic Unit Label

Potomac Group - Interbedded quartzose gravels; protoquartzitic to orthoquartzitic argillaceous sands; and white, dark gray, and multicolored silts and clays; thickness 0 to 800 feet. Includes Raritan and Patapsco Formations - Gray, brown, and red variegated silts and clays; lenticular, cross-bedded, argillaceous, subrounded sands; minor gravels; thickness 0 to 400 feet; Arundel Clay - Dark gray and maroon lignitic clays; abundant siderite concretions; present only in Baltimore-Washington area; thickness 0 to 100 feet; and Patuxent Formation - White or light gray to orange-brown, moderately sorted, cross-bedded, argillaceous, angular sands and subrounded quartz gravels; silts and clays subordinate, predominantly pale gray; thickness 0 to 250 feet.

— USGS

Taxonomy

Classified As

Geologic Formation