The Geology of Delaware

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Columbia Formation

Qcl
Geologic Time Period: 
lower Pleistocene
Coastal Plain - Primarily Surficial Unit

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Yellowish- to reddish-brown, fine to coarse, feldspathic quartz sand with varying amounts of gravel. Typically cross-bedded with cross-sets ranging from a few inches to over three feet in thickness. Scattered beds of tan to reddish-gray clayey silt are common. In places, the upper 5 to 25 feet consists of grayish- to reddish-brown silt to very fine sand overlying medium to coarse sand. Near the base, clasts of cobble to small boulder size have been found in a gravel bed ranging from a few inches to three feet thick. Gravel fraction primarily quartz with lesser amounts of chert. Clasts of sandstone, siltstone and shale from the Valley and Ridge, and pegmatite, micaceous schist, and amphibolite from the Piedmont are also present. Fills a topographically irregular surface, is less than 50 feet thick, and is interpreted to be primarily a body of fluvial glacial outwash sediment (Jordan, 1964; Ramsey, 1997). Pollen indicate deposition in a cold climate during the middle Pleistocene (Groot and Jordan, 1999). Ramsey (2010) considered the Columbia to be lower Pleistocene.

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Yellowish- to reddish-brown, fine to coarse, feldspathic quartz sand with varying amounts of gravel. Typically cross-bedded with cross-sets ranging from a few inches to over three ft in thickness. Scattered beds of tan to reddish-gray clayey silt common. In places, the upper 5 to 25 ft a grayish- to reddish-brown silt to very fine sand overlying medium to coarse sand. Near base of unit, clasts of cobble to small boulder size found in gravel bed ranging from a few inches to three ft thick. Gravel fraction consists primarily of quartz with lesser amounts of chert. Clasts of sandstone, siltstone, and shale from the Valley and Ridge Province, and pegmatite, micaceous schist, and amphibolite from the Piedmont are present. The Columbia fills an eroded surface and ranges from less than 10 ft thick to over 100 ft. Primarily a body of glacial outwash sediment (Jordan, 1964; Ramsey, 1997). Pollen indicate deposition in a cold climate during middle Pleistocene (Groot and Jordan, 1999).

Reference(s): 

Groot, J.J., and Jordan, R.R., 1999, The Pliocene and Quaternary deposits of Delaware: palynology, ages, and paleoenvironments: Delaware Geological Survey Report of Investigations No. 58, 19 p.

Jordan, R.R., 1964, The Columbia sediments of Delaware: Delaware Geological Survey Bulletin No. 12, 69 p.

Ramsey, K.W., 1997, Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55, 40 p.

Ramsey, K.W., 2010, Stratigraphy, correlation, and depositional environments of the middle to late Pleistocene interglacial deposits of southern Delaware: Delaware Geological Survey Report of Investigations No. 76, 43 p.