Stratigraphic test well, Nantucket Island, Massachusetts
The U.S. Geological Survey, in cooperation with the Massachusetts Water Resources Commission and the Nantucket Conservation Foundation, continuously cored 514 m of sediment and volcanic rock in a stratigraphic and water-quality test near the geographic center of Nantucket Island. Stratified sediments were divided texturally into three zones: the upper zone (0-128 m) contains mostly coarse sand and gravel; the middle zone (128-349 m) contains mostly silty clay and a few beds of sand and silt; and the lower zone (349-457 m) contains soft, unconsolidated, clayey sand. Below the lower zone, a saprolite, composed mostly of clay, grades abruptly downward at 470 m into partially altered basalt that extends to the bottom of the hole at 514 m. Calculations based on the Ghyben-Herzberg principle predicted a zone of freshwater 120-150 m thick. This principle is the theory of hydrostatic equilibrium between freshwater and more dense seawater in a coastal aquifer; it states that for each meter of ground-water elevation above sea level, the freshwater lens will depress the saltwater interface about 40 m below sea level. Freshwater or low-salinity brackish water was found in sediments far below the depth predicted by the Ghyben-Herzberg principle. These interstitial waters are probably relict ground water emplaced during times of low sea level during the Pleistocene. (Woodard-USGS)
Citation Information
Publication Year | 1978 |
---|---|
Title | Stratigraphic test well, Nantucket Island, Massachusetts |
DOI | 10.3133/cir773 |
Authors | David W. Folger, J.C. Hathaway, R. A. Christopher, P. C. Valentine, C. W. Poag |
Publication Type | Report |
Publication Subtype | USGS Numbered Series |
Series Title | Circular |
Series Number | 773 |
Index ID | cir773 |
Record Source | USGS Publications Warehouse |