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National Geologic Map Database
Map showing publication footprint
  • Usage in publication:
    • Islesboro Formation*
  • Modifications:
    • Age modified
  • AAPG geologic province:
    • New England province
Publication:

Rankin, D.W. (editor), Chiarenzelli, J.R., Drake, A.A., Jr., Goldsmith, Richard, Hall, L.M., Hinze, W.J., Isachsen, Y.W., Lidiak, E.G., McLelland, James, Mosher, Sharon, Ratcliffe, N.M., Secor, D.T., Jr., and Whitney, P.R., 1993, Proterozoic rocks east and southeast of the Grenville Front, IN Reed, J.C., Jr., and others, eds., Precambrian; conterminous U.S.: Geological Society of America, The Geology of North America, The Decade of North American Geology (DNAG), v. C-2, p. 335-461.


Summary:

Islesboro Formation is of Late Proterozoic age. Consists of interbedded pelite, siltstone and sandstone, limestone and dolomite, conglomerate, rhyolite, and basalt. D.B. Stewart (1990, oral commun.) considers Islesboro to be distal facies of North Haven Greenstone, Ellsworth Schist and schist at Columbia Falls (eastern coastal ME).

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Islesboro Formation*
  • Modifications:
    • Revised
    • Age modified
  • AAPG geologic province:
    • New England province
Publication:

Stewart, D.B., and Tucker, R.D., 1999, Geology of northern Penobscot Bay, Maine; with contributions to geochronology: U.S. Geological Survey Miscellaneous Investigations Series Map, I-2551, scale 1:62,500


Summary:

Age of Islesboro Formation changed to Late Proterozoic(?) and Ordovician(?). Some carbonate rocks previously designated as Coombs Limestone Member are reassigned to Seven Hundred Acre Island Formation (new name). Because the carbonate sequences within Islesboro Formation have different stratigraphic positions, variable thickness and lithology along strike, and may resemble each other locally, continued regional use of the name Coombs Limestone Member is unwarranted.

Source: GNU records (USGS DDS-6; Reston GNULEX).


For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).