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NGMDB
Geologic Unit: Walloomsac
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Map showing publication footprint
  • Usage in publication:
    • Walloomsac Formation*
  • Modifications:
    • Age modified
    • Biostratigraphic dating
  • AAPG geologic province:
    • New England province
Publication: Summary:

Basal limestone of Walloomsac contains pelmatozoans, bryozoans, algae remains, and conodonts. Conodonts exposed at No Bottom Pond indicate a Middle Ordovician or slightly younger age (according to J. Huddleston, USGS). Age of whole unit is Middle and Late(?) Ordovician.

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

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Walloomsac Formation*
  • Modifications:
    • Isotopic dating
  • AAPG geologic province:
    • New England province
Publication: Summary:

Pg. 15, geologic time scale (inside front cover). Walloomsac Formation (Middle Ordovician). Sample from staurolite-garnet schist, at Lat. 41 deg. 59 min. 45 sec. N., Long. 73 deg. 25 min. 00 sec. W., Sharon quadrangle, Litchfield County, Connecticut, yielded a Rb-Sr age of 368 +/-19 Ma (biotite). Age recalculated, using decay constants of Steiger and Jager (1977, Earth Planet. Sci. Letters, v. 36, p. 359-362), from Zen and Hartshorn's (1966) published age of 355 Ma for this sample. Zartman and others (1970) reported a K-Ar age of 390 Ma (muscovite). Initial age of schist (Middle Ordovician) disturbed by later metamorphism [Devonian].

Source: Publication.

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Walloomsac Formation*
  • Modifications:
    • Overview
  • AAPG geologic province:
    • New England province
Publication: Summary:

Used as Walloomsac Formation of Middle Ordovician age. Mapped as one main unit and three informal, unnamed subunits. Subunit consisting of tan to dark-blue laminated quartzite and calcareous quartzite was previously mapped by other workers as Bellowspipe Quartzite [name not used on this map].

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

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Walloomsac Formation*
  • Modifications:
    • Revised
    • Areal extent
Publication: Summary:

In this map area, Manhattan Schist member A is replaced by Walloomsac Formation based on work by Jackson and Hall (1982), Hall (in press), and A.A. Drake (1990., pers. commun.).

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

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Walloomsac Formation*
  • Modifications:
    • Age modified
    • Biostratigraphic dating
  • AAPG geologic province:
    • New England province
Publication: Summary:

Thin limestone unit near base of Walloomsac locally contains abundant bryozoan fragments, cup corals, pelmatozoan hash, and conodonts that indicate that the base of the Walloomsac is Rocklandian (middle and late Caradocian) or younger. Age of unit is Middle Ordovician.

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

NGMDB
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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 ([ ]).

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