- Usage in publication:
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- Indian Run Formation*
- Modifications:
-
- Named
- Dominant lithology:
-
- Schist
- AAPG geologic province:
-
- Piedmont-Blue Ridge province
Summary:
The Indian Run Formation, here named, was previously mapped as the Sykesville Formation in VA. It is a sedimentary melange with a matrix of quartz-plagioclase-muscovite-biotite-chlorite-garnet containing abundant olistoliths of Accotink Schist and Lake Barcroft Metasandstone of the Annandale Group. It is a precursory melange unit believed to have been emplaced by subaqueous sliding, but its base is not exposed and the unit serving as the slide surface is not known. It tectonically underlies the Annandale Group on the Red Fox thrust fault; it is intruded by the Occoquan Granite. Age is Late Proterozoic or Cambrian based on isotopic ages from the Occoquan Granite.
Source: GNU records (USGS DDS-6; Reston GNULEX).
- Usage in publication:
-
- Indian Run Formation*
- Modifications:
-
- Age modified
- AAPG geologic province:
-
- Piedmont-Blue Ridge province
Summary:
Age of Indian Run Formation changed from Late Proterozoic or Cambrian to Late Proterozoic and (or) Early Cambrian.
Source: GNU records (USGS DDS-6; Reston GNULEX).
- Usage in publication:
-
- Indian Run Formation*
- Modifications:
-
- Overview
- AAPG geologic province:
-
- Piedmont-Blue Ridge province
Summary:
Annandale Group is older than Indian Run Formation because Indian Run contains olistoliths of Annandale Group rocks. Annandale Group underwent major deformation before emplacement of Falls Church Intrusive Suite (revised) (Drake and Froelich, 1986; Drake, 1987). Age is Late Proterozoic and (or) Early Cambrian.
Source: GNU records (USGS DDS-6; Reston GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"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 conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).