- Usage in publication:
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- Portuguese tuff bed*
- Modifications:
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- Named
- Dominant lithology:
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- Tuff
- AAPG geologic province:
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- Los Angeles basin
Summary:
Named for Portuguese Bend on S coast, Palos Verdes Hills, CA. Type region [area]: along Portuguese Canyon [San Pedro 7.5' quad, Los Angeles Co, CA]. Is bentonitic tuff bed at top of lower part of Altamira shale member of Monterey Shale in Palos Verdes Hills. Is 55 ft thick. Is middle Miocene age based on Foraminifera in lower part of Altamira shale member.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
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- Portuguese tuff bed*
- Modifications:
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- Overview
- AAPG geologic province:
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- Los Angeles basin
Summary:
Type region [area] redesignated as Klondike Canyon, near Portuguese Bend [San Pedro 7.5' quad, Los Angeles Co, CA] because in Woodring and others (1936) erroneously cited in Portuguese Canyon. Portuguese tuff bed consists of light-colored bentonitic tuff, 55 ft thick in type region. Included at top in measured section of lower part of Altamira shale member of Monterey shale in unnamed canyon .25 mi E of Portuguese Canyon. At Inspiration Point is about 60 ft thick. Probably acted as lubricant for mass of rocks that slid down structural basin and moving seaward overriding lower marine terraces. Shown on map as middle Miocene age.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
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- Portuguese Tuff Bed*
- Modifications:
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- Geochronologic dating
- AAPG geologic province:
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- Los Angeles basin
Summary:
Sample of bentonite containing plagioclase and minor quartz collected on W wall of Klondike Canyon at 325 ft elevation from Portuguese Tuff Bed yielded K-Ar age of 14.5 +/-1.1 Ma on plagioclase.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
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- Portuguese Tuff Bed*
- Modifications:
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- Geochronologic dating
- AAPG geologic province:
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- Los Angeles basin
Summary:
Portuguese Tuff Bed in Altamira Shale Member of Monterey Formation dated by Turner (1970) at 14.9 +/-1.1 Ma is close to Relizian-Luisian boundary. [All K-Ar ages have been calculated using decay constants recommended by Steiger and Jager (1977).]
Source: GNU records (USGS DDS-6; Menlo 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 ([ ]).