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National Geologic Map Database
Geologic Unit: Blacho
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  • Usage in publication:
    • Blacho Tuff Member*
  • Modifications:
    • Named
  • Dominant lithology:
    • Tuff
    • Conglomerate
  • AAPG geologic province:
    • Caribbean region
Publication:

Berryhill, H.L., Jr., 1965, Geology of the Ciales quadrangle, Puerto Rico: U.S. Geological Survey Bulletin, 1184, 116 p.


Summary:

The Blacho Tuff Member of the Pozas Formation, here named, consists of a sequence of reddish lenticular ash-flow deposits and interbedded fluvial conglomerate, lapillistone, reworked tuff, and volcanic breccia. Base of the unit is not exposed, overlies Minguillo Lava Member of the Pozas north of Quebrada Manicaboa and the Manicaboa Formation south of Quebrada Manicaboa. Conformably underlies the informal upper breccia member of the Pozas. Thickness is 500 m. Age is Late Cretaceous (Maastrichtian) based on rudistids in similar rocks.

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