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National Geologic Map Database

Geologic Unit: Walnut

Usage:

Walnut Clay of Fredericksburg Group (AR*,OK*,TX*, and LA*-subsurface)
Walnut Formation of Fredericksburg Group (NM,TX*)
Walnut Marl of Fredericksburg Group (OK,TX)
Walnut Member of Goodland Limestone of Fredericksburg Group (recognized locally in northeast TX* and southeast OK)


Subunits:

(alphabetical): Bee Cave Member, Cedar Park Member, Keys Valley Marl Member.


Geologic age:

late Early Cretaceous (Albian)*


Type section, locality, area and/or origin of name:

Not designated. Named from their characteristic occurrence at Walnut [Walnut Springs], Bosque Co., TX (Hill, 1891).


AAPG geologic province:

Ouachita folded belt*
Arkla basin*
East Texas basin*
Strawn basin*
Llano uplift*
Kerr basin*
Permian basin*
South Oklahoma folded belt*
Fort Worth syncline*


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 ([ ]).