GYPSUM  PLAIN

 

The Gypsum Plain occurs between the Delaware Mountains and the Rustler Hills of West Texas and adjacent New Mexico, USA.  It principally consists of gently rolling hills of rock gypsum (originally rock anhydrite).  A world-class locality for seeing rocks of the Gypsum Plain is State Line outcrop, on the New Mexico-Texas border.

 

State Line outcrop exposes banded gypsum-calcite rocks of the Castile Formation, deposited during the latest Permian (251 m.y.).  The gypsum component was originally anhydrite (CaSO4), which has been altered by hydration.  The rocks here were formed in a paleoequatorial marine evaporitic setting.  They have since been deformed by anhydrite-to-gypsum volume expansion and regional orogenesis.  The rocks are pervasively microfolded, resulting in an attractive contorted appearance.

 

Locality: State Line outcrop, roadcut on either side of Rt. 180/Rt. 62, between Carlsbad Caverns National Park and Guadalupe Mountains National Park, immediately north of the Texas border, southern Eddy County, southeastern New Mexico, USA.  GPS of cut: 32 00.570 N, 104 29.917 W.

 

State Line outcrop, along Rt. 180/Rt. 62 at the New Mexico-Texas border.  The mountain range is the distance is the main scenery of Guadalupe Mountains National Park (western Texas).  Looking WSW.

 


 

State Line outcrop - banded gypsum-calcite rocks of the Castile Formation (uppermost Upper Permian, 251 m.y.).

 


 

State Line outcrop - banded gypsum-calcite rocks of the Castile Formation (uppermost Upper Permian, 251 m.y.).  The whitish layers are gypsum.  The dark brown layers are calcite.  Each gypsum-calcite couplet represents one year's worth of deposition.  These layers can be called varves.  The calcite-gypsum (or -anhydrite) couplets have been successfully correlated throughout the Delaware Basin.  Note the microfolding and the many small-scale reverse faults.

 


 

State Line outcrop - banded gypsum-calcite rock of the Castile Formation (upper Upper Permian, 251 m.y.) showing convoluted crumpling and microfolding, plus small-scale faults (normal & reverse).

 


 

State Line outcrop - microfolding and small-scale normal & reverse faults in banded gypsum-calcite rocks of the Castile Formation (upper Upper Permian, 251 m.y.).

 


 

State Line outcrop - microfolding and small-scale reverse faults in banded gypsum-calcite rocks of the Castile Formation (upper Upper Permian, 251 m.y.).

 


 

State Line outcrop - convoluted folding in banded gypsum-calcite rock of the Castile Formation (upper Upper Permian, 251 m.y.).

 


 

State Line outcrop - microfolding in banded gypsum-calcite rocks of the Castile Formation (upper Upper Permian, 251 m.y.).  Such patterns are thought to have inspired the decorations seen on some southwestern American Indian pottery (see below).

 

Flagstaff-style Indian pottery from Arizona, USA, dating to the 12th century A.D. (FMNH 707.81976, Field Museum of Natural History, Chicago, Illinois, USA).

 


 

State Line outcrop - nodular gypsum (irregular whitish masses above geology hammer) within banded gypsum-calcite rocks of the Castile Formation (upper Upper Permian, 251 m.y.).

 


 

Info. mostly synthesized from:

 

Anderson & Kirkland (1987) - Banded Castile evaporites, Delaware Basin, New Mexico.  Rocky Mountain Section of the Geological Society of America, Centennial Field Guide 2: 455-458.

 


 

 

Home page