One of the world's most impressive angular unconformities is located just alongside Interstate 70 in Salina Canyon, Sevier County, central Utah, USA (see map).


Angular unconformities are formed by structural tilting of flat-lying sedimentary rocks, followed by erosion, followed by deposition of more flat-lying sedimentary rocks.  The Salina Canyon angular unconformity can't get more angular than it is already.  You've got flat-lying beds atop vertical beds, separated by an erosion surface having small-scale irregular topography.


This angular unconformity is exposed throughout the lower parts of Salina Canyon (Salina Creek valley), east of the town of Salina, on both sides of Interstate 70 (but better seen on the northern side of the highway).  Eastward of the 1st photo shown below, the underlying rocks become less vertical, and eventually have a disconformable relationship with the overlying rocks.


Salina Canyon angular unconformity - reddish vertical beds below the contact are part of the Twist Gulch Formation (Middle Jurassic).  The light-colored horizontal beds above the contact include a thin interval of Flagstaff Formation (mid-Paleocene), the Colton Formation, and the Green River Formation (upper Paleocene to Eocene).



Salina Canyon angular unconformity - reddish vertical beds below are the Twist Gulch Formation (Middle Jurassic) - mainly siltstones, sandstones, and shales.  The whitish horizontal beds above are sandstones of the Flagstaff Formation (mid-Paleocene).  Halite salt casts, a rare sedimentary structure, occur on some of the bedding planes in the Twist Gulch Fm. at this locality.



The structural tilting of the Twist Gulch in Salina Canyon has been attributed to local salt dome tectonics.  Evaporites occurs in the underlying Arapien Formation (Middle Jurassic).  Some of the Arapien's rock salt intervals have domed upward (salt diapirs), resulting in tilting of overlying beds.  The Salina Canyon angular unconformity provides information about the timing of Arapien rock salt diapirism (post-Jurassic & pre-Paleocene - in other words, during the Cretaceous).



For more info. on the geology of this area, see:


Lawton & Willis (1987) - The geology of Salina Canyon, Utah.  in  Rocky Mountain Section of the Geological Society of America.  Geological Society of America Centennial Field Guide 2: 265-268.



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