GPS Location:

38^o 19.342' N

111^o 20.263' W

 

Ages:

Triassic

 

Rock Units:

Shinarump Conglomerate Member (Chinle Formation)

Moenkopi Formation

 

Features Present:

In the Moenkopi Formation, many varieties of ripples along bedding planes and in cross-sectional view are present in loose rock slabs around the Twin rocks. Above the contact of the Moenkopi , mud rip -up clasts are common in the base of the Shinarump channel sandstones.

 

Depositional Environment:

The Moenkopi Formation regionally preserves environments of shallow marine to continental alluvial fans and also includes marginal marine, deltaic, shoreline, mudflat, tidal, estuarine, sabkha (arid supratidal - above tide level), fluvial (river), and eolian (wind blown) deposits (Dubield 1994).  In this locality, the deposits are largely thin-bedded tidal and floodplain deposits.  The Chinle depositional environments are typically fluvial. The Shinarump Member here is a tabular planar stratified sandstone with an irregular distribution that may be thick in some areas where it filled in paleovalleys.

 

Interpretation:

During the Late Triassic, the supercontinent Pangaea was symmetrically straddling the equator and Utah was located around a paleolatitude of 10° north and was continuing to shift northward entering a more subtropical zone. The Chinle Formation as a whole is a fluvial-lacustrine system with a tropical monsoonal climate. Meaning the region would receive a good amount of precipitation but would be interrupted by seasonally dry periods.  (Dubiel, 1991.) Tectonically, the Chinle was deposited in a continental back-arc basin on the west coast of Pangea.