Sedimentology and cyclicity in the Lower Permian De Chelly Sandstone on the Defiance Plateau: Eastern Arizona

The Lower Permian (Leonardian) De Chelly Sandstone crops out along a north-south trend on the Defiance Plateau of eastern Arizona. It is divided into lower and upper members separated by a tongue of the Supai Formation that pinches out to the north.

Lithofacies in the De Chelly Sandstone consist of (1) a large-scale trough to tabular- and/or wedge-planar cross-stratified sandstone facies of large-scale eolian dune origin, (2) a small- to medium-scale, trough cross-stratified sandstone also of eolian dune origin, (3) a horizontally stratified, wind-rippled sandstone of sand sheet origin, (4) a wavy, horizontally stratified, wind-rippled sandstone of sabkha origin, and (5) a mud-draped ripple-laminated sandstone of mud-flat origin.

The De Chelly Sandstone in the northern Defiance Plateau consists mainly of large-scale dune deposits. Stratigraphic sections in the middle of the plateau are dominated by small- to medium-scale dune and sand sheet deposits whereas those along the southern end of the plateau are composed largely of sabkha and supratidal mud-flat deposits. The lateral distribution of these facies suggests a north-south juxtaposition of central-erg, fore-erg, and mixed sabkha-supratidal depositional environments. Repetitive interbedding of facies in the De Chelly indicates at least twelve depositional cycles in which sabkha and/or supratidal to coastal-plain mud-flats were sequentially overridden by eolian sand sheets and cross-stratified dunes.

Lateral and vertical facies relations within the lower and upper members of the De Chelly Sandstone record episodic expansion of the De Chelly erg southward, The comparative abundance of large-scale dune deposits in the upper member suggests that progradation was more extensive during latter stages of deposition. The intervening tongue of Supai Formation and the redbeds that overlie the upper member of the De Chelly at Bonito Canyon document northward transgression of sabkha and supratidal to coastal-plain mud-flat environments. Eolian dune deposition was restricted to the northern Defiance Plateau during deposition of these units.