Recognition of shallow water and tidal flat aspects of the Abrigo formation (Cambrian) in southeastern Arizona

Abstract

A study of the Abrigo Formation (Middle and Upper Cambrian) in southeastern Arizona was made to describe tidal flat and shallow water characteristics in the field and laboratory, and to compare these characteristics with similar modern and ancient environments. Tidal flats are well developed on coasts of low relief with a marked tidal range. The movement of water in response to tidal forces produces three depositional zones. The relative position and composition of available sediments are the controlling factors that influence lithologic associations and sedimentary structures that form in the terrigenous and the carbonate tidal flat and shallow water environments. Tidal flat and shallow water environments in the Abrigo Formation are represented at the Seven Dash Ranch, J-Six Ranch, Dry Canyon, and Colossal Cave localities. The lithologies and sedimentary structures are remarkably similar to those that form on a carbonate platform in an epeiric sea. Terrigenous sediments associated with the carbonates may have resulted from emergence of the Cambrian landmass. No one sedimentation model can account for the stratigraphic sequence in the Abrigo, but each Abrigo section contains numerous lithologies, sedimentary structures, and paleontologic examples that are characteristic of tidal flat and shallow water environments.