Abstract

In northern Arizona, the Toroweap Formation of Permian age is divided into three members that record a major west to east transgression, followed by a regression. The basal member, the Seligman Member, represents supratidal and continental environments at the land margin of the advancing Toroweap sea. Sabkha deposition gave way to marine carbonate deposition represented by the Brady Canyon Member. The Woods Ranch Member represents a regression of the Toroweap sea, as indicated by a return to supratidal and continental deposition.

Facies in the Brady Canyon Member include grain-supported skeletal limestone, mud-supported skeletal micrite, pelleted micrite and dolomicrite, sandy dolomite, and aphanitic limestone and dolomite. Three minor transgressions and regressions are recorded by shifts in the carbonate facies. No facies in the Brady Canyon Member is micrite-free, suggesting that low-energy conditions prevailed throughout most of Toroweap deposition in northern Arizona; the higher energy environments are farther west.

Evidence for supratidal facies within the Seligman and Woods Ranch Members includes the presence of thick evaporite deposits, algal stromatolites, dolomitization of carbonate units, and the scarcity of fossils. Evidence for a continental sabkha/dune facies within the Seligman and Woods Ranch Members includes horizontally bedded sandstones; the presence of solution-collapse breccias, contorted bedding, and minor diapiric structures, suggesting the former presence of gypsum; and bimodal sandstones and large-scale crossbeds, indicating an eolian environment.

Continental sabkha and dune deposition continued to the south and east of marine deposition during Toroweap time. The entire Toroweap Formation, therefore, is a good example of marine carbonate-sabkha-eolian deposition.