Triassic Sedimentary Rocks
In most of the ranges of the EMNSA that contain latest Proterozoic and Paleozoic
sequences (see previous section), these strata are conformably overlain by reddish sandstone,
limestone, and shaley limestone, or their metamorphosed equivalents. These rocks are
correlated with the Early to Middle Triassic Moenkopi Formation (Burchfiel and Davis, 1971,
1977; Walker, 1987). In the Providence Mountains, this unit is approximately 300 m thick
and contains Early Triassic fossils. In many ranges, these rocks are metamorphosed to
distinctive calc-silicate rock (Stone and others, 1983).
In the Mescal Range, a unit of sandstone, shale, and limestone stratigraphically above the
Moenkopi Formation and below a Jurassic sandstone unit was correlated with the Late Triassic
Chinle Formation by Hewett (1956). This correlation was questioned by Marzolf (1983), who
considered several Jurassic units to lie directly on the Moenkopi. Possible Chinle-correlative
rocks have not been reported elsewhere in the EMNSA.