Nonmarine Triassic strata have wide distributions on all the world's continents. Their precise correlation is an obvious step towards better elucidating the Triassic history of physical and biological events on land. At present, Triassic chronology has been developed almost exclusively on the basis of marine rocks and fossils. To that end, standard sections of strata and stratotype sections have been identified for the Triassic portion of the Standard Global Chronostratigraphic Scale (SGCS) (Tozer, 1984). Although much work remains to be done on the Triassic portion of the SGCS, a workable Triassic biochronology, based principally on ammonoids and conodonts, is already in place, rooted in standard and stratotype sections of marine strata.

In regard to the nonmarine stratigraphic terranes of the Triassic, quite a different situation exists. No such standard or stratotype rock sections have been identified for nonmarine Triassic strata, and their correlations are made either by direct (though usually imprecise) reference to the marine SGCS or by nonmarine biochronologic constructs such as the Lystrosaurus “Zone.” Recently, however, Lucas (1992) and Lozovsky (1993) have suggested that standard sections of nonmarine Triassic strata be identified for use in correlation. These would not be intended to be the stratotypes of stages, but rather reference sections to aid in the correlation of nonmarine Triassic strata. Here, I follow their lead, arguing that the Upper Triassic nonmarine Chinle Group of the western United States (Figure 23.1) provides an excellent standard section for Upper Triassic nonmarine chronology.