US Geological Survey


Date of this Version



Journal of the Arizona-Nevada Academy of Science, Vol. 22, No. 1, Triassic Continental Deposits of the American Southwest (1987), pp. 35-45.


The Upper Triassic Chinle Formation in southeastern Utah was deposited in a complex fluvial-deltaic-lacustrine system. The Chinle records the evolution of a continental system in response to variations in climate, tectonics, and sediment supply. Chinle strata represent deposits of fluvial channels and floodplains, lacustrine deltas, lacustrine basins, and lacustrine and playa mudflats. These rocks include a variety of vertebrate, invertebrate, and plant fossils, trace fossils, and paleosols that provide information on depositional environments, water tables, and paleoclimate.

Sedimentologic and paleontologic interpretations both support an interpretation of abundant lakes, streams, and marshes with high, but fluctuating water tables for all but the last phase of Chinle deposition. This final phase represents a transition to eolian deposition of the Wingate erg. The Chinle climate is interpreted to have been characterised by tropical monsoons, with abundant precipitation and seasonally drier periods. This interpretation agrees with Late Triassic paleoclimates predicted from theoretical models.