Architectural Facies Analysis of Nonmarine Depositional Systems in Upper Triassic Chinle Formation, Southeastern Utah

Russell F. Dubiel

The Upper Triassic Chinle Formation in southeastern Utah consists of nonmarine strata deposited in a back-arc cratonic basin. Architectural analysis of exposures in subparallel canyons reveals an intricately interbedded fluvial-deltaic-lacustrine system characterized by (1) mobile fluvial-channel belts consisting of stacked channel complexes; (2) overbank deposits of levees, paleosols, marshes, and small floodplain lakes interfingered with crevasse splays and lacustrine deltas; and (3) extensive lacustrine strata deposited over the entire study area. Stratigraphic panels using closely spaced measured sections drawn either perpendicular or parallel to depositional dip show lateral facies relations within the extra-channel strata and the relations to channel complexes. Succ ssions of panels through several canyons depict the three-dimensional architecture of the Chinle depositional system.

In the Shinarump and Monitor Butte Members at the base of the Chinle, fluvial-channel complexes grade laterally over short distances into deposits of levees and crevasse splays and then into wetland complexes of lake and marsh deposits. In the Moss Back and Petrified Forest Members in the middle of the Chinle, fluvial-channel complexes grade laterally into flood-plain strata characterized by calcic and vertic paleosols. In the lower and middle Chinle, fluvial-channel belts can be traced across the study area. Locally, paleosol and wetland strata serve as marker beds in three dimensions and provide estimates on the size of flood-plain environments. The Owl Rock and Church Rock Members of the upper Chinle are dominated by thin to medium-bedded, laterally extensive lacustrine strata reco nizable throughout the study area. The three-dimensional continuity of these units indicates the lacustrine environment extended throughout the study area. The complex facies relations in the Chinle were the result of variations in climate, tectonics, and sediment supply.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.