Abstract

Basal Triassic strata in southeastern Utah provide evidence of local tectonic activity that occurred at approximately the time of formation of the Permian-Triassic unconformity. In southeastern Utah, the lowermost part of the Moenkopi Formation, the primarily fluvial chert-pebble conglomerate facies (CPCF) of the Black Dragon Member, exhibits eastward-directed paleocurrent indicators. Because paleocurrent indicators and provenance studies of non-eolian Permian strata underlying the unconformity in southeastern Utah indicate dominantly westward-directed transport, the eastward-directed flow indicators observed in lowermost Triassic strata are interpreted to record a reversal of paleoslope that occurred between deposition of mid-Permian and lowermost Triassic strata Tectonic activity is interpreted to be responsible for the paleoslope reversal. Based on clast size and composition data for the CPCF and analysis of surface and subsurface stratigraphy, the beta member of the Lower Permian Kaibab Limestone in an area that includes the Circle Cliffs of southern Utah is the inferred source of the chert pebbles in the CPCF. The source area is considered part of the Emery uplift, a previously recognized paleotectonic element that influenced depositional patterns in southern Utah during many geologic periods.

In the Early Triassic, the Emery uplift acted as a drainage divide in southern Utah, separating marine and marginal-marine deposition to the west from sabkha deposition to the east. The basin on the east side of the Emery uplift, called the Hoskinnini basin, may have had intermittent or restricted contact with the marine environment across its northern margin. It was fully separated, however, from the Early Triassic sea by the Emery uplift along its western boundary. The Hoskinnini basin continued to be present and distinct from the marine environment throughout deposition of the entire Black Dragon Member of the Moenkopi.