| Description |
The supercontinent Pangea was at its maximum subaerial exposure during the Late Triassic, causing an extreme paleoclimatic state. Seasonal, potentially monsoonal weather patterns affected the supercontinent and influenced depositional environments. The Upper Triassic Chinle Formation in Paria, Utah within Grand Staircase-Escalante National Monument provides an excellent exposure of rocks, mostly paleosols, which contain paleoclimatic indicators. This research presents an interpretation of Late Triassic depositional history and paleoclimate in southern Utah using stratigraphy, sedimentology, clay mineralogy, and QEMSCAN analyses from the Chinle Formation at Paria, Utah. The stratigraphic section was divided into three lithostratigraphic intervals based on outcrop descriptions, combined with petrographic, mineralogical, and geochemical analyses. The lowermost unit, interval 1 (0-68.8 m) contains low chroma paleosols with a relative abundance of the clay mineral kaolinite, reducing features and trace amounts of sand. Bk and k-horizons (pedogenic carbonate which forms from the repeated wetting and drying of soils) are present only in the upper 10 m of this interval. Interval 1 represents a more humid environment than the upper intervals, and potentially correlates to the Blue Mesa and Sonsela members of the Chinle Formation. The Bk and k-horizons in the lowermost interval may indicate that seasonality became more pronounced near the upper part of the section. Compared to interval 1, interval 2 (68.8-170.3 m) has fewer reducing features and an increase in pedogenic carbonate and slickensides, indicating climatic seasonality was still present. Interval 2 probably correlates to the Petrified Forest Member of the Chinle Formation. Interval 3 (170.3-237.4 m) contains an increase in sand from fluvial deposits such as sandstone and conglomerates, and may correlate to the Owl Rock Member of the Chinle Formation. This change in deposition is most likely related to either avulsing river systems or ephemeral stream deposits. Overlying the Chinle Formation in Paria is the Wingate/Moenave Formations that contain eolian dune deposits in addition to fluvial and lacustrine environments indicating more prolonged aridity. The Chinle Formation at Paria, UT thus appears to support existing regional interpretations of a regional paleoclimatic shift from wetter to drier conditions as Pangea drifted northward through the Late Triassic. |
