CHEMOSTRATIGRAPHY OF THE LOWER MEMBER OF THE CHINLE FORMATION, CEDAR CITY, UTAH

The Late Triassic Chinle Formation is a fluvial and floodplain deposit found in Utah, Arizona, New Mexico, and Colorado. The sediment for this formation is believed to be sourced from large river systems that flowed northwest from highlands near the modern US-Mexico border. In most areas, the basal unit of the Chinle Formation is the Shinarump Conglomerate Member, which sits unconformably on the Triassic Moenkopi Formation. However, in certain areas of southwestern Utah there is a lower member of the Chinle Formation that is mapped below the Shinarump member. The lesser-studied Lower Member of the Chinle Formation is a floodplain deposit composed of mudstones, siltstones, and paleosols. It is most notable for its multicolored mottled layers of orange, green, yellow, red, and purple. In the Cedar City, Utah area, there is also an abundance of concretions, nodules, and mottles with metallic appearances. This project measured section in the Lower Chinle member, and identified 11 distinct subunits based on lithology and color variations. SEM analysis of samples taken from this layer are currently being conducted, and indicate concentrations of uncommon alkali earth and transition metals within the sedimentary deposits. With information gained from these tests chemical compositions of the different units will be determined. This will be important in determining the type of paleosols that are present as well as make hypotheses as to the paleoclimate and tectonic settings of this area at the time of deposition.