Sequence Stratigraphy of the lower portion of the Upper Trissic Chinle Formation, southcentral Utah, USA

Joseph Beer, University of Minnesota Duluth, Department of Geological Sciences, Duluth, MN, [email protected]

Field and well log data from central Utah identify three sequence bounding unconformities in the lower portion of the Chinle (Shinarump, Monitor Butte, Temple Mountain, and Moss Back Members) which function to divide these deposits into three periods of incision and subsequent valley fill. The initial period of degradation is marked by interfluve paleosols and truncation of the underlying Moenkopi Formation creating a paleovalley which constrains the deposition of these four members. The first paleovalley fill, represented by the Shinarump Member, is interpreted as a confined sandy low-sinuosity river system. A second period of incision is marked by truncation of the Shinarump and correlative paleosols and pedogenically modified strata. The Monitor Butte and correlative Temple Mountain Members overlie this unconformity and consist of mudstones and sandstones representing fluvio-lacustrine deposition and vertisols and interbedded mudstones and sandstones deposited in a high-sinuosity river system. A final cut and fill within the pre-Shinarump paleovalley is filled by the high- and low-sinuosity fluvial deposits of the Moss Back Member. Truncation of the Monitor Butte and Temple Mountain Members and the Moenkopi Fm. and interfluve pedogenesis mark the preceding surface of degradation.