A CHEMOSTRATIGRAPHIC ANALYSIS OF UPPER CRETACEOUS STRATA, BOOK CLIFFS, UTAH

The precise timing and development of incised valley fills (IVF) is difficult to ascertain due to their erosive nature and the complex character of these systems. Lack of chronological constraint and the variable diachroneity of fluvial deposits make detailed sequence stratigraphic analysis difficult. This study attempts to extract a more precise timing of the development and infill of two IVFs by using stable isotope chemostratigraphy (d¹³C_OM, d¹³C_calcite, d¹⁸O_calcite) as a high-resolution chronostratigraphic tool. This dating method was tested on a ~450 ft. section of shallow marine to fluvial deposits from the Book Cliffs, Utah: The Blackhawk and Castlegate formations, and the Buck Tongue member of the Mancos Shale. Data was generated from four locations near Green River Utah, an ExxonMobil drill core taken from Sego Canyon, and three outcrops: Blaze, Tusher, and Thompson canyons. Preliminary results extracted from over 1,000 data points have revealed at least four correlative positive or negative d¹³C_OM events which span across the entire study interval. For example: A 3 per mil d¹³C_OM positive excursion located in lower shoreface deposits in the more distal Thompson and Sego Canyon locations is found in paleosols and raised-mire deposits further inland. This may indicate a period of simultaneous deposition in different but stratigraphically correct environments. If these events truly act as datums, and they are globally driven, then a positive correlation to a dated reference curve will allow the duration of depositional and erosive events at various locations within one IVF to be estimated. Work is still being done processing for calcite values, finalizing the excursion correlations and a global tie should be accomplished by fall 2014.