Carbonate cementation in a sequence-stratigraphic framework: Upper Cretaceous sandstones, Book Cliffs, Utah-Colorado

Three macroscopic diagenetic features can be recognized in the sandstones o f the Upper Cretaceous Desert Member of the Blackhawk Formation and Castleg ate Sandstone of the Mesaverde Group exposed in the Book Cliffs, Utah, each of which have distinctive form, geometry, and stratigraphic distribution. Diagenetic alterations are: (1) leached zones ("whitecaps"), up to 10 m thi ck, beneath coal beds; (2) large (up to 8 m) concretionary carbonate-cement ed bodies in amalgamated shoreface and thin fluvial sandstones; and (3) thi n (up to 2 m), laterally extensive carbonate-cemented horizons beneath majo r marine flooding surfaces. Each feature has distinct petrographic and geoc hemical signatures, and formed through discrete diagenetic processes. Large isolated carbonate-cemented bodies are composed of ferroan dolomite, most of which precipitated during early diagenesis. Field and petrographic data, coupled with stable-isotope data (early cements, delta(13)C = -2.5 to +3.4 parts per thousand VPDB; delta(18)O = -7.8 to -12.0 parts per thousand VPD B; Sr-87/Sr-86 = 0.7078; later cements, delta(13)C = -3.1 to -5.7 parts per thousand VPDB; delta(18)O = -12.0 to -15.1 parts per thousand VPDB; Sr-87/ Sr-86 = 0.7093) suggest precipitation from meteoric fluids, input into sedi ments during times of relative sea-level fall. The source of carbonate for the dolomite cement was dissolution of detrital dolomite from beneath coals by organic acids and subsequent mobilization by meteoric fluids. Carbonate precipitation in laterally extensive cement horizons appears to have start ed as a result of hiatus in sediment accumulation during marine flooding ev ents (relative sea-level rise). Cement precipitation in these horizons cont inued through sediment burial as a result of organic-matter oxidation react ions in overlying organic-rich mudstones. The results of this study show a link between sedimentation (related to changes in relative sea level) and d iagenesis, leading to the potential for the development of process-based, p redictive models of early diagenesis in depositional successions.