CORRELATING PALYNOFACIES ASSEMBLAGES WITH SEQUENCE STRATIGRAPHY IN UPPER CRETACEOUS (CAMPANIAN) SEDIMENTARY-ROCKS OF THE BOOK CLIFFS, EAST-CENTRAL UTAH

Some of the most important factors that govern the preservation of dep ositional sequences in passive margins are the rate of sediment supply , the type of sediment, subsidence history, sea-level changes, and cli mate. These factors also control the nature of components, such as org anic matter, palynomorphs, and other fossils incorporated within the s ediments. Because detrital organic matter (palynodebris) behave like s edimentary particles, their distribution in sediments can be used to i nfer palynofacies, and consequently depositional conditions. This stud y correlates palynofacies assemblages with sequence stratigraphic inte rpretations of Upper Cretaceous (Campanian) sedimentary rocks in the B ook Cliffs, east-central Utah, namely the Kenilworth, Grassy, and Dese rt Members of the Blackhawk Formation, Mancos Shale, Castlegate Sandst one, and Buck Tongue of the Mancos Shale. Sedimentological criteria ha ve been used to identify the depositional framework at 8 localities, a nd 12 palynodebris types have been identified in the sediments: sporom orphs, marine palynomorphs, fresh-water algae, fungal remains, amorpho us organic matter, resins, cuticles, parenchyma, degraded bundles, woo d, black debris, and degraded debris. The samples and palynodebris wer e analyzed statistically using average linkage cluster analysis, princ ipal components analysis, and detrended correspondence analysis. Clust er analysis yielded seven palynofacies assemblages, which have been in tegrated with sedimentological criteria, and correlated with sequence stratigraphic interpretations. Although all the samples are dominated by woody debris, the palynofacies assemblages are defined primarily by marine palynomorphs, degraded bundles, black debris, and sporomorphs, and to a lesser extent by cuticles and resins. Highstand systems trac ts and lowstand systems tracts are each represented by major palynofac ies assemblages, indicating that there is some correlation with sequen ce stratigraphy. Two other minor assemblages are indicative of the hig hstand systems tract. In addition, three assemblages, which are domina ted by siltstone and shale samples interbedded with sandstones, are ri cher in black debris; this is probably due to the effect of oxidation in the depositional environment and, possibly, microbial respiration i n the interbedded sandstones. Marine environments are usually characte rized by an abundance of marine palynomorphs and palynodebris over spo romorphs and other nonmarine palynodebris, and this characteristic has been used to recognize initial marine flooding events and maximum flo oding intervals (condensed sections) in several palynological studies. In this study, however, one possible initial marine flooding event wa s not easily detected palynologically. In situations such as this, the re is a need to integrate palynology with sedimentological and other c riteria in order to establish valid regional sequence stratigraphic in terpretations.