PALYNOLOGICAL CONTENT AND PALYNOFACIES ANALYSIS OF A MIXED TIDE- AND WAVE-INFLUENCED DELTAIC DEPOSIT: THE CRETACEOUS SEGO SANDSTONE, UTAH, USA

Palynological analysis has been performed on samples from different facies associations of the Campanian Sego Sandstone, Utah. Very little palynological analysis has been undertaken on these deposits and it is a common misconception that predominantly sand-rich deltaic deposits produce poor assemblages of palynomorphs. A diverse suite of sporomorphs and dinocysts has been recovered and analysed for their taxonomic and palaeoenvironmental information potential.

The sporomorph assemblages consist of a diverse range of Pteridophytes, Lycophytes, angiosperms and conifers. Of note are fern spores of cicatricose nature, other ferns such as Deltoidospora and Dictyophyllidites, bisaccate and inaperturerate gymnosperm pollen. The Bisaccates, predominantly Pityosporites-types (Pinus), are likely washed in from the hinterland, whereas Inaperturopollenites hiatus (Cupressaceae) demonstrates a potential riparian swamp-like environment.

While Fern spores and Gymnosperm pollen make up the majority of terrestrial palynological material, the angiosperm component is more telling. It is dominated by Retitricolpites, representing a Platanus-type parent plant, Aquilapollenites, a triprojectate with a proposed link to the Loranthaceae, and Cupaneidites, possibly of Cupania-type affinity (Sapindaceae), which would suggest a warm climate, probably temperate to subtropical in nature given the presence of Cycad pollen in more than half of the samples.

The dinocyst assemblage is dominated by weakly tabulated, cavate cysts. Dinoflagellates are not consistent, occurring in half of the samples analysed with the diversity varying between only two and eleven taxa.

Van Cappelle et al. (in press) have introduced a facies association scheme for the deposits. The simple and practical palynofacies analysis undertaken in the current study provides strong evidence to support sedimentological facies analysis of the "Sego Delta" deposits. The dominant variable in this and many marginal marine settings is the types of phytoclast, which are dominant in such settings due to their proximity to fluvial input.