GEOMORPHOLOGY AND SEQUENCE STRATIGRAPHY, LINKING EOLIAN STRATA TO SEA LEVEL CHANGE, PERMIAN CEDAR MESA SANDSTONE SE, UTAH

The Permian (Wolfcampian) Cedar Mesa Sandstone of Southeastern Utah is known for the prominent erosion surfaces that divide the formation into 20 to 40 m thick units. Previous studies have shown that some of these erosion surfaces are continuous across the entire Cedar Mesa and represent successive dune seas that formed after the previous ergs were stabilized and partly eroded. Petrographic analysis of thin sections from samples collected in the needles district of Canyonlands National Park show that two of these horizons contain sandstone bearing fragmented marine fossils. Biota include brachiopods, crinoids and bryozoans. Sandstones above and below the rooted horizons were devoid of fossil fragments indicating that development of the erosion surfaces marked a change in eolian sediment source. The erosion surfaces are associated with large ponds, and are extensively vegetated, suggesting a high water table possibly associated with sea-level rise. Pond lithologies vary depending on the amount of sediment balanced with the water availability and can be classified into distinguishable pond types. Therefore, the erosion surfaces are correlated with transgressions associated with Permian glacio-eustatic sea level highstands. Pond locations and vegetation are controlled by eolian paleotopography preserved on the surfaces. Up to 8 m of relief is preserved, with highs correlated to underlying megadunes.

This correlation of erosion surfaces allows development of a sequence stratigraphic model for this and similar Permian eolianites, which are found on most continents. The erosion surfaces mark highstands, which must have resulted from transgression and flooding of eolian sand sources. The intervening dune fields mark lowstands that are associated with sediment source recharge. In several intervals in the Cedar Mesa, eolianites contain numerous ponds and flooding surfaces that formed later in their development. This may mark higher water tables associated with sea-level rise.