SOUTHWARD SEDIMENT TRANSPORT OF THE PANTHER TONGUE PALEODELTA AND ITS CAUSES

Abstract

The Cretaceous Panther Tongue sandstone, part of the Star Point Formation, represents a more than fifty-kilometer long, north-south regression into the shallow waters of the western interior seaway. The Panther Tongue is well exposed and studied in the Book Cliffs area, east-central Utah. Its deposits are interpreted as a southward-prograding fluvial-dominated river delta with upward coarsening parasequences. Despite the north-south oriented western shoreline of the western interior seaway, paleocurrents indicate a southward sediment transport direction. This could be explained in three ways: (1) During the early stages of filling the basin, the deposition was parallel to the orogen, but the reduction in accommodation space by initial deposition of the Panther Tongue caused the delta to avulse to the south. A change in flow direction would suggest this. (2) A north-south oriented structural high east of the delta forced a shoreline parallel flow direction because sediment transport was confined to the paleo-low inboard of the proposed high. The indicator for this scenario would be paleoflow direction that reflect consistent southward transport and sedimentary structures and ichnofacies indicative of upward shoaling. (3) The third possibility is that the Panther Tongue represents a north-south-oriented spit that was reworked during the subsequent transgression. Lagoon-like environments as well as lacustrine sediments in the basal portion of the Panther Tongue would support this hypothesis. These three paleogeographic models will be tested by measuring and analyzing several stratigraphic sections and documenting paleocurrent flow directions, sedimentary structures (i.e. flow regimes, grain size), and ichnofacies along an east-west transect within the delta lobe