STRATIGRAPHIC PARTITIONING OF WAVE- AND RIVER-INFLUENCED DELTAIC FACIES UTILIZING ICHNOLOGY, FERRON SANDSTONE, UTAH

Ichnology provides a high-resolution tool for the interpretation of depositional systems due to the sensitivity to environmental parameters of sediment-dwelling animals. Within an integrated sedimentological-ichnological framework, trace fossils have been instrumental in subdividing deltaic deposits into hydrodynamic end members (fluvial-, tide-, and wave-dominated). Recent studies differentiate wave-modification of the delta front from river-dominated delta front deposits at a scale as small as two vertical meters within a parasequence. This study builds upon those efforts by examining both the vertical and lateral relationships in Parasequence 2d of the Ferron Sandstone in central Utah. This is accomplished by examining five closely spaced cores from the Muddy Creek area of the Cretaceous Ferron Sandstone that penetrate the parasequence. The parasequence ranges in thickness from 18 meters in the south to 31 meters basinward in the north. The exposed outcrop a few hundred meters in front of the drilled wells allows for the establishment of accurate lateral relationships along this 2-kilometer stretch.

Facies of Parasequence 2d are interpreted as river-dominated deltaic deposits with a moderate degree of wave-reworking. The trace fossil assemblage present in the middle to distal delta-front deposits of river-dominated facies in this parasequence are comparable to Archetypal-Distal Skolithos Ichnofacies, whereas the proximal prodelta deposits are represented by Proximal Cruziana Ichnofacies. Conversely, the trace fossils of the wave-reworked middle to distal delta-front deposits are ascribed to the Distal Skolithos Ichnofacies, whereas the proximal prodelta is characterized by mixed a Skolithos-Cruziana Ichnofacies. Greater abundances and higher diversities of trace fossils are also observed in the wave-reworked deposits. The proximal portions of the delta front and distal distributaries of both processes are similar to an Archetypal Skolithos Ichnofacies, but many of these traces are related to deep-tiered overprinting initiating from the overlying transgressive scour. This scour is associated with shallow tidal channels that incise the top of the progradational portion of the parasequence.