Master of Science / Department of Geology / Allen W. Archer / Abstract This study compares the tidally influenced facies found within the Tonganoxie Sandstone Member (Stranger Formation, Douglas Group) (Upper Pennsylvanian) of northeastern Kansas with similar facies directly observed in the upper intertidal mudflats of Turnagain Arm of Cook Inlet (Alaska, USA). The two settings contain strikingly similar facies that are characteristic of upper macrotidal estuaries with a strong influence of tidal activities. Identical aspects and features found within both settings include rhythmic vertical variation in stratum thicknesses (cyclic tidal rhythmites), high estimated sedimentation and aggradation rates, and biogenic and physical sedimentary structures (e.g., drag marks, raindrop impressions, arthropod traces and tetrapod trackways, zigzag burrows, runoff washouts, and upright trees, among others). Tidal rhythmites are the most important evidence that is indicative of the tidal influence on the depositional processes of these two study areas. Such cyclic tidal rhythmites have been reported and described from several Carboniferous settings in the eastern USA. Modern analogs to these Carboniferous rhythmites are usually found within upper macrotidal estuarine depositional environments, especially within fluvio-estuarine transitional zones. These environments are distributed over a wide range of modern latitudes. Using cyclic tidal rhythmites as modern analogs for interpreting similar ancient facies is a powerful tool for paleogeographic and paleoenvironmental reconstructions, although it is somewhat a new approach.

Master of Science / Department of Geology / Allen W. Archer / Turnagain Arm is the hypertidal (commonly exceeding 9 m) west-east trending extension of Cook Inlet in south-central Alaska. The inlet formed from a drowned glacial valley that was subsequently filled with tidal deposits of silt and fine sand. The tidal system is semidiurnal with a prominent diurnal inequality. There are also variations due to spring and neap tides. Turnagain Arm is home to a tidal bore generated during spring tides that can reach heights of up to 2 m and travel at speeds of up to 5 m/s. Current reversals can be dramatic with ebb tidal velocities of 6 m/s changing to flood velocities of 10 m/s over a period of a few minutes. During the initial flood tide, highly turbid water can rise as fast as 10 cm/min. This combination of elements results in a highly dynamic depositional setting. Measurements taken in the inner estuary during several neap-spring cycles in the summers of 2007-08 documented deposition upon mud bars of as much as 8.9 cm per tidal event. Conversely, erosion of up to 13.5 cm per tidal event has been measured. The highest rates of deposition and erosion occurred during the spring tides while much lower rates occur during the neap tides. Some portions of the inner estuary are only submerged during the extreme high tides. The magnitude of the high tide needed to cover each site increases with increasing distance into the upper estuary. Even if submerged, deposition does not always occur. Such a high percentage of non-depositional events has real implications when interpreting tidal cyclicity of the rhythmites found at these sites.