DEPOSITION AND PRESERVATION OF ESTUARINE SEDIMENT, TURNAGAIN ARM, COOK INLET, ALASKA by DARRON G DEBOER B.S., Kansas State University, 2007 A THESIS submitted in partial fulfillment of the requirements for the degree MASTER OF SCIENCE Department of Geology College of Arts and Sciences KANSAS STATE UNIVERSITY Manhattan, Kansas 2009 Approved by: Major Professor Allen W. Archer Copyright DARRON GRANT DEBOER 2009 Abstract 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. Table of Contents List of Figures.................................................................................................................... vi List of Tables ...................................................................................................................... x Acknowledgements............................................................................................................ xi Dedication......................................................................................................................... xii CHAPTER 1 - Introduction ................................................................................................ 1 Study Area ......................................................................................................................1 CHAPTER 2 - Background ................................................................................................ 4 Geography and Geology ................................................................................................. 4 Climate............................................................................................................................ 6 Tidal Setting.................................................................................................................... 7 Sediment ......................................................................................................................... 8 CHAPTER 3 - Methods.................................................................................................... 10 CHAPTER 4 - Sedimentary Structures............................................................................. 13 Depositional Structures................................................................................................. 13 Erosional Structures...................................................................................................... 18 Deformation Structures................................................................................................. 21 Biogenic Structures....................................................................................................... 25 CHAPTER 5 - Observations............................................................................................. 27 Bird Point...................................................................................................................... 28 Tidal Bore Overlook #4 ................................................................................................ 46 Glacier Creek ................................................................................................................ 60 Peterson Creek .............................................................................................................. 79 Portage Creek #2........................................................................................................... 88 CHAPTER 6 - Summary of Observations...................................................................... 105 CHAPTER 7 - Conclusions ............................................................................................ 108 References....................................................................................................................... 109 Appendix A - EBP Photos .............................................................................................. 110 Appendix B - TBO4 Photos............................................................................................ 113 iv Appendix C - GC Photos ................................................................................................ 116 Appendix D - PEC Photos .............................................................................................. 119 Appendix E - PC2 Photos ............................................................................................... 121 v List of Figures Figure 1-1: Location map of Turnagain Arm and the surrounding area............................. 2 Figure 1-2: Location of major study sites within Turnagain Arm...................................... 3 Figure 2-1: View from Peterson Creek toward Bird Point. ................................................ 4 Figure 2-2 Portage Lake in May, 2007. .............................................................................. 5 Figure 2-3: The flooded village of Portage, shortly after the earthquake........................... 6 Figure 2-4: Generalized tidal curve for Turnagain Arm..................................................... 7 Figure 2-5: Tidal bore advancing up Turnagain Arm......................................................... 8 Figure 2-6: Microphotograph of fine grained Turnagain Arm tidal sediment.................... 9 Figure 3-1: Schematic of rod system used to measure deposition/erosion....................... 11 Figure 4-1: Rhythmite section from Glacier Creek. ......................................................... 14 Figure 4-2: Simplified Hjulström diagram. ...................................................................... 14 Figure 4-3: Asymmetrical lingoid current ripples. ........................................................... 15 Figure 4-4: Symmetrical branching ripples at EBP. ......................................................... 16 Figure 4-5: Interference ripples (ladder-back ripples) at EBP.......................................... 17 Figure 4-6: Climbing ripples on the upper surface of a cut bank at PC2.......................... 18 Figure 4-7: Small scale rills at EBP.................................................................................. 19 Figure 4-8: Large gully at EBP......................................................................................... 19 Figure 4-9: Large sour containing ripples at PEC. ........................................................... 20 Figure 4-10: Adhesion warts at the EBP study site. ......................................................... 21 Figure 4-11: Soft-sediment deformation in a cut bank at Glacier Creek.......................... 22 Figure 4-12: Soft-sediment deformation as seen on the surface of the TBO4 bar. .......... 22 Figure 4-13: Small mud volcano on left and dewatering pit on right at the PEC site. ..... 23 Figure 4-14: Large dewatering pits at the PEC site. ......................................................... 24 Figure 4-15: Mud cracks with small dewatering pits at the GC site................................. 25 Figure 4-16: Salmon fin drag marks (arrow), gull tracks and rain-drop prints at the GC site............................................................................................................................. 26 Figure 4-17: Insect burrows at the GC site. ...................................................................... 26 vi Figure 5-1: Schematic of data plot.................................................................................... 27 Figure 5-2: Air photo and schematic of EBP study site.................................................... 29 Figure 5-3: Photo of EBP taken on August 3, 2007. ........................................................ 30 Figure 5-4: EBP transect 1, May 2007.............................................................................. 32 Figure 5-5: EBP transect 2, May 2007.............................................................................. 33 Figure 5-6: EBP partially flooded on May 20, 2007, after high tide #12......................... 34 Figure 5-7: EBP at low tide on May 23, 2007, after high #17.........................................