A GUIDE TO THE LATE QUATERNARY HISTORY OF NORTHERN AND WESTERN KENAI PENINSULA, ALASKA by R.D. Reger, A.G. Sturmann, E.E. Berg, and P.A.C. Burns Guidebook 8 Published by STATE OF ALASKA DEPARTMENT OF NATURAL RESOURCES DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYS 2007 A GUIDE TO THE LATE QUATERNARY HISTORY OF NORTHERN AND WESTERN KENAI PENINSULA, ALASKA by R.D. Reger, A.G. Sturmann, E.E. Berg, and P.A.C. Burns Division of Geological & Geophysical Surveys Guidebook 8 Cover photo: Granitic erratic, measuring 15 m (50 ft) high by 30 m (100 ft) long, was probably carried southward at least 160 km (100 mi) from the Talkeetna Mountains by ice of the Moosehorn stade of the last major glaciation and deposited in the southwest quarter of Kenai C-3 SW Quadrangle. This huge block is one of a series of granitic monoliths that form a north-trending block train across northeastern Kenai Peninsula lowland. STATE OF ALASKA Sarah Palin, Governor DEPARTMENT OF NATURAL RESOURCES Tom Irwin, Commissioner DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYS Robert F. Swenson, State Geologist and Acting Director Division of Geological & Geophysical Surveys publications can be inspected at the following locations. Address mail orders to the Fairbanks offi ce. Alaska Division of Geological University of Alaska Anchorage Library & Geophysical Surveys 3211 Providence Drive 3354 College Road Anchorage, Alaska 99508 Fairbanks, Alaska 99709-3707 Elmer E. Rasmuson Library Alaska Resource Library University of Alaska Fairbanks and Information Services (ARLIS) Fairbanks, Alaska 99775-1005 3150 C Street, Suite 100 Anchorage, Alaska 99503 Alaska State Library State Offi ce Building, 8th Floor 333 Willoughby Avenue Juneau, Alaska 99811-0571 This publication released by the Division of Geological & Geophysical Surveys was produced and printed in Anchorage, Alaska at a cost of $25.00 per copy. Publication is required by Alaska Statute 41, “to determine the potential of Alaskan land for production of metals, minerals, fuels, and geothermal resources; the location and supplies of groundwater and construction materials; the potential geologic hazards to buildings, roads, bridges, and other installations and structures; and shall conduct such other surveys and investigations as will advance knowledge of the geology of Alaska.” ii CONTENTS Page Introduction ............................................................................................................................................................... 1 Acknowledgments ..................................................................................................................................................... 1 Glacial History .......................................................................................................................................................... 3 Subdivision of last major glaciation ........................................................................................................... 4 Establishing a chronology .......................................................................................................................... 4 Summary of Naptowne events .................................................................................................................... 8 Moosehorn stade.................................................................................................................................. 8 Killey stade ....................................................................................................................................... 10 Skilak stade ....................................................................................................................................... 10 Elmendorf stade ................................................................................................................................... 10 Holocene glaciation of northern Kenai Mountains .................................................................................... 10 Vegetation History .................................................................................................................................................... 14 Climate Change ......................................................................................................................................................... 15 Stop Descriptions and Road Log .............................................................................................................................. 15 Stop 1. Turnagain Pass ............................................................................................................................. 15 Stop 2. Tern Lake ..................................................................................................................................... 20 Stop 3. Killey-age outwash fan ................................................................................................................ 33 Stop 4. Sterling ....................................................................................................................................... 38 Swanson River Road localities ................................................................................................................... 44 Paradox Lake ....................................................................................................................................... 44 Rainbow Lake...................................................................................................................................... 47 Discovery Pond ................................................................................................................................... 47 Swanson Fen ....................................................................................................................................... 49 Jigsaw Lake ....................................................................................................................................... 49 Stop 5. Soldotna ....................................................................................................................................... 54 Stop 6. Captain Cook State Park picnic area ............................................................................................ 64 Stop 7. River bluff at Kenai ...................................................................................................................... 66 Bluff section ................................................................................................................................. 66 Changes in relative sea level ........................................................................................................ 69 Land-level changes ............................................................................................................... 69 Eustatic sea level rise ............................................................................................................ 70 Basal peat dates as evidence of climatic change .......................................................................... 71 Other evidence of climatic change ............................................................................................... 74 Stop 8. North Cohoe Loop gravel pit ....................................................................................................... 81 Stop 9. Clam Gulch .................................................................................................................................. 84 Stop 10. Paleochannel of ancestral Happy Valley Creek............................................................................ 88 Stop 11. Mouth of Anchor River ................................................................................................................ 91 Stop 12. Bluff Point overlook ..................................................................................................................... 94 Stop 13. Karen A. Hornaday Hillside Park................................................................................................. 96 End of road log .................................................................................................................................... 99 Stop 14. Terminal zone of Grewingk Glacier ............................................................................................. 99 Holocene glaciation of southern Kenai Mountains ...................................................................... 99 Massive landslide-induced fl ood .................................................................................................. 101 References Cited ....................................................................................................................................................... 104 Appendix A. Calibration of radiocarbon ages ........................................................................................................... 112 iii TABLES Table 1. Summary fi eld description of soil profi le near Stop 1 on crest of latest-Naptowne moraine in Turnagain Pass .................................................................................................................................... 18 2. Defi nitions of symbols in summary soil descriptions ............................................................................. 19 3. Changes in Soldotna reach of lower Kenai River during and after Naptowne glaciation ...................... 55 4. Names and location data of peat