Morphology, sedimentation, and seismic characteristics of an arctic beach, Nome, Alaska - with economic significances
<p>Arctic beaches exhibit characteristics that do not occur on beaches in more temperate zones. In the summer of 1967 morphological, sedimentological, and…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: pubs.usgs.gov.
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tfillgtp UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY MORPHOLOGY, SEDIMENTATION, AND SEISMIC CHARACTERISTICS OF AN ARCTIC BEACH, NOME, ALASKA -- WITH ECONOMIC SIGNIFICANCES By H. Gary Greene Open-file report This report is preliminary and has not been edited or reviewed for conformity with Geological Survey standards
ABSTRACT Arctic beaches exhibit characteristics that do not occur on beaches in more temperate zones. In the summer of 1967 morphological, sedimentological, and seismic refraction studies were made on an arctic beach near Nome, Alaska, in order to better define these distinguishing characteristics. Several distinct microrelief structures are developed during ice break-up and the melting of ice and snow on the beaches including ice-pushed ridges, kaimoo ridge and deposits, sea-ice kettles, seaice sand and sea-ice gravel cones, micro-outwash deposits, and microdeltaic deposits. Sedimentological studies showed that sediment distribution along the beach is random with no increasing or decreasing median diameters, or sorting coefficients, or sand-gravel percentages, either along the strandline or along the beach profile. This random grain size distribution is attributed to the relatively low energy along the coast of the Seward Peninsula. Further, the beaches are insulated from the elements by ice for about 6 months out of the year and the beach sediments are disturbed annually by ice-push. Longshore drift appeared to vary from east to west during the summer of 1967 with a net transport to the east. The seismic refraction study on the Nome beach indicated that internal stratigraphy of the overburden could be interpreted and correlated with known onshore and offshore stratigraphic units. Bedrock was well defined in the seismograms and exhibited a gently
undulating topography with several buried channels that may be sites of gold placer deposits.
TABLE OF CONTENTS PAGE INTRODUCTION I. General II. Purpose and Scope of Investigation III. Location IV. Equipment V. Geologic Setting VI. Previous Investigations PART I - BEACH MORPHOLOGY I. Introduction II. Beach Profile III. Beach Features Rill Marks Swash Marks Cusps IV. Microrelief Structures Microrelief Features of the Lower Beach Ice-pushed Ridges Kaimoo Ridge and Deposits Sea-ice Kettles Sea-ice Sand Cones and Sea-ice Gravel Cones Microrelief Features of the Upper Beach Microfluvial Deposits 1. Micro-outwash Deposits 2. Micro-deltaic Deposits PART II - ASPECTS OF BEACH SEDIMENTATION AND TRANSPORT I. Introduction II. Procedures and Sampling Methods Procedures Methods III. Grain Size Distribution Swash Zone Foreshore (or Lower Foreshore) Kaimoo Ridge Deposits and Kaimoo Deposits Backshore (or Upper Foreshore) Micro-outwash Deposits Stream Deposits Offshore
PAGE IV. Processes Affecting Coastal Features. Wind Waves Littoral Currents Ice V. Offshore Features River Mouth Bars and Spits Longshore VI. Conclusions PART III - SEISMIC INVESTIGATION Introduction II. Equipment and Procedures Description of Equipment Procedures Summary III. Interpretation of Seismograms Theory Analysis of Data IV. Results General Beach Profile Seismic Velocities Depths Bedrock Topography Tundra Survey Seismic Velocities Depths V. Discussion and Conclusions General Interpretation Potential Placer Sites Conclusions PART IV - SUMMARY BIBLIOGRAPHY APPENDIX Table I. Grain Size Analysis of Nome Beach Sediment Samples Table II. Textural Analysis of Nome Beach Sediment Samples by Folk and Ward Method
LIST OF FIGURES FIGURE PAGE 1. Index map of Alaska 2. Map of southwestern Seward Peninsula 3. Generalized geologic map and cross section of coastal plain at Nome 4. View of the Nome coastal plain and beaches 5. General beach profile 6. Swash marks near Snake River 7. Cusps on the Nome Beach 8. Ice-pushed ridges 9. Kaimoo 10. Scarp of kaimoo ridge 11. Diagram illustrating the formation of kaimoo ridge, kaimoo deposit, and micro-outwash deposit 12. Sea-ice kettles in swash zone 13. Sea-ice kettle with chunk of melting ice 14. Diagram illustrating the formation of sea-ice kettles 15. Sea-ice sand cone 16. Sea-ice gravel cone 17. Formation of sea-ice sand and sea-ice gravel cones by melting of sediment-laden brash ice 18. Melting block of sea-ice showing sand flowing down sides to form a sand ridge 19. Fairy-castle structured ridges 20. Micro-deltaic deposit
FIGURE PAGE 21. Grain size distribution map of the Nome beach between Penny and Snake Rivers 22. Mean Size vs. Standard Deviation plot for swash zone, longshore trough and longshore bar samples 23. Mean Size vs. Sorting plot for swash zone, longshore trough and bar, foreshore, and backshore samples 24. Small crashing breakers on the Nome beach 25. Generalized wave refraction diagram of the northwestern Norton Sound area 26. Storm wave-cut escarpment 27. Nome dump 28. The Snake River jetties showing accumulation of sediment on the west side and erosion on the east 29. River mouth bars and spits 30. Barrier spit with small lagoon built at the mouth of a stream east of Nome 31. Old barrier spit and previous outlet of Penny River 32. Mean Size vs. Sorting plot for kaimoo, kaimoo ridge and micro-outwash deposits samples 33. Seismograms obtained with blasting caps and dynamite sound sources 34. Time-distance graph and schematic representation of refraction of seismic energy at three acoustical interfaces and the resultant timedistance graph 35. Refraction seismograms showing how first-arrival times are picked and plotted on a time-distance graph is
FIGURE PAGE 36. Beach survey. Map showing location of beach seismic stations and composite basement contours, with cross section, expanded beach profile, and geophone spreads 37. Time-distance graphs constructed from data of beach station 49 38. Time-distance graphs constructed from data of beach station 27 39. Time-distance graphs constructed from data of beach station 45 40. Profile of beach seismic refraction line relating travel-time curves to bedrock topography 41. Tundra survey. Map showing location of tundra seismic line and USSR&M drill-hole lines with block diagram and geophone spread 42. Profile of tundra seismic refraction line relating travel-time curves with bedrock topography 43. Idealized cross sections and stratigraphic column of Nome beach and tundra survey areas
Appendix
TABLE I GRAIN SIZE ANALYSIS OF NOME BEACH SEDIMENT SAMPLES Sample Size Class in mm -- Fractional %/Cumulative % No. G-14-la G-14-2a G-14-4 G-17-2a G-17-3 G-20-1 G-20-2 G-20-3b G-20-5 F-, VXIGNaddV
TABLE I (Continued) Sample No. Size Class in Fractional %/Cumulative % G-14-la G-14-2a G-14-4 G-17-2a G-20-1 G-20- 3b G-20-5
TABLE I (Continued) Sample No. Md. Moment Measures -- So. Sk. TraAk `1 Q 3 Percentage Gravel Sand G-14-la G-14-2a G-14-4 G-17-2a G-17-3 G-20-1 G-20-2 G-20-3b G-20-5
Sample No. TABLE I (Continued) Size Class in mm -- Fractional %/Cumulative % G- 21-1 G-21-2 G-22-1 G-22-2a G-22-3 G-23-1 G-23-2a G-23-3 G-25-1
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % G-21-1 G-21-2 G-22-1 G-22-2a G-22-3 G-23-1 G-23-2a G-23-3 G-25-1
TABLE I (Continued) Sample No. Md. Moment Measures -- So. Sk. TrasX n. Q 3 Percentage Gravel Sand G-21-1 G-21-2 G-22-1 G-22-2a G-22-3 G-23-1 G-23-2a G-23-3 G-25-1
TABLE I (Continued) Sample No. Size Class in mm -- Fractional %/Cumulative % G-25-3a G-25-4 G-27-1a G-27-2 G-27-3 G-27-4 G-27-5 G-27-6 G -29 -la
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % G-25-3a G-25-4 G-27-la G-27-2 G-27-3 G-27-4 G-27-5 G-27-6 G-29-la
TABLE I (Continued) Sample Moment Measures -- Tras Percentage Q No. Md. So. Sk. Gravel Sand G-25-3a G-25-4 G-27-la G-27-2 G-27-3 G-27-4 G-27-5 G-27-6 G-29-la
TABLE I (Continued) Sample No. Size Class in mm -- Fractional %/Cumulative % G -29 -2a G-29-3a G-29-4 G-31-la
G-31-3
G-33-2 G-33-3
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % G-29-2a G-29-3a G-29-4 G-31-la
G-31-3
G-33-2 G-33-3
TABLE I (Continued) Sample Moment Measures -- Trask Percentage Q No. Md. So. Sk. `41 Gravel Sand G-29-2a G-29-3a 0-31-la
G-31-3
G-33-2 G-33-3
Sample No. TABLE I (Continued) Size Class in mm -- Fractional %/Cumulative % G-33-4 G-34-1 G-34-81 G-35-la G-35-5b G-35-6a G-35-7 G-35-8 G-37-1
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % G-33-4 G-34-1 G-34-8I G-35-la G-35-5b G-35-6a G-35-7 G-35-8 G-37-1
TABLE I (Continued) Sample No. Md. Moment Measures -- Trash So. Sk. Q 3 Percentage Gravel Sand G-33-4 G-34-1 G-34-81 G-35-la G-35-5b G-35-6a G-35-7 G-35-8 G-37-1
TABLE I (Continued) Sample Size Class in mm -- Fractional %/Cumulative % No. G-37-2a G-37-3 G -37 -4a G-37-5a G-37-6a G-39 -la G-39-2a G -39 -3a G-39-4a N.)
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % G-37-2a G-37-3 G-37-4a G-37-5a G-37-6a G-39-la G-39-2a G-39-3a G-39-4a
TABLE I (Continued) Sample No. Md. Moment Measures -- So. Sk. Trask `1 Q 3 Percentage Gravel Sand G-37-2a G-37-3 G-37-4a G-37-5a G-37-6a G-39-la G-39-2a G-39-3a G-39-4a
TABLE I (Continued) Sample No. Size Class in mm -- Fractional %/Cumulative % G-39-5a G-40-la G-40-2b G-40-3d G-40-4a 0-43-la G-43-3 G-43-4a G-45-la N.)w
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % ‹.031 G-39-5a G-40-la G-40-2b G-40-3d G-40-4a G-43-la G-43-3 G-43-4a G-45-la
TABLE I (Continued) Sample No. Md. Moment Measures -- So. Sk. Trash Q 3 Percentage Gravel Sand G-39-5a G-40-la G-40-2b G-40-3d G-40-4a G-43-la G-43-3 G-43-4a G-45-la
TABLE I (Continued) Sample Size Class in mm -- Fractional %/Cumulative % No. G-45-2a G-45-3a G-45-4a G-46-la G-46-2 G-46-3a G-46-4b G-46-5a G-47-1
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % G -45 -2a G-45-3a G-45-4a G-46-la G-46-2 G-46-3a G-46-4b G-46-5a G-47-1
TABLE I (Continued) Sample No. Md. Moment Measures So. Sk. TraAk Q 3 Percentage Gravel Sand G-45-2a G-45-3a G-45-4a G-46-la G-46-2 G-46-3a G-46-4b G-46-5a G-47-1
TABLE I (Continued) Sample No. Size Class in mm -- Fractional %/Cumulative % G-47-2a G-47-3 G-47-4a G-47-5a G-R-48-la G-R-48-2a G-R-48-3b G-48-4a G-R-49-la
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % G-47-2a G-47-3 G-47-4a G-47-5a G-R-48-la G-R-48-2a G-R-48-3b G-48-4a G-R-49-la
TABLE I (Continued) Sample Moment Measures -- Trask Percentage Q No. Md. So. Sk. Gravel Sand G-47-2a G-47-3 G-47-4a G-47-5a G-R-48-la G-R-48-2a G-R-48-3b G-48-4a G-R-49-la
Sample No. TABLE I (Continued) Size Class in mm -- Fractional %/Cumulative % G-R-49-2a G-R-49-3a L-1-1 1'
TABLE I (Continued) Sample No. Size Class in mm (continued) -- Fractional %/Cumulative % G-R-49-2a G-R-49-3a L-1-1 1'
TABLE I (Continued) Sample No. Md. Moment Measures -- So. Sk. Trash n. Q3 Percentage Gravel Sand G-R-49-2a G-R-49-3a L-1-1 1'
TABLE I (Continued) Sample Size Class in mm -- Fractional %/Cumulative % No.
TABLE I (Continued) Sale No. Size Class in mm (continued) -- Fractional %/Cumulative %
TABLE I (Continued) Sample Moment Measures -- Trash Percentage Q No. Md. So. Sk. '<1 Gravel Sand
APPENDIX B TABLE II TEXTURAL ANALYSIS OF NOME BEACH SEDIMENT SAMPLES BY FOLK AND WARD METHOD Sample No. M Ski z6i G-17-3 G-20-5 G-22-3 G-23-3 G-25-4 G-27-6 G-29-4 G-31-3 G-33-4 G-34-8 G-35-8 G-37-6 G-39-4 G-40-3 G-43-4 G-45-4 G-46-5 G-47-5 G-48-4 G-49-3
TABLE II (Continued) Sample No. M z (5i Sk. -0.49 -0.14 -1.48 -1.07
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