U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY MISCELLANEOUS FIELD STUDIES MF-2335, Version 1.0

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INTRODUCTION AREAS OF SEA-FLOOR DATA concentrations of winnowed (lag) gravel on Tarr Bank and on the outer Knik Arm The U.S. Geological Survey has a long history of exploring marine Cook Inlet -- Hazards studies in this embayment emphasized sediment shelf southeast of Yakutat Bay. Between Kayak Island and Yakutat Bay Evans, K.R., 1997, Offshore geologic framework and sedimentology of geology in the Gulf of Alaska. As part of a cooperative program with distribution, sediment dynamics, bedforms, shallow faults, and seafloor the outer shelf consists of pebbly mud (diamict). This diamict is a product the Gulf of Alaska: selected bibliography of U.S. Geological E X P L A N A T I O N other federal and state agencies, the USGS is investigating the relations stability. Migrating mega-sandwaves, driven by strong tidal currents, of glacial marine sedimentation during the Pleistocene and is present today Survey Studies (1970-present): U.S. Geological Survey Open-File Report, OF 97-26, 15 p. The sediment categories, shown at left, are between ocean-floor geology and benthic marine biohabitats. This bottom influence seabed habitats and stability of the seafloor, especially near as a relict sediment. A prograding wedge of Holocene sediment consisting organized according to grain size and sediment map, compiled from published literature (Carlson and others, pipelines and drilling platforms (Bouma and others, 1980). The of nearshore sand grading seaward into clayey silt and silty clay covers the Folk, R.L., 1954, The distinction between grain size and mineral sorting. Grains are classified by their Gravelly sand Fire Island Anchorage 1977; Hampton and others, 1986; Evans, 1997), will help marine coarseness of the bottom sediment reinforces the influence of the strong relict pebbly mud to mid-shelf and beyond (Carlson and others, 1977). composition in sedimentary-rock nomenclature: Journal of maximum dimension. Gravel includes biologists develop an understanding of sea-floor geology in relation to tidal currents on the seafloor habitats. Shelf and slope channel systems transport glacially derived sediment Geology, v. 62, p. 344-359. Muddy to sandy gravel Valdez particles larger than 2.0 mm in diameter, various biological habitats. across the continental margin into Surveyor channel, an abyssal fan and Gravelly mud sand grains range from 0.0625 to 2.0 mm The pattern of sea-floor sedimentation and bottom morphology in Kodiak Shelf -- Tectonic framework studies demonstrate the development channel system that reaches over 1,000 km to the Aleutian Trench Hampton, M.A., 1989, Geotechnical properties of sediment on the across, silt ranges from 0.039 to 0.0625 mm the Gulf of Alaska reflects a complex interplay of regional tectonism, of an accretionary wedge as the Pacific Plate underthrusts the Alaskan (Carlson and others, 1996). Kodiak continental shelf and upper slope: Marine Geotechnology, 61˚ Sand across, and clay includes all particles Turnagain Arm glacial advances and retreats, oceanic and tidal currents, waves, storms, landmass (von Huene and others, 1987). Seismic data across the v. 8, p. 159-180. Sandy silt to silty sand smaller than silt. Mud consists of silt plus Glacier Is. eustatic change, and gravity-driven processes. This map, based on accretionary wedge reveal anomalies indicative of fluid/gas vent sites in REFERENCES CITED Hampton, M.A., Carlson, P.R., Lee, H.J., and Feely, R.A., 1986, Geo- clay. Sorting was determined through sieve numerous cruises during the period of 1970-1996, shows distribution of this segment of the continental margin. Geologic hazards research shows Bouma, A.H., Rappeport, M.L., Orlando, R.C., and Hampton, M.A., 1980, Clayey silt to silt Port Wells Esther morphology, sediment, and sedimentary processes, in Hood, D.W., analyses. The ternary diagrams below, Island Identification of bedforms in lower Cook Inlet, Alaska: Sedimentary bottom sediments in areas of study on the continental shelf. The samples that movement along numerous shallow faults poses a risk to sea-floor and Zimmerman, S.T., eds., The Gulf of Alaska, Physical based on classification schemes modified Geology, v. 26, p. 157-177. Silty clay Whittier Prince were collected with piston, box, and gravity corers, and grab samplers. structures (Hampton, 1989). Sea-floor sediment on shallow banks is Environment and Biological Resources: Washington, D.C., U.S. from Shepard (1954) and Folk (1954) Perry Island The interpretations of sediment distribution are the products of sediment eroded by seasonal wave-generated currents. The winnowing action of the Department of Commerce, p. 93-143. Bedrock Bruns, T.R., 1983, A model for the origin of the Yakutat block, an accreting illustrate the proportional relationships of size analyses combined with interpretations of high-resolution seismic- large storm waves results in concentrations of gravel over broad segments Chenega Naked William terrane in the northern Gulf of Alaska: Geology, v. 11, p. 718-721. sediment sizes to the key sediment textures. Island Is. reflection profiles (Carlson and others, 1977; Hampton and others, 1986). of the Kodiak shelf (Hampton and others, 1986). Plafker, George, 1987, Regional geology and petroleum of the northern Blank area at bottom of triangle on right Gulf of Alaska continental margin, in Scholl, D.W., Grantz, Arthur, C o o k I n l e t Carlson, P.R., Molnia, B.F., Kittelson, S.C., and Hampson, J.C., Jr., 1977, Orca Bay and Vedder, J.G., eds., Geology and Resource Potential of the represents sediment with less than 1% Northeastern Gulf of Alaska -- Tectonic framework studies demonstrate Distribution of bottom sediments on the continental shelf, northern Gulf of Kenai Sound Continental Margin of western North America and Adjacent Ocean gravel, as shown in triangle on left. Cordova that rocks of distant origin (Yakutat terrane) are currently attached to and Alaska: U. S. Geological Survey Miscellaneous Field Studies Map, MF- Basins--Beaufort Sea to Baja California: Circum-Pacific Council moving with the Pacific Plate, as it collides with and is subducted beneath 876, 2 sheets, 13 p. -200 for Energy and Mineral Resources Earth Science Series, v. 6, p. -100 Clay Gravel Kalgin Island southern Alaska (Bruns, 1983; Plafker, 1987). This collision process has 229-268. Knight Island Hinchinbrook Island Copper Carlson, P.R., Stevenson, A.J., Bruns, T.R., Mann, D.M., and Huggett, Quentin, River led to pronounced structural deformation of the continental margin and -100 Delta 1996, Sediment pathways in Gulf of Alaska from beach to abyssal plain, in adjacent southern Alaska. Consequences include rapidly rising mountains Shepard, F.P., 1954, Nomenclature based on sand-silt-clay ratios: 25 75 Gardner, J.V., Field, M.E., and Twichell, D.C., eds., The Geology of the Green and high fluvial and glacial sedimentation rates on the adjacent margin Journal of Sedimentary Petrology, v. 24, p. 151-158. Is. United States' Seafloor: The View from GLORIA: London, Cambridge 50 and ocean floor. The northeastern Gulf of Alaska shelf also has Press, Chapter 15, p.255-277. Tuxedni Bay Smith, W. H. F. and Sandwell, D.T., 1997, Global seafloor topography from satellite altimetry and ship depth soundings: Science, vol. 75 25 70 30 Chisik Is. Seward Evans Island 277, p. 1956-1962. Bainbridge Resurrection Is. Controller Bay 1 Bay Latouche Sand 25 50 75 Silt Sand 50 Mud Island von Huene, Roland, Fisher, M.A., and Bruns, T.R., 1987, Geology and -100 Russell Fjor evolution of the Kodiak margin, Gulf of Alaska, in Scholl, D.W., 60˚ <1% Gravel >1% Gravel Icy Bay Elrington Is. Montague Island Kayak Island Grantz, Arthur, and Vedder, J.G., eds., Geology and Resource

-100 d Potential of the Continental Margin of western North America and TARR BANK -100 Adjacent Ocean Basins--Beaufort Sea to Baja California: Circum- Pacific Council for Energy and Mineral Resources Earth Science -200 Yakutat Series, v. 6, p. 191-212. -100 Bay Homer K e n a i P e n i n s u l a Wessel, Paul, and Smith, W.H.F., 1995, The Generic Mapping Tools (GMT), Version 3, technical reference and cookbook: Manoa, Kachemak Bay SOEST, University of Hawaii, 70 p.

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-3000 -4000 Figure 1. Map showing locations of samples collected by the USGS and used to determine distribution of sea-floor sediments.

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Distribution of bottom sediments digitized by K.R. Evans, 1997, from Carlson and others (1977) Alaskan coastline, alaska.cst (USGS), http://walrus.wr.usgs.gov/infobank/bear/poly/ak/alaska.cst MAP OF DISTRIBUTION OF BOTTOM SEDIMENTS ON THE CONTINENTAL SHELF, GULF OF ALASKA SCALE 1:1,000,000 at 60 and Hampton and others (1986). Bathymetry modified from Etopo2 database (Smith and Sandwell, 1997). KILOMETERS A L A S K A The authors gratefully acknowledge the assistance given by Carolyn Degnan for geographic By 010 20 40 60 80 100 Base grid plotted with Generic Mapping Tools, Version 3.0 (Wessel and Smith, 1995). and bathymetric basemaps, and by Christina Gutmacher for final editing changes in Kevin R. Evans, Paul R. Carlson, Monty A. Hampton, Michael S. Marlow, and Peter W. Barnes STATUTE MILES preparation for publication. 10 0 50 Mercator projection This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronic plotters and 2000 Map Area Isobath contours shown in meters (100, 200, then 1000s) between X and Y directions on the same plotter, and paper may change size due to atmospheric conditions; therefore, scale and proportions NOTE: THIS MAP IS NOT INTENDED FOR NAVIGATION may not be true on plots of this map. INDEX MAP SHOWING For sale by U.S. Geological Survey, Map Distribution, Box 25286, Federal Center, Denver, CO 80225 LOCATION OF MAP AREA Available on World Wide Web at http://pubs.usgs.gov/mf/2000/2335/