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Marine Geology of Astoria Deep-Sea Fan

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Marine Geology of Astoria Deep-Sea Fan AN ABSTRACT OF THE THESIS OF CARLTON HANS NELSON for the Ph. D, (Name) (Degree) inOCEANOGRAPHY presented on _j _ (Major) (Date) Title: MARINE GELGY OFSTORIA DEEP-SEA FAN Abstract approved: Redacted for privacy JohnV. By Astoria Fan lies on the continental rise off Northern Oregon and has its apex near the mouth of Astoria Canyon.The fan has an asymmetrical shape, evidently because the structurally controlled Cascadia deep-sea channel borders it and because the fan valleys have migrated southward ("left") during the fan construction. A few narrow, deep channels occur on the steep upper fan (gradient < 1:100) and these divide into many depositional distributaries on the flatter middle and lower fan (gradient 1:400 to> 1:1000).The olive gray postglacial clay, which is characterized by radiolarian fauna, is one meter thick in interchannel regions and more than five meters thick in main channels.Underlying the postglacial clay is a late glacial gray silty clay that contains numerous gravel, sand and silt interbeds (coarse layers), and that has a dominant fauna of planktonic foraminifera. Hemipelagic fan deposits are characterized by high clay and faunal content,, and are dominant in the postglacial section.Coarse layers deposited by density currents are distinguished by dominance of Columbia River detrital minerals and displaced benthic foramini- fera, moderate sorting, grading of size and composition, and typical turbidite sequence of sedimentary structures.Thetail" deposits from density currents are characterized by clayey-silt size and by a coarse fraction of platy constituents (mica and plant fragments). Denity-current deposition predominates in the late-glacial sediments. Fan ash layers are correlated with continental deposits from the cat3clysmic eruption of Mt. Mazama 6, 600 B. P. by position in the stratigraphic column, refractive index, and radiocarbon dating. Textural and compositional gradation, Columbia River mineral suites, and upper slope fauna within the tuffaceous layers indicate that ash was spread throughout the fan by density currents. Thickness and distribution of the tuffaceous layers and coarse layers reveal that transportation and deposition of the main, coarsest portion of density currents is restricted to fan valleys and distributaries; fine, sorted "tail" debris spreads beyond even the deepest channels (> 100 fathoms) and builds upper fan interchannel regions.High coarse layer:shale ratios throughout the main fan valleys and the middle and lower fan result from this density-current depo sition. Because of density-current processes, proximal regions of the fan can beidentified by the low coarse layer:shale ratios in inter- channel regions, by, poorly, sorted, massive, and gravelly coarse layers, andbya stratigraphy of coarse beds with sharp upper con- tacts, irregularthickness, and poorly developed clay partings. Away from the proximal regions, coarse layers progressively: (1) decrease in skewness, and content of clay, platy constituents, and heavy minerals, (2) increase in content of detrital minerals, (3) have better sorting, and. development of sedimentary structures.Herni- pelagic deposits grade out from the continental terrace and Columbia river plume, which is the source of clay; they contain more clay and planktonic remains, but less terrigenous debris toward the open ocean. The aforementioned data of Astoria Fan provide criteria for a fan model that helps in identifying fan deposits of the geological record, and that permits speculation on the history of Astoria Fan. In the Pleistocene, deep channels were eroded in the upper fan into older clays with "ice rafted(?)" pebbles.Coarse density-current debris was funneled through the channels to depositional distribu- taries of the middle and lower fan1With shift of the shoreline to the east, which is shown by change to finer texture and greater plank- tonic composition of the postglacial hemipelagic sediments, and with rise of sea level, density-current activity slackened.In thepost- glacial,period influxofivlazama ash provided material for the last large density currents on the fan; it also may have contributed to rapid filling of fan valleys which is indicated by the following sedimentation rates calculated from faunal reversal and Mazama ash horizons: Channel Interchannel Postglacial 25 cmjlO'3 yrs 8 cm/tO3 yrs Pleistocene > 40cm/tO3yrs Based on observed sedimentation rates, present sediment loads of the Columbia River, and seismic thickness of unconsolidated fan sediments, it appears that the fan was built mainly during the Pleistocene. Marine Geology of Astoria Deep-Sea Fan by Canton Hans Nelson A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 1968 APPROVED: Redacted for privacy Pr essor of Oce graphy in charge of major Redacted for privacy irman of Delartment of Ocgraphy Redacted for privacy DeanbiGraduate School Date thesis is presented c'cN \))\T_ Typed by Marion F. Palmateer ACKNOWLEDGEMENTS I would like to express my appreciation to my major professor, Dr. John V.. Byrne, for:his guidance throughout the project, andfor his critical review of the manuscript and figures. Dr. Vern Kulm provided considerable assistance in perfecting techniques of piston.coring,and sediment size analysis.Dr. Gerald Fowler confirmed identification of and depth ranges for for.ammnifera species.The help of Sue Bordon. in computer programming and. data processing is gratefully acknowledged. Many, beneficial discussions were held with the aforementioned faculty members and the following graduate students: Paul Carison, Erwin Runge, John Duncan, Gary.Griggs, Dick Boettcher, Jim Ridlon, Dave Allen,. and Arthur Hunger.I would. like to express my gratitude to all of these people and,.to the crews of the R. V. Acona and the R. V. Yaquina.. for help with the difficult task of collecting piston cores. The author also wishes to express great. appreciation to his wife, Jane, for many.hours spent typing, drafting,. and editing the disserta- tion, .and. for her helpand encouragement throughout the entire course of study. This study was madepossible 'through the financial support of the office of' Naval Research (Contract Nonr1286 (10) and the research facilities of the Oceanography.. Department, Oregon State Tjniver sity. TABLE OF CONTENTS Page L INTRODUCTION 1 Purpose 1 Previous Work 3 II. GEOLOGIC SETTING 5 Continental Geology 5 Columbia River Drainage 6 IlL, OCEANOGRAPHIC SETTING 8 General 8 Water:Masses 8 Currents 9 Biological Oceanography 14 IV. PHYSIOGRAPHY 16 General 16 Continental Terrace 16 Astoria Canyon 17 Astoria Fan 18 Channel Systems of Astoria Fan 28 Comparison of Astoria Fan Valleys with Astoria Canyon, and Cascadia Channel 36 Comparison of Astoria Fan Valleys with Other Fan Valleys 37 Comparison of Astoria Fan with Other Deep-sea Fans 39 Astoria Fan Compared with Alluvial Fans 43 V. SEDIMENTS 45 Sampling Methods 45 General Stratigraphy of the Fan 48 Lithology, Texture, andCoarse Fraction of Sediment Types 52 Composition 78 Summary of Characteristics of Displaced Foraminifera 86 Comparison with Coarse Layers of Other Regions 109 Page VL STRATIGRAPHY 114 Correlation and Age of the Stratigraphic Units 114 Establishment of a CorrelatingAsh Horizon 117 Summary of Astoria Fan Stratigraphy 124 Comparison with Stratigraphy of Other Regions 126 VII. SOURCEOF SEDIMENTS 131 Terrigenous Materials 131 VIII. SEDIMENTARY PROCESSES 138 Hem ipelagic Sedimentation 1 38 Transportation and Deposition of Exotic Materials 139 Other Sedimentary Processes 151 IX. RATES OF DEPOSITION 157 General 157 Interchannel Regions 160 Channels 161 Sedimentation Rates Compared with Other Regions 162 X. GEOLOGIC HISTORY OF ASTORIA FAN 166 History of the Region 166 Sequence of Events in Astoria Fan History 169 Estimates of Astoria Fan Age 177 Age of Fan Based on Sedimentation Rates 179 XI. GEOLOGIC SIGNIFICANCE 186 General Characteristics of Fans 186 Review of the Density-Current Process 187 Significance of Deep-sea Fans in Geologic History 193 Application to Ancient Rocks 198 BIBLIOGRAPHY 208 APPENDICES 225 LIST OF FIGURES Figure Page 1 Submarine and continental physiographic features in the vicinity of Astoria Fan. 2 2 Sample station locations and bathymetric sounding lines completed on Astoria Fan. 19 3 Bathymetric chart of Astoria Fan, 20 4 Transverse profiles of Astoria Channel and Slope Base Fan Valley. 22 5 Physiographic divisions and fan valley systems of Astoria Fan. 6 Longitudinal profiles and Precision Depth Recorder profiles of Astoria Fan. 25 7 Physiography of the apex region of Astoria Fan. 29 8 Sediment types of Astoria Fan. 47 9 Thickness of brown clay and of olive gray clay. 49 10 Representative lithology of Astoria Fan. 51 11 Relation between sorting versus mean grain size, physiographic location, and coarse fraction con- tent of Astoria Fan coarse layers. 56 12 Relation between sorting versus mean grain size, physiographic location, and coarse fraction con- tent of fine-size sediments of Astoria Fan. 57 13 Relation between skewness versus mean grain size and stratigraphic units of Astoria Fan sedi- ment types. 58 14 Sand-silt--clay content of sediment types in the various physiographic regions of Astoria Fan. 59 15 Terrigenousplaty-terrigenous, and biogenous content of sediment types in the various physio- graphic regions of Astoria Fan. 60 LIST OF FIGURES (continued) Figure Page 16 Representative cumulative size frequency curves for Astoria Fan sediment types. 62 17 Triangular diagram of the
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