The Geology of Lummi and Eliza Islands Whatcom
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THE GEOLOGY OF LUMMI AND ELIZA ISLANDS WHATCOM COUNTY, WASHINGTON by PARKER EMERSON CALKIN B.S. Tufts University, Medford, Mass. A Thesis submitted in partial fulfilment of the requirements for the degree of MASTER OF SCIENCE in the Department of GEOLOGY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April, 1959 ABSTRACT Lummi and Eliza Islands form the northeast part of the San Juan Island group in northwest Washington. Lummi is a long, narrow island characterized by a rocky, mountainous southern half and a low, northern half. Eliza is a small T-shaped island southeast of Lummi Island. Lummi Island is underlain by igneous, metamorphic, and sedimentary rocks of Paleozoic to Lower Cenozoic age. The oldest rocks are believed to be those of the Lummi Island Metamorphic and Igneous Complex which form a small, isolated knob in the middle of the island. These are hornblendic rocks, intruded by quartz-albite rocks and cut by numerous aplite and lamprophyric dikes. The age and origin of these rocks is un• known but they may be older "basement" rocks brought to their present position through faulting. Shale, graywacke and granule conglomerate of the Carter Point formation (Paleozoic or Mesozoic) underly most of southern Lummi Island. These rocks show all the character• istics of the typical "graywacke suite" such as great thick• ness, clastic character, rhythmic bedding, and graded bedding. The only fossils found were a few carbonized plant stems im• bedded in fine-grained graywacke. The rocks forming the bed• rock of Eliza Island may be a more metamorphosed equivalent of these. Overlying the Carter Point formation on the southeast side of Lummi Island and directly underlying the sandstone at the northern end are the Reil Harbor volcanics. Although they occur in five isolated outcrops these rocks are grouped together on the basis of lithology and outcrop features. In contrast to an earlier intrusive interpretation these occur as submarine (pillow) lavas and interbedded breccia with tuffaceous - argillaceous rocks rather than as dikes or sills. The lavas of some of the outcrops are spilitic and in most cases are extremely altered. The breccias are dominantly vol• canic - clastic types which show some reworking. The age of the volcanics and underlying Carter Point formation is unknown; however, interbedded sedimentary rocks contain radiolarian tests suggestive of Mesozoic age. Northern Lummi Island is underlain by plant-bearing lithic-feldspathic arenites and conglomerates of the Chuckanut formation (Paleocene). These are believed to have a contin• ental fluviatile origin on the basis of: absence of marine fossils; conspicuous amounts of hematite imbedded in the sand• stone; moderate sorting and rounding; apparent large-scale heterogeneity evidenced by internal structures such as prom- inant cross bedding and cut - fill structures, and the domin• ance of sandstone and conglomerate facies. The Carter Point formation and the overlying volcanics on the southeast side of Lummi Island strike N 40 W and dip 45 degrees NW. Drag folds suggest that southern Lummi Island represents the eastern limb of a northwest plunging anticline. The Chuckanut formation and the underlying Reil Harbor vol- canics at the north end of the island have been folded into three synclines which strike northwest-southeast and plunge gently northwest. During the Pleistocene, northern Lummi Island was blanketed with glacial drift while the higher knobs here and the rocks of southern Lummi were grooved, polished or eroded by the glaciers. In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Parker E». Galkin Department of Geology The University of British Columbia, Vancouver 8\ Canada. Date 29- A^rll, 1959 CONTENTS Chapter Page I. INTRODUCTION 1 Location and access 1 Previous geological work 1 Field Work 4 Acknowledgments . 5 II. GEOGRAPHY 6 Surface Features 6 Lummi Island 6 Eliza Island , 8 Climate 9 Vegetation 9 Culture ' 10 Water supply and drainage 11 III. GEOLOGY 12 General Features 12 Lummi Island Metamorphic and Igneous Complex ... 14 Introduction 14 Description 15 Hornblendic rocks ..... 16 Quartz-albite rocks 19 Dikes 21 Veins and albitization 22 Sequence of events 22 Discussion 23 Carter Point Formation 25 Introduction 25 Previous Work 25 Stratigraphies relations on Lummi Island .... 26 Sedimentary structures 30 Graded-bedding 30 Cross-bedding 31 Slump structures 31 Intraformational breccia 31 Lithology at the coarse fraction 32 Diagenesis and the graywacke problem 37 Lithology of the fine fraction . 39 Veins 40 Origin and conditions of deposition 40 Age and correlation 42 Reil Harbor volcanics 45 General 45 Outcrop features 46 Description 51 Pillow Lavas 51 Amygdules, veins, and vugs 54 Alteration 54 Page Breccias 56 Origin of the clastic breccias 61 The spilite problem 62 Tuffs 68 Previous geological work 70 Age Relations 72 Chuckanut formation 75 General 75 Previous work 75 General stratigraphy - Lummi Island 77 Lithology 80 Conglomerate 80 Sandstone 82 Diagenesis 90 Sedimentary structures 91 Cross-bedding 91 Graded-bedding 93 Concretions 93 Intraformational breccias 95 Mud balls . 95 Carbonaceous deposits of Lummi Island 96 Origin and conditions of deposition 105 Paleoclimatology 106 Age and correlation 107 Glaeiation 108 Geomorphology 114 Coastlines 114 Lithologic control of weathering 114 Marine cliffs and terraces 115 Fretted surfaces 117 Lummi Point 117 Structure . 119 Regional structure 119 Carter Point formation and Reil Harbor vol• canics of the southern half of Lummi Island 120 Eliza Island 123 Structure of the sedimentary and volcanic rocks a.t the northern half of Lummi Island 123 Cross-island faults 126 Bibliography 128 Appendix 133 ILLUSTRATIONS Plate Page 1. Geologic map of Lummi and Eliza Islands in pocke4^^p 2. Diagramatic Structural Sections, Lummi Island . in pe^ekWc^s. 3. Map showing location of water wells on the ( s northern half of Lummi Island in poefce-15) View looking East from Orcas Island showing the southern two-thirds of Lummi Island . frontispiece Figure 1. Index Map 3 ''2, Eliza Island looking southeast from Lummi Island . 18 3. Hand specimen of hornblendic rock, Lummi Island Metamorphic and Igneous complex 18 4. Section of the Carter Point formation 28 5. Laminated siltstone and fine-grained graywacke, Carter Point formation 29 6. Photomicrograph of graywacke, Carter Point formation 29 7. Photomicrograph showing graded bedding in laminated siltstone, Carter Point formation . 33 8. Hand specimen of shale granule breccia, Carter Point formation 33 9. Mineral composition, Carter Point formation, graywackes 35 10. Carbonized plant stems in a specimen of fine• grained graywacke, Carter Point formation ... 47 11. Pillow lavas, Reil Harbor volcanics ... 47 12. Limestone pod interbedded with ribbon chert , Reil Harbor volcanics 50 13. Contorted ribbon chert, Reil Harbor volcanics ... 50 14. Photomicrograph of spilitic lava, Reil Harbor volcanics 57 15. Breccia of the Reil Harbor volcanics 57 16. Photomicrograph of tuffaceous argillite, Reil Harbor volcanics 67 17. Photomicrograph of specimen 5/7/6-2A from the tuff sequence overlying the Reil Harbor volcanics 67 18. View looking SE at Migley Point showing con• glomerate of the Chuckanut formation lying upon the eroded surface of the pillow lavas of the Reil Harbor volcanics 78 19. Short stratigraphic section of the Chuckanut formation at its base on Lummi Island 79 20. View of the Chuckanut formation at Fern Point ... 92 21. Cumulative frequency, curve of a typical sand• stone, Chuckanut formation 84 Figure Page 22. Mineral composition, Chuckanut formation, sandstone 86 23. Petrography of representative samples of the Chuckanut formation,sandstone ... 87 24. View N. showing cross-bedded sandstone, Chuckanut formation 94 25. View SW of spine-like pattern in sandstone, Chuckanut formation 94 26. Hand specimen of black micaceous sandstone lens, Chuckanut formation 97 27. Photomicrograph of the micaceous sandstone shown above (Figure 25) 97 28. Coalified wood fragment interbedded with sand• stone, Chuckanut formation 99 29. Irregular masses of coalified vegetal material with radiating stringers occurring in sandstone,Chuckanut formation 99 30. Photomicrograph of a tangential section from a specimen of coalified wood, Chuckanut formation 102 31. View NE showing a coalified log (A) cutting across beds of the Chuckanut formation 104 32. View SW showing glacial grooves and polished surfaces in Reil Harbor volcanics , 104 33. Folds in stratified outwash deposits (A) formed by thrust of glacier 116 34. Wave-cut cliff and bench in Reil Harbor volcanics . 116 35. (a and b) Fretted surface, formed by differ• ential wave erosion of sandstone, Chuckanut formation 118 36. View NE of Chuckanut formation showing small scale fault 125 TABLES Page Table 1. Table of formations 14 Table 2. Comparison of outcrop features of the Reil Harbor volcanics 48 Table 3. Petrography of the outcrops of the Reil Harbor volcanics 52 View looking E. from Orcas Island shov; ing the southern two-thirds of Lummi Island and Mt. Baker in the background W.R.Danner, July, 1957. CHAPTER I INTRODUCTION LOCATION AND ACCESS Lummi Island and adjacent Eliza Island are located in western Whatcom County in northwestern Washington (see Figure 1). They form the northeastern part of the San Juan Island group. The area included in the geologic map of this report is that occupying the northern half of the Anacortes Topo• graphic Quadrangle between 122° - 34' and 122° - 44' west longitude, and between 40° - 30' and 48° - 45' north latitude. The mainland opposite Lummi Island is easily reached by car and is an approximate two hours drive from Vancouver, British Columbia or a fifteen minute drive from Bellingham.