Lower Matanuska Valley Alaska
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DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, DIRECTOK BTTLI/ETIN 500 *- J 0 GEOLOGY AND COAL FIELDS OF THE LOWER MATANUSKA VALLEY ALASKA BY G. C. MARTIN AND F. J. KATZ WASHINGTON GOVERNMENT PRINTING OFFICE 1912 CONTENTS. Page. Preface, by Alfred H. Brooks.............................................. 7 Introduction....................;......................................... 9 Location.............................................................. 9 Account of investigations............................................... 9 Exploratory and reconnaissance surveys............................. 9 Detailed surveys.................................................. 10 General description of the district....................................... 10 Geography............................... .*. ........................ 10 Climate............................................................ 11 Vegetation......................................................... 13 Accessibility....................................................... 13 Commercial development........................................... 14 Outline of the geology of the Matanuska Valley.......................... 14 General features................................................... 14 Mica schists....................................................... 15 Gray wackes and slates of the Knik Eiver region..................... 16 Lower Jurassic rocks................................................ 17 Granitic rocks.................................................... 19 Middle and Upper Jurassic rocks.................................... 20 Lower Cretaceous rocks............................................. 22 Upper Cretaceous rocks............................................ 23 Tertiary rocks..................................................... 24 Quaternary deposits............................................... 25 Detailed description of the rocks of the lower Matanuska Valley.............. 26 Granitic and gneissic rocks.............................:................ 26 Areal distribution................................................. 26 Lithologic character............................................... 27 Age and relations................................................... 27 Lower Jurassic rocks................................................... 29 Volcanic breccia, agglomerate and tuff.............................. 29 Areal distribution............................................. 29 Lithologic character........................................... 29 Fauna........................................................ 30 Age and correlation............................................. 31 Lower Cretaceous (?) rocks ............................................ 32 Limestone........................................................ 32 Areal distribution............................................. 32 Lithologic character..................................%......... 32 Stratigraphic relations......................................... 33 Age and correlation............................................. 33 Upper Cretaceous rocks................................................ 34 Areal distribution................................................. 34 Lithologic character............................;.................. 34 Fauna and flora...............................:................... 36 Age and correlation................................................. 38 3 140213 4 CONTENTS. Detailed description of the rocks of the lower Matanuska Valley Continued. Page. Tertiary rocks....................................... ,................. 39 Arkose, conglomerate, and shale..................................... 39 Areal distribution............................................. 39 Lithologic character........................................... 39 Stratigraphic relations......................................... 41 Flora......................................................... 42 Chickaloon formation.............................................. 42 Areal distribution............................................. 42 Lithologic character........................................... 43 Flora and fauna.............................................. 49 Age and correlation........................................... 52 Eska conglomerate................................................ 52 Areal distribution............................................. 52 Lithologic character........................................... 53 Age and correlation^.......................................... 54 Basaltic lavas and tuffs............................................ 54 Tertiary intrusive rocks............................................ 55 Diorite porphyries............................................. 56 Areal distribution.......................................... 56 Petrographic character. .................................. 56 Local relations............................................ 58 Trachytic rocks................................................ 61 Areal distribution......................................... 61 Petrographic character..................................... 61 Local relations............................................ 62 Diabase and gabbro.......................................... 63 Areal distribution......................................... 63 Petrographic character..................................... 63 Local relations............................................ 64 Quaternary deposits................................................... 67 Morainic deposits................................................. 68 Terrace gravels.................................................. 69 Alluvium........................................................ 71 Structure................................................................ 72 Mineral resources........................................................ 75 Coal................................................................. 75 Areal distribution................................................. 75 Stratigraphic occxirrence.......................................... 77 Description of beds............................................... 77 Character of the coal............................................... 88 Physical properties............................................ 88 Chemical analyses and tests.................................... 89 Coking qualities............................................. 92 Mining conditions................................................ 92 Mine sites................................................... 92 Local supplies............................................... 93 Underground water and gas.................................... 93 Effect of intrusive rocks....................................... 93 Effect of folding and faulting.................................. 94 Metals............................................................... 95 Index.................................................................... 97 ILLUSTRATIONS. Page. PLATE I. Map of central Alaska, showing position of the coal fields........ 10 II. A, Talkeetna Mountains from the west side of Kings River; B, North wall of Matanuska Valley about 12 miles above Chicka- loon River................................................. 10 .. III. Geologic reconnaissance map of the Matanuska Valley....... In pocket, p IV. Topographic map of the lower Matanuska Valley........... In pocket, t/'j V. Geologic map of the lower Matanuska Valley.............. In pocket, y VI. A) Granite and Tertiary arkose in gulch on the west side of Sheep Valley; B, Granite and Tertiary arkose in the west wall of Sheep Valley.............................................. 28 VII. A, Granite overlain by arkose at the head of Sheep Valley; B, Sheep Valley from a point near its lower end-.................. 28 VIII. A, Exposure of arkose in cliffs on north slope of ridge north of Moose Creek; B, Gently dipping arkose in west end of ridge north of Moose Creek........................................ 40 I.. A, Eska conglomerate on west wall of valley of Eska Creek, at east end of Wishbone Hill; B, Eska conglomerate in west end of Castle Mountain......................................... 52 X. A, Tertiary lavas, unconformably overlying Eska conglomerate on Castle Mountain; B, Eska conglomerate overlain by small cap of Tertiary lava on southeast spur of Castle Mountain...... 56 XI. A, Porphyry sill (?) in valley of Young Creek overlying Chicka- loon formation; B, Porphyry sills and dikes in Upper Creta ceous rocks on south bank of Matanuska River 2.7 miles below Chickaloon River.......................................... 56 XII. A, Diabase dike on fault in Chickaloon formation at base of Castle Mountain; B, Diabase dikes and sills in Chickaloon formation on north bank of Boulder Creek............................. 64 XIII. A, Stratified gravels on east bank of Kings River near lower bridge; B, Gravel cliffs on north bank of Matanuska River 1 mile above Moose Creek................................................ 70 XIV. A, Fault on north edge of Matanuska Valley near headwaters of Young Creek; B, Fault between granite and Upper Cretaceous rocks....................................................... 72 XV. Structure sections in lower Matanuska Valley................... 72 XVI. Structure sections in lower Matanuska Valley................. 72 XVII. A, Coal beds in west bank of Eska Creek 2.7 miles north of Mata nuska River; B, Coal bed in west bank of Eska Creek 2.4 miles north of Matanuska River...................................