1
MIS 2—FRASER GLACIATION MIS 4—POSSESSION GLACIATION MIS 5 AND EARLIER INTERVALS MIS 3—OLYMPIA NONGLACIAL INTERVAL ? ? ? ? Qgo Qaf Qls Qp Qa Qmw af Qpu Qgaf Qgic Qgt Qps Qgos Qc o ml Qpt Qgas Qga Ev p Qcg o …En …Ec …vt Evs pg KJm w …vt …Ec EOCENE TERTIARY PLEISTOCENE QUATERNARY HOLOCENE OLIGOCENE MIOCENE CRETACEOUS JURASSIC 11.700 ±0.099 ka 33.9 ±0.1 Ma 43.4 ±0.4 Ma (this study) 23.03 ±0.05 Ma 27.8 ±0.4 Ma (this study) 145.5 ±4.0 Ma 170–74 Ma CORRELATION OF MAP UNITS NONGLACIAL UNITS GLACIAL AND NONGLACIAL UNITS, UNDIVIDED GLACIAL UNITS PERIODS AND EPOCHS BASED ON USGS FACT SHEET 2010-3059 Vashon ice arrival in map area—likely between 18 and 17.5 ka (Polenz and others, 2015) contact not observed Vashon ice retreat from map area—likely between 16 and 15 ka (Polenz and others, 2015) UNCONFORMITY 36–47 Ma (Dragovich and others, 2013) (Tabor and others, 1993) (Dragovich and others, 2014a) UNCONFORMITY Ei p 2 1 COMPOSITE COLUMNAR SECTION 1 near High Bridge (sec. 34, T28N R6E) COMPOSITE COLUMNAR SECTION 2 SR 2 (sec. 23, T27N R6E) Qga Qgt covered 10-28D: >43,500 yrs BP (elev. 21 ft) (Dragovich and others, 2010a,b) GD7: 67,100 ±3,700 yr (IRSL) 62,000 ±3,720 yr (OSL) (elev. 26 ft) (elev. 81 ft) GD9: 53,030 ±4,510 yr (IRSL) 52,120 ±3,910 yr (OSL) (elev. 95 ft) GD8: 34,890 ±2,790 yr (IRSL) 27,430 ±2,750 yr (OSL) (elev. 115 ft) GD5: 28,140–27,810 yr BP GD10: 21,700 ±1,520 (IRSL) 20,890 ±1,775 (OSL) (elev. 133 ft) (elev. 141 ft) GD1: 21,885–21,615 yr BP unconformity Qc o Qgas Qgt elev. 40 ft elev. 100 ft 90 ft GD12: 32,220 ±2,090 yr (IRSL) (elev. 55 ft) GD3: 27,410–27,140 yr BP (elev. 73 ft) (Snohomish quadrangle) Snoqualmie River (active channel) 40 ft 83 ft 150 ft 173 ft elev. 20 ft elev. 210 ft 25 ft Qpu Qps Qps Qcg o Qc o (Snohomish quadrangle) 0 200 400 600 800 -600 -400 -200 200 400 600 800 -600 -400 -200 0 ? ? ? ? ? FIDDLERS BLUFF ANTICLINE …En …En …En …En Qpu Qpu Qpu Qga Qga Qcg o Qc o …Ec Qpu Ev p Evs pg KJm w …Ec? Qgaf Qgaf Qgaf Qgo Qgt Qgt Qgt Qgt Qgt Qgic Qgic Qa Qa Qaf ml Qgic Qp Qgo Qgic Qp Qgic …vt Qgic ml Qa Qp Qgas Ei p Ei p Ei p W68 W63 W64 W65 W62 W61 W53 W51 W54 W52 W47 W46 W43 W37 W35 W18 W24 W23 W25 B12 W2 Snohomish River Crystal Lake Road Paradise Lake Road State Route 522 U.S. Route 2 GEOPHYSICAL LINEAMENT B GEOPHYSICAL LINEAMENT A $ƍ A 3x vertical exaggeration Elevation (ft) Elevation (ft) SOUTHERN WHIDBEY ISLAND FAULT SOUTHERN WHIDBEY ISLAND FAULT ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? CROSS SECTION EXPLANATION W43 Geologic units too thin to show as polygons at the scale of the cross section. Bedding form lines—solid where accurate; long dashed where inferred Water well or boring Qa GP1 A Aƍ cross section A Southern Whidbey Island fault geophysical lineament Fiddlers Bluff anticline 1 mGal interval 5 mGal interval Bouguer anomaly contours Aƍ A MALTBY QUADRANGLE MALTBY QUADRANGLE Seattle Basin Everett Basin -95 -90 -85 -80 -75 -70 -65 -60 -55 -50 -45 -85 -45 -50 -45 -55 -45 -40 -35 -30 -25 -40 -40 -35 -45 -50 -40 -60 -65 -70 -70 -65 -60 -55 -60 GEOPHYSICAL LINEAMENT B G E O P H Y SIC AL LINEAMENT A SB EB SB EB 0 2 4 mi 52.5 -276.9 -255.3 -237.1 -225.0 -211.6 -197.5 -186.7 -174.3 -155.5 -133.4 -103.4 -4.1 40.7 93.3 Magnetic anomalies (nanoteslas) ƍƎ ƍƎ ƍƎ ƍƎ Figure M2. Reduced-to-pole aeromagnetic anomaly imagery is from Richard Blakely (USGS, written commun., 2016). Isostatic gravity anomaly contours are from this study. The Maltby quadrangle boundary is shown in red. Faults within the quadrangle boundary correspond to the Grace and Cottage Lake lineaments of Sherrod and others (2008). The Fiddlers Bluff anticline and geophysical lineaments are from this study (see pamphlet, Geophysical Observations). ? ? ? ? ? ? EVERETT BASIN SEATTLE BASIN SW K A SS SD U S MALTBY MALTBY LAKE CHAPLAIN SNOHOMISH REDMOND BOTHELL EVERETT KIRKLAND SEATTLE NORTH EDMONDS EAST MUKILTEO LAKE ROESIGER GRANITE FALLS VERLOT LAKE STEVENS MONROE CARNATION SULTAN LAKE JOY 2 90 5 405 5 Lynnwood Marysville CF C C F Z Sultan Bellevue S E A T T L E F A U L T P u g e t S o u n d TCFZ MF MF S O U T H E R N W H I D B E Y I S L A N D F A U L T Z O N E PF EFB MS Everett RMFZ Seattle FBA MA MS S n o q u a l m ie R i v e r S k y k o mis h R i ver S n o h o m is h R iv e r Duvall Snohomish Woodinville Monroe Cathcart Woods Creek K I N G S T O N A R C H GFFZ ƍ Ǝ 1 ƍ 1 ƍ : ƍ : Quaternary deposits Holocene nonglacial Pleistocene glacial and nonglacial Pre-Quaternary sedimentary rocks Miocene Oligocene–Eocene Eocene, undifferentiated Eocene Tukwilla Formation oil and gas well A fault, undivided ? ? syncline geophysical lineament anticline fault, reverse fault / fold queried where questionable Igneous rocks Eocene rhyolite of Hansen Lake Eocene volcanic rocks of Mount Persis Eocene Pilchuck stock and Bald Mountain pluton Metamorphic rocks Cretaceous–Jurassic :estern mélange belt Geologic structures 0 5 10 mi Figure M1. Regional geologic map of the Maltby quadrangle. Geologic units are from 1:100,000-scale mapping (WADGER, 2016). Locations of the Seattle Fault and Kingston arch are from 1:250,000-scale mapping (WADGER, 2010). Seattle and Everett basins modified from Pratt and others (1997, plate 1) and Dragovich and others (2015, 2016, fig.1). The westernmost extents of the Monroe fault (MF), Monroe anticline (MA), and Monroe syncline (MS) are simplified from Dragovich and others (2015, fig. 10). The Southern Whidbey Island fault zone traces are simplified from Dragovich and others (2002) and Sherrod and others (2008). Geophysical lineaments (green) and the Fiddlers Bluff anticline (FBA) are from this study. Structures east of the quadrangle are simplified from Tabor and others (1993, 2002) and Dragovich and others, (2007, 2009, 2010a, 2011a, 2012, 2013, 2014a, 2015, 2016). RMFZ, Rattlesnake Mountain fault zone; CF, Carnation fault; EFB, Explorer Falls basin; TCFZ, Tokul Creek fault zone; CCFZ, Cherry Creek fault zone; GFFZ, Granite Falls fault zone; PF, Pilchuck fault. Oil and gas exploration wells are from Washington Geological Survey records: A, Alderwood No. 1; SS, Socal-Schroeder No. 1; K, Kingston No. 1; SW, Socal-Whidbey No. 1; S, Snohomish No. 1; SD, Sol Duc Delfel No. 1; U, unnamed. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? S O U T H E R N W H I D B E Y I S L A N D F A U L T SOUTHERN W H I D B E Y I S L A N D F A U L T ? ? $ƍ A G E OP H Y SI CA L LI N E AME N T — A GE OPHY S I CAL L INEAMENT — B …vt …vt ? ? ? ? ? ? ? F I D D L E R S B L U F F A N T I C L I N E FL-12 FL-228 GD14 GD21 10-28D GD5 GD10 GD20 GD27 GD11 09-54Z GD1 GD8 GD24 GD 17 GD23 GD26 GD16 GD19 GD4 GD7 GD6 GD2 GD13 GD28 GD18 GD15 GD9 GD25 W33 W41 GP4 G15-16 W5 S1 G5 W53 W10 G1-2 B4 W59 W44 W55 W58 W2 W64 MBFT W1 G9 W25 W67 W17 G13 B11 GP3 W30 W31 W38 W14 G10 CS2 B6 …vt B1 W66 W19 W37 S5 B8 S3 DNRFT1 B9 W34 P4 B2 W9 W27 W51 G11 S2 FSFT B5 W8 P5 G19 B3 W63 W50 CS1 G8 W39 W7 W35 W11 P1 W4 GP6 W60 W13 W65 W48 W20 W43 P6 W40 W18 W3 W12 G14 B10 GP2 G6 W23 W80 P7 G4 W61 GP1 W49 GP5 GP7 W54 S4 W42 B7 W62 W24 G3 G12 W36 G17- 18 W45 W15 W46 W57 W56 W32 W16 G7 W21 W28 W47 W52 W29 W6 W22 DNRFT2 W26 4 18 28 27 77 16 63 82 4 59 8 26 82 26 22 73 85 58 7 16 61 11 5 9 18 73 26 6 31 15 78 21 34 59 78 14 9 10 18 13 59 5 19 4 84 72 32 3 80 13 66 12 28 23 13 82 61 28 9 4 29 70 59 15 35 31 13 32 27 29 29 33 30 15 70 27 18 57 ml ml ml ml ml ml ml ml ml ml ml ml ml Ev p Ev p Ev p Ev p Ev p Ev p Ev p Ev p Ev p Ev p Ev p Ev p Ei p af af af af af af af af af af af …Ec …Ec …Ec …Ec …Ec …Ec …Ec …Ec? …En …En …En …En …En …En …En …En …En …En …En …En …En …En …En …En Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Qa Ei p Ei p Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qaf Qpu Qpt Qc o Qc o Qc o Qc o Qc o Qc o Qc o Qcg o Qcg o Qcg o Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qga Qgaf Qgaf Qgaf Qgaf Qgaf Qgaf Qgaf Qgaf Qgaf Qgaf Qgaf Qgaf Qgas Qgas Qgas Qgas Qgas Qgas Qgas Qgas Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgic Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgo Qgos Qgos Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qgt Qls Qls Qls Qls Qls Qls Qls Qls Qls Qls Qls Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qmw Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qp Qps Qpt Qpu Qpu Fiddlers Bluff Fryelands trough 122°07ƍ 30Ǝ 47°52ƍ 30Ǝ 50ƍ 00Ǝ 47ƍ 30Ǝ 47°45ƍ 00Ǝ 122°07ƍ 30Ǝ 05ƍ 00Ǝ 02ƍ 30Ǝ 122°00ƍ 00Ǝ 47°45ƍ 00Ǝ 05ƍ 00Ǝ 02ƍ 30Ǝ 122°00ƍ 00Ǝ 47°52ƍ 30Ǝ 50ƍ 00Ǝ 47ƍ 30Ǝ T 28 N T 27 N R 5 E R 6 E T 27 N T 26 N T 28 N T 27 N R 5 E R 6 E T 27 N T 26 N This geologic map was funded in part by the U.S. Geological Survey National Cooperative Geologic Mapping Program under USGS award number G16AC00286, 2016–2017. 7000 FEET 1000 1000 0 2000 3000 4000 5000 6000 0.5 1 KILOMETER 1 0 0.5 1 0 1 MILE SCALE 1:24,000 contour interval 20 feet APPROXIMATE MEAN DECLINATION, 2017 MAGNETIC NORTH TRUE NORTH 16° Disclaimer: This product is provided ‘as is’ without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular use. The Washington Department of Natural Resources and the authors of this product will not be liable to the user of this product for any activity involving the product with respect to the following: (a) lost profits, lost savings, or any other consequential damages; (b) fitness of the product for a particular purpose; or (c) use of the product or results obtained from use of the product. This product is considered to be exempt from the Geologist Licensing Act [RCW 18.220.190 (4)] because it is draft geological research conducted by or for the State of Washington, Department of Natural Resources, Washington Geological Survey. Research supported by the U.S. Geological Survey, National Cooperative Geologic Mapping Program, under USGS award number G16AC00286. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. Lambert conformal conic projection North American Datum of 1927; to place on North American Datum of 1983, move the projection lines approximately 26 meters north and 92 meters east as shown by crosshair corner ticks Base map from scanned and rectified U.S. Geological Survey Maltby 7.5-minute quadrangle, 1981—base map modified to reflect mapped lakes. Shaded relief generated from a lidar bare-earth digital elevation model (available from the Washington Geological Survey, http://lidarportal.dnr.wa.gov/) GIS by Mitchell D. Allen and Skyler P. Mavor Digital cartography by Daniel E. Coe Editing and production by Jessica L. Czajkowski, Jaretta M. Roloff, and Daniel E. Coe WASHINGTON GEOLOGICAL SURVEY MAP SERIES 2017-02 Geologic Map of the Maltby 7.5-minute Quadrangle Pamphlet accompanies map Duvall Maltby Monroe Redmond Bothell Everett Cathcart Snohomish Woodinville MALTBY MONROE BOTHELL EVERETT KIRKLAND REDMOND CARNATION SNOHOMISH LAKE ROESIGER 2 405 5 202 9 96 522 203 527 © 2017 Washington Geological Survey http://www.dnr.wa.gov/geology/ Geologic Map of the Maltby 7.5-minute Quadrangle, Snohomish and King Counties, Washington Mitchell D. Allen, Skyler P. Mavor, Jeffrey H. Tepper, Elizabeth A. Nesbitt, Shannon A. Mahan, Recep Cakir, Bruce A. Stoker, and Megan L. Anderson October 2017 af ml Qa Qaf …Ec Qp Qps Qgos Qgic Qgo Qc o Qga Qcg o Qgt Qls Qmw …En Qpu Qpt Ev p Qgaf Qgas …vt Evs pg KJm w Ei p …vt MAJOR FINDINGS • Eighteen new geochemical samples and a new ~44 Ma U-Pb date from the volcanic rocks of Mount Persis reflect signatures of the nascent Cascade arc in the mid-Eocene. • Refugian-stage foraminiferal and Galvinian-stage molluscan biostratigraphy below a ~28 Ma U-Pb date of interbedded tuff shows that sedimentary rocks are older than previously inferred and record an Eocene or early Oligocene marine transgression. • Luminescence and finite radiocarbon chronology constrain glacial and nonglacial Quaternary deposits between Marine Isotope Stage 2 (MIS 2), and MIS 4. Results may demark a minimum limiting age for the Possession glaciation. • A west-northwest tracing bedrock anticline records late Oligocene or younger north-northeast-directed shortening and may connect to other regional structures. DESCRIPTION OF MAP UNITS (see pamphlet for detailed map unit descriptions) Quaternary Unconsolidated Deposits HOLOCENE NONGLACIAL DEPOSITS Artificial fill—Major road fill placed to elevate the land along road or railways; likely engineered; may include sand, cobbles, pebbles, boulders, silt, clay, organic matter, rip-rap, and concrete, in varied amounts; includes industrial or household waste in landfills. Modified land—Boulders, cobbles, pebbles, sand, silt, clay, diamicton, and organic matter, in varied amounts; locally derived but redistributed to modify topography; underlying units exposed in some areas. LATEST PLEISTOCENE TO HOLOCENE NONGLACIAL DEPOSITS Peat—Organic material and organic-rich sediment; includes peat, gyttja, muck, silt, and clay, with plant or woody debris; rare volcanic ash or pumicite; dark brown or olive-brown; soft; typically wet and may include standing water. Landslide deposits—Cobbles, pebbles, sand, silt, clay, boulders, and diamicton, in varied amounts; in slide bodies and toes; angular to rounded clasts and grains; unsorted; generally loose, jumbled, and unstratified. Mass-wasting deposits—Cobbles, pebbles, sand, silt, clay, boulders, and diamicton, in varied amounts; loose; often wet; generally unsorted; shown along potentially or demonstrably unstable slopes; includes colluvium and (or) landslides too small to map separately. Alluvium—Sand, pebbles, silt, clay, peat, cobbles, and organic material; dark brown to gray; loose; moderately to well sorted; stratified; deposited in flood plains, stream channels, and on terraces. Alluvial fan deposits—Pebbles, sand, silt, cobbles, and boulders, in varied amounts; typically brown to gray; loose; moderately to poorly sorted; weakly to well stratified; forms gently dipping lobe-shaped surfaces where streams emerge from confining valleys. PLEISTOCENE GLACIAL AND NONGLACIAL DEPOSITS Deposits of the Vashon Stade of the Fraser Glaciation Vashon recessional outwash—Sand and pebble to cobble gravel; some silt and clay; gray to tan where fresh; loose or soft to medium soft; subangular to well-rounded polymict clasts; moderately to well sorted; weakly to well stratified. Locally subdivided into: Vashon recessional outwash, sand—Sand with silt, rare pebbles, and clay; gray to pale brown where fresh, orange-brown where weathered; sand subangular to subrounded; moderately to well sorted; loose to medium dense; massive to poorly bedded. Vashon ice-contact deposits—Diamicton (ablation till, flow till, or melt-out till and supraglacial sediment); includes poorly compacted or patchy lodgment till; pale gray, tan, or brown where fresh, orange-brown where weathered; compaction, sorting, and degree of stratification varied; supraglacial, subglacial, or ice-marginal origin; often associated with hummocky or irregular morphology. Vashon lodgment till—Diamicton; gray to brown; lightly to unweathered; unsorted; unstratified; compact; stiff to very stiff; gravel to very large boulders angular to subrounded and supported in a matrix of sand, silt, and clay. Vashon advance outwash, undivided—Sand, pebble to cobble gravel, silt, and clay, in varied amounts; blueish gray, brown, or gray to tan; orange-stained where weathered; compact; sand medium dense to dense; mud medium soft to very stiff; clasts typically rounded and moderately sorted; commonly stratified. Locally subdivided into: Vashon advance outwash, sand—Sand and sparse gravel; pale gray to pale brown; orange-brown where weathered; loose to dense; clasts subangular to subrounded; well sorted; massive to planar-bedded; local thin, planar silt interbeds. Vashon advance outwash, silt and clay—Silt and clay with sparse gravel; blue-gray to gray-brown where fresh, dark brown where weathered; stiff to hard; well sorted; locally sandy; mostly glaciolacustrine with dropstones; thinly bedded to laminated with rhythmic bedding. Pre-Vashon Glacial and Nonglacial Deposits Deposits of the Olympia nonglacial interval (MIS 2–3), sand and silt—Sand and silt with minor clay and gravel; blue-gray to brown-gray where fresh, orange-brown where oxidized, dark brown where organic-rich; very stiff to hard; moderately to very well sorted; micaceous; medium bedded to laminated. Deposits of the Olympia nonglacial interval (MIS 2–3), gravel—Pebble and cobble gravel in coarse sand matrix, rare small boulders; gray-brown to dark brown, orange-brown where weathered; matrix- to clast-supported; clasts subrounded to rounded; moderately to well sorted; weakly stratified and imbricated. Pre-Vashon sand—Medium sand; pale brown to light gray where fresh, orange-brown to gray-brown on weathered faces; medium dense to dense; well sorted; massive or thin to medium planar bedded; discontinuous, thin lens-shaped beds of pebbly sand; centimeter-scale ripple bedforms. Pre-Vashon till—Diamicton; locally sandy; gray, blue-gray, or brown where fresh, orange brown on weathered faces; massive; compact, locally resembles concrete; local shear fabric; polymict clasts. Mapped based on stratigraphic position; poorly exposed. Pre-Vashon glacial and nonglacial deposits, undivided—Sand, silt, clay, pebble gravel, diamicton, organic debris, and boulders, in varied amounts; color, weathering, rounding, sorting, and bedding varied; compact. Tertiary Bedrock Nearshore sedimentary rocks (Oligocene to late Eocene)—Siltstone to coarse-grained sandstone rare pebble conglomerate; brown or gray to dark gray; orange-brown or tan to dark gray on weathered surfaces with hackly concentric weathering pattern; typically tuffaceous and fossiliferous; well lithified to friable; massive to very thickly planar bedded; rare crossbedding. Locally subdivided into: Tuff (Oligocene)—Coarse rhyolitic crystal vitric (ash) tuff; white to light gray on fresh faces, tan to gray on weathered surfaces; very strongly lithified; massive with local faint stratification; line and point units only. Continental sedimentary rocks (early Oligocene to Eocene)—Sandstone and pebble and cobble conglomerate, with minor siltstone and shale; tan to brown or gray-brown when fresh, tan to red-brown where weathered; well indurated but locally friable; clasts subrounded; crossbedded and imbricated; terrestrial plant fossils and thin coal stringers common. Volcanic rocks of Mount Persis of Tabor and others (1993), undivided (mid- to late Eocene)— Andesite and dacite flows, autoclastic breccia, block-and-ash flows, dikes, rare tuff, and volcaniclastic boulder breccia; gray to dark gray; well indurated; fine to coarse grained; massive; columnar jointed. Locally subdivided into: Dikes—Andesite and dacite dikes around the flanks of Lord Hill; steeply dipping with various orientations; planar to gently undulating; locally glassy with rare andesite xenoliths. Puget Group, undivided (Eocene)(cross sections only)—Arkosic sandstone, tuffaceous sandstone, tuff, tuff breccia, andesitic conglomerate, and less common siltstone and coal; not exposed in outcrop; inferred from oil and gas wells west of the map area. Western mélange belt of Frizzell and others (1987), undivided (Cretaceous to Jurassic)(cross sections only)—Metamorphosed argillite, sandstone, chert, pebble conglomerate, tuff, and intermediate to mafic volcanic flows; less common gabbro, diabase, and tonalite; rare marble and ultramafic rocks; not exposed in outcrop or known from subsurface explorations; inferred from geophysical and regional mapping and susbsurface data. 11 A A ƍ GD1 GD25 G3 W50 S2 CS1 GP7 P1 29 57 59 20 16 0 Inclined bedding—showing strike and dip Horizontal bedding Approximate orientation of inclined bedding in unconsolidated deposits or bedrock—showing approximate strike and dip Inclined bedding, where top direction of beds known from local features—showing strike and dip Small, minor inclined joint—showing strike and dip Small, minor inclined fault—showing strike and dip Inclined generic small, minor fold axial surface—showing strike and dip Inclined slickenline, groove, or striation on fault surface—showing bearing and plunge Slickenside—showing strike and dip Inclined flow direction, including sole mark, tool mark, scour mark, flute mark, groove, or channel in sedimentary materials—showing bearing and plunge Inclined bedding in unconsolidated sedimentary deposits—showing strike and dip Inclined foreset bedding in unconsolidated sedimentary deposits—showing strike and dip Inclined flow bands, lamination, layering, or foliation in igneous rock—showing strike and dip Age site, fossil Age site, U-Pb, uranium-lead Age site, 14 C, carbon-14 Age site, luminescence (OSL and (or) IRSL) Geochemistry sample location Water well Significant site Geologic unit too small to show as a polygon at map scale Location of columnar section (CS) Geophysical data collection location Drill hole or test pit Pollen sample ? ? ? ? ? GEOLOGIC SYMBOLS Contact—Solid where location accurate; long-dashed where approximate; short-dashed where inferred; dotted where concealed; queried where identity or existence questionable Gradational contact—Identity or existence questionable; location inferred Fault, unknown offset—inferred; identity or existence questionable Anticline—Long-dashed where approximate; short-dashed where inferred; dotted where concealed; queried where identity or existence questionable Geologic unit too thin to show as a polygon—Solid where location accurate; long-dashed where approximate; short-dashed where inferred; dotted where concealed; queried where identity or existence questionable Dike—Identity or existence certain; Solid where location accurate; long-dashed where approximate; ; short-dashed where inferred; showing dip value and direction Cross section line Fluvial terrace—Identity and existence certain, location accurate; hachures point downslope Landslide scarp—Solid where identity or existence certain; location accurate; hachures on downslope side Geophysical lineament Stream—Perrennial where solid; dotted and dashed where intermittent …vt ? 70 8 09-54Z GD10 5 73 B10 59 …vt Ei p 61 0 20 40 60 80 100 120 140 160 48 52 56 60 64 68 72 76 80 Ba/Nb SiO 2 (weight %) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 48 52 56 60 64 68 72 76 80 K 2 O (weight %) SiO 2 (weight %) 0 10 20 30 40 50 60 0 200 800 400 600 1000 Sr/Y Sr (ppm) 10 12 14 16 18 20 22 24 48 52 56 60 64 68 72 76 80 Al 2 O 3 (weight %) SiO 2 (weight %) North Bend Snoqualmie Carnation Monroe Maltby Lake Joy Sultan Miocene–Recent Cascades Oligocene Cascades Abstract—No. 387-4 (304000): We present a new geologic map of the Maltby 7.5-minute quadrangle at 1:24,000 scale. The densely populated quadrangle located 30 km northeast of Seattle, which has not been mapped in detail since the 1980s, spans the projected intersections of several active regional tectonic structures. We support the map with new field work, lidar, existing subsurface explora- tions, geochemistry, palynology, and U-Pb, luminescence, radiocarbon, and biostratigraphic chronology. We compare mapped geology with new iso- static gravity and existing aeromagnetic data for further observations of structural features in this complex area. New radiocarbon and luminescence chronology constrains pre-Vashon stra- tigraphy of the Olympia non-glacial interval and may provide a limiting date for the end of the Possession Glaciation. New U-Pb zircon ages for both volcanic (~44 Ma) and sedimentary (~28 Ma) bedrock units are pre- sented. Geochemical analyses of 18 samples of the volcanic rocks of Mount Persis range from andesite to dacite and most have adakite affinities. Skyler P. Mavor—Washington Geological Survey, Department of Natural Resources; Colorado State University Mitchell Allen—Forest Practices Division, Washington Geological Survey, Department of Natural Resources Jeffrey H. Tepper—University of Puget Sound Elizbeth A. Nesbitt—Burke Museum, University of Washington Shannon A. Mahan—U.S. Geological Survey, Denver Federal Center Recep Cakir—Washington Geological Survey, Department of Natural Resources Bruce A. Stoker—Earth Systems M.L. Anderson—Colorado College GEOLOGIC MAP OF THE MALTBY 7.5-MINUTE QUADRANGLE, SNOHOMISH AND KING COUNTIES, WASHINGTON We compare these data with existing analyses of the volcanics and discuss a relation to the earliest stages of subduction-related magmatism as the modern Cascade arc initiated in the Eocene. We refine the stratigraphy of fossiliferous Tertiary sedimentary bedrock with constraints from U-Pb zircon chronology, as well as foraminiferal and molluscan biostratigraphy, and de- scribe an Eocene-Oligocene transition from continental to mid-shelf environ- ments with evidence for diffuse methane seep colonies. Biostratigraphy leads us to infer that most of the exposed sedimentary bedrock predates the Blake- ley Formation type section, in contrast to correlations drawn by previous workers. A major bedrock anticline in the map area reflects Oligocene or later NNE-SSW compression and may be tied to a complex interaction of re- gional structures concealed by Quaternary cover. Detailed mapping is unable to further constrain the surficial trace of the active Southern Whidbey Island Fault zone or Monroe Fault, though geophysical lineaments indicate that strands of these structures extend through the quadrangle and merge with previously mapped faults to the southeast. Our new map concludes a de- cade-long campaign of detailed geologic mapping by the Washington Geo- logical Survey in the eastern Puget Lowland. direction of maximum shortening 3 Rhythmic, planar-bedded silt and clay of unit Qgaf representing cyclical lacustrine sedimentation. SiO 2 K 2 O 45 50 55 60 65 70 75 0 1 2 3 4 5 6 7 Tholeiite &DOFíDONDOLQH +LJKí. FDOFíDONDOLQH 6KRVKRQLWH 0.05 0.50 5.00 50.00 Sr K Rb Ba Th Ta Nb Ce P Zr Hf Sm Ti Y Yb Sample / MORB * WXII XQLW …vt) 1.0 10.0 100.0 La Ce Pr Nd Sm EX Gd Tb Dy Ho Er Tm Yb LX Sample / MORB * WXII XQLW …vt) A M F Tholeiite &DOFíDONDOLQH 40 50 60 70 80 0 5 10 15 Picrobasalt Basalt Basaltic DQGHVLWH $QGHVLWH Dacite Rhyolite Trachyte Trachydacite 7UDFK\í DQGHVLWH Basaltic WUDFK\í DQGHVLWH 7UDFK\í basalt Tephrite %DVDQLWH 3KRQRí tephrite 7HSKULí SKRQROLWH 3KRQROLWH Foidite $ONDOLQH 6XEDONDOLQH7KROHLLWLF Ultrabasic Basic ,QWHrmediate Acid SiO 2 Na 2 2. 2 O Deciduous and coniferous terrestrial plant fossils preserved in a detached boulder of unit …Ec. Luminescence age site GD8 in a 60 cm (24 in.)-thick interbed of well-sorted, fine to coarse sand, with sparse pebbles concentrated along bedding. Typical weathered exposure of unit …En siltstone and sandstone at age site GD15. Clast-supported monomict andesitic boulder breccia of unit Evp exposed along the Snohomish River at site S3. Geochemistry data illustrating the compositional diversity of the volcanic rocks of Mount Persis , including data from nearby Monroe, Carnation, Sultan, Lake Joy, Snoqualmie, and North Bend quadrangles. Stereonet of poles to bedding measurements from units …Ec and …En across the Fiddlers Bluff anticline (n=38). U-Pb dating results for site GD28 (left) and GD27 (right). Download the publication data-point error ellipses are 2ı Intercept at 43.47 ±0.15 [±0.16] Ma MSWD = 1.09 238 U / 206 Pb 207 Pb / 206 Pb 42 44 46 48 0.04 0.05 0.06 0.07 0.08 130 134 138 142 146 150 154 158 A. Kernel density estimate and histograms (Sample GD27) Number of zircon grains 206 Pb/ 238 U age (Ma) Relative probability 0 20 40 60 80 100 120 140 160 180 200 0 9 19 28 38 (n=60)
