Geologic Map of the Coupeville and Part of the Port Townsend North 7.5
Total Page：16
File Type：pdf, Size：1020Kb
WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES GEOLOGIC MAP GM-58 Geologic Map of the Coupeville and Part of the Port Townsend North R1W R1E 42¢30² 122°45¢ 40¢ 122°37¢30² 48°15¢ 48°15¢ Qgtv Qco Qb Qgoge Qco Qgdp 7.5-minute Quadrangles, Island County, Washington Qml 1 Qco schematic section Qgog Qgd 5 e Qcw from top to Qgav; Qgav Qgdme elev. 197 ft schematic section elev. 160 ft measured section Qgdp Qml Qgav Qgoge elev. 150 ft Qs <10 ft sand by Michael Polenz, Stephen L. Slaughter, and Gerald W. Thorsen ~10 ft below Qgav Qd active dune sand Qp Qs 110,124,182 6 to 12 ft 5 ft Qs sand Qgdm 18 ft sand and gravel Qgdm Qco silt and clay e Qgav 7 ft Qgdm diamict e Qb liquefaction features e Qgdme Qml Qc 15 ft silt 9 ft Qgd diamict Qcw o and small shears in Qd Qgoge Qgd 9 ft Qgt till 188 p 10 ft silt and clay silt and sand at ~100 ft June 2005 v Qgtv <75 ft Qgoge 11 ft Qgav sandy gravel Qcw Qp Qmw 177,178 gravel with ~30 ft mixed deposits—sand, Qmw silt boulders silt, and minor gravel Qgd Qp Qgomee? Qm Qgdmels? ~20 ft lahar runout (Table 2, samples 188 and 182*) GEOLOGIC SETTING AND DEVELOPMENT We suggest that this sediment source is partly documented by a high-energy outwash Deposits of the Fraser Glaciation (Pleistocene) alluvial facies reflect ancestral Skagit River provenance. Sparse, local Glacier REFERENCES CITED channel deposits— Qgomee Qcw Qgd 79 ft p clean sand with Qls Qb Qcw ~15 ft channel deposits—sand and minor gravel gravel unit (unit Qgoge), which locally grades up into Partridge Gravel, and which we Peak dacite and pumice pebbles, such as those found to the east of Long Point very sparse gravel Like most of the Puget Lowland, the map area is dominated by glacial sediment and lacks Armstrong, J. E.; Brown, W. L., 1954, Late Wisconsin marine drift and associated sediments of the ~10 ft lahar runout (Table 2, samples 110, interpret as mostly subglacial flow deposit. EVERSON INTERSTADE (columnar section 7; Table 2, samples 136-1 and 136-2), are chemically Qgd Qb lower Fraser Valley, British Columbia, Canada: Geological Society of America Bulletin, v. 65, p Qc 124, 177, 178, and 04-5H*) bedrock exposures. Jones (1999) inferred between 1800 ft (west of Point Partridge) and ???? Qgoge Qf The Partridge Gravel outwash channels east and west of Ebeys Prairie terminate at a indistinguishable from lahar runout deposits within the Whidbey Formation no. 4, p. 349-364. channel deposits—sand Qgoge 3300 ft (east of Penn Cove) of unconsolidated deposits in the area; Mosher and others Glaciomarine drift, emergence (beach) facies—Sand and gravel, locally Qb 6 ~10 ft channel deposits—sand and minor gravel Qgom 30 ft Qcw with very sparse gravel Qs slope break, which represents the upper slope break of marine kame-delta fronts ee (unit Qcw), but no lahar runout deposits were recognized in this unit. The age elev. 6 ft beach (2000) and Johnson and others (2001) used geophysical data to suggest that the top of silty; loose; typically only a few feet thick; underlain by glaciomarine drift Armstrong, J. E.; Crandell, D. R.; Easterbrook, D. J.; Noble, J. B., 1965, Late Pleistocene Qgdm elev. 205 ft measured section ~20 ft floodplain deposits—sand, silt, prograding into Ebeys Prairie (Carlstad, 1992) and therefore approximates paleo–sea of the West Beach silt is constrained in the map area to between about 37,000 Qc floodplain deposits— e a, b clay, peat, and minor gravel stratigraphy and chronology in southwestern British Columbia and northwestern Washington: w 5 ft Qgdme silt and clay *sample 188 from column location; Miocene(?) (Johnson and others, 1996) bedrock in the map area is about 1150 to 2600 ft (unit Qgdme) or Partridge Gravel (unit Qgome), but may rest on older 14 31 ft silt, clay, and sand; Qf Qgdme? Qf level (Thorson, 1981). Consequently, we agree with Carlstad (1992) that Ebeys Prairie and 27,000 C yr B.P. by dates from overlying and underlying units (Table 1, samples 177 and 178 from Geological Society of America Bulletin, v. 76, no. 3, p. 321-330. 8 ft peat and organics Qgomee Qf below the surface (depending on location). The oldest sediment exposed in the map area sediments north and west of Penn Cove and along parts of the slope east of Qgdm ? Qmfe? Qgog ? ~300 ft southwest of column location; was sea floor on which glaciomarine drift was deposited while Partridge Gravel was sample nos. Beta 154508 and Beta 169086). The age of the entire unit may be elev. 7 ft beach covered Qgdm e e is thought to be Double Bluff Drift, which is found at beach level south of Ebeys Landing Ebeys Prairie; represents emergence deposits (Domack, 1983) that record a Berger, G. W.; Easterbrook, D. J., 1993, Thermoluminescence dating tests for lacustrine, e samples 110, 124, 182 and 04-5H from deposited to the east and west. The two units interfinger and grade into each other limited to between about 37,000 and 16,800 14C yr B.P. by six radiocarbon a, b Qf Qm? 3 96 ft Qgome loose sand, some ~1200 ft northeast of column location (shoreline section B; Easterbrook, 1968; Thorsen, 2001). Based on stratigraphic position, falling relative sea level at the end of the Everson Interstade. Subtle benches at glaciomarine, and floodplain sediments from western Washington and British Columbia: Qp? pebble gravel 14 Qf elev. 40 ft beneath Ebeys Prairie (Carlstad, 1992; cross section A). Together, the two units fill dates from the field area and the above-mentioned 37,000 C yr B.P. date Canadian Journal of Earth Sciences, v. 30, no. 9, p. 1815-1828. Qb 4 7 Double Bluff Drift would likely date to marine oxygen-isotope stage (hereinafter “stage”) varying elevations are characteristic of the unit and represent paleo–beach Qp? irregularities in an underlying surface that may represent the subglacial topography that from West Beach just north of the field area (Table 1). Alternatively, undated Qml? Qs ~3 ft schematic section elev. 91 ft schematic section Bloom, A. L., 1983, Sea level and coastal morphology of the United States through the late Qb elev. 71 ft 6, or about 185 to 125 ka (thousands of calendar years before 1950) (references to berms (Carlstad, 1992). This unit is partly the youngest facies of glaciomarine Qp Qgoge preceded the Everson Interstade incursion of marine water (cross section A). strata within the unit may include significantly older deposits of the Olympia Qgom Qgdme 6 ft 18 ft Qgdm silt and clay Qgdm oxygen-isotope stages in this report are as defined in fig. 4 of Morrison, 1991), although drift but may also include terrestrial deposits (Domack, 1983). It is mapped as Wisconsin glacial maximum. In Porter, S. C., editor, The late Pleistocene; Volume 1 of Wright, Qp e e 10 ft e silt and clay Partridge outwash channels truncate some drumlins (Fig. 1), implying that a former nonglacial interval. This unit may include fine-grained early Vashon advance >2 to <35 ft Qgt till and subglacial gravel 15 to 75 ft Qgt till direct age estimates suggest that some exposures may be older (Berger and Easterbrook, outwash to maintain continuity with maps to the north (Dragovich and others, H. E., Jr., editor, Late-Quaternary environments of the United States: University of Minnesota Qf v v Qgoge Qc peat, <6 in. thick; till plain was locally obliterated by the meltwater that deposited the Partridge Gravel. deposits ("Transitional beds” of Pessl and others (1989)), such as at North Press, p. 215-229. 45 ft o silt and clay 73 ft Qu compact sand and silt 1993; Blunt and others, 1987; Easterbrook, 1994a,b). 2005). Qgdme 14 ft organic sediment fraction However, some till plain likely remains preserved beneath Ebeys Prairie and the Partridge Penn Cove (columnar section 4), where the upper radiocarbon date and Qgome Qgog 16,790 ±70 14C yr B.P. on 34,610 ±510 14C yr B.P. Blunt, D. J.; Easterbrook, D. J.; Rutter, N. W., 1987, Chronology of Pleistocene sediments in the e elev. 17 ft The oldest widely exposed unit is the interglacial Whidbey Formation, which forms Qb Qp elev. 6 ft shells (Table 1, loc. 11) <6 ft diamictons (Table 1, loc. 16) Gravel (cross section A). A partial underlayment of till plain is supported by well records Fan deposits—Sand, fine gravel, silt, and clay; variably sorted; loose; bedded; sedimentary characteristics of overlying silty sediment may be compatible Qf Qf beach Qmf Puget Lowland, Washington. In Schuster, J. E., editor, Selected papers on the geology of covered 10–12 ft 22,160 ±90 14C yr B.P. on Qb the base of the section along West Beach and Blowers Bluff, where it is as much as about e Qb 0 to 60 ft Qco sand, silt, and clay southwest of Penn Cove, weak drumlinization(?) at relatively low elevation southeast of consists of either terrigenous nearshore marine deltaic or terrestrial alluvial with early Vashon association. ~30 ft (to beach at elev. 7 ft) shell (Table 1, loc. 14) Qf Washington: Washington Division of Geology and Earth Resources Bulletin 77, p. 321-353. Qp 31 ft covered elev. 6 ft peat, <6 in. thick 120 ft thick (columnar section 5). We believe the formation to be correlative in the map silt blocks highlighted for Qb beach Ebeys Landing and around the Coupeville moraine (Fig. 1), and till exposures along the fans that record a late Everson Interstade (?), onshore hydrologic regime Qs? area with stage 5, or about 125 to 80 ka, based on stratigraphic position and dates from Booth, D.