Quaternary Maps
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Depth to Base of Quaternary Map
Arc Explorer
Themes visible in the above map: QDEPTH (Image), LATITUDE/LONGITUDE and COASTLINE. When the gravity data is viewed in Arc Explorer, please note that the QDEPTH(Image) theme is an image and therefore not able to be queried. The QDEPTBAR (Image) provides a scale for QTHICK(Image). However, the DEPTH TO QUATERNARY CONTOURS theme may be queried. The contour values are contained in the CONTOUR field.

Depth to the base-of-Quaternary in the eastern Juan de Fuca Strait region
Samuel Y. Johnson, Susan B. Rhea, David C. Mosher, Robert B. Kung, and Shawn V. Dadisman

This map shows the depth to the base of Quaternary strata in the eastern Juan de Fuca Strait region and is a companion to the map showing the thickness of Quaternary strata. For offshore areas, this value is determined entirely on the basis of interpretation of seismic-reflection data. These data include high-resolution and conventional seismic-reflection surveys of the U.S. Geological Survey and Geological Survey of Canada as well as parts of four conventional industry seismic-reflection surveys. Tracklines and data-acquisition parameters are described elsewhere in this report. Examples of seismic reflection data from which these maps were generated can be accessed through the trackline or the structure map sheets or by activating the following links: PGC96006, SHIPS, USGS and Industry. For onshore areas, we relied on geologic mapping of Tabor and Cady (1978), Roddick and others (1979), Muller (1983), and Whetten and others (1988), and on logs of a few deep boreholes (Brocher and Ruebel, 1998; Rau and Johnson, 1999). North and northeast of the southern Whidbey Island and Leech River faults (Neotectonics Map), Quaternary strata are mainly underlain by pre-Tertiary meta-sedimentary, volcanic, plutonic, and metamorphic rocks. South of these faults, Quaternary strata are underlain by Tertiary sedimentary and volcanic rocks (Roddick and others, 1979; Johnson and others,1996). The base of Quaternary strata is typically most distinct on conventional industry seismic-reflection data, where it is recognized on the basis of contrasts in seismic facies (e.g., Mitchum and others, 1977; Johnson and others, 1996).

Quaternary strata are generally characterized by low to moderate amplitude, discontinuous to continuous, irregular hummocky, divergent, and parallel reflections. Internal truncation, onlap, and offlap of reflections are all common. In contrast, reflections from underlying Tertiary strata have higher amplitude, are more continuous, and are typically parallel to subparallel. Where Tertiary rocks are folded, this contact is generally an angular unconformity that may pass laterally into a disconformity. Underlying pre-Tertiary rocks are generally non-reflective. Examples of conventional seismic-reflection data that show the base-of-Quaternary horizon in the eastern Juan de Fuca Strait are in Johnson and others (1996) and Figures 7, 8, and 14.

On high-resolution seismic-reflection profiles, this contact and the contrast in seismic facies between Tertiary and Quaternary strata may not be as distinct (e.g., Figures 3, 6, 9, 13, and 16). For these profiles, the location of the contact is generally based on projection from nearby conventional industry profiles or on the basis of locally distinct unconformities and onlapping surfaces. Once the contact at the base of the Quaternary was identified at one or more locations on individual high-resolution profiles, it was traced across the profiles to yield fairly complete regional coverage.

This map shows both the onshore and offshore data points used to generate contour surfaces. For onshore areas, data points are mainly the boundaries of exposed bedrock and depths from a few deep boreholes. For offshore data points, we converted two-way travel time to depth by assuming velocities of 1500 m/sec for the water column and 1800 m/sec for Quaternary strata. The data were contoured using the following smoothed inverse-distance weighting function with a distance decay value of d-5, a radius of 12 km, and a cell size of 100 m:

In this function, z = the elevation of the base of the Quaternary section, d = distance to a data point, i = distance to all data points within the radius, and r = radius.

Quaternary deposits in the Puget Lowland of western Washington comprise a stratigraphically complex basin fill of glacial and interglacial deposits that are locally as thick as 1,100 m (Yount and others, 1985; Jones, 1996). Easterbrook (1994a, b) described six distinct glacial-drift units, three of which are exposed on Whidbey Island. Onland glacial and interglacial strata in the eastern Juan de Fuca Strait region consist mainly of till, fluvial channel and floodplain deposits, and coarse- to fine-grained glaciomarine deposits. Given the physiography of the eastern Juan de Fuca Strait, it is likely that much of the Quaternary strata imaged on offshore seismic-reflection profiles consists of recessional glaciomarine drift. Present day seafloor morphology is largely governed by these drift deposits (Mosher and Johnson, 2000). Many of the Quaternary stratigraphic units exposed onshore are well dated (Yount and others, 1980; Easterbrook, 1994a, b), however determining the age of the Quaternary deposits imaged on seismic-reflection data in Puget Lowland waterways is problematic. No boreholes have penetrated the submerged section, and multiple pulses of subglacial scour and subsequent filling make correlation with adjacent, dated units on land untenable. We did not recognize specific sequences in the offshore Quaternary data that could be correlated with different glaciations, and we think it likely that much of the Quaternary strata in the subsurface of the eastern Juan de Fuca Strait was deposited during retreat of the most recent (Fraser) glaciation.

The depth to base of Quaternary is inferred to be controlled by both tectonic structures and large-scale erosion and deposition associated with multiple Quaternary glaciations. Maximum depths occur in two locations. The first area is beneath Camano Island in the southeastern part of the map region, where Quaternary strata reach a thickness of more than 1,000 m. This trough is part of the Everett basin (Johnson and others, 1996), a structural low bounded by the southern Whidbey Island fault to the southwest and the Strawberry Point and Utsulady Point faults (Johnson and others, 2000) to the north. This area corresponds to both a gravity and aeromagnetic low (Gravity Map, Aeromagnetic Map). The second area where the depth to the base of the Quaternary reaches as much as 1,000 m lies in the southeastern Juan de Fuca Strait, north of the Miller Peninsula and eastern Quimper Peninsula. This trough lies southwest of and within the northwest portion of the southern Whidbey Island fault zone and is cut by several northwest-trending faults (Neotectonics Map). This region overlies an aeromagnetic high (Aeromagnetic Map) and does not form a distinct gravity anomaly (Gravity Map). Thus it appears that this region is underlain partly by relatively shallow, dense magnetic rocks (inferred Crescent Formation) and is not a long-lived structural low like the Everett basin. Instead, the increased depth to the base of the Quaternary section in this area suggests either a site of locally enhanced glacial erosion and (or) a structural inversion.

With the exception of the Whidbey and Camano Island areas, the depth to the base of the Quaternary section is less in onshore areas than in offshore areas. Depths in the offshore area north of the Devils Mountain, Strawberry Point, and Utsulady Point faults (Neotectonics map; Johnson and others, 2000) are notably lower than in areas south of the fault, strongly suggesting Quaternary structural control.

References

Brocher, T. M., and Ruebel, A.L., 1998, Compilation of 29 sonic and density logs from 23 oil test wells in western Washington State: U.S. Geological Survey Open-File Report 98-249, 59 p.

Easterbrook, D.J., 1994a, Chronology of pre-late Wisconsin Pleistocene sediments in the Puget Lowland, Washington, in Lasmanis, R., and Cheney, E.S., eds., Regional geology of Washington State: Washington Division of Geology and Earth Resources Bulletin 80, 191-206.

Easterbrook, D.J., 1994b, Stratigraphy and chronology of early to late Pleistocene glacial and interglacial sediments in the Puget Lowland, Washington, in Swanson, D.A., and Haugerud, R.A., eds., Geologic field trips in the Pacific Northwest (published for the 1994 Annual Meeting of the Geological Society of America): Seattle, University of Washington, p. 1J-1-38.

Johnson, S.Y., Potter, C.J., Armentrout, J.M., Miller, J.J., Finn, C., and Weaver, C.S., 1996, The southern Whidbey Island fault, an active structure in the Puget Lowland, Washington: Geological Society of America Bulletin, v. 108, p. 334-354 and oversize insert.

Johnson, S.Y., Dadisman, S.V., Mosher, D.C., Blakely, R.J., and Childs, J.R., 2000, Late Quaternary tectonics of the Devils Mountain fault and related structures, northern Puget Lowland: Geological Society of America Abstracts with Programs, v. 32, p. XX.

Jones, M.A., 1996, Thickness of unconsolidated deposits in the Puget Sound Lowland, Washington and British Columbia: U.S. Geological Survey Water Resources Investigations Report 94-4133.

Mitchum, R.M., Jr., Vail, P.R., and Sangree, J.B., 1977, Seismic stratigraphy and global changes in sea level, part 6 -- Stratigraphic interpretation of seismic reflection patterns in depositional sequences, in Payton, C.E., ed., Seismic stratigraphy - applications to hydrocarbon exploration: American Association of Petroleum Geologists Memoir 26, p. 117-143.

Mosher, D.C., and Johnson, S.Y., 2000, Mapping the Quaternary under the eastern Juan de Fuca Strait - A digital atlas: Geological Society of America Abstracts with Programs, v. 32, p. XX.

Muller, J.E., 1983, Geology, Victoria: Geological Survey of Canada Map 1553A, scale 1:100,000.

Rau, W.W., and Johnson, S.Y., 1999, Well stratigraphy and correlations, western Washington and northwest Oregon: U.S. Geological Survey Map I-2621, 3 oversized sheets/charts, 31 p.

Roddick, J.A., Muller, J.E., and Okulitch, A.V., 1979, Fraser River, British Columbia-Washington: Geological Survey of Canada Map 1386A, Sheet 92, scale 1:1,000,000.

Tabor, R.W., and Cady, W.M., 1978, Geologic Map of the Olympic Peninsula, Washington: U.S. Geological Survey Map I-994, scale 1:125,000.

Whetten, J.T., Carroll, P.I., Gower, H.D., Brown, E.H., and Pessl, F., Jr., 1988, Bedrock geologic map of the Port Townsend 30- by 60-minute quadrangle, Puget Sound Region, Washington: U.S. Geological Survey Map I-1198-G, scale 1:100,000.

Yount, J.C., Marcus, K.L., and Mozley, P.S., 1980, Radiocarbon-dated localities from the Puget Lowland, Washington: U.S. Geological Survey Open File Report 80-780, 51p, 1 map.

Yount, J.C., Dembroff, G.R., and Barats, G.M., 1985, Map showing depth to bedrock in the Seattle 30' by 60' quadrangle, Washington: U.S. Geological Survey Map MF-1692, scale 1:100,000.

Reference citation:
Johnson, S.Y., Rhea, S.B., Dadisman, S.V., and Mosher, D.C., 2000. Depth to the base-of-Quaternary in the eastern Juan de Fuca Strait region, in: Mosher, D.C. and Johnson, S.Y. (Eds.), Rathwell, G.J., Kung, R.B., And Rhea, S.B. (Compilers), Neotectonics of the eastern Juan de Fuca Strait; a digital geological and geophysical
atlas. Geological Survey of Canada Open File Report 3931

Quaternary Thickness Map
Arc Explorer
Themes visible in the above map: QTHICK (Image), LATITUDE/LONGITUDE and COASTLINE. When the gravity data is viewed in Arc Explorer, please note that the QTHICK (Image) theme is an image and therefore not able to be queried. The QTHICBAR (Image) provides a scale for QTHICK(Image). However, the QUATERNARY THICKNESS CONTOURS theme may be queried. The contour values are contained in the CONTOUR field.

Thickness of Quaternary strata in the eastern Juan de Fuca Strait region
Susan B. Rhea, Samuel Y. Johnson, David C. Mosher, Robert B. Kung, and Shawn V. Dadisman

This map shows the thickness of Quaternary strata in the eastern Juan de Fuca Strait region, and is a companion to the map showing the depth to the base of the Quaternary section. For offshore areas, the thickness is determined entirely on the basis of aninterpretation of seismic-reflection data. These data include high-resolution and conventional seismic-reflection surveys of the U.S. Geological Survey and Geological Survey of Canada as well as parts of four conventional industry seismic-reflection surveys. Tracklines and data-acquisition parameters are described elsewhere in this report. Examples of seismic reflection data from which these maps were generated can be accessed through the trackline or the structure map sheets or by activating the following links: PGC96006, SHIPS, USGS and Industry. For onshore areas, we relied on geologic mapping of Tabor and Cady (1978), Roddick and others (1979), Muller (1983), and Whetten and others (1988), and on logs of a few deep boreholes (Brocher and Ruebel, 1998; Rau and Johnson, 1999). North and northeast of the southern Whidbey Island and Leech River faults (Neotectonics Map), Quaternary strata are mainly underlain by pre-Tertiary meta-sedimentary, volcanic, plutonic, and metamorphic rocks. South of these faults, Quaternary strata are underlain by Tertiary sedimentary and volcanic rocks (Roddick and others, 1979, Johnson and others, 1996).

The base of Quaternary strata is typically most distinct on conventional industry seismic-reflection data, where it is recognized on the basis of contrasts in seismic facies (e.g., Mitchum and others, 1977; Johnson and others, 1996). Quaternary strata are generally characterized by low to moderate amplitude, discontinuous to continuous, irregular hummocky, divergent, and parallel reflections. Internal truncation, onlap, and offlap of reflections are all common. In contrast, reflections from underlying Tertiary strata have higher amplitude, are more continuous, and are typically parallel to subparallel. Where Tertiary rocks are folded, this contact is generally an angular unconformity that may pass laterally into a disconformity. Underlying pre-Tertiary rocks are generally non-reflective. Examples of conventional seismic-reflection data that show the base-of-Quaternary horizon in the eastern Juan de Fuca Strait are in Johnson and others (1996) and Figures 7, 8, and 14.

On high-resolution seismic-reflection profiles, this contact and the contrast in seismic facies between Tertiary and Quaternary strata may not be as distinct (e.g., Figures 3, 6, 9, 13, and 16). For these profiles, the location of the contact is generally based on projection from nearby conventional industry profiles or on the basis of locally distinct unconformities and onlapping surfaces. Once the contact at the base of the Quaternary was identified at one or more locations on individual high-resolution profiles, it was traced across the profiles to yield fairly complete regional coverage. This map shows both the onshore and offshore data points used to generate contour surfaces. For onshore areas, data points are mainly the boundaries of exposed bedrock and depths from a few deep boreholes. For offshore data points, we converted two-way travel time to depth by assuming velocities of 1500 m/sec for the water column and 1800 m/sec for Quaternary strata. To determine thickness in offshore areas, we subtracted the thickness of the water column from the depth to the base of the Quaternary. The data were contoured using the following smoothed inverse-distance weighting function with a distance decay value of d-5, a radius of 12 km, and a cell size of 100 m:


In this function, z = the elevation of the base of the Quaternary section, d = distance to a data point, i = distance to all data points within the radius, and r = radius.

References

Brocher, T. M., and Ruebel, A.L., 1998, Compilation of 29 sonic and density logs from 23 oil test wells in western Washington State: U.S. Geological Survey Open-File Report 98-249, 59 p.

Johnson, S.Y., Potter, C.J., Armentrout, J.M., Miller, J.J., Finn, C., and Weaver, C.S., 1996, The southern Whidbey Island fault, an active structure in the Puget Lowland, Washington: Geological Society of America Bulletin, v. 108, p. 334-354 and oversize insert.

Mitchum, R.M., Jr., Vail, P.R., and Sangree, J.B., 1977, Seismic stratigraphy and global changes in sea level, part 6 -- Stratigraphic interpretation of seismic reflection patterns in depositional sequences, in Payton, C.E., ed., Seismic stratigraphy - applications to hydrocarbon exploration: American Association of Petroleum Geologists Memoir 26, p. 117-143.

Muller, J.E., 1983, Geology, Victoria: Geological Survey of Canada Map 1553A, scale 1:100,000.

Rau, W.W., and Johnson, S.Y., 1999, Well stratigraphy and correlations, western Washington and northwest Oregon: U.S. Geological Survey Map I-2621, 3 oversized sheets/charts, 31 p.

Roddick, J.A., Muller, J.E., and Okulitch, A.V., 1979, Fraser River, British Columbia-Washington: Geological Survey of Canada Map 1386A, Sheet 92, scale 1:1,000,000.

Tabor, R.W., and Cady, W.M., 1978, Geologic Map of the Olympic Peninsula, Washington: U.S. Geological Survey Map I-994, scale 1:125,000.

Whetten, J.T., Carroll, P.I., Gower, H.D., Brown, E.H., and Pessl, F., Jr., 1988, Bedrock geologic map of the Port Townsend 30- by 60-minute quadrangle, Puget Sound Region, Washington: U.S. Geological Survey Map I-1198-G, scale 1:100,000.

 

Reference citation:
Johnson, S.Y., Rhea, S.B., Dadisman, S.V., and Mosher, D.C., 2000. Thickness of Quaternary strata in the eastern Juan de Fuca Strait region, in: Mosher, D.C. and Johnson, S.Y. (Eds.), Rathwell, G.J., Kung, R.B., and Rhea, S.B. (Compilers), Neotectonics of the eastern Juan de Fuca Strait; a digital geological and geophysical atlas. Geological Survey of Canada Open File Report 3931

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