Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks

Sedimentary and volcanic rocks, undivided. Graywacke, argillite, siltstone, slate, volcanic rocks, phyllite, greenschist, and greenstone.
State Washington
Name Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks
Geologic age Late Cretaceous-Jurassic
Lithologic constituents
Sedimentary > Clastic > Siltstone (Bed)
Metamorphic > Metasedimentary > Metaclastic > Argillite
Sedimentary > Clastic > Sandstone > Graywacke (Bed)
Metamorphic > Schist (Greenschist)
Metamorphic > Metasedimentary > Metaclastic > Phyllite
Metamorphic > Metasedimentary > Metaclastic > Slate
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Volcaniclastic-volcanic breccia, Pyroclastic-tuff)
Metamorphic > Metaigneous > GreenstoneMay be minor in rank.
Comments Volcanic rocks include andesite flows, tuff, and breccia with minor dacite and basalt, and minor volcaniclastic sandstone, conglomerate, and siltstone (Barksdale, 1975, Tabor and others, 1993--NOTE: Tabor and others, 1993, does not differentiate between WAJK and WAJKv). Huntting and others, 1961, originally listed"Leech River Group" in the stratigraphy of this unit; obsolete term and now considered part of Lummi and Constitution Formations (Brandon and others, 1988).
Stratigraphic units Spieden Group; Obstruction Formation; Fidalgo Complex (in part); Lummi Group (including James Island Formation); Lopez Structural Complex; Newby Group: Buck Mountain Formation (in part), Twisp Formation

Huntting, M.T., Bennett, W.A.G., Livingston, V.E.Jr., and Moen, W.S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.

Brandon, M.T., 1989, Geology of the San Juan-Cascade Nappes, northwestern Cascade Range and San Juan Islands, in Joseph, N. L. (Ed.), Geologic Guidebook for Washington and Adjacent Areas: prepared for the 85th Annual Meeting of the Cordilleran Section, Geological Society of America, May 8-11, 1989, Spokane, Washington: Washington Division of Geology and Earth Resource Infomation Circular 86, p. 137-162.

Barksdale, J.D., 1975, Geology of the Methow Valley, Okanogan County, Washington: Washington Division of Geology and Earth Resources Bulletin no. 48, 72 p.

Tabor, R.W., Frizzell, V.A.,Jr., Booth, D.B., Waitt, R.B., Whetten, J.T., Zartman, R.E., 1993, Geologic Map of the Skykomish River 30- by 60-Minute Quadrangle, Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-1963, scale 1:100,000.

Johnson, S.Y., 1981, Stratigraphy, Sedimentology, and Paleogeographic Significance of Spieden Group, San Juan Islands, Washington: American Association of Petroleum Geologists (AAPG) Bulletin, v. 65, no. 5, p. 942.

Garver, J., 1988, Stratigraphy, depositional setting, and tectonic significance of the clastic cover to the Fidalgo Ophiolite, San Juan Islands, Washington: Canadian Journal of Earth Sciences, v. 25, p. 417-432.

Brandon, M.T., Cowan, D.S., Vance, J.A., 1988, The Late Cretaceous San Juan thrust system, San Juan Islands, Washington: Geological Society of America Special Paper 221, 81 p. 1 pl.

Whetten, J.T., Carroll, P.I., Gower, H.D., Brown, E.H., Pessl, F., Jr., 1988, Bedrock Geologic Map of the Port Townsend 30- by 60-Minute Quadrangle, Puget Sound Region, Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-1198-G, scale 1:100,000.

NGMDB product
Counties Island - King - Okanogan - San Juan - Skagit - Snohomish - Whatcom