Pre-Middle Jurassic sedimentary and volcanic rocks

Predominantly sedimentary rocks. Graywacke, argillite, and slate; includes minor marble, siltstone, arkose, conglomerate, ribbon cherts, and volcanic rocks.
State Washington
Name Pre-Middle Jurassic sedimentary and volcanic rocks
Geologic age Jurassic
Lithologic constituents
Major
Metamorphic > Metasedimentary > Metaclastic > Slate
Metamorphic > Metasedimentary > Metaclastic > Argillite
Sedimentary > Clastic > Sandstone > Graywacke (Bed)
Minor
Sedimentary > Clastic > Sandstone > Arkose (Bed)
Sedimentary > Chemical > Chert (Bed)
Sedimentary > Clastic > Conglomerate (Bed)
Sedimentary > Clastic > Siltstone (Bed)
Metamorphic > Metasedimentary > Metacarbonate > Marble
Comments Includes rocks of both the western and eastern melange belts. The western melange in Washington State is chiefly graywacke, argillite and phyllite whereas the eastern melange is primarily greenstone and chert (Tabor and others, 1988); each appears to be equally represented in this unit; argillite and graywacke are dominant because they are subordinate in the eastern melange as well. Includes "semi-schist" (Tabor and others, 1988).
References

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.

Dragovich, J.D., Logan, R.L., Schasse, H.W., Walsh, T.J., Lingley, W.S., Jr., Norman, D.K., Gerstel, W.J., Lapen, T.J., Schuster, J.E., Meyers, K.D., 2002, Geologic Map of Washington-Northwest Quadrant: Washington Division of Geology and Earth Resources Geologic Map GM-50, scale 1:250,000.

Tabor, R.W., Booth, D.B., Vance, J.A., Ford, A.B., Ort, M.H., 1988, Preliminary geologic map of the Sauk River 30 by 60 minute quadrangle, Washington: U. S. Geological Survey Open File Report 88-692, 51 p., 1 pl.

NGMDB product
Counties King - Snohomish