Marine sedimentary rocks (middle and lower Miocene) (ORTms;0)

Fine- to medium-grained Marine siltstone and sandstone that commonly contains tuff beds. Includes the Astoria Formation, which is mostly micaceous and carbonaceous sandstone, and the middle Miocene Gnat Creek Formation of Niem and Niem (1985), which overlies Frenchmen Springs Member of the Wanapum Basalt east of Astoria. The Astoria Formation locally contains calcareous concretions and sulfide nodules; foraminifers in formation are assigned to the Saucesian and Relizian Stages (Kleinpell, 1938; Rau, 1981) and molluscan fossils to the Newportian Stage of Addicott (1976, 1981). Also includes Nye Mudstone, which is massive to poorly bedded siltstone and mudstone; foraminiferal assemblages assigned to the Saucesian Stage (Kleinpell, 1938; Rau, 1981) and molluscan fauna to Pillarian(?) Stage (Armentrout, 1981)

State	Oregon
Name	Marine sedimentary rocks (middle and lower Miocene)
Geologic age	Early Miocene to Middle Miocene
Original map label	Tms
Primary rock type	siltstone
Secondary rock type	sandstone
Other rock types	tuff
Lithologic constituents	Major Sedimentary > Clastic > Sandstone (Bed) Sedimentary > Clastic > Siltstone (Bed) Incidental Igneous > Volcanic (Pyroclastic, tuff)
Map references	Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.
Unit references	Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000. Niem, A.R., and Niem, W.A., 1985, Oil and tgas investigation of the Astoria Basin, Clatsop and northernmost Tillamook Counties, northwest Oregon: Oregon Department of Geology and Mineral Industries Oil and Gas Investigation OGI-14, scale 1:100,000. Kleinpell, R.M., 1938, Miocene stratigraphy of California: Tulsa, Oklahoma, American Association of Petroleum Geologists, 450 p. Rau, W.W., 1981, Pacific Northwest Tertiary benthic foraminiferal biostratigraphic framework-an overview, in Armentrout, J.M., ed., Pacific Northwest Cenozoic Biostratigraphy: Geological Society of America Special Paper 184, p. 67-84. Addicott, W.O., 1976, Neogene mulluscan stages of Oregon and Washington, in Wornardt, W.W., ed., Symposium of the Neogene of the Pacific Coast: Society of Ecoonomic Paleontologists and Mineralogists, Pacific Section, San Francisco, California, April 1976, p. 95-115. Addicott, W.O., 1981, Signifiance of pectinids in the Tertiary bgiochronology of the Pacific Northwest, in Armentrout, J.M., ed., Pacific Northwest Cenozoic Biostratigraphy: Geological Society of America Special Paper 184, p. 17-37. Armentrout, J.M., 1981, Correlation and ages of Cenozoic chronostratigraphic units in Oregon and Washington, in Armentrout, J.M., ed., Pacific Northwest Cenozoic Biostratigraphy: Geological Society of America Special Paper 184, p. 137-148.
Geographic coverage	Clatsop - Columbia - Lincoln - Tillamook