The ''Tukwila Formation'' is a geological formation in

King County, Washington King County is located in the U.S. state of Washington. The population was 2,269,675 in the 2020 census, making it the most populous county in Washington, and the 13th-most populous in the United States. The county seat is Seattle, also the st ...

within the

Puget Group The Puget Group is a geologic group in Washington (state). It preserves fossils dating back to the Paleogene period. Two key formations include the Renton Formation and the Tukwila Formation. See also * List of fossiliferous stratigraphic ...

. It is named after Tukwila area, which is close to the formation. The formation consists of various fossils of marine origin. The Tukwila formation is mainly composed of

andesitic Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

dacitic Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite ...

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...

, tuff,

lahar A lahar (, from jv, ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley. Lahars are extreme ...

, and carbonaceous shales. The tuff-breccia has an approximate age of 42 Ma.

Fauna

Vertebrate fauna

Vertebrate fauna mainly consists of just shark remains. Mainly one unnamed species of Goblin shark and one unnamed species belonging to the same genus as the Whitetip reef shark. * Triaenodon.sp *

Mitsukurina ''Mitsukurina'' is a genus of mackerel shark in the family Mitsukurinidae. It contains one extant species, the goblin shark (''M. owstoni'') and more extinct species. The genus was described by American ichthyologist David Starr Jordan in 18 ...

.sp

Invertebrate fauna

Are the following: *? Coeloma martinezensis *Zanthopsis vulgaris *Terebratulina washingtoniana *Protula sp. *Glycymeris saggittata *Venericardia clarki *Colwellia bretzi *Brisaster sp.

References

Eocene United States Tuff formations Shale formations Lahars {{US-geologic-formation-stub