The Renton Formation is a geologic formation in Washington (state) within the Puget Group . It preserves fossils dating back to the Paleogene period .
6-537: Most of the formation consists of fine- to medium-grained arkosic and feldspathic sandstone, interbedded with lesser amounts of siltstone, sandy shale, coal, and carbonaceous shale. Sandstone typically contains at least 40 percent subangular to subrounded quartz grains, 10 to 25 percent feldspar, and some mica and rock fragments, in a matrix of calcite, clay, and silt. Chert fragments constitute as much as 20 percent of some sandstones. Unoxidized rocks are mostly light gray but are light brown or buff where oxidized. The sandstone
12-488: A sand). These sediments must be deposited rapidly and/or in a cold or arid environment such that the feldspar does not undergo significant chemical weathering and decomposition; therefore arkose is designated a texturally immature sedimentary rock. Arkose is often associated with conglomerate deposits sourced from granitic terrain and is often found above unconformities in the immediate vicinity of granite terrains. The central Australian inselberg Uluru (Ayers Rock)
18-533: Is a detrital sedimentary rock , specifically a type of sandstone containing at least 25% feldspar . Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose. Quartz is commonly the dominant mineral component, and some mica is often present. Apart from the mineral content, rock fragments may also be a significant component. Arkose usually contains small amounts of calcite cement, which causes it to effervesce (fizz) slightly in dilute hydrochloric acid ; sometimes
24-548: Is weakly cemented, most commonly with calcite, but in places matrix silt and clay act as the binding agent. The sandstone and siltstone commonly are well sorted and thinly bedded; locally, the sandstone is massive or crossbedded. Some beds in the formation are very soft and plastic when wet, owing to the weathering or alteration of feldspar to a montmorillonitic clay. The Renton formation is a nonmarine arkosic sandstone and siltstone , with carbonaceous shale , and noted for its Muldoon coal seams . Lidar-Revised Geologic Map of
30-620: The Des Moines 7.5' Quadrangle, King County, Washington |url= https://pubs.usgs.gov/sim/3384/sim3384_pamphlet.pdf= 4 May 2020 This article about a specific stratigraphic formation in Washington is a stub . You can help Misplaced Pages by expanding it . This article related to the Paleogene period is a stub . You can help Misplaced Pages by expanding it . Arkosic Arkose ( / ˈ ɑːr k oʊ s , - k oʊ z / ) or arkosic sandstone
36-525: The cement also contains iron oxide . Arkose is typically grey to reddish in colour. The sand grains making up an arkose may range from fine to very coarse, but tend toward the coarser end of the scale. Fossils are rare in arkose, due to the depositional processes that form it, although bedding is frequently visible. Arkose is generally formed from the weathering of feldspar-rich igneous or metamorphic , most commonly granitic, rocks , which are primarily composed of quartz and feldspar (called ' grus ' as
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