Arapahoe Formation
Open-knowledge reference entry
The Arapahoe Formation is a geological formation of latest Cretaceous (Maastrichtian) age that is present within the Denver Basin that underlies the Denver, Colorado, area. The formation includes fossil leaves and dinosaur remains, although none of the latter have yet been referred to a specific genus. It also includes aquifers that are important sources of water for the area.
The Arapahoe Formation consists of alluvial fan and fluvial deposits that prograded eastward from the growing Rocky Mountain Front Ranges. It rests unconformably on the Laramie Formation, and is conformably overlain by the Denver Formation. It reaches a maximum thickness of about 300 ft (91 m).
The base of the Arapahoe Formation is marked by a discontinuous conglomerate, or where the conglomerate is absent, by sandstone beds that commonly contain large ironstone concretions. The conglomerate is composed principally of chert pebbles, but pebbles of granite, gneiss and schist are also present. Medium grey to brown claystone makes up the majority of the formation, with lesser amounts of light grey to light brown quartzose sandstone. The formation top is marked by a change from sandstone and claystone to the tuffaceous sediments of the overlying Denver Formation.
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This entry incorporates text from “Arapahoe Formation” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.