Golden Valley Formation
The Golden Valley Formation is a stratigraphic unit of Late Paleocene to Early Eocene age in the Williston Basin of North Dakota. It is present in western North Dakota and was named for the city of Golden Valley by W.E. Benson and W.M. Laird in 1947. It preserves significant assemblages of fossil plants and vertebrates, as well as mollusk and insect fossils. Stratigraphy. The Golden Valley Formation is present as a series of outliers in western North Dakota. It is underlain by the Sentinel Butte Formation and unconformably overlain by the White River Group. It reaches thicknesses  of up to and is subdivided into two members: the "Bear Den Member" (lower) and the "Camels Butte Member" (upper). Lithologies. The base of the Bear Den Member consists of kaolinitic claystone, mudstone and sandstone that weather to white, light grey, orange, and purple. These are overlain by grey or brownish carbonaceous sediments and, in some areas, a bed of lignite (the "Alamo Bluff lignite"). In places the sequence is capped by a siliceous bed (the "Taylor bed") that represents a weathering surface or paleosol. The Bear Den Member reaches a maximum thickness of about . The Camels Butte Member consists  of montmorillonitic and micaceous claystone, siltstone, lignite, poorly cemented sandstone and conglomerate. The upper part includes a massive fluvial sandstone that caps many of the major buttes in southwestern North Dakota. The Camels Butte Member reaches a maximum thickness of about . Depositional environment. The Golden Valley Formation was deposited in a broad swampy lowland crossed by fluvial channels. Deposition occurred during late Paleocene (Clarkforkian) to early Eocene (Wasatchian) time, a period that spans the Paleocene-Eocene Thermal Maximum. Paleontology. Plant fossils collected from throughout the formation include floating and rooted aquatic plants such as "Salvinia", "Nelumbo" and "Isoetes", and lowland  forest plants such as the ferns "Onoclea" and "Osmunda", the conifers "Glyptostrobus" and "Metasequoia", and the dicots "Platanus" and "Cercidiphyllum". The vertebrate fossils have come primarily from the upper, early Eocene Camels Butte Member. They include the remains of mammals such as "Coryphodon", "Hyracotherium", "Homogalax", "Sinopa", "Didymictis", "Hyopsodus", "Paramys" and others; there are also remains of fish, amphibians, and reptiles such as "Trionyx", "Peltosaurus", and four genera of crocodilians. Invertebrate fossils include shells of freshwater mollusks such as "Viviparus", "Unio", "Hydrobia", and "Planorbis", and the wing casing of a crabid beetle.