[F] Cedar Mountain Formation - Utah - US
Utah - US
The Lower Cretaceous of the Colorado Plateau is represented by the Cedar Mountain Formation in Utah and the largely correlative [Burro Canyon Formation] east of the Colorado River. When first named, the Cedar Mountain Formation was characterized as differing from the underlying Upper Jurassic Morrison Formation in having an abundance of dinosaur gizzard stones (gastrolites) and in lacking preserved dinosaur bone.
Its age was based on palynology and is was assumed to be largely correlative to the Aptian to middle Albian Cloverly Formation of Wyoming and Montana. Research has shown that there are are considerably dinosaur remains in the Cedar Mountain Formation and that instead of preserving only one dinosaur fauna correlative with the Cloverly Formation, it preserves three successive distinct dinosaur fauna’s. [ * = Upper Cedar Mountain Formation] (Garrison et al.)
The Cretaceous Cedar Mountain Formation first described by Stokes (1944). It is at least 137 m in thickness is an alluvial plain/lacustrine deposit lying unconformably upon the flood plain deposits of the Tithonian-Berriasian (uppermost Jurassic) Brushy Basin Member of the Morrison Formation (Currie, 1998).
Coarse-grained braided fluvial deposits of the lower Cenomanian Dakota Formation lie unconformably on the top of the Cedar Mountain Formation. The Cedar Mountain Formation is correlative with the [Burro Canyon Formation] cropping out east of the Colorado River (Young, 1960; Craig, 1981) (Figure 1). Young (1960), believing a genetic relationship, included both the Cedar Mountain Formation and the Dakota Formation in the Dakota Group.
Craig (1981) suggested that the Cedar Mountain and Burro Canyon Formations represent upper Barremian to upper Albian deposits (125 Ma to 100 Ma). An 40Ar/39Ar age determination from a volcanic ash bed from the upper part of the Cedar Mountain Formation produced an Albian age of 97.0 Ma (recalculated with MMhb-1 with an age of 513.9 Ma) (Cifelli et al., 1999). The age determination suggests that the uppermost part of the Cedar Mountain Formation is latest Albian to earliest Cenomanian.
The Cedar Mountain Formation has been sub-divided by previous workers into the: Buckhorn Conglomerate Member (Stokes, 1952), a discontinuous very coarse-grained sandstone to pebble conglomerate, containing pebbles up to 20 cm in diameter. In central Utah, it averages 4-11 m in thickness. The Buckhorn Conglomerate Member appears to have formed within incised-valleys eroded into the underlying Brushy Basin Member of the Morrison Formation (Currie, 1998).
It is thickest and best developed in the northern and northwestern portion of the San Rafael Swell (Kirkland et al., 1997; Currie, 1998). Stokes (1952) assigned the Buckhorn Conglomerate as the basal unit of the Cedar Mountain Formation in the San Rafael Swell. Kirkland et al. (1997) also assigned the Buckhorn Conglomerate to the Cedar Mountain Formation.
Yellow Cat Member, dominantly a mauve to pale green mudstone containing thin sandstone and limestone interlayers (Kirkland et al., 1997). It ranges in average thickness from 20 m to 75 m, and occurs at the base of the Cedar Mountain Formation in the area surrounding Arches National Park.
The Yellow Cat Member most commonly lies unconformably upon a paleosol horizon at the top of the Brushy Basin Member of the Morrison Formation. In some areas, the boundary between the Yellow Cat Member and the Brushy Basin Member is marked by a (deflation?) pebble lag deposit at the top of the Morrison Formation (Kirkland et al. , 1997). The stratigraphic position of the Yellow Cat Member above the paleosol horizon on the top of the Morrison Formation suggests that it is younger than the Buckhorn Conglomerate Member.
The Yellow Cat Member contains elements of the iguanodontid-polacanthid-brachiosaurid fauna (Yellow Cat Fauna) of Carpenter et al. (2002). Kirkland et al. (1999) and Carpenter et al. (2002) have suggested that the Yellow Cat Fauna is similar to Barremian age faunas in Europe. The fauna recovered from the Yellow Cat Member includes the theropods Utahraptor ostrommaysorum and Nedcolbertia justinhofmanni and the ankylosaur Gastonia burgei.
Poison Strip Sandstone (Member), (Kirkland et al., 1997) a cliff-forming sandstone horizon lying above the Yellow Cat Member in eastern Utah from Green River to the Colorado border. It averages 5 m in thickness. It consists of a fine to mediumgrained sandstone containing scattered chert pebbles. The unit contains greenish mudstone partings near the top. The Poison Strip Sandstone Member contains a dinosaur fauna belonging to the Yellow Cat Fauna of Carpenter et al. (2002). Carpenter et al (2002) suggested that the Poison Strip Sandstone is likely of Barremian-Aptian age.
Ruby Ranch Member, (Kirkland et al., 1999;), a purple to dark gray, muddy sandstone, siltstone, and mudstone deposit containing thin conglomerate layers, fluvial sandstone beds, and several calcareous paleosol horizons. It ranges in thickness from about 9 to 90 m. It lies on top of the Poison Strip Sandstone Member in the eastern part of Utah and upon the Buckhorn Conglomerate Member in the San Rafael Swell. The Ruby Ranch Member contains a poorly understood dinosaur fauna. The lowermost part of the unit has been assigned to the Yellow Cat Fauna and the upper part has been assigned to the shamosaurine-neoceratopsian-therizinosauroid-gobiconodontid Mussentuchit Fauna (Carpenter et al., 2002).
Mussentuchit Member (Kirkland et al., 1997) a grayish, muddy sandstone to mudstone containing minor sandstone beds and several altered volcanic ash layers. In the northern part of the San Rafael Swell, it contains several calcareous paleosols near the top. It lies, apparently conformably, upon the underlying Ruby Ranch Member. In the Mussentuchit Wash area, the base of the Mussentuchit Member is a laterally continuous sandstone unit. In the Price River area, the lower boundary coincides with the occurrence of a freshwater limestone unit. The Mussentuchit Member contains an abundant vertebrate fauna consisting of more than 80 taxa of vertebrates (Kirkland et al., 1999).
Abydosaurus mcintoshi - Sauropoda Brachiosauridae - Cretaceous Early Cretaceous Late Albian Cenomanian
Acrocanthosaurus atokensis - Carnosauria Carcharodontosauridae - Cretaceous Early Aptian Albian
Animantarx ramaljonesi - Ankylosauria Nodosauridae - Cretaceous Late, Cenomanian Turonian
Bilbeyhallorum - Eurypoda Ankylosauria - Cretaceous Early Aptian Albian
Brontomerus mcintoshi - Sauropoda Camarasauridae - Cretaceous Early Aptian Albian
Cedarosaurus weiskopfae - Sauropoda Brachiosauridae - Cretaceous Early Barremian
Cedarpelta bilbeyhallorum - Eurypoda Ankylosauria - Cretaceous Early Aptian Albian
Cedrorestes crichtoni - Ornithopoda Hadrosauridae - Cretaceous Early
Eohadrosaurus caroljonesi - Lambeosaurinae Nomen Nudem - Cretaceous Early Cretaceous Late Albian Cenomanian
Eolambia caroljonesa - Hadrosauridae Lambeosaurinae - Cretaceous Early Cretaceous Late Albian Cenomanian
Falcarius utahensis - Therizinosauroidea Therizinosauridae - Cretaceous Early Barremian Aptian
Gastonia burgei - Nodosauridae [Polacanthidae] - Cretaceous Early Barremian
Geminiraptor suarezarum - Maniraptora Troodontidae - Cretaceous Early ?Barremian
Hippodraco scutodens - Ornithopoda Iguanodontia - Cretaceous Early Barremian Aptian
Iguanacolossus fortis - Ornithopoda Iguanodontia - Cretaceous Early ?Barremian
Iguanodon ottingeri - Iguanodontia Nomina Dubia - Cretaceous Early Albian
Martharaptor greenriverensis - Therizinosauridae - Cretaceous Early Aptian
Moabosaurus utahensis - Sauropoda [Macronaria] Nomen Nudem - Cretaceous Early Barremian Aptian
Nedcolbertia justinhofmanni - Tetanurae Coelurosauria - Cretaceous Early Barremian
Planicoxa venenica - Ornithopoda ?Iguanodontia - Cretaceous Early
Sauropelta edwardsorum - Ankylosauria Nodosauridae - Cretaceous Early Cretaceous Late Aptian Albian Cenomanian
Tenontosaurus“dossi” - Iguanodontia Iguanodontidae - Cretaceous Early Aptian Albian
Tenontosaurus tilletorum - Iguanodontia Iguanodontidae - Cretaceous Early Aptian
Utahraptor ostrommaysorum - Coelurosauria Dromaeosauridae - Cretaceous Early Barremian
Venenosaurus dicrocei - Sauropodomorpha Sauropoda - Cretaceous Early
Yurgovuchia doellingi - Coelurosauria Dromaeosauridae - Cretaceous Early Barremian? Aptian
?Hadrosaurid indet. - Ornithopoda - Cretaceous Early Albian
Ankylosaurid indet. - Ankylosauria - Cretaceous Early Albian
Brachiosaurid indet. [teeth (OMNH coll.) from the Mussentuchit Member of the Cedar Mountain Fm] - Sauropoda Brachiosauridae - Cretaceous Early Cretaceous Late - Albian Cenomanian
cf. Deinonychus sp. - Theropoda Dromaeosauridae - Cretaceous Early Albian
Dromaeosaurid indet. - Theropoda Dromaeosauridae - Cretaceous Early Albian
Ornithischia indet. - Ornithischia - Cretaceous Early Albian
Sauropoda indet. - Sauropoda - Cretaceous Early Albian
Theropoda indet. - Theropoda - Cretaceous Early Albian
Troodontid indet. - Theropoda Troodontidae - Cretaceous Early Albian
Undescribed ? iguanodontid (?2 species; Britt. pers. comm.) - Ornithopoda ? Iguanodontidae - Cretaceous Early Albian