Marginal-marine facies of the Spring Canyon Member of the Upper Cretaceous Blackhawk Formation in east-central Utah were deposited in a complex set of channel-fill, delta, and lagoon-fill environments. Twelve trace fossils have been identified from 27 measured sections in the transition zone between nonmarine and marine facies. None is unique to the marginal-marine environment. Abundant trace fossils occur in three assemblages: channel-fill, delta and lagoon-fill. Trace fossils in the channel-fill sandstones include Ophiomorpha, Skolithos, Teredolites, Thalassinoides, collapse structures, and rayhole structures. Thalassinoides is restricted to the base of channels at erosional contacts with coal and is present as exichnia in the upper portion of the coal. Arenicolites, Pholeus, Ophiomorpha, Teredolites, collapse structures, and rayhole structures are found in deltaic sandstones. Planolites, Palaeophycus, Pelecypodichnus, Thalassinoides, Ophiomorpha and horizontal sand-filled burrows are present in lagoonal siltstone and sandstone; Palaeophycus, Thalassinoides, Planolites, and horizontal sand-filled burrows are found in the delta/lagoon transition beds.--Modified journal abstract.

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