Abstract
The Spence Shale of northern Utah is the oldest North American middle Cambrian (∼506–505 Ma) Burgess Shale-type (BST) deposit and, unlike previously thought for BST deposits, has a very diverse ichnofauna. Twenty-four ichnogenera and 35 ichnospecies were identified: Archaeonassa (A. fossulata and A. jamisoni isp. nov.), Arenicolites carbonaria, Aulichnites, Bergaueria (B. hemispherica and B. aff. perata), Conichnus conicus, Cruziana (C. barbata and C. problematica), Dimorphichnus, Diplichnites (D. cf. binatus, D. gouldi, and D. cf. govenderi), Gordia marnia, Gyrophyllites kwassizensis, Halopoa aff. imbricata, Lockeia siliquaria, Monomorphichnus (M. bilinearis, M. lineatus, and M. cf. multilineatus), Nereites cf. macleayi, Phycodes curvipalmatum, Phycosiphon incertum, Planolites (P. annularius, P. beverleyensis, and P. montanus), Protovirgularia (P. dichotoma and P. cf. pennatus), Rusophycus (R. carbonarius, R. cf. pudicus, and R. cf. cerecedensis), Sagittichnus lincki, Scolicia, Taenidium cf. satanassi, Teichichnus cf. nodosus, and Treptichnus (T. bifurcus, T. pedum, and T. vagans). The ichnofossils comprise three ichnocoenoses—Rusophycus-Cruziana, Sagittichnus, and Arenicolites-Conichnus—representing dwelling, deposit- and filter-feeding, grazing, locomotion, and predation behaviors of organisms (e.g., annelid worms and trilobites). Two ichnofossil associations are suggestive of predation: (1) Planolites terminating at a Rusophycus; and (2) Archaeonassa crosscutting a Taenidium. The Spence Shale ichnofauna represent a distal Cruziana Ichnofacies and depauperate, distal Skolithos Ichnofacies. A new ichnospecies of Archaeonassa is proposed, A. jamisoni isp. nov., and Ptychoplasma (Protovirgularia) vagans is herein transferred to Treptichnus. This study is the first ichnotaxonomic study of the Spence Shale and North American BST deposits and shows highly diverse ichnofaunas can be present in BST deposits.
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