Trace fossils and depositional sequences in a clastic shelf setting, Upper Cretaceous of Utah

Abstract

In Coal Creek Canyon, Utah, the Spring Canyon Member of the Blackhawk Formation is divisible into four regressive hemicycles of deposition, each representing the downdip part of a nearshore-to-offshore sequence. The first and fourth hemicycles are best developed. Individual bedding units span middle-shoreface to lower-offshore lithofacies, the latter corresponding to a thin intertongue of Mancos Shale.Trace fossil assemblages include ~22 ichnospecies and 17 ichnogenera: Ancorichnus, Aulichnites, Chondrites, Cylindrichnus, Ophiomorpha, Palaeophycus, Phoebichnus, Planolites, Rosselia, Schaubcylindrichnus, Scolicia, Skolithos, Taenidium, Teichichnus, Terebellina, Thalassinoides, and Uchirites. Diversity and abundance of ichnospecies are greater in nearshore than in offshore lithofacies. Distal deposits are typified by obscure bioturbate textures: Cylindrichnus concentricus, Palaeophycus heberti, and Rosselia socialis are prevalent through the remainder of the lithofacies suite. Ophiomorpha irregulaire and Schaubcylindrichnus coronus are most common in middle-shoreface beds and Chondrites ichnosp. in upper-offshore beds; Ophiomorpha nodosa and O. annulata also are common in this part of the sequence.

Ordovician sponges from west-central and east-central Alaska and western Yukon Territory, Canada

“…Some Ordovician sponges were previously described from the White Mountain area by Rigby et al (1988;see Fig. 2A therein for the locality location).…”

“…2B therein for the locality location). The current collection includes specimens of: Corymbospongia betella Rigby, Potter & Blodgett, 1988, C. mica Rigby & Potter, 1986 perforata Rigby & Potter, 1986, Pseudoimperatoria minima? (Rigby & Potter, 1986), Pseudoimperatoria media (Rigby & Potter, 1986), and Nucha naucum?…”

“…The short columnar specimen (Fig. 3I) is partially overgrown with four adnate chambers of exaulos-bearing Corymbospongia betella Rigby, Potter & Blodgett, 1988, and a fragment of a finely (? )spiculed, massive unidentified (?)sponge.…”

“…As noted by Rigby et al (1988), the Early Paleozoic record of sphinctozoan sponges is essentially a circum-Pacific record. Sphinctozoan sponges are seemingly abundant in Ordovician-Devonian carbonate rocks of Alaska (Rigby & Blodgett 1983;Rigby et al 1988Rigby et al , 1994Rigby et al , 2005Rigby et al , 2008.…”

“…Sphinctozoan sponges are seemingly abundant in Ordovician-Devonian carbonate rocks of Alaska (Rigby & Blodgett 1983;Rigby et al 1988Rigby et al , 1994Rigby et al , 2005Rigby et al , 2008. Their Alaskan occurrences are primarily in the accreted terranes (i.e., Farewell, Livengood, White Mountains, and Alexander terranes), which make up the bulk of the state, but they are also found in Ashgillian (late Late Ordovician) strata of the uppermost Jones Ridge Limestone, situated along the Alaska-Yukon border in autochthonous rocks belonging to Laurentia.…”