CHONDRICHTHYANS FROM THE LOWER FERRON SANDSTONE MEMBER OF THE MANCOS SHALE (UPPER CRETACEOUS: MIDDLE TURONIAN) OF EMERY AND CARBON COUNTIES, UTAH, USA

摘要

The Lower Ferron Sandstone Member of the Mancos Shale in southeastern Utah preserves a chondrichthyan assemblage of at least 13 taxa that include: Hybodus sp., Ptychodus cf. P. mammillaris Agassiz, 1843, Ptychodus whipplei Marcou, 1858, cf. Chiloscyllium sp., Scapanorhynchus raphiodon (Agassiz, 1843), Cretodus crassidens (Dixon, 1850), cf. Leptostyrax sp., cf. Cretalamna appendiculata (Agassiz, 1835), Squalicorax sp., Pseudohypolophus mcnultyi (Thurmond, 1971), Protoplatyrhina hopii Williamson, Kirkland and Lucas, 1993, Ischyrhiza schneideri (Slaughter and Steiner, 1968), and Ptychotrygon triangularis (Reuss, 1844). Although this assemblage is typical of other Turonian chondrichthyan faunas in North America, fossil teeth are preserved in two unique facies associations that consist of arenitic sandstones with mud interclasts and rounded chert, feldspar, and quartz pebbles. The coarser beds within these facies associations are previously interpreted to represent storm events and turbidity flows associated with a sea level lowstand. Chondrichthyan teeth occurring within these coarser beds are indicative of extensive transport and reworking and attest to the durable nature of chondrichthyan teeth for biostratigraphic and paleoecological interpretations. Similar studies of chondrichthyan teeth in shelf marine settings may also provide new insights for facies interpretations related to sequence stratigraphy and regional stratigraphic correlations.