Fossil fishes from a lag deposit within the Upper Cretaceous Mancos Shale in New Mexico, USA, with comments on correlative Turonian–Coniacian time-transgressive lags in the Western Interior Seaway of North America

Abstract

A lag deposit between the Tocito Sandstone and Mulatto Tongue of the Upper Cretaceous Mancos Shale in Sandoval County, New Mexico, USA, contains a fossil assemblage of late Turonian–early Coniacian chondrichthyans and osteichthyans. This assemblage consists primarily of isolated teeth that derive from at least 26 taxa including: Meristodonoides sp.; Ptychodus mortoni; P. mammillaris; Scapanorhyncus raphiodon; Protolamna sp.; Cretodus cf. C. semiplicatus; Cretodus sp.; Cretalamna “appendiculata”; cf. Eostriatolamia tenuiplicatus; Archaeolamna cf. A. kopingensis; Squalicorax cf. S. falcatus; S. deckeri; Squalicorax sp.; Paranomotodon(?) sp.; Rhinobatos lobatus; Ptychotrygon triangularis; Texatrygon hooveri; Pseudohypolophus mcnultyi; Ischyrhiza mira; Chondrichthyes indet.; Micropycnodon cf. M. kansasensis; Pycnodontiformes indet.; Aspidorhynchidae indet.; Protosphyraena sp.; and Enchodus cf. E. gladiolus. The lag deposit formed along a series of outer shoreface and discontinuous sandbars in the southeastern corner of the San Juan Basin during eustatic sea-level fluctuation herein referred to as the Turonian–Coniacian Time Transgressive (TCTT) Event. This sea-level event and the concentration of fish remains into a lag deposit is also recorded at several other states within the Western Interior Seaway of North America. These stratigraphic properties have correlative potential across basins and states and provide a framework by which regional and eustatic sea-level events can be interpreted. Differences in coeval faunas found within these TCTT lags are bathymetrically controlled, related to the degree of taphonomic reworking, and proximity of the ancestral shoreline.