Special papers in Palaeontology: 64
<br />Inoceramid faunas and biostratigraphy of the Lower Turonian - Lower Coniacian, U.S. Western Interior
<br />Walaszczyk & W.A. Cobban
<br />811 pp., 32 pls, 27 figs
<br />ABSTRACT. Twenty-seven inoceramid species and subspecies of the genera Inoceramus J. Sowerby, 1814, My/iloides Brongniart, 1822, Cremnoceramus Cox, 1969, and Te/hyoceramus Sornay, 1980 are described from the Upper Turonian and Lower Coniacian of the Western Interior of the United States. One Inoceramus species, I. dako/ensis, and two My/iloides species, M. ra/onensis, and M. bellefourchensis, are described as new, and four forms are left in open nomenclature. Four widely used North American species, I. dimidius White, 1874, I. perplexus Whitfield, 1877, C. deformis ereclus (Meek, 1877), and C. deformis deformis (Meek, 1871), are thoroughly discussed for the first time and illustrated. The inoceramids allow a subdivision of the Upper Turonian and Lower Coniacian into eight zones, and their precise correlation with the European succession and the standard substage subdivision of the Turonian and Coniacian, as well as with the ammonite zonation used in the US Western Interior. The base of the Upper Turonian, corresponding to the base of the European I. coslellalus Zone, corresponds to the base of the I. perplexus Zone, and to the base of the Scaphi/es whilfieldi ammonite Zone. The Upper Turonian is divided into zones of Inoceramus perplexus, I. dakolensis, Myliloides incerlus, M. scupini, and Cremnoceramus wallersdoifensis wal/ersdoifensis. The Lower Coniacian has the zones of Cremnoceramus deformis ereCIUS, C. deformis dobrogensis, and C. crassus crassus. In the upper part of the ereclus Zone and in the dobrogensis Zone, the Te/hyoceramus wandereri and Cremnoceramus crassus inconSlans zones may be distinguished. Cremnoceramus deformis ereclus (Meek) is the basal member of the deformis lineage and the proper name for forms referred to C. rolunda/us (sensu Troger 1967 non Fiege 1930), and, accordingly, is the basal boundary marker of the Coniacian. So defined, the first Forresleria have already appeared in the topmost Turonian. The Turonian/Coniacian boundary is marked by a series of short-lived events beuer recognized in Europe (DidymOlis I Event, wallersdoifensis Event, herbichi Event, ereclus I Event).