Acanthoceras

Abstract: The Lower Chalk of south-eastern England is a richly fossiliferous sequence 54-104 m. thick, spanning most of the Cenomanian Stage. It rests with a slight break or without interruption on Upper Albian dispar-perinflatum Sub-zone sediments of Gault or Upper Greensand facies. The upper limit as here adopted is marked by a slight break at the base of the Cenomanian-Turonian plenus Marls (Metoicoceras gourdoni Zone), the sub-plenus erosion surface of Jefferies (1962, 1963). Of the many groups of fossils present, the ammonites provide the most useful means of subdivision and correlation. The distribution of these, and of other originally aragonitic fossils, is largely controlled by preservation, and there are levels at which there is evidence of seafloor dissolution of aragonite. Nevertheless, three ammonite zones can be recognised: 3. Zone of Calycoceras naviculare 2. Zone of Acanthoceras rhotomagense 1. Zone of Mantelliceras mantelli Within the M. mantelli Zone three assemblages are identified, characterised by: (a) Hypoturrilites carcitanensis, (b) Mantelliceras saxbii, (c) Mantelliceras gr. dixoni. There are also three assemblages in the Zone of A. rhotomagense, characterised by: (a) Turrilites costatus, (b) Turrilites acutus, (c) Acanthoceras jukes-brownei. The C. naviculare Zone is not subdivided. These zones are comparable to those proposed by Hancock (1959) for the type Cenomanian, and are equivalent to the Lower, Middle and Upper parts of the Stage. Bivalves, corals and brachiopods also have a use in correlation, and even fragments of the commonest fossils—Inoceramus and Holaster—are of local use.

Abstract: The ammonite faunas of the Woodbine Formation and lower part of the Eagle Ford Group of north-east and central Texas can be referred to five successive zonal assemblages of the standard sequence recognized for the southern part of the US Western Interior. The upper lower Cenomanian Forbesiceras brundrettei zone is represented by a limited assemblage in old collections believed to be from the Pepper Shale Member of the Woodbine, and from the Waco area. The middle Cenomanian Conlinoceras tarrantense zone is represented in the Tarrant Formation of the Eagle Ford in the area west of Dallas. The succeeding Acanthoceras bellense zone is a new biostratigraphic unit in the area, occurring only at the base of the Bluebonnet Member of the Lake Waco Formation of the Eagle Ford Group near Belton in Bell County. The Acanthoceras amphibolum zone is represented by the type species in the Lewisville Member of the Woodbine. The Six Flags Limestone Member of the Woodbine and the lower part of the bentonitic member of the Eagle Ford Group yield the index species and Tarrantoceras west of Dallas. The highest fauna described is that of the Plesiacanthoceras wyomingense zone, known only from the Templeton Member of the Woodbine in the northeastern part of the study area. -from Authors

Abstract: The comparison of superposed praealveolinid assemblages from the well exposed outcrops in the Iberian Range and the Pyrenees with Prealveolina species from the type localities in Reichel's collection have allowed us to evaluate the stratigraphical range of each species. The species Praealveolina iberica, P. pennensis and P. debilis successively replace each other from Early to Mid Cenomanian; they have been correlated with Mantelliceras mantelli and Acanthoceras rotomagense ammonite zones, and with Rotalipora brotzeni and the lower part of the R. cushmanni planktonic foraminiferal zones. Praealveolina brevis and P. tenuis appear successively during the Upper Cenomanian, but the range of P. tenuis may overlap with the one of P. brevis in the Early Upper Cenomanian; they have been correlated with Calycoceras naviculare and Metoicoceras geslinianum and with R. cushmannni zone. P simplex occurs together with P. brevis and P. tenuis in the Upper Cenomanian. The stratigraphic relationship of P. cretace...