A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #0-9

Hoedemaeker P.J. (1983) Reconsideration of the stratigraphic position of the boundary between the Berriasian and the Nemausian (= Valanginian sensu stricto) // Zitteliana. Vol. 10. Pp. 447-457.

The study of the ammonite distribution in the Lower Cretaceous beds N and NW of Los Miravetes (Rio Argos, W of Caravaca, SE Spain), compels us to draw the boundary between the Berriasian and Valanginian sensu stricto between the Berriasella (Berriasella) picteti Subzone and the Tirnovella alpillensis Subzone. The latter subzone was introduced as a substitute for the Berriasella (Berriasella) calhsto Subzone of Le Hégarat (1971), because, although both subzones embrace the same biochronologic interval, the ammonite associations of the two differ fundamentally: in addition to the known callisto association of merely Berriasian ammonites, the T. alpillensis Subzone contains an equally large number of renownedly ´Valanginian´ ammonite forms appearing at its base. The boundary proposed here coincides with the appearance of Lorenziella hungarica, which provides a means to correlate this level outside the Mediterranean faunal province. The transformation from a pure Berriasian ammonite association into a clear Valanginian association definitely has not the abruptness that invited so many stratigraphers to choose this boundary as the one between the Jurassic and Cretaceous systems. Finally arguments are adduced to return to the old concept of the Valanginian Stage and to regard the Berriasian as its lower substage. For the upper substage of the Valanginian (= Valanginian sensu stricto) the name Nemausian (Sarran d´Allard, 1875, 1881) is available, which has explicitly been introduced to cover the stratigraphic interval between the Berriasian and the Hauterivian.