Cephalopodes

Cephalopods

The Cephalopods of the chalk are represented by two groups:

In the Anglo-Parisian Pond, Cephalopods are rather rare. This rarity is due to the fact that their shell is initially made of aragonite, unstable mineral in the pure chalky mud and which restarts in solution. Their preservation takes place only if they are prematurely cemented or if they are buried in a more marly chalk. Cephalopods meet mainly in Cénomanien, in the base of Turonien and in Campanien. Thus it is not this group which allows globally to date chalks and we substitute him a scale macrofaunique based on Inocérames (Bivalves) and the Echinoderms which possess a test calcitique more resistant.

Zonation from Cénomanien to Coniacien

From of the ammonites, resumed of F. Amédro and F. Robaszynski (2008):

Ammonites du Cénomanien's zones - Turonien, compared to the zones of Foraminifères, extracts of F. Amédro and F. Robaszynski (2008)

Here is a representation of the main sorts of ammonites used for the stratigraphy of Cénomanien (slide of F. Robaszynski):

Ammonites of Cénomanien (slide F. Robaszynski)

Bélemnites is confined in certain levels (upper Cénomanien, Santonien superior, Campanien). The geologic association auboise gives some illustrations.

Illustration of some sorts-types met in the chalk

Cénomanien

Cénomanien inferior:Mantelliceras mantelli (Link GCR, fig. In, link ammonites.fr)
Cénomanien lower than superior: Schloenbachia varians (+ + link GCR, fig. B1 to B3, Link ammonites.fr, AGBP, link f.diebold)
Cénomanien:Hypoturrilites gravesianus (Link GCR, fig. C1)
Hypoturrilites tuberculatus (Link GCR, fig. C2)
Cénomanien means:Turrilites costatus (Link GCR, fig. F, link ammonites.fr)
Cénomanien means:Sciponoceras baculoides (link f.diebold)
Turrilites scheuchzerianus (Link GCR, fig. G, link ammonites.fr)
Mantelliceras cantianum (Link GCR, fig. In, link ammonites.fr)
Cénomanien inferior:Mantelliceras dixoni (link f.diebold)
Cénomanien inferior:Mantelliceras saxbii (link f.diebold)
Cunningtoniceras inerme (Link GCR, fig. C, link ammonites.fr)
Cénomanien means: Acanthoceras rhotomagense
Calycoceras gentoni
Calycoceras asiaticum
Scaphites aequalis
Scaphites obliquus (link f.diebold)
Schloenbachia coupei
Turrilites acutus
Turrilites costatus
Eutrophoceras laevigatus
Forbesiceras bicarinatum
Cénomanien superior:Metoicoceras geslinianum (Link GCR, fig. In, link ammonites.fr)
Cénomanien superior:Proeucalycoceras guerangeri (link f.diebold)
Cénomanien lower than average Turonien: Parapuzosia (Austiniceras) austeni (LLink GCR, fig. B, link ammonites.fr

Turonien (zonation: Link ammonites.fr)

Turonien inferior:Mammites nodosoides (Link GCR, fig. B, link ammonites.fr, link f.diebold)
Turonien means:Collignoniceras woollgari (Link GCR, fig. In, link f.diebold))
Turonien superior: Lewesiceras mantelli (Link GCR, fig. C, link ammonites.fr)
Turonien superior:Subprionocyclus neptuni (Link GCR, figs. In, B, D)
Sciponoceras bohemicum (Link GCR, figs. W, X)

mammites_nodosoides

Mammites nodosoides