Arkell.1956.Jurassic..

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THE PARIS BASIN
UPPER OXFORDIAN (up to 150 m. or more)
Zone of Epipeltoceras bimammatum. To this zone certainly belongs
the lower half (30-40 m.) of the 'Corallien compacte', from which de
Loriol, Royer & Tombeck (1872) figured E. bimammatum Quenst. sp.
(pi. v, fig. 3), Ochetoceras marantianum d'Orb. sp. (pi. v, fig. 4), Decipia
sp. (pi. iv, fig. 3), and Ringsteadia frequens Salfeld (pi. iv, fig. 2). The
first two guide-fossils are found in various places on the east and southeast
of the Paris Basin (Lemoine, 1911, pp. 113-117). The basal part of
the zone, corresponding to the Cautisnigrae Subzone of England, is
represented in at least the upper part of the Calcaire de Creue, Meuse
(or in similar beds taken for it), with Perisphinctes mosensis Bayle, P. aff.
damoni Arkell, etc. (Maubeuge, 1953, p. 1909).
Zone of Gregoryceras transversarium. The species of Gregoryceras
have been revised and figured by de Grossouvre (1917). To this zone
belong the thick coral rags and coralline oolites, such as those of St
Mihiel, Meuse (Buvignier, 1852), with wonderfully rich faunas of
pelecypods, gastropods, echinoids, etc. in which ammonites are either
very scarce or wanting. In the chalky Calcaire de Creue ammonites are
commoner but crushed; most are certainly of Transversarium Zone age
(Dechaseaux, 1931, p. 354; Bonte, 1938; Maubeuge, 1953, p. 1909).
The sorting-out of the ammonite succession in these coralline facies,
mainly from isolated marly lenticles, remains one of the major problems
in the stratigraphy of the Paris Basin. The most promising attempt was
made by de Grossouvre (1897), who sought to establish a number of
ammonite zones, but it is difficult to relate these to the stratigraphy.
His conclusions seem to indicate a more gradual passage into both
Cordatum Zone faunas below and Bimammatum Zone faunas above,
the fauna of the Transversarium Zone being less distinctly demarcated
than in NW. Europe and the Jura ranges, probably as the result of
continuity of deposition and environment. The same result emerges
from the researches of Maubeuge (19516) in the Verdun region and on
the Etain sheet (19520"). Here, as in the Swiss Jura, the fauna of the
Plicatilis Zone occurs below the coralline beds, in the 'Chailles'; and
in the Ardennes (Arkell, 1948, p. 390) and Cote d'Or (Collot, 1917)
the base of the zone, already with Gregoryceras transversarium or G.
toucasi near Dijon, is found in the top of the ironshot oolites which so
often underlie the coralline oolites and coral rags. Much time has been
wasted in sterile attempts to classify the beds into 'Oxfordian s.s.',
'Argovian', 'Rauracian', and 'Sequanian' (e.g. Reyre, 1944) without
regard to ammonites and oblivious of the fact that in the type-area of
the Jura Mountains the Rauracian and Argovian have long ago been shown
to be the same, and that both are equivalent to d'Orbigny's Upper
Oxfordian. In the Nievre this tendency has been carried to extremes
with four substages for each of these stages (Panthier, 1931-35);
but a useful set of ammonites has been figured, all belonging to the
Upper Oxfordian and typical of the Plicatilis-Transversarium Zone.
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