Arkell.1956.Jurassic..

THE JURA MOUNTAINS
Subzone of Catulloceras sp.
Subzone of Phlyseogrammoceras dispansum
Subzone of Hammatoceras insigne, Lytoceras germaini and Paroniceras
sternale
Subzone of Grammoceras fallaciosum
Subzone of Haugia variabilis and Phymatoceras erbaense
Subzone of Hildoceras levisoni and H. boreale
Subzone of Dactylioceras annulatum, D. mucronatum, and Catacoeloceras
raquineanum
MIDDLE AND LOWER LIAS (up to c. 50 m.)
The outcrops along the outer edge of the Jura south of Besancon and
the Langres portal are a continuation of those on the east of the Paris
Basin and of those along the east side of the Massif Central. Their
stratigraphy and faunas have not been the subject of illustrated studies
and they call for no special comment. All the stages and principal zones,
from marls with Amaltheus margaritatus down to Lower Hettangian with
Psiloceras, are present (Guerin, 1954), even to the southernmost extremity
of the He Cremieu (de Riaz, Riche & Roman, 1913, pp. 82-6). The
outcrops of the northern Jura similarly are a continuation of those of
Wiirttemberg, except that thicknesses are reduced (maximum less than
50 m.); the successions have been tabulated by Heim (1919, table,
p. 486); for sections and fossil lists see Brandlin (1911). Notoriety has
been achieved by a Liassic sequence on the inner edge of the Jura west of
Geneva, at Champfromier, north of Bellegarde, dept. of Ain, described
by Bovier (1931). Bovier recorded here a sequence of ammonite epiboles
in the Sinemurian and Pliensbachian widely different from those
established by Lang's collecting on the Dorset coast, and his results were
publicized by Spath (1931) who used them to discredit Buckman's 'polyhemeral'
system of correlation. It appears to have been only some years
after publishing this paper, however, and after it had been widely quoted,
that Dr Spath examined the material, and in consequence he asserted
that, so far as the Liparoceratidae were concerned, 'the apparent
anomalies in the succession are easily explained by misidentification'
(Spath, 1938, 'Cat. Amm. Liassic family Liparoceratidae', Brit. Mus.,
p. 36). Unfortunately no reference was made to the other anomalies;
but doubt is inevitably cast on them also, and is enhanced by Mouterde's
observation that the order of certain beds may have been disturbed by
slipping (1953, Bull. Serv. Carte Geol. France, no. 236, p. 407). In the
light of this the Champfromier succession urgently needs reinvestigation.
Its importance far transcends local interest. (Roche, 1939, pp. 31-3,
in his enthusiasm for Buckman's polyhemeral system proclaimed, somewhat
cryptically, that the fact that it does not work at Champfromier
confirms its value; if now the anomalies turn out to be illusory, presumably
one should draw the opposite conclusion ?)
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