Arkell.1956.Jurassic..

EAST OF THE PARIS BASIN 55
collections were determined by S. S. Buckman and are in the museum
of the Faculte des Sciences at Poitiers.
TOARCIAN (8-10 m.)
In its type region the Toarcian consists uniformly of blue marl with
blue marly limestone bands and pyritized ammonites. Although the
stage is so thin, the following ammonite zones are distinguishable at
Thouars (Welsch, 1903, p. 821; 1928; for farther east, in Indre, see
Mouterde, 1948). Locally the stage transgresses on to the crystalline
basement.
Zone of Pleydellia aalensis
Zone of Dumortieria radians
Zone of Hammatoceras insigne, with Polyplectus discoides
Zone of Grammoceras thouarsense, with G. striatulum
Zone of Haugia variabilis, with Pseudolioceras compactile
Zone of Hildoceras bifrons, with H. levisoni and Dactylioceras commune
Zone of Harpoceras falcifer, with Dactylioceras annulatum and Frechiella
PLIENSBACHIAN (5-15 m.)
Limestones and sandy limestones of this stage yield Pleuroceras
spinatum, Amaltheus margaritatus, Prodactylioceras davoei, Androgynoceras
capricornum, Protogrammoceras normannianum, etc. (Welsch, 1903,
pp. 815-21, 945; Couffon & Dolfuss, 1928, p. 32). Locally the stage
transgresses on to the crystallines.
SINEMURIAN AND HETTANGIAN (up to 20 m.)
Where not cut out by Pliensbachian or Toarcian overlaps, there are
limestones assigned to the Lower Lias but containing a meagre fauna.
An Arietites is recorded (Welsch, 1903, pp. 812-5; Glangeaud, 1895,
pp. 22 ff.).
EAST OF THE PARIS BASIN
From the departments of Indre and Nievre in the south, a continuous
broad band of Jurassic,—the most extensive outcrop in Europe—, encircles
the Chalk of the Paris Basin on the east as far north as the Ardennes.
South-eastwards it spreads over continuously by way of the Plateau of
Langres and the department of Doubs to join up with the Jura chain,
and it is continued eastward in south Belgium, Luxemburg and Alsace.
In this great Jurassic area are Hettange and Semur, type localities of the
Hettangian and Sinemurian stages.
Against the Palaeozoic horsts of the Massif Central, Morvan, Vosges
and Ardennes, various members of the Jurassic change facies or wedge
out, overlapped by higher members or by the Cretaceous. For instance,
in the Ardennes area the Cretaceous usually rests on the Oxfordian,
though occasionally there is some Lower Kimeridge left below the unconformity;
parts of the Lower Lias are sometimes missing; and the
http://jurassic.ru/