Arkell.1956.Jurassic..

IOO THE JURA MOUNTAINS
blagdeni, occurs also. In the Staffelberg area a coral reef started to grow
at the time of the Blagdeni Zone and continues upwards well into the
Lower Hauptrogenstein, showing continuity of conditions.
MIDDLE BAJOCIAN (up to 190 m.)
Zone of Stephanoceras humphriesianum. This is divisible into Blagdeni
Beds above (sandy limestones and marls, 3-20 m.) and Humphriesianum
Beds below (largely ironshot marls and ironshot oolites, 1-7 m.). As
remarked above, Teloceras sp. or spp. customarily identified as blagdeni
pass up into the Subfurcatum Zone. The Humphriesianum Zone yields
large Stephanoceras and Skirroceras, and also Sphaeroceras brongniarti,
Chondroceras gervillii, Poecilomorphus cycloides, Oppelia subradiata (Greppin,
1898, pp. 23-7, 34-5) and Strigoceras strigifer Buck. sp. (Maubeuge &
Lieb, 1950). Some areas have considerable coral growth in this zone.
Zone of Otoites sauzei. Marls and sandy limestones, up to c. 30 m.,
passing in places into crinoidal limestones and coralline limestones:
Emileia polymer a (Waag.), E. polyschides (Waag.), Otoites sauzei (Greppin,
1898, pis. i-iii), Normannites cf. braikenridgei (Sow.), Skirroceras macrum
Quenst. sp. (Pelletier, 1950).
Zone of Sonninia sowerbyi. In the southern Jura this zone reaches
a thickness of 130 m., consisting chiefly of marly to sparry limestones,
with some bands of chert nodules and a coral band (15 m.) in the
Laeviuscula Subzone (Pelletier, 1950). In the lowest n m. Pelletier
records a large Euhoploceras and, immediately above, a bed (o-6 m.)
with Hyperlioceras, Graphoceras, Reynesella and Sonninia. In the Basel
region the thickness of the zone is only 12-35 m. at a section described in
detail by Striibin (1900), which yielded Sonninia, Poecilomorphus and
Hyperlioceras. In this region Maubeuge & Lieb (1950) find all three
subzones identifiable by distinctive ammonites.
The details of this and other Bajocian zones in the Rhine valley near
Lorrach are described by Wittmann (1949).
LOWER BAJOCIAN (up to 125 m.)
The Lower Bajocian consists of very variable beds of limestone, marl
and ironshot oolite (2-18 m.), which pass down into the Opalinum Clays
(Miihlberg, 1900). The normal thickness for the Opalinum Clays is
about 50 m., but in a boring at Buix near Porrentruy they were 157 m.
thick and, although no fossils were found in them, they overlay Toarcian
shales with Posidonia, under which were pyritized Pleuroceras spinatum
and Spiriferina, so that no mistake was possible (Schmidt & others, 1924).
Probably, however, the Jurense Zone is represented in this great thickness,
for there is a gradual passage in some places at outcrop. Often, also,
the upper part of the Opalinum Zone is represented in the base of the
overlying limestones and ferruginous beds.
In the north-eastern part of the Jura an exceptionally valuable ammonite
succession, correlating with Germany and England, has been established
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