Arkell.1956.Jurassic..

THE JURA MOUNTAINS
Paris basin. The ammonites have been monographed by de Loriol
(1898-99, 1900), whose plates show the usual profusion of beautiful,
small, pyritized Oppeliidae, Cardioceratidae, Aspidoceratidae and Perisphinctidae.
Sowerbyceras and some other Phylloceratids also occur.
The swarms of Scarburgiceras alphacordatum Spath (de Loriol, 1898-99,
pi. ii, 1-3), S. lahuseni Maire (fig. 9) and their allies, with Pavloviceras
mariae d'Orb. sp. (pi. iii), Hecticoceras, Proscaphites (pis. iii, iv) and
Creniceras are accompanied by Poculisphinctes petitclerci de Loriol sp.
(pi. v, 16), Properisphinctes bernensis (de Loriol), Euaspidoceras babeanum
(d'Orb.) and inner whorls of various Peltoceratids difficult to place, all
just as in the same zone in England. Interesting aberrant Oppeliids are
Scaphitodites scaphitoides (Coquand), Sphaerodomites calcaratus (Coquand)
and Berniceras inconspicuum (de Loriol). A few specimens may have
come from the Cordatum Zone: e.g. Vertebriceras sequanicum Maire (de
Loriol, 1898-99, pi. ii, 10), which occurs in the Yorkshire Ball Beds.
CALLOVIAN (0-5-82 m.)
The Callovian is condensed and richly fossiliferous, excepting the
Macrocephalus Zone, which is often unrepresented by fauna, either
owing to absence or owing to development in the facies of crinoidal
limestone (Dalle nacree), which in places has yielded large Macrocephalitidae.
Apart from this the prevalent facies is oolitic ironstone
or ironshot marls. For the most part the ores belong to the Middle
Callovian and the upper part of the Lower (Calloviense and Koenigi Zones).
At Herznach mines, near the north extremity of the Jura, the whole
Callovian is only 3-25 m. thick and at Chanaz, near the south extremity,
even less. At both places the ironstone has yielded magnificent ammonite
faunas, monographed respectively by Jeannet (1951) and Parona &
Bonarelli (1897). At Chanaz the Upper Callovian (and Lower Oxfordian)
is missing, the Transversarium Zone resting on the Anceps Zone, but
at Herznach, although less than half a metre thick it is separable into
Lamberti Zone above and Athleta Zone below. In the Hauenstein area
near Olten both Upper and Middle Callovian are missing (Erni, 1942,
p. 162), while in the He Cremieu the Middle alone is present (de Riaz,
1895, p. 368). The detailed ammonite succession at Herznach (Jeannet,
1951) makes it a type section; but the order of occurrence of some of the
genera and species within the Middle Callovian (beds B2-7 and Ci, total
1-95 m.) is probably valid only locally. For instance, Erymnoceras has
its maximum abundance above Reineckeia anceps (Jeannet, 1951, p. 7)
whereas at Salins in the west-central Jura, where the development is
similar, the order is reversed (Piroutet, 1919). Reversibility of the
anceps and coronatum epiboles was noted also on the outcrops of the
eastern Paris Basin (above, p. 60).
A particularly important ammonite succession has been published
for the Weissenstein area near Solothurn (Erni, 1934):
Upper Oxfordian, Birmensdorf Beds, above.
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