Arkell.1956.Jurassic..

BORDERS OF THE MASSIF CENTRAL 77
part contains bituminous limestones with lignite, rootlet beds, and
several horizons with assemblages of small gastropods and pelecypods
referred to the freshwater and brackish genera Planorbis, Cyrena, etc.
(e.g. Glangeaud, 1895, pp. 154-72; Nickles, 1907, p. 582). These
supposedly brackish beds extend for 250 miles along the south and west
of the Plateau Central. A fauna from the Causses du Larzac recently
studied (Maubeuge, 1949 ; Cox & Maubeuge, 1950) is for the most part
a normal marine one and bears a striking resemblance to that of the
Upper Great Oolite (Bladon Beds) of Oxfordshire. The genera Viviparus
(Paludina), Ampullaria and Paludestrina previously recorded are held to
have been misidentified. This does not, however, dispose of the records
of Planorbis and Chara, and of lignites with cycads, in the Tournemire
area (south of Millau, Aveyron) published by Nickles (1907, p. 583).
These beds form the local base of the Bathonian but may be Upper
Bathonian in date and disconformable on the Bajocian. This tends to
support the conclusion of Agadele (1937) that the dolomites of the Causses
include the Callovian and even Oxfordian and Kimeridgian. The subject
calls for a research with fascinating possibilities, in view of the transgressive
'estuarine' late Bathonian beds reported from so many parts of
the world (e.g. Southern Tunisia, Egypt, Cutch, Burma).
UPPER BAJOCIAN (up to 77 m.)
Zone of Parkinsonia parkinsoni. In the Maconnais an ironshot oolite,
c. 6 m., contains P. parkinsoni, Cadomites deslongchampsi, Morphoceras
dimorphum, as well as Garantiana garantiana (Roche, 1939), but at Crussol
the zone seems to be missing, and it is usually recessive or absent, or
devoid of ammonites. It may be represented in the Privas ironstone,
which embraces from Lower Bathonian down to Toarcian (Roman, 1935,
p. 22).
Zone of Garantiana garantiana. Persistent and fossiliferous in many
places. Reaches a great development in the Mont d'Or Lyonnais where
it is developed as the Ciret, 70 m. of homogeneous fine-grained limestone
with wonderfully-preserved silicified fossils (Roman & Petouraud, 1927;
Marzloff & others, 1936). The fauna consists predominantly of Garantiana
spp., Pseudogarantiana dichotoma Bentz (Roman & Petouraud, 1927,
pi. vi, figs. 1-6, 12-17), and Spiroceras spp., with rather numerous
Phylloceratidae and Lytoceratidae and Vermisphinctes (ibid., 1927, pi. v,
figs. 1, 3, 4), Cleistosphinctes (pi. v, fig. 2), Lissoceras oolithicum, Oppelia
subradiata, Cadomites, etc. A small specimen figured as Parkinsonia
parkinsoni (pi. vi, fig. 22) is certainly not that species and is not evidence
of any admixture of the Parkinsoni Zone. In the Maconnais the zone is
represented by about 12 m. of compact limestone with rare Garantiana.
Zone of Strenoceras subfurcatum. Recognized in the Maconnais (Roche,
1939, p. 114) as limestone (1-65 m.) with silicified brachiopods and a
mixture of ammonites of the Blagdeni, Subfurcatum and Garantiana
Zones, some believed to be derived. At Mont d'Or it occurs as a bed
http://jurassic.ru/