Arkell.1956.Jurassic..

WESTERN AND CENTRAL ALPS 155
landmass took place during the Toarcian and probably reached its climax
with the basal Bajocian (Opalinum Zone) (Triimpy, 1949, p. 178).
The prevalence of breccias in the Alpine Jurassic and the spectacular
transgressions, with wedging out of the whole Lias in short distances
in Glarus and on the Aar and Aiguilles massifs, suggest rapid movements
of orogenic type. Both in the central and eastern Alps, however, the
movements are considered to have been essentially epeirogenic, progressive
and continuous, though evidently jerky (Brinkmann & others, 1937;
Triimpy, 1952). The whole Lias thins out piecemeal against the
Vindelician foreland.
The most remarkable of all the evidences for geanticlines active during
the Jurassic are contained in the Breccia Nappe of the Prealps, where
almost the whole Jurassic consists of breccias, to a total thickness of
1600 m. A submarine fault scarp is indicated. Contemporaneous fossils
are rare and the breccias have to be dated chiefly by reference to underlying
(Rhaetian) and overlying (Albian) beds. Debris from the Prealps
nappes in the Tertiaries of the foreland proves that they had reached
approximately their present positions, as nappes, before the end of the
Oligocene; but where they stood before the nappes began to move, when
the breccias were accumulating, it is still impossible to say. The breccias
are built up of a series of superimposed submarine slides, which travelled
a maximum distance of 5 km. and seem to have slid off the rear of
a rising geanticline in the north-west (Kuenen & Carozzi, 1953). The
succession in the Breccia Nappe is so remarkable that it merits separate
tabulation before considering the general succession in the Alps (Gagnebin,
1934; Schroeder, 1939).
Succession in the Breccia Nappe, Prealps
Flysch
Albian shales, a few metres thick, micaceous, with glauconitic
sandstone, passing up into red beds
Upper Breccia, less coarse on the whole than the Lower Breccia ;
believed to be Upper Jurassic and Lower Cretaceous: 200-300 m.
Slaty shales with bands of radiolarite: supposed Oxfordian
Lower Breccia, probably representing the Lower and Middle Jurassic,
thickening to the north-west, 300-1300 m.
Lower shales, early Lower Liassic, passing up into the breccia
Rhaetian Beds, in Swabian facies
[BERRIASIAN
Perhaps the best fauna occurs in the region between Interlaken and
Glarus, south of Lake Lucerne, especially between Brunig and Urirotstock,
where the Cementstone beds (marls and marly limestones) yield
Berriasella boissieri (Pict.), B. callistoides (Behr.), B. pontica (Ret.)
Neocomites occitanicus (Ret.), Acanthodiscus euthymi (Pict.), A. curelensis
(Kil.), Spiticeras negreli (Math.), S. ducalis (Math.), and forms such as
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