Arkell.1956.Jurassic..

154 THE ALPS AND NORTHERN CARPATHIANS
The Central Geosynclinal Facies: the Schistes Lustre's or Biindnerschiefer
The monotonous 'comprehensive series' of the central geosyncline
is 2000-5000 m. thick and consists mainly of mica schists and black and
grey phyllites, passing where less metamorphosed into calcareous shales
and sandstones. Greenstone intrusions are common and increase
southwards: their age is still undetermined, but, from their association
with radiolarites, they are believed to be late Upper Jurassic or early
Cretaceous (Routhier, 1944).
Despite the prevalent metamorphism, macro-fossils are found in
places, especially towards the base. Most of those hitherto found have
been of Lower Liassic age—belemnites, Pentacrinus, Gryphaea, Cardinia
listeri, distorted Arietitid ammonites, and occasionally corals and logs
of silicified wood. Higher in the sequence are Upper Jurassic and
Cretaceous radiolarites; and in some places there is gradual upward
passage into Eocene flysch, with, locally, nummulites occurring in rock
indistinguishable from Schistes lustres.
The lower limit of the Schistes lustres is as inconstant stratigraphically
as the upper. In some places typical Schistes lustres begin with the
Middle Trias; in other places the lowest layers contain Sinemurian
fossils and rest conformably on Upper Triassic quartzite; in others the
basal layers are believed to be Pliensbachian. Locally there is a basal
conglomerate, and bands of conglomerate and thick breccia may occur
higher up in the series. From all this it is inferred that the bottom of
the geosyncline from as early as Triassic times was corrugated with
rising geanticlinal ridges similar to those on the foreland margin. In
the later stages of the Tertiary orogeny the Palaeozoic cores of these
geanticlines burst through the Mesozoic sedimentary cover to form the
Pennine nappes.
The Foreland Margin
The foreland in the west (Dauphine and Provence) has already been
discussed. For a more comprehensive and detailed structural study
reference should be made to Goguel (1944). On the north of both the
Swiss and Austro-Bavarian Alps the immediate foreland was the Vindelician
(Alemannian) landmass—either a string of islands or an elongated
projection from the Bohemian Forest—which divided the Alpine from the
Swabian trough of deposition during Liassic times and probably survived
at first as islands, later as a submerged swell, through the Middle and
Upper Jurassic. Study of the southern margin of this barrier during
Liassic times (Frank, 1930; Triimpy, 1949, 1952) has revealed an extremely
rapid southerly thickening of the Lias, followed twice by gradual thinning
and then repeated rapid thickening. These changes are attributed to a
stepwise foundering and outward tilting of strips of the geosynclinal
margin, perhaps even under tension, due to profound subsidence of the
axial region to the south. Rapid transgression over the Vindelician
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