Arkell.1956.Jurassic..

THE ATLAS RANGES 26l
500 m.; the Berriasian is not separable lithologically. The Mesozoic
sequence begins with thick Triassic marls and red sandstones, capped by
basalt. On this lies the first Jurassic formation, some 80 m. of red and
white sandstones and marls with gypsum, known as the Jurassic 'lagunaire'.
It has yielded only indeterminable brachiopods, pelecypods, gastropods
and a belemnite, and its age therefore still remains to be established.
There follow up to 100 m. of beds in which marine limestones predominate.
They have yielded a rich Upper Jurassic fauna, but very few
ammonites. Roch (1930, p. 205) records small Peltoceratids comparable
with French Lower Oxfordian forms. Half a Perisphinctid has been
figured (Gentil & Lemoine, 1905, pi. iv, fig. 6); it was first identified
with a Swiss Upper Oxfordian species of the Transversarium Zone, but
Roch thought it Callovian. In my opinion it is highest Upper Oxfordian,
Bimammatum Zone, comparable with the group of Perisphinctes fontannesi
UPPER JURASSIC AND P-^.
BERRIASIAN WITH GYPSUM OLD DUNES
LOWER KIMERIDGIAN rl-ll
OXFORDIAN E=3 TILTED PALAEOZOIC V/////M
FIG. 33.—Horizontal section illustrating the overlap of the Upper Jurassic against the
Palaeozoic of the High Atlas in western Morocco. After Roch, 1930 (the Jurassic
formations reclassified as in the present text).
Choffat (1893, pi. ix) and P. lusitanicus Siem. as figured by Wegele (1929,
pi. ii, fig. 3) from the Planula Subzone.
Next follow 80 m. of limestones in coralline facies with Nerinea beds,
which pass eastwards, towards the shoreline, into dolomitic limestones and
finally sandstones. They have yielded no cephalopods but are presumably
Lower Kimeridgian. Finally there is a series of 250 m. of limestones
and marls with lenticular masses of gypsum up to 100 m. thick. The
lower parts have yielded echinoids and lamellibranchs believed to be
Kimeridgian, while at the top there is a rich ammonite fauna of the
Berriasian, in which species of Spiticeras predominate. Berriasella
boissieri (Pictet), zonal index of the lowest Cretaceous, occurs in this
assemblage (Roch, 1930, p. 257). These highest 250 m. of beds overlap
all the earlier formations and transgress far across the folded Palaeozoics.
HIGH ATLAS, MIDDLE ATLAS AND SAHARAN ATLAS
The sediments in the north-eastern part of the basin just described wedge
out against the core of the High Atlas, a range of Palaeozoic sediments and
granites folded and solidified in the Variscan orogeny and refolded in the
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