Arkell.1956.Jurassic..

212 ITALY AND CORSICA
Calabria and Sardinia, on opposite sides of the marine trough that connected
the central Apennines with Sicily. Lias is absent in Sardinia,
complete and very thick in Calabria. In Calabria the Liassic marine
cycle ends with ammonitiferous Lower Bajocian, which is about the same
age as the continental sandstone that begins the sequence in Sardinia.
The predominant formation in Sardinia, transgressive on the basement,
is the Middle Bajocian-Bathonian (250 m.), which stages are absent in
Calabria. The only feature in common is the transgressive Upper Jurassic,
in both regions only vaguely dated but embracing the Tithonian.
THE APENNINES
Between the small Jurassic outcrops of northern Calabria, on the
'instep' of the Italian 'foot', and the main complex of scattered outcrops
higher up the 'leg', in the central Apennines, there is a gap of some 200
miles. On old maps, the gap is to some extent bridged by an inlier of
reef-facies limestones assigned to the Tithonian (Viola & Cassetti, 1893),
in the core of a dome forming Monte Gargano (the 'spur', on the Adriatic
coast). But on the new Geological Survey maps (1928) and Dainelli's
atlas (1948) all these limestones have been transferred to the Cretaceous
on the strength of more recent palaeontological discoveries (Checchia-
Rispoli, 1925). No ammonites occur.
In the central and northern Apennines, especially in Tuscany and
Umbria, the Jurassic is thin but complete, or nearly complete, and the
Lias is well dated by beds rich in ammonites belonging to all the stages.
As pointed out by Haug (1910, Traite, p. 984) in passing north from
Calabria we have crossed from a neritic zone to a 'bathyal' zone with marls
as well as limestones, and including in the Toarcian Posidonia bronni
shales and Ammonitico rosso, extremely rich in cephalopods; they were
deposited in a Liassic trough which was certainly continuous from the
southern Alps of Lombardy, through the Apennines to Sicily and (as has
since been proved) Algeria and Morocco. As in all these places, too, the
Upper Bajocian and probably Bathonian are represented by shales with
limestone bands and cherts, crowded with Posidonia alpina. Above
follow shales and cherts with Aptychus (Lamellaptychus) of uncertain
Upper Jurassic age, in part containing Tithonian foraminifera; and
locally typical Lower and Middle Tithonian cephalopod limestone with
the fauna of Rogoznik.
This succession, first established by Zittel (1869), has been proved over
the whole breadth of the peninsula, from Monte Catria, inland from
Ancona, to the foothills behind Rome. Particularly good marker formations
are the Toarcian Ammonitico rosso and Posidonia bronni shales like
those of central Europe, and the Upper Bajocian cherty beds with Posidonia
alpina (ornati Roemer) which stretch from the Lombardy Alps to Sicily
and Greece; also the Tithonian aptychus and foraminiferal limestones with
Cadosina and Stomiosphaera (Renz, 1949).
As in all such large areas there are more or less extensive variations of
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