Arkell.1956.Jurassic..

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THE BALKAN PENINSULA
DOBROGEA
More than 100 miles north of the outer folds of the Balkan Mountains,
where they run out into the Black Sea, and far out in the foreland of both
Balkans and Carpathians, Mesozoic and Palaeozoic rocks rise from the
alluvial plains and loess in the Dobrogea. The isolated group of hills
so formed is enclosed in a peninsula between the sea and the right-angled
bends and marshes of the Danube, before it enters the delta. The chief
Jurassic inliers protrude from loess across the neck of the peninsula
and some are well exposed in cliffs on the Danube near Harsova, and in
large quarries worked for cement.
The Jurassic sequence (Simionescu, 1910) rests unconformably on
green schists of Lower Palaeozoic age and begins with sandstone and a
ferruginous limestone, both of uncertain date: perhaps Lower Oxfordian
or Upper Callovian, judging by some echinoids and Rhynchonella
thurntanni. Above this comes a thick series of limestones with a wonderful
Upper Oxfordian ammonite fauna monographed by Simionescu (1907),
passing laterally into sponge limestones and coralline sand, followed
without distinct break by similar Lower Kimeridgian limestones which
pass laterally and upward into coral limestones. At the top are regularly
bedded limestones and dolomites without diagnostic fossils, probably
Middle Kimeridgian in date, overlain by Cretaceous conglomerate.
Many of the ammonites figured in Simionescu's excellent monograph
have been discussed by me in my monograph on the ammonites of the
English Corallian Beds. One of Simionescu's species, Perisphinctes
cotovui, proved to be the commonest and most characteristic form in the
English Plicatilis Zone and his name was adopted. Many of the other
Perisphinctids are also of this age, though most show subtle differences
in some character or other from their closely allied counterparts in Britain
and NW. Europe, no doubt due to geographical distance. Many are
identical with forms in the similar thick Upper Oxfordian limestones of
the Cracow district (p. 479), others with those of Trept (p. 95).
Peltoceras arduennense (d'Orb.), recorded from the basal bed, above the
undated ferruginous limestone, indicates that the main limestone series
begins with the Lower Oxfordian, and several other ammonites not tied
down stratigraphically are also Lower Oxfordian, for instance Protophites
christoli (Baud.), Perisphinctes michalskii Buk., Peltoceras cf. constantii
(d'Orb.), Euaspidoceras babeanum (d'Orb.), E. edwardsianum (d'Orb.);
but there are no Cardioceratids, and very few Phylloceratids at any level.
The greater part of the fauna, however, belongs to the Bimammatum
Zone, which is represented by Epipeltoceras bimammatum (Quenst.),
E. berrense (Favre), Euaspidoceras oegir (Oppel), E. hypselum (Oppel),
Clambites clambus (Oppel) and remarkable Perisphinctids. Lower
Kimeridgian elements are certainly present also, for instance Ataxioceras
cf. inconditum (Font.), Physodoceras liparum (Oppel), Aspidoceras cf.
uhlandi (Oppel). As indicated by these records, the Bimammatum and
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