THE MEDITERRANEAN LOWER CRETACEOUS

2.2.2. Foraminifera
Foraminifera are among the most important Early Cretaceous groups of microorganisms,
playing a great role both in rock-formation and for the stratigraphy of the
series (Bartcnstein, 1962-1979; S i g a 1, 1965; 1977; M о u 1 1 a d e, 1966;
К о в a ч e в a, 1968-1986, and others).
There are two important specificities in the evolution of the Early Cretaceous
foraminifera: (1) the populations explosion of the so-called conic foraminifera —
Orbitolinidae, whose root is in the Late Jurassic, and (2) the sharp increase in the
planktonic Globigerina-Wkz groups,which started during the Hauterivian and reached
its maximum during the Aptian and Albian, in order to prepare the extensive development
of Globigerina and the explosion of Rosalina during the Later Cretaceous
(Si gal, 1965).
2.2.3. Calpionellids
Calpionellids are the only group of organisms which competes with the chronostratigraphic
significance of the ammonites. However, they are more general compared
with the ammonites, therefore permitting detailed division and precise correlation
(R e m a n e, 1963-1974; A 1 1 e m a n n et al., 1971). Calpionellids are extremely
widespread in the Mediterranean Region. The following genera outline characteristic
successions in the Lower Cretaceous: Tintinnopsella, Crassicollaria, Lorenziella,
Calpionella, Remanniella, Calpionellopsis and Calpionellites. They are most
widespread in pelagic clayey-calcareous sediments, but they occur, although more
rarely, among neritic clayey-carbonate rocks as well.
2.3. Some Invertebrates Metazoa
2.3.1. Ostraeoda
The first considerable phenomenon in the evolution of the Early Cretaceous marine
ostracods is the explosive development of the Trachyleberidinac populations with
many species belonging to the genera Cythereis, Isocythereis and Platycythereis.
Protocythere forms characteristic associations.
The following taxa form clear successions: Protocythere, Schuleridea, Dolocythere,
Cythereis, Cytherella, Centr осу there, Protocythere, Vaenia, Platycythereis,
Neocythere, Xestoleberis, Bairdia, Monoceratina and Cytherelloidea (D о n z e,
1958-1975; О e r 11 i, 1965; D a m о t t e, 1965, 1979).
2.3.2. Spongia and Coelenterata
These are mainly facial organisms whose distribution is tied predominantly to neritic
sediments. This is particularly characteristic of Ca-spongia and corals.
Si-spongia flourished on clayey and clayey-calcareous bottom, predominantly
in deep-sea zones or in calm waters.
A characteristic feature of the Mediterranean Lower Cretaceous is the development
of coral reefs. Single corals are also extensively developed.
Hydrozoa also take a considerable part in rock formation during the Early
Cretaceous.
2.3.3. Echinodermata
The crinoids are widespread, but they play mainly a rock-forming role. The socalled
spathic limestones in Jura Mountains, the Alps and the Carpathians are mainly
built of crinoid members.
Echinids manifest a considerable upsurge in their evolution with the considerable
spreading of the irregular sea-urchins which are tied mainly to the clayey-
157