THE MEDITERRANEAN LOWER CRETACEOUS

with many representatives of Ammonitina and Phylloceratina (biotope with clayeycalcareous
ooze bottom).
Neritic biotopes with different combination of bivalvs, gastropods, brachiopods,
echinids, corals, serpulae, algae and benthonic foraminifera were developed
in the Moesian Platform from the Berriasian to the Early Hauterivian.
Pelagic limestones are the richest in macro- and microfauna (biotope with chayeycalcareous
ooze bottom). This type is also widespread in the Mediterranean Region.
The configuration and the character of Valanginian biotopes are very similar
to the Berriasian ones. The sandy flysch zone (biotope with clayey-calcareous bottom)
began to widen gradually in the Fore-Balkan. Among the ammonites the Ammonitina
representatives are exceptionally widespread, whereas Phylloceratina
and Lytoceratina have a considerably more limited distribution compared with
the Berriasian.
Among the neritic Valanginian biotopes there are bivalvs: Camptonectes, Cucullaea,
Prohinnites and Hinnites; gastropods: Nerinea and Natica, many serpulae,
which build in some places entire limestone beds. Benthonic foraminifera are rare.
Four main Hauterivian biotopes are established : (1) bathyal biotope with clayeycalcareous
bottom in the Fore-Balkan, inhabited by Ammonitina and Lytoceratina,
concurrent belemnites and rare bivalvs; (2) neritic biotope with clayey-calcareous
ooze bottom in Northeastern and Central North Bulgaria, inhabited by extremely
rich ammonite and belemnite faunas, characteristic brachiopods and
foraminifera, concurrent bivalvs and rare echinids; (3) bathyal biotope with
ooze (marly) bottom in Northwestern Bulgaria, inhabited mainly by ammonites
and concurrent belemnites. Here ammonites are much more varied compared with
the other biotopes and especially compared with the first biotope; (4) transitional
biotope between the neritic and the bathyal biotope. ft is characterized by unstable
conditions. The biotope is inhabited by different Ancyloceratidae, late Neocomitinae,
some Hibolites and Duvalia, as well as bivalvs (Arcomytilus, Camptonectes
and Chlamys), gastropods (Pleurotomaria, Purpuroides and Ampullina), brachiopods
and benthonic foraminifera.
The development of the Barremian ecosystems manifests considerable differences
between the Early and Late Barremian in the Fore-Balkan, whereas stable biotopes
were developed throughout the entire Stage in the Moesian Platform.
The Early Barremian biotopes in the Central and Eastern Fore-Balkan are with
clayey-sandy bottom, and they are inhabited by a number of ammonites (Costidiscus,
Crioceratites, Acrioceras, Paraspinoceras, Leptoceratidae, various Barremitinae,
Pseudothurmannia, Holcodiacidae, Anahamulina, Hamulina, etc.) and comparatively
rare belemnites.
Biotopes were formed on carbonate platforms (Urgonian facies) during the Late
Barremian, inhabited by rudists, various other bivalvs, gastropods, corals, echinids,
brachiopods, Orbitolinidae, as well as other benthonic foraminifera and algae. Various
microbiotopes with specific population and different density were formed
within the Urgonian biotopes.
Three basic biotopes are outlined in the Moesian Platform: (1) Southern biotope
with ooze (marly) bottom with extremely many belemnites (mainly Mesohibolites)
and ammonites; (2) Middle biotope with ooze (clayey-calcareous) bottom,
inhabited mainly by ammonites. This is biotope of the outer shelf, which is the richest
in ammonites, including large forms. There are concurrent belemnites, rare
brachiopods, echinids and bivalvs. Benthonic foraminifera are also found; (3) Biotope
with calcareous bottom, inhabited by sublittoral benthos bivalvs, gastropods,
concurrent echinids and rare corals. This biotope is well outlined in Northeastern
Bulgaria (Ruse Formation.) The biotope of the Urgonian in Provence (France) is
of the same type.
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