THE MEDITERRANEAN LOWER CRETACEOUS

a gradual lithological transition, while in the Komarevo region they overlie the denuded
surface of the Valanginian limestones(KaspiSan Formation). In the north, in
the Brest-Gigen region, Barremian sediments are absent. In the remaining boreholes
the Barremian is developed in a continuous succession, its presence being accurately
proved palaeontologically in many places.
Characteristic Barremian ammonites are found in a number of boreholes (H иколов
et al., 1974).
The Barremian is characterized by rich foraminifera associations by means of
which this stage is clearly differentiated in many areas.
In borehole R-l Dolni Dâbnik at a depth of 1605-1608 m T. Kovatchev
a (oral communication) has established characteristic Upper Barremian foraminifera:
Astacolus planiusculus (R e u s s), A. incurvatus (Reus s), Lamarckina
lamplughl (S h.), Lenticulina ouachensis ouachensis (S i g.), Frondicularia in
versa R e u s s, Marssonella subtrochus Bart., Marginulinopsis djaffaensis S i g.,
Gaudryina borimensis К о v. and Epistomina caracolla (Roe m.).
In borehole R-l Umarevci the Barremian comprises the base of the Lovec
Urgonian Group (approximately the lower 100 m) and the upper part of the Gorna
Orjahovica Formation, i. e. it is about 600 m thick. At two levels in this borehole
Kovatcheva (unpublished data) has found characteristic Barremian foraminifera:
— At 1049-1052 m: Epistomina hechti Bart., В e t t., В о 1 1 i, Arenobulimina
meltae К о v., Marssonella subtrochus Bart., Lamarckina lamplughi S h.,
Conorboides bulgaricus В a r t., В e t t., Ko v., Gaudryina borimensis К о v.,
Planularia crepidularis (Roe m.) and Lenticulina nodosa (Reus s).
— At 1481-1484 m: Epistomina hechti В a r t., В e t t., В о 1 I i, E. caracolla
(Roe m.), Gaudryina borimensis К о v. and Lenticulina nodosa (R e u s s).
Tn borehole R-37 Komarevo, at a depth of 1071 m T. Kovatcheva
has found the following foraminifera at the beds with Barremian ammonites: Conorotalites
intercedens (Bet t.), Gavelinella barremiana В e t t., Gaudryina praedividens
N e a g u, G. borimensis К о v., Marginulinopsis djaffaensis S i g., Lenticulina
ouachensis ouachensis (S i g.), Trochammina gerochi Bart., К о v. and Marssonella
kummi Z e d I.
The thickness of the Barremian in the southern part of the area (the villages
Kalenik— Umarevci — Devetaki) is 600-750 m, in the central part (the town of
Gorni Dabnik and the villages Dolni Dàbnik, Grivica, Slavjanovo and Stezerovo) —
191-453 m, in the northwestern and northern part — 50 to 123 m.
The Aptian is widely developed in Central Northern Bulgaria, occurring in many
outcrops. It is extremely facially heterogeneous and it is connected with the following
lithostratigraphic units: Mramoren, Sumer, Roman and Trambes Formations,
as well as the Vraca and Lovec Urgonian Groups.
The Aptian is differentiated in the boreholes mainly according to data on the vertical
distribution of the foraminifera. In some boreholes it is indicated by macrofauna
as well. The boreholes from the northwestern part of the area are also correlated
with the borehole sections from the Western Fore-Balkan and the Lorn Depression,
where this stage is well characterized palaeontologically.
The complete section of the Aptian is found in a number of outcrops between
the villages Kozar-Belene and Sanadinovo, Pleven District, in the valley of Osâm
river. In these outcrops, as well as in the east towards the valley of Jantra river between
the villages Polski Trâmbes and Cenovo this stage is represented by marls
and it is characterized by many molluscs:
— For the Bedoulian: Cheloniceras (C.) beltzovensis D i т., С. (C.) crassum
S p., С. (C.) seminodosum S i n z., Deshayesites deshayesi Le y m,, С, callidiscus
С a s., Deshayesites spp.. etc.
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