THE MEDITERRANEAN LOWER CRETACEOUS

of Ruse limestones deposited in the intertidal flat; (2) peripheral, slightly deepersea
part of the same sublidal flat of the shelf, in which clayey-calcareous sediments
with small amounts of glauconite are formed (R u s к о v a, 1982). In the
western region the relief becomes gradually lower in the deep part of the shelf (southwest
of the Slavjanovo-Totleben line). The characteristic Salas limestones are deposited
there, their faunistic and lithological composition being a confirmation of
the indicated bathymétrie level. Inheritance of the shallow-water Kaspican Limestones
is found only in two isolated places in the basin (moreover, during the Early
Hauterivian — Fig. 28 — at Bardaski Geran and Kneza, as well as to the north
of Novi Pazar). As regards the carbonate-reef builtup of the Brestnica Limestones,
which is sharply prominent among the deep shelf, during the Hauterivian it gradually
decreased its surface to the west of Iskâr river, sinking progressively with its
peripheral parts. (This is indicated on the palaeogeographic sketch of the Early
and Late Hauterivian — Fig. 28, whereby the second sketch of the Early Hauterivian
clearly demonstrates the entrainment of some of the peripheral deeper-water
part of the carbonate builtup towards the slope of the basin with flyschoid sedimentation
— Fig. 28 b). Insular dry lands (shallow-water areas) are discovered in
two regions: at Brest—Gigen and in the northwesternmost part of Bulgaria, in
Vidin District (Николов, 1972).
The influx of material during the Hauterivian continued mainly at the expense
of the rapidly denuded Thracian land. The géosynclinal depression underwent
compensatory sinking, with increased gradient in its eastern part. Conversely, the
regime was stable in the area of the Moesian Platform, though in the northeasternmost
part the supply of material was bilateral, i. e. already involving the participation
of the Dobrogea dry land.
The beginning of the Barremian indicates direct depositional continuation of
the Hauterivian. This concerns above all the marly-sandy deposits of the depression
from the south which progress slightly northward (Fig. 28). The sedimentation
environment is practically preserved in the same places. Considerable retention is
observed in the Western Balkanides and in the Western part of the Moesian Platform,
where only the clayey and partly the terrigenous-clastic components of the
sediments increase. In fact, in the more northwestern regions, close to the carbonate
lands, the marly sediments are replaced by pure micritic limestones whose faunistic
composition already indicates sedimentation under conditions of shallower
but also calm waters. This process is probably due to a certain elevation of the deep
shelf. A more essential change in the sedimentation environment occurred in the
depression region from the south, which already represents a compensated basin
of marly-sandy sedimentation. The influx of material, although predominantly
terrigenous, was from the same sources in the south and the Dobrogea land in
the north (P у сков a, 1970), and it continued, though in reduced amounts. This
is evidenced by the reduced thicknesses of the Barremian in general. In the central
and southernmost parts (e. g. west of Omurtag) the basin is considerably shallower:
the denuded structures with diagenetic type of cement, as in the surface oolites in
some places, are evidence even for the existence of bathymétrie levels in the zone
of the intertidal plane. Towards the end of the Barremian the first symptoms о
change in the sedimentation position occurred in the depression zone: Urgonian terrif
genous-carbonate sediments became imposed in the Veliko Tarnovo-Lovec area.-
Their lithological composition (Bahama-type carbonate) suggests extremely shallowwater
environment with impulsive influx of terrigenous material, bilaterally dispersed
in the adjacent regions to the east and to the west (Fig. 29) (Хрисчев,
1969; 1972).
The sedimentation situation during the Early Aptian (Fig. 30) is characterized
by great variety. In fact, it has inherited the basic sedimentation tendencies from
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