DACIAN BASIN - GeoEcoMar

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Chapter 2. Dacian Basin paleogeography. Sedimentological interpretation
the southern margin of the Dacian Basin migrated small distances during the Early
and Middle Pontian, and larger distances during the Late Pontian.
Both sets of paleogeographic maps indicate that only the central and centraleastern
parts of the southern Dacian Basin limit are subject to migration. In contrast
the southern shift is not apparent in the southwestern part of the Dacian Basin.
Sediment thickness distribution. The sediment thickness (isopach maps) from the
initial stage of existence of the Dacian Basin indicates that the accumulation of
detrital material was more active in the eastern part of the basin, less active in the
western part, while the area in between was sediment-starved (Fig. 2.12).
Starting from the Maeotian at the southern periphery of the basin an area
with low sedimentation rate and reduced sediment thickness appeared. During
the Maeotian time this area was narrow and apparently insignificant, but its width
became several times larger during the Early Pontian and Late Pontian-Dacian
time. Taking into consideration the southern migration of the basin, as previously
discussed, we believe that the thin-sediment area from the southern periphery of
the basin (hatched in Fig. 2.12) represents the region of southward extension of
the Dacian Basin. Following the southward widening trend of the basin, the area
with thin sediment extended only in the central and central-eastern periphery
of the basin.
Paleoenvironment in the Late Pontian Dacian Basin. According to Saulea et al.
(1969), during the Late Pontian-Dacian in the northern, sub-Carpathian area of the
Dacian Basin the cardiid shells are characteristically thick and large. In contrast, in
the southern part of the basin, the mollusks associations consist of numerous small
size specimens, with thin shells. These features indicate a shallow water environment
with low relief coast and lower energy for the southern area of the Dacian
Basin.
2.2.3. Nature of the southward extension process
Previous interpretations considered the southward enlargement of the Dacian Basin
as common transgression (Saulea et al., 1969; Papaianopol et al., 1987; Marinescu
and Papaianopol, 1989). Here we discuss possible alternative interpretations.
Processes of transgression. Transgressive events affected the Dacian Basin during
the Late Neogene time. The sub-Carpathian coast of the Dacian Basin exhibits clear
evidences for these processes. Late Neogene sedimentary deposits overlie directly
Early Miocene or Paleogene deposits. The transgressive episodes are restricted to
short periods of time, like Late Maeotian and Late Pontian (see Chapter 1.5).
Based on information offered by the paleogeographic maps (Saulea et al. 1969)
(Fig. 2.10), the southward enlargement of the Dacian Basin may be viewed as a
long-term process, which progressed through the whole time-span of existence of