DACIAN BASIN - GeoEcoMar

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Chapter 4. Dacian Basin Physiography
4.3. DACIAN BASIN SEDIMENTATION DEPTH
Estimation of the sedimentation depth in the Dacian Basin brackish-sea, have always
been a subject of utmost importance for the Dacian Basin enthusiasts. The
reduced possibility to compare data resulted from deposits on the margins and in
the central part of the basin was – and still is – a factor limiting the understanding
of the subject. We are going to approach the sedimentation depth problem with
data coming from the two end zones of the Dacian Basin area.
The northern end zone of the Dacian Basin is singled out by Saulea et al. (1969)
as the area of the basin where extensive fresh-water or fresh-water influenced deposits
have been observed (Fig. 4.5). A Late Sarmatian (s. l.) detrital-continental facies
with mammal remains (Ichtiterium, Hipparion near the town of Iasi) is mentioned
by Saulea et al. (1969). The brackish character (with Limnocardium) developed in
the northernmost Dacian Basin area during the Early Pontian, but the continental
facies appeared again during the Late Pontian.
The shallow water characteristic of the deposits in the northern part of the Dacian
Basin near Focşani is substantiated by the fluvial facies of the sediments. Sand
beds, several meter thick and fining upward with erosional bottom features are intercalated
in homogeneous (showing no bedding) silty clay, with rare fresh-water
fossils. This aspect dominates the area at the west of Focşani, but southward of
Buzău the homogeneous silty clay are progressively replaced by littoral brackish
sand and clay sequences with wave ripples.
A fine-grained sand and silt sequence with large scale inclined bedding (clinoforms)
developed at the western margin of the Dacian Basin. The prograding facies
was mentioned by Tărăpoancă (2004) and further investigated by Leveer (2007)
(Fig. 4.6). The sequence is significant for the assessment of the sedimentation
depth, as the thickness of the genetically unitary clinoform sequence indicates the
minimal sediment accumulation water depth. On this base, a sedimentation depth
of several hundred meters (around 300 m; Tărăpoancă, 2004; Leveer, 2007) can be
appreciated for the Meotian-Pontian clinoform sedimentary succession.
The evaluation of the sedimentation depth presented above suggests the image
of a Dacian Basin brackish-marine trough which is fluvial to very shallow in
the northern basin extremity, but shows a considerably deeper water depth at the
opposite, western end (Fig. 4.7). The dominant longitudinal and southward flowing,
paleocurrent trend, together with the sedimentation depth evaluated at the
two extremities of the basin, are indications leading to the image of a Dacian Basin
trough getting deeper and deeper from a fluvial environment in the north to a
several meter depth marine setting in the western part.