DACIAN BASIN - GeoEcoMar

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128 Chapter 5. Littoral Sedimentary Environment in the Dacian Basin FIGURE 5.36. Sediment slumping structures in the littoral deposits from the Dacian Basin. A. Coherent syn-depositional deformation. Early Dacian, Bădislava River, Bălileşti village (Argeş County). B. Syndepositional distortion (a), followed by erosion before the accumulation of the covering, undeformed sediments (b). Note clastic dykes (c), showing little or no compaction. Early Dacian, Râmnicu Sărat River, Chiojdeni village (Vrancea County). C. Large scale mass-transport breccia. Early Dacian, Râmnicu Sărat River, Chiojdeni village (Vrancea County). D. Mass-flow breccia consisting of shells and fragments of shells in a silty matrix. Early Dacian, Râmnicu Sărat River, Chiojdeni village (Vrancea County) Clastic dykes can be observed in the undeformed sediments just above the slumped beds. The geometry of the dykes suggests that post-slumping compaction was not significant. In contrast with the coherent deformations, in the littoral deposits syndepositional, highly destructed deposits have been also noticed. They probably represent the mass-flow events triggered by sediment sliding. The mass-transported sediment consists of fragments of rocks, hard and soft pebbles and shells, embedded in a fine-grained matrix. This type of breccias occurs either at a large scale (Fig. 5.36 C) or at a small scale (Fig. 3.36 D). 5.5. <strong>DACIAN</strong> <strong>BASIN</strong> SEDIMENTARY ENvIRONMENT BELOw THE FAIRwEATHER wAvE BASE The sedimentary environments analysis depends a great deal on the interpretation of the sedimentary structures and implicitly on outcrop observation. Most of the Dacian Basin extent is covered with Quaternary deposits (Fig. 1.2). Practically, all
5.5. Dacian Basin sedimentary environment below the fairweather wave base the good outcrops are located in the sub-Carpathian proximal (littoral) zone of the basin. This is why at the present time we know very little about the sediment accumulation environments of the axial and external parts of the Dacian Basin. 5.5.1. Deeper-water sediment accumulation in the Dacian Basin The western end of the Dacian Basin is the only area where there are arguments for deeper-water sedimentation depth. This is based on the presence of a large scale progradation structure (Fig. 4.6), whose thickness approximates the sediment accumulation water depth. On this basis, Leever (2007) appreciates the minimal water depth in the western Dacian Basin to 300 m. The deeper-water sediments accumulated in the western part of the Dacian Basin are fine-grained. The well logs and the drill cuttings of the Băleni 1 well (Mehedinţi County) (Fig. 5.37) show that Maeotian-Pontian sediments consist of clay or silty clay, with very thin fine-grained sand (or silt) intercalations. The persistent absence of any wave or storm sedimentary structure within a Dacian Basin littoral sequence is regarded as a possible indication of an environment placed under the fair-weather wave and storm base. However, a supplementary indication is necessary to validate such interpretation. This reasoning was applied to a sand dominated facies investigated in the Olteţ River geological section (Cireşu village, Vâlcea County). One of the facies of the Maeotian deposits cropping out along the Olteţ River consists dominantly of sand, with thin clayey intercalations (Fig. 5.39). Some of the sand beds are lens-like and their bottom limit cuts discordantly the underlying thin clay and sand beds. Other sand beds are tabular and extensive. The internal structures of the sandy Maeotian facies are current generated. Parallel and larger scale cross lamination, as well as small channel fills (Fig. 5.39 A) are displayed by the thicker (up to 50 cm) beds. Smaller scale current ripples associated with parallel lamination are frequent in thinner bedded sediments (Fig. 5.39 B and C). No fair-weather wave or storm generated sedimentary structures have been observed in the sandy deposits from the Olteţ River section. This suggests a possible deeper-water sediment accumulation. Other features of the Maeotian Olteţ River sequence are corroborating the deeper water indication suggested by the absence of the wave and storm ripples. Sediment mass flow processes are pointed out by the occurrences of breccias, consisting of resedimented clay and sand pebbles enclosed in a sandy matrix. Two levels of breccias occur in the basal part of the Olteţ River sequence. The Maeotian-Pontian sedimentary succession shows a large scale fining upward trend, a feature which is frequent to submarine fans. 129
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Dan C. Jipa, Cornel Olariu DACIAN B
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Dedicated to the memory of Prof. Gh
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NATIONAL INSTITUTE OF MARINE GEOLOG
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CONTENTS Foreword and Acknowledgeme
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Contents Chapter 7. The Point Bar F
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FOREwORD AND ACkNOwLEDgEMENTS The s
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PLATE 1. Location of the Dacian Bas
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18 Chapter 1. Dacian Basin. General
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The analysis of the paleogeographic
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42 Chapter 2. Dacian Basin paleogeo
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58 FIGURE 2.14. Paleogeography and
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68 Chapter 3. Sediment Thickness Di
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Page 84 and 85: Sedimentation in the brackish-water
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178 Chapter 7. The Point Bar Facies
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190 Chapter 8. The Paleoenvironment
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The evolution and architecture of a
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200 Chapter 9. Source-Areas in the
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10.1. SEDIMENT ACCUMULATION AREAS I
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214 Chapter 10. History of the Daci
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230 Chapter 11. From Brackish-Marin
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Ai n s w o r t h r. B., Cr o w l e
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258 References hA m o r, g., et al.
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260 References mA C A r o V iC i, n
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262 References ră d A n, s.C., 200
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264 References VAsilieV, i., Kr iJ
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