DACIAN BASIN - GeoEcoMar

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142 Chapter 6. Upper Neogene Fluvial Sedimentation in the Dacian Basin FIGURE 6.8. Thick fining upward sandy beds in the Romanian fluvial deposits. The fining upward is obvious at the upper part of the beds (the sand/clay limit). Buzău River, Berca (Buzău County). Index map - location of the study area in the Dacian Basin and in Romania FIGURE 6.9. Conglomeratic bed with fining upward grading and erosional basal limit. Late Sarmatian (s. l.) . Valea Morilor Creek, Colibaşi village (east of Drobeta - Turnu Severin)
6.1. Sedimentary characteristics of the fluvial deposits in the Dacian Basin Coarsening upward grading also occurs in the fluvial environment. This grain size trend is related to processes of progradation that take place in the crevasse splay development. The well logs offer the best way to examine the grain size grading. The Dobretu well logs point out four main grading types, each one with varieties (Fig. 6.10). 6.1.3. Sedimentary structures The Dacian Basin fluvial deposits display the whole array of current lamination structures, in accordance with the general characteristic of the sediment accumulations generated by alluvial processes. The current structures evolve within the fluvial graded sequences, following the fining upward trend and the corresponding level of sedimentary dynamics (Figs. 6.7; 6.11 and 6.12). Frequently, the fluvial unit displays structures showing the effect of discharge pulses. The apparently unitary sequence in the figure 6.11A has three stages of clay pebbles accumulation, but the grain size of the consecutive pebble levels is fining upward. Closely successive sedimentary events can generate polygenetic units (Fig. 6.12 A) or separate units narrowly superposed (Fig. 6.12 C and D). The characteristic erosional lower limit of the fluvial sequence has been observed in many cases in the fluvial sequences of the Dacian Basin (Figs 6.3C and 6.9), excepting the sedimentary units with fine-grained detrital material at the base (Fig. 6.8 C). Channels with basal erosional surface are sometimes present in the outcrops (Fig. 6.3 B), showing erosional irregularities at the decimetric scale. But the erosion within the Dacian-Romanian fluvial deposits can locally reach hundreds of meters, expressed by the absence of Late Dacian or Early Romanian deposits (Papaianopol, Marinescu, 2003). The magnitude of the fluvial transport in the Dacian Basin is indicated by large scale current structures, occurring in coarse-grained deposits (Fig. 6.3 A) but also in sandy accumulations (Figs 6.4 C and 6.15). 6.1.4. Inclined bedded units The lateral migration of the fluvial channels is the main process that generates large scale inclined stratification (Thomas et al., 1987), as the characteristic of the point bar facies. In the fluvial sediments of the Dacian Basin, a few point bar accumulations have been identified. One of the studied point bar unit has been observed in the terminal Dacian-aged deposits from Călugăreni village (Prahova County) (Fig. 6.13). Another point bar, cropping out in a coal quarry from Oltenia (west of Romania), is an outstanding feature which will be described in a separate chapter of this book (see Chapter 7). 143
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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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Sedimentation in the brackish-water
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84 Chapter 4. Dacian Basin Physiogr
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Page 94 and 95: 92 Chapter 4. Dacian Basin Physiogr
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Page 192 and 193: 190 Chapter 8. The Paleoenvironment
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192 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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DACIAN BASIN - GeoEcoMar

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