DACIAN BASIN - GeoEcoMar

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132 Chapter 5. Littoral Sedimentary Environment in the Dacian Basin Presently no specific sedimentation depth can be assigned to the sedimentary sequence cropping out along the Olteţ River. The only depth range which can be argued is the accumulation environment bellow the base of the fair-weather wave and storm action. 5.5.2. Littoral clay deposits: offshore or sediment-starved facies Clay deposits are quantitatively dominant in the cropping out littoral sediment sequences from the central and western part of the Dacian Basin. Usually, these sediments have frequent intercalation of sand, mostly fine-grained. In the Bădislava River geological section, there are clay intervals, several tens of meters thick, practically devoid of any sandy or silty interbeds (Fig. 5.38). The clayey intervals like those occurring on Bădislava River have been considered as offshore-type facies (Jipa et al., 1999). This interpretation is based on the lack of sand or silt intercalations, which suggests a calm sedimentation environment, outside the sand material influxes. Presently, we believe that the calm environment aspect is better explained as a result of the lack of sand particles supply, because the clay deposits occur in the proximal, sub-Carpathian margin of the basin. Consequently, the littoral clay deposits could serve as markers of the sediment-starved time intervals. 5.6. CONCLUSIONS The Dacian Basin sediment accumulation displaying features generated by wave and storm action have been attributed to the shoreline environment. A separation was made between lower energy and higher energy wave-dominated shoreline environment, according to the thickness of the sandy units intercalated in the clayey sequence and to the presence of the coarsening upward trend. The sequences attributed to the lower or higher energy shoreface might also represent sediment accumulation in the lower or middle shoreface area. The rate of sediment influx could also control the character of the two types of shoreline sequences. Parallel laminated shoreface sediments accumulated in a very high energy shoreline environment. The trough cross lamination and/or wave ripples at the upper part of sequence indicate that the environment was getting more tranquil at the end of the high energy event. Shell beds in the Dacian Basin shoreline environment are of detrital origin, resulting by current transport and sedimentation. The shell accumulation required a high energy transport agent, acting in the shoreline or near shore environment. The storm-generated currents represent the agent able to transport, concentrate and accumulate the shells.
5.6. Conclusions The storm-generated, hummocky-type structures occur in sequences with coarsening upward trend (prograding shoreline), as well as in non-graded sequences (stable, aggrading shoreline). The alternation of hummocky cross lamination and smaller structures, probably wave ripple lamination, reflects the fluctuation of storm and fair weather conditions. The Dacian Basin fluvial-dominated delta-front deposits are coarsening upward and do not show (but very seldom) sedimentary structures produced by basinal agents (waves and storms). A special type is the deltaic body with delta-front mass transported sediment. This character is indicated by the presence of small quartzitic pebbles randomly distributed in fine-grained sand. The deltaic plain environment of the Dacian Basin is represented by sedimentary sequences with both fresh-water and brackish-marine features. The picture which emerges is that of a fluvial network (distributary channels and their flooding plain) which switched laterally by avulsion and allowed brackish-marine shoreline sediments to accumulate in the same area. 133
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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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182 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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DACIAN BASIN - GeoEcoMar

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