DACIAN BASIN - GeoEcoMar

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184 Chapter 7. The Point Bar Facies in the Jilţ Quarry (Romanian Deposits) FIGURE 7.27. Accumulation of clay pebbles resulting from the erosion of the down-slope mud drapes endings. A. Row of clay pebbles on the bedding plane, in the median part of the Jilţ point bar deposit. B. Clay pebbles breccia. C. Clay pebbles accumulated as a discrete breccia unit or dispersed in the sand mass. D. Trough cross bedding with clay pebbles. Jilţ South Quarry, Mining front A13
7.4. Genetic significance of the sand body with mud drapes from the Jilţ Quarry Clay pebble accumulation. During the evolution of the Jilţ point bar, the mud drapes have been partly eroded in different circumstances. In the lower part of the fine-grained sand facies, well above the basal higher energy section of the Jilţ point bar, mud drapes appear occasionally eroded at the contact with small channels. The energy of the channel was probably insufficient to completely remove the clay pebbles produced during erosion. Consequently, a clay pebbles breccia accumulated inside the small channel, sometime in the vicinity of the eroded mud drape (Fig. 7.27). When the mud drapes have been eroded in the basal, fluvial channel section of the point bar, the resulting clay pebbles have been transported and redeposited. In this way clay pebble breccia units have been generated within the basal sediments with large scale trough-cross lamination (Fig. 7.28 B, C and D). Occasionally, the dipping clay pebble breccia units show the presence of inclined stratification in the basal part of the point bar (Figs. 7.10; 7.18 C). 7.4. gENETIC SIgNIFICANCE OF THE SAND BODY wITH MUD DRAPES FROM THE JILţ QUARRY 7.4.1. The sedimentation environment The sediments exposed by the coal mining activity in the mining fronts A12 and A13 have been accumulated in a fresh-water environment, as attested by the fauna (Pană et al.,1981, Stănescu et al., 1983; manuscript 1 ). The cross and parallel lamination are common internal structures of the studied sand accumulation. These two main sedimentary structures indicate that Jilţ deposits were formed in a fluvial environment, by unidirectional currents. The fining upward, scoured base with lag deposits and the large participation of clay deposits in the general sedimentary succession are characteristic to the fluvial environment of the meandering rivers (Walker, 1979; Miall, 1996). The main sedimentary architecture element for the identification of the sedimentation environment of the sand body with thin clay intercalations cropping out in Jilţ Quarry is the large scale inclined stratification. This geometry of the beds shows that the Jilţ South deposits accumulated by lateral sedimentation. The relatively orthogonal relationships between the dip direction of the large scale inclined stratification of the Jilţ sand bodies and the dominant paleocurrent directions (Fig. 7.24) confirm that the lateral sedimentation is of lateral accretion type, eliminating the possibility of forward progradation. The fact that the two directions are approximately rectangular indicates that the sediments were carried to the north through fluvial channels, while the channels were migrating eastward. 1 Op. cit., p. 140 185
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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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94 Chapter 5. Littoral Sedimentary
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Page 136 and 137: Fluvial sedimentation played a majo
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Page 192 and 193: 190 Chapter 8. The Paleoenvironment
Page 200 and 201: The evolution and architecture of a
Page 202 and 203: 200 Chapter 9. Source-Areas in the
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Page 216 and 217: 214 Chapter 10. History of the Daci
Page 232 and 233: 230 Chapter 11. From Brackish-Marin
Page 234 and 235: 232 Chapter 11. From Brackish-Marin
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234 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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