DACIAN BASIN - GeoEcoMar

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186 Chapter 7. The Point Bar Facies in the Jilţ Quarry (Romanian Deposits) FIGURE 7.28. Mud drapes endings in a Jilţ point bar segment. To be noted the limited down-dip extent of the mud drapes, irrespective of the facies dominant grain size. Not to scale. 1. Medium and coarse-grained sand. 2. Fine and very fine-grained sand. 3. Clayey-sitty deposits. 4. Coal. 5. Mud drapes. 6. Erosional ending. 7. Erosional ending with a row of day pebbles. 8. Pinching out ending.
7.4. Genetic significance of the sand body with mud drapes from the Jilţ Quarry Into an environment of fresh-water mollusk fauna such as the Jilţ South sand (Stănescu et al., 1983, manuscript 1 ), the environment of the lateral accretion process may be identified as the point bar environment (Stewart, 1983; Thomas et al., 1987). 7.4.2. genetic significance of the facies All the facies of the Jilţ sand - except for the homogeneous upper clay - are associated through the common inclined stratification. The genetic relationship results from the fact that the thin clay intercalations start from the silty-clay facies and extend down-slope to the upper part of the medium and large grain size sand, crossing the fine and very fine sand deposits. Therefore, the Jilţ South point-bar sequence does not express a simple geometric superposition, but also a lateraloblique continuity of the facies. The continuity relationship along the inclined stratification reveals the distribution of the deposits on the inner, convex bank of the fluvial channel that accreted laterally and generated the point-bar. During the lateral accretion the sedimentation unit consisted of (1) clayey-siltic sediments (upper Jilţ sand facies) of the marsh behind the channel, (2) fine and very fine-grained sand on the slope, and (3) coarse (later fine) grained sand in the trough of the fluvial channel. The basal facies of the Jilţ sand is characterized by large cross lamination units and the coarsest-grained sediments of the point bar deposit. This basal point bar facies hosts rudaceous elements, consisting of quartzitic pebbles, most of them concentrated at the basal erosional limit. There are also clay pebbles assembled as breccia intercalations, or dispersed in the sand matrix. These features indicate that the basal Jilţ sand facies reflects the highest energy of the Jilţ deposits; that is the axial zone of the alluvial channel. The middle facies of the point-bar sequence consists of very fine and fine sand. In this facies the inclined mud drapes are fully developed. Consequently, there are arguments to consider that the sediments of the middle facies accumulated on the depositional slope, which is the convex, accretional fluvial bank (the front of the point bar). Its reduced grain size and smaller cross-lamination units reflect the lower depositional energy of these deposits, as compared with the environment of the basal point bar facies. The silty-clay subfacies is the place wherefrom the system of mud drapes starts. This indicates that the silty-clay subfacies is part of the large scale, inclined structure of the Jilţ sand. Therefore, we may consider that this subfacies includes sediments accumulated on the upper slope of the point bar, at the edge of the river, in the area with the shallowest water. 1 Op. cit., p. 140 187
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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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Fluvial sedimentation played a majo
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Page 192 and 193: 190 Chapter 8. The Paleoenvironment
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Page 232 and 233: 230 Chapter 11. From Brackish-Marin
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236 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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