jeanflop/post-ocr-correction huggingface dataset:
[14], [15]), la sédimentation du complexe de Llestui a eu lieu pendant une phase de stabilisation glaciaire Post-maximum. La géométrie de l'unité glacio-lacustre nous montre une migration vers l'amont de l'environnement glacio-lacustre, résultat d'une progression glaciaire (fig. 2). Par conséquent, on peut estimer que, pendant cette phase, le glacier de Llauset a subi une réavance. DATATIONS PAR RADIOCARBONE. — Quatre datations des rythmites glacio-lacustres de Llestui ont été présentées par Vilaplana [15], avec les résultats suivants : égaux ou plus anciens que 34 000 (Ly-3045), 31 500 (Ly-3046) et 33 000 ans BP (Ly-2942 et Ly-2943). D'après ces dates, deux
000 ans BP (Ly-2942 et Ly-2943). D'après ces dates, deux hypothèses ont été formulées pour la chronologie du paléolac de Llestui : entre 65 000 et 31 500 ans BP [15] et entre 45 000 et 34 000 ans BP [6]. La présence de graphite dans les argiles de Llestui, provenant des ardoises graphiteuses du Silurien qui affleurent dans le bassin de ce paléolac, a cependant pu modifier l'âge de ces sédiments [19]. Pour le prouver, trois nouveaux échantillons ont été prélevés et analysés (fig. 2). Les datations obtenues avec une combustion des échantillons à 400°C sont les suivantes :
une combustion des échantillons à 400°C sont les suivantes : Llestui A : 21 650±900 ans BP; avec δ13C: -20.42 °/oo (Gif-8778 bis). — Llestui B : Insuffisante quantité de gaz (Gif-8779 bis). CORRECTION ### SPOSITO, The chemistry of soils, Oxford University Press, Inc., 1985, 277 L'estimation C : 18 240 ±600 ans BP; avec δ13C: -21.68 °/oo (Gif-8780 bis). Par contre, l'âge des échantillons obtenus à partir d'une combustion du résidu à 900°C est plus ancien que 40 000 ans BP. Ces résultats nous indiquent le vieillissement, dû au graphite, des rythmites glacio-lacustres de Llestui. CONCLUSIONS. — Les nouvelles
graphite, des rythmites glacio-lacustres de Llestui. CONCLUSIONS. — Les nouvelles datations du complexe de Llestui nous permettent de dater ce paléolac entre 18 000 et 20 000 ans BP. Les âges qui avaient été proposés antérieurement [6], [7], [15] doivent être considérés comme trop anciens, à cause de la contamination des sédiments glacio-lacustres par du graphite silurien. La nouvelle chronologie du complexe de Llestui nous indique clairement que la dernière extension maximale glaciaire des Pyrénées est antérieure au Dernier Maximum Glaciaire Global. Pendant la période 18 000-20 000 ans BP, les glaciers pyrénéens avaient subi un important rétrait par rapport
les glaciers pyrénéens avaient subi un important rétrait par rapport à leur extension durant la phase maximale régionale. La dynamique du glacier de Llauset, pendant la mise en place du paléolac juxtaglaciaire de Llestui, se caractérise par une réavancée. Cette récurrence glaciaire pourrait être interprétée comme une réponse locale dans les Pyrénées au refroidissement global qui a eu lieu pendant le Dernier Maximum Glaciaire. INTRODUCTION. — The maximum expansion of ice sheets in northern Europe during the last glacial cycle is established between 18,000 and 20,000 years before present (BP) [1], [2]. However, Seret et al. [3] demonstrated that in
[1], [2]. However, Seret et al. [3] demonstrated that in the French Vosges, at approximately 48°N, both the ice volume and extent were considerably larger between 50,000 and 30,000 years BP than during the Last Glacial Maximum. Thus, the glacial maximum may not have occurred at the same time around the world. According to Seret et al. [3] and Guiot et al. [4], the coldest phase was dry (700 mm less than modern values) and the maximum growth of the Vosges ice sheet occurred in an early phase of the last glacial cycle as a result of a large snow
last glacial cycle as a result of a large snow supply in a somewhat warmer climate. In the same way, the last glacial maximum in the Pyrenees, at a latitude between 42°43’N, is also previous to 18,000-20,000 years BP. In the southern Pyrenees, on the basis of available modern data arising from both regional geomorphological studies and detailed analysis of glacial and glaciolacustrine sequences, a glacial maximum and several deglaciation phases being characterized by glacial pulsations have been defined [5] to [8]. The last glacial maximum in the northern Pyrenees is observed to have occurred before 38,400 years BP [9],
is observed to have occurred before 38,400 years BP [9], [10]. Well before 20,000 years BP, Pyrenean glaciers had retreated upstream of the limits achieved during their phase of maximum development [11], [12] without any significant glacier readvance being recorded at around 20,000 years BP [10]. In this paper, new radiocarbon dates of glaciolacustrine rhythmites from the juxtaglacial complex of Llestui, a key locality for the last glacial cycle in the Pyrenees, will be presented and discussed. THE LLESTUI GLACIOLACUSTRINE COMPLEX. — Ice-marginal till complexes, mainly those in an ice-lateral (juxtaglacial) position in relation to the main valley glacier, are
(juxtaglacial) position in relation to the main valley glacier, are quite common in the Southern Pyrenees [13]. These complexes are related to a major phase of deposition that took place shortly after the last glacial maximum during the so-called Post-maximum stabilization phase [6] to [8]. Several ice-lateral till complexes have been recognized and studied in the Noguera Pallaresa, Noguera Ribagorçana, Esera and Ara basins [14] to [17], [6]. Ice-lateral till complexes were formed when the glacial tongues flowing down the main valleys blocked up the drainage of either ice-free or glacial tributary valleys. Thus, several sedimentary environments and their related
glacial tributary valleys. Thus, several sedimentary environments and their related deposits can be distinguished: glacial, glaciolacustrine, fluvio-torrential and slope deposits. All these formations are useful in order to reconstruct both the extension and the dynamics of Pleistocene glaciers. Moreover, they serve to define and characterize the different glacial phases within the Pyrenean deglaciation. One of the best examples of these complexes hitherto studied in the Pyrenees is the Llestui glaciolacustrine complex in the Llauset valley, a tributary of the Noguera Ribagorçana river (fig. 1). A glacial tongue about 10 kilometres long flowed through Llauset valley to join onto the main
long flowed through Llauset valley to join onto the main glacier in the Noguera Ribagorçana valley. The ice-lateral till complex of Llestui was formed on the left margin of Llauset glacier as a result of the drainage obstruction of two small fluviotorrential basins devoid of glaciers, giving way to the formation of a small juxtaglacial lake [14], [15]. Three sedimentary units have been distinguished in the Llestui complex [14], [15] (fig. 2) : — Glacial deposits: They are constituted by a lower subglacial till and an upper supraglacial till. These tills constitute the left lateral moraine of the Llauset glacier
tills constitute the left lateral moraine of the Llauset glacier which blocked up the glaciolacustrine environment. Glaciolacustrine deposits: They are mainly constituted by rhythmites consisting of millimetric to centimetric laminae of clays and sands, with common dropstones. However, gravels and diamictons are also interlayered in this unit. — Alluvial fan deposits: They consist of gravels and pebbles corresponding to two coalescent alluvial fans that were once functioning as a delta. These deposits cover the top of the glaciolacustrine unit and even lean on the lateral moraine. Vilaplana and Bordonau [18] and Bordonau [6] have described the sedimentary processes which can
and Bordonau [6] have described the sedimentary processes which can be recognized from the study of the glaciolacustrine sequence. CORRECTION ### L'estimation C : 18 240 ±600 ans BP; avec δ13C: -21.68 °/00 (Gif-8780 bis). Par contre, l'âge des échantillons obtenus à partir d'une combustion du résidu à 900°C est plus ancien que 40 000 ans BP. Ces résultats nous indiquent le vieillissement, dû au graphite, des rythmites glacio-lacustres de Llestui. CONCLUSIONS. — Les nouvelles datations du complexe de Llestui nous permettent de dater ce paléolac entre 18 000 et 20 000 ans BP. Les âges qui avaient été proposés
20 000 ans BP. Les âges qui avaient été proposés antérieurement [6], [7], [15] doivent être considérés comme trop anciens, à cause de la contamination des sédiments glacio-lacustres par du graphite silurien. La nouvelle chronologie du complexe de Llestui nous indique clairement que la dernière extension maximale glaciaire des Pyrénées est antérieure au Dernier Maximum Glaciaire Global. Pendant la période 18 000-20 000 ans BP, les glaciers pyrénéens avaient subi un important rétrait par rapport à leur extension durant la phase maximale régionale. La dynamique du glacier de Llauset, pendant la mise en place du paléolac juxtaglaciaire de Llestui, se
la mise en place du paléolac juxtaglaciaire de Llestui, se caractérise par une réavancée. Cette récurrence glaciaire pourrait être interprétée comme une réponse locale dans les Pyrénées au refroidissement global qui a eu lieu pendant le Dernier Maximum Glaciaire. INTRODUCTION. — The maximum expansion of ice sheets in northern Europe during the last glacial cycle is established between 18,000 and 20,000 years before present (BP) [1], [2]. However, Seret et al. [3] demonstrated that in the French Vosges, at approximately 48°N, both the ice volume and extent were considerably larger between 50,000 and 30,000 years BP than during the Last
between 50,000 and 30,000 years BP than during the Last Glacial Maximum. Thus, the glacial maximum may not have occurred at the same time around the world. According to Seret et al. [3] and Guiot et al. [4], the coldest phase was dry (700 mm less than modern values) and the maximum growth of the Vosges ice sheet occurred in an early phase of the last glacial cycle as a result of a large snow supply in a somewhat warmer climate. In the same way, the last glacial maximum in the Pyrenees, at a latitude between 42°43’N, is also previous
the Pyrenees, at a latitude between 42°43’N, is also previous to 18,000-20,000 years BP. In the southern Pyrenees, on the basis of available modern data arising from both regional geomorphological studies and detailed analysis of glacial and glaciolacustrine sequences, a glacial maximum and several deglaciation phases being characterized by glacial pulsations have been defined [5] to [8]. The last glacial maximum in the northern Pyrenees is observed to have occurred before 38,400 years BP [9], [10]. Well before 20,000 years BP, Pyrenean glaciers had retreated upstream of the limits achieved during their phase of maximum development [11], [12] without any
during their phase of maximum development [11], [12] without any significant glacier readvance being recorded at around 20,000 years BP [10]. In this paper, new radiocarbon dates of glaciolacustrine rhythmites from the juxtaglacial complex of Llestui, a key locality for the last glacial cycle in the Pyrenees, will be presented and discussed. THE LLESTUI GLACIOLACUSTRINE COMPLEX. — Ice-marginal till complexes, mainly those in an ice-lateral (juxtaglacial) position in relation to the main valley glacier, are quite common in the Southern Pyrenees [13]. These complexes are related to a major phase of deposition that took place shortly after the last glacial
of deposition that took place shortly after the last glacial maximum during the so-called Post-maximum stabilization phase [6] to [8]. Several ice-lateral till complexes have been recognized and studied in the Noguera Pallaresa, Noguera Ribagorçana, Esera and Ara basins [14] to [17], [6]. Ice-lateral till complexes were formed when the glacial tongues flowing down the main valleys blocked up the drainage of either ice-free or glacial tributary valleys. Thus, several sedimentary environments and their related deposits can be distinguished: glacial, glaciolacustrine, fluvio-torrential and slope deposits. All these formations are useful in order to reconstruct both the extension and the dynamics
in order to reconstruct both the extension and the dynamics of Pleistocene glaciers. Moreover, they serve to define and characterize the different glacial phases within the Pyrenean deglaciation. One of the best examples of these complexes hitherto studied in the Pyrenees is the Llestui glaciolacustrine complex in the Llauset valley, a tributary of the Noguera Ribagorçana river (fig. 1). A glacial tongue about 10 kilometres long flowed through Llauset valley to join onto the main glacier in the Noguera Ribagorçana valley. The ice-lateral till complex of Llestui was formed on the left margin of Llauset glacier as a result of
the left margin of Llauset glacier as a result of the drainage obstruction of two small fluviotorrential basins devoid of glaciers, giving way to the formation of a small juxtaglacial lake [14], [15]. Three sedimentary units have been distinguished in the Llestui complex [14], [15] (fig. 2) : — Glacial deposits: They are constituted by a lower subglacial till and an upper supraglacial till. These tills constitute the left lateral moraine of the Llauset glacier which blocked up the glaciolacustrine environment. Glaciolacustrine deposits: They are mainly constituted by rhythmites consisting of millimetric to centimetric laminae of clays and sands, with
of millimetric to centimetric laminae of clays and sands, with common dropstones. However, gravels and diamictons are also interlayered in this unit. — Alluvial fan deposits: They consist of gravels and pebbles corresponding to two coalescent alluvial fans that were once functioning as a delta. These deposits cover the top of the glaciolacustrine unit and even lean on the lateral moraine. Vilaplana and Bordonau [18] and Bordonau [6] have described the sedimentary processes which can be recognized from the study of the glaciolacustrine sequence. The dominant processes responsible for the high rate of detritical sedimentation in paleolake Llestui were: —
high rate of detritical sedimentation in paleolake Llestui were: — Processes related with instabilities (mass movements) in the subaerial or subaquatic slopes of the glaciolacustrine basin. — Processes related both with supraglacial and subglacial meltwater streams and mainly with inflowing streams coming from the two small tributary torrential basins. — Processes related with the seasonal existence of an ice-layer in the surface of lake Llestui. Fig. 2. — Geological cross-section of the glaciolacustrine complex of Llestui. Legend: 1. Alluvial-fan deposits; 2. Glaciolacustrine deposits; 3. Supraglacial till; 4. Subglacial till; 5. Paleozoic bedrock. Location of 14C samples in the glaciolacustrine unit.
Paleozoic bedrock. Location of 14C samples in the glaciolacustrine unit. White dots correspond to radiocarbon dates presented by Vilaplana [15]: ≧ 34,000 yr BP (Ly-3045); ≧31,500 yr BP (Ly-3046); ≧33,000 yr BP (Ly-2942) and ≧ 33,000 yr BP (Ly-2943). Black dots correspond to radiocarbon dates presented in this paper: Llestui A, 21,650 ±900 yr BP (Gif-8778 bis); Llestui B, Not enough gas obtained (Gif-8779 bis) and Llestui C, 18,240 ±600 yr BP (Gif-8780 bis). Fig. 2. — Coupe géologique du complexe glacio-lacustre de Llestui. Légende: 1. Dépôts de cône de déjection; 2. Dépôts glacio-lacustres; 3. Till supra-glaciaire; 4. Till sous-glaciaire;
déjection; 2. Dépôts glacio-lacustres; 3. Till supra-glaciaire; 4. Till sous-glaciaire; 5. Substrat paléozoïque. Situation des échantillons datés dans l'unité glacio-lacustre. Les points blancs correspondent aux datations présentées par Vilaplana [15]: ≧ 34 000 ans BP (Ly-3045); ≧ 31 500 ans BP (Ly-3046); ≧ 33 000 ans BP (Ly-2942) et ≧ 33 000 ans BP (Ly-2943). Les points noirs correspondent aux nouvelles datations présentées dans cette note : Llestui A, 21 650± 900 ans BP (Gif-8778 bis); Llestui B, Insuffisante quantité de gaz (Gif-8779 bis) et Llestui C, 18 240 ±600 ans BP (Gif-8780 bis). The relative position of Llestui complex
ans BP (Gif-8780 bis). The relative position of Llestui complex within the general context of the last glacial cycle in the Pyrenees was established after the geomorphological study of the whole Noguera Ribagorçana glacial basin. According to several authors ([6], [14], [15]), the sedimentation of several units took place during a period of glacial stabilization within the long deglaciation period which followed the last glacial maximum. However, the geometry of the glaciolacustrine unit shows an upstream migration of the glaciolacustrine environment as a result of a glacial progression (fig. 2). Thus, during the so-called Postmaximum stabilization phase, Llauset glacier was
Thus, during the so-called Postmaximum stabilization phase, Llauset glacier was active and even showed a small pulsation or readvance. RADIOCARBON DATES. — Four radiocarbon dates of glaciolacustrine rhythmites from Llestui were presented by Vilaplana [15] being older or equal to 34,000 (Ly-3045), 31,500 (Ly-3046) and 33,000 years BP (Ly-2942 and Ly-2943). According to these dates, several ages have been proposed and discussed for the Llestui complex: between 65,000 and 31,500 years BP [15], between 45,000 and 34,000 years BP [6]. Contamination of glaciolacustrine sediments by allochthonous material (e.g. dead carbon) and/or the hard water effect may cause an aging of
and/or the hard water effect may cause an aging of the 14C dates obtained. Silurian shales containing graphite crop out extensively in Llauset basin and the presence of inactive carbon (graphite) in the glaciolacustrine rhythmites can significantly modify the age of the sediments [19]. In order to demonstrate the aging of the former dates from Llestui, three new samples corresponding to the bottom, middle and top of the glaciolacustrine sequence were taken for 14C dating (fig. 2). Combustion of the sample within a furnace, at low temperature under pure oxygen flow, would provide the CO2 gas deriving from organic matter
flow, would provide the CO2 gas deriving from organic matter and, therefore, the representative fraction to be dated. The ideal combustion temperature for soot carbon contained in aerosol collected on a glass fibre filter was determined by Cachier et al. [20] to be 340°C. However, we were obliged to perform the combustion at a temperature of 400°C, due to the nature of the sample itself and to the large amount (1 kg) needed, resulting in an abrupt temperature decrease towards the centre of the furnace. Thus, the 14C ages obtained are: Llestui A: 21,650±900 years BP; with δ13C : -20.42‰
are: Llestui A: 21,650±900 years BP; with δ13C : -20.42‰ (Gif-8778 bis). Llestui B: Not enough gas obtained (Gif-8779 bis). Llestui C : 18,240 ±600 years BP; with δ13C: -21.68‰ (Gif-8780 bis). The ages of the three samples (Llestui A, B and C) from the combustion of the residue at 900°C, are older than 40,000 years BP. These ages may reflect the aging due to the graphite content in the glaciolacustrine rhythmites of Llestui. However, age inversion between Llestui A and C has to be noted. If we agree with the fact that either contamination by modern carbon that might
the fact that either contamination by modern carbon that might have occurred during sampling or aging due to slightly higher temperature combustion are unlikely, an explanation would be the large variations of atmospheric 14C content at that time, resulting in a variable 14C age drift ranging between 1,000 and 3,000 years [21]. According to these new 14C dates, the age of Llestui complex cannot be more accurately fixed than around 18,000-21,000 years BP. Former dates presented by Vilaplana [15] show an aging due to contamination of glaciolacustrine sediments by allochthonous material coming from the Silurian graphitic shales. CONCLUSIONS. — The
material coming from the Silurian graphitic shales. CONCLUSIONS. — The juxtaglacial complex of Llestui was formed during the so-called Post-maximum stabilization phase corresponding to the long deglaciation period which followed the last glacial maximum in the Pyrenees ([6], [14], [15]). This complex is placed in a margin of Llauset glacier, at a middle altitude (about 1,600 m a.s.l.) and far away from the maximum extent achieved by the Noguera Ribagorçana glacier (fig. 1). New 14C dates presented in this note allow us to date the Llestui complex at around 18,000-21,000 years BP. Former ages proposed for this complex ([6], [7],
years BP. Former ages proposed for this complex ([6], [7], [15]) are to be considered as too old due to an aging of 14C dates resulting from contamination of glaciolacustrine sediments by Silurian graphite. The proposed age for the Llestui complex clearly shows that the last glacial maximum extent in the Pyrenees is previous to the Last Glacial Maximum. Surely, at around 18,000-20,000 years BP Pyrenean glaciers had significantly regressed with respect to their position during their phase of maximum development. Moreover, Jalut et al. 10] asserted that no advance of Pyrenean glaciers took place between 18,000 and 20,000 years
of Pyrenean glaciers took place between 18,000 and 20,000 years BP. In any case, the age which has been proposed for the Llestui complex in this note suggests that during the Last Glacial Maximum, a major phase of deposition is recorded in the Pyrenees. The glacial dynamics of Llauset glacier was characterized by a pulsation which gave way to the formation of the juxtaglacial complex of Llestui. This glacial pulsation could be the local response in the Pyrenees to the global cooling recorded throughout the world during the Last Glacial Maximum. However, the narrowness of Pyrenean valleys has not allowed
Maximum. However, the narrowness of Pyrenean valleys has not allowed the preservation of terminal morainic complexes related to the glacial pulsation which took place during the Post-maximum stabilization phase, and only juxtaglacial complexes such as the Llestui complex are preserved in the Pyrenees. Financial support has been provided from the DGICYT Project PB88-0209. Note remise le 20 août 1992, acceptée après revision le 8 janvier 1993. REFERENCES [1] W. F. RUDDIMAN and A. McINTYRE, Palaeogeogr., Palaeoclimatol., Palaeoecol., 35, 1981, pp. 145-214. [2] D. G. MARTINSON, N. G. PISIAS, J. H. HAYS, J. IMBRIE, T. C. MOORE and N. J. SHACKLETON,
HAYS, J. IMBRIE, T. C. MOORE and N. J. SHACKLETON, Quaternary Research, 27, 1987, pp. 1-29. [3] G. SERET, E. DRICOT and G. WANSARD, Nature, 346, 1990, pp. 453-456. [4] J. GUIOT, A. PONS, J. L. DE BEAULIEU and M. REILLE, Nature, 338, 1989, pp. 309-313. [5] J. BRU, A. GÓMEZ, D. SERRAT, J. VENTURA and J. M. VILAPLANA, Actas de la 1 Reunión del Cuaternario Ibérico, GETC-GTPEQ, 1985, pp. 165-183. [6] J. BORDONAU, Els complexos glacio-lacustres relacionats amb el darrer cicle glacial als Pirineus, Geoforma Ediciones, Logroño, 1992, 251 p. [7] J. BORDONAU, III Congreso Geológico de España y
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and R. JULIA, Quaternary Science Reviews, 11, 1992, pp. 449-480. [11] M. BAKALOWICZ, P. SORRIAUX and D. C. FORD, Norsk Geografisk Tidsskrift, 38, 1984, pp. 193-197. [12] J. MONTSERRAT MARTI, Monografías del Instituto Pirenaico de Ecología (CSIC), 6, 1992, 147 p. [13] J. BORDONAU, J. BRO, D. SERRAT and J. M. VILAPLANA, Abstracts XIIth INQUA International Congress, Ottawa, 1987, p. 133. [14] D. SERRAT, J. M. VILAPLANA and C. E. MARTI BONO, in E. B. EVENSON, Ch. SCHLOCHTER and J. RABASSA Eds., Tills and related deposits, A. A. Balkema, Rotterdam, 1983, pp. 132-144. [15] J. M. VILAPLANA, Acta Geolólgica Hispanica,