Exploration of Mg isotope compositions of marine carbonates as paleoenvironnemental proxy

L'utilisation des compositions isotopiques en Mg des carbonates marins peut permettre l'étude du cycle biogéochimique de cet élément. Ainsi, les carbonates sont susceptibles d'enregistrer la composition isotopique de Mg de l'océan lors de leur précipitation. Cependant, il est nécessaire de comprendre les facteurs environnementaux (e.g. température, pH, Mg/Ca de la solution) qui peuvent contrôler ces compositions. Le premier objectif de cette thèse a donc été de déterminer les paramètres pouvant impacter les compositions isotopiques de Mg des carbonates par des précipitations expérimentales en conditions contrôlées. Il a ainsi été mis en évidence, dans les gammes considérées, mais qui restent restreintes, l'absence de contrôle de la température, du pH et du Mg/Ca de la solution sur le fractionnement isotopique du Mg lors de la précipitation des carbonates. Le fractionnement isotopique du Mg entre la solution et la calcite, à l'équilibre, a été évalué à -2,13 ± 0,24 pour mille (2sigma) à partir de cette étude, combinée à des données de la littérature. Ces résultats ont ensuite été appliqués à l'étude des compositions isotopiques de Mg dans des coquilles de brachiopodes à la fois modernes et anciens. Pour cela, une quantification des effets vitaux vis-à-vis des isotopes du Mg lors de la croissance du brachiopodes a été réalisée. Ainsi, les zones en équilibre isotopique pour Mg, O et C et donc susceptibles d'être utilisables lors des reconstructions paléoenvironnementales sont situées au sein de la calcite interne sur les bords de la coquille. Les premières mesures des compositions isotopiques de Mg sur les derniers 60 Ma suggèrent des variations de la composition isotopique du Mg de l'océan qui pourraient être liées à un changement du flux de carbonate à l'océanStudying the Mg isotopic composition in marine carbonate can help to understand the biogeochemical cycle of this element. Indeed, carbonates may record seawater Mg isotopic composition during their precipitation. However, it is necessary to understand the possible control of some environmental factors (e.g. temperature, pH, Mg/Ca of the solution) on those compositions. Therefore, the first goal of this thesis was to determine parameters impacting carbonate Mg isotopic composition with experimental precipitations under controlled conditions. Thus, it has been shown, in restricted ranges, that temperature, pH and solution Mg/Ca have no influence on Mg isotopic fractionation during calcite precipitation. Equilibrium Mg isotopic fractionation between solution and calcite has been evaluated to -2.13 ± 0.24 per thousand (2sigma) from this study, combined with published data. These results were then applied to a study of Mg isotopic compositions in modern and past brachiopod shells. For this, a quantification of vital effects with respect to Mg isotopes during the brachiopod growth was realized. The zones in isotopic equilibrium for Mg, O and C, and thus susceptible to be used for paleoenvironnemental reconstruction, are in the inner calcite at the edge of the shell. The first measurements of Mg isotopic compositions for the last 60 Ma suggest variations of Mg isotopic compositions of the seawater which could be linked to changes of carbonate flux in the ocea

Exploration des compositions isotopiques en magnésium des carbonates marins comme traceurs paléoenvironnementaux

Studying the Mg isotopic composition in marine carbonate can help to understand the biogeochemical cycle of this element. Indeed, carbonates may record seawater Mg isotopic composition during their precipitation. However, it is necessary to understand the possible control of some environmental factors (e.g. temperature, pH, Mg/Ca of the solution) on those compositions. Therefore, the first goal of this thesis was to determine parameters impacting carbonate Mg isotopic composition with experimental precipitations under controlled conditions. Thus, it has been shown, in restricted ranges, that temperature, pH and solution Mg/Ca have no influence on Mg isotopic fractionation during calcite precipitation. Equilibrium Mg isotopic fractionation between solution and calcite has been evaluated to -2.13 ± 0.24 per thousand (2sigma) from this study, combined with published data. These results were then applied to a study of Mg isotopic compositions in modern and past brachiopod shells. For this, a quantification of vital effects with respect to Mg isotopes during the brachiopod growth was realized. The zones in isotopic equilibrium for Mg, O and C, and thus susceptible to be used for paleoenvironnemental reconstruction, are in the inner calcite at the edge of the shell. The first measurements of Mg isotopic compositions for the last 60 Ma suggest variations of Mg isotopic compositions of the seawater which could be linked to changes of carbonate flux in the oceanL'utilisation des compositions isotopiques en Mg des carbonates marins peut permettre l'étude du cycle biogéochimique de cet élément. Ainsi, les carbonates sont susceptibles d'enregistrer la composition isotopique de Mg de l'océan lors de leur précipitation. Cependant, il est nécessaire de comprendre les facteurs environnementaux (e.g. température, pH, Mg/Ca de la solution) qui peuvent contrôler ces compositions. Le premier objectif de cette thèse a donc été de déterminer les paramètres pouvant impacter les compositions isotopiques de Mg des carbonates par des précipitations expérimentales en conditions contrôlées. Il a ainsi été mis en évidence, dans les gammes considérées, mais qui restent restreintes, l'absence de contrôle de la température, du pH et du Mg/Ca de la solution sur le fractionnement isotopique du Mg lors de la précipitation des carbonates. Le fractionnement isotopique du Mg entre la solution et la calcite, à l'équilibre, a été évalué à -2,13 ± 0,24 pour mille (2sigma) à partir de cette étude, combinée à des données de la littérature. Ces résultats ont ensuite été appliqués à l'étude des compositions isotopiques de Mg dans des coquilles de brachiopodes à la fois modernes et anciens. Pour cela, une quantification des effets vitaux vis-à-vis des isotopes du Mg lors de la croissance du brachiopodes a été réalisée. Ainsi, les zones en équilibre isotopique pour Mg, O et C et donc susceptibles d'être utilisables lors des reconstructions paléoenvironnementales sont situées au sein de la calcite interne sur les bords de la coquille. Les premières mesures des compositions isotopiques de Mg sur les derniers 60 Ma suggèrent des variations de la composition isotopique du Mg de l'océan qui pourraient être liées à un changement du flux de carbonate à l'océa

Sediment records of lake level changes in the Simav Graben (western Turkey

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Palaeoenvironmental records in and around PPN Aşıklı site in the Melendiz Valley (Kızılkaya, Aksaray)

International audienc

Palaeoenvironmental records in and around PPN Aşıklı site in the Melendiz Valley (Kızılkaya, Aksaray)

International audienc

Geomorphological and Palaeoenvironmental Setting of Asikli Hoyük

Archaeology, PalaeoenvironmentInternational audienceGeomorphological research at PPN Asikli Hüyük (ascertained 8.5-7.3 ka cal BP occupation time) started in the early 1990's in the framework of the archaeological excavation and associated projects run by Prof. Dr. U. Esin (1996, 1999a). A first geomorphological field work was done by Prof. Dr. O. Erol, whose unpublished report we were unable to access .In 1995, Prof. Esin asked us to undertake geomorphological research in the Melendiz valley, where the Asikli Höyük settlement was founded. Prof. Esin's main question for us was whether the Melendiz river ever flew at the time of the first settlement, along the eastern sicle of the mound (contrary to today, as it flows west of the mound the edges of which floods currently erodes the site. In 1995 and 1996 , field survey and three cores in the valley (Kuzucuoglu, 2013) did not allow us to answer this question. However, the survey did allow us to define a suite of terraces within the valley, to determine the position of the roof of the bedrock below the terraces in the western part of the mound at only -5 m depth, and to develop hypotheses regarding the possible occurrence of a buried river palaeobed east of the mound (Kuzucuoglu, 2013). In 2010, additional questions were proposed to us by the new director of the excavation, Prof. M. Özbasaran. The first question concerned the "paved road" in Level 3 that descends toward the river bed, and its possible role in establishing some kind of continuity with the Late PPN Musular site established on the opposite flank of the valley. Second question concerned the reconstruction of palaeogeographies at time of the mound PPN occupation. Was there a relationship between the road and an erosion phase during the occupation of the mound? or did its riverward slope correspond to the normal mound-morphology accumulation at the time ? What kind of environment was present in the valley when PPN people first settled at the site, and was there a specific reason for the site location choice ? The efforts to answer these questions included mainly fieldwork (including several coring episodes) around the mound, in, accross and along the valley between 2010 and 2015. The present paper provides some answers to the questions posed by U. Esin and Özbasaran

Palaeoenvironmental records in and around PPN Aşıklı site in the Melendiz Valley (Kızılkaya, Aksaray)

International audienc

Geomorphological and Palaeoenvironmental Setting of Asikli Hoyük

Archaeology, PalaeoenvironmentInternational audienceGeomorphological research at PPN Asikli Hüyük (ascertained 8.5-7.3 ka cal BP occupation time) started in the early 1990's in the framework of the archaeological excavation and associated projects run by Prof. Dr. U. Esin (1996, 1999a). A first geomorphological field work was done by Prof. Dr. O. Erol, whose unpublished report we were unable to access .In 1995, Prof. Esin asked us to undertake geomorphological research in the Melendiz valley, where the Asikli Höyük settlement was founded. Prof. Esin's main question for us was whether the Melendiz river ever flew at the time of the first settlement, along the eastern sicle of the mound (contrary to today, as it flows west of the mound the edges of which floods currently erodes the site. In 1995 and 1996 , field survey and three cores in the valley (Kuzucuoglu, 2013) did not allow us to answer this question. However, the survey did allow us to define a suite of terraces within the valley, to determine the position of the roof of the bedrock below the terraces in the western part of the mound at only -5 m depth, and to develop hypotheses regarding the possible occurrence of a buried river palaeobed east of the mound (Kuzucuoglu, 2013). In 2010, additional questions were proposed to us by the new director of the excavation, Prof. M. Özbasaran. The first question concerned the "paved road" in Level 3 that descends toward the river bed, and its possible role in establishing some kind of continuity with the Late PPN Musular site established on the opposite flank of the valley. Second question concerned the reconstruction of palaeogeographies at time of the mound PPN occupation. Was there a relationship between the road and an erosion phase during the occupation of the mound? or did its riverward slope correspond to the normal mound-morphology accumulation at the time ? What kind of environment was present in the valley when PPN people first settled at the site, and was there a specific reason for the site location choice ? The efforts to answer these questions included mainly fieldwork (including several coring episodes) around the mound, in, accross and along the valley between 2010 and 2015. The present paper provides some answers to the questions posed by U. Esin and Özbasaran

Geomorphological and Palaeoenvironmental Setting of Asikli Hoyük

Archaeology, PalaeoenvironmentInternational audienceGeomorphological research at PPN Asikli Hüyük (ascertained 8.5-7.3 ka cal BP occupation time) started in the early 1990's in the framework of the archaeological excavation and associated projects run by Prof. Dr. U. Esin (1996, 1999a). A first geomorphological field work was done by Prof. Dr. O. Erol, whose unpublished report we were unable to access .In 1995, Prof. Esin asked us to undertake geomorphological research in the Melendiz valley, where the Asikli Höyük settlement was founded. Prof. Esin's main question for us was whether the Melendiz river ever flew at the time of the first settlement, along the eastern sicle of the mound (contrary to today, as it flows west of the mound the edges of which floods currently erodes the site. In 1995 and 1996 , field survey and three cores in the valley (Kuzucuoglu, 2013) did not allow us to answer this question. However, the survey did allow us to define a suite of terraces within the valley, to determine the position of the roof of the bedrock below the terraces in the western part of the mound at only -5 m depth, and to develop hypotheses regarding the possible occurrence of a buried river palaeobed east of the mound (Kuzucuoglu, 2013). In 2010, additional questions were proposed to us by the new director of the excavation, Prof. M. Özbasaran. The first question concerned the "paved road" in Level 3 that descends toward the river bed, and its possible role in establishing some kind of continuity with the Late PPN Musular site established on the opposite flank of the valley. Second question concerned the reconstruction of palaeogeographies at time of the mound PPN occupation. Was there a relationship between the road and an erosion phase during the occupation of the mound? or did its riverward slope correspond to the normal mound-morphology accumulation at the time ? What kind of environment was present in the valley when PPN people first settled at the site, and was there a specific reason for the site location choice ? The efforts to answer these questions included mainly fieldwork (including several coring episodes) around the mound, in, accross and along the valley between 2010 and 2015. The present paper provides some answers to the questions posed by U. Esin and Özbasaran