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FIG. 18 in Fossil wood from the lower Miocene of Myanmar (Natma Formation): palaeoenvironmental and biogeographic implications
No full textFIG. 18. — Shoreoxylon sp. 2, MNHN.F.50195: A, Ts, vessel arrangement, often solitary, sometimes in groups and clusters, with one parenchyma band (arrow); B, Ts, mostly vasicentric to slightly aliform parenchyma as well as some diffuse parenchyma (arrow); C, E, Tls, 1-5-seriate rays; D, Ts, long tangential line of secretory canals embedded in parenchyma band (arrow); F, Rls, heterocellular ray with one line of upright marginal cells (arrow); G, Ts, synthetic drawing of the transversal section (only some vessels and rays are displayed) with bands of parenchyma as grey lines and secretory canals as red dots, arranged in long tangential lines; doubtful canals are displayed as orange dots; H, Rls, crystals in possibly chambered parenchyma cells (arrow); I, tyloses in vessels (black arrow) and vasicentric tracheids (white arrow) J, Tls, alternate, vestured (arrow) intervessel pits; K, simple vessel-ray pits with reduced borders and ovoid shape (arrow). Scale bars: G, 1 cm; A, D-E, 500 µm; B-C, F, 200 µm; H-I, 100 µm; K, 50 µm; J, 20 µm. Abbreviations: see Fig. 2.Published as part of Gentis, Nicolas, Licht, Alexis, Boura, Anaïs, Aung, Dario De Franceschi Zaw Win Day Wa & Dupont-Nivet, Guillaume, 2022, Fossil wood from the lower Miocene of Myanmar (Natma Formation): palaeoenvironmental and biogeographic implications, pp. 853-909 in Geodiversitas 44 (28) on page 888, DOI: 10.5252/geodiversitas2022v44a28, http://zenodo.org/record/714530
Cenozoic evolution of the Pamir plateau recorded in surrounding basins, implications on Asian climate and land-sea distribution.
No full textEocene-Oligocene continental sediment natural gamma radiation data of the CDB1 drill-core (Rennes Basin, France)
No full textThe natural gamma radiation (NGR) data were acquired each 10 cm (see details below) on fluvio-lacustrine and palustrine sediment materials, from the continental CDB1 drill-core located in the Rennes Basin (Chartres de Bretagne, France, geographic coordinates: 48.04412074N; 1.71899076W, Elevation: +37m NGF, Nivellement Général de France). The studied geological time interval covers the Eocene-Oligocene transition interval, roughly from 31 to 38.5 Ma.
NGR measurements were conducted by the Semm Logging company during the drilling campaign of the CINERGY project (CDB1 borehole) during summer 2010, under the supervision of BRGM (Bureau de Recherches Géologiques et Minières, France), on behalf the contracting authority of Chartres-de Bretagne. The main objective of the CINERGY project was to explore the Cenozoic cover of the Armorican shield preserved in a small strike-slip basin. The CINERGY Project was funded by the BRGM, the AELB (Agence de l'Eau Loire-Bretagne) and the ADEME (Agence de l'Environnement et de la Maitrise de l'Energie) French agencies.
The NGR probe used during the CDB1 well logging consists of a scintillation detector (sodium iodide crystal coupled to a photo-multiplication tube), which converts gamma rays into electric pulses. The measured values are expressed in API (American Petroleum Institute) unit. This unit was calculated using a linear interpolation of raw data expressed in pulses per second (pps) according to a calibration set with a very stable source, the radioactivity of which is known in API unit. Because disintegration is a random phenomenon, raw measurements taken every 2 cm are integrated over a 25 cm long window and restored at a 10 cm step, which is consistent both with the crystal size and the average dip of the strata, nearly 15 degrees
Tectonic evolution of the Tian Shan and Western Kunlun Shan : evidence from magnetostratigraphic and thermochronological analyses
No full textDeux questions scientifiques critiques sont adressées dans cette thèse présentées comme suit. ( 1 ) L’évolution mésozoïque du bassin d’avant-pays dans les piémonts nord et sud du Tian Shan. ( 2 ) L’évolution au Cénozoïque précoce du soulèvement du Tian Shan. Dans le chapitre 1, l'évolution du nord Tian Shan est étudiée par datation U/Pb (LA- ICP-MS) de zircons détritiques sur 14 échantillons de grès d'une série continue d’âge fin Paléozoïque à Quaternaire dans la marge sud du bassin de Junggar (région de Manasi). Dans le chapitre 2, l'évolution encore mal contrainte entre le Mésozoïque et le début du Cénozoïque de la marge sud-ouest du Tian Shan est étudiée en utilisant les datations U/Pb ( LA- ICP-MS ) sur zircons détritiques et les traces de fission sur apatites détritiques. Dans le chapitre 3, nous présentons une étude magnétostratigraphique détaillée de la zone Ulugqat au sud-ouest du Tian Shan, dans le but d'améliorer la compréhension de son soulèvement et de l'histoire de la déformation de la région au cours du Cénozoïque. Ce travail à permis de montrer que l'érosion du paléo-Tian Shan commencée au Trias moyen s’est traduite par le pénéplanation générale au Mésozoïque du Tian Shan qui était dominé par un système de drainage large pendant une longue période de quiescence tectonique. Le piémont nord du Tian Shan était caractérisé par un bassin en subsidence thermique post- extensive avec peu d'activité tectonique, et le piémont sud a également connu un aplanissement général de la topographie. Au cours du début du Jurassique, du Crétacé inférieur et du Crétacé supérieur, trois inversions tectoniques mineures sont identifiées avec des ajustements du bassin d’avant-pays du Tian Shan. Ces inversions peuvent correspondre respectivement à l’accrétion des terrains Cimmérien, de Lhassa, et du Kohistan-Dras à la limite sud de la plaque eurasienne. Les données U-Pb sur zircons détritiques et les données traces de fission sur apatite indiquent une première réorganisation du bassin à la fin du Crétacé – début du tertiaire, contemporaine d’une réactivation de l’érosion le long du piémont sud du Tian Shan. Nous avons interprété cette réactivation fin Crétacé – début Paléogène du Tian Shan sud à la réponse initiale des effets lointains de la collision Inde-Eurasie. Pendant le reste du Cénozoïque, la principale réactivation du Tian Shan est initiée fin Oligocène – début Miocène. Cela est attesté dans le piémont nord du Tian Shan par nos données U-Pb sur zircons détritiques et dans le piémont sud du Tian Shan par les données traces de fission sur apatite suggérant des chevauchements entre 18 et 16 Ma, par les résultats magnétostratigraphiques révélant une importante lacune de sédimentation oligocène ainsi que l’augmentation des taux d’accumulation à ~ 18.5 Ma.Two critical scientific issues are adressed in the présent thesis as follows. (1) Mesozoic basin-range relationship in the northern and southern piedmonts of the Tian Shan. (2) Spatio-temporal differences in the Early Cenozoic uplift of the Tian Shan. In chapter 1, the évolution of the northern Tian Shan is investigated through U/Pb (LA-ICP-MS) dating of detrital zircons from 14 sandstone samples from a continuous series ranging in age from latest Palaeozoic to Quaternary in the southern margin of the Junggar Basin (Manasi area). In chapter 2, the still poorly constrained Mezosoic to early Cenozoic evolution of the southwestern Tian Shan piedmont is investigated using U/Pb (LA-ICP-MS) dating of detrital zircons and fission track analysis on detrital apatites. In chapter 3, we present a detailed magnetostratigraphic study from the Ulugqat area in piedmont of the Southwest Tian Shan, in order to improve understanding of the uplift and deformation history of the Southwest Tian Shan during the Cenozoic. This work enabled to show that erosion of the Paleo-Tian Shan initiated in the Middle Triassic results in the general peneplanation of the Mesozoic Tian Shan dominated by a wide drainage system and long-lasting tectonic quiescence. The northern piedmont of the Tian Shan was characterized by a post-extensional thermally subsiding basin without much tectonic activity, and the southern piedmont also experienced a general flattening of topography. During the Early Jurassic, Early Cretaceous and Late Cretaceous, three identified minor tectonic inversions and adjustments of basin-range pattern in the Tian Shan, may potentially correspond respectively to the accretions of Cimmerian, Lhasa, and Kohistan-Dras in the southern margin of the Eurasian plate. Detrital zircon U-Pb and apatite fission-track data indicate an initial late Cretaceous – Early Tertiary basin reorganization and coeval renewed erosion along the southern Tian Shan piedmont. We interpreted this late Cretacesou to Paleogene activity in STS as the initial response of the distant effects of India-Eurasia collision as previously argued. During the Late Cenozoic, the major reactivation of the Tian Shan initiated around the Late Oligocene-Early Miocene times. This is evidenced mainly from the detrital zircon U-Pb geochronology in the northern piedmont of the Tian Shan, the apatite fission-track data suggesting a possible activation of the Talas Fergana Fault between 18 and 16 Ma, the major Oligocene depositional hiatus and conspicuous increase in accumulation rates at ~ 18.5 Ma revealed by the magnetostratigraphic results in the southern piedmont of the Tian Shan
Paleogene seasonal variability in Central Asia : constraints from high-resolution geochemistry on oyster shells
No full textLe climat asiatique est aujourd'hui caractérisé par une forte dualité entre un climat de moussons au Sud-Est et un climat aride en Asie centrale. Ces climats sont tous les deux définis par une saisonnalité marquée, que ce soit en terme de précipitations pour le premier ou de températures pour le second. Si l'intensification des moussons asiatiques au Néogène, liée à l'influence du soulèvement final du plateau tibétain sur les climats asiatiques, semble faire consensus dans la communauté scientifique, la caractérisation des climats paléogènes est encore peu établie. Ainsi la question de savoir quand cette dualité climatique s'est installée en Asie reste encore ouverte. Au Paléogène, les reliefs liés à la collision entre les plaques indienne et eurasiatique étaient encore naissant et la distribution entre les terres et les mers très différente de l'actuelle. Notablement, une vaste mer épicontinentale et peu profonde (la Proto-Paratethys) s'étendait à travers l'Europe et l'Asie Centrale. À la fin du Paléogène, la Proto-Parathetys se retire de l'Asie Centrale, et les hautes topographies asiatiques se mettent en place. Dans ce contexte géodynamique, cette thèse cherche à caractériser les fluctuations à haute fréquence du climat en Asie Centrale afin de comprendre l'évolution de la saisonnalité au cours du Paléogène, et plus précisément pendant la période de l'Éocène (-55 à -34 Ma). Pour cela une approche originale utilisant une méthode géochimique multi- proxy sur des coquilles d'huîtres a été établie. Grâce à l'apport de l'analyse incrémentielle de marqueurs élémentaires et isotopiques sur les coquilles nous accédons aux variations saisonnières de la température et de la salinité de l'eau de mer. Ceci nous permet de mieux cerner les bilans hydriques et thermiques à l'échelle de l'année et ainsi de caractériser le climat d'Asie Centrale à très haute résolution. Combinant cette approche géochimique avec une étude sédimentologique et une étude numérique à plus grande échelle, cette thèse cherche à mieux établir les causes de l'évolution du climat régional au cours du Paléogène.The modern Asian climate is mainly characterized by a monsoonal duality between humid summers in southern and eastern Asia and arid winters in Central Asia resulting in a strong seasonality in terms of precipitation and temperature in these respective regions. Although Neogene monsoonal intensification - mainly attributed to Tibetan plateau uplift - is well established, Paleogene Asian climate is still poorly understood such that the question of how and when this climate duality was established remains open. During Paleogene times, paleoreliefs due to the ongoing Indo-Asia collision and the land-sea distribution were very different compared to modern. Notably, a shallow epicontinental sea (the Proto-Paratethys) covered part of Europe and Central Asia. During the Eocene (-55 to -34 Ma), the Proto-Paratethys retreated westward while high Asian topographies formed. In this peculiar context, this PhD thesis aims to characterize the evolution of high-frequency climatic fluctuations in Central Asia in order to better constrain the seasonality changes associated with sea retreat, topographic uplift or nascent monsoons. We develop a novel approach using a geochemical multi-proxy methodology on oyster shells. Thanks to incremental analyses of elements and isotopes on bivalve shells, we estimate seasonal variations of temperature and salinity in seawater at high resolution. This enables to constrain precisely the annual-scale water and thermal balances and, by applying this technique to successive oyster bearing deposits widely distributed over Central Asia, aims to characterize Central Asian climate evolution. Combining this geochemical approach with a sedimentological and a numerical studies at larger time- and geographic- scale, this PhD thesis is aiming at better understanding the causes of the Eocene regional climate evolution
Datations et quantifications des forçages externes et internes des paléoenvironnements dans le cadre des changements régionaux et globaux
No full textQuel est le défi des sciences de la terre et de l'environnement aujourd'hui? Depuis la révolution de la théorie de la tectonique des plaques, l'évolution des surfaces continentales a été associée aux interactions des plaques lithosphériques. Plus récemment, la révolution de la modélisation numérique a bousculé le paradigme de la tectonique en montrant l'importance des interactions entre processus externes (ex. climat, érosion, altération) et processus internes (ex. géodynamique, topographie dynamique). D'une part, les modèles climatiques montrent que les changements régionaux (moussons, aridification...) ainsi que globaux (refroidissement, pCO2...) peuvent être attribués à des phénomènes d'origine interne par le biais de variations dans la distribution des reliefs, des mers et des continents. D'autre part, les modèles géomorphologiques montrent que ces processus internes peuvent être influencés en retour par les variations climatiques par le biais de l'érosion de la surface des continents. Ce qui est nécessaire aujourd'hui, pour tester et calibrer les modèles, c'est une méthodologie qui permette de différencier et de quantifier les contributions respectives des processus internes et externes sur les variations paleoenvironnementales observées pendant les changements régionaux et globaux. En utilisant les outils et l'expérience acquis pendant mes travaux antérieurs, je développe cette méthodologie dans le cadre des travaux de recherche présenté dans cette thèse. La clef de la méthodologie préconisée est basée sur la chronologie fine par datation haute-résolution des enregistrements sédimentaires dans les bassins en utilisant les techniques de magnéto- et cyclostratigraphiques. En effet, une résolution en âge suffisante permet de corréler (ou pas) des variations paleoenvironnementales locales aux cycles astronomiques modulés par la géométrie orbitale de la terre, aux archives marines du climat global ou aux évènements géodynamiques et tectoniques. Cette approche ne prend sa réelle mesure que dans le cadre d'une intégration stratigraphique multidisciplinaire. Je présenterai mon projet principal portant sur les forçages internes et externes des variations paleoenvironnementales dans le contexte de la collision Inde-Asie pendant les évènements climatiques globaux paléogènes. De plus, je décrirai deux autres applications chrono-stratigraphique sur les couplages tectonique-érosion-sédimentation dans l'Himalaya et les interactions climat-évolution dans les bassins à hominidés du rift Est Africain
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Constraints on the mechanism of the Altyn Tagh fault from paleomagnetism
No full textFirst, paleomagnetic data were obtained from Tertiary red beds at two localities separated by several hundred kilometers within the Qaidam Basin. When compared with equivalent-age expected directions for Eurasia, the mean paleomagnetic directions indicate no Neogene vertical-axis rotation of the Qaidam Basin or the Altyn Tagh fault. The Qaidam Basin may act as an indentor translating without rotation toward the Sino-Korean craton. Second, the observed paleomagnetic direction from Miocene red beds in the central Tarim Basin indicates 30.8° ± 5.5° flattening of inclination and 15.3° ± 6.7° clockwise vertical-axis rotation. Anisotropy of magnetic susceptibility measurements indicate a rock-magnetic (depositional or compaction shallowed) origin for the inclination flattening. Local deformation is the preferred interpretation for the vertical-axis rotation. Third, paleomagnetic data were obtained along the arcuate Tula syncline to test whether its strike curvature is due to oroclinal bending. The observed 13.3° ± 8.8° declination difference between the two halves of the Tula syncline is far less than the ∼40° difference predicted by oroclinal bending. Instead the arc shape of the syncline is an original configuration produced by transport above an arcuate thrust ramp. Along with paleomagnetic data from the Qaidam Basin, this result indicates that crustal displacement between the Tarim Basin and the Tibetan Plateau is accommodated by strike-slip motion on the Altyn Tagh fault rather than distributed shear within the northern Tibetan Plateau. Finally, we present results from red beds in the Altun Shan, the Qilian Shan/Nan Shan fold-thrust-belt and the Hexi corridor. In the Altun Shan, results from Miocene beds indicate no significant vertical-axis rotation confirming that the Altyn Tagh fault has not rotated and that sinistral shear strain is concentrated on the fault. Paleomagnetic results from Nan Shan/Qilian Shan fold-thrust-belt indicate no rotation since 30 Ma contrasting with prediction from previous kinematic models. This result indicates that there is no transrotation of the belt associated with motion on the Altyn Tagh fault. In the Hexi corridor, the observed mean paleomagnetic direction is concordant with the expected direction at 110 Ma providing a new local paleomagnetic reference for the Sino-Korean craton in agreement with published reference paleomagnetic poles for Eurasia
Continental temperature seasonality from Eocene Warmhouse to Oligocene Coolhouse
No full textThis dataset combines model outputs from five experiments which aim at reconstructing the middle Eocene to early Oligocene greenhouse-icehouse transition (Toumoulin et al., 2021, Clim. Past).
Simulations are characterized by a 40 Ma paleogeography (Poblete et al., 2021, Earth-Sci. Rev.), different pCO2 (1120, 840, 560 ppm), and an antarctic ice-sheet or not. When present, antarctic ice-sheet is represented alone or associated with a sea-level decrease of -70 m, which is applied homogeneously to the 40 Ma paleogeography map. All experiments were performed with the general circulation model IPSL-CM5A2 (Sepulchre et al., 2020, Geosci. Model Dev.) and ran for 4000 years to a quasi-equilibrium state (change in deep ocean temperature < 0.1°C/century). Data are monthly averages over the last 100 years
The paleogeography of the India-Asia collision: a review of ongoing models and controversies
No full textNational audienceThe reconstruction of the "India-Asia Collision" and the development of the Tibetan-Himalayan orogen remain highly controversial despite over a century of research on the shoulders of early giants such as Emile Argand (1922). The motivations for reconstructing the evolution of the most dramatic ongoing geodynamic event forming the highest and largest orogenic plateau, is not only "because it's there". It also holds clues to constrain proposed models of underlying geodynamic and surface processes as well as associated climatic and biotic impacts. As such it represents, arguably, the most important conundrum challenging the Earth Science community today. We present here a review of reliable constraints, with a focus on paleomagnetic data, selected in the current overwhelming tsunami of related publications on (1) the convergence between the Indian and Asian plates with intermingled terranes; and (2) the growth of the Himalaya-Tibetan orogen. Results are integrated into Terra Antiqua, a plugin for QGIS to make paleogeographic reconstructions with a user-friendly graphical interface (Aminov et al., 2023). Three major types of collision models are currently competing with a plethora of variations that make contrasting predictions on the timing, amount and location of tectonic deformation and associated rock and surface uplift. These predictions compared to a review of various constraints on the Himalaya-Tibetan orogen paleogeography enable, together with plate configuration considerations, to evaluate the most likely collisional models and propose a new one. Argand, E., 1922, La tectonique de l'Asie, Congrès géologique international (XIIIe session), Extrait du compte rendu, 372pp Aminov, J., Dupont-Nivet, G., Ruiz, D., Gailleton, B., (2023), The Terra Antiqua QGIS plugin for palaeogeography: application to 30 and 50 Ma reconstructions, Earth Science Reviews, https://doi.org/10.1016/j.earscirev.2023.104401
The paleogeography of the India-Asia collision: a review of ongoing models and controversies
No full textNational audienceThe reconstruction of the "India-Asia Collision" and the development of the Tibetan-Himalayan orogen remain highly controversial despite over a century of research on the shoulders of early giants such as Emile Argand (1922). The motivations for reconstructing the evolution of the most dramatic ongoing geodynamic event forming the highest and largest orogenic plateau, is not only "because it's there". It also holds clues to constrain proposed models of underlying geodynamic and surface processes as well as associated climatic and biotic impacts. As such it represents, arguably, the most important conundrum challenging the Earth Science community today. We present here a review of reliable constraints, with a focus on paleomagnetic data, selected in the current overwhelming tsunami of related publications on (1) the convergence between the Indian and Asian plates with intermingled terranes; and (2) the growth of the Himalaya-Tibetan orogen. Results are integrated into Terra Antiqua, a plugin for QGIS to make paleogeographic reconstructions with a user-friendly graphical interface (Aminov et al., 2023). Three major types of collision models are currently competing with a plethora of variations that make contrasting predictions on the timing, amount and location of tectonic deformation and associated rock and surface uplift. These predictions compared to a review of various constraints on the Himalaya-Tibetan orogen paleogeography enable, together with plate configuration considerations, to evaluate the most likely collisional models and propose a new one. Argand, E., 1922, La tectonique de l'Asie, Congrès géologique international (XIIIe session), Extrait du compte rendu, 372pp Aminov, J., Dupont-Nivet, G., Ruiz, D., Gailleton, B., (2023), The Terra Antiqua QGIS plugin for palaeogeography: application to 30 and 50 Ma reconstructions, Earth Science Reviews, https://doi.org/10.1016/j.earscirev.2023.104401
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