DI-UMONS : Dépôt institutionnel de l’université de Mons

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2014-06-16 - Colloque/Présentation - communication orale - Anglais - 2 page(s)

Quesnel Florence, Baele Jean-Marc , Ricordel-Prognon Caroline, Dupuis Christian , "Reconstructing the P/E continental paleosurface in and around the Paris and adjacent basins: new insights for paleogeographic, geodynamic and climatic studies" in Puddingstones and related silcretes of the Anglo-Paris Basin. The Geological Society, London, Great Britain, 2014

  • Codes CREF : Géologie et minéralogie (DI1410), Sédimentologie (DI1415), Stratigraphie (DI1414)
  • Unités de recherche UMONS : Géologie fondamentale et appliquée (F401)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux)

Abstract(s) :

(Anglais) A pluridisciplinary study of the Sparnacian facies preserved within the Paris and adjacent basins and the weathered neighbouring basements has been performed. Its initial purpose was to integrate the upstream to downstream sequences of diversified coastal to terrestrial paleoenvironments, their landscapes and ecosystems, in order to assess the impact of the PETM climate crisis. These different parts of the landscapes and coeval paleoweathering features have been examined and then related to the continental paleosurface of the Late Paleocene - Early Eocene interval. Terrestrial sediments (often deposited in fluvial environments), pedogenic, quartzitic and oxidized silcretes and puddingstones are the main features used as geological markers of that paleosurface. These and others have been locally dated using paleomagnetism, geochronology, and litho-, bio-, and chemo- stratigraphy. Here we focus on the reconstruction of the paleosurface’s current geometry and on the paleogeography of the Paris and adjacent basins and their surroundings. The chronological frame of silcretes and paleoweathering markers has first been revised. Their development is stratigraphically well-constrained around the P/E boundary in the lowlands of the studied area, but less well on the uplands, where the hiatus may seem longer, because of a much reduced sedimentation rate. Upstream the continental paleosurface’s shaping probably began during the Late Paleocene, after a few millions years of kaolinitic paleoweathering upon old basements and Mesozoic cover, and the development of deep Clay-with-flints profiles upon Cretaceous chalks. Pedogenic silcretes are more often found there, with diagnostic illuviation features such as caps on top of gravels of flint and other lithologies , but the quartzitic facies occur as well, formed upon fluvial sands and gravels, originally pyritic and organic. Downstream its shaping was probably much shorter and can be dated around the P/E boundary; the quartzitic silcretes are more often found, also formed upon fluvial lignitic and pyritic sandy units, occasionally upon glauconitic marine Upper Thanetian sands, but illuviation features are evidenced as well. The shaping of this continental paleosurface is related to regional uplift occurring between the North Atlantic Igneous Province and the Pyreneo-Alpine orogeny and evolved through warm climates of the Early Paleogene, silcrete development being probably favored during hyperthermic events such as the PETM. The main processes involved appear to be linked to extreme events and enhanced hydrologic cycles, with deposition of organic and pyritic fluvial units, soon leached after emersion, triggering silica and kaolinite dissolution. Sands, nodules and clay illuviation have also been induced by rapid percolation of meteoric waters in the porosity and soil cracks, followed by dry phases saturating the ground solutions, and precipitation of several phases of neoformed silica, depending on ground water chemistry. Once established the continental paleosurface’s geometry and paleogeography of the P/E transition in the Paris and adjacent basins, we are now aiming at: (i) studying and dating other weathering features from uplands to lowlands, (ii) refining the calendar of successive paleoweathering steps, (iii) deciphering the paleosoils, biologic and hydrologic processes affecting various compartments of the P/E continental surface and their intensities along toposequences. In addition, this regional study may be directly usable in improving the tools for simulating landscape evolution and Earth's climate in paleoenvironmental modeling. Key Words: continental paleosurface, paleogeography, paleoweathering, pedogenic and quartzitic silcrete, puddingstone, Paleocene, Eocene, PETM.