The Late Ordovician glacial record

• Main Authors: Ghienne, Jean-François, Loi, Alfredo, Paris, Florentin, Rubino, Jean-Loup
• Other Authors: Centre de géochimie de la surface (CGS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Louis Pasteur - Strasbourg I-Centre National de la Recherche Scientifique (CNRS), Géosciences Rennes (GR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2008
• Subjects: [SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy; [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology; Ice Sheet
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-00377126

1 p. An outline of the North Gondwanan, Late Ordovician glacial record is proposed. The related palaeogeographic domain extended from southern high palaeo-latitudes (southeastern Mauritania, Niger) to northern lower palaeo-latitudes (Morocco, Turkey, Sardinia) and covered a more than 4000 km-wide section perpendicular to ice-flow lines. Glacial advances are spatially and stratigraphically evidenced by subglacial structures (tunnel valley, shear zones) delineating glacial erosion surfaces, while deglaciation periods and interglacial intervals are reflected in fluvio-deltaic, glaciomarine or shallow shelf successions. A major mid-Hirnantian deglaciation event subdividing the Hirnantian glaciation in two first-order cycles is recognised. Each cycle comprises 2-3 glacial phases separated by several hundreds kilometres ice-front retreats. From ice-proximal to ice-distal regions, the number of glacial surfaces differentiates (i) a continental interior with post-glacial reworking of the glacial surfaces, (ii) a glaciated continental shelf that is subdivided into inner (1-2 surfaces), middle (2-5 surfaces) and outer (a single surface related to the glacial maximum) glaciated shelves, and (iii) the non-glaciated shelf. Glaciomarine outwash diamictites are developed at or near the maximum position of the ice-front. During ice-sheet recession, a relatively thin sediment cover blankets the erosion surfaces in foredeepened ice-stream areas. Marine-terminating ice fronts then evolve later into more slowly retreating, land-terminating ice fronts. In adjacent areas (inter ice-stream) where a more gradual ice-sheet recession occurred, fluvio-glacial deposits prevailed. The progradation of a delta-shelf system, coeval with fluvial aggradation, characterises the late glacial retreat to interglacial conditions (Ghienne et al., 2007, The Late Ordovician glacial sedimentary system of the North Gondwana platform. Special Publication n°39, International Association of Sedimentologists, Blackwells, pp. 295-319). This model for ...