Fluvial aggradation phases in the Upper Rhine Graben : New insights by quartz OSL dating

The Upper Rhine Graben (URG) is characterized by a thickness of up to 500 m of unconsolidated Quaternary sediments, providing excellent records of the Rhine river system and its responses to tectonic and climatic changes. The most complete Quaternary sequence of fluvial and limnic-fluvial deposits is found in the Heidelberg Basin, due to its long-term subsidence since the mid-Eocene. The aim of this study is to provide a chronological framework using optically stimulated luminescence (OSL) dating of aeolian and fluvial sands derived from the upper 33 m of a sediment core, which was drilled into the Heidelberg Basin infill close to the village of Viernheim, Germany. The OSL ages demonstrate that the dated fluvial sediments were deposited during the last glacial period (Weichselian) and that there were at least three aggradation periods during this episode. The coversands that cap the sequence were emplaced during the early Holocene

The Heidelberg Drilling Project (Upper Rhine Graben, Germany)

The Heidelberg basin hosts one of the thickest successions of unconsolidated Pliocene and Quaternary deposits in continental middle Europe, and certainly the thickest succession built by the Geosystem Rhine, connecting Alps, Rhine Graben, North Sea and English Channel. Also local Geosystems, first place the Neckar System, contribute to the basin infill. The more or less continuous subsidence of the Upper Rhine Graben (URG) during all periods of tertiary Graben history, but especially during the last few million years, led to a succession of alternating fluvial and lacustrine environments of various provenances. This archive contains not only various proxies of the mid-European climate evolution during the Plio-Quaternary, but also signals of geodynamic processes controlled by tectonics. Various pre project activities during the last years prove the feasibility of an extensive research project to begin in late 2005. In its centre will be three drillings envisaged to become 300 m, 350 m and 500 m deep which are all designed to expose the Plio-Quaternary transition. The various techniques of facies analysis, geophysical exploration, geochronology, climate and tectonics modelling, to be combined in a comprehensive 3D evolutionary scenario, will – hopefully – enable us to read and understand the archive of the Heidelberg basin fill. The expected results will not only contribute to the data pools of palaeoclimate and neotectonics, but are also a methodological test in handling complex Geosystems. A considerable fallout with regard to societal use and handling of the geo-environment is also expected: from use of geothermal energy, hydrogeology and pollution handling in a highly industrialized region, right to assessment of climate and seismic risks.The project will be run by a Co-operation of the Leibniz Institute for Applied Geosciences (Hannover) and the Geological Services of the three German federal States sharing the territories of the Heidelberg basin (Baden-Württemberg, Hessen, Rheinland-Pfalz). This paper is designed to outline the project, present some very preliminary results of pre-project research and stimulate further collaboration into the main project to come.Le bassin d’Heidelberg présente une des successions de dépôts quaternaires non consolidés les plus épaisses d’Europe continentale moyenne et certainement la succession la plus épaisse du géosystème Rhin, connectant les Alpes, le graben du Rhin, la Mer du Nord et la Manche. Des géosystèmes locaux, avec en premier lieu celui du Neckar, contribuent également au remplissage du bassin. La subsidence plus ou moins continue de cette partie du graben du Rhin durant toute son histoire cénozoïque, mais en particulier durant les derniers millions d’années, a conduit à la mise en place d’une succession d’environnements fluviaux et lacustres de différentes provenances. Cette archive ne contient pas seulement différents proxies de l’évolution climatique durant le Plio-Quaternaire, mais également des signaux des processus géodynamiques controlés par le climat et la tectonique.Différentes activités pré-projet menées durant ces dernières années ont montré la faisabilité d’un programme de recherche important qui a pris corps autour d’un projet de carottage profond prévue pour commencer à la fin 2005. Les différentes techniques d’analyse de faciès, d’exploration géophysique, de géochronologie, de modélisation du climat et de la tectonique, prévues pour être intégrées dans un modèle compréhensif d’évolution 3D, permettront de lire et de comprendre l’archive d’Heidelberg. Les résultats escomptés ne contribueront pas seulement à documenter les aspects paléoclimatiques et néotectoniques, mais fourniront également un apport méthodologique pour l´appréhension des géosystèmes complexes. Des retombées importantes sont également attendues par rapport aux usages sociaux et à la gestion des géo-environnements, en ce qui concerne l’énergie géothermique, l’hydrogéologie et la maîtrise des pollutions dans une région très industrialisée, sensible aux modifications climatiques et au risque sismique.Le projet sera mis en œuvre grâce à une coopération de l’Institut GGA pour les Géosciences appliquées de Hanovre et les services géologiques des trois Länder recouvrant le bassin d’Heidelberg (Baden-Württemberg, Hesse, Rhénanie-Palatinat). Cet article expose le projet, présente quelques résultats préliminaires ou recherches pré-projets et propose des opportunités de collaboration

Infrared radiofluorescence (IR-RF) dating of middle pleistocene fluvial archives of the Heidelberg Basin (Southwest Germany)

The infrared radiofluorescence (IR-RF) dating technique was applied to eight fluvial samples that were collected from two sediment cores at the Heidelberg Basin located near Viernheim and Ludwigshafen in southwest Germany. Based on the IR-RF derived ages of the samples it was possible to establish a chronological framework for the Mid-Pleistocene fluvial deposits of the Heidelberg Basin. The results allow us to distinguish between four main periods of aggradation. The lowermost sample taken from 100 m core depth lead to an IR-RF age of 643 ± 28 ka pointing to a Cromerian period of aggradation (OIS 17–16). For the Elsterian it is now possible to distinguish between two aggradation periods, one occurring during the Lower Elsterian period (OIS 15) and a second during the Upper Elsterian period (OIS 12–11). For the so called Upper interlayer (or “Oberer Zwischenhorizont” — a layer of organic-rich and finer-grained deposits), the IR-RF results point to a deposition age of around 300 ka, with samples taken directly on top and out of this layer yielding IR-RF ages of 288 ± 19 ka and 302 ± 19 ka, respectively. Hence, the measured IR-RF ages clearly point to a deposition during the Lower Saalian period (OIS 9–8) whereas earlier studies assumed a Cromerian age for the sediments of the Upper Interlayer based on pollen records and also mollusc fauna. The new IR-RF dataset indicates that significant hiatuses are present within the fluvial sediment successions. In particular the Eemian and Upper Saalian deposits are missing in this part of the northern Upper Rhine Graben, as the 300 ka deposits are directly overlain by Weichselian fluvial sediments. It is obvious that time periods of increased fluvial aggradation were interrupted by time periods of almost no aggradation or erosion which should have been mainly triggered by phases of increased and decreased subsidence of the Heidelberg Basin

Q4 Continuité et discontinuité dans les enregistrements quaternaires - Première partie

Organisé par l’AFEQ et le CNF-INQUA dans le cadre de la Réunion des Sciences de la Terre (RST) (Strasbourg 22 - 23 Septembre 2004