Variations climatiques et morphogenese au Maroc atlantique (3 degrees -33 degrees N) a la limite Pleistocene-Holocene

International audienc

SAHARAN DUST ON FUERTEVENTURA ISLAND (CANARIES): CHEMICAL AND MINERALOGICAL CHARACTERISTICS, AIR MASS TRAJECTORIES, AND PROBABLE SOURCES

International audienceFrom April 12 to 19, 1984, dust was [Windom, 1975; Chester et al., 1979; Sarnthein et collected by cascade impactor on Fuerteventura al., 1982] and, probably, to the mineral feeding Island, 100 km from the Saharan coast. The sam-of marine plankton. The dust outbreaks from ples were analyzed by X ray fluorescence spectro-northwestern Africa to the middle Atlantic and metry (elemental composition), by X ray diffrac-Western Europe have been much less studied. The tion (mineral constituents), and by scanning only samplings were carried out during oceanic electron microscope (SEM) and energy dispersive X cruises [Chester and Johnson, 1971; Parkin et ray analyzer (EDXA) examination (shape, surface al., 1972] and the results were compared to the features, and mineralogy of particles), with the marine sedimentation [Tetzlaff and Wolter, 198

Mission archéologique de Madâ'in Sâlih (Arabie Saoudite) : Recherches menées de 2001 à 2003 dans l'ancienne Hijrâ des Nabatéens

84 pagesInternational audienceThis contribution presents the preliminary results of the Madâ'in Sâlih archaeological project, which started in 2001 and which, in December 2004, completed its fourth field season. The aims of this five-year project are a systematic recording of the archaeological remains at the site as well as an analysis of its agricultural potential. The former include not only the tombs, sanctuaries, wells, quarries, walls, buildings, etc., but also the inscriptions written in various scripts and languages. Parallel to this exploration of what is visible on the surface, an extensive geophysical survey was undertaken in the so-called residential area, in the central part of the site, in order to obtain an image of the sub-surface remains. This contribution begins with a presentation of the sources, followed by a brief history of the exploration of Madâ'in Sâlih. The focus is on the conditions which allowed this project to be established as well as the problematics which guided it. J.-B. Rigot then presents his analysis of the agricultural potential of the site, demonstrating the existence, in antiquity, of a large oasis. Finally, a preliminary description of the main components of the sites: the necropoleis, the sanctuaries and the residential area, is given

Sediments of the Moon and Earth as End-Members for Comparative Planetology

Processes of production, transport, deposition, lithification, and preservation of sediments of the Moon and Earth are extremely different. The differences arise primarily from the dissimilarity in the origins and sizes of the Moon and Earth. The consequence is that the Moon does not have an atmosphere, a hydrosphere (the Moon is totally dry), a biosphere (the Moon is totally life-less), a magnetosphere, and any tectonic force. Pristine rocks on the exposed surface of the Moon are principally anorthositic and basaltic, but those on the Earth are granitic (discounting suboceanic rocks). Sediments on these two bodies probably represent two end-members on rocky planetary bodies. Sediments on other rocky planetary bodies (atmosphere-free Mercury and asteroids, Venus with a thick atmosphere but possibly no water on its surface, and Mars with a currently dry surface sculptured by running water in the past) afe intermediate in character. New evidence suggests that characteristics of Martian sediments may be in-between those of the Moon and Earth. For example, impacts generate most Martian sediments as on the Moon, and, Martian sediments are wind-blown to form dunes as on Earth. A comparative understanding of sediments of the Moon and Earth helps us anticipate and interpret the sedimentary record of other planetary bodies. Impact processes, large and small, have produced the sediments of the Moon. Unlike Earth, the surface of the Moon is continuously bombarded by micrometeorites and solar wind. Processes of chemical and mechanical weathering aided by biological activity produce sediments on Earth, fixing a significant amount of carbon in the solid state. Whereas solar wind produces minor chemical changes in lunar sediments, chemical weathering significantly alters and affects the character of Earth sediments. Primarily ballistic and electrostatic forces transport lunar sediments but Earth sediments are transported by air, water, and ice. Whereas Earth sediments accumulate mostly in basins created slowly by tectonic forces, lunar sediments are deposited in craters (excavated instantaneously by impacts) or even on high grounds. Rubble, sand, mud, and carbonate material on Earth are lithified through burial, expulsion of water, and precipitation of cement from H2O-so1utions. In contrast, lunar sediments are lithified through presumably low-energy shock waves that sinter and bind clastic grains into regolith breccias. Surface processes and morphological features on the Moon are dominated by impact cratering and ejecta deposition, while those on Earth are sculptured by water, ice, and air. However, comparisons in two areas assist in planning planetary exploration. (l) Dust, i.e., small particles elevated above the solid surface of a planetary body, is ubiquitous on the Moon and Earth. The composition of dust is related to but is different from the source rocks, especially where dust is transported aver long distances as on Earth. Dust obscures observation of a planetary body and interferes with remote sensing; dust may also affect climate on planetary bodies with an atmosphere. (2) Because Earth's lithosphere has been recycled many times, sediments shed from rocks and regions that do not exist any more are the principal guides to the ancient Earth and its crustal evolution. Because the lunar surface is completely covered by regolith, and no bedrock has been directly observed or sampled, sediment is the principal guide to the lunar crust, past and presento Provenance analysis of lunar and terrestrial sediments is accomplished using the same methods and principles