Distribution of heavy and clay minerals in coastal sediment of Jijel, East of Algeria: indicators of sediment sources and transport and deposition environments

摘要

The identification of bulk, clay (< 2 mu m), and heavy (63-200 mu m) minerals has been investigated on 42 coastal samples along the Jijel bay (Eastern Algeria). The mineralogical assemblages are used to identify the mineral sources and to interpret the mineral distribution. The samples were subjected to grain-size analysis by sieving and by X-ray diffraction on powder (bulk mineralogy) and on oriented aggregates (clay fraction). The bulk fraction is composed by muscovite, plagioclase, calcite, anhydrite, clay fraction, and a predominance of quartz (11 to 45 %). Clay fraction is composed of kaolinite, chlorite, smectite, interstratified minerals, and a predominance of illite (43-65 %). In addition, the heavy minerals assemblages of sediments have been identified by binocular observation, X-ray diffraction, and optical microscope. The heavy minerals are dominated by opaque minerals (16-65 %) associated with variable proportions of muscovite, chlorite, kyanite, sillimanite, biotite, pyroxene, amphibole, garnet, epidote, zircon, tourmaline, and rutile. Both fluvial hydrodynamic and marine agents control the sediment distribution along the coast. Indeed, the passage from areas in accretion toward those in erosion has caused a concentration in heavy minerals on coastal sections in recession; however, the light minerals were moved selectively toward accretional areas. The heavy mineral assemblages present in rivers sediment indicate that they were delivered to the coast in a highly selective manner. This assemblage of heavy mineral is also present with high concentration in a variety of fluvio-marine environments such as river mouths, coastal dunes, and beaches. These sediments are derived from the various geological formations (metamorphic formations of the basement, magmatic rocks, and other sedimentary rocks) observed in the watershed.