| Popis: |
A sediment-geochemical study was performed on unconsolidated Upper Cenozoic siliclastic sediments from an area in the south of the Netherlands. Glauconite-rich sediments (Breda Fm) show high K contents and low Ba/K ratios. Major shifts in sediment composition as a result of changes in the Rhine system and of shifts between Rhine and Scheldt provenance, as known from heavy-mineral studies, are also recorded in changes in the grain-size-dependent variations between Al, Na and K. Pleistocene Rhine sediments (Tegelen Fm) show higher Na contents than Pliocene Rhine sediments (Oosterhout and Kiezelooliet Fms) and Scheldt-derived material (Kedichem Fm), probably as a result of larger contents of sodic plagioclase. Scheldt-derived sediments show low K/Al ratios as a result of a smectite-dominated clay-mineralogical composition and low contents of micas, whereas Rhine-derived sediments have high K/Al ratios which reflect an illite-kaolinite-dominated clay mineralogy and higher contents of muscovite. The presence of siderite causes high Fe contents in the Tegelen Fm in the east of the area, suggesting a fresh-water depositional environment. Increased Mg contents in the siderite-bearing sections of the Tegelen Fm and in parts of the Oosterhout and Kiezelooliet Fms are probably caused by the presence of minor amounts of dolomite. Localized high concentrations of (pyrite-) S are not only found in the marine Oosterhout Fm and the estuarine Tegelen Fm, but also in the fluviatile Kiezelooliet and Kedichem Fms, which indicates at least minor marine transgressions during their deposition. |
