Geochemical compositional changes at the Pliocene-Pleistocene transition in fluviodeltaic deposits in the Tegelen-Reuver area (southeastern Netherlands)
article
At the Pliocene-Pleistocene transition, major changes occurred in the Rhine system: Climatic cooling, extension of the drainage area into the Alps and a marine regression. We studied the geochemistry, clay mineralogy and micromorphology of several sections with Pliocene and Early Pleistocene Rhine deposits to determine the effects of this change on the bulk geochemical record. We found a general increase in Na<sub>2</sub>O contents, which can be attributed to the Alpine source supplying fresh, sodic plagioclase-rich material instead of the local, strongly weathered sediments. Increasing K<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub> can be attributed to a similar decrease in degree of weathering. However, this trend is disturbed by the loss of K from clay minerals during weathering in organic-rich layers. Local high TiO<sub>2</sub> anomalies, caused by preferential sorting and concentration, are found in most Pliocene sections, but they are absent in the Upper Pliocene and Lower Pleistocene Alpine-derived deposits. This change is probably due to a change in the energy of the fluvial system. Finally, (pyrite-) S contents drop (soderite-) Fe contents rise. Micromorphological observations indicate that the Pliocene pyrite was formed when freshwater deposits were flooded with seawater during short-term events. The decrease in S, and the increase in siderite-Fe, can be attributed to decreasing marine influence, as a result of the marine regression at the Pliocene-Pleistocene transition.
Topics
TNO Identifier
280415
ISSN
14373254
Source
International Journal of Earth Sciences, 89(1), pp. 154-169.
Pages
154-169
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