LOESSFEST'09 | Aug. 31st – Sept. 3rd, 2009 |Novi Sad-Serbia
Loess Along the River Rhine
Manfred Frechen1
1Leibniz Institute for Applied Geophysics, Section S3: Geochronology and Isotope Hydrology, Stilleweg 2, 30655 Hannover, Germany
Loess-palaeosol sequences have been intensively studied along the river Rhine over the past century. These deposits display a wide variety of climate proxies for periglacial periods and, therefore, supply some major clues concerning the climate and environmental changes on land. Middle Pleistocene loess deposits are exposed in the Lower Rhine area (e.g. Rheindahlen section), the Middle Rhine area (e.g. Kärlich section) and in the Upper Rhine area (e.g. Kaiserstuhl). The oldest loess from the Kärlich section was most likely deposited between 600 and 650 ka BP. However, the Middle Pleistocene loess record is difficult to investigate because reliable dating results are rare.
The onset of the Upper Pleistocene loess deposition is related to the first cold stadial following the last interglacial optimum at c. 115 ka. In northern Central Europe, increased aridity, dust storms and a decline of thermophilous trees at the time of glacial inception were typical for the post-Eemian period. Several cycles of slope erosion and sediment accumulation also occurred, as well as soil forming processes. At the Tönchesberg section in the Eifel area, four A horizons are intercalated; the lowermost chernozem-like palaeosol correlates most likely to the Early Weichselian (Marine Isotope Stage (MIS) 5c), the uppermost one, a chernozemlike palaeosol with strong clay illuviation, correlates to MIS 5a. Loess beds, up to 20 cm thick, accumulated at the early stage of the Middle Pleniglacial and correlate to the boundary between MIS 5a and MIS 4, in the Eifel. This loess most likely correlates to a Europe-wide dust storm, which occurred at that time and which has many small frost cracks and ice-wedge pseudomorphs indicative of a cold and stadial environment following interstadial conditions. Dust accumulation was followed by a period of erosion, as documented by the presence of a hiatus and/or pellet sands in many Central European loess regions. In the Rhine area, the pedosediments underwent at least two periods of soil formation, as documented by two weak A horizons. In early MIS 3, weak soil formations also occurred in the Middle Rhine area, as evidenced by the presence of A horizons. At the Remagen-Schwalbenberg section near the confluence of the rivers Rhine and Ahr, MIS 3 is characterized by the presence of loess and reworked loess intercalated by six weak soils within the time period ranging from 45 to 25 ka BP. The high number of palaeosols was most likely due to increased slope dynamics. The upper part of the Middle Pleniglacial is characterised by loess-like deposits with two intercalated weak brown soils indicating interstadial intervals, a correlation with the Hengelo (39 – 36 ka) and the Denekamp (32 – 28 ka) interstadials of the Middle Weichselian is likely. During MIS 2, two main periods of loess accumulation occurred between 24 and 20 ka BP and between 17 and 13 ka.
High mass accumulation rates of dust most likely occurred in the transition between the Pleniglacial and the Late Glacial periods. Early summer floods were able to transport a substantial amount of fluvial sediments; whereas the remainder of the year was characterized by aridity. The resulting dry surfaces and flood plains facilitated extensive deflation of silt- and sand-sized material along the river Rhine.