Das Holstein-Interglazial von Tönisberg im Rahmen des Niederrheinischen Pleistozäns
Abstract. Near the village of Tönisberg (Lower Rhine district) a new shaft penetrated the Schaephuysen hills, which is an upsqueezed terminal moraine of the Saale glaciation. It turned out that the Pleistocene amounts to almost 180 feet; from base to top it consists of Middle Middle-Terrace (Mittlere Mittelterrasse), Kempen-Krefeld-Beds (Holstein-Interglacial), and Lower Middle-Terrace (Untere Mittelterrasse). Pleistocene rests on marine sands of Upper Oligocene age. Within the sediments of the Middle Middle-Terrace the occurence of reworked fossils seems to be a significant character. The assemblage is composed of three major constituents: marine faunal relicts of Upper Oligocene age as well as Tertiary and Quaternary plant remains. The reworked fossils and additional features made it possible to trace the Middle Middle-Terrace farther to the north. It could be concluded that the "Moers-Beds" („Moerser Schichten") ought to be placed in the early Holstein-Interglacial. There is a gradual change from the deposits of the Middle Middle-Terrace to the interglacial sediments. Therefore the Middle Middle-Terrace can be regarded as a transitional layer between the Elster-Glacial and the Holstein-Interglacial. The great thickness of interglacial deposits is due to the upsqueezing effects of the Saale ice sheet. The interglacial sediments (sand, chalky gyttja, argillaceous peat) yielded many fossils of which the molluscs, the ostracods, and the macroscopic plant remains (mainly fruits and seeds) were studied in detail. Furthermore palynological investigations were undertaken. The samples from some new boreholes allowed comparative investigations with the „Krefeld-Beds" of the isolated hills west of Moers (Inselberge) and the „Kempen-Beds" which are distributed below the city of Krefeld. As redards fossils and stratigraphical sequence several similarities could be detected. Therefore the „Krefeld-Beds" of the Schaephuysen hills and those of Moers are regarded as time equivalents of the „Kempen-Beds". The term Kempen-Krefeld-Beds was chosen for these Holstein-Interglacial deposits in the Lower Rhine district. The description of the prevailing climatic conditions during the deposition of the Holstein-Interglacial beds in the Lower Rhine district is based on the nature of the fossil content. The recent distribution of the identified plant species within the Lower Rhine district was noted by means of publications on local plant communities covering more than a century. According to these data the climate of the Holstein-Interglacial essentially corresponded to that of the present day. A greater rainfall and slightly higher temperatures allowed, however, some plant species to thrive which nowadays do not occur in this area. The sequence and structure of the Pleistocene, exposed in the shaft of Tönisberg, proves the opinions of K. N. Thome (1958, 195,9), regarding the origin of the upsqueezed terminal moraines in the Lower Rhine district, to be right. This is further underlined by observations which could be made during shaft sinking, as a freezing technique was applied. In contrast to the opinions of K. N. Thome reasons are advanced to show that, within the area of the Moers ice lobe (Moerser Lobus), the Kamp ridge (Kamper Staffel) was the first to be squeezed up and that the squeezing up of the Neuss ridge (Neußer Staffel) was the later event. Also in connection with this the stratigraphical position of the Krefeld Middle-Terrace (Krefelder Mittelterrasse) within the Drenthe stage (Drenthe-Stadium) of the Saale-Glacial appears to be most probable. On figure 15 the stratigraphical sequence of middle and late Pleistocene deposits of the Lower Rhine district is listed, according to the results indicated above.