SEDIMENT-PETROLOGIC CHARACTERISTICS OF SAALIAN AND WEICHSELIAN DEPOSITS IN THE HUMMLING REGION, NW GERMANY

In the lowlands of northwest Germany, Saalian (fluvio-)glacial plateau s and ice-pushed hills are surrounded by flat and low-lying terrain co nsisting of Weichselian fluvial to aeolian sands. The present work ref ers to the Ems-Hase fluvial basin and the adjacent part of the fluviog lacial Hummling plateau. On the basis of heavy-mineral analyses and ot her data it was found that: (i) The Weichselian deposits are significa ntly richer in garnet and alterite than the Saalian meltwater sands wh ich flank and underlie them in the Ems-Hase fluvial basin. It is thoug ht that Weichselian fluvial deposition was preceded by a period of ero sion related to the low sea level of the last ice age. During that pha se, the ancient riversystem extended its course in upstream direction and cut down into the headwater portion of its drainage basin. As a re sult, the subsequent infilling of the valleys was primarily by materia l derived from pre-Cenozoic rocks with the share of the Saalian substr ate being subordinate only. (ii) There is no significant difference in unstable-species content between fluvial and aeolian sands but for th e occurrence of traces of glaucophane only in the second type. The lat ter feature suggests that, during the Late Weichselian Pleniglacial, d eflation from the then dry part of the North Sea floor contributed to the deposition of the windborne coversands in the study area. Yet, the effect of the long-distance aeolian transport must have been slight o nly, and the buildup of the coversands resulted mainly from the local reworking by wind of the fluvial-sand substrate. (iii) Mineralogically , there is a distinct contrast between the fluvial sands from the nort hern part and those from the southern part of the study area. The pert inent heavy-mineral spectra, supplemented with previously published an alyses, reveal downstream trends in the composition of the Weichselian fluvial sand. These trends reflect changes in the sediment supply fro m Cretaceous and older rocks in the south to thick Cenozoic beds in th e north. The northern strata include shallow marine deposits of Tertia ry and Pleistocene (mainly Holsteinian) age and material laid down by the Late Tertiary to Elsterian north German riversystem.