Zur stratigraphischen Gliederung der jungpleistozänen Sedimente im nördlichen Oberrheintalgraben

Abstract. In the Quarternary the northern Upper Rhine rift valley was filled with the fluviatile deposits (pebbles and sands) of the rivers Rhine, Main and Neckar. During the Würm ice age and in the Holocene the surface of these fluviatile deposits was covered with eolian sand plains and dune fields of varying thickness and extension. The most complete stratigraphie sequence of the eolian cover was found in the Lower Main district. In this region the eolian deposits cover, over large areas, the remnants of a Riß-Würm interglacial involution layer at the surface of the Old-to Middle Pleistocene Kelsterbach terrace. Based on the stratigraphie sequence of the dunes in the Main region and by comparison with the loess stratigraphy of Hesse it was possible to reconstruct the following chronology: In early Würm intensive soil erosion and solifluction perdominated on the terrace surfaces. A basal alternation of loamy and sandy layers presumably at the end of this cool-wet climatic epoch originated. These basal layers are limited upward by an involution layer of slight thickness, which is possibly equal to the fossil soil Würm I/II of the loess sequence. In the Maddle Würm this horizon was covered by dune-sands of great thickness. The dunes may be correlated with Würm III loess. A rare tundra gley (Naßfleckenboden) is found in the basal parts of the dunes in places. During the last Glacial the dune-sands weathered to a sandy grey-brown podsolic soil (Sand-Parabraunerde) comparable to the grey-brown soil (Parabraunerde) found on loess. An absolute age marker is given by a pumice layer (Laacher See eruption) intercalated in Middle Alleröd. The Laacher See pumice is mixed with drift sand and probably weathered in Upper Alleröd to a brown earth (Braunerde). In the Younger Dryas epoch the pumice brown earth was covered by drift sand again. In the Holocene this drift sand weathered to brown earth of great thickness, stratifically comparable to the chernosem in Rhinehesse and the „Lockerbraun-erden" in the mountainous regions of Hesse. It has been demonstrated by palaeolithic findings and the C14 method that this intensive pedogenesis was interrupted in the 6-7th century B. C. by new sand drift. This youngest drift sand is weathered to a lesser extent. A special section deals with the genesis of the clay-iron bands (sandy grey-brown podsolic soil). The enrichment in bands is the result of leaching and migration by chemical and mechanical processes extending through the whole eolian complex.