Seven steps towards a terrace model of the Middle Rhine Valley

Climate, tectonic and fluvial processes are the forces and river-terraces the product. Between Bingen and Bonn, the Rhine crosses the uplifted Rhenish slate mountains and is supported by Graben-building processes. We could find 28 separate sediment-bodies of the Rhine with bedrock surfaces by drilling. We were using the palaeomagnetic dating of sediments by Scheidt et al. (2015) of two drillings in the Rhine-Graben to force an entry into the palaeomagnetic time-model.From 2006 to 2013 a geomorphological project between Bad Kreuznach and Bingen was revived, that was started in the 1980-ies by Görg and Preuß. It was enlarged to Boppard (Preuß et al. 2015, 2019; Preuß 2017).From the data a Downstream Correlation Diagram (see Fig. 1) for more than 60 river-kilometers was created, in which 726 drillings are summarized. It was used to construct a composite sequence (Collected Sequence) of the recorded 28 sediment bodies resting on bedrock surfaces (see Fig. 1 & 2). The Collected Sequence was inserted in the Quaternary temperature curve derived from pollen by Zagwijn (1985, 1998), into the cold intervals with temperatures of the warmest month below 10°C. The ages of the intervals with maximum cooling were taken from the MIS (Cohen & Gibbard, 2011). This is the Chrono-Sequence (1) with MIS time-model. The Chrono-Sequence (1), in their chronological order, was transferred by mathematical calculation into two paleomagnetically dated drill cores from Heidelberg (307 m) and Viernheim (221 m). (For the cores: Gabriel, Ellwanger, Hoselmann & Weidenfeller, (2008), for paleomagnetic dating: Scheidt, Hambach & Rolf (2015). In the underlying and overlying stratum of the transferred points, the lower boundary (coarse sediments) and upper boundary (fine sediments, organic material, paleosols) were identified in photographs of the cores. Their ages were calculated using the paleomagnetic depth-functions of the respective cores and subsequently combined into mean values of both cores (red column in Fig. 2). This is Chrono-Sequence (2) with a palaeomagnetic time-model. In Fig. 3, Chrono-Sequence (1) was plotted on the x-axis (time) and the elevation of bedrock-surfaces on the y-axis. Linear equations were calculated (see Fig 3). The gradients amount to 52 m/Ma (upper) and 66 m/Ma (lower). The lower curve segment corresponds to the uplift rate (= rate of incision). In the upper curve segment, the uplift rate was reduced by subsidence of about 14 m/Ma. According to its assumed age, the bedrock surface of the oldest terrace (tRh1.1) would have been lowered from 311 m a. s. l. by 37 m to its present level at 274 m a. s. l. To the initial elevation of 311 m a. s. l., the present-day thalweg of the Rhine was inserted into the model as a third-order polynomial line (see Fig. 6 (=5/2). The terrace model was evaluated using two independent datasets from the Lower Middle Rhine Valley (Bibus (1980); Hoselmann (1994)) (see Fig. 7). The latest (“paper”-)model fits well with the real situations of the rock-bases.