Characteristics of the sediments hosting the Thracian settlement near the town of Letnitsa

The Thracian settlement near the town of Letnitsa is situated on the left fluvial terrace of the Osam River. Hosting sediments are determined as sandy clayey silts, limy in various degrees. Deposits from the western and central parts are compared and both show similar mineralogical composition. These from the central parts contain more fine silt and clayey fraction, which supposes that these parts could have been flooded by the river.

Integrated geological and geophysical study of the Tagil river valley morphology in its middle course

Relevance. Integrated geological and geophysical studies of a bridge in the Makhnevo village area are considered in the frame of the Urals eastern slope geology. Research objective is to study the lithology of the underlying part of the valley floor, determine soil physical and mechanical characteristics, and study a complex of fluvial terraces. Results. Relief elevations across the river valley have been studied, and four main fluvial terrace levels typical of the Urals eastern slope have been identified. An unstable section of the streambed with a canyonshaped valley above the neotectonic unwarping zone has been identified. The geological section of the river’s floodplain and streambed were studied based on geological and geophysical data. A change in the physical properties of glauconite sandstones and clays of Paleogene age in the recent underlying part of the river valley has been established. Layers of sand and glauconite sandstone that can be developed have been found at the new bridge site near the existing sand and gravel deposit. Conclusions. A complex of terraces of the Tagil river valley in its middle course is typical for the Urals eastern slope. The paleovalley is cut into a Paleogene glauconite sandstone layer. In the underlying part of the valley floor, changes in sandstones and clays physical properties have been recorded, and the presence of hypogene minerals was revealed. These are the signs of possible neotectonic processes in the series of the Cenozoic and Quaternary deposits.

Impacts of climatic changes on fluvial sediment fluxes in north western Europe: The Middle and Late Pleistocene Meuse river system

<p>Climate change and tectonics can generate signals in a source-to-sink system in the form of changing sediment supply. The study of the propagation of this signal through the system might elucidate how different source-to-sink systems respond to a given perturbation, for instance, the Early to Middle-Pleistocene climate transition. Knowledge on the temporal and spatial responses to such perturbations in a catchment is still limited. Previous studies, with the support of landscape evolution models, demonstrate that several thousands of years might be needed for an extreme-climate-transition-induced signal to propagate through a river catchment (an example of source-to-sink system). The present work aims to contribute to the understanding of how such systems might react when submitted to rapid climate change events by studying the Meuse river catchment. The primary goals are to characterize and quantify the main controls on sediment flux of this fluvial system as a response to the Early to Middle Pleistocene climate transition as well as to assess how climate signals propagated through this source-to-sink system during the last four glacial-interglacial cycles, starting around 450.000 years ago.</p><p>To achieve our goals, three main tasks are proposed. In the first stage of this project, with the support of high-resolution DEM and high-resolution sedimentary cores, the different Meuse fluvial terrace maps are updated. For that, a new cross-border fluvial terrace map between the Netherlands, Belgium and Germany is produced. Characterization and mapping of sediment grain-size and provenance is also carried out. The new Meuse terrace map will guide the sampling campaign of Meuse terrace sediments. The samples will be used for cosmogenic-nuclide age-dating of the sampled terraces. Two dating methods will be used depending on how deeply buried and well-preserved the terraces are: burial isochrone (<sup>26</sup>Al/<sup>10</sup>Be) where sediment cover thickness is greater than 4,5 – 5 m, and depth profile (<sup>10</sup>Be) when the terrace surface is well preserved. These methods will be applied to specific terrace steps, in order to date those around the Mid-Pleistocene transition. Beryllium-10 age-dating will possibly also be applied to specific sedimentary levels (cores, outcrops), in order to infer averaged denudation rates and, consequently, the sediment fluxes, during the investigated climatic cycles. During the latter part of the project, all the data will be set in a temporal framework using the cosmogenic dating results and existing age controls.</p>

Steady-state valley width revealed by alluvial terrace sequences

<div> <p>Lateral erosion by rivers drives valley widening and controls valley-bottom width. The current lack of a comprehensive valley-widening model complicates the reproduction of the full range of valley shapes that we find in nature as well as the prediction of valley evolution under different climatic and tectonic boundary conditions. Field data have shown that water discharge and valley wall lithology control lateral erosion rates. However, order-of magnitude variations in valley width formed in uniform lithology and under similar discharge conditions suggest additional, so far unquantified controls on valley width.</p> <p>Fluvial terrace sequences offer an opportunity to study valley-width evolution under comparable discharge and lithologic conditions. Alluvial terraces are composed of flat surfaces and steep walls carved into previously deposited river sediments. They form where a river alternates between phases of lateral valley widening by lateral planation and vertical incision and terrace formation. In order to form an entire terrace staircase, such alternations have to repeat and many Quaternary terrace staircases are interpreted to be driven by cyclic climate changes. Because Quaternary climate cycles have had comparable amplitudes and durations, individual surfaces in paired climate-driven terrace sequences preserve the widths of valleys that have formed under similar discharge conditions, lithologies and over comparable time-intervals. We use a global compilation of 16 climatically formed alluvial terrace sequences to investigate controls on valley width.</p> <p>Between 90 and 99% of the variance in valley width can be explained by a linear relationship of the width with the total valley depth. Hence, at least one of the missing controls on valley width must scale (close to) linearly with valley depth. Ruling-out a preservation bias and a number of parameters that are unrelated to valley depth, we propose a model that relates valley width to a competition between the sediment supplied from valley walls and the river’s capacity to rework sediment, such that a lateral sediment-flux steady state is reached. According to our model the valley width-depth relationship is controlled by (1) the horizontal hillslope-erosion rate, (2) the lateral sediment-transport capacity of the river and (3) the valley-width which forms in the absence of lateral-sediment input. Hence, the model allows to predict valley width when all of the above parameters are quantified in the field. Alternatively, any of the three parameters can be predicted when valley width is measured. The new model is able to reproduce the first-order trend observed in terrace-derived valley widths and it can explain the evolution of paired terrace sequences, which has so far been a major challenge.</p> </div>

Late Pliocene-Pleistocene incision in the Ebro Basin (North Spain)

The Ebro Basin constitutes the central part of the southern foreland of the Pyrenees. It was endorheic during the Cenozoic and accumulated sediments. By the end of the Miocene, erosion and river incision reconnected the basin to the Mediterranean Sea, establishing a post-opening drainage network. Those rivers left terraces that we study in this work. We first synthesize previous works on river terraces that are widely dispersed in the basin. We provide new age constraints, up to 3 Ma, obtained thanks to cosmogenic nuclides using both profile and burial methods. We derive a unified fluvial terrace chronology and a homogenized map of the highest terraces over the entire Ebro Basin. The dated terraces labeled A, B, C, D, and E are dated to 2.8 ± 0.7 Ma, 1.15 ± 0.15 Ma, 850 ± 70 ka, 650 ± 130 ka, and 400 ± 120 ka, respectively. The chronology proposed here is similar to other sequences of river terraces dated in the Iberian Peninsula, around the Pyrenees, and elsewhere in Europe. The oldest terraces (A, B, C) are extensive, indicating they form a mobile fluvial network while from D to present, the network was stable and entrenched in 100 to 200 m-deep valleys. The transition from mobile to fixed fluvial network is likely to have occurred during the Middle Pleistocene Transition (MPT, between 0.7 and 1.3 Ma), when long-period/high-intensity climate fluctuations were established in Europe. We estimate that between 2.8–1.15 Ma and present, the incision rates have tripled.