Abstract
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.
Highlights
Intracontinental endorheic basins occupy ∼ 20% of the Earth’s land surface
We report new chronological constraints obtained with various cosmogenic nuclide techniques: exposure depth profiles, simple burial and P-PINI, which is an adaptation of the isochron burial method
A unified fluvial terrace chronology and mapping have been produced for the Ebro Basin
Summary
Intracontinental endorheic basins (or closed basins) occupy ∼ 20% of the Earth’s land surface They develop mostly in response to the tectonic uplift of surrounding ranges, generally under arid climatic conditions Sobel et al, 2003; García-Castellanos et al, 2003) and are infilled by lowerodible sedimentary rocks They represent key elements of source-to-sink systems as they preserve eroded products from surrounding catchments and large areas, as for the Tibetan Plateau and Tarim basin (Sobel et al, 2003; Han et al, 2019) or the Altiplano (Fornari et al, 2001; Sobel et al, 2003). Despite the development of analogical and numerical modelling tools, processes by which the river network grows and propagates into a captured endorheic basin remain unclear
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