Post-tectonic landscape evolution in NE Iberia using staircase terraces: combined effects of uplift and climate.
Lewis, C. J., Sancho, C., McDonald, E.V., Peña-Monné, J.L., Pueyo, E.L., Rhodes, E., Calle, M., Soto, R., 2017. Post-tectonic landscape evolution in NE Iberia using staircase terraces: combined effects of uplift and climate. Geomorphology, 292, 85-103. http://dx.doi.org/10.1016/j.geomorph.2017.04.037
River incision into bedrock resulting from the combined effects of tectonic uplift and climate governs long-term regional landscape evolution. We determined spatial and temporal patterns of post-orogenic stream incision from a sequence of well-preserved staircase terraces developed over the last 1 Ma in the Central Pyrenees and its southern foreland Ebro basin (NE Spain). Extensive remnants of ten vertically separated terraces (Qt1 to Qt10, from oldest to youngest) were mapped along 170 km of the Cinca River valley, transverse to the Pyrenean mountain belt. Multiple outcrops appear in the upper reach of the valley (Ainsa sector, 50 km from headwaters) as well as in the lower reach (Albalate sector, 125 km from headwaters). Fluvial incision into bedrock was calculated using (i) differentially corrected GPS measurements of the altitude of straths and (ii) numerical dating of alluvial sediments from the lower terraces (Qt5 to Qt9) by Optically Stimulated Luminescence, previously reported by Lewis et al. (2009), and supplemented with new dates for the upper terraces (Qt1, Qt2 and Qt3) based on paleomagnetism and supported by soil development. Considering altitude differences and the elapsed time between successive well preserved terrace couples (Qt3–Qt7, Qt7–Qt9 and Qt9-Active channel), mean bedrock incision rates ranged from 0.76 to 0.38 m ka−1, at the upper reach of the valley (Ainsa section), and from 0.61 to 0.20 m ka−1, at the lower reach (Albalate section). River incision along the valley produced vertically separated, near-parallel longitudinal terrace profiles evidencing a rapid near-uniform regional uplift as response to (i) the tectonic lithospheric thickening in NE Iberia and (ii) the erosional download rebound related to the Ebro basin exorheism. Moreover, a subtle upstream divergence of strath profiles may have been a consequence of an increase in uplift rate toward the head of the valley. Additionally, incision rates changed over time as indicate results from the lower reach (Albalate section); the maximum rate was 1.48 m ka−1 between Qt7 (61 ka) and Qt8 (47 ka), and the minimum rate was 0.11 m ka−1 between Qt3 (401 ka) and Qt5 (178 ka). The highest incision rates were produced after the Marine Isotope Stage 4 most likely in response to (i) an increased snowmelt discharge during the subsequent deglaciation related to the last maximum advance of glaciers in the southern Pyrenees, and (ii) a limited width of the valley after Qt7 formation, resulting from the deactivation of the westward river migration. Therefore, incision rates over the last 1 Ma in the Cinca River valley were basically controlled by near-uniform bedrock uplift, in the context of climate variability. The results reported in this study represent significant data on fluvial incision in NE Iberia, and provide an assessment of the regional post-tectonic landscape evolution.