Post-Miocene landscape rejuvenation at the eastern end of the Alps

Abstract

In the debate on the causes of uplift and landscape evolution of the Alps, most studies focus on regions that were glaciated at some stage during the last 2 m.y. In these areas, it is difficult to separate glacial-driven versus tectonically driven rates of erosion. Here, we present 10 Be-derived erosion rates from unglaciated catchments in the Koralpe range at the eastern end of the Alps. This region features strong geomorphologic evidence for landscape transience with young valleys incised into a smooth relict landscape. Erosion rates average 49 ± 8 mm/k.y. for catchments located on the relict landscape and 137 ± 15 mm/k.y. for catchments in the incised landscape. From these data, we estimate the onset of incision at 4 ± 1 Ma, the surface uplift at 350 ± 90 m, and a total relative base-level fall of 540 ± 140 m. Our results are in close agreement with both the magnitude and the age of onset of uplift of the Styrian Basin and the northern Molasse Basin, as well as the incision rate of the Mur River into the Styrian karst. The inferred timing of the onset of uplift around 4 Ma relates to interpreted basin inversion in the Pannonian Basin. Since this uplift event appears to have involved both the Pannonian Basin and the entire eastern end of the Alpine mountain range, we suggest that it may have occurred in response to a deep-seated process in the lithosphere. As such, we argue for tectonic drivers for the post-Miocene uplift in the eastern Alps.

Response to Reviewers

“…7a). The highest rates measured in our study region are amongst Norton (2010) W mann (2007) Delunel (2010) Norton (2008) Norton (2011) This study Legrain (2015) Glotzbach (2014) Wittmann (2016) Savi ( Published erosion rates across the European Alps range from ∼ 40 to 2100 mm ky −1 , recorded by over 100 cosmogenic samples from nine studies that report both mean catchment slope and erosion rates. Published erosion rates were rescaled to a consistent sea level, high-latitude production rate of 4.0 atoms g −1 year −1 .…”

“…In unglaciated portions of our study area, previous geomorphic work has recognized two distinct landscape morphologies: a low-gradient, low-relief upland region and a higher-gradient, higher-relief region downstream of river knickpoints (Legrain et al, 2014;Robl et al, 2008). Millennial erosion rates from small basins within these regions correlate with slope and the degree of incision (Legrain et al, 2015). These two morphologies are interpreted as representing the relict and incising portions of a landscape responding to incision initiated at ∼ 4 Ma .…”

“…3b). Legrain et al (2015) in this same region show little systematic variation in slope with elevation (small open circles). Instead of reflecting the broader regional signal, mean slopes of these smaller basins are likely controlled by their position with respect to river knickpoints and the proportion of the catchment that is actively incising.…”

“…www.earth-surf-dynam.net/4/895/2016/ across the Alps to gain a regional picture of Holocene erosion. These rates, published in nine different prior studies (Delunel et al, 2010;Glotzbach et al, 2013;Legrain et al, 2015;Norton et al, 2008Norton et al, , 2010bNorton et al, , 2011Savi et al, 2014;Wittmann et al, 2007Wittmann et al, , 2016, were derived assuming different sea level, high-latitude (SLHL) production rates. To aid comparison of rates across disparate studies, we recalculate all compiled rates using a consistent SLHL production rate of 4.0 atoms g −1 yr −1 , regardless of original scaling factors.…”

Evaluating process domains in small arid granitic watersheds: Case study of Pima Wash, South Mountains, Sonoran Desert, USA

“…These rates, surprisingly (Gudmundsdottir et al, 2013;Legrain et al, 2015), do not relate to the distribution of knickpoints and major knickzones along Pima Wash (Fig. 12).…”