Miocene high elevation in the Central Alps

Abstract

Abstract. Reconstructing Oligocene–Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps remain scarce. Here we present stable and clumped isotope measurements to provide a new paleoelevation estimate for the mid-Miocene (∼14.5 Ma) European Central Alps. We apply stable isotope δ–δ paleoaltimetry to near-sea-level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30±5 ∘C) yield a near-sea-level precipitation δ18Ow value of -5.8±1.2 ‰ and, in conjunction with the high-Alpine phyllosilicate δD value of -14.6±0.3 ‰, suggest that the region surrounding the Simplon Fault Zone attained surface elevations of >4000 m no later than the mid-Miocene. Our near-sea-level δ18Ow estimate is supported by paleoclimate (iGCM ECHAM5-wiso) modeled δ18O values, which vary between −4.2 ‰ and −7.6 ‰ for the Northern Alpine Foreland Basin.

Slab Load Controls Beneath the Alps on the Source-to-Sink Sedimentary Pathways in the Molasse Basin

“…Based on their conclusion we thus infer that surface loading in the Alps was not the primary driving mechanism for the deflection of the foreland plate. Admittedly, a recent research contribution documented that the Alps reached a high topography during Miocene times [115] particularly in the hangingwall area of the Simplon fault (Figure 2). However, these high elevations were possibly local in nature [115] and could have reflected a transient state in the rearrangement of the Alpine drainage network, which started at c. 20 Ma [116][117][118].…”

“…Admittedly, a recent research contribution documented that the Alps reached a high topography during Miocene times [115] particularly in the hangingwall area of the Simplon fault (Figure 2). However, these high elevations were possibly local in nature [115] and could have reflected a transient state in the rearrangement of the Alpine drainage network, which started at c. 20 Ma [116][117][118]. In addition, at the same time, tectonic exhumation in the Lepontine area through slip along the Simplon fault (Figure 2) reached a peak shortly after 20 Ma [119], which would correspond to a phase of surface unloading in the orogen.…”

Middle Miocene Climate and Stable Oxygen Isotopes in Europe Based on Numerical Modeling

“…We reduce the elevation in the area covering the Alps and the Alpine forelands to 250 m elevation (Mio_278_noAlps, Mio_450_noAlps; Figure 1d) and increase the elevation to twice the reconstructed height (Mio_278_plusAlps, Mio_450_plusAlps; Figure 1e) compared to the original paleogeographic reconstruction of Herold et al. (2011) (used in Mio_278 and Mio_450 experiments), which reflects recent hypotheses of very high Alpine elevations in the Middle Miocene (Krsnik et al., 2021). We also tested the influence of a marine transgression and regression within Europe on regional climate and stable water isotopes.…”

“…Surface uplift of the Alps has previously been suggested to influence European climate (Botsyun et al., 2020; Campani et al., 2012; Krsnik et al., 2021; Boateng et al., 2022), but detailed time‐specific studies quantifying the magnitude of spatial and temporal variations and dynamics of regional climate change are still lacking. Moreover, the timing and rate of the surface uplift of the Alps is still controversial and ranges from reconstructed elevations of 1,900 ± 1,000 m (Schlunegger & Kissling, 2015) to elevations >4,000 m (Jäger & Hantke, 1984; Krsnik et al., 2021; Sharp, 2005). Thus, in order to reconstruct past climate in Europe, the elevation history of the Alps plays a key role.…”

“…The Late Cretaceous to Paleogene closure of the Alpine Tethys, the collision between the Adriatic and the European continental plates (Handy et al., 2010; Schmid et al., 1996; Stampfli et al., 1998) and subsequent post‐collisional convergence (e.g., Schmid et al., 1996) ultimately resulted in the surface uplift of the Alps. However, the timing and rate of this uplift is still controversial, with Miocene stable‐isotope‐based paleoelevation estimates ranging from mean elevations of 1,900 ± 1,000 m (Schlunegger & Kissling, 2015) and 2,300 ± 650 m (Kocsis et al., 2007) to 2,850 + 800/‐600 m (Campani et al., 2012), and >4,000 m (Krsnik et al., 2021; Sharp, 2005). Based on combined evidence from sediment budget curves, thermochronology, and sediment facies, the maximum elevation of the Western and central Alps has been estimated at 2,500–3,000 m for the middle Miocene (Kuhlemann, 2007).…”