Chemical versus mechanical denudation in meta-clastic and carbonate bedrock catchments on Crete, Greece, and mechanisms for steep and high carbonate topography

Abstract

On Crete — as is common elsewhere in the Mediterranean — carbonate massifs form high mountain ranges whereas topography is lower in areas with meta-clastic rocks. This observation suggests that differences in denudational processes between carbonate-rich rocks and quartzofeldspathic units impart a fundamental control on landscape evolution. Here we present new cosmogenic basin-average denudation rate measurements from both 10Be and 36Cl in meta-clastic and carbonate bedrock catchments, respectively, to assess relationships between denudation rates, processes, and topographic form. We compare total denudation rates to dissolution rates calculated from 49 new and previously published water samples. Basin-average denudation rates of meta-clastic and carbonate catchments are similar, with mean values of ~ 0.10 mm/a and ~ 0.13 mm/a, respectively. The contribution of dissolution to total denudation rate was < 10% in the one measured meta-clastic catchment, and ~ 40% for carbonate catchments (~ 0.05 mm/a), suggesting the dominance of physical over chemical weathering at the catchment scale in both rock types. Water mass-balance calculations for three carbonate catchments suggests 40-90% of surface runoff is lost to groundwater. To explore the impact of dissolution and infiltration to groundwater on relief, we develop a numerical model for carbonate denudation. We find that dissolution modifies the river profile channel steepness, and infiltration changes the fluvial response time to external forcing. Furthermore, we show that infiltration of surface runoff to groundwater in karst regions is an efficient way to steepen topography and generate the dramatic relief in carbonates observed throughout Crete and the Mediterranean.

Reassessing Eastern Mediterranean Tectonics and Earthquake Hazard From the 365 CE Earthquake

“…Uplift of sedimentary basins also indicates minimum Neogene uplift rates of ∼0.2 mm/a (Meulenkamp et al., 1994), while Pleistocene paleoshorelines indicate uplift of 0.5–1 mm/a for the south and west coast and lower, non‐uplift, or subsidence in the east and north of the island (Gallen et al., 2014; Ott, Gallen, Wegmann, et al., 2019; Robertson et al., 2019). Rock uplift is mostly driven by tectonics since erosion rates are only ∼0.1 mm/a, indicating that the component of isostatic adjustment due to erosional unloading is likely negligible (Ott, Gallen, Caves Rugenstein, et al., 2019). The uplift of Pleistocene paleoshorelines is interpreted to be related to a regional‐scale uplift signal augmented by local uplift in the footwalls of large normal fault systems (Gallen et al., 2014; Ott, Gallen, Wegmann, et al., 2019; Robertson et al., 2019).…”

How Lithology Impacts Global Topography, Vegetation, and Animal Biodiversity: A Global‐Scale Analysis of Mountainous Regions

“…This could be related to a bias in the exposure of different lithologies in certain tectonic regions; metamorphic rocks are commonly exposed in the interior of mountain ranges with typically high uplift rates, whereas carbonates are often removed earlier during orogeny. This could suggest higher‐average erosional resistance of carbonate rocks compared to metamorphic rocks, or it may indicate that carbonate mountains are steeper due to higher rates of surface water infiltration, which can reduce discharge and stream power and therefore cause channels to steepen (Ott et al, 2019). Overall, these topographically inferred differences in erodibility are consistent with the findings from previous local‐ and regional‐scale studies (Gabet, 2020a; Garcia‐Castellanos & O'Connor, 2018; Harel et al, 2016; Kühni & Pfiffner, 2001).…”

Cosmogenic nuclide weathering biases: corrections and potential for denudation and weathering rate measurements

“…Yet, carbonate regions are interesting because their topography is highly sensitive to the interplay between tectonics and climate, owing to their greater chemical reactivity relative to more silica-rich rocks, and they exert a significant influence on flora and fauna distributions (Ott, 2020). The number of studies measuring 36 Cl on calcite in carbonate catchments for denudation rates is increasing (Avni et al, 2018;Ott et al, 2019;Ryb et al, 2014a, b;Thomas et al, 2017), and therefore the effect of weathering on soluble target mineral CRN concentrations needs to be assessed. This effort is worthwhile because it will allow for the extension of tectonic geomorphology and centennial-tomillennial timescale denudation rate studies in a significant portion of the globe that has been traditionally understudied.…”

“…Hence, caution needs to be observed when combining the two methods. Climate models can be used to check if climatic conditions, such as precipitation and temperature, have changed significantly throughout the cosmogenic nuclide averaging window, and can help to assess whether water chemistry-derived weathering rates could be biased (Ott et al, 2019).…”

“…The same holds true for measurements of soluble target minerals such as 36 Cl in regolith and alluvial sediments. Most studies measure 36 Cl on bedrock exposures (Avni et al, 2018;Godard et al, 2016;Matsushi et al, 2010;Stone et al, 1994;Thomas et al, 2018;Xu et al, 2013) and only a few in the regolith or in alluvial sediments (Ott et al, 2019;Ryb et al, 2014b, a;Thomas et al, 2017). Studying limestone regions and other areas with soluble minerals is of particular interest because the high weatherability makes them more susceptible to the interplay of tectonics and climate (Ott et al, 2019;Simms, 2004).…”