EGU22-6474
https://doi.org/10.5194/egusphere-egu22-6474
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Punctuated river incision: implications for deriving climate signals, river incision and rock uplift rates from Quaternary strath terraces

Jesse Zondervan1,2, Martin Stokes1, Anne Mather1, Matt Telfer1, Sarah Boulton1, Jan-Pieter Buylaert3, Mayank Jain3, Andrew Murray4, and Mhamed Belfoul5
Jesse Zondervan et al.
  • 1School of Geography, Earth & Environmental Sciences, University of Plymouth, Plymouth, United Kingdom
  • 2Now at: Department of Earth Sciences, University of Oxford, Oxford, United Kingdom
  • 3Department of Physics, Technical University of Denmark, Roskilde, Denmark
  • 4Nordic Laboratory for Luminescence Dating, Department of Geoscience, Aarhus University, Denmark
  • 5Structural Geology and Thematic Mapping Laboratory, Earth Sciences Department, Ibn Zohr University, Morocco

We demonstrate how assumptions about strath terrace formation affect the interpretation of climatic control on landscapes, calculation of incision and rock uplift rates, and recommend strategies for geochronological sampling and interpretation. An innovative approach to OSL dating terrace gravels allows us to produce a detailed ~200 kyr history of punctuated river incision and strath terrace formation spanning two stratigraphic landform levels in the High Atlas Mountains (NW Africa). Extensive preservation and exposure of strath-top gravels, within a post-orogenic setting unaffected by eustatic influences, enables the derivation of rates of base-level fall, integrated over periods of strath-top deposition, metastable equilibrium, and incision, that are consistent with independently constrained regional rock uplift rates. Combining a punctuated river incision model with our well-constrained terrace formation history allows us to demonstrate how assumptions concerning Quaternary river incision and deposition can lead to the problematic Sadler Effect, an apparent dependence of incision rates on measured time interval. Subsequently, we demonstrate that an approach to reinterpreting previously published data using the punctuated incision model, even when combined with limited terrace age data, results in more consistent and parsimonious conclusions about rates of river incision, rock uplift and base-level lowering across the mountain belt. Our recommendations for sampling strategies to constrain rock uplift rates require samples to be taken just above the strath surface, and in addition towards the top of the deposit for river incision rates. In a setting with punctuated river incision and strath terrace formation, both rock uplift and incision rates require burial dates, as exclusive use of abandonment ages will not yield constraints on accurate rates of rock uplift or incision. Furthermore, we find that only with multiple along-stream locations and multiple burial dates in each terrace deposit, could a reliable climatic signal be extracted; this signal would not have shown up in terrace abandonment ages such as those derived from cosmogenic exposure dates. The demonstrated effects of assumptions about strath terrace formation, and the recommended approaches for sampling and interpretation, have implications for those attempting to constrain palaeoclimatic, tectonic, and geomorphic histories from strath terrace records in regions exhibiting punctuated river incision.

How to cite: Zondervan, J., Stokes, M., Mather, A., Telfer, M., Boulton, S., Buylaert, J.-P., Jain, M., Murray, A., and Belfoul, M.: Punctuated river incision: implications for deriving climate signals, river incision and rock uplift rates from Quaternary strath terraces, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6474, https://doi.org/10.5194/egusphere-egu22-6474, 2022.