IAP2-22-406

Relict landscapes as archives of past climatic and tectonic conditions

‘Relict’ landscapes are low-relief, high elevation surfaces that are often interpreted as an archive of previously stable tectonic and/or climatic conditions. These landscapes are commonly recognised in mountain ranges that have been interpreted to be undergoing late-Cenozoic acceleration in tectonic uplift that means they are being rejuvenated by an erosional response (e.g., Clark et al., 2006). Relict topography (and the information it contains about past conditions) will eventually be lost through such erosion (e.g., Whittaker & Boulton, 2012).

These remnants of Earth’s geologic past have been identified across various landscapes on Earth. Several alternative mechanisms have been proposed for the formation of low relief, high elevation uplands, including emerging from dynamic reorganisation of drainage networks through divide migration and drainage capture (Yang et al., 2015; Whipple et al., 2017), or due to lateral advection of landscapes over mid-crustal, subsurface structural ramps (Eizenhöfer et al 2019). Yet the mechanisms of formation from the nature of the topography remains unclear. Building on these recent studies, the primary goals of this project are: (i) identifying the processes that can lead to low relief upland preservation, and identify topographic metrics to distinguish different mechanisms of formation; and (ii) deciphering their geomorphological record of past tectonic and climatic conditions across the globe. These goals will be achieved through state-of-the-art, coupled, process-based numerical models of geodynamics and landscape evolution and applied to case study areas across the Himalaya, Central Asia, and South Africa.

Locations have been identified where such ancient landscapes are presumably preserved, such as in Bhutan (e.g., Adams et al., 2016), Mongolia (e.g., Jolivet et al., 2007) or the Kaapvaal craton (e.g., Stanley et al., 2017) despite significant differences in their present-day climate and tectonic conditions. Across the Himalaya tectonic convergence is ongoing while the region is being influenced by the Monsoon (e.g., Bookhagen & Burbank, 2006). Mongolia witnessed reactivation of its Palaeozoic tectonic framework (e.g., Allen & Vincent, 1997) due to the India-Asia collision while aridification commenced since at least the Miocene (e.g., Miao et al., 2012). The topography of South Africa is driven by deeper-seated geodynamic processes (e.g., Cox, 1989) with more humid conditions during Late Cretaceous times (e.g., Braun et al., 2014). Understanding the mechanisms to create and preserve such relict landscapes and being able to reconstruct their geomorphological archive of Earth’s past is crucial to understand the interaction of physical processes within the Earth System and to unlock feedbacks between tectonics, climate, and topography. Such knowledge will help to understand spatial landscape responses and response times to changes due to external forcings, improving efforts in earthquake risk assessments and mitigating the consequences of climate change.

Over geologic time, fluvial erosion is the predominant driver of landscape decay. Fluvial erosion is often described through a stream-power relation (e.g., Whipple & Tucker, 1999) which quantifies changes in topography as a function of discharge, local relief, and substrate erodibility. In turn, discharge and local relief are governed by climatic and tectonic conditions. Hence, a favourable combination of these parameters is required to achieve the preservation of relict landscapes, which is often unknown. In active convergent mountain ranges advection of rock over mid-crustal, structural ramps may produce landscapes that have recorded past rock uplift (Eizenhöfer et al., 2019). Arid climatic conditions in the presence of tectonic activity may facilitate non-steady-state landscapes. Similarly, this might be the case for tectonically inactive regions where lithology determines the preservation potential (e.g., Peifer et al., 2021) or where drainage reorganisation has resulted in stranded landscapes due to drainage area loss (Whipple et al. 2017). A systematic understanding of landscape preservation under variable climatic, tectonic, and lithologic conditions is currently not available.

The primary objectives of this project are:
• Implement coupled numerical geodynamic and landscape evolution forward models to establish systematics that promote the emergence of relict landscapes.
• Automated extraction and interpretation of geomorphological metrics across climatically and tectonically distinct regions to establish a global database of relict landscapes.
• Model inversions to identify the range of climatic, geodynamic and tectonic parameters that shaped the three study regions.

Click on an image to expand

Image Captions

Fig. 1. Landscape response and emergence of ‘relict’ landscapes due to the lateral advection of rock over a mid-crustal, subsurface structural ramp (e.g., Himalaya) modified after Eizenhöfer et al. (2019).

Methodology

The project will integrate multidisciplinary empirical and modelling data in the fields of palaeo-climate, geomorphology, tectonics, and geodynamics to drive numerical landscape evolution models.

Topographic analyses of commonly available digital elevation models will map geomorphic metrics (river steepness, local relief, knickpoint locations, landscape transience) using the MATLAB software package TopoToolbox and/or LSDTopoTools. Automated algorithms will be developed to identify and characterise relict landscapes worldwide and for the three case study areas Mongolia, Southern Africa and the Himalaya.

Existing palaeo-climate models (e.g., Mutz & Ehlers, 2018) and proxy-data (e.g., Zachos et al., 2008) will be accessed to quantify climate change over geologic time in the study regions. Geodynamic scenarios will be explored from existing studies. The upper lithospheric tectonic evolution of the three regions will be reconstructed based on literature data.

Numerical landscape evolution forward models (FastScape) coupled to geodynamic models (ASPECT) will systematically explore conditions for the preservation of relict landscape with respect to climatic and tectonic parameters. Data obtained for the three case study regions will then inform model inversions to reconstruct climatic and tectonic conditions during and after the formation of relict landscapes.

Project Timeline

Year 1

The student will set up coupled numerical landscape evolution and geodynamic models to systematically explore conditions for the emergence of relict landscapes. High resolution numerical landscape evolution forward models will implement climatic, tectonic, and geodynamic input and evaluate the model output.

Year 2

The student will undertake literature work and geomorphic analyses across the three study regions informed by the numerical models. Remote geomorphological analyses of landscapes will be performed using LSDTopoTools and/or TopoToolbox software packages. The results of this analysis will be placed in relation to the climatic, tectonic, and geodynamic evolution of the study regions.

Year 3

The student will set up inversions of numerical landscape evolution models to reconstruct climatic/tectonic parameter space for the evolution of the three study regions. These will explore climatic, tectonic, and geodynamic conditions that led to the formation of the relict landscapes, and also extract the information archived in the relict landscapes prior to their formation.

Year 3.5

The student will finalise the results, write manuscripts for publications, and complete thesis.

Training
& Skills

The student will be trained by leading experts of geomorphology and tectonics to achieve a holistic understanding of System Earth. This training involves analyses of remote sensing data, as well as data in the fields of climate, tectonics, and geodynamics to reconstruct the mid- to long-term (kyr to Myr) evolution of landscapes. Such data analysis will expose the student to high-level programming environments (e.g., Python, MATLAB, C++, Fortran). Furthermore, the student will apply and develop further process-based numerical models in both forward and inverse modes in a high-performance cluster (HPC) environment. This also implies the statistical evaluation of a large number (>10000) of model runs and big (environmental) data analysis (e.g., misfit analysis, multivariate statistics, geospatial data analysis). Visits to worldwide leading institutions (GFZ Potsdam/Germany and CSDMS Boulder, Colorado / USA) supplement this training. The training also constitutes ‘soft’ skills: project management, scientific writing, grant acquisition, (oral and written) project reporting. These skills make the student highly competitive to a career in computationally driven Earth System science. Beyond academia the student will be able to analyse and manipulate large data sets, apply, and evolve process-based numerical models, make data-driven model predictions towards machine learning capabilities. Hence, the student will be highly employable in the fields of environmental consulting, hazard research, land management and software development.

References & further reading

Adams, B. A., Whipple, K. X., Hodges, K. V., & Heimsath, A. M. (2016). In situ development of high‐elevation, low‐relief landscapes via duplex deformation in the Eastern Himalayan hinterland, Bhutan. Journal of Geophysical Research: Earth Surface, 121(2), 294-319.
Allen, M. B., & Vincent, S. J. (1997). Fault reactivation in the Junggar region, northwest China: the role of basement structures during Mesozoic-Cenozoic compression. Journal of the Geological Society, 154(1), 151-155.
Bookhagen, B., & Burbank, D. W. (2006). Topography, relief, and TRMM‐derived rainfall variations along the Himalaya. Geophysical Research Letters, 33(8).
Braun, J., Guillocheau, F., Robin, C., Baby, G., & Jelsma, H. (2014). Rapid erosion of the Southern African Plateau as it climbs over a mantle superswell. Journal of Geophysical Research: Solid Earth, 119(7), 6093-6112.
Clark, M. K., Royden, L. H., Whipple, K. X., Burchfiel, B. C., Zhang, X., & Tang, W. (2006). Use of a regional, relict landscape to measure vertical deformation of the eastern Tibetan Plateau. Journal of Geophysical Research: Earth Surface, 111(F3).
Cox, K. G. (1989). The role of mantle plumes in the development of continental drainage patterns. Nature, 342(6252), 873-877.
Eizenhöfer, P. R., McQuarrie, N., Shelef, E., & Ehlers, T. A. (2019). Landscape response to lateral advection in convergent orogens over geologic time scales. Journal of Geophysical Research: Earth Surface, 124(8), 2056-2078.
Jolivet, M., Ritz, J. F., Vassallo, R., Larroque, C., Braucher, R., Todbileg, M., … & Arzhanikov, S. (2007). Mongolian summits: an uplifted, flat, old but still preserved erosion surface. Geology, 35(10), 871-874.
Miao, Y., Herrmann, M., Wu, F., Yan, X., & Yang, S. (2012). What controlled Mid–Late Miocene long-term aridification in Central Asia?—Global cooling or Tibetan Plateau uplift: A review. Earth-Science Reviews, 112(3-4), 155-172.
Mutz, S. G., & Ehlers, T. A. (2019). Detection and explanation of spatiotemporal patterns in Late Cenozoic palaeoclimate change relevant to Earth surface processes. Earth Surface Dynamics, 7(3), 663-679.
Peifer, D., Persano, C., Hurst, M. D., Bishop, P., & Fabel, D. (2021). Growing topography due to contrasting rock types in a tectonically dead landscape. Earth Surface Dynamics, 9(2), 167-181.
Whipple, K. X., Forte, A. M., DiBiase, R. A., Gasparini, N. M., & Ouimet, W. B. (2017). Timescales of landscape response to divide migration and drainage capture: Implications for the role of divide mobility in landscape evolution. Journal of Geophysical Research: Earth Surface, 122(1), 248-273.
Whipple, K. X., & Tucker, G. E. (1999). Dynamics of the stream‐power river incision model: Implications for height limits of mountain ranges, landscape response timescales, and research needs. Journal of Geophysical Research: Solid Earth, 104(B8), 17661-17674.
Whittaker, A. C., & Boulton, S. J. (2012). Tectonic and climatic controls on knickpoint retreat rates and landscape response times. Journal of Geophysical Research: Earth Surface, 117(F2).
Yang, R., Willett, S. D., & Goren, L. (2015). In situ low-relief landscape formation as a result of river network disruption. Nature, 520(7548), 526-529.
Zachos, J. C., Dickens, G. R., & Zeebe, R. E. (2008). An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics. nature, 451(7176), 279-283.

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