Overview

Many landscapes have been subject to detailed study to understand their response to environmental change and to reconstruct their evolutionary history.  Typically, the depositional history of a landform may be studied in depth at one or a few locations (e.g. alluvial fan, lake basin, or a dune) and implications for wider landscape evolution / palaeoclimate may be generalised/synthesised into a regional history.  Much less emphasis has been placed on understanding heterogeneity of landscape response to environmental change, even though it is widely recognised that landscapes with similar boundary conditions (climate, lithology, relief), subject to similar forcing (climate change, tectonics,) can follow different evolutionary pathways.  For instance, the adjustment of river systems to supplies of water and sediment is often indeterminate; landforms may display divergence due to initial conditions or position with respect to thresholds, or may have varied reaction and relaxation times (Schumm, 1985).  A greater awareness and understanding of the potential heterogeneity(ies?) of landscape response to changing geomorphological drivers is, thus, fundamental to developing robust histories and models of landscape/climate evolution. The Mojave region (California, USA) provides a useful case study. Pleistocene climates have left a clear landscape legacy, evidenced in the form of palaeo-lakes, aeolian landforms (Figure 1) and widespread, large-scale alluvial fans (Reheis et al. 2014). There have been significant developments for Quaternary geochronology relevant to this region, particularly luminescence dating methods and refinements to K-feldspar IRSL dating. These have led to improvements in the accuracy, precision and age range of luminescence dating in the Mojave (McGuire and Rhodes, 2015; Rhodes, 2015). This presents new opportunities to re-assess existing chronologies, and in conjunction with new approaches to desert surface dating (Fuchs et al., 2015), to develop an understanding of potential variabilities in landscape responses to perturbations. Building on ongoing work concerning the age of aeolian landforms in the southwest Mojave, this project will (re)evaluate the nature and timing of alluvial landscape responses in piedmont zones. The project will focus on the development of luminescence chronologies for alluvial fan emplacement and entrenchment, with a focus on the diversity of the preserved landscape record and responses in settings with similar boundary conditions.

Figure 1: A sequence of inter-bedded alluvial – aeolian sediments and associated palaeosol in the North Cady Mountains, California. Luminescence ages indicate ages from ~70ka to 10 ka.

Methodology

The project will focus on the construction of landscape depositional chronologies, largely using luminescence dating. This method will be applied, in conjunction with detailed field mapping and stratigraphic logging, in piedmont zones to develop accumulation histories of alluvial sediments. New sampling and analytical approaches associated with the dating of desert pavements (Fuchs et al. 2015) suggest that this method can also be used to estimate the age of stabilised surfaces (e.g. alluvial fan surfaces) and the project will also involve further development and refinement of this approach. There may also be potential to apply cosmogenic dating methods should suitable materials be identified, as well as geochemical methods for the consideration of sediment provenance. The fieldwork will focus on piedmont sedimentary accumulations in the Baker-Barstow region where the supervisory team have conducted preliminary fieldwork. Previous studies in this region provide initial ages for potential field sites (Harvey and Wells, 2003).

Training and Skills

CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to CENTA research themes. The successful student will obtain extensive skills in luminescence dating method, using a variety of dosimeter minerals and potentially a range of measurement approaches. Luminescence dating and sediment provenance analyses also provide scope for training in geochemical analyses, notably ICP-MS methods. The project will also provide training geomorphic field mapping and interpretation, sedimentology and basic remote sensing methods.

 

Timeline

Year 1: Initial field reconnaissance, site identification and field mapping training (via the annual Mojave field class), collection of initial luminescence dating training samples, and later training in basic dating methods. Analysis of climate data, remote sensing and digital elevation data for proposed study sites.

Year 2: Major field mapping and sampling, extended period of luminescence dating analyses, secondary field sampling campaign, geochemical and cosmogenic dating analyses (if appropriate)

Year 3: Integration of stratigraphic/morphological data, finalising geochronological data

Partners and collaboration (including CASE)

The project will be jointly supervised by Professor Ian Livingstone (Northampton). There may be additional scope to develop collaborations at other institutions, with whom the supervisors have collaborated in this region.

Further Details

Contact Dr Mark Powell, University of Leicester, dmp6@le.ac.uk