Geomorphic complexity in the stratigraphic record: the importance of sediment storage and recycling in real landscapes
Harries, Rebekah Maud
The sedimentary record preserves a history of erosion in upland catchments. It is the refore key to deciphering the topographic evolution of the Earth's surface in response to climatic and tectonic change. However, an ability to make sensitive inversions of landscape evolution from this record is currently limited as we do not yet understand how the geomorphic evolution of depositional systems impacts their long term mass balance at geological timescales. Physical parameters such as grain size and composition, which are frequently used to reconstruct the evolution of landscapes, are deposited by dynamic river systems that have highly non-linear responses to external forcing at geomorphic timescales. This thesis explores the complexity of sediment dynamics in active source to sink systems and evaluate the extent to which sediment grain size and composition records tectonic, climatic and autogenic forcing. The research focuses on three large catchment alluvial fan systems within the arid south-central Argentine Andes, a landscape dominated by physical transport processes. To characterise the sediment exported from the Frontal Cordillera and to map the spatial distribution of sediment in the Iglesia basin, the size and composition of clasts deposited along the length of three alluvial fans was measured. These datasets are used to investigate three key questions: (1) What controls sorting on alluvial fans? (2) Are downstream grain size fining trends on alluvial fans sensitive to their catchment sediment flux and basin structure? (3) Do riverbed gravels provide a spatially integrated sample of erosional processes in their upstream mountain catchments?