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Sink to source modelling of sedimentary histories

Sink to source modelling of sedimentary histories

Earth surface landforms are shaped by geomorphological processes which are either erosive or depositional in nature. There is, therefore, a strong link between landscape morphology and sedimentology and, in turn, this opens the possibility of interpreting landforms and their preserved sediments to unravel records of formative conditions. Indeed, there have been a number of studies that have sought to use Landscape Evolution Models (LEMs) to reconstruct palaeo-environmental histories (Howard, 1997, 1999; Coulthard et al. 2000, 2002; Leyland and Darby, 2009). These studies use suites of hindcast simulations in an attempt to match contemporary observed landscape morphologies with those simulated by the models, but such studies have thus far been based only on morphological reconstructions, without consideration of the additional insights afforded by interpretation of the associated sedimentary record. This is because existing LEMs do not have the ability to track the provenance, movement and deposition of multiple fine grain sizes. Lacustrine and marine fans or deltas are depositional features found at the mouths of rivers around the world (e.g. Mekong, Mississippi, Nile, Selenga), many of which have very poorly constrained long term (>Holocene) climatic and environmental histories. Due to the nature of their formation, these fans contain an archive of past formative conditions within the sediment layers of which they are made. The deciphering of such archives is not without its challenges, as often fan sediments can be re-worked many times through the action of river avulsions. Nonetheless with carefully selected sampling sites, sediment cores can be recovered that represent continuous deposition over many thousands of years. Previous research has attempted to make links between sediment characteristics and flow conditions (Liu et al., 2004) and a number of 2D and 3D delta building models have been developed (Hutton and Syvitski, 2008) which allow the study of formative rates of sediment delivery and river discharge. However, nobody has yet attempted to link the sediment and water discharge from a catchment scale LEM to the geomorphology and sedimentology of a fan or delta, thereby allowing holistic scenarios of environmental change resulting in plausible fan development to be identified. This proposal seeks to address this gap by developing the very first nested modelling approach in which fan morphology and stratigraphy will be simulated as a tool for identifying plausible scenarios of catchment scale palaeo-environmental change. In this proof of concept research, the approach will be applied to a lacustrine study site, The Loch Insh (Scotland) which has extensive fan development, thereby removing the complexities of sea-level change and wave climate associated with deltas.