Using grain size analysis to understand transverse versus axial sediment supply to a rift: Example from the Sperchios rift, Greece
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In order to better understand the interaction between different controlling variables in fluvial systems in a rift basin, and the differences between transverse and axial drainage in the same setting, I present the results of numerical modelling in which downstream grain size trends along the fluvial systems in the Sperchios rift basin in Central Greece are analysed. The model is used to explore the relationship between (1) the spatial distribution of subsidence, (2) sediment supply and (3) downstream grain size fining trends in such systems. The transverse systems drain from the footwall, across the border faults, and feed coarse alluvial fans that prograde into the centre of the rift whereas the axial system supplies sediment to a fine grained birds foot delta in the Maliakos Gulf. The model used has been developed in recent years by Fedele and Paola (2007) and Duller et al. (2010). I first demonstrate how the grain size data from the Sperchios rift is obtained and quantified, and then present the modelling results based on the obtained grain size data, where the effects of - and interaction between - the controlling variables is explored. Furthermore, I demonstrate how the amplitude and spatial distribution of subsidence impacts grain size fining trends and the distribution of deposition and bypassing. I also show how the sediment supplied to the system impacts the grain size fining trends and distribution of deposition and bypassing. For the fluvial systems in the Sperchios rift, I then compare the transverse systems with the axial system. This study indicates that the model developed by Fedele and Paola (2007) and Duller et al. (2010), despite some weaknesses and necessary assumptions, provides a greater understanding of the interaction between the controlling variables impacting fluvial deposition in rifts.