Investigating the autogenic process response to allogenic forcing: Experimental geomorphology and stratigraphy

Summary: Decoupling the preserved signal of environmental (allogenic) forcing from those of internally generated (autogenic) processes is at the centre of understanding the evolution of the Earth's surface preserved in the sedimentary record. A major stumbling block for distinguishing between allogenic versus autogenic signatures in the stratigraphic record is the lack of quantitative understanding of autogenic processes and their interactions with allogenic forcing. Physical experiments with moving sediment and water construct topography through dynamic self-organised fluvial systems, thus providing an opportunity to investigate autogenic processes under controlled boundary conditions (e.g. sediment supply and tectonics). This paper presents a set of tank experiments that are used to examine quantitatively 1) the autocyclic storage and release of sediment in the delta top surface associated with river-pattern changes between channel and sheet flow and 2) changes in fluvial autocyclic behaviour driven by external forcing (e.g. sea-level change and tectonics). The time and event scales of the autogenic processes observed in the experiments conducted without external forcing have provided the first-order quantitative understanding of the autogenic processes. Changes in the frequency of autogenic processes through base-level changes and lateral ground tilting have provided a new view into the coupled allogenic and autogenic controls on stratigraphic development. Coupled experiments that test the effects of allogenic forcing on autogenic process are presented here: one experiment was conducted with constant external forcing and the other was conducted with cyclic changes in external controls. This review provides 1) quantitative measurements of fluvial autogenic processes and thorough comparisons of cyclic strata attributed to allogenic versus autogenic controls and 2) suggestions for future experimental studies of fluvial autogenic processes that will enhance our ability to interpret the mixed signals of environmental variation and internal dynamics in the sedimentary record.