Quantitative analogue flume-model study of river-shelf systems: principlesand verification exemplified by the Late Quaternary Colorado river-delta evolution

Physical modelling of clastic sedimentary systems over geological time span s has to resort to analogue modelling since full scaling cannot be achieved within the spatial and temporal restrictions that are imposed by a laborat ory set-up, Such analogue models are suitable for systematic investigation of a sedimentary system's sensitivity to allocyclic changes by isolating go verning parameters. Until now, analogue models of landscape evolution were mainly qualitative in nature. In this paper, we present a quantitative appr oach. The quantitative experimental results are verified and discussed by c omparison with high-resolution data from the Colorado river-shelf system of the Texas shelf that we used as a prototype. The model's dimensions are proportionally scaled to the prototype, except f or a vertical exaggeration. Time is scaled using a Basin Response factor to maintain a similar ratio between the period of change and the system's equ ilibrium time for model and prototype. A Basin Fill factor was used to comp are the ratio between the time-averaged sedimentation rate and the rate of change in accommodation space of model and prototype. The flume-model resul ts are in the form of sediment budgets that are related to shelf cannibalis m and fluvial supply, which are compared with the ancestral Colorado river- delta evolution of the last 40 kyr. Model and prototype have similarities in delta evolution in response to one cycle of sea-level change. With sea-level change as the isolated variable, the flume model generates a significant supply pulse caused by headward er osion of the shelf in response to the sea-level fall. This pulse adds to th e yield of the hinterland. The supply induced by sea-level change persists during the early rise, although its rate declines. A similar trend is obser ved on the east Texas shelf. We argue that shelfal and fluvial degradation cycles induced by sea-level changes can significantly influence the timing and amount of sediment supply to basins and Must therefore be taken into co nsideration.