Abstract
The Experimental Earthscape Facility (XES) at St. Anthony Falls Laboratory of the University of Minnesota, is a 6 meter by 13 meter by 1.3 meter deep basin with a programmable subsiding floor. We used this system to model a braided fluvial-deltaic system evolving under varying subsidence rates and sediment to water discharge ratios. The experiment was intended to examine the effect of tectonic subsidence and climate on an active river system and on the resultant stratigraphy. It comprised four stages in which subsidence varied both spatially and temporally, with additional variation in the water supply. We used two types of sediment to simulate a natural braided river system, coal as an analog to mud and sand for the coarser-grained sand component. Here we examine the distribution, in three dimensions, of sand and coal, sheet and ribbon deposits, and single-storey and multi-storey channel stacking patterns as produced in the experimental basin. We find that, 1) overall sand content decreases downstream, 2) most of the vertical changes in channel stacking produced by changes in subsidence rate can be attributed to facies migration rather than to any direct effect of subsidence rate on architecture, 3) lateral variation in subsidence has at most a weak effect on channel stacking, and 4) there are autocyclic patterns in the stratigraphy on at least two length and time scales, one of which does not appear to have been recognized previously.