Basin Evolution Controls on Grain Size Fining: Beyond the 1D Solution

Abstract

Interpretation of the sedimentary record requires a thorough understanding of both external forcing and autogenic dynamics within sedimentary basins. This research analyzes the influence of autogenic and basin dynamics on grain size fining through landscape evolution modeling (Myr timescales) of a flexural foreland basin and observations from real-world basins with well-known underlying subsidence for comparison. In previous work, we have incorporated the Fedele and Paola (2007) self-similar gravel grain size method in two dimensions allowing for the formation of multichannels (2D) into the FastScape (Braun and Willett, 2013) landscape evolution model. We have validated this modelling approach against the self-similar grain size results of Duller et al. (2010) without multiple channels (1D). Here, we analyze different upstream precipitation and flexural elastic thicknesses (impacting the pattern and rate of subsidence) on the evolution of grain size fining, stratigraphic thickness, topography, and channel dynamics. We use real world scenarios with known underlying subsidence, grain size fining, and surface ages (such as the Grapevine Mountain fans of Death Valley) to compare with model results. Underlying subsidence controls on grain size have been well described by Duller et al. (2010), but never with the consideration of channel and topographic dynamics that vary the deposition rate relative to the subsidence rate across the basin. Braun (2022) has described the upstream area and precipitation influence relative to downstream on fan extents, but has not yet applied this to grain size fining trends. Our results show that multiple channels influence the grain size fining solution (more fining) compared to solutions with a single set channel pathway in conditions ranging from full sediment capture in the basin to full bypass, and these results vary depending on fan extents and the pattern of underlying subsidence. The model can be also used to estimate a variance range in grain size fining in which autogenic dynamics may be playing a greater role to statistically rule out or acknowledge a potential autogenic control induced by channel dynamics. Braun & Willet (2013). Geomorphology: 180. Braun (2022). ESP: 10(2). Duller et al. (2010). JGR: ES 115(F3). Fedele & Paola (2007). JGR: ES 112(F2).