Capturing or Shredding Milankovitch Climate Cyclicity within Death Valley Alluvial Fans

The distribution of grain size in sedimentary fans is commonly used as a record of past climate fluctuations. The fidelity of this record can, however, be affected by several processes such as highly condensed stratigraphy or strong autogenic geomorphic processes that tend to ‘shred’ the climate signal. In this study, we use a coupled FastScape erosional–depositional landscape evolution model with a gravel grain-size model to identify the environmental and geomorphic conditions that optimize the generation and preservation of climate-driven grain-size signals. Our results indicate that such signals are most reliably recorded in low-bypass, transient, and topographically constrained alluvial fans.

To illustrate this, we apply an optimization approach to a gravel fining dataset, catchment wide erosion rates, and topographic profiles from two alluvial fans in Death Valley described in D’Arcy et al. (2017). These fans were interpreted as preserving climate signals tied to Milankovitch-scale rainfall variability despite some channel incision on a neighbouring fan surface (D’Arcy et al, 2017). Our analysis suggests that these systems are near-optimally configured for archiving climatic fluctuations. The methodological framework we present can be used to inform the design of future grain-size data collection strategies and offers a tool for assessing the potential of other fan systems to preserve paleoclimate signals in their depositional stratigraphy.

D’Arcy, M. et al. (2017). Sedimentology, 64(2), 388–424