CHANGES IN PRECIPITATION DRIVE STRATIGRAPHIC PRESERVATION OF CLIMATE SIGNALS: INSIGHTS FROM LANDSCAPE EVOLUTION MODELING

Geomorphologic and stratigraphic records from proximal depositional systems (e.g., alluvial fans) have long been used to study the influence of external forcings (e.g., tectonics, climate) on sedimentary systems. Such alluvial basins may be particularly sensitive to changes in boundary conditions as they have a direct connection with their upstream erosional domains and lack large transfer zones. However, sediment supply often exceeds accommodation in proximal environments, resulting in a high degree of sediment bypass and variable stratigraphic preservation. To address the sensitivity of stratigraphic preservation to conditions of changing climate, we employ the ‘Fastscape’ library, a coupled erosional-depositional landscape evolution model that incorporates detachment-limited bedrock channel erosion, hillslope diffusion, and sediment deposition. Our results suggest that stratigraphic completeness, the fraction of model time steps that leave a record of deposition, is intrinsically linked to variability in relative precipitation in proximal, overfilled basins. For example, a stepped increase and decrease in relative precipitation results in a temporary decrease and increase in stratigraphic completeness, respectively. Cyclic variations in relative precipitation produce periods of low stratigraphic completeness during periods of increasing precipitation when erosional recycling of the upper basin stratigraphy is greater than when precipitation is decreasing. An instantaneous increase followed by linear decrease in relative precipitation results in poorer stratigraphic preservation before the event versus after. Although shredding of paleoclimate proxies has been explored in the content of autogenic variability, we show that preservation of stratigraphic records (and the paleoclimate proxies they contain) is unlikely to be independent of allogenic forcings. Further efforts to couple erosional and depositional numerical models across a wider range of depositional settings may elucidate the complex relationships between geomorphic processes and stratigraphic preservation.