Morphodynamic limits to environmental signal propagation across landscapes and into strata

Abstract

The sedimentary record contains unique information about landscape response to environmental forcing at timescales that far exceed landscape observations over human timescales. However, stochastic processes can overprint and shred evidence of environmental signals, such as sediment flux signals, and so inhibit their transfer to strata. Our community currently lacks a quantitative framework to differentiate between environmental signals and autogenic signals in field-scale analysis of strata. Here we develop a framework and workflow to estimate autogenic thresholds for ancient sediment routing systems. Crucially these thresholds can be approximated using measurements that are readily attainable from field systems, circumventing the low temporal resolution offered by strata. This work demonstrates how short-term system dynamics can be accessed from ancient sediment routing systems to place morphodynamic limits on environmental signal propagation across ancient landscapes and into strata.

The degradation and detection of environmental signals in sediment transport systems

“…As autogenic processes have no role within a diffusion framework due to the averaging of lateral stochastic system dynamics, T rw does not exist and signals can therefore only be related to T eq . This leads to a loss of predictive capability when evaluating the limits of environmental signal propagation across Earth’s surface, as only long time scale signals can be assessed ( 65 ). As autogenic processes are inherent to 3D STS and set a lower limit for signal propagation and preservation, any theoretical framework must incorporate stochastic dynamics.…”

“…The specific sediment transport and storage mechanisms within an STS will determine the nature and time scales of autogenic processes, which mediates how STSs might transmit environmental signals ( 15 , 33 , 65 ). In the physical rice pile, the temporal extent of correlation (i.e., red noise up to T rw ) is defined by the duration of individual avalanche events.…”

“…If the hillslope-fluvial system is well connected, sediment delivered from the hillslope segment is fed directly into the fluvial segment; hence, we hypothesize that time required to evacuate sediment from the catchment is short, and hence, T rw is short. This also means that the STS could convey sediment flux signals effectively through consecutive STS segments ( 7 ), depending on the autogenic processes and storage capacity of the STS segment in question ( 65 ). On the other hand, if a hillslope-fluvial system is disconnected, sediment is stored on the hillslope ( 7 , 70 ) where it is gradually removed and transported to the river network.…”

“…This means that although the absolute landslide duration on the hillslope is short-lived, the time to evacuate the associated sediment from the catchment by fluvial processes is much longer, which we hypothesize will extend the time scales of temporal correlation (e.g., red noise) ( 54 ) and hence the time scales over which signals will experience shredding. From the above, it is evident that the interconnection of STS segments strongly influences the spectral geometry of influx at the outlet of the connected segments and controls how signals propagate between and through them [e.g., ( 65 )].…”

The Incomplete Record of Autogenic Processes Sets Limits on Signal Detectability

“…However, the statistics of these fluxes are not linked to the same processes at play in field‐scale systems; hence, we do not focus on the specific processes but rather the ramifications of having a stochastic time series of sediment flux bound by process timescales and finite size effects. Although the rice pile does not directly generate strata, it produces a time series of sediment flux from a single location, which is a measurable attribute that links both Earth surface processes and strata (Toby et al., 2022). The time series generated is comparable to a time series of stratigraphic measurables collected from a 1D vertical section, which provides insight into the complex internal dynamics operating up‐system of this location (Figure 1).…”