Surface Process Control on Stratigraphic Completeness in Simple Experimental Deltas

Abstract:

The ability to measure and understand stratigraphic completeness is fundamental to the interpretation of the sedimentary record. It provides the epistemic basis that allows us to predict the preservation potential of input signals to sedimentary systems, and gives us a null hypothesis of sorts against which real stratigraphic sequences can be compared. Stratigraphic completeness essentially sets the resolution of a seismic section. However, despite the importance of stratigraphic completeness, significant gaps remain in our understanding, especially as regards the mechanistic underpinnings of how real geomorphic and transport processes influence completeness.

Here we use a suite of reduced complexity numerical models of a delta to investigate what degree of realism in representation of surface processes is required to match measured completeness-timescale relationships in real systems. Target data is drawn from experimental deltas, where input variables are known and well constrained. We explore the extent to which surface processes – in particular, expressed as the spatial restriction of and correlation between loci of erosion and deposition on the delta top and front – control completeness, independent of the forcing parameters of sediment input and base level. We illustrate the importance of data resolution in controlling measured completeness, and demonstrate that these resolution effects can combine with trends driven by process localization on the delta top. We discuss the extent to which these two effects can or cannot be distinguished in real data. We argue that signals of localized erosion on the delta top and localized deposition on the delta front are key drivers of completeness-timescale trends, even for simple Gilbert-style deltas under elementary experimental boundary conditions.