QUANTIFYING THE COMPLETENESS OF SHORELINE TRAJECTORIES IN THE STRATIGRAPHIC RECORD

Understanding the incomplete nature of the stratigraphic record is fundamental for interpreting stratigraphic sequences. Methods for quantifying stratigraphic completeness for one-dimensional stratigraphic columns are now commonplace; however, quantitative solutions of stratigraphic completeness in higher dimensions are generally lacking. We present a metric for the stratigraphic completeness of 2-D shoreline trajectories from topset-foreset rollover positions in dip-sections. From analysis of a pair of cut sections from an experimental Gilbert-type delta, we observed that a significant portion of the record of shoreline migration is removed or never deposited due to both imposed sea level fluctuations and autogenic processes. Shoreline completeness in 2-D is shown to be higher in our experimental dataset than 1-D completeness along the same transects for a distribution of time intervals. This is consistent with the notion, derived from mass conservation that completeness should increase with higher dimensions of observation. Applying the concept of stratigraphic completeness to a simplified two-dimensional framework of a shoreline trajectory provides a first-approach to up-scaling current thinking of completeness to higher dimensions.

We observe two end-member cases between which the removal of antecedent trajectories occurs primarily dependent on whether or not erosion of topsets occurs during lowstand – a feature not necessarily evident from trajectories alone. We present a pair of kinematic and geometric numerical forward models for describing the portions of shoreline trajectories likely to be preserved. Forward-modeled stratigraphy is then used to determine the expected values for shoreline completeness given particular shoreline trajectories. We vetted the models against transects from our experimental delta for which geomorphic and stratigraphic trajectories are known, with excellent results. This concept of stratigraphic completeness as applied to 2-D shoreline trajectory analysis, and the development of constrained forward model end-members can be a powerful tool for describing both the ability of a particular shoreline trajectory to be preserved and can inform basin-scale interpretations of outcrop and seismic data.