Reconstruction of Geomorphic Surfaces Using Stratigraphic Surfaces: Application in the Analysis of Supercritical-Flow Bedform Dynamics from Sedimentary Structures

Sedimentary structures comprise the (commonly incomplete) preservation of the sediment-flow interface at the time of active bedform migration. Bedform dynamicists are challenged with reconstructing flow processes from this incomplete record. Geomorphic surfaces are key to this challenge, representing timelines of the evolving bed-flow interface that are crucial to the reconstruction of the morphodynamic evolution of bedforms. We studied tens-of-meters long stratification patterns in several-meters-thick beds, deposited by supercritical density flows on a now exposed Pleistocene subaqueous slope, by line drawing of the internal stratification. Strata are correlated using the ‘bar-code principle’, which is based on the assumption that layers have properties such as relative thickness, grain-size distribution, and boundary sharpness, that can be observed and traced along discontinuous exposures. A higher-frequency pulsation in the flow led to a periodic repetition of erosion and deposition related to the formation of individual laminae of 1 to 15 cm thick. Temporal variations in the intensity of these fluctuations and associated rates of deposition created a bar-code-like pattern in the deposits. Such patterns occur at both sides of composite erosion surfaces that separate individual bedform sets. The careful counting of laminations between more-pronounced marker laminae adds to the certainty of the method. The missing part of laminae comprised within the composite erosion surface can be inferred from the preserved portions. Here, we demonstrate how bed-flow interfaces (i.e., the sea floor and the flow that reshaped it) can be reconstructed from discontinuous strata in juxtaposed stratigraphic units to reconstruct the morphodynamic evolution of bedforms.