Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published August 2019 | Published
Journal Article Open

Autogenic Erosional Surfaces in Fluvio-deltaic Stratigraphy from Floods, Avulsions, and Backwater Hydrodynamics

Abstract

Erosional surfaces set the architecture of fluvio-deltaic stratigraphy, and they have classically been interpreted in terms of changes in boundary conditions such as climate, tectonics, and base level (allogenic forces). Intrinsic dynamics of sedimentary systems (autogenic dynamics) can also create a rich stratigraphic architecture, and a major knowledge gap exists in parsing the relative roles of autogenic versus allogenic processes. Emerging theoretical and experimental work suggests that backwater hydrodynamics play an important role in driving transient channel incision in river deltas, even those experiencing net aggradation. Here, we identify and quantify two autogenic mechanisms that produce broad erosional surfaces in fluvio-deltaic stratigraphy, namely, floods and avulsions. Using a simple mass-balance model for single-threaded delta channel systems, we show that flood-induced scours begin near the shoreline, and avulsion-induced scours begin at the avulsion site, and both propagate upstream over a distance that scales with the backwater length, bed slope, and bed grain size. We also develop scaling relationships for the maximum scour depths arising from these mechanisms, which are functions of characteristic flow depth and formative flood variability. We test our theoretical predictions using a flume experiment of river delta evolution governed by persistent backwater hydrodynamics under constant relative sea level. Results indicate that autogenic dynamics of backwater-mediated deltas under conditions of constant base level can result in stratigraphic surfaces and shoreline trajectories similar to those often interpreted to represent multiple sea-level cycles. Our work provides a quantitative framework to decouple autogenic and allogenic controls on erosional surfaces preserved in fluvio-deltaic stratigraphy.

Additional Information

© 2019 SEPM (Society for Sedimentary Geology). Received 26 November 2018; accepted 3 May 2019. We thank Woodward Fischer and Elizabeth Trower for useful discussions. This work was supported by the Caltech Terrestrial Hazard Observation and Reporting program and National Science Foundation grant 1427177 to MPL. VG and MPL acknowledge additional support from the Junior Research Fellowship and the Royal Academy of Engineering Distinguished Visiting Professor Fellowship from the Imperial College London, respectively.

Attached Files

Published - i1527-1404-89-8-815.pdf

Files

i1527-1404-89-8-815.pdf
Files (3.9 MB)
Name Size Download all
md5:f7569b9eff76812f169bb8ca13ecd726
3.9 MB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 18, 2023