The evolution and preservation of flood deposits on continental shelves offshore river mouths is influenced by the dynamic relationship between punctuated discharge events and post-deposition processes. These short-term dynamic changes at the seafloor that ultimately shape the sedimentary record are difficult to monitor and not well understood. The aim of this study was to examine how punctuated deposition of flood sediments from a coastal river on the continental shelf, biological mixing and winnowing interplay in shaping grain size profiles and their transient evolution, and the preservation of flood layers in the sedimentary record. For this end an observations-based model was devised for the northern shelf of the sheltered, hyper-arid Gulf of Aqaba-Eilat, where infrequent floods from ephemeral rivers occur ∼ yr−1 and there is low physical perturbation by currents and waves in between, conditions that facilitate the examination of grain size profiles' evolution in time. The model shows that in between floods mixing and winnowing shape grain size profiles in the seafloor, causing the sediment to coarsen from the top down and shape a subsurface peak of the fine flood-sediments. Over longer time periods, without additional floods, mixing and winnowing gradually erase the peak of fines, coarsening the entire mixed layer thus nulling the flood layers' chances of preservation. This important role of winnowing near the sediment surface is missing in previous studies. Concurrently, our modelling suggests that long-term positive sedimentation, usually estimated on the years' time-scale, is comprised of a series of short-term, steep sediment deposition events brought by the punctuated floods (lasting hours to days) and followed by a gradual (months to years' time-scale) winnowing of finer sediments (erosion). These high-resolution dynamics that were captured by the model and included short-term flood depositions and their reoccurrence, could not be deduced from the long-term sedimentary records.
Bibliographical noteFunding Information:
We wish to thank the Schulich Foundation and IUI for supporting the initial fieldwork that inspired this research (TK/BGT) and the Admiral Yohay Ben-Nun Foundation of NAF-IOLR for supporting AK. We are very grateful to Alysse Mathalon and Paul Hill for sharing data, work and resources. We also thank Yoni Shaked for his great help with obtaining the wave data, the Israel National Monitoring Program at the Gulf of Eilat for making available their wind data and Mor Kanari for his help with the map and the bathymetric data from the study area.
© 2022 Elsevier Ltd
- Grain-size profiles
ASJC Scopus subject areas
- Aquatic Science