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Sediment transport due to large storms: Multiple tools for a complex problem

Applicant Douillet Guilhem Amin
Number 185856
Funding scheme Ambizione
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geology
Start/End 01.12.2019 - 30.11.2023
Approved amount 942'908.00
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All Disciplines (2)

Discipline
Geology
Other disciplines of Earth Sciences

Keywords (24)

Sedimentology; Hummocky-Cross-Stratification; Tempestites; Storm; Waves; Froude Supercritical Flows; Sand; Siliciclastic; Shallow Marine; Density Currents; Combined Flow; Flow Dynamics; CFD; Sediment Transport; Stratigraphy; Gondwana; Ordovician; Permian; Ktawa; Bani; Tubeilliat; Mukorob; Ecca; Karoo Kalahari

Lay Summary (French)

Lead
Le terme "tempestite" se réfère à des couches ponctuelles de sable attribuées à l'action de tempêtes dans l'enregistrement de séries sédimentaires marines anciennes. Les figures les plus caractéristique des tempestites sont les "litages-obliques-en-mamelons" (HCS, Hummocky-Cross-Stratifications). Ces structures ondulantes, métriques et à faible pente sont comprises comme formées entre 5 et 100 m de profondeur, sous l'effet de courants vers le large combinés à l'oscillation de vagues de tempêtes. Des structures semblables aux HCS peuvent cependant aussi être formées indépendamment de l'effet des vagues par des courants de sédiments profonds (turbiditiques). Bien qu'il y ait consensus sur l'interprétation générale, un verrou subsiste pour extraire des informations quantitatives sur l'amplitude des tempêtes et les profondeurs d'eau à partir de l'observation sédimentaire.
Lay summary
Objectifs du travail de recherche :
Le projet combinera quatre approches pour tester des hypothèses indépendantes, apporter des données quantitatives, et réconcilier la théorie au terrain:
1. Surveillance in-situ: installation de matériel d'observation sur les fonds marins autour de Taïwan (caractérisation de typhons)
2. Modèles numériques: étude de courants turbiditiques
2. Expériences analogiques: un canal expérimental pour l'étude de taux de sédimentation extrêmes
4. Géologie de terrain: sédimentologie/stratigraphie sur des affleurements de qualité exceptionnelle (Maroc/Jordanie/Namibie).

Contexte scientifique et implications societales:
Les informations contenues dans les HCS concernant l’évolution des niveaux marins et changements climatiques dans l'ancien peuvent s'avérer cruciales pour la compréhension du passé et futur de notre Planète. De nombreux réservoirs sont de plus exploités autour de séries à tempêtes. Enfin, la compréhension des transferts de sable des cotes au large renseigne sur les processus d’érosion côtière.

Direct link to Lay Summary Last update: 29.08.2019

Responsible applicant and co-applicants

Employees

Abstract

"Tempestites" refer to punctual layers of sand in the sedimentary record of shallow-marine environments that are interpreted as being related to tempests, or storms events. Although there is a general agreement on this basic assumption, major questions remain unsolved, in particular regarding the agent and mechanism of transport (flow), the origin of the source material, dynamics conditions of deposition, paleo-bathymetric significance, and stratigraphic position. This gap results from concurrent theories, the nature of the topic that overlaps on different disciplines, the difficulty in scaling analogue models, and the scarcity of observational and monitoring data directly linked to the sedimentary information. This project aspires to bridge the gap between methods and knowledge, and provide data from in-situ observations, numerical models, analogue experiments, as well as sedimentological and stratigraphic field studies, in an effort to reconcile the various aspects of tempestites and the signature of storms in marine sediments.Tempestites generally consist of decimeter to meter thick units of sand that form sheets over several kilometers in extent and that are found as "event layers" in otherwise finer-grained muddy successions. They contain sedimentary structures known as "Hummocky Cross Stratifications" (HCS), which are flat, meter-scale dune forms that aggrade and cross-cut each other without preferential orientation. HCS are often envisioned as deposited by the combined action of a flow and oscillations related to large storm-waves. Alternatively or complementarily, tempestite beds have also been related to turbidity currents, with HCS representing bedforms produced by thin and rapid currents (Froude-supercritical regime). Tempestites and HCS are widespread in many sedimentary basins around the world, in association with sediments from the lower-shoreface (<5 m depth) and down to depths of >100 m in offshore transitions.Where does the sand that forms tempestites come from and how is it transported? If HCS structures are influenced by storm-waves, can the size of these waves be inferred from the study of their sedimentary signature? Is there only one type of tempestite? Are alternative interpretations of tempestite units viable? Four different approaches will be used to test existing and alternative theories on the origin of tempestites in order to reconcile observations and constrain a framework for quantitative interpretation:- In-situ monitoring of modern offshore environments subjected to large storms. A joint survey will be deployed on the marine sea floor around Taiwan, impacted yearly by typhoons. The installation of flow-meters (ADCPs) combined with the in-situ sampling of sedimentary structures will provide direct data about the influence of storms on a seabed and allow to frame a quantitative interpretation of these beds regarding wave influence and water depth.- Numerical modeling of density currents in a Froude-supercritical regime and their sedimentary signature. A long debate in the literature between interpretation of storm-wave reworking vs. supercritical turbidity current will be addressed with quantitative results. The goal is to test whether such density currents can produce HCS-like bedforms. - Analogue flume-tank experiments with the aim of reproducing the aggrading nature of HCS bedforms in environments where the main characteristic is the high rate of sedimentation within slow currents. More than 30 years of field research in various sedimentary environments has put forward this possibility, yet the question remains, up to date, fundamentally lacking data from analogue experiments.- Field-based study of ancient sedimentary successions attributed to storms, assisted by a PhD student, in three key locations: 1) the shore to offshore Bani and Ktawa Groups (Late Ordovician, Morocco), 2) the lower-shoreface Auob sandstones (Early Permian, Karoo-Kalahari basin in Namibia) and 3) the upper-offshore Khreim Group (Late Ordovician, Jordan). The objective is to analyze tempestite beds within a stratigraphic framework from the shore to offshore, their spatial extent and architecture as well as their correlation with climatic signals.The combination of the proposed methods, technically impossible ca. 10 years ago, will shed light on the origin of one of the most important sedimentological units in stratigraphic archives, and it will establish a new standard to lead research in process-sedimentology.
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