Grain size as a record of tectono-climatic forcing: examples from fluvial and deltaic systems
File(s)
Author(s)
Rezwan, Nahin
Type
Thesis
Abstract
This thesis explores how grain size can be used as a physical signal to decode tectonic and climatic forcing in sedimentary systems. Two natural field-based settings are presented: Pleistocene uplifted and modern Gilbert-type deltas in the Gulf of Corinth, Greece, and a near-natural gravel-bed river in western Switzerland (Sense River).
Methodologically, the thesis integrates classical field sampling of sediment calibre (Wolman counts and photo-granulometry) with UAV structure-from-motion and machine-learning segmentation to produce spatially continuous, grain-resolved datasets. A self-similarity framework places modern and stratigraphic grain-size distributions within common, dimensionless axes, allowing grain-size distributions to be interpreted without constraining detailed hydraulics.
Applied to rift-margin deltas, I show that topset grain fining and stratal architecture jointly quantify fault growth, interaction, and linkage. Steep-to-gentle shifts in fining correspond to changes in accommodation, sediment supply, and sediment routing, illustrating how fault configuration governs accommodation and sedimentation preservation. In the modern river case study, I use high-resolution mapping (ca. 1.86 million grains) to show spatially organised grain mobility in response to a moderately large flood event. Despite substantial patch-scale reworking, reach-scale distributions retain a stable self-similar form, validating dynamic equilibrium maintained by particle exchange.
I use these data to establish a grain-size framework enabling comparison between modern fluvial dynamics and long-term stratigraphic records. The thesis resolves distinct controls across scales; climate acts at seasonal scales by reorganising patches and bars in ways predictable from local hydraulics, while tectonics modulates accommodation and sediment routing over 10⁴-10⁵ years, shaping grain-size distributions preserved in basin fills.
My approach is transferable across fluvial, deltaic, and coastal systems. It enhances the interpretability of grain-size records, enables reconstruction of tectonic forcing, and clarifies which components of hydrologic variability are likely to be archived in modern and stratigraphic systems, offering a practical tool for decoding past landscape dynamics.
Methodologically, the thesis integrates classical field sampling of sediment calibre (Wolman counts and photo-granulometry) with UAV structure-from-motion and machine-learning segmentation to produce spatially continuous, grain-resolved datasets. A self-similarity framework places modern and stratigraphic grain-size distributions within common, dimensionless axes, allowing grain-size distributions to be interpreted without constraining detailed hydraulics.
Applied to rift-margin deltas, I show that topset grain fining and stratal architecture jointly quantify fault growth, interaction, and linkage. Steep-to-gentle shifts in fining correspond to changes in accommodation, sediment supply, and sediment routing, illustrating how fault configuration governs accommodation and sedimentation preservation. In the modern river case study, I use high-resolution mapping (ca. 1.86 million grains) to show spatially organised grain mobility in response to a moderately large flood event. Despite substantial patch-scale reworking, reach-scale distributions retain a stable self-similar form, validating dynamic equilibrium maintained by particle exchange.
I use these data to establish a grain-size framework enabling comparison between modern fluvial dynamics and long-term stratigraphic records. The thesis resolves distinct controls across scales; climate acts at seasonal scales by reorganising patches and bars in ways predictable from local hydraulics, while tectonics modulates accommodation and sediment routing over 10⁴-10⁵ years, shaping grain-size distributions preserved in basin fills.
My approach is transferable across fluvial, deltaic, and coastal systems. It enhances the interpretability of grain-size records, enables reconstruction of tectonic forcing, and clarifies which components of hydrologic variability are likely to be archived in modern and stratigraphic systems, offering a practical tool for decoding past landscape dynamics.
Version
Open Access
Date Issued
2025-10-10
Date Awarded
01/02/2026
License URL
Advisor
Whittaker, Alexander
Gupta, Sanjeev
Sponsor
European Commission
Grant Number
860383
Publisher Department
Department of Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)