Quantifying normal fault growth histories from Gilbert Delta stratigraphy using downstream grain size trends: Examples from the Kerinitis and Akrata Delta, Gulf of Corinth. 

Abstract

Gilbert-type deltas, built into rift basins, record interactions between fault-driven uplift and subsidence, sediment supply, and drainage network evolution. Typically forming at the junction of progressive fault segments, the syn-rift stratigraphy of uplifted Gilbert deltas offers a preserved record of the dynamic behavior of sedimentary source-to-sink systems through geological time. Of the physical parameters preserved in delta stratigraphy, grain size distributions contain unique information about sedimentary source-to-sink system dynamics over time. Specifically, downstream fining trends in syn-rift deposits reflect interactions between sediment supply to the basin and accommodation space creation driven by active faulting and subsidence. This work aims to understand how grain size distribution can quantify the syn-linkage phase of normal fault segments in the Gulf of Corinth. We examined two Pleistocene geological examples of uplifted Gilbert deltas with distinct tectonic configurations: 1) The Kerinitis Delta, formed by the relatively simple interaction of two same-aged fault segments, the Pirgaki and Mermoussia (P-M) Faults, which experienced a single linkage event; and 2) the more complicated Akrata Delta, formed by multiple linkage events between fault segments of the East Heliki Fault (EHF) and Derveni Fault (DF). We collected gravel grain size distribution data across 62 localities. Additionally, we captured scaled grain-size photographs in inaccessible areas. By tracing stratigraphic units and measuring their thicknesses, we reconstructed hanging-wall subsidence and paleo-fault slip rates. Using a self-similarity-based grain size fining model, we are able to reconstruct sediment supply rates and paleo-catchment erosion rates during the evolution of the fault systems. Further, we reconstructed the catchment averaged erosion rate to be markedly lower than the reconstructed footwall uplift, implying the landscape's transient response to fault growth. Our analysis demonstrates that grain size trends serve as a powerful tool for quantifying the complete growth histories of faults underlying normal fault-driven Gilbert delta systems. We demonstrate the feasibility of converting high-resolution grain size fining patterns preserved in Gilbert delta stratigraphy into reconstructed records of fault slip rates, hanging wall subsidence rates, sediment flux changes, and other key forcing parameters over 105 year timescales. This significantly expands the quantitative toolbox available to translate syn-rift sedimentary architecture into rich chronologies unravelling structural deformation patterns, including fault interactions, segment linkage, and overall progression.