Constraints on fault interaction and linkage from grain size fining and stratigraphy in the Gilbert-type deltas: Examples from the Gulf of Corinth, Greece

Stratigraphy and grain-size distributions have the potential to quantitatively record fault growth, and interaction between fault segments over geological timescales. This study demonstrates how grain-size fining trends can reflect fault linkage, using Gilbert-type delta stratigraphy in the Gulf of Corinth, Greece as a natural laboratory. In the upper-Pleistocene Akrata Gilbert Delta, located on the southern margin of the gulf, we analysed two transects, traced along a discrete stratigraphic interval from upstream to downstream: an older fluvial-to-shoalwater delta (T1; ca. 285-240 ka); and a relatively younger Gilbert-type topset (T2; ca. 220-200 ka), which were controlled by interactions between the East Helike and Derveni faults. Both units exhibited exponential grain-size fining; however, T1 showed rapid fining due to limited sediment supply relative to accommodation space formation, while T2 demonstrated slower fining, reflecting the response to a larger sediment flux and a broader dispersal. Reconstructed subsidence rates increased from ca. 0.3 mm/yr (T1) to 0.5 mm/yr (T2), alongside a significant rise in sediment flux from ca. 430-600 m³/yr (T1) to ca. 2130-2770 m³/yr (T2), illustrating the impact of fault interaction on deposition efficiency. Final breaching of relay zone (ca. 200 ka) resulted in the formation of the fully linked Krathis fault, with the consequence that slip rates accelerated significantly. Comparisons with the lower Pleistocene Kerinitis Gilbert Delta, located along strike, and the Holocene Krathis delta, the modern equivalent of the Akrata system, highlight how fault geometry and interaction fundamentally control sediment supply and grain-size trends across different settings, enabling quantitative reconstructions of sedimentary processes over 10⁴-10⁵ year timescales.