Decoding downstream trends in stratigraphic grain size distribution: examples from the Kerinitis Gilbert type delta, Greece.

Stratigraphy represents a physical record of the behavior of source to sink sedimentary systems in the geological past. Grain-size fining in stratigraphy toward the downstream direction is driven by the sediment supply, subsidence rate and accommodation space generation. In principle these grain size trends can be inverted to quantify the temporal and spatial variation in these driving forces. This work addresses this challenge to understand how stratigraphic grain size fining reflects sediment flux and accommodation space generation in a normal fault bounded sedimentary system in the Gulf of Corinth, Greece. A SW to NE 2.6 km exposed natural cliff cut section of the middle Pleistocene Kerinitis Gilbert type delta has been selected for its accessibility, where the stratigraphic units are traceable, and where the timing of sediment deposition is well constrained (500 to 800 ka). The qualitative evolution of the fault is also understood as the three mapped depositional packages (lower part, middle part and the upper part) in the Kerinitis delta are thought to represent the initiation, development, and termination of the Pirgaki-Marmoussia fault. Down-system grain size data has been collected using the Wolman point count method at 25 measurement stations, predominantly from fluvial top-sets following for several timelines. Furthermore, high-resolution grain size photographs have been captured to study the inaccessible higher stratigraphic units. Paleoflow direction is reconstructed using a pebble imbrication dataset, which indicates the source to sink direction. For the grain size datasets, we have applied several self-similarity tests to evaluate the mutual relationship among the datasets. Our result shows that almost all the datasets exhibit significantly self-similarity with each other. We reconstruct grain size fining trends for each of the units, which we quantitatively relate to the spatial distribution of subsidence and sediment flux using a self-similarity based fining model. Our analysis gives new insights into the evolution of the delta bounding Pirgaki-Marmoussia fault and show how grain size data can be used to reconstruct landscape dynamics in the past.