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Keywords:

  • Gilbert-type delta;
  • incised-valley system;
  • relay ramp;
  • sedimentary facies;
  • sequence stratigraphy;
  • shoal-water delta

Abstract

This study from the southern margin of the Gulf of Corinth documents a Late Pleistocene incised valley-fill succession that differs from the existing facies models, because it comprises gravelly shoal-water and Gilbert-type deltaic deposits, shows strong wave influence and lacks evidence of tidal activity. The valley-fill is at least 140 m thick, formed in 50 to 100 ka between the interglacials Marine Isotope Stage 9a and Marine Isotope Stage 7c. The relative sea-level rise left its record both inside and outside the incised valley, and the age of the valley-fill is estimated from a U/Th date of coral-bearing deposits directly outside the palaeovalley outlet. Tectonic up-warping due to formation of a valley-parallel structural relay ramp contributed to the valley segmentation and limited the landward extent of marine invasions. The valley segment upstream of the ramp crest was filled with a gravelly alluvium, whereas the downstream segment accumulated fluvio-deltaic deposits. The consecutive deltaic systems nucleated in the ramp-crest zone, forming a bathymetric gradient that promoted the ultimate growth of thick Gilbert-type delta. The case study contributes to the spectrum of conceptual models for incised valley-fill architecture. Four key models are discussed with reference to the rates of sediment supply and accommodation development, and it is pointed out that not only similarity, but also all departures of particular field cases from these end-member models may provide valuable information on the system formative conditions. The Akrata incised valley-fill represents conditions of high sediment supply and a rapid, but stepwise development of accommodation that resulted from the spatiotemporal evolution of normal faulting at the rift margin and overprinted glacioeustatic signals. This study adds to an understanding of valley-fill architecture and provides new insights into the Pleistocene tectonics and palaeogeography of the Corinth Rift margin.