Shoal-water deltas in high-accommodation settings: Insights from the lacustrine Valimi Formation (Gulf of Corinth, Greece)

The stratigraphic architecture of shoal-water deltaic systems developed in low-accommodation settings is relatively well-known. In contrast, the features of shoal-water deltas developed in high-accommodation settings remain relatively poorly documented, especially when compared with the available data sets for Gilbert-type deltaic systems developed in the same settings. The lacustrine Valimi Formation (Gulf of Corinth, Greece) provides an opportunity to investigate the facies assemblage and architectural style of shoal-water deltaic systems developed in high-accommodation settings. The studied interval accumulated during the Pliocene and Pleistocene and represents part of the early syn-rift Gulf of Corinth succession. Six facies associations, each described in terms of depositional processes and geometries, have been identified and interpreted to represent a range of proximal to distal deltaic sub-environments: delta plain, distributary channel, mouth-bar, delta front, prodelta and open lake. The facies associations and their architectural elements reveal characteristics which are not common in traditionally described shoal-water deltas. Of note, different facies arrangements are observed in the distributary channels in different sectors of the delta, passing from thick single-storey channel fills embedded within delta-plain fines in landward positions, to thin, amalgamated and multi-storey channels closer to the river mouth. This study proposes a new depositional model for shoal-water deltas in high-accommodation settings documenting, for the first time, that shoal-water delta deposits can form a substantial part of stratigraphic successions that accumulate in these settings. The proposed depositional model provides new criteria for the recognition and interpretation of these deposits; the results of this study have applied significance for reservoir characterization.