Stratigraphic Architecture, Sedimentology and Structure of the Vouraikos Gilbert‐Type Fan Delta, Gulf of Corinth, Greece

Abstract

In the Aegion to Kalavrita region of the Gulf of Corinth, Greece, Plio-Pleistocene syn-rift stratigraphy comprises a fluvial-dominated lower group and an upper group dominated by Gilbert-type deltas separated by an erosive unconformity. The lower group records substantial accumulation (1.3 km) of fluvial sediment across a broad area of fault-controlled grabens and half grabens, which was terminated by a marine transgression. The upper group records a great increase in accommodation space, the migration of the depocentre to the north and an increase in sediment supply. It is dominated by large gravel-rich systems that were sourced in the footwalls of active normal faults. The Vouraikos Delta is an exceptionally well-exposed Gilbert-type fan delta complex, which is > 800 m thick, with a surface area of 32 km2. It lies in the hangingwall of the Pirgaki-Mamoussia Fault and has been exhumed in the footwall of the Eastern Helike Fault. Preliminary palynological results from topset and pro-delta fine-grained facies and from lower group strata indicate that the Vouraikos Delta began forming some time before 1.1 Ma and was terminated soon after 0.7 Ma. These preliminary Early to Middle Pleistocene age estimates are coherent with published models of the uplift history of the Eastern Helike Fault. Sedimentation rates are thus estimated between 1.3 and 2 mm yr−1. While the earliest delta infilled an incised palaeovalley, accommodation space was primarily tectonically controlled, first by an extensional forced fold and later by a system of major normal faults (Pirgaki-Mamoussia Fault and its splays). Several families of syn-sedimentary and late normal faults cut the delta. A listric growth fault controlled a large rollover anticline in the lowest stratigraphic package. The delta prograded (to the north-northwest) into water that reached depths of 200–600 m. Topset limestones associated with coastal conglomerate facies indicate that the delta built into a water body that was wholly or periodically marine. Internally, the Vouraikos Delta comprises five stratigraphic packages each characterized by a distinctive organization of topsets, foresets, bottomsets and pro-delta facies and bounded by major stratigraphic surfaces. These packages are tentatively correlated with regressive glacio-eustatic interglacial periods. The trajectory of the offlap break in the centre of the Vouraikos reflects early progradationdominated behaviour followed by increasingly aggradational behaviour.