Late Quaternary depositional history of the North Evvoikos Gulf, Aegean Sea, Greece

摘要

A high-resolution seismic reflection survey was carried out in the North Evvoikos Gulf, a deep (450 m) semi-enclosed basin in east-central Greece connected to the Aegean sea via a 45-m sill to the north and a 30-m wide, 10-m deep straight to the south. This active extensional basin is bound by major normal faults, that switch polarity along strike, thereby controlling the asymmetric shape of the basin. The survey records show a continuous upper unit in the marine strata deposited since the post-glacial transgression on an erosion surface generated during the last glacial. The upper unit can be traced downslope into the basin plain where it merges into a unit of laterally continuous interbedded turbidites and hemipelagic deposits. The buried erosion surface has many terraces distributed over several depth zones, between 65 m and 165 m below present sea-level that are evidence for a fluctuating water level when, in the last glacial interval, the sill depth in the north was about 55 m below today's sealevel and the gulf became isolated from the Aegean Sea. Thus during the last 70 kyr the water level of the lowstand lakes fluctuated in correspondence with the Oxygen Isotope Stages (OIS) and the climatic conditions. In the dryer stages (OIS 4, 2) the lake water level was lower, in the wetter stages (OIS 1, 3) the lake water level was higher. These events are also con-elated with sediment budgets input from the surrounding land to the basin. Researches carried out in many other gulfs of variable depth in the Ionian and Aegean seas indicated presence of sills at today's depths between -50 and -70 m. The generation of these features is postulated as sedimentary as many sea level fluctuations ranged in this depth interval.