Anthropogenic turbidity current deposits in a seismically active graben, the Gulf of Corinth, Greece: A useful tool for studying turbidity current transport processes

Abstract

A detailed marine survey in Antikyra Bay in the northern margin of the Gulf of Corinth graben in Greece was carried out to examine the distribution and dispersion of bauxitic "red mud" tailings. The red mud tailings have been discharged at a rate of 500 000 to 640 000 tonnes/year via submerged outfalls on the shelf at a water depth of 100 m. The red mud tailings at the mouth of the outfalls have formed three oval shaped mounds. These mounds have a maximum thickness of about 27 m and thin out radially in the downslope direction along the longitudinal axis of the bay in a south-southwestward direction forming a common depositional lobe. The "red mud" tailings are transported by turbidity currents, via channels which incise the slope, to the basin floor at a water depth of 800 m and over a distance of 17 km, where they form small sheet-like deposits. High-resolution sedimentological analysis of 30 short cores using visual inspection, X-radiography, grain size measurements, X-ray diffraction and smear slides have shown the presence of seven (7) distinct turbidity flow events which were activated on the shelf and the slope and have occurred during the 24 years of tailing discharge. Five of these have their source at the "red-mud" mounds at the mouths of the outfalls and two of them have their source at the shelf break and the upper slope. The analysis revealed that the former consist of (a) graded structureless red mud deposits and/or bioturbated red mud deposits, or (b) laminated red mud deposits, whereas the latter are mostly structureless and poorly graded.