Tsunami as Triggering Mechanism of Homogenites Recorded in Areas of the Eastern Mediterranean Characterized by the “Cobblestone Topography”
A several meters thick lithologic unit characterized by a very fine grained, homogeneous, structureless marl, a sharp basal contact and a rapidly fining upwards sequence was recovered in eleven piston cores of the “Cobblestone Project”: 8 from the southern Calabrian Ridge (Area 4) and 3 from the western Mediterranean Ridge (Area 3). All these cores are located in the floor of flat bottomed depressions like troughs, basins, perched basins and craters.
The unit — called homogenite —is conspicuously absent on plateaus, where pelagic sedimentation occurs with oozes, sapropels and tephras, and on basin flanks, where pre-late Pleistocene sediments are consistently recorded.
Homogenite deposition is a Holocene event: the unit is over-and underlain by decimetric thick normal pelagic oozes. Sapropel S-1 (top approximately 8000 y BP) is found beneath the base of homogenites in all homogenite-bearing cores.
The tsunami induced by the collapse of the caldera of Santorini 3500 y BP (Minoan eruption) is considered the causative mechanism of homogenite.
Calculations by K.A. Kastens show that oscillating currents accompanying the tsunami were above the threshold erosion velocity, and that pressure pulse was sufficient to cause liquefaction of loose sediments draping the basin walls.
Grain-size analysis carried out on homogenite samples from two cores where the unit is approximately 500 cm thick support the theoretical calculations that a higher energy was available in the western Mediterranean Ridge Site (∿500 km from Santorini) than in the southern Calabrian Ridge Site (∿800 km from Santorini).
KeywordsSedimentation Holocene Refraction Lithology Azimuth
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