Abstract

Coring and acoustic-reflection data show that coarse-grained sediment layers are remarkably continuous throughout the Tyrrhenian Abyssal Plain. Contrasts in acoustic impedance at the interfaces of these layers with the finer pelagic clay produce discrete sub-bottom echoes that have been correlated with the in situ strata by coring.

Observations of grain size, bed thickness, and mineralogy have been used to identify the origin and transportation routes for two distinct types of sand. One type consists of eolian-transported tephra; several individual beds have been tentatively correlated with historic volcanic eruptions. The other type appears to have been transported through submarine canyons to the abyssal plain by turbidity currents. Three extensive turbidite layers have been traced to Naples Canyon, and one layer to a canyon originating off the eastern coast of Sardinia.

Photographs of the sea floor on the abyssal plain show no evidence of bottom currents; however, those at the mouth of Naples Canyon depict large sand waves and drifted sediments which suggest that strong transient currents have recently flowed there.

The vast areal extent of the individual turbidite layers within the abyssal plain supports the hypothesis that the turbidity currents arrive at the abyssal plain with sufficient energy to pond their suspension over the basin floor. Seismic-reflection records indicate that this process has been active throughout the modern history of the Tyrrhenian Basin, and more than 1000 m of sediment has accumulated in its deepest depression.

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