Evidence for sea-level oscillations by the “characteristic thickness” of marine deposits from raised terraces of Southern Calabria (Italy)

Abstract

Clastic deposits associated with marine terraces can provide evidence for detecting eustatic oscillations. The method is based on the characteristic thickness (CT) of beach formations, which are generally deposited on a wave-cut platform, between the breakpoint and the swash upper limit. On any present-day coast, CT reflects equilibrium related to current shore processes with a constant sea level. It represents a local threshold ( T cr) as, when sea-level rises, CT increases by a value equal to the rise amplitude. This amount is reduced in uplifted areas by the magnitude of coeval uplifting. The amplitude of sea level variations (detected by CT) can be calculated knowing CT −T cr, uplift rate, and the duration of an oscillation. The method is applied to the clastic deposits of 23 marine terraces stepped between 52 and 172 m and shaped over the MIS 5–MIS 4 period, along the Calabria coast of the Messina Strait. Not only the great orbital oscillations MIS 5.5, MIS 5.3, MIS 5.1 and MIS 3 are recorded, but also several rapid and low-amplitude events are detected into each substage. The most surprising result is the ten small oscillations during MIS 5.5, the duration of which ranges between 2 ka and less than 1 ka, while sea-level oscillates from 0.5 to 12 m in amplitude. By calculating initial relative sea level highstands and also lowstands preceding them, detailed eustatic oscillations of the curve are drawn.