Middle–Upper Pleistocene record of 100-ka depositional cycles on the Southern Tuscany continental margin (Tyrrhenian Sea, Italy): Sequence architecture and margin growth pattern

Abstract

Five unconformity-bounded depositional sequences have been seismically defined on the Tyrrhenian margin offshore Southern Tuscany, Italy. The set of sequences encompasses a ~500ka interval, each sequence recording a ~100-ka orbitally-driven climate-eustatic cycle. Similarly to most of Quaternary continental margins, sequences on the Southern Tuscany margin show an overall regressive motif reflecting shelf sediment progradation basically during the prolonged phases of sea level fall that characterise the Middle–Upper Pleistocene 100-ka cyclicity. On seismic profiles, however, progradational units within each sequence display a variable clinoform geometry, interpreted as a record of the alternation of highstand, falling and lowstand intervals within 100-kacycles. The observed geometric variability is thus used as a key for separating systems tracts otherwise merging into a general progradational/regressive sedimentary body composing the bulk of each sequence. On a longer term, the interplay between sea level changes modulated by 100-kacycles and regional subsidence controls the stratigraphic architecture and the growth pattern of the continental margin. This effect is documented by the overall aggradational/retrogradational stacking pattern of sequences, superimposed on shelf margin progradation and reflecting the renewal of accommodation space landward of the shelf margin and its exploitation at each cycle.