Interplay between tectonics and glacio-eustasy: Pleistocene of the Crotone Basin, Calabria (Southern Italy)

On a global scale, the Crotone basin preserves one of the best-developed and most complete Pleistocene marine records available in outcrop, as important as those in California, New Zealand, and Japan. A deformed, markedly cyclothemic, lower to middle Pleistocene succession is present in the territory of San Mauro Marchesato (Crotone area, southern Italy), showing an overall shallowing trend from slope mudstones to marginal marine and continental deposits. Preservation and high resolution of cyclothems occurred through the interaction between high-amplitude relative sea-level fluctuations, a particular pattern of differential subsidence due to intrabasinal tectonics, and high rates of sediment supply. The studied succession was laid down in the Crotone basin under an extensional tectonic regime, following a major, middle Pliocene contractional phase probably of transpressional nature. Two major unconformities, locally accompanied by angular discordances, occur within the succession. The former, centered at ca. 1.2 Ma, is thought to reflect the opening of the San Mauro subbasin within the Crotone basin in the early Pleistocene, following dextral transtensional motion along north- to north-northeast-trending faults. The latter, with a hiatus lasting from ca. 0.65 to 0.45 Ma, may reflect the decoupling of the Calabrian block with respect to Adria and Sicily, allowing further advancing of the Calabrian arc in the Ionian area, where subduction could continue until the present time. The lower part of the succession (the H. sellii and "large Gephyrocapsa" Zones, from ca. 1.67 to ca. 1.23 Ma) consists of slope to outer-shelf monotonous mudstones and is bounded at the top by the first unconformity, whose gap suppresses the upper part of to locally the entire "large Gephyrocapsa" Zone (1.608-1.235 Ma) and the lower part of the "small Gephyrocapsa" Zone (1.235-0.96 Ma). A number of cyclothems developed in an outer- to inner-shelf environment within the "small Gephyrocapsa" Zone. Biomagnetostratigraphic constraints strongly support a correlation between the condensed sections of cyclothems and MIS (marine isotope stage) 33 to MIS 25. From the base of the R lacunosa Zone (at ca. 0.96 Ma) upward, the succession rapidly becomes sand dominated, a change that can be confidently correlated with the major climatic shift associated with MIS 24 to MIS 22. In the following succession, two tephra layers, named "Pitagora ash" and "Parmenide ash," provide mappable isochronous surfaces across the subbasin. The sedimentary record is remarkably cyclothemic, characterized by a stack of simple or composite, seaward-prograding, sand-dominated tongues and intervening aggradational deposits related to transgressive-deepening episodes. The cyclothems can be confidently correlated with the oxygen isotope record up to the Matuyama-Brunhes inversion, i.e., up to MIS 19, whereas the stratigraphic record postdating MIS 19 has poorer chronological constraints. Dating is provided by tracing the Parmenide ash in the deeper-water coeval succession of the southern part of the Crotone basin, where the deposits including the ash can be correlated by means of nannofossil biostratigwith termination V (transition from MIS 12 to MIS 11). The second unconformity marks an abrupt increase in the proximal character of the sedimentary deposits forming the cyclothems, which incorporate increasing amounts of marginal-marine to continental deposits in the upper part of the subbasin infill. Several lines of direct and indirect evidence indicate that, in spite of the dramatic role of tectonics in shaping stratigraphic architecture, the roles of tectonics and eustasy can be disentangled, owing to the different time scales of the tectonic events. and the high-frequency, high-amplitude glacioeustatic Pleistocene cycles. Interaction between intrabasinal tectonics and high rates of sediment supply allowed forced regressive and possibly also lowstand systems tracts to be preserved in some cyclothems, particularly in the lower part of the succession, an unusual fact in shelf deposits. Considering the far younger age of marine terraces on the Ionian side of Calabria when compared to the Tyrrhenian side, it is thought that, during ongoing subduction of the Ionian crust, a wave of uplift and related extensional tectonics migrated southeastward in the rear of the frontal accretionary wedge.