Sequence stratigraphy in the context of rapid regional uplift and high-amplitude glacio-eustatic changes: the Pleistocene Cutro Terrace (Calabria, southern Italy)

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Abstract

The Cutro Terrace is a mixed marine to continental terrace, where deposits up to 15 m thick discontinuously crop out in an area extending for ca 360 km2 near Crotone (southern Italy). The terrace represents the oldest and highest terrace of the Crotone area, and it has been ascribed to marine isotope stage 7 (ca 200 kyr bp). Detailed facies and sequence-stratigraphic analyses of the terrace deposits allow the recognition of a suite of depositional environments ranging from middle shelf to fluvial, and of two stacked transgressive–regressive cycles (Cutro 1 and Cutro 2) bounded by ravinement surfaces and by surfaces of sub-aerial exposure. In particular, carbonate sedimentation, consisting of algal build-ups and biocalcarenites, characterizes the Cutro 1 cycle in the southern sector of the terrace, and passes into shoreface and foreshore sandstones and calcarenites towards the north-west. The Cutro 2 cycle is mostly siliciclastic and consists of shoreface, lagoon-estuarine, fluvial channel fill, floodplain and lacustrine deposits. The Cutro 1 cycle is characterized by very thin transgressive marine strata, represented by lags and shell beds upon a ravinement surface, and thicker regressive deposits. Moreover, the cycle appears foreshortened basinwards, which suggests that the accumulation of its distal and upper part occurred during forced regressive conditions. The Cutro 2 cycle displays a marked aggradational component of transgressive to highstand paralic and continental deposits, in places strongly influenced by local physiography, whereas forced regressive sediments are absent and probably accumulated further basinwards. The maximum flooding shoreline of the second cycle is translated ca 15 km basinward with respect to that of the first cycle, and this reflects a long-term regressive trend mostly driven by regional uplift. The stratigraphic architecture of the Cutro Terrace deposits is the result of the interplay between regional uplift and high amplitude, Late Quaternary glacio-eustatic changes. In particular, rapid transgressions, linked to glacio-eustatic rises that outpaced regional uplift, favoured the accumulation of thin transgressive marine strata at the base of the two cycles. In contrast, the combined effect of glacio-eustatic falls and regional uplift led to high-magnitude forced regressions. The superposition of the two cycles was favoured by a relatively flat topography, which allowed relatively complete preservation of stratal geometries that record large shoreline displacements during transgression and regression. The absence of a palaeo-coastal cliff at the inner margin of the terrace supports this interpretation. The Cutro Terrace provides a case study of sequence architecture developed in uplifting settings and controlled by high-amplitude glacio-eustatic changes. This case study also demonstrates how the interplay of relative sea-level change, sediment supply and physiography may determine either the superposition of cycles forming a single terrace or the formation of a staircase of terraces each recording an individual eustatic pulse.

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