DEVELOPMENT OF THE BELVEDERE SEDIMENTARY BASIN IN SOUTHERN ITALY: INTEGRATION OF STRUCTURAL DATA AND ANALOGUE MODELING

The Tyrrhenian Belvedere basin of southern Italy is a transgressive sequence of upper Miocene sediments deposited on crystalline units of the Calabrian Arc. The evolution of this basin is not well known and much debated. There are two widely accepted, significantly different hypotheses: 1) it is a piggy-back basin that formed during the latest contractional phase of the Apenninic orogen; 2) the basin formed during post-contractional rifting of the Tyrrhenian Sea.

Results of fieldwork and analyses of mesostructures demonstrate there are two principal fault sets in the Belvedere basin. The primary fault set strikes NNW-SSE, records dip-slip motion, occurs commonly in conjugate pairs, and have structures common to growth faults. This fault set accommodated significant ENE-WSW extension consistent with early rifting of the Tyrrhenian Sea. The secondary fault set strikes primarily ENE-WSW and accommodated minor oblique to strike-slip displacements. This fault set transferred slip among faults in the primary fault set. Biostratigraphy for the two principal sedimentary cycles in the Belvedere Basin are consistent with a Serravalian age for the first sedimentary cycle and middle to upper Tortonian age for the second one. Consequently, formation and deformation of the basin had to begin at least during the Serravalian and continued until the upper Tortonian.

The absence of a boundary fault at the basin’s margin, the presence of a progressive unconformity within the basin, and the rotation of conjugate faults are consistent with the Belvedere Basin having formed above a décollement in the crystalline units. Analogue modeling of a detachment basin was capable of producing the structures and unconformity very similar to those observed in the field. The Belvedere basin therefore probably formed during early rifting of the Tyrrhenian Sea when extension-related slip localized in a basement-hosted décollement below the evolving sedimentary basin.