High-frequency cyclicity, palaeoclimate and palaeoenvironments in the upper Messinian Lago-Mare deposits of the Fonte dei Pulcini section (Majella Mts., central Italy).

Late Messinian Lago-Mare deposits show high-frequency cyclicity in the whole Mediterranean Basin. Both mm- and cm-scale cyclicities have been observed in several ODP sites as well as in stratigraphic sections from the Mediterranean borderland. We have analyzed a well-exposed late Messinian Lago-Mare section from the Adriatic side of the central Apennines (Italy). At the Fonte dei Pulcini section (SE Majella Mts.), mm- and cm-scale white-and-dark couplets have been observed in the field. A 50cm regular-spaced sampling has been performed in the uppermost 53m of the late Messinian Lago-Mare clays. On the 107 collected samples, geochemical (CaCO3 content), mineralogical (XRD analyses) and micropalaeontological investigations have been performed. In addition, SEM and Microprobe investigations as well as mineralogical and micropalaeontological analyses have been carried out on single lamina from a 34cm-thick interval of mm-scale laminites.The uppermost Messinian Lago-Mare facies of the Fonte dei Pulcini section (southeastern Majella), which developed in the pre-orogenic Adriatic foreland basin, shows high-frequency cyclicities that consist of mm- and cm-scale white-and-dark couplets (fig. 1). Similar cyclicities characterize the uppermost Messinian Lago-Mare deposits recovered in several western Mediterranean ODP sites (Iaccarino and Bossio, 1999) as well as on the Mediterranean borderlands (Vismara-Schilling et al., 1976; Fortuin et al., 1995; Bassetti et al., 1994; 1998; Roveri et al., 2001). Since these high-frequency sedimentary signatures are widespread in the whole Mediterranean Basin, allocyclic mechanisms (e.g. climatic changes) have to be considered as a primary cause for generating these rhythmic deposits.Besides the mm- and cm-scale rhythmites found in the field, spectral analyses performed on the CaCO3 data set from the Fonte dei Pulcini A section evidenced higher periodicities of about 2.1 m (f = 0.47 cycles/m), 2.8 m (f = 0.35 cycles/m) and 5.6 m (f = 0.17 cycles/m). Using the estimated sedimentation rate (about 1 m/ky) for the late Messinian Lago-Mare episode of the Majella area, the computed depth periodicities have been time converted into 2.1 ky, 2.8 ky and 5.6 ky. These periodicities are tentatively related to hypercycles of the sunspot activity since similar cyclicity values have been found by cosmogenic isotope data (Vitinsky et al., 1986; Usoskin and Mursula, 2003) or recognized in Carboniferous varves (Milana and Lopez, 1998).Taking into account the estimated sedimentation rate, the lowest periodicity observed in the analyzed section as mm-scale laminites should represent an annual cyclicity. Then, each individual white-and-dark couplet can be considered as a “varve” since it represents a sedimentary cycle produced during the course of a year.The varved sediments in the upper Messinian deposits of the Majella area show a marked seasonality with the alternation of humid and more arid conditions. This marked seasonality could be explained with the climate conditions related to the monsoon system developed in the Mediterranean region during the late Miocene (Griffin, 2002).Relevant climatic oscillations from drier to moister and colder conditions in the late Messinian of the Mediterranean realm are revealed by both palynological (Bertolani Marchetti and Marzi, 1988; Bertini, 1992; 1994; Bertini, in press) and mineralogical investigations (Chamley, 1975; Chamley and Robert, 1980; Martìnez-Ruìz et al., 1999). In th