Morfoevoluzione, sedimentazione e tettonica recente dell’alta piana del Sele e delle sue valli tributarie (Campania)

Morphological, sedimentary and neotectonic evolution of the inner Sele River Plain and its tributary valleys (Campania,Italy)

Abstract

The Sele River alluvial coastal plain, occupying the innermost portion of a structural depression (the Gulf of Salerno Grahen), cuts almost transversally the Tyrrhenian slope of the Apennin chain and attains a total maximum throw of abont 4 000 m. The western half of this graben (i.e. the portion which is nowday submerged into the Tyrrhenian Sea) has experienced a complex neotectonic history. It may be made to start from the modelling of a mature erosional landscape on the top of the complex thrust system forming the Campanian Apennines. The modelling of this paleosurface was probably accomplished by the end of Pliocene. During Lower Pleistocene a period of intense block-faulting broke up the said mature landscape, lifted fragments of it several hundred meters above the sea level and caused a phase of moderate subsidence on the inner portion of Salerno graben. Depending of the increased relief of the interland, the depression experienced a huge and coarse clastis deposition which gave rise to the thick Conglomerati di Eboli group, whose age covers at least the interval 1,5-0.9 Myrs. Possibly during the late Lower Pleistocene two distinct fases of block-faulting and tilting affected the inner margin of the plain. These resulted in the 400 m uplift of Conglomerati di Eboli and in the reshaping of the graben outline. On the subsiding sectors, that reached much closer to the mountain front than during the Lower Pleistocene, a complex and variable set of transitional to fluvial coastal plain environments established leading to the formation of a thick sedimentary sequence (Complesso di Persano). The top surface of said sequenee forms a wide terrace resting at 30 to 100 m a.s.l. and deeply dissected by Sele and Calore rivers. This terrace continues upstream of the coastal plain within the lower reaches of Calore and Tanagro valleys. Both on the coastal plain and within the valleys the morphology of the terrace is affected by faults of little throw and few degrees tilting. Based on its relations to some beach deposits outcropping along the outer rim of the terrace and dated 130.000 yrs B.P., it was possible to infer that the sedimentation of the Complesso di Persano stopped sometime before that age. The attribution to the Middle Pleistocene of these deposits, coupled with the correlations we succeded to trace between the latter and other terraced formations of the tributary valleys, allowed us to propose a Lower Pleistocene age for several undated detrital and fluvial units occurring well inside the chain and morphostratigraphically comprised between the Late Tertiary paleosurface and the Middle Pleistocene terraced formations.