Last interglacial paleoshoreline location and tectono-stratigraphic evolution of the peri-Tyrrhenian Sarno basin, southern Italy, constrained by tephrostratigraphy

Abstract

In this paper, we provide chronological constraints to reconstruct the Late Middle Pleistocene to Holocene geomorphological, stratigraphical and tectonic evolution of the inner Sarno plain, along the Tyrrhenian flank of Southern Italy. These constraints derive from tephrostratigraphical analysis and ⁴⁰Ar/³⁹Ar dating of volcanic deposits, chronologically constrained between ca. 40 ka and 184 ka, recovered from a borehole located in the pediment of the Sarno Mts. The lack of marine to transitional deposits in the borehole testifies that the entire area has been above sea level during this period. Conversely, analysis of previously drilled borehole data indicates the presence of an at least 200 m thick sequence of marine and transitional deposits beneath the Sarno Plain. The top of the marine to transitional deposits in the Sarno basin has been correlated with those in the San Valentino Torio High to the SW, dated to the MIS 5. Consequently, it may be envisaged that the upper portion of the marine deposits in the Sarno Plain also correlates with the MIS 5. This allows to estimate a mean subsidence rate in the last 125 ka, which is 0.32 mm/a. On the other hand, the uninterrupted 200 m-thick marine succession means that subsidence in the Sarno basin was ≥0.7 mm/a during the preceding interval between ~285 ka and the last interglacial (LIG; MIS 9-MIS 5). The subsidence was likely driven by the activity of the Sarno Fault, whose slip rate in the last 40 ka was significantly lower than the subsidence rate since the LIG and the MIS 9-LIG interval. This implies that the fault slip rate has decreased during the last 285 ka. This paper provides a valuable contribution to the study of the complex interplay between glacio-eustatic oscillations and tectonics to assess reliable paleo-sea level indicators.