Paleovalley fills as terrestrial archives of Mediterranean Sapropel S1: insights from the Biferno Paleovalley System (Southern Italy)

Sapropel S1 corresponds to the latest deoxygenation event that occurred in the Mediterranean Sea between ∼10.2 and 6.8 cal kyr BP. However, terrestrial deposition coeval with Mediterranean Sapropel S1 remains poorly understood. Through the integration of sedimentological, paleontological, geochemical (TOC, TN, δ13C, δ15N) and chronological data within a regional onshore-offshore framework, this study investigates the Upper Pleistocene-Holocene fill of the Biferno paleovalley system (Southern Italy) and characterizes the S1-equivalent (S1eq) succession. The results document a continuous S1eq record comprising three stratigraphic intervals (S1aeq, S1breakeq, and S1beq) that can be correlated with the corresponding offshore S1 phases. Facies evolution from poorly-drained floodplain to estuarine deposits reflects Holocene relative sea-level rise and paleovalley drowning. Bulk geochemical proxies display strong stratigraphic control, with δ13C and δ15N trends closely tracking facies shifts and Organic Matter (OM) sources. Onshore-offshore correlation and comparison with other Adriatic paleovalley systems reveal a marked decoupling in organic-carbon accumulation during the S1 break, consistent with the progressive landward migration of river mouths during the Holocene transgression. This evolution promoted enhanced terrigenous OM storage within paleovalleys while reducing its export toward deeper basin sectors. These findings indicate that paleovalley systems constitute key transient repositories of sediment and organic carbon during rapid transgression and provide a valuable terrestrial archive for reconstructing the evolution of the Adriatic source-to-sink system during Mediterranean Sapropel S1 deposition. Their stratigraphic record offers a critical link between continental and marine systems, providing new constraints on the environmental processes accompanying S1 deposition in the Adriatic and Mediterranean regions.