Organic matter properties in buried paleosols sequence of the middle Pleistocene as a biomarker in Vulsini Volcanic District (Central Italy)

A sequence of three paleosols (PIT3, CAN2, CAN1) of the Quaternary Latera pyroclastic succession (western Vulsini Volcanic District) was investigated with the aim of reconstructing the paleoenvironment of the Middle Pleistocene focusing on soil biomarkers. Wide variability (from 85 to 3 %) of extracted organic carbon on total (ExC/OC) was found along the depth. Py-GC/MS analysis of extractable soil organic matter (ExOM) revealed significant vertical variations in aromatic and aliphatic hydrocarbons. Paleoproxies derived from n-alkane chains—including non-diagenetic (L/H, ACL, n-C29/n-C31, TAR) and diagenetic (CPI, OEP, LSR) indices— indicated dominant input from terrestrial higher plants in paleosols buried by Sovana (PIT3) and Farnese (CAN2) eruptions, while microbial-aquatic sources prevailed in that buried by Canino (CAN1). Bioma reconstructions suggest a mixed woody-herbaceous cover in CAN2 and a stratigraphic transition from herbaceous to woodyshrub vegetation in PIT3. Presence of phytoliths in PIT3 supported grassland soils. Diagenetic indices revealed moderate to high degradation of aliphatic hydrocarbons, likely driven by paleoclimatic variability. FT-IR spectra from PIT3 showed n-alkane dominance, suggesting organo-mineral stabilization due to interaction with kaolinite, halloysite and allophanes. Pedological analyses and pedogenetic indices evidenced low OC content in CAN1 and intense weathering, consistent with paleoproxy data and δ18O records indicating increase of hothumid conditions during MIS 7.5. In contrast, PIT3 and CAN2 showed OC accumulation and moderate pedogenesis, with vitric features exclusively in PIT3. These findings align with CAN2 development under initially warm and humid conditions followed by temperate climate, whereas alternating dry-moist phases in PIT3 under progressively cooler conditions toward MIS 7.4.