Long-term palaeoenvironmental changes from the Late Aptian to Late Cenomanian in the western Tethys: New evidence from the Umbria-Marche Basin (central Italy)

A high-resolution reconstruction of detrital input, chemical weathering, freshwater influx, and palaeoproductivity trends from the late Aptian to the late Cenomanian (~25 Myr) is presented, based on quantitative geochemical data from the Umbria-Marche Basin (central Italy, western Tethys). This record captures a key environmental transition from the multicolored marlstone and black shale-rich sediments of the Marne a Fucoidi Formation to the widespread chalk deposits of the Scaglia Bianca Formation (Gambacorta et al., 2015; Giorgioni et al., 2015). During the late Aptian “cold snap,” oligotrophic surface waters coexisted with oxygenated bottom waters, punctuated by cyclic redox fluctuations recorded in the alternation of reddish and greenish marlstones and marly limestones. Following this cooling phase, a marked warming across the Aptian–Albian boundary was characterized by a dissolution phase and the onset of repeated seafloor deoxygenation cycles. In the early–middle Albian, intensified chemical weathering and increased nutrient supply promoted meso–eutrophic conditions, favoring widespread black shale deposition under stratified surface waters. A major environmental shift occurred during the late Albian, marked by the establishment of stable, arid conditions. These conditions reduced chemical weathering and runoff, leading to oligotrophic surface waters and a persistent thermocline, which lasted until the latest Cenomanian onset of Oceanic Anoxic Event 2 (OAE 2). The geochemical record documents large-scale climatic-oceanic changes with a transition from an unstable palaeoclimatic–palaeoceanographic regime during the Aptian–Albian to a more stable circulation pattern during the late Albian–Cenomanian.