Long-term variations in palaeoenvironmental conditions in the Western Tethys during the late Aptian–late Cenomanian time interval: From an unstable to a stable ocean

A high-resolution record of long-term variations in detrital input, chemical weathering, freshwater influx, and palaeoproductivity from a pelagic environment of the Western Tethys spanning the late Aptian to late Cenomanian (∼25 million years) is presented, based on quantitative elemental data from the Umbria-Marche Basin (Monte Petrano section and Piobbico Core, central Italy). This interval captures a major environmental transition from the multicolored marlstone and black shale-dominated sediments of the Marne a Fucoidi Formation to the extensive limy deposits of the Scaglia Bianca Formation but also highlights three main distinct palaeoenvironmental phases during the deposition of the Marne a Fucoidi. During the late Aptian cooling episode, semi-arid conditions prevailed, with surface waters being oligo- to mesotrophic and stratified, while bottom waters remained oxygenated. A marked warming started at the Aptian/Albian boundary paralleled by increased surface water fertility and seafloor deoxygenation. The early to middle Albian experienced intensified weathering and nutrient supply under warm and humid conditions, fostering meso- to eutrophic conditions and promoting the deposition of alternated marlstones and black shales. A major transition took place in the late Albian, with the emergence of arid conditions that reduced runoff and chemical weathering, coinciding with progressively more oligotrophic surface waters and a stable thermocline that persisted until just prior to the onset of Oceanic Anoxic Event 2 in the latest Cenomanian.