Long-term variations in palaeoenvironmental conditions during the Late Aptian–Late Cenomanian in the western Tethys: Insights from the Umbria-Marche Basin (central Italy)

We present a high-resolution record of long-term changes in detrital input, chemical weathering, freshwater influx, and palaeoproductivity across the late Aptian to late Cenomanian (~25 Myr), based on quantitative elemental data from the Umbria-Marche Basin (central Italy, western Tethys). This interval captures a major environmental transition, from multicolored marlstone and black shale-dominated sediments of the Marne a Fucoidi Formation to the widespread chalk deposition of the Scaglia Bianca Formation. During the late Aptian "cold snap" surface water were oligotrophic and stratified while bottom waters were oxygenated although subject to cyclic redox shifts evidenced by the deposition of reddish and greenish marlstones and marly limestones. The Aptian cooling was followed by significant warming across the Aptian-Albian boundary characterized by a dissolution phase and the onset of seafloor deoxygenation cycles that persisted throughout most of the Albian. The early–middle Albian was characterized by intensified weathering and nutrient supply supporting meso–eutrophic conditions and favoring black shale deposition under stratified surface waters. A major shift occurred in the late Albian, with the onset of stable arid conditions that reduced runoff and chemical weathering associated to oligotrophic surface waters and a stable thermocline that persisted until the onset of Oceanic Anoxic Event 2 in the latest Cenomanian. Geochemical data confirm a shift from an unstable palaeoclimatic/palaeoceanographic mode in the Aptian-Albian to stable circulation in the late Albian-Cenomanian. The Western Tethys recorded large-scale climatic-oceanic changes, but its peculiar palaeogeographic position also allowed recording regional variations in weathering/runoff, productivity, and redox conditions at the seafloor.