Trophism, climate and paleoweathering conditions across the Eocene-Oligocene transition in the Massignano section (northern Apennines, Italy)

Abstract

The Eocene-Oligocene transition represents the latest greenhouse-icehouse shift faced by Earth, a major global climate change associated with carbon cycle perturbation. In this paper, we investigate the Massignano stratigraphic section (northern Apennines, Italy), GSSP of the Eocene-Oligocene boundary, by X-ray diffraction analysis of clay minerals and carbon and oxygen stable isotopes to explore the link among climate, paleoweathering and runoff, and carbon cycle in the Neotethys across this major climatic transition. We examine the interplay between global climate forcing and orogen evolution controlling the Massignano hemipelagic sedimentation. The late Eocene clay mineral assemblages indicate that the Neotethys was sensitive to global eustatic changes as well as changes in composition and rates of weathered sediments accumulating into the basin. The carbon isotope record matches with the global signal, showing productivity pulses linked to cooling phases and sea-level drops before 34.8 Ma. Subsequently, a constant negative trend is recorded, which is consistent with the global carbon isotope curve, and attests for a decrease of primary productivity linked to decreasing atmospheric CO2. This negative trend ends at the Eocene-Oligocene boundary, when the onset of the global carbon isotope positive excursion is recorded also within the Massignano hemipelagic succession. On the contrary, the clay mineral assemblage is quite constant across the Eocene-Oligocene boundary reflecting the complex interplay among fluvial discharge, sea level changes and orogen dynamics which clouded the global climate shift. In this context, the enhanced fluvial discharge likely contributed to sustain high trophic conditions in the Adriatic waters and, in turn, the Oligocene positive carbon isotope shift. These results highlight how clay minerals proved to be a useful proxy to identify the interplay between global and regional controlling factors on hemipelagic sedimentation and, their integration with the carbon isotope record, provides insights into carbon cycle dynamics.