A palynological and organic geochemical study of the early Aptian Selli unit (oceanic anoxic event 1a) of the western Tethys provides new information about paleoceanography and documents pronounced changes in the regional climate pattern. It also emphasizes the role of oxic degradation of organic matter, even at horizons with the highest rates of organic carbon (Corg) accumulation. The absence of anoxia indicates that enhanced primary production is the main reason for these organic carbon accumulations, and variations in preservation are related to pulses in primary production and nutrient recycling. Despite the high-productivity character of the Selli unit black shales, the δ13Ccarb values are not marked by a positive shift, but by an interval of unchanged values. Warm climatic conditions for deposition of the Selli unit are inferred from the presence of southern provenance pollen and low δ18O values. For the interval above the Selli unit, changes in the pollen spectrum and an increase in δ18O values reflect a hitherto undocumented late early Aptian cooler and more humid climate and/or a reorganization of the Tethyan oceanographic circulation pattern.
- Geological Society of America