New Data on the Expression of the Early Eocene Hyperthermals in Northern Bulgaria: Riben Section Revisited

Abstract

We present new lithologic, nannofossil biostratigraphic and benthic carbon and oxygen isotope records for a marly-rich, 11 m thick Paleocene-Eocene section, now exposed at an old quarry at Riben Village, northern Bulgaria. The occurrence of NP9, NP10 and NP11 nannofossil zones is evidenced by detailed high-resolution nannofossil biostratigraphy. The carbon dissolution interval is marked by the abrupt drop of CaCO3 content and deposition of a clay interval at the onset of the Paleocene-Eocene Thermal Maximum (PETM). Stable isotope analyses of δ13C and δ18O were performed on benthic-foraminiferal tests. An unusual two-fold carbon isotope excursion (CIE) in the PETM interval is documented (total negative shift of 2.89‰). Moreover, three paired negative excursions: two in the Paleocene within the PETM interval, upper NP9 zone, and one within the early Eocene, NP11 zone are identified. The most prominent negative carbon isotope excursion (4.90‰ negative shift) is related with ETM3 (or “X” event), 52.84 Ma ago. Integration of nannofossil biostratigraphy, benthic stable isotope data sets and lithology unravel two separate early Eocene hyperthermal events: the PETM (= ETM1) and the ETM3 (= “X” event), recorded at Riben section.