An improved correlation of the multi-event Aptian/Albian OAE 1b

The Aptian/Albian oceanic anoxic event 1b (OAE 1b; ca 114-109 Ma) contains the record of several perturbations in the global carbon cycle and multiple black shale horizons, particularly in the North Atlantic and Western Tethys. The second sub-event of OAE 1b, the Early Albian Paquier Event, is generally assumed to represent the episode of most widespread black shale deposition during OAE 1b. For this reason, Paquier Event and OAE 1b have become synonyms in the geological literature. We have studied Upper Aptian/Lower Albian sediments from three DSDP/ODP sites in the North Atlantic (DSDP 545 and ODP sites 1049 and 1276) using a combination of sedimentological and geochemical methodologies. We compared our results between studied sites in the North Atlantic and to available data from sites in the Vocontian and Pacific basins thereby improving our knowledge of the Aptian/Albian stratigraphy of the North Atlantic. We were able to correlate the studied sections using chemostratigraphy and recently published biostratigraphy and thus determine that the most widespread of the OAE 1b black shale horizons is in fact the Upper Aptian Kilian Level. The Paquier Level is not as widespread as previously thought and it should therefore not be regarded as ‘OAE 1b’. Our results, which are in agreement with recent paleontological data by other authors, illustrate well the problems associated with correlating black shale horizons deposited during OAE 1b. The geographical extent of black shale deposition during one such event may not always carry implications for the nature of the global forcing mechanisms. The perturbations in the global carbon cycle that resulted in the negative excursions recorded in Aptian/Albian sediments have a global forcing mechanism. However, whether black shales or organic-lean sedimentary rocks be associated with these excursions further depends on local sedimentary processes.