Correlating environmental changes during early Albian oceanic anoxic event 1B using benthic foraminiferal paleoecology

Abstract

The nature and consequences of mid-Cretaceous oceanic anoxic events (OAEs) are the subject of ongoing debate, and recent studies have shown that different scenarios are needed to explain each of these events. Nevertheless, similarities between the different OAEs can be observed. Here, we have reconstructed paleoenvironmental changes during the early Albian OAE 1b using benthic foraminiferal distributions and lithologies in three sections from different basins and paleowater depths. Eutrophic conditions, as indicated by the presence of infaunal as well as opportunistic genera such as Gyroidinoides, Pseudobolivina, Pleurostomella and bolivinitids, prevailed before and during the OAE and led to dysoxic to anoxic conditions. Dysoxia was most intense in the bathyal sections but also occurred in the outer shelf where more heterogeneous patterns of foraminiferal distributions are believed to reflect fluctuations of the upper boundary of an oxygen-minimum zone. A change from eutrophic to mesotrophic conditions caused the termination of OAE 1b and opportunistic benthic foraminifera (e.g. Pseudobolivina, Pleurostomella) were the first to subsequently repopulate the bathyal sea floor. Repopulation occurred rapidly in the shallow settings and gradually in the deeper sites, where a normal, diverse pre-event fauna was established a few tens of thousands of years after OAE 1b.