How bioturbation obscured the Cretaceous-Palaeogene boundary record

The Cretaceous–Palaeogene (K/Pg) boundary interval is often penetrated by burrows, which may obscure stratigraphic and micropalaeontological records, leading to misinterpretations of the sequence of events spanning the K/Pg boundary. Here, we assess the role of burrowing organisms in the redistribution of benthic foraminifera across the boundary at Bidart (France), and report a strong relationship between the behaviour represented by pre- and post-K/Pg trace fossils and their benthic foraminiferal content. We further infer a brief interval of eutrophic conditions at the seafloor, as reported from other locations, which disappeared from the lowermost Danian stratigraphic record and is represented only inside post-K/Pg trace fossils hosted in Cretaceous strata. The combined study of trace fossils and microfossils is a powerful tool in eco-stratigraphy and event-stratigraphy, and can yield important insights into the completeness of the K/Pg record, especially at locations such as Bidart where this interval has traditionally been assumed to be complete.