A POST-EXTINCTION CACO3 SATURATION STATE CRISIS IN THE EARLIEST PALEOGENE (Invited Presentation)

Recent work has focused on how the K-Pg extinction of marine pelagic calcifiers impacted biogeochemical cycling, but the full impact of the extinction on carbon cycling in the ocean remains unknown. Furthermore, the nature and duration of disruption to carbon cycling in the oceans may have implications for the biotic recovery following this extinction event. Here, we suggest that biogeochemical changes associated with the Cretaceous-Paleogene extinction had direct consequences for biodiversity dynamics during the ensuing recovery interval in the Danian. It is well known that carbonate accumulated on the deep seafloor in the earliest Paleogene, in areas that previously were at or below the CCD. This carbonate accumulation is notable in the South Pacific at IODP Site 329-U1370. Here, benthic and planktic foraminifera in carbonate-rich layers provisionally assigned to lower Paleocene planktic foraminiferal Zones P1a and P1b reveal the same collapse in the carbonate carbon isotopic gradient that has been documented from many locations globally. One interpretation of these data is that a temporary decline in the export of organic carbon from the surface ocean to the deep caused a flattening of the surface-deep CaCO₃ gradient, such that saturation decreased in shallow waters while increasing at depth. This scenario is consistent with biodiversity dynamics in the early Paleogene: an analysis of marine animal genera suggests that the pattern of extinction during the Danian was physiologically selective, with unbuffered organisms experiencing the highest extinction rates among all marine taxa, followed by buffered and then non-calcareous organisms. Interestingly, other work has shown that benthic foraminifera did not experience extinction during the K-Pg or its aftermath. Our results suggest that shallow marine organisms may have suffered from a saturation state crisis, perhaps tied to a temporary shutdown in the export of organic carbon. In this way, the aftermath of the K-Pg extinction helped shape the course of the biotic recovery.