Astronomical calibration of paleoclimatic and planktic foraminiferal events of the Cretaceous-Paleogene transition at Zumaia, Spain
Résumé
The main trigger for the Cretaceous/Paleogene boundary (KPB) mass extinction is still subject ofintense debate. The co-occurrence of the Chicxulub impact (Yucatan, Mexico) and massive DeccanTraps volcanism (India) during Chron C29r hinders disentangling their climatic and environmentaleffects. Unravelling the influence of Deccan volcanism on the KPB extinction and otherMaastrichtian and Danian perturbations requires more accurate age calibrations and durationestimates of biotic and climatic events. Here we integrate existing astrochronologies of the Zumaiasection, allowing us to produce a refined cyclostratigraphic calibration of the main plankticforaminiferal and paleoclimatic events recorded across the KPB in the well-know Zumaia section(NW, Spain).At Zumaia, the KPB is marked by a ~8 cm-thick dark clay bed, with low values of %CaCO3 and δ13C.The Chicxulub ejecta-rich airfall layer has been identified at the base of the dark clay bed, but it ispartially masked within a 1–2 cm-thick diagenetic calcitic layer. At Zumaia, the KPB has beenastronomically calibrated at 66 Ma (compatible with radioisotopic ages), and the duration of darkclay bed is estimated at ~10 kyr. The first appearances (FA) of the Danian planktic foraminiferalindex-species Parvularugoglobigerina longiapertura, Parvularugoglobigerina eugubina,Eoglobigerina simplicissima, Parasubbotina pseudobulloides, Subbotina triloculinoides andGlobanomalina compressa have been orbitally tuned at Zumaia, to have occurred at 8, 30, 45, 70,210, and 475 kyr after the KPB. Specimens of Plummerita hantkeninoides have been identifiedfor the first time in the Maastrichtian of Zumaia, and its first occurrence is dated at ~100 kyrbefore the KPB. Based on d13C data, we have identified the late Maastrichtian Warming Event(LMWE), the early Danian Dan-C2 and the Lower-C29N events. Additionally, a bloom of theeutrophic/opportunist genus Chiloguembelitria, interpreted as a period of environmental stress,has also been recognized above and separate from the KPB clay bed. Besides the KPB, the mainpaleoclimatic/paleoenvironmental events have been astronomically calibrated at Zumaia asfollows: the LMWE between 270 and 120 kyr before the KPB, the Dan-C2 event between 205 and305 kyr after the KPB, the Lower-C29N event between 520 and 595 kyr after the KPB, and theChiloguembelitria bloom between 100 and 305 kyr after the KPB. According to this chronology, weconclude that the LMWE and early Danian Chiloguembelitria bloom seems to coincide in timewith major volcanic pulses of the Deccan Traps, unlike the Dan-C2 and Lower-C29N events, which
appear to have been driven by orbital forcing. Regardless of the cause of climatic andenvironmental events, all these perturbations appear unrelated to the KPB mass extinction event.It supports the hypothesis that the influence of Deccan volcanism on planktic foraminiferalassemblages during the Maastrichtian and Danian was limited.