Chicxulub Impact Predates the KPB Mass Extinction by 200-230 kyr;Deccan Volcanism, Mercury and Climate change are main causes

Discovery of impact glass in deep water at El Penon, NE Mexico, revealed a 2m thick impact spherule deposit during excavation of an 8m thick late Maastrichtian sequence ^[1]. The impact spherules are pristine and undisturbed in the late Maastrichtian. Marly sediments prevailed at the base followed mainly by small rip-up clasts overlain by a 10cm thick layer, which consists only of amorphous molten glass containing occasional planktic foraminifera. Large impact glass spherules 3-5mm in size followed and gradually reduced in size. Up-section the impact spherule size gradually reduced (2mm) but remained abundant and devoid of sediments. Near the top, spherules reduced in size and abundance mixed with marls, ending the impact deposit quietly. Marls and marly limestones followed. Preliminary age determinations identified the impact based on various indicators. 1) Biostratigraphy: First appearance of planktic foraminifer Plummerita hantkeninoides zone CF1 age ~200-kyr pre-KPB. 2) U-Pb dating of Deccan volcanism ~230-kyr pre-KPB. 3) Mercury anomalies of Deccan volcanism EE6 ~215-kyr pre-KPB. 4) Cyclostratigraphy ~230-kyr pre-KPB^[2]. Impact glass spherules are ubiquitous in the late Maastrichtian of NE Mexico and the impact is believed to be the source. But these spherules are almost always reworked from older into younger sediments, which eliminates age control. Nevertheless, the reworked Chicxulub impact spherules were always believed the source – but this is no longer tenable. The discovery of pristine impact spherules in NE Mexico at the much older age of 200-kyr to 230-kyr places the Chicxulub impact outside the realm of the KPB mass extinction. However, we know since 2003 the Chicxulub crater predates the KPB, although this fact was always neglected. New mercury data from a dozen localities in NE Mexico reveals further evidence that the Chicxulub impact is linked to the older impact crater. Our data supports Deccan volcanism as primary cause for the KPB mass extinction.

 

 

References:

[1] Keller et al., 2009, Journal of the Geological Society, London

[2] Keller et al., 2020, Global Planetary Change