Can the initial phase of the K/Pg boundary fern spike be reconciled with contemporary models of the Chicxulub impact? New insights from the birthplace of the fern spike concept

• Published in: Review of palaeobotany and palynology 2023-02, Vol.309, p.104824, Article 104824
• Main Author: Berry, Keith
• Format: Article
• Language: English
• Subjects: Chicxulub; Dennstaedtiaceae; Fern spore abundance anomaly; Mass extinction; Raton Basin
• ISSN: 0034-6667; 1879-0615
• DOI: 10.1016/j.revpalbo.2022.104824

Researchers at Tanis, North Dakota, U.S.A., cited faulting associated with soft sediment deformation of the K/Pg boundary clay at Madrid East in the Raton Basin, U.S.A., as additional evidence of “more-instantaneous effects” that preceded the longer-term, climatic effects of the Chicxulub impact. However, Madrid East is among numerous localities where the initial phase of the K/Pg boundary fern spike initiated within rather than above the K/Pg boundary clay crosscut by this fault. Accordingly, this phase of the K/Pg boundary fern spike must have preceded the cessation of seismic aftershocks of the Chicxulub impact—a conclusion also reached by researchers at the deep marine depositional setting of Gorgonilla Island in Colombia, South America. The observation that the Chicxulub impact winter was shorter in duration than post-impact seismicity need not signify a major dilemma for contemporary climate models of the Chicxulub impact, a dilemma originally exacerbated by the common perception that this phase of the fern spike was dominated by tropical tree ferns. Because tree ferns have exceptionally long generation times (ca. 100 y according to contemporary estimates), they could not have had ample time to reach sporing stage if they were killed back to rhizomes or other belowground reserves by a complete shutdown of photosynthesis and subsequent impact winter. Alternatively, the dennstaedtiaceous affinity of spores at Madrid East suggests that these ferns had a generation time of only 2–4 y, which better fits contemporary estimates on how long it took for the effects of Chicxulub to wind down. •Tanis researchers suggest seismic aftershocks preceded the K/Pg impact winter.•The first phase of the fern spike preceded the cessation of aftershocks.•The generation time of Dennstaedtiaceae, not Cyatheaceae, fits Chicxulub models.•Seismic aftershocks occur many years after major mainshocks.•The first plants recovered within a few years of the impact.