The first day of the Cenozoic.

Highly expanded Cretaceous-Paleogene (K-Pg) boundary section from the Chicxulub peak ring, recovered by International Ocean Discovery Program (IODP)-International Continental Scientific Drilling Program (ICDP) Expedition 364, provides an unprecedented window into the immediate aftermath of the impact. Site M0077 includes ∼130 m of impact melt rock and suevite deposited the first day of the Cenozoic covered by <1 m of micrite-rich carbonate deposited over subsequent weeks to years. We present an interpreted series of events based on analyses of these drill cores. Within minutes of the impact, centrally uplifted basement rock collapsed outward to form a peak ring capped in melt rock. Within tens of minutes, the peak ring was covered in ∼40 m of brecciated impact melt rock and coarse-grained suevite, including clasts possibly generated by melt-water interactions during ocean resurge. Within an hour, resurge crested the peak ring, depositing a 10-m-thick layer of suevite with increased particle roundness and sorting. Within hours, the full resurge deposit formed through settling and seiches, resulting in an 80-m-thick fining-upward, sorted suevite in the flooded crater. Within a day, the reflected rim-wave tsunami reached the crater, depositing a cross-bedded sand-to-fine gravel layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal fragments. Generation of a deep crater open to the ocean allowed rapid flooding and sediment accumulation rates among the highest known in the geologic record. The high-resolution section provides insight into the impact environmental effects, including charcoal as evidence for impact-induced wildfires and a paucity of sulfur-rich evaporites from the target supporting rapid global cooling and darkness as extinction mechanisms.

Hot carbonates deep within the Chicxulub impact structure.

Constraining the thermodynamic conditions within an impact structure during and after hypervelocity impacts is extremely challenging due to the transient thermal regimes. This work uses carbonate clumped-isotope thermometry to reconstruct absolute temperatures of impact lithologies within and close to the ∼66 Myr old Chicxulub crater (Yucatán, México). We present stable oxygen (δ18O), carbon (δ13C), and clumped-isotope (Δ47) data for carbonate-bearing impact breccias, impact melt rock, and target lithologies from four drill cores on a transect through the Chicxulub structure from the northern peak ring to the southern proximal ejecta blanket. Clumped isotope-derived temperatures (T(Δ47)) are consistently higher than maximum Late Cretaceous sea surface temperatures (35.5°C), except in the case of Paleogene limestones and melt-poor impact breccias outside of the crater, confirming the influence of burial diagenesis and a widespread and long-lived hydrothermal system. The melt-poor breccia unit outside the crater is overlain by melt-rich impact breccia yielding a much higher T(Δ47) of 111 ± 10°C (1 standard error [SE]), which likely traces the thermal processing of carbonate material during ejection. Finally, T(Δ47) up to 327 ± 33°C (1 SE) is determined for the lower suevite and impact melt rock intervals within the crater. The highest temperatures are related to distinct petrological features associated with decarbonation and rapid back-reaction, in which highly reactive CaO recombines with impact-released CO2 to form secondary CaCO3 phases. These observations have important climatic implications for the Cretaceous-Paleogene mass extinction event, as current numerical models likely overestimate the release of CO2 from the Chicxulub impact event.

Amplified seasonality in western Europe in a warmer world.

Documenting the seasonal temperature cycle constitutes an essential step toward mitigating risks associated with extreme weather events in a future warmer world. The mid-Piacenzian Warm Period (mPWP), 3.3 to 3.0 million years ago, featured global temperatures approximately 3°C above preindustrial levels. It represents an ideal period for directed paleoclimate reconstructions equivalent to model projections for 2100 under moderate Shared Socioeconomic Pathway SSP2-4.5. Here, seasonal clumped isotope analyses of fossil mollusk shells from the North Sea are presented to test Pliocene Model Intercomparison Project 2 outcomes. Joint data and model evidence reveals enhanced summer warming (+4.3° ± 1.0°C) compared to winter (+2.5° ± 1.5°C) during the mPWP, equivalent to SSP2-4.5 outcomes for future climate. We show that Arctic amplification of global warming weakens mid-latitude summer circulation while intensifying seasonal contrast in temperature and precipitation, leading to an increased risk of summer heat waves and other extreme weather events in Europe's future.

Life before impact in the Chicxulub area: unique marine ichnological signatures preserved in crater suevite.

To fully assess the resilience and recovery of life in response to the Cretaceous-Paleogene (K-Pg) boundary mass extinction ~ 66 million years ago, it is paramount to understand biodiversity prior to the Chicxulub impact event. The peak ring of the Chicxulub impact structure offshore the Yucatán Peninsula (México) was recently drilled and extracted a ~ 100 m thick impact-generated, melt-bearing, polymict breccia (crater suevite), which preserved carbonate clasts with common biogenic structures. We pieced this information to reproduce for the first time the macrobenthic tracemaker community and marine paleoenvironment prior to a large impact event at the crater area by combining paleoichnology with micropaleontology. A variable macrobenthic tracemaker community was present prior to the impact (Cenomanian-Maastrichtian), which included soft bodied organisms such as annelids, crustaceans and bivalves, mainly colonizing softgrounds in marine oxygenated, nutrient rich, conditions. Trace fossil assemblage from these upper Cretaceous core lithologies, with dominant Planolites and frequent Chondrites, corresponds well with that in the overlying post-impact Paleogene sediments. This reveals that the K-Pg impact event had no significant effects (i.e., extinction) on the composition of the macroinvertebrate tracemaker community in the Chicxulub region.

Shaping of the Present-Day Deep Biosphere at Chicxulub by the Impact Catastrophe That Ended the Cretaceous.

We report on the effect of the end-Cretaceous impact event on the present-day deep microbial biosphere at the impact site. IODP-ICDP Expedition 364 drilled into the peak ring of the Chicxulub crater, México, allowing us to investigate the microbial communities within this structure. Increased cell biomass was found in the impact suevite, which was deposited within the first few hours of the Cenozoic, demonstrating that the impact produced a new lithological horizon that caused a long-term improvement in deep subsurface colonization potential. In the biologically impoverished granitic rocks, we observed increased cell abundances at impact-induced geological interfaces, that can be attributed to the nutritionally diverse substrates and/or elevated fluid flow. 16S rRNA gene amplicon sequencing revealed taxonomically distinct microbial communities in each crater lithology. These observations show that the impact caused geological deformation that continues to shape the deep subsurface biosphere at Chicxulub in the present day.

Globally distributed iridium layer preserved within the Chicxulub impact structure.

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.