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Abstract Core from Hole M0077 from IODP/ICDP Expedition 364 provides unprecedented evidence for the physical processes in effect during the interaction of impact melt with rock-debris-laden seawater, following a large meteorite impact into waters of the Yucatán shelf. Evidence for this interaction is based on petrographic, microstructural and chemical examination of the 46.37-m-thick impact melt rock sequence, which overlies shocked granitoid target rock of the peak ring of the Chicxulub impact structure. The melt rock sequence consists of two visually distinct phases, one is black and the other is green in colour. The black phase is aphanitic and trachyandesitic in composition and similar to melt rock from other sites within the impact structure. The green phase consists chiefly of clay minerals and sparitic calcite, which likely formed from a solidified water–rock debris mixture under hydrothermal conditions. We suggest that the layering and internal structure of the melt rock sequence resulted from a single process, i.e., violent contact of initially superheated silicate impact melt with the ocean resurge-induced water–rock mixture overriding the impact melt. Differences in density, temperature, viscosity, and velocity of this mixture and impact melt triggered Kelvin–Helmholtz and Rayleigh–Taylor instabilities at their phase boundary. As a consequence, shearing at the boundary perturbed and, thus, mingled both immiscible phases, and was accompanied by phreatomagmatic processes. These processes led to the brecciation at the top of the impact melt rock sequence. Quenching of this breccia by the seawater prevented reworking of the solidified breccia layers upon subsequent deposition of suevite. Solid-state deformation, notably in the uppermost brecciated impact melt rock layers, attests to long-term gravitational settling of the peak ring. 

An asteroid impact in the Yucatán Peninsula set off a sequence of events that led to the Cretaceous–Paleogene (K–Pg) mass extinction of 76% species, including the nonavian dinosaurs. The impact hit a carbonate platform and released sulfate aerosols and dust into Earth’s upper atmosphere, which cooled and darkened the planet—a scenario known as an impact winter. Organic burn markers are observed in K–Pg boundary records globally, but their source is debated. If some were derived from sedimentary carbon, and not solely wildfires, it implies soot from the target rock also contributed to the impact winter. Characteristics of polycyclic aromatic hydrocarbons (PAHs) in the Chicxulub crater sediments and at two deep ocean sites indicate a fossil carbon source that experienced rapid heating, consistent with organic matter ejected during the formation of the crater. Furthermore, PAH size distributions proximal and distal to the crater indicate the ejected carbon was dispersed globally by atmospheric processes. Molecular and charcoal evidence indicates wildfires were also present but more delayed and protracted and likely played a less acute role in biotic extinctions than previously suggested. Based on stratigraphy near the crater, between 7.5 × 10 14 and 2.5 × 10 15 g of black carbon was released from the target and ejected into the atmosphere, where it circulated the globe within a few hours. This carbon, together with sulfate aerosols and dust, initiated an impact winter and global darkening that curtailed photosynthesis and is widely considered to have caused the K–Pg mass extinction. 

Solander Basin is characterized by subduction initiation at the Pacific-Australia plate boundary, where high biological productivity is found at the northern edge of the Antarctic Circumpolar Current. Sedimentary architecture results from tectonic in-fluences on accommodation space, sediment supply and ocean currents (via physi-ography); and climate influence on ocean currents and biological productivity. We present the first seismic-stratigraphic analysis of Solander Basin based on high-fold seismic-reflection data (voyage MGL1803, SISIE). Solander Trough physiography formed by Eocene rifting, but basinal strata are mostly younger than ca. 17Ma, when we infer Puysegur Ridge formed and sheltered Solander Basin from bottom currents, and mountain growth onshore increased sediment supply. Initial inversion on the Tauru Fault started at ca. 15Ma, but reverse faulting from 12 to ca. 8Ma on both the Tauru and Parara Faults was likely associated with reorganization and formation of the subduction thrust. The new seabed topography forced sediment pathways to be-come channelized at low points or antecedent gorges. Since 5Ma, southern Puysegur Ridge and Fiordland mountains spread out towards the east and Solander Anticline grew in response to ongoing subduction and growth of a slab. Solander Basin had high sedimentation rates because (1) it is sheltered from bottom currents by Puysegur Ridge; and (2) it has a mountainous land area that supplies sediment to its northern end. Sedimentary architecture is asymmetric due to the Subtropical Front, which moves pelagic and hemi-pelagic sediment, including dilute parts of gravity flows, eastward and accretes contourites to the shelf south of Stewart Island. Levees, scours, drifts and ridges of folded sediment characterize western Solander Basin, whereas hemi-pelagic drape and secondary gravity flows are found east of the meandering axial Solander Channel. The high-resolution record of climate and tectonics that Solander Basin contains may yield excellent sites for future scientific ocean drilling. 

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. 

Oral presentation of radioisotopic age data for allanite crystals in granitic rocks of drill core samples from the peak ring of the Chicxulub impact crater.