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During International Ocean Discovery Program (IODP)/Inter- national Continental Drilling Project (ICDP) Expedition 364, the peak ring of the Chicxulub impact crater was drilled in April–May 2016. The expedition recovered 829 m of core, from 505.7 to 1334.7 meters below seafloor (mbsf). Because the geographic in situ orien- tation of the core is not preserved during the drilling process, we report orientation corrections for all core sections. Angular correc- tion values were determined by comparing and matching fractures and lithologic contacts between computed tomography scans of the cores and downhole acoustic borehole images as well as comparing fractures and contacts from one core section to another. The orien- tation correction values can be used to reorient cores to true geo- graphic north, enabling proper assessment of directionality for structural deformation, paleomagnetic indicators, and sedimentary transport data with the Expedition 364 cores. 

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. 

Abstract. Expedition 364 was a joint IODP and ICDP mission-specific platform (MSP)expedition to explore the Chicxulub impact crater buried below the surface ofthe Yucatán continental shelf seafloor. In April and May 2016, thisexpedition drilled a single borehole at Site M0077 into the crater's peakring. Excellent quality cores were recovered from ∼505 to ∼1335mbelow seafloor (mb.s.f.), and high-resolution open hole logs were acquiredbetween the surface and total drill depth. Downhole logs are used to imagethe borehole wall, measure the physical properties of rocks that surround theborehole, and assess borehole quality during drilling and coringoperations. When making geological interpretations of downhole logs, it isessential to be able to distinguish between features that are geological andthose that are operation-related. During Expedition 364 some drilling-inducedand logging-related features were observed and include the following: effects caused by thepresence of casing and metal debris in the hole, logging-tool eccentering,drilling-induced corkscrew shape of the hole, possible re-magnetization oflow-coercivity grains within sedimentary rocks, markings on the boreholewall, and drilling-induced changes in the borehole diameter andtrajectory. 

The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 10 5 km 3 of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 10 6 years. 

Abstract Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small‐scale petrographic and petrophysical measurements with larger‐scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock‐induced microfracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak ring formation, can accurately predict the distribution and orientation of impact‐induced microfractures in large craters, which plays an important role in the geophysical signature of impact structures.