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

Abstract

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.

Keywords: chicxulub; craters; deep biosphere; drilling; impact crater.

FIGURE 1

Location of the drilling site M0077 in the Chicxulub crater, Yucatán peninsula, México as seen using gravity data. Figure is adapted from Gulick et al. (2008).

FIGURE 2

Microbial abundance through the Chicxulub Expedition 364 (site 0077A) core. Diagram showing cell enumerations alongside total extracted DNA and total organic carbon (TOC) content, porosity, and open fractures. The limit of detection is taken as 1 × 10⁴ cells/g. The horizontal lines separate the sections of suevite. TOC and porosity are displayed as moving averages of each 20 m depth. The classification of the geological units adopted by the drilling expedition scientists are shown alongside (see section “Materials and methods”).

FIGURE 3

Box plots of cell numbers associated with Chicxulub impact lithologies. Lithologies shown are postimpact sedimentary rocks, suevite (cell enumerations in all suevite units), granite basement alone (elevated cell counts in non-granitic material removed), and non-granite rocks in the granitic unit (i.e., geological interfaces within the granitic unit). Logarithmically transformed data are shown as a box plot.

FIGURE 4

Venn diagram showing the number of microbial taxa (assigned at the lowest identified taxonomic levels) in the three lithologies. The non-overlapping parts of the circles show the number of taxa that are unique to each lithology, whereas the overlapping parts of the circles display the number of taxa that are shared between the lithologies.

FIGURE 5

Canonical analysis of principal coordinates (CAP) showing the spatial distribution of the microbial communities at the lowest taxonomic level in the three crater lithologies. Also shown are the probabilities for pairwise comparisons of the crater units. Vector overlay shows the dominant significant indicator species for each lithology. For details about the ISA, see Supplementary Tables 3, 4.

FIGURE 6

Bar graphs showing the average distribution of the major phyla (A), classes (B), and orders for Proteobacteria (C) in the three lithologies: postimpact Cenozoic interval (n = 32 samples), suevite (n = 23), and granitic basement (n = 7). See Supplementary Figure 5 for details on the relative abundance of the main phyla and classes in the three lithologies.

FIGURE 7

PCA plot based on SIMPER analysis of environmental parameters (porosity, TOC, temperature, Fe, S, and Mn). Vectors overlay represents each of these parameters contributing to each lithological interval.