Deep subsurface microbial communities shaped by the Chicxulub impactor

Author(s): Cockell, C. S.; Coolen, Marco; Schaefer, Bettina; Grice, K.; Gulick, Sean P. S.; Morgan, J. V.; Kring, D. A.; Osinski, G.
Author Affiliation(s): Primary:
University of Edinburgh, Edinburgh, United Kingdom
Curtin University, Australia
University of Texas at Austin, United States
Imperial College London, United Kingdom
Lunar and Planetary Institute, United States
University of Western Ontario, Canada
Volume Title: AGU 2017 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2017; American Geophysical Union 2017 fall meeting, New Orleans, LA, Dec. 11-15, 2017. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Fresh core material was obtained by drilling of the Chicxulub impact crater during IODP-ICDP Expedition 364 to assess the present-day biosphere in the crater structure. Cell enumerations through the core show that beneath the post-impact sedimentary rock there is a region of enhanced cell abundance that corresponds to the upper impact suevite layer (Units 1G/2A). We also observed a peak in cell numbers in samples at the bottom of suevite Unit 2C and between the suevitic and grainitoid interface (Unit 3/4). These patterns may reflect preferential movement of fluid and/or availability of nutrients and energy at interfaces. 16S rDNA analysis allows us to rule out contamination of the suevite material since no taxa associated with the drilling mud were observed. Two hundred and fifty microbial enrichments were established using diverse culture media for heterotrophs, autotrophs and chemolithotrophs at temperatures consistent with measured core temperatures. Six yielded growth in the breccia, lower breccia and upper granitoid layer and they affiliated with Acidiphilium, Thermoanaerobacteracea and Desulfohalbiaceae. The latter exhibited visible microbial sulfate-reduction. By contrast, the granitoid material exhibited low cell abundances, most samples were below direct cell detection. DNA extraction revealed pervasive low level contamination by drilling mud taxa, consistent with the highly fractured, high porosity of the impact-shocked granitoids. Few taxa can be attributed to an indigenous biota and no enrichments (at 60 and 70°C) yielded growth. These data show that even with a porosity approximately an order of magnitude greater than most unshocked granites, the uplifted granites have not experienced sufficient fluid flow to establish a significant deep biosphere. Paleosterilisation of the material during impact may have re-set colonisation and the material may have originally been below the depth at which temperatures exceeded the upper temperature limit for life. These data show that the deep biosphere can preserve the imprint of catastrophe long after these events. In this case, the distribution of deep subsurface microbial communities reflects the lithological sequence established during the substantial impact-induced geological rearrangements that occurred in the first hours of the Cenozoic.
Year of Publication: 2017
Research Program: IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Atlantic Ocean; Chicxulub Crater; Cores; Ecology; Expedition 364; Geomorphology; Gulf of Mexico; Impact craters; Impact features; International Ocean Discovery Program; Marine environment; Marine sediments; North Atlantic; Sediments
Coordinates: N212701 N212701 W0895658 W0895658
Record ID: 2019092035
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