252 | Nature | Vol 579 | 12 March 2020
Article
sequence was annotated to Chroococcidiopsis sp., a cyanobacterial
taxon that may contribute to anaerobic production of cobalamin or
pseudocobalamin in the lower crust using a hydrogen-based lithoau-
totrophic metabolism^20.
Although we observed the production of methane in long-term
enrichments (Extended Data Fig. 2), methanogens appear to be rare
in our samples, explaining the low recovery of transcripts involved
in methane metabolism (Supplementary Table 4), and no ribosomal
RNA gene sequences of know methanogens were recovered (Extended
Data Fig. 3). However, the abundance of SAR324 Deltaproteobacteria
in our iTAG libraries indicates potential methanotrophy^15 ,^16 coupled
with methane production in our long-term enrichments (Extended
Data Fig. 2). Some methane metabolism is probably present, but its
importance is unclear in these samples. Detection of glycosidic archaeol
and acyclic GDGT (GDGT-0) may indicate the presence of methanogens;
however, these lipids may also derive from other archaeal sources.0Depth below sea oor CCSF (m)ATP
(pg cm–3)0
Carb veins
(rank)0
Clay veins
(rank)0
All veins
(rank,
1-m average)0
Alteration
(intensity,
1-m average)0
Fracturing
(intensity,
2-m average)102 104
Average cells
(per cm^3 )01020
Volatile content
(wt%)00 .51.0
Clay OH
(150–300 °C)800700600500400300200100U1473A lithology
(recovered
2-m average)Fault
zoneFault0 100%Drilled,
no
coreFaultFaultFaultFaultFaultFault80070060050040030020010080070060050040030020010080070060050040030020010080070060050040030020010080070060050040030020010080070060050040030020010080070060050040030020010080070060050040030020010080070060050040030020010024655 5 55Diabase Diorite/felsic veins Oxide gabbros Oxide-bearing gabbros Disseminated oxide gabbros Oxide gabbronorite Gabbro Olivine gabbroFig. 2 | Summary of hole U1473A of IODP Expedition 360. Downhole
properties of the gabbroic section determined by shipboard macroscopic
descriptions and measured microbiological indicators. Labels indicate the
property shown in each panel. Carb, carbonate. A key to lithology is included;
rank and intensity range between 0 and 5. Faults are indicated by pale-green
lines. Microbiological sample depths are highlighted by dashed blue lines. The
light-grey horizontal zone around 500 mbsf indicates a zone that was drilled
but not cored. ATP was measured once per sample. CCSF, core composite
depth below seaf loor. Replicate cell-count data are provided in Supplementary
Table 3b. Source data are available at http://web.iodp.tamu.edu/DESCReport/
(file name, 360_U1473A_macroscopic.xlsx).