Title: 1' Sherwood Lollar et al' Evidence for Pervasive Methanogenesis and H2Based autotrophy in the deep s
1Papers underway from Toronto
- 1. Sherwood Lollar et al. Evidence for Pervasive
Methanogenesis and H2-Based autotrophy in the
deep subsurface (for subm. to PNAS) - 2. Ward et al. Origin of Hydrocarbon Gases in the
Witwatersrand Basin (in revision for GCA Special
Volume) - 3. Slater et al. Radiocarbon constraints on the
timing of Methanogenesis in the Witwatersrand
Basin
2Paper 1 Evidence for Pervasive Methanogenesis
and H2-based autotrophy in the deep subsurface
- 1. Based on samples from 4 new sites (1 in Canada
and 3 in South Africa) abiogenic hydrocarbons
pervasive in PreC Shield - 2. Compositional and isotopic variability
controlled by abiogenic-microbial mixing - 3. H2 concentrations and CH4 isotopic
compositions consistent with coupled oxidation of
H2 and reduction of CO2 to CH4 via autotrophic
methanogens
3Figure 1 Abiogenic end-members
C4
C3
C2
739
C1
Drie
Kloof
C4
C3
d2H ()
Aump
C2
MP104
Dr938-3
Mponeng
Dr548
C1
Kidd Creek
CCS-3
d13C ()
4Figure 2 Abiogenic-Microbial mixing
Thermogenic
Kloof
441
d2HCH4 ()
Dr938-1
739
Dr938-3
Microbial
Kidd Creek
Dr548
CCS-3
d13CCH4 ()
5Figure 3 Microbial-Abiogenic mixing
Microbial
Dr938-1
Kloof
441
CH4/C2
443
Dr938-3
739
Abiogenic 13C-enriched end-members
CCS-3
Dr548
KC7792
d13CCH4 ()
6Figure 4 H2-rich 13CCH4-enriched abiogenic
end-member
H2 ()
d13CCH4 ()
7Figure 4 Methanogenesis and H2-based autotrophy
- high H2 associated with the most 13C-enriched
abiogenic CH4 we have a disagreement on the
amount of mixing in end members - when released due to tectonics/mining, deep
subsurface microbes gain access to the abundant
geologically old stored H2-we disagree with
origin of H2-it is continuously produced by
radiolysis - CH4-H2 rich abiogenic gases support a
redox-driven ecosystem where rapid depletion of
H2 and methanogenic 13C-depleted CH4 overprints
abiogenic signature-just the H2 supports
autotrophy-not the CH4
8 Samples fall in overlap between Microbial and
Microbial Mixing-according to this diagram the
microbial looks thermogenic
Thermogenic
Beatrix
d2HCH4 ()
MB
Evander
Microbial
Kidd Creek
d13CCH4 ()
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10Pretoria Precipitation
d2Ho/ooVMSOW
Mine Water
Mean Precipitation
Ev219
0.2
0.6
Karoo
Ev818
0.8
d18Oo/ooVMSOW
Ev522
Mixing Line
11Cl- (ppm)
Karoo
Mine Water
d18Oo/ooVMSOW
Ev522
Ev219
Ev820
Ev818
Mixing Line
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13Paper 2 Origin of Hydrocarbon Gases in
Witwatersrand Basin (J. Ward thesis)
- 1. Predominantly microbial origin for
hydrocarbons at Beatrix, Evander and Middlebult. - 2. But some degree of mixing.
- 3. Geological controls on mixing samples in
Witwatersrand mainly microbial - 4. Samples from Ventersdorp greatest degree of
mixing of microbial with more 13C-enriched CH4
not true-all samples from Witwatersrand
quartzites at Evander
14Maximum mixing in Ventersdorp
Microbial
Beatrix
Witwatersrand
Ventersdorp
CH4/C2
Evander
Kidd Creek
d13CCH4 ()
15Paper 3 14C in DIC and CH4 in South African gold
mines evidence for current methanogenesis?
Slater et al. STATUS???
- This study examines the stable and radiocarbon
relationship between DIC and methane in three
gold mines where there is evidence of microbial
methanogenesis - Goal to determine whether this microbial
contribution represents methanogenesis from
current DIC pools, or is evidence of bacterial
activity over geologic timescales