1' Sherwood Lollar et al' Evidence for Pervasive Methanogenesis and H2Based autotrophy in the deep s

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Papers 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

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Paper 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

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Figure 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 ()
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Figure 2 Abiogenic-Microbial mixing
Thermogenic
Kloof
441
d2HCH4 ()
Dr938-1
739
Dr938-3
Microbial
Kidd Creek
Dr548
CCS-3
d13CCH4 ()
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Figure 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 ()
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Figure 4 H2-rich 13CCH4-enriched abiogenic
end-member
H2 ()
d13CCH4 ()
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Figure 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

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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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Pretoria Precipitation
d2Ho/ooVMSOW
Mine Water
Mean Precipitation
Ev219
0.2
0.6
Karoo
Ev818
0.8
d18Oo/ooVMSOW
Ev522
Mixing Line
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Cl- (ppm)
Karoo
Mine Water
d18Oo/ooVMSOW
Ev522
Ev219
Ev820
Ev818
Mixing Line
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Paper 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

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Maximum mixing in Ventersdorp
Microbial
Beatrix
Witwatersrand
Ventersdorp
CH4/C2
Evander
Kidd Creek
d13CCH4 ()
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Paper 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