Origin of Gases

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Origin of Gases

• Biological gases produced by microbial processes
  (fermentation or reduction)
• Thermogenic gases produced by the thermal
  breakdown of higher organic molecules
• Abiogenic metal oxide/sulfide catalyzed
  reactions.
• Radiolytic radioactive destruction of water.
• Atmospheric brought in from surface recharge.

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Isotope Background

• Hydrogen (1H 2H) (VSMOW)
• Carbon (12C 13C) (PDB)
• Sulfur (34S 32S) (CDT)

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Sampling of dissolved gases
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Gas Compositions

• CH4 (up to 94)
• N2 (up to 48)
• He (up to 23)
• H2 (up to 12)
• C2H6 (up to 3.5)
• C3H8 (up to 0.34)
• C4H10(up to 0.05)
• Trace amounts of Ar, CO, NH3, H2S CO2

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Lin et al. submitted to Science
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Atlantic Coastal Plain
aquifer
1
-1
-3
-5
-7
Log CO2 production rate (M/yr)
-9
-11
-13
-15
Surface soils
Lake sed.
Deep sea sed.
Sub-surface aquifers
Sub-surface aquitards
Deep vadose zones
Deep rocks consolidated sed.
From Kieft and Phelps (1997)
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Typical thermogenic gas
Kloof Mine gases
Abiogenic gas from Canadian Shield
Sherwood-LollarWard-Univ. Toronto
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Pratt Boice-Indiana University
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Radiation driven ecosystem?
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If rock matrix not accessible to bacteria, then
radiolytic products diffuse into colonized
fractures effectively localizing, yet raising the
potential respiration rates well above 1 nM/yr.
1 cm.
H2
SO4
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Ore
H2
SO4
Groundwater ages
Quartzite
Mining-induced fractures
Avg. Wits.
Geological Fractures
Atlantic Coastal Plain
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H2
H2