Hydrocarbon gar in sediments of the Costa Rica ubduction zone
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| Natura: | Dataset Open Access |
| Lingua: | en |
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PANGAEA
2002
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| _version_ | 1867169502953734144 |
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| author | Lückge, Andreas Kastner, Miriam Littke, Ralf Cramer, Bernhard |
| author_facet | Lückge, Andreas Kastner, Miriam Littke, Ralf Cramer, Bernhard |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | At the active continental margin off Costa Rica substantial amounts of hydrocarbon gases are encountered in sediments. The molecular composition (C1-C3) of free hydrocarbon gas as well as the isotopic composition (d13C of methane and ethane and D of methane) was analysed on core samples (ranging between 50 and 380 m depth) collected at sites 1040-1043 which was drilled during ODP Leg 170. In addition, the molecular composition of the C1-C3 hydrocarbons and the d13C composition of C1 and C2 hydrocarbons was determined on adsorbed gas from selected depth intervals at Site 1041 (50-380 mbsf). The molecular composition, and stable carbon and hydrogen isotope signature of low molecular weight hydrocarbons from core sediments and gas pockets indicate that most of the gas was generated by microbial CO2-reduction. Beside d13C values of about -80 per mil for methane (which is typical for microbially- generated methane) extremely light d13C values of -55 per mil were measured for ethane. The carbon isotope composition of methane and ethane, as well as the C1/(C2+C3) ratio display distinct trends with increasing depth. Gas mixing calculations indicate that the percentage of thermally-generated ethane increases from 10% at about 75 mbsf to almost 80% at 380 mbsf. The fraction of thermogenic methane in this depth interval is calculated to range from 0.03 to 1.8% of the total methane. The small contribution of thermogenic methane would increase the d13C value by <1 per mil. Therefore, the increase of d13C of methane (by about 12 per mil) with depth cannot be explained by gas mixing alone. Instead, the observed d13C trend is caused by successive isotope depletion of the methane precursor within the sedimentary organic matter due to progressing microbial gas generation. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_757214 |
| institution | PANGAEA |
| language | en |
| publishDate | 2002 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | Hydrocarbon gar in sediments of the Costa Rica ubduction zone Lückge, Andreas Kastner, Miriam Littke, Ralf Cramer, Bernhard 170-1040B; 170-1041; 170-1041A; 170-1041B; COMPCORE; Composite Core; Costa Rica margin, North Pacific Ocean; Costa Rica subduction complex, North Pacific Ocean; DRILL; Drilling/drill rig; Joides Resolution; Leg170; Ocean Drilling Program; ODP At the active continental margin off Costa Rica substantial amounts of hydrocarbon gases are encountered in sediments. The molecular composition (C1-C3) of free hydrocarbon gas as well as the isotopic composition (d13C of methane and ethane and D of methane) was analysed on core samples (ranging between 50 and 380 m depth) collected at sites 1040-1043 which was drilled during ODP Leg 170. In addition, the molecular composition of the C1-C3 hydrocarbons and the d13C composition of C1 and C2 hydrocarbons was determined on adsorbed gas from selected depth intervals at Site 1041 (50-380 mbsf). The molecular composition, and stable carbon and hydrogen isotope signature of low molecular weight hydrocarbons from core sediments and gas pockets indicate that most of the gas was generated by microbial CO2-reduction. Beside d13C values of about -80 per mil for methane (which is typical for microbially- generated methane) extremely light d13C values of -55 per mil were measured for ethane. The carbon isotope composition of methane and ethane, as well as the C1/(C2+C3) ratio display distinct trends with increasing depth. Gas mixing calculations indicate that the percentage of thermally-generated ethane increases from 10% at about 75 mbsf to almost 80% at 380 mbsf. The fraction of thermogenic methane in this depth interval is calculated to range from 0.03 to 1.8% of the total methane. The small contribution of thermogenic methane would increase the d13C value by <1 per mil. Therefore, the increase of d13C of methane (by about 12 per mil) with depth cannot be explained by gas mixing alone. Instead, the observed d13C trend is caused by successive isotope depletion of the methane precursor within the sedimentary organic matter due to progressing microbial gas generation. |
| title | Hydrocarbon gar in sediments of the Costa Rica ubduction zone |
| topic | 170-1040B; 170-1041; 170-1041A; 170-1041B; COMPCORE; Composite Core; Costa Rica margin, North Pacific Ocean; Costa Rica subduction complex, North Pacific Ocean; DRILL; Drilling/drill rig; Joides Resolution; Leg170; Ocean Drilling Program; ODP |
| url | https://doi.org/10.1594/PANGAEA.757214 |