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- Title
ISOTOPIC EVIDENCE FOR THE MIGRATION OF THERMOGENIC METHANE INTO A SULFIDIC CAVE, CUEVA DE VILLA LUZ, TABASCO, MEXICO.
- Authors
WEBSTER, KEVIN D.; LAGARDE, LAURA ROSALES; SAUER, PETER E.; SCHIMMELMANN, ARNDT; LENNON, JAY T.; BOSTON, PENELOPE J.
- Abstract
Methane (CH4) is an economic resource and a greenhouse gas, but its migration through rocks is not immediately associated with speleogenesis. Sulfuric-acid speleogenesis is a cave-forming mechanism that has produced a variety of economically important oil fields and aquifers, and is theorized to be related to the oxidation of CH4 and hydrocarbons. Despite hypotheses that the oxidation of CH4 may provide a basis for the generation of sulfides during sulfuric-acid speleogenesis, evidence from active systems has not yet been obtained. In this study, we address how CH4 influences the development of sulfidic cave systems by sampling the CH4, H2S, and CO2 concentrations, as well as δ1313CCH4 , δ2HCH4 , and δ13CCO2 values, in a cave currently forming by sulfuric-acid speleogenesis, Cueva de Villa Luz. CH4, H2S, and CO2 concentrations were highest directly above springs in the cave, showing that all three gases enter by means of the spring water. The δ13CCH4 and δ2HCH4 in the air of CVL ranged from -47.92 ±15 to -35.47 ±12 % (VPDB) and -117 to -83 % (VSMOW), respectively. Keeling plots suggest that CH4 with δ13CCH4-24 ± 3 % and δ2HCH4-40 ± 50 % was outgassing from spring water. This stable-isotope signature does not fall within traditional published δ13CCH4 versus δ2HCH4 fields. Our data suggest that the CH4 entering Cueva de Villa Luz is the remnant of a larger thermogenic CH4 flux that is incompletely oxidized in the subsurface as it travels to Cueva de Villa Luz. Our data support links between the processes forming Cueva de Villa Luz and the proposed mechanisms for other caves associated with sulfuric acid.
- Subjects
MEXICO; CAVES; METHANE analysis; SPELEOTHEMS; SULFURIC acid; GREENHOUSE gas analysis
- Publication
Journal of Cave & Karst Studies, 2017, Vol 79, Issue 1, p24
- ISSN
1090-6924
- Publication type
Article
- DOI
10.4311/2016ES0125