Recent, deep-sourced methane/mud discharge at the most active mud volcano in the western Mediterranean

Carmina López-Rodríguez; Gert J. De Lange; Menchu Comas; Francisca Martínez-Ruiz; Fernando Nieto; Célia J. Sapart; José M. Mogollón

doi:10.1016/j.margeo.2018.11.013

Recent, deep-sourced methane/mud discharge at the most active mud volcano in the western Mediterranean

Carmina López-Rodríguez^*, Gert J. De Lange, Menchu Comas, Francisca Martínez-Ruiz, Fernando Nieto, Célia J. Sapart, José M. Mogollón

^*Corresponding author for this work

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

Active mud volcanism in the West Alboran Basin (WAB) is closely associated with tectonically mobilized, overpressurized shales and shale-diapirism. This appears to control mud expulsion at Carmen mud volcano, a cone-shaped structure 65 m high and 1 km in basal diameter. The presence of gas-rich mud breccia, living chemosynthetic fauna, the absence of hemipelagic draping and the abrupt transition that occurs between high dissolved sulfate in the uppermost interval and low sulfate together with high methane concentrations in the lowermost sediment interval all point to a recent expulsion of mud breccia at the summit of Carmen MV. For the lowermost interval, the depletion of major elements (i.e., Ca²⁺ and Mg²⁺) and the enrichment of trace species (i.e., Li and B) in the pore water all indicate a deep fluid source. The δ¹⁸O_pw (5.7‰ VSMOW) and δD_pw (−10‰ VSMOW) of pore water in the lowermost interval correspond with smectite dehydration as the main pore-water freshening mechanism. Water-formation temperatures calculated with empirical geo-thermometers (K-Na, K-Mg; δ¹⁸O_pw, δD_pw, and dissolved B) reveal that fluids were generated at temperatures of ~140 ± 20 °C. Taking a regional geothermal gradient for the WAB of 25–27 °C/km, this points to a fluid source from ~5 ± 1 km sediment depth. This is not only consistent with the depth of overpressurized shales and megabreccia of Lower to Middle Miocene age, but it also fits nicely with the Upper/Middle-Miocene seawater value for the porewater ⁸⁷Sr/⁸⁶Sr derived from dissolving carbonates. The stable carbon and hydrogen isotopic composition of methane (δ¹³C_methane ~ −59.4‰ VPDB and δD_methane −184‰ VSMOW) for the deepest samples of summit-core GP05PC is consistent with the mentioned deep origin. Mud breccia expulsion of overpressurized deep sedimentary units would be accompanied by rigorous degassing, leading to rapid, ‘instantaneous’ replacement of pore fluid by bottom water in the upper sediments. The absence of oxidized sediment draping, the seawater-like pore-water composition in the uppermost part of the mud breccia interval, and the abrupt methane to sulfate transition all provide evidence for a very recent mud expulsion. The distinctively kink-shaped pore-water Cl⁻ profile in core GP05PC has been used in a numerical transport-reaction model to derive the timing for this event. This eruptive event appears to have taken place very recently, namely 12 ± 5 yrs prior to the 2012 coring, thus in the year 2000 CE.

Original language	English
Pages (from-to)	1-17
Number of pages	17
Journal	Marine Geology
Volume	408
DOIs	https://doi.org/10.1016/j.margeo.2018.11.013
Publication status	Published - Feb 2019

Funding

The authors gratefully acknowledge the GASALB-Pelagia Shipboard Party, technicians as well as Captain and crew of R / V Pelagia for support and collaboration during the cruise as well as TTR-17 Leg 1 Shipboard Party and R / V Professor Logachev Captain and crew. We thank H. De Haas for providing cruise technical details and J.M.R Alpiste for multibeam data processing. In addition, we thank the Pelagia shipboard scientific party and in particular K. Bakker and S. Ossebaar for on-board nutrient analyses, D. Gallego-Torres, D. Apostolova, and L. López-Alcaide for on-board methane and alkalinity analyses. A. van Dijk is thanked for his helpful assistance during stable isotopes analyses, C. van der Veen and T. Röckmann at IMAU - laboratory for methane isotope analyses, and P. Böning and K. Pahnke at ICBM, University of Oldenburg, for Sr isotope determination. Special thanks go to R. Hennekam, M.L. Goudeau and E. Grimoldi for their work and nice cooperation in pore-water extractions and sub-sampling. This work was supported by MINECO Spanish Projects [ CTM2009-07715 , CGL2011-1441 , CGL2012-32659 and CGL2015-66830-R ]; and the Andalusian Government Research Group [ RNM-179 and RNM-215 ]. C. F. López-Rodríguez was funded by a JAE-PhD fellowship from the CSIC (Spain); she acknowledges subsequent funding from the STSM in the framework of COST action ES1301. Appendix A

Keywords

Alboran Sea
Clay minerals
Deep fluids
Isotopes
Mud volcanoes
Pore waters

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@article{ef74b8a6dd3f468fa3ddfad62a999731,

title = "Recent, deep-sourced methane/mud discharge at the most active mud volcano in the western Mediterranean",

abstract = "Active mud volcanism in the West Alboran Basin (WAB) is closely associated with tectonically mobilized, overpressurized shales and shale-diapirism. This appears to control mud expulsion at Carmen mud volcano, a cone-shaped structure 65 m high and 1 km in basal diameter. The presence of gas-rich mud breccia, living chemosynthetic fauna, the absence of hemipelagic draping and the abrupt transition that occurs between high dissolved sulfate in the uppermost interval and low sulfate together with high methane concentrations in the lowermost sediment interval all point to a recent expulsion of mud breccia at the summit of Carmen MV. For the lowermost interval, the depletion of major elements (i.e., Ca2+ and Mg2+) and the enrichment of trace species (i.e., Li and B) in the pore water all indicate a deep fluid source. The δ18Opw (5.7‰ VSMOW) and δDpw (−10‰ VSMOW) of pore water in the lowermost interval correspond with smectite dehydration as the main pore-water freshening mechanism. Water-formation temperatures calculated with empirical geo-thermometers (K-Na, K-Mg; δ18Opw, δDpw, and dissolved B) reveal that fluids were generated at temperatures of ~140 ± 20 °C. Taking a regional geothermal gradient for the WAB of 25–27 °C/km, this points to a fluid source from ~5 ± 1 km sediment depth. This is not only consistent with the depth of overpressurized shales and megabreccia of Lower to Middle Miocene age, but it also fits nicely with the Upper/Middle-Miocene seawater value for the porewater 87Sr/86Sr derived from dissolving carbonates. The stable carbon and hydrogen isotopic composition of methane (δ13Cmethane ~ −59.4‰ VPDB and δDmethane −184‰ VSMOW) for the deepest samples of summit-core GP05PC is consistent with the mentioned deep origin. Mud breccia expulsion of overpressurized deep sedimentary units would be accompanied by rigorous degassing, leading to rapid, {\textquoteleft}instantaneous{\textquoteright} replacement of pore fluid by bottom water in the upper sediments. The absence of oxidized sediment draping, the seawater-like pore-water composition in the uppermost part of the mud breccia interval, and the abrupt methane to sulfate transition all provide evidence for a very recent mud expulsion. The distinctively kink-shaped pore-water Cl− profile in core GP05PC has been used in a numerical transport-reaction model to derive the timing for this event. This eruptive event appears to have taken place very recently, namely 12 ± 5 yrs prior to the 2012 coring, thus in the year 2000 CE.",

keywords = "Alboran Sea, Clay minerals, Deep fluids, Isotopes, Mud volcanoes, Pore waters",

author = "Carmina L{\'o}pez-Rodr{\'i}guez and {De Lange}, {Gert J.} and Menchu Comas and Francisca Mart{\'i}nez-Ruiz and Fernando Nieto and Sapart, {C{\'e}lia J.} and Mogoll{\'o}n, {Jos{\'e} M.}",

year = "2019",

month = feb,

doi = "10.1016/j.margeo.2018.11.013",

language = "English",

volume = "408",

pages = "1--17",

journal = "Marine Geology",

issn = "0025-3227",

publisher = "Elsevier BV",

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TY - JOUR

T1 - Recent, deep-sourced methane/mud discharge at the most active mud volcano in the western Mediterranean

AU - López-Rodríguez, Carmina

AU - De Lange, Gert J.

AU - Comas, Menchu

AU - Martínez-Ruiz, Francisca

AU - Nieto, Fernando

AU - Sapart, Célia J.

AU - Mogollón, José M.

PY - 2019/2

Y1 - 2019/2

N2 - Active mud volcanism in the West Alboran Basin (WAB) is closely associated with tectonically mobilized, overpressurized shales and shale-diapirism. This appears to control mud expulsion at Carmen mud volcano, a cone-shaped structure 65 m high and 1 km in basal diameter. The presence of gas-rich mud breccia, living chemosynthetic fauna, the absence of hemipelagic draping and the abrupt transition that occurs between high dissolved sulfate in the uppermost interval and low sulfate together with high methane concentrations in the lowermost sediment interval all point to a recent expulsion of mud breccia at the summit of Carmen MV. For the lowermost interval, the depletion of major elements (i.e., Ca2+ and Mg2+) and the enrichment of trace species (i.e., Li and B) in the pore water all indicate a deep fluid source. The δ18Opw (5.7‰ VSMOW) and δDpw (−10‰ VSMOW) of pore water in the lowermost interval correspond with smectite dehydration as the main pore-water freshening mechanism. Water-formation temperatures calculated with empirical geo-thermometers (K-Na, K-Mg; δ18Opw, δDpw, and dissolved B) reveal that fluids were generated at temperatures of ~140 ± 20 °C. Taking a regional geothermal gradient for the WAB of 25–27 °C/km, this points to a fluid source from ~5 ± 1 km sediment depth. This is not only consistent with the depth of overpressurized shales and megabreccia of Lower to Middle Miocene age, but it also fits nicely with the Upper/Middle-Miocene seawater value for the porewater 87Sr/86Sr derived from dissolving carbonates. The stable carbon and hydrogen isotopic composition of methane (δ13Cmethane ~ −59.4‰ VPDB and δDmethane −184‰ VSMOW) for the deepest samples of summit-core GP05PC is consistent with the mentioned deep origin. Mud breccia expulsion of overpressurized deep sedimentary units would be accompanied by rigorous degassing, leading to rapid, ‘instantaneous’ replacement of pore fluid by bottom water in the upper sediments. The absence of oxidized sediment draping, the seawater-like pore-water composition in the uppermost part of the mud breccia interval, and the abrupt methane to sulfate transition all provide evidence for a very recent mud expulsion. The distinctively kink-shaped pore-water Cl− profile in core GP05PC has been used in a numerical transport-reaction model to derive the timing for this event. This eruptive event appears to have taken place very recently, namely 12 ± 5 yrs prior to the 2012 coring, thus in the year 2000 CE.

AB - Active mud volcanism in the West Alboran Basin (WAB) is closely associated with tectonically mobilized, overpressurized shales and shale-diapirism. This appears to control mud expulsion at Carmen mud volcano, a cone-shaped structure 65 m high and 1 km in basal diameter. The presence of gas-rich mud breccia, living chemosynthetic fauna, the absence of hemipelagic draping and the abrupt transition that occurs between high dissolved sulfate in the uppermost interval and low sulfate together with high methane concentrations in the lowermost sediment interval all point to a recent expulsion of mud breccia at the summit of Carmen MV. For the lowermost interval, the depletion of major elements (i.e., Ca2+ and Mg2+) and the enrichment of trace species (i.e., Li and B) in the pore water all indicate a deep fluid source. The δ18Opw (5.7‰ VSMOW) and δDpw (−10‰ VSMOW) of pore water in the lowermost interval correspond with smectite dehydration as the main pore-water freshening mechanism. Water-formation temperatures calculated with empirical geo-thermometers (K-Na, K-Mg; δ18Opw, δDpw, and dissolved B) reveal that fluids were generated at temperatures of ~140 ± 20 °C. Taking a regional geothermal gradient for the WAB of 25–27 °C/km, this points to a fluid source from ~5 ± 1 km sediment depth. This is not only consistent with the depth of overpressurized shales and megabreccia of Lower to Middle Miocene age, but it also fits nicely with the Upper/Middle-Miocene seawater value for the porewater 87Sr/86Sr derived from dissolving carbonates. The stable carbon and hydrogen isotopic composition of methane (δ13Cmethane ~ −59.4‰ VPDB and δDmethane −184‰ VSMOW) for the deepest samples of summit-core GP05PC is consistent with the mentioned deep origin. Mud breccia expulsion of overpressurized deep sedimentary units would be accompanied by rigorous degassing, leading to rapid, ‘instantaneous’ replacement of pore fluid by bottom water in the upper sediments. The absence of oxidized sediment draping, the seawater-like pore-water composition in the uppermost part of the mud breccia interval, and the abrupt methane to sulfate transition all provide evidence for a very recent mud expulsion. The distinctively kink-shaped pore-water Cl− profile in core GP05PC has been used in a numerical transport-reaction model to derive the timing for this event. This eruptive event appears to have taken place very recently, namely 12 ± 5 yrs prior to the 2012 coring, thus in the year 2000 CE.

KW - Alboran Sea

KW - Clay minerals

KW - Deep fluids

KW - Isotopes

KW - Mud volcanoes

KW - Pore waters

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DO - 10.1016/j.margeo.2018.11.013

M3 - Article

AN - SCOPUS:85057838143

SN - 0025-3227

VL - 408

SP - 1

EP - 17

JO - Marine Geology

JF - Marine Geology

ER -

Recent, deep-sourced methane/mud discharge at the most active mud volcano in the western Mediterranean

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Keywords

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