HAL Id: hal-02335918
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Submitted on 28 Oct 2019
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A Sulfuric Acid Speleogenesis in the Northern Pyrenees (France)?
Dimitri Laurent, E. Gaucher, Christophe Durlet, Cédric Carpentier, Guillaume Barre, Pauline Collon, Guillaume Paris, Jacques Pironon
To cite this version:
Dimitri Laurent, E. Gaucher, Christophe Durlet, Cédric Carpentier, Guillaume Barre, et al.. A Sulfuric Acid Speleogenesis in the Northern Pyrenees (France)?. Réunion des Sciences de la Terre 2018, Oct 2018, Lille, France. �hal-02335918�
6- Collaborations
2- Thermochemical Sulfate Reduction (TSR) and SAS
1- Introduction:
hypogenic caves in the Northern Pyrenees?
5- Conclusions:
1
sthypothesis and Perspectives
4- Sulfur isotopes:
origin and processes
3- Field evidences of cave sulfates in the Arbailles massif:
SAS or evaporite leaching ?
notch
Audra, 2007
D. Laurent (1)*, E. C. Gaucher (2), C. Durlet (3), C. Carpentier (1), G. Barré (4), P. Collon (1), G. Paris(1), J. Pironon (1) (1) CREGU, GeoRessources, ENSG, CRPG, Univ. Lorraine (Nancy, France), (2) Total (Pau, France),
(3) UMR/CNRS Biogeosciences, Univ. Bourgogne Franche-Comté (Dijon, France), (4) UPPA (Pau, France)
A Sulfuric Acid Speleogenesis in the Northern Pyrenees (France)?
P. & S. Degouve (GSHP Tarbes) M. Douat (ARSIP, ICE Himalayas)
Collectif Nébélé
P. Sorriaux & CDS09/SCHS CDS64
Data base Karsteau
-> Problematic (in Total «Fluid» program):
Reposition Sulfuric Acid Speleogenesis (SAS) in the continuum of fluid-rock interactions in the foothills.
Biodegradation
Top gasTop oil
Foothills
Deep exotic fluids (H, He,
CO2, CH4) H2S, CO2, H2O from TSR
Sedimentary brines
Modified from TOTAL 1km
Meteoric fluids N 500 500 m 0 Apoura Lechara Aussurucq NNE SSW Albian-Ceno.: conglomerates
Up. Triassic/Lo. Lias: limestones and dolomites
Lias/Dogger: marls and limestones
Kimmeridgian: limestones Oxfordian: Hosta Marls
Supposed hypogenic caves and thermo-mineral springs
Lo. Aptian: Ste Suzanne marls Aptian: Urgonian limestones Up. Aptian/Albian: black schistose marls
Up. Triassic: gypsum-rich marls
H
2S
TSR ? Meteoric water
Meteoric water Nébélé cave
Cross section of the Arbailles Massif (modified from Viaud, 1991)
Albian Aptian Jurassic Up. Triassic Thermo-mineral springs Oxygenated water TSR
H2S-rich fluids (derived from TSR) Meteoric fluids
Perspectives
Preliminary conceptual model
NW SE
Paleokarst cavities
Carbonate veins
NW SE
Calcite Pyrite + Pyrrhotite
SD2 Hydrothermal saddle dolomite SD1 Calcite PPL 500 µm Garaybie spring
Modified from Bauer, 1998
Thermochemical sulfate reduction: CH4 + SO42- => H
2S + CO2 + 2OH
-Oxidation of H2S:
H2S + 2O2 <=> H2SO4 (SO42- + 2H+ in solution)
Sulfate precipitation in replacement of carbonate:
SO42- + 2H+ + CaCO
3 + 2H2O
=> CaSO4-2H2O (gypsum) + CO2 + H2O
D.Laurent (Grotte du Chat)
Gypsum crust
Iron oxides
The Arbailles Massif, a good candidate for SAS...
-> Numerous caves in Aptian and Dogger limestones
-> Caves located close to regional faults connected to Triassic evaporites
-> Current thermo-mineral springs = sulfate/sulfur-rich deep fluids circulation -> Gypsum precipitation in karst systems
-> Relative proximity with oil seeps and hydrocarbon fields
... But several processes may be responsible for cave sulfate precipitation:
-> SAS
-> Pyrite oxidation
-> Leaching of sulfate-rich sediments (evaporite, carbonate...) -> Decomposition of organic matter (guano...)
Nébélé cave Garaybie spr. Landanoby cave Arbailles massif Camou Cross section Bexanka cave Aussurucq Azalegui cave Maddalen cave Camou spr. Mainaltea spr.
Cave gypsum Sulfur- & sulfate-rich springs
Compatible SAS morphologies
Ω Ω Ω Ω Ω Ω Hibou cave Cents sources spr. 1km Compac tion (M+ , H 2O) TSR and hy drocarbon cr acking (H 2S, CO 2, HC, H 2O) Crustal (M+, CH 4, CO 2) Marine 1 5 9 Depth (km) Meteoric B asin burial +
-Source SO 4 2-TransportH 2S H2SO4 Condensation-corrosion Corrosion-replacement Font Estramar Arbailles Massif Pierre St Martin Massif St-Pé-de-Bigorre Massif Esparros Labastide Cigalère Bagnères-de-Bigorre Massif NPF NPFT Ermite Vapeur France
Supposed SAS (cave gypsum) Oil/gas fields with H2S
Ariège Massif Lacq 15-20% H2S Meillon-Saint Faust 4-7% H 2S Andouins 11% H2S Cassourat 15% H2S Sulfuric thermal springs Sarrance Massif Ossau Valley
Modified after Clerc, 2013
-> Main questions:
- Timing of karst formation
(hyper-extension, compression…)? - Controlling factors of karst
development (structural, geochemical...)? - Nature and origin of fluids involved in the dissolution (CO2, H2S, meteoric...)? - Link with petroleum and ore deposits?
D ogger limest one Gypsum Replacement pocket 20 cm
Plan view: collectif Nébélé (in Vanara, 1998) Entrance
Salle du pendule Salle du Parpaing Le Bain (riv.) Grande faille Tubes est (riv.) La Flemme Galerie du Scrouitch Tubes ouest
Les Herses Sablier
Damoclès La Roume (riv.) Aval de l’Oasis (riv.) Méandre de l’Oasis (riv.) Noël Spirales 0 100 200 m -159 -160 -152 -99 -100 -150 -127 -104 -147 Regional fault Fossil level Scrouitch
High δ34S fractionation between Triassic evaporites and cave sulfates
-> Evidence of TSR and H2S-rich fluid migration
200
500 m 0
A typical example of SAS: Grotte du Chat (Alpes-Maritimes) Mean temp. = 15°C Cond. = 550µS/cm In Vanara, 1998 10 cm Geological map
of the Arbailles Massif
Potential sources of sulfur in the sedimentary basin
Notch and corrosion table
Replacement pocket
H2S-rich hydrothermal carbonate veins in Aptian limestones Pyrite in veins Diagenetic pyrite Sulfate/sulfur-rich thermo-mineral springs
N120-80N diaclases coated by gypsum crust
Convection niches, sulfuric karren and corrosion table Mirabilite flower (Na2SO4-10H2O)
S isotopes on gypsum & water
O isotopes on gypsum & water
C isotopes on water & veins Fluid inclusions in veins U/Th on gypsum H2S-rich veins S species & origin Conditions during SAS Organic matter involved in TSR P/T of fluids & S species Absolute dating of SAS
Methods
Lessons
(i) TSR of Triassic evaporites starting during Cretaceous extension (ii) Migration of H2S-rich fluids towards basin margins (timing?)
(iii) Mixing between deep fluids and oxygen source -> SAS
Convective hot air
Corrosion table with gypsum
Convection niches Gypsum crusts 1m Notch Gypsum + mir abilite
Ancient sulfuric river? Convective hot air
Condensa
tion sur face
Projected cross section of the Nébélé cave (Collectif Nébélé) Entrance
Vertical scale x1.5
0 100 200 m Regional faults: pathways for fluids
Fossil level: -85 to -120m
50m 0
Typical morphologies and mineral markers of SAS
observed along a fossil level (-85 to -120m)
W E Liassic limestones Aptian limestones Condensa tion sur face
Example of the Nébélé Cave
SAS
SAS
SAS
Cave sulfates are not linked to evaporite leaching or pyrite oxidation:
- such processes do not involve significant δ34S fractionation
- very few pyrites in sediments
Semi-active level (-145 to -177m)
Ascending flux?
Condensation
Corrosion table
Sulfuric river or feeders
Replacement pocket & gypsum
Isotherms in host rocks
H2S H2SO4 Fluid inclusion 15µm TSR Δ33S (‰) δ34S CDT (‰) -0.2 -0.1 +0.1 +0.2 -30 -20 -10 0 +10 +20 +30 Nébélé Cave
Gypsum & mirabilite
Azalegui Cave
Gypsum
Liassic limestones
Diagenetic pyrite
Aptian limestones
Pyrite & Pyrrhotite
Triassic evaporites
Liassic limestones
Pyrite in veins
Garaybie spr. (SO42-) Cents sources spr. (SO42-) Mainaltea spr. (SO42-) Oxidation of pyrite S N *dimitri.laurent@univ-lorraine.fr error <0.02‰ (0.2‰ for springs) H2S H2SO4 H2S H2SO4 H2SO4 H2S Mainaltea spring Mean temp. = 12°C Cond. = 655µS/cm Gas Liq.
