Gas hydrates, fluid venting and slope stability on the upper Amazon deep-sea fan

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Gas hydrates, fluid venting and slope stability on the upper Amazon deep-sea fan

D. Praeg, C Silva, A Reis, J-M Ketzer, S Migeon, Vikram Unnithan, Rodrigo Perovano, Alberto Cruz, Christian Gorini

To cite this version:

D. Praeg, C Silva, A Reis, J-M Ketzer, S Migeon, et al.. Gas hydrates, fluid venting and slope stability on the upper Amazon deep-sea fan. I Simpósio Brasileiro �de Geologia e Geofísica Marinha (I SBGGM), Nov 2018, Rio de Janeiro, Brazil. P2GM Projetos e Produções, Rio de Janeiro, Brasil, 31, pp.217-218, Anais do I Simpósio Brasileiro�de Geologia e Geofísica Marinha (I SBGGM). �hal-02156661�

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Gebco 2008, 250 m contours 5˚N 4˚N 3˚N 50˚W 49˚W 48˚W 47˚W

References

Carlson RL et al. (1986). Empirical reflection travel time versus depth and velocity versus depth functions for the deep-sea sediment column. Journal of Geophysical Research 91 (B8), 8249-8266.

Ketzer JM et al. (2018) Gas seeps and gas hydrates in the Amazon deep-sea fan. Geo-Marine Letters 38 (5), 429-438

Maslin M et al. (1998) Sea-level and gas-hydrate–controlled catastrophic sediment failures of the Amazon Fan. Geology 26:1107-1110. Perovano R (2012) Análise estrutural da tectônica gravitacional na bacia da Foz do Amazonas a partir da interpretação de dados

sísmicos e de modelagem experimental. PhD thesis, Universidade Federal Fluminense, Niterói, pp. 296.

Reis AT et al. (2016) Effects of a regional décollement level for gravity tectonics on late Neogene to recent large-scale slope instabilities in the Foz do Amazonas Basin, Brazil. Marine and Petroleum Geology 75:29-52.

Riedel M et al. (2010) Characterizing the thermal regime of cold vents at the northern Cascadia margin from bottom-simulating reflector distributions, heat-probe measurements and borehole temperature data. Marine Geophysical Research 31 : 1-16.

Gas Hydrates, Fluid Venting and Slope Stability on the Upper Amazon Deep-Sea Fan

Praeg D (

daniel.praeg@geoazur.unice.fr

)

1-3

_{; Silva C}

1

_{; Reis AT}

4

_{; Ketzer JM}

5

_{; Migeon S}

3

_{; Unnithan V}

6

_{; Perovano R}

4

_{; Cruz A}

7

_{; Gorini C}

7

1

_{Universidade Federal Fluminense (UFF), Niterói RJ;}

2

_{Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS),}

Porto Alegre RS;

3

_{Géoazur, Valbonne, France;}

4

_{Faculdade de Oceanografia, Universidade do Estado do Rio de Janeiro}

(UERJ);

5

_{Linnéuniversitetet, Sweden;}

6

_{Jacobs University Bremen, Germany;}

7

_{Sorbonne Université, Paris, France}

0 20 40 60 80 100 0 2 4 6 8 10 12 T g ra d ie n t (˚C /k m )

BSR

? 1500 T W T (ms) vents

Evidence of

upward flux of

warm gas-rich

fluids through

thrust-folds

(rooted on

detachments at

depths of kms)

TWT ( ms ) fluid vents vents 10 0 KM 3 0 KM 2000 Te m p er atu re g ra d ie n t B SR -s ea fl o o r (˚C /k m ) 100 80 60 40

A

B

A

1170 m WD

Gradients 1.5-10 x

background

1-BP-1A-APS (projected 1.5 km) 30.4˚C/km

4. BSR patches à spatially variable temperature gradients + seafloor fluid vents

BSR

base MHSZ@ 20˚C/km

5. Bottom-up gas hydrate & slope dynamics

•  Changes in upward flux of fluid (heat) will modify gas hydrate stability from below

•  Increased flux during thrust episodes will thin hydrate-rich zone over wide areas

•  Reduced sediment strength at base of stability zone may trigger large landslides

≈ 1 km

≈ 10 km

①  thrust-faulting

② 

③ 

④ 

_⑤

②  upward flux of

fluids & heat

③  thinning of

hydrate-rich

stability zone

④  enhanced

fluid venting

⑤  upper fan slope

failure

past

failures

potential failure

volume

Ø  Elongate BSR patches on the upper Amazon fan linked to upward flux of gas-rich

fluids through thrust-folds recording collapse above deep detachments

Ø  Tectonically-driven changes in fluid flux will thin gas hydrate-rich zones from below

and may trigger recurrent giant slope failures from the upper fan

Ø  Bottom-up mechanism independent of climate-driven changes in hydrate stability

6. Conclusions

3. BSR depth inversion to temperatures

Inversion method (after Riedel et al. 2010)

•  BSR TWT à depth (velocity profile from Carlson et al. 1986)

•  Depth of BSR à hydrostatic pressure

•  Pressure at BSR à temperature at phase boundary (MHSZ*)

•  Bottom water temperatures (WOD) à geothermal gradients

y = -‐6.246E-‐04x2_{+
5.751E+00x
-‐}

7.604E+03 0 200 400 600 800 1000 1200 1500 1750 2000 Dep th b sf ( m) Interval Velocity bsf (m/s) Carlson et al. 1986 Riedel 2001 0 10 20 30 40 50 60 70 80 90 0 20 40 Pr es su re (MP a) Temperature (˚C) Methane hydrate in seawater 3.5% salinity) from Sloan 1998)

Bottom water

temperatures

Temperature (˚C)

Velocity-depth

profiles

Hydrate phase

boundary*

DSDP global correlation to seismic (Carlson et al. 1986) To compare, seismic stack velocities Cascadia

(Riedel 2001) Amazon fan

data in World Ocean Database Wa ter d ep th (m)

2. Mapping bottom simulating reflections (BSRs)

Thrust-fold axes (this study) Normal faults (Perovano 2012) Multichannel seismic lines (ANP)

Results :

•  linear BSR

‘patches’

•  water depths

700-2250 m

•  aligned with

thrust-folds

•  total area

>6800 km

2

1. Amazon fan & slope instabilities

R ei s et a l. (2 01 6)

2D/3D BSR inversion (250 m grid)

Spatial variation at

two wavelengths :

•  22-50˚C/km

(10

3

_-10

4

_{m areas)}

- mainly >30˚C/km

•  50-100˚C/km

(10

1

_-10

2

_{m – vents)}

3D seismic area

Multibeam_{survey area}

(Ketzer et a_{l. 2018)}

From Ketzer et al. (2018) :

gas hydrate sample water column gas flare

3D seismic BSR inversion

(25 m grid)

B

A

C

C’

fluid vents 1-BP-1A-APS Te m p er atu re g ra d ie n t B SR -s ea fl o o r (˚C /k m ) 22 30 40 50 60 70 80 90 200

*

C’

B

750-900 m WD Mud volcanoes + pockmarks

Mud

volcanoes

3D seismic bathymetry (12.5 m)

Te

m

p

er

atu

re

g

ra

d

ie

n

t

B

SR

-s

ea

fl

o

r

(˚C

/k

m

)

22 30 40 50 60 70 80 90 95

① 

Acknowledgement : This work is funded in part by CAPES-IODP (PVE, UFF 2018-2019) and in part by

the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement No. 656821 (project SEAGAS, PUCRS 2016-2018, Géazur 2019-2020).

Gas hydrates, fluid venting and slope stability on the upper Amazon deep-sea fan

References

Gas Hydrates, Fluid Venting and Slope Stability on the Upper Amazon Deep-Sea Fan

Praeg D (

daniel.praeg@geoazur.unice.fr

)

; Silva C

; Reis AT

; Ketzer JM

; Migeon S

; Unnithan V

; Perovano R

; Cruz A

; Gorini C

Universidade Federal Fluminense (UFF), Niterói RJ;

Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS),

Porto Alegre RS;

Géoazur, Valbonne, France;

Faculdade de Oceanografia, Universidade do Estado do Rio de Janeiro

(UERJ);

Linnéuniversitetet, Sweden;

Jacobs University Bremen, Germany;

Sorbonne Université, Paris, France

BSR

Evidence of

upward flux of

warm gas-rich

fluids through

thrust-folds

(rooted on

detachments at

depths of kms)

A

B

A

A

Gradients 1.5-10 x

background

4. BSR patches à spatially variable temperature gradients + seafloor fluid vents

BSR

5. Bottom-up gas hydrate & slope dynamics

• Changes in upward flux of fluid (heat) will modify gas hydrate stability from below

• Increased flux during thrust episodes will thin hydrate-rich zone over wide areas

• Reduced sediment strength at base of stability zone may trigger large landslides

≈ 1 km

≈ 10 km

① thrust-faulting

②

③

④

⑤

② upward flux of

fluids & heat

③ thinning of

hydrate-rich

stability zone

④ enhanced

fluid venting

⑤ upper fan slope

failure

past

failures

potential failure

volume

Ø Elongate BSR patches on the upper Amazon fan linked to upward flux of gas-rich

fluids through thrust-folds recording collapse above deep detachments

Ø Tectonically-driven changes in fluid flux will thin gas hydrate-rich zones from below

and may trigger recurrent giant slope failures from the upper fan

Ø Bottom-up mechanism independent of climate-driven changes in hydrate stability

6. Conclusions

3. BSR depth inversion to temperatures

Inversion method (after Riedel et al. 2010)

• BSR TWT à depth (velocity profile from Carlson et al. 1986)

• Depth of BSR à hydrostatic pressure

• Pressure at BSR à temperature at phase boundary (MHSZ*)

• Bottom water temperatures (WOD) à geothermal gradients

Bottom water

temperatures

Velocity-depth

profiles

_{; Silva C}

_{; Reis AT}

_{; Ketzer JM}

_{; Migeon S}

_{; Unnithan V}

_{; Perovano R}

_{; Cruz A}

_{; Gorini C}

_{Universidade Federal Fluminense (UFF), Niterói RJ;}

_{Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS),}

_{Géoazur, Valbonne, France;}

_{Faculdade de Oceanografia, Universidade do Estado do Rio de Janeiro}

_{Linnéuniversitetet, Sweden;}

_{Jacobs University Bremen, Germany;}

_{Sorbonne Université, Paris, France}

•  Changes in upward flux of fluid (heat) will modify gas hydrate stability from below

•  Increased flux during thrust episodes will thin hydrate-rich zone over wide areas

•  Reduced sediment strength at base of stability zone may trigger large landslides

①  thrust-faulting

② 

③ 

④ 

_⑤

②  upward flux of

③  thinning of

④  enhanced

⑤  upper fan slope

Ø  Elongate BSR patches on the upper Amazon fan linked to upward flux of gas-rich

Ø  Tectonically-driven changes in fluid flux will thin gas hydrate-rich zones from below

Ø  Bottom-up mechanism independent of climate-driven changes in hydrate stability

•  BSR TWT à depth (velocity profile from Carlson et al. 1986)

•  Depth of BSR à hydrostatic pressure

•  Pressure at BSR à temperature at phase boundary (MHSZ*)

•  Bottom water temperatures (WOD) à geothermal gradients

•  linear BSR

•  water depths

•  aligned with

•  total area

•  22-50˚C/km

_-10

_{m areas)}

•  50-100˚C/km

_-10

_{m – vents)}

① 