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Seafloor Pockmarks identifying ancient submarine canyons, Equatorial Guinea Zane Jobe Don Lowe.

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Presentation on theme: "Seafloor Pockmarks identifying ancient submarine canyons, Equatorial Guinea Zane Jobe Don Lowe."— Presentation transcript:

1 Seafloor Pockmarks identifying ancient submarine canyons, Equatorial Guinea
Zane Jobe Don Lowe

2 Acknowledgements

3 Why should you care about pockmarks?
Offshore drilling hazards Sites of methane release Pore water migration and release Under-represented in outcrops This study Possibility to identify subsurface features

4 Take home messages Pockmarks on the modern seafloor identify ancient submarine canyons Pockmark evolution (Ma) Canyon ridge formation ‘Peanuts’ Discrete pockmarks Only canyons that lose access to upslope flows evolve into pockmarks

5 Road map Pockmarks Equatorial Guinea Pockmarks in Equatorial Guinea
Identify ancient canyons Have a distinct evolution Canyons losing upslope access to flows evolve into pockmarks

6 Road map Pockmarks Equatorial Guinea Pockmarks in Equatorial Guinea
Identify ancient canyons Have a distinct evolution Canyons losing upslope access to flows evolve into pockmarks

7 Pockmarks: size and distribution
“Cone shaped depressions” (King and MacLean, 1970) Formation Upward fluid “percolation” Pore water (Whiticar and Werner, 1981) Methane (Hovland and Sommerville, 1985) Size (Hovland et al, 2002) m x 5-40 m Distribution Random Aligned in trains Lastras et al., 2004 10 km Pilcher and Argent, 2007

8 Road map Pockmarks Equatorial Guinea Pockmarks in Equatorial Guinea
Identify ancient canyons Have a distinct evolution Canyons losing upslope access to flows evolve into pockmarks

9 Surface currents transport sediment (mud) into the study area
longshore wind

10 3D seismic reflection dataset
15 x 26 km 12.5 x 12.5 m 2 ms 70 Hz Water depth 1200 m

11 Dip attribute map of the seafloor
2 km degrees Perception

12 Bright amplitudes concentrated in canyons & pockmarks

13 Canyons are highly aggradational and long lived (> 10 Ma) = pockmarks

14 Canyons are highly aggradational and long lived (> 10 Ma) = pockmarks
K/T (65 Ma) ~3 Ma 1 km

15 Road map Pockmarks Equatorial Guinea Pockmarks in Equatorial Guinea
Identify ancient canyons Have a distinct evolution Canyons losing upslope access to flows evolve into pockmarks

16 Pockmark trains overlie ancient canyons

17 Across canyon view: Pockmarks overlie ancient canyons
450 m wide 60 ms deep A A’

18 Dip view – chaotic canyon deposits
giving way to conformable reflectors 350 m wide 50 ms deep B B’ B’ B

19 Canyon piracy and abandonment
Time structure Colors

20 Pockmark trains overlie ancient canyons
+ 2 km =

21 Road map Pockmarks Equatorial Guinea Pockmarks in Equatorial Guinea
Identify ancient canyons Have a distinct evolution Canyons losing upslope access to flows evolve into pockmarks

22 Cross-canyon ridges formed by slumps (sediment waves)
2 km A’ 2 km A

23 Pockmark evolution Across-canyon ridges ‘Peanuts’ Pockmarks 2 2 3 2 1

24 Road map Pockmarks Equatorial Guinea Pockmarks in Equatorial Guinea
Identify ancient canyons Have a distinct evolution Canyons losing upslope access to flows evolve into pockmarks

25 Canyon piracy and abandonment
WB 4 1x1

26 Canyon evolution Slate newer

27 Canyon piracy and abandonment
Above slate

28 Canyon piracy and abandonment
BS2_newer

29 Canyon piracy and abandonment

30 Canyon piracy and abandonment
Below below WB

31 Canyon piracy and abandonment
Below WB

32 Canyon piracy and abandonment
WB 4 1x1

33 Canyon  Pockmark Abandoned canyon with ridges (slumps)
Thinning canyon with ‘peanuts’ Discrete & aligned pockmarks Active canyon

34 High permeability canyon deposits act as fluid migration pathways
2 km

35 Channel-pockmark association: Other examples
Heinio and Davies, 2009 Channel morphology much different (sandiness) Channel margin faults Sediment wave interaction

36 Channel-pockmark association: Other examples
Heinio and Davies, 2009

37 Channel-pockmark association: Other examples
Heinio and Davies, 2009

38 Canyon  Pockmark Abandoned canyon with ridges (slumps)
Thinning canyon with ‘peanuts’ Discrete & aligned pockmarks Active canyon

39 Conclusions Pockmarks on the modern seafloor identify ancient submarine canyons Pockmark evolution (Ma) Canyon ridge formation ‘Peanuts’ Discrete pockmarks Only canyons that lose access to upslope flows evolve into pockmarks

40 Keep a lookout for pockmarks!

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