Pockmarks

forestsaintregisOil and Offshore

Nov 8, 2013 (3 years and 9 months ago)

72 views

Seafloor Pockmarks
identifying ancient
submarine canyons,
Equatorial Guinea

Zane Jobe

Don Lowe

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

1)
Pockmarks on the modern
seafloor identify ancient
submarine canyons

2)
Pockmark evolution (Ma)

1)
Canyon ridge formation

2)
‘Peanuts’

3)
Discrete pockmarks

3)
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)


100
-
700 m x 5
-
40 m


Distribution


Random


Aligned in trains

Lastras et al., 2004

Pilcher and Argent, 2007

10 km

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

wind

longshore

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

d
e
g
r
e
e
s

2 km

Perception

12

Bright amplitudes concentrated in

canyons & pockmarks

2 km

13

Canyons are highly aggradational

and long lived (> 10 Ma) = pockmarks

14

Canyons are highly aggradational

and long lived (> 10 Ma) = pockmarks

15.5 Ma

8.2 Ma

6.3 Ma

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

1 km

17

Across canyon view:

Pockmarks overlie ancient canyons


450 m wide


60 ms deep

A’

A

A’

A

18


350 m wide


50 ms deep

B

B’

B

B’

Dip view


chaotic canyon deposits

giving way to conformable reflectors

19

Canyon piracy and abandonment

Time

structure

Colors

Pockmark trains overlie ancient canyons

20

2 km

+

=

2 km

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)

A’

A’

A

A

2 km

2 km

23

Pockmark evolution


Across
-
canyon
ridges


‘Peanuts’


Pockmarks

1

1

2

3

2

2

2

2

3

2 km

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


偯P歭慲k

Active
canyon

Abandoned
canyon with
ridges (slumps)

Thinning
canyon with
‘peanuts’

Discrete &
aligned
pockmarks

34

High permeability canyon deposits act as

fluid migration pathways

2 km

35

Channel
-
pockmark association:

Other examples

Heinio and Davies, 2009

2 km


Channel morphology much different (sandiness)


Channel margin faults


Sediment wave interaction

36

2 km

Heinio and Davies, 2009

Channel
-
pockmark association:

Other examples

37

2 km

Heinio and Davies, 2009

Channel
-
pockmark association:

Other examples

38

Canyon


偯P歭慲k

Active
canyon

Abandoned
canyon with
ridges (slumps)

Thinning
canyon with
‘peanuts’

Discrete &
aligned
pockmarks

39

1)
Pockmarks on the modern
seafloor identify ancient
submarine canyons

2)
Pockmark evolution (Ma)

1)
Canyon ridge formation

2)
‘Peanuts’

3)
Discrete pockmarks

3)
Only canyons that lose
access to upslope flows
evolve into pockmarks

Conclusions

40

Keep a lookout for pockmarks!