G.S.I. Seabed Survey G.S.I. Seabed Survey SeminarSeminar

Possible Carbonate Mound Possible Carbonate Mound DistributionDistribution

November 2001November 2001Thomas FureyThomas Furey

Presentation OverviewPresentation Overview

Introduction.Introduction. Overview of carbonate mound Overview of carbonate mound

distribution to date offshore distribution to date offshore Ireland.Ireland.

Mounds and their settings, data Mounds and their settings, data examples, data resolution.examples, data resolution.

Summary and conclusions.Summary and conclusions.

What Are Mounds?What Are Mounds? Topographic highs - circular & ridge morphologyTopographic highs - circular & ridge morphology

Of what importance are Of what importance are they?they?

Environmental – Associated coral Environmental – Associated coral ecosystemsecosystems

Hazards – trawling damage, shallow gasHazards – trawling damage, shallow gas

Line 140, Area 3A

30 m

500 m

Interested GroupsInterested Groups•GEOMOUND – htttp://geomound.ucd.ieGEOMOUND – htttp://geomound.ucd.ie

•ECOMOUNDECOMOUND•ACES - Atlantic Coral Ecosystem StudyACES - Atlantic Coral Ecosystem Study•CORSAIRESCORSAIRES•ENAM-2ENAM-2

Recent Irish StudiesRecent Irish Studies•1996 AIRS survey - Gloria1996 AIRS survey - Gloria•Logachev 1997 - Seismic & Logachev 1997 - Seismic &

SidescanSidescan•Belgica 1997 - SeismicBelgica 1997 - Seismic

Mound Identification Mound Identification

•Trawling, sidescan sonar, seismic.Trawling, sidescan sonar, seismic.•Sub bottom profiler.Sub bottom profiler.•Multibeam – bathymetry & backscatter.Multibeam – bathymetry & backscatter.

Problems incurred:Problems incurred:

How are they How are they identified?identified?

•Multibeam Chart Resolution:Multibeam Chart Resolution:1 Pixel = 100 m1 Pixel = 100 m22

Contour Interval = 50 mContour Interval = 50 m

•Sub Bottom Profiles: 2D, Digital Sub Bottom Profiles: 2D, Digital InterpretationInterpretation

Mound CharacteristicsMound Characteristics

• Water Depth Ranges: 550-2500 mWater Depth Ranges: 550-2500 m• Size:Size:

– Height Range: 20 - 400 m Height Range: 20 - 400 m approximatelyapproximately

– Diameter: 250 metres - 1.5 kmDiameter: 250 metres - 1.5 km– Elongate Reefs (?) : Several Km’s Elongate Reefs (?) : Several Km’s

GEOMOUND Carbonate GEOMOUND Carbonate MoundsMounds

24ºW 20 ºW 16 ºW 12 ºW 8 ºW 4 ºW

24ºW 20 ºW 16 ºW 12 ºW 8 ºW 4 ºW

56 ºN

54ºN

52 ºN

50 ºN

48 ºN

56 ºN

54ºN

52 ºN

50 ºN

48 ºN

NWRT

SERT

MPB

SPB

Mound GroupsMound Groups•South Porcupine Bite – SPBSouth Porcupine Bite – SPB•Main Porcupine Basin – MPBMain Porcupine Basin – MPB•South East Rockall Trough – South East Rockall Trough – SERTSERT•North West Rockall Trough – North West Rockall Trough – NWRTNWRT•West Rockall Bank – WRBWest Rockall Bank – WRB•Edoras Bank - EBEdoras Bank - EB•Fangorn Bank - FBFangorn Bank - FB

24ºW 20 ºW 16 ºW 12 ºW 8 ºW 4 ºW

24ºW 20 ºW 16 ºW 12 ºW 8 ºW 4 ºW

56 ºN

54ºN

52 ºN

50 ºN

48 ºN

56 ºN

54ºN

52 ºN

50 ºN

48 ºN

Possible Mound Distribution Possible Mound Distribution 20012001

EB

FB

WRB

Bathymetric Mound Bathymetric Mound DistributionDistribution

23º W 18º W 13º W 8º W

23º W 18º W 13º W 8º W

57º N

52º N

57º N

52º N

500 m

1000 m

1500 m

2000 m

23º W 18º W 13º W 8º W

23º W 18º W 13º W 8º W

57º N

52º N

57º N

52º N

PAD Structural Map & PAD Structural Map & MoundsMounds

NEXT SLIDE

West Rockall Bank MoundsWest Rockall Bank Mounds

PINCH MICKS IMAGE – add transects

Mounds

Ridge

0 20 km

N

West Rockall BankWest Rockall Bank Mound Example Mound Example

Mound Location

30 metres

500 metres

Acoustic Blanking

Sub Bottom Profile – Line 144

WSW ENE

Shaded Relief with Bathymetric Contours.

WRB Mounds

N

Line 156 Line 155 Line 154 Line 153

• Tracklines 153 - 156

• Ridge

• Isolated Mound• Contour Parallel Mounds

Raw Backscatter Data - Raw Backscatter Data - WRBWRB

5 km

50 km

WSW ENE

Raw Backscatter Data - Raw Backscatter Data - WRBWRB

Individual Individual MoundsMounds

Grouped MoundsGrouped Mounds Elongate:Elongate:

North-SouthNorth-SouthContour ParallelContour Parallel

Line 154

Line 153

5 km

10 km

Line 144, Area 3A 500 metres

40 metres

Small Mound - 250 x 20 metresSmall Mound - 250 x 20 metres

155

144

WRB

WRB WRB MoundsMounds

130 metres1 km

Line 155, Area 3A

Large Mound - 130 metres x 1.5 kmLarge Mound - 130 metres x 1.5 km

20 metres

Line 145, Area 3A500 metres

Acoustic Blanking

Acousting Blanking BeneathAcousting Blanking Beneath

Possible Gasified Mounds Possible Gasified Mounds

Conical Mound with Moat FeatureConical Mound with Moat Feature

500 metres AcousticBlanking

Line 150, Area 3A

40 metres

Moat

WRB WRB MoundsMounds

150 145

Fangorn BankFangorn Bank Bathymetry Map Sheet 28 Bathymetry Map Sheet 28

N

Mound features

0 25 km

Next Slide

N

0 25 km

Fangorn BankFangorn BankShaded Relief Map Sheet 28Shaded Relief Map Sheet 28

Fangorn BankFangorn Bank Sub bottom record - Line 1353Sub bottom record - Line 1353

seabed

40 metres

SE NW

500 metres

MPB & SPB MPB & SPB MoundsMounds

3D Surface 3D Surface

NorthNorth Area 3EArea 3E

40 km

Shaded Shaded

ReliefRelief

MBP

SPB

ConclusionsConclusions Additional Mound locations Additional Mound locations identified.identified. Relief useful Mound identification Relief useful Mound identification tool.tool. Raw Backscatter is good quality.Raw Backscatter is good quality. Small features require reprocessing. Small features require reprocessing. West Rockall Bank study proposed.West Rockall Bank study proposed. Ground truthing required.Ground truthing required. Large uninterpreted dataset Large uninterpreted dataset available.available.

Zone 3Zone 3

3A

W.P.

3E

3F

3H

Area 3E colour contoured map of area coveredArea 3E colour contoured map of area covered

N

Ship track lines

Depth Range200 m to 4500 m

0 150 km

Area 3E sun illuminated map of area coveredArea 3E sun illuminated map of area covered

Next slide

Gollum Channel Complex

0 150 km

Area 3E, Line 3564.Area 3E, Line 3564.Possible gas associated with Carbonate Mound.Possible gas associated with Carbonate Mound.

seabed

Gas bearing sediment

SW NE

500 metres