near-bottom sedimentation offshore southwestern taiwan from echo character study jui-kun chiu,...
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Near-Bottom Sedimentation Near-Bottom Sedimentation Offshore Southwestern Taiwan Offshore Southwestern Taiwan
from Echo Character Studyfrom Echo Character Study
Jui-kun ChiuJui-kun Chiu, Cher-Shine Liu, Cher-Shine Liu
Institute of OceanographyInstitute of Oceanography
National Taiwan UniversityNational Taiwan University
2009/03/252009/03/25
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AcknowledgementAcknowledgement
• The crew of the R/V Ocean Research I
• Central Geological Survey, MOEA
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Offshore SW Taiwan
Liu et al., 1998
TAIWANTransition from Subduction toCollisionAccretionary Wedge: folds and faultsPassive margin: normal faultsDeformation frontRapid sediment depositionSlumps on continental slope
Liu et al., 1997
Deform
ation Front
AccretionaryWedge
Passive
Continen
tal
Margin
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PurposePurpose• To find the possible mechanisms of the
different sedimentary processes and their geological implications offshore area Southwestern Taiwan
http://www.marum.de/
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How to conduct researches How to conduct researches in this big area?in this big area?
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Yellow Sea
South China Sea
(Chough et al., 2002)(Damuth, 1980)
Echo Character
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1B
2A
2B
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Yellow Sea
(Chough et al., 2002)
Echo Character
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Methods and DataMethods and Data• Bathymetry data• Chirp sonar profiles(Bathy-2000P on OR1)
Taiwan
Ship Track Map
> 7 cruises>10,000 km
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Unconformity
Chirp Sonar ProfileChirp Sonar Profile
2 km
100mSW NE
We identified and classified discrete echo types on the basis of reflection characters (e.g. clarity, continuity, amplitude and geometry of bottom and sub-bottom echoes).
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Four categories of echo types are recognized in this study:
(1) Distinct echoes (Type I-1 and I-2)
(2) Indistinct echoes (Type II-1 and II-2)
(3) Hyperbolic echoes (Type III)
(4) Irregular echoes (Type IV-1, IV-2 and IV-3)
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Echo Characters (1)Echo Characters (1)
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Echo Characters (2)Echo Characters (2)
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Type Line drawing Description Occurrence Interpretation
I-1
Sharp surfloor reflector without or with few subbottom echoes
Passive and active continental shelf
Coarse-grained sediments (Chen, 1983; Lee et al., 2004)
I-2
Distinct bottom echo with continuous, parallel internal reflectors; the penetration depth ranges from 40 to 100 m; seafloor is generally flat
Intra-slope basin of the Kaoping Slope and the lower part of the passive continental slope
Pelagic deposition (Lee et al., 1999); submarine fan
II-1Indistinct bottom echo and bushy, prolonged sub-bottom echoes
Upper China continental slope Creep sediments
II-2Wavy, prolonged sub-bottom echoes; the penetration depth varies from 10 to 50 meters
Troughs or depressions of the Kaoping Slope
Turbidites
III
Single or irregular overlapping hyperbolae with widely varied vertex elevations and no sub-bottom reflectors
Summits and outcrops of the Kaoping Slope and small hills or rugged area of the upper China continental slope
Basement high or outcrops (Damuth, 1980) , Escarpments
IV-1
Slope failure planes within a short distance; down-slope slumps by the gravity sliding
Steep slope and gullies of the SCS continental margin and canyon systems of the Kaoping Slope
Slope failure (Lee et al., 2002; Lee et al., 2005)
IV-2Acoustic blanking zone between continuous reflectors; the width of the blanking signals varied from 200 meter to several kilometers
Mud dirpir zone of the upper Kaoping Slope
Gassy sediments (Chiu et al., 2006)
IV-3Uppermost transparent blanketing layer below the sea floor
lower SCS continental slope and around the lower section of the Penghu Canyon
Debris flow deposits (Lee et al., 1999)
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Echo Character MapEcho Character Map
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What we observedWhat we observed1. In the submarine Taiwan orogenic wedge offshore SW Taiwan,
and fill-and-spill processes have smoothed the seafloor topography of the upper Kaoping slope there. In the lower Kaoping slope, steep slopes of the ridge flanks and submarine canyon walls generate frequent slope failures.
2. In the passive SCS continental margin, the steep slope of the upper continental slope forms an erosional environment while the mass wasting materials are deposited in the lower continental slope.
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Accretionary Wedge
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Kaoping River
NE
Kaoping Submarine Canyon
Penghu Submarine Canyon
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100 m
2 km
Flood Layer thinner
(OR1-647)
Kaoping Submarine Canyon
Taiwan
Type 1-2
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( Huh , 2008 )
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Kaoping River
OR1-716-4
Kaoping Submarine Canyon
Penghu Submarine Canyon
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Gullies
Penghu Submarine Canyon Kaoping Submarine Canyon
Passive margin
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• Differences in the occurrence of slope failures and sea-floor gradients from NE (near Taiwan) to SW (away from Taiwan) along the passive SCS continental margin.
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Line ANW SE
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Continental Shelf
Clift
Mass movement
2 km
100m
SE NW
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• This reflects the influence of the loading of Taiwan orogenic wedge on the passive SCS continental margin.
(Lin & Watts, 2002)
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• Continuous, parallel, general conformable sub-bottom reflections are observed on the lower SCS continental slope
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Continuous Reflectors
Mass movement
2 km
100m
SE NW
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Summary(1)Summary(1)• There is a major difference between the sedimentary
environments of the passive SCS continental margin and the submarine orogenic wedge offshore southwestern Taiwan.
• The echo distribution map clearly indicates that in the passive SCS continental margin province, the sedimentary environment in the upper to mid-slope is erosional, whereas the lower continental slope of the SCS continental margin is depositional.
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Summary(2)Summary(2)
• On the other hand, in the active submarine Taiwan orogenic wedge, the upper slope domain appears to be a depositional environment, whereas the lower slope domain is erosional in nature.
• The main reason for this big contrast is the supply of terrigenous sediment.
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Thanks for your attention!Thanks for your attention!