from Echo Character Study

choppedspleenMechanics

Feb 21, 2014 (2 years and 9 months ago)

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Near
-
Bottom Sedimentation

Offshore Southwestern Taiwan

from Echo Character Study

Jui
-
kun Chiu
, Cher
-
Shine Liu

Institute of Oceanography

National Taiwan University

2009/03/25

Acknowledgement




The crew of the R/V Ocean Research I


Central Geological Survey, MOEA




Offshore SW Taiwan

Liu et al., 1998

TAIWAN

Transition from Subduction to

Collision

Accretionary Wedge: folds and faults

Passive margin: normal faults

Deformation front

Rapid sediment deposition

Slumps on continental slope

Liu et al., 1997

Accretionary

Wedge

Purpose


To find the possible mechanisms of the
different sedimentary processes and their
geological implications offshore area
Southwestern Taiwan


http://www.marum.de/

How to conduct researches
in this big area?


Yellow Sea

South China Sea

(Chough et al., 2002)

(Damuth, 1980)

Echo Character

1B

2A

2B


Yellow Sea

(Chough et al., 2002)

Echo Character

Methods and Data


Bathymetry data


Chirp sonar profiles

(Bathy
-
2000P on OR1)


Taiwan

Ship Track Map

> 7 cruises

>10,000 km

Unconformity

Mud Volcano

Flow disturb

Fault

Chirp Sonar Profile

2 km

100m

SW

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).

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)

Echo Characters (1)


Echo Characters (2)


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
-
1

Indistinct bottom echo and bushy, prolonged
sub
-
bottom echoes

Upper China continental slope

Creep sediments

II
-
2

Wavy, 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
-
2

Acoustic 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
-
3

Uppermost 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)

Echo Character Map


What we observed

1.
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.

Accretionary Wedge


Kaoping River

NE

Kaoping Submarine Canyon

Penghu Submarine Canyon

100 m

2 km



Flood Layer

thinner

(OR1
-
647
)

Kaoping Submarine Canyon

Taiwan

Type 1
-
2



Huh

2008



Kaoping River

OR1
-
716
-
4

Kaoping Submarine Canyon

Penghu Submarine Canyon



Gullies

Penghu Submarine Canyon

Kaoping Submarine Canyon

Passive margin


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.


Line A

NW

SE

Continental

Shelf

Clift

Mass movement

2 km

100m

SE

NW


This reflects the influence of the loading of
Taiwan orogenic wedge on the passive
SCS continental margin.

(Lin & Watts, 2002)


Continuous, parallel, general
conformable sub
-
bottom reflections are
observed on the lower SCS continental
slope

Continuous Reflectors

Mass movement

2 km

100m

SE

NW

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.

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.

Thanks for your attention!