Where have all the

sediments gone?The fate of sediments in the

Taiwan Strait: A reassesment

Where have all the

sediments gone?The fate of sediments in the

Taiwan Strait: A reassesment

Chih-Chieh Su, Man-Shan Chang, Horn-Ru Liao, Ho-

Shing Yu Institute of Oceanography, NTU

20, Feb, 2008

Chih-Chieh Su, Man-Shan Chang, Horn-Ru Liao, Ho-

Shing Yu Institute of Oceanography, NTU

20, Feb, 2008

Outline

• Previous study– Relict sediments?

• Short-term changes• Chronology of sediment cores• Where have all the sediments gone?

– What we know…– What we “don’t” know…

Changyun Ridge

Wuchu Depression

Kuanyin Depression

Taiwan Banks

Penghu Channel

Emery (1952; 1961)

In general, any shelf sediment belongs to one or more of five main groups:

• Authigenic (glauconite and phosphorite)

• Organic (Foraminifera and shells)• Residual (weathered from underlying

rocks)• Relict (remnant from a different

earlier environment － such as a now-submerged beach or dune)

• Detrital (presently supplied chiefly from adjacent river mouths, beaches, or sea cliffs)

Emery ( 1968 )

Boggs ( 1975; 1979 )

• continued using Emery’s concept of relict sediments

• mud belt along the coast of mainland China→ modern sediments

• sandy sediments in Taiwan Strait– in the nearshore area of Taiwan→Holocene

to modern sand– central part of Taiwan Strait →relict

sediments from mainland China• A large area of the Strait surrounding

the Penghu Island was covered by palimpsest sediment formed by mixing of modern and relict sediment.

Boggs et al. ( 1979 )

Chiu ( 2000 )

Modern muddy sediment

Relict sediment

Palimpsest sediment

Modern sandy sediment

Chang ( 2002 )

Modern muddy sediment

Relict sediment

Palimpsest sediment

Modern sandy sediment

Liu et al., 1998

Liao ( 2005 ); Liao et al. (2008)

Outline

• Previous study– Relict sediments?

• Short-term changes• Chronology of sediment cores• Where have all the sediments gone?

– What we know…– What we “don’t” know…

Location map of the surface sediment

median sorting

Milliman et al., 2007

Outline

• Previous study– Relict sediments?

• Short-term changes• Chronology of sediment cores• Where have all the sediments gone?

– What we know…– What we “don’t” know…

Location Map

(060721-24)(060406-09)(050705-07)

790-1

790-2

790-3

790-4

790-5

790-6

790-7

1.00 cm/a0.12 cm/a

1.46 cm/a0.18 cm/a

1.06 cm/a

1.25 cm/a0.21 cm/a

1.08 cm/a0.18 cm/a

0.05 cm/a

0.70 cm/a

OR542 BC9(1999/3/9)

Outline

• Previous study– Relict sediments?

• Short-term changes• Chronology of sediment cores• Where have all the sediments

gone?– What we know…– What we “don’t” know…

What we know…

• The sediments in the Taiwan Strait are not the so called “relict sediments”, they are the products of the action of modern tidal currents.

• Taiwan is the major source of modern sediments in the Taiwan Strait.

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What we don’t know…

• Where did the “old” sediments in the Taiwan Strait (Chanyun Ridge) come from?– mainland China?– Taiwan?– Penghu Channel?

2008 Joint Hydrographic Survey

• Grain Size Analysis• Clay Mineral

Composition• Trace Element

Distribution• Thermoluminesce

nce Dating (TLD)

It’s not complicated, but “VERY” dynamic!