Near-Bottom Sedimentation Offshore Southwestern Taiwan from Echo Character Study

1. 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

2. Acknowledgement • The crew of the R/V Ocean Research I • Central Geological Survey, MOEA

3. Offshore SW 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 Passive Continental Margin TAIWAN Accretionary Wedge Deformation Front Liu et al., 1998

4. Purpose • To find the possible mechanisms of the different sedimentary processes and their geological implications offshore area Southwestern Taiwan http://www.marum.de/

5. How to conduct researches in this big area?

6. Echo Character Yellow Sea South China Sea (Damuth, 1980) (Chough et al., 2002)

7. 1B 2A 2B

8. Echo Character Yellow Sea (Chough et al., 2002)

9. Taiwan Methods and Data • Bathymetry data • Chirp sonar profiles (Bathy-2000P on OR1) > 7 cruises >10,000 km Ship Track Map

10. 100m Mud Volcano 2 km Unconformity Flow disturb Fault Chirp Sonar Profile 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). SW NE

11. 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)

12. Echo Characters (1)

13. Echo Characters (2)

15. Echo Character Map

16. What we observed • 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. • 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.

17. Accretionary Wedge

18. NE Kaoping River Kaoping Submarine Canyon Penghu Submarine Canyon

19. Type 1-2 Taiwan Flood Layer thinner 100 m 2 km (OR1-647) Kaoping Submarine Canyon

20. （Huh，2008）

21. Kaoping River Kaoping Submarine Canyon OR1-716-4 Penghu Submarine Canyon

23. Passive margin Gullies Penghu Submarine Canyon Kaoping Submarine Canyon

24. 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.

25. Line A NW SE

26. 100m 2 km NW SE Continental Shelf Mass movement Clift

27. This reflects the influence of the loading of Taiwan orogenic wedge on the passive SCS continental margin. (Lin & Watts, 2002)

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

29. Mass movement 100m 2 km Continuous Reflectors NW SE

30. 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.

31. 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.

32. Thanks for your attention!