Cyclic steps along the South Taiwan Shoal and West Penghu submarine canyons on the northeastern continental slope of the South China Sea
Cyclic steps along the South Taiwan Shoal and West Penghu submarine canyons on the northeastern continental slope of the South China Sea
Large-scale step-like features within the South Taiwan Shoal and West Penghu submarine canyons on the northeastern continental slope of the South China Sea are investigated by integrating high-resolution multibeam bathymetric data and multichannel seismic profiles. These step-like features, ranging from 1.2 to 10.0 km in wavelength and 5.4–80.9 m in wave height, are mostly interpreted as cyclic steps formed by turbidity currents flowing through the canyons, based on their characteristic step-like morphology, in-train alignment, large wavelengths and aspect ratios (ratio of wavelength to wave height), and typical upstream-sloping backset bedding, among others. A train of 19 continuous steps delineated along the thalweg of the South Taiwan Shoal canyon measures up to 100 km and may be the longest ever reported. Nine short trains of scours identified on a terrace of the South Taiwan Shoal canyon are oriented parallel to the distributaries draining over the terrace and roughly perpendicular to the main canyon thalweg, indicating a complicated flow pattern within the canyon valley. Two trains of scours separated by an intracanyon high in the steeper middle reach of the West Penghu canyon are interpreted as transitional bed forms between antidunes and cyclic steps, which develop downstream into a train of five net-depositional cyclic steps with typical backset bedding in the gentler-sloping lower reach of the canyon. Average slope gradients for the canyon reaches with cyclic steps range from 0.26° to 1.24°. Along each thalweg step train, a slope break is identified to separate the net-erosional cyclic steps in the steeper upstream segment from the net-depositional ones in the gentler downstream segment. Rough estimations indicate that the paleoflows are 100 to 300 m thick with maximum velocities of up to 10 m s–1. The estimated flow depths match well with those inferred from geomorphologic analysis. Estimated paleodischarges of ?7–23 × 105 m3 s–1 are equivalent to ten times the discharge of the modern Amazon River.
804-824
Zhong, Guangfa
19231e09-7606-4f63-a821-dddfe3b191f6
Cartigny, Matthieu J.B.
d252d7b1-16c6-47b1-bf86-8087070934ce
Kuang, Zenggui
953a3f2f-c9d5-4c96-a5dd-cf702f4ec429
Wang, Liaoliang
b7a8d8b9-c5a1-412e-acee-4c8eca2da06a
2015
Zhong, Guangfa
19231e09-7606-4f63-a821-dddfe3b191f6
Cartigny, Matthieu J.B.
d252d7b1-16c6-47b1-bf86-8087070934ce
Kuang, Zenggui
953a3f2f-c9d5-4c96-a5dd-cf702f4ec429
Wang, Liaoliang
b7a8d8b9-c5a1-412e-acee-4c8eca2da06a
Zhong, Guangfa, Cartigny, Matthieu J.B., Kuang, Zenggui and Wang, Liaoliang
(2015)
Cyclic steps along the South Taiwan Shoal and West Penghu submarine canyons on the northeastern continental slope of the South China Sea.
Geological Society of America Bulletin, 127 (5-6), .
(doi:10.1130/B31003.1).
Abstract
Large-scale step-like features within the South Taiwan Shoal and West Penghu submarine canyons on the northeastern continental slope of the South China Sea are investigated by integrating high-resolution multibeam bathymetric data and multichannel seismic profiles. These step-like features, ranging from 1.2 to 10.0 km in wavelength and 5.4–80.9 m in wave height, are mostly interpreted as cyclic steps formed by turbidity currents flowing through the canyons, based on their characteristic step-like morphology, in-train alignment, large wavelengths and aspect ratios (ratio of wavelength to wave height), and typical upstream-sloping backset bedding, among others. A train of 19 continuous steps delineated along the thalweg of the South Taiwan Shoal canyon measures up to 100 km and may be the longest ever reported. Nine short trains of scours identified on a terrace of the South Taiwan Shoal canyon are oriented parallel to the distributaries draining over the terrace and roughly perpendicular to the main canyon thalweg, indicating a complicated flow pattern within the canyon valley. Two trains of scours separated by an intracanyon high in the steeper middle reach of the West Penghu canyon are interpreted as transitional bed forms between antidunes and cyclic steps, which develop downstream into a train of five net-depositional cyclic steps with typical backset bedding in the gentler-sloping lower reach of the canyon. Average slope gradients for the canyon reaches with cyclic steps range from 0.26° to 1.24°. Along each thalweg step train, a slope break is identified to separate the net-erosional cyclic steps in the steeper upstream segment from the net-depositional ones in the gentler downstream segment. Rough estimations indicate that the paleoflows are 100 to 300 m thick with maximum velocities of up to 10 m s–1. The estimated flow depths match well with those inferred from geomorphologic analysis. Estimated paleodischarges of ?7–23 × 105 m3 s–1 are equivalent to ten times the discharge of the modern Amazon River.
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Published date: 2015
Organisations:
Marine Geoscience
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Local EPrints ID: 377286
URI: http://eprints.soton.ac.uk/id/eprint/377286
ISSN: 0016-7606
PURE UUID: 09c7e4b6-5d59-4309-98fe-804c52bc0918
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Date deposited: 19 May 2015 15:53
Last modified: 14 Mar 2024 20:00
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Author:
Guangfa Zhong
Author:
Matthieu J.B. Cartigny
Author:
Zenggui Kuang
Author:
Liaoliang Wang
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