Late Pleistocene-Holocene seismic stratigraphy of the Southeast Vietnam Shelf.

Dung, B. V., Stattegger, Karl, Unverricht, D., Phach, P. V. and Thanh, N. T. (2013) Late Pleistocene-Holocene seismic stratigraphy of the Southeast Vietnam Shelf. Global and Planetary Change, 110 . pp. 156-169. DOI 10.1016/j.gloplacha.2013.09.010.

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The Late Pleistocene–Holocene sedimentary architecture of the Southeast (SE) Vietnam Shelf was investigated using high-resolution seismic profiles and core samples. Three systems tracts and a prominent seismic reflection surface at the base of the sequence were revealed. This surface (SB1) is interpreted as a sequence boundary formed by subaerial processes during the Late Pleistocene sea-level fall and subsequent marine reworking during transgression. A surface map of the lowstand surface, compiled from seismic profiles and sediment cores, revealed the W–E to N–S oriented incised-valley system of the paleo-Mekong River. The incised valleys show a clear change in morphology from the north to the south in the study area. The northern incised-valley system off Vung Tau appears as a narrow and deep V-shape in cross-section (< 5 km wide and tens of meters deep) likely as a result of the high-gradient morphology of the paleo-shelf. In contrast, the wide and low-gradient paleo-shelf off the modern Mekong Delta and Ca Mau Peninsula created shallow incised-valleys (5–15 km wide and < 15 m deep) on the exposed shelf. The lowstand systems tract (LST) consists of a prograding outer shelf delta-wedge formed during the Last Glacial Maximum (LGM) sea-level lowstand period. The transgressive systems tract (TST) was well preserved in the incised-valleys, where its thickness reaches 15–25 m. Sediment core analysis results and seismic facies reveal that the TST deposits within the incised-channels were marked by a transition from fluvial deposits at the base to marine deposits in the upper part of the channels. On the exposed shelf and the interfluvial area of the incised-channels, the TST is a sandy layer overlying the sequence boundary SB1. Thickness of the TST on the shelf varies from 0 to 15 m. The highstand systems tract (HST) consists of thick mud clinoforms of the modern Mekong subaqueous delta. The HST wedge prograded onto the shelf primarily after the mid-Holocene sea-level highstand was at approximately 6.5–5.5 kyr BP ago. The HST wedge extends along the southwestern shore, and its maximum thickness (30 m) was recorded in the Cape Ca Mau area. The HST wedge pinches out at modern water depths of 20–30 m, resulting in a thin HST layer on the middle and outer shelf. The proposed post-Pleistocene sequence-stratigraphic model for the SE Vietnam Shelf is a variation on the theoretical model of Vail (1987). The thick highstand wedge on the SE Vietnam Shelf is confined to the inner shelf due to the broad and low-gradient shelf morphology and the strong local hydrodynamic conditions driven by the monsoon system. Except for the one deposited within the incised-valley system, the TST deposits on the SE Vietnam Shelf tend to disperse over the shelf instead of forming a thick backstepping unit. The accommodation space was probably created faster than the sediment supply during the rapid transgression.

Document Type: Article
Additional Information: Times Cited: 0 Bui Viet Dung Stattegger, Karl Unverricht, Daniel Phung Van Phach Nguyen Trung Thanh Si B
Keywords: sequence stratigraphy, LGM sea-level, SE Vietnam Shelf
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.gloplacha.2013.09.010
ISSN: 0921-8181
Projects: Future Ocean
Date Deposited: 08 Jul 2014 09:00
Last Modified: 16 Jul 2019 10:04

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