Evolution of holocene depositional environments in the coastal area from the Tien river to the Hau river mouths
Main Article Content
Abstract
Abstract. The Holocene coastal zone o f Mekong river plain is the result o f prolonged marinefluvial interaction. Lithofacies association in time and space IS characterized by three depositional
system ưact belonged to the upper part o f a sequence sưatigraphy. Based on lithology should be
divided 5 sedimentary types and 18 lithofacies distributed in stratigraphical colum n and in sea
bottom varying from 25m water depth to mainland coastal area. A ccording to sequence
stratigraphy the ưansgressive systems tract at 5 Ky Bp, while from geochronology point o f view
the boundary between Middle Holocene and Late H olocene is 3 Ky Bp - a regressive stage.
During Early-Middle Holocene stage ưansgressive depositional system tract is characterized by
two associated lilhofacies upward section: delta front swamp mud rich in organic materials facies
and marine shallow grey-greenish clay facies corresponded with marine flooding plain. And then
Late Holocene regressive phase corresponding with Highstand system s tract com posed o f delta
plain clayish Slit facies in which there are different sandy ndges generations distributed younger
seaward. Each sand ridge generation was mark by a coastal zone and associated lithofacies.
In circumstance o f global climate change and sea-leve! rising, the M ekong river coastal zone will
be changed much more in framework o f modem tectonic subsidence. If the rate o f sea-level rising
is 2mm/ycar then sea bed will be subsided with a rate o f 4mm/year. But recent rate o f sediment
accumulation is over 4mm/year, so the modem coastline continue to prograde seaward with a rate
o f 40m/year. The Mekong river mouths are migrating to East-North, and as a result geosystems
and landscapes arc changing.
system ưact belonged to the upper part o f a sequence sưatigraphy. Based on lithology should be
divided 5 sedimentary types and 18 lithofacies distributed in stratigraphical colum n and in sea
bottom varying from 25m water depth to mainland coastal area. A ccording to sequence
stratigraphy the ưansgressive systems tract at 5 Ky Bp, while from geochronology point o f view
the boundary between Middle Holocene and Late H olocene is 3 Ky Bp - a regressive stage.
During Early-Middle Holocene stage ưansgressive depositional system tract is characterized by
two associated lilhofacies upward section: delta front swamp mud rich in organic materials facies
and marine shallow grey-greenish clay facies corresponded with marine flooding plain. And then
Late Holocene regressive phase corresponding with Highstand system s tract com posed o f delta
plain clayish Slit facies in which there are different sandy ndges generations distributed younger
seaward. Each sand ridge generation was mark by a coastal zone and associated lithofacies.
In circumstance o f global climate change and sea-leve! rising, the M ekong river coastal zone will
be changed much more in framework o f modem tectonic subsidence. If the rate o f sea-level rising
is 2mm/ycar then sea bed will be subsided with a rate o f 4mm/year. But recent rate o f sediment
accumulation is over 4mm/year, so the modem coastline continue to prograde seaward with a rate
o f 40m/year. The Mekong river mouths are migrating to East-North, and as a result geosystems
and landscapes arc changing.
References
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Minerals of VN. Hanoi.
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Long delta. Proceedings o f International
Seminar "Quaternary stratigraphy o f deltas in
Viet Nam", 124-132, Ha Noi.
[2] G.p Allen, H .w Posamentier, Sequence
stratigraphy and facies model o f an incided
valley fill: The Gironde estuary, France.
Journal o f sedim entary Petrology 3 (1993)
378.
[3] Nguyen Huy Dung, 2003, Report o f Project
"Division, correlation o f Neogen-Quatemary
stratigraphy and study on structure o f Nam Bo
plain, scale 1:500.000", Archive in Informative - Gcological Archive Centre.
[4] Nguyen Huy Dung, Ngo Quang Toan, 2004,
Quaternary stratigraphy o f the Mekong delta.
Proceedings o f International Seminar
"Quaternary stratigraphy o f deltas in Viet
Nam", 133-147, Ha Noi.
[5] Nguyen Ngoc Hoa, 1991. Report on geological
mapping group sheets o f the Nam Bo Plain,
sheet An Bien-Soc Trang and Soc Trang-Con
Dao, scale 1: 200.000", Archive in Informative - Geological Archive Centre.
[6] Tran Nghi, 1999. Report "Map of surface
sediments and petro-dynamic of neashore area
(0-30m water depth) Bac Lieu-Ham Luong, scale
1:500,000. Archive in Informative-Geological
Archive Centre.
[7] Tran Nghi, Nguyen Huy Dung, Nguyen Thanh
Lan, Dinh Xuan Thanh, Pham Nguyen Ha Vu,
Law o f ancient river channel facies transition in
late Neogene- Quartemary in relation to tectonic
activity in Nambo plain. Jour. Of Marine
Science and Technology 5/3 (2005) 45. A.ST.
Vietnam.
[8] V.L. Nguyen, T.K.O. Ta, M. Tateishi, Late
Holocene depositional environments and coastal
evolution of the Mekong River Delta, Southern
Vietnam, Journal o f Asian Earth Sciences 18
(2000) 427.
[9] E. Saurin, Le substratum de Saigon et la
formation du Delta du Mekong. C.R.Som. Geol.,
France, fasc. 8 (1964) 306. Paris.
[10] Vu Truong Son, 2009. Report "Survey, evaluate
o f minerals potential of nearshore area of
Province Soc Trang, scale 1: 100,000". Archive
in Informative-Geological Archive Centre.
[11] T.K.O. Ta, V.L. Nguyen. M. Tateishi, I.
Kobayashi, Y., Sailo, Sedimentary facies,
diatom and foraminifera assemplagcs in a late
Pleistocene - Holocene incised-valley sequence
from the Mekong River Delta, Bentre Province,
Southern Vietnam: the BT2 core, Journal of
Asian Earth Sciences 20 (2001) 83.
[12] T.K.O. Ta, V.L. Nguyen. M. Tateishi, I.
Kobayashi, Y., Saito, T. Nakamura, Sediment
facies and Late Holoccne progradation of the
Mekong River Delta in Bentre Province,
Southern Vietnam: an example of evolution
from a tide-dominated to a tide-and wavedominate delta. Sedimentary Geology 152
(2002)313.
[13] Dao Manh Tien, 2004. Report "Study on
physical conditions and minerals o f nearshore
area (0 -30m water depth ) for sustainable
development of coastal zone in Soc Trang
Province” Archive in Marine Geology and
Mineral resources Centre.
[14] C.D. Woodroffe, Late Quaternary evolution of
coastal and lowland riverine plains of Southeast
Asia and nouthem Australia: an overview.
Sedimentary Geology 83 (1993) 163.
[15] Saito Y., S. Tanabe, Q.L. Vu, T.J.J. Hanebuth,
A. Kitamura. Q.T. Ngo (Eds.), 2004.
Stratigraphy and Hoiocene evolution o f the Song
Hong (Red River) delta, Vietnam. In
Stratigraphy of Quaternary system in deltas of
Vietnam, pp. 101-108. Dpt of Geology and
Minerals of VN. Hanoi.