Initiation of the Mekong River delta at 8 ka: evidence from the sedimentary succession in the Cambodian lowland

Tamura, Takeshi; Saito, Yoshiki; Sieng, Sotham; Ben, Bunnarin; Kong, Meng; Sim, Im; Choup, Sokuntheara; Akiba, Fumio

doi:10.1016/j.quascirev.2008.10.010

Cited by 187 publications

(144 citation statements)

References 38 publications

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“…Sediment age 0.5 m above the peat decreases to 3.8 ka (Table 2), indicating a relatively low sediment accumulation rate of 0.3 m ka -1 (see Electronic Annex) -within the range of 0.3 -0.7 m ka -1 measured for a comparable floodplain facies unit near our field site (Tamura et al, 2009). As the profile transitions from gray floodplain sediments to the overlying brown natural levee sediments, the measured sediment accumulation rate generally increases to 1 m k a -1 .…”

Section: Micro X-ray Fluorescence ( Xrf) Mapping and Xanes Spectroscopymentioning

confidence: 58%

“…The peat at 6 m depth in our site, aged 5.675 ± 0.020 ka, which directly underlies gray sediments representative of a flood plain depositional environment, likely corresponds to the "organic mud" of similar depth in sediment cores collected proximal to our field site (Tamura et al, 2009). Thus, the peat developed in a saline environment that likely continued even as the coastline receded southeast to present-day Vietnam, as saltwater intrusion may have occurred up to tens of kilometers along the Mekong during high tide in the dry season -the extent of present-day seawater intrusion (Hori, 2000;Tamura et al, 2007).…”

Section: Authigenic Arsenian Pyrite Formationmentioning

confidence: 66%

“…A ~ 6.3 to 6.5 ka mangrove peat layer over 5 m thick extends through a large portion of Mekong River lowland, from Phnom Penh to the Vietnam border (Tamura et al, 2009). Similarly, mangrove peat of 6.0 to 6.5 ka is found in the innermost part of the Mekong Delta in Vietnam (Nguyen et al, 2005).…”

Section: Discussionmentioning

confidence: 96%

“…Our site transitioned from a salt marsh to mangrove forest containing brackish water between 8.5 to 6.3 cal ka BP owing to sea level rise accompanying sediment aggradation and delta progradation, producing peat layers throughout the surrounding upper Mekong Delta (Nguyen et al, 2005;Tamura et al, 2009). The peat at 6 m depth in our site, aged 5.675 ± 0.020 ka, which directly underlies gray sediments representative of a flood plain depositional environment, likely corresponds to the "organic mud" of similar depth in sediment cores collected proximal to our field site (Tamura et al, 2009).…”

Section: Authigenic Arsenian Pyrite Formationmentioning

confidence: 99%

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Peat formation concentrates arsenic within sediment deposits of the Mekong Delta

Stuckey

Schaefer

Kocar

et al. 2015

Geochimica et Cosmochimica Acta

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This is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found online at Geochimica et Cosmochimica Acta, published by Elsevier. Copyright restrictions may apply. doi: 10.1016/j.gca.2014.10.021 Mekong River Delta sediment bears arsenic that is released to groundwater under anaerobic conditions over the past several thousand years. The oxidation state, speciation, and distribution of arsenic and the associated iron bearing phases are crucial determinants of As reactivity in sediments. Peat from buried mangrove swamps in particular may be an important host, source, or sink of arsenic in the Mekong Delta. The total concentration, speciation, and reactivity of arsenic and iron were examined in sediments in a Mekong Delta wetland by X-ray fluorescence spectrometry (XRF), X-ray absorption spectroscopy (XA S), and selective chemical extractions. Total solid-phase arsenic concentrations in a peat layer at a depth of 6 m below ground increased 10-fold relative to the overlying sediment. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that arsenic in the peat was predominantly in the form of arsenian pyrite. Arsenic speciation in the peat was examined further at the micron-scale using XRF and X-ray absorption near-edge structure (XANES) spectroscopy coupled with principal component analysis. The multiple energy XRF mapping and XANES routine was repeated for both iron and sulfur phase analyses. Our XRF/ XANES analyses confirm arsenic association with pyrite -a less reactive host phase than iron (hydr)oxides under anaerobic conditions. The arsenian pyrite likely formed upon deposition/formation of the peat in a past estuarine environment (~ 5.5 ka BP), a process that is not expected under current geochemical conditions. Presently, arsenian pyrite is neither a source nor a sink for aqueous arsenic in our sediment profile, and under present geochemical conditions represents a stable host of As under the reducing aquifer conditions of the Mekong Delta. AbstractThis is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found online at Geochimica et Cosmochimica Acta, published by Elsevier.

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Section: Micro X-ray Fluorescence ( Xrf) Mapping and Xanes Spectroscopymentioning

confidence: 58%

Section: Authigenic Arsenian Pyrite Formationmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 96%

Section: Authigenic Arsenian Pyrite Formationmentioning

confidence: 99%

See 2 more Smart Citations

Peat formation concentrates arsenic within sediment deposits of the Mekong Delta

Stuckey

Schaefer

Kocar

et al. 2015

Geochimica et Cosmochimica Acta

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“…When the Mekong River reaches northern Cambodia, alluvial channel deposits with exposures of Triassic sedimentary rocks and Neogene basalts become the primary riverbed material. The river ultimately runs into the Mekong River Delta (MRD), which is composed of Holocene alluvial sediments and has experienced a rapid progradation since 8000 yr BP (Tamura et al, 2009;Xue et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Changes in hydrology and sediment delivery of the Mekong River in the last 50 years: connection to damming, monsoon, and ENSO

Xue

Liu

2011

Earth Surf Processes Landf

147

111

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As the population and economy boom, more and more dams are being built in the Mekong River basin. Previous studies have revealed that Manwan Dam had little infl uence on the runoff-SSC (suspended sediment concentration) relationship, and the sediment load was relatively stable over the past 40 years. However, little is known at present on the relationship among monsoons, El Niño Southern Oscillation (ENSO), precipitation, runoff, and the impact of dams on the delta dynamics. A comprehensive hydropower GIS database covering the entire Mekong basin is presented in this study. Mann-Kendall trend analysis showed no signifi cant change in precipitation and runoff over the past 50 years. Spectral analysis showed that the runoffs of the middle to lower reach of Mekong River are correlated with the Indian Monsoon, where as the East Asian Monsoon's infl uence is mainly on the lower reach. With another 200 new dams to be added to the basin in the next couple of decades, changes are expected in both hydrological regime and delta dynamics. On one hand, the runoff showed a closer connection with the regional precipitation and ENSO in the post-dam period (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) than in the pre-dam period . Such a relationship is expected to be even closer when more dams are completed. On the other hand, both daily maximum and minimum water levels on the delta plain have shown an abrupt drop since the end of 1994. This reduced water-level gradient between the river and sea inevitably weakens the sediment discharge to the coast, which might intensify the ongoing coastal erosion on the eastern part of the delta plain.

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Evidence for sea level and monsoonally driven variations in terrigenous input to the northern East China Sea during the last 24.3 ka

Chang

Xiong

et al. 2015

Paleoceanography

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Geochemical and sedimentological analyses of core PC-1 recovered from the northern East China Sea (ECS) provide insights into variations in terrigenous input associated with sea level and climate changes over the past 24.3 ka. Based on high-resolution multiproxy records, our results suggest that the competing processes of sea level and monsoonally driven precipitation determined terrigenous input to the northern ECS. Dominance of terrigenous material, along with relatively light Globigerinoides ruber δ 18 O, indicates that the Last Glacial Maximum (LGM) lowstand of sea level has occurred during the period 21.5-19.6 ka, not suggesting an early slow rise but supporting the conventional LGM age of 21 ka. This LGM lowstand was terminated by the rapid sea level rise of 19 ka meltwater pulse (MWP), which is well expressed by the nearly synchronous decreases in both terrigenous detritus and mean grain size from 19.6 to 18.9 ka. MWP-1A is clearly marked in our records by a sharp reduction in terrigenous input and pronounced maxima of G. ruber δ 18 O at 15.3-14.8 ka, given the considerable age uncertainties of deglacial marine radiocarbon samples. A slightly increasing input of terrigenous matter is noted after 13.4 ka, potentially pointing to a sea level fall following the Inter-Allerød Cooling Period, which was seldom reported previously. Although MWP-1B did not leave robust signatures in terrigenous input, it is explicitly captured by the heavy δ 18 O of G. ruber and decline in mean grain size at 11.5-10.9 ka. MWP-1c probably occurred in a broad millennial interval with multiple peaks, which are robustly marked by the abrupt variations in terrigenous input and marine organic matter at 9.7-9.3 and 9.1 ka, respectively. During the late Holocene, the effect of continuously weakening monsoon precipitation overwhelmed that of stable sea level resulting in a uniform increase in the proportion of marine-derived organic matter after 5.5 ka.

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Initiation of the Mekong River delta at 8 ka: evidence from the sedimentary succession in the Cambodian lowland

Cited by 187 publications

References 38 publications

Peat formation concentrates arsenic within sediment deposits of the Mekong Delta

Peat formation concentrates arsenic within sediment deposits of the Mekong Delta

Changes in hydrology and sediment delivery of the Mekong River in the last 50 years: connection to damming, monsoon, and ENSO

Evidence for sea level and monsoonally driven variations in terrigenous input to the northern East China Sea during the last 24.3 ka

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