VNUJournalofScience,EarthSciences23(2007)170‐176
170

CharacteristicsofQuaternarysedimentaryfacies
inrelationtowaterbearingcapacityofaquifers
andaquicludesintheRedRiverDelta,Vietnam
NguyenThanhLan*,TranNghi,DangMai,DinhXuanThanh
CollegeofScience,VNU
Received07March2007
Abstract.There are five Quaternary sedimentary sequences in the Red River Delta, Vietnam. The
formingofeachsequenceisrelated to transgressionandregressionphases.Thesequences, which
was formed in transgression period, composed mainly of fine grained size leading to the water
bearingcapacityisvery
lowandplaysaroleasaquicludes.Besides,inthesefinegrainsizelayers,
thecontentsofarsenicandironarehigh,especiallyindarkclay,siltyclayrichinorganic material
ofswampfaciesandbrown,darkbrown clay of flood facies sothattheyarestated  as a sourceof
arsenic contamination in the groundwater. For the sequences formed in regression period
composed mainly of gravel, cobbles, pebbles, and coarse sand of fluvial, river channel facies are
goodaquif e r s .Theseaquif e r s arethemainsupplysourcesforhumanactivitiesintheRedRiverDelta.
Keywords:Aquiclude;Aquifer;RedRiverDelta;Sedimentaryfacies.
1.Introduction
*

LikemanycitiesandprovincesofVietnam,
the provinces in the Red River Delta receive
watersupplyfromgroundwaterinQuaternary
sediments. The characteristics, potential and
variation trend of this water resource depends
much on the distribution of sedimentary facies
in the stratigraphic column. The depositional
environment and material composition

Pleistocene and corresponded with Le Chi
Formation. The sediments of this sequence are
composed mainly of cobbles, pebbles, and
coarsesandofriverchannelenvironmentinthe
lower part
 and medium sand, silt and clay of
floodplainintheupperpart.
‐ The second sequence that corresponds
with the second depositional cycle, formed in
Middle to Lowermost Late Pleistocene. This
sequence corresponds with Hanoi Formation
and consisting of cobbles, pebbles, gravel of
proluvialandmountainousriverbedfacies.
‐ The
third sequence corresponds with the
third depositional cycle and was formed in
Uppermost of Late Pleistocene. It corresponds
with Vinh Phuc Formation which contains
coarse to medium grained sand of plain river
bed facies and chan gin g up war ds into finer
sediments co nsisting mainly silty clay mixed
with fine sand of flood plain
 facies and clay of
lagoonalfacies.
‐ The fourth sequence was formed in
Lowermost of Late Pleistocene to Early‐
Middle Holocene, corresponding with the
fourth depositional cycle of Hai Hung
Formation,composedofgreenishgrayclayand
peatoflagoonandcoastalswampfacies.

90
100
110
120
130
140
Depth
(m)
BH59-64
605
BH-11
105
To Lich
River
Red River
BH2-HN
156
BH3-HN
180
BH4-HN
ta.amQ
tb
2
3
am lbQ hh
2
1-2
amQ vp
III
2

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tb
2
3
aQ
tb
2
3
amQ
vp
1
3a
a,am Q
vp
1
3a

Fig.1.QuaternarysedimentaryfacialcrosssectionintheRedRiverDelta[5].
NguyenThanhLan etal./VNUJournalofScience,EarthSciences 23(2007)170‐176
172
of the Quaternary sediments in the Red River
Delta,thereisaclearchangeofsedimentaryfacies
associations and corresponding with changing
in lithological composition and sedimentation
parameters such as: Md, Ro,  So, Me, 
permeabilityandpaleogeographicenvironments
in each period, which represent the water
bearing properties as well as
the quality of the
groundwater in the region. Therefore, the
important aquiferswithgoodqualit ycorrespon ds

0.02‐0.11mm,So=1.21‐2.85,pH
sediments
 =5.5‐8.2,
Eh
sediments
=‐5÷‐10mV.Inthislayer,thespecific
capacityofwellsisverylowandchangingfrom
2to3l/sm.
Especially, the groundwater regime is
affected directly by river and rain water
percolating through the overlying Thai Binh
Formation. The fluctuation amplitude of the
waterleveldecreases
withthedistancefromthe
river. Therefore, this aquifer is mainly
rechargedbytherain waterand surfacewater,
especially in some big rivers in the Red River
system. The groundwater is discharged mainly
through the evaporation process and
percolation to the Pleistocene aquifer. Water
qualityofthislayerisfresh,
softtoslightlyhard
withtotaldissolvedsolid(TDS)content<1mg/l
and bicarbonate calcium, bicarbonate sodium
calcium type. According to the results of
chemical analysis, the groundwater in the
Holocene aquifer has a
r
Na
/r

Formation which serve as an aquiclude and
aquitard. The particle size distribution is as
follows: cobbles, pebbles, gravel 2.5%, sand
56.7%,silt‐clay40.8%.Thesedimentindicators
areMd=0.25,So=3.2,pH
sediments
=6.7.However,
these layers are very thin and were formed as
small lenses due to erosion and sheet washing
during regression phases before the formation
of the overlying coarse sediments. The specific
capacityofboreholesdrilledintothisaquiferis
higher than that into the Holocene aquifer (in
the
sedimentlayerofVinhPhucFormation:2‐9
l/ms, Hanoi and Le Chi formations: 26‐51 l/ms).
Thegroundwaterinthisaquiferisfresh(TDS<
lg/l),ofbicarbonatecalcium,bicarbonatesodium
‐ calcium type, with
r
Na
/r
Cl
 ratio = 0.98‐5.6,
pH
water
=1.0‐8.1,TDS=0.1‐0.5g/landveryhigh
iron content (2‐25 mg/l). However, the iron
content in this aquifer is lower than that in the
Holoceneaquifer.

cont ent equals0.1‐0.05,TOC
is changing from 0.23 to 0.26µg/g in deltaic
sediments; and Fe
2+
/Fe
3+
 = 1.7, TOC = 0.54 in
NguyenThanhLan etal./VNUJournalofScience,EarthSciences 23(2007)170‐176
174
marinesediments.The
r
Na
/r
Cl
ra tio ofthislayer
is 0.66, pH
water
 = 1‐8 and the water hardness is
1.5‐1.6mg/l.
ThesedimentofHaiHungFormation,which
corresponds to Early‐Middle Holocene, is
composedmainlyofsiltyclayandfinesandmixed
clayofdeltaicfacies.Thislayerischaracterized
byoxidationenvironmentthatindicatedbylow
value
ofTOCandratioofFe
2+
/Fe
3+
.

of high
 storage and water bearing capacity.
These areʺhydrogeological windowsʺ (Fig. 8).
The hydrogeological windows are areas where
the groundwater in the Holocene aquifer is
interconnectedwiththePleistoceneaquifer.
3.4.Middle‐LowermostofLatePleistoceneaquiclude
TheupperpartoftheHanoiFormationwith
green gray to dark gray clay
and silt of lagoon
facies, lens of lacustrine clay formed during the
Middle‐LatePleistocene transgression is called
Middle‐Late Pleistocene aquiclude. However,
as it is eroded during the regression phase and
its dis tribution area is small  and is associated
with silty sand of tidal flat facies  and alluvial
cobbles,pebbles,
thisaquicludehassmallerextent
than the Pleistocene ~ Holocene aquiclude
above. Also for this reason, it is usually
neglectedandattributedtothelocalaquicludein
the Pleistocene aquifer.  The pa rticle size
distribution is: sand: 46%, silt‐clay: 60%. The
sedimentindicatorsare:Md=0.15mm,So=
4.5,
Eh
sediments
=50mV,pH
sediments
=7.5.Ther

> 1 and TOC
arehigh)andhavehighcontentoftotalarsenic.
Besides, the upper part of Holocene aquiclude
appeared brown and dark brown clay of flood
facies what are in high content of arsenic.
Arsenicabsorbedbyironhydroxidewhileiron
hydroxide absorbing by clay mineral.
Therefore, this layer
 was considered as a main
source of arsenic contamination in the
groundwater.
NguyenThanhLan etal./VNUJournalofScience,EarthSciences 23(2007)170‐176
175

Fig.6.Siltyclay,clayspottedweatheringofmarinesedimentinVP1borehole,
Hanoiarea(13‐13.74mdepth).CourtesyofESTNV‐2Project.

Fig.7.Clay,siltyclayrichinorganicmaterialofswampfacies
inVP2borehole,Hanoiarea(0.95‐1.0mdepth).CourtesyofESTNV‐2Project.

Fig.8.HydrogeologicalwindowbetweenPleistoceneaquiferandHoloceneaquiferin
HanoiareaaccordingtoNguyenVanDan[3].
Acknowledgements
This paper is completed within the
framework of Fundamental Research Program
funded by Vietnam Ministry of Science and
Technology. The pictures in this paper were
published by courtesy of ESTNV‐2 Project
(Environmental Science and Technology in
Top

[5] Tran Nghi,Relationshipbetweenthelithofacies
and ground water of Quaternary sediments in
the Red River Delta, Journal of Geology 226A
(1995)11(inVietnamese).