Báo cáo " Characteristics of Quaternary sedimentary facies in relation to water bearing capacity of aquifers and aquicludes in the Red River Delta, Vietnam " ppt

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

express
different paleogeographic environments such
as marine, continental environment or
transitionalenvironment.IntheRedRiverDelta
area, the facial association rule is examined in
_______
*
Correspondingauthor.Tel.:84‐4‐5587059.
E‐mail:
three spatial directions: vertical, perpendicular
andparallelwiththepresentcoastline.
2. Characteristics of Quaternary sedimentary
sequences
In Quaternary, the Red River Delta
experienced glaciation stages: Gunz, Mindel,
Riss,Wurm1,Wurm2,andcorrespondingwith
them transgression phases. These stages have
left behind 5 sedimentary sequences
corresponding with 5 sedimentary
 cycles in
Quaternary each began. The coarse grain size
sediments were formed in regressions phase
and fine grain size sediments were formed in
transgression phases. Accordingly, the
NguyenThanhLan etal./VNUJournalofScience,EarthSciences 23(2007)170‐176
171
Quaternary sediments in the Red River Delta
are identified by the following sedimentary
sequences:
‐ The first sequence was formed in Early

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.

‐ The fifth sequence was formed in
Late
Holocene and composed of sand, silt and clay
of deltaic facies, corresponding with the fifth
depositionalcycleofThaiBinhFormation.
In spatial distribution,the sediments of the
first and second sequences are rather
widespreadintheplain.Thethirdsequencehas
a continuous change of facies from sand, silt

and clay of alluvial facies to clayey silt mixed
with sand of deltaic facies and silty clay of
lagoonal facies in the central part passing into
siltyclayofflood plain, oxbow,coastalswamp
andpeatfaciesinthedirectionfromtheplainto
the modern coastline. The fourth sequence
consistsofswampclay,lagoonalclayandpeat.
Inthedirectiontowardsthecenteroftheplain,
eachofthesesequencesappearsmoreandmore
particular facies that forms a quite complete
faciesassociation.Thus,intheevolutionprocess
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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

with the coarse grained sediment layers of
alluvialandproluvialfacies(formedinthefirst
stage of each cycle), while the aquicludes are
fine sediments of deltaic, coastal swamp and
marinefacies(formedinthe
finalstageofeach
cycle). Based on this point of view, the
Quaternarysedim e ntsintheRedRiverDeltacan
be divided into the following hydrogeological
units: Holocene aquifer (Qh); Pleistocene
aquifer(Qp),Pleistocene‐Holoceneaquiclude,
Middle‐LatePleistoceneaquiclude.
3. Facial characteristics and water bearing
properties of the aquifers
and aquicludes in
theRedRiverDelta
3.1.Holoceneaquifer(Qh)
The Holocene aquifer is distributed at a
shallow depth where the water fluctuates in a
widerangefrom2‐4mupto36m, withthickness
increasing towards the center of plain. It is
composedofsand,silt,clay
ofalluvialfaciesof
Thai Binh Formation (Fig. 2) in the upper part
and lens of sand, silt, clay of Hai Hung
Formation in the lower part which are low
water bearing capacity layers. The particle size
distribution is: gravel 2%, sand 30‐85%, silt‐
clay15‐70%.Thesediment
indicatorsare:Md=

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

Cl
 ratio of 1.56, a
hardness of 2‐9, a pH of 7.5, a TDS content of
1.2‐11.7g/l,inparticularitsironcontentreaches
1.24to33.5mg/l.

Fig.2.Laminatedfinesandinterclatedwithsiltof
alluvialfaciesofHoloceneaquiferinVP2borehole,
Hanoiarea(6.9‐7.2mdepth).CourtesyofESTNV‐2
Project(EnvironmentalScienceandTechnologyin
NorthernVietnam)supportedbySDCand
implementedbyCETASDandEawag.
3.2.Pleistoceneaquifer(Qp)
ThePleistoceneaquiferiswidelydistributed
in the Red River Delta and is overlain by the
younger sedimentary layer which is the
Pleistocene‐Holoceneaquiclude.Thesediments
of this layer consist of 3 formations: Le Chi
Formation, Hanoi Formation, and Vinh Phuc
Formation (Fig. 3‐5). These
 sediments are
intercalatedbyfinesedimentsofclayeymudof
lagoon environment of Le Chi Formation, the
NguyenThanhLan etal./VNUJournalofScience,EarthSciences 23(2007)170‐176
173
tidalflatsiltysandandlagoonalclayandlenses
of lacustrine clay of Ha noi Formation, the
laterizedlagoonalclayofVinhPhucFormation,
the alternating greenish gray clay and peat
bearing swamp clayey mud of Hanoi

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.

3.3. Uppermost of Late Pleistocene‐Holocene
aquiclude
The Holocene and Pleistocene aquifers are
separatedbythePleistoceneHoloc ene
aquiclude.

Fig.3.LatePleistocenecoarsegrainedsand
ofriverchannelfaciesinVP2borehole,Hanoiarea
(28‐28.3mdepth)CourtesyofESTNV‐2Project.

Fig.4.LatePleistocenecoarsegrainedsand,gravelof
riverchannelfaciesinVP2borehole,Hanoiarea
(39.2‐41.2mdepth).CourtesyofESTNV‐2Project.

Fig5.EarlyPleistocenepebble,cobbleoffluvialfacies
inVP2borehole,Hanoiarea(55‐57mdepth).
CourtesyofESTNV‐2Project.
The Pleistocene‐Holocene aquiclude is
composed mainly of greenish gray fine clayey
sand of lago onal and coastal swamp facies of
HaiHungFormationintheuppersequenceand
thefinesedimentsofdeltaicandmarinefaciesof
VinhPhucFormationinthelowersequence.
The sedimentof Vinh Phuc Formation was

weathered (Fig. 6) that created reddish brown
toorange.Fe
2+
/Fe
3+

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+
.

Besides, silty clay and clay rich in organic
material of swamp facies that formed in early
Flandrian transgression (10.000 to 6.000 year
BP, Fig. 7) are in high values of TOC and
Fe
2+
/Fe
3+
, which indicated for reduction
environment.Moreover,contentoftotalarsenic
in sediment of this facies are very high (6‐33.0
mg/g)[1,2,4].
Regressionphase happened afterFlandrian
transgression that formed sandy silt clay and
siltyclayofdeltaicanddarkbrownclayofriver
flood facies. The sediments
 what took in dark
brownclayofriverfloodinPhapVanborehole
havecontentofarsenicreachto2‐12um/g.
The combination of them created as thick
sedimentary layer playing a role of  relatively
thick aquiclude that separating the overlying
Holocene aquifer above and the Pleistocene
aquiferbelow.
ThethicknessofthePleistocene‐
Holoceneaquiclude varies from 6 m to 11.5 m.
However,duetotheactionofoldriversystems,
insomeplacesthereisnotraceofthefinegrain
sediments, but there remain only the coarse
grainedsedimentsofriverbedfacies,whichare

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

Na
/r
Cl
ratio
of the groundwater equals 0.8, pHwater= 7.5.
The iron content in the water is relatively high
(>10mg/l).
4.Resultsanddiscussion
The relationship between sedimentary
facies and aquifers, aquicludes is very strong.
The primary and secondary sedimentary
sequences are composed mainly of coarse‐
grained sand, cobbles and
pebbles of
mountainous river facies in the lowerpart that
is a good potential and quality layer. Besides,
the upper part of each layer was covered
mainlybysiltyclay;clayishsiltmixedfinesand
of flood and deltaic facies is a bad aquiclude.
The Pleistocene‐Holocene aquiclude, which
contained mainly
 of fine grained size such as
clay, silt, silty clay, clayey silt and rich in
organic material is good regional aquiclude.
These sediments are mainly formed in
reduction environment (Fe
2+
/Fe
3+


> 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

Botto
m
Top
Bottom
NguyenThanhLan etal./VNUJournalofScience,EarthSciences 23(2007)170‐176
176
Northern Vietnam) implemented by CETASD
andEawagunderfinancialsupportofSDC.

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