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島根大学地球資源環境学研究報告 30, 31～45 ページ（2011年 12月）Geoscience Rept. Shimane Univ., 30, p.31～45（2011）
Major and trace element compositions of Tertiary sedimentary successions in the NW and SE Bengal basin, Bangladesh
Dhiman Kumer Roy＊ and Barry P. Roser＊
AbstractThe Bengal basin in Bangladesh occupies the vast peripheral Himalayan foreland basin, and is divided into three
geological provinces: 1) NW shelf (NWS); 2) the Northeastern foredeep (Surma basin); and 3) the southeastern Chittagong-Tripura Folded Belt (CTFB). These geological provinces contain sediments derived from the Himalaya and Proto-Himalaya that record the exhumation history of the Himalayan orogen. This study reports whole-rock major and trace element analyses of Paleogene and Neogene sediments from the NWS (n = 66) and Neogene sediments from the CTFB (n = 219). Both the NWS and the CTFB sample suites show marked compositional contrasts between sandstones and mudrocks, and systematic stratigraphic changes in composition. These geochemical variations are the end product of processes which include hydrodynamic sorting, weathering, diagenesis, and heavy mineral concentration, coupled with contrasting depositional environments related to Himalayan tectonics and climate change. The role of these fac-tors in determining the geochemical variations will be evaluated further in future work, along with comparison with published data for geological province 2 (Surma basin), to explore the links between provenance, tectonism, and climate in the Himalaya-Bengal Basin depositional system.
Key words: Geochemistry, sandstone, mudstone, Bengal Basin, Bangladesh
Introduction
Geological processes and the erosion and deposition of sediments from nearby sources or orogens play an important role in crustal evolution. Erosion of Himalayan sediments and their deposition in the peripheral foreland basin has contributed significantly to changes in global geodynamics, climate and ocean geochemistry, as estab-lished in the literature (Raymo and Ruddiman, 1992; Richter et al. 1992). The geochemical compositions of sediments respond to various tectonic, sedimentological, and climatic processes. Retention of the fingerprints of such processes is the basis of geochemical studies of sediments used to infer past geological environments. Geochemical compositions of sediments and their variations can be used to link provenance (Roser and Korsch, 1988; McLennan et al. 1993), tectonic setting (Roser and Korsch, 1986), climate (Nesbitt and Young, 1982), and other earth surface processes operating at geological time scales. However, it remains a challenge to differentiate tectonically- and climatically-driven sedimentation, and the influence of these two primary factors on sedimentary environments and depositional patterns.
The Bengal basin fill is a record of Himalayan-derived sediments that can be used to infer the interaction of tectonism and climate. The Bengal basin began to receive sediments during the Oligocene period (38 Ma) (Najman et al. 2008). The Bengal basin encompasses the northeastern
part of the Indian subcontinent, and is located between the Indian Shield and the Indo-Burman Ranges (Fig. 1). It is divided into three geological provinces: i) Province 1, or the Northwest shelf (NWS); ii) Province 2, or the Northeastern foredeep (Surma basin); and iii) Province 3, the Chittagong Tripura Folded Belt (CTFB); each province varies in their facies and potential provenance (Reimann, 1993; Alam et al. 2003; Najman, 2006). The Bengal basin thus occupies a vast region, and receives a large volume of sediments that may hold the key to resolving many basic problems, such as the geochemical variation of sediments in relation to Himalayan uplift and climate change. Understanding the effects of these processes helps in developing models of tectonic-climatic evolution in the regional context. The geochemical composition of sediments can also help iden-tify past depositional environments.
Early work on the geochemical composition of sediments in the Bengal basin by Rahman and Faupl (2003) dealt with Neogene Surma Group sediments of the Surma basin (Province 2). Rahman and Suzuki (2007a, b) also inferred the provenance and tectonic setting of the Surma Group depositional basin. The Paleogene succession of the Bengal basin was studied by Najman et al. (2008) to identify the provenance of the sediments. They found that significant contribution of sediments from the Himalaya began at 38 Ma, some 17 Ma earlier than previously thought. Strati-graphic and lithologic limitations of earlier work in the Surma basin (Rahman and Faupl 2003; Rahman and Suzuki (2007a, b) were addressed by Hossain et al. (2010), who examined the geochemical compositions of both Paleogene and Neogene sandstones and mudrocks from the Surma
Article
＊ Department of Geoscience, Shimane University, 1060 Nishikawatsu,
Matsue 690-8504, Japan
31
succession (Province 2) to identify geochemical variations in the sediments in relation to provenance and weather-ing. However, Najman (2006) noted that amalgamation of datasets from more than one geological province for provenance studies could obscure regional details. To date, no geochemical studies have been carried out in Province 1 (NWS) or 3 (CTFB). Therefore, it is essential to study the geochemical composition of the sediments from each province individually.
In this paper, we present a geochemical database of sandstones and mudstones from the Paleogene and Neogene succession of Province 1 (NWS) and the Neogene succes-sion of Province 3 (CTFB). This new geochemical data and previously published data from Province 2 (Hossain et al. 2010) will contribute to better understanding of the regional context of proto-Himalayan and Himalaya-derived sedimentation in the Bengal basin. This geochemical dataset will be interpreted and discussed in depth in future work to examine climatically and tectonically-induced sedimentation in relation to drifting of the Indian plate, and Himalayan uplift and climate change.
Geology of the Bengal Basin
Tectonic evolutionThe tectonic evolution of the Bengal basin is related to
the continent-continent collision of the Indian and Eurasian (Tibetan) plates, development of the Himalaya, and oblique subduction of oceanic crust beneath the Burmese plate, with associated development of an accretionary wedge (Alam et al. 2003; Mukherjee et al. 2009). India was part of Gondwana before collision of the Indian and Eurasian plates. The Gondwana supercontinent began to break up at ~126 Ma, and India started to move northward from the South Pole (Lindsay et al. 1991). The Bengal basin started to form during that time, with rifting of the Indian plate from Antarctica and Australia. However, collision of the Indian and Asian plates took place during Eocene time (55 Ma) (Molnar and Tapponier, 1975). Recent work by Aitchison et al. (2007) noted that soft collision started at the Eocene-Oligocene boundary (34 Ma ago). The Tethys Sea disappeared due to the collision between the Indian and Asian plates, and subsequent formation of the Himalaya fed sediments into the Bengal basin via gigantic river systems.Stratigraphy
The stratigraphic successions of the NWS and CTFB are summarized in Table 1 (a, b). The depositional patterns and sedimentation within them are controlled by rise and fall of sea level, and uplift and subsidence of the source region and depositional basin, respectively (Alam et al. 2003).
In the NWS the lowermost Jaintia Group (Paleocene-Late Eocene) is represented by the Tura Sandstone, Sylhet Limestone, and Kopili Shale, in ascending order. The Tura Sandstone Formation (Paleogene-E. Eocene) consists of poorly sorted sandstone, siltstone, mudstone, fossiliferous
marl, and thin coal seams (Reimann, 1993; Uddin and Lundberg, 1999; Alam et al. 2003). The overlying Sylhet Limestone Formation (E.-M. Eocene) is composed of massive and compact limestone containing abundant fora-minifera (Alam et al. 2003), and the Kopili Shale consists of thinly-bedded sandstone and shale (Uddin and Lundberg, 1999; Alam et al. 2003). The Barail Group of late Eocene to early Miocene age overlies the Jaintia Group, and is composed of interbedded sandstones and mudstones with high sand/mud ratio that were deposited in distal deltaic to marine environments (Alam et al. 2003; Najman et al. 2008). The Barail Group is succeeded by the Neogene Surma Group, which consists of sandstones, siltstones and mudstones deposited in a large deltaic system (Alam et al. 2003), followed by fluvial sandstones and mudstones of the Dupitila Group (Table 1).
The CTFB succession is all of Neogene age (Table 1b). The basal Surma Group is divided into the Bhuban and Bok-abil Formations, in ascending order. Both consist of deltaic sandstones and mudrocks. In the CTFB the Surma Group is succeeded by the Tipam Group, which is subdivided into the Tipam Sandstone Formation and the overlying Girujan Clay Formation. The Tipam Group sediments consist of coarse grained sandstones, siltstones and mudstones that represent bedload-dominated braided fluvial and fluvial overbank deposits (Reimann, 1993; Alam et al. 2003). Tipam Group sediment are absent from the NWS, but also occur in Prov-ince 2. In the CTFB the Tipam Group is succeeded by the Dupitila Group, which consists of sandstones, siltstones, and mudstones that were laid down by a meandering river system (Johnson and Alam, 1991).
Sampling and Sample Preparation
Sample sitesThis study presents whole-rock X-ray fluorescence (XRF)
analyses of Paleogene and Neogene sandstones and mudrocks from Province 1 (NW shelf; n = 66) and Neogene sandstones and mudrocks from Province 3 (CTFB; n = 219). The samples were collected from both deep and shallow exploration bore-holes, and also from outcrop (see Tables 2 and 3, respectively). The number of samples collected for each formation or group was determined by availability from drill core.
Samples from the NWS represent the Jaintia (n = 14), Barail (n = 6), Surma (n = 22) and Dupitila Groups (n = 24), in ascending order (Table 2). All samples were taken from drillcore. The Jaintia Group samples consist of 11 sandstones from the Tura Sandstone Formation, and three mudstones from the Kopili Shale; all of which were taken from the Bogra-2 well. Barail Group is represented by only six samples (one sandstone, five mudrocks), all of which were from the Singra-1 well. Surma Group samples (two sandstones, seven siltstones, 13 mudstones) were collected from the Bogra-2 and Singra-1 wells, whereas Dupitila Group samples (five sandstones, 13 siltstones, six mud-
Dhiman Kumer Roy and Barry P. Roser32
stones) were drawn from several wells (see Table 2).The CTFB suite is much larger (n = 219), but spans only
the Surma (n = 155), Tipam (n = 42) and Dupitila Groups (n = 22). The Surma samples are divided almost equally between the Bhuban (n = 80; 20 sandstones, 60 mudrocks) and the Bokabil Formations (n = 75; 14 sandstones, 64 mudrocks), collected from both drillcore and outcrop (Table 3, Fig. 1). Tipam Group samples represent the lower-most Tipam Sandstone Formation (n = 32; 16 sandstones, 16 mudrocks) and the Girujan Clay Formation (10 mudstones). Of these, five were taken from the Shahbajpur-1 well, and the remainder from outcrop (Fig. 1). The Dupitila Group samples (seven sandstones, 15 mudstones) were all col-lected from outcrop (Fig. 1).
Analytical proceduresClean drill core and outcrop samples were chipped to
< 1 cm using a manual splitter to remove any veins or thin weathering rinds. The chips were then repeatedly rinsed and soaked in deionized distilled water to remove dust and then dried in an oven at 110°C for 24 h. The dried chips were then crushed in a tungsten carbide ring mill, with mills time generally of 30-45 seconds, following the methodology of
Roser et al. (1998). Subsamples (10 g) of the pulps were placed in glass vials and returned to the oven at 110°C for > 24 h. Total loss on ignition (LOI) was subsequently deter-mined gravimetrically by ignition for at least 2 h at 1020°C. The ignited samples from the LOI determination were hand-ground in an agate pestle and mortar, and returned to a 110 °C oven before preparation of glass fusion beads for the XRF analysis.
The XRF analysis was performed at Shimane University, using a Rigaku RIX 2000 spectrometer equipped with a Rh-anode X-ray tube. Major element and 14 trace element (Ba, Ce, Cr, Ga, Nb, Ni, Pb, Rb, Sc, Sr, Th, V, Y, Zr) abun-dances were determined from glass fusion beads prepared with an alkali flux (80% lithium tetraborate (Li2B4O7) and 20% lithium metaborate (LiBO2)), in a flux to sample ratio of 2:1 (Kimura and Yamada, 1996). Calibration and correc-tion for spectral interferences followed the methodology of Kimura and Yamada (1996). Internal correction for intra-run drift was made using secondary calibration against ten Geological Survey of Japan standard rocks spanning the compositional range from gabbro (JGb-1) through to granite (JG-2).
Deposi'onal environment
Neogene Dupi*la Dupi*la Sandstones, mudstones Fluvial
Neogene Surma Surma Sandstones, mudstones Deltaic
L. Eocene-‐E. Miocene Barail Barail Sandstones, minor mudstones Deltaic
L. Eocene Kopili Shale Shales, minor limestone Shallow marine
E. to M. Eocene Sylhet Limestone Limestone Shallow marine
Paleocene-‐E. Eocene Tura Sandstone Quartz arenites Shallow marine
Deposi'onal environment
Neogene Dupi*la Dupi*la Sandstones, mudstones Meandering
Neogene Girujan Clay Mudstones Overbank
Neogene Tipam Sandstone Sandstones, mudstones Braided
Neogene Bokabil Sandstones, mudstones Deltaic
Neogene Bhuban Sandstones, mudstones DeltaicSurma
LithologyForma'onGroup
(A) NW shelf (Province 1)
Jain*a
(B) CTFB (Province 3)
Age
Age Group Forma'on Lithology
Tipam
Table 1. Stratigraphy, facies and depositional environments of (a) NW shelf (NWS; Province 1) and (b) CTFB (Province 3) of the Bengal basin in Bangladesh (modified from Reimann, 1993; Alam et al. 2003; Najman et al. 2008). Data are presented for the shaded formations.
Major and trace element compositions of Tertiary sedimentary successions in the NW and SE Bengal basin, Bangladesh 33
Beach and dune sandAlluvial silt and clayValley alluvium and colluvium
} Thrust and fault
Lake
Dihing and Dupitila Formation (undifferentiated)
Dihing Formation
Dupitila Formation Tipam Group
Surma Group
LEGEND
revirR anhga
M
reviR segnaG
reviR anu
maJ
BAY OF BENGAL
West Bengal(INDIA)
Meghalaya (INDIA)
Assam(INIDA)
Tripura(INDIA)
Mizoram (INDIA)
RAJSHAHI
KHULNA
SYLHET
DHAKA
Main city Main riverCountry border
LEGEND
40 0 40 80 km
CHITTAGONG
BARISAL
1
2
3
92
22
24
26
88 90 92
9088
45
67
22
24
26
°
°
° ° °
°
°
°
°°°
°
D 61-70, 92-101
D 1-10, 23-24,34-40, 71-76,102-110
D 11-14, 25-26, 41-44, 77-83, 111-114
Geological map of the CTFB
D 15-22, 27-33,
45-60, 84-91
Fig 1. Map showing the location of drill hole and areas sampled in the NW shelf and CTFB, Bengal basin, Bangladesh. Drill hole No. (1) AS-13, 14, 27, 28, DOB-1, SOB-11/4, MS-13, 14, 15, 17, 19 (2) Bogra-2 (3) Singra-1 (4) Begumganj-2 (5) Feni-1 (6) Sitakund-5 and (7) Shahbajpur-1 (modified after Alam et al. 1990).
Dhiman Kumer Roy and Barry P. Roser34
Results and Discussion
Major and trace elements analyses (anhydrous normal-ized basis) of the NWS and CTFB samples are listed in Tables 2 and 3, respectively. The normalizing factors used to adjust the major element data to 100% were also applied to the trace element data. The tabulated data can be cor-rected to a hydrous basis if desired, using the original “as analyzed” total (anhydrous), and the LOI values determined from the original hydrous powders.
NW shelf (NWS, Province 1)Major elements
Major element abundances show significant variation within the NWS succession. Hydrodynamic separation of quartz and clay minerals during deposition strongly influ-ences SiO2 and Al2O3 contents, and hence largely controls the bulk composition of individual samples. Mean SiO2
contents in sandstones are high in all formations, with an extreme average value of 97.16 wt% and very narrow range (96.03-97.96 wt%) in the Tura Sandstone Formation of the Jaintia Group, and 87.05 wt% for the single sandstone ana-lyzed from the Barail Group. Average SiO2 content in the two Surma Group sandstones analyzed is 83.73 wt%, rising to 89.64 wt% (86.34-92.60 wt%) for the Dupitila Group sandstones.
Average SiO2 contents in the mudrocks show much wider variation. An average value of 61.40 wt% in the three Kopili Shale (Jaintia Group) samples analyzed is typical of shales, but disguises very low content (35.44 wt%) in one sample (DK-3) caused by abnormal Fe2O3 (35.01 wt%), and high SiO2 (89.28 wt%) in another (DK-5; Table 2). Average SiO2 content in the Barail mudrocks is also uniformly very high (90.28 wt%; range 83.40-94.61), well above the values typical of this lithotype (<~70 wt%). Average values fall to more normal values in the Surma (75.16 wt%) and Dupitila Groups (77.46 wt%). In these two groups the higher aver-ages in the mudrocks are caused by significantly higher SiO2 contents in siltstones versus mudstones. This is especially marked in the Dupitila samples, where SiO2 contents in silt-stones range from 80.40 to 88.31 wt%, slightly overlapping the range in sandstones (86.34-92.4 wt%), but well above that of companion mudstones (60.66-67.08 wt%), a range more typical of fine-grained sediments. These features indicate the NWS siltstones contain appreciable quantities of fine-grained quartz, and attest to the maturity and well-sorted nature of the NWS sediments in general.
As expected from hydrodynamic sorting, Al2O3 is the next most abundant major element in all formations. Aver-age content in the Tura sandstones is only 1.29 wt%, rising to 6.47 wt% in the single Barail sandstone, 8.33 wt% in the Surma Group, before falling to 6.57 wt% in the Dupitila sandstones. Mudrock averages show the opposite pattern, falling from 12.30 wt% in the Kopili Shale to 5.18 wt% in the Barail Group, returning to higher values more typical of
fine-grained sediments of 13.88 wt% in the Surma Group, and falling slightly to 11.62 wt% in the Dupitila Group.
Due to the covariations of SiO2 and Al2O3, Surma Group sediments thus tend to have higher contents of TiO2, Fe2O3, MnO, MgO, Na2O and P2O5 than underlying Barail and overlying Dupitila equivalents. Tura Sandstone exhibits remarkably low Na2O and K2O contents, with Na2O below theoretical lower limit of detection (0.10 wt%) in all except one sample, and maximum K2O of only 0.11 wt%. CaO con-tents are also very low in all Tura sandstones, with all < 1 wt% (Table 3), and in most mudrocks. Average CaO in the Kopili Shale (4.06 wt%) is biased by one high value (11.67 wt% in DK-3), and falls to 0.09 wt% in Barail mudrocks and 0.43 wt% in the Surma Group, before rising to 2.40 wt% in the Dupitila Group. However, Dupitila siltstones have much lower CaO contents (range 0.04-0.92 wt%) than their com-panion mudstones (5.97-7.87 wt%). The high abundances in these mudstones are also accompanied by relatively high LOI values (9.27-10.15 wt%), indicative of presence of authigenic CaCO3. In general, LOI values are low (< 5 wt%) in most of the NWS samples. However, higher LOI values (5-15 wt%) are seen in the Kopili Shale (11.51-14.07 wt%) and in many Surma mudrocks, where they appear to be associated with high Fe2O3 or Al2O3 contents, rather than CaO. This implies influence in these samples of other diagenetic phases, such as Fe oxy-hydroxides, siderite, or hydrous clays.
Overall the major element data for the NWS samples thus show marked fractionation between sandstones, siltstones, and mudstones; very high maturity, as indicated by high SiO2 contents; severe depletion in mobile elements such as Na2O, K2O, and CaO; and irregularities in the distribution of fluid-mobile elements. These features indicate their bulk chemistry has been strongly influenced by factors other than source composition, including sorting, weathering, and diagenesis.
Trace elementsThe effects of hydrodynamic sorting are seen clearly in
the NWS trace element data, with average abundances in the mudstones in each group almost always greater than in companion mudstones. This is true for all trace elements analyzed in the Dupitila and Jaintia Groups, with concen-trations in the mudrocks generally more than double those in the sandstones. In the Surma Group samples average contents in the mudrocks are higher for all except Ba, which is marginally higher (average 289 ppm) in the average of the two sandstones analyzed than in the 233 ppm mean from 20 mudrocks. The single sandstone analyzed in the Barail Group has higher Ba, Ga, Pb, Rb and Sr than the mudstone average (n = 6), but this contrast may not be significant.
The effects of quartz dilution are clearly seen in the Tura Sandstone samples, which are characterized by lower trace element abundances than all other sandstones. In the Tura sandstones average contents of all elements except Ba (80
Major and trace element compositions of Tertiary sedimentary successions in the NW and SE Bengal basin, Bangladesh 35
Tabl
e 2.
Who
le ro
ck m
ajor
(wt %
) and
trac
e el
emen
t (pp
m) a
naly
ses o
f san
dsto
nes a
nd m
udro
cks f
rom
the
NW
She
lf (P
rovi
nce
1), B
angl
ades
h.In
dex:
SaN
R –
sam
ple
num
ber;
Lith
– li
thol
ogy;
tota
l iro
n as
Fe 2
O3;
LOI–
Los
s on
igni
tion.
Not
e th
at d
ata
are
tabu
late
d on
an
anhy
drou
s nor
mal
ized
bas
is. T
he n
orm
aliz
ing
fact
ors
wer
e ap
plie
d to
bot
h th
e m
ajor
and
trac
e el
emen
t dat
a. O
rigin
al a
nhyd
rous
ana
lysi
s tot
al (T
otal
*) a
nd L
OI d
ata
are
incl
uded
to a
llow
reca
lcul
atio
n to
a h
ydro
us b
asis
if d
esire
d.Li
thol
ogy
code
s: c
sst -
coa
rse
sand
ston
e; m
sst -
med
ium
sand
ston
e; f
sst -
fine
sand
ston
e; z
st -s
iltst
one;
mst
- m
udst
one.
SaN
rD
epth
(m)
Wel
lLi
thSi
O2
TiO
2A
l 2O3
Fe2O
3M
nOM
gOC
aON
a 2O
K2O
P 2O
5B
aC
eC
rG
aN
bN
iPb
Rb
ScSr
ThV
YZr
LOI
Tota
l*D
upiti
la G
roup
Dup
itila
For
mat
ion
DD
-01
901
Sing
ra-1
mst
66.3
90.
7013
.30
5.02
0.09
3.37
6.27
1.40
3.32
0.14
503
8562
1716
2823
154
12.1
126
20.0
8931
297
9.39
99.3
9D
D-0
290
1.5
Sing
ra-1
mst
60.6
60.
7316
.35
6.76
0.11
3.72
5.97
1.24
4.32
0.14
668
8289
2217
3532
193
14.1
136
20.7
115
3320
010
.15
99.4
4D
D-0
490
2.5
Sing
ra-1
mst
66.6
70.
7113
.06
5.11
0.09
3.33
6.25
1.35
3.30
0.14
534
9364
1616
2926
151
12.8
128
20.8
8833
337
9.27
99.2
4D
D-0
590
3Si
ngra
-1m
st63
.91
0.71
14.3
86.
080.
113.
526.
281.
233.
640.
1458
886
7818
1733
2616
814
.213
320
.610
433
257
9.84
99.4
3D
D-0
690
3.5
Sing
ra-1
mst
63.5
90.
7215
.04
5.46
0.08
3.61
6.26
1.24
3.86
0.13
589
8373
2017
3226
177
14.1
130
19.6
100
3123
810
.02
99.4
9D
D-0
716
AS-3
zst
80.4
00.
3210
.98
2.50
0.04
0.91
0.86
1.60
2.32
0.06
363
5427
129
1123
131
6.7
8813
.537
2415
11.
3499
.77
DD
-08
24AS
-5zs
t82
.87
0.26
9.79
1.98
0.04
0.71
0.92
1.52
1.87
0.04
330
4529
126
1019
934.
111
410
.333
1613
01.
3010
0.40
DD
-09
64AS
-14
zst
80.8
00.
3611
.13
2.99
0.02
0.71
0.56
0.97
2.43
0.03
409
4838
139
1821
120
5.1
909.
744
1413
83.
2110
0.22
DD
-10
118
AS-2
7zs
t84
.64
0.57
13.5
40.
480.
010.
210.
140.
180.
220.
0344
753
102
1522
58
1711
.728
12.5
7323
287
5.04
99.6
0D
D-1
112
7AS
-28
zst
88.3
10.
3411
.04
0.05
0.01
0.15
0.04
0.01
0.03
0.01
449
8157
1218
026
109.
110
6.7
4514
185
3.94
99.9
1D
D-1
214
-16
DO
B-1
f sst
88.3
70.
157.
181.
210.
010.
360.
180.
462.
040.
0333
441
138
44
2210
73.
242
7.8
1611
117
1.18
100.
54D
D-1
332
-34
DO
B-1
m s
st86
.34
0.19
8.03
1.43
0.02
0.41
0.65
1.07
1.83
0.03
304
4226
95
718
872.
097
8.8
2215
981.
1810
0.25
DD
-14
62-6
4D
OB-
1m
sst
89.8
40.
176.
251.
090.
010.
320.
270.
621.
420.
0221
133
147
57
1575
2.4
499.
314
1398
1.09
101.
18D
D-1
596
-98
DO
B-1
m s
st91
.27
0.12
5.27
0.90
0.01
0.27
0.20
0.34
1.62
0.02
241
2811
64
315
812.
045
5.2
28
860.
9099
.69
DD
-16
126-
128
DO
B-1
m s
st92
.40
0.28
6.11
0.79
0.01
0.20
0.10
0.01
0.11
0.02
1147
368
105
1915
4.1
268.
029
1925
72.
3599
.29
DD
-17
14-1
6SO
B-11
/4m
st67
.08
0.58
14.2
24.
930.
051.
347.
871.
042.
810.
0846
910
367
1713
3388
165
13.2
110
27.9
7034
254
9.11
98.9
4D
D-1
882
-84
SOB-
11/4
zst
85.3
80.
308.
262.
880.
040.
460.
440.
561.
640.
0529
272
4610
718
2389
3.5
6210
.749
1915
02.
4910
0.07
DD
-19
88-9
0SO
B-11
/4zs
t83
.01
0.34
9.72
2.67
0.03
0.57
0.79
0.81
2.00
0.04
335
5232
118
1723
108
6.2
7511
.741
2015
72.
9899
.97
DD
-20
108-
110
SOB-
11/4
zst
83.9
80.
349.
312.
410.
030.
520.
530.
851.
980.
0431
952
2412
813
2310
44.
478
11.4
3818
149
2.53
99.9
4D
D-2
162
MS-
13zs
t85
.35
0.22
8.30
2.49
0.01
0.44
0.59
0.88
1.67
0.05
296
4821
106
1017
856.
184
10.8
2617
106
1.95
99.3
6D
D-2
268
MS-
14zs
t81
.40
0.36
10.7
82.
890.
020.
580.
711.
062.
160.
0438
556
3610
916
2010
66.
910
311
.444
1714
62.
9199
.12
DD
-23
73M
S-15
zst
82.8
90.
2710
.18
2.27
0.01
0.54
0.59
1.05
2.17
0.03
373
3936
117
1219
105
4.3
957.
735
1511
72.
5699
.39
DD
-24
77M
S-17
zst
81.2
20.
3711
.28
3.39
0.04
0.63
0.04
0.68
2.32
0.04
392
4936
119
1521
127
7.0
7111
.941
1916
03.
5510
0.24
DD
-25
88M
S-19
zst
83.2
10.
3110
.19
2.61
0.03
0.42
0.43
0.74
2.02
0.04
327
4826
117
1120
100
8.1
7810
.041
1713
12.
8899
.39
Surm
a G
roup
DS-
0113
00Si
ngra
-1m
st65
.23
0.81
17.3
16.
820.
112.
831.
701.
343.
700.
1454
080
106
2218
5531
174
15.7
112
17.8
126
3219
66.
5599
.87
DS-
0218
01Si
ngra
-1m
st74
.76
1.24
14.3
85.
600.
031.
020.
200.
911.
770.
0927
111
214
216
2651
2296
13.6
132
19.3
145
3748
06.
3399
.56
DS-
0318
02Si
ngra
-1m
st79
.06
1.03
11.3
85.
070.
050.
880.
250.
801.
390.
0822
310
711
814
2237
1876
10.0
104
15.1
105
3254
94.
5799
.17
DS-
0518
04Si
ngra
-1m
st74
.30
1.25
14.7
15.
740.
031.
010.
240.
871.
750.
1027
912
314
418
2651
2295
13.0
135
18.0
142
3756
66.
4099
.73
DS-
0616
00Bo
gra-
2m
st85
.62
1.01
8.69
3.47
0.01
0.50
0.12
0.09
0.45
0.03
9197
128
1023
2517
387.
885
11.1
114
2453
54.
2999
.79
DS-
0716
02Bo
gra-
2f s
st84
.87
0.32
7.80
2.70
0.06
0.77
0.60
1.39
1.43
0.05
273
4528
86
2215
613.
111
76.
636
1510
01.
5399
.73
DS-
0816
03Bo
gra-
2f s
st82
.59
0.43
8.86
3.44
0.05
0.94
0.63
1.44
1.57
0.07
305
6061
109
2318
688.
112
010
.454
2117
71.
7899
.33
DS-
0916
04Bo
gra-
2m
st82
.35
1.02
8.20
6.75
0.12
0.69
0.27
0.08
0.43
0.08
9910
713
510
2334
1735
10.8
8812
.212
430
713
5.22
99.5
5D
S-10
1606
Bogr
a-2
mst
61.3
20.
8918
.99
7.73
0.13
3.42
2.00
1.18
4.20
0.15
550
7813
026
2070
3419
518
.612
419
.713
934
190
7.86
99.8
8D
S-11
1608
Bogr
a-2
mst
67.0
61.
4217
.72
10.3
90.
121.
200.
450.
341.
150.
1519
212
117
022
3266
2979
20.9
188
20.2
226
3936
19.
7210
0.53
DS-
1217
23-1
724
Bogr
a-2
zst
85.7
11.
007.
724.
290.
010.
550.
220.
090.
390.
0397
115
144
823
2716
338.
974
13.5
110
2870
44.
3799
.28
DS-
1317
23-1
724
Bogr
a-2
mst
68.0
51.
2916
.87
8.45
0.20
1.52
0.53
0.36
2.55
0.18
310
131
156
2228
5618
134
17.9
179
21.6
172
4249
510
.52
99.4
0D
S-15
1724
-172
5Bo
gra-
2zs
t74
.35
1.40
16.6
83.
810.
031.
020.
140.
352.
110.
1024
113
415
922
3048
911
614
.415
219
.716
241
469
9.89
99.3
2
Tabl
e 2.
Who
le ro
ck m
ajor
(wt%
) and
trac
e el
emen
t (pp
m) a
naly
ses o
f san
dsto
nes a
nd m
udro
cks f
rom
the
NW
She
lf (P
rovi
nce
1), B
angl
ades
h.In
dex:
SaN
R-sa
mpl
e nu
mbe
r; Li
th-li
thol
ogy;
tota
l iro
n as
Fe 2
O3;
LOI-
Loss
on
igni
tion.
Not
e th
at d
ata
are
tabu
late
d on
an
anhy
drou
s nor
mal
ized
bas
is. T
he n
orm
aliz
ing
fact
ors
wer
e ap
plie
d to
bot
h th
e m
ajor
and
trac
e el
emen
t dat
a. O
rigin
al a
nhyd
rous
ana
lysi
s tot
al (T
otal
*) a
nd L
OI d
ata
are
incl
uded
to a
llow
reca
lcul
atio
n to
a h
ydro
us b
asis
if d
esire
d.Li
thol
ogy
code
s: c
sst -
coa
rse
sand
ston
e; m
sst -
med
ium
sand
ston
e; f
sst -
fine
sand
ston
e; z
st -s
iltst
one;
mst
- m
udst
one.
Dhiman Kumer Roy and Barry P. Roser36
Tabl
e 2
(ctd
). W
hole
rock
maj
or (w
t%) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e N
W S
helf
(Pro
vinc
e 1)
, Ban
glad
esh.
Tabl
e 2
(ctd
). W
hole
rock
maj
or (w
t %) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e N
W S
helf
(Pro
vinc
e 1)
, Ban
glad
esh.
SaN
rD
epth
(m)
Wel
lLi
thSi
O2
TiO
2A
l 2O3
Fe2O
3M
nOM
gOC
aON
a 2O
K2O
P 2O
5B
aC
eC
rG
aN
bN
iPb
Rb
ScSr
ThV
YZr
LOI
Tota
l*Su
rma
Gro
up c
td)
DS-
1617
25-1
726
Bogr
a-2
mst
70.6
41.
4919
.10
4.47
0.06
1.19
0.18
0.38
2.37
0.10
274
145
166
2432
704
129
16.1
198
24.0
202
4341
015
.71
99.2
7D
S-17
1725
-172
6Bo
gra-
2zs
t70
.64
1.71
17.8
66.
130.
080.
980.
290.
401.
810.
1124
014
218
324
3747
2110
718
.720
021
.519
644
457
9.76
99.7
7D
S-18
1726
-172
7Bo
gra-
2m
st68
.01
1.59
20.4
15.
280.
091.
310.
280.
322.
580.
1228
514
217
626
3561
1014
217
.218
724
.919
847
385
12.0
299
.66
DS-
1917
26-1
727
Bogr
a-2
zst
85.4
91.
007.
884.
330.
040.
550.
160.
110.
390.
0477
104
143
1023
2416
349.
979
12.2
108
2670
84.
1899
.49
DS-
2017
27-1
728
Bogr
a-2
mst
69.1
11.
2617
.38
7.21
0.11
1.39
0.42
0.35
2.58
0.18
310
119
164
2028
6421
140
18.3
180
23.1
175
3938
49.
9699
.35
DS-
2117
27-1
728
Bogr
a-2
zst
79.8
51.
4512
.57
4.30
0.01
0.69
0.10
0.21
0.80
0.04
140
130
189
1732
4724
6110
.313
317
.916
930
636
6.09
99.1
7D
S-22
1728
-172
9Bo
gra-
2m
st59
.40
1.14
16.0
616
.59
0.39
2.28
0.98
0.37
2.49
0.31
297
103
133
1726
5326
123
16.0
197
20.9
170
4227
513
.16
99.1
3D
S-23
1728
-172
9Bo
gra-
2zs
t91
.05
0.21
7.46
0.53
0.01
0.23
0.07
0.06
0.37
0.03
6451
303
66
620
2.0
235.
422
1029
27.
5199
.75
DS-
2417
29-1
730
Bogr
a-2
zst
91.1
60.
396.
241.
110.
010.
280.
070.
190.
510.
0475
6940
59
88
293.
439
9.4
5014
319
3.96
100.
34
Bar
ail G
roup
DB-
120
01Si
ngra
-1m
sst
87.0
50.
346.
472.
370.
040.
600.
741.
101.
250.
0571
945
406
611
1349
5.4
122
9.6
4018
118
6.08
100.
37D
B-2
2002
Sing
ra-1
mst
83.4
01.
298.
555.
480.
010.
610.
070.
200.
360.
0392
175
188
1028
3121
3010
.588
19.4
154
3811
575.
3010
0.67
DB-
420
02.5
Sing
ra-1
zst
89.8
30.
785.
792.
930.
010.
400.
070.
070.
110.
0242
106
942
1816
1014
5.3
3711
.571
2387
83.
3999
.60
DB-
520
03Si
ngra
-1zs
t94
.25
0.69
2.86
1.62
0.01
0.30
0.12
0.01
0.10
0.04
5410
184
316
89
130.
436
8.6
4322
793
1.75
99.0
9D
B-6
2004
Sing
ra-1
zst
94.6
10.
652.
651.
580.
020.
300.
080.
010.
080.
0246
102
821
158
813
3.4
329.
646
2175
71.
6099
.06
DB-
720
04.5
Sing
ra-1
mst
89.2
80.
836.
032.
990.
010.
440.
100.
080.
210.
0368
9398
619
1812
205.
148
8.5
7424
668
3.13
99.5
4Ja
intia
Gro
upK
opili
Sha
le F
orm
atio
nD
K-3
1765
Bogr
a-2
mst
35.4
40.
748.
7635
.01
0.84
6.55
11.6
70.
340.
530.
1313
415
815
49
1370
2827
25.8
403
30.4
546
5152
213
.59
95.5
2D
K-4
1766
Bogr
a-2
mst
59.4
91.
8022
.12
11.6
00.
082.
090.
400.
421.
920.
0821
315
618
827
3868
3210
923
.122
925
.025
236
523
14.0
799
.63
DK-
517
67Bo
gra-
2m
st89
.28
0.83
6.03
2.99
0.01
0.44
0.10
0.08
0.21
0.03
6893
986
1918
1220
5.1
488.
574
2466
811
.51
96.1
3Tu
ra S
ands
tone
For
mat
ion
DC
-119
91-1
992
Bogr
a-2
c ss
t97
.74
0.05
0.79
0.68
0.01
0.18
0.52
0.01
0.01
0.01
7119
10
21
63
0.6
130.
75
481
1.71
100.
12D
C-2
1991
-199
2Bo
gra-
2m
sst
97.4
70.
070.
960.
840.
010.
170.
460.
010.
010.
0171
173
13
12
32.
013
2.0
64
912.
4410
0.49
DC
-319
92-1
993
Bogr
a-2
m s
st97
.12
0.13
1.51
0.67
0.01
0.18
0.35
0.01
0.01
0.01
8029
21
41
45
2.0
132.
610
716
42.
5810
0.71
DC
-419
92-1
993
Bogr
a-2
m s
st97
.37
0.09
0.96
0.74
0.01
0.18
0.62
0.01
0.01
0.01
9316
11
32
42
0.5
161.
85
511
01.
9999
.10
DC
-619
94-1
995
Bogr
a-2
m s
st96
.03
0.15
2.29
0.87
0.01
0.18
0.34
0.06
0.06
0.01
5223
43
44
45
1.2
153.
91
712
03.
3198
.84
DC
-819
94-1
995
Bogr
a-2
c ss
t97
.96
0.13
0.77
0.39
0.01
0.18
0.54
0.01
0.01
0.01
104
291
13
14
40.
815
2.7
09
204
1.24
97.5
4D
C-9
1995
-199
6Bo
gra-
2f s
st96
.48
0.23
1.62
1.13
0.01
0.17
0.34
0.01
0.01
0.01
6728
51
50
86
0.8
143.
214
818
83.
6010
1.02
DC
-10
1995
-199
6Bo
gra-
2c
sst
97.5
80.
070.
950.
610.
010.
180.
560.
010.
010.
0188
181
03
15
41.
115
1.6
54
792.
1610
0.58
DC
-11
1996
-199
7Bo
gra-
2m
sst
97.0
70.
101.
370.
530.
010.
170.
450.
190.
100.
0198
332
13
15
82.
016
2.1
68
242
1.79
100.
51D
C-1
219
96-1
997
Bogr
a-2
m s
st97
.27
0.26
1.08
0.84
0.01
0.16
0.36
0.01
0.01
0.01
7631
51
51
64
1.9
132.
811
919
92.
9210
0.61
DC
-13
1997
-199
8Bo
gra-
2f s
st96
.65
0.13
1.88
0.71
0.01
0.16
0.32
0.01
0.11
0.01
7834
61
41
69
2.0
162.
56
826
03.
0810
0.83
Major and trace element compositions of Tertiary sedimentary successions in the NW and SE Bengal basin, Bangladesh 37
ppm), Ce (25 ppm), Sr (14 ppm) and Zr (158 ppm) are < 10 ppm. Among the mudrocks, average contents of Ce, Cr, Ni, Sc, Sr, Th, V, and Y in the Kopili Shale mudstones are greater than equivalents in the Barail, Surma and Dupitila Groups, suggesting differing provenance. Another feature of the mudrock analyses is the relatively high concentra-tions of several elements (Ce, Y, Zr) that are typically found in resistant heavy minerals such as monazite, apatite and zircon, especially in the Jaintia, Barail, and Surma Groups. For example, average Zr concentrations in the mudrocks in these three groups are 571, 851, and 456 ppm, respectively, well above the 190 ppm value in average upper continental crust (UCC; Taylor and McLennan, 1985). This suggests significant zircon concentration in the NWS mudrocks. Conversely, average concentrations of more mobile trace elements (Ba, Sr) are significantly lower in both sandstones and mudrocks within groups than in UCC (550 and 350 ppm, respectively). In clastic sediments both elements are typically associated with feldspars, and values in the NWS lower than UCC thus suggest significant loss during weath-ering or diagenesis.
The above features indicate that the trace element abun-dances in the NWS sediments have also been influenced by sorting, weathering, diagenesis, and heavy mineral con-centration, and hence do not directly reflect original source rock compositions.
CTFB (Province 3)Major elements
As in the NWS suite, the CTFB sandstones analyzed here have higher concentrations of SiO2 and lower concentra-tions of Al2O3 than the mudstones. Average SiO2 contents increase stratigraphically upward. SiO2 contents of the sand-stones range from 59.33-80.15 wt% (mean 74.21 wt%) in the Bhuban Formation, 71.97-83.06 wt% (mean 77.39 wt%) in the Bokabil Formation, 60.31-86.84 wt% (mean 80.71 wt%) in the Tipam Sandstone Formation, and 77.36-95.49 wt% (mean 85.60 wt%) for the Dupitila Formation. Lowest SiO2 in some samples, e.g. D-92, D-94 and D-109 (Bhuban) and D-42 (Tipam) are due to high CaO contents from authigenic CaCO3 cements. Average SiO2 contents in the mudrocks are similar in the Bhuban (67.55 wt%), Bokabil (67.77 wt%), Tipam (71.01 wt%) and Girujan Clay (69.60 wt%) Forma-tions. However, average SiO2 increases slightly in the Dupitila mudrocks (74.56 wt%), due to unusually high concentrations (80.19-92.32 wt%) in four siltstones.
Al2O3 concentrations in the Girujan Clay mudrocks tend to be a little higher than in equivalents in the other forma-tions, with a range of 14.90-19.79 wt% (mean 16.98 wt%), compared to 10.56-20.37 wt% (mean 16.06 wt%) in Bhuban mudrocks, 9.64-19.79 wt% (mean, 16.24 wt%) in Bokabil mudrocks, 10.02-19.79 wt% (mean, 14.65 wt%) in Tipam Sandstone Formation mudrocks and 4.40-18.55 wt% (mean, 14.15 wt%) in the Dupitila Formation. Average concentra-tions of Al2O3 in the mudrocks are 44% (Bhuban) to 80%
(Dupitila) greater than in the sandstones within each forma-tion, with relative enrichment increasing stratigraphically upward.
Average concentrations of the remaining major elements are naturally constrained by the sum of the SiO2 and Al2O3
contents. The next most abundant oxides are Fe2O3 and K2O, with ranges of averages by lithotype and formation of 2.36-6.53 and 1.47-3.16 wt%, respectively. Average Fe2O3 content in the sandstones falls progressively from 4.63 wt% in the Bhuban Formation through to 2.36 in the Bhuban Forma-tion, whereas mudrocks averages fall at a lower rate, from 6.53 wt% to 4.64 wt% respectively. This reflects a steady rise in relative enrichment between average mudrock and sandstone of 1.41 times (Bhuban), through 1.54 (Bokabil) and 1.61 (Tipam Sandstone), to 2.36 times in the Dupitila Formation. This suggests increasing fractionation between sandstone and mudrock end-members stratigraphically upward, as a result of improved sorting. The same pattern is observed for K2O, with the mudstone to sandstone enrich-ment factor increasing from 1.42 (Bhuban) through to 1.69 (Dupitila).
The most notable feature of the remaining major ele-ments is the low levels of the mobile oxides CaO and Na2O. Average CaO content in the sandstones falls from 3.91 wt% (Bhuban), through 1.76 wt% (Bokabil), to 2.16 wt% (Tipam Sandstone), to 0.68 wt% in the Dupitila Forma-tion. Comparable averages for the mudrocks are 1.96, 1.72, 1.47 and 0.85 wt%, respectively, and that in Girujan Clay mudrocks is even lower (mean 0.48 wt%, range 0.26-0.85 wt%). Sandstone Na2O contents are also low, averaging 1.16 wt% (Bhuban), 1.23 wt% (Bokabil), 0.89 wt% (Tipam) and 0.76 wt% (Dupitila); mudrock averages are lower still, fall-ing steadily from 1.10 wt% in the Bhuban Formation to 0.86 wt% in the Dupitila. With the exception of a few samples enriched in CaO from carbonate cements, CaO and Na2O contents in the CTFB sediments are considerably less than in UCC (4.2 and 3.9 wt% respectively; Taylor and McLen-nan, 1985). This points to considerable modification of bulk sediment compositions from the source to the depocenter. Moreover, the consistent trend towards lower abundances of these elements with stratigraphic position points to pro-gressive modification with time.
The remaining major elements (TiO2, MnO, MgO, P2O5) all share a common feature in greater abundances in the mudrocks than in the sandstones, with average enrichment factors ranging from 1.11 to 2.04. Furthermore, abundances in both sandstones and mudrocks generally decrease strati-graphically upwards, in response to increased SiO2 content. This again points to progressive change of modifying fac-tors with time.
Trace elementsThe CTFB trace element data also show marked
fractionation between sandstones and mudrocks. Within each formation almost all elements are enriched in the
Dhiman Kumer Roy and Barry P. Roser38
Tabl
e 3.
Who
le ro
ck m
ajor
(wt %
) and
trac
e el
emen
t (pp
m) a
naly
ses o
f san
dsto
nes a
nd m
udro
cks f
rom
the
CTF
B (P
rovi
nce
3), B
angl
ades
h.
SaN
rD
epth
(m)
Wel
lLi
thSi
O2
TiO
2A
l 2O3
Fe2O
3M
nOM
gOC
aON
a 2O
K2O
P 2O
5B
aC
eC
rG
aN
bN
iPb
Rb
ScSr
ThV
YZr
LOI
Tota
l*
Dup
itila
Gro
upD
upiti
la F
orm
atio
nD
-01
OC
mst
72.6
40.
6814
.25
4.25
0.06
1.68
1.56
1.73
2.99
0.15
435
8474
1615
3127
133
10.7
163
20.2
9232
315
2.31
100.
14D
-02
OC
zst
68.2
00.
7415
.78
5.75
0.08
2.62
1.66
1.51
3.52
0.14
485
8383
1917
4432
162
12.0
137
19.9
104
3421
73.
8210
0.10
D-0
3O
Czs
t67
.03
0.76
15.7
86.
030.
092.
662.
501.
623.
390.
1547
379
9416
1648
3216
514
.117
322
.310
833
214
4.11
98.8
8D
-04
OC
zst
66.7
50.
7717
.34
6.18
0.07
2.35
1.21
1.50
3.67
0.14
523
7998
2118
4637
190
16.1
142
21.1
114
3519
43.
3810
0.54
D-0
5O
Cm
st64
.89
0.77
17.3
96.
320.
082.
772.
561.
463.
610.
1552
278
9721
1744
4218
217
.015
620
.811
833
190
4.79
101.
73D
-06
OC
zst
75.6
30.
7012
.86
4.79
0.05
1.37
1.02
1.08
2.41
0.08
399
7310
715
1542
1813
110
.812
914
.293
3028
02.
7410
0.49
D-0
7O
Czs
t72
.04
0.79
14.6
55.
950.
071.
640.
911.
102.
740.
1144
675
113
1416
5723
145
12.5
130
18.3
107
3223
93.
3099
.48
D-0
8O
Cm
sst
77.9
20.
6111
.03
3.91
0.06
1.31
1.32
1.50
2.23
0.10
371
8081
913
4620
114
9.2
138
17.8
7236
303
1.67
99.6
5D
-09
OC
f sst
77.3
60.
5311
.14
4.15
0.06
1.65
1.24
1.44
2.34
0.08
373
5173
1212
4017
122
9.4
137
11.4
7422
194
1.75
100.
09D
-10
OC
m s
st80
.66
0.51
10.1
43.
260.
050.
841.
251.
321.
900.
0634
971
688
1123
1687
8.1
157
16.9
6325
205
1.47
99.1
4D
-11
OC
mst
77.9
20.
7713
.68
4.36
0.03
0.84
0.11
0.23
2.04
0.02
360
8810
215
1668
1812
313
.753
14.4
9745
283
3.74
100.
63D
-12
OC
f sst
83.0
80.
459.
313.
130.
060.
670.
800.
771.
710.
0332
272
6910
1116
1681
8.9
106
18.0
5524
203
1.82
100.
06D
-13
OC
mst
68.7
40.
9218
.55
5.44
0.14
1.71
0.72
0.62
3.12
0.04
481
9113
222
1952
2716
019
.111
922
.515
042
223
4.70
99.2
2D
-14
OC
zst
80.2
80.
7712
.23
3.10
0.02
0.99
0.07
0.58
1.96
0.01
366
7410
914
1569
1511
18.
954
13.2
8032
298
2.99
100.
56D
-15
OC
zst
92.3
20.
404.
401.
240.
020.
250.
100.
340.
950.
0017
178
713
910
1448
2.7
3013
.426
1328
81.
2198
.34
D-1
6O
Cm
sst
95.4
90.
082.
760.
490.
010.
190.
050.
130.
800.
0114
633
83
44
1142
0.6
252.
16
859
0.78
98.5
8D
-17
OC
zst
76.1
90.
9817
.11
2.67
0.01
0.59
0.05
0.24
2.14
0.01
322
106
163
1919
2821
111
16.3
5318
.613
241
316
4.61
99.8
5D
-18
OC
zst
85.8
30.
5610
.49
1.76
0.01
0.32
0.04
0.10
0.89
0.00
152
6093
1311
1513
619.
927
13.9
7316
311
3.36
100.
25D
-19
OC
m s
st91
.34
0.31
6.30
0.64
0.01
0.22
0.05
0.14
0.99
0.01
184
5444
47
615
515.
828
10.1
2814
172
1.84
98.5
1D
-20
OC
m s
st93
.33
0.32
4.48
0.92
0.01
0.20
0.04
0.04
0.66
0.01
127
3736
58
411
371.
620
8.6
1910
185
1.37
97.6
2D
-21
OC
zst
80.1
90.
7310
.42
5.93
0.02
0.47
0.07
0.23
1.92
0.02
366
9710
29
1433
2312
710
.144
20.2
8332
494
3.19
99.0
0D
-22
OC
mst
69.7
80.
8917
.32
5.80
0.05
2.02
0.23
0.57
3.26
0.07
497
111
118
2219
9230
175
15.6
7717
.312
757
206
4.34
100.
26
Tipa
m G
roup
Giru
jan
Cla
y Fo
rmat
ion
D-2
3O
Cm
st62
.80
0.92
19.4
68.
110.
112.
650.
851.
203.
730.
1651
185
158
2118
8437
187
20.9
132
21.2
159
3517
55.
0599
.58
D-2
4O
Cm
st63
.05
0.92
19.7
97.
990.
122.
520.
681.
143.
630.
1650
882
147
2518
7637
185
20.1
126
18.5
158
3517
25.
0910
0.68
D-2
5O
Cm
st63
.48
0.95
19.4
77.
580.
072.
890.
661.
083.
710.
1251
983
175
2519
107
3719
021
.311
320
.316
036
178
4.83
100.
15D
-26
OC
mst
69.4
00.
8916
.37
6.09
0.06
1.98
0.81
1.16
3.13
0.11
480
8415
517
1784
2816
015
.512
219
.713
333
215
3.71
99.1
6D
-27
OC
mst
73.3
20.
8315
.32
4.71
0.04
1.71
0.29
1.04
2.68
0.05
382
8312
218
1662
2314
413
.483
16.4
117
3025
73.
9910
0.45
D-2
9O
Cm
st73
.94
0.85
15.6
93.
980.
031.
500.
291.
012.
670.
0437
985
126
1917
5322
140
16.5
8615
.611
129
290
3.91
100.
49D
-30
OC
mst
74.3
40.
8315
.06
4.28
0.03
1.46
0.30
1.01
2.64
0.06
372
9112
315
1758
2213
816
.984
19.2
113
3132
23.
7299
.33
D-3
1O
Cm
st73
.70
0.81
14.9
05.
240.
041.
500.
260.
972.
510.
0637
481
123
1816
5924
137
15.8
8515
.611
731
281
3.58
100.
58D
-32
OC
mst
70.5
20.
8916
.81
6.24
0.04
1.72
0.26
0.73
2.76
0.03
390
9715
417
1778
2814
219
.987
21.6
150
3635
14.
4199
.32
D-3
3O
Cm
st71
.40
0.89
16.9
95.
330.
091.
510.
390.
762.
620.
0338
710
815
320
1778
3213
919
.298
18.6
137
3734
63.
4810
0.84
Tipa
m S
ands
tone
For
mat
ion
D-3
4O
Cf s
st81
.43
0.46
9.76
3.08
0.05
0.79
0.96
1.34
2.08
0.06
361
5659
811
2818
100
6.1
142
13.4
5220
175
1.58
98.5
4D
-35
OC
mst
65.2
60.
9619
.79
6.44
0.05
2.46
0.52
0.91
3.50
0.11
496
8214
026
1998
3618
020
.411
520
.115
637
198
4.84
100.
74D
-36
OC
m s
st80
.82
0.48
9.54
3.67
0.07
0.94
1.11
1.42
1.88
0.06
328
7262
1110
2216
907.
714
713
.157
2320
11.
2999
.80
D-3
7O
Cf s
st78
.54
0.55
10.7
24.
030.
051.
200.
991.
582.
250.
0938
364
6511
1333
2011
79.
814
313
.062
2421
41.
6399
.17
Inde
x:Sa
NR
–sa
mpl
enu
mbe
r;Li
th–
litho
logy
;to
tal
iron
asFe
2O3;
LOI–
Loss
onig
nitio
n.N
ote
that
data
are
tabu
late
don
ananhydrousnormalized
basi
s.Th
eno
rmal
izin
gfa
ctor
sw
ere
appl
ied
tobo
thth
em
ajor
and
trace
elem
entd
ata.
Orig
inal
anhy
drou
san
alys
isto
tal(
Tota
l*)a
ndLO
Idat
aar
ein
clud
edto
allo
wre
calc
ulat
ion
toa
hydr
ous
basi
sif
desi
red.
Lith
olog
yco
des:
css
t-co
arse
-gra
ined
sand
ston
e;m
sst-
med
ium
sand
ston
e;fs
st-f
ine
and
very
fine
grai
ned
sand
ston
e;zs
t-si
ltsto
ne;
mst
- m
udst
one.
OC
- ou
tcro
p sa
mpl
e; se
e Fi
g. 1
for l
ocat
ions
.
Tabl
e 3.
Who
le ro
ck m
ajor
(wt%
) and
trac
e el
emen
t (pp
m) a
naly
ses o
f san
dsto
nes a
nd m
udro
cks f
rom
the
CTF
B (P
rovi
nce
3), B
angl
ades
h.In
dex:
SaN
R-sa
mpl
e nu
mbe
r; Li
th-li
thol
ogy;
tota
l iro
n as
Fe2
O3;
LO
I-Lo
ss o
n ig
nitio
n. N
ote
that
dat
a ar
e ta
bula
ted
on a
n an
hydr
ous n
orm
aliz
ed b
asis
. The
nor
mal
izin
g fa
ctor
s w
ere
appl
ied
to b
oth
the
maj
or a
nd tr
ace
elem
ent d
ata.
Orig
inal
anh
ydro
us a
naly
sis t
otal
(Tot
al*)
and
LO
I dat
a ar
e in
clud
ed to
allo
w re
calc
ulat
ion
to a
hyd
rous
bas
is if
des
ired.
Li
thol
ogy
code
s: c
sst-c
oars
e-gr
aine
d sa
ndst
one;
m ss
t-med
ium
sand
ston
e; f
sst-fi
ne a
nd v
ery
fine
grai
ned
sand
ston
e; z
st -s
iltst
one;
mst
-mud
ston
e. O
C-o
utcr
op sa
mpl
e; se
e Fi
g. 1
for l
ocat
ions
.
Major and trace element compositions of Tertiary sedimentary successions in the NW and SE Bengal basin, Bangladesh 39
Tabl
e 3
(ctd
). W
hole
rock
maj
or (w
t %) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e C
TFB
(Pro
vinc
e 3)
, Ban
glad
esh.
SaN
rD
epth
(m)
Wel
lLi
thSi
O2
TiO
2A
l 2O3
Fe2O
3M
nOM
gOC
aON
a 2O
K2O
P 2O
5B
aC
eC
rG
aN
bN
iPb
Rb
ScSr
ThV
YZr
LOI
Tota
l*
Tipa
m G
roup
(ctd
)Ti
pam
San
dsto
ne F
orm
atio
n (c
td)
D-3
8O
Czs
t68
.43
0.85
16.0
37.
220.
102.
250.
731.
173.
080.
1348
480
117
2017
6032
163
15.8
107
18.4
126
3423
43.
8699
.92
D-3
9O
Cm
st68
.11
0.67
10.4
84.
930.
371.
8210
.07
1.27
2.16
0.13
342
7089
814
4218
103
12.1
267
18.2
8231
261
9.08
98.3
5D
-40
OC
zst
70.0
80.
9214
.82
6.36
0.08
2.23
1.29
1.25
2.81
0.16
437
111
143
1818
5923
146
14.8
112
21.7
128
3945
93.
8799
.84
D-4
1O
Czs
t69
.57
0.86
15.6
46.
180.
082.
361.
061.
232.
910.
1143
984
104
1917
5226
148
13.5
128
17.1
132
3322
63.
7499
.75
D-4
2O
Cm
sst
60.3
10.
427.
492.
980.
611.
7523
.89
0.95
1.53
0.07
224
5110
81
814
312
638.
018
818
.354
2716
615
.57
96.5
3D
-43
OC
f sst
77.5
70.
5510
.62
5.77
0.09
1.29
0.64
1.19
2.19
0.10
346
5072
1312
5218
127
9.5
115
10.1
9422
181
2.26
99.3
0D
-44
OC
zst
80.9
70.
5110
.02
3.74
0.05
0.91
0.75
1.14
1.87
0.04
349
6168
611
3517
958.
113
516
.773
2119
91.
6498
.65
D-4
5O
Cm
sst
79.1
10.
5511
.09
4.81
0.07
1.04
0.59
0.72
1.97
0.06
327
7681
1212
3625
106
11.3
100
14.8
9230
290
2.36
99.6
2D
-46
OC
m s
st83
.52
0.48
8.47
3.20
0.06
0.72
0.87
0.94
1.69
0.05
292
8265
410
2123
859.
311
220
.267
2633
91.
1898
.43
D-4
7O
Cf s
st83
.16
0.46
8.94
3.46
0.07
0.86
0.60
0.68
1.69
0.09
289
6169
1010
3119
897.
696
12.3
6022
235
1.53
99.5
7D
-48
OC
f sst
83.1
00.
458.
873.
370.
050.
800.
730.
761.
800.
0630
869
616
1026
2191
8.1
107
16.2
6724
284
1.37
98.2
9D
-49
OC
zst
72.2
40.
8515
.91
5.49
0.06
1.59
0.39
0.61
2.80
0.06
411
8611
919
1759
2515
516
.696
17.2
136
3426
53.
5099
.41
D-5
0O
Cf s
st86
.84
0.31
6.84
2.66
0.05
0.59
0.63
0.57
1.47
0.03
256
4738
38
1822
724.
692
14.2
4719
167
0.99
98.6
1D
-51
OC
f sst
81.7
20.
449.
483.
670.
070.
870.
850.
981.
870.
0532
264
5211
1024
2298
6.3
117
12.4
7223
201
1.83
99.3
9D
-52
OC
zst
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roup
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Form
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1992
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f sst
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4
Tabl
e 3
(ctd
). W
hole
rock
maj
or (w
t%) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e C
TFB
(Pro
vinc
e 3)
, Ban
glad
esh.
Dhiman Kumer Roy and Barry P. Roser40
Tabl
e 3
(ctd
). W
hole
rock
maj
or (w
t %) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e C
TFB
(Pro
vinc
e 3)
, Ban
glad
esh.
SaN
rD
epth
(m)
Wel
lLi
thSi
O2
TiO
2A
l 2O3
Fe2O
3M
nOM
gOC
aON
a 2O
K2O
P 2O
5B
aC
eC
rG
aN
bN
iPb
Rb
ScSr
ThV
YZr
LOI
Tota
l*
Surm
a G
roup
(ctd
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il Fo
rmat
ion
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2417
015
.014
820
.711
133
262
5.23
98.4
6D
R 7
418
01-1
802
Shah
bajp
ur-1
zst
71.8
20.
7312
.87
5.58
0.07
2.39
2.32
1.34
2.77
0.12
469
7577
1516
4025
150
13.2
137
16.9
9529
278
4.45
98.4
4D
R 7
520
11-2
012
Shah
bajp
ur-1
zst
69.6
70.
8314
.39
5.90
0.06
2.49
2.08
1.55
2.89
0.15
486
8793
1817
4821
146
13.0
143
18.8
104
3325
64.
5998
.64
DR
76
2012
-201
3Sh
ahba
jpur
-1zs
t69
.14
0.82
14.8
55.
910.
062.
452.
021.
652.
950.
1547
488
9518
1749
2915
015
.614
619
.811
334
280
4.64
98.9
6D
R 7
720
13-2
014
Shah
bajp
ur-1
zst
67.3
90.
8715
.86
6.44
0.06
2.64
1.93
1.48
3.18
0.15
509
8795
1918
5329
160
14.3
147
21.1
130
3426
05.
0298
.66
DR
78
2014
-201
5Sh
ahba
jpur
-1zs
t70
.01
0.83
14.3
25.
800.
062.
412.
091.
482.
850.
1447
195
9816
1746
2214
414
.114
421
.011
634
316
4.55
98.9
4D
R 7
920
16-2
017
Shah
bajp
ur-1
zst
68.0
60.
8415
.26
6.49
0.06
2.62
2.01
1.47
3.06
0.14
497
9010
117
1752
2615
513
.414
320
.811
534
263
4.93
98.8
2D
R 8
022
89-2
290
Shah
bajp
ur-1
zst
65.7
10.
8416
.49
6.62
0.08
2.71
2.61
1.14
3.64
0.15
567
8496
1919
4734
189
15.9
123
22.3
122
3422
35.
8698
.67
DR
81
2292
-229
3Sh
ahba
jpur
-1zs
t65
.61
0.85
15.9
96.
260.
092.
733.
591.
123.
610.
1456
588
9218
1945
3218
716
.712
324
.111
733
233
6.58
98.1
8D
R 8
222
93-2
294
Shah
bajp
ur-1
f sst
72.9
70.
7012
.63
5.04
0.07
2.17
2.32
1.29
2.71
0.11
465
7469
1515
3922
148
11.2
134
15.8
8427
240
4.09
98.9
9D
R 8
322
95-2
296
Shah
bajp
ur-1
mst
66.2
20.
8215
.59
6.18
0.09
2.65
3.60
1.17
3.52
0.15
544
8394
1818
4633
184
15.3
124
21.9
124
3524
46.
3498
.48
DR
94
373-
374
Sita
kund
-5zs
t64
.67
0.89
17.8
37.
150.
112.
911.
581.
163.
560.
1652
187
136
2319
7939
178
17.0
143
19.6
149
3420
65.
9698
.79
DR
95
374-
375
Sita
kund
-5m
st70
.38
0.78
14.4
06.
170.
122.
391.
761.
022.
810.
1745
986
110
1516
6429
142
17.2
134
20.5
105
3427
65.
2298
.77
DR
96
375-
376
Sita
kund
-5zs
t67
.92
0.86
15.7
46.
280.
122.
622.
191.
013.
120.
1548
179
126
2018
6932
157
15.7
147
18.8
121
3121
45.
8698
.04
Tabl
e 3
(ctd
). W
hole
rock
maj
or (w
t%) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e C
TFB
(Pro
vinc
e 3)
, Ban
glad
esh.
Major and trace element compositions of Tertiary sedimentary successions in the NW and SE Bengal basin, Bangladesh 41
Tabl
e 3
(ctd
). W
hole
rock
maj
or (w
t %) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e C
TFB
(Pro
vinc
e 3)
, Ban
glad
esh.
SaN
rD
epth
(m)
Wel
lLi
thSi
O2
TiO
2A
l 2O3
Fe2O
3M
nOM
gOC
aON
a 2O
K2O
P 2O
5B
aC
eC
rG
aN
bN
iPb
Rb
ScSr
ThV
YZr
LOI
Tota
l*
Surm
a G
roup
(ctd
)B
okab
il Fo
rmat
ion
(ctd
)D
R 9
737
6-37
7Si
taku
nd -5
mst
61.6
90.
9719
.79
7.80
0.10
3.16
1.37
0.97
4.01
0.14
553
9016
122
1992
3620
219
.015
024
.316
133
193
6.66
97.8
2D
R 9
861
2-61
3Si
taku
nd -5
mst
64.8
20.
9416
.91
6.95
0.08
2.99
2.68
1.07
3.44
0.13
494
9412
521
1869
3216
817
.314
120
.614
932
246
6.58
97.9
6D
R 9
997
5-97
6Si
taku
nd -5
m s
st78
.55
0.53
7.76
3.72
0.12
1.09
5.90
0.78
1.49
0.07
360
6910
68
1039
1968
7.2
393
14.9
4923
285
5.93
98.1
4D
R 1
0097
6-97
7Si
taku
nd -5
m s
st79
.96
0.47
9.18
4.22
0.06
1.47
1.86
0.92
1.79
0.07
378
5894
1110
6424
848.
117
210
.151
1817
03.
4998
.75
DR
101
1096
-109
7Si
taku
nd -5
mst
67.3
40.
9317
.37
6.76
0.06
2.38
0.64
0.99
3.42
0.11
594
9613
721
1868
3117
417
.414
821
.513
835
274
5.07
98.1
7D
R 1
0210
97-1
098
Sita
kund
-5m
st68
.02
0.89
16.7
36.
550.
072.
290.
791.
253.
310.
1160
086
127
2117
6930
164
18.6
159
18.8
141
3023
35.
0097
.85
DR
103
1098
-109
9Si
taku
nd -5
mst
65.6
80.
9418
.28
7.08
0.07
2.52
0.71
0.97
3.66
0.11
626
9013
922
1977
3118
618
.015
022
.714
731
262
5.40
98.0
8D
R 1
0410
99-1
100
Sita
kund
-5m
st63
.15
0.97
19.2
47.
930.
082.
770.
681.
113.
960.
1165
992
155
2520
7827
198
21.3
141
20.4
173
3421
85.
5798
.05
DR
105
1543
-154
4Si
taku
nd -5
mst
63.1
80.
9518
.41
7.59
0.11
3.08
1.65
1.20
3.67
0.17
523
8715
221
1987
3418
320
.114
323
.115
837
200
6.52
98.2
2D
R 1
0919
36-1
937
Sita
kund
-5m
st66
.56
0.82
16.4
26.
370.
142.
602.
551.
033.
360.
1486
478
133
2116
7130
167
16.3
155
17.5
120
3120
15.
9797
.40
DR
110
1937
-193
8Si
taku
nd -5
mst
66.4
30.
8517
.26
6.40
0.09
2.70
1.45
1.22
3.45
0.14
608
7913
320
1776
3017
717
.513
721
.013
630
213
5.74
98.5
8B
huba
n Fo
rmat
ion
D-9
2O
Cf s
st61
.15
0.62
8.88
4.06
0.82
2.20
19.5
70.
671.
890.
1330
766
739
1231
1684
8.1
2915
.668
2827
915
.32
98.0
6D
-93
OC
mst
75.6
40.
7310
.75
4.07
0.06
2.30
2.95
1.08
2.27
0.14
393
8988
1315
3418
106
10.7
115
18.0
9227
382
4.76
98.7
5D
-94
OC
f sst
59.3
30.
709.
054.
320.
892.
4720
.49
0.57
2.02
0.16
339
7974
1014
3013
919.
021
018
.078
3035
715
.70
98.0
5D
-95
OC
zst
61.3
30.
8818
.86
8.33
0.08
2.80
3.09
0.55
3.93
0.16
560
8415
024
1874
3319
519
.312
21.6
163
3617
86.
6599
.20
D-9
6O
Czs
t65
.13
0.87
17.0
27.
170.
132.
562.
850.
783.
320.
1748
184
129
2117
7131
166
19.6
126
19.5
144
3622
65.
8599
.44
D-9
7O
Czs
t63
.21
0.96
19.8
28.
050.
152.
490.
600.
683.
870.
1753
391
144
2620
8937
202
21.1
115
21.5
177
3818
74.
6299
.33
D-9
8O
Cm
st67
.88
0.83
14.9
66.
150.
142.
303.
760.
932.
900.
1545
485
110
1817
6227
147
18.7
123
18.9
133
3525
15.
9198
.96
D-9
9O
Cm
st66
.27
0.92
16.9
36.
320.
082.
412.
860.
803.
250.
1546
092
135
2118
6233
163
19.4
117
19.5
147
3624
05.
6599
.44
D-1
00O
Cf s
st78
.98
0.63
10.7
64.
080.
081.
420.
910.
972.
060.
1138
577
9112
1237
1810
410
.199
15.6
8827
318
2.54
99.3
8D
-101
OC
mst
70.2
00.
7914
.09
5.63
0.20
2.05
3.20
0.91
2.79
0.13
438
9210
717
1554
2414
114
.112
817
.812
135
270
2.60
98.6
7D
-102
OC
f sst
75.4
40.
6611
.83
6.32
0.09
1.53
0.64
0.92
2.48
0.09
444
6683
1614
6626
135
12.9
113
12.8
110
2622
35.
2299
.37
D-1
03O
Czs
t68
.66
0.90
16.1
96.
530.
052.
461.
100.
943.
030.
1445
981
126
1918
6226
155
17.8
113
19.0
148
3324
84.
3899
.47
D-1
04O
Czs
t72
.82
0.81
14.3
55.
850.
061.
660.
591.
062.
650.
1343
177
112
1716
5322
137
15.0
108
17.8
127
3227
32.
9999
.68
D-1
05O
Cf s
st77
.16
0.69
11.6
04.
380.
051.
721.
090.
982.
210.
1338
479
9313
1437
2111
312
.010
315
.896
3029
92.
9999
.13
D-1
06O
Cm
st80
.32
0.61
10.5
63.
400.
030.
960.
681.
222.
120.
1038
780
7111
1229
1910
78.
212
116
.376
2532
03.
5299
.42
D-1
07O
Cf s
st71
.86
0.77
14.8
96.
090.
041.
740.
691.
002.
810.
1144
974
9719
1551
2414
517
.611
216
.813
430
216
1.75
99.6
8D
-108
OC
mst
73.4
30.
7713
.32
5.39
0.06
2.08
1.15
1.15
2.49
0.14
410
8310
016
1545
2112
716
.510
716
.212
033
263
3.24
99.7
3D
-109
OC
f sst
68.2
40.
588.
433.
440.
681.
3414
.55
0.87
1.78
0.09
296
7275
911
2817
819.
234
715
.167
2732
611
.12
98.2
5D
-110
OC
zst
67.9
30.
6510
.75
4.81
0.58
1.88
10.3
50.
832.
120.
1133
772
9112
1342
1610
412
.326
114
.390
3025
79.
2598
.69
D-1
11O
Czs
t71
.15
0.80
14.7
95.
680.
082.
121.
081.
382.
760.
1443
985
101
1817
4823
141
15.9
137
16.7
126
3425
43.
3599
.00
D-1
12O
Czs
t72
.14
0.80
14.2
25.
660.
081.
951.
101.
262.
630.
1743
794
113
1616
4524
135
14.8
145
19.2
124
3629
83.
2399
.54
D-1
13O
Czs
t73
.47
0.87
15.8
55.
600.
041.
300.
040.
092.
630.
0951
511
794
1817
5534
137
14.4
7620
.613
038
360
4.15
99.2
9D
-114
OC
mst
66.9
50.
8617
.13
7.03
0.13
2.25
1.11
1.10
3.26
0.18
483
8710
820
1756
3116
717
.813
821
.514
336
227
4.31
98.9
9D
R 1
330
33-3
034
Begu
mga
nj-1
f sst
73.8
80.
6411
.73
4.71
0.20
1.98
3.14
1.25
2.32
0.15
389
7376
1513
3923
115
12.8
172
15.4
7729
265
4.65
98.4
7D
R 1
430
34-3
035
Begu
mga
nj-1
zst
64.6
50.
9419
.11
7.65
0.07
3.16
1.21
1.16
1.88
0.15
551
8312
625
1967
3819
522
.515
019
.415
332
183
5.44
98.3
7D
R 1
530
35-3
036
Begu
mga
nj-1
mst
65.1
70.
9617
.49
7.33
0.06
2.96
1.09
1.25
3.53
0.16
513
8812
923
1970
3217
820
.814
020
.214
936
236
5.08
98.3
8D
R 1
630
36-3
037
Begu
mga
nj-1
zst
64.0
40.
9018
.33
7.31
0.07
3.03
1.21
1.19
3.75
0.16
554
7912
623
1965
4018
619
.514
018
.914
233
186
5.57
98.8
6D
R 1
730
37-3
038
Begu
mga
nj-1
zst
64.7
70.
8516
.23
6.83
0.25
2.78
3.63
1.16
3.30
0.19
474
7811
120
1762
3316
416
.218
517
.512
232
193
6.66
98.1
6D
R 1
830
47-3
048
Begu
mga
nj-1
mst
66.5
10.
9216
.49
6.84
0.08
2.92
1.52
1.25
3.31
0.16
512
8611
921
1860
3516
517
.413
519
.012
833
250
5.25
98.9
2D
R 1
930
48-3
049
Begu
mga
nj-1
f sst
70.8
30.
7613
.67
6.14
0.09
2.54
1.81
1.30
2.70
0.15
496
7697
1716
4930
137
11.3
131
15.2
107
2623
84.
7099
.09
DR
20
3049
-305
0Be
gum
ganj
-1m
st63
.53
0.94
18.7
07.
430.
093.
031.
221.
143.
770.
1451
182
130
2419
7238
187
19.8
140
19.8
153
3019
35.
5598
.83
DR
21
3050
-305
1Be
gum
ganj
-1m
st63
.22
0.97
18.5
97.
680.
083.
121.
251.
143.
800.
1652
181
125
2419
6741
186
20.6
140
20.0
144
3120
85.
4498
.43
DR
22
3476
-347
7Be
gum
ganj
-1f s
st74
.48
0.61
10.2
64.
210.
101.
795.
221.
172.
020.
1334
876
7213
1341
1810
09.
817
214
.161
2729
86.
0698
.46
DR
23
3477
-347
8Be
gum
ganj
-1m
st64
.58
0.97
17.4
67.
080.
062.
991.
911.
193.
630.
1353
510
012
423
2070
3317
716
.912
720
.414
433
274
5.75
98.4
9D
R 2
434
78-3
479
Begu
mga
nj-1
mst
67.3
10.
9015
.60
6.33
0.06
2.75
2.46
1.23
3.20
0.15
494
107
114
2019
5932
157
15.5
128
19.8
118
3530
15.
7198
.71
Tabl
e 3
(ctd
). W
hole
rock
maj
or (w
t%) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e C
TFB
(Pro
vinc
e 3)
, Ban
glad
esh.
Dhiman Kumer Roy and Barry P. Roser42
Tabl
e 3
(ctd
). W
hole
rock
maj
or (w
t %) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e C
TFB
(Pro
vinc
e 3)
, Ban
glad
esh.
SaN
rD
epth
(m)
Wel
lLi
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33
3661
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34
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35
3663
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DR
36
3664
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gum
ganj
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R 5
228
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53
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258
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139
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156
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112
2494
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446
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314
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823
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283
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496
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126
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7630
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130
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144
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114
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512
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316
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423
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933
214
6.22
97.7
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R 1
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162
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116
2649
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taku
nd -5
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68.7
20.
8414
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6.51
0.07
2.95
1.90
1.17
3.02
0.12
555
8112
218
1864
2515
014
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618
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430
262
5.51
97.9
4D
R 1
1726
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36.
120.
072.
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242.
820.
1249
090
117
1817
5823
140
11.5
122
18.4
105
3228
35.
3798
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DR
118
2651
-265
2Si
taku
nd -5
zst
71.0
70.
7613
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6.04
0.07
2.70
1.84
1.18
2.75
0.11
591
8311
117
1659
2313
811
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916
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2826
74.
9998
.53
DR
119
2793
-279
4Si
taku
nd -5
zst
68.8
00.
8715
.23
6.49
0.06
2.63
1.37
1.26
3.16
0.14
551
8811
619
1857
2715
815
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817
.911
831
277
4.94
98.5
4D
R 1
2027
94-2
795
Sita
kund
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sst
78.2
80.
5810
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4.61
0.05
1.74
1.03
1.21
2.09
0.10
410
7273
1211
4126
106
8.8
9514
.160
2526
53.
1798
.56
DR
121
2795
-279
6Si
taku
nd -5
m s
st80
.15
0.54
9.69
3.75
0.04
1.47
1.06
1.21
1.99
0.10
516
7066
1111
3120
968.
698
14.5
4724
276
2.86
98.4
6
Tabl
e 3
(ctd
). W
hole
rock
maj
or (w
t%) a
nd tr
ace
elem
ent (
ppm
) ana
lyse
s of s
ands
tone
s and
mud
rock
s fro
m th
e C
TFB
(Pro
vinc
e 3)
, Ban
glad
esh.
Major and trace element compositions of Tertiary sedimentary successions in the NW and SE Bengal basin, Bangladesh 43
mudrocks, with enrichment factors generally greater than 1.25, with a maximum of 2.30 for Ni in the Dupitila Forma-tion. The exceptions are Sr in the Bhuban Formation, which is fractionally enriched in the sandstone average (134 ppm) compared to the mudrocks (132 ppm); and Zr, which is clearly enriched in the sandstones in both the Bhuban (287 ppm) and Bokabil (287 ppm) Formations relative to their mudrocks (245 and 232 ppm, respectively).
As for most of the major elements, trace element abun-dances in both the sandstones and the mudrocks tend to decrease from the Bhuban through to the Dupitila Forma-tions due to quartz dilution, although the decrease is not always regular. Strontium shows the least change, falling from an average of 134 ppm in Bhuban sandstones through to 88 ppm in Dupitila sandstones; for the equivalent mudrocks contents fall from 132 ppm to 99 ppm, respec-tively. Strontium also shows the least contrast between the mudrocks and the sandstones, with enrichment factors of 0.99 to 1.13 throughout the succession. Furthermore, concentrations of Sr in all CTFB samples are considerably lower than in UCC (350 ppm; Taylor and McLennan, 1985), suggesting significant loss of this mobile element. This is also the case for Ba, with average contents by lithology and formation ranging from 267 to 486 ppm, well below the UCC value of 550 ppm (Taylor and McLennan, 1985). Contents of less mobile trace elements (Ce. Cr, Nb, Sc, Sr, Th, V, Y, Zr) are close to or are greater than UCC values, indicating they have not been affected by the processes which reduced Sr and Ba abundances.
Conclusions
Geochemical compositions of Paleogene and Neogene mudstones and sandstones from Province 1 (NWS) and Province 3 (CTFB) in Bangladesh show significant and systematic variations, between both formations and groups, and between lithotypes. These variations reflect the operation of several processes, among which hydrodynamic sorting, source change, weathering, and preferential heavy mineral concentration are likely to be significant. These systematic variations may hold potential keys to resolve the exhumation history of the Himalaya in relation to tectonic and climatic factors. Detailed interpretation of the geochemical variations in the NWS and CTFB in the light of tectonic and climate factors will be made in future work, along with comparison and correlation with published data for Province 2 (Surma Basin), in an effort to improve under-standing of Himalayan erosion in a regional context.
Acknowledgements
We thank Professor Mrinal Kanti Roy (Geology and Mining, University of Rajshahi, Bangladesh) for his help and encouragement during fieldwork and sampling, and Muhammad Imadduddin (Managing Director), Bangladesh
Petroleum Exploration (BAPEX) for permission to access drill cores from exploration wells. Special thanks are also due to Professor Syed Samsuddin Ahmed and Md. Sultan-Ul-Islam (Geology and Mining, University of Rajshahi) for their encouragement and valuable suggestions. This work was supported by a Monbukagakusho (MEXT) Special Program scholarship (to DKR) and by internal research funding (to BPR).
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(Received: Oct. 3, 2011, Accepted: Oct. 28, 2011)
Major and trace element compositions of Tertiary sedimentary successions in the NW and SE Bengal basin, Bangladesh 45