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Geochemistry of the Mural Formation (Aptian-Albian) of the Bisbee Group,

publicité
Cretaceous Research 31 (2010) 400e414
Contents lists available at ScienceDirect
Cretaceous Research
journal homepage: www.elsevier.com/locate/CretRes
Geochemistry of the Mural Formation (Aptian-Albian) of the Bisbee Group,
Northern Sonora, Mexico
J. Madhavaraju a, *, C.M. González-León a, Yong Il Lee b, J.S. Armstrong-Altrin c, L.M. Reyes-Campero d
a
Estación Regional del Noroeste, Instituto de Geologia, Universidad Nacional Autónoma de México, Apartado Postal 1039, Hermosillo, Sonora 83000, México
School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Republic of Korea
c
Instituto de Ciencias del Mar y Limnología, Geología Marina y Ambiental, Universidad Nacional Autónoma de México, Circuito Exterior s/n, 04510 México D.F., México
d
Servicio Geológico Mexicano, Gerencia de Hidrogeología y Geología Ambiental, Blvd. Felipe Ángeles Km. 93.50-4, Pachuca de Soto, Hidalgo 42080, México
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 May 2008
Accepted in revised form 14 May 2010
Available online 20 May 2010
The elemental content (major, trace and rare earth elements) of 35 AptianeAlbian limestone samples
from the Mural Formation has been determined to provide information on depositional conditions and
provenance. The limestones of the Mural Formation show large variations in terrigenous and carbonate
contents (1.2 to 42.3% and 57.7 to 98.8% respectively). Small variations are observed in CaO concentrations in the Tuape Shale, Cerro La Puerta and Mesa Quemada members whereas large variations are
found in the Cerro La Ceja, Los Coyotes and Cerro La Espina members. The majority of the limestones
show high values of Th, Sc and Zr. Large variations in SREE content are observed among different
members of the Mural Formation. Most limestones from the Mural Formation record non-seawater-like
REEþY signatures. The limestones show large variations in Ce anomalies which may be due to mixing of
sediment components (biogenic and authigenic phases) and detrital materials including Fe-colloids from
fluvial input. Most of the limestones show positive Eu anomalies, but some samples show negative Eu
anomalies (Eu/Eu*: 0.42 to 2.62).
The large variations in terrigenous percentage, high Al2O3 and SREE contents, high LaN/YbN ratios, low
Y/Ho ratios and non-seawater-like REE patterns suggest that the observed variations in SREE contents
are mainly controlled by the amount of detrital sediments in the limestones of the Mural Formation. The
limestones of the Mural Formation were deposited under both coastal and open shelf environments, and
they exhibit non-seawater-like REE þ Y patterns. The presence of terrigenous materials in these
carbonates as contaminants effectively masks the seawater signature due to their high concentration of
the REE. Thus, trying to decipher the palaeoceanographic conditions represented by ancient carbonate
rocks should be done cautiously since limestones deposited under open marine environments may also
be contaminated by some amount of terrigenous particles. The presence of small quantities of terrigenous materials in the limestones can also reveal source rock information. The La/Sc, La/Co, Th/Sc, Th/Cr,
Th/Co and Cr/Th ratios suggest that the terrigenous materials present in the limestones were mainly
derived from a nearby exposed basement of intermediate to felsic igneous rocks.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Geochemistry
Rare Earth Element
Provenance
AptianeAlbian Limestone
Mural Formation
Northern Sonora
México
1. Introduction
Rare Earth Element (REE) concentrations, REE patterns, and the
Eu and Ce anomalies in marine sediments provide useful information on marine depositional environments. Many workers have
undertaken detailed studies on the REE to understand the pathways of biogenic and terrigenous fluxes from the source to the
marine sediments (Piper, 1974; Murray and Leinen, 1993;
Sholkovitz et al., 1994). The REE concentrations in seawater are
mainly controlled by factors relating to different input sources (e.g.,
* Corresponding author.
E-mail address: [email protected] (J. Madhavaraju).
0195-6671/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cretres.2010.05.006
terrestrial input from continental weathering, hydrothermal input)
and scavenging processes related to depth, salinity and oxygen
levels (Elderfield, 1988; Piepgras and Jacobsen, 1992; Greaves et al.,
1999). Rare Earth Elements generally reflect uniform trivalent
behaviour except for Ce and Eu which exhibit multiple oxidation
states. Shale-normalized seawater REE patterns are characterized
by i) LREE depletion, ii) negative Ce anomalies and iii) a slight
positive La anomaly (e.g. de Baar et al., 1991; Bau and Dulski, 1996).
Y and Ho are chemically similar in charge and ionic radius, but Ho is
more readily removed from seawater than Y because of its surface
complexation behaviour (Nozaki et al., 1997), thus seawater
exhibits distinctly a high Y/Ho ratio than the terrigenous materials
(e.g. Bau, 1996).
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
The distribution of REEs and Ce anomalies in marine sediments
may be influenced by depositional environments such as proximity
to source area (Murray et al., 1991a), widespread marine anoxia (Liu
et al., 1988; German and Elderfield, 1990; Murray et al., 1991b),
surface productivity variation (Toyoda et al., 1990), oceanic redox
conditions (Liu et al., 1988; German and Elderfield, 1990) and
lithology and diagenesis (Nath et al., 1992; Madhavaraju and
Ramasamy, 1999; Armstrong-Altrin et al., 2003; Madhavaraju and
Lee, 2009). Ce anomalies in marine sediments are considered by
some as reliable indicators for understanding the paleoredox
conditions (Liu et al., 1988), although several workers have raised
doubts about their effectiveness (German and Elderfield, 1990;
Murray et al., 1991b; Nath et al., 1992, 1997).
The REE signatures in ancient marine environment provide
information on secular changes in detrital influx and oxygenation
conditions in the water column (e.g. Holser, 1997; Kamber and
Webb, 2001). The seawater signatures are, however, completely
masked by the incorporation of terrigenous materials, which have
relatively high, non-seawater-like REE contents (Murray et al., 1992;
Webb and Kamber, 2000; Nothdurft et al., 2004; Madhavaraju and
Lee, 2009). The identification of the terrigenous particles present
in the marine carbonate rocks as contaminants is an important
aspect to understand the geochemistry of carbonate rocks.
The Lower Cretaceous, shallow marine siliciclastic and calcareous strata of the Mural Formation are exposed in northern Sonora,
northwest Mexico in a 300 km long transect that extends from
Sierra El Chanate (westernmost part) to Cerro El Caloso Pitaycachi
(northeastern most outcrop). Along this transect, González-León
et al. (2008) reported the stratigraphy and biostratigraphy of
several sections, including the Cerro Pimas and Sierra San José
sections (Figs. 1 and 2) of which we discuss herein the major, trace
and REE geochemistry of their limestone beds. The aims of our
study are to determine the influence of terrigenous materials on the
REE characteristics of carbonate rocks, to document the variations
in Ce anomalies and to unravel the probable reason for significant
positive Eu anomalies in the limestones of the Mural Formation.
110 00
113 00
San Luis
R. C.
SONORA
Sonoita
ARIZONA
Naco Agua Prieta
Nogales
Caborca
Cananea
31 00
Sierra
San Jose
Santa Ana
Cerro
Pimas
HERMOSILLO
0 20
29 00
60
120
Km
Guaymas
Obregon
Navojoa
Mexico
Fig. 1. Location map of the studied sections of the Mural Formation.
27 00
401
2. Geology and Stratigraphy
The Lower Cretaceous sedimentary succession assigned to the
Bisbee Group is well exposed in the north-central part of the state
of Sonora, Mexico. This succession has similar stratigraphic and
lithologic characteristics to the younger formations of the Bisbee
Group (Ransome, 1904) of southern Arizona and New Mexico in the
United States of America, and is correlative with strata exposed in
northern Mexico (Cantu-Chapa, 1976; Bilodeau and Lindberg, 1983;
Mack et al., 1986; Dickinson et al., 1989; Jacques-Ayala, 1995;
Lawton et al., 2004). In Arizona the Bisbee Group consists of the
Glance Conglomerate and the Morita, Mural and Cintura Formations that were deposited in a rift basin, termed the Bisbee Basin.
The older unit is the Glance Conglomerate composed of cobble- to
boulder-conglomerate with local interbeds of volcanic flows and
tuffs, which represent syntectonic rift deposits (Bilodeau et al.,
1987; Lawton et al., 2004).
The Morita and Cintura Formations are composed of reddish
brown siltstone and lenticular beds of arkose and feldspathic
arenite (Dickinson et al., 1986; Klute, 1991) that were deposited
under fluvial conditions. These two formations are difficult to
distinguish based only on their lithological characteristics. Hence,
the intervening marine Mural Formation is key to understanding
Lower Cretaceous stratigraphy and basin configuration in the area.
The fossiliferous clastic and carbonate strata of the Mural
Formation were deposited during a major marine transgression
during AptianeAlbian time (Scott, 1987) in the region of Sonora and
Arizona where it overlies the Morita Formation on a sharp ravinement surface and grades upward into the Cintura Formation.
Lawton et al. (2004) defined six members in the Mural Formation in
north-central Sonora (Fig. 2), which from the base upwards are the
Cerro La Ceja, Tuape Shale, Los Coyotes, Cerro La Puerta, Cerro La
Espina and Mesa Quemada members. The lithostratigraphic studies
of different members of the Mural Formation show minor facies
changes from west to east. The facies characteristics and regional
correlation of different members of the Mural Formation indicate
that the depositional environments of this formation varied from
restricted shelf with deltaic and fluvial influence to open shelf with
coral rudist buildups, to offshore shelf. For the present study, we
have collected limestone samples from the western part (Cerro
Pimas e CP) and the eastern part (Sierra San José e SSJ) of the
Bisbee Basin in northern Sonora. Here the limestones of the Mural
Formation were deposited in a nearshore environment with deltaic
and fluvial influence to open marine environments (González-León
et al., 2008). Most of the limestone samples contain varied amounts
of terrigenous materials.
The Cerro La Ceja (CLC) Member consists of interbedded bioclastic limestone, siltstone and calcareous sandstone. The limestone
beds are grey, brown and dark yellowish brown, bioturbated and
locally sandy. Siltstone beds are grey, green and reddish brown with
calcareous nodules. The Tuape Shale (TS) Member is mainly
composed of grey to black mudstone and shale, shaly limestone and
subordinate amount of siltstone and fine grained sandstone.
Limestone occurs as thin beds which contain oysters and ammonites. The Los Coyotes (LC) Member consists of thin beds of brown
mudstone, calcareous siltstone, shaly limestone, massive brown
siltstone, fine-grained sandstone and bioclastic limestone. This
member contains abundant fossils such as oysters, trigoniids,
gastropods, bivalves and echinoderms. The Cerro La Puerta (CLP)
Member is composed of mostly black shale and thin beds of finegrained sandstone and fossiliferous limestone. The limestone
exhibits distinct bedding-parallel burrows on the upper bed
surfaces, and it contains fossils including oysters and Orbitolina; the
black shale contains calcareous nodules. The Cerro La Espina (CLE)
Member consists mainly of massive limestone with thin beds of
402
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
Fig. 2. Lithostratigraphic sections of the Mural Formation in Cerro Pimas and Sierra San José areas (modified after González-León et al., 2008).
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
siltstone, mudstone, fine grained sandstone and shaly limestone.
The limestone beds are lenticular and fossiliferous with Orbitolina,
gastropods, corals, rudists and other bivalves and the shaly limestones contain abundant oysters. The Mesa Quemada (MQ)
Member includes green mudstone, light grey or red siltstone,
sandstone and bioclastic limestone. Sandstone beds are fine- to
very fine-grained with local parallel laminations. The bioclastic
limestone contains numerous oysters.
3. Material and methods
The stratigraphy of several sections of the Mural Formation
exposed in the northern part of Sonora has recently been studied by
Lawton et al. (2004) and González-León et al. (2008). Among them,
carbonate rocks are well exposed at the Cerro Pimas and Sierra San
José sections (Fig. 2). In our present study, thirty-five limestone
samples from these two sections were analyzed e twenty from the
Cerro Pimas section and fifteen from the Sierra San José section. We
consider these to be representative limestone samples from the
western and northeastern part of the Bisbee Basin in order to
establish the geochemical variations in the two sections that are
separated by about 150 km within the Bisbee Basin.
Care was taken to remove the weathered materials from the
surface of the limestone samples. The selected samples were
washed with distilled water several times, air dried and powdered
in an agate mortar. Then, fused glass beads were prepared for major
element analysis using a Phillip PW 1480 X-ray fluorescence
spectrometer with a rhodium X-ray source (see Norrish and Hutton,
1969; Giles et al., 1995). The accuracy of SiO2, Al2O3 and K2O are
better than 1%, MnO is better than 2% and that of Fe2O3, CaO and
MgO are better than 4%. Na2O, P2O5 and TiO2 are better than 6%,
Trace elements (Cr, Sc, Sr and Zr) were measured using a Jobin Yvon
138 Ultrace Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). Rare Earth Elements and certain other trace
elements (Co, Y, Th and Pb) were analyzed using a VG elemental PQ
II plus Inductively Coupled Plasma Mass Spectrometer (ICP-MS)
(see Jarvis, 1988). The sedimentary geochemical standard rock,
MAG-1, obtained from the USGS, was used for calibration. The
result from the analyses of MAG-1 are compared with the published values compiled by Govindaraju (1994) which shows better
precision of our data and also compatible with the published values
(Table 1). The precision for trace elements like Co, Zr and Th are
better than 3% whereas Cr, Sr, Y and Pb are better than 10%. The
analytical accuracy of all REEs is better than 4% (except Tb, Dy, Ho,
Tm and Lu). The precision of Tb, Dy, Ho, Tm and Lu are more than
10%. The limits of detection for the analytical procedure are also
listed in Table 1. They mainly agree with the findings mentioned by
earlier workers (Verma et al., 2002; Santoyo and Verma, 2003;
Verma and Santoyo, 2005). Major, trace and Rare Earth elements
were analyzed at the Korea Basic Science Institute. Three analyses
were made for each sample and then averaged. Yttrium is inserted
between Dy and Ho in the REE pattern according to its identical
charge and similar radius (REE þ Y pattern, Bau, 1996). Rare Earth
Elements were normalized to the Post Archaean Australian Shale
(PAAS) values of Taylor and McLennan (1985) for preparing REEnormalized diagrams. The Ce/Ce* (Ce anomaly) is calculated using
the value of Ce (Cesample/CePAAS) and the predicted value of Ce* is
obtained from the interpolation from the PAAS-normalised values
of La and Pr. The Eu/Eu* (Eu anomaly) is also calculated in similar
way using the values of Sm, Eu and Gd.
Thirty-five samples were analyzed using standard XRD procedures (Biscaye, 1965; Muller, 1967; Grim, 1968; Hardy & Tucker,
1988) for whole rock mineralogy. The powder samples were
scanned from 2e70 (2q) per minute. X-ray diffraction was used in
a computer controlled Shimadzu Diffractometer system model
403
Table 1
Comparison of data of major oxides, trace and rare-earth elements for USGS reference sample MAG-1 (marine sediment) with the literature USGS certificate of
analysis (Govindaraju 1994; see also USGS website).
Oxide/Elements
This Study*
SiO2
Al2O3
Fe2O3
CaO
MgO
K2O
Na2O
MnO
TiO2
P2O5
LOI
Co
Cr
Sc
Y
Sr
Zr
Pb
Th
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
50.72
16.48
7.11
1.42
3.11
3.59
3.60
0.10
0.70
0.17
14.09
20.2
77.1
e
24.91
133.7
125.6
28.44
11.96
41.46
87.32
10.06
38.10
7.61
1.66
5.89
1.28
5.92
1.16
3.09
0.56
2.70
0.53
Govindaraju 1994
Mean
50.4
16.4
6.8
1.37
3.0
3.55
3.83
0.098
0.75
0.16
e
20
97
17
28
150
130
24
12
43
88
e
38
7.5
1.6
5.8
0.960
5.2
1.0
3.0
0.43
2.6
0.4
0.96
0.30
0.60
0.10
0.10
0.17
0.11
0.009
0.07
0.021
e
1.6
8
1
3
15
13
3
1
4
9
e
5
0.6
0.14
0.7
0.090
0.3
0.1
e
0.43
0.3
0.04
Limits of detection**
e
5
20
5
5
5
50
5
15
15
e
0.0287
e
e
0.0075
e
e
0.0598
0.0473
0.0044
0.0030
0.0031
0.0034
0.0034
0.0031
0.0036
0.0024
0.0024
0.0027
0.0024
0.0023
0.0029
0.0018
*
Major oxides in wt% are analysed by XRF (average of 43 measurements); trace
elements in ppm by ICP-AES and ICP-MS (average of 6 measurements). The obtained
data were not tested statistically to find out the discordant outliers and it will be
undertaken in our future work (Barnett and Lewis, 1994; Verma, 2005; Verma and
Quiroz-Ruiz, 2006a, 2006b, 2008; Verma et al., 2008).
**
Limit of Detection: Three times the standard deviation of seven blank measurements; For major elements in mg/L and for trace elements in ng/L.
e not determined or not reported.
6000 with Cu ka radiation to estimate semi-quantitatively the
minerals present. The dominant minerals identified in these limestone samples are quartz, feldspar and calcite. The clastic and
carbonate percentages are given in Table 2.
4. Results
The concentrations of major elements in the studied limestones
samples of the Mural Formation are given in Table 2. Large variations are observed in SiO2 and Al2O3 contents (Table 2) among
different members of the Mural Formation in both sections. In the
Cerro Pimas section, the CaO content in the CLC, TS, LC, CLE and MQ
varies significantly (Table 2). Small variations are observed in CaO
concentrations in the CLC, TS, CLP, CLE and MQ members whereas
large variations are found only in the LC Member of Sierra San José
section (Table 2). The limestones from both sections show low
contents of Fe2O3 (Table 2). Those major and trace elements which
are enriched in silicate minerals (eg. SiO2 and Al2O3) are higher in
the CLC, TS, CLE and MQ members than the LC member from the
Cerro Pimas sections. In contrast, major and trace elements that are
housed in the carbonate minerals (eg. CaO and Sr) are higher in the
LC member than the other members of the Cerro Pimas section. The
CLC, TS, LC and MQ members from the Sierra San José section are
404
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
Table 2
Major oxides (wt%), trace and rare earth elements (ppm) concentrations for limestones of the Mural Formationa.
Member/Sample no Clastic % Carbonate % SiO2 Al2O3 Fe2O3 CaO
Cerro Pimas section
Mesa Quemada
CP47
CP45
Cerro La Espina
CP43
CP41
CP38
CP36
CP33
Los Coyotes
CP28
CP26
CP24
CP22
CP18
CP15
Tuape Shale
CP12
CP10
CP9
CP6
Cerro La Ceja
CP4
CP3
CP1
10.8
5.1
89.2
94.9
29.5
4.8
11.0
5.2
7.7
70.5
95.2
89.0
94.8
92.3
23.7
3.0
7.8
3.3
5.6
2.8
5.5
3.9
1.9
6.1
6.6
97.2
94.5
96.1
98.1
93.9
93.4
19.6
14.9
17.0
20.8
3.9
5.8
29.3
Sierra San José section
Mesa Quemada
SSJ27
11.3
Cerro La Espina
SSJ25
6.7
SSJ23
7.9
SSJ21
5.9
SSJ18
1.2
SSJ16
5.9
Cerro La Puerta
SSJ11
7.3
SSJ10
6.1
SSJ9
7.8
Los Coyotes
SSJ7
8.4
SSJ6
38.1
Tuape Shale
SSJ5
17.0
SSJ4
17.9
Cerro La Ceja
SSJ3
42.3
SSJ2
39.2
Member/Sample no
Cerro Pimas section
Mesa Quemada
CP47
CP45
Cerro La Espina
CP43
CP41
CP38
CP36
CP33
Los Coyotes
CP28
CP26
CP24
CP22
CP18
CP15
Tuape Shale
CP12
CP10
C P9
CP6
Cerro La Ceja
CP4
Th
Na2O MnO TiO2 P2O5 LOI
Total
Co
Cr
Sc
Zr
0.03 0.13
0.16 0.09
0.08
0.05
0.03
0.04
0.05
0.02
39.0
41.3
99.82
99.74
4.2
2.9
2.99
0.27
1.10
0.58
0.46
1.46
0.34
1.27
0.56
0.66
38.7
53.3
48.7
53.0
51.2
0.67
0.35
1.26
0.68
0.73
0.82
0.05
0.07
0.08
0.01
n.d.
n.d.
n.d.
n.d.
n.d.
0.15
0.06
0.12
0.09
0.08
0.12
0.02
0.05
0.02
0.03
0.03
0.02
0.02
0.02
0.02
31.4 100.00
42.0
99.41
39.1
99.49
41.4
99.73
40.8
99.59
4.3
2.8
6.9
4.6
3.2
9.1
1.0
4.9
3.5
4.6
1.8
3.9
2.9
1.5
3.4
5.4
0.14
0.65
0.48
0.10
0.48
0.47
0.28
0.65
0.65
0.25
1.81
0.78
54.1
52.0
53.2
54.9
51.9
51.5
0.35
0.41
0.26
0.09
0.51
0.18
0.01
0.14
0.10
0.01
0.08
0.12
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.06
0.08
0.06
0.07
0.25
0.25
0.01
0.04
0.03
0.01
0.02
0.02
n.d.
0.02
0.02
0.01
0.02
0.01
42.7
41.3
41.9
42.4
41.1
40.5
99.45
2.9
99.19
3.7
99.60
4.3
99.34
3.0
99.57 10.1
99.23
4.5
80.4
85.1
83.0
79.2
14.2
9.9
13.1
16.9
2.75
1.73
1.33
2.04
1.66
1.33
1.37
1.36
44.2
46.8
46.1
43.5
0.69
1.20
0.32
0.45
0.44
0.20
0.14
0.45
n.d.
0.02
0.26
0.03
0.15
0.12
0.16
0.08
0.12
0.08
0.07
0.10
0.05
0.04
0.05
0.02
35.5
37.7
36.6
34.6
99.76
99.12
99.50
99.53
4.6
3.6
3.0
3.2
96.1
94.2
70.7
2.0 0.49
3.1 0.77
23.3 2.84
0.26
0.41
1.59
53.3 0.38
53.3 0.23
38.0 0.52
0.10 n.d.
0.17 0.02
0.29 0.66
0.01
0.07
0.69
0.03
0.04
0.12
0.02
0.04
0.06
42.5
41.4
31.1
99.09
99.55
99.17
2.2
5.3
3.4
7.7 0.61
6.8 0.87
9.1 1.78
2.5
1.6
6.6
1.9
9.5 24.8
510
391
298
88.7
8.2 1.56
0.59
49.1 0.50
0.29 0.05
0.44
0.06
0.03
38.8
99.62
3.2
2.0 1.39
5.4
6.6
983
93.3
92.1
94.1
98.8
94.1
4.3
6.5
4.2
0.3
4.6
0.51
0.46
0.44
0.08
0.21
0.60
0.12
0.10
0.06
0.16
51.7
50.7
52.6
54.6
52.5
n.d.
0.07
0.04
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.07
0.02
0.01
0.01
0.01
0.02
0.02
0.01
0.01
0.02
0.01
0.01
0.01
0.01
0.01
41.3
40.7
41.7
43.4
41.4
99.39
99.53
99.84
99.15
99.76
2.8
2.2
2.1
2.1
1.98
4.0
3.6
2.8
2.7
3.0
4.3
3.8
1.5 10.1
1.2
6.2
0.8
1.8
1.5
5.0
313
390
439
407
434
92.7
93.7
93.2
4.7 0.90
3.9 0.84
4.8 0.78
0.50
0.44
0.37
51.7 0.96
52.6 0.90
52.3 0.78
0.06 n.d.
0.08 n.d.
0.10 n.d.
0.07
0.02
0.02
0.03
0.03
0.03
0.01
0.02
0.01
40.6
40.3
40.2
99.53
99.13
99.39
2.2
2.1
1.8
6.3 0.60
5.9 0.60
7.4 0.60
3.3
4.4
3.6
827
849
673
91.6
61.9
5.7 0.54
31.5 3.00
0.96
1.20
51.2 0.84
36.2 0.73
0.03 0.01
0.24 0.86
0.08
0.09
0.02
0.23
0.06
0.06
39.7
25.6
99.11
99.71
1.6
2.3
8.6 0.61
5.7
6.5 1183
11.9 1.59 18.0 70.3
753
83.0
82.1
12.5 1.78
13.5 1.92
0.86
0.92
46.1 0.72
49.7 0.78
0.20 0.34
0.21 0.37
0.08
0.09
0.10
0.11
0.04
0.04
36.5
31.6
99.22
99.24
2.2
1.9
15.2 1.42
8.0 52.2
19.3 2.00 13.8 43.8
699
520
57.7
60.8
31.7 6.26
29.6 6.00
0.94
1.48
37.3 0.80
32.8 1.03
0.59 2.03
1.21 0.07
0.29
0.07
0.21
0.30
0.08
0.08
19.9 100.10
27.3
99.94
2.7
2.8
10.5 2.42 11.3 57.4
21.4 4.20 12.1 50.6
528
481
La
Ce
Pr
Nd
1.0
1.0
425
631
2.21
6.1 24.1
0.41
5.2
0.6
1.40 10.7
9.4
1.20 14.1
2.6
0.60
9.5
2.8
554
405
544
529
746
1.4
11.0
6.0
3.5
7.7
6.3
0.20
1.7
0.60
4.1
0.60
4.4
0.20 10.3
0.60
6.0
0.60
6.5
540
428
440
218
368
471
10.8
13.6
9.0
15.3
1.79
7.1 14.4
866
1.39 18.2 42.1 1116
0.81
8.4
5.9
503
2.19 13.2 24.1
705
0.40
0.20
0.20
0.20
0.20
5.1
4.7
Sr
49.9 0.20
53.0 0.31
0.88
0.93
0.73
0.68
0.85
11.3 1.00
10.4 1.00
Y
0.80
0.41
Pb
9.1 0.50
3.5 0.86
MgO K2O
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
1.0
4.4
4.2
1.0
2.6
4.4
6.0
6.2
5.4
SREE
0.25
0.39
8
29
5.57
5.91
5.63
10.27
0.98
1.52
4.68
7.46
0.86
1.15
0.23
0.23
1.07
1.24
0.13
0.15
0.74
0.83
0.14
0.16
0.39
0.45
0.04
0.05
0.28
0.35
0.04
0.04
20.78
29.81
1.55
0.23
1.01
0.81
0.64
254
47
22
58
43
6.16
3.25
7.75
8.62
6.78
12.44
6.21
17.38
19.69
13.62
1.38
0.69
1.85
2.07
1.49
7.28
3.73
10.06
11.45
8.07
1.31
0.70
1.67
1.98
1.39
0.39
0.18
0.43
0.43
0.36
1.62
1.00
2.38
2.91
2.07
0.21
0.14
0.32
0.40
0.28
1.03
0.75
1.62
2.06
1.40
0.22
0.16
0.33
0.42
0.28
0.62
0.45
0.91
1.16
0.76
0.09
0.06
0.12
0.16
0.10
0.59
0.39
0.77
1.02
0.61
0.09
0.06
0.11
0.15
0.09
33.43
17.77
45.70
52.52
37.27
e
0.33
0.39
0.09
0.57
0.50
93
49
135
18
25
46
1.07
3.66
3.19
2.23
4.74
5.31
1.70
6.45
5.65
2.69
9.17
9.18
0.19
0.73
0.66
0.38
1.04
1.04
1.03
3.87
3.52
1.92
5.51
5.60
0.20
0.68
0.67
0.44
1.10
1.12
0.06
0.20
0.18
0.14
0.37
0.36
0.30
0.89
0.90
0.57
1.34
1.40
0.04
0.12
0.13
0.08
0.18
0.19
0.22
0.56
0.66
0.44
0.92
0.93
0.05
0.12
0.14
0.10
0.18
0.19
0.14
0.32
0.39
0.27
0.55
0.50
0.02
0.04
0.05
0.04
0.07
0.06
0.12
0.26
0.34
0.21
0.43
0.39
0.02
0.04
0.05
0.03
0.06
0.06
5.22
17.94
16.53
9.54
25.66
26.33
1.27
1.68
1.44
2.34
40
117
79
14
9.18
11.98
20.88
7.72
18.68
27.18
50.49
14.32
2.04
3.26
4.53
2.01
10.97
17.25
26.72
10.33
1.78
2.42
2.87
1.94
0.69
0.78
1.03
0.47
2.12
2.94
3.69
2.43
0.26
0.35
0.40
0.35
1.19
1.42
1.52
1.98
0.23
0.26
0.28
0.41
0.65
0.70
0.82
1.21
0.08
0.08
0.09
0.16
0.53
0.54
0.56
1.09
0.08
0.08
0.08
0.17
48.48
69.24
113.96
44.59
1.51
19
4.63
7.40
1.03
5.05
0.75
0.17
0.89
0.12
0.45
0.09
0.24
0.04
0.19
0.03
21.08
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
405
Table 2 (continued )
Th
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
CP3
CP1
1.13
1.34
67
41
6.49
13.51
11.50
28.94
1.59
3.05
8.04
16.52
1.32
2.17
0.36
0.49
1.57
2.77
0.20
0.33
1.07
1.45
0.21
0.28
0.58
0.85
0.07
0.12
0.48
0.77
0.07
0.12
33.55
71.37
0.72
25
6.69
13.64
1.39
7.54
1.21
0.75
1.48
0.18
0.83
0.17
0.48
0.06
0.40
0.06
34.88
0.35
0.12
0.08
0.01
0.07
13
7
17
9
26
3.77
1.06
0.91
0.53
0.92
7.77
1.87
1.59
0.73
1.26
0.81
0.21
0.19
0.09
0.16
4.44
1.10
0.98
0.45
0.82
0.70
0.18
0.16
0.09
0.14
0.19
0.05
0.04
0.028
0.04
6.50
0.24
0.23
0.14
0.21
0.12
0.03
0.03
0.014
0.03
0.56
0.17
0.17
0.08
0.15
0.12
0.04
0.037
0.017
0.03
0.31
0.115
0.11
0.05
0.10
0.04
0.018
0.017
0.007
0.01
0.36
0.11
0.114
0.043
0.09
0.04
0.017
0.018
0.006
0.012
25.73
5.21
4.60
2.28
3.97
0.44
0.31
0.36
14
34
9
2.95
2.37
2.51
4.64
3.55
3.71
0.55
0.46
0.48
2.83
2.34
2.44
0.46
0.41
0.42
0.13
0.11
0.12
0.61
0.55
0.63
0.08
0.08
0.08
0.41
0.40
0.43
0.09
0.09
0.09
0.26
0.24
0.27
0.04
0.03
0.04
0.22
0.21
0.22
0.03
0.03
0.03
13.30
10.87
11.47
0.77
3.11
11
15
9.36
19.48
21.51
43.03
2.56
4.57
13.45
24.40
1.78
3.38
0.37
0.68
2.10
4.45
0.25
0.62
1.06
3.10
0.19
0.65
0.54
1.91
0.07
0.27
0.42
1.77
0.07
0.27
53.73
108.58
1.19
1.97
21
34
6.66
12.19
13.26
19.72
1.68
2.58
8.62
13.31
1.27
2.06
0.39
0.44
1.50
2.65
0.20
0.36
0.94
1.81
0.19
0.39
0.56
1.14
0.08
0.15
0.50
0.98
0.08
0.15
35.93
57.93
2.80
3.23
15
6
10.55
12.68
21.80
27.70
2.41
3.35
12.68
17.51
1.93
2.80
0.52
0.81
2.37
3.18
0.34
0.44
1.77
2.18
0.38
0.44
1.11
1.29
0.16
0.18
1.06
1.19
0.16
0.18
57.24
73.93
Sierra San José section
Mesa Quemada
SSJ27
Cerro La Espina
SSJ25
SSJ23
SSJ21
SSJ18
SSJ16
Cerro La Puerta
SSJ11
SSJ10
SSJ9
Los Coyotes
SSJ7
SSJ6
Tuape Shale
SSJ5
SSJ4
Cerro La
CejaSSJ3
SSJ2
a
Pb
SREE
Member/Sample no
Before data presentation, an attempt was made to round the data to the number of significant digits as suggested by Verma (2005).
more enriched in silicate minerals than the CLP and CLE members.
In contrast, the CLP and CLE members are more enriched in
carbonate minerals than the CLC, TS, LC and MQ members. The
observed variations in the major oxides concentrations within the
same member from different localities may be due to the amount of
clastic materials included in them.
The bivariate plots of major oxides including certain trace
elements vs the percentage of clastic materials present in the
carbonate rocks provide useful information regarding the source of
these materials (Parekh et al., 1977; Cullers, 2002). In addition,
statistical approach will also useful to understand the statistically
valid or invalid correlation (Verma et al., 2006). A Plot of the
S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs the percentage of clastic materials show excellent linear correlation and
also the linear plot extending from the origin (Fig. 3a). This suggests
as expected that these oxides are mainly incorporated into the
clastic materials rather than the calcite. In contrast, CaO and LOI
have a perfect negative correlation with the percentage of clastic
materials, suggesting that they are incorporated into the carbonate
phase (Fig. 3b and c). These results are consistent with the other
published studies (Parekh et al., 1977; Cullers, 2002).
Trace elements concentrations and their ratios are given in
Tables 2 and 3. The high field strength elements (HFSE), namely Zr,
Y and Th, are resistant to weathering and alteration processes when
compared with other trace elements (Taylor and McLennan, 1985).
The limestones from the LC and MQ members contain a low
concentration of Zr when compared with other members at the
Cerro Pimas section (Table 2). The CLC, TS and LC members have
higher concentrations of Zr than the CLP, CLE and MQ members at
Sierra San José section (Table 2). Maximum concentrations of Y are
found in the CLC, TS, LC and CLE members whereas low concentrations are found in the MQ Member at Cerro Pimas section
(Table 2). In the Sierra San José section, the higher concentrations of
Y are observed in the CLC, TS, LC and MQ members than the CLP and
CLE members. Overall, the limestones of the Mural Formation
contain high Sr content (Table 2).
Plots of La, Ce, Sc and Th vs S(SiO2 þ Al2O3 þ Fe2O3 þ MgO
þ Na2O þ K2O þ TiO2) yield significant positive correlation with the
linear plots emanating slightly above the intersects of the X and Y
axes (Fig. 4aed). This suggests that these elements are mainly
housed in the clastic materials. Likewise, Sm, Eu, Tb, Yb, and Lu
show a positive correlation with S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ
Na2O þ K2O þ TiO2) which suggest that these elements are mainly
associated with terrigenous particles (statistically significant at
a strict significance level of 0.001; linear correlation coefficient
r ¼ 0.64; 0.63; 0.71; 0.78; 0.79; respectively, n ¼ 35). These results
are consistent with the other published studies (Parekh et al., 1977;
Cullers, 2002).
The enrichment and depletion of REE in the sediment are
controlled by the major processes such as the terrigenous input
from the continental area, authigenic removal of REE from the
water column and early diagenesis (Sholkovitz, 1988). Seawater
contributes lesser amount of REE to the sediments where as the
sediments contain high REE concentration show non-seawater-like
pattern (Nothdurft et al., 2004). The PAAS normalized Seawater REE
patterns (Fig. 5) are characterized by (1) uniform light REE depletion, (2) a negative Ce anomaly, and (3) a slight positive La anomaly
(e.g., De Baar et al., 1991; Bau and Dulski, 1996) and higher Y/Ho
ratios (e.g., Bau, 1996). The limestones from the CP and SSJ
sections show non-seawater-like REE þ Y patterns (CLC:
NdN/YbN ¼ 1.52 0.42, n ¼ 5; TS: 1.95 1.17, n ¼ 6; LC: 1.18 0.65,
n ¼ 8; CLP: 0.97 0.08, n ¼ 3, CLE: 0.92 0.15, n ¼ 10; MQ:
1.57 0.19, n ¼ 3; Fig. 6aef). Most of the samples contain positive La
and negative Ce anomalies although some samples show slightly
positive La and negative Ce anomalies to no anomalies. Most of the
limestones from the CP and SSJ sections contain chondritic Y/Ho
ratios (CLC: 30.1 2.7, n ¼ 5; TS: 34.2 5.0, n ¼ 5; LC: 32.1 2.4,
n ¼ 7; CLE: 35.4 6.1, n ¼ 10; MQ: 32.5 3.3, n ¼ 3; respectively,
Y/Ho Chondritic ratio: w28), but the limestones of the CLP member
from the SSJ section contain slightly higher Y/Ho ratios (CLP:
41.8 6.4, n ¼ 3). Two samples contain high Y/Ho ratios (CP10:
70.15 and CP22: 102.5) which have been statistically proved as
outliers using the method proposed by Verma and Quiroz-Ruiz
(2006a,b). So, we have not included those samples with discordant outliers while calculating the mean and standard deviation to
improve the authenticity of the data set (Verma et al., 2008).
406
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
a
b
c
Fig. 3. a, plot of the S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs clastic
percentage in the limestones of the Mural Formation provides a linear plot with
a correlation coefficient of 0.99. b, plot of the clastic (%) vs CaO content gives significant
negative correlation with a correlation coefficient of 0.98. c, clastic (%) vs LOI plot
exhibits a linear plot with a correlation coefficient of 0.98.
5. Discussion
5.1. Ce Anomaly
Ce/Ce* ratios in limestones of the Cerro Pimas section ranges
from 0.56 to 1.20, with a mean value of 0.91 (n ¼ 20); in limestones
of the Sierra San José section this ratio ranges from 0.73 to 1.05 with
a mean value of 0.90 (n ¼ 15). Noticeable variations are observed
among different members of the Mural Formation. Many limestones of the Mural Formation exhibit less negative Ce anomalies
than the deep-sea Indian Ocean carbonates (Nath et al., 1992),
Arabian sea sediments (Nath et al., 1997), Cretaceous carbonates
from Southern Alps (Bellanca et al., 1997), Maastrichtian carbonates
of Southern India (Madhavaraju and Ramasamy, 1999), Indian
Ocean waters (Bertram and Elderfield, 1993) and Pacific Ocean
waters (Zhang and Nozaki, 1996).
The depletion of Ce relative to the adjacent REE is one of the
characteristic features of modern seawater. In seawater Ce/Ce*
values range from <0.1 to 0.4 (Elderfield and Greaves, 1982;
Piepgras and Jacobsen, 1992), but it is 1 in average shale
(Murray et al., 1991a). The deficiency of Ce in seawater result
from the oxidation of Ceþ3 to the less soluble Ceþ4 and subsequently its removal from the seawater through scavenging by
suspended particles which settle through the water column
(Sholkovitz et al., 1994).
The Ce/Ce* values are not correlated very well with Al, Th and Zr
(r ¼ 0.40; 0.35; 0.33; respectively), but Ce values are positively
correlated with Al, Th and Zr (statistically significant at a strict
significance level of 0.001; linear correlation coefficient r ¼ 0.55;
0.53; 0.58; respectively). Such moderate correlation of Ce and Ce/
Ce* with Al, Th and Zr suggests that other factors in addition to
detrital input might have controlled the Ce distribution in the
studied limestones.
Seawater and marine carbonates exhibit a Ce deficient nature
due to the scavenging of Ceþ4 by FeeMn oxides in the deep sea
environments (Elderfield, 1988). The deep sea regions having a low
sedimentation rate with a well developed oxic water column with
a more active scavenging processes which initiate the coprecipitation of Ce(OH) on to FeeMn coatings on sedimentary particles. In
the studied limestones the Ce/Ce* values, however, are not correlated with a scavenging-type particle reactive element (Ce/Ce* vs
Pb: r ¼ 0.24), which indicates that the observed variations in Ce
anomalies are probably unrelated to a scavenging process.
Furthermore, the limestones of the Mural Formation were
deposited in shallow marine environments (Lawton et al., 2004;
González-León et al., 2008) where scavenging processes are
limited when compared with deep sea regions.
Many limestone samples from the Mural Formation contain
positive Ce anomalies. The positive Ce anomalies mainly occur due
to the paleoredox conditions (German and Elderfield, 1990),
lithology and diagenesis (Nath et al., 1992; Madhavaraju and
Ramasamy, 1999; Armstrong-Altrin et al., 2003; Madhavaraju and
Lee, 2009) and Fe-organiceREE rich colloids from the riverine
input (Sholkovitz, 1992).
The variations in the bottom water oxygenation level in the
carbonate rocks have been estimated using Ce/Ce* ratios (Wang
et al., 1986; Piper, 1991). In the present study, Ce anomalies are
inversely correlated with CaO contents (r ¼ 0.48) suggesting
that the Ce/Ce* values, however, not related to bottom water
oxygenation. The inclusion of REE-rich river-borne colloids in the
coastal fringing reef resulted in the lack of a negative Ce anomaly
(Nothdurft et al., 2004). The fluvial deltaic-influenced facies are
present in the Cerro la Puerta and Cerro la Espina members at
Cerro Pimas locations (González-León et al., 2008). The absence
of a large Ce anomaly requires inclusion of material with a positive Ce anomaly relative to PAAS, and Fe-colloids from riverine
input have such positive Ce anomaly (Sholkovitz, 1992).
A comparison of Ce/Ce* values with the concentrations of Fe
indicates that there is a moderate correlation ((statistically
significant at a strict significance level of 0.001; linear correlation
coefficient r ¼ 0.57) between them in these limestones. Hence,
the observed variations in Ce content and Ce anomalies in the
limestones of the Mural Formation may be due to the mixing of
different portions of sediment components (dominantly biogenic
and authigenic phases) which inherited the seawater-like Ce
anomaly and of detrital materials (mainly alumino-silicates) with
crust-like Ce anomaly. In addition, incorporation of Fe-colloids
from riverine input might be partially responsible for the variations in Ce anomalies.
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
407
Table 3
Elemental ratios for limestones of the Mural Formation.
Member/Sample no
Cerro Pimas section
Mesa Quemada
CP47
CP45
Cerro La Espina
CP43
CP41
CP38
CP36
CP33
Los Coyotes
CP28
CP26
CP24
CP22
CP18
CP15
Tuape Shale
CP12
CP10
C P9
CP6
Cerro La Ceja
CP4
CP3
CP1
Sierra San José section
Mesa Quemada
SSJ27
Cerro La Espina
SSJ25
SSJ23
SSJ21
SSJ18
SSJ16
Cerro La Puerta
SSJ11
SSJ10
SSJ9
Los Coyotes
SSJ7
SSJ6
Tuape Shale
SSJ5
SSJ4
Cerro La Ceja
SSJ3
SSJ2
La/Co
Th/Sc
Th/Co
Th/Cr
Cr/Th
Ce/Ce*
Eu/Eu*
LaN/YbN
NdN/YbN
5.57
5.91
1.33
2.05
0.25
0.39
0.06
0.14
0.02
0.04
45.00
26.69
0.56
0.79
1.13
0.91
1.47
1.25
1.39
1.77
36.07
29.56
2.79
7.93
5.54
7.18
11.3
1.44
1.17
1.12
1.89
2.13
0.70
0.56
0.72
0.68
1.07
0.36
0.08
0.15
0.18
0.20
0.17
0.23
0.21
0.23
0.14
5.89
4.43
4.84
4.32
7.14
0.99
0.95
1.05
1.07
0.99
1.26
1.01
1.02
0.84
1.00
0.77
0.62
0.74
0.62
0.82
1.10
0.80
1.09
0.93
1.10
27.68
32.75
32.33
33.45
33.96
5.35
6.10
5.32
11.15
7.90
8.85
0.37
0.99
0.73
0.74
0.47
1.17
e
0.55
0.65
0.45
0.95
0.83
e
0.09
0.09
0.03
0.06
0.11
e
0.03
0.07
0.03
0.07
0.08
e
33.27
15.26
38.78
13.44
12.54
0.84
0.91
0.89
0.67
0.95
0.89
1.17
1.21
1.09
1.33
1.44
1.35
0.44
1.04
0.69
0.78
0.82
1.01
0.70
1.24
0.86
0.77
1.07
1.20
33.60
34.00
31.57
102.50
33.28
34.05
5.13
8.62
25.78
3.53
2.02
3.32
7.01
2.40
0.71
1.21
1.78
1.07
0.28
0.47
0.48
0.73
0.12
0.12
0.16
0.15
8.47
8.10
6.23
6.54
1.00
1.00
1.20
0.84
1.67
1.38
1.49
1.02
1.28
1.64
2.75
0.52
1.72
2.66
3.96
0.79
31.04
70.15
29.89
32.12
7.59
7.46
7.59
2.10
1.22
4.01
2.48
1.30
0.75
0.68
0.21
0.40
0.20
0.17
0.15
5.09
6.01
6.81
0.78
0.82
1.04
0.98
1.17
0.94
1.81
0.99
1.30
2.22
1.39
1.78
28.00
31.48
34.00
4.81
2.12
0.52
0.23
0.36
2.76
1.00
2.64
1.23
1.56
31.88
9.43
5.30
4.55
2.65
4.60
1.35
0.49
0.43
0.25
0.46
0.88
0.60
0.40
0.05
0.35
0.13
0.06
0.04
e
0.04
0.09
0.03
0.03
e
0.02
11.37
29.58
34.88
e
42.71
1.03
0.88
0.87
0.75
0.73
0.42
1.12
0.98
1.22
1.09
0.77
0.72
0.62
1.00
0.75
1.02
0.83
0.73
0.87
0.75
35.42
40.00
32.70
48.24
45.94
4.92
3.95
4.18
1.34
1.11
1.38
0.73
0.52
0.60
0.20
0.15
0.20
0.07
0.05
0.05
14.39
19.10
20.58
0.83
0.79
0.77
1.15
1.10
1.10
0.99
0.85
0.84
1.06
0.93
0.91
36.22
51.65
39.14
15.34
12.25
5.78
8.66
1.26
1.96
0.48
1.38
0.09
0.26
11.16
3.83
1.01
1.05
0.90
0.83
1.64
0.81
2.66
1.15
30.11
27.71
4.69
6.10
3.03
6.45
0.84
0.99
0.54
1.04
0.08
0.10
12.75
9.80
0.92
0.82
1.33
0.89
0.98
0.92
1.44
1.13
42.32
35.46
4.36
3.02
3.89
4.59
1.16
0.77
1.03
1.17
0.27
0.15
3.74
6.63
1.00
1.00
1.14
1.28
0.73
0.79
0.99
1.23
29.66
27.34
La/Sc
5.2. Behaviour of Europium
The limestones from Cerro Pimas and Sierra San Jose sections
show large variations in Eu anomalies (Eu/Eu*: 0.84 to 1.67; 0.42 to
2.64; respectively). Most of the limestone samples contain positive
Eu anomalies, whereas few samples contain negative Eu anomalies.
Positive Eu anomalies are mainly found either in sediments affected
by hydrothermal solutions (Michard et al., 1983; German et al.,
1993; Siby et al., 2008); intense diagenesis (Murray et al., 1991b;
MacRae et al., 1992) or variations in plagioclase content (Nath
et al., 1992). Positive Eu anomalies are not common in seawater,
which resulted due to hydrothermal discharges along mid-ocean
ridges (Klinkhammer et al., 1983, 1994). Positive Eu anomalies have
been well documented for hydrothermal vent fluids and sediment
particulates in active ridge system (Michard et al., 1983; German
et al., 1990, 1999; Douville et al., 1999). Hydrothermal solutions
mainly originate in the deep marine environments but such an
origin is unlikely for the limestones of the Mural Formation which
were deposited in shallow marine environments (Lawton et al.,
2004; González-León et al., 2008).
Y/Ho
Positive Eu anomalies have been reported from Amazon fan
muds in which Eu2þ is precipitated from pore waters during
diagenesis (MacRae et al., 1992). Unlike Ce which can undergo
oxidation state changes in ambient seawater conditions, redox
transformations from Eu3þ to Eu2þ require low oxidation-reduction
potentials (pH 2e4) and high temperatures (>200 C) (Sverjensky,
1984; Bau, 1991). These conditions are generally absent in shallow
marine environments. Petrographic and geochemical studies,
suggest that the studied limestones were not subjected to intense
diagenesis. The positive correlation between Eu and the immobile
elements such as Y, Th and Zr (statistically significant at a strict
significance level of 0.001; linear correlation coefficient r ¼ 0.69;
0.74; 0.53; respectively) supports the nondiagenetic influence on
this element. The inclusion of small amount of feldspars may lead
to positive Eu anomalies in the bulk sediments (Murray et al.,
1991b). In the present study, Eu contents show significant positive correlation with Al2O3 which suggest the detrital origin of this
element. Hence, the observed variations in Eu anomalies in the
limestones of the Mural Formation may be due to the presence of
feldspar content rather than hydrothermal events and diagenesis.
408
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
Seawater/PAAS x 10-6
10
1
NPSW
Coral Sea
South Fiji basin
Bay of Bengal
Andaman Sea
0.1
0.01
La
Ce
Pr
Nd Sm Eu
Gd
Tb
Dy
Y
Ho
Er
Tm Yb
Lu
Elements
Fig. 5. PAAS normalized REE patterns of modern seawaters (NPSW: North Pacific
shallow water, Sagami trough (Alibio and Nozaki, 1999), Coral Sea: Coral sea (South
Pacific shallow seawater, Zhang and Nozaki, 1996), South Fiji Basin: South Fiji Basin e
Station SA12 (Zhang and Nozaki, 1996), Bay of Bengal: Bay of Bengal shallow water
(Nozaki and Alibio, 2003) and Andaman Sea: Andaman Sea shallow water (Nozaki and
Alibio, 2003).
This interpretation is further supported by the enrichment of Sr in
these limestone samples.
5.3. Source of REE
Fig. 4. a, S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs Sc show significant
positive correlation with correlation coefficient of 0.85. b, plot of the S(SiO2 þ Al2O3
þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs Th content provides positive correlation with
coefficient of 0.72. c, S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs La plot
exhibits positive correlation (correlation coefficient of 0.70). d, plot of the
S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs Ce content gives positive
correlation with a correlation coefficient of 0.67.
REE data have been used extensively to assess the pathways of
biogenic and terrigenous fluxes from the source to the marine
sediments (Piper, 1974; Murray and Leinen, 1993; Sholkovitz et al.,
1994; Wray, 1995; Cullers, 1995). The concentration of REEs in
seawater is mainly controlled by factors relating to input sources
and scavenging processes related to depth, salinity, and oxygen
levels (Elderfield, 1988; Piepgras and Jacobsen, 1992; Bertram and
Elderfield, 1993; Greaves et al., 1999).
The limestones of the Mural Formation exhibit distinctly nonseawater-like patterns (Fig. 6aef) which resulted from the presence
of a variety of contaminants. The major source of contaminants are
likely: 1) terrigenous fine-grained sediments having high REE
content with non-seawater-like pattern (Elderfield et al., 1990), 2)
Fe and Mn oxides (Bau et al., 1996) and 3) phosphates having a high
affinity for REEs in diagenetic fluids (Byrne et al., 1996).
The concentration of Al2O3 is closely related to clay content. So,
Al2O3 concentration is considered as a proxy for shale contamination (Nothdurft et al., 2004). Most of the limestones from the Mural
Formation show high values for Al2O3 (0.44 to 6.26%; except five
samples which show low concentration) when compared to the
average values of siliciclastic-contaminated carbonate rocks (0.42%;
Veizer, 1983). The Al2O3 concentration shows positive correlation
P
with the REE content (statistically significant at a strict significance level of 0.001; linear correlation coefficient r ¼ 0.59, n ¼ 35)
which suggest a moderate contamination.
Trace elements such as Th and Sc have been used as indicators of
shale contamination because of their higher concentrations in the
PAAS than in marine carbonates (Webb and Kamber, 2000). The Th
and Sc concentrations correlate well with Al2O3 contents (statistically
significant at a strict significance level of 0.001; linear correlation
coefficient r ¼ 0.81, r ¼ 0.90; respectively) which suggest the presence of shale contamination in the limestones of the Mural Formation.
Many modern carbonates (particularly foraminifera) were
contaminated by ferromanganese crusts (Palmer, 1985), which
show a high affinity for the REEs, and the crusts incorporate them
disproportionately (Bau et al., 1996). The limestones of the present
P
study show a positive correlation between the
REE and Fe
contents (statistically significant at a strict significance level of
1
0.1
CP1
SSJ2
CP3
SSJ3
CP4
d
1
Sample/PAAS
a
Sample/PAAS
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
0.1
409
SSJ9
La
Ce
Pr
Nd Sm Eu Gd Tb Dy
Y
Ho
La
Er Tm Yb Lu
Ce
Pr
Nd Sm Eu Gd Tb Dy
CP9
SSJ4
CP10
SSJ5
1
e
10
Sample/PAAS
Sample/PAAS
10
CP6
CP12
1
La
CP33
SSJ16
Ce
Pr
Nd Sm Eu Gd Tb Dy
Y
Ho
CP36
SSJ18
CP38
SSJ21
CP41
SSJ23
CP43
SSJ25
0.01
La
Er Tm Yb Lu
Ce
Pr
f
CP15
CP18
CP22
CP24
CP26
CP28
SSJ6
SSJ7
0.01
La
Ce
Pr
Nd Sm Eu Gd Tb Dy
Nd Sm Eu Gd Tb Dy
Y
Ho
Er Tm Yb Lu
Elements
Sample/PAAS
Sample/PAAS
Er Tm Yb Lu
0.1
Elements
0.1
Ho
0.001
0.1
1
Y
Elements
Elements
c
SSJ11
0.01
0.01
b
SSJ10
Y
Ho
Er Tm Yb Lu
Elements
1
CP45
CP47
SSJ27
0.1
0.01
La
Ce
Pr
Nd Sm Eu Gd Tb Dy
Y
Ho
Er Tm Yb Lu
Elements
Fig. 6. a, REE patterns of limestones of the CLC Member. b, PAAS normalised REE patterns of the TS Member. c, REE patterns of the LC Member. d, REE patterns of limestones of the
CLP Member. e, REE patterns of limestones of the CLE Member. f, PAAS normalized REE patterns of limestones of the MQ Member.
0.001; linear correlation coefficient r ¼ 0.70). The average Fe2O3
concentrations (0.27%, n ¼ 35) of the present study is within the
range of average carbonate (0.38%, Veizer, 1983) which suggest that
the diagenetic Fe2O3 does not play a significant role in controlling
the REE patterns in these limestones.
Phosphates mainly incorporate REE disproportionally and they
are altered easily by diagenesis (Reynard et al., 1999). The limestones of the present study show a positive correlation between
P
REE and P2O5 (statistically significant at a strict significance level
of 0.001; linear correlation coefficient r ¼ 0.74). A poor correlation
has been observed between P and NdN/YbN ratios (statistically
significant at a strict significance level of 0.01; linear correlation
coefficient r ¼ 0.42) in the limestones of the Mural Formation.
Hence it is unlikely that the presence of minor quantity of P2O5
could affect the REE patterns of limestones of the Mural Formation.
Thus, our data suggest that contamination by phosphate minerals
or ferromanganese coatings is not likely.
Yttrium is not removed from the seawater effectively when
compared with its geological twin Ho, due to differing surface
complex stabilities, thereby leading to a significant superchondritic
marine Y/Ho ratio (Hogdahl et al., 1968; Zhang et al., 1994; Bau et al.,
1995; Bau, 1996; Nozaki et al., 1997). The chemical sediments free
from contamination generally display Y/Ho ratios between 44 and 74.
But contaminations due to terrestrial detritus and volcanic ash have
fairly constant chondritic Y/Ho values of w28. The limestones of the
Mural Formation contain large variations in Y/Ho ratio (27.34 to
102.50). Like the Y/Ho ratio, Th and Sc also show significant variations
among different members of the Mural Formation. Such variations in
these limestones may be due to contamination by terrestrial detritus
(Webb and Kamber, 2000). In the present study, most of the limestones of the Mural Formation show high values of Th, Sc and Zr and
chondritic Y/Ho ratios, which suggests that these limestones appear
to have been contaminated by terrigenous materials.
The different members of the Mural Formation show slight
variations in LaN/YbN ratios (Table 4). The LaN/YbN ratios of the CLC,
TS and MQ members are more or less similar to the values proposed
by Condie (1991; about 1.0) and Sholkovitz (1990; about 1.3) for
terrigenous materials whereas the LC, CLP and CLE members show
lower LaN/YbN ratios. The observed variations in the LaN/YbN ratios
in the limestones of the Mural Formation suggest that the REE
signals were mainly influenced by the incorporation of terrigenous
materials into them. The LaN/YbN ratios of the Mural Formation are
more or less similar to the Arabian Sea carbonate sediments (Nath
et al., 1997) and Indian Ocean carbonate sediments (Nath et al.,
1992) and lower than the shallow marine Albian and Maastrichtian limestones (Madhavaraju and Lee, 2009; Madhavaraju and
Ramasamy, 1999; Table 4) of the Cauvery Basin and Kudankulam
Formation (Armstrong-Altrin et al., 2003) of South India (Table 4).
The limestones from the Mural Formation show non-seawaterlike patterns. The representative samples of the present study were
compared with the limestones having non-seawater-like patterns
(Fig. 7; Late Devonian coastal fringing reef, Nothdurft et al., 2004;
Albian limestone, Madhavaraju and Lee, 2009; Maastrichtian
limestone, Madhavaraju and Ramasamy, 1999; Miocene limestone,
Armstrong-Altrin et al., 2003) which suggests that the inclusions of
terrigenous materials in the carbonates as contaminants will mask
410
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
Sample/PAAS
0.56
1.03
e
36.6
e
0.84 0.1
0.8 0.2
78 40
29 12
1.15 0.1
0.1
Y
Ho Er Tm Yb Lu
0.91 0.13
1.0 0.45
35 28
49 6
1.16 0.34
0.97 0.13
1.91 0.22
39 25
48 6
1.2 0.08
0.76 0.2
1.8 0.5
73 20
42 8
0.58 0.1
Fig. 7. Representative samples of the Mural Formation with non-seawater-like signatures are compared with limestones exhibit LREE enriched REE þ Y pattern (DCFR: Late
Devonian coastal fringing reef (Nothdurft et al., 2004), AL: Albian limestone
(Madhavaraju and Lee, 2009), MAL: Maastrichtian limestone (Madhavaraju and
Ramasamy, 1999) and ML: Miocene limestone (Kudankulam Formation, ArmstrongAltrin et al., 2003).
0.78 0.22
1.32 0.13
28 7
51 2
1.6 0.9
l
k
i
j
h
f
g
e
c
d
Present study, n ¼ 5.
Present study, n ¼ 6.
Present study, n ¼ 8.
Present study, n ¼ 3.
Present study, n ¼ 10.
Present study, n ¼ 3.
Present study, n ¼ 35.
Madhavaraju and Lee, 2009, n ¼ 8.
Madhavaraju and Ramasamy, 1999, n ¼ 8.
Armstrong-Altrin et al., 2003, n ¼ 9.
Nath et al., 1997, n ¼ 9.
Nath et al., 1992, n ¼ 4.
a
b
MQ
CP10
SSJ6
ML
Elements
0.93 0.12
0.74 0.12
23 19
51 5
1.0 0.24
CLE
CP9
SSJ3
MAL
1
La Ce Pr Nd Sm Eu Gd Tb Dy
0.80 0.03
0.89 0.08
12 1
52 0.5
1.12 0.03
CLP
CP4
SSJ2
DCFR
0.01
0.90 0.12
0.90 0.35
33 34
51 6
1.17 0.22
LC
TS
0.96 0.14
1.35 0.80
62 28
46 2
1.3 0.29
0.93 0.12
1.12 0.40
51 23
43 10
1.1 0.14
Ce/Ce*
LaN/YbN
SREE
CaO
Eu/Eu*
CLC
CP1
CP33
AL
0.9 0.1
2.7 1.4
80 40
49 3
0.78 0.3
Indian Ocean
carbonate
sedimentsl
Arabian Sea
carbonate
sedimentsk
Kudankulam
Formationj
Maastrichtian
limestonei
Albian
limestoneh
Mural
Formationg
(average)
f
e
d
c
b
a
Mural Formationaef
Table 4
Average geochemical values of the Mural Formation compared to shallow and deep marine sediments.
10
the seawater signature due to their high concentration of the REE.
The high content of Al2O3 and SREE, the elevated concentrations of
Th and Sc, chondritic Y/Ho ratios, high LaN/YbN ratios and nonseawater-like REE patterns indicate that the terrigenous contaminations in the limestones of the Mural Formation are responsible
for such variations in REE signals.
The preservation of seawater REEþY pattern in limestone will
only occur if detrital materials, marine or diagenetic authigenic
phosphates (eg. Rasmussen et al., 1998) and ferromanganese
encrustations (eg. Reitner, 1993) are nearly absent from the limestones. The inclusions of terrigenous materials in the carbonates as
contaminants will mask the seawater signature due to their high
concentration of REE in them. So, the depositional environment of
limestone is more important to understand the REE geochemistry.
In the present study, the limestone samples from LC Member (at CP
section) and CLP and CLE members (at SSJ section) were deposited
in an open shelf environment with little terrigneous contamination
whereas the limestones from CLE (at CP section) and LC (at SSJ
section) members contain high concentrations of terrigenous
materials, respectively due to fluvial deltaic influence and deltafront depositional environments (González-León et al., 2008). Thus,
the limestones deposited under both coastal and open shelf environments exhibit non-seawater-like REE þ Y patterns.
The present study reveals that the limestones deposited in open
shelf environments are also contaminated by some terrigenous
particles. Hence, care may be taken to study the REE geochemistry
of ancient limestone. The limestones devoid of terrigenous particles
are suitable for understanding the REE patterns of ancient shallow
seawater and also they serve as a valuable seawater proxy. The
presence of a small quantity of terrigenous materials in the limestones will also reveal source rock information.
The concentrations of certain immobile elements like La and Th
are higher in silicic than in basic igneous rocks (Cullers, 1995). The
felsic and mafic rocks show significant variations in La/Sc, La/Co, Th/
Sc, Th/Co and Th/Cr ratios which are most useful in understanding
the provenance composition (Wronkiewicz and Condie, 1990; Cox
et al., 1995; Cullers, 1995). The extent to which these elemental
ratios that are useful in unraveling the provenance of terrigenous
materials present in the carbonate rock is clearly addressed by
Cullers (2002). In the present study, La/Sc, La/Co, Th/Co, Th/Cr, Cr/
Th, and Th/Sc are similar over a range of the
S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) (Fig. 8). Our
results are generally consistent with other studies (Cullers, 2002).
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
411
Fig. 8. Bivariate plots for the limestones of the Mural Formation. a, S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs La/Sc. b, S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2)
vs La/Co. c, S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs Th/Sc. d, S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs Th/Co. e, S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O
þ K2O þ TiO2) vs Th/Cr. f, S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2) vs Eu/Eu*.
Table 5
Range of elemental ratios of the Mural Formation compared to felsic rocks, mafic rocks, Upper Continental Crust (UCC) and Post-Archaean Australian Shale (PAAS).
Range of Mural Formationa
Eu/Eu*
La/Sc
La/Co
Th/Sc
Th/Co
Th/Cr
Cr/Th
a
b
c
0.42e2.64
2.65e25.78
0.25e8.66
0.05e2.48
0.03e1.38
0.02e0.36
2.76e45.0
Range of sedimentsb
Felsic rocks
Mafic rocks
0.40e0.94
2.50e16.3
1.80e13.8
0.84e20.5
0.67e19.4
0.13e2.7
4.00e15.0
0.71e0.95
0.43e0.86
0.14e0.38
0.05e0.22
0.04e1.40
0.018e0.046
25e500
Upper Continental Crustc
Post-Archaean Australian
average shalec
0.63
2.21
1.76
0.79
0.63
0.13
7.76
0.66
2.40
1.65
0.90
0.63
0.13
7.53
Present study, n ¼ 35.
Cullers (1994, 2000); Cullers and Podkovyrov (2000); Cullers et al. (1988).
Taylor and McLennan (1985).
The La/Sc, La/Co, Th/Co, Th/Cr, Cr/Th, and Th/Sc ratios of the limestones of the Mural Formation have been compared with felsic and
mafic rocks (fine fraction) as well as to upper continental crust
(UCC) and PAAS values (Table 5) which suggest that these ratios are
within the range of intermediate to felsic rocks.
6. Conclusions
The high content of Al2O3, SREE, Th and Sc, low Y/Ho ratios, high
LaN/YbN ratios and non-seawater-like REE patterns in the
limestones of the Mural Formation indicate that the terrigenous
contaminations is responsible for the variations in REE signals. The
limestones of the Mural Formation were compared with the limestones having non-seawater-like patterns that indicate the inclusion of terrigenous materials in the carbonates, as contaminants
will mask the seawater signature due to their high concentration of
the REE in them. The limestone samples from CLP member show
negative Ce anomalies (Ce/Ce*: 0.77 to 0.83, ave. 0.80 0.03, n ¼ 3)
whereas CLC, TS, LC, CLE and MQ members show both negative and
positive Ce anomalies (Ce/Ce*: 0.78 to 1.04, ave. 0.93 0.12, n ¼ 5;
412
J. Madhavaraju et al. / Cretaceous Research 31 (2010) 400e414
0.82 to 1.20, ave. 0.96 0.14, n ¼ 6; 0.67 to 1.05, ave. 0.90 0.12,
n ¼ 8; 0.73 to 1.07, ave. 0.93 0.12, n ¼ 10; 0.56 to 1.00, ave.
0.78 0.22, n ¼ 3; respectively). The observed variations in Ce
anomalies resulted from the inclusion of terrigenous materials as
well as Fe-rich colloids from rivers. The limestones of the Mural
Formation contain both negative and positive Eu anomalies relative
to the PAAS. The CLP member shows least variations in Eu anomalies (Eu/Eu*: 1.10 to 1.15, ave. 1.12 0.03, n ¼ 3) whereas CLC, TS,
LC, CLE and MQ members exhibit large variations in Eu anomalies
(Eu/Eu*: 0.94 to 1.28, ave. 1.10 0.14, n ¼ 5; 0.89 to 1.67, ave.
1.30 0.29, n ¼ 6; 0.83 to 1.44, ave. 1.17 0.22, n ¼ 8; 0.42 to 1.26,
ave. 1.0 0.24, n ¼ 10; 0.91 to 2.64, ave. 1.6 0.9, n ¼ 3; respectively). The observed positive Eu anomalies in the limestones are
likely controlled by the feldspar content.
The elemental ratios (La/Sc, La/Co, Th/Co, Th/Cr, Cr/Th, and Th/Sc)
which are characteristics of provenance of terrigenous materials
show the minimal variations with the changing percentage of the
S(SiO2 þ Al2O3 þ Fe2O3 þ MgO þ Na2O þ K2O þ TiO2). The La/Sc, La/
Co, Th/Co, Th/Cr, Cr/Th, and Th/Sc ratios of the limestones of the Mural
Formation have been compared with felsic and mafic rocks, upper
continental crust (UCC) and PAAS values which indicate that the
terrigenous materials included in the limestones of the Mural
Formations were mainly derived from the intermediate to felsic rocks.
Acknowledgements
The first author would like to thank Dr. Thierry Calmus, ERNO,
Instituto de Geología, Universidad Nacional Autónoma de Mexico
for his support and encouragement during this work. We would
like to thank Prof. S.P. Verma and Prof. R.L. Cullers for their critical
reviews and constructive comments. We would like to thank Dr.
Hannes Löser for his help during the field work. We acknowledge
the support rendered by Universidad Nacional Autónoma de
Mexico through PAPIIT Project No.IN121506-3. The field study of
this work is partly supported by PAPIIT Project No. IN107803-3. We
thank Mr. Pablo Peñaflor for powdering of limestone samples for
geochemical studies. We also thank Dr. Teresa Pi I Puig, Instituto de
Geología, Universidad Nacional Autónoma de México, México for
her help in XRD analysis. This research was partly supported by
Korea Science and Engineering Foundation (KOSEF) grants (R012000-000-00056-0 to YIL).
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