Chinese Science Bulletin
© 2008
SCIENCE IN CHINA PRESS
Springer
Geochemical environmental changes and dinosaur
extinction during the Cretaceous-Paleogene (K/T)
transition in the Nanxiong Basin, South China:
Evidence from dinosaur eggshells
ZHAO ZiKui1†, MAO XueYing2, CHAI ZhiFang2, YANG GaoChuang2, ZHANG FuCheng1 & YAN Zheng3
1
Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese
Academy of Sciences, Beijing 100044, China;
2
Institute of High Energy Physics and Laboratory of Nuclear Analytical Techniques, Chinese Academy of Sciences, Beijing 100080,
China;
3
Institute of Geology, State Seismological Bureau, Beijing 100029, China
The complex patterns of trace elements including Ir and isotope distributions in the three K/T sections
of the Nanxiong Basin prove the existence of two environmental events in the latest Cretaceous and
earliest Paleocene. The first geochemical environmental event occurred at about 2 Ma prior to the K/T
boundary interval, where the dinosaur diversity was hardly reduced, except that a number of pathological eggshells appeared. The second one was larger and occurred just at and near the Cretaceous-Paleogene (K/T) boundary. The extinction of the dinosaurs spread out within 250 ka with major
extinction beginning at the boundary interval. This is even later than their extinction in Montana, North
America and in India. The cause of the dinosaur extinction may be the result of a complex multiple
events brought about by the coincidence of global environment change marked by multiple Ir and δ 18O
anomalies, and environmental poisoning characterized by other trace elements derived from the local
source. Successive short- and long-term conditions of geochemically induced environmental stress
negatively affected the reproductive process and thus contributed to the extinction of the dinosaurs.
Nanxiong Basin of Guangdong Province, Cretaceous-Paleogene (K/T) boundary, Ir anomaly, trace element, stable isotope, dinosaur
eggshell, dinosaur extinction
One of the most striking events in the Mesozoic era was
the almost complete extinction of the dinosaurs at the end
of the Cretaceous. The observation of a widespread Ir
―
anomaly at the K/T boundary led by Alvarez et al.[1 3] to
propose that the extinction event at the boundary results
from the impact of an extraterrestrial body on earth.
However, it is difficult to find strong support for this hypothesis, because of the paucity of suitable stratigraphic
sections and the comparative scarcity of fossil material.
Virtually all the evidence or debates that have been drawn
about the final dinosaur extinction derive from a few sec―
tions in the North American Western Interior[4 9].
The “red beds” in the Nanxiong Basin of Guangdong
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Province are a relatively continuous sequence containing
a record of dinosaur egg fauna spanning the K/T boundary and Paleocene mammals, and seem to provide some
direct evidence for interpreting the dinosaur extinction.
―
Previously published data[10 16] from the CGY-CGD and
CGT-CGF sections (Figure 1) showed that the geochemical environmental changes and the dinosaur extinction in South China may have been a rather longReceived February 20, 2008; accepted October 30, 2008;
published online December 14, 2008
doi: 10.1007/s11434-008-0565-1
†
Corresponding author (email: [email protected])
Supported by National Natural Science Foundation of China (Grant No. 40472018)
and the Chinese Academy of Sciences (Grant No. 21039751)
Chinese Science Bulletin | March 2009 | vol. 54 | no. 5 | 806-815
Figure 1 Locations of the studied K/T boundary sections in the
Nanxiong Basin.
To obtain a better idea on how the cause and timing of
the dinosaur extinction took place, we have investigated
trace elements including Ir, stable isotope composition,
and eggshell structures in a series of dinosaur eggshells
from the third K/T section (the CGN section) in this basin.
The purpose of the present paper is to establish the
environmental change pattern across the K/T boundary
and the geochemical environmental stress played a role
in dinosaur extinction, based on the geochemical signals
(e.g. trace elements including Ir, stable carbon- and
oxygen-isotope composition), histo-structures of dinosaur eggshells with other data regarding stratigraphy
taken from the above-mentioned three sections (CGYCGD, CGT-CGF and CGN sections).
1 Element and isotope distribution in
dinosaur eggshells from the CGN Section
The CGN Section is situated south of the Nanxiong
county town (Figure 1). Lithologically, the section is
essentially similar to both the CGY-CGD Section and
the CGT-CGF Section. However, the Pingling Formation
here attains a thickness of about 270 m, and its uppermost part and the overlying strata, the Shanghu Formation, are not exposed because of the town buildings in
this area.
According to the field observation, complete eggs in
nest and eggshell fragments are more frequent and
widespread in the sedimentary sequence of the Pingling
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Formation, from which about 10 clutches of eggs have
been collected by the local museums (the Nanxiong
Museum and the Shaoguan Museum) and the Shanghai
Museum of Natural History from 1972 to 1994. The
complete clutches preserved in situ show no evidence of
transport. Excellent preservation of the clutch geometry
indicates that the egg laying and sediment formation
were nearly synchronous. Many eggshell fragments
were found in heaps in this section, and may represent
clutches destroyed in situ or nearby. It suggests that the
sediments with abundant eggshell fragments were
clearly not reworked. Because palynomorphs were
scarcer than expected, the exact location of the K/T
boundary interval has not yet been determined in this
section[15], but it should be present at CGN 220―240 m,
as discussed later.
Fifteen eggshell samples, belonging to Macroolithus
yaotunensis, collected at 15 levels from this section by
the Sino-German team in 1984[10,15] have been analyzed
by radiochemical neutron activation analysis (RNAA)
for their iridium concentration, and by instrumental neutron activation analysis (INAA) for other trace elements;
besides, another 15 eggshell samples collected at the
same levels of this section were used for stable-isotope
analysis. The eggshell samples for the chemical analysis
have been examined using a light microscope and/or
SEM, and display a well-preserved microstructure with
primary calcite growth and little or no recrystallization.
The eggshell samples were then abraded on the outer
and inner surfaces in order to remove any contamination
by the surrounding sediments.
Theoretically, Ir is nonexistent in eggshell and/or
bone because this element is not vital to life. Eggshell
samples of living ostrich (Struthio camelus) from Beijing Zoo, wild Chinese alligator (Alligator sinensis)
from Anhui Province, and chickens (Gallus gallus)
showed no detectable Ir with limits of <6―<10 ppt[12,17].
The results of Ir abundances and the stable carbonand oxygen-isotope composition in the eggshell samples
from the CGN Section are given in Table 1. Four
Ir-bearing levels have been identified. The highest Ir
abundance occurs in eggshell sample CGN 912 from
215.5 m in the CGN Section, and reaches 236.8 ppt
(normalized to Ca) over a background level of <10 ppt.
The three other Ir peaks (of 42.7 ppt, 53.3 ppt and 179.7
ppt) were detected in the eggshell samples CGN 909,
CGN 903 and CGN 901 from 202―203 m, 85.5 m and
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duration process rather than an instantaneous event that
only lasted a few years or centuries as is often portrayed
in the asteroid hypothesis.
Table 1 Iridium concentration and stable-isotope composition in the dinosaur eggshell samples of Macroolithus yaotunensis from the CGN
Section of the Pingling Formation
Ir concentration normalized to
Ca (ppt, 10−12g/g)
Sample number
Depth (m)
Ir concentration
(ppt, 10−12g/g)
CGN 915
235―235.5
29.7
39.5
28.0
39.6
27.6
Ca (%)
CGN 914
231.5―232
29.4
CGN 913
223.5―225
<16.3
CGN 912
215.5
268
42.1
<18.5
41.4
CGN 911
213.5
CGN 910
208
CGN 909
202―203
CGN 908
198―199.5
CGN 907
186
CGN 906
176.5
CGN 905
110―112
CGN 904
104.5―106
−10.93
+5.50
−10.27
−3.29
−10.18
−3.85
−10.85
+0.36
−10.09
−1.63
−9.62
+1.45
8.1
48.4
42.2
42.7
−9.90
−2.19
23
42.8
20.0
−12.01
−6.75
25.1
40.5
23.1
−11.13
−2.31
26.5
40
24.6
−10.55
−3.26
29.3
42.5
25.6
−10.77
−2.20
<11.6
41.9
85.5
60.6
42.3
CGN 902
76.5
<20.9
41.8
CGN 901
44
185
38.3
44 m of the section, respectively. The distribution of
some other trace elements (As, Br, K, La, Na, Au, U, Yb,
Fe, Co, Sc and Sr) shows (Figure 2(c)) that most of them
are distinctly the most abundant in eggshell sample
CGN 913 from 223.5―225 m of the same section, excepting Au, U and Fe whose maximum levels occur in
the eggshell sample CGN 901 from 44 m.
The stable-isotope values (Table 1) of the eggshell
samples belonging to Macroolithus yaotunensis from the
CGN Section range for δ 13C from −12.01‰ to −9.09‰
(PDB), and for δ 18O from −6.75‰ to +5.50‰ (PDB),
respectively. The values of δ 13C oscillate within a narrow range of about 3‰. The values of δ 18O, by contrast,
have a range of about 12‰, and is characterized by multiple positive δ 18O perturbations within the CGN Section interval of 208―235.5 m, except for the δ 18O value
of +1.11‰ for sample CGN 902 from 76.5 m. The three
eggshell samples (CGN 910, CGN 912 and CGN 915)
from 208 m, 215.5 m and 235―235.5 m have δ 18O
values of +1.45‰, +0.36‰ and +5.50‰, respectively.
This shows that the oxygen-isotope record in the CGN
Section is comparable to that of the two other sections
(CGY-CGD and CGT-CGF)[13].
2 Pathologic dinosaur eggshells from
the CGN Section
Dinosaur eggs and eggshell fragments collected at the
CGN Section are represented by eight distinct eggshell
808
236.8
δ 18O (‰, PDB)
41.4
CGN 903
8.91
9.25
δ 13C (‰, PDB)
−10.46
−3.36
53.3
−9.54
−4.54
−9.09
+1.11
179.7
−9.23
−0.97
oospecies: Macroolithus yaotunensis, Macroolithus rugustus, Elongatoolithus andrewsi, Elongatoolithus elongatus, Elongatoolithus oosp., Apheloolithus shuinanensis, Nanshiungoolithus chuetienensis and Shixingoolithus
erbeni.
Normal eggshells of different oospecies have each
structural pattern and a normal range of shell thickness.
According to Zhao et al.[14], in the CGH Section of the
Yuanpu Formation the eggshell thickness of
Macroolithus yaotunensis range between 1.70 and 2.52
mm, those of Macroolithus rugustus between 1.66 and
2.38 mm, those of Elongatoolithus andrewsi between
1.36 and 1.58 mm, and Elongatoolithus elongatus between 0.9 and 1.26 mm. Obviously, each oospecies has a
small variation in eggshell thickness. The average values
of eggshell thickness in each oospecies at various levels
show almost no change, and represent the normal range
of predominating variation (see Figure 6(a) published in
Zhao et al.[14]).
Measurements of the eggshell thicknesses involve
1758 eggshell fragments of the above-mentioned four
oospecies from the CGN Section. The eggshell thickness
of Macroolithus yaotunensis ranges from 0.9 to 2.36 mm,
that of Macroolithus rugustus from 0.92 to1.96 mm, that
of Elongatoolithus andrewsi from 0.6 to 1.52 mm, and
that of Elongatoolithus elongatus from 0.6 to 1.16 mm,
indicating an abnormal variation in eggshell thickness.
The mean values of eggshell thickness of each oospecies
from successive horizons of this section vary distinctly
(Figure 3), and are similar to those from the CGY-CGD
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Figure 2 Variations in the trace-element concentration in the dinosaur eggshells from the studied K/T sections in the Nanxiong Basin. (a)
CGY-CGD Section; (b) CGT-CGF Section; (c) CGN Section.
and CGT-CGF sections (see Figure 6(b), (c) published in
Zhao et al.[14]).
Figure 4(a) shows the healthy eggshell with a well-
defined cone layer and a columnar layer in Macroolithus
yaotunensis.
An examination of the eggshells with the polarizing
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spaces in the columnar layer of the eggshell (Figure 4(b),
(c), (d)). By random analysis of Macroolithus yaotunensis from this section, the frequency of histopathological
eggshells of this oospecies was found to be a confidence
interval of 17% to 53% in the levels of 44 to 106 m, and
12% to 46% in those from 110 to 199 m. In the levels of
202 to 235 m (i.e. at the K/T boundary interval, as discussed later), the frequency increases to 50% to 85%
(Table 2). This is one more proof that anomalous concentrations of trace elements including Ir are associated
with the formation of pathological eggshells[10,11,14,18].
The enrichment of Ir and other trace elements in the
eggshells may have been caused by the assimilation of
these elements into the dinosaur body through food
(mechanisms discussed in Zhao[18]; Zhao et al.[10,14];
Yang et al.[17]).
Figure 3 Variations in the average values of eggshell thickness of
the four oospecies from the successive horizons in the CGN Section.
○ Elongatoolithus elongatus; ● Elongatoolithus andrewsi; □
Macroolithus rugustus; ■ Macroolithus yaotunensis.
light microscope and the scanning electron microscope
shows that many of them have various histopathological
patterns such as a bi- or multi-layered cone and disorderly arranged crystallines, and irregular or dendritic
Table 2 Frequency of pathological eggshells in Macroolithus yaotunensis from successive horizons in the CGN Section
Sampling
interval (m)
CGN 235―
Number of
eggshell
samples
−
Number of
pathologic
eggshells
−
Frequency: confidence interval
(%)
−
CGN 202―235
30
21
50―85
CGN 110―199
30
8
12―46
CGN 44―106
30
10
17―53
Figure 4 Radial section of healthy and pathologic eggshells from the CGN Section. (a) Healthy eggshell of the Macroolithus yaotunensis (CGN
908). Note a well-defined cone layer and a columnar layer, an undulating demarcation between both the layers, thin outer secondary deposit
(arrow). (b) Pathologic eggshell of the Macroolithus yaotunensis, (CGN 912). Note multi-layered cone (MC) and disorderly arranged crystallines
(DC) in the lower part of the columnar layer, outer secondary deposit (arrow). (c) Pathologic eggshell of the Macroolithus yaotunensis, (CGN 903).
A secondary cone layer or a multi-layered cone is formed between the original cone layer and the columnar layer (arrows). (d) Pathologic eggshell
of the Elongatoolithus andrewsi, (CGN 913). Note irregular or dendritic spaces in the upper part of the columnar layer (arrows).
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3.1 Position of the Cretaceous-Paleogene (K/T) boundary interval at the CGN Section
The distribution of Ir and some other trace elements in
the three studied K/T sections (e. g. CGY-CGD, CGTCGF and CGN sections) is shown in Figure 2. It is clear
that the distribution pattern of the various trace elements
including Ir is, in general, similar in each succession.
The CGY-CGD Section has relatively continuous sequence from the Late Cretaceous to early Paleocene and
has been exposed very well. The section has been studied in detail by biostratigraphy, magnetostratigraphy,
sedimentology and geochemistry, and presently serves
as a reference section for the K/T boundary[10,15]. Based
on a palynofloral study[15,16], the K/T chronostratigraphic
boundary is placed in the upper part of the Pingling
Formation, which occurs in a stratigraphic interval of
approximately 20 m (CGD 57―78 m). This corresponds
to a time span of about 50 ka, assuming a sedimentation
rate of 40 cm/ka.
It is very interesting that six levels of Ir enhancement
have been identified[14] in the CGY-CGD Section (Figure 2(a)); the two highest peaks (118 ppt in CGD 111
and 117.6 ppt in CGD 109) occur exactly within the palynological K/T boundary interval (CGD 111) and at 2―
5 m (CGD 109) below the boundary interval, respectively. It is worth noting that most other trace elements,
such as Ni, Co, Pb, Cu and Mn, all reach a maximum
level (CGD 110) at the base of the palynological boundary interval, which is just sandwiched between both Ir
peaks (CGD 111 and CGD 109) mentioned above (Figure 2(a)). The distinct geochemical anomalies found in
the palynological K/T boundary interval are seen as conformable to the international K/T boundary standards.
Therefore, this section can be used as a reference for the
interpretation and comparison of data from other K/T
boundary sections in the Nanxiong Basin.
A comparison of the concentrations of trace elements
including Ir measured in the CGN Section (Figure 2(c))
with the other two sections (the CGY-CGD Section and
the CGT-CGF Section) shows that the level (CGN 913)
from 223.5―225 m with the anomalous abundances of
some other trace elements and the underlying level with
an Ir anomaly (236.8 ppt in CGN 912) at 215.5 m in the
CGN Section correspond with the level (CGD 110) at
the base of the palynological boundary interval and with
3.2 Geochemical environment during the Cretaceous-Paleogene (K/T) transition
Eggshell formation is a relatively fast process (19―21 h
for most birds)[20,21]. Generally, the eggshell chemistry
reflects the animal’s diet (and hence the characteristics
of their living environment) over the few days of the
laying period. In feeding experiments of ostrich and
chickens, the changes in the drinking water supply were
fully recorded in the eggshell δ 18O after 10 days[22,23].
Experiments with a flock of domestic hens show that
changes in the supply of a forage containing (NH4)2IrCl6
are fully recorded in the eggshell Ir concentration after
4―6 days, and the accumulation rate of Ir from the feed
in the eggshell is about 0.08%[17], similar to that of REE
(rare earth elements) in mammals[24]. It seems logical,
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the underlying level (CGD 109) in the CGD Section
(Figure 2(a)); these levels correspond also with levels
CGF 402 and CGF 401, respectively, in the CGT-CGF
Section (Figure 2(b)). In addition, the δ 18O record (Table 1) is characterized by three positive perturbations
within the CGN Section interval of 208―235.5 m, and
seems to have coincided with that of the CGY-CGD and
CGT-CGF sections[13]. Based on all the geochemical
data mentioned above, the placement K/T boundary interval of this section consequently probably lies within
the 220―240 m interval.
The eight oospecies were found up to 215.5―235.5
m of CGN (Table 1) in 1984, and no eggshell specimens
were collected in the levels above 235.5 m. However, a
clutch with 16 eggs, belonging to Elongatoolithus oosp.,
collected by the Shanghai Museum of Natural History in
1972, may come from about 240―250 m of CGN. Four
clutches containing a few dozen eggs belonging to
Macroolithus yaotunensis, and a large number of elongatoolithid eggshells as well as a badly preserved oviraptorid skull with lower jaws[19], have been discovered
within a range of about 0.6 km2 by workers at about
250―280 m of CGN during the construction of buildings in the 1980―1990s. The material has been deposited in the local museum (the Nanxiong Museum). This
case indicates that the Paleocene beds with dinosaur
eggs and eggshell fragments were clearly not reworked.
Thus, the dinosaur population represented by the elongatoolithids did overstep the boundary interval and survived into the early Paleocene, as those observed in the
CGY-CGD and CGT-CGF sections[14].
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3 Discussion and conclusion
therefore, that the Ir concentration in the geological environment during the K/T transition time in the Nanxiong Basin would be of the order of 10−7―10−9 g/g,
which is roughly consistent with the Ir value at various
K/T boundaries on earth.
Figures 2 and 5 show that, when the relative abundances of Ir and other trace elements from the three
studied sections are plotted, there are two events marked
by these elemental abundances from the latest Cretaceous into the earliest Paleocene. The earlier geochemical environmental event occurs at 67 Ma in magnetic
chron 31N below the K/T boundary interval, where three
distinct Ir anomalies are identified in the CGY-CGD Section[14], four Ir anomalies in the CGT-CGF Section[14], and
two Ir anomalies in the CGN Section.
The second one occurs just at and near the K/T
boundary interval. The iridium concentrations in the
three sections show maxima with varying strength: 118
ppt in the boundary interval and 117.6 ppt at 2―5 m
below the boundary interval in the CGY-CGD Section,
168 ppt at 2―3 m below the boundary interval in the
CGT-CGF Section, and 236.8 ppt at about 6 m below the
boundary interval in the CGN Section.
In addition, the oxygen-18 records from the CGYCGD and CGT-CGF sections are also characterized by
multiple positive δ18O perturbations occurring just in the
interval of around 50 m at and near the boundary interval, indicating the existence of unusually fluctuating
climatic changes (Figure 5). The various above-mentioned lines of evidence further demonstrate that the
geochemical environmental changes that occurred locally during the K/T transition did not occur instantaneously, but stretched out over a considerable time interval.
It is noteworthy, however, that the maximum concentrations of Ir and most other trace elements were not
produced during the same time span, as they invariably
occur at different levels at and near the boundary interval in each section (Figure 2). The distribution pattern of
these elements shows that Ir and other trace elements
apparently had a different genesis. Possibly, the anomalous concentrations of the other trace elements contained
Figure 5 Ir and oxygen isotope anomalies, magnetochron, and stratigraphic occurrence of oospecies of dinosaur eggshells from the studied
[14]
18
K/T sections in the Nanxiong Basin (Ir abundance data of the CGY-CGD and CGT-CGF sections from Zhao et al. ; δ O from Zhao and
[13]
[10]
Yan . (a) Magnetic chrons ; (b) stratigraphic occurrence of different oospecies (solid bars).
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3.3 Extinction and survivorship of dinosaurs across
the K/T boundary
The Nanxiong dinosaur eggs occur as nests, eggs and
eggshell fragments. Parataxonomically, the eggs have
been classified into 12 oospecies belonging to eight
oogenera and four oofamilies (Elongatoolithidae, Prismatoolithidae, Ovaloolithidae and Megaloolithidae).
Though the available data do not permit to relate a particular type of egg with a particular dinosaur species,
correlation at higher taxonomic levels is possible. The
Elongatoolithidae and Prismatoolithidae are related to
theropods. Based on embryonic remains within eggs
from southern Central Mongolia[25,26] and western Montana (North America)[27,28], the similarity of the eggshell
structure, and the pattern of the egg arrangement in the
nest, the eggs of these two oofamilies can be safely related to the families of the Oviraptoridae[29] and Troodontidae[30], respectively.
The combined record of oospecies from the three
studied sections (right side of Figure 5) shows that the
dinosaur diversity, represented by these oospecies in the
interval corresponding to magnetic chron 31N (67 Ma)
where about three Ir anomalies occurred, was hardly
reduced, except that a number of pathological eggshells
appeared.
The major extinction occurred at the K/T boundary
interval. However, only seven rare oospecies became
extinct exactly at this interval. The remaining five oospecies belonging to elongatoolithids overstepped the
boundary interval and survived into the early Paleocene,
subsequently disappearing one after another over an interval of about 100 m. Only one oospecies, Macroolithus
yaotunensis, is found up to the contact between the
Pingling Formation and the Shanghu Formation. This
corresponds to a time span of 250 ka, assuming a sedimentation rate of 40 cm/ka[15].
In the light of presently available data, this group might
well have disappeared in Montana, North American at the
K/T boundary[8,9], about 3 m below it[5], or even have extended 1.3 m above the K/T boundary[6,7]. Most recently,
Mohabey[31] further investigated dinosaur eggs and eggshells in west India based on an interdisciplinary research
―
by Hansen et al.[32 34], and demonstrated that the last dinosaurs in India disappeared 300 ka before the K/T
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boundary, coevally with the major eruptive period of the
Deccan volcanism (also see below). The results gained in
the Nanxiong Basin, therefore, again indicate that the
disappearance of the dinosaurs in different parts of the
world appears not to be synchronous but to vary in time
from one part to another.
3.4 Cause of the dinosaur extinction
The current data indicate that the mass extinctions at the
K/T boundary are generally attributed to impact or major
flood basalt volcanism (e.g. Deccan Traps) and associated
environmental extremes. With the discovery of the Chic―
xulub crater on the Yucatan Peninsula of Mexico[35 37],
many scientists believe that the impact of a massive asteroid or comet immediately caused the global extinction
of the dinosaurs and many other organisms at the end of
the Cretaceous.
However, no other direct evidence for an asteroid or
comet impact at the K/T boundary has been found thus
far within the Nanxiong Basin sediments[15], except for
the multiple Ir anomalies. Neither shocked quartz grains
nor microtektites have been reported. It is possible,
therefore, that it had no decisive or direct sudden influence on the paleoenvironment and the dinosaur groups
in the Nanxiong Basin in southeastern China.
The Deccan volcanism in India is the largest volcanic
event in the past 245 Ma. The 40Ar/39Ar ages and Re-Os
isotopic data for Deccan basalts indicate that the erup―
tive phase occurred around 67―64 Ma[38 45], and the
major pulse is dated between 65.2 and 65.4 Ma[46]. According to Cox[47], the Deccan traps consists of 100―
500 volcanic events separated by relatively short repose
periods in between.
Recently, Sant et al.[48] have found the concordant
distribution of cristobalite (a silica polymorph of volcanic origin) and Ir peaks during the K/T transition (65
Ma) in the intertrappean beds at Anjar, western India,
and suggested that the Ir anomalies there may be of volcanic source. It has been established that the hotspot
volcano on Reunion Island that produced the Deccan
traps is yet liberating iridium[49].
The geochemical data and the stepwise extinction
pattern gained in the Nanxiong Basin nearly coincide
with the duration of the Deccan volcanism. The occurrence of multiple volcanic events could explain the
complex patterns of element and isotope distributions
found across the K/T boundary interval in the Nanxiong
Basin. However, the Ir and other trace elements in the
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in the eggshells could be introduced from an unknown
source of the locality[10], or other volcanic centers
nearby.
eggshells at and near the K/T boundary apparently had a
different genesis, as mentioned above. The anomalous
concentrations of the other trace elements contained in
the eggshells could be introduced from an unknown
source of the locality, or other volcanic centers nearly.
Reviewing all the data collected by our group, it is
possible that the cause of the dinosaur extinction may be
the result of a complex multiple events brought about by
the coincidence of global environment change marked
by multiple Ir and δ 18O anomalies, and environmental
poisoning characterized by other trace elements derived
from the local source. Successive short- and long-term
conditions of geochemically induced environmental
stress negatively affected the reproductive process and
1
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This geochemical study of dinosaur eggshells reveals
a strong influence of the environment on the elemental
and isotope composition of eggshell and on the formation of pathologic eggshells, and also shows the importance of working within a detailed stratigraphic framework. Fortunately, rather continuous outcrops of the K/T
boundary interval are available for study in several basins of China, and work in progress should help to test
the above scenario.
The authors thank Dr. Gerta Keller (Princeton University), Dr. Desui
Miao (Kansas University), Dr. Monique Vianey-Liaud (Universite de
Montpellier), and Dr. A. J. van Loon (University of Silesiua) for helpful
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