Versão online: http://www.lneg.pt/iedt/unidades/16/paginas/26/30/185
Comunicações Geológicas (2014) 101, Especial III, 1435-1437
IX CNG/2º CoGePLiP, Porto 2014
ISSN: 0873-948X; e-ISSN: 1647-581X
Deccan Volcanism: a main trigger of environmental changes
leading to the K/Pg mass extinction?
O vulcanismo do Deccan: maior responsável pelas mudanças
ambientais que levaram à extinção em massa do K/Pg?
T. Adatte1, A. Fantasia1, B. Samant2, D. Mohabey2, E. Font3, G. Keller4,
H. Khozyem5, B. Gertsch1
.
Artigo Curto
Short Article
© 2014 LNEG – Laboratório Nacional de Geologia e Energia IP
Abstract: Recent studies indicate that the bulk (80%) of Deccan trap
eruptions occurred over a relatively short time interval in magnetic
polarity C29r, whereas multi-proxy studies from central and southeastern India place the Cretaceous-Paleogene (K/Pg) mass extinction
near the end of this main phase of Deccan volcanism suggesting a
cause-and-effect relationship. Beyond India multi-proxy studies also
place the main Deccan phase in the uppermost Maastrichtian C29r
below the K/Pg (planktic foraminiferal zones CF2-CF1), as indicated
by a rapid shift in 187Os/188Os ratios in deep-sea sections from the
Atlantic, Pacific and Indian Oceans, coincident with rapid climate
warming, coeval increase in weathering, a significant decrease in
bulk carbonate indicative of acidification due to volcanic SO2, and
major biotic stress conditions expressed in species dwarfing and
decreased abundance in calcareous microfossils (planktic
foraminifera and nannofossils).
Keywords: Mass extinction, Deccan volcanism.
Resumo: Estudos recentes indicam que a maior parte (80%) das
erupções das Trapas do Deccan ocorreram em um curto intervalo de
tempo, durante o crono 29r, enquanto estudos multidisciplinares
sobre a parte central e sul-leste da India colocam o limite K/Pg e a
extinção em massa correspondente no fim desta fase principal do
Deccan, o que sugere uma relação de causa a efeito. Além da India,
os estudos multidisciplinares colocam a fase principal do Deccan no
fim do Maestrichtiano, no crono 29r, abaixo do limite K/Pg
(correspondente as biozonas dos foraminíferos planctónicos CF1CF2), como sugerido pelos variações rápidas do 187Os/188Os das
series marinhas profundas do Atlântico, Pacífico e Índico,
coincidindo com o rápido aquecimento do clima, aumento da
meteorização, diminuição significativa no volume de carbonato
indicativa de acidificação devido ao SO2 vulcânica, e as principais
condições de stress biótico expressos em espécie de nanismo e
diminuição da abundância em microfósseis calcários (foraminíferos
planctónicos e nanofósseis).
Palavras-chave: Extinção em massa, Vulcanismo do Deccan.
1
ISTE, Lausanne University, 1015 Lausanne, Switzerland.
Department of Geology, Nagpur University, Nagpur 440 001, India.
3
IDL-FCUL, Faculdade de Ciências de Lisboa, Lisboa, Portugal.
4
Department of Geosciences, Princeton University, Princeton NJ 08540, USA.
5
Geology Department, Faculty of Sciences, University of Aswan, Aswan,
Egypt.
*
Corresponding author / Autor correspondente: [email protected]
2
Recent studies indicate that the bulk (80%) of Deccan trap
eruptions occurred over a relatively short time interval in
magnetic polarity C29r, whereas multi-proxy studies from
central and south-eastern India place the CretaceousPaleogene (K/Pg) mass extinction near the end of this
main phase of Deccan volcanism suggesting a cause-andeffect relationship. Beyond India multi-proxy studies also
place the main Deccan phase in the uppermost
Maastrichtian C29r below the K/Pg (planktic foraminiferal
zones CF2-CF1), as indicated by a rapid shift in
187
Os/188Os ratios in deep-sea sections from the Atlantic,
Pacific and Indian Oceans, coincident with rapid climate
warming, coeval increase in weathering, a significant
decrease in bulk carbonate indicative of acidification due
to volcanic SO2, and major biotic stress conditions
expressed in species dwarfing and decreased abundance in
calcareous microfossils (planktic foraminifera and
nannofossils). These observations indicate that Deccan
volcanism played a key role in increasing atmospheric CO2
and SO2 levels that resulted in global warming and
acidified oceans, respectively, increasing biotic stress that
predisposed faunas to eventual extinction at the K/Pg.
The nature and causes of mass extinctions in the
geological past have remained topics of intense scientific
debate for the past three decades. Central to this debate is
the question of whether one, or several large bolide
impacts, the eruption of large igneous provinces (LIP) or a
combination of all them were the primary mechanisms
driving the environmental changes that caused four of the
five major extinction events recorded during the
Phanerozoic.
The K/Pg is the only mass extinction associated with
both impact (Chixculub) and flood basalts (Deccan Traps)
and therefore an excellent case study to evaluate the
potential causes and effects. Deccan eruptions were
pulsating, with some gigantic megaflows 1500 km across
India and with estimated volumes >10,000 km3 that may
have erupted over very short time intervals. Deccan
volcanism started in the late Maastrichtian (67.4 Ma) with
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T. Adatte et al. / Comunicações Geológicas (2014) 101, Especial III, 1435-1437
the two main eruptive phases identified, in the latest
Maastrichtian and the early Danian, respectively (Chenet
et al., 2007). For comparison, the largest historical basalt
eruption in 1783 in Iceland (Laki) ejected some 15 km3 of
lava in about a year (Chenet et al., 2005). A single Deccan
megaflow would have been equivalent to 667 Laki
eruptions. The vast amount of carbon and sulphur dioxides
injected into the atmosphere from just one Deccan
megaflow probably was on the same order of magnitude as
those estimated for the Chicxulub impact.
Model results predict that Deccan Traps emplacement
was responsible for a strong increase in atmospheric pCO2
accompanied by rapid warming of 4°C (Dessert et al.,
2001), followed by global cooling. During the warming
phase, increased continental weathering of silicates
associated with consumption of atmospheric CO2 likely
resulted in a subsequent drawdown of greenhouse gases,
leading to global cooling at the end of the Maastrichtian.
Massive CO2 input together with massive release of SO2
may thus have triggered a global carbon crisis and the
mass extinctions recorded in both the marine realm, as a
result of ocean acidification, and the terrestrial areas due to
acid rains (Fig. 1). Global stress conditions related to these
climatic changes are well known and documented in
planktic foraminifera by a marked diversity decrease,
species dwarfing, dominance of opportunistic species and
near disappearance of specialized species (e.g. Keller &
Abramovich, 2009). Recent studies indicate that the bulk
(80%) of Deccan trap eruptions (phase-2) occurred over a
relatively short time interval in magnetic polarity C29r
(Chenet et al., 2007). Multi-proxy studies from central and
south-eastern India place the Cretaceous-Tertiary (KT)
mass extinction near the end of this main phase of Deccan
volcanism suggesting a potential cause-and-effect
relationship (Keller et al., 2012).
upper Rajahmundry trap was deposited during zone P1b
corresponding to the lower part of magnetic polarity C29n.
Data from infra- and intertrappean sediments drilled in the
Krishna-Godavari Basin by India’s Oil and Natural Gas
Corporation reveal swift and devastating effects on marine
plankton in India. A 50% drop in diversity of planktic
foraminifera preceded the first megaflow, another 50%
drop thereafter, leaving just 7 to 8 survivor species. No
recovery occurred between the next three mega-flows and
the mass extinction was complete with the last phase-2
megaflow at the K/Pg.
Fig. 2. Map of India (Adatte & Keller, 2013) with locations of
Rajhamundry and Jhilmili sections. Planktic foraminiferal
biostratigraphy places the lower trap in the latest Maastrichtian with the
uppermost lava flow near the K/Pg mass extinction; numerical ages
from Cande & Kent (1995). Panorama view of Rajhamundry intertrappean sequence (Balaji Quarry) showing upper and lower basalt trap
flows.
Fig. 2. Mapa da Índia (Adatte & Keller, 2013) com a localização das
seções de Rajhamundry e de Jhilmili. A biostratigrafia dos
foraminíferos planctónicos coloca a parte inferior das Trapas de
Deccan no Maestrichtiano Superior, com a unidade de lava superior
cerca da extinção em massa do K/Pg; idades numéricas de Cande &
Kent (1995). Vista panorâmica da sequência sedimentares dos
intertrappeanos de Rajhamundry (Balaji Pedreira) mostrando as
unidades de lava inferior e superior.
Fig. 1. Flow chart for the model of massive Deccan volcanism as a
main trigger of environmental changes leading to the K/Pg mass
extinction.
Fig. 1. Fluxograma do modelo do vulcanismo massivo do Deccan como
principal responsável pelas mudanças ambientais que levaram à
extinção em massa do K/Pg.
In the Rajhamundry area (Fig. 2), two Deccan basalt
flows, known as the Rajahmundry traps, mark the largest
lava flows extending for at least 1000 km across the Indian
continent and into the Bay of Bengal (Keller et al., 2008).
The sediments directly overlying the lower Rajahmundry
trap contain the earliest Danian planktic foraminiferal
assemblages of zones P0-P1a and mark the initial
evolution in the aftermath of the K-T mass extinction. The
In Central India a strong floral turnover is observed as
a direct response to Deccan volcanic phase-2. In Lameta,
in the sediments preceding the volcanic eruptions
(infratrappean), a palynoflora of gymnosperms and
angiosperms with a rich canopy of gymnosperms (Conifers
and Podocarpaceae) and an understory of palms and herbs
dominates (Samant & Mohabey, 2009). Immediately after
the onset of Deccan phase-2, this floral association
changed abruptly to a dominance of angiosperms and
pteridophytes, at the expense of gymnosperms. In the
overlying intertrappean sediments a sharp decrease in
pollen and spores coupled with the appearance of fungi
mark increasing stress conditions, apparently as a direct
result of volcanic activity. The intertrappean sediments
corresponding to Phase-2 (80% of Deccan basalt
Deccan Volcanism and K/Pg Mass Extinction
emissions, latest Maastrichtian) are characterized by the
highest Chemical Index of Alteration (CIA) values (Fig.
3). This can be explained by increased acid rains due to
SO2 emissions rather than a global climatic shift, because
clay minerals from the corresponding sediments do not
reflect a significant climate change. The increased
weathering is coeval with the sharp decline in pollen and
an increase in fungal spores observed by Samant &
Mohabey (2009) and corresponds to the main phase-2 of
Deccan activity.
1437
Fig. 3. Ti/Al, index de alteração química (CIA), intensidade da alteração dos
basaltos (K/Fe+Mg) nos sedimentos infra- e inter-trappeanos de Nagpur, India
Central, comparação com os dados palinológicos. Note-se que os valores mais
elevados da CIA são observados em sedimentos inter-trappeanos localizados
dentro de fluxos da Fase 2 (Chron 29r, Maestrichtiano Superior- Daniano
Inferior), o que corresponde a 80% das emissões de lava.
Beyond India, multi-proxy studies also place the main
Deccan phase in the uppermost Maastrichtian C29r below
the K/Pg (planktic foraminiferal zones CF2-CF1 spanning
120ky and 160ky respectively), as indicated by a rapid
shift in 187Os/188Os ratios in deep-sea sections from the
Atlantic, Pacific and Indian Oceans (Robinson et al., 2009)
, coincident with rapid climate warming, coeval increase in
weathering, a significant decrease in bulk carbonate
(indicative of acidification due to volcanic SO2), and major
biotic stress conditions expressed in species dwarfing and
decreased abundance in calcareous microfossils (planktic
foraminifera and nannofossils). These observations
indicate that Deccan volcanism played a key role in
increasing atmospheric CO2 and SO2 levels that resulted in
global warming and acidified oceans, leading to increased
biotic stress and predisposing faunas to eventual extinction
at the K/Pg.
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Fig. 3. Ti/Al ratio, Chemical Index of Alteration (CIA), basalt weathering
intensity (K/Fe+Mg) in infra and intertrappean sediments from Nagpur,
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CIA values are observed in intertrappean sediments located within flows
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