Environmental Engineering Reference
In-Depth Information
12.7 Environmental implications
As sedimentary basins are among the main crustal reservoirs of organic and
inorganic carbon (e.g. IPCC,
2007
), there is a huge potential for CH
4
and CO
2
generation in volcanic basins. A link between contact metamorphism and the
PETM was suggested in 2004, based on detailed seismic imaging and borehole
studies in the Vøring and Møre basins, offshore Norway (Svensen
et al
.,
2004
),
and this provided a new framework for investigating LIP processes and the link to
environmental changes. The cornerstone of this hypothesis is rapid gas generation
from contact metamorphism of organic material and subsequent release of green-
house gases to the atmosphere.
Recent work has provided evidence that degassing from volcanic basins
can be linked to other climate events, including the Toarcian (Lower Jurassic),
the Triassic
Jurassic, the end-Permian, and the end-Guadalupian (e.g. Svensen
et al
.,
2007
; Svensen
et al
.,
2009
; Ganino and Arndt,
2009
;McElwain
et al
.,
2005
; Beerling
et al
.,
2007
). This hypothesis is supported by geological
constraints (e.g. observed contact aureoles, sill intrusions, and vertical pipe
structures) as well as the fact that metamorphism of organic carbon leads
to the generation of
-
12
C-enriched CH
4
. This can better explain the available
geochemical data than the emission of
12
C-depleted mantle CO
2
due to LIP lava
degassing.
In eastern Siberia, the sill emplacement event took place at the end of
the Permian, and thick sills are present throughout the basin. Mass balance
calculations suggest that 10,000
-
30,000 Gt C could have been generated during
contact metamorphism of organic matter, accompanied by 4,500
13,000 Gt
CH
3
Cl (Svensen
et al
.,
2009
). The presence of a large number of pipe structures
rooted in evaporite lithologies suggests that the gases were released to the
atmosphere. Violent degassing of sulfur-, carbon-, and halogen-rich gases,
as suggested by the pipes in Siberia, makes it likely that the gases could
have passed through the otherwise rather undisturbed tropopause and been
injected into the stratosphere. This may explain some of the terrestrial conse-
quences of the end-Permian mass extinctions, as mutated pollen grains are
ascribed to ozone-layer breakdown and damaging ultraviolet-B radiation
(Visscher
et al
.,
2004
; Foster and Afonin,
2005
). This hypothesis is suppor-
ted by the heating experiments mentioned here and atmospheric chemistry
modelling of end-Permian ozone stability (Black
et al
.,
2014
). Contact meta-
morphism of coal and other carbonaceous sediments in the Tunguska Basin
in eastern Siberia generated carbon gases that induced global warming
(Svensen
et al
.,
2004
; Retallack and Krull,
2006
; Visscher
et al
.,
2004
; Svensen
et al
.,
2009
).
-
