Environmental Engineering Reference
In-Depth Information
pillow lavas and hyaloclastites with intercalated marine limestones and submarine
tuffs (Zhu
et al
.,
2014
). Eruptions transitioned to phreatomagmatic lapilli-tuffs
and tuff-breccias intercalated with basaltic lava sheet
flows displaying peperitic
basal zones and carbonates (
c
. 2000 m: Zhu
et al
.,
2014
), suggesting a very
shallow subaqueous to subaerial depositional environment. This is overlain by
>
2500 m of thick a
'
a and pahoehoe basalts and rhyolite lavas, intercalated with
minor, thin (
1 m), oxidized basaltic tuffs dominated by glassy vesicular ash
shards (Zhu
et al
.,
2014
), likely derived from subaerial phreatomagmatic to
magmatic pyroclastic eruptions.
~
1.3.3 Siberian
flood basalts
The Siberian
flood basalts contain intercalated volcaniclastics to varying extent
throughout the most studied sections of that province, for example in Noril
'
sk
(e.g. Fedorenko
et al
., 1996). A vast literature on the Siberian province exists, but
here we focus on the understudied volcaniclastics and present some new results.
The most signi
cant volcaniclastics in the Siberian province are the thick, primar-
ily phreatomagmatic deposits underlying the lavas. In the northeast and northwest
sections the majority of the basal volcaniclastics are less than 30 m in thickness,
and are sometimes absent (
Figure 1.2
). In the central, eastern and southern
regions, however, the volcaniclastics are voluminously present in largely massive,
featureless outcrops.
Along almost 200 km of the Angara River north of Ust Ilim
'
sk, all the river
cliffs consist of volcaniclastics, and visible outcrops are as much as 250 m thick,
with erosional upper and unexposed basal contacts (Naumov and Ankudimova,
1995
). Volcaniclastic units are massive, unbedded and sediment-rich, though
near the Kata River there is local bedding and accretionary lapilli. Some outcrops
have lithic blocks of underlying sedimentary strata; peperites and sediment dikes
indicate an active aquifer and driving force for eruption from depth. Notably absent
are pillow basalts and hyaloclastites.
Similar deposits occur along 200 km of the Nizhnaya Tunguska River, stretch-
ing east
west past the middle Siberian town of Tura. In Tura, drill cores indicate
at least 500 m of tuffs transitioning to overlying effusive lavas (Drenov,
1985
).
These drill cores demonstrate that voluminous phreatomagmatism immediately
preceded the main stage of effusive lava emplacement.
-
1.4 Evidence for volatile loads, temperatures and plume heights
Chemicals released by volcanism will have the greatest effect on global climate,
both in terms of destructive chemical reactions and longevity, if they reach the
