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Australia: The Land Where Time Began |
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Siberian flood basalts
Intercalated volcaniclastics are present in the
Siberian flood basalts to varying extent throughout the sections of that
province that have been most studied e.g., in Noril’sk (e.g. Fedorenko
et
al., 1996). There is a
vast literature on the Siberian province. The thick, primary
phreatomagmatic deposits that underlie the lavas are the most
significant volcaniclastics in the Siberian province. The majority of
the basal volcaniclastics are less than 30 m thick in the northeast and
northwest sections, and are sometimes absent. The volcaniclastics are,
however voluminously present as largely massive, featureless outcrops in
the central, eastern and southern regions. All the river cliffs along almost 200 km of the
Angara River north of Ust Ilim’sk consist of volcaniclastics with
visible outcrops as much as 250 m thick with erosional upper and
unexposed basal contacts (Naumov & Ankudimova, 1995). Volcaniclastic
units are massive, with no bedding and are rich in sediment, but near
the Kata River there is local bedding and accretionary lapilli. Lithic
blocks of underlying sedimentary strata are present in some outcrops; an
active aquifer and driving force for eruption from depth are indicated
by peperites and sediment dykes. Pillow basalts and hyaloclastites are
notably absent. Along the Nizhnaya Tunguska River there are similar
deposits extending for 200 km east-west past the town of Tura in middle
Siberia. Drill cores indicate that in Tura thee are at least 500 m of
tuffs that transition to overlying effusive lavas (Drenov, 1985).
Voluminous phreatomagmatism immediately prior to the main stage of
effusive lava emplacement is demonstrated by these cores.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |