Environmental Engineering Reference
In-Depth Information
DGs and three IDs in the Ergalakh section, and nine DGs and six IDs in the
Sunduk section (
Table 5.2
and
Figure 5.4
).
The same approach has been applied to the composite section containing the
Listvjanka, Icon and Abagalakh sections studied earlier by Heunemann
et al
.
(
2004
) in the Norilsk region. In this composite section, which includes 76 flows
and represents the majority of the trap volcanic sequence in the Norilsk region, we
have isolated 23 DGs and 12 IDs (
Figure 5.4
). In our analysis, we did not consider
the Talnakh section because it is located in immediate proximity to the Listvjanka
section and virtually repeats its lower part.
Correlating directional groups (individual directions) with volcanic pulses (indi-
vidual eruptions) and taking into account the time constraints discussed in Chenet
et al
.(
2008
,
2009
), we conclude that the duration of active volcanism that
produced the composite Kotuy and Norilsk sections does not exceed 9000 and
11 000 years respectively.
These estimates do not include, of course, periods of quiescence separating
volcanic pulses and individual eruptions. The absence of sedimentary layers and
developed weathering crusts between the
flows, however, is a clear indication that
such quiescent periods were brief (nevertheless, we must mention that quiescent
periods can also be marked by an absence of any evidence).
This conclusion is also supported by the rather high values of the non-random-
ordering factor (Biggin
et al
.,
2008
), calculated for the composite Kotuy and
Norilsk sections (0.9999 and 0.8750 respectively). The non-random-ordering
factor was suggested by Biggin
et al
.(
2008
) as a measure of serial correlation
of the successive directions in lava sections. The calculated values point to high
correlation of ID and DG directions in the studied sections and, therefore, indicate
brief time gaps within them.
Heunemann
et al
.(
2004
) and Gurevitch
et al
.(
2004
) subdivided the composite
Norilsk section (Listvjanka, Icon and Abagalakh) into consecutive R, T, E and
N intervals, each recording reversed, transitional, excursional and normal states,
respectively, of the geomagnetic
field. They note also that between the transitional
and excursional intervals (
y
reaches normal polarity. The authors further suggest that the excursional interval
may correspond to a post-transitional rebound effect (Merrill
et al
.,
1996
; Valet
et al
.,
2012
).
We observe the same features in the Ergalakh and Sunduk sections. While
in the Ergalakh section only the reversed and transitional intervals can be
identi
(flows gd5, tk7, tk6), the geomagnetic
field brie
ed (levels DG1, DG2 and DG3, ID1, ID2, ID3, DG4, respectively),
the Sunduk section contains almost all (
Figure 5.5
) of the intervals isolated
in the composite Listvjanka
-
Icon
-
Abagalakh section by Heunemann
et al
.
(
2004
).
