Environmental Engineering Reference
In-Depth Information
from insuf
cient averaging of the secular variation, or from weak contamination
by the low-temperature component.
Several of the lowest
flows in the Ivakinsky Formation in both the Sunduk and
Ergalakh sections yield a reverse polarity. All upper-lying flows in these sections
are magnetized in normal polarity.
The primary origin of the high-temperature component isolated in these rocks
relies on:
(1) the close proximity of these mean directions to the expected Permo-Triassic
directions for this region (Pavlov
et al
.,
2007
), and their distinction from
(2) a positive conglomerate test for the Arydzhangsky Formation;
(3) the fact that normal and reversed polarity directions are virtually antiparallel;
(4) a positive fold test for the Morongovsky Formation (Pavlov
et al
.,
2013
); and
(5) the existence of primary magmatic magnetic minerals (Latyshev
et al
.,
2012
).
A primary origin of the isolated magnetization is also supported by the statistically
different mean directions of the directional groups (see
Section 5.4
).
5.4 Discussion
In total we have studied 79
flows from the Kotuy region (Medvejia and Truba
sections) and 54
flows from the Norilsk region (Sunduk and Ergalakh sections). In
116 out of 133 sampled sites, we have isolated the high-temperature component,
which we interpret to be primary.
To estimate the time interval during which the studied trap sections were
formed, we applied the procedure described in Chenet
et al
.(
2008
,
2009
). This
procedure, based on the analysis of the secular variations recorded in lava
ows,
has permitted the identification of 17 directional groups (DGs) and 13 individual
directions (IDs) in the composite Kotuy section (
Table 5.1
and
Figure 5.4
), four
Figure 5.3 (
cont.
) plots for samples from the Ergalakh (g) and Sunduk (j) sections.
Closed (open) circles represent projection onto the horizontal (vertical) plane. (b),
(e) Equal area projections showing mean ID and DG directions for the Arydz-
hangsky (b) and Onkuchaksky (e) formations. (h), (k) Equal area projections
showing mean
flow directions for the Ergalakh (h) and Sunduk (k) sections. (c)
Equal area projection showing the result of the conglomerate test for the Arydz-
hangsky Formation. Closed (open) circles on the equal area net indicate down
(up) direction. (f) Magnetic polarity of volcanic traps of the Kotuy River valley.
(Ar
Onkuchaksky Formation.). (i), (l) Magnetic
polarity of Ergalakh (i) and Sunduk (l) sections (Iv
¼
Arydzhangsky Formation, On
¼
¼
Ivakinsky, Sv
¼
Syver-
minsky, Gd
¼
Gudchikhinsky, Kh
¼
Khakanchansky, Tk
¼
Tuklonsky, Nd
¼
Nadezhdinsky formations). Black (white)
¼
normal (reversed) polarity.
