Geology Reference
In-Depth Information
1 E -4
χ
(m
3
/kg) residuals
1 E -4
χ
(m
3
/kg) residuals
Obliquity (°)
Precession
-0.4 -0.2
0
0.2 0.4
0.6 0.8
1. 0
2524.52423.52322.52221. 5 0.4-0.20 0.20.4
0.60.8
1. 0
0.040.020-0.02 -0.04
1. 8
2.0
2.2
2.4
2.6
2.8
3.0
Figure 6.3
Figure taken from Gunderson et al. (2012) showing how detrended MS data (low frequencies
removed, black curve on left) is tied to theoretical obliquity (blue curve second from left). The obliquity-tuned
data series is then Gaussian filtered at precession scale (red curve second from right) and tied to theoretical
precession (blue curve, far right). Source: Gunderson, Kodama, Anastasio & Pazzaglia 2012. Copyright 2012 by
the Geological Society of London.
the 10.2 m peak (41.8 kyr) would be close to obliquity in duration. Therefore,
the susceptibility record was tuned to theoretical obliquity for the Plio-
Pleistocence and the 5-6 m peaks emerged as precession with periods of 23.5
and 21 kyr. The tuning also leads to a spectral peak near to 95 kyr which could
be short eccentricity, but it does not reach the 95% confidence limits above the
robust red noise calculated for the time series using the algorhythm of Mann
and Lees (1996). A strong spectral peak does arise at about 350 kyr, but
Gunderson et al. (2012) do not identify it as being astronomically forced.
One interesting story that is not in Gunderson et al.'s (2012) paper is that
the data were collected in two field seasons, with some of the oriented sam-
ples collected in each season and all the unoriented samples collected in the
first season. Based on the identification of obliquity in the MS data series,
Kellen Gunderson predicted where the base of the Olduvai event (C2n) and
the Gauss-Matuyama boundary (C2r.1n-C2An.1n) should be found in the
stratigraphic section. Sampling during the second field season in this part of
the section found the reversal boundaries exactly as predicted, a strong
testament to the accurate identification of the obliquity cycle.
The final high-resolution age model was produced by band-pass filtering
the obliquity-tuned data series at the precession scale (mean period = 21.3
kyr) and retuning the record to theoretical precession (Figure 6.3).
