Geology Reference
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top normal polarity interval correlated to the Jaramillo event (C1r.1n;
Gunderson et al. 2012). The tie to the geomagnetic polarity time scale (GPTS)
indicates that the section ranges from 3 to 1 Ma in age and has an average sed-
iment accumulation rate of 24 cm/kyr that was used as a first approximation to
determine the duration of the cycles observed by the rock magnetics.
Magnetic susceptibility (MS), and ARM were measured for the unoriented
cyclostratigraphic samples. IRM acquisition results suggested two coercivity
components identified by Gunderson et al. (2012) as low coercivity (~20 mT)
depositional magnetite and higher coercivity (~80 mT) iron sulfides. The iron
sulfide component was much stronger than the magnetite component, so iron
sulfides control a good portion of the ferromagnetic signal and hence could
potentially obscure the cyclostratigraphy.
Multitaper method (MTM) spectral analysis showed that the susceptibility
record was best at recording cycles in the data. Spectral peaks were observed
with periods of 85 m, 10 m, and two peaks near to 5-6 m (Figure 6.2). The sed-
iment accumulation rate derived from the magnetostratigraphy suggested that
(a)
0.030
348.3 ky
0.025
85.3 m
0.020
0.015
41.8 ky
10.2 m
25.8ky 23.6 ky
0.010
6.3 m
5.8 m
0.005
0
0
0.02
0.04
0.06
0.08 0.10
Frequency (1/m)
0.12
0.14
0.16
0.18
0.20
(b)
0.030
356.1 ky
85.4 m
0.025
0.020
Figure 6.2
MTM power
spectra for the Stirone
Formation MS data series.
(a) is untuned and (b) is
tuned to theoretical obliquity.
Source: Gunderson, Kodama,
Anastasio & Pazzaglia 2012.
Copyright 2012 by the
Geological Society of
London.
43.5 ky
0.015
21.0 ky
10.4 m
5.2 m
0.010
23.5 ky
5.6 m
0.005
0
0
0.02
0.04
0.06
0.08 0.10
Frequency (1/m)
0.12
0.14
0.16
0.18
0.20
