Geology Reference
In-Depth Information
can be critical to understanding many important Earth processes. Rock
magnetic cyclostratigraphies have already been used to study tectonic
processes. Gunderson et al. (2012) have used a susceptibility record of
obliquity in Plio-Pleistocene marine sediments from the Po River Valley
in northern Italy to time the deposition of growth strata that, in turn,
constrain the folding of the Salsomaggiore anticline, and hence fault slip
on the blind thrust pushing up the folded rocks. A similar study of folded
Eocene marine growth strata in the Spanish Pyrenees is the ultimate goal
for the ARM cyclostratigraphy already produced for the Arguis Formation
marine marls (Kodama et al. 2010). Not only high-resolution chro-
nostratigraphies will result from rock magnetic cyclostratigraphies, but
high-resolution correlation of sedimentary sections that are distant
globally, or even cores drilled from an oil or gas field for petroleum
exploration and exploitation.
Rock magnetic cyclostratigraphy also has the potential for outperforming
the resolution of radioisotope geochronology, particularly for very ancient
rocks. Minguez et al. (2014) have demonstrated rock magnetic cyclostratig-
raphies at different localities of the Neoproterozoic Johnnie Formation from
near Death Valley, CA. These chronostratigraphies yield precession-scale
resolution that in the Neoproterozoic is on the order of 15 kyr. Bowring
and Schmitz (2003) indicate errors of approximately ±0.3-3 Ma on
Neoproterozoic age (~550 Ma) rocks in their discussion of the problems
dating the Cambrian-Neoproterozoic boundary with zircon U-Pb ages.
Even the 555.0 ± 0.3 Ma age they report for the Neoproterozoic has an error
20 times larger than the precision realized by the Johnnie Formation
rock magnetic cyclostratigraphy. Furthermore, radioisotopic dates give spot
ages at irregular intervals, whereas cyclostratigraphy yields a continuous
chronology and preserves high-precision ages through several million year
intervals.
1.4
Layout of the Topic
This topic is organized to provide the background information needed to
conduct a rock magnetic cyclostratigraphic study of a sedimentary
sequence. Chapter 2 covers the important points about rock magnetics
necessary for conducting rock magnetic cyclostratigraphy studies and for
understanding the interpretation of rock magnetic data. Chapter 3 is a
primer for the basics of conducting a magnetostratigraphic study needed to
assign time at a coarse scale to the data series acquired in a cyclostrati-
graphic study. Chapter 4 covers the basics of time series analysis needed
to extract and interpret cycles in rock magnetic data series; step-by-step
procedures and commands are demonstrated with MATLAB
®
scripts.
Chapter 5 gives the theoretical background of astronomical forcing
mechanisms and provides step-by-step description for how to calculate
