Geology Reference
In-Depth Information
2
Rock Magnetism
Abstract:
This chapter covers the basics of rock magnetism needed for conducting
a rock magnetic cyclostratigraphy study. The fundamental types of material
magnetic behavior,
diamagnetism, paramagnetism, and ferromagnetism
, and
their causes are discussed. The basic characteristics and properties of the impor-
tant ferromagnetic minerals—the iron oxides, iron oxyhydroxides, and iron sul-
fides—are summarized. The fine particle magnetic behavior that governs the
magnetic particles carrying a rock magnetic cyclostratigraphy is introduced. Fine
particle magnetism topics that are discussed include hysteresis, individual
magnetic particle anisotropy, and magnetic domains. Finally, the environmental
magnetic parameters, and their ratios, that are important to rock magnetic
cyclostratigraphy are explained. The chapter ends by discussing the importance
of identifying the magnetic mineralogy in a sedimentary sequence targeted for a
rock magnetic cyclostratigraphy study and choosing the best environmental
magnetic parameter for the cyclostratigraphic study.
2.1
Introduction
The basic idea of rock magnetic cyclostratigraphy is to measure the variations
in one or several rock magnetic parameters throughout a sequence of sedimen-
tary rocks. The rock magnetic parameter is selected based on its ability to be a
proxy for an environmental or climate process at the time of the sediment's
deposition. Rock magnetic cyclostratigraphy uses the principles of environ-
mental magnetism, an important subdiscipline of rock magnetism (Thompson
& Oldfield 1986; Evans & Heller 2003; Tauxe 2010; Kodama 2012), in which
magnetic measurements of a sample can detect one of the three important
magnetic characteristics: the concentration of a particular magnetic mineral,
the grain size of the magnetic mineral particles, and the different types of
magnetic minerals in a sample. These measurements, which will be covered
in more detail later in this chapter, are typically done by the application of
