Geology Reference
In-Depth Information
6
Case Studies
of Rock Magnetic
Cyclostratigraphy
Abstract:
Details of rock magnetic cyclostratigraphy studies are given in this
chapter to illustrate how the technique is applied to sedimentary sequences depos-
ited in a variety of environments, including shallow marine, platform carbonate,
and fluvial settings. These case studies show that rock magnetic cyclostratigraphy
can detect astronomically forced climate cycles in rocks that vary in age from
Plio-Pleistocene to Neoproterozoic. The rock magnetics appear to encode climate
variations by different techniques, including eolian dust driven by aridity or
continental flux driven by runoff.
6.1
Introduction and Environmental Shredding
This chapter will present examples of rock magnetic cyclostratigraphy
studies to illustrate the details of conducting a study and show how those
details can vary on a case-by-case basis. The general guidelines for con-
ducting a rock magnetic cyclostratigraphy study listed in Chapter 1 are,
just that, guidelines. As in any creative enterprise, the researcher must
adjust their techniques and methodologies to fit the specific characteristics
of the rocks being studied in order to answer the important question: are
the cycles observed truly due to astronomically forced climate cycles? As
the examples in this chapter will show, the rock magnetic parameter that
gives the best result, whether its susceptibility, anhysteretic remanent mag-
netization (ARM), or isothermal remanent magnetization (IRM) or some
ratio of parameters, will need to be tailored to the rocks being studied. The
magnetic minerals carrying the signal also need to be identified and their
age of creation needs to be pinned down, so the mechanism by which the
astronomically forced cycles are encoded can be understood. Unraveling
the encoding mechanism is an important goal for any rock magnetic
cyclostratigraphy study. Not only does it lend credence to the identification
