Geology Reference
In-Depth Information
1
Introduction
Abstract:
Rock magnetic
cyclostratigraphy
is a new technique that allows a
high-resolution chronostratigraphy to be assigned to a sequence of sedimentary
rocks. Concentration variations of magnetic minerals in a sedimentary rock can
be tied to astronomically forced global climate cycles with little or no facies inter-
pretation needed. The rock magnetic measurements are nondestructive, relatively
quick, and inexpensive. This chapter outlines the basic steps of a rock magnetic
cyclostratigraphy study and serves as an introduction to the monograph.
1.1
Rock Magnetic Cyclostratigraphy
The purpose of this monograph is to provide an overview and the practical
“how to” for a relatively new technique that can yield high-resolution chro-
nostratigraphy for sequences of sedimentary rocks. Rock magnetic cyclostratig-
raphy is the result of the merging of environmental magnetism, in which
rock magnetic measurements can detect past environmental conditions, and
cyclostratigraphy, in which cyclic variations of lithology or a rock's physical
properties are tied to orbitally forced changes in global climate. Orbitally forced
cyclic variations in the lithology of sedimentary sequences has been an impor-
tant research focus for stratigraphers since Hays et al.'s (1976) pioneering study
of Late Pleistocene marine sediments. The main reason for this intense interest
is that if lithologic variations can be tied to the well-known cyclic variations of
solar
insolation
at periods of ~20 kyr, ~40 kyr, ~100 kyr, and 405 kyr, a detailed
and high-resolution chronostratigraphy can be established for the rocks, even
at distant times in Earth's history.
Lithologic cyclostratigraphy relies on identifying facies changes in a rock
sequence and interpreting them as indicators of cyclic variations in the
rock's depositional environment. These cyclic variations are then tied to
astronomically forced climate change. Deep-sea cyclostratigraphy has been
