Geology Reference
In-Depth Information
(a)
10 2
1
Figure 6.1 Figure from
Jerolmack and Paola (2010)
showing their modeling
of numerical rice-pile
experiments in which the input
signal (with period T, (a)) has a
longer period than the
characteristic frequency of the
rice-pile processes (landsliding
primarily, Tx) or a shorter
period (b). In the bottom
example, the amplitude of the
input signal keeps it from
being completely shredded.
Source: Jerolmack & Paola 2010.
Reproduced with permission of
John Wiley & Sons, Inc.
T
0.75
10 0
0.5
0.25
T x
10 -2
0
(b)
1
10 2
0.75
T
0.5
10 0
0.25
T x
0
10 -2
of the cycles, but it teaches us the important details about surficial processes
in the Earth system and is a satisfying intellectual reward.
Another important consequence of examining specific examples of rock
magnetic cyclostratigraphy studies is to illustrate the limitations of the tech-
nique and the important role of “shredding” of the input signal by the sedi-
ment transport processes for a given depositional environment. Jerolmack
and Paola (2010) propose that the sediment transported through a landscape
will be affected by processes that act, in concert, as a nonlinear filter that can
“shred” an environmental signal. Jerolmack and Paola (2010) point out that
processes such as landsliding, bed load transport, and river avulsion will act
as a low-pass filter for the environmental signal input into the system. Their
modeling of rice-pile analogues of sedimentary systems suggests that if the
frequency of the input signal is longer than the periods of the shredding
processes, then the signal will make it through the system and be recorded
in the stratigraphy (Figure 6.1). However, for input signals with periods
shorter than a “threshold frequency,” the input signal will be lost, unless the
amplitude of the input signal is very large. Furthermore, the size of the
depositional system, e.g., the size of the fluvial system carrying the sediment
to the depositional basin, determines the “threshold frequency” that charac-
terizes the system.
Jerolmack and Paola's (2010) idea of environmental “shredding” must be
considered when interpreting the origin of the cycles observed in any rock
magnetic cyclostratigraphic study. Furthermore, the successful identification
of eccentricity and precession-scale signals in a rock magnetic record helps
constrain the size of the threshold frequency for a given depositional environ-
ment. Jerolmack and Paola's (2010) model should also inform the researcher in
the choice of depositional systems to investigate and estimates for the chances
of success. For instance, the expected nearly continuous sedimentation of a
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