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to that at the shoreline. This change in amplitude
of the autogenic variability is mainly controlled
by changes in the axial length of the alluvial sys-
tem, i.e. shortening the length results in a decrease
in the alluvial-bedrock transition autogenic varia-
bility; and vice versa. A simple geometric, mass-
balance model similar to one in Kim
et al
. (2006a)
was also employed in this study. The model again
used varying fluvial slopes to express sediment
transport efficiency in the fluvial system and cap-
tured the patterns of the autogenic signature in the
both moving boundaries. The dimensionless vari-
ability of the shoreline and alluvial-bedrock
boundaries, enhanced by the base-level forcing,
indicated that the autogenic response has the
same order of magnitude as the allogenic response.
This suggests the possibility of overlap in time
and event scales across the autogenic and allo-
genic stratigraphic products, even though the allo-
genic signal is mostly expected to be coherent
over much longer length and time scales.
Paola, 1996; Kim
et al
., 2010; Leeder, 1978; Leeder
et al
., 1996). However, stratigraphic evolution in
active tectonic basins cannot be properly under-
stood without consideration of the dynamic
interactions of autogenic process with tectonic
forcing. The following experimental example
shows a complex autogenic response to tectonic
activity.
The XES 05 experiment further considered the
influence of subsidence on autogenically-driven
stratigraphy. XES 05 had an initial stage with no
tectonic component, in which the results for
quantifying the autogenic process were presented
in the previous sections. The experiment was
composed of two separated normal fault segments
that set up a relay-ramp. Constant fault slip rates
were applied to both faults in the experiment
(Kim
et al
., 2010). Topographic displacement
occurred across the upstream footwall and down-
stream hangingwall basins, which substantially
lengthened the time for the fluvial channel system
to redistribute sediment and to reach a quasi-
steady-state landscape. Analysis using time inte-
grated maps of wetted surface by channel flow in
the tectonic stage (Fig. 4) indicates an increase in
the characteristic time scale of the fluvial auto-
genic variation from 13 hours (non-tectonic stage)
to 65 hours (tectonic stage) (Kim & Paola, 2007).
The five-fold increase in the autogenic time
scale (i.e. slow channel lateral migration) caused
temporal variation in sediment supply to the
position of the maximum subsidence in the
hangingwall basin. The slow redistribution of
Tectonics: Lateral ground tilting
The response of rivers to tectonic activity is gener-
ally accepted as a key control for spatial distribu-
tion of the subsurface channel sandbodies.
Stacking density of channel deposits therefore has
been used to infer changes in 1) tectonic activity
and 2) sediment supply (as a proxy for climate
changes) from catchments (e.g. Alexander
et al
.,
1994; Alexander & Leeder, 1987; Allen, 2008;
Bridge, 1993; Bridge & Leeder, 1979; Heller &
(A)
(B)
1. 2
1. 2
65 hours
1. 0
13 hours
1. 0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
14.5 hours
56 hours
0
0
140
145
150
155
160
165
170
0
10
20
30
40
50
60
70
80
90
Stage 1, runtime [hr]
Stage 0, runtime [hr]
Fig. 4.
Characteristic measurement of channel activity in the delta top surface (low value represents rapid migration (and/
or avulsion) of channels). (A) Channel activity cycles every ~ 13 hours in the first non-tectonic stage, but (B) the cycle
period increases to 65 hours due to lateral ground tilting imposed during the second tectonic stage.
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