Investigating the autogenic process response to allogenic forcing: experimental geomorphology and stratigraphy - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 132

The following sections describe the complex
responses of autogenic processes to external forc-
ing (i.e. base-level change, tectonic tilting) in
physical experiments. Both time scale and event
size of the fluvial autogenic processes are different
when base-level and tectonic controls are manipu-
lated in the experiments compared to those con-
ducted without the external forcing. Some elongated
and magnified internal processes observed from
the previous studies suggest stratigraphic signals
exhibiting periodicity close to or longer than the
equilibrium time scale could also be attributed
to autogenic processes that have comparable
stratigraphic results to allogenic controls.

exhibited high-frequency shoreline fluctuations
superimposed over long-term responses (see
studies about stratigraphic (allogenic) responses
to the base-level cycles in Kim et al . (2006b) and
Martin et al . (2009a)). The first base-level cycle
started at 26 hours in run time and lasted for 108
hours which is a longer duration than a rapid
cycle that was applied for 18 hours after the ini-
tial slow cycle. The amplitude of the first slow
base-level cycle was 0.11m, which is ten times
larger than the averaged channel depth in the
experiment. In the study, shoreline migration
rates were calculated using 10 min laterally aver-
aged downstream positions of the shoreline and
roughly show a 3-fold increase in autogenic vari-
ability during the base-level rise than that during
the base-level fall (Fig. 3).
Topographic scans reveal that the slope of
the delta top surface varies cyclically during the
autogenic processes: The slope decreases during
release events and increases during storage events.
This slope fluctuation is casted in a geometric
model in Kim et al . (2006a), the results of which

Base-level change

Changes in the magnitude of autogenic fluctua-
tions in shoreline migration rates during base-
level rise and fall were first quantified in Kim
et al . (2006a) using the XES 02 experiment. The
deltaic shoreline responded to multiple sinusoidal
base-level cycles applied in the experiment and

(A) (B) (C) (D)

200

150

100

50

0

-0.1 -0.2 -0.3 123 4 -3 -2 -1 012300.2 0.40.6 0.8 1.0 1.2

standard deviation
[10 -4 m s -1 ]

base-level [m] shoreline [m] migration rate

[10 -4 m s -1 ]

Fig. 3. Shoreline data in XES 02 (note that the time series includes only the first 200 hours of the total 310 run time). (A)
Imposed base-level cycles; (B) maximum, minimum and laterally averaged shoreline downstream positions; (C) migration
rate calculated using the averaged shoreline positions; and (D) standard deviations of the shoreline migration rates.