Investigating the autogenic process response to allogenic forcing: experimental geomorphology and stratigraphy - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 127

Investigating the autogenic process response to allogenic forcing:
experimental geomorphology and stratigraphy

WONSUCK KIM*, ANDREW PETTER † , KYLE STRAUB ‡ and DAVID MOHRIG*
* Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin,
Austin, 78712 TX, USA (E-mail: [e-mail])
† St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA
‡ Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118, USA

ABSTRACT

Decoupling the preserved signal of environmental (allogenic) forcing from those of inter-
nally generated (autogenic) processes is at the centre of understanding the evolution of
the Earth's surface preserved in the sedimentary record. A major stumbling block for
distinguishing between allogenic versus autogenic signatures in the stratigraphic record
is the lack of quantitative understanding of autogenic processes and their interactions
with allogenic forcing. Physical experiments with moving sediment and water construct
topography through dynamic self-organised fluvial systems, thus providing an opportu-
nity to investigate autogenic processes under controlled boundary conditions (e.g. sedi-
ment supply and tectonics). This paper presents a set of tank experiments that are used
to examine quantitatively 1) the autocyclic storage and release of sediment in the delta
top surface associated with river-pattern changes between channel and sheet flow and 2)
changes in fluvial autocyclic behaviour driven by external forcing (e.g. sea-level change
and tectonics). The time and event scales of the autogenic processes observed in the
experiments conducted without external forcing have provided the first-order quantita-
tive understanding of the autogenic processes. Changes in the frequency of autogenic
processes through base-level changes and lateral ground tilting have provided a new
view into the coupled allogenic and autogenic controls on stratigraphic development.
Coupled experiments that test the effects of allogenic forcing on autogenic process are
presented here: one experiment was conducted with constant external forcing and the
other was conducted with cyclic changes in external controls. This review provides 1)
quantitative measurements of fluvial autogenic processes and thorough comparisons of
cyclic strata attributed to allogenic versus autogenic controls and 2) suggestions for
future experimental studies of fluvial autogenic processes that will enhance our ability
to interpret the mixed signals of environmental variation and internal dynamics in the
sedimentary record.

Keywords: Autogenic process, stratigraphy, experiment, geomorphology, shoreline.

INTRODUCTION in the sedimentary record remains as a fundamen-

tal goal of sedimentary geosciences. Classically
allogenic deposits have been recognised by their
cyclic nature. Their cyclicity is interpreted as the
signature of periodic changes in climate, base-level,
sediment supply, and/or tectonics. On the other
hand, it has also been generally accepted that non-
linearity in sediment transport (e.g. delta lobe
switching, channel avulsion) results in random or
scale-free (fractal) deposits, i.e. autogenic-driven
deposits (Jerolmack & Paola, 2007; Jerolmack &

Sedimentary deposits in basins are sensitive
indicators of environmental variations, e.g. global
sea-level change, river floods, coastal storms and
earthquakes. These environmental conditions exert
a crucial influence on the shape of Earth's surface
which, in turn, influences the development of sub-
surface architecture (stratigraphy). Decoupling the
products of environmental (allogenic) forcing from
the internally generated (autogenic) 'noise' written