The autostratigraphic view of responses of river deltas to external forcing: a review of the concepts - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 147

tectonic subsidence trend of the basin which was
determined independently through geohistory
analysis (Schellpeper, 2002). On the other hand,
if relative sea-level had been rising steadily
(R slr = const), Q s would have had to increase very
rapidly, as exponential with time (Fig. 8). These
possibilities of unsteady changes in R slr and Q s
would not have been recognised quantitatively
until the deterministic autogenesis was fully
explored in the analysis of the stratigraphic
succession.

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REMAINING PROBLEMS

Autostratigraphy is essential to the understand-
ing of any depositional system, not simply
because it deals with autogenic processes that
have been unknown or insufficiently under-
stood but primarily because it explores the
inherent responses of depositional systems to
external forcing. Autostratigraphy encompasses
both equilibrium and non-equilibrium responses
and takes full account of both steady and
unsteady dynamic external forcing (Muto et al .,
2007). Further exploration of non-equilibrium
responses in river deltas will further clarify the
stratigraphic responses to both dynamic and
static external forcing.
The present framework of autostratigraphy
treats only river deltas unaffected by waves and
tides. There is no reason that non-equilibrium
responses are limited in this way. The challenge is
thus to extend the autostratigraphic view to other
sedimentary systems/environments including
wave-dominated systems, tide-dominated sys-
tems, inland fluvial basins which have no influ-
ence of sea-level forcing, deep water systems and
even non-clastic depositional systems. Different
environments would have a wide variety of strati-
graphic responses to external forcing. The key to
further exploration of autostratigraphy will be the
recognition of non-equilibrium response in rock
successions.

ACKNOWLEDGMENTS

The present work was financially supported
in part by JSPS (20340140) and the RioMAR
Industry Consortium at University of Texas in
Austin.