Autogenic Processes in Physical Stratigraphy by Chris Paola, #50093 (2008)

*Adapted from oral presentation at AAPG Annual Convention, San Antonio, TX, April 20-23, 2008

¹Dept. Geology and Geophysics, University of Minnesota, Minneapolis, MN ([email protected])

²Dept. Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA

³Dept of Geology, University of Illinois Urbana-Champaign, Urbana, IL; currently ExxonMobil Upstream

Depositional systems have a remarkable capacity to create and record internal (autogenic) dynamics. We illustrate this with experimental cases including shoreline fluctuations, terraces, and spontaneously formed lakes. Consistent features of autogenic processes emerging from the experiments include: (1) they are commonly associated with local sediment storage and release caused by the strongly nonlinear nature of sediment transport, and (2) in many cases they have characteristic scales (time, space, and amplitude) that can be constrained using relatively simple geometric arguments. The maximum autogenic time scale appears to be significantly larger than commonly thought: of the order of 10 - 100 kyr. We close with initial evidence that autogenic sediment storage and release can destroy input signals that fall within well defined limits of frequency and amplitude.

	Stochastic vs. deterministic autogenic processes.
	Case 1: Updip signal loss.
	Case 2: Stochastic shoreline migration.
	Case 3: Signal destruction "in transmission."

Conclusions

· Stochastic autogenic processes in channelized systems.

§ self-organized sediment storage and release.

§ often associated with process thresholds.

§ a kind of “stratigraphic turbulence”?

· Mask allogenic signals if amplitude is reduced to ~ autogenic amplitude.

· Can be amplified or attenuated by interaction with allogenic signals.

· Can destroy (“shred”) allogenic signals if time scales overlap.

Challenge 1: quantify length, time, and amplitude scales of expected fluctuations in specific environments.

Challenge 2: Understand quantitatively how these scales govern what signals are preservable in the stratigraphic record.

References

Frette, V., 1993, Sandpile models with dynamically varying critical slopes: Physical Review Letters, v. 70, p. 2762-2765.

Kim, W., C. Paola, V.R. Voller, and J.B. Swenson, 2006, Experimental measurement of the relative importance of controls on shoreline migration: Journal of Sedimentary Research, v. 76/2, p. 270-283.

Kim, W., and T. Muto, 2007, Autogenic response of alluvial-bedrock transition to base-level variation; experiment and theory: Journal of Geophysical Research, v. 112/F3, p. FO3514.

Muto, T., 2001, Shoreline autoretreat substantiated in flume experiments: Journal of Sedimentary Research, v. 71/2, p. 246-254.

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