Chris Paola¹, Ben Sheets¹, Dan Cazanacli², Tom Hickson², Nikki Strong²

(1) University of Minnesota, Minneapolis, MN
(2) University of Minnesota

ABSTRACT: (Keynote): Intrinsic Time Scales in Fluvial Basins

The relative influence of various kinds of tectonic forcing on basin stratigraphy, the way in which these influences are recorded, and the relative importance of autocyclic versus external forcing, are fundamentally dependent on a set of intrinsic time scales that govern basin response. One time scale, called the 'equilibrium time', arises from the diffusional nature of fluvial surface dynamics on long time scales. The effect of this time scale on deposition can be analyzed using concepts from filter theory: basins act as low-pass filters for subsidence signals and high-pass filters for rainfall signals. They record sediment-supply signals at all frequencies but with frequency-dependent phase and unconformity patterns. Another time scale controls the transition from flow-controlled to subsidence-controlled deposition. This time scale can be thought of as setting the upper limit to the autocyclic frequency band. In an experimental fluvial system the transition to subsidence control occurs over a time equivalent to that required to deposit several mean scour depths' worth of sediment. It is not clear how external signals that fall within the autocyclic band are recorded, but some modeling results suggest that the general effect of autocyclic noise is to destroy, as opposed to simply masking, superimposed external signals.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado