Sediment Mass
Extraction as a Key to Quantifying the Interplay of Tectonic Subsidence and
Sedimentation
Paola, Chris1, John Martin1,
Sean Connnell2, Wonsuck Kim1
(1) University of Minnesota, Minneapolis, MN (2) Univesity
of New
Mexico, Albuquerque,
The most direct influence of tectonics on
sedimentation, nicely illustrated by Crowell's work on the Ridge Basin, is through downstream
sediment mass extraction in response to tectonic subsidence. For example, in
sedimentary basins, the classical idea of fluvial “grade” is replaced by an
overall balance between subsidence and sedimentation, in which the transport
surface is adjusted to provide the downstream rate of sediment loss required to
balance subsidence. It is this persistent mass loss, not changes in slope or
stream power per se, that are responsible for most downstream changes in
depositional environments and architecture. We illustrate some of the main
effects of downstream sediment extraction via theoretical analysis and data
from the field and from an experimental basin with a fully programmable
subsiding floor. Primary among these effects are downstream decreases in grain
size and channel stacking density. We also show how to quantify the mass
extraction via a bypass ratio or extracted fraction. Finally, we illustrate how
mass extraction determines the relative extents of transverse and longitudinal
depositional packages in a system with multiple interacting sediment sources.