Net Pumping of
Sediment Into Deep Water Due To Base-Level Cycling
Kim, Wonsuck1, Chris Paola1,
John Martin2, Marty Perlmutter3, Frederick Tapaha4
(1) University of Minnesota, Minneapolis, MN (2) St Anthony Falls Laboratory,
University of Minnesota, Minneapolis, MN (3) Chevron Energy Technology Company,
Houston, TX (4) New Mexico Institute of Mining and Technology, Socorro, NM
The general tendency for sediment supply
to deep water to be maximized during eustatic fall
and lowstand, and minimized during rise and high stand, is well
established in the sequence-stratigraphy literature.
Much less is known about the cumulative effect of repeated eustatic
cycles on net deep-water sediment delivery. Here we investigate the possibility
that repeated eustatic cycles can increase the net
delivery of sediment to deep water averaged over several cycles, an effect we
term sediment pumping. We present two sets of experimental results collected
from the Experimental EarthScape (XES) and Delta
basins at the St. Anthony Falls Laboratory, University of Minnesota. XES run in 2002
modeled the effect of slow and rapid base-level cycles on stratigraphic
configuration under a passive margin type subsidence with constant water and
sediment supply. Two Delta basin experiments in 2005 were run to address the
effects of water and sediment supply variation with +90° and -90° phase shifts
from the imposed base-level cycle on stratal
development. These experiments provide clear examples of stratigraphic
fluvial and marine facies partitioning driven by
base-level change and coupled supply and base-level cycling, respectively.
Combining data from these laboratory experiments (sliced sections and scanned
topographic profiles) and a 2D geometric model, we find that net sediment
pumping depends on (1) the relative timescale of the external perturbation to
the basin equilibrium time, i.e., a ‘slow' or ‘rapid' base-level cycle, (2) the
spatial subsidence pattern, and (3) the phase of sediment supply relative to eustatic variation. Slow base-level cycling results in a
rather poor sediment pump, actually resulting in a smaller marine fraction
compared to constant base-level conditions (i.e. no perturbation). A backtilting subsidence pattern produces a substantially
stronger pumping than a foretilting
geometry, and pumping is maximized when the sediment supply maximum occurs
during eustatic falling stage or lowstand.