Basal Pressure
in Turbidity Currents: Experimental Data on Causes for Substrate Deformation
Eggenhuisen, Joris1, William
McCaffrey1 (1)
After a turbidity
current has passed and waned, the turbidite bed is still located at the
sediment water interface where it is subject to a range of processes that may
alter its appearance. A particular set of processes involves the impact of
subsequent turbidity currents on the recently deposited substrate.
An experimental program has been devised
to look into the common denominator of substrate deformation by gravity flows:
the stresses exerted by such flows on the topography they flow over.
The development of a pressure sensitive
laboratory setup allows for quantitative analysis of base-of-flow pressure and
stresses exerted on the substrate. A first set of experiments regards the
dynamic pressure variations under gravity currents over flat, featureless
surfaces. The reason for looking into this subject lies in the possibility that
these pressure variations are responsible for liquefaction occurrences at the
base of flows. This could take place either: 1) In the
non-depositing phase, where liquefaction may cause failure or slurryfication of
the pre-event substrate. Or: 2) During aggradation of
the bed, where it may cause periodic remobilisation of compacting substrate.
This type of flow induced reorganisation of grains may play an important role
in creating the post-event grain packing in turbidite beds. A second set of
experiments determines stress fields exerted by flows on substrate with
topography. The generic results of these experiments give information about
what eroding interaction to expect around irregularities in the substrate. One
application of these results is the expected preferred geometry of scour zones
where connectivity is enhanced through removal of fine grained deposits that
would normally present a barrier between subsequent turbidite beds.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California