Eur. Phys. J. E 1, 127-135
Grain segregation mechanism in aeolian sand ripples
H.A. Makse
Schlumberger-Doll Research, Old Quarry Road, Ridgefield, CT 06877, USA
makse@ridgefield.sdr.slb.com
Received 19 July 1999 and Received in final form 4 August 1999
Abstract
Many sedimentary rocks are formed by migration of sand ripples.
Thin layers of coarse and fine sand are present in these rocks,
and understanding how layers in sandstone are created
has been a longstanding question.
Here, we propose a mechanism for the origin of the most common
layered sedimentary structures such as inverse graded climbing
ripple lamination and cross-stratification patterns.
The mechanism involves a
competition between
three segregation processes:
(i) size-segregation and (ii)
shape-segregation during transport and rolling,
and (iii) size segregation due to different hopping lengths of the
small and large grains.
We develop a discrete model of grain dynamics
which incorporates
the coupling between
moving grains and the static sand surface,
as well as the different properties
of grains, such as size and roughness,
in order to test the plausibility of this physical mechanism.
PACS
81.05.Rm Porous materials; granular materials -
91.65.Ti Sedimentary petrology
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
