Eolian Environments - Trace Fossils as Indicators of Sedimentary Environments - page 407

Chapter 14
Eolian Environments
Allan A. Ekdale * ,1 and Richard G. Bromley †
*Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, USA,
† Geological Museum—SNM, Copenhagen, Denmark
1 Corresponding author: e-mail: [e-mail]
1. INTRODUCTION
On his epic voyage home to Greece following the Trojan War, Odysseus met
and became fast friends with Aeolus, keeper of the four winds. Aeolus presented
his Greek friend with an ox-hide bag tied with a silver cord, which contained all
the necessary breezes to carry Odysseus' ships toward their beloved homeland.
But while at sea, the unruly crew ripped open the bag and unleashed all the
howling winds at once, thus creating a great tempest that blew them hopelessly
off course (from Homer's Odyssey , Chapter X).
Winds have been blowing across Earth's surface since our planet's
origin, and the geologic record of windy environments is contained within
eolianites, aptly named after the mythical custodian of all winds. Deciphering
the direction, intensity, and constancy of ancient wind regimes from eolianites
is a challenge to continental sedimentologists because sedimentary structures
and bed forms in such deposits can be quite confusing. Deciphering the ecology
of ancient wind-blown environments from eolianites is a challenge to paleon-
tologists because fossils in such deposits are notoriously sparse. Ichnologic
evidence may provide welcome assistance to both.
2. ICHNOFACIES
2.1 Ichnology in Eolian Environments
A sand dune is a subaerial substrate on the move. It is at once an erosional envi-
ronment and a depositional environment. The gently dipping, windward, and
sometimes partially vegetated stoss side of a dune is a site of uphill sediment
transport by saltation (or less commonly by traction or suspension). The more
steeply dipping, leeward, and generally unvegetated slip face side of a dune is a
site of sedimentation, largely by grain flow and/or avalanche depositional
mechanisms. The dune moves grain by grain, thus providing a mobile substrate