EOLIAN SEDIMENTS
"Eolian" refers to wind-blown
sediments. Sand dunes can be found in many deserts, and the principal
sediment transportation agent in such settings is wind. Wind-blown
sediments are expected to be fairly well-sorted to very well-sorted (all
sediment grains are about the same size), and are going to be sand-sized.
The most unusual & scenic place on Earth for
eolian sands is the White
Sands area of southern New Mexico. There, abundant loose gypsum
sediment (CaSO4·2H2O - hydrous calcium sulfate) occurs,
which is not common elsewhere on Earth. White Sands is world-famous for
its dunes of white, wind-blown gypsum sand. The area consists of a gypsum
dune field in the Tularosa Valley, just downwind of evaporitic Lake
Lucero. The gypsum sediment in this area ultimately originates from
leaching of Yeso Formation outcrops (Leonardian Series, upper Lower Permian) in
adjacent mountain ranges.
White Eolian Gypsum Sand (modern), White Sands Dune Field, Tularosa Valley,
southern New Mexico, USA. Microphotograph by Sara Beth Kopczynski.
White Eolian Gypsum Sand (modern), White Sands Dune Field, Tularosa Valley,
southern New Mexico, USA. All three cleavage planes of this gypsum grain
are visible. The original sharp cleavage corners have been slightly
rounded by abrasion. Microphotograph by Sara Beth Kopczynski.
Another nice concentration of eolian (wind-blown) sand
is Bruneau Sand Dunes in southeastern Idaho's Eagle Cove Depression. The
sand is dominantly subangular to subrounded, and consists of a mixture of
quartz, feldspar, and ferromagnesian rock fragments. These sediments are
principally derived from weathering of Plio-Pleistocene Idaho Group sedimentary
rocks (fluvial & lacustrine deposits). The sand dunes themselves have
formed during the Holocene, since the catastrophic flood that drained Lake
Bonneville in the Late Pleistocene.
Modern eolian quartzose-lithic sand from Bruneau Sand Dunes, Eagle Cove Depression, Snake
River Plain, southwestern Idaho, USA. Microphotograph by Sara Beth
Kopczynski.