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.