2 Continental Sediments
2.3 Eolian Sediments
2.3.1 Introduction
2.3.2 Source, Migration, and Specific Properties of
Eolian Sands
Sand Sources
Composition of Sand
Color of Eolian Sands
Transport and Texture ofEolian Sands
2.3.3 Bed Forms and Sedimentary Structures of
Eolian Dunes
Inland Dunes
Sedimentary S tructures of Inland Dunes
Coastal Dunes
2.3.4 Large-Scale Facies Associations ofEolian Sands
Interaction with Fluvial and Playa Sediments
Thickness of Eolian Sands
Interaction with Shallow-Marine Sediments
2.3.5 Distinctive Features ofEolian Sandstones
(Summary)
2.3.6 Clay Dunes
2.3.7 Eolian Dust, Loess
General Aspects
Dust Deposition
Pleistocene Loess
2.3.8 Remarks to Ancient Eolian Sediments
2.3.9 Summary (Eolian Sediments)
2.3.1 Introduction
Eolian sediments are deposited under the direct influence of wind without the influence of running or
standing water. They therefore exhibit primary features typical of eolian environments. Various other
types of sediments may contain considerable
amounts of wind-blown dust and sand, but they ultimately accumulated in fluvial or subaquatic environments. Well-known examples of these non-eolian
sediments form on floodplains of desert rivers, in
coastal areas, and even deep-sea muds may contain
significant proportions of air-borne dust.
Ancient eolian sediments have been understood by
geologists for a long time, because their accumulation can be readily observed in the present-day
deserts.
Numerous articles and most textbooks on physical and
sedlmentary geology present descriptions of eolian proces ses and sediments (e.g., Bigarella 1972; McKee 1979;
Blatt et al. 1980; Galloway and Hobday 1983; Chorley et
al. 1984; Frostick 1987; Pettijohn et al. 1987; Pye and Lancaster 1993; Nickling 1994; Kocurek 1996). Climatic aspects and shifting of desert belts are dealt with, e.g., by
Leinen and Samthein (1989), Lancaster (1990), Goudie
and Wells (1995). Specific topics such as sorting, sedimentary structures, and reddening of eolian sand are addressed,
e.g., by (Folk 1971), Hunter (1981), Collinson and Thompson (1982), Wopfner and Twidale (1988). Interactions of
eolian and fluvial deposits are described, e.g., by Langford
(1989), Langford and Chan (1989) and many others.
The medium of transport of eolian sediments is the
atmosphere. Planets or moons without an atmosphere
are devoid of eolian processes and sediment, but
even a very thin atmosphere such as that on Mars is
sufficient to produce sand dunes. Deserts constitute
about 20% of the present-day land surface of the
Earth, but only 20% to 45% of the area classified as
arid is covered by "sand seas" (ergs).
The major part of deserts comprises highlands, stony
plains, alluvial fans, and closed depressions (pans
and playas). Many of these depressions have been
formed by the combined action of salt weathering
and eolian deflation (Fig. 2.2la).
Deserts range from low-latitude, hot and arid regions within the zones of trade winds and monsoons
to cold and dry polar regions. Prominent deserts occur along the western margins of continents which
are affected by cold ocean currents. Furthermore,
land-locked continental interiors, particularly on the
leeward side of the principle wind directions, may
acquire the characteristics of deserts. Beaches with
high sand supply can cause dune fields of limited
extent under various climatic conditions.
Winds are an effective agent for taking up and transporting fine to medium-grained, unconsolidated materials, if the sediment particles do not adhere to each
other, for example by moisture. Hence, the land surface must be dry and not be protected by vegetation.
Fine silt is whirled up and kept in suspension as long
as the turbulence of the air is sufficiently high to
counteract the settling of particles by gravity (Fig.
2.21). Thus, silt may travel from desert areas over
distances of tens to several hundreds to a thousand
kilometers and reach vegetated land. The larger and
heavier sand grains move near the land surface by
saltation, and therefore migrate much more slowly
than dust. Both dust and sand can, in contrast to flu-
2.3 Eolian Sediments
2.3.1 Introduction
2.3.2 Source, Migration, and Specific Properties of
Eolian Sands
Sand Sources
Composition of Sand
Color of Eolian Sands
Transport and Texture ofEolian Sands
2.3.3 Bed Forms and Sedimentary Structures of
Eolian Dunes
Inland Dunes
Sedimentary S tructures of Inland Dunes
Coastal Dunes
2.3.4 Large-Scale Facies Associations ofEolian Sands
Interaction with Fluvial and Playa Sediments
Thickness of Eolian Sands
Interaction with Shallow-Marine Sediments
2.3.5 Distinctive Features ofEolian Sandstones
(Summary)
2.3.6 Clay Dunes
2.3.7 Eolian Dust, Loess
General Aspects
Dust Deposition
Pleistocene Loess
2.3.8 Remarks to Ancient Eolian Sediments
2.3.9 Summary (Eolian Sediments)
2.3.1 Introduction
Eolian sediments are deposited under the direct influence of wind without the influence of running or
standing water. They therefore exhibit primary features typical of eolian environments. Various other
types of sediments may contain considerable
amounts of wind-blown dust and sand, but they ultimately accumulated in fluvial or subaquatic environments. Well-known examples of these non-eolian
sediments form on floodplains of desert rivers, in
coastal areas, and even deep-sea muds may contain
significant proportions of air-borne dust.
Ancient eolian sediments have been understood by
geologists for a long time, because their accumulation can be readily observed in the present-day
deserts.
Numerous articles and most textbooks on physical and
sedlmentary geology present descriptions of eolian proces ses and sediments (e.g., Bigarella 1972; McKee 1979;
Blatt et al. 1980; Galloway and Hobday 1983; Chorley et
al. 1984; Frostick 1987; Pettijohn et al. 1987; Pye and Lancaster 1993; Nickling 1994; Kocurek 1996). Climatic aspects and shifting of desert belts are dealt with, e.g., by
Leinen and Samthein (1989), Lancaster (1990), Goudie
and Wells (1995). Specific topics such as sorting, sedimentary structures, and reddening of eolian sand are addressed,
e.g., by (Folk 1971), Hunter (1981), Collinson and Thompson (1982), Wopfner and Twidale (1988). Interactions of
eolian and fluvial deposits are described, e.g., by Langford
(1989), Langford and Chan (1989) and many others.
The medium of transport of eolian sediments is the
atmosphere. Planets or moons without an atmosphere
are devoid of eolian processes and sediment, but
even a very thin atmosphere such as that on Mars is
sufficient to produce sand dunes. Deserts constitute
about 20% of the present-day land surface of the
Earth, but only 20% to 45% of the area classified as
arid is covered by "sand seas" (ergs).
The major part of deserts comprises highlands, stony
plains, alluvial fans, and closed depressions (pans
and playas). Many of these depressions have been
formed by the combined action of salt weathering
and eolian deflation (Fig. 2.2la).
Deserts range from low-latitude, hot and arid regions within the zones of trade winds and monsoons
to cold and dry polar regions. Prominent deserts occur along the western margins of continents which
are affected by cold ocean currents. Furthermore,
land-locked continental interiors, particularly on the
leeward side of the principle wind directions, may
acquire the characteristics of deserts. Beaches with
high sand supply can cause dune fields of limited
extent under various climatic conditions.
Winds are an effective agent for taking up and transporting fine to medium-grained, unconsolidated materials, if the sediment particles do not adhere to each
other, for example by moisture. Hence, the land surface must be dry and not be protected by vegetation.
Fine silt is whirled up and kept in suspension as long
as the turbulence of the air is sufficiently high to
counteract the settling of particles by gravity (Fig.
2.21). Thus, silt may travel from desert areas over
distances of tens to several hundreds to a thousand
kilometers and reach vegetated land. The larger and
heavier sand grains move near the land surface by
saltation, and therefore migrate much more slowly
than dust. Both dust and sand can, in contrast to flu-