2.3 EoIian Sediments
Pleistocene, the climatic belts and thus also the large
subtropical deserts shifted poleward and gained in
extent. Continental drift and the changing configuration of the oceans and land masses significantly affected the global climate and thus the areal extent of
deserts and the proportion of eolian sediments in the
geological record.
In the Permo-Triassic, for example, when the older
continents had created one supercontinent (Pangea),
arid climates and eolian sediments played a much
greater role than today. Since eolian sediment transport is favored by the lack or absence of vegetation,
the evolution of land plants during the Earth's history
2.3.9
Summary (EoIian Sediments)
Windblown sands and dust originate from dry
deflation surfaces and abrasion of rocks.
Sand transport occurs close to the land surface
and slows with the increasing height of sand
dunes; dust can be easily kept in suspension in
the atmosphere and travel over long distances.
Eolian sands tend to become weil rounded, yellowish and later red in color. They often form
characteristic large-scale planar cross-bedding
and minor ripple cross-bedding. Transport directions preserved in dune sands greatly vary.
Many eolian sands show goundwater-controlled
deflation surfaces and interactions with fluvial
63
has to be taken into consideration. Prior to the Devonian, plant life was limited, and also in the pre-Upper
Cretaceous, soil protection by dense roots of angiosperms did not yet exist. In general, long persisting
dry climate, sufficient subsidence, and the inability
of plants to grow in desert environments favored the
accumulation of eolian sands.
Colder climate and the advance of glaciers during
glacial periods led to areduction in land surface covered by vegetation. For all these reasons, the contribution of eolian processes to sediment accumulation
and basin filling can have been much greater or
lower during some periods in the past than it is today.
and playa deposits. Other distinctive criteria are
summarized in Sect. 2.3.5.
- Eolian dust, derived from glaciofluvial outwash
or from deserts, can generate loess covers of
various thicknesses on the land surface. Dust
contributes considerably to the composition of
lake deposits in arid zones as weil as to deepsea sediments in regions where offshore winds
from deserts reach the open ocean.
- Clay dunes along drying lakes, consisting of
wind-blown aggregates, represent a specific
type of eolian deposit.
Pleistocene, the climatic belts and thus also the large
subtropical deserts shifted poleward and gained in
extent. Continental drift and the changing configuration of the oceans and land masses significantly affected the global climate and thus the areal extent of
deserts and the proportion of eolian sediments in the
geological record.
In the Permo-Triassic, for example, when the older
continents had created one supercontinent (Pangea),
arid climates and eolian sediments played a much
greater role than today. Since eolian sediment transport is favored by the lack or absence of vegetation,
the evolution of land plants during the Earth's history
2.3.9
Summary (EoIian Sediments)
Windblown sands and dust originate from dry
deflation surfaces and abrasion of rocks.
Sand transport occurs close to the land surface
and slows with the increasing height of sand
dunes; dust can be easily kept in suspension in
the atmosphere and travel over long distances.
Eolian sands tend to become weil rounded, yellowish and later red in color. They often form
characteristic large-scale planar cross-bedding
and minor ripple cross-bedding. Transport directions preserved in dune sands greatly vary.
Many eolian sands show goundwater-controlled
deflation surfaces and interactions with fluvial
63
has to be taken into consideration. Prior to the Devonian, plant life was limited, and also in the pre-Upper
Cretaceous, soil protection by dense roots of angiosperms did not yet exist. In general, long persisting
dry climate, sufficient subsidence, and the inability
of plants to grow in desert environments favored the
accumulation of eolian sands.
Colder climate and the advance of glaciers during
glacial periods led to areduction in land surface covered by vegetation. For all these reasons, the contribution of eolian processes to sediment accumulation
and basin filling can have been much greater or
lower during some periods in the past than it is today.
and playa deposits. Other distinctive criteria are
summarized in Sect. 2.3.5.
- Eolian dust, derived from glaciofluvial outwash
or from deserts, can generate loess covers of
various thicknesses on the land surface. Dust
contributes considerably to the composition of
lake deposits in arid zones as weil as to deepsea sediments in regions where offshore winds
from deserts reach the open ocean.
- Clay dunes along drying lakes, consisting of
wind-blown aggregates, represent a specific
type of eolian deposit.