Geoscience Reference
In-Depth Information
Figure 15.7. Contorted Cenozoic salt lake sediments, Negev Desert, Israel.
processes engendered by insects, such as ants or termites, and of the subsequent
erosional reworking of material brought to the surface by insects and other soil
fauna.
The presence of relict soils, or paleosols, in areas that are now arid indicates
that conditions were previously sufficiently humid for plant growth to occur there.
However, it is not always possible to distinguish between the effects of short intervals
of intense humidity and rapid soil development and longer intervals of lesser humidity
and slower soil development, given that the end results may be very similar.
Stratified sequences of buried soils within loess deposits, river and lake sediments,
and volcanic ash beds can provide potentially useful information about past phases
of landscape stability during which the climate was wetter, widespread plant growth
was possible and soils could form.
The soils that develop under extreme aridity reflect the influence of sporadic rainfall
events and the precipitation of gypsum, halite and/or calcium carbonate within the
soil profile. Progressive accumulation of gypsum or calcium carbonate within the
soil profile can ultimately lead to the formation of hard beds or crusts of calcrete or
gypcrete and no further soil development. In the Negev Desert, laminated sediments
composed of alternating layers of gypsum and silt have been contorted by recent earth
movements (
Figure 15.7
).
