Geoscience Reference
In-Depth Information
Magnetic properties are important indicators about the quality of past soil devel-
opment. Great magnetic enhancement was estimated in the top horizon of well-
drained paleo-cambisols where weathering had contributed to the concentration of
magnetic silt-sized fi ne grains and cutans. Generally, the well-drained and intermit-
tent wet/dry soils manifest enhanced magnetic properties on the ultra-microscale
even a hundred thousand years after their genesis. On the other hand, the excessive
arid or wet and acid soils were not able to form signifi cant amounts of micro-
ferrimagnets in paleosols. The initial stages of the weathering of loess can also be
identifi ed by changing concentrations of micro-ferrimagnets.
Soluble silica absorbed by plant roots from the soil is carried up through the plant
to some of its organs, and after the plant or its parts die and break down, this “skel-
eton” - usually of microscopic size - remains in the soil. Its scientifi c name is phy-
tolith, derived from the Greek
phyton
meaning plant and
lithos
meaning stone.
When phytoliths are found and used for the detection of the type of vegetation, the
paleo-soil scientist has in hand one of the important soil-forming factors that can be
used to confi rm or reject a hypothesis regarding the genesis and existence of an
actual soil during a specifi c geological era. The phytoliths are hidden primarily
under old river sediments (alluvium) or loess layers that originated in glacial/inter-
glacial cycles during the last 2.588 million years (Pleistocene). In some instances,
residues of paleosols are under the colluvium splashed downslope, or their parts are
hidden below a layer of volcanic ash. Generally, the occurrence of a complete or
substantial part of an entire soil profi le is a rarity. Paleo-soil scientists and geologists
usually fi nd only microscopic to small traces of past soils. Each such discovery has
helped us to separate individual glacials since if two layers are separated by traces
of soil, the meaning is simple - a glacial there could not exist because soil evolution
is impossible in the presence of ice. In a similar way, volcanic ash sedimentation
was interrupted by a time period when the ash was a parent material of new develop-
ing soil and the volcanic activity stopped for a time period of suffi cient length for
soil development. Generally, we could also compare results from numerous other
methods to detect memoirs of paleosols.
When we know the age and type of soil in a certain region, we can change our
research upside down and own a tool for estimating the climate during times of
paleosol evolution. Paleo-soil scientists found the remnants of Terra Rossa in the
Rendzina region of Central Europe. The climate typical for the evolution of Terra
Rossa was 2-3 °C higher than the recent annual average temperatures of contempo-
rary Rendzina. Moreover, there were dry seasons lasting each year for several
months - a condition required for the evolution of Terra Rossa in the time of the last
interglacial Sangamonian (Eemian) 130,000-115,000 years BP. A couple of other
paleosols originating in the last interglacial further document that the climate was
warmer than in our recent interglacial Holocene.
Layers of sand in several regions of present-day deserts cover thick crusts con-
taining CaCO
3
- a reliable sign of the past existence of soils across large areas.
Somewhere there must be remnants of dark gray A horizons indicative of a less arid
climate with rains coming regularly each year. We have proxies about the existence
of either low or even high savanna with lots of animals in signifi cant regions of
