Paleo soil
A paleo- soil ( old Gr. Παλαιός palaiós 'old' + dt. ' Soil ') is an "old soil " according to the meaning of the word . Paleo soils are soils created under different environmental conditions . Fully preserved old floors are very rare. Paleo soil as a term also includes the remains of an erosively cut soil. Paleo floors are archives of past environmental conditions. Fossil soils in sedimentary sequences provide information about phases of morphodynamic stability (sedimentation pauses) of the earth's surface and the existing ecological and thus climatic conditions. Paleopedology is a sub-area of soil science (pedology) that deals with the scientific investigation of paleo soils .
definition
Paleo soil is often equated with fossil soil , but according to the meaning of the word simply means "old soil". The term paleo-soil is mostly used for buried (fossil) soils that are older than the Holocene . Fossil soils are not affected by recent soil formation . Their formation was also subject to environmental conditions that differed from the recent (Holocene) conditions. In contrast, relict soils are areas of recent soils that were formed under different environmental conditions. They may be subject to further soil formation, provided that the substrate can still be significantly processed by recent soil-forming processes. In addition to fossil soils, paleopedologists also devote themselves to relict soils.
Difficulty of definition
The definition of paleo soils depends on the definition of soil. Chemical weathering alone is not a soil-forming process, so the result is not soil in the pedological sense. When geologists refer to fossil saprolith as paleo soil, for example, this contradicts pedological soil definitions. On the other hand, saprolite represents stability of the land surface as in-situ weathering progresses , which is an important characteristic of soils and a key property of paleo soils.
Paleo soils as environmental archives
With the same initial substrate and comparable relief position, climate and time are the main factors in soil formation. If the time is known, paleo soils can contain information about the climatic conditions at the time of their formation. This principle is used, among other things, in Quaternary research . In Quaternary loose sediments, paleo soils have been preserved which, in terms of their physiochemical characteristics, are still relatively similar to recent soils. Paleo soils, however, have been passed down from almost all phases of the earth's history in sedimentary rocks or even metamorphic rocks . Changes due to diagenesis and especially due to metamorphosis make identification as paleo-soil more difficult. If it can be proven by appropriate scientific methods that a layer was subject to soil formation before it was fossilized , it can be referred to as paleo soil.
The potential of paleo-floors for the reconstruction of past environments is expanded by the fact that paleo-floors trace the relief at the time of their formation. In general, paleo soils represent phases of the stability of the landscape surface. Stability means changing the original substrate through weathering and other soil-forming processes without erosion , accumulation or redistribution taking place. As a rule, the vegetation cover is closed.
Paleo soils in Quaternary research
The quaternary climate changes are documented in the oxygen isotope curves as changes in global average temperatures over the past 2.6 million years. The regional characteristics of the climate - mediated by the atmospheric circulation, influenced by the topography - can only be studied in regional archives. A number of environmental archives exist for the last 100 ka. Loess paleo-soil sequences are the most suitable archives for understanding the corresponding environmental changes depending on the basic oscillation of the climate according to the Milanković cycles . Tephra-paleo-soil sequences, which are also scientifically investigated, are distributed globally.
Loess paleo-soil sequences
Paleo soils that are switched on in sufficiently thick loess deposits of the moderate latitudes show the climatic fluctuations and environmental changes of cold phases and warm phases due to the alternation of loess and soil formation. Difficulties arise when erosion or redistribution events have occurred. In general, fossil soils that have been capped by erosion are still referred to as paleoboils. For example, the change from warm period to cold period due to the change in landscape dynamics results in major relocation events, so that in Central Europe mostly only the dense Bt horizons of parabrown earths are preserved from the last warm period , while the easily erodible Ah and Al horizons have been removed. The scientific investigation of the loess-paleo- soil sequences is carried out primarily with pedological , geological , mineralogical , paleontological and also archaeological field and laboratory methods.
Tephra-paleo-soil sequences
Also tephra -Paläoboden sequences are examined by Quartärforschern. However, the rhythms of sedimentation and soil formation are subject to the dynamics of the respective volcano. For this, the archives are available in all climatic zones and not only limited to the moderate latitudes.
credentials
Retallack, GJ: Soils of the Past - an introduction to paleopedology . 2nd ed., Blackwell Science, 2001.
Individual evidence
- ↑ Collective of authors: Lexicon of Geosciences , Volume 4, Spectrum Academic Publishing House, Berlin, Heidelberg 2001, ISBN 3-8274-0423-1 , p. 306
- ^ Retallack, GJ: Soils of the Past - an introduction to paleopedology . 2nd ed., Blackwell Science, 2001. p. 7.