Sonntag, 9. Mai 2010

The first geological map depicting loess (1865)

Loess is silt dominated sediment with minor amounts of sand and clay. This homogenous particle distribution is a result of the formation of the up to hundred of meters thick massive deposit; it's a terrestrial, windblown sediment, most time with homogenous bright, yellowish colour. Primary sedimentary structures in loess are subtle, so the true origin of this sediment was for a very long time unclear. Lyell in his first editions of Geology books interpreted loess as fluviatile loam.*

Loess covers a significant amount of the Earth's land surface, perhaps as much as 10%. Because of its widespread distribution, texture and mineralogy, it forms some of the world's most important agricultural soils.

There exist two main models to explain the formation and distribution of loess. The classical hypothesis interpret it as primarily glacial eroded and reworked material, from where the finer fractions become subsequently selective transported and accumulated by wind. The second model explain the main source of the windblown material to coming from deserts or arid areas, not necessarily related to glaciers, as a result of dry climate conditions during glacial periods.

Fig.1. Carl Maria PAUL, Guido STACHE and in the middle Franz Ritter VON HAUER, the author of the first loess map of Central Europe.

The geologist Franz Ritter von Hauer was the second Director of the Geological Survey in Vienna (1866-1885). One of his main contributions to Quaternary science was the geology textbook of the former Austro-Hungarian Monarchy, which provided a resource to access recent developments in geology and notably loess research to many scientists. In the middle of the 19th century he also coordinated the geological mapping of the monarchy, initiated mainly for economical reasons to record the mining activities and map future potential mineralogical resources.
Even if quaternary sediments were not the primary interest of the project, Hauer tried to establish a first approach to mapping and classification of these deposits.

Fig.2. The second edition of the General Geological General Map of the Austro-Hungarian Monarchy compiled by von Hauer (Archive of the Austrian Federal Geological Survey) compare to Fig.4. for the loess formation (mainly yellow and ligth green coloured area), from GAUDENYI & JOVANOVIC 2010.

Fig.3. Enlargement of the map in Fig.2.

The General Geological Map of the Austro-Hungarian Monarchy presented in 1865, and produced between 1850 and 1856, was one of the most comprehensive and complete geological map of Central Europe during that period of time.


The Quaternary formations were subdivided in two groups: Pleistocene and Holocene formations. The Pleistocene formations identified as "Dilluvial" included predominantly fluvial gravels and sand, but also loess.
The Holocene formations were denominated "Alluvial" and included peat, lime tuff, quicksand and other formations summarized only as "Alluvial formations".
Loess was mentioned exclusively as a Pleistocene ("Dilluvial") formation and the distribution clearly outlined, even if, for lack of detailed knowledge, the definition differs from the modern understanding of loess . In the Austrian geological map for example, the loess formation in some areas also included "loess-like" sediments, as for example colluvial deposits.


Nevertheless it was one of the first maps which documented the extent of loess deposits in Europe and West Asia.

Fig.4. Modern map of loess distribution, from HAASE et al. 2007.


*The Student's Elements of Geology (1870): "In some parts of the valley of the Rhine the accumulation of similar loam, called in Germany "loess," has taken place on an enormous scale [several hundred feet thick]. Its colour is yellowish-grey, and very homogeneous; and Professor Bischoff has ascertained, by analysis, that it agrees in composition with the mud of the Nile. Although for the most part unstratified, it betrays in some places marks of stratification, especially where it contains calcareous concretions, or in its lower part where it rests on subjacent gravel and sand which alternate with each other near the junction. Although this loam of the Rhine is unsolidified, it usually terminates where it has been undermined by running water in a vertical cliff, from the face of which shells of terrestrial, freshwater and amphibious mollusks project in relief. These shells do not imply the permanent sojourn of a body of freshwater on the spot, for the most aquatic of them, the Succinea, inhabits marshes and wet grassy meadows."


REFERENCES:

GAUDENYI, T. & JOVANOVIC, M. (2010): Franz Ritter von Hauer's work and one of the first loess map of Central Europe. Quaternary International. 10.1016/j.quaint.2010.04.008

HAASE, D., FINK, J., HAASE, G., RUSKE, R., PECSI, M., RICHTER, H., ALTERMANN, M., JÄGER, K. D. (2007): Loess in Europe - its spatial distribution based on a European Loess Map, scale 1:2,500,000. Quaternary Science Reviews 26 (9-10), 1301-1312

Kommentare:

Silver Fox hat gesagt…

I love loess! Great post.

David Bressan hat gesagt…

Thanks - who doesnt´t love loess ;) loess often shows beautiful soil horizonts, and is good to grow hop to make beer ;)

Just for curiosity: Is there research or made mapping efforts in the U.S. dealing especially with loess?