Donnerstag, 18. Juni 2009

The Ehringsdorf-Formation: or travertine trouble

Even if the first descriptions of the travertine* deposits from Weimar can be traced back to J.C.W.Voigt (1781), and later Goethe draw the first stratigraphic section, only in the years after 1965 they were studied intensively and with modern methods.
STEINER (1983) described three facies in the travertine body, that in 2007 was defined as Ehringsdorf-Formation.

Spring near or marginal facies: characterized by a low topographic gradient and slow running water. In the developing shallow ponds Chara “lawn” developed and fine chalk sand or lake marls were deposited

Slope facies: strong topographic gradient with riffle-pool sequence, the water flows fast and loosing his dissolved carbonate deposits compact travertine layers, the calcification of organic material is very strong.

Valley facies: the slope changes in the broad alluvial plain of the Paleo – Ilm River, the travertine interfingers with loamy and pebbly river sediments. Then follows an alternation of lake marls, an travertine with imprints of reed.

The three-dimensional standard section of the Pleistocene travertine near Weimar is distinguished by three facies ranges following one after another in the direction of the flow of the karst spring waters which are characterized by characteristics or type rocks showing typical structural marks. From the results of the investigation the conclusion is that other occurrences of travertine probably have a similar facial, and, by this, stratigraphically complicated division. This must be taken in consideration much more than until now in all further discussions of stratigraphic questions, also in the discussion of the dating and the absolute age and coordination of paleontological finds in geological sections.

Idealized cross section trough the travertine deposits of Ehringsdorf (after STEINER 1979). White= travertine, black= "Pariser". Notable the coal bearing horizonts in the lower travertine, showing human presence.

The age of the travertine of Ehringsdorf is highly controversial. The position between sediments deposited in cold environments (the fluvial conglomerate represents a braided river system, the uppermost loess layers show ice wedges and cryoturbation) let conclude an interglacial age.

The faunal assemblage supports in part an interglacial position, with the upper part belonging to the Eemian (ca. 130.000y), and the lower part, or at least the base, dating back much further to an Intrasaalian age (OIS7 - 200.000y). The presence of Cricetus major in the soil of the Pariser seems in part to support an Eemian or older date for the upper part of the formation. The malacology on the other side seems to support older ages for both travertine bodies, typical Eemian species are lacking.
The study of human "Präneanderthalian"artefacts, with wedge like utensils and scrapers/spires showed similarities with artefacts found in Eemian to early Würmian (or in this case better Weichsel) ages sites.

The radiometric dating in 2000 using the U/Th method resulted in ages of 236+-13ka for the lower, and 198+-10ka BP for the upper travertine. Unfortunately these results are not universally accepted, the travertine is not a closed system, and water can easily enter the rock and falsifying the isotopic composition.

So still the age remains a trouble.


KATZSCHMANN (2007): The Ehringsdorf Formation. In LithoLex [Online-Datenbank]. Hannover: BGR. Last updated 30.11.2007. [cited 20.06.2009]. Record No. 1000002

*Unfortunately the term “travertine” is somehow vague in different languages. Travertine limestone in English is referred to form around hot springs or by inorganic processes. Calcareous tufa forms by precipitation of calcium carbonate from “cool” springs and river waters, also improved by organic processes. To remain as near as possible to the meaning and use of the word “Travertin” in German, where the distinction is not so clear, here also travertine is used in sense of calcareous tufa.

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