Samstag, 25. Juli 2009

Ice age gravel deposits

Gravel pits are widespread in northern Germany - they exploit the vast gravel deposits that underlay the flat landscape. This gravels were of fluvioglacial origin, deposited in braided river systems feed by the vast ice shields that covered the northern german territory in the main ice ages. During interglacial periods, the rivers, freed of the sediment bedload, eroded they way trough the formely deposited sediments, and cut valleys, that in the next glacial were refilled partially with new material. Based on this principle, the german quaternary sediments were subdivided in different fluvial terraces, mainly four - corresponding – in a simplified view- to the four mayor ice advances – Brüggen- Menap, Elster, Saale and Weichsel, named after the area of the rivers the single highstand reached.

The age and the deposition environment of the gravels can also be inferred by fossils and artefacts that can found in them, in fact the vast area that they cover, and the thickness makes them to one of the major source of such finds in Europe.
In the sand-lenses, alternating with glaziofluvial gravels outcropping in the baroque park of the castle of Hundisburg, westward of the thuringian city of Magdeburg, already 1921 an silex biface and some artefacts were discovered.

A memorial plaque recalls the discoveries of Hundisburg.

Based on the stratigraphy, and the interpretation of some lithogies as morains, the site was attributed to pre-Saale or pre-Elster in age. In recent excavations more artefacts were found, also bones and teeths of different mammals.

This fossils, comprising parts of molars attributet to Mammuthus, seems to confirm a deposition in a cold environment. The artefacts and silex instruments are attributed to the cultural epoch of the Acheuléen, ranging from 1,5 million years to 150.000 years ago, so unfortunately they are not very helpful to determinate the age of the gravels. But also the “morains”, after modern observations, can be interpreted as cryogenic disturbed sediments, so the relative age – early to middle Pleistocene - of this finds is highly controversial.


Silex artefact

Lthic flake of quartzite, processecd by early man, found in gravel deposits in the vicinity of Quedlinburg.

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