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Quaternary Stratigraphy between Danube and Rhine

Dietrich Ellwanger1, Ulrike Wielandt-Schuster1, Matthias Franz1
1 Referat 92, RPF LGRB, Freiburg

V 1.10 in Fortschritte der Quartärstratigraphie

17.09.2012, 15:10-15:30, H8

 

The newly assigned Quaternary Lithostratigraphy of the alpine foreland between Bodensee and Danube Valley will be discussed. Traditional chronostratigraphy as established by Penck serves as background (1). Overdeepened glacial basins are considered as elements only little observed by Penck (2). Finally, the new lithostratigraphical units (Formations) are introduced and discussed (3). Conclusive remarks include scenarios applying the new lithostratigraphy and a hint towards unique features of the Rhineglacier area .



(1) The Pleistocene Rhineglacier and its meltwaters have shaped most of the actual topography of the area between Bodensee and Danube valley. Here and everywhere around the Alps, Quaternary Stratigraphy traditionally comprises the units of Würm, Riss, Mindel & Günz, as established by Penck & Brückner since 1901. This alpine version of Quaternary Stratigraphy is primarily based on terrace stratigraphy. All four units were supposed to represent glacier advances, based on the “partial” evidence that many of the Würm and Riss aged terraces originate at or within the adjacent moraine topography (the two landsystems were correlated by the “Glaziale Serie” – Penck’s classical facies model). – Until today Penck’s scheme is still widely in use, though several major upgrades and re-adjustments had to be included as more data became available. In our region between Bodensee and Danube, all geological maps in scale 1 : 25000 were worked out accordingly. This map series has been completed in 2008 – but it is difficult to handle due to the upgrades.

The latest re-adjustments were based on lithofacies patterns of the sediment infill of overdeepened glacial basins and actual sedimentological results, and supported by time markers from palaeontological and palaeomagnetical investigations (not yet by physical dating techniques). The resulting Quaternary Chronostratigraphy (Table 1) consists of

three Middle and Late Pleistocene major ice advances (glacial stages, glaciations), grading up into the Holsteinian, Eemian and Holocene interglacial stages, and

three Early Pleistocene Deckenschotter units of mainly fluvial origin, related to the Tiglian and Bavelian.

Holocene

Late Pleistocene

Middle Pleistocene

Major Ice Advances

Würm (==> Holocene)

Riss (==> Eem)

Hoßkirch (==> Holstein)

Early Pleistocene

Deckenschotter

Mindel (==> Bavel)

Günz

Donau (Tiglian)



(2) Although most units in Penck’s original scheme, including update-schemes, represent glacier advances of some kind, one major effect of the glacial environment has been given surprisingly little attention: the overdeepening beneath the ice. By this process, the surface at the alpine margin has been transformed from a preglacial ramp of foothills and valleys into the actual deep valleys and foreland amphitheatres. The amphitheatres comprise areas covered with till and overdeepened basins that are, partially or wholly, filled up with glaciolacustrine and lacustrine deposits. – Each “Major Ice Advance” also represents a generation of major glacial basins, i.e. we recognise three transformation steps from ramp to amphitheatre.

Related to the glacial basins we find not only the deep erosion events with their major unconformities, but also the thickest depositional sequences of this puzzle of discontinuous Pleistocene sediment units. The transition from erosion to deposition is a matter of the subglacial environment, i.e. in terms of chronostratigraphy both processes happen at a glacial stage. After meltdown of the ice, sufficient accommodation space will usually be available for further sediment infill. I.e., deposition may continue as sediment input goes on. Subglacial deposits may be followed by proglacial, periglacial and post-glacial deposits (the latter finally representing the interglacial stage to follow. The boundary between glacial and interglacial deposits usually shows no or little difference in lithology).

In a similar way can be argued with regard to the fluvial environment, although this is a more input-controlled system, set up even more discontinuously.



(3) Some years ago the task came up in the Geological Survey, to re-describe the subsurface with main focus upon litho-units. In this approach, the prime boundaries of the main sediment units are inevitably related to the major unconformities, whilst there is less need to subdivide a continuous sediment sequence by means of chronological marks (if available). This leads into a dilemma using the Quaternary chronostratigraphy as outlined above, where the main unconformities lie in the midst of chronostratigraphical stages, and chrono-boundaries within litho-successions. All these processes can be described in terms and patterns sensu Penck, but this may become complicated. We felt it more convenient to use the major unconformities as prime boundaries of major units, in this case formations and members (not stages).

This simple idea has been further developed to a new and very simple lithostratigraphical system. Each recognized generation of major glacial basins represents an “unconformity-bounded” unit (formation) that is, as required, further subdivided into subunits (members, facies units etc.). It has been thoroughly and successfully tested in projects of applied geology, in mapping in different scales, in short and long distant correlation (after all, lithostratigraphy is supposed to be a “correlation method”), and now it has been officially assigned as Quaternary Lithostratigraphy of the new digital map of Baden-Württemberg.

three “Major Ice Advances”

D1-unconformity ==> Hasenweiler-Fm

D2-unconformity ==> Illmensee-Fm

D3-unconformity ==> Dietmanns-Fm

Eldest glacial deposits ==> Steinental-Fm

Oberschwaben-Deckenschotter

Mindel-Deckenschotter

Günz-Deckenschotter

Donau-Deckenschotter



This new lithostratigraphy is helpful solving many though not all questions in the Quaternary daily routine. It is easy to use whenever sediment bodies are to be considered or correlated, esp. regarding the 3D-architecture of the subsurface. It is though inexpedient in some questions regarding pedology. The main challenge we experienced with many friends of the Quaternary is, however, how to handle the phase-shifted units of this purely spatial approach, as opposed to the long practiced glacial-interglacial pattern.



The new lithostratigraphy refers to a major transformation of topography. This scenario has been worked out in some detail, and has been applied for an event-correlation from the alpine foreland into the southern Upper Rhinegraben, maybe far beyond. – The possibility to work out this new scheme is owed to some special features of the area between Bodensee and Danube that are unique in the alpine foreland. They are related to the evolution of the Rhine valley at the alpine margin in the Early Pleistocene, and to the re-orientation of the Rhine and the Rhineglacier from the Danube system towards the Rhine system in the Middle and Late Pleistocene.



Literatur s. http://www.bgr.bund.de/litholex



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Letzte Änderung 19.07.2012