Tuesday, November 11, 2008

The Hauptrogenstein-Formation

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I recently noticed a number of visitors coming from Wikipedia. There are several posts on the Hauptrogenstein on my blog. Please click on the tags Carbonate Sedimentology and Germany to find most of them.

The majority of rocks and formations within my mapping area are from the Middle Jurassic. During the Bajocian (Middle Jurassic) a shallow-marine carbonate platform - the Burgundy Platform - stretched from France towards the SE and prograded slowly into modern Germany and Switzerland. It represents the so called Celtic facies realm that grades into the Swabian facies realm E of Strasbourg and Bern. In Germany this transition is not preserved. The platform carbonates are composed of the oolitic complex of the Hauptrogenstein-Formation and the uppermost Ostreenkalk-Formation.

Paleogeography

While the W is mostly dominated by the deposition of marls the E is dominated by N-S trending oolitic barries and tidal areas. Back barrier facies belts developed W of these. Off-barrier deposition is again characterised by marls and intercalated strom deposits. A good map says more than a 1000 words though:


Paleogeographic reconstruction of the late Bajocian (from Gonzales & Wetzel, 1996)

Three facies belt can be distinguished in the geological record. A shallow-marine, high-energy oolitic barrier system controlled by tidal currents. A backbarrier with calmer water and deposition of micrites, oncolites and patch reefes and a off-barrier dominated by marls and tempestites.

In SW-Germany, in the S edge of my own field area, the interfingering of marls at the bottom, oolitic sands in the middle and backbarrier patch reefes can be very nicely observed in several profiles also indicating the slow progradation of the different facies over time and the growth of the platform towards the NE and SE.


References:

  1. Ramon Gonzales & Andreas Wetzel (1996): Stratigraphy and paleogeography of the Hauptrogenstein and Klingau Formations (middle Bajocian to late Bathonian), northern Switzerland, Eclogea. geol. Helv. 89/1
  2. Martin Ernst (1991): Lithostratigraphische und fazielle Untersuchungen des Hauptrogensteins (Bajocium) im SE-Oberrheingraben, Jber. Mitt. oberrhein. geol. Ver., N.F. 73

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