Alsace Part 2: The Geology - The Vosges and the Black Forest Mountain

In my previous post Alsace Part 2: The Geology - The Location of the Upper Rhine Graben, I gave a 35,000 foot view of the location of the Upper Rhine Graben and it's context in the European continent. The Upper Rhine Graben (URG) is an important geological feature in the Alsatian Wine growing region. The topological map of the Upper Rhine Graben and the location of major cities is shown in the illustration below:

On the left side of the above illustration, the topographical map shows that the highest features, the Vosges Mountains on the west and the Black Forest Mountains on the east, occur in the southern Upper Rhine Graben. The map also shows that as one goes farther north, the terrain becomes lower in elevation.
My focus will be on the southern URG because most of the Alsatian vineyards are located on the eastern slopes of the Vosges Mountains, in the region known as the sub-Vosgian Hills that stretches from Mulhouse in the south to Strasbourg in the north.

The illustration that was shown in Alsace Part 2: The Geology - The Location of the Upper Rhine Graben as well as the above two illustrations serves to set the stage for understanding where the various soil types that exist in the Alsace came from.
Also helpful to me was the time line⁴ shown below so that I could put events that were happening in the Alsace into geological context.

Some of the oldest rocks in the southern URG, known as the basement rocks are exposed on the flanks of the graben, mostly in the Black Forest and the Vosges Mountains. They include a variety of intrusive, metamorphic and Cambrian to Visean sedimentary and volcanic rocks of the Variscan Internides.³ (The Variscan Internides are built up either from the so-called Armorican Terrane Assemblage, that is peri-Gondwana crust initially situated south of the Rheic Ocean, or rock complexes that formed along the active margin of the Rheic Suture Zone.⁵)

A geological conundrum in the URG is that although some of the oldest rocks are known to exist in the Vosges and the Black Forest Mountains, the exposure of these rocks, or the uplift of the Vosges and Black Forest Mountains is generally thought to have occurred during the Miocene, or even during the Upper Pliocene 􏰀Pleistocene, quite late in the history of the URG.³
Having set this stage of the ancient geological history of the Vosges and Black Mountains, what is next is to explore the soil types that were being formed during the intervening years of the Variscan Orogeny and the uplift of the Vosges and Black Mountains that resulted in the soils that are so conducive to wine growing in the Alsace. Stay tuned.
References:
1. Li, Y., Tsukamoto, S., Frechen, M. & Gabriel, G. 2018 (January): Timing of fluvial sedimentation in the Upper Rhine Graben since the Middle Pleistocene: constraints from quartz and feldspar luminescence dating. Boreas, Vol. 47, pp. 256–270. https://doi.org/10.1111/bor.12266. ISSN 0300-9483.
2. Markus E. Schumacher, Upper Rhine Graben: Role of preexisting structures during rift evolution, TECTONICS, VOL. 21, NO. 1, 1006, 10.1029/2001TC900022, 2002.
3. Yair Rotstein, Marc Schaming, Tectonic implications of faulting styles along a rift margin: The boundary between the Rhine Graben and the Vosges Mountains, Tectonics, 04 March 2008, https://doi.org/10.1029/2007TC002149.
4. The Geological Society of America, GSA Geologic Time Scale v.5.0.
5. Kroner, Uwe, MANSY, JEAN-LOUIS, Mazur, Stanisław, Paweł, Aleksandrowski, Hann, Horst, Huckriede, Hermann, Lacquement, Fréderic, Lamarche, Juliette, Ledru, Patrick, PHARAO, TIMOTHY, ZEDLER, HUBERT, Zeh, Armin, Zulauf, Gernold, Variscan Tectonics, In book: The Geology of Central Europe, volume 1: Precambrian and Palaeozoic, Edition: 1, Chapter: Variscan Tectonics, Publisher: The Geological Society, Editors: Tom McCann, pp.599-664,