Alsace Part 2: The Geology - The Location of the Upper Rhine Graben

I ended the previous blog on the Geology of Alsace with an illustration of the diversity of soil types that occur in the Alsace wine region.
Little did I know that when I said that I would write a blog about the Geology of the Alsace that I was embarking on an adventure that would take me back in time some 380 million years ago when the continental land masses were in a state of flux and the world as we know it today was still being jigsaw-puzzled together.
The region of Alsace is located on a geological feature called a graben. A graben is the German word for a grave-like trench.¹ The Upper Rhine Graben (URG), where Alsace is located, is part of the 1100‐km‐long European Cenozoic rift system which formed some 50 milion years ago.²
First, in order to understand where the Upper Rhine Graben (URG) is located we need to get a 35,000 foot view of the area:³

In the illustration above, the URG is the area shown in the rectangle. The URG is bordered by the Rhenish Massif to the north and the Jura Mountains to the south. It has a length of some 300 km, extending from Basel in the south to near Mainz in the north and a width between 30-40 km.³

In the above illustration, the left side shows a closeup of the area in the rectangle in the first illustration. This is the Upper Rhine graben.³ The cross hatched areas in that illustration shows something that the inset key identifies as "the basement".
Our major focus will be on the area shown on the right side, the southern URG, flanked by two main mountain ranges, the Black Forest Mountains on the east and the Vosges Mountains on the west.² It's a little strange that the cross hatched area, known as the basement is the location of the Vosges and Black Forest Mountains, but that is because those areas are of very ancient origin.
This will be the focus of the upcoming blogs, an area known as the Southern Upper Rhine Graben, what the various soil types are and when they were formed.
References:
1. James E. Wilson, Terroir The Role of Geology, Climate and Culture in the Making of French Wines, Reed Consumer Books Limited, 1998, ppg 82-107.
2. 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.
3. Markus E. Schumacher, Upper Rhine Graben: Role of preexisting structures during rift evolution, TECTONICS, VOL. 21, NO. 1, 1006, 10.1029/2001TC900022, 2002.
4. Jeanne Vidal, Albert Genter, Overview of naturally permeable fractured reservoirs in the central and southern Upper Rhine Graben: Insights from geothermal wells, Geothermics, 74 (2018) 57–73.
5. Vincent Maurer, Coralie Aichholzer, Alexandre Richard, Pauline Harlé, Régis Hehn, Albert Genter, Philippe Duringer, Geothermal reservoir temperature estimation derived from gradient wells in a continental rift context (Upper Rhine Graben), PROCEEDINGS, 43rd Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, February 12-14, 2018.
6. Etienne Skrzypek, Karel Schulmann, Anne-Sophie Tabaud and Jean-Bernard Edel, (Palaeozoic evolution of the Variscan Vosges Mountains) in K., Martınez Catalan, J. R., Lardeaux, J. M., Janousek,V.&Oggiano, G. (eds) The Variscan Orogeny: Extent, Timescale and the Formation of the European Crust, Geological Society, London, Special Publications, 405, http://dx.doi.org/10.1144/SP405.8, The Geological Society of London 2014.