What is Giessen nappe?

The Giessen nappe is a tectonic nappe in the southeastern part of the Rhenish Massif in western Germany. The nappe is an "alien" unit in the Rhenohercynian zone of the Hercynian orogeny, it was thrust over the usual slightly metamorphosed Devonian and Carboniferous sedimentary rocks in this zone.

The Giessen nappe is often correlated with the Harz nappe in the Harz and similar units in the Bohemian Massif in the Czech Republic. These units form the rare erosional leftovers of small microcontinents that were during the Hercynian orogeny squeezed between the paleocontinents Gondwana to the south and Laurussia to the north.