International Field Workshop on 'The Triassic of eastern France'

Stop 4.4 - Bitche (Citadel): Middle Buntsandstein (Karlstal facies of the ‘Grès
vosgien’ Fm)
In this outcrop (Fig. 44), the Karlstal facies of the ‘Grès vosgien’ Formation are well exposed (Fig.
47). These facies are characterized by fluvial and aeolian deposits.
Figure 47: Outcrops of Bitche Cidatel.
Facies association: Fluvio-aeolian overbank environments
This facies association is observed in the upper ‘Grès vosgiens’ Formation, so-called the Karlstal
Formation (Fig. II.3, II.4). This association is very sandy and characterized by vertical pattern, from the base
to top (defined on the cores of the Soultz-sous-Forêts well):
- planar laminated sands containing cm-thick coarse sand layers,
- cm-thick planar laminations of fine to medium sand, that sometimes grade upward into
oscillatory ripples
- laminated silstones, or fine sandstones, along with red mudstones, sometimes bioturbated.
These facies can be more or less bioturbated. They form fining-upward sequences ranging in thickness
from dm up to 5 m, with frequent mud-crack structures at their top. Locally, aeolian facies can be
interbedded within these deposits. The first facies, interpreted as fluvial sheet flood deposit evolves vertically
into wave-ripple facies that suggest flood currents entering a subaqueous environment, a hypothesis
73