Complex sentence: Before the formation of the Alps in the lower and middle Tertiary period, the Austroalpine rocks experienced another deformation phase: the Eo-Alpine phase of mountain building that took place in the Cretaceous.
Split into simpler sentences: Before the formation of the Alps in the lower and middle Tertiary period, the Austroalpine rocks experienced another deformation phase. The Eo-Alpine phase of mountain building took place in the Cretaceous.