Station 12, Malbun Geology Trail: The Triassic Stratigraphy

The north face of the cliffs stretching from below Alp Turna up to the summit of the Augstenberg displays the sequence of all the Triassic rock layers found in the Malbun area. Here, they lie one above the other in the order in which they were deposited in the sea. The oldest layers are at the bottom, and the youngest at the top. Depending on the type of rock, the layers weather differently. Limestone forms steep rock faces. Clay-rich rocks, such as marl and shale, weather into gently sloping meadows. Dolomite forms steep faces similar to limestone but with abundant scree slopes.

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Different deposits due to different environmental conditions

Why did such different types of rock form in the same sea? The lowest layers of limestone were deposited 240 million years ago. The dolomite at the summit was deposited about 200 million years ago. From where we stand to the summit, we can thus see 40 million years of continuous rock deposition. Over this long period, water depth and climate changed. The limestones at the bottom and the shale clays above them formed in deeper water than the limestones further up and the gypsum and dolomites above them. In general, the north face shows a transition from a deeper to a shallower sea and an increasing influence of evaporation. The seafloor slowly rose, and the climate became warmer and drier.