4th Swiss Geoscience Meeting, Bern 2006 Gravel with crystalline components on the helvetic border chain (Sieben Hengste area)

is part of the helvetic border chain. The helvetic border chain consists of cretaceous and tertiary sediments. Surprisingly gravel with crystalline components is found on the surface and in caves at places where no alpine glaciers are known to have ever overflowed. Due to the cretaceous Schrattenkalk the Sieben Hengste form today a karst plateau of ca. 2 km2. At the southern margin, the Schrattenkalk is overlaid by the Tertiary Hohgant-Formation, consisting mostly of more or less quartz-rich sandstones and Globigerinen-Mergel. Nearby outcrops of Habkern- / Schlierenflysch and of the prealpine Klippen nappe (Giswiler Klippen) exist also. From 1600-1870 m (asl) a sandy, loamy gravel is found in different sediment traps, as caves, hollows, dolines and waterless runs (Fig. 1). The largest outcrop lies in a line of hollows and runs in a length of about 1 km between Oberberg and Wagenmoos (Coord. 629.375/177.875). A 2 m deep profile not reaching the bedrock shows an unlayered, compact sediment under 50 cm of Braunerde. It looks like a mudflow, in no way adjusted and woozily poured. Half of the pebbles are non