THE SEDIMENTS OF THE UPPER MARINE MOLASSE (OMM) OF THE SOUTH-WESTERN HORNLI FAN (EASTERN SWITZERLAND) AND THE PALEOECOLOGICAL INTERPRETATION OF ITS FOSSIL CONTENT

Due to strong constructing activities in the region of Jona before 199 0, the study of the lithological relationships of the younger portion of the Upper marine Molasse (OMM) became possible. The petrography of the sediments, and their fossil contents showed up a rather clear pict ure of the ecological conditions of their surrounding. Basically there were near-coastal and shallow marine conditions. The molluscs indicat e a rather turbulent water body. The sharks and rays reflect mainly a shallow marine environment, although bathyal forms also occur. In spit e of nearby delta-sequences, the conditions almost never were really b rackish. Occasional weak decrease of salinity is partly indicated. The age of the sediments is considered to be approximately 18 million yea rs old, based onto Sr-isotope analysis. This would be equivalent to th e Neogene mammal zone MN 4, according to correlations of the somewhat younger site of Tagernaustrasse and the correlation with the mammal be aring profiles of the nearby Goldinger Tobel.