EVOLUTION OF THE HELVETIC CARBONATE PLATF ORM IN EASTERN SWITZERLAND (TITHONIAN-BERRIASIAN) - A SEQUENCE STRATIGRAPHIC APPROACH

The paleogeographic evolution of a part of the northern Tethys margin (Helvetic area of the eastern Swiss Alps) has been analysed in the lim e window of the late Tithonian to the early Valanginian. On this open shelf, three intervals of southward migration of a carbonate platform can be distinguished. Unfavourable environmental conditions obstructed a continuous evolution; at times the platform emerged or was even ero ded. Reasons for these disturbances were changes in relative sea level , climatic changes and nutrient availability. Time correlation was pos sible for the lower part of the distal sections with the help of biost ratigraphy (calpionellids and ammonites). Sequence stratigraphic analy ses proved to be a useful tool for correlating the platform with the o uter shelf especially in the upper part of the sedimentary record. Thi s led to the reconstruction of a series of paleogeographic maps.