MICROBIAL ECOSYSTEMS AS MARKERS OF CHANGE S IN LACRUSTRINE ENVIRONMENTS IN FAN DELTAS - SOUTHERN RHINE RIFT (WESTERN-EUROPE)

The Rhine Graben begins to develop in the Upper Eocene. During the fir st paroxysmal stage a belt of sandstones and conglomerates, the so-cal led ''Conglomerats cotiers'', is deposited on the rift border. In the graben an euryhaline lacustrine basin regulates the extension of fan-d eltas which are developing along the boundary faults of the rift. Stro matolites preferentially colonize the littoral fringe of the lake wher e they find indurated substratums. So they appear to be excellent mark ers of the transgressive movements of the lake and its palaeomargins. The stromatolites also allow an excellent sequential subdivision to re construct the history of the basin.