de GRACIANSKY, PIERRE CHARLES, Ecole des Mines de Paris, Paris, France, G. DARDEAU, Institut de Geodynamisme, Nice, France, T. JACQUIN, Ecole des Mines de Paris, Paris, France, R. MOUTERDE, Laboratoire de Geologie, Lyon, France, and P. R. VAIL, Rice University, Houston, TX

ABSTRACT: Stratigraphic Signatures of the Tectonic and Eustatic Effects During the Synrift History of the South European Tethyan Margin in the Daupine Zone, Subalpin Range, France

The Dauphine basin comprises a complex system of extensional and transfer faults that developed during the rifting phase of the south European Tethyan margin in the Early to Middle Jurassic. During that period, the surrounding highs were covered by carbonate platforms such as the Jura, the Provence, and the Brianconnais; whereas hundreds of meters of marls and shales accumulated in the troughs. Ten sections along a 50-km transect have been measured between the Digne trough and the Provence platform. The dating is high resolution by ammonite horizon. They provide an exceptional opportunity to discriminate tectonic from eustatic effects.

Five major transgressive-regressive cycles have been documented for the Liassic and the Middle Jurassic along this transect. These are controlled by episodic phases of extension dated as Sinemurian, middle Pliensbachian, late Bajocian, and latest Bathonian; these were well established from field observations.

Extensional phases are followed by rapid subsidence giving rise to sediment starvation in the basins and to peak transgressions on the platform. Subsequently, basinal areas were progressively infilled by shales. These long-term cycles coincide extremely well in time with other European basins showing that Tethyan rifting influenced the disintegration of the late Variscan European platform.

Higher frequency events are thought to be of eustatic origin. Their stratigraphic signature depends widely on their place within major cycles. The high-frequency cycles around peak transgressions may be highly condensed but cover wide surfaces on the platforms (e.g., Bifrons zone). High-frequency cycles close to peak transgressions are characterized by the thick lowstand deposits in the basins, such as those of the early Aalenian. Some of them may even have been removed from the highs by subaerial erosion when block tilting induced enhanced unconformities.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.