STRATIGRAPHIC CYCLES IN ALPINE LIAS AND A ALENIEN SERIES FROM BOTH SIDES OF THE PENNIC THRUST (SAVOY, FRANCE) - TECTONIC CONTROL VERSUS EUSTATISM

Along a NW-SE transect in Savoy, stratigraphy of ''Delphino-helvetic Z one'', ''Breches de Tarentaise Zone'' and ''Subbrianconnais Zone'', is revised by using sequential analysis and all available biostratigraph ic data. From the early Rhetian to the late Aalenian, four to six unco nformities were identified from one structural and paleogeographical u nit to the other. They are boundaries of 2nd order cycles of a duratio n between 3 and 16 Ma. The Rhetian cycle is common to the different do mains and shows the predominant eustatic control on its origin. Howeve r, the boundary at the top is weekly marked because of the beginning o f regional subsidence. A Hettangian-Sinemurian cycle is specifically e videnced in the ''Dauphinois Basin'' in Savoy (Mont-Joly Nappe) and on the ''Subbrianconnais'' slope (Perron des Encombres Unit). The unconf ormity at the top of this cycle (Turneri-Obtusum boundary) is not obse rved in the other Zones but is recorded in all the West European basin s. It is considered as a tectonically enhanced unconformity where eust atic and tectonic effects were added. In the other Zones, Hettangian-e arly Carixian versus Hettangian-early Domerian 2nd order cycles are di fferent on both sides of the Penninic Thrust. The transgressive half c ycle ended earlier in the West (Angulata zone) than in the East (Semic ostatum zone) and earlier in the northern (Savoy) part of the ''Dauphi nois Basin'' than in the South (Digne Basin). On the ''Valaisan'' plat form and ''Subbrianconnais'' slope, the unconformity at the cycle boun dary corresponds to a significant distensive and block tilting episode throughout the Carixian (Jamesoni-Ibex zone boundary or intra Ibex zo ne). On the Mont-Blanc and Rocheray shoals (horsts), significant diste nsive events with block tilting were post-Carixian (post Davoei, proba bly Margaritatus zone). An additional cycle is differentiated through the Pliensbachian at the East of the Penninic Thrust. The unconformity surface in the early part of Margaritatus zone seems to be common to all the Units of the studied area and is known in all West European ba sins showing that it was influenced by eustatic effects and was tecton ically enhanced. The ''Valaisan'' platform was drowned during and afte r Domerian. Most of the Toarcian seems to be characterized by an overa ll starvation hiatus.