Jp. Loreau et al., STRATIGRAPHIC CYCLES IN ALPINE LIAS AND A ALENIEN SERIES FROM BOTH SIDES OF THE PENNIC THRUST (SAVOY, FRANCE) - TECTONIC CONTROL VERSUS EUSTATISM, Eclogae Geologicae Helvetiae, 88(3), 1995, pp. 529-551
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.