The Cenomanian–Turonian Boundary Event (CTBE) on the southern slope of the Subalpine Basin (SE France) and its bearing on a probable tectonic pulse on a larger scale
Résumé
The CenomanianeTuronian Boundary Event (CTBE) event is not associated with a transgression on the
southern margin of the Subalpine Basin, but with a steady shallowing-up trend beginning in the lower
half of the d13 C positive shift. The SWeNE Rouaine Fault had a complex role, first in isolating a black shale
basin to the west and a large, deep submarine plateau devoid of black shale to the east, then by a strike-
slip movement that induced a forced progradation to the north of the southern platform in the eastern
compartment. This compressive tectonic reactivation of the southern margin began around the depo-
sition of the local equivalent of the Plenus bed of boreal basins, as shown by correlation supported by
both isotope and palaeontological data. Other local data are pieced together to suggest that the whole of
SE France underwent a short-lived transpressive tectonic pulse around the CenomanianeTuronian
boundary, probably connected with the early compressive movement of Africa vs. Europe. On a larger
scale, other published data suggest that this pulse could be a global one. It is coeval with renewed thrust
loading, volcanism and transgression in the North-American Western Interior, local emergences during
the event along the eastern Atlantic margin, suggesting a slight tendency to inversion of the margin, and
a tilting to the east of the North-Africa plate that could explain the large transgression recorded from
Morocco to Tunisia on the Saharan Craton.
New isotope and palaeontological (coiling ratio of Muricohedbergella delrioensis) data from SE France
suggest that two coolings of suprabasinal importance occurred just before and during the build-up of the
d13C shift, including the boreal “Plenus Marls“, especially its middle limestone bed and its SE France
equivalent.
Regarding the extinction of the genus Thalmaninella and Rotalipora and during the event, neither
anoxia nor climate changes can fully explain the palaeontological crisis, given that Rotalipora cushmani
crosses the first phase of anoxia without harm, as well as the two coolings, not only in SE France but on a
large scale, as shown by the correlation of the published data. This extinction needs alternative expla-
nations as we challenge both anoxia and climate as major causes