Subsidence of the Paris Basin

Abstract

We discuss the main results of a systematic quantitative analysis of the subsidence of the Paris basin made on 100 wells. Backstripping techniques with decompaction as well as sea level and water depth corrections are used to derive tectonic subsidence curves (in the absence of water and sediment loading) assuming local as well as regional compensation. A best fitting sea level variations curve is derived for the deepest central part on the basis of the resulting tectonic subsidence curve. The adopted amplitude of the regression since Upper Cretaceous is 330 m. The spatial and temporal distribution of tectonic subsidence is reconstructed and discussed. It is shown that rigidity of the lithosphere (with an adopted 50‐km flexural parameter) plays a significant role. These results are then quantitatively interpreted in terms of the lithospheric stretching model. This interpretation is reasonable provided it is made in terms of volumetric subsidence over the whole basin, because of the thermal conduction and the rigidity low‐pass filtering effects. The subsidence can be explained if the axial zone was thinned during Permo‐Triassic by a factor of about 1.3 with respect to the adjacent lithosphere. It is shown that either the initial altitude was more than 500 m above sea level or the lower part of the lithosphere was lost at the beginning of the Permo‐Triassic phase of extension, resulting in a rapid uplift of several hundreds of meters. The similarity of the Permo‐Triassic initiating extensional phase with active continental rifting is shown.