Mode d'empilement et distorsion de sequences genetiques en milieu marin restreint; facies et architecture des depots hettangiens du sud-ouest du bassin de Paris

Abstract

Abstract In the southwestern part of the Paris Basin (Sologne region), dolomite and limestone deposits of Hettangian age represent an excellent cover for a thick sandstone reservoir, which is being worked by "Gaz de France" for natural gas storage in underground aquifers. The "genetic sequences" of these shallow marine deposits and their stacking patterns are associated with two orders of relative sea-level fluctuations. The thinnest genetic sequences are arranged in transgressive/regressive hemicycles that include distinct facies assemblages. The facies changes are related to rapid palaeogeographic variations that occur during the onset of each genetic sequence. On a different scale, the stacked genetic sequences are organized into three geometric patterns, which are related to long-term eustatic fluctuations (eg. aggradational, retrogradational, and progradational patterns). For each of these stacked geometries, the partitioning of sediment volumes, the degree of symmetry, and the two-dimensional architecture of the genetic sequences had been modified through time. These changes are related to the effects of two superimposed short-term and long-term sea-level oscillations that distort the stratigraphic record.