A 3-D model of the Paris basin was constructed to reconstitute its 248 m.y. geologic history from the Trias to the present. The model is based on detailed stratigraphic and lithographic data from about 1,100 petroleum drillings. Its scale is regional and it covers a surface area of 700,000 km2, which exceeds the present extent of the basin in order to allow the paleogeographic evolution of the European plate to be taken into account. The geological history is simulated with the numerical model NEWBAS from the Ecole des Mines de Paris.
The model simulates sedimentation, erosion, compaction, fluid flow and processes of solute and heat transport. The objective of this article is to demonstrate the value of this type of modelling for estimating and quantifying the role of fluid circulation in geological processes. Studies of diagenetic cements in the Dogger and Keuper aquifers in the Paris basin have often led their authors to consider the involvement of regional fluid circulation. These studies provide estimates of paleotemperature and paleosalinity which impose constraints on the modelling but the latter may, in turn, contribute to date the events and estimate the relevant processes. By reconstructing heat and salt transport, as proposed in this article, it is therefore possible to define the influence of hydrodynamics on these processes. The history of heat and salt in the basin is shown at various stages on a representative NW-SE cross-section of a present-day flow line which is also valid for Tertiary times. We demonstrate that the role of hydrodynamics may be predominant for salt transport by gravity-driven flow, which explains the salinity increase in the Keuper aquifer and the role of the Bray fault in the salinisation of the Dogger. Although the heat transport is dominated by the conductive component, it is also influenced by the hydrodynamics with a possible convective cooling effect when the head in the aquifers increased at the end of the Tertiary erosion period. This may partly explain the higher temperatures, deduced from fluid inclusions in the Keuper, at the end of the chalk deposition as compared to present ones. According to our simulations, the early Tertiary is the period most compatible with the diagenetic observations for thermal (maximum burial and convective cooling effect) and chemical reasons (topography allowing migration of brines in the Keuper and the Dogger).