Spatial correlation of fluid inclusion generations: reconstructing fluid flow during basin evolution

Abstract

Fluid inclusion analysis is used to reconstruct the spatial and temporal variation of fluid composition and thermal properties within the NE-German intracontinental basin. Microthermometric and SEM–EDS analyses of fluid inclusions allow the distinction of palaeo-fluid systems and show their lateral and vertical distribution and variation through time. Early fluids, migrating in the deeper parts of the basin, are characterised by complex salinities. Sulphur content of these fluids increases towards the contact with the Zechstein, suggesting a partial exchange with the evaporites. Coexisting fluids, restricted to authigenic minerals in the Upper Carboniferous sediments and Rotliegend volcanics are dominated by NaCl, CaCl2 and KCl. Younger, secondary fluid inclusions, sometimes containing gas phases, indicate increasing temperatures. Thermal properties of the fluid inclusions indicate steep thermal gradients below the base of the Zechstein and Rotliegend sediments. This is interpreted as documentation of convective or advective heat flow in the deeper parts of the basin, with the Zechstein salt as a seal to this convective system.