Middle muschelkalk evaporitic deposits in eastern Paris basin

Abstract

Middle Muschelkalk of the eastern Paris Basin is an extension of the large German Basin than an unit by itself. It allows us to study the effects of continental influences on evaporitic sedimentation: fresh water and detrital supplies, and salt dissolution. More or less evaporated sea water flowing into the basin causes a cyclic evolution of salinity throughout the series.

The deposit is generally layered and shows millimetric to centimetric primary depositional sequences which prove the complexity of the internal organization of the filling in the basin. They reflect elementary changes in the depositional environment: fresh water supplies carring detrital particles, fresh water and sea water inflow introducing dilution, increasing evaporation rate causing precipitation of carbonates, Ca-sulfate or halite. In fact, the main factors controlling sedimentation which are working at this fine scale and the evolution at a larger sequential scale depends upon which one of these factors becomes dominant. The general evolution results in a typical sedimentary cycle.

The structural behavior of the Hercynian basement controls distribution and sometimes preservation of the depsits. Diagenesis may also preserve or totally destory primary sedimentary structures. Algal mat-like deposits undergo extensive Ca-sulfate diagenesis in the middle of the sedimentary cycle and toward its top, dolomites and magnesium-rich corrensites develop layer by layer.

Middle Muschelkalk of the eastern Paris Basin is a very good example for the study of sedimentary processes involoved on the edges of a large evaporitic basin.