Controls on sedimentary deposits in the coastal environments of the Paris Basin at the Eocene-Oligocene transition.

The Eocene-Oligocene Transition (‘EOT’) marks a global deterioration in climate associated with the establishment of the Antarctic polar ice cap, but is poorly constrained in continental areas. In Europe, a marked seasonality and a major replacement of European flora and fauna by Asian species (the ‘Grande Coupure’ described by Stehlin, 1909) were recorded during this period. Deposits at the ocean-continent interface are recorded in the Paris Basin at the EOT, from the lagoon-marine to the lacustrine domains. Lithology and facies distribution are therefore controlled by mechanisms on a global and local scale (tectono and glacio-eustatism, climate, tectonic), which need to be differentiated and highlighted. We present a mineralogical, elemental and isotopic geochemistry record of three Upper Priabonian to Upper Rupelian sections located in the northern Paris basin (Cormeilles-en-Parisis, Le Pin-Villeparisis and Saint-Soupplets), near the Bray anticline. Cormeilles-en-Parisis, the westernmost, is located in the Saint-Denis synclinal and shows the most complete sedimentary sequence, more clayey and carbonaceous. It is fossiliferous but not very diverse. The Saint-Soupplets section, located on the eastern flank of the perianticlinal end of the Bray, shows the same sequence of formations as the Cormeilles-en-Parisis section, but is characterised by sandier deposits with current and erosive figures. The Le Pin-Villeparisis section, located on the western flank of the Bray anticline and between the two other sections, is truncated in its upper part and relatively condensed. It is essentially clayey and mostly barren of fossils.

In the Upper Priabonian, the sedimentary record shows a tectonic pulse at the origin of terrigenous inputs and the creation of positive topography, then the Late Eocene regression and the decrease of the tectonic activity inducing the progradation of continental deposits. In the Lower Rupelian, the long-term increase in detrital terrigenous deposits and the environmental changes suggested by floral and faunal data are probably due to the combination of tectonics and eustatism. To the west (Cormeilles-en-Parisis section), a few evaporitic levels show a lagoonal environment that is almost always submerged. To the east, the sections are incomplete (erosive levels and missing formations), influenced by the structure of the anticline, which forms a topographic barrier and a positive relief. The absence of certain formations and the presence of a clearly lacustrine formation at the top of the Le Pin-Villeparisis section show the proximity of the coastline, which is more prone to emersion when subjected to tectonic uplift. 

 

Reference: 

Stehlin, H., 1909. Remarque sur les faunules de mammifères des couches éocènes et oligocènes du Bassin de Paris. Bull. Société Géologique Fr. 19, 488–520.