Lacustrine sedimentation in a Permian intermontane basin: The Villé graben (Vosges, France)

Abstract

The Permian Villé graben, located on a major fault of the Vosges basement, has several stages of fluvial fill interrupted by a period of lacustrine sedimentation. The lacustrine deposits of the Autunian 2 series include various facies: marginal and fan-delta clastics and permanent lacustrine carbonate facies evolving into evaporitic playa facies. Differential subsidence of tectonic blocks controlled the facies patterns from the margin to the centre of the basin. The sedimentation is determined by three components: terrigenous, volcanosedimentary and carbonate. Fan-delta progradation with resedimentation processes provided the clastic material. In the upper part of the lacustrine formation, volcanosedimentary material was deposited. Primary ash-fall sedimentation was followed by sub-aqueous erosion and redeposition. Towards the edge of the basin, the lacustrine facies is thin and was subject to frequent emergence. Sediments were occasionally oxidized and iron was redistributed to give mottled horizons. Cabonate crusts were precipitated and some silicification took place. In the centre of the basin, sapropelic carbonate sedimentation develops into a eutrophic lake with anoxic bottom waters. The sapropels are massive to finely laminated; they include monospecific ostracod faunas, type II to type III kerogens and a total organic carbon content reaching 2.7%. Cyanobacterial and microbial activity in these organic-rich sediments produced early diagenetic carbonate, phosphate and sulfide phases. At the top of the formation, important sedimentological changes follow a lacustrine regression. A restricted and evaporative environment leads to the development of an evaporitic playa lake with stromatolites.