|Name: La Voulte-sur-Rhône
Location: Ardèche, France
Age: Lower Callovian, Jurassic
The rocks at La Voulte-sur-Rhône are fine-grained, sedimentary rocks called silty shales, which contain pyrite (iron sulphide, FeS2). In some areas they are red due to the oxidation of iron minerals. Some horizons contain concretions (a calcareous or siliceous mass formed around an object), and others show simple horizontal burrows. The rocks of La Voulte-sur-Rhône have an unusually high metallic mineral content.
The sediment was probably deposited in a low energy, shallow marine basin. The water column was episodically stratified (no mixing of water at different depths).
Evidence for low or no oxygen in the water
A turbidity flow (an underwater sediment flow driven by gravity) introduced organisms from a neighbouring oxygenated area (allocthonous fauna).
The lack of plant matter indicates that deposition occurred far from land.
The Lagerstatte at La Voulte-sur-Rhône is Lower Callovian in age. This stage occurs at the end of the mid Jurassic, approximately 160 million years ago.