Saint-Dié formation
The Saint-Dié Formation is a sedimentary formation of the central Vosges . It was deposited in the uppermost Rotliegend during the Permian .
etymology
The Saint-Dié formation, French Formation de Saint-Dié , was named after Saint-Dié .
Geography and geology
The Saint-Dié formation is in the Saint-Dié basin , in the Villé basin , and further north in the Champenay basin , in the Plaine basin and in the Nideck basin . The first two basins mentioned are pull-apart basins that arose along the east-northeast-trending Vittel Fault . The Vittel Fault, also Vittel-Loubine-Lalaye Fault (VLL), is an important Terrang boundary in the central Vosges, which separates the Saxothuringian zone in the north from the Moldanubian zone or Morvan-Vosges zone in the south. It should find its western continuation in the Bray fault . In the southwest, the Saint-Dié formation extends to Bruyères , in the southeast to south of Orbey .
stratigraphy
The Saint-Dié formation is the uppermost formation of the Rotliegend in the Vosges. It follows discordant to the Champenay formation and in turn is discordant from the among Triassic Senones formation ( Low red sandstone superimposed). It is difficult to estimate the thickness of the Senones Formation erosively removed; in any case, in the northern basin it reaches down quite deep into the Saint-Dié Formation.
The more than 120 m thick Saint-Dié formation consists essentially of brown-red, arkosischen Fanglomeraten . They represent former alluvial deposits which, based on the marginal faults of the pull-aparts, filled the tectonic basins. The very small particle size control of coarse clastic sediments and lack of stratification can be liquefied on mass transports ( Engl. Grain flows and debris flows ) close to the meter range. The individual transport packages are closed off by relatively thin, continuous layers of silt, which indicate that they will be washed out by running water.
The debris that is carried along consists of granites , volcanites and detritic sedimentary rocks from the Devonian , Lower Carboniferous and Permian. These pebbles are only slightly rounded, so their transport should have only been a few kilometers. As the marginal faults ( paleoreliefs ) approach, the size and angularity of the rubble fraction noticeably increase. The rubble and, above all, the sand fraction also have clearly rounded elements, which suggest a partial reprocessing of previously deposited formations.
The rich, silty - clayey matrix can be hardened in places by a dolomitic cement that replaces the clay fraction , which then gives the rock a light color.
Mostly in the lower section of the Saint-Dié formation there are layers with dolomitic crusts, so-called dolcretes or dolocretes, which are likely to be of pedogenic origin . The crusts can be several meters thick. They contain microcrystalline silica bulbs made from chalcedony and carnelian .
Several stages of soil formation can be observed. Vertically oriented tubers were likely caused by root rhizomes . The sub-horizontal formations, on the other hand, speak in favor of longer sedimentation pauses. Several growth phases can also be seen in the thicker crusts. They also often contain red carnelian layers.
Two of these horizontal crust layers are amazingly durable. The first is at the base of the formation and was mined on fluorite . It is assumed that it arose from lacustrine or palustrine limestone layers . The second layer in the hanging wall of the formation occurs in all basins.
Here and there, between the horizontal crust layers, there are also isolated, structureless dolomite lenses, which can become quite thick and which are difficult to interpret.
Age
Absolute ages for the Saint-Dié formation are not known. As the last Rotliegendformation it should belong to the Guadalupian and have an age of around 265 million years BP .