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Trossingen Formation
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Trossingen Formation
The Trossingen Formation, formerly the Knollenmergel (also known as the Arnstadt Formation), is a geological formation in Germany and Switzerland. It dates back to the late Norian-Rhaetian. It belongs to the Keuper Group of the Germanic Triassic. The Trossingen Formation is underlain by the Löwenstein Formation and erosively overlain by the Exter Formation, in part also directly by the Black Jurassic.
The horizontal boundary of the Trossingen Formation is a diachronous facies boundary and is characterized by the exposure of the sandstones of the Löwenstein Formation. The hanging wall boundary is also sharply defined facially and characterized by the erosive overburden with terrestrial sediments of various locally widespread strata of the Exter Formation (Malschenberg Clay or Sandstone, Contorta Clay, Tübingen Sandstone) or, in the case of the more extensive Upper Keuper Hiatus, directly with the dark marine mudstones of the Hettangian onwards Black Jurassic.
The Trossingen Formation itself consists of fairly uniform, reddish-brown to red, sometimes purple claystones with occasional layers of calcareous nodules (hence the name "Knollenmergel"). In northern Franconia, continuous limestone crusts several meters thick can also occur. Carbonaceous mudstones and silicified limestones also occur locally at the top of the succession.
The Trossingen Formation is restricted to the edge area of the Vindelizian Threshold and thus to the South German stratigraphic zone. The average thickness is about 40 to 50 m, in northern Franconia values between 55 and 60 m are reached. In southern Württemberg (Wutach area), the thickness decreases to 10 m. The differences in thickness are due on the one hand to the interlocking with the Löwenstein Formation and on the other hand to the Rhaetian/Early Jurassic erosion.
Chronostratigraphically, the Trossingen Formation is placed in the uppermost Norian or lower Rhaetian (upper Upper Triassic). The type locality or type profile is the impact slope of the Trosselbach near Trossingen (Tuttlingen district). It was named after the town of Trossingen. The type region is southwestern Baden-Württemberg.
The outcrops of the Trossingen Formation are characterized by so-called "hummocky" meadows. It forms very heavy soils (minute soil), which can be recognized by typical tree growth (crooked and leaning trees), and is prone to frequent landslides after rainfall. Tuberous marl landscapes can often only be used for orchards.
Due to its richness in claystone, the Knollenmergel, like many Keuper formations, is a difficult subsoil for buildings of any kind because the claystones contain three-layer clay minerals that are swellable due to water retention in the intermediate layers. Intensive arable farming is therefore also problematic due to the fact that it is highly dependent on weather conditions. Like many claystone-dominated rock sequences, nodular marl tends to creep on slopes. This manifests itself in the sabre growth of trees on slopes.
The lithology of the Trossingen Formation, particularly at the Trossingen dinosaur site, is dominated by fine-grained sediments with minimal stratification, indicating post-depositional disturbance. Sandstones are rare, appearing only as thin intercalations in certain areas. Is dominated by mudstones with varying compositions and colors, divided into three main stratigraphic units: the lower beds, dark purple, marbled mudstones rich in carbonates. They contain calcitic replacements of small roots and show signs of pedogenic processes, including mud cracks and pseudobreccias. The presence of carbonate is highest in these beds, contributing to their distinctive texture and appearance. Next are homogeneous red-brown beds of light reddish-brown mudstones with lower carbonate content. They contain occasional small, round carbonate nodules, which increase in size and clustering towards the lower part of the unit. The last beds range from light purple to brown mudstones and have moderate carbonate content. Some layers contain calcitic root replacements, scattered carbonate nodules, and mud cracks that transition into pseudobreccias. This unit lacks the marbled appearance of the Lower Beds but shares similarities in texture and composition.
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Trossingen Formation
The Trossingen Formation, formerly the Knollenmergel (also known as the Arnstadt Formation), is a geological formation in Germany and Switzerland. It dates back to the late Norian-Rhaetian. It belongs to the Keuper Group of the Germanic Triassic. The Trossingen Formation is underlain by the Löwenstein Formation and erosively overlain by the Exter Formation, in part also directly by the Black Jurassic.
The horizontal boundary of the Trossingen Formation is a diachronous facies boundary and is characterized by the exposure of the sandstones of the Löwenstein Formation. The hanging wall boundary is also sharply defined facially and characterized by the erosive overburden with terrestrial sediments of various locally widespread strata of the Exter Formation (Malschenberg Clay or Sandstone, Contorta Clay, Tübingen Sandstone) or, in the case of the more extensive Upper Keuper Hiatus, directly with the dark marine mudstones of the Hettangian onwards Black Jurassic.
The Trossingen Formation itself consists of fairly uniform, reddish-brown to red, sometimes purple claystones with occasional layers of calcareous nodules (hence the name "Knollenmergel"). In northern Franconia, continuous limestone crusts several meters thick can also occur. Carbonaceous mudstones and silicified limestones also occur locally at the top of the succession.
The Trossingen Formation is restricted to the edge area of the Vindelizian Threshold and thus to the South German stratigraphic zone. The average thickness is about 40 to 50 m, in northern Franconia values between 55 and 60 m are reached. In southern Württemberg (Wutach area), the thickness decreases to 10 m. The differences in thickness are due on the one hand to the interlocking with the Löwenstein Formation and on the other hand to the Rhaetian/Early Jurassic erosion.
Chronostratigraphically, the Trossingen Formation is placed in the uppermost Norian or lower Rhaetian (upper Upper Triassic). The type locality or type profile is the impact slope of the Trosselbach near Trossingen (Tuttlingen district). It was named after the town of Trossingen. The type region is southwestern Baden-Württemberg.
The outcrops of the Trossingen Formation are characterized by so-called "hummocky" meadows. It forms very heavy soils (minute soil), which can be recognized by typical tree growth (crooked and leaning trees), and is prone to frequent landslides after rainfall. Tuberous marl landscapes can often only be used for orchards.
Due to its richness in claystone, the Knollenmergel, like many Keuper formations, is a difficult subsoil for buildings of any kind because the claystones contain three-layer clay minerals that are swellable due to water retention in the intermediate layers. Intensive arable farming is therefore also problematic due to the fact that it is highly dependent on weather conditions. Like many claystone-dominated rock sequences, nodular marl tends to creep on slopes. This manifests itself in the sabre growth of trees on slopes.
The lithology of the Trossingen Formation, particularly at the Trossingen dinosaur site, is dominated by fine-grained sediments with minimal stratification, indicating post-depositional disturbance. Sandstones are rare, appearing only as thin intercalations in certain areas. Is dominated by mudstones with varying compositions and colors, divided into three main stratigraphic units: the lower beds, dark purple, marbled mudstones rich in carbonates. They contain calcitic replacements of small roots and show signs of pedogenic processes, including mud cracks and pseudobreccias. The presence of carbonate is highest in these beds, contributing to their distinctive texture and appearance. Next are homogeneous red-brown beds of light reddish-brown mudstones with lower carbonate content. They contain occasional small, round carbonate nodules, which increase in size and clustering towards the lower part of the unit. The last beds range from light purple to brown mudstones and have moderate carbonate content. Some layers contain calcitic root replacements, scattered carbonate nodules, and mud cracks that transition into pseudobreccias. This unit lacks the marbled appearance of the Lower Beds but shares similarities in texture and composition.
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