نتایج جستجو برای: middle ordovician
تعداد نتایج: 156546 فیلتر نتایج به سال:
This is the first description of Ordovician cephalopods from Morocco. Although their occurrence has been known for a long time, only a poorly preserved conch from the late Katian of Ikhf n’Ouzerg (central Anti-Atlas) was described as “Orthoceras hastile Barrande” by Termier & Termier (1950). In some cases Ordovician cephalopods were mentioned within faunal lists without classification (e.g., Gu...
Middle Ordovician phosphatic ironstone of the Welsh Basin provides new insight into paleoenvironmental significance and ocean chemistry. Deposition occurred in a back-arc basin along southern margin Avalonia as Rheic Ocean opened to south. Ironstone is interpreted have accumulated part an aggradational parasequence on storm-dominated shelf with coastal upwelling. This has laminated pyritic muds...
Phytoplankton form the base of most marine trophic chains and studying their past diversity at regional global scales can provide valuable insights into evolution ecosystems climate history. Using a new database more than 4000 species acritarchs prasinophytes, comprehensive investigation taxonomic trajectories this (micro)phytoplankton throughout Paleozoic is performed for first time. This data...
In the wake of the end-Permian mass extinction, the Early Triassic (~251.9 to 247 million years ago) is portrayed as an environmentally unstable interval characterized by several biotic crises and heavily depauperate marine benthic ecosystems. We describe a new fossil assemblage-the Paris Biota-from the earliest Spathian (middle Olenekian, ~250.6 million years ago) of the Bear Lake area, southe...
isotope data from bulk carbonates, micrite, marine calcite cements, non-skeletal grains and brachiopods indicate deposition of a wide spectrum of warm to cold water carbonates during the ordovician and the jurassic. this isotopic interpretation is supported by warm to cold climatic models proposed for the ordovician and the jurassic. these carbonates formed during the greenhouse mode (condition...
The pre-Variscan sequence of the Carnic Alps is exposed across state border between north-east Italy and Austria. It includes Middle Ordovician to Lower Pennsylvanian rocks that, although affected by both Variscan Alpine orogeny, preserve continuous non-metamorphosed successions. Depositional settings vary from shallow water open marine environments. Remarkable presence largest Devonian reefs E...
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