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| Ammonoid and gastropod coquina, Wetterstein Limestone |
The lovely example of the Wetterstein limestone you see here is equivalent in age to the typically creamy orange limestones from nearby Hallstatt. The Wetterstein limestones are an adjacent Ladinian to Lower Carnian reef facies that provide a window into the end of the Carnian Pluvial Event (CPE).
The Carnian Pluvial Event is sometimes called the Carnian Pluvial Episode and is also known as Reingrabener Wende (meaning Reingrabener turnover), or Raibl Event — named after the Raibl area, Friuli-Venezia Giulia region of northeastern Italy.
By any name, the Carnian Pluvial Event (CPE) was a time of major change in our global climate and biotic turnover in the early Late Triassic, between 234 and 232 million years ago. For its significance, it is all but neglected in the body of our palaeontological studies that favour other global ecosystem turnovers during the Mesozoic. It had a huge impact on marine and terrestrial ecosystems. This interval saw a climatic shift from the arid climate of the Late Triassic to the markedly more humid conditions of the Carnian Pluvial Event (CPE), then back to arid again.
A ≈1.5‰ negative shift in oxygen stable isotopes (δ18O) of conodont apatite suggests a global warming of 3 to 4 °C and a change in seawater salinity.
Major changes in organisms responsible for calcium carbonate production occurred during the CPE. In the world's oceans, we see mass biological turnover. Conodonts, ammonoids, bryozoa, and green algae were severely hit by the CPE and experienced high extinction rates.
Most noticeable were the radiations of, among other groups, calcareous nanofossils, corals, and crinoids.
This is especially interesting as ammonoids and conodonts, the two most important groups for the biostratigraphy of the Triassic, had a significant turnover.
Outside of Austria, many localities in Itlay place a primary role in our understanding of the CPE as paradigmatic examples of the geological and biotic processes that were occurring during this interesting moment in time — particularly concerning our future understanding of the evolution of shallow marine and terrestrial groups.
The collective research to date has been focussed on more global and on the deepwater records of the CRP. Italy boasts the most expanded and complete shallow-water successions in the Raible area of northeastern Italy and the most prolific amber site with reef associations in the Dolomites near Veneto.
A halt of carbonate sedimentation is observed in nearby southern Italy in deepwater settings that were probably caused by the rise of the carbonate compensation depth (CCD). High extinction rates occurred among ammonoids, conodonts, bryozoa, and crinoids.
Major evolutionary innovations followed the CPE, as the first occurrence of dinosaurs, lepidosaurs, an expansion of coniferous trees, calcareous nanofossils and scleractinian corals
After the CPE, reef growth starts again. We see this as the Dachsteinkalk — the Dachstein Formation or Dachstein Limestones — a Norian geologic formation in the Alps and other Tethyan mountain ranges in Austria
The beautiful block you see here was kindly prepared by mother nature. She did most of the prep but Andreas did the excavation, soaked it for a few days in water and carefully washed it clean to photograph. A very special thank you to him for continuing to inspire me with his wonderful eye and deep knowledge of our world.
Photo: Andreas / Size: 15 cm x 15 cm.
