Rocks documenting the Carnian Pluvial Episode, a period about 232 million years ago when global rainfall increased dramatically for about a million years. The climate shift may have given dinosaurs the opening they needed to become dominant.
Paolo Mietto, Public domain
A world interrupted by rain
Before 234 million years ago, the supercontinent of Pangea was a mostly dry place. In the tropical sea of Tethys, of which the Dolomites are a remnant, vast carbonate platforms similar to the modern Bahamas were growing. The rock layers visible in this part of the Dolomites, known as the Cassian Dolomite, record this environment. Then, the world changed. The geological record here shows a dramatic shift. The bright carbonates are overlain by darker, silica-rich mudstones and shales of the Heiligkreuz Formation. This darker layer, visible as a distinct band across the mountainsides, documents the Carnian Pluvial Episode (CPE).
This episode was a 1- to 2-million-year-long period of intense, sustained rainfall that significantly altered global ecosystems. The humid conditions increased weathering on land, washing enormous quantities of sand and mud into the sea and shutting down the carbonate platforms. The geological evidence for this climatic shift was first identified in the Carnic Alps, giving the geological stage its name. Dinosaur footprints, absent in the lower rock layers of the Dolomites, become abundant just above the layers corresponding to the CPE, representing a fundamental change in the planet's fauna.
Volcanic trigger, biological revolution
The leading cause for the Carnian Pluvial Episode was a series of massive volcanic eruptions. Geologists link the event to the formation of the Wrangellia Large Igneous Province, a huge oceanic plateau whose remnants are now part of western North America, from British Columbia to Alaska. For up to five million years, these eruptions pumped immense volumes of greenhouse gases, like carbon dioxide, into the atmosphere. This triggered a spike in global temperatures, which in turn intensified the hydrological cycle and caused the period of extreme rainfall.
The consequences for life were severe. The volcanic gases produced acid rain, and the warmer water led to ocean anoxia and acidification. This resulted in a mass extinction event that eliminated about 33% of marine genera. On land, dominant herbivores like dicynodonts and rhynchosaurs were decimated. In the aftermath, new groups became common. Dinosaurs, which had existed for about 20 million years but comprised only 5% of terrestrial fauna, diversified explosively into the vacant ecological niches. The CPE also spurred the evolution of many modern groups, including the first turtles, crocodiles, lizards, and mammals. In the oceans, the first modern stony corals appeared, building reefs in a way that had not been seen before.
💡Fun Facts
The name "Carnian" is derived from the Carnic Alps, where geologists first studied rocks from this time period.
Before the event, dinosaurs were a relatively minor group, making up only about 5% of vertebrate animal life on land.
The volcanic eruptions of the Wrangellia Large Igneous Province released enough CO2 to potentially raise global temperatures by 3–9 °C.
The event is also linked to the first appearance of significant amounts of amber in the fossil record, possibly due to environmental stress on resin-producing trees.
Always open. The area is part of the Puez-Odle Nature Park and is accessible via public hiking trails, subject to weather conditions.
Admission
Free.
Accessibility
This point of interest is in a high alpine environment. Reaching the specific geological sections requires hiking on mountain trails that can be steep and uneven. Sturdy footwear is essential.
