TRIASSIC

Paleogeography

In the Triassic period, Pangea was located around the equator. A deep rift valley opened up in this zone, where Laurasia met Gondwana, stretching from the east toward the west. Waters from the already formed Tethys Ocean flooded the valley. Parts of the shallow-marine shelf detached from Gondwana as a result of substantial tectonic activity in the Middle Triassic and continued their journey toward the northeast in the Tethys Ocean. The Adriatic Microplate or Adria was one of them.

The fragmentation of Pangea continued with the formation of a new rift valley at the western point of contact between Laurasia and Gondwana. The new Atlantic Ocean began to open between North America and Africa.

Paleoclimate

Climate conditions in the Triassic closely resembled those in the Permian. Only the coastal areas received higher amounts of precipitation, and the interior of the continent remained dry, with very hot summers and cold winters. Powerful Monsoonal winds swept through the equatorial zone, leading to the sedimentation of red sandstones and evaporites in large areas. There are no traces of glaciation, not even on the poles, where the climate was wet and moderately warm.

Terrestrial life

Fauna – Terrestrial fauna was wiped out almost entirely by the global catastrophe at the end of the Permian period. Rare amphibian groups survived the extinction event. Some new groups appeared as well, such as frogs. Among the reptiles of the Therapsida (1) group, those originating from the Thecodontia were best adapted. Two-legged movement gave them exceptional speed and agility. Their hind legs were stronger, and their front legs weaker (2). The first “real” dinosaurs of the genii Saurischia (3) and Ornitischia (4) developed from this group. The first flying reptiles from the Pterosauria (5) order and the first flying lizards from the Lepidosauria (6) subclass also appeared at this time. The first mammals (7) developed in the Triassic too, no larger than modern cats.

Flora – The amount of Lycopodiaceae and Fungi spores increased at the beginning of the Triassic, which is associated with large-scale plant mass decomposition after the global catastrophe. Only certain plant groups survived, such as ferns from the Dicrodium genus, some Lycopodiaceae (8) and Cycadophytina (9).

Marine life

It took a long time for life on Earth to recover after the mass extinction at the end of the Permian period. Bivalve and brachiopod diversity was lost. Only one group of corals existed, building small coral mounds at the beginning of the Triassic. The formerly dominant sea lilies of the Echinodermata phylum were replaced by Asteroidea, and two ammonite genii (10) were the only survivors among the brachiopods. The algae only recovered in the Middle Triassic. A diversity of reptiles appeared in the oceans, including legged and fingered reptiles from the Crocodilia order, the Nothosauria (11) and the Placodonta, as well as finned reptiles from the Plesiosauria order (12), who ruled the oceans, and the fishlike reptiles of the Ichthycosauria order (13).

Proto-Velebit sedimentary basins

The sedimentation of dolomites continued in the early Triassic in the very shallow sea along the northern edge of Gondwana, with the addition of particles borne by rivers and winds from the mainland. Tectonic movements on Gondwana’s north-eastern edge started to open a deep marine rift valley separating the shallow-marine shelf from the future Adriatic Microplate. The Proto-Velebit sedimentary basin was a part of this shelf. The tectonic movements went hand-in-hand with powerful volcanic eruptions and lava effusions, uplifting parts of the newly formed plate. This was followed by erosion of the uplifted older rocks, with rivers flushing their material to the depressions where they sedimented, cemented, and formed sandstones and conglomerates. Global sea levels rose again at the end of the Triassic, flooding the Adriatic Microplate. The sedimentation of dolomites in this very shallow sea started all over again.

Extinction

The Triassic followed the mass extinction event in late Permian, and ended with another extinction event. Almost 50% organisms became extinct in only 10,000 years. Among marine organisms, cephalopods, gastropods, brachiopods, and reef communities were reduced in numbers, and conodonts disappeared entirely. Many marine and terrestrial reptiles became extinct, with the exception of dinosaurs, who emerged out of this catastrophe as the winners, taking advantage of the void created by the extinction of smaller and weaker reptiles. The cause of the extinction has not yet been fully clarified, but it is assumed that it was associated with Pangea breaking apart. Rift valleys, flood basalts and the opening of the Atlantic Ocean, coupled with volcanic eruptions and increased concentrations of carbon dioxide and methane released from massive carbon deposits, contributed to the extinction of many species. Short cold periods, also a result of the dust and sulphur aerosol released by volcanic eruptions, are believed to have had an equally negative impact on ecosystems as global warming.