PERMIAN - CARBONIFEROUS

Paleogeography

At the beginning of the Carboniferous, there were two supercontinents on Earth, Laurasia (the northern supercontinent) and Gondwana (the southern supercontinent), plus two smaller cratons, Siberia and China. Laurasia and Gondwana were separated by the Paleo-Tethys Ocean.

Gondwana ‘travelled’ north toward Laurasia and collided with it amid powerful tectonic movements and volcanic eruptions, forming a larger supercontinent that was pushed toward the northeast by tectonic movements and collided with Siberia and China. The largest continental mass in the Earth’s geological history, the supercontinent Pangea, was thus born. Pangea extended from the North to the South Pole. At the end of the Palaeozoic period, lava-spewing rift basins started to form on the eastern side of Pangea’s centre, along the north-eastern edge of Gondwana. As the sea floor was formed and the new ocean expanded, shallow water marine shelves called the Cimmerian blocks detached. This new ocean space was the predecessor of the new ocean, the Neotethys.

Paleoclimate

In early Carboniferous, the climate was wet. The fusion of Laurasia and Gondwana resulted in a sudden temperature drop south of the equator. The formation of glaciers in southern geographical latitudes caused a drop in sea levels and the emersion of shallow-marine environments along the edge of the ocean (shelves). The resulting climate was cold and dry, but the newly uplifted mountain ranges also caused severe temperature differences between the equatorial and polar zones. The climate changed during the Permian, becoming gradually warmer, and the last glaciers melted by the end of the period. Pangea’s enormous surface weakened the circulation of air masses from the ocean, and a dry, arid climate prevailed as a result.

Terrestrial life

Fauna – Amphibians ruled the vast wetlands of the Carboniferous. Some resembled modern crocodiles (the Eryops genus) (1), while others lacked extremities and looked much like modern snakes. Actinopterygii, freshwater bivalves, worms and arthropods, most notably cockroaches, inhabited fresh waters and nearby land. The largest insects in Earth history, with a wing span of about 70 cm (2), surrounded the wetlands. The first primitive reptiles of the Hylonomus genus (3) appeared at the very end of the Carboniferous. The huge evolutionary leap in the development of the amniotic egg (4), whose shell protected the embryo from dehydration, helped them assert dominance over amphibians. New types of reptiles of the Pelycosauria (5) order developed. As of the Middle Permian, a new order of reptiles emerged, the Therapsida (6), whose superior speed and agility made them the dominant group. The Therapsida’s bodies were covered in fur, making them less dependent on the Sun for warmth. These adaptations made them the dominant group of vertebrates on Earth.

Fauna – No other period in Earth history saw such a wide distribution and diversity of plant life forms like the Carboniferous. Plants thrived mostly in the vast swampy forests, where the massive carbon deposits that the period was named after were formed. Forests made up of large ligneous plants and pteridophytes (7) were the dominant form of plant life. When the arrangement of the land masses and oceans changed in the Permian and the ice sheets started spreading from the South Pole northwards, the first gymnosperms from the conifer subclass appeared (8). Since they reproduced using seeds, they did not depend on wet areas like the pteridophytes. Fungi grew both on land and in the sea. All modern fungi species were developed.

Marine life

Oceans were mostly inhabited by bivalves (9), crustaceans, brachiopods, coelenterates (10), cephalopods (11), trilobites (12) and Echinodermata, especially sea lilies (13) and sponges (14). Single-cell eukaryotic organisms (foraminifera) also developed fast. There was an abundance of red algae, which helped build massive reef structures during the Permian, as well as calcareous algae, especially from the Mizzia Velebitana genus.  Smaller reefs made up of this algae, Bryozoa and Parazoa are found in the Baške Oštarije area of Mount Velebit. Ocean inhabitants included fish, such as sharks and Dipnoi.

Proto-Velebit sedimentary basin

At the beginning of the Carboniferous period, the Proto-Velebit sedimentary basin was located along the north-eastern edge of the Gondwana supercontinent, in spacious sea-floor valleys. The sea floor was covered in algae meadows that formed limestones. As the global sea levels dropped, shallow-marine environments were replaced by terrestrial environments where wetlands filled with mud, sand and gravel borne by the ancient rivers were the dominant landscape. As the climate changed in the Permian, some of the wetlands dried up, and the rivers formed sedimentary environment systems of intertwined rivers. Sedimentary deposits, siltstones, sandstones and conglomerates were formed. As the Permian neared its end, the climate changed once again: temperatures rose, glaciers melted, rivers and marshlands dried up, and global sea levels rose, flooding the low coastal and island landscapes of Proto-Velebit. Carbonate deposits and the remains of dead marine organisms sedimented, initially forming limestones and dolomites.

Extinction

The biggest extinction event in Earth history happened at the end of the Permian period. 95% marine organisms and 70% terrestrial organisms became extinct. Almost all types of reef communities died out in the oceans and the seas, and the number of amphibians decreased as well. Many groups of insects, large predators and herbivores became extinct on land. Terrestrial plant communities went through the probably biggest crisis in Earth history. The cause of this mass extinction has not been positively identified, but one of the hypothesis is that intensive volcanic activity released enormous amounts of gases and dust into the atmosphere, reducing sunlight intensity and causing glaciation. The surface area affected by the vulcanisms is believed to have been larger than modern Europe and to have occurred in present-day Siberia. It lasted for about a million years.