Tournaisian

The Tournaisian is the oldest part of the Mississippian, which itself is the earliest subsystem of the Carboniferous period. In the world of geology, the Tournaisian is like the first chapter of a very important book. It lasted from about 358.86 million years ago to 346.7 million years ago.

Before the Tournaisian came the Famennian, the last part of the Devonian period. After the Tournaisian, the next part of the Carboniferous, called the Viséan, began.

Scientists divide the Tournaisian into two smaller parts, called substages. The first is called the Hastarian, and the second is called the Ivorian. These names come from places in Europe where important rock layers from this time were first studied. The Tournaisian helps us understand how Earth’s surface and life changed a very long time ago.

Name and regional alternatives

The Tournaisian was named after the city of Tournai in Belgium. It was first used in scientific writing by Belgian geologist André Hubert Dumont in 1832. This time period is part of the official international timeline for Earth's history.

The Tournaisian is related to other regional names in different parts of the world. In North America, it is linked to the Kinderhookian and lower Osagean stages, and in China, it matches the Tangbagouan stage. In the British Isles, the Tournaisian is often called the Courceyan stage.

Stratigraphy

The Tournaisian is the oldest part of the Carboniferous period. Scientists identify its beginning by looking for a special type of tiny fossil called Siphonodella sulcata. These fossils help them determine the exact start of this time period.

The end of the Tournaisian is marked by the appearance of another fossil called Eoparastaffella simplex. During the Tournaisian, scientists have found eight different groups of these tiny fossils, called biozones, which help them study and divide this time period into smaller parts.

Paleoenvironments

The Tournaisian period was a time of interesting changes in Earth's plant and animal life. It coincided with a gap in the fossil record known as Romer's gap, meaning scientists find very few fossils from land animals during this time. This gap marks a break between the life forms of the Devonian period and those that came later in the Carboniferous period.

During this time, a cold period called glaciation happened in the southern parts of the world. South America was near the South Pole and was part of a large landmass called Gondwana. Even though coal wasn't very common yet and forests were not as thick as they would later become, some trees still grew very tall—up to 40 meters, or about 131 feet! The rivers back then looked different from today's, more like those from even earlier times.

Notable formations

Some important rock layers from the Tournaisian time period include the Albert Formation in New Brunswick, Canada, and the Agua de Lucho Formation in Argentina. Other notable formations are the Ballagan Formation and Cementstone Group in Scotland, and the Herbesskaya Formation in Russia. Additional formations include the Horton Bluff Formation in Nova Scotia, Canada, the Mansfield Group in Australia, the Price Formation in West Virginia and Virginia, United States, and the Tournai Formation in Belgium.