Furongian

The Furongian, also called the Late Cambrian, was the last part of the Cambrian period. It happened from about 497 to 486.85 million years ago. This time was very important because it was when many animal groups first showed up in fossils.

The Furongian came after the Miaolingian and before the Lower Ordovician Tremadocian Stage. During this time, the oceans had many new species, and some old ones disappeared.

Scientists split the Furongian into three parts: the Paibian, the Jiangshanian, and one stage that does not have a name. Learning about this time helps us know how life on Earth changed millions of years ago.

History and naming

The Furongian was also called the Cambrian Series 4. It replaced an older name, Upper Cambrian. The name Furongian was approved by the International Commission on Stratigraphy in 2003. The word Fúróng (芙蓉) means 'lotus' in Mandarin and connects to Hunan, a region known as the "lotus state".

Definition

The Furongian, also called the Late Cambrian, began around 497 million years ago. It started when a special trilobite called Glyptagnostus reticulatus first appeared. This also marks the start of the Paibian Stage. The Furongian ended around 486.85 million years ago. This is when another fossil, a conodont named Iapetognathus fluctivagus, first appeared. The end of the Furongian is also the start of the Tremadocian Stage in the Lower Ordovician period.

Subdivisions

The Furongian, also called the Late Cambrian, is split into smaller parts. This helps scientists study events from millions of years ago. The table below shows these parts and how the Furongian is organized.

Main article: Cambrian

Biostratigraphy

The Furongian is the last part of the Cambrian period. Its stages are marked by the first appearance of certain trilobites. For example, the Paibian Stage starts when the trilobite Glyptagnostus reticulatus first appears. The Jiangshanian Stage starts when Agnostotes orientalis first appears. The Cambrian Stage 10 might be defined by the first appearance of either Lotagnostus americanus or the conodont Eoconodontus notchpeakensis.

The Furongian can be divided into several trilobite zones. These zones help scientists understand the order of rock layers from this time.

Major events

At the start of the Furongian epoch, the number of species stopped dropping. The amount of different species grew back to what it had been before. Later, another drop happened, reducing the variety of species.

There was also an important change in the chemistry of carbon in the oceans during this time, called the Steptoean positive carbon isotope excursion. Scientists aren't exactly sure why this happened, but they think it might be connected to big changes in sea levels or in the amount of oxygen in the ocean.

During this period, there was a lot of volcanic activity under the Earth's surface in a place that is now part of the Iberian Peninsula.

Paleontology

Scientists noticed that many important soft-bodied animals from a time between the Cambrian Explosion and the Great Ordovician Biodiversification Event were not found until recently. In 2019, this missing period was named the Furongian Biodiversity Gap. Researchers think this gap happened because there weren’t enough rocks from that time to study, or because scientists hadn’t looked closely enough. New discoveries, especially in South China, are helping us learn more about life during this time.

Many fossils of trilobite-agnostoid animals have been found in Furongian rock layers in the Alum Shale Formation of Bornholm, Denmark. Some of these include Ctenopyge, Eurycare, Leptoplastus, Olenus, Parabolina, Peltura, Protopeltura, Sphaerophthalmus, Lotagnostus, and Triangulopyge. Scientists also found benthic graptolites in South China, such as Rhabdopleura, Dendrograptus, Callograptus, and Siberiograptus.