Furongian

The Furongian, also known as the Late Cambrian, was the fourth and final epoch of the Cambrian period. It lasted from about 497 to 486.85 million years ago. This time period was very important in Earth's history because it marked the end of the Cambrian Explosion, a time when many animal groups first appeared in the fossil record.

The Furongian came after the Miaolingian series and was followed by the Lower Ordovician Tremadocian Stage. During this epoch, the world saw continued changes in marine life, with many new species evolving and some going extinct.

Scientists divide the Furongian into three stages: the Paibian, the Jiangshanian, and an unnamed tenth stage of the Cambrian. Studying this period helps us understand how life on Earth developed and changed millions of years ago.

History and naming

The Furongian was also called the Cambrian Series 4. It replaced an older name, Upper Cambrian, and is similar to a local term called Hunanian. The name Furongian was officially 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 with the first appearance of a special trilobite called Glyptagnostus reticulatus. This marks the start of both the Furongian and the earlier Paibian Stage. The Furongian ended around 486.85 million years ago, which is when another fossil, a conodont named Iapetognathus fluctivagus, first appeared. This ending also marks the beginning of the Tremadocian Stage in the following period, the Lower Ordovician.

Subdivisions

The Furongian, also known as the Late Cambrian, is divided into smaller parts to help scientists study this time period. These divisions help us understand the order of events and changes that happened millions of years ago. The table below shows these subdivisions, giving a clear view of how the Furongian is organized.

Main article: Cambrian

Biostratigraphy

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

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

Major events

At the start of the Furongian epoch, a major drop in the number of species ended. The amount of different species grew back to what it had been before. Later, another drop happened, reducing the variety of species quite a bit.

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 also a lot of volcanic activity under the Earth's surface in a place that is now part of the Iberian Peninsula.

Paleontology

Scientists have 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.