Tremadocian

The GSSP for the beginning of the Tremadocian is the Green Point section (49°40′58″N 57°57′55″W / 49.6829°N 57.9653°W / 49.6829; -57.9653)[7] in Gros Morne National Park, in western Newfoundland.

[5] The Tremadocian ends with the beginning of the Floian which is defined as the first appearance of Tetragraptus approximatus at the GSSP in Diabasbrottet quarry, Västergötland, Sweden.

In addition to the first appearance datum of I. fluctivagus, fossils of olenid trilobite Jujuyaspis and planktonic graptolite Anisograptus matanensis are present in a nearby section.

[13] However, in 2021, the International Union of Geological Sciences (IUGS) proposed to deny the use of specific points and replace them by Standard Auxiliary Boundary Stratotypes (SABS) for more "flexible" correlations with GSSPs.

[17] At the beginning of the Tremadocian, about 485.4 million years ago, biodiversity, which had been at a low level, began its long increase phase, known as the Great Ordovician Biodiversification Event.

Above the disappearance of Ceratopyge fauna, sediments are presented in a more depleted form due to the decreased sea level in the Late Tremadocian.

Specimens of Ellesmeroceras and possibly Bassleroceras, found in Santa Rosita Formation, northwestern Argentina, show that cephalopods first migrated to the waters off western Gondwana already in the early Tremadocian.