Usolka Section

Geological natural monument. Formed in 2007.

Usolka Geological Section is a reference (”Golden Nail”) of the Sakmarian stage of the Permian system according to the International Stratigraphic Scale (ISS). Also, it is an additional standard (paralimitotype) of the Asselian Stage of the Permian. The Usolka Geological Section is a candidate for the “Golden Nail” of the Gzhelian Stage. It is considered one of the best sections in the world revealing the lower boundary of the Kasimovian Stage of the Carboniferous.

A golden nail is a point selected in a specific section and is the standard of a stage lower border of the International geologic time scale.

Border Biomarkers

Each “Golden nail” of ISS has its own biomarker which defines the lower boundary of the stage and allows it to be tracked around the world. In the Carboniferous and Permian, the biomarkers of the boundaries are conodonts that reached a significant variety in the waters of the late Paleozoic seas and evolved incredibly fast. The lower border of the Sakmarian stage is defined with the first appearance of the species Mesogondolella monstra Chernykh, the Asselian is determined with Streptognathodus isolatus Chernykh, Ritter and Wardlaw, the Gzhelian is defined with Streptognathodus simulator Ellison, the Kasimovian stage is defined with Swadelina subexcelsa (Alekseev et Goreva).

Conodonts on the border of the Asselian and Sakmarian stages of the Permian