Baissa is a locality situated on the banks of the Vitim River in the northeastern region of Buryatia, Russia. It is primarily recognized for its significance within the Zaza Formation, a geological structure dating to the Lower Cretaceous period.
The area is characterized by its location on a large granite plateau and contains sedimentary deposits including sandstones, siltstones, marls, and bituminous shales. These materials were originally deposited in a stratified lake environment. The Baissa locality is specifically noted for containing numerous compression fossils of various insect varieties found across multiple beds within the formation.
The preservation of these insect fossils varies depending on the specific geological facies; while they are predominantly found in finer-grained layers, they exhibit good preservation in marl and poor preservation in shale beds. The exact age of the surrounding formation remains a subject of geological dispute, with estimates ranging from Valanginian-Hauterivian to Aptian.