The article provides a lithological description of the sections of the Lower Frasnian Stage of the Upper Devonian: the Zhelon Regional Stage and the Saria Beds of the Sargaevo Regional Stage, exposing in the basin of the Saryanka river, the Latvian Saddle. The complete lithological description of the Sargaevo and Semiluki sediments of the Frasnian Stage in the Gralevo quarry of the Vitebsk region, Orsha Depression has been presented. Macro- and micro-dimensional remains of heterostracans, placoderms, acanthodians, sarcopterygians, actinopterygians, as well as scolecodonts and conodonts have been found in the Lower Frasnian sediments; their photographic images are presented. For the first time, the Sr isotope composition was measured in the remains of ichthyofauna from the Zhelon and Sargaevo sediments of Belarus. On the basis of palaeoichthyological and taphonomic data, lithology and Sr isotope composition of ichthyofauna fragments, depositional environments in the Zhelon and Saria times were clarified, and the distant sections were correlated. The 87Sr/86Sr values in ichthyofauna samples from the Saria Beds in sections of the Latvian Saddle (sections of Kalyuty 5a and 6, Virenka 1) and the Orsha Depression (Gralevo quarry) lie within similar ranges: 0.70825–0.70842 and 0.70837–0.70856, respectively. The 87Sr/86Sr values in the ichthyofauna from the Zhelon sediments in the Kalyuty 2 and Obukhovo 1 sections (Latvian Saddle) vary within 0.70898–0.70932 and 0.71065–0.71102, respectively. High 87Sr/86Sr values in the fossil ichthyofauna of both regional stages suggest that the Early Frasnian palaeobassin was significantly desalinated, and the salinity in the Saria palaeobassin was comparable to the salinity of the modern Baltic Sea.