A complex detailed study of lithology, petrophysics, and distribution of hydrocarbon biomarkers and hydrocarbons of diamond-like structure in a soluble organic matter and products of thermolysis of insoluble organic matter (kerogen) of the Lower Cambrian Eastern Siberian сarbonate reservoir rocks (osinsky horizon) showed that these rocks  are source rocks at the same time. An additional research validation of this conclusion is the close distribution of the hydrocarbon composition at the molecular level of crude oils taken from the same deposits.