Lacustrine sediments are unique paleoenvironmental and paleoclimatic archives. Geochemical analyses have long been an integral part of lacustrine basin studies. They proved valuable in investigating the past lake conditions and processes operating in lakes and record the lake evolution. This is of particular interest when lake sediments host economically valuable resources (e.g., hydrocarbons, coal, uranium). The main goal of this PhD thesis is to explore the processes controlling syn-rift source-rock deposition in the Gulf of Tonkin, Vietnam and more generally in tropical rift basins using geochemical analysis. The work is based on analysis of core material from the 500 m deep, fully cored ENRECA-3 well that penetrated an upper Oligocene, lacustrine syn-rift succession deposited in the Bach Long Vi Graben, offshore Vietnam. The results of this study offer a unique insight into the controls on formation of organic carbon and petroleum source rock in a non-marine rift graben. The collected data allowed for establishing the path and provenance of the sediments deposited in the graben. Characterization of the depositional conditions prevailing in the graben allowed for identification of further factors controlling the development of organic-rich deposits. It showed how setting and composition of the hinterland affect productivity and source rock development in the basin, while the rift basin morphology influences organic matter preservation potential. The study determines the role of the lake setting and climate on in-lake isotope fractionation processes and establishes two models of in-lake fractionation present in the lake. Finally, by significantly improving the age estimates of the cored succession it shows that carbon isotope records of terrestrial organic matter can be used to improve dating of lacustrine deposits in SE-Asia. All these findings further the understanding of the factors controlling source rock development and deposition in lacustrine basins.