Abstract: Multiple sets of pre-Paleogene strata with relatively low exploration levels have developed in the Jiyang Depression. The Lower Paleozoic Cambrian-Ordovician, Upper Paleozoic Carboniferous-Permian and Mesozoic all host source rocks and thus can theoretically generate oil and gas for accumulation in the study area. Different tectonic and sedimentary backgrounds lead to different geochemical characteristics among different sets of source rocks. This study comprehensively analyzes  data of geology, source rock pyrolysis and TOC, vitrinite reflectance, whole rock microscopic composition, and gas chromatography-mass spectrometry of saturated and aromatic hydrocarbons. The distribution, geochemistry and resource potential of the pre-Paleogene source rocks in the Jiyang Depression were determined. The Lower Paleozoic marine carbonate source rocks have limited distribution and low abundance of organic matter, but have organic matter types favourable for certain hydrocarbon generation capacity. The widely distributed Upper Paleozoic coaly source rocks, with high abundance of organic matter and relatively poor organic matter types, are dominated by gas generation. As a result of complex tectonic evolution, this set of source rock is characterized by secondary hydrocarbon generation. The Mesozoic has developed two sets of source rocks (i.e., coaly source rocks and lacustrine mudstones) with medium organic matter types. Medium- to good-quality source rocks are developed locally with varying maturity spatially. Overall, among the thr ee sets of pre -Paleogene source rocks in the Jiyang Depression, the Upper Paleozoic coal-measure source rocks have the best quality, followed by the Mesozoic, and the Lower Paleozoic is relatively poor.

Key words: pre-Paleogene, coaly source rocks, maceral compositions, secondary hydrocarbon generation, Jiyang Depression