Hydrocarbon Generative Potentials of Middle and Lower Jurassic Source Rocks in Northern Margin of Qaidam Basin

The Middle and Lower Jurassic coal-bearing mudstone source rocks occur widely in the northern margin of Qaidam basin.The depositional area in the Middle Jurassic is larger than that in the Lower Jurassic,with a relatively deeper water depth.This indicates that the lake boundary of the Middle Jurassic is wider.Also,the Middle Jurassic source rock has a higher abundance of algae and a lower abundance of cutinite than the Lower Jurassic source rock,showing that the Middle Jurassic source rock is better than the Lower Jurassic one in organic matter type.However,the distribution of present-day residual source rock and the total organic carbon abundance indicate that the hydrocarbon generative potential of the Lower Jurassic source rock is better than that of the Middle Jurassic one.Because the Lower Jurassic source rock has entered into highly maturated evolution stage(Ro2.0%),the Middle Jurassic one is dominated by differential thermal evolution in different structural elements.Therefore,both the Lower and Middle Jurassic source rocks are all in good hydrocarbon generative potentials.This implies that not only the Lower Jurassic source rock,but also the Middle Jurassic ones should be equally placed enough importance for petroleum geological research and exploration in the future.