南华海泥盆纪烃源岩的古氧相和缺氧环境模式——以广西中、上泥盆统为例

缺氧条件是形成和保存优质烃源岩的重要条件。古氧相的研究对查明海相优质烃源岩时空分布、恢复地史时期古环境演化具有重要意义。泥盆纪时期,南华海受陆内裂陷作用影响,形成台地(滨岸台地和孤立台地)与台沟间列的盆地格局。不同的控制因素控制了古氧相的类型。在台沟和钦防裂陷海槽中,海水分层控制了泥盆纪的古氧相类型和变化。台沟和钦防裂陷海槽以厌氧相与准厌氧相为主。在台地相区,海平面变化控制了古氧相的类型和分布。台地相区的古氧相主要是常氧相和贫氧相。南华海中、晚泥盆世硅质沉积、磷质沉积发育,有机质丰富,形成了有机质-硅质-磷质沉积三位一体的特征,指示上升流作用明显。南华海地区泥盆纪位于赤道附近的信风带,向西的表面洋流越过南华海在西部形成离岸流,海底海水向东补充形成上升的底流,也说明了泥盆纪南华海上升流存在的可能性。

Paleoxygenation facies and oxygen-deficient environmental model of the Devonian source rocks from southern South China Sea: An example from the Middle and Upper Devonian of Guangxi

xygen deficient environment is an important condition for formation and preservation of marine source rocks. The study of paleoxygenation facies is significant for tracing spatial temporal distribution of high quality marine source rocks and interpreting the evolution of depositional environments. During the Devonian， carbonate platform(nearshore and isolated platforms)and inner platform taphrogenic trough resulting from intracontinental rifting were simultaneously developed in the southern South China Sea. The Devonian paleoxygenation facies types are controlled by sea water layering in platform troughs and the Qinzhou Fangcheng taphrogenic trough， where quasi anaerobic and anaerobic facies were dominant. The paleoxygenation facies is controlled by sea level changes in platform in which developed aerobic and dysaerobic facies. Siliceous， phosphorus and organic carbon rich deposits of the Devonian indicate the upwelling flows influence. The southern South China Sea was located in the trade wind zone near the equator in the Devonian. Westward surface ocean current passed over the southern South China Sea and formed off shore currents. Eastward bottom current compensated toward shore and formed the upwelling flow. The Devonian upwelling flow led to the formation of an oxygen deficient environment in the southern South China Sea.