塔里木盆地中、上奥陶统烃源岩的碳同位素宏观证据

Macro-evidence of Carbon Isotopes for the Middle-Upper Ordovician Source Rocks in the Tarim Basin

经过十余年的勘探,已在塔里木盆地探明13个大、中型油气田和33个工业性含油构造,但关于塔里木盆地的古生界主力烃源岩一直有争议。本文根据两条有代表性的地表剖面和两条钻井剖面的海相碳酸盐岩碳、氧稳定同位素分析与研究,发现了中、上奥陶统碳同位素组成的大幅度正向波动,认为这是当时全球范围大陆冰川作用的结果,这一时期有利于沉积有机质的保存。结合有机质丰度、成熟度指标(R_o)以及沉积相等地质因素综合分析,提出了塔里木盆地中、上奥陶统烃源岩的碳同位素宏观证据。同时,论述了中、上奥陶统海相碳酸盐岩作为我国下扬子地区及华北地台西缘海相下古生界寻找有效烃源岩重点层系的可能性与前提条件。

Studies of δ 13C and δ18O of the marine carbonate sedimentary in four geological sections in the Tarim basin, northwest China, show an obviously positive shift, the δ 13C values changing from - 2‰-0‰ in the Lower Ordovician up to +0. 5‰- + 3‰ (PDB) in the Middle-Upper Ordovician, and the δ 18O values from -9‰ up to -5. 5‰ for the Kalpin section of shallow water platform fades; whereas the δ13C and δ 18O values from -1‰-0 ‰ up to +1‰- + 2‰ (PDB) and from -9. 2‰-8. 1 % up to -6. 4‰-5. 3‰ respectively for the Kuruktag section of deep water facies, corresponding in time to the major continental glaciation in Gond-wana. The corresponding carbon isotopic positive excursions can be found in South China and North America, Argentina, Greenland, and some areas in Europe, including in both marine carbonate , well-preserved brachiopods, and sedimentary organic carbons.