CARBON AND HYDROGEN ISOTOPIC CHARACTERISTICS AND THEIR GEOLOGICAL SIGNIFICANCE OF PYROLYSIS PRODUCTS OF MODERN PINEAL POLLENS
Wang Wanchun;Ji Liming (Lanzhou Institute of Geology, Chinese Academy of Sciences, Lanzhou 730000)
Methane produced under lower temperatures (lower than 250℃) of the pyrolysis of pineal pollens is richer in 13C than that produced under higher temperatures (350-550℃), and this is due to that the products of lower temperature pyrolysis are mainly from the protoplasm of pineal pollens, while the products of higher temperature pyrolysis are mainly from sporopollenin. When the temperature of pyrolysis is higher than 350℃, methane, ethane and propane produced from the pyrolysis of pineal pollens become richer in 13C with the increasing temperature,indicating that 13C values of the gaseous hydrocarbons are closely related to the thermal maturity of the oil-generating organic materials. Under same temperature,methane, ethane and propane produced from the pyrolysis become rich in 13C from methane to propane and this is similar to the carbon isotopic distribution character of methane, ethane, propane in the oil accompanying gas. The shell of pineal pollens (sporopollenin) is relatively rich in lighter carbon isotopes than the whole pineal pollens. The hydrogen isotopic composition of the methane produced from the pyrolysis of pineal pollens is similar to that of the methane produced from the source rock of fresh water deposition. Under lower temperatures, because of the decomposing and losing of most of protoplasm, the kerogen from the pyrolysis of pineal pollens is slightly richer in 12C than original pineal pollens. Under higher temperatures the 13C value of the kerogen from the pyrolysis of pineal pollens doesn' t correlate obviously with heating temperature, this shows that the degree of thermal evolution has no obvious effect on the 13C value of kerogen.