太平洋海底富钴结壳中的烃类有机质及其成因意义

Hydrocarbons in ferromanganese crusts from Pacific seamounts and their implications for the genesis.

用气相色谱-质谱(GC-MS)联测方法测定了中西太平洋海底海山富钴结壳中的可溶有机质,对其丰度、生源构成、沉积环境、成熟度等方面进行了初步的探讨。富钴结壳的烃类生物标志化合物大多具成熟烃特征,个别具低成熟烃特点,"A"/C高达9.81～21.15,显示出运移烃的特征;藿烷C_(31)-R/(S+R)为0.43～0.46,Tm/(Tm+Ts)为0.40～0.59,C_(30)αβ藿烷/(αβ藿烷+βα莫烷)为0.85～0.89,C_(29)αβ藿烷/(αβ藿烷+βα莫烷)为0.81～0.85,C_(29)甾烷20S/(20S+20R)为0.45～0.60,从而计算出R_(sc)(%)为0.73%～0.81%,个别达到1.06%;C_(29)αββ(αββ+ααα)为0.35～0.42。甾烷丰度顺序为C_(29)甾烷>C_(27)甾烷>C_(28)甾烷,同时检出了孕甾烷和4-甲基甾烷,重排甾烷三角图显示该有机质为Ⅱ型。Pr/Ph值介于0.35～0.82,显示植烷优势,说明烃类形成于强还原环境。链状烷烃、类异戊二烯烷烃、萜烷、甾烷化合物的组成和分布都说明菌藻类低等水生生物和陆源高等植物混合生源输入。洋底热液活动是富钴结壳中有机质热演化的重要热源。有机质在特定的海底条件下生成,并被运移到海山上,通过扩散和浸染由外层进入结壳。

Trace hydrocarbons in the ferromanganese crusts collected from central and west Pacific seamounts were detected by GC and GC-MS, and abundance, biological source, sedimentary environment and maturity of the soluble hydrocarbons in the crusts were investigated preliminarily. The results indicate that the organic matters are mostly of mature hydrocarbons, excepting one. sample. 'A'/C ratios reach as high as 9.81 to 21.15. The ratios of 22S/(22S +22R) to C(31)-homohopane are 0.43 similar to 0.46, Tm/(Tm + Ts) are 0.40 similar to 0.59. The ratios of C(29) and C(30) hopanes alpha beta/ (alpha beta +beta alpha) are 0.81 similar to 0.85 and 0.85 similar to 0.89, respectively. Besides, the ratio of C(29)20S/(20S + 20R) rearranged-sterane and C(29) alpha beta beta/(alpha beta beta + alpha alpha alpha) sterane gave values of 0.45 similar to 0.60 and 0.35 similar to 0.42, respectively. Consequently, the calculated vitrinite reflectance, R(sc) ( %), varies between 0.73 % to 0.81 %, occasionally 1.06%. Abundance sequence of the measured sterane is C(29)-sterane > C(27)-sterane > C(28)-sterane, pregnane and 4-methy steranes are also identified. The organic matters in ferromanganese crusts are composed predominantly of Type II ones. The pristane/phytane ( Pr/Ph) ratios for the ferromanganese crusts are 0.35 similar to 0.82, indicating that the hydrocarbon were probably deposited in a strong reducing environment. Composition and distribution of n-alkanes, acyclic isopenoid, terpanes and steranes seem to show that the organic matters sourced from algae or microbes and terrestrial plants. Submarine hydrothermal activity might have supplied heat energy for thermal evolution of hydrocarbon in the crusts. It is proposed that the hydrocarbons were generated in a strong reducing submarine environment, transported to the seamounts and finally entered the crusts by pervasion or infiltration.