(Table 1) Total and organic carbon in sediments at DSDP Holes 69-504 and 69-505

Sediments from Deep Sea Drilling Project Sites 504 and 505 near the Costa Rica Rift were examined by thermal methods. It was found that production index (P.I.) values, which measure the degree of thermal hydrocarbon generation in the sediment, were slightly different for the two sites when compared for sediments with similar types of organic matter. Highly burrowed sections of these immature sediments gave anomalously low values of pyrolyzable hydrocarbons, suggesting production of inert organic carbon by purely biological processes. Organic carbon levels correlate with pyrolyzable hydrocarbons at both sites and show that samples with less than 1 % organic carbon are inert to hydrocarbon generation under any conditions of time and temperature.

针对哥斯达黎加裂谷附近的深海钻探计划（Deep Sea Drilling Project）504与505站位的沉积物，采用热学方法开展了系统检测分析。研究发现，在有机质类型相近的沉积物组间对比时，两个站位的产率指数（production index, P.I.）——该指标用于表征沉积物内热生烃作用的发育程度——存在细微差异。这些未成熟沉积物中生物潜穴发育强烈的层段，其热解烃（pyrolyzable hydrocarbons）含量呈现异常偏低的特征，这提示纯生物过程可生成惰性有机碳。两个站位的有机碳含量均与热解烃含量呈显著相关，且结果表明：有机碳含量低于1%的样品，在任意时间与温度条件下均无法发生烃类生成反应，表现为惰性特征。