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

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深海钻探计划（Deep Sea Drilling Project）504与505站位采集的沉积物，本研究采用热解方法（thermal methods）开展了分析检测。结果显示，当选取有机质类型相近的沉积物进行对比时，两处站位的生成指数（production index, P.I.）数值存在细微差异——该指数用于表征沉积物内热成因烃类的生成程度。进一步研究发现，上述未成熟沉积物（immature sediments）中具强烈生物扰动的层段，其可热解烃类（pyrolyzable hydrocarbons）数值呈现异常偏低的特征，这表明仅通过生物过程便可生成惰性有机碳。此外，两处站位的有机碳含量均与可热解烃类呈现显著相关性，且数据表明，有机碳含量低于1%的样品，在任意时间与温度条件下均对烃类生成呈惰性。