Vitrinite reflectance of ODP Leg 139 samples (Table 1)@en

Isolated kerogens from four sites in the Middle Valley hydrothermal region of the Juan de Fuca Ridge (Ocean Drilling Project (ODP) Leg 139) were analysed by electron paramagnetic resonance (EPR) spectroscopy. Measurements of peak width, spin density and power saturation for site 857 kerogens, which increased regularly in maturity downhole, show correlation with vitrinite reflectance values from 0.61 to 2.5%, indicating the start of the oil window at depths from 200 to 400 m. Spin density increases to 1.56 * 10**17 spins per gram and peak width decreases to 3.45 G (gauss) with increasing depth. The tendency to power saturate also decreases with increasing maturity and increasing vitrinite reflectance within the oil window. These trends are consistent with a model in which exchange processes are occurring and cause changes in the EPR behavior of samples from this site. Sediments from other Middle Valley sites, 855, 856 and 858 contain large quantities of pyrite with Mn2+ impurities which interact with the carbon radical to distort the EPR measurements.本研究对胡安·德·富卡脊（Juan de Fuca Ridge）中谷热液区大洋钻探计划（Ocean Drilling Project, ODP）第139航次的四个站位的分离干酪根（kerogen）开展了电子顺磁共振波谱（electron paramagnetic resonance, EPR）分析。针对站位857的干酪根，其成熟度随井下深度呈规律性升高，对其峰宽、自旋密度与功率饱和特性的测量结果显示，上述三项参数与0.61%至2.5%区间的镜质体反射率值存在相关性，表明石油生成窗口的起始深度为200至400米。随着深度增加，干酪根的自旋密度升高至1.56×10^17自旋/克，峰宽则降低至3.45高斯（G）。在石油生成窗口范围内，功率饱和倾向也随成熟度与镜质体反射率的升高而减弱。上述变化趋势与该站位样品发生交换过程并由此改变电子顺磁共振波谱特性的模型相符。中谷其他三个站位（855、856与858）的沉积物中含有大量掺杂Mn²+杂质的黄铁矿，此类杂质可与碳自由基发生相互作用，进而干扰电子顺磁共振波谱的测量结果。