(Table 1) Comparison of adjacent Cenomanian black shales with green claystones from DSDP Hole 75-530A

Black shales possessing high concentrations of organic carbon (Foresman, 1978, doi:10.2973/dsdp.proc.40.111.1978) were deposited in many parts of the proto South Atlantic Ocean during the Cretaceous period (Bolli et al., 1978, doi:10.2973/dsdp.proc.40.104.1978). The way such sediments accumulated is not fully understood, but is likely to have occurred through a combination of low oxygen availability and abundant supply of organic matter. Thin, centimetre-thick layers of black shales are commonly interbedded with thicker layers of organic carbon-deficient, green claystones, as found in strata of Aptian to Coniacian age, at Deep Sea Drilling Project (DSDP) Site 530, in the southern Angola Basin (Hay et al., 1982, doi:10.1130/0016-7606(1982)93<1038:SAAOOC>2.0.CO;2) and elsewhere. These differences in carbon content and colour reflect the conditions of deposition, and possibly variations in the supply of organic matter (Summerhayes and Masran, 1983, doi:10.2973/dsdp.proc.76.116.1983; Dean and Gardner, 1982). We have compared, using organic geochemical methods the compositions of organic matter in three pairs of closely-bedded black and green Cenomanian claystones obtained from Site 530. Kerogen analyses and distributions of biological markers show that the organic matter of the black shales is more marine and better preserved than that of the green claystones.

富有机碳含量的黑色页岩（Foresman，1978，doi:10.2973/dsdp.proc.40.111.1978）于白垩纪时期沉积于原南大西洋的众多区域（Bolli等，1978，doi:10.2973/dsdp.proc.40.104.1978）。此类沉积物的堆积机制尚未完全阐明，但推测其形成与低氧环境和充足的有机质供给共同作用相关。在安哥拉南部盆地的深海钻探计划（Deep Sea Drilling Project, DSDP）530站位以及其他区域的阿普第期至科尼亚克阶地层中，常见厘米级厚度的黑色页岩薄层与有机碳匮乏的绿色泥岩厚层互层产出（Hay等，1982，doi:10.1130/0016-7606(1982)93<1038:SAAOOC>2.0.CO;2）。碳含量与颜色的此类差异反映了沉积环境差异，同时也可能与有机质供给量的变化有关（Summerhayes与Masran，1983，doi:10.2973/dsdp.proc.76.116.1983；Dean与Gardner，1982）。本研究采用有机地球化学方法，对从530站位获取的三套紧密互层的塞诺曼期黑色与绿色泥岩中的有机质组成进行了对比分析。干酪根分析与生物标志物分布特征表明，黑色页岩中的有机质相较于绿色泥岩，具有更强的海源特性且保存程度更佳。