Cape Kalamba oil seeps occur at the south end of the Ubwari Peninsula, at the intersection of faults controlling the morphology of the northern basin of the Tanganyika Rift, East Africa. Oil samples collected at the surface of the lake 3-4 km offshore from Cape Kalamba have been studied. The aliphatic hydrocarbon and biomarker compositions, with the absence of the typical suite of polynuclear aromatic hydrocarbons, indicate an origin from hydrothermal alteration of immature microbial biomass in the sediments. These data show a similarity between a tar sample from the beach and the petroleum from the oil seeps, and confirm that the source of these oils is from organic matter consisting mainly of bacterial and degraded algal biomass, altered by hydrothermal activity. The compositions also demonstrate a < 200 degrees C temperature for formation/generation of this hydrothermal petroleum, similar to the fluid temperature identified for the Pemba hydrothermal site located 150 km north of Cape Kalamba. The 14C age of 25.6 ka B.P. obtained for the tar ball suggests that Pleistocene lake sediments could be the source rock. Hydrothermal generation may have occurred slightly before 25 ka B.P., during a dry climatic environment, when the lake level was lower than today. These results also suggest that the Cape Kalamba hydrothermal activity did not occur in connection with an increased flux of meteoric water, higher water tables and lake levels as demonstrated in the Kenya Rift and for the Pemba site. Hydrothermal petroleum formation is a facile process also in continental rift systems and should be considered in exploration for energy resources in such locales.

中文翻译：

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来自东非裂谷湖相沉积有机质的热液石油

Cape Kalamba 石油渗漏发生在 Ubwari 半岛的南端，位于控制东非坦噶尼喀裂谷北部盆地形态的断层交叉点。已经研究了从卡兰巴角离岸 3-4 公里的湖面收集的油样。脂肪烃和生物标志物组成，没有典型的多核芳香烃套件，表明沉积物中未成熟微生物生物量的热液蚀变起源。这些数据显示了海滩焦油样品和油渗出的石油之间的相似性，并确认这些油的来源主要是由细菌和降解的藻类生物质组成的有机物质，被热液活动改变了。该组合物还表现出 < 这种热液石油的形成/生成温度为 200 摄氏度，类似于为位于卡兰巴角以北 150 公里处的奔巴热液场确定的流体温度。为焦油球获得的 25.6 ka BP 的 14C 年龄表明更新世湖泊沉积物可能是烃源岩。热液产生可能发生在 25 ka BP 之前，在干燥的气候环境中，当时湖水位低于今天。这些结果还表明，卡兰巴角热液活动的发生与大气水通量的增​​加、更高的地下水位和湖水位无关，如肯尼亚裂谷和奔巴遗址所证明的那样。