Geochemical characteristics and sedimentary environment of upper Miocene-lower Pliocene source rocks in the Albertine Basin, East African Rift Valley

Abstract

The Albertine Basin is an important rift basin in the East African Rift System, enriched in oil and gas resources. The upper Miocene to lower Pliocene hydrocarbon source rocks are important source rocks in the basin, but the research is relatively limited. In this work, we evaluate the source rocks of the upper Miocene and lower Pliocene in the Albertine Basin by integrations of geological, rock pyrolysis and elemental geochemistry data and analyses the paleoenvironmental evolutions of the late Miocene to early Pliocene. These results show that the two sets of source rocks are under the mature stage, but the abundance and type of organic matter are different. The lower Pliocene source rocks have higher organic matter abundance and belong to middle-good source rocks, yielding type Ⅱ1 -Ⅱ2 kerogen. The upper Miocene source rocks have lower organic matter abundance and belong to poor source rocks, yielding type Ⅱ2-Ⅲ kerogen. The sedimentary environment is an important controlling factor for the difference in source rocks. During the late Miocene to early Pliocene, the study area was a freshwater lake with strong reducibility, gradually increasing water depth, a warmer climate, flourishing bacteria and microorganisms, and better organic matter types. At the same time, lake productivity is elevated, the sedimentation rate is accelerated, and organic matter can be preserved more efficiently, so the abundance of organic matter in source rocks is higher.

Keywords

• source rock evaluation
• elemental geochemistry
• sedimentary environment
• albertine basin
• east african rift valley