Developing a Coherent Stratigraphic Scheme of the Albertine Graben, East Africa

摘要

The Albertine graben is one the most petroliferous onshore rifts in Africa. It forms the northernmost termination of the western arm of the East African Rift System. Its surface exposures were first studied by Wayland (1925) and Pickford et al. (1993) among others. Pickford et al. (1993) especially developed the basic stratigraphic framework of the graben, which was later modified by the Government geoscientists and international oil companies using subsurface data. However, the stratigraphic units have not fully and formally described and have been used informally in different and often confusing ways. The current study therefore aims to solve this challenge by establishing a coherent stratigraphic scheme for the entire graben through an integral study of surface and subsurface data. The study involves precise description of the type and reference sections for various formations both in exposure and wells and has therefore led to the development of lithostratigraphic columns of different basins in the graben. The approach reveals that the Semliki area,south of Lake Albert, has the most complete sedimentary succession in the graben, spanning the period from middle Miocene (ca 15 Ma) to Recent. It also reveals that platform deposits, which form a small fraction of the thickness of the basinal succession, represent a highly condensed sequence which only saw deposition at times of lake highstand.