Integrated Geophysical Mapping of Turonian-Maastrichtian Bitumen Saturated Sand in Selected Part of Central Portion of Eastern Dahomey Basin


 A.O. Opatola*, S.I. Bankole, S.A. Saheed,
Department of Geosciences, University of Lagos, Akoka, Lagos, Nigeria.

O.A. Oluwajana
Department of Earth Sciences, Adekunle Ajasin University, Akoko-Akungba, Nigeria.


Bitumen, also known as oil sand, across Nigeria is hosted in the Eastern Dahomey Basin spanning over several kilometers. Integration of five (5) traverses of 2D electrical resistivity tomography (ERT), four (4) vertical electrical sounding (VES) and two (2) borehole lithological logs have led to delineation of five geoelectric layers – namely topsoil, lateritic soil, clay, shale/ marly limestone, bituminous sand and sandstone geoelectric units. The bituminous sand is characterized with high resistivity value as contrast to previous values obtained in other regions of the basin, ranging from 4177 Ωm to 70,000 kΩm with thickness ranges from 15 m to 28m. 2D ERT shown that the bituminous sands occur within a relatively shallow depth with a resistivity value ranging from 3225 Ωm to about 80,000 Ωm and a thickness range of 5 to about 30m. The survey shown that bitumen occurrences are overlain by relatively thin overburden (0-25m), and underlain by mudstone facies and limestone facies. Similarly, relatively deeper bituminous sands have higher resistivity range and are laterally continuous than the shallow occurrences. This suggests the sands comprising the shallow and deeper occurrences are probably deposited under different geologic setting.