Sediment Loading and Subsidence in the Niger Delta Sedimentary Basin

INTRODUCTION Geological and geophysical investigations reveal that maximum subsidence of the basement and active downwarping of the lithosphere have occurred around the axis of symmetry of the Niger Delta. A great bulk 6f sediments h~ accumulated:in this sedimentary basin stn~~ Tertiary, and during the period of accumula- . tion, vertical tect()nic movementS took place. This is evidenced by the presence of shallow water sediments ia deeper parts. of the basin. It is obvious from the overall thickness of the sediments (10 to 12km in some places), that purely eustatic sea-level changes could not have been the primary cause of sedimentation. The center of the basin coincides with the area of-greatest sediment preservation, and the presence of deeper water sediments near this area indicates that the basin was an area of rapid subsidence. during depositions. - ~though much is now known about the structure of the Niger Delta as a result of commercial oil exploration, the mode of basin formation and the cause of the subsidence have not been properly investigated. It is now generally accepted that the subsidence of rifted Atlantic-type continental margins results from thermal contraction of the lithosphere (Sleep 1971). Based on the thermal cooling model for the oceanic lithosphere, a "similarity solution" for the subsidence of sedimentary basins has been given by Turcotte and Ahem (1977). Details of the method and its applications have also been discussed by Steckler and Watts (1978) and Keen (1979).