Sequence Stratigraphy, Chronostratigraphy, and Spatio-Temporal Stratigraphic Thickness Variation of the Agbada Formation, Robertkiri and Delta Fields, Niger Delta, Nigeria

The Miocene-aged deltaic Agbada Formation, Niger Delta, Nigeria, is composed of prograding sediments deposited on a series of basin-ward tilted normal faults, characterized by structural collapse. It consists of shallow marine and non-marine deposits over- lying faulted collapsing sub-formation shale deposits. Sequence stratigraphic analysis of gamma ray wireline well logs shows that the Agbada Formation consists of at least four third order sequences. Thickness maps of the sequences and structural analysis of the sequence surfaces indicate rollover anticlinal structures reflecting the orientation of the underlying faults. Generally stratigraphic thinning of older sequences covers a wider areal extent than that of younger sequences and the sequences become thinner upward and landward. Chronostratigraphic analysis reveals the spatial variation in the location and zones of stratigraphic thinning. The stratigraphic thinning may be the result of erosion, non-deposition, or slower deposition. The spatial variation may be related to shift in fluvial deltaic deposition combined with a fall in the relative sea level.