Sequence Stratigraphic Appraisal: Coastal Swamp Depobelt In The Niger Delta Basin Nigeria

Abstract

Mid-Lower Miocene Agbada sedimentary intercalations of “AB” Field in the coastal swamp depobelt, Western Niger-Delta, were evaluated to determine their sequence stratigraphic character. The analysis was based on a combination of data sets including logs of six wells to describe lithic variations of the Agbada Formation within the ‘AB' Field. These well logs were integrated with biostratigraphic data to develop a sequence stratigraphic framework. The results revealed two maximum flooding surfaces dated 10.4Ma and 9.5Ma. A sequence boundary dated at 10.35Mya was also identified across the field. The strata in the study area were divided into lowstand system tracts (basin floor fan, slope fan and prograding wedge), transgressive and highstand systems tracts. Biostratigraphic data suggested that these sediments were deposited in coastal deltaic to bathyal marine environments. Basal deposits directly overlying sequence boundaries where formed by the migration of large distributary channels. Upward coarsening sets of inclined beds, hundreds of feet thick, record progradation of deltas into slope. Blocky and upward fining well-log patterns are interpreted to reflect deposition in shoreline, paralic, and fluvial environments. The thick sequences of highly microfossiliferous are the probable petroleum source rocks. The massive sand formation of the basin floor fan, the sand-rich prograding wedge and the highstand sands as well as the transgressive sands constitute good reservoirs. The distal shale toes of the prograding wedge and transgressive shales as well as highstand shales form seals for the stratigraphic traps formed in the study area.

Keywords: Sequence stratigraphic tool, system tract deposits.

Global Journal of Geological Sciences Vol. 6 (2) 2008: pp. 129-137