Sedimentology and Palynological Study of Maastrichtian to Danian Sedimentary Succession in Alo-1 Well, Anambra Basin
Lucas, F. A. & Osezele, E. I.
Department of Geology University of Benin, Benin City, Nigeria
Geology and Geophysics Department, Skangix Development Limited Lagos, Nigeria
Email: drfalucas@gmail.com, preshyose143@gmail.com
ABSTRACT
One hundred and five (105) cutting samples recovered from depths between 540ft to 8,600ft in Alo-1 well sedimentary succession, Anambra basin were subjected to sedimentological and palynological study. Three Lithofacies were established: shale, sandy-shale and shaly-sand respectively. Mineral contents of these lithofacies include mica, carbonate, iron oxide and quartz. A total of 81 species of miospores and 19 dinocysts were identified, evaluated and appraised for their biostratigraphic utilities. Danian to Maastrichtian stage is assigned for the succession penetrated. The Cretaceous -Tertiary (K-T) boundary is delineated by both the FAD of a dinocysts species, Damassadinium californicum and LAD of a pollen species, Constructipollenites ineffectus at intervals 3,600ft and 4,360ft respectively. A shelf environment was established for intervals between 540ft- 5340ft marked by interfingering of miospores and dinocysts. The paleoenvironment between intervals 5340ft-8600ft was undiagnostic because of absence of sufficient palynological evidence. Palynomorph abundance pattern and the age of the succession penetrated were used to delineate stratal surfaces: two maximum flooding surfaces (MFS) and one sequence boundary (SB) were defined in the Danian, three maximum flooding surfaces (MFS) and two sequence boundaries (SB) were defined in the Maastrichtian. Based on the age established for the succession penetrated, the formations likely penetrated by the well were established to be the Imo (Danian) from 540ft-3600ft and Nsukka (3600ft-4570ft)-Ajali (4570ft-5170ft) and the Mamu (5170ft-8600ft) these have been dated Danian-Maastrichtian. The two maximum flooding surfaces were mainly delineated and defined on the basis of palynological signals while the sequence was identified on the basis of the high resolution lithofacies model generated for the well sedimentary succession. This work has therefore, demonstrated the utilities of palynology for the definition and characterization of stratal surfaces.
Keywords: Danian; dinocysts; K-T boundary; Lithofacies; Maastrichtian; pollen; Paleoenvironment; Sequence stratigraphy.
