Soft-Sediment Deformation in the Campanian-Maastrichtian Deltaic Deposits of the Afikpo Sub-basin, South-eastern Nigeria: Recognition of Endogenic Trigger

In this research, soft-sediment deformation structures are studied and analyzed from the Cretaceous deltaic deposits of the Afikpo Sandstone Member of the Nkporo Formation in Afikpo Sub-basin. These deformation structures are grouped into three morphological and deformational styles which include load structures (load casts, ball-and pillow-structures, flame structures, and pseudonodules), ductile disturbed structures (loop bedding, recumbent folding, and deformed lamination), and brittle deformation (synsedimentary fractures). The facies analysis revealed sedimentary structures that are indicative of storm and wave processes and rapid sedimentation. Though the trace fossils have a low to moderate diversity and abundance, the Skolithos ichnofacies, particularly the Diplocraterion and Skolithos burrows, are relatively frequent. These ichnofossils are indicative of high-energy conditions and rapid sedimentation. The recognition of the deformation processes and their triggers suggests that the soft sediment deformation structures in the study area are not tectonic in origin as they are associated with storm-generated sedimentary structures and structures formed due to rapid sedimentation. Furthermore, the deformational structures are restricted to a single stratigraphic layer, and are not laterally extensive suggesting an endogenic or non-seismic trigger mechanisms such as storm events, overloading, and rapid sedimentation.