The sediment fill in the Niger Delta basin is characterized by three major depobelts. These three cycles show that the basin experienced an overall regression throughout time as the sediments go from deep sea mud sized grains to fluvial denser sand sized grains. The lithologies of the area experience changes due to several factors. The sediment provenance from the onshore highlands which feed into the delta control the mineralogy of the grains. Additionally, the impact of sea level on sediment deposition is well known; relative sea level will control the basinward extent of lithologies (see sequence stratigraphy). Volcanic activity in the area may also result in thin deposits of ash (bentonite). The early Cretaceous sediments are thought to be from a tide-dominated system that were deposited on a concave shoreline, and throughout time the shoreline became and it is currently a wave-dominated system.