Significance of Textural and Petrographic Attributes of several Cretaceous Sandstones, Southern Nigeria

Textural and petrographic attributes of sandstones of several Cretaceous formations of southern Nigeria sedimentary basin have been evaluated. Sandstones of the first sedimentary cycle (Albian-Santonian) confined mainly to the Abakaliki basin are feldspathic and those of the second sedimentary cycle (Campanian-Eocene) confined mainly to the Anambra-Afikpo basin are quartz arenites. Nearness of the Abakaliki basin to the source region of Cameroun basement complex was the governing factor in the survival and accumulation of feldspars in the sand of the first cycle. Although detritus of the second cycle was derived from the same source region, it underwent intense chemical weathering in a humid climate and during long transportation to the Anambra site of deposition, and thereby attained a high degree of mineralogical maturity. In both cases, duration of erosion played a critical role in the presence or absence of feldspar in sediments. Quartz arenites with low textural index are perhaps indicative of a miogeosynclinal deposition whereas texturally mature quartz arenites are characteristic of cratonic or stable platform. Fragmentation of large polycrystalline quartz grains into finer subindividuals in a dynamic environment is advanced as an adequate mechanism to account for the origin of fine and silt-size particles in a sedimentary system.