Forty-two ditch cutting samples of the KR-1 offshore well from depths of 9660 ft to 10,920 ft composited at 90-ft intervals were subjected to sedimentological, micropaleontological, and geochemical analyses using standard procedures and the laser ablation-induced coupled plasma mass spectrometry technique, respectively. Sedimentological analysis revealed the presence of glauconites and the rare occurrence of framboidal pyrites, indicative of deposition in a slightly anoxic marine environment. Palynomorph percentage distribution shows that there are more terrestrially derived miospores (dominated by Zonocostites ramonae (Rhizophora spp.), Psilatricolporites crassus (Tabernaemontana crassa), Acrotichum aureum, and Laevigatosporites sp.) than marine phytoplanktons. Rare occurrence of Globoquadrina venezuelana, Globigerinoides promordius, and Globigerina sp. denotes an Early Miocene age and proximal shelf. These indicate that the main environment of deposition in the KR-1 well is coastal to marginal marine consisting of coastal deltaic-inner neritic, made up of tidal channel and shoreface deposits. Geochemical results show that the average concentrations of considered rare earth elements are less than their concentrations in world average shale. Trace metal ratios (such as Th/Cr, Cr/Th, Th/Co, and Cr/Ni) suggest that the investigated sediments were derived from felsic source rocks. Rare earth element patterns (such as La/Yb, Gd/Yb, La/Sm, and Eu/Eu) and Th data established the felsic composition of the source rocks. Ratios of U/Th, Ni/Co, Cu/Zn, and V/Sc suggest a well-oxygenated bottom water condition. Estimated europium and cerium anomalies of the studied samples suggest an oxidizing environment of deposition. Nonetheless, the ratios of V/Cr suggest a range of environmental conditions. Moreover, ratios of V/(V+Ni) suggest the rare occurrence of suboxic to anoxic environments of deposition.
Sedimentology, palynomorphs, traces elements, rare earth element, environment of deposition, Niger Delta, Nigeria
ADEBAYO, OLAJIDE FEMI; AKINYEMI, SEGUN AJAYI; MADUKWE, HENRY YEMAGU; ATURAMU, ADEYINKA OLUYEMI; and OJO, ADEBAYO OLUFEMI
"Geochemical characterization and palynological studies of some Agbada Formation deposits of the Niger Delta basin: implications for paleodepositional environments,"
Turkish Journal of Earth Sciences: Vol. 25:
6, Article 4.
Available at: https://journals.tubitak.gov.tr/earth/vol25/iss6/4