Origin, Depositional Environment and Thermal Maturity of some Source Rocks from Niger Delta Basin, Nigeria

Abstract

Eleven (11) core samples from Agbada and Akata formations in the Niger Delta, Nigeria, were analyzed using gas chromatography-mass spectrometry to evaluate their paleodepositional conditions and source input as well as to determine their thermal maturity. The distribution of n-alkanes, isoprenoids, and biomarkers indicate a mixture (marine/terrigenous) organic matter source input for Agbada and Akata formation sediments deposited in marine environment. Low values of Phytane/nC18 (0.45 to 1.32) and Pristane/nC17 (0.37 to 1.8) indicates Marine organic matter contribution and anoxic-suboxic (Type II/III kerogens) depositional conditions of extract for Agbada and Akata Formations. The Carbon Preference Index (CPI) values for all analysed samples are slightly greater than 1.0 indicate a mixed input of marine and terrigenous organic matter deposited under relatively reducing (dysoxic) conditions. The high concentration of Oleanane in studied samples reveals that source rocks are tertiary age and belong to marine deltaic depositional environment. Moderate to higher Gammacerane index values ranging from 0.06 to 0.11, suggests water-column stratification, potentially due to hypersalinity for Isan oilfield well samples from Agbada formation. Biomarker maturity parameters suggest that the sediments have reached the early stages of hydrocarbon generation.