Geochemical record for the depositional condition and petroleum potential of the Late Cretaceous Mamu Formation in the western flank of Anambra Basin, Nigeria

作     者：Gbenga O.Ogungbesan Taofik AAdedosu Gbenga O.Ogungbesan;Taofik A.Adedosu

作者机构：Department of Earth SciencesLadoke Akintola University of TechnologyP.M.B.4000OgbomosoNigeria Department of ChemistryLadoke Akintola University of TechnologyP.M.B.4000OgbomosoNigeria 

出 版 物：《Green Energy & Environment》 (绿色能源与环境（英文版）)

年 卷 期：2020年第5卷第1期

页      面：83-96页

核心收录：

学科分类：081803[工学-地质工程] 08[工学] 0818[工学-地质资源与地质工程] 

基　　金：7th CAS-TWAS symposium on Green Technology University of Ilorin Tertiary Education Trust Fund, TETFund 

主　　题：Anambra Basin Mamu formation Paleoenvironment Kerogen Thermal maturity 

摘      要：Carbonaceous shale exposures of the Late Cretaceous Mamu Formation along Ifon-Uzebba road in western arm(Benin Flank) of Anambra Basin, southwestern Nigeria, were analyzed for bulk organic geochemical, molecular biological and poly-aromatic hydrocarbon(PAH) compositions to investigate the organic matter source, paleo-depositional condition, thermal maturity and petroleum potential of the unit. The bulk organic geochemistry was determined using Leco and Rock-Eval pyrolysis analyses while the biomarkers and PAH compositions were investigated using gas chromatography-mass spectrometer(GC-MS).The bulk organic geochemical parameters of the shale samples showed total organic carbon(TOC)(1.11-6.03 wt%), S2(0.49-11.73 mg HC/g Rock), HI(38-242 mg HC/g TOC) and Tmax(425-435 C) indicating good to excellent hydrocarbon source-rock. Typical HI-Tmax diagram revealed the shale samples mostly in the gas-prone Type Ⅲ kerogen region with few gas and oil-prone Type Ⅱ-Ⅲ kerogen. The investigated biomarkers(n-alkane, isoprenoid, terpane, hopane, sterane) and PAH(alkylnaphthalene, methylphenanthrene and dibenzothiophene) indicated that the carbonaceous shales contain mix contributions of terrestrial and marine organic matter inputs that were deposited in a deltaic to shallow marine settings and preserved under relatively anoxic to suboxic *** maturity parameters computed from Rock-Eval pyrolysis, biomarkers(hopane, sterane) and PAH(alkylnaphthalene, alkylphenanthrene, alkyldibenzothiophene) suggested that these carbonaceous shales in Anambra Basin have entered an early-mature stage for hydrocarbon generation. This is also supported by fluoranthene/pyrene(0.27-1.12), fluoranthene/(fluoranthene + pyrene)(0.21-0.53) ratios and calculated vitrinite reflectance values(0.49-0.63% Ro) indicative that these shales have mostly reached early oil window maturity, thereby having low hydrocarbon source potential.