keywords: Anambra basin, coal, mamu formation, paleoredox history, trace elements
Thirteen coal samples from the Maastrichtian Mamu Formationin the Anambra Basin (SE Nigeria) were analysed for total organic carbon (TOC), major and trace elements using LECO C-230 analyser and inductively coupled plasma-optical emission spectrometry (ICP-OES) in order to assess the paleoredox depositional conditions of sedimentation and the role of clastic input. TOC contents of up to 65% were recorded in the coal samples. The organic richness of the coals (average TOC = 34.7%) was due to high organic carbon flux resulting from high primary productivity and enhanced organic preservation. The chemical composition of the major oxides in the coals are dominated by SiO2 (1.02–52.77%), Al2O3 (0.66 to 20.69%), TiO2 (0.01-2.14%), Fe2O3 (0.04-2.01%) and K2O (0.01-1.36%), indicating high detrital quartz and clay mineral content. The SiO2/Al2O3 ratios (1.43 to 3.03), TiO2/Al2O3 (0.01-0.11) and K2O/Al2O3 (0.02-0.07) are consistent with limited clastic influx during coal formation. Ternary plots of TOC-S-Fe2O3 associations and redox-sensitive trace element ratios indicate dominantly oxic environments of deposition for the coal samples. Ni/Co and V/Cr ratios indicate mainlyoxic environments and V/(V+Ni) ratios inferred variable paleoredox (oxic, anoxic and euxinic) conditions during accumulation of these coals.