THE GEOCHEMISTRY, PALYNOLOGY AND PALYNOFACIES CHARACTERISTICS OF MAIGANGA COAL DEPOSIT, UPPER BENUE TROUGH, NIGERIA

Abstract

Geochemical, palynological and palynofacies studies had been carried out on samples from 24 boreholes that penetrated Gombe Formation around Maiganga coal mine. The aim of the study was to establish their microfloral assemblages, age, paleoclimate, paleoenvironment and biozonation as well as evaluating the petroleum generative potentials of the Formation. The standard maceration and Rock Eval 6 methods were employed for the palynological/palynofacies and organic geochemical analyses respectively. The studied boreholes are considerably rich in palynomorphs which permitted some adequate deductions, such as the age, paleoclimate and paleoenvironment of the formation. Majority of the pollen and spores observed from the study area included Proteacidites sigalii, Retidiporites magdalensis, Monoporites annulatus, Cingulastisporites ornatus, Rugulatisporites caperatus, Scabratriporites annellus, Proteacidites longispinosis, Distaverrusporites simplex and Foveotrilete margaritae. The recovered marker species have been used to date the studied sections Maastrichtian age. Palynomacerals types I, II and III were found in the studied sections with little type – IV and Armophous Organic Matter (AOM). The analyses of these palynofacies were used to interpret the paleoclimate and paleoenvironment of the studied sections as well as zoning the sections into two palyzones, namely, Proteacidites sigalii – Echitriporites trianguliformis zone and Cyathidites spp-Laevigatosporites haardtii zone. The analyzed palynoforms showed that the paleoenvironment of the study sections were swamps and flood plains while the coal seam intercalation was an indication of swampy environment under anoxic condition. The paleoclimatic conditions were inferred to belong to the Late Cretaceous Palmae province based on the analyzed palynomorphs. The geochemical analyses showed that the analyzed samples were organic rich and contained kerogen types (II and III). They were however considered thermally immature based on the analyzed Tmax values which were considered low. The results of the Rock-Eval analyses showed that the samples in boreholes BA-7 and BA-16 contain Type II kerogen while those from borehole BA-17 contain Type III kerogen. This study also revealed that the analyzed samples especially those from boreholes BA-7 and BA-16 may constitute a good source rocks capable of generating petroleum and gas. The Rock-Eval Tmax data available for thermal maturity assessment of the samples suggest that the analyzed samples from the three boreholes are thermally immature. This assessment was consistent with the immaturity status of their coeval formations in other part of the Benue Trough. These contemporaneous formations may be related in depth and/or have experienced similar geothermal gradient with those of the Gombe Formation.