Optical (visual) Kerogen assessment of Enugu Shale, Anambra Basin, Southeastern Nigeria: Implications for source rock potential and thermal maturation

Abstract

Palynological analysis was carried out on Ten (10) samples from outcrops of the Campanian Enugu Formation, a component lithostratigraphic unit of the Anambra Basin, using the acid maceration techniques for recovering acidinsoluble organic-walled microfossils. Two main lithological units were encountered, which include: carbonaceous shale and siltstone. Result from kerogen laboratory examination reveals two (2) main groups of palynofacies association namely; palynofacies (A and B), based on the change in particulate organic matter constituents of organic residue extract. Palynofacies A is characterized by abundant opaques debris with common terrestrial phytoclasts, which occupy the southwestern and northwestern parts of the studied area, whereas palynofacies B dominates in the northeastern part, characterised by abundant phytoclasts followed by frequent opaques debris. Kerogen type III with gas-prone material is suggested for both palynofacies. The examined exine of spore/ pollen grain are pale yellow – yellow, with Thermal Alteration Index TAI of 1+ to 2- and Vitrinite Reflectane (R o) (0.3 % - 0.4 %) in palynofacies A, and yellow – yellow brown, with Thermal Alteration Index TAI of 2- to 2, and Vitrinite Reflectane (R o) of 0.3% - 0.5% in palynofacies B. These revealed source rock that is thermally immature to slightly mature but has potential to generate mainly gas. The kerogen data generated using transmitted light microscopy correlated well with geochemical data obtained using rock-eval pyrolysis method, and this shows the method a reliable tool for assessing petroleum potential in any given sedimentary basins.

Integrated Geological and Geophysical Mapping for Groundwater Potential Studies at Ekwegbe-Agu and Environs, Enugu State, Nigeria

“…The study area lies within the Anambra Basin. The basin is a NE-SW trending syncline that is part of the Central African Rift System which developed in response to the stretching and subsidence of major crustal blocks during a Lower Cretaceous break-up phase of the Gondwana super-continent [17]. It's the oldest sedimentary basin in Nigeria and originated in the early Cretaceous as the failed rift associated with the opening of the South Atlantic [18].…”

Palynostratigraphy, Paleoenvironments and Kerogen Evaluation of the Campanian-Maastrichtian Enugu Shale, Anambra Basin, Nigeria

“…However, palynofacies type I (P-I) and type III (P-III) could be classified as type III kerogen (mainly gas prone, could be related to the high phytoclasts input) as deduced mainly from Tyson (1993) ternary plot (Jaeger, 2013;Tahoun et al, 2013;Makled & Baioumi 2013). The kerogen investigation indicates that particulate organic matter, spore coloration and thermal maturity results obtained from the Enugu outcrop samples is at an immature thermal oil maturity stage (Atta-Peters & Kyorku, 2013;Makled et al, 2013;Ribeiro et al, 2013;Chiaghanam et al, 2014;Atta-Peters et al, 2015).…”

“…Palynostratigraphy is the use of palynomorphs in sedimentary strata delineation, correlation and relative age dating. Several workers have used palynomorph distributions in stratigraphic differentiation of rock sequence over various geological periods (Umeji, 2010;Nwojiji et al, 2013;El Atfy et al, 2013;Onoduku & Okosun, 2014;Chiaghanam et al, 2014;Stephenson, 2016). In addition, palynostratigraphic analysis can be used to establish stratigraphic boundaries.…”

“…However, few works have been done on the palynofacies of the Anambra Basin (Oboh-Ikuenobe et al, 2005;Chiaghanam et al, 2014;Maju-Oyovwikowhe & Malomi 2019;Onyedikachi, 2019;Lucas, 2018;Oke & Onoduku, 2018;Durugbo & Ogundipe, 2019). Dinoflagellate cysts study have received very little attention in the study area even though they have proven to be very useful in the interpretation of depositional environments (Li and Habib 1996).…”

Mineralogy and Geochemistry of Shales of Mamu Formation in Nigeria: Effects of Deposition, Source Rock, and Tectonic Background

“…In addition, it is typically overlain by the intercalation of sand and shale facies sequence with coal inter-beds previously deposited under surface marine settings [1]. Selected studies have examined the Mamu Formation, Anambra Basin based on the following; stratigraphic/biostratigraphy [2][3][4][5], sedimentology and depositional environments [6], sequence stratigraphy [7,8], palynology [1,[9][10][11], coal characterization [12][13][14], petroleum potential [15][16][17], palynofacies and kerogen analysis [18], geochemical indicator [19][20][21] and ichnology and lithofacies [22].…”