Geochemical characterization of a Cretaceous black shale from the Mamfe Basin, Cameroon

Abstract

Shale from Cretaceous strata of the Mamfe Basin has been characterized by petrological and geochemical techniques. The aims of this study were to assess the quality of its organic matter, evaluate its thermal evolution and highlight its potential as a source rock. The total organic carbon (TOC) (4.45 wt%) of the shale constitutes that of a good source rock with oil-prone kerogen indicated by Rock-Eval S2/S3 (26.1). The low oxygen index (OI) (8 mgCO 2 g −1 TOC), pr/ph (1.79) and high gammacerane index (22) suggest deposition in a highly saline reducing environment. The n -alkane distribution dominated by n -C 15 and infrared spectrum dominated by aliphatic and aromatic functional groups are considered to be indicators of Type II kerogen. The CPI (1.1), T max (441° C), C 31 (S/S+R) ratio (0.6), Rr (0.7%) and MPI-1 (0.6) all indicate the maturity of this rock. This thermal evolution is thought to account for its current hydrogen index (HI) (222 mgHC g −1 TOC). Expulsion may have occurred before uplift and erosion but a more elaborate study is required to evaluate the petroleum systems of the basin.

Composition and applied sedimentology of salt from brines of the Mamfe Basin, Cameroon

“…Therefore, the presence of organic matter in brines may inhibit the formation of certain minerals such as gypsum (Schreiber et al, 1986). Mature shale from the basin studied by Eseme et al (2006) was attributed to the Manyu sandy clay series described by Le Fur (1965). The shale contained 4.2 wt.% organic carbon that largely exceeds the 0.5-1 wt.% threshold for petroleum source rocks (Tissot and Welte, 1984;Bordenave et al, 1993;Hunt, 1996).…”

“…Fig. 2 adapted from Eseme et al (2006) shows the stratigraphy of the Mamfe Basin compared to the relatively well studied adjacent lower Benue Trough. The lower Benue Trough was open to marine transgression, whereas the Mamfe basin only experienced restricted incursions.…”

“…Eseme et al (2002) proposed that, the springs in the Mamfe basin originate from dissolution of ancient evaporites, whereas Uma (1998) concluded that similar springs in Nigeria result from connate waters pressed out during tectonic compaction and subsequently stored in Eseme et al (2002Eseme et al ( , 2006. resulting fractures.…”

Petro-geochemistry, Genesis and Economic Aspects of Mafic Volcanic Rocks in the West and Southern Part of The Mamfe Basin (SW Cameroon, Central Africa)

“…It is suggested to be genetically related to that of the Benue Trough as they both have similar structures [24,37]. The Mamfe Sedimentary Basin is filled by very fine to very coarse-grained immature and mature siliciclastic lithified sediments (e.g., conglomerates, sandstones, arkoses, shales and mudstones) [22,[37][38][39][40][41][42]. These are locally associated with evaporites [23,24,[43][44][45].…”

“…%) and lower MgO (≤ 10 wt. %) and Mg# (40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59) [1]. Some of those major element contents are within the ranges of basanite found in Mount Bamenda, Cameroon volcanic line basalts although the basanites there are consistently higher in Na 2 O contents [34].…”