Stable isotopes of oxygen and carbon compositions in the Neoproterozoic of South Gabon (Schisto-Calcaire Subgroup, Nyanga Basin): Are cap carbonates and lithoherms recording a particular destabilization event after the Marinoan glaciation?

Geochemical characterization of the Marinoan “Cap Carbonate” of the Niari-Nyanga Basin (Central Africa)

“…Moreover, tepee structures observed in the Nkengué and Mouyengo Cap Carbonate sequences do not reveal any influence by carbon of methane origin (␦ 13 C ∼ −41‰), as observed in some Chinese Cap Carbonate (Jiang et al, 2003). At a regional scale, the obtained ␦ 13 C values are entirely consistent with those reported by Préat et al (2011) for samples collected from the SCIa member close to the Lébamba section. The chemostratigraphical correlation of our ␦ 13 C records from the SCIa member of the Niari-Nyanga basin (Central Africa) with those from coeval West-African or South-American sequences shows a consistent picture (Fig.…”

“…Recent studies have reported stable isotope variations for Marinoan carbonate sequences of the West-Congolian basin, documenting mainly the different formations of the thick "Schistocalcaire" Group (Frimmel et al, 2006;Préat et al, 2011). Our work focuses on a detailed study of the Cap Carbonate representing the lowest part (the SCIa member) of the Schisto-calcaire Group, overlying unconformably the Upper Diamictite and materializing the early stage of the Marinoan deglaciation/transgression.…”

“…Two main glacial formations or diamictites called Lower and Upper Diamictite are defined within the West-Congolian Supergroup of the Niari-Nyanga basin. In absence of geochronological data, the Upper Diamictite was attributed to Marinoan glacial deposits (Frimmel et al, 2006;Poidevin, 2007;Préat et al, 2011). This diamictite unconformably overlies the Bouenzian Group and underlies the "Schisto-Calcaire Group".…”

“…Two distinct glacial deposits were recognized in the lower part of the mega cover sequence: they are considered as the Lower and the Upper Diamictites (Dadet, 1969;Boudzoumou, 1986). The thin sequence mainly made up of carbonates and lying unconformably on the Upper Diamictite is known as the SCIa member and usually defined as the Marinoan Cap Carbonate (Frimmel et al, 2006;Préat et al, 2011). High-resolution sedimentological and isotopic studies focusing on this "Cap Carbonate" are relatively sparse (Caron et al, 2010(Caron et al, , 2011.…”

Pre- and post-Marinoan carbonate facies of the Democratic Republic of the Congo: Glacially- or tectonically-influenced deep-water sediments?

“…6F). Under SEM, the laminae revealed well-preserved tubules and spheroidal unicells, which are comparable (morphology and size) with the mat builders of the fossil species Siphonophycus septatum (Schopf, 1968;Delpomdor, 2007;Préat et al, 2011). Smooth planar laminated limestones are associated with disrupted fenestral and crinkled fabrics.…”