Re-assessment of the northern Guinean “Koubia–Lessere unconformity” (KLU): Consequences on the geological correlations throughout West Africa

Abstract

International audienceNew radiometric data from recent cartographic projects (2007, 2010) lead to a reinterpretation of the "Koubia-Lessere Unconformity" (KLU). This unconformity is evidenced in the Bassaride Ranges (northern Guinea) and in two western inliers (Tomine and Kemberra). The KLU was previously correlated with the main unconformity (Jbeliat unconformity [JU]) separating the lower "super group 1" from the middle "super group 2" of the large Taoudeni basin. Consequently, the brecciated level (partly glaciogenic) that underlines the "KLU" was correlated with the "tillitic" level located at the base of the super group 2. The latter is linked to the worldwide "Marinhoan" glacial event (650-635 Ma). However, 32 recently published U/Pb age data on detrital or new formed zircons show clearly that the Bassarides groups (ante KLU), deformed and slightly metamorphosed by the Panafrican-II orogen, belong to the super group 2 of the Taoudeni basin. Consequently, the overlying "Koubia-Lessere unconformity" (KLU) cannot be linked to the "Jbeliats unconformity" (JU) that separates the super groups 1 and 2 in the Taoudeni basin. The KLU is younger than the Panafrican-II orogen and probably younger than the last volcanic basaltic flows (492 Ma) outcropping in the Bassaride belt. Consequently, the glaciogenic levels that outcrop in the KLU should be distinguished from the numerous "Marinhoan" glacial levels of West Africa. This new KLU interpretation implies some important changes in the stratigraphic correlations and interpretations all over the West African domain

Reservoir Characteristics and Main Factors Controlling Carboniferous Volcanic Rocks in the Well CH471 Area of the Hongche Fault Zone: Northwest Margin of Junggar Basin, China

“…Volcanic rocks have strong heterogeneity, and it is impossible to track reservoirs simply by the distribution of the dominant lithology. As the basis of reservoir development, the dominant lithology is not a decisive factor [63,64]. The main body of the study area is located on the hanging wall of the Hongche fault zone.…”

Linking the Neoproterozoic to Early Paleozoic Belts Bordering the West African and Amazonian Cratons

“…It initiated with intercontinental troughs infilling by sediments corresponding to two different groups. The lower Mali-Rokel River Group started with a diamictite level (Koubia-Lessere diamictite) evidenced in Guinea and Sierra Leone [13]. These diamictites cover the 480 Ma micro-gabbros in the Tominé inlier.…”

“…From the Mesoproterozoic to the end of Palaeozoic, four orogenic events have been evidenced on the western side of the WAC [13] and are thus taken as references for assessing the geological evolution of West Africa and north Brazil and propose correlations between African and South American Neoproterozoic to Early Palaeozoic belts. Of course, each of these orogenic events is not recorded by every belt ascribed to the Brasiliano -Panafrican cycle, and some orogenic events are missing depending on the position of the belts in the Gondwana continent.…”

“…In this work, we review new data on the western branch of the West African Craton (e.g., [12][13][14]) and on the eastern side of the Amazonian Craton (e.g., [15,16]). This allows proposing a new hypothesis for correlating Neoproterozoic belts on both sides of the Equatorial Atlantic Ocean.…”

Linking the Neoproterozoic to Early Paleozoic Belts Bordering the West African and Amazonian Cratons: Review and New Hypothesis

“…In this work, we review new geochronological and geodynamical data on the western branch of the West African Craton (e.g., [14][15][16]) and on the eastern side of the Amazonian Craton (e.g., [17,18]). This allows proposing a new hypothesis for correlating Neoproterozoic belts on both sides of the Equatorial Atlantic Ocean.…”