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Cyclicity and sequence stratigraphy of the Neoproterozoic uppermost Haut Shiloango-Lukala carbonate ramp system in the Lower Congo region (Democratic Republic of the Congo): example of tectonostratigraphic control versus climatic changes
Delpomdor, F.; Kant, F.; Tack, L.; Préat, A. (2019). Cyclicity and sequence stratigraphy of the Neoproterozoic uppermost Haut Shiloango-Lukala carbonate ramp system in the Lower Congo region (Democratic Republic of the Congo): example of tectonostratigraphic control versus climatic changes. J. Afr. Earth Sci. 160: 103636. https://dx.doi.org/10.1016/j.jafrearsci.2019.103636
In: Journal of African Earth Sciences. Elsevier: Oxford & Amsterdam. ISSN 1464-343X; e-ISSN 1879-1956, meer
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Neoproterozoic; West Congo supergroup; Sea-level changes; Tectonics;Climate |
| Abstract |
During the Cryogenian-Ediacaran, tectonically- and climatically-driven perturbations created sea level changes. Snowball Earth-type glaciations suggest ~500–800 m sea level fall or at least 1,000–1,500 m in eustatic sea-level change as a result of severe climate changes. However, in Central Africa, geologic evidence of such processes is lacking. In the Lower Congo region (Democratic Republic of the Congo), detailed facies analysis and sequence stratigraphy of the Neoproterozoic uppermost Haut Shiloango-Lukala carbonate ramp system allowed to reconstruct the multiple order relative sea-level changes. Two hundred twenty-three fifth-order elementary parasequences, grouped into eleven fourth-order depositional sequences or parasequence sets, recorded a severe sea-level fall up to 15 m for slope-outer-to-outer ramp facies of the uppermost Haut Shiloango Subgroup-Upper Diamictite Formation followed by two distinct sea-level rises for the slope-outer-to-inner ramp facies of the Lukala Subgroup. First marine transgression shows a cumulative ~60 m of sea-level rise throughout C1 to C3 (Lukala Subgroup) sediment accumulations. Second marine transgression shows a cumulative ~50 m sea-level rise throughout C4 to C5 sediment accumulations. The transition from uppermost Haut Shiloango to Upper Diamictite ramp system points to an isostatic rebound and uplift of the rift flanks of the Congo Craton, creating paleoreliefs, potentially allowing local glaciation and periglacial sedimentation. This rebound can be ascribed to a diachronous far-field effect of ~660 Ma Macaúbas Basin opening in Brazil. First marine transgression is interpreted as a consequence of syn-to post-rifting related to sea-floor spreading, which initiated the subsidence of the basin. A ~30 m of sea-level rise drowned the C1 formation carbonate ramp, which turned on the oversupply and progradation of offshore to nearshore marine deposits on the wedges of the basin. An abrupt change from both marine transgressions points to ~25 m of sea-level rise that is interpreted as the consequence of the development of ~585-560 Ma Araçuaì-West Congo Orogen, which significantly increased the siliciclastic supply in the basin. Our results show that no anomalous climatic or eustatic events such as those proposed in the Snowball Earth model are recorded in DRC. On the contrary, relative sea-level changes result from long-term overriding regional tectonic processes controlling diachronous sedimentation along the western passive margin of the Congo Craton. |
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