6533b7d1fe1ef96bd125d8e0

RESEARCH PRODUCT

Facies and facies association of the siliciclastic Brak River and carbonate Gemsbok formations in the Lower Ugab River valley, Namibia, W. Africa

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Abstract The Neoproterozoic Zerrissene Turbidite Complex of central-western Namibia comprises five turbiditic units. From the base to the top they are the Zebraputs Formation (greywacke and pelite), Brandberg West Formation (marble and pelite), Brak River Formation (greywacke and pelite with dropstones), Gemsbok River Formation (marble and pelite) and Amis River Formation (greywacke and pelites with rare carbonates and quartz-wacke). In the Lower Ugab River valley, five siliciclastic facies were recognised in the Brak River Formation. These are massive and laminated sandstones, classical turbidites (thick- and thin-bedded), mudrock, rare conglomerate and breccia. For the carbonate Gemsbok River Formation four facies were identified including massive non-graded and graded calcarenite, fine grained evenly bedded blue marble and calcareous mudrock. Most of these facies are also present in the other siliciclastic units of the Zerrissene Turbidite Complex as observed in other areas. The vertical facies association of the siliciclastic Brak River Formation is interpreted as representing sheet sand lobe to lobe-fringe palaeoenvironment with the abandonment of siliciclastic deposition at the top of the succession. The vertical facies association of the carbonate Gemsbok Formation is interpreted as the slope apron succession overlain by periplatform facies, suggesting a carbonate slope sedimentation of a prograding depositional shelf margin. If the siliciclastic–carbonate paired succession would represent a lowstand relative sea-level and highstand relative sea-level, respectively, the entire turbidite succession of the Zerrissene Turbidite Complex can be interpreted as three depositional sequences including two paired siliciclastic–carbonate units (Zebraputs-Brandberg West formations; Brak River–Gemsbok formations) and an incomplete succession without carbonate at the top (Amis River Formation).