Gross Brukkaros, Namibia, is a broad (10 km diameter) dome structure in Nama Group country rocks, with a crater-shaped central depression. Formation of the dome structure has recently been attributed to a shallow intrusion, which subsequently became partly depleted during volcanic activity in the Brukkaros Volcanic Field, causing cauldron subsidence. The subsiding depocentre became filled by a sedimentary sequence corresponding to alluvial fan delta / lacustrine environments. Here we give a detailed petrographical and chemical description of the Brukkaros sediments and their lithic and mineral constituents. As main sources for the Brukkaros sediments we identified shales, cherts, sandstones, and quartzites from Karoo Sequence and Nama Group rocks as well as Karoo dolerites. A contribution of aeolian deposits (early Kalahari?) is also identified. No primary pyroclastic deposits were found within the Brukkaros depocentre. Volcanogenic fragments in the form of carbonatitic lapilli, however, are described from the Brukkaros sediments for the first time and are attributed to redeposition of tephra deposits of the common carbonatitic diatremes at and around Brukkaros. Basement fragments within the Brukkaros sediments might well have been derived from the same source. Metasomatichydrothermal alteration and cementation of the Brukkaros rocks can be shown to have operated already during sedimentation. Metasomatic alkali feldspar compositions indicate that fenitization took place mainly at subsolvus temperatures.