Cisuralian palynological associations of the Owambo Basin, Namibia: biostratigraphic implications in southwestern Gondwana

Abstract

A detailed palynological study of the Strat Test-1 (ST-1) borehole in the Owambo Basin, Namibia, is presented, covering the depth interval between 348.1 and 596.3 m below the surface (mbs). The analyzed section includes rocks from the Ecca Group (348.1–498.3 mbs) and the Dwyka Group (528.2–596.3 mbs). The diverse and well- preserved microfloras comprise spores (32 genera and 80 species), pollen grains (45 genera and 142 species), algal cysts (4 genera and 5 species), and fungal spores (2 genera and 2 species). In addition, more than 20 reworked taxa of older strata were identified, particularly within the Dwyka Group (596.3 mbs). Four new species are proposed: a trilete spore Anapiculatisporites grossus sp. nov., a monolete spore Tuberculatosporites tricaricoi sp. nov., a bisaccate pollen grain Ovalipollis namibiensis sp. nov., and a colpate pollen grain Sverdrupollenites zavattierii sp. nov. The analyzed interval refers to the Cisuralian (middle Asselian-middle Kungurian). Its correlation with contemporary basins in South America and southern Africa is discussed. The microflora reflects the replacement of cold-temperate forests composed of conifers and seed ferns by more open vegetation consisting of ferns, along with gymnosperms, probably more tolerant of environmental stress, under warm-temperate and humid climatic conditions, related to the postglacial climatic conditions of the Asselian.