Correlation of Carnian to Rhaetian palynological, foraminiferal, calcareous nannofossil, and ostracode biostratigraphy, Wombat Plateau

During Ocean Drilling Program Leg 122, Upper Triassic sediments were recovered at four sites (Sites 759, 760, 761, and 764) on the Wombat Plateau, a small horst on the northern margin of the Exmouth Plateau. Biostratigraphic results vary at each site, because of environment changes from prodeltaic in the late Carnian to marginal-marine and fluvial non marine in the Norian, and finally to reefal and mudftat in the Rhaetian. Sediments from these sites have been examined for calcareous nannofossils, dinoflagellates, foraminifers, ostracodes, radiolarians, and spores and pollen. The biostratigraphy of the Carnian-Norian sequence is based primarily on organic microfossils, since the rare occurrence of calcareous microfossils minimizes the stratigraphic potential of those groups. The carbonates of the overlying Rhaetian sequence, however, contain rich foraminifers, ostracodes, and calcareous nannofossil assemblages. Siliceous microfossils in the Carnian to Rhaetian sequence are nearly absent, except for rare fragments of radiolarians. The near-continuous late Carnian to Rhaetian sequence recovered on the Wombat Plateau allows us to compile a biostratigraphic framework for different fossil groups

Sea-level changes, river capture and the evolution of populations of the Eastern Cape and fiery redfins (Pseudobarbus afer and Pseudobarbus phlegethon, Cyprinidae) across multiple river systems in South Africa

AIM: The phylogeography of the two closely related species Pseudobarbus afer and Pseudobarbus phlegethon was investigated to assess the association of evolutionary processes, inferred from mitochondrial DNA (mtDNA) sequence variation, with hypothetical palaeoriver systems and other climatic and landscape changes. Location One western and several southern river systems in South Africa. METHODS: We sampled known populations and confirmed known distribution gaps. This was followed by an assessment of mtDNA control region sequence variation for 31 localities across 17 river systems across the range of the species complex. A map of possible offshore drainage patterns during the last major regression event was constructed based on bathymetry and geological studies. RESULTS: The genetic distinction of four major lineages of P. afer strongly correspond with proposed palaeoriver systems. However, a western ‘Forest’ lineage, is widespread across two such proposed systems and is closely related to P. phlegethon on the west coast of South Africa. Both the ‘Krom’ and ‘St Francis’ lineages were identified in the single palaeoriver system proposed for St Francis Bay. A fourth ‘Mandela’ lineage is restricted to the one or two palaeoriver systems proposed for Nelson Mandela Bay. Four minor lineages were identified within the Forest lineage and two within the Mandela lineage. Main conclusions The close relationship between P. phlegethon and the Forest lineage of P. afer can only be explained by a series of river captures. We suggest the Gourits River system as a historical link that could account for this relationship. On the south coast, lower sea levels than at present allowed confluence between currently isolated river systems, offering opportunities for dispersal among these populations. At present, isolation between different river systems rather than dispersal appears to have a dominant influence on mtDNA diversity