KeywordsCape Province region
Cape Province South Africa
Gauteng South Africa
Natal South Africa
Orange Free State South Africa
Pretoria South Africa
Transvaal South Africa
MetadataShow full item record
CitationVogel, J. C., Fuls, A., & Visser, E. (1986). Pretoria radiocarbon dates III. Radiocarbon, 28(3), 1133-1172.
PublisherAmerican Journal of Science
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Response of the Black Mountain, South Africa, sulfide deposit to various geophysical techniques and implications for exploration of similar depositsStevenson, Frederick (The University of Arizona., 1985)
Oceanic Radiocarbon Between Antarctica and South Africa Along WOCE Section 16 at 30 Degrees ELeboucher, Viviane; Orr, James; Jean-Baptiste, Philippe; Arnold, Maurice; Monfray, Patrick; Tisnérat-Laborde Nadine; Poisson, Alain; Duplessy, Jean-Claude (Department of Geosciences, The University of Arizona, 1999-01-01)Accelerator mass spectrometry (AMS) radiocarbon measurements were made on 120 samples collected between Antarctica and South Africa along 30 degrees E during the WOCE-France CIVA1 campaign in February 1993. Our principal objective was to complement the Southern Ocean's sparse existing data set in order to improve the 14C benchmark used for validating ocean carbon-cycle models, which disagree considerably in this region. Measured 14C is consistent with the theta -S characteristics of CIVA1. Antarctic Intermediate Water (AAIW) forming north of the Polar Front (PF) is rich in 14C, whereas surface waters south of the PF are depleted in 14C. A distinct old 14C signal was found for the contribution of the Pacific Deep Water (PDW) to the return flow of Circumpolar Deep Waters (CDW). Comparison to previous measurements shows a 14C decrease in surface waters, consistent with northward displacement of surface waters, replacement by old deep waters upwelled at the Antarctic Divergence, and atmospheric decline in 14C. Conversely, an increase was found in deeper layers, in the AAIW. Large uncertainties, associated with previous methods for separating natural and bomb 14C when in the Southern Ocean south of 45 degrees S, motivated us to develop a new approach that relies on a simple mixing model and on chlorofluorocarbon (CFC) measurements also taken during CIVA1. This approach leads to inventories for CIVA1 that are equal to or higher than those calculated with previous methods. Differences between old and new methods are especially high south of approximately 55 degrees S, where bomb 14C inventories are relatively modest.
MICROSTROMATOLITES FROM THE 2.3 G.A. TRANSVAAL SEQUENCE, SOUTH AFRICA (STROMATOLITES, MICROFOSSIL, CHERT).Nagy, Bartholomew; LANIER, WILLIAM PAUL.; Baker, Victor R.; Kidwell, Susan; Sinclair, Norval A.; Schrieber, Joseph F. (The University of Arizona., 1984)A unique assemblage of in situ microstromatolites, articulated intraclastic microstromatolites, and disarticulated stromatolites has been identified from drill cores of the 2.3 G.a. Transvaal Sequence, South Africa. These structures occur in organic-rich lenticular and nodular replacement black cherts which are associated with early diagenetic dolomite. Petrographic evidence indicates that the chert has formed via a primary carbonate and organic matrix--partial dolomitization--silicification paragenetic sequence; and that dolomitization and silicification were closely contemporaneous diagenetic events. Microstructures which resemble three dimensionally preserved microfossils are found in the majority of the silicified Transvaal cores. These fossil-like microstructures can be grouped broadly into three morphological types: (1) filaments, (2) ovoid or spheroidal forms, and (3) bacteria-like microstructures. Certain of the filamentous forms which are associated with pyrite mineral grains are clearly of abiological origin, and their formation can be explained in the context of sedimentary diagenesis and mineral paragenesis. The three dimensional association of the ovoid and bacteria-like microstructures to the microstromatolites is such as would be predicted from studies of modern cyanobacterial/microbial mat ecosystems. Hence, these microstructures are considered to be potential microfossils. The Transvaal microstromatolitic materials represent some of the smallest stromatolites yet described from either Proterozoic or Phanerozoic sedimentary rocks. Nearly all of the basic stromatolite growth forms (i.e. columnar, bulbous, nodular, and stratiform) are represented in the Transvaal assemblage. Thus, stromatolite diversity at the "basic growth form" level apparently did not evolve through geologic time. Physical and chemical environmental parameters probably controlled stromatolite morphogenesis only to the extent that they influenced the steady state balance of microstromatolite microbial communities. Indirect evidence suggests that the Transvaal microstromatolites grew via the precipitation of primary carbonate at some level within the structures and that a correlation exists between the degradation of primary producer organic carbon and the precipitation of a structurally supportive carbonate mineral matrix.