Browsing by Author "Siesser, W G"

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    Depositional processes in Saldanha Bay and Langebaan Lagoon
    (1977) Flemming, B W; Siesser, W G
    This study deals with the physical aspects of sedimentation in Saldanha Bay and Langebaan Lagoon. On the basis of detailed textural investigations the depositional history of the study area has been established. The sediments in the bay and in the lagoon consist of a fine terrigenous quartz population and a coarser skeletal carbonate population, which have been mixed in various proportions. In order to gain size parameters that are more closely related to the hydraulic nature of depositional processes observed in the marine environment, grain size analyses were performed with an automatically recording settling tube system. The instrument was developed in the course of this study. Construction costs were kept extremely low without, however, impairing the scientific requirements of the instrument. Over 500 sediment samples were recovered on a closely-spaced grid; in each case, a size analysis was performed on the total sample and on the insoluble, terrigenous fraction. By subtracting the terrigenous size distribution from that of the total sediment, the relevant size parameters of the bioclastic component were calculated. In this manner 1500 individual size distributions were available for interpretation.
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    Sediments on the continental margin off South West Africa between latitudes 17⁰ and 25⁰ S
    (1978) Bremner, James Michael; Siesser, W G
    The study area lies on the north-central part of the South West African continental margin. It covers approximately 57 000 n.miles² , and extends from 2 n.miles offshore to a depth of about 1 500 m. Four cruises of the R.V. THOMAS B. DAVIE were undertaken over a two year period (May, 1972 to May, 1974) to collect 555 sediment samples, 38 rock samples, and bathymetric data. The main effort of the study has been directed at the unconsolidated sediments of the continental margin, and particular emphasis was placed on the authigenic mineral deposits. On sedimentological grounds, the continental margin is divided by a latitudinal boundary at 18°40' S. This boundary coincides with the northern flank of the Walvis Ridge Abutment, and separates the morphologically distinct Kunene and Walvis Continental Margins. To the north, the Kunene Shelf is narrow (~24 n.miles) and breaks at about 200 m depth whereas in the south, the Walvis Shelf is wide (~64 n.miles) with a poorly defined shelf break at about 360 m depth, and features an inner shelf break over most of its length.